UMTS Planning

Radio Planning Issues

Understanding UMTS ©Informa

Telecoms

Radio Planning Issues 1

W-CDMA PLANNING 1.1

2

Own and Adjacent Cell Interference Multi-path Effects Interference Sharing and Soft Capacity Limitations User Data Rates and Number of Users Sectorisation Smart Antennas Multi-Carrier Cells Planning the Frequency Spectrum The Layered Architecture GSM Co – Planning Use Of Existing Sites W-CDMA, EDGE and GSM Coverage Areas Planning Tools Monte Carlo Simulations

SUMM SUMMAR ARY Y – PLAN PLANNI NING NG CONS CONSID IDER ERA ATION TIONS S

Understanding UMTS ©Informa

Telecoms

11 13 15 17 19 21 23 25 27 28 31 33 35

RAD RADIO PLANN LANNIN ING G AND SIMUL IMULA ATIO TIONS 5.1 5.2

6

3 5 7 9

REDU REDUCI CING NG INTE INTERF RFER EREN ENCE CE/I /INC NCRE REAS ASIN ING G CAP CAPACIT ACITY Y 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8

5

Traditional Cell Planning W-CDMA Cellular Planning Principles Soft Handover Regions Cell Breathing

INTERFERENCE EFFECTS 3.1 3.2 3.3 3.4 3.5

4

1

CELL PLANNING 2.1 2.2 2.3 2.4

3

The Requirements

37 37 39

Radio Planning Issues

1. W-CDMA PLANNING 1.1 1.1 The The Requ Requir irem emen ents ts When planning any radio network there are three overall requirements to be satisfied. Coverage planning should allow services to be provided continuously over the area of operation. Fortunately in UMTS, the UTRAN can exist alongside the GSM radio network, or any other compatible (radio or fixed) access network, with handovers allowed between the different systems. This, together with the different different W-CDMA modes of operation (FDD and TDD) allows a great deal of flexibility in coverage planning. Sufficient capacity should ensure that calls can be completed, or data transferred with a high probability of success. The higher the success rate (Grade of Service) planned for, the more equipment that will need to be provided. Quality of Service must be maintained at an acceptable level. This becomes much more of an issue with UMTS due to the range of services (all with varying needs of data rate, delay tolerance, error rates etc.) which can be supported.

Understanding UMTS 1

©Informa

Telecoms

• Coverage • Capacity • Quality

Fig. 1 – Planning Requirements ©Informa

Telecoms

2

Radio Planning Issues

2. CELL PLANNING 2.1 Traditi raditiona onall Cell Cell Planni Planning ng For second generation Time Division Multiple Access (TDMA) systems, including GSM, the air interface was organised into equally spaced carrier frequencies, each of which could support a finite number of users separated by the use of recurring time slots (in GSM, eight timeslots existed per carrier frequency). The TDMA notation refers to the use of timeslots, but the equal spacing of the carrier frequencies is described as Frequency Division Multiple Access (FDMA). Hence GSM is actually a TDMA / FDMA system. In addition, for each uplink frequency there is a separate, but corresponding downlink frequency. This is known as Frequency Division Duplex (FDD). The frequency and time allocation in second generation networks ensures that the different control data and user data can be kept separate within a given geographical area. This can only work if the available carrier frequencies are planned to minimise interference. This is achieved by careful control of transmitter powers, and stipulating a minimum distance between transmitters using the same frequency (minimum re-use distance) for a given quality of signal. The radius of the nominated coverage area for each base site (cell) is therefore planned to be significantly smaller than the stipulated re-use distance. This ratio depends on the interference that can be tolerated in each system (GSM is fairly tolerant, hence the re-use distance for a given power is relatively small). Since power is generally set to provide sufficient coverage for the cell in question, the smaller the cells, the lower the re-use distance. Hence, with careful power control, cell planning becomes purely a geometrical problem. In general, a tessellating pattern is used to provide coverage over the required geographical area, as shown opposite. The greater the tolerance to interference, the lower the ratio between re-use distance and cell radius need be, and hence the smaller the number of cells in the pattern. GSM is more tolerant than the analogue TACS system and can cope with a four cell repeat pattern rather than the minimum of seven needed in TACS. However, as always, quality must be taken into account when deciding on the repeat pattern. For a finite set of available carrier frequencies, the larger the pattern, the lower the number of available frequencies per cell. Therefore more cells may be needed within the required geographical area in order to provide the same capacity. This leads to higher infrastructure costs.

