Mobile Assignment I

MOBILE COMPUTING:

ASSIGNMENT NO 1

Q1: Is a directional antenna useful for mobile phones? Why? How can the gain of antenna be improved? Ans : Antennas couple electromagnetic energy to and from space to and from a wire or coaxial cable (or any other appropriate conductor). A theoretical reference antenna is the isotropic radiator, a point in space radiating equal power in all directions, i.e., all points with equal power are located on a sphere with the antenna as its center. The radiation pattern is symmetric in all directions . However, such an antenna does not exist in reality. Real antennas all exhibit directive effects, i.e., the intensity of radiation is not the same in all directions from the antenna. The simplest real antenna is a thin, center-fed dipole, also called Hertzian dipole.

The dipole consists of two collinear conductors of equal length, separated by a small feeding gap. The length of the dipole is not arbitrary, but, for example ,half the wavelength λ of the signal to transmit results in a very efficient radiation of the

energy. If mounted on the roof of a car, the length of λ/4 is efficient. This is also known as Marconi antenna.

A λ/2 dipole has a uniform or omni-directional radiation pattern in one plane and a figure eight pattern in the other two planes . This type of antenna can only overcome environmental challenges by boosting the power level of the signal. Challenges could be mountains, valleys, buildings etc.

Q2: What are the main problems of signal propagation? Why do radio waves not always follow a straight line? Why is reflection both useful & harmful?

Ans: In wireless networks, the signal has no wire to determine the direction of propagation, whereas signals in wired networks only travel along the wire (which can be twisted pair copper wires, a coax cable, but also a fiber etc.). As long as the wire is not interrupted or damaged, it typically exhibits the same characteristics at each point. One can precisely determine the behavior of a signal travelling along

this wire, e.g., received power depending on the length. For wireless transmission, this predictable behavior is only valid in a vacuum, i.e., without matter between the sender and the receiver.

Transmission range: Within a certain radius of the sender transmission is possible, i.e., a receiver receives the signals with an error rate low enough to be able to communicate and can also act as sender. Detection range: Within a second radius, detection of the transmission is possible, i.e., the transmitted power is large enough to differ from background noise. However, the error rate is too high to establish communication. Interference range: Within a third even larger radius, the sender may interfere with other transmission by adding to the background noise. A receiver will not be able to detect the signals, but the signals may disturb other signals. Radio signal propagation faces the following problems: • Attenuation (amplitude of the wave loses strength thereby the signal power) • Refraction • Reflection • Shadowing • Scattering • Diffraction

Radio waves do not follow a straight line because of blocking objects in its path. Reflection is useful because in non-line-of-sight environments (where there is no direct path from the transmitter to receiver for example in offices, town and cities) it allows the radio signal to reach from the transmitter to the receiver. Reflection can be harmful because multiple copies of the same signal can reach the receiver at different times.

Q3: What are the main reasons for using cellular systems? How is SDM typically realized and combined with FDM? How does DCA influnence the frequencies available in other cells? Answer :Cellular systems for mobile communications implement SDM. Each transmitter, typically called a base station, covers a certain area, a cell. Cell radii can vary from tens of meters in buildings, and hundreds of meters in cities, up to tens of kilometers in the countryside. The shape of cells are never perfect circles or hexagons , but depend on the environment (buildings, mountains, valleys etc.), on weather conditions, and sometimes even on system load. Typical systems using this approach are mobile telecommunication systems , where a mobile station

within the cell around a base station communicates with this base station and vice versa.

Advantages of cellular systems with small cells are the following: ● Higher capacity: Implementing SDM allows frequency reuse. If one transmitter is far away from another, i.e., outside the interference range, it can reuse the same frequencies. As most mobile phone systems assign frequencies to certain users (or certain hopping patterns), this frequency is blocked for other users. But frequencies are a scarce resource and, the number of concurrent users per cell is very limited. Huge cells do not allow for more users. On the contrary, they are limited to less possible users per km2. This is also the reason for using very small cells in cities where many more people use mobile phones. ● Less transmission power: While power aspects are not a big problem for base stations, they are indeed problematic for mobile stations. A receiver far away from a base station would need much more transmit power than the current few Watts. But energy is a serious problem for mobile handheld devices. ● Local interference only: Having long distances between sender and receiver results in even more interference problems. With small cells, mobile stations and base stations only have to deal with ‘local’ interference. ● Robustness: Cellular systems are decentralized and so, more robust against the failure of single components. If one antenna fails, this only influences communication within a small area. Small cells also have some disadvantages: Infrastructure needed: Cellular systems need a complex infrastructure to connect all base stations. This includes many antennas, switches for call forwarding, location registers to find a mobile station etc, which makes the whole system quite expensive.

Handover needed: The mobile station has to perform a handover when changing from one cell to another. Depending on the cell size and the speed of movement, this can happen quite often. Frequency planning: To avoid interference between transmitters using the same frequencies, frequencies have to be distributed carefully. On the one hand, interference should be avoided, on the other, only a limited number of frequencies is available. Higher capacity, higher number of the users: cellular systems can reuse spectrum according to certain patterns. Each cell can support a maximum number of users. Support user localisation and location based services: Less transmission power needed. Smaller cells also allow for less transmission power ( thus less radiation). The mobile systems can enjoy longer runtime. Typically each cell holds a certain number of frequency bands. Neighboring cells are not allowed to use the same frequencies. Whether or not DCA depends on the current load. It can react upon sudden increase in traffic by borrowing capacity from other cells. However the ”borrowed” frequency must then be blocked in neighboring cells. Q4: What limits the number of simultaneous users in a TDM/FDM system compared to a CDM system? What happens to the transmission quality of connections if the load gets higher in a cell, i.e., how does an additional user influence the other users in the cell, for both TDM/FDM and CDM systems?

Ans: FDM/TDM system have a hard upper limit of simultaneous users. The system assigns a certain time-slot at a certain frequency to a user. If all time-slots at all frequencies are occupied no more users can be accepted. Compared to this ”hard capacity” a CDM system has a so-called ”soft-capacity”. The signal-to-noise-ratio typically limits the number of simultaneous users. The system can always accept an additional user. However, the noise level may then increase above a certain threshold where transmission is impossible. In TDM/FDM systems additional users, if accepted, do not influence other users as users are separated in time and frequency( well, there is some interference; however,this can be neglected in this context). In CDM systems, each additional user decreases transmission quality of all other users.

Q.5 Recall the problem of hidden and exposed terminals. What is the effect of such terminals if Aloha, slotted Aloha, reservation Aloha, or MACA is used? Ans:

• In Aloha, hidden station is a serious problem. Stations start sending their data, and because of runtime to the satellite, it needs long time till the satellite has repeated the information and sent it down to all stations. Thus there can be lots of hidden stations we will learn about only very late. On the other hand, exposed

stations don’t exist – a potential sender does not listen to the medium before sending, thus he cannot be exposed.

• For Slotted Aloha, it is the same as for traditional Aloha. • For Reservation-Aloha, both problems don’t exist. Because we work with reservations, all other stations know about ours at well at their own sending times. Only in the reservation phase we can have problems with placing reservations, but because we will recognize if someone else tried to do the same reservation as we, the other stations are not really hidden to us. • MACA was designed to avoid both, hidden and exposed stations. (Note: exposed stations in principle are avoided because a station which can hear the RTS but not the CTS could interpret it as not influencing the receiver. But in reality, also a station which cannot hear the CTS but hears a transmission begin after an RTS has to wait, because each sender also becomes a receiver – even if only for an ACK after finishing its transmission.) Nevertheless, if we have changing topology (i.e. mobile devices) or asymmetric connections, a station can miss the RTS/CTS messages and send without knowing that something is destroyed.

Q 6. Explain the term interference in the space, time, frequency, and code domain. What are countermeasures in SDMA, TDMA, FDMA, and CDMA systems? Ans: Interference and countermeasures are: • SDMA: Interference is overlapping of cells. Just leave a protective distance between base stations and/or devices.

• TDMA: Interference is simultaneous transmission of several stations. Synchronization and time gaps between time slots are countermeasures. • FDMA: Interference means transmission on the same carrier frequency. Countermeasures are protective gaps on the frequency band. • CDMA: Interference is sending with correlated codes. Thus orthogonal or quasiorthogonal codes have to be used (i.e. the gap in this example is in code orthogonality).

