LTE Radio Link Budgeting

LTE Radio Link Budgeting and RF Planning 1. Introduction

The initial planning of any Radio Access Network begins with a Radio Link Budget. As the name suggests, a link budget is simply the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system. In this page, we will briefly discuss link budget calculations for LTE.

2. LTE Radio Link Budgeting

2.1. Typical Parameter Values The link budget calculations estimate the maximum allowed signal attenuation g between the mobile and the base station antenna. The maximum path loss allows the maximum cell range to be estimated with a suitable propagation model. The cell range gives the number of base station sites required to cover the target geographical area.The following table shows typical (practical) parameter values used for doing an LTE Radio Link Budget.

a b c

Parameter Typical Value Base Station maximum transmission power. A typical value for macro cell base 43 – 48 dBm station is 20-69 W at the antenna connector. Base Station Antenna Gain Manufacturer   Dependent Cable loss between the base station antenna connector and the antenna. The 1 – 6 dB cable loss value depends on the cable length, cable thickness and frequency band. Many installations today use RF heads where the power amplifiers are close to the antenna making the cable loss very small. Base Station EIRP, Calculated as A + B - C

d e UE RF noise figure. Depends on the frequency band. Duplex separation and on 6 – 11 dB f 

the allocated bandwidth. Terminal noise can be calculated as:

-104.5 dBm for 50 resource blocks (9 MHz)

“K (Boltzmann constant) x T (290K) x bandwidth”. The bandwidth depends on bit rate, which defines the number of resource blocks. We assume 50 resource blocks, equal 9 MHz, transmission for 1 Mbps downlink. Calculated as E + F

g h Signal-to-noise ratio from link simulations or measurements. The value depends -9 to -7 dB i  j

on the modulation and coding schemes, which again depend on the data rate and the number of resource blocks allocated. Calculated as G + H

k

Interference margin accounts for the increase in the terminal noise level caused 3 – 8 dB by the other cell. If we assume a minimum G-factor of -4 dB, that corresponds to 10*Log10(1+10^(4/10)) = 5.5 dB interference margin. Control channel overhead includes the overhead from reference signals, 10 – 25 % =

L

PBCH, PDCCH and PHICH. UE antenna gain.

M Body loss

2.2. Uplink Budget

0.4 – 1.0 dB Manufacturer   Dependent Device Dependent

The table below shows an example LTE link budget for the uplink from [1], assuming a 64 kbps data rate and two resource block allocation (giving a 360 kHz transmission bandwidth). The UE terminal power is assumed to be 24 dBm (without any body loss for a data connection). It is assumed that the eNode B receiver has a noise figure of 2.0 dB, and the required Signal to Noise and Interference Ratio (SINR) has been taken from link level simulations performed in [1]. An interference margin of 2.0 dB is assumed. A cable loss of 2 dB is considered, which is compensated by assuming a masthead amplifier  (MHA) that introduces a gain of 2.0 dB. An RX antenna gain of 18.0 is assumed considering a 3-sector macro-cell (with 65degree antennas). In conclusion the maximum allowed path loss becomes 163.4 dB. Uplink Link Budget for 64 kbps with dual-antenna receiver base station

Data rate (kbps) Transmitter – UE 

64

a b c d

24.0 0.0 0.0 24.0 = a + b + c

Max. TX power (dBm) TX antenna gain (dBi) Body loss (dB) EIRP (dBm)

Receiver – eNode B e f  g h i  j k l m

Node B noise figure (dB) Thermal noise (dBm) Receiver noise floor (dBm) SINR (dB) Receiver sensitivity (dBm) Interference Margin (dB) Cable Loss (dB) RX antenna gain (dBi) MHA gain (dB)

Maximum path loss

2.0 -118.4 = k( Boltzmann ) * T( 290K )* B( 360kHz ) -116.4 = e + f   -7.0 From Simulations performed in [1] -123.4 = g + h 2.0 2.0 18.0 2.0 163.4 = d – i – j – k + l - m

The table below shows an example LTE link budget

2.3. Downlink Budget The table below shows an example LTE link budget for the downlink from [1], assuming a 1 Mbps data rate (assuming antenna diversity) and 10 MHz bandwidth. The eNode B power is assumed to be 46 dBm, a value typical among most manufacturers. Again the SINR value is taken from link level simulations performed in [1]. A 3 dB interference margin and a 1 dB control channel overhead are assumed, and the maximum allowed path loss becomes 165.5 dB. Downlink Link Budget for 1 Mbps with dual-antenna receiver terminal