Understanding UMTS 3

©Informa

Telecoms

eg: 7 Cell Re-use Pattern

R 2 7

3 1

D

6

4 5

2 7

3 1

6

4 5

Re use distance D: D = R 3N Interference considerations dictate that for:   TACS, TACS, Cluster size 7 GSM, Cluster size 4

N

=

Cluster size

3

=

Indicates cell with set frequency (s)

=

Cluster of cells

Fig. 2 – Traditional Cell Planning ©Informa

Telecoms

4

Radio Planning Issues

2.2 W-CDMA -CDMA Cell Cellula ularr Planni Planning ng Prin Princip ciples les The W-CDMA planning concept initially seems simpler than for TDMA systems. It is based generally on a single cell repeat pattern, where the same W-CDMA carrier frequency can be used in adjacent cells continually throughout the network. Users and control data are separated by the use of codes within the spreading and despreading process. The ability to despread however mainly depends on the data rate and therefore spreading factor / processing gain, and on the overall interference received along with the wanted signal. The received interference originates from both the same cell (as the wanted signal), and from adjacent cells. In both cases, interference can be minimised by careful power control (fast power control in UMTS is performed 1500 times per second) and by controlling the overall loading of each cell (number of users and their aggregate data rates). The recovery of the wanted signal depends not only on the despreading process, but also on the rejection of the interfering signals. So long as different spreading codes are used, and they are orthogonal (with good cross correlation characteristics), the interfering signals will remain spread during the despreading process of t he wanted signal. In addition, code allocation and required data rates are linked in W-CDMA by the nature of the code tree (used to ensure orthogonality). For both these reasons, code planning is essential.

Understanding UMTS 5

©Informa

Telecoms

1

1

1

1

• Spread Spread signals signals from same same and adjacent adjacent cells contribu contribute te to interfere interference nce levels levels - GOOD POWER CONTROL REQUIRED - CAPACITY CAPACITY OF EACH CELL NEEDS PLANNING

• This interfer interference ence remains remains spread spread on despreading despreading wanted wanted signal, signal, unless unless same spreading codes are used, or poor correlation characteristics exist – CODE PLANNING REQUIRED.

Fig. 3 – W-CDMA W-CDMA Cellular Planning Planning Principles ©Informa

Telecoms

6

Radio Planning Issues

2.3 2.3 Soft Soft Hand Handov over er Regi Region ons s The soft handover (between cells provided by different Node Bs) and softer handover (between cells provided by the same Node B) allows mobiles to be served by more than one radio interface connection at the same time. This is an important concept in W-CDMA in that it allows the mobile to use each separate signal to enhance the overall recovered signal. The soft and softer handover regions occur generally at the edge of cells where power requirements would otherwise be at their greatest. However, the gain introduced by the soft and softer handover allows for lower powers to be used, minimising the contribution to overall interference levels. The near-far effect is also mitigated, (where a mobile closer to the Node B introduces a level of interference into the system that precludes successful despreading of a mobile on the edge of a cell). When planning the network, the soft and softer handover regions must allow continuous coverage, whilst minimising overall interference under all cell load conditions. The trade off is that more hardware is required if the average time spent in soft or softer handover increases. This includes Rake Receivers in the Node B, and UTRAN transmission links for soft handover (where combining is done at the RNC). Note that combining techniques for soft and softer handover are different. Softer handover utilises the Rake receiver to combine the signals in much the same way that multi-path signals can be combined. Whilst soft handover combining is achieved in the RNC, where the different signals are assessed, and the best signal is chosen for inclusion in the combined signal (choice made every 10-80ms). Realistic figures for connections spent in soft handover may be 20-40%, whilst those spent in softer handover may be 10%.

