UMTS Link Budget

P R O P O S A L T O

Customer Name, Location

Estimation of UMTS Cell Range based upon Link Budget.

Date, RFP#

1 Introduction Sophisticated Network Planning tools exist today to produce accurate, detailed predictions of UMTS coverage and capacity performance. The accuracy of these tools is heavily dependant on the effort spent configuring the parameters to match the geographic location and proposed network topology. This is an extremely time consuming and complex process that can require multiple iterations.

In the initial stages of a network design it can be more effective to produce quick budgetary designs that may be used to estimate initial Capital Expenditure and facilitate business modelling. A practical method of constructing a budgetary design is to determine the cell radius for sites in different environments and then use this to determine the total number of sites required for the total area to be covered.

The effective cell range of a site under certain conditions can be approximated using a Link Budget calculation. Link budgets may be produced independently for the Uplink and the Downlink in order to determine the maximum allowable pathloss to meet certain specifications. Pathloss can then be substituted into a standard propagation model to estimate the cell range.

Supplementary to providing an estimate of the number of sites required, for a given set of conditions, calculating the cell range will determine whether the Uplink or the Downlink is the limiting link. Comparing cell ranges for different conditions provides a quick method of analysing the effects of changing parameters such as coverage criteria or site configurations.

2 Basic UMTS Link Budget To characterise a given area the distribution of environment types (Clutter) must be determined. The telecommunications industry has adopted the following general definitions.

High Dense Urban (Indoor and Outdoor). Low Dense Urban (Indoor and Outdoor). Suburban (Indoor and Outdoor). Rural (Indoor and Outdoor).

Clutter types can generally be split up into groups based on the number of subscribers per Km2 and building height and density.

High dense urban clutter types have the most subs/ Km2 and a high density of building(s) in a small area. Buildings are typically tall.

Rural clutter types have the lowest subs/ Km2. Buildings are generally sparsely distributed.

Once the area to be simulated has been assigned clutter types, the environments can be defined.

Figure 1 shows an example of a clutter map. The different colours represent the different clutter types.

XXXX 2005 Motorola Confidential Proprietary Page 2 of 10

Type Colour Bldg Loss

Subs/Km2(x 1,000)

% of area

High Dense Urban Red 18dB 10 10%Low Dense Urban Orange 16 dB 5 25%Suburban Yellow 12 dB 1 50%Rural Purple 8 dB <0.5 15%

Figure 1: Example clutter map

2.1 Link Budget Parameters ExplainedEach environment can be defined by the attributes described in Table 1.

Table 1: Uplink Dense Urban Link Budget

Parameter Unit Parameter Description

Chip Rate C/s

CDMA uses unique spreading codes to spread the baseband data before transmission. Codes take the form of a carefully designed one/zero sequence produced at a much higher rate than that of the baseband data. The rate of a spreading code is referred to as chip rate.

Bit Rate bit/s Bit Rate is the number of bits per second

Base Station Noise Figure dB

Noise figure of an active device, over a bandwidth of interest is the contribution by the device itself to thermal noise at its output. The noise figure is usually expressed in decibels (dB), and is with respect to thermal noise power at the system impedance, at a standard noise temperature (usually 20o C, 293 K) over the bandwidth of interest.

K J/KK is Boltzmann constant (k = 1.380 6505(24)×10−23

joules/kelvin)

T KT is the temperature measured on the Kelvin temperature scale

kT dBW/HzIs the wideband thermal noise floor which is equal to the temperature (T) multiplied by Boltzmann constant.

kTW dB

Is the noise floor measured in the receiver bandwidth. This is equal to the wideband thermal noise multiplied by the chip rate.

NthW dB

Is the noise floor of the BTS receiver system. This is equal to the noise floor measured in the receiver bandwidth (kTW) added to the Base station Noise Figure

Base Ant. Gain dBi The gain attributed to the BTS antennaMobile Ant. Gain dBi The gain attributed to the mobile antenna

Body Loss dBThe loss attributed to your head or hands holding the mobile. This is typically fixed at 3dB


http://en.wikipedia.org/wiki/Kelvin

Parameter Unit Parameter Description

Building/Vehicle Penetration Loss dBThe loss attributed to a signal travelling through a building or car body.

Base Cable Loss dBThe loss in the system due to the cable coupling the antenna to the BTS.