Q 7.What is the main physical reason for the failure of many MAC schemes known from wired networks? What is done in wired networks to avoid this effect? Ans: Stations in a wired network “hear” each other. I.e., the length of wires is limited in a way that attenuation is not strong enough to cancel the signal. Thus, if one station transmits a signal all other stations connected to the wire receive the signal. The best example for this is the classical Ethernet, 10Base2, which has a bus topology and uses CSMA/CD as access scheme. Today’s wired networks are star shaped in the local area and many direct connections forming a mesh in wide area networks. In wireless networks, it is quite often the case that stations are able to communicate with a central station but not with each other. This lead in the early seventies to the Aloha access scheme (University of Hawaii). So what is CS (Carrier Sense) good for in wireless networks? The problem is that collisions of data packets cause problems at the receiver – but carrier sensing takes place at the sender. In wired networks this doesn’t really matter as signal strength is almost the same (ok, within certain limits) all along the wire. In wireless networks CS and CD at the sender doesn’t make sense, senders will quite often not hear other stations’ signals or the collisions at the receiver. Q9: Describe the functions of the MS and SIM. Why does GSM sperate the MS & SIM? How & where is User-related data represented/stored in the GSM system? Ans:

Mobile station (MS): The MS comprises all user equipment and softwareneeded for communication with a GSM network. An MS consists of user independent hard- and software and of the subscriber identity module(SIM), which stores all user-specific data that is relevant to GSM.3 While and MS can be identified via the international mobile equipment identity (IMEI), a user can personalize any MS using his or her SIM, i.e., user-specific mechanisms like charging and authentication are based on the SIM, not on the device itself. Device-specific mechanisms, e.g., theft protection, use the device specific IMEI. Without the SIM, only emergency calls are possible. The SIM card contains many identifiers and tables, such as card-type, serial number, a list of subscribed services, a personal identity number (PIN), PIN unblocking key (PUK), an authentication key Ki, and the internationalmobile subscriber identity (IMSI) (ETSI, 1991c). The PIN is used to unlock the MS. Using the wrong PIN three times will lock the SIM. In suchcases, the PUK is needed to unlock the SIM. The MS stores dynamic information while logged onto the GSM system, such as, e.g., the cipher key Kc andthe location information consisting of a temporary mobile subscriber identity(TMSI) and the location area identification (LAI). Typical MSs for GSM 900 have a transmit power of up to 2 W, whereas for GSM 1800 1 W isenough due to the smaller cell size. Apart from the telephone interface, an3 Many additional items can be stored on the mobile device. However, this is irrelevant to GSM.MS can also offer other types of interfaces to users with display, loudspeaker,microphone, and programmable soft keys. Further interfaces comprise computermodems, IrDA, or Bluetooth. Typical MSs, e.g., mobile phones,comprise many more vendor-specific functions and components, such ascameras, fingerprint sensors, calendars, address books, games, and Internet browsers. Personal digital assistants (PDA) with mobile phone functions are also available. The reader should be aware that an MS could also be integrated into a car or be used for location tracking of a container.

Q10: How is user data protected from unautheraised access,especially over the air interface? How could the position of an MS be localised? Think of the MS reports regarding signal quality? Ans: Authentication centre (AuC): As the radio interface and mobile stations are particularly vulnerable, a separate AuC has been defined to protect user identity and data transmission. The AuC contains the algorithms for authentication as well as the keys for encryption and generates the values needed for user authentication in the HLR. The AuC may, in fact, be situated in a special protected part of the HLR. ● Equipment identity register (EIR): The EIR is a database for all IMEIs, i.e., it stores all device identifications registered for this network. As MSs are mobile, they can be easily stolen. With a valid SIM, anyone could use the stolen MS. The EIR has a blacklist of stolen (or locked) devices. In theory an MS is useless as soon as the owner has reported a theft. Unfortunately, the blacklists of different providers are not usually synchronized and the illegal use of a device in another operator’s network is possible (the reader may speculate as to why this is the case). The EIR also contains a list of valid IMEIs (white list), and a list of malfunctioning devices (gray list). •

Security: GSM offers several security services using confidential information stored in the AuC and in the individual SIM (which is plugged into an arbitrary MS). The SIM stores personal, secret data and is protected with a PIN against unauthorized use. (For example, the secret key Ki used for authentication and encryption procedures is stored in the SIM.) The security services offered by GSM are explained below:

● Access control and authentication: The first step includes the authentication of a valid user for the SIM. The user needs a secret PIN to access the SIM.The next step is the subscriber authentication (see Figure 4.10). This step is based on a challenge-response scheme as presented in section 4.1.7.1. ● Confidentiality: All user-related data is encrypted. After authentication, BTS and MS apply encryption to voice, data, and signaling as shown in section 4.1.7.2.

This confidentiality exists only between MS and BTS, but it does not exist end-toend or within the whole fixed GSM/telephone network. ● Anonymity: To provide user anonymity, all data is encrypted before transmission, and user identifiers (which would reveal an identity) are not used over the air. Instead, GSM transmits a temporary identifier (TMSI), which is newly assigned by the VLR after each location update. Additionally, the VLR can change the TMSI at any time. Three algorithms have been specified to provide security services in GSM. Q11: How is localisation, location update,roaming,etc done in GSM & reflected in the database? What are typical roaming scenarios? List the enities of mobile IP & describe data transfer from mobile node to a fixed node & vice versa? Why & where encapsulation needed? Ans:One fundamental feature of the GSM system is the automatic, worldwide localization of users. The system always knows where a user currently is, and the same phone number is valid worldwide. To provide this service, GSM performs periodiclocation updates even if a user does not use the mobile station (provided that the MS is still logged into the GSM network and is not completely switched off). The HLR always contains information about the current location (only the location area, not the precise geographical location), and the VLR currently responsible for the MS informs the HLR about location changes. As soon as an MS moves into the range of a new VLR (a new location area), the HLR sends all user data needed to the new VLR. Changing VLRs with uninterrupted availability of all services is also called roaming. Roaming can take place within the network of one provider, between two providers in one country (national roaming is,often not supported due to competition between operators), but also between different providers in different countries (international roaming). Typically, people associate international roaming with the term roaming as it is this type of roaming that makes GSM very attractive: one device, over 190 countries!To locate an MS and to address the MS, several numbers are needed: ● Mobile node (MN): A mobile node is an end-system or router that can change its point of attachment to the internet using mobile IP. The MN

keeps its IP address and can continuously communicate with any other system in the internet as long as link-layer connectivity is given. Mobile nodes are not necessarily small devices such as laptops with antennas or mobile phones; a router onboard an aircraft can be a powerful mobile node.

● Correspondent node (CN): At least one partner is needed for communication. In the following the CN represents this partner for the MN. The CN can be a fixed or mobile node. ● Home network: The home network is the subnet the MN belongs to with respect to its IP address. No mobile IP support is needed within the home network. ● Foreign network: The foreign network is the current subnet the MN visits and which is not the home network. ● Foreign agent (FA): The FA can provide several services to the MN during its visit to the foreign network. The FA can have the COA (defined below), acting as tunnel endpoint and forwarding packets to the MN. The FA can be the default router for the MN. FAs can also provide security services because they belong to the foreign network as opposed to the MN which is only visiting. For mobile IP functioning, FAs are not necessarily needed. Typically, an FA is implemented on a router for the subnet the MN attaches to. ● Care-of address (COA): The COA defines the current location of the MN from an IP point of view. All IP packets sent to the MN are delivered to the

COA, not directly to the IP address of the MN. Packet delivery toward the MN is done using a tunnel, as explained later. To be more precise, the COA marks the tunnel endpoint, i.e., the address where packets exit the tunnel. There are two different possibilities for the location of the COA: ● Foreign agent COA: The COA could be located at the FA, i.e., the COA is an IP address of the FA. The FA is the tunnel end-point and forwards packets to the MN. Many MN using the FA can share this COA as common COA. ● Co-located COA: The COA is co-located if the MN temporarily acquired an additional IP address which acts as COA. This address is now topologically correct, and the tunnel endpoint is at the MN. Co-located addresses can be acquired using services such as DHCP (see section 8.2). One problem associated with this approach is the need for additional addresses if MNs request a COA. This is not always a good idea considering the scarcity of IPv4 addresses. ● Home agent (HA): The HA provides several services for the MN and is located in the home network. The tunnel for packets toward the MN starts at the HA. The HA maintains a location registry, i.e., it is informed of the MN’s location by the current COA. Three alternatives for the implementation of an HA exist. ● The HA can be implemented on a router that is responsible for the home network. This is obviously the best position, because without optimizations to mobile IP, all packets for the MN have to go through

the router anyway. ● If changing the router’s software is not possible, the HA could also be implemented on an arbitrary node in the subnet. One disadvantage of this solution is the double crossing of the router by the packet if the MN is in a foreign network. A packet for the MN comes in via the router; the HA sends it through the tunnel which again crosses the router. ● Finally, a home network is not necessary at all. The HA could be again on the ‘router’ but this time only acting as a manager for MNs belonging to a virtual home network. All MNs are always in a foreign network with this solution. The example network in Figure 8.1 shows the following situation: A CN is connected via a router to the internet, as are the home network and the foreign network. The HA is implemented on the router connecting the home network with the internet, an FA is implemented on the router to the foreign network. The MN is currently in the foreign network. The tunnel for packets toward the MN starts at the HA and ends at the FA, for the FA has the COA in this example.

