
2/35

Mobile Com-

munications


Figueras

Agenda

Topic 1: Fundamental of Cellular Radio Networks

1 General Concepts of Telecommunication Networks2 Link Budget and Interference

3 Experimental Propagation Models for Cellular Radio

Networks

4 Basic Traffic Concepts


3/35

Mobile Com-

munications


Figueras

Environment is not perfect....

There are several effects that could affect the qualityexperienced by the end user in a mobile communication system

Noise

From external sources.

From the receiver.

Interference experienced at the receiver

Co-channel interferer: other MS transmit at same frequency (frequency reuse) as the receiver listens.

Adjacent interferer: other MS uses adjacent frequencies for transmissio.

Fading

Due to mobile channel effects: houses .

Multipath Shadowing.


4/35

Mobile Com-

munications


Figueras

Link Budget

Link budgets are used to calculate the coverage or cell range inthe UL and in the DL.

BTS use higher power that mobile.

TOTAL Coverage= Minimum (coverage in DL, coverage in UL)

For this reason, the coverage in UL is always the limiting factor.

The minimum performance requirements regarding the BTSreceiver and the MS receiver are fixed by the standardizationbodies.

This minimum performance requirements determine the MS andBTS receiver sensitivity.

Example from 3GPP for TU50iFH for EDGE in 900Mhz bandand Coding MCS5 BLER 10%

BTS receiver sensitivity= -97dBm.

MS receiver sensitivity= -94dBm


5/35

Mobile Com-

munications


Figueras

Link Budget

Receiver sensitivity (minimum accepted received signal level) for BTSand MS are specified in the standard 3GPP:

For frequency bandFor different channels Typical urban, rural areaFor the queality levelSNR.

Receiver Sensibility=SNR+Noise.Noise=Thermal Noise+Noise Bandwidth+Fr

Thermal Noise = -174dBm / Hz.

Noise Bandwidth (depends on the receiver filter) typical value forGSM 52.6 dB.

Noise Figure, typicall value 5 dB.

Typical noise value at the receiver filter output = -116.4 dBm

The receiver sensitivity determine the maximum allowed pathloss and

hence, the maximum cell range


6/35

Mobile Com-

munications


Figueras

Link Budget

General Link Budget Equation

PTX+

G L LPathloss=SRXWhere

PTX: Transmitter Power.

G: Gain of the diff

erent equipment (dB).L: Losses of the different equipment (dB).

SRX: Receiver Sensibility.


7/35

Mobile Com-

munications


Figueras

Link Budget

Free Space Pathloss

LFreePathloss= 32 + 20Log(f) + 20Log(d)

Where

f: Frequency in MHz.

d: Distance in Km.


8/35

Mobile Com-

munications


Figueras

Propagation Models

We have obtained previously the values for the total pathloss and our first estimation of the range using the freespace formulation.

However it is straight forward to see that we are not in afree space environment so we have to study some other

methods.Propagation methods may be classified into two maincategories:

Theoretical Models: They come from theoreticalsimulations and mathematical studies.

Simulation of Wave Propagation.Ray Theory.

Experimental models: They come from measures in realworld

COST 231 Hata ModelCOST 231 Walkfish Ikegami.PCS


9/35

Mobile Com-

munications


Figueras

COST 231 - Hata Model

Path loss estimation is performed by empirical models ifland cover is known only roughly, and the parametersrequired for semi-deterministic models cannot bedetermined.

One of the most extended model is the Okumura Hata.This model was developed by Y. Okumura using a set ofequation which required to go to a large set of curvesobtained from empirical measurements.

M. Hata performs the first extension of this equations.

The model is based in four parameters

1 Frequency f (MHz).2 Distance d (Km).3 BTS antenna height hBTS (m).4 Mobile antenna height hMobile (m).


10/35

Mobile Com-

munications


Figueras


The basic transmission loss Lbcan be calculated asfollows.

