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Tuesday, July 10, 2012

Link Budget Calculation Example for UMTS

The following assumption are aplied Three sectored base station site Uplink is designed for 64 kbit/s service with 3dB noise rise ( 50% cell

loading) Downlink for 128 kbit/s with 6 dB average noise rise (75% cell loading)

Uplink Dense Urban Link Budget for Indoor 64 kbit/s Coverage

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

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The link budgets parameters are used to calculate the maximum allowablepathloss for the specified conditions at the edge of the cell. Maximum isotropicpathloss,

Maximum Uplink Isotropic PathlossMax = - NthW + Tottal effective Gain - Mean Noise Rise - average Eb/No +Processing Gain + Soft Handoff Gain + Power for UE DL connection - Shadow FadeMarginso, maximum uplink isotropic pathloss = 127.8 dBm

Maximum Downlink Isotropic PathlossMax = - NthW + Tottal effective Gain - Mean Noise Rise - average Eb/No +Processing Gain + Soft Handoff Gain + Power for UE DL connection - Shadow FadeMarginso, maximum downlink isotropic pathloss = 129.8 dBm

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

Modified Hata COST231 for cell ranges over greater than 1km. COST 231 Walfish-Ikegami for cell ranges less than 1km

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Modified Hata COST231 Propagation Model ( > 1 km)The basic propagation model used for UMTS is the COST 231 Hata model forfrequencies above 1500MHz. This model is detailed in the ETSI GSM specificationTR 101 362 V6.0.1 (1987-07). While Hatas standard equations are for use up to1000MHz, COST 231 modifies Hatas equations to cover propagation losses for

systems operating between 1500 and 2000 MHz. Also, strictly speaking, Hatasmodel is basically for cell ranges greater than 1km and therefore, an alternativepropagation model is included for cell ranges below 1km.Definitions for Equations f = frequency (MHz) Hm = mobile station antenna height (m) Hb = base station antenna height (m) d = distance (km)a. Urban Area : COST 231 Hata Model

Propagation 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) 0.8b. Suburban Area: COST 231 Hata Model

Pathloss is Lp Lps, whereLps = - 2Log2 { f / 28 } 5.4

c. Rural Area: COST 231 Hata ModelPathloss is Lp Lpr, where

Lpr = - 4.78Log2 (f) + 18.33Log(f) 35.94d. Open Rural Area: COST 231 Hata Model

Pathloss is, Lp Lpo, where

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

Hata COST231 Propagation Model ExampleThe following example is based on using a macro base station. The assumptionsmade 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 simpleequations for each environment:Error: Reference source not found

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Lp refers to the propagation loss between the base station antenna and themobile station antenna and can be calculated from the link budget. d is thedistance between the UE and Node B antennae. Thus once the propagation loss iscalculated for a certain environment, the variable d can be obtained toestablish the maximum range of the cell.The propagation loss Lp must be derived for each specific case using a standardlink budget calculation. These equations may be used for macro cells only andnot micro or pico cells. In the propagation loss table, the COST 231 Hataequation 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 maximumindoor range of a tri-sectored cell with 50% mean loading is 0.50 km.

COST 231 Walfish-Ikegami Propagation ModelThis model provides a method of estimating small cell ranges (

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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 theequation for Lmsd have variable values depending upon antenna height relativeto 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 ) + LcriLcri = 2.5 + 0.75 = 3.25

Therefore, Lrts = 31.55Lmsd = -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 canbe substitutedinto this equation in order to estimate the maximum cell range.

Uplink Dense Urban Pathloss = 127.8dB

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

Uplink cell range, d = 0.37 km

This alternative (COST 231 Walfish-Ikegami) model has produced a cell range of0.37km compared to the range of 0.50km obtained with the COST 231 Hatamodel. It is recommended that the Hata model is used only for Suburban andrural environments where cell ranges greater than 1km are predicted.