Understanding UMTS 7

©Informa

Telecoms

1

1

1

1

• Mobiles Mobiles may be served served by more more than one one base station station site in in soft handover handover (shaded) areas • Conti Continuous nuous coverag coverage e should should be maintained maintained (if (if required) required) under under all load load conditions • The combinin combining g process process enhance enhances s the signal signal in soft soft handover handover

Fig. 4 – Soft Handover Regions ©Informa

Telecoms

8

Radio Planning Issues

2.4 2.4 Cell ell Br Breath eathiing If the number of users in a particular area increases, or their aggregate data rates increase, more interference is introduced into the overall system. Despreading of signals for mobiles in that area becomes more difficult, and the effective cell range for a given power reduces. Unfortunately, the adjacent cells, which may also be serving the same area (soft handover), will encounter the same problem. This means that for higher loading, the effective radius of all cells serving the area in question will reduce (for the given power), reducing the area of soft handover. The variation in effective radius with loading is a phenomenon known as cell breathing, and it must be taken into account when planning the handover regions.

Understanding UMTS 9

©Informa

Telecoms

Lower Load

2

1

3

Higher Load

2

1

3

• Effective Effective range range of cell is reduced reduced on higher higher loading loading due to interfe interferenc rence e caused by additional channels • Adjace Adjacent nt cells cells also also bre breath athe e • Soft Soft hando handover ver regio region n redu reduces ces

Fig. 5 – Cell Breathing ©Informa

Telecoms

10

Radio Planning Issues

3. INTERFERENCE EFFECTS 3.1 Own and Adjace Adjacent nt Cell Cell Interf Interfer erenc ence e Since the same W-CDMA frequency is used in each cell, the total interference in a system is a combination of that generated within the same cell, and that generated in adjacent, or nearby cells. The figure opposite shows the relationship between the spread wanted signal, the interference contribution from own cell and adjacent / nearby cells, data rates (and therefore the subsequent processing gain), power and range. The result is that power, coverage area, data rates (and subsequent spreading factor /  processing gain) per user, and the overall loading of the cell all need careful consideration when implementing a W-CDMA network. Interference, capacity and coverage are interdependent and must be considered together.

Understanding UMTS 11

©Informa

Telecoms

Interference

Wanted Signal

• Wanted signal despread and raised sufficiently to recover signal (Processing Gain is sufficient/dat sufficient/data a rate is low enough)

Interference Spread Wanted signal

• Higher data rate, therefore lower processing gain – insufficient to raise wanted signal sufficiently sufficient ly above noise

Interference Spread Wanted signal

• Power of spread wanted signal is increased by reducing range, or increasing transmitted power (Increasing transmitted power adds more interference for other users)

Interference Increased power of spread wanted signal Need to control:

• • • •

Power Range (coverage) Processing Processin g Gain/Spreading Factor per user Overall loading

Fig. 6 – Interference, Capacity and Coverage ©Informa

Telecoms

12

Radio Planning Issues

3.2 3.2 Mult Multii-pa path th Eff Effec ects ts Unlike in most radio systems, the Rake reception of the W-CDMA signals means that multi-path effects can be used to enhance the signal.  Any signals that take different paths from source to destination will travel different distances and arrive at the destination at slightly different times. In W-CDMA however, however, the different different multi-path components of the same original signal can then be despread separately by the same code, so long as the code has been delayed by an appropriate amount to account for the path differences. Once the multi-path components have been despread, they can be adjusted in time so that the despread signals coincide with each other, and then added together to give a composite signal.

Understanding UMTS 13

©Informa

Telecoms

Multi-path Propagation

Received Components

Rake Output

Delay due to different paths • By delaying delaying code generatio generation n in the Rake Receiver Receiver,, multi-path multi-path can be used to enhance recovered signal.

Fig. 7 – Multi-path Effect ©Informa

Telecoms

14

Radio Planning Issues

3.3 Interf Interfer erenc ence e Sharin Sharing g and Soft Soft Capac Capacity ity  Another effect of W-CDMA is called interference sharing. If a W-CDMA network is planned for equal loading of the cells, the interference contributed by each cell to the average system interference will be roughly the same. Based on this, each cell will be planned to expect a certain level of interference from its neighbouring cells. Hence its loading / capacity will be planned with an upper limit which ensures that wanted signals can be despread and raised (by the processing gain) sufficiently above the interference (e.g. 7dB). However, However, if neighbouring cells are lightly loaded, the adjacent cell interference contribution is lower. lower. The cell in question can benefit by providing higher data rates per user (lower processing gain, but with less total interference to raise the wanted signal above), or to accept a higher interference contribution from users in its own cell. This effectively means more users. In both cases, the capacity in the cell increases due to lower usage of (or interference from) adjacent cells. Since different cells throughout the network may be benefiting from this effect at any one time, there is an overall gain in capacity, and this can be planned for in the capacity calculations. The effect is known as soft capacity, and can only be taken advantage of if there is spare capacity (hardware and processing) available in the base sites. If there isn’t spare capacity, then hard blocking will occur, where calls or data transfer is blocked due to lack of resources.