IP packet delivery packet delivery to and from the MN using the example network of Figure 8.1. A correspondent node CN wants to send an IP packet to the MN. One of the requirements of mobile IP was to support hiding the mobility of the MN. CN does not need to know anything about the MN’s current location

and sends the packet as usual to the IP address of MN (step 1). This means that CN sends an IP packet with MN as a destination address and CN as a source address. The internet, not having information on the current location of MN, routes the packet to the router responsible for the home network of MN. This is done using the standard routing mechanisms of the internet. The HA now intercepts the packet, knowing that MN is currently not in its home network. The packet is not forwarded into the subnet as usual, but encapsulated and tunnelled to the COA. A new header is put in front of the old IP header showing the COA as new destination and HA as source of the encapsulated packet (step 2). (Tunneling and encapsulation is described in more detail in section 8.1.6.) The foreign agent now decapsulates the packet, i.e., removes the additional header, and forwards the original packet with CN as source and MN as destination to the MN (step 3). Again, for the MN mobility is not visible. It receives the packet with the same sender and receiver address as it would have done in the home network.

Ans:- 12

Wireless access techinques used are: 1G:- FDMA 2G:- FDMA/ TDMA 2.5G:- TDMA based GSM System/CDMA 3G:- CDMA2000/WCDMA

Three Classes of wireless data networking are: 1. Wireless Personal Area Networks (WPANs) 2. Wireless LAN 3. Wireless MAN 4. WirelessWAN Q13: Define the roles of WPAN technology in wireless data networking? Ans: IEEE 802.15.4-2003 standard for Low-Rate Wireless Personal Area Networks (LR-WPANs), such as wireless light switches with lamps, electrical meters with in-home-displays, consumer electronics equipment via short-range radio needing low rates of data transfer. The technology defined by the ZigBee specification is intended to be simpler and less expensive than other WPANs, such as Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low data rate, long battery life, and secure networking. WPAN technologies enable users to establish ad hoc, wireless communications for devices (such as PDAs, cellular phones, or laptops) that are used within a personal operating space (POS). A POS is the space surrounding a person, up to a distance of 10 meters. Currently, the two key WPAN technologies are Bluetooth and infrared light. Bluetooth is a cable replacement technology that uses radio waves to transmit data to a distance of up to 30 feet. Bluetooth data can be transferred through walls, pockets, and briefcases. Technology development for Bluetooth is driven by the Bluetooth Special Interest Group (SIG), which published the Bluetooth version 1.0 specification in 1999. Alternatively, to connect devices at a very close range (1 meter or less), users can create infrared links. To standardize the development of WPAN technologies, IEEE has established the 802.15 working group for WPANs. This working group is developing a WPAN standard, based on the Bluetooth version 1.0 specification. Key goals for this draft standard are low complexity, low power consumption, interoperability, and coexistence with 802.11 networks. Q14: List the main features of 3G systems? Ans:Main features of 3G System are:

The most significant features of the 3G technology is that is supports greater voice and data capacity and higher data transfer rate at the lowest cost both in the rural and urban areas. 3G uses the radio spectrum, which allows the transmission of 384 kb/s for the mobile systems and the 2mb/s for the stationary systems. Today more telecommunication networks in the world are being upgraded to the 3G technologies because of its greater features, scalability, higher voice and data transfer rates and better performance than the 2G tec Combines a mobile phone, laptop PC and TV Features includes: - Phone calls/fax - Global roaming - Send/receive large email messages - High-speed Web Navigation/maps Videoconferencing - TV streaming - Electronic agenda meeting reminder. Speed: 144kb/sec-2mb/sec Time to download a 3min MP3 song: 11sec-1.5min

Q15. What is the role of GPRS in enhancing 2G GSM system? ANS: General Packet Radio Service (GPRS) in GSM GPRS has been standardized to optimally support a wide range of applications ranging from very frequent transmission of medium to large data volume and infrequent transmission of large data volume. Services of GPRS have been developed to reduce connection setup time and allow an optimum usage of radio resources. GPRS provides a packet data service for GSM where time slots on the air interface can be assigned to GPRS over which packet data from several mobile stations is multiplexed.

GPRS provides a core network platform for current GSM operators not only to expand the wireless data market in preparation for the introduction of 3G services, but also a platform on which to build IMT-2000 frequencies should they acquire them. GPRS enhances GSM data services significantly by providing end-to-end packetswitched data connections. This is particularly efficient in Internet/intranet traffic, where short bursts of intense data communications activity are interspersed with relatively long periods of inactivity. Because there is no real end-to-end connection to be established, setting up a GPRS call is almost instantaneous and users can be continuously online. Users have the additional benefit of paying for the actual data transmitted, rather than for connection time. Because GPRS does not require any dedicated end-to-end connection, it only uses network resources and bandwidth when data is actually being transmitted. This means that a given amount of radio bandwidth can be shared efficiently and simultaneously among many users. The implementation of GPRS has a limited impact on the GSM core network. It simply requires the addition of new packet data switching and gateway nodes, and an upgrade to existing nodes to provide a routing path for packet data between the wireless terminal and a gateway node. The gateway node provides interworking with external packet data networks

for access to Internet, intranets, and databases.

A GPRS architecture for GSM is shown in Figure…… GPRS will support all widely used data communications protocols, including IP, so it will be possible to connect with any data source from anywhere in the world using a GPRS mobile terminal. GPRS will support applications ranging from low-speed short messages to high-speed corporate LAN communications. However, one of the key benefits of GPRS—that it is connected through the existing GSM air interface modulation scheme—is also a limitation, restricting its potential for delivering data rates higher than 115 kbps. To build even higher rate data capabilities into GSM, a new modulation scheme is needed. GPRS can be implemented in the existing GSM systems. It requires only minor changes in an existing GSM network. The base station subsystem (BSS) consists of base

station controller (BSC) and packet control unit (PCU). The PCU supports all GPRS protocols for communication over the air interface. Its function is to set up, supervise, and disconnect packet-switched calls. PCU supports cell change, radio resource configuration, and channel assignment. The base transceiver station (BTS) is a relay station without protocol functions. It performs modulation and demodulation. The GPRS standard introduces two new nodes, the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN). The home location register (HLR) is enhanced with GPRS subscriber data and routing information. Two types of services are provided by GPRS: • Point-to-point (PTP) • Point-to-multipoint (PTM) Packet data transmission speeds were later increased via EDGE for 2G GSM. Enhanced Data rates for GSM Evolution (EDGE) (also known as Enhanced GPRS (EGPRS) is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM. EDGE is considered a pre-3G radio technology and is part of ITU's 3G definition. EDGE is standardized by 3GPP as part of the GSM family. EDGE can be used for any packet switched application, such as an Internet connection. EDGE provides an evolutionary path that enables existing 2G systems (GSM, IS136) to deliver 3G services in existing spectrum bands. The advantages of EDGE include fast availability, reuse of existing GSM, IS-136, and PDC infrastructure, as well as support for gradual introduction of 3G capabilities. EDGE reuses the GSM carrier bandwidth and time slot structure. EDGE can be seen

as a generic air interface for efficiently providing high bit rates, facilitating an evolution of existing 2G systems toward 3G systems. EDGE (2.5G system) [7,8] was designed to enhance user bandwidth through GPRS. This is achieved through the use of higher-level modulation schemes. Although EDGE reuses the GSM carrier bandwidth and time slot structure, the technique is by no means restricted to GSM systems; it can be used as a generic air interface for efficient provision of higher bit rates in other TDMA systems. In the Universal Wireless Communications Consortium (UWCC), the 136 high-speed (136 HS) radio interface was proposed as a means of satisfying the requirements for an IMT-2000 RTT. EDGE was adopted by UWCC in 1998 as the outdoor component of 136 HS to provide 384-kbps data service. The standardization effort for EDGE has two phases. In the first phase the emphasis has been placed on enhanced GPRS (EGPRS) and enhanced CSD (ECSD). The second phase is being defined with improvements for multimedia and real-time services as possible work items. EDGE is primarily a radio interface improvement, but it can also be viewed as a system concept that allows GSM and IS-136 networks to offer a set of new services. EDGE has been designed to improve S/I by using link quality control. Link quality control adapts the protection of the data to the channel quality so that an optimal bit rate is achieved for all channel qualities. The EDGE air interface is designed to facilitate higher bit rates than those currently achievable in existing 2G systems. The modulation scheme based on 8-PSK is used to

increase the gross bit rate. GMSK modulation as defined in GSM is also part of the EDGE system. The symbol rate is 271 kbps for both GMSK and 8-PSK, leading to gross bit rates per time slot of 22.8 kbps and 69.2 kbps, respectively. The 8-PSK pulse shape is linearized GMSK to allow 8-PSK to fit into the GSM spectrum mask. The 8-PSK burst format is similar to GSM

In order to achieve a higher gross rate, a new modulation scheme, quaternary offset quadrature amplitude modulation (QOQAM), has been proposed for EDGE, since it can provide higher data rates and good spectral efficiency. An offset modulation scheme is proposed because it gives smaller amplitude variation than 16-QAM, which can be beneficial when using nonlinear amplifiers. EDGE will coexist with GSM in the existing frequency plan and will provide link adaptation (i.e., modulation and coding are adapted for channel conditions). Radio Protocol Design The radio protocol strategy in EDGE is to reuse the protocols of GSM/GPRS whenever possible, thus minimizing the need for new protocol implementation. EDGE enhances both GSM circuit-switched (HSCSD) and packet-switched (GPRS) mode operation. EDGE includes one packet-switched (PS) and one circuit-switched (CS) mode, EGPRS and ECSD, respectively. Enhanced GPRS (EGPRS). The EDGE radio link control (RLC) protocol is somewhat different from the corresponding GPRS protocol. The main changes are related to improvements

in the link quality control scheme. A link adaptation scheme regularly estimates the link quality and subsequently selects the most appropriate modulation and coding scheme for transmission to maximize the user bit rate. The link adaptation scheme offers mechanisms for choosing the best modulation and coding alternative for the radio link. In GPRS, only the coding schemes can be changed between two consecutive link layer control (LLC) frames. In the EGPRS, even the modulation can be changed. Different coding and modulation schemes enable adjustment for the robustness of the transmission according to the environment.

