Module 9 Advanced Radio Systems

8/4/2019 Module 9 Advanced Radio Systems

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The Medium ofRadio


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Objectives


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The EM SpectrumWavelength Designation

10-15

Gamma Rays10-14

10-13

10-12

10-11

X-Rays10-10

10-9

10-8

10-7 Ultraviolet1m Visible Light

10m Near Infrared

100mFar Infrared

1mm

10mm

Microwave100mm

1m UHF

10m

Radio

VHF

100m HF

1km MF

10km LF


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The EM Spectrum

RadioThe radio spectrum ranges from a frequency of 30 KHz 30 GHz.Within this range there are many applications that have beendeveloped.

MicrowaveMicrowaves range from 1Ghz 30Ghz.

Infra-redFar infrared are heat waves. Near infrared are used for optic fibrecommunications.

UltravioletHave a higher frequency than visible light. Used in optic fibres.

X-rays

Very high energy radiation that can pass through objects. Widely used inmedical diagnostics

Gamma rays


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Low Frequency Transmission

Low frequency signals such as those in theLF,MF cover frequencies of up to 2 Mhz.They can propagate using ground waves.

Earth


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High Frequency Transmission

High frequencies can be refracted by theupper layers of the atmosphere especially theionosphere and troposphere. When the signal

reaches a highly ionized layer its bent backto a lower ionization region. This is known assky wave propagation.


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Sky Wave Propagation

Earth

Ionosphere

Radio signalis refractedback to earth

by theionosphere


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Very High Frequency Transmission

At the VHF, UHF and SHF bands most of theradio propagation is transmitted by directwaves. Most of the signal relies on line of

sight propagation. As the frequencyincreases, attenuation also increases makingit necessary to have highly focused,

directional antennas for microwavetransmission.


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Line of Sight Transmission


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UHF Propagation

Refrection


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Refraction

UHF radio waves will

bend slightly over thehorizon. The amountof refraction dependson the ambienttemperature,humidity, frequencyand air density.


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Penetration

UHF radio wavesare capable ofpenetratingthrough solidmaterial such asconcrete orglass. On passingthrough suchobstacles thewaves undergoattenuation.


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Diffraction

Diffraction is thebending of thewavefront which occurs

when the waves meetan object such as abuilding.


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Multipath Propagation


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Signal Cancellation and addition

Signal Cancellation Signal Addition

+ = + =


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Rician Fading

In a ricianfading channelthere is adominant radiopath whichmay be theline of sightpath or strongreflection. Thedominant pathwill be distortedby minorreflections. The

magnitude offading is of theorder of 1030 dB.


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Rayleigh Fading

In a rayleighfading channelthere is nodominant radiopath . All theenergy receivedconsists of low

power reflectedsignals, whichleads to fastfading . Themagnitude offading can beup to 40 dBcompared to thenon fadingchannel.


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Principles ofPropagation


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Electromagnetic Wave


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EM Wave

Electric and magnetic fields oscillate togetherbut perpendicular to each other and theelectromagnetic wave moves in a direction

perpendicular to both of the fields. Electromagnetic waves are formed when an

electric field couples with a magnetic field

The magnetic and electric fields of anelectromagnetic wave are perpendicular toeach other and to the direction of the wave.


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Radiation of EM Waves

Omni-Directional Radiation

Directional Radiationusing Reflector


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Shadows

Solid Object

Shadow


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Radio shadow

Antenna

Radio Shadow


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Attenuation

RadioEnergy

Distance

Attenuation refers to the fact that the radio energydecreases as the distance from the source antennaincreases. There are several methods used to calculateattenuation


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Fresnel Zone


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Fresnel Zone

If unobstructed, radio waves will travel in a straightline from the transmitter to the receiver. But if thereare obstacles near the path, the radio wavesreflecting off those objects may arrive out of phasewith the signals that travel directly and reduce thepower of the received signal. On the other hand, thereflection can enhance the power of the receivedsignal if the reflection and the direct signals arrive inphase. The point at which the loss reaches 0 dB forthe first time is called the first Fresnel zone.


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Clutter

Buildings and foliage obstruct transmissionpath.

Radio Waves diffract over rooftops. Waves penetrate buildings

Waves reflect from buildings.


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Clutter

Clutter refers to actual radio frequency (RF)echoes returned from targets. Such targetsmostly include natural objects such as

ground, sea, precipitation (such as rain, snowor hail), atmospheric turbulence, and otheratmospheric effects, such as ionospherereflections and meteor trails. Clutter may alsobe returned from man-made objects such asbuildings.


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Ducting

Waveguide effect in:

TunnelsStreet CanyonsAtmospheric layers

Inside Buildings


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Ducting

Ducting can result in better than free spacepropagation. It is a waveguide effect, whichis used in optical fibres and cables. This good

propagation mainly causes problems withinterference and with cell areas beingextended beyond what was intended.