Understanding UMTS 15

©Informa

Telecoms

Interference over whole system reflects dimensioning for average usage per cell

Cell Usage Equally Loaded Cells

Interference over whole system Interference may remain the same

Higher Capacity is possible in middle cell due to reduced interference from neighbouring cells

Known as “Soft Capacity” Capacity”

Fig. 8 – Interference Sharing ©Informa

Telecoms

16

Radio Planning Issues

3.4 Limitations It is useful to note the limitations of the system in terms of coverage and capacity.  A significant factor is that in the downlink, the maximum transmitted power remains the same regardless of the number of users, and each user has to share the power available, whilst in the uplink, each mobile has its own power amplifier. Even with low downlink load, the coverage will depend on the interference contributed by the total number of users in the uplink (more users, less coverage), whilst in the downlink, for a given power, the higher the data rate, the lower the range for acceptable service. Range and capacity are, of course, traded off against each other in both the uplink and downlink. However, it is the plotted graphs of maximum path loss (range amongst other considerations) against load for given conditions, including interference, which illustrate the limitations. Below about 600kbps in the downlink, the uplink limits the range and hence coverage, whilst in the downlink, anything above about 700kbps can only be provided at low range (low coverage area). It is worth noting that a 2Mbps service can be provided using three separate codes and combining the results.  As the capacity limits are approached, it becomes much more difficult to increase the capacity within the coverage area without adding more cells. Increasing downlink power to increase capacity is inefficient, whereas splitting the power between two WCDMA carrier frequencies would be much more efficient, but requires additional hardware. The figures quoted are only for illustration, and many factors will affect the performance, including improved improved antenna design for increasing the coverage (e.g. receive antenna diversity), and asymmetric services.

Understanding UMTS 17

©Informa

Telecoms

C a  a p  pa     c  a c i i t  ty  y   l i i m  mi  t  t e  ed     i n  d n t h  h e  e d o  ow    n  w   l l  i i n  n C o  nk  ov   ve  k     e r  ra     g  a ge     l i i m  e mi  t  t e  ed     i n  d n t h  he     u p  e pl l  i i n  nk  k   

• Note that for for a 2 Mbps service, service, three three codes codes would would be used used

Fig. 9 – Limitations ©Informa

Telecoms

18

Radio Planning Issues

3.5 User User Data Data Rate Rates s and and Numb Number er of of Users Users Since acceptable service depends on despreading the wanted signal, which in turn depends on the level of interference in the system, there is generally a trade-off between the number of users and their average data rates. This is because an upper limit on total t otal interference determines the capacity. For lower data rate users, the processing gain is relatively high and each signal will be raised significantly above the interference for average planned cell load conditions. However, However, as the number of users increase, so the interference increases, increases, and an upper limit on the number of users will be reached (this is maximised by effective power control). For higher data rate users, the processing gain is not so high, which results in the signal being raised less effectively above the interference. The maximum interference level will be reached earlier, hence a lower number of users will be tolerated for acceptable higher data rate services to be provided. The total user data capacity is affected by the control information, in that more lower data rate users will require more control information, leaving less user data. However, higher data rate users will have a less even distribution over the system, which makes capacity planning less efficient. Therefore on average, overall cell loading may be lower if higher data rate users dominated and had been planned for. In practice, of course, a mix of users would generally be expected. Asymmetric services may also be provided.

Understanding UMTS 19

©Informa

Telecoms

144

   )   s   p    b    k    (   s   e    t   a   r   r   e   s    U

Note: Figures are for illustration only

64

32 16 12.2 0

10

20

30

40

50

60

Number of channels per cell • Total capacity (Users x User Rates) is not constant due to dimensioning and also the greater control overhead required for more lower rate users