Services Offered by EDGE PS Services. The GPRS architecture provides IP connectivity from mobile station to an

external fixed IP network. For each service, a quality of service (QoS) profile is defined. The QoS parameters include priority, reliability, delay, and maximum and mean bit rate. A specified combination of these parameters defines a service, and different services can be selected to suit the needs of different applications. CS Services. The current GSM standard supports both transparent and nontransparent services. Eight transparent services are defined, offering constant bit rates in the range of 9.6 to 64 kbps. Thus, EDGE CS transmission makes the high-bit-rate services available with fewer time slots, which is advantageous from a terminal implementation perspective. Additionally, more users can be accepted since each user needs fewer time slots, which increases the capacity of the system. Q16..show how CDMA IS-95 systems are moving to provide 3G services.? Soluiton16.. 2G CDMA Cellular (IS-95) GSM uses TDMA, but who uses CDMA in 2G? While some systems have appeared, IS-95 is the best-known example of 2G with CDMA. Recall that in the case of CDMA, each user is assigned a unique code that differentiates one user from others. This is in contrast to TDMA where each user is assigned a time slot. Why use CDMA for cellular? Although the debate between CDMA versus TDMA has been raging for a while (see Section 8.5.5), there are

several advantages of CDMA for cellular networks. The main advantage of CDMA is that many more users (up to 10 times more) can be supported as compared to TDMA. Although this leads to some complications (see Section 8.5.5), the advantage of supporting more users far outweighs the disadvantage of added complexity. The IS-95 cellular system has different structures for its forward (base station to mobile station) and backward links. The forward link consists of up to 64 logical CDMA channels, each occupying the same 1228 kHz bandwidth. The forward channel supports 4 different types of channels: � Traffic channels (channels 8 to 31 and 33 to 63) – these 55 channels are used to carry the user traffic (originally at 9.6 Kbps, revised at 14.4 Kbps). � Pilot (Channel 0) – used for signal strength comparison, among other things, to determine handoffs � Synchronization (Channel 32) – a 1200 bps channel used to identify the cellular system (system time, protocol revision, etc.). � Paging (channels 1 to 7) – messages for mobile stations

All these channels use the same frequency band – the chipping code (a 64-bit code) is used to distinguish between users. Thus 64 users can theoretically use the same band by using different codes. This is in contrast to TDMA where the band has to be divided into slots – one slot per user. The voice and data traffic is encoded, assigned a chipping code, modulated and sent to its destination. The data in the reverse travels on the IS-95 reverse links. The reverse links consist of up to 94 logical CDMA channels, each occupying the 1228 kHz bandwidth. The reverse link supports up to 32 access channels and up to 62 traffic channels. The reverse links support many mobile unit-specific features to initiate calls, and to update location during handoffs. The overall architecture of 2G CDMA-based systems are similar to the TDMAbased GSM systems (see Figure 8-10). The main difference is that the radio communication between the Base Station Subsystem and Mobile System uses CDMA instead of TDMA. Of course, the MSC now has to worry about handling soft handoffs, but the overall structure stays the same. 8.5.5 Controversy: CDMA Versus TDMA

There are conflicting performance claims for CDMA and TDMA. The debate is raging because hardware vendors have chosen sides and consequently the standardizing bodies have been lobbied hard. The primary motivation for this level of debate is that vendors want their selection to become the industry standard. Since both TDMA and CDMA have become TIA (Telecom Industry Association) standards – IS-54 and IS-95, respectively – the debate goes on to determine which standard is better. Technically speaking, CDMA has the following advantages over TDMA. � Network capacity: In CDMA, the same frequency can be reused in adjacent cells because the user signals differentiate from each other by a code. Thus frequency reuse can be very high and many more users (up to 10 times more) can be supported as compared to TDMA. � Privacy: Privacy is inherent in CDMA since spread spectrum modulates data to signals randomly (you cannot understand the signal unless you know the randomizing code). � Reliability and graceful degradation: CDMA-based networks only gradually degrade

as more users access the system. This is in contrast to the sudden degradation of TDMAbased systems. For example, if the channel is divided between ten users, then the eleventh user can get a busy signal in a TDMA system. This is not the case with CDMA because there is no hard division of channel capacity – CDMA can handle users as long as it can differentiate between them. In case of CDMA, the noise and interference increases gradually as more users are added because it becomes harder to differentiate between various codes. � Frequency diversity: CDMA uses spread spectrum, thus transmissions are spread over a larger frequency bandwidth. Consequently, frequency-dependent transmission impairments that occur in certain frequency ranges have less effect on the signal. � Environmental: Since existing cells can be upgraded to handle more users, the need for new cell towers decreases.

But, there are some drawbacks of CDMA cellular also: � Relatively immature. As compared to TDMA, CDMA is a relatively new technology; but it is catching up fast. � Self-jamming. CDMA works better if all mobile users are perfectly aligned on chip (code) boundaries. If this is not the case, then some interference can happen. This situation is better with TDMA and FDMA because time and frequency guard bands can be used to avoid the overlap.

� Soft handoff. An advantage of CDMA is that it uses soft handoff (i.e., two cells can own a mobile user for a while before the handoff is complete). However, this requires that the mobile user acquires the new cell before it relinquishes the old – a more complex process than hard handoff used in FDMA and TDMA schemes. The main advantage of CDMA is that the frequency reuse can be very high and many more users can be supported in a cell as compared to TDMA. Although this leads to a soft handoff that is more complicated than the hard handoff used in TDMA, the advantage of supporting more users far outweighs the disadvantage of added complexity

Q17..show how 2G GSm systems are moving to achieve 3G services? ANS:

: A Step-by-Step Towards IMT-2000 (UMTS) 3G

UMTS: atat384 UMTS: 384 Kbps and Kbps andaamax max speed of speed of22Mbps Mbps

EDGE: up EDGE: up to 384 384Kbps Kbps

2.5G

2G

GPRS: variable GPRS: variable speeds, speeds,depending depending on configuration. configuration. on ~~57 14and and114 28Kbps Kbps 2001 by midmid-2001

HSCSD: dial HSCSD: dial-up -up access atatup access uptoto 57.6 Kbps 57.6 Kbps

GSM GSMatat 9.6 Kbps 9.6 Kbps

2G SYSTEMS The development of the digital technology, on one hand, and frequent cases when analog systems reached their full capacity, especially in big cities, on the other hand, led to the development of the second-generation (2G) systems. 

The main aim in the design of the 2G systems was the maximization of the system capacity measured as the number of users per spectrum per unit area.

 2G networks are digital, both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system. 

Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted, more efficient on the spectrum allowing for far greater mobile phone penetration levels; and data services for mobile, starting with SMS. CAPACITY OF 2G SYSTEM Using digital signals system capacity in two key ways:

 Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be packed into the same amount of radio bandwidth.  The digital systems were designed to emit less radio power from the handsets. The cells are smaller, so more cells could be placed in the same amount of space. DRAWBACKS OF 2G  There are drawbacks to the current GSM: 

The GSM is a circuit switched, connection oriented technology, where the end systems are dedicated for the entire call session. This causes inefficiency in usage of bandwidth and resources.



The GSM-enabled systems do not support high data rates.



They are unable to handle complex data such as video.



These devices have small hardware configurations with less powerful CPUs, memory and display units, and support simple functionality.



Only basic messaging services such as SMS can be supported.