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Free Space Path Loss

2

4

d

PPtr


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Propagation Models

A radio propagation model, also known as the RadioWave Propagation Model or the Radio FrequencyPropagation Model, is an empirical mathematicalformulation for the characterization of radio wave

propagation as a function of frequency, distance andother conditions. A single model is usuallydeveloped to predict the behavior of propagation forall similar links under similar constraints. Createdwith the goal of formalizing the way radio waves arepropagated from one place to another, such modelstypically predict the path loss along a link or theeffective coverage area of a transmitter.


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Plane Earth Path Loss Model

The plane earth propagation model is relatively simple, consistingonly of two paths which can be analyzed mathematically. The modelfits extremely well to measurements made over a flat surface, suchas a tarmac car park.


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Okumura-Hata

In wireless communication, the Okumura-Hatamodel is the most widely used radio frequencypropagation model for predicting the behaviour ofcellular transmissions in built up areas. This model

incorporates the graphical information fromOkumura model and develops it further to realize theeffects of diffraction, reflection and scatteringcaused by city structures. This model also has twomore varieties for transmission in Suburban Areasand Open Areas. The Hata Model predicts the totalpath loss along a link of terrestrial microwave orother type of cellular communications.


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Radio Spectrum Sharing

Bodies that administer radio spectrum

ITU (International Telecommunications Union)

CEPT (Conference Europeen de Post etTelegraph)

ETSI (European Telecommunications StandardsInstitute)


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Multiple AccessMethods


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Multiple Access Techniques

Multiple Access Achieved by dividing the available radiofrequency spectrum, so that multiple users can be given accessat the same time.

FDMA - Frequency Division Multiple Access

( eg: GSM each Frequency channel is 200KHz) TDMA - Time Division Multiple Access

( eg: GSM each frequency channel is divided into 8timeslots)

CDMA - Code Division Multiple Access (eg: CDMAOne - Each User data is coded with a unique

code)


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Duplex Technique

Duplex - How the up link and Down link of a user is

separated

FDD - Frequency Division Duplex

(eg:In GSM the up link and down link of a user is separated

by 45MHz ) TDD - Time Division Duplex

(the up link and down link of a user will be at the samefrequency but at different Time )


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GSM Frequencies

GSM-900 (Channels 125, operating band 900Mhz, carrierspacing 200khz, spacing 45Mhz)

GSM -1800 (Channels 374 spacing 95Mhz)

GSM -1900(Used in USA)


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GSM Band Allocations (MHz)

Carrier frequency = ARFCN =Absolute Radio Frequency Channel Number

Frequencies are in MHz

GSMsystems

Uplink Downlink BandDuplexSpacing

Duplexchannels

GSM 900E-GSM (900)

890-915880-915

935-960925-960

2x252x35

4545

124174

GSM 1800

GSM 1900

1710-1785

1850-1910

1805-1880

1930-1990

2x75

2x60

95

80

374

299


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GSM in Kenya

GSM Frequency Allocation (MHz)

880 882.5 Orange 925 927.5

882.5 890 Yu 927.5 935

890 900 Safaricom 935 945

900 905 Orange 945 950

905 - 915 Zain 950 960


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Frequency Division Multiple Access

1 2 3 4 5 6 7 . . . . .

200KHz

In FDMA the allocated frequency band is subdivided into multipleequal channels.


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Time Division Multiple Access

1 2 3 4 5 6 7 . .

0 1 2 3 4 5 6 7

TDMA Frame = 8 Time Slots


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TDMA

Each frequency channel is divided into aframe of 8 time slots.

Each mobile is assigned a time slot

Mobiles use Burst transmission. Only duringthe allotted time slot will the mobile beactually radiating power.


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TDMA Frame


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TDMA frame structure

Bit rate of the radio carrier is 270.833 Kbps

Bit duration =1/270.833=3.69 sec

One time slot =148 bits+8.25 guard bits=156.25bits

Time slot duration =156.25x3.69 sec= 0.577msec

Frame duration=0.577x8= 4.615 msec


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Cellular FrequencyReuse


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Cellular Principles

BTS-1 BTS-2

BTS


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Cellular Principles

Mobile networks require high capacity to support millionsof users. Traditional techniques such as PMR use asingle radio channel which cannot support a largenumber of users.

Cellular radio is based on re-use of frequencies. Lowpower transmitters are used to limit the range. Eachfrequency can be used multiple times as long as co-

channel cells are spaced apart.


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Frequency Reuse

Reuse Distance


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Frequency Reuse

A given radio carrier used at a particularlocation may be reused at some minimumdistance provided the distance is sufficient to

reduce mutual interference to a manageablelevel. GSM specifications require a minimumCarrier to Interference (C/I) ratio of 9 dB.