Fig. 10 – User Data Rates and Number of Users ©Informa

Telecoms

20

Radio Planning Issues

4. REDUCING INTERFERENCE/INCREASING CAPACITY 4.1 4.1 Sec Sector torisat isatiion One simple way to reduce interference is to use sectored cells, where a single base site can support up to six sectors (or cells) at a time. The directional antennas mean that antenna gain acts to enhance the signals from mobiles in the sector, and reject those outside the sector. At the same time, interference in the downlink is reduced due to the confinement of power within the sector, which ensures a lower contribution to overall interference. In addition, the cells are effectively smaller (for the same number of sites) and therefore lower powers can be used. Softer handover now becomes a factor in that mobiles can be in handover between sectors of the same Node B, with the signal combined in the Rake receiver (an advantage in terms of reduced power requirement). The Soft handover region, rather than the Softer handover region still provides the greater area. Effectively, Effectively, the reduced interference allows greater capacity for the same number of base sites, or reduced hardware costs for the same capacity if the system is planned as a sectored system from initial rollout.

Understanding UMTS 21

©Informa

Telecoms

• Reduced Co-Channel Interference • Increase Increased d Capacity • Reduced Hardware Costs

Soft Handover Region Softer Handover Region Base Station Sites with  Axis of sectorisation

Fig. 11 – Sectorisation ©Informa

Telecoms

22

Radio Planning Issues

4.2 4.2 Sma Smart Ante Anten nnas nas The sectored cell benefits can be taken to the extreme with the use of smart antennas, where multiple beams can be generated, each serving a specified user. user. The beams are effectively very narrow sectors, with all the benefits in terms of reduced interference. Antenna gain is generally higher than for the three or six sector sites. The beams are formed and steered by antenna arrays. The broadcast channel is configured for normal cell coverage since it must be available to mobiles in idle mode. Smart antennas may well be a feature in UMTS networks.

Understanding UMTS 23

©Informa

Telecoms

Narrow Beam

Broadcast Channel

User

• • • •

Multiple Multiple beams beams can be genera generated ted for multiple multiple users users Co-Channel interference interference in Uplink and Downlink is reduced reduced Range Range increase increased d due to higher higher antenna antenna gain gain Capacity increased increased due to reduced reduced co-channel co-channel interference interference

Fig. 12 – Smart Antennas ©Informa

Telecoms

24

Radio Planning Issues

4.3 4.3 Mult Multii-Ca Carr rrie ierr Cells Cells Multi-carrier cells offer an efficient way to increase capacity (limited generally by the downlink). Unlike power increases in a single frequency (which provide little improvement in capacity as the higher data rates, or user numbers are approached), a second carrier frequency allows the data rates, or user numbers to remain in the part of the load curve considered efficient in terms of capacity provision. Each frequency can then use power control to increase capacity until each now approaches the limit again (as defined by the load curve). In general, the frequencies used will be adjacent channels (adjacent W-CDMA frequencies), frequencies), and will therefore cause adjacent channel interference. However, However, this can be minimised by co-locating the transmitter / receivers and using the same antennas. This concept can be extended to different network operators who may be using adjacent frequencies. They could both benefit from reduced adjacent channel interference if they co-located their transmitter / receivers.  A mobile required to change frequencies for capacity, capacity, coverage, or quality reasons would use the hard handover technique.

Understanding UMTS 25

©Informa

Telecoms

Frequency 2 Frequency 1

Hard Handover can be employed • Adjacent Adjacent channel channel interfer interference ence is minimis minimised ed by co-locatin co-locating g and using using same antennas. • Differen Differentt operators operators using adjacent adjacent frequenc frequency y bands would would benefit from from colocation to reduce adjacent channel interference

Fig. 13 – Multi-Carrier Cells ©Informa

Telecoms

26

Radio Planning Issues

4.4 Planni Planning ng the Frequ Frequenc ency y Spec Spectru trum m Within the available frequency band, the actual carrier frequency and spacing can be set in steps of 200kHz. This can be used effectively to decrease the spacing between frequencies within the operators band (where the increased adjacent channel interference can be minimised by co-locating the transmitters / receivers, and using the same antennas). This allows increased separation (at the edge of the operator's band) with the adjacent frequencies used by another operator, as shown opposite.