Data rate (Mbps) Transmitter – eNode B

1

a b c d

46.0 18.0 2.0 62.0 = a + b + c

HS-DSCH power (dBm) TX antenna gain (dBi) Cable loss (dB) EIRP (dBm)

Receiver – UE  e f  g h i  j k l m

UE noise figure (dB) Thermal noise (dBm) Receiver noise floor (dBm) SINR (dB) Receiver sensitivity (dBm) Interference Margin (dB) Control Channel Overhead (dB) RX antenna gain (dBi) Body Loss (dB)

Maximum path loss

7.0 -104.5 = k( Boltzmann ) * T( 290K )* B( 360kHz ) -97.5 = e + f   -10.0 From Simulations performed in [1] -107.5 = g + h 3.0 1.0 0.0 0.0 165.5 = d – i – j – k + l - m

The table below shows an example LTE link budget

2.4. Propagation (Path Loss) Models  A propagation model describes the average signal propagation, and it converts the maximum allowed propagation loss to the maximum cell range. It depends on: 

Environment : urban, rural, dense urban, suburban, open, forest, sea…

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Distance

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Frequency

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atmospheric conditions

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Indoor/outdoor 

Common examples include Free space, Walfish–Ikegami, Okumura–Hata, Longley–Rice, Lee and Young's models. The most commonly used model in urban environments is the Okumura-Hata.

2.5. Mapping of Path Losses to Cell Sizes For a path loss of 164 dB, based on the assumptions shown in the table below the following cell ranges can be attained with LTE. The cell range is shown for 900, 1800, 2100 and 2500 MHz frequency bands. Assumptions

Okumura–Hata parameter

Urban Indoor 

Suburban Indoor 

Rural Indoor 

Base station antenna height (m) Mobile antenna height (m) Mobile antenna gain (dBi) 0 Slow fading standard deviation (dB) Location probability (%) Correction factor (dB) Indoor loss (dB) Slow fading margin (dB)

30 1.5 0.0 8.0 95 0 20 8.8

50 1.5 0.0 8.0 95 -5 15 8.8

80 1.5 0.0 8.0 95 -15 0 8.8

Rural outdoor  fixed 80 5 5.0 8.0 95 -15 0 8.8

Cell Size in Km

2.6. Comparison to Other Radio Access Technologies In comparison to other Radio Access Technologies such as GSM or UMTS, LTE does not provide a significant increase in cell size or path loss measurements, however, the data rate (services) provided is much superior. In contrast to HSPA link budgets, the LTE Link budgets show up to roughly 2 dB higher values, which is mainly a result of low interference margins that can be achieved with orthogonal modulation. For a detailed comparison please refer to LTE Link Budget Comparison.

LTE Link Budget Comparison 1. Introduction

The tables below show a link budget comparison between LTE, GSM and UMTS HSPA.

2. Uplink Budget Comparison The following table based on [1],[2] compares the uplink budget for LTE, HSPA and GSM

RAN Technology Data rate (kbps) Transmitter – UE  a b c d

GSM 12.2

Max. TX power (dBm) TX antenna gain (dBi) Body loss (dB) EIRP (dBm)

HSPA 64

LTE 64

33 0 3 30

23 0 0 23

23 0 0 23

-114 0 0 18 0 0

2 -108.2 -106.2 -17.3 -123.4 3 0 18 1.8 2

2 -118.4 -116.4 -7 -123.4 1 0 18 0 0

162

161.6

163.4

Receiver – BTS/Node B/eNode B e f  g h i  j k l m n

Node B noise figure (dB) Thermal noise (dBm) Receiver noise floor (dBm) SINR (dB) Receiver sensitivity (dBm) Interference Margin (dB) Cable Loss (dB) RX antenna gain (dBi) Fast fade margin (dB) Soft handover gain (dB)

Maximum path loss

The uplink link budget has some differences in comparison to HSPA: specifically the smaller interference margin, no macro diversity gain (Soft handover gain) and no fast fading margin. As can be seen from the table above the link budget was calculated for 64 kbps uplink, which is cannot be classified as a high enough data rate for true broadband service. To guarantee higher data rates for LTE, a low frequency deployment may be required in addition to additional sites, active antenna solutions or local area solutions.