The GSM networks are not compatible with the current TCP/IP and other common networks because of differences in network hardware, software and protocols Evolution of Wireless Sys. (2.5G)

• 2G telephony is highly successful • Enhancement to 2G on data service – GSM: HSCSD and GPRS – IS-95: IS-95b – IS-136: D-AMPS+ and CDPD

• The improved data rate is still too low to support multimedia traffic • ITU initiated 3G standardization effort in 1992, and the outcome is IMT2000. Goals of 3G Systems  More services  Web browsing  VoD  Video phone call  Mobile computation  Improved quality  Higher rates: 2.048 Mbps for low speed users, 384 Kbps for modest speed users and 144 Kbps for high speed users  More reliable and larger capacity  Compatible with 2G systems  More flexible  Support both circuit-switching and packet-switching  Work in hierarchical mode with pico-/micro-/macro-cells Support asymmetric services Paradigm From 1G to Beyond 3G

2G EVOLUTION TO 3G

Q18:what are the data rate requirements for 3g system Third generation cellular systems are being designed to support wideband services like high speed Internet access, video and high quality image transmission with the same quality as the fixed networks. The primary requirements of the next generation cellular systems are [1]: • Voice quality comparable to Public Switched Telephone Network (PSTN). • Support of high data rate. The following table shows the data rate requirement of the 3G systems Table 1.1: 3G Data Rate Requirements Mobility Needs Vehicular

Minimum Data Rate 144 kbps

Outdoor to indoor and pedestrian

384 kbps

Indoor Office

2 Mbps

• Support of both packet-switched and circuit-switched data services. • More efficient usage of the available radio spectrum • Support of a wide variety of mobile equipment • Backward Compatibility with pre-existing networks and flexible introduction of new services and technology • An adaptive radio interface suited to the highly asymmetric nature of most

Internet co Q 19: define ip wireless tecnology IPWireless is the broadband technology based upon UMTS(Universal Mobile Telecommunications System). It uses either 5 or 10 MHz TDD carriers and QPSK(quadrature phase shift keying ) modulation. The theoretical peak transmission speeds for a 10MHz deployment are 6 Mbps downlink and 3 Mbps uplink. The IPWireless system only uses QPSK modulation and no advanced antenna technologies. With the inclusion of advanced antenna technologies and the development of High-Speed Downlink Packet Access (HSDPA), IPWireless has signifi cant potential. SOMA networks has also developed a wireless broadband technology based on UMTS. Like UMTS, SOMA’s technology uses 5 MHz FHSS carriers. Peak throughput is claimed to be as high as 12 Mbps, making SOMA one of the faster wireless broadband technologies. mmunications: a much greater bandwidth for the downlink than the uplink.

Q20: compare 3g and 4g. Motivation for 4G Research Before 3G Has Not Been Deployed? 1. 3G performance may not be sufficient to meet needs of future highperformance applications like multi-media, full-motion video, wireless teleconferencing. We need a network technology that extends 3G capacity by an order of magnitude. 2. There are multiple standards for 3G making it difficult to roam and interoperate across networks. we need global mobility and service portability

3. 3G is based on primarily a wide-area concept. We need hybrid networks that utilize both wireless LAN (hot spot) concept and cell or base-station wide area network design. 4. We need wider bandwidth 5. Researchers have come up with spectrally more efficient modulation schemes that can not be retrofitted into 3G infrastructure 6. We need all digital packet network that utilizes IP in its fullest form with converged voice and data capability. Comparing Key Parameters of 4G with 3G 3G (including 2.5G, sub3G)

4G

Predominantly voice driven - data was always add on

Converged data and voice over IP

Network Architecture

Wide area cell-based

Hybrid - Integration of Wireless LAN (WiFi, Bluetooth) and wide area

Speeds

384 Kbps to 2 Mbps

20 to 100 Mbps in mobile mode

Major Requirement Driving Architecture

Frequency Band Dependent on country Higher frequency or continent (1800bands (2-8 GHz) 2400 MHz) Bandwidth

5-20 MHz

100 MHz (or more)

Switching Design Basis

Circuit and Packet

All digital with packetized voice

Access Technologies

W-CDMA, 1xRTT, Edge

OFDM and MCCDMA (Multi Carrier CDMA)

Forward Error Correction

Convolutional rate 1/2, 1/3

Concatenated coding scheme

Component Design

Optimized antenna design, multi-band adapters

Smarter Antennas, software multiband and wideband radios

IP

A number of air link protocols, including IP 5.0

All IP (IP6.0)

Ques21 What is multi input multi output (MIMO) system? Explain. Answer Systems with more than one input or more than one output are known as Multi-Input Multi-Output systems. MIMO is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology. The terms input and output refer to the radio channel carrying the signal, not to the devices having antennas. MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency have more bits per second per hertz of bandwidth and link reliability or diversity. Because of these properties, MIMO is an important part of modern wireless communication standards such as IEEE 802.11n (Wifi), 4G, WiMAX etc. MIMO Technology Uses Multiple Radios to Transfer More Data at the Same Time

MIMO technology leverages multipath behavior by using multiple, “smart” transmitters and receivers with an added “spatial” dimension to dramatically increase performance and range. MIMO allows multiple antennas to send and receive multiple spatial streams at the same time. This allows antennas to transmit and receive simultaneously. MIMO makes antennas work smarter by enabling them to combine data streams arriving from different paths and at different times to effectively increase receiver signal-capturing power. Smart antennas use spatial diversity technology, which puts surplus antennas to good use. In order to implement MIMO, either the station (mobile device) or the access point (AP) need to support MIMO. Optimal performance and range can only be obtained when both the station and the AP support MIMO. Legacy wireless devices can’t take advantage of multipath because they use a Single Input, Single Output (SISO) technology. Systems that use SISO can only send or receive a single spatial stream at one time. MIMO technology takes advantage of a radio-wave phenomenon called multipath where transmitted information bounces off walls, ceilings and other objects, reaching the receiving antenna multiple times via different angles and at slightly different times. Question 22 What is the software defined radio system? Answer Software Defined Radio (SDR) refers to the technology wherein software modules running on a generic hardware platform consisting of DSPs

and general purpose microprocessors are used to implement radio functions such as generation of transmitted signal (modulation) at transmitter and tuning/detection of received radio signal (demodulation) at receiver. A radio that includes a transmitter in which the operating parameters of the transmitter including the frequency range, modulation type or maximum radiated or conducted output power can be altered by making a change in software without making any hardware changes. A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as a waveforms) based solely on the software used. Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time. Software-defined radios are expected by proponents like the SDRForum (now The Wireless Innovation Forum) to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio. Motivation of SDR Commercial wireless communication industry is currently facing problems due to constant evolution of link-layer protocol standards (2.5G, 3G, and 4G) existence of incompatible wireless network technologies in different countries inhibiting deployment of global roaming facilities problems in rolling-out new features due to wide-spread presence of legacy subscriber handsets. Applications Military, Real-time flexibility, Secure International connectivity, Portable command for crisis management, Bluetooth, WLAN, GPS, Radar, WCDMA, GPRS, GSM, AM, FM, etc. Features Reconfigurability, future-proof, multi-service, multi-mode, multiband, multistandard terminals and infrastructure equipment, Ubiquitous Connectivity, Interoperability, SDR facilitates implementation of open architecture radio

systems. Programmability Hardware radio, no software changes, Software controlled radio in PDR, BB operations and link layer protocols are implemented in software. Question 23 List some of the new technologies that will be used in the 4G system? Answer The new technologies used in the 4G system are 4G mobile systems focus on seamless integration of existing wireless technologies including WWAN, WLAN and Bluetooth. 4G standards setting peak speed requirements for 4G service at 100 Mbit/s for high mobility communication (such as from trains and cars) and 1 Gbit/s for low mobility communication (such as pedestrians and stationary users). The 4G systems will encompass all systems from various networks, public to private, operator-driven broadband networks to personal areas, and ad hoc networks. The 4G intends to integrate from satellite broadband to high altitude platform to cellular 2G and 3G systems to wireless local loop (WLL) and broadband wireless access (BWA) to WLAN, and wireless personal area networks (WPANs). A 4G system is expected to provide a comprehensive and secure all-IP based mobile broadband solution to laptop computer wireless modems, smartphones and other mobile devices. Facilities such as ultrabroadband Internet access, IP telephony, gaming services and streamed multimedia may be provided to users. A 4G system can provide a comprehensive IP solution where voice, data and streamed multimedia can be provided to users on an "Anytime, Anywhere" basis. The data transfer rates are also much higher than previous generations. The main objectives of 4G are:1) 4G will be a fully IP-based integrated system. 2) This will be capable of providing 100 Mbit/s and 1 Gbit/s speeds both indoors and outdoors. 3) It can provide premium quality and high security. 4) 4G offer all types of services at an affordable cost. 4G is developed to provide high quality of service (QoS) and rate requirements set by forthcoming applications such as wireless broadband access, Multimedia Messaging, Video Chat, Mobile TV, High definition TV content, DVB, minimal service like voice and data and other streaming services. 4G technology allow high-quality smooth video transmission. It will enable fast downloading of full-