Total Effective Gain - antennas dB

Is the term given to: (Base antenna gain + Mobile antenna gain) – (Body loss + Building/Vehicle loss + cable loss)

Mean Noise Rise dB

Is the design goal margin that is allowed for due to average cell load. A typical value may be 3dB (50% cell loading). When increasing the Noise rise design goal, more users are traded off against lower cell ranges.

Average Eb/No dB

The Eb/No value is a measure of the signal quality required by the UE or Node B in order to recover the required signal from the received signal. Eb/No is highly dependant upon many different parameters such as Bearer Rate, UE speed, Fading profile, Block Error Rate, etc.

Further description is provided below table

Processing Gain dB The ratio of the chip rate / bit rate.

BTS Rx sensitivity dBm

The minimum signal level that the receiver can decode the wanted signal from whilst meeting the specified BER rate.

Soft Handoff Gain dB Gain attributed to the macro diversity combining.

Max Power for UE dBW

Maximum power of the handset which is typically +21dBm. An optional margin of typically 2-3dB may be included to offset power control errors due to fast fading

Fade Margin (single cell) dB

Margin to compensate for slow fading.

Further description is provided below table

2.1.1 Eb/No PerformanceThe Eb/No value is a measure of the signal quality required by the UE or Node B in order to recover the required signal from the received signal. Eb/No is highly dependant upon many different parameters such as Bearer Rate, UE speed, Fading profile, Block Error Rate, etc.

Motorola has produced many curve sets from both link level simulations and equipment measurements. Error: Reference source not found shows a summary of a small set of measured Eb/No values for the Node B.

In Table 3, the value of 1.7dB was used corresponding to 64kbit/s, Pedestrian A model at 3km/hr.

Table 2: Summary of measured Uplink Eb/No values

BLER=1% Ped. A 3km/hr Veh. A 50km/hr Veh. A 120km/hr12.2k 5.0 6.0 6.464k 1.7 2.7 2.9128k 1.6 2.6 2.8


384k 3.7 5.1 5.2

2.1.2 Fade MarginCoverage for all cases is for 90% cell coverage reliability, indoor and outdoor, at 64 kbit/s Uplink and 128kbit/s Downlink. This is implemented within the link budget using a lognormal fading standard deviation of 8dB, which produces a fade margin of 5.4dB for 90% cell coverage reliability. Error: Reference source not found shows how the fade margin varies against cell coverage and fading standard deviation.

Figure 2: Fade margin variation for various UMTS cell coverage reliabilities

For example with 8dB standard deviation, a cell coverage reliability of 95% requires a fade margin of 8.6dB to be added to the link budget. In dense Urban environments, higher standard deviation such as 10dB may be used. This requires 11.7dB fade margin for 95% cell coverage reliability, thus reducing the cell range significantly.

2.1.3 Maximum Transmit Power per User connectionIn the Uplink direction, the standard maximum transmit power for a typical handset is +21dBm (equivalent to -9dBW or 125mW). An additional margin may be used to account for power control error due to fast fading at the edge of the cell. This is typically 2dB, which means that a value of +19dBm is actually used in the link budget for handset transmit power.In the downlink, different maximum power levels per UE connection are used depending upon the service bearer rate. For example, 1W (+33dBm) may be used for a voice user at he edge of the cell but 4W may be available for a 384k data connection. The maximum downlink power per user is set in the database at a level relative to the common pilot channel power and is based upon customer specifications. Within the link budget, a Fast Fade margin may again be used with the maximum power per link.

2.2 Link Budget Parameters Example


Table 3 and Table 4 show examples of link budgets parameter values that would be used to predict indoor coverage in a Dense Urban environment. The following assumptions are applied

Tri-sectored base station site. Uplink is designed for 64kbit/s service with 3dB noise rise (50% cell loading), Downlink for 128kbit/s with 6dB average noise rise (75% cell loading).

Table 3: Uplink Dense Urban Link Budget for Indoor 64 kbit/s CoverageParameter Unit Parameter Definition Value

Chip Rate C/s a 3840000Bit Rate bit/s b 64000Base Station Noise Figure dB c 3.5K J/K d 1.381e-23T K e 290kT dB/Hz f = 10 * Log(d.e) -204.0kTW dB g = 10 * Log(a.d.e) -138.1NthW dB h = c + g -134.6Base Ant. Gain dBi I 18Mobile Ant. Gain dBi j 0Body Loss dB k 2Building/Vehicle Penetration Loss dB m 18Base Cable Loss dB N 3.5Total Effective Gain - antennas dB p = i + j – k – m - n -5.5Mean Noise Rise dB q 3.0Average Eb/No (1% FER) dB r 1.7Processing Gain dB s = 10 * Log (a / b ) 17.8BTS Rx sensitivity dBm u = f + 10*Log(b)+30+r+c -120.7Soft Handoff Gain dB v 2.0Max Power for UE dBW w -11.0Shadow Fade Margin (single cell) dB x 5.4