Lb= 66.95 + 26.16Log(f)13.82Log(hBTS)a(hMobile)+(44.95

6.55Log(hBTS))Log(d)

Where:

a(hMobile) = (1.1logf 0.7)hMobile (1.56log(f) 0.8)


11/35

Mobile Com-

munications


Figueras


The model is restricted to:

f : 150...1000MHzhBTS : 30...200m.hMobile : 1...10m.d : 1...20Km

COST 231 has extended Hatas model to the frequencyband 1500


12/35

Mobile Com-

municationsJose Antonio

PortillaFigueras


Lb= 46.3 + 33.9Log(f)

13.82

Log(hBTS)a(hMobile)+(44.95 6.55Log(hBTS))Log(d) +Cm

Where a(hMobile) is defined as in the previous model and Cm:

Cm =

0dB for medium sized cities and suburban centres3dB for metropolitan centres


13/35

Mobile Com-


PortillaFigueras


The model is restricted to:

f : 150...2000MHzhBTS : 30...200m.hMobile : 1...10m.d : 1...20Km

The application of the COST-Hata-Model is restricted to

large and small macro-cells,


14/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

COST 231 proposed a combination of the Walfisch andIkegami model that is called theCOST-Walfisch-Ikegami-Model (COST-WI).It calculates improved path-loss estimation byconsideration of more data to describe the character of the

urban environment:Heights of buildings hRoof.Widths of roads wbuilding separation broad orientation with respect to the direct radio path .

Note that although we use some special values this modelis still statistical because we only use characteristic values.


15/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

The model distinguishes between line-of-sight (LOS) andnon-line-of-sight (NLOS) situations.

In the LOS case -between base and mobile antennas

within a street canyon - a simple propagation loss formuladifferent from free space loss is applied.

The loss is based on measurements performed in the cityof Stockholm

COST 231 - WI for LOS

Lb= 42.6 + 26Log(d) + 20Log(f) for d 20m


16/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

In the NLOS-case the basic transmission loss Lb iscomposed of the terms:

Free space loss L0,

Multiple screen diffraction loss LmsdRoof-top-to-street diffraction and scatter loss Lrts.

COST 231 - WI for LOS

Lb=

L0+Lrts+Lmsd Lrts+Lmsd>0L0 Lrts+Lmsd 0


17/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

Lets study the diff

erent terms that composes the model

The term Lrtsdescribes the coupling of the wave along themultiple path into the street where the mobile terminal is

located, that is, the roof-top-to-street diffraction andscatter loss.

Lrts= 16.9 10Log(w)+10Log(f) + 20Log(hMobile) +LOri

hMobile=hRoof hMobilehBase=hBase hRoof

The values for LOriand its explanation are in the following

slide


18/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

LOri=

10 + 0.354 0 352.5 + 0.075( 35) 35 554.0 + 0.114

( 55) 55 90


19/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

Now we have to deal with the effect of the multi screendiffraction, that is, Lmsd.

This part of the model is usually used when the antennaheight of the BTS is below the roof-top.

Lmsd=Lbsh+ka+kdLog(d) +kf Log(f) 9Log(b)

Where:

Lbsh =

18Log(1 + hBase) hBase>hRoof0 hBase hRoof


20/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

The term ka represents the increase of the path loss forbase station antennas below the roof tops of the adjacentbuildings.

ka =

54 hBase>hRoof

54 0.8 hBase d 0.5 hBase hRoof54 0.8 hBase d0.5 d


21/35

Mobile Com-


PortillaFigueras

COST 231 - WI Model

The terms kd and kfcontrol the dependence of themulti-screen diffraction loss versus distance and radiofrequency, respectively.

kd =

18 hBase>hRoof18 15 hBase

hRoofhBase hRoof

kf =

0.7( f925 1) Medium sized cities and suburban

1.5( f925 1) Metropolitan centers


22/35

Mobile Com-munications


Figueras

COST 231 - WI Model: We are finishing

An important problem in this method is to obtain values of thedifferent parameters.

Note that is most cases these models are used to perform studies inseveral and quite different cities, and hence not all parameters areknow.

If the data on the structure of buildings and roads are unknown thefollowing default values are recommended:

Recommended Values

hRoof = 3(Number of floors) + (roof height)

(roof height) =

3 pitched0 flat

b= 20...50.w=b/2= 90


23/35



Figueras

COST 231 - WI Model: The last slide

Conditions

The model is restricted to:f : 800...2000MHzhBTS : 4...50m.hMobile : 1...4m.d : 0.02...5Km

C


24/35



Figueras

Interference Calculations

When number of users start to increase (higher traffic) itis needed to calculate the interference in the system inorder to know if the quality criteria are fulfil.