length songs or music pieces in real time. 4G mobile data transmission rates are planned to be up to 20 megabits per second which means that it will be about 1020 times faster than standard ASDL services. Technologies Multicarrier Modulation Multicarrier modulation (MCM) is a derivative of frequency-division multiplexing. It is not a new technology. Forms of multicarrier systems are currently used in DSL modems and digital audio/video broadcast (DAB/DVB). MCM is a baseband process that uses parallel equal bandwidth sub channels to transmit information and is normally implemented with fast Fourier transform (FFT) techniques. MCM’s advantages are better performance in the inter-symbol-interference environment and avoidance of single-frequency interferers. Smart Antenna Techniques Smart antenna techniques, such as multiple-input multiple-output (MIMO) systems, can extend the capabilities of the 3G and 4G systems to provide customers with increased data throughput for mobile highspeed data applications. MIMO systems use multiple antennas at both the transmitter and receiver to increase the capacity of the wireless channel. Single-input, multiple-output There are N antennas at the receiver. If the signals received on the antennas have on average the same amplitude, then they can be added coherently to produce an N2 increase in signal power. Multiple-input, single-output We have M transmitting antennas. The total power is divided into M transmitter branches. Multiple-input, multiple-output MIMO systems can be viewed as a combination of MISO and SIMO channels. OFDM-MIMO Systems OFDM and MIMO techniques can be combined to achieve high spectral efficiency and increased throughput. The OFDM-MIMO system transmits independent OFDM modulated data from multiple antennas simultaneously. At the receiver, after OFDM demodulation, MIMO decodes each subchannel to extract data from all transmit antennas on all the subchannels. Q.no 24 What is the basic requirement & entity involed for the mobility management? Ans: MOBILITY MANAGEMENT

Mobility management contains two components:Location management and handoff management [2]. A. Location Management Location management is a two-stage process that enablesthe network to discover the current attachment point of themobile user for call delivery, as shown in Fig. 1. The firststage is location registration (or location update). In this stage,the mobile terminal periodically notifies the network of its newaccess point, allowing the network to authenticate the user andrevise the user’s location profile. The second stage is call delivery. Here the network is queried for the user location profile and the current position of the mobile host is found

Fig.1. Location management operations

B. Handoff Management Handover (or handover) management enables the network tomaintain a user’s connection as the mobile terminal continues Mobility Management in NextGenerationWireless Systems

Fig. 2. Handoff management operations To move and change its access point to the network. The threestage process for handoff first involves initiation, where either the user, a network agent, or changing network conditions identify the need for handoff. The second stage is new connection generation, where the network must find new resources for the handoff connection and perform any additional routing operations. Under networkcontrolled handoff (NCHO)[11], or mobile-assisted handoff (MAHO), the network generates a new connection, finding new resources for the handoff and performing any additional routing operations. For mobile-controlled handoff (MCHO)[10], the mobile terminal finds the new resources and the network approves. The final stage is data-flow control, where the delivery of the data from the old connection path to the new connection path is maintained according to agreed upon service mobile terminal finds the new resources and the network approves. The final stage is dataflow control, wherethe delivery of the data from the old connection path to the new connection path is maintained according to agreed-upon service guarantees. The handoff management operations are presented in Fig. 2. Handoff management includes two conditions:

Intracell handoff and intercell handoff. Intracell handoff occurs when the user moves within a service area (or cell) and experiences signal strength deterioration below a certain threshold that results in the transfer of the user’s calls to new radio channels of appropriate strength at the same base station (BS) [11]. Intercell handoff occurs when the user moves into an adjacent cell and all of the terminal’s connections must be transferred to a new BS. While performing handoff, the terminal may connect to multiple BS’s simultaneously and use some form of signaling diversity to combine the multiple signals. This is called soft handoff. On the other hand, if the terminal stays connected to only one BS at a time, clearing the connection with the former BS immediately before or after establishing a connection with the target BS, then the process is referred to as hard handoff. MOBILITY MANAGEMENT FOR THE PLMN In ordinary wire line networks, such as the telephonenetwork, there is a fixed relationship between a terminal andits location[8]. Changing the location of a terminal generally involves the network administration and it cannot easily be performed by a user. Incoming calls for a particular terminal are always routed to its associated location as there is no distinction between a terminal and its location [9]. In contrast, mobile terminals (MT’s) are free to travel and thus the network access point of an MT changes as it moves around the network coverage area. As a result, the ID of an MT does not implicitly provide the location information of the MT and the call delivery process becomes more complex. In order to perform the registration, update, and call delivery operations described above, the network stores the location information of each MT in the location databases. Then the information can be retrieved for call delivery.Current schemes[3] for PLMN location management arebased on a two-level data hierarchy such that two types of network location database, the home location register (HLR) and the visitor location register (VLR), are involved in tracking an MT. In general, there is an HLR for each network and a User is permanently associated with an HLR in his/her subscribed network. Information about each user, such as the types of services subscribed and location information are stored in a user profile located at the HLR. The number of VLR’s and their placements vary among networks. Each

VLR stores the information of the MT’s (downloaded from the HLR) visiting its associated area.

Fig. 3. SS7 signaling network. Network management functions, such as call processing and location registration, are achieved by the exchange of signaling messages through a signaling network. Signaling System 7 (SS7) [5] is the protocol used for signaling exchange, and the signaling network is referred to as the SS7 network the type of CSS currently implemented for the PLMN is known as a mobile switching center (MSC). Fig. 3 shows the SS7 signaling network which connects the HLR, the VLR’s, and the MSC’s in a PLMN based network. The signal transfer points (STP’s) as shown in Fig. 3 are responsible for routing signaling. Messages within the SS7 network. For reliability reason, the STP’s are installed in pairs. As mentioned previously, location management includes two major tasks: location registration (or update) and calldelivery (see Fig. 1). For PLMN, the location registrationprocedures update the location databases (HLR and VLR’s)and authenticate the MT when up-to-date location informationof an MT is available. The call delivery procedures locate the MT based on the information available at the HLR and the VLR’s when a call for an MT is initiated. The IS-41 and the GSM MAP location management strategies are very similar to each other. While GSM MAP is designed to facilitate personal mobility and to enable user selection of network provider, there are a lot of commonalities between the two standards.

1. Location Registration: In order to correctly deliver calls, the PLMN must keep track of the location of each MT. As described previously, location information is stored in two types of databases, VLR and HLR. As the MT’s move around the network coverage area, the data stored in these databases. To ensure that calls can be delivered successfully, the databases are periodically updated through the process called location registration.Location registration is initiated by an MT when it reports its current location to the network. We call this reporting process location update. Current systems adopt an approach such that the MT performs a location update whenever it enters a new LA. Recall that each LA consists of a number of cells and, in general, all BTS’s belonging to the same LA is connected to the same MSC. When an MT enters an LA, if the new LA belongs to the same VLR as the old LA, the record at the VLR is updated to record the ID of the new LA [14]. Otherwise, if the new LA belongs to a different VLR, a number of extra steps are required to: 1) register the MT at the new serving VLR; 2) update the HLR to record the ID of the new serving VLR; and3) deregister the MT at the old serving VLR. Fig. 4 shows the location registration procedure when an MT moves to a newLA. The following is the ordered list of tasks that areperformed during location registration. The MT enters a new LA and transmits a location updatemessage to the new BS. The BS forwards the location update message to the MSC which launches a registration query to its associated VLR. The VLR updates its record on the location of the MT. If the new LA belongs to a different VLR, the new VLR determines the address of the HLR of the MT from its mobile identification number (MIN) [10]. This is achieved by a table lookup procedure called global title translation. The new VLR then sends a location registration message to the HLR. Otherwise, location registration is complete.The HLR performs the required procedures to authenticate the MT and records the ID of the new serving VLR of the MT.

Fig. 4. Location registration procedures.

The HLR then sends a registration acknowledgment messageto the new VLR. The HLR sends a registration cancellation message to the old VLR. The old VLR removes the record of the MT and returns a cancellation acknowledgment message to the HLR. Depending on the distance between the current and the home locations of the MT, in steps 3)–6), the signaling messages may have to go through several intermediate STP’s before reaching their destinations. For example, a user who subscribes to wireless services in Atlanta will normally be assigned to an HLR located in the Atlanta area. When this user is roaming in London, each location update performed by his/her mobile phone will result in the transmission of four transatlantic SS7 messages [messages (3)–(6) as shown in Fig.6]. These messages may transverse a number of STP’s in the SS7[10] network before reaching their destinations, which generate additional load to the network elements and the transmission links. The location registration may, therefore, result in significant traffic load to the SS7 network. As the number of mobile subscribers keeps increasing, the delay for completing a location registration may increase.

Fig.6. Mobile IP location registration. Call Delivery: Two major steps are involved in calldelivery: 1) determining the serving VLR of the called MT and 2) locating the visiting cell of the called MT. Locating the serving VLR of the MT involves the following database ookup procedure (see Fig. 5).