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Cellular Reuse Pattern

R

D

kRD 3Where:

D is the reuse distanceR is cell radiusk is cluster size


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Co-Channel C/I Ratio

To calculate the level of interference for agiven reuse pattern the distance between theco-channel cells must be known and some

assumptions made about the way the radiosignal propagates over the system.

/


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Co-Channel C/I Ratio

4

1

DP

31D

P

Urban :

Rural :

If these assumptions aremade its possible to

approximate the C/I

ratio in cellular systems.

/


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C/I Ratio

R

D

D - R

/


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C/I Ratio

ni

RDP

)(

1

nC

RP

1

Pc is the carrier power (wanted signal)Pi is the interference power (unwanted signal)n is the index of propagation

The Carrier to Interference ratio is given by:

n

i

C

R

D

I

C

P

P

1log10

and

f d


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Interference and Reuse Pattern Size

k n = 3 n = 4

3 9 dB 12 dB

4 11 dB 15 dB

7 16 dB 21 dB

9 18 dB 24 dB

12 23 dB 31 dB

Adj Ch l I f


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Adjacent Channel Interference

This is interference that results from channelsthat are next to each other on the frequencyspectrum.

In practice theres a minimum adjacentchannel separation between frequencieswithin a given cell. (typically 4 carriers).


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The GSM AirInterface

R di Li k A


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Radio Link Aspects From Speech to RF Signal

Blah Blah Blah...Blah... Blah... Blah...

Digitizing andSource Coding

Channel Coding

Interleaving

Ciphering

Burst Formatting

Modulating Demodulating

Burst De-formatting

Deciphering

De-interleaving

Channel Decoding

Source Decoding

GSM B d All ti (MH )


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GSM Band Allocations (MHz)

Carrier frequency = ARFCN =Absolute Radio Frequency Channel Number

Frequencies are in MHz

GSMsystems

Uplink Downlink BandDuplexSpacing

Duplexchannels

GSM 450GSM 480GSM 850

450.4-57.6478.8-486824-849

460.4-467.6488.8-496869-894

2x7.22x7.22x25

101045

3535124

GSM 900

E-GSM (900)R-GSM (900)

890-915

880-915876-880

935-960

925-960921-925

2x25

2x352x04

45

4541

124

17440

GSM 1800GSM 1900

1710-17851850-1910

1805-18801930-1990

2x752x60

9580

374299


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Air InterfaceUplink and downlinkTwo carriers make up the radio channel required forcommunication between the Mobile Station and the BaseTransceiver Station.


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Frequency bandUplink 890 - 915 MHzDownlink 935 - 960MHz

Duplex Frequency Spacing 45MHz

Carrier separation 200KHzFrequency Channels 124Time Slots /Frame(Full Rate) 8Voice Coder Bit Rate 13KbpsModulation GMSKAir transmission rate 270.833333 KbpsAccess method FDMA/TDMASpeech Coder RPE-LTP-LPC

GSM 900 System specifications

P i d R di Ch l i GSM


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890 MHz 915 MHz 935 MHz 960 MHz

Uplink Downlink

Example:

Channel 48

0 124channel # 0 124channel #

Frequency Frequency

Duplex spacing = 45 MHzFrequency band spectrum = 2 x 25 MHzChannel spacing = 200 kHz

BTS

Paired Radio Channels in GSMCase of GSM 900


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AIR INTERFACE Types of channels

1. Physical channels

2. Logic channels

Physical Channels


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Physical Channels

TS TS TS TS TS TS TS TS

0 1 2 3 4 5 6 7

Time

4.615 ms

TDMA frame

Physical channel # 2 = recurrence of time-slot # 2

TDMA frame

0 9.23 ms

Time-slot

(frames repeat continuously)

TS TS TS TS TS TS TS TS

0 1 2 3 4 5 6 7

Ph i l Ch l


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Physical Channels

A TDMA frame contains 8 successive Time-Slots(TS) with a duration of 60/13 ms or4.615385 ms.

A TS, has a duration of 15/26 ms or 0.576923 ms.

A physical channel is made of the recurrence ofthe same TS taken from successive frames of thesame channel.

GSM Delays Uplink TDMA Frames


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Downlink TDMA

T T T T T T T T

R TMS1

R TMS2

Downlink

Uplink

Fixed transmitdelay of three

time-slots

R R R R R R R R

0 1 2 3 4 5 6 7

The start of the uplink TDMAis delayed of three time-slots

BTS side

MSs side

BTS

TDMA Frame (4.615 ms)



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The start of an uplink TDMA frame is delayed with respectto the downlink by a fixed period of three Time Slots. Why?