So we have to two factors to analyze.

Receiver sensibility that comes from the SNR of the serviceand the Noise.Carrier to Interference ratio C/I.

In urban environments the C/I will be often the limitingfactor

I f C l l i


25/35



Figueras


We would like to evaluate C/I en certain position.

C= carrier power.

I= Interference power.

We may have two situations

Interference downlink: Received by the MS and generatedby transmission of other BTS using same frequencies(cochannel).Interference uplink : Received by BTS listening to certainMS. Interference generated by other MS (located in othercells) using same frequencies (cochannel).

It is straight forward to see that the most dominant one will be the

downlink.There are two ways to evaluate that we fulfill the quality criteria:

C/I> C/I threshold where C/I threshold is the designcriteria at the end of the cell that result in certain quality.Prob(C/I>C/I threshold),

p example: 90 % (More

Exact)

I f C l l i


26/35



Figueras


This illustration shows the C over I calculation scenario.

I t f C l l ti


27/35



Figueras


Interference Equations

I = 6 PTD

+ 6 PT(

3D)+ 6 PT(2D)

C = PTR

Where:

I: Interference power.

C: Carrier power

D: Reuse distance.

: Power depravement ratio.

R: Cell Range.

Only considered three circumferences over the target cell.

I t f C l l ti


28/35



Figueras


The minimum physical distance between two transmittersusing the same frequency required to achieve certain linkquality is denoted at Reuse Distance, D.

Note the influence ofD

with

.Values of

Free space propagation = 2.

In mobile communications = 3 5

= 3 correspond with rural areas.

= 5 correspond with high-rise buildings areas.

R s All ti


29/35



Figueras

Resource Allocation

Our most scarce resource is the frequency.

In figure above the coverage area is organized in 4 groupsof 7 cells marked in different colors Cluster.

Each MS will connect with a BTS depending on thelocation

In this case each BTS has been located in the middle ofthe cell, using Omni directional antenna.

Resource Allocation


30/35



Figueras

Resource Allocation

Each BTS is able to use n frequencies

The total number of frequencies is 7n

Frequencies are reused in neighboring clusters

Example number of frequencies

In the 900 MHz band the bandwidth for GSM is 25 MHz,divided by 3 operators it is about 8 MHz.

This means 40 different frequencies (GSMBW= 200KHz)for each operator.

Hence about 5 frequencies will be assigned for each cell.

Resource Allocation


31/35



Figueras

Resource Allocation

If we have Nfrequencies available, each cell can use N/Kwhere K is the size of the group

We define frequency reuse factor as Reuse= K where

K is number of cells that belong to same cluster.

Reuse factor or cluster size is a compromise betweencapacity and quality

Small reuse factors result in high interference & highcapacity (more channels)High reuse factors result in low interference & low capacity(less channels)

Resource Allocation


32/35



Figueras

Resource Allocation

If we have Cavailable channels, we divide them into Kgroups of approximately equal size.

Each BTS will have assigned a group ofnf = CK.The number nf is orientation of the capacity of the system

Channel could not be reused in a cell that is to closebecause is needed to maintain quality requirements and we

saw that Reuse Distance=f(S.I.R required))


33/35

Resource Allocation


34/35



Figueras

Resource Allocation

Symmetric cell plans exist for K = 1, 3, 4, 7, 9, 12, .

Formulation for the Cluster definition

K = (i+j)2 i

j i,j= 0, 1, 2, 3...

It is possible to demonstrate that the distance D betweentwo cells with the same channels is.

6 Closest channels, distance D.Next circumference, other 6 cochannels

3D

Next circumference, 2D.

Resource Allocation additional information


35/35



Figueras

Resource Allocation, additional information

In the previous examples the BTS was located in themiddle of the cell using an omni directional antenna.

In urban environments and indoor coverage is more

complicated and BTS usually use directive antennas.

In this way the cell is divided typically in three Sectors

Each antenna reaching 120.

Each sector has its own frequency set and it is basically a

cell.In highways typically cells with 2 sectors are used (180).

mobile communications topic 12 link budget interference

Documents