Fig. 5. Mobile IP architecture. 1. The calling MT sends a call initiation signal to the serving MSC of the MT through a nearby BS. 2. The MSC determines the address of the HLR of the called MT by global title translation and sends a location request message to the HLR.

3. The HLR determines the serving VLR of the called MT and sends a route request message to the VLR. This VLR then forward the message to the MSC serving the MT. 4. The MSC allocates a temporary identifier called temporary local directory number (TLDN) to the MT and sends a reply to the HLR together with the TLDN. 5. The HLR forward this information to the MSC of the calling MT. 6. The calling MSC requests a call set up to the called MSC through the SS7 network. The procedure described above allows the network to set upa connection from the calling MT to the serving MSC of the called MT. Since each MSC is associated with an LA and there are more than one cell in each LA, a mechanism is therefore necessary to determine the cell location of the called MT. In current PLMN networks, this is achieved by a paging (or alerting) procedure, such that polling signals are broadcast to all cells within the residing LA of the called MT. On receiving the polling signal, the MT sends a reply which allows the MSC to determine its current residing cell. As the number of MT’s increases, sending polling signals to all cells in an LA whenever a call arrives may consume excessivewireless bandwidth Q.No 25 : Compare various mobile devices like smartphone, pc tablet and its various model available in the market? Ans: Comparision b/w smartphone and pc tablet Technically, both Tablet and Smartphone are designed to serve different purposes. But, these days every type of gadget is trying to incorporate into it the best features of other category gadgets to claim the title of an ‘All Purpose Machine’. A smartphone fulfills the criteria to a great extent. In case you are not bewildered with the amazing feats that high end mobile handsets (affectionately referred to as smartphones these days) are capable of performing, rewind your memory to one and a half decade back. Back then, mobile handsets usually had pathetic resolution and were ‘technically deficient’ (yup! This is the term I would like to use) when compared with the phones of the present generation. Ever since then, the mobile market has tried hard to bridge the gap between a high resolution display system and a computer and simple mobile handset. As a result of this, smartphones today

are in a position to take head on the other devices in the broad spectrum of sleek electronic gadgets. While the smartphone may have become really smart, still it has a long way to go to replace tablet PC’s. The presence of a thriving market for tablet PC’s is a testimony to the fact there the consumers love tablet PC’s too as do they love smartphones. In fact, there are many tasks which are enjoyable on a tablet PC rather than a mobile handset. Let’s talk about the unique strong points of both gadgets. First and foremost, the high resolution fully touch screen feature of tablet PC’s provides an ideal platform for content consumption. The basic idea is to compromise on processing power (as compared to a laptop) to give a sizeable screen which resembles the size of a book. The large screen with exceptional clarity which the Tablet PC has to offer can’t be replaced by a smartphone. Whether you wish to chalk out business plans or check your mail, a bigger screen is always better than a smaller one. If content consumption with exceptional screen resolution is your forte, then, a tablet PC is simply irresistible. Touching a pointing on a larger screen is definitely more fun. Also, if one is interested in light content creation, then too the tablet PC scores above a smartphone. Writing mail or social networking on a laptop, netbook or a tablet PC is always better than typing the same text on phone. It’s true that mobile handsets these days boast of QWERTY keyboards, but still the miniature sized keys can never offer great speed. Also, for e-book reading, nothing beats i-Pad (Apple’s tablet PC). For students too, an i-Pad can supplement other sources and can make the process of learning easier and more efficient. Coming to smartphones, they are the hottest gadgets in demand these days. Reason – they can be comfortably carried around in a pocket and have processing power similar to a basic computer. A smartphone is essentially designed to be handy throughout the day. Checking mail, sending business documents, text messaging, video calling, social networking, savoring music, etc. is achieved effortlessly at the push of a button. It ideally connects you to the world. To top all this, AMOLED screens, innumerable amazing apps, nice cameras (resolution up to 8-10 mega pixels) further make life enjoyable. Their popularity stems from the fact that you don’t feel carrying something while at work which is not the case with netbooks, laptops or tablet PC’s.

Swype Technology, AllShare via DLNA, Wireless Tethering, Operation System (Google’s Android is in vogue), Mobile tracker, Augmented Reality browser, ebook reader, LAYAR REALITY BROWSER, Google™ Turn-by-Turn Navigation, and Social Hub are some cool features offered by smartphones. They also boast of good RAM, ROM and external memory. Other regular features include Bluetooth, Wifi, calendar, scheduler, world time, alarm, currency converter, memo book, stopwatch, countdown timer and a GPS mobile tracker. So, the selection of one of the two (Tablet PC or Smartphone) depends basically on the type of use. If you wish to consume content and engage in light content creation in your office or at home then, a tablet PC offers exceptional visual experience. Otherwise, for business purpose (for being connected) a smartphone would be suitable. Some people may need both. So, understand your needs and decide what you have to buy. Both are priced at around Rs. 25,000. Models of smartphone:Smartphones have emerged as the benchmark against which every mobile phone manufacturer seems to be judged by the market and the users alike. There is a constant competition among the mobile phone vendors to outsmart each other by launching the most technologically advanced smartphone loaded with every possible application. Whether it is Apple or Nokia, Samsung, HTC or BlackBerry they all offer such an amazing ensemble of smartphones that it becomes too hard to pick the best ones. Keeping in mind not just what is offered but also what is desired, some of the best or perhaps more appropriately better than the rest smartphones would be; Apple iPhone 3G S: Apple's iPhone may not have been the first smartphone but it definitely was the one that made the biggest impact and was perhaps one of the most awaited launches ever. Taking the same tradition forward Apple's latest offering iPhone 3G S is also hits the spot. It is faster than most, looks impressive, battery backup is better and of course works on 3G. Moreover, one of the hallmarks of iPhone that still remains is that owning one is treated by most as an honor. (Buy iPhone 3G S in India)

RIM BlackBerry Curve 8900: RIM's BlackBerry was the harbinger of smartphones and what RIM adds to its range still keeps enthralling users. Any list of top smartphones can never be complete without at least one of the BlackBerry's, case in point Curve 8900. This BlackBerry works brilliantly, has 3.2 megapixel camera and overall is so good that the fact that it doesn't support 3G doesn't take anything away from the phone. The GPS, BlackBerry Maps, Corporate Data Access, and Entertainment features make BlackBerry Curve 8900 a great smartphone choice. (BlackBerry Curve in India) Nokia N97: Nokia is one of the most trusted names and best manufacturers in the mobile phones market and the same impact is carried into the smartphones segment with N97. To begin with it has great looks and supports 3G. Its 5 megapixel camera takes great pictures and 32GB internal flash memory ensures it works amazingly well. Its price could be a bit of a dampener but otherwise it sure is a good buy. See Nokia N97 Review for more details. (Buy Nokia N97 in India) LG KM900 Arena: LG offers many really cool smartphones and Arena is one of the best not only among LG's phones but also across other major smartphone brands. It features a great TFT touchscreen supported by impressive interface. Its 5 megapixel autofocus camera with LED flash captures pictures that you'll love. It supports 3G, has decent battery and on a whole is a really good package. The LG KM900 Arena introduces new LG UI technology that uses 3D cubes to make the display stunningly beautiful. (Buy LG KM900 Arena in India) Samsung Memoir T929: What strikes most about Samsung Memoir T929 is its sleek and slim design and the fact that it actually looks like a camera. It also looks great when you hold it in your hands and use of TouchWiz ensures that you will be using one of the most impressive navigation interfaces that are available among the smartphones. Backed by great performance it sure deserves to be among the top five smartphones.

There are many other smartphones like Motorola MotoSurf A3100, Palm Pre, Pharos Traveler 137, etc. that all deserve to be right at the top. As for buying one, you take your pick and have all the fun you want. Q.No: 26 Describe Symbian OS Development for mobile or iphone? Ans: Symbian OS Development for mobile or iPhone Features of Symbian Operating System In: Symbian Operating System Symbian is basically an Operating System consisting libraries, UI, frameworks and reference implementations of common tools. Symbian had been made for mobile devices and smartphones. Under the establishment of non-profit foundation, Symbian was acquired by Nokia. Symbian OS were also contributed by its user with developing interfaces like S60, UIQ and MOAP(s). To make Symbian royalty-free the process of publishing the source code under EPL (Eclipse Public License) met completion in recent time in 2010. Symbian is being used in more than 45% of the smartphone market, which clearly shows how popular Symbian OS is. Symbian OS has been powering 330 million phones till date and increasing day by day. Although some of the market experts are suggesting an early market entrance to Symbian OS, expecting more popularity across the world and the cell phone market. 1) Generally, the language C++ is used in most of the symbian operating systems. But in many Symbian Operating System the operating system can also use languages like Python, Visual Basic, OPL and Perl 2) Symbian Operating System was built in such a way that it follows the three basic design rules.