In GSM, all radio frequency channels in a given cell aresynchronized such that the frame and time slot boundaries

on all downlink radio frequency channels occur at the sametime. The same is true for the uplink radio frequencychannels in that cell. However, the uplink frames aredelayed by three time slots from the downlink frames. Thisprevents an MS using a single time slot in each direction

from having to transmit and receive simultaneously andreduces the cost and complexity of GSM handsets.

Ti i Ad


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Timing Advance1 - Propagation Delay

M2 M1d1>>d2d2

BTS Frame reference

MSs transmit

Propagation Delay tp

TS0 TS1 TS2 TS3 TS4 TS6TS5 TS7

Bits Overlapping

Timin Ad n


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Timing Advance

On the radio path, propagation delays cannot be ignored.Indeed, 1 km corresponds to a propagation delay of 3.33s (compared with a bit period of 48/13 = 3.7 s).

But the BTS receives continuously, and has its own

scheduling. The mobile station must itself balance thepropagation delay, in order to avoid overlapping in theframe received by the BTS.

This is why the system takes into account these timingdelays and orders the mobile station to transmit with an

anticipation called the Timing Advance.

Timing Advance


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Timing Advance

For technical reasons, it is necessary that the MS and the BTS do nottransmit simultaneously. Therefore, the MS is transmits threetimeslots after the BTS. The time between sending and receiving datais used by the MS to perform various measurements on the signal

quality of the receivable neighbor cells. Depending on the distancebetween the two, a considerable propagation delay needs to be takeninto account. That propagation delay, known as timing advance (TA),requires the MS to transmit its data a little earlier


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Types of Logical Channels Types of logic channels

1. Traffic channels

2. Control channels

TDMA frame Structure


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TDMA frame Structure

Normal Burst

3113 57 5726

Normal Burst


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Normal Burst

3 start and stop bits A 26 bit training sequence in the middle f each

burst. Its used to estimate the channel distortioncaused by multipath fading, a process known asequalisation.

114 data bits. This represents the digital data to betransmitted and is equivalent to an overall bit rate of22.8 kbps. In all cases this capacity includes someredundancy used for error control.

2bits either side of the training sequence are used toindicate the presence of a signaling channel knownas the FACCH.


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The GSM LogicalChannels

Hyperframe, Superframe, Multiframe and Burst


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Hyperframe, Superframe, Multiframe and Burst

TDMA Frame and Burst


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TDMA Frame and Burst

Hyperframe Superframe Multiframe


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Hyperframe, Superframe, Multiframe

In a GSM system, every TDMA frame is assigned a fixednumber, which repeats itself in a time period of 3 hours, 28minutes, 53 seconds, and 760 milliseconds. This time period isreferred to as hyperframe.

Two variants of multiframes, with different lengths, need to be

distinguished. There is the 26-multiframe, which contains 26 TDMA frames with

a duration of 120 ms and which carries only traffic channels andthe associated control channels.

A 51-multiframe, which contains 51 TDMA frames with a durationof 235.8 ms and which carries signaling data exclusively.

Each superframe consists of twenty-six 51-multiframes or fifty-one 26-multiframes.

Why 26 and 51 Frames per Multiframe?


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Downlink

message

Uplinkmessage

Neighboring BTS(downlink)

Measurement Windows

C CF SC CF SC CF SC CCBF S F S F S

0 1 12 25 0 1 12 25

0 1 10 20 30 40 50 0 1

T AT T T T T T T T T T TT T T T T T T T T T T T T AT T T T T T T T T T TT T T T T T T T T T T T

Mobile

activity

Rx Rx Tx Rx Rx Tx Rx Rx Tx

(n) (n) (n)

y p

Channels : Differentiating between


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Channels : Differentiating between

Physical and Logical channels

Physical channels : The combination of an ARFCNand a time slot defines a physical channel.

Logical channels : These are channels specified byGSM which are mapped on physical channels.

Ch l


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Physical channel:

One timeslot of a TDMA-frame on one carrieris referred to as a physical channel.There are 8 physical channels per carrier inGSM, channel 0-7(timeslot 0-7)

Logical channel:A great variety of information must be transmittedbetween BTS and the MS,for e.g. user data andcontrol signaling. Depending on the kind of

information transmitted we refer to different logicalchannels.These logical channels are mapped onphysical channel.

Channel concept

GSM Channels


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GSM Channels

Control ChannelsTraffic Channels(TCHs)

Fullrate

Halfrate

Dedicated ControlChannels

(DCCHs)

SlowFast

Downlink

BroadcastChannels

(BCHs)

Common ControlChannels

(CCCHs)

Downlink Uplink

TCH /F TCH /H FCCH SCH BCCH PCH CBCH RACHAGCH SDCCH SACCHFACCH

Traffic Multiframing Signaling Multiframing Traffic Multiframing

(down uplink)

Broadcast channels BCH


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Broadcast Channel-BCH

Alloted one ARFCN & is ON all the time in every cell. Present inTS0 and other 7 TS used by TCH.