Understanding UMTS 27

©Informa

Telecoms

Operator 1 (10MHz)

Operator 2 (15MHz)

frequency

4.6MHz

> 5MHz

4.6MHz

Larger spacing (Minimises interfere interference) nce) • Carrier Carrier spacing spacing can be set set in steps of 200kHz 200kHz within within band band to minimise minimise adjacent adjacent channel interference • Operators Operators can minimise minimise adjacent adjacent channel channel interfer interference ence from from their own own carriers carriers by co-location (hence spacing can be reduced in order to maximise spacing between operators)

Fig. 14 – Setting the Carrier Spacing ©Informa

Telecoms

28

Radio Planning Issues

4.5 4.5 The The Laye Layere red d Arch Archit itec ectu ture re  A layered architecture may be employed for coverage, capacity, capacity, or quality reasons, with the different layers operating on different frequencies (required in order to minimise the effects of interference in each cell).  At the micro / pico-cell level, TDD mode may be utilised. Its reduced range can be used to advantage in areas requiring higher data rates. The TDD cell power can be controlled sufficiently sufficiently to provide coverage only in selected areas (such as offices). This ensures that interference is kept to a minimum in other coverage areas where the TDD frequency is re-used. Hence, higher data rates / loading can be provided for "hot spots", while more general coverage is provided by FDD operation. If more than one FDD frequency is available, an umbrella layer can also be used for wider area coverage. The loading of each layer needs careful consideration. Different data rates can be traded off against the number of users. Hard handovers must be used between different modes and frequencies (and also, therefore, between layers).

Understanding UMTS 29

©Informa

Telecoms

FDD f1

FDD f2

FDD f2

 TDD f3 • Differen Differentt Carrier Carrier Frequenci Frequencies es may be employed employed at differ different ent layers layers (hard handovers can be used) • Lower range, range, higher higher bit rate rate services services may may be provided provided by by TDD mode mode (eg: office environments)

Fig. 15 – The Layered Architecture ©Informa

Telecoms

30

Radio Planning Issues

4.6 4.6 GSM GSM Co Co – Pla Plan nning ning The way in which UMTS has been specified allows for an evolutionary strategy from existing 2G GSM networks. In fact in the first phase of UMTS, the core network is essentially an evolved GSM Phase 2+ network, incorporating circuit switched and packet switch (GPRS) infrastructures. infrastructures. It is a general assumption that GSM and UMTS will co-exist in a similar way that first and second generation systems did. However for UMTS, the core network will initially be that of the existing GSM network, and it follows that operators will also want to maximise use of the existing radio infrastructure. Re-using existing GSM base transceiver sites will provide a huge cost saving to operators. The feasibility of this is illustrated opposite in a comparison of effective ranges for both GSM (900 and 1800MHz frequencies) and UMTS (at varying data rates). GSM 900 clearly allows for greater range, whereas GSM 1800 and low to moderate W-CDMA data rate ranges are more comparable. Range is more limited for the W-CDMA at higher data rates.

Understanding UMTS 31

©Informa

Telecoms

Relative Coverage (Range)

WCDMA 384kbps

WCDMA 144kbps

WCDMA SPEECH

GSM 1800 SPEECH

GSM 900 SPEECH

Fig. 16 – GSM Co Planning – Range Comparisons ©Informa

Telecoms

32

Radio Planning Issues

4.7 4.7 Use Use Of Of Exi Exist stin ing g Sit Sites es Existing GSM sites may therefore be used for UMTS, so long as the cell range /  coverage area required for the planned UMTS system can be provided with the existing base site spacing. If not, then additional sites will be needed. Remote, or rural areas, where GSM has been planned simply to provide continuous coverage (with a low capacity requirement), will generally provide more of a problem than urban areas due to the greater cell sizes. GSM 900 cell sizes will usually be greater than GSM 1800 in these areas. For urban areas, capacity is often the major planning issue. Here, the available frequencies must be re-used more often in order to provide the required resources. This is achieved by carefully controlling the transmitted power and reducing the cell sizes. The GSM cell sites will be closer together and therefore more likely to support UMTS cells with the required coverage areas. In urban areas, GSM 900 and 1800 are likely to have similar cell sizes, and therefore are more equally likely to be able to provide UMTS coverage from existing sites. The UMTS soft and softer handover regions (including under higher load conditions) must be taken into account when planning coverage from existing GSM cell sites.