Table 4: Downlink Dense Urban Link Budget for Indoor 128 kbit/s Coverage

Parameter Unit Parameter Definition ValueChip Rate C/s a 3840000Bit Rate bit/s b 128000Base Station Noise Figure dB c 7.0K J/K d 1.381e-23T K e 290kT dB/Hz f = 10 * Log(d.e) -204.0kTW dB g = 10 * Log(a.d.e) -138.1NthW dB h = c + g -131.1Base Ant. Gain dBi i 18Mobile Ant. Gain dBi j 0Body Loss dB k 2Building/Vehicle Penetration Loss dB m 18Base Cable Loss dB n 3.5


Total Effective Gain – antennas dB p = i + j – k – m - n -5.5Mean Noise Rise dB q 6.0Average Eb/No (1% FER) dB r 4.2Processing Gain dB s = 10 * Log (a / b ) 14.8BTS Rx sensitivity dBm u = f + 10*Log(b)+30+r+c -111.7Soft Handoff Gain dB v 2.0Power for UE DL connection dBW w 3.0Shadow Fade Margin (single cell) dB x 5.4

The link budgets parameters are used to calculate the maximum allowable pathloss for the specified conditions at the edge of the cell. These are given in Table 5.

Table 5: Maximum Isotropic PathlossParameter Unit Parameter Definition Value

Max Uplink Isotropic Pathloss dB y = -h + p – q – r + s + v + w - x 127.8Max Downlink Isotropic Pathloss dB y = -h + p – q – r + s + v + w - x 129.8

3 Propagation Models

Propagation models provide a mathematical formula that can be solved to provide the cell range. Due to the deterministic nature of the models they are generally only valid over a certain range and therefore cannot be generally applied to all situations. For UMTS modelling there are two main models.

I. Modified Hata COST231 for cell ranges over greater than 1km.

II. COST 231 Walfish-Ikegami for cell ranges less than 1km

3.1 Modified Hata COST231 Propagation Model

The basic propagation model used for UMTS is the COST 231 Hata model for frequencies above 1500MHz. This model is detailed in the ETSI GSM specification TR 101 362 V6.0.1 (1987-07).

While Hata’s standard equations are for use up to 1000MHz, COST 231 modifies Hata’s equations to cover propagation losses for systems operating between 1500 and 2000 MHz. Also, strictly speaking, Hata’s model is basically for cell ranges greater than 1km and therefore, an alternative propagation model is included for cell ranges below 1km.

3.1.1 Definitions for Equations

f = frequency (MHz) Hm = mobile station antenna height (m) Hb = base station antenna height (m) d = distance (km)


3.1.2 Urban Area : COST 231 – Hata ModelPropagation loss, Lp = 46.3 +33.9 Log (f) – 13.82 Log (Hb) – A (Hm)

+ {44.9 – 6.55Log (Hb)} * Log (d) + Cm

Correction factor, Cm = 0dB (for medium sized city areas) = 3dB (for high density urban areas)

Mobile correction factor, A (Hm) = {1.1Log (f) – 0.7} * Hm - 1.56 Log (f) – 0.8

3.1.3 Suburban Area: COST 231 – Hata Model Pathloss is Lp – Lps, where

Lps = - 2Log2 { f / 28 } – 5.4

3.1.4 Rural Area: COST 231 – Hata ModelPathloss is Lp – Lpr, where

Lpr = - 4.78Log2 (f) + 18.33Log(f) – 35.94

3.1.5 Open Rural Area: COST 231 – Hata Model

Pathloss is, Lp – Lpo, where

Lpo = - 4.78Log2 (f) + 18.33Log(f) – 40.94

3.1.6 Hata COST231 Propagation Model Example

The following example is based on using a macro base station. The assumptions made for the macro base station are provided:

Uplink frequency of 1940MHz, Downlink frequency 2140MHz, 1.5m mobile antenna height, 25m base station antenna height for all environments.