Frequency correction channel-FCCH

To make sure this is the BCCH carrier.

Allow the MS to synchronize to the frequency.

Carries a 142 bit zero sequence and repeats once in every 10frames on the BCH.

Synchronization Channel-SCH

This is used by the MS to synchronize to the TDMA frame

structure within the particular cell. Listening to the SCH the MS receives the TDMA frame number

and also the BSIC ( in the coded part- 39 bits).

Repeats once in every 10 frames.



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Broadcast channels BCH ...

BCCH

The last information the MS must receive in order to receivecalls or make calls is some information concerning the cell. Thisis BCCH.

This include the information of Max power allowed in the cell.

List of channels in use in the cell.

BCCH carriers for the neighboring cells,Location Area Identityetc.

BCCH occupies 4 frames (normal bursts) on BCH andrepeats once every Multiframe.

This is transmitted Downlink point to multipoint. Cell Broadcast Channel - CBCH

Used for the Transmission of generally accessible informationlike Short Message Services(SMS)

Common Control Channels CCCH


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CCCH-

Shares TS-0 with BCH on a Multiframe.

Random access channel-RACH:

Used by Mobile Station for requesting for a channel. When the

mobile realizes it is paged it answers by requesting a signalingchannel (SDCCH) on RACH. RACH is also used by the MS if itwants to originate a call.

Initially MS doesnt know the path delay (timing advance), hence

uses a short burst (with a large guard period = 68.25 bits).

MS sends normal burst only after getting the timing advance info onthe SACCH.

It is transmitted in Uplink point to point.



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Common Control Channels CCCH ..

Access Grant Channel-AGCH On request for a signaling channel by MS the network assigns a

signaling channel(SDCCH) through AGCH. AGCH is transmittedon the downlink point to point.

Paging Channel-PCH

The information on this channel is a paging message includingthe MSs identity(IMSI/TMSI).This is transmitted on Downlink,

point-to-multipoint.

Dedicated Control Channels-DCCH


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Dedicated Control Channels DCCH

Stand alone dedicated control channel(SDCCH) AGCH assigns SDCCH as signaling channel on request by MS.The

MS is informed about which frequency(ARFCN) & timeslot to use fortraffic.

Used for location update, subscriber authentication, ciphering

information, equipment validation and assignment of TCH. This is used both sides, up and Downlink point-point.

Dedicated Control Channels-DCCH


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Dedicated Control Channels DCCH

Slow associated control channel-SACCH Transmission of radio link signal measurement, power control etc.

Average signal strengths (RXLev) and quality of service (RXQual)of the serving base station and of the neighboring cells is sent onSACCH (on uplink).

Mobile receives information like what TX power it has to transmitand the timing advance. It is associated with TCH or SDCCH

Fast associated control channel-FACCH

Used for Hand over commands and during call setup and release.

FACCH data is sent over TCH with stealing flag set

Traffic Channels-TCH


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Traffic Channels TCH

TCH carries the voice data. Two blocks of 57 bits contain voice data in the normal burst.

One TCH is allocated for every active call.

Full rate traffic channel occupies one physical channel(one TS on

a carrier) and carries voice data at 13kbps Two half rate (6.5kbps) TCHs can share one physical channel.

GSM Channels


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GSM Channels

Control ChannelsTraffic Channels(TCHs)

Fullrate

Halfrate

Dedicated ControlChannels

(DCCHs)

SlowFast

Downlink

BroadcastChannels

(BCHs)

Common ControlChannels

(CCCHs)

Downlink Uplink

TCH /F TCH /H FCCH SCH BCCH PCH CBCH RACHAGCH SDCCH SACCHFACCH

Traffic Multiframing Signaling Multiframing Traffic Multiframing

(down uplink)

The Logical Channels on Radio Interface


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FACCH

BTS

0 1 2 3 4 5 6 7TS

MS

FCCH

SCH

BCCH

PCH

AGCH

CBCH

SDCCH

SACCH

TCH

TCH

FACCH

SDCCHSACCH

FCCH

SCH

BCCH

RACH

PCH

AGCH

RACH

CBCH

Synchronization

Frequency correction

Broadcast control

Access request

Subscriber paging

Answer to Access request

Broadcast info

Dedicated Signaling

Sys InFo 5, 6 + SMS

Traffic (speech data)

Associated Signaling

Associated Signaling

Traffic (speech-data)

Radio Measurement + SMS

Dedicated Signaling

Broadcast info

M.S. Pre-synchronization

Access request

Subscriber paging

Answer to Access request

Logical Channel Description


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FACCH MESSAGES Connection establishment from