2. Downlink Budget Comparison The following table based on [1],[2] compares the downlink budget for LTE, HSPA and GSM

RAN Technology Data rate (kbps) Transmitter – BTS/Node eNode B a b c d

Max. TX power (dBm) TX antenna gain (dBi) Cable loss (dB) EIRP (dBm)

GSM 12.2

HSPA 1024

LTE 1024

B, 44.5 18 2 60.5

46 18 2 62

46 18 2 62

-119.7 -104 0 0 0

7 -108.2 -101.2 -5.2 -106.4 4 20 0

7 -104.5 -97.5 -9 -106.4 4 20 0

Receiver – UE  e f  g h i  j k l

UE noise figure (dB) Thermal noise (dBm) Receiver noise floor (dBm) SINR (dB) Receiver sensitivity (dBm) Interference Margin (dB) Control channel overhead (%) RX antenna gain (dBi)

m

Body loss (dB)

Maximum path loss

3

0

0

161.5

163.4

163.5

The LTE link budget in downlink has several similarities with HSPA and the maximum path loss is similar. The link budgets show that LTE can be deployed using existing GSM and HSPA sites assuming that the same frequency is used for LTE as for GSM and HSPA. LTE itself does not provide any major boost in the coverage. That is because the transmission power  levels and the RF noise figures are also similar in GSM and HSPA technologies, and the link performance at low data rates is not much different in LTE than in HSPA.

LTE RF Planning Introduction In the context of mobile and cellular communication systems, RF Planning is the process of assigning frequencies, transmitter locations and parameters of a wireless communications system to provide sufficient coverage and capacity for  the services required (e.g. mobile telephony). The RF plan of a cellular communication system revolves around two principal objectives; Coverage and Capacity Coverage relates to the geographical footprint within the system that has sufficient RF signal strength to provide for a call/data session. Capacity relates to the capability of the system to sustain a given number  of subscribers. In 3GPP LTE systems, both capacity and coverage are interrelated. To improve quality some coverage, capacity has to be sacrificed, while to improve capacity, coverage will have to be sacrificed. The LTE RF planning process mainly consists four phases:

Phase 1: Initial RF Link Budget The first level of the RF planning process is a budgetary level. It uses the RF link budget along with a statistical propagation model (e.g. Hata, COST-231 Hata or Erceg-Greenstein) to approximate the coverage area of the planned sites and to eventually determine how many sites are required for the particular RF communication system. The statistical propagation model does not include terrain effects and has a slope and intercept value for each type of  environment (Rural, Urban, Suburban, etc.). This fairly simplistic approach allows for a quick analysis of the number of  sites that may be required to cover a certain area. Following is a typical list of outputs produced at this stage: 

Estimated Number of Sites

Phase 2: Detailed RF Propagation Modelling The second level of the RF Planning process relies a more detailed propagation model. Automatic planning tools are often employed in this phase to perform detailed predictions. The propagation model takes into account the characteristics of the selected antenna, the terrain, and the land use and land clutter surrounding each site. Since these factors are considered, this propagation model provides a better estimate of the coverage of the sites than the initial statistical propagation model. Thus, its use, in conjunction with the RF link budget, produces a more accurate determination of the number of sites required. Following is a typical list of outputs produced at this stage: 

Number of Sites and Site Locations (and Height)

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 Antenna Directions and Downtilts

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Neighbour Cell Lists for each site

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Mobility (Handover and Cell Reselection) Parameters for each site.

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Frequency Plan

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Detailed Coverage Predictions (e.g. Signal Strength (RSRP), Signal Quality (RSRQ) Best CINR, Best Server Areas, Uplink and Downlink Throughput)

The following figure shows a typical coverage prediction out (All Sites coverage by Signal Strength).

Phase 3: Fine Tuninig and Optimisation The third phase of the RF planning process incorporates further detail into the RF plan. This stage includes items such as collecting drive data to be used to tune or calibrate the propagation prediction model, predicting the available data throughput at each site, fine tuning of parameter settings (e.g. antenna orientation, downtilting, frequency plan). This process is required in the deployment of the system or in determining service contract based coverage. Following is a typical list of outputs produced at this stage: 

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 A final List of Sites and Site Locations (and Height) Optimised Antenna Directions and Downtilts  An optimised Neighbour Cell Lists for each site Mobility (Handover and Cell Reselection) Parameters for each site.  An optimised Frequency Plan Detailed Coverage Predictions (e.g. Signal Strength (RSRP), Signal Quality (RSRQ) Best CINR, Best Server   Areas, Uplink and Downlink Throughput)

Phase 4: Continuous Optimisation The final phase of the RF planning process involves continuous optimisation of the RF plan to accommodate for changes in the environment or additional service requirements (e.g. additional coverage or capacity). This phase starts from initial network deployment and involves collecting measurement data on a regular basis that could be via drive testing or  centralised collection. The data is then used to plan new sites or to optimize the parameter settings (e.g. antenna orientation, downtilting, frequency plan) of existing sites.