Understanding UMTS 33

©Informa

Telecoms

Remote Areas (GSM Coverage Planned)

WCDMA Range GSM Range

 Additional Base Sites Required for Continuous Coverage

Urban Areas (GSM Capacity Planned)

Cell boundary less than GSM or WCDMA maximum range

Possible to Provide Continuous Coverage using Existing Sites

Fig. 17 – Using Existing 2G Sites ©Informa

Telecoms

34

Radio Planning Issues

4.8 W-CDMA, -CDMA, EDGE EDGE and and GSM GSM Cover Coverage age Areas Areas  A network may be planned with the different W-CDMA modes, EDGE (Enhanced Data rates for Global Evolution) and GSM providing different areas of coverage. Each would be able to support different data rates and Qualities of Service. The reasons for this approach could include cost, speed of rollout, coverage, capacity, capacity, or overall quality. It makes sense in many ways to leave basic (voice subscribers) on the GSM network, since a large initial migration to UMTS would increase interference, reducing reducing the ability to provide higher data rate services for potentially high revenue (usually corporate) users. The high value users will usually be concentrated in business areas.  As more users start using higher data rate services, a gradual migration would allow operators to use GSM sites initially for UMTS coverage, increasing capacity as the network grows. The cut off between a likely GSM and UMTS subscriber is not clear cut. EDGE could provide an extra step, with the flexibility of higher data rate services without increasing the UMTS load. UMTS services could be sold at a premium, with higher capacity provided initially in urban areas (where GSM co-planning is most feasible). TDD can be used to provide higher data rates in the required "hotspots".

Understanding UMTS 35

©Informa

Telecoms

EDGE URBAN COVERAGE GSM Continuous Coverage

WCDMA TDD Hot Spots (Offices etc)

WCDMA FDD Business Coverage

Fig. 18 – Coverage Areas ©Informa

Telecoms

36

Radio Planning Issues

5. RADIO PLANNING AND SIMULATIONS 5.1 5.1 Plan Planni ning ng Tools ools The complex nature of the iterative process necessitates a software planning tool. This allows much of the external data to be loaded, including the radio propagation and geographical data for the area in question. The operator can then ask for iterations under various conditions. Various visual representations are used to covey the coverage and capacity results on screen, as shown.

5.2 5.2 Mont Monte e Car Carlo lo Simu Simula lati tion ons s The Monte Carlo method is a general technique applied to many systems to model the outcomes, from economics to physics. The basis is random numbers and statistical probability calculations. There are many forms of Monte Carlo simulations. In UMTS, the simulation is applied to the radio network to model the coverage and therefore capacity of the radio system under various conditions. The planning tools used at this stage of the planning process use the Monte Carlo method because it allows complex systems to be analysed by sampling a number of random configurations. It then uses this data to describe the system as a whole.

Understanding UMTS 37

©Informa

Telecoms

Supplied courtesy of Ericsson

Fig. 19 – Planning Tools ©Informa

Telecoms

38

Radio Planning Issues

6. SUMMARY – PLANNING CONSIDERATIONS The planning considerations for UMTS are summarised in the figure shown opposite.

Understanding UMTS 39

©Informa

Telecoms

• Cell Cellul ular ar stru struct ctur ure e used used • Sam Same e freque frequency ncy can can be used used in in each each cell cell • Codes need to be planned to prevent co-channel interference (64 groups to choose from) • In general, general, the the greater greater the bit bit rate per user user,, the lower lower the number number of users per cell • Gre Greater ater cell cell range range gives gives reduced reduced capacity capacity (and (and vice vice versa) for a given power • The greater greater the instantan instantaneous eous cell cell usage, usage, the smaller smaller the effective cell range (cell breathing) • Inter Interfere ference nce decreases decreases range range and/or and/or capacity capacity for for a given power power • Overa Overallll system system noise/inter noise/interfere ference nce must must be kept as low as possible possible • Inter Interfere ference nce reduc reducing ing techni techniques ques may be used – Diversity – Multi user detection – Smart antennas – Repeaters • Incr Increased eased downlink downlink power power gives increa increased sed capacity capacity only to a certain certain limit • Pl Plan anni ning ng ma may y use use:: – more than one frequency for capacity or coverage purposes (eg: hierarchical cells) – GSM/EDGE to offer more complete coverage around UMTS “Islands” • TDD mode mode suited suited to shorter shorter range range (and (and possibly possibly higher higher data data rates) rates) • FDD mod mode e suite suited d to lon longer ger ran range ge • Asy Asymme mmetri tric c servic services es must must be plann planned ed for

Fig. 20 – W-CDMA Planning Considerations - Summary ©Informa

Telecoms

40