SDCCH to TCH

End validation of a SDCCH-TCHcommutation

Characteristics of the future used BS

after handover

Connection establishment to BS afterhandover

Validation of an handover

SACCH MESSAGES

Measures:

-power level of the communication-quality level of the communication

- level on the beacon frequency ofthe neighboring cells

Timing Advance

Power Control

SMS

TCH MESSAGES

Speech

Data

Handover Access message (uplink)

SDCCH MESSAGES

Request for a SDCCH assignment

Request for the end of channelassignment

Order of commutation from SDCCH toTCH

SMS




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FCCH MESSAGES

no message is sent (all bits 0)

BCCH MESSAGES

System Information type 1, 2, 2bis,2ter, 3, 4, 7, 8

(idle mode)

SCH MESSAGES

Frame Number

Base Station Identity Code (BSIC)

AGCH MESSAGES

For dedicated channel assignment:

-frequency number-slot number-frequency hopping description-Timing Advance (1st estimation)-MS identification

PCH MESSAGES

messages containing a mobileidentity for a call, a short messageor an authentication

RACH MESSAGES

Service request:

-emergency call-answer to an incoming call-outgoing call-short message-call re-establishment- inscription

CBCH MESSAGES

Specific information(weather, road information


Logical Channel Mapping


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Full Rate - Downlink & Uplink

T : TCH A : SACCH : IDLETi: TCHsub-channel no. i

Ai: SACCHsub-channel no. i

time

26 frames = 120 ms

T0 A0T0 T0 T0 T0 T0 T0 T0 T0 T0 T0 T0T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 A1 time

Half Rate - Downlink & Uplink

T AT T T T T T T T T T TT T T T T T T T T T T T

T

26 frames = 120 ms

1 - Traffic Channel Combination


D di d Si li Ch l C bi i


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A : SACCH D : SDCCH : IDLE

51 frames = 235 ms

A1 A2 A3A0D7D6D5D4D3D2D1D0

A5 A6 A7A4D7D6D5D4D3D2D1D0

time

Downlink

51 frames = 235 ms

A5 A6 A7 A0

A4

D7D6D5D4D3D2D1D0

D7D6D5D4D3D2D1D0A1 A2 A3

time

Uplink

AAAA

Dedicated Signaling Channel Combination


3 C Ch l C bi i


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51 frames = 235.38 ms

Downlink

time

51 frames = 235.38 ms

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Uplink

time

B : BCCHS : SCHF : FCCH : IDLE: PCH /AGCHC R : RACH

BTS MSPhysical Channel

ARFCN (n) TS (s)

FCCH

SCH BCCH

PCH/AGCH

Frames repeat continuously

Multiframem+1

Multiframem-1

Multiframe m

C CF SC CF SC CF SC CCBF S F S BF SC

3 - Common Channel Combination


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The GSM RadioLink

Speech

From Speech to Radio Transmission


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Speech

Sourcedecoding

Channeldecoding

De-interleaving

Burst deformatting

Deciphering

Demodulationequalization

Digitizing andsource coding

Channelcoding

Modulation

Ciphering

Burst formatting

Interleaving

Step 1

Step 2

Step 3

Step 4

Transmission

Step 5

Step 6 Diversity

GSM Radio Link


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GSM Radio Link

Speech Coding -Done at Transcoder of BSC and MS

The Linear Predictive Coder uses RPE-LTP(Regular PulseExcitation- Long Term Prediction)

Converts 64kbps voice to 13kbps(260 bits every 20ms)

Channel Coding - Done at BTS and MS

Uses Convolution Coding and CRC (Cyclic RedundancyCheck)

Converts 13 kbps to 22.8 kbps (456 bits per 20ms)

GSM Radio Link


101/195

Bit Interleaving - Done at BTS and MS Encryption - Done at BTS and MS

EX OR data with cipher block, which is generated by applying A5Algorithm to the Ciphering Key(Kc)

Multiplexing - Done at BTS

Modulation - Done at BTS and MS

GMSK(Gaussian filtered Minimum Shift Keying)

Phase change of +90 for 0 and -90 for 1

Speech Coding


102/195

BP A/D SPEECHENCODERCHANNEL

CODING

LP D/A SPEECHDECODERCHANNELDECODING

BANDPASS

300 Hz -3.4 kHZ

Every 125 s value issampled from analogsignal and quantised by13 bit wordData rate = 13/125*10 -6

= 104 kbps

Every 20ms 160 samplestakenData rate = 160 * 13/20ms

= 104 kbps

Linear Predictive Coding & RegularPulse Excitation Analysis

1. Generates 160 filter coeff2. These blocks sorted in 4 sequence

1,5,9,37 / 2,6,10----38/3,7,1139/8,12,1640

3. Selects the sequence with mostenergy

So data rate = 104/4 = 26 kbps

Long term prediction analysis1. Previous sequences stored in memory2. Find out the correlation between thepresent seq. And previous sequences3. Select the highest correlation sequence4. Find a value representing the differencebetween the two sequences.