The integrity and security of user data is of paramount importance. Response time must not be as small as possible. All resources are scarce. 3) Symbian OS programming is said to be event-based, and the Central Processing Unit is switched off when the running applications and programs are not linked to the event. This is achieved through a programming logic called active objects. 5) The Symbian Operating system is compatible with all kinds of devices, mostly removable media file systems. 6) Symbian Operating system 9.x which is one of the latest models has adopted a better model. 7) The Symbian system is not an Open Source software. Cell phone manufacturers, though have some parts of its source code. The Symbian applications like the Themes, games, wall papers and software’s are all SIS files which can also be easily transferred by using Bluetooth, or through the internet or through transfer using cables. Features: Location Based Services (LBS): Location Based Services (LBS) have become almost omnipresent today in all smartphones just like the ubiquitous camera, without which, a mobile phone is hard to find. LBS require smartphones with GPS functionality and are very useful to determine the exact location of self and others in real time. FreeWay: Previously, broadband or 3G speeds weren't possible on mobile phones but with today's motto of office on the go using your mobile, quick net access speeds with easy switching between different networks and connections has become an absolute must. FreeWay, which is a Symbian IP networking architecture, makes this possible and more. FreeWay delivers crystal clear and high quality audio/video streaming, VoiP calls, robust WiMax and Super 3G experience with its lightening quick download speeds. FreeWay can be easily integrated within the existing web browsers thus doing away with the need for additional development. ScreenPlay: ScreenPlay is the powerful new graphics architecture within the Symbian OS meant to deliver high-end graphics that have not been seen previously on any

mobile phone and are life-like and crystal clear. ScreenPlay offers big canvass effects on your smartphone and is specially designed for mobile interfaces that integrate HD video with high-detail games and animations. ScreenPlay ensures that your visual mobile experience is enhanced manifold while the interface remains simple and versatile. ScreenPlay is mean for both, intermediate and high-end mobile devices with hardware acceleration. Symbian OS ScreenPlay delivers all these benefits without compromising your mobile's battery life in any way. Symmetric Multi-Processing (SMP): With increasing use of resource gulping applications like high-end games, high definition videos, GPS services and others, Symbian has introduced the SMP technology for its Symbian OS. The SMP divides a resource-heavy task among multiple processors on the same chip to finish it quickly and once the task is completed, the additional processors fall dormant, thus conserving your mobile's battery life. A technology to look out for in the near future. Demand Paging: Demand Paging is a technology developed by Symbian for use in its Symbian OS versions 9.3 onwards, which makes more efficient use of the mobile's RAM by selectively loading the data and read-only code only when demanded. Previously entire DLLs were copied into the RAM by the Symbian OS whenever required but with Demand Paging only the needed DLL page is copied onto the RAM, thus conserving the onboard RAM usage. Simply, only the code that is currently needed or demanded is loaded into the RAM and not the whole code or ?page' thus, it is a more efficient way of utilizing the RAM. Q.no. 27: Describe Component & feature of Google Android, Apple iPhone, Mac OS X, Windows Mobile? Ans: Google Android Android is a software stack for mobile devices that includes an operating system, middleware and key applications. The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language. Features • • •

Application framework enabling reuse and replacement of components Dalvik virtual machine optimized for mobile devices Integrated browser based on the open source WebKit engine

• • • • • • •

Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional) SQLite for structured data storage Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF) GSM Telephony (hardware dependent) Bluetooth, EDGE, 3G, and WiFi (hardware dependent) Camera, GPS, compass, and accelerometer (hardware dependent) Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Android Architecture The following diagram shows the major components of the Android operating system. Each section is described in more detail below.

Applications Android will ship with a set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others. All applications are written using the Java programming language. Application Framework By providing an open development platform, Android offers developers the ability to build extremely rich and innovative applications. Developers are free to take advantage of the device hardware, access location information, run background services, set alarms, add notifications to the status bar, and much, much more. Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by

the framework). This same mechanism allows components to be replaced by the user. Underlying all applications is a set of services and systems, including: •

• • • •

A rich and extensible set of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data A Resource Manager, providing access to non-code resources such as localized strings, graphics, and layout files A Notification Manager that enables all applications to display custom alerts in the status bar An Activity Manager that manages the lifecycle of applications and provides a common navigation backstack

For more details and a walkthrough of an application, see the Notepad Tutorial. Libraries Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework. Some of the core libraries are listed below: • •

• • • •

System C library - a BSD-derived implementation of the standard C system library (libc), tuned for embedded Linux-based devices Media Libraries - based on PacketVideo's OpenCORE; the libraries support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG Surface Manager - manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications LibWebCore - a modern web browser engine which powers both the Android browser and an embeddable web view SGL - the underlying 2D graphics engine 3D libraries - an implementation based on OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration (where available) or the included, highly optimized 3D software rasterizer

• •

FreeType - bitmap and vector font rendering SQLite - a powerful and lightweight relational database engine available to all applications

Android Runtime Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language. Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is registerbased, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included "dx" tool. The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management. Linux Kernel Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model. The kernel also acts as an abstraction layer between the hardware and the rest of the software stack. The iPhone 4 and its predecessors are more than just fancy cell phones. With their range of features – from phone to web browser, from iPod to mobile game device – the iPhone is more like a computer that fits in your pocket and your hand than any cell phone. iPhone Specfications Physically, the iPhone 4 differs a decent amount from the iPhone 3GS and previous models, all of which were broadly similar in shape. While the overall presentation of the iPhone 4 is similar to its predecessors, it's different in that it's no longer tapered on the edges, includes a glass face on the front and back, wraps the antenna around the outside of the phone (which has caused antenna some problems), and is slightly thinner.

All iPhones offer a 3.5-inch touchscreen that employs multi-touch technology. Multi-touch allows users to control items on the screen with more than one finger simultaneously (thus the name). It’s multi-touch that enables some of the iPhone’s most famous features, such as tapping the screen twice to zoom in or “pinching” and dragging your fingers to zoom out. Other major differences between the iPhone 4 and earlier models include use of the Apple A4 processor, the inclusion of two cameras, a high-resolution screen, and improved battery life. Both phones use a trio of sensors to produce some of their best usability features, though neither model offers expandable or upgradeable memory. iPhone Features Because the iPhone is like a mini-computer, it offers the same wide range of features and functions that a computer does. The major areas of function for the iPhone are: Phone – The iPhone’s phone features are solid. It includes innovative features like Visual Voicemail and standard features like text messaging and voice dialing. Web browsing – The iPhone offers the best, most complete mobile browsing experience. Though it doesn’t support the standard Flash browser plug in, it doesn’t require dumbed-down “mobile” versions of websites, instead offering the real thing on a phone. Email – Like all good smartphones, the iPhone has robust email features and can sync to corporate email servers running Exchange. Calendar/PDA – The iPhone is a personal information manager, too, with calendar, address book, stock-tracking, weather update, and related features. iPod – A shortcut description of an iPhone is a combined cell phone and iPod, so of course its music player features offer all the advantages and coolness of iPods. Video playback – With its big, beautiful, 3.5-inch screen, the iPhone is a great choice for mobile video playback, whether using the built-in YouTube application, adding your own video, or buying or renting content from the iTunes Store. Apps – With the addition of the App Store, iPhones can now run all kinds of thirdparty programs, from games (both free and paid) to Facebook and Twitter to

restaurant finders and productivity apps. The App Store makes the iPhone the most useful smartphone around. Cameras - One major change in the iPhone is the inclusion of two camera, whereas previous models only had one. The camera on the back of the phone shoots 5megapxzel still images and takes 720p HD video. The user-facing camera allows FaceTime video chats.iPhone Home Screen With the release of iPhone firmware – the software that runs the phone - version 1.1.3, users can re-arrange the icons on their home screen. This is especially helpful once you start adding programs from the App Store, as you can group similar applications, or the ones you use the most often, together. Of course, being able to re-arrange icons also leads to some unexpected events, like all the icons on your screen shaking. iPhone Controls Though the iPhone’s coolest control features are based around the multi-touch screen, it also has a number of buttons on its face that are used for control. Home button – This button, at the bottom of the phone right below the screen, is used to wake the phone from sleep and control some onscreen features. Hold button – At the top right corner of the iPhone, you’ll find the hold button. Pressing this button locks the screen and/or puts the phone to sleep. It’s also the button used to restart the phone. Volume button – On the left side of the phone, a long button that moves up and down controls the volume of music, video, and the phone’s ringer. Ringer button – Just above the volume control is a smaller rectangular button. This is the ringer button, which allows you to put the phone into silent mode so the ringer won’t sound when calls come in. Dock Connector – This port, at the bottom of the phone, is where you plug in the cable to sync the phone with a computer, as well as accessories. Using iPhone with iTunes Like an iPod, the iPhone is synced with and managed using iTunes.

Activation - When you first get an iPhone, you activate it through iTunes and select your monthly phone plan using the software. Sync - Once the phone is activated, iTunes is used to sync music, videos, calendars and other information to the phone. Restore and Reset – Lastly, iTunes is also used to reset data on the iPhone and restore contents from backup if problems cause you to need to erase the contents of the phone.