Using these numbers, the above equation for Lp yields the following simple equations for each environment:Error: Reference source not found

Table 6: Summary of COST231 Propagation Model Values

Clutter Type Propagation model - UL Propagation model - DL

Dense urban Lp = 138.5 + 35.7*Log (d) Lp = 139.8 + 35.7*Log (d)

Urban Lp = 135.5 + 35.7*Log (d) Lp = 136.8+ 35.7*Log (d)

Suburban Lp = 126.3 + 35.7*Log (d) Lp = 127.3+ 35.7*Log (d)

Rural Lp = 111.1 + 35.7*Log (d) Lp = 111.9 + 35.7*Log (d)


Lp refers to the propagation loss between the base station antenna and the mobile station antenna and can be calculated from the link budget. ’d’ is the distance between the UE and Node B antennae. Thus once the propagation loss is calculated for a certain environment, the variable ‘d’ can be obtained to establish the maximum range of the cell.

The propagation loss Lp must be derived for each specific case using a standard link budget calculation. These equations may be used for macro cells only and not micro or pico cells.

In the propagation loss table, the COST 231 Hata equation for Dense urban environments is:

Lp = 138.5 + 35.7 * Log (d)

Substituting Lp for the Uplink Pathloss of 127.8dB from Table 3:

Uplink Cell Range (d) = 0.50 km

Therefore, in a dense urban environment, for 64 kbit/s service, the maximum indoor range of a tri-sectored cell with 50% mean loading is 0.50 km.

3.2 COST 231 Walfish-Ikegami Propagation Model This model provides a method of estimating small cell ranges (<1km), in dense metropolitan urban areas, where there is no line of sight between the Node B and UE. This model has been simplified slightly for the purpose of this document, an explanation of which will be given as the equations are defined.

3.2.1 COST 231 Walfish-Ikegami Propagation Model Pathloss, Lb = Lo + Lrts + Lmsd

Free space loss, Lo = 32.4 + 20 * log( d ) + 20 * log( f )

Roof top to street diffraction and scatter loss; Lrts = -16.9 – 10 * log( w ) + 10 * log( f ) + 20 * log ( Hr – Hm ) + LcriLcri = -10 + 0.354 * Phi { 0 <= phi < 35 deg)Lcri = 2.5 + 0.075 * ( Phi -35) { 35 <= phi < 55 deg)Lcri = 4.0 - 0.114 * ( Phi – 55 ) { 55 <= phi < 90 deg)

Multiscreen diffraction loss;Lmsd = Lbsh + 54 +18 * log( d ) – 2.34 * log( f ) – 9 * log( b )

Lbsh = -18 * log( 1 + Hb – Hr )

Where; d = cell range (to be calculated)f = frequency (UL = 1940MHz, DL = 2150MHz)w = width of road (assume 20m)Hr = height of roof (assume 20m)Hm = height of mobile (assume 1.5m)Hb = height of Node B antenna (assume 30m, i.e. 10m above average roof level)Phi = road orientation with respect to direct radio path (assume 45 deg)b = building separation (assume 30m)


The model has only been considered for cases where the Node B antenna is above the average building height to simplify the examples shown. All the terms in the equation for Lmsd have variable values depending upon antenna height relative to roof height.

Therefore, for Uplink dense urban environment;

Lo = 32.4 + 20 * log (1940) + 20 * log (d) = 98.2 + 20 * log (d)

Lrts = -16.9 – 10 * log (20) + 10 * log( 1940 ) + 20 * log( 18.5 ) + Lcri

Lcri = 2.5 + 0.75 = 3.25

Therefore, Lrts = 31.55

Lmsd = -18 * log (11) + 54 + 18 * log (d) – 2.34 * log (1940) – 9 * log (30) = 14.27 + 18 * log (d)

Therefore, Lb = Lo + Lrts + Lmsd

Uplink Pathloss, Lb = 98.2 + 20 * log (d) + 31.55 + 14.27 + 18 * log (d) = 144.0 + 38 * log (d)

As before, with the Hata Model, the pathloss calculated from the link budget can be substituted into this equation in order to estimate the maximum cell range.

From Table 3 Uplink Dense Urban Pathloss = 127.8dB

Therefore, 127.8 = 144.0 + 38 * log( d )

Uplink cell range, d = 0.37 km

3.3 Propagation Model Summary

This alternative (COST 231 Walfish-Ikegami) model has produced a cell range of 0.37km compared to the range of 0.50km obtained with the COST 231 Hata model.

It is recommended that the Hata model is used only for Suburban and rural environments where cell ranges greater than 1km are predicted.


Documents

UMTS Link Budget