Reduces data rate = 26 kbps/2 = 13 kbpsie 260 bits in 20ms

50 132 78

1A 1B 2

1A = Filter Coeffblock ampl, LTPparams

1B = RPE pointers &pulses2 = RPE pulse & filterparams

50 3 132 4

3 crc bitsFour 0 bits for codec

378 coded bits

Conv coding rate = 1/2 delay = 4

78

456 bits in 20 ms = 22.8 kbps57 x 8 = 456

To modulator

Channel Processing in GSM

Overview for Full Rate


103/195

C

20 ms20 ms

A

A8

A7

A6

A5

B4

B3

B2

B1

B8

B7

B6

B5

C4

C3

C2

C1

57 bits

Information

1 1

CRL CRL

3 3

Tail Tail

26 bits

Training

8 Bursts

8 Sub blocksof 57 bits

Source coding

Channel coding

Interleaving

Normalburst

20 ms

B

456 bitsA 456 bitsB 456 bitsC

57 bits

Information

A8B4A7B3A6B2A5B1 B8C4B7C3B6C2B5C1

Speech blocks

Codec dependent Codec dependentCodec dependent

Overview for Full Rate

Voice Coding


104/195

g

After having transformed speech blocks (20 ms) into digital blocks, channelcoding adds redundancy.

The purpose of channel coding is to improve poor transmission quality due todisturbances such as noise, interference, or multipath propagation (resultingfrom the reflections of the transmitted signal from buildings, etc.).

Channel coding consist in adding redundant information to the source datacalculated from this source information:

Convolutional codes and block codes: for correction purposes. Fire code: detection and correction of bursty errors. Parity code: error detection.

Each channel has its own coding and interleaving scheme. A common structure of 456 (for full rate) or 228 (for half rate) coded bit is

interleaved and mapped onto bursts. The blocks are interleaved and spread into segments which are combined with

flags and a training sequence to build up the burst. Ciphering is applied to the bursts, and the resulting data is used to modulate the

carriers.

Speech Channel Coding


105/195

Speech Channel Coding

Channel Processing in GSMOverview for Half Rate


106/195

C

20 ms20 ms

A

A4

A3

A2

A1

B2

B1

B4

B3

C4

C3

C2

C1

4 Bursts

4 Sub blocksof 57 bits

Source coding

Channel coding

Interleaving

20 ms

B

228 bitsA 228 bitsB 228 bitsC

A4B2A3B1 B4C2B3C1

Speech blocks

Codec dependent Codec dependentCodec dependent

Normalburst 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Overview for Half Rate

0 1 2 3 4 5 6 7 8 452 453 454 455456

Interleaving: TCH Full Rate


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0 1 2 3 4 5 6 7 8 ... ... 452 453 454 455

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15

448 449 450 451 452 453 454 455

57Rows

Divide 456 bits in 8 sub-blocks

765432107654 0 1 2 3

reordering&

partitioningout

diagonalinterleaving

456coded bits

burst

b0 b1 b56 b1 b56b0

bitinterleaving

Interleaving


108/195

g

After channel coding, speech coded information (TCH Full rate) areclassified into 456 bits blocks. They are then spread into bursts. These 456 bits are reordered into a 8 x 57 array, line by line. The

initially close bits are separated. The array is split into 8 columns of 57bits. In this way, each 57 bits block contains bits which were all distanteach other.

Each 57 bits block shall be grouped with another one in order to createa burst which contains 114 information bits. Each of the 4 first blocks isgrouped with each of the 4 last blocks of the previous segment. In thesame way, each of the 4 last blocks is grouped with each of the 4 firstblocks of the next segment.

In a burst, containing 2 x 57 bits blocks, it is possible to increase bitspreading. The first block uses the even positions and the second one

uses the odd positions inside the burst. The proximity of initiallysuccessive bits are now destroyed. Each speech block of 456 bits (20 ms) is so spread over 8 bursts.

Burst Formatting


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1 frame:4.615 ms

0 1 2 3 4 5 6 7

Guard

157 126 57

DATA

156.25 bits duration(0.577 ms)

Trainingsequence

33

DATA

8.25

S SGuardBand

Burst

148 bits

Normal Burst

Burst Formats


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Synchronization Burst(SCH)

Tail Data Extended Training Sequence Data Tail


3 bits 39 encrypted bits 64 synchronization bits 39 bits 3 bits 8.25 bits

GuardPeriod

Frequency Correction Burst(FCCH)

Tail Data Tail


3 bits 142 fixed bits (0) 3 bits 8.25 bits

Guard

Period

Normal Burst

Burst Formats


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Access Burst

Tail TrainingSequence Guard PeriodTail

156.25 bits (0.577 ms)

8 bits 36 encrypted bits 68.25 bits3 bits41 synch bits

Data

Dummy Burst

Tail Dummy Sequence Training Sequence Dummy Sequence Tail

3 bits 58 mixed bits 26 midamble bits 58 mixed bits 3 bits 8.25 bits

Guard

Period

156.25 bits (0.577 ms)

156.25 bits (0.577 ms)

13 bits 57 encrypted bits 1 26 bits 57 encrypted bits 3 bits 8.25 bits

Tail Data Training Sequence Data Tail GuardPeriod

Normal Burst

D S S DBurst to be

Ciphering


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Plain data: 0 1 1 1 0 0 1 0.....Ciphering sequence: 0 0 0 1 1 0 1 0.....XOR:Ciphered data (transmitted): 0 1 1 0 1 0 0 0.....

Ciphered sequence: 0 0 0 1 1 0 1 0.....XOR:Recovered data: 0 1 1 1 0 0 1 0.....

Data S S DataBurst to betransmitted

Data S STraining

sequenceData

Receivedburst

Interleaving


113/195

57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57

57 57 57 57

57 57 57 57

57 57 57 57

57 57 57 5757 57 57 57

57 57 57 57 57 57 57 57

57 57 57 57

Encoded speech blocks - Diagonal Interleaving

Even bits

Odd bits

Tb3

Coded Data57

F1

Training Sequence26

F1

Coded Data57

Tb3

Gp8.25

Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57

57 57 57 57

57 57 57 57

57 57 57 57

57 57 57 5757 57 57 57

57 57 57 57

Encoded control channel blocks - Rectangular Interleaving

Even bits

Odd bits

Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

Burst


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The information format transmitted during one timeslot in theTDMA frame is called a burst.

Different Types of Bursts

Normal Burst

Random Access Burst

Frequency Correction Burst

Synchronization Burst


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Normal Burst

T3

Coded Data57

S1

T. Seq.26

S1

Coded Data57

T3

GP8.25

Tail Bit(T) :Used as Guard TimeCoded Data :It is the Data part associated with the burstStealing Flag :This indicates whether the burst is carrying

Signaling data (FACCH) or user info (TCH).Training Seq. :This is a fixed bit sequence known both to

the BTS & the MS.This takes care of thesignal deterioration.

156.25 bits 0.577 ms

T Training Sequence Coded Data T GP

156.25 bits 0.577 ms


116/195

T3

Training Sequence41

Coded Data36

T3

GP68.25

Random Access Burst

T3

Fixed Bit Sequence142

T3

GP8.25

T

3

Coded Data

39

Training Sequence

64

Coded

Data 39

T

3

GP

8.25

Freq. Correc. Burst

Synchronization Burst

156.25 bits 0.577 ms

156.25 bits 0.577 ms


117/195

The GSM Idle ModeProcedures

PLMN Selection


118/195

No

automaticmode

The MS selects the firstPLMN from the preferredPLMNs list (if it is not in

the forbidden PLMNs list)

The user selects aPLMN from the

displayed PLMNs

manualmode

YesYes

Creation of a foundPLMN list

Is there an up to datefound PLMNs list?

End of PLMNselection

YesNo (automatic)

Cell Selectionsucceed?

Selection of thenext preferredpossible PLMN

No (manual)

PLMN Selection

C tit ti f th "F d PLMN li t"


119/195

Listen to all the

frequencies of the GSMspectrum:

power level measurementand average on these

measurements

Select the best

frequenciesaccording to the

power level

(124 channels in GSM900, 374 in GSM 1800and 299 in GSM 1900

(30 in GSM 900 and 40 in GSM 1800)

Memorize thebeacon

frequencies in the

precedentselection

=> Create theFound PLMN list

Constitution of the "Found PLMN list"

List of the

Initial Cell Selection


120/195

Suitable cell:

- cell of the selected PLMN- cell not barred- C1 > 0

Eligible cell

List of thefrequencies of the

selected PLMN

IMSI Attach

Look for the cell with the bestC1 in the suitable cells list

Eligible cell?

Yes

Selection ofanother PLMN

No

C1 Computation foreligible cells

Suitable cell?

Yes

No

Rejected?

Yes

PLMN set in the forbiddenPLMN list

End of Cell Selection

No

Cell Selection


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BTS-2

BTS-1

This cell

BTS-3

BTS-4

BTS-5

1

1

1

1

2

3

45

Purpose: get synchronizationwith the GSM networkprior establishing any communication.

1

Registration: the Very First Location

Update


122/195

Update

LAI HLR

IMSIVLR id

TMSI

IMSI

TMSI

Release

VLR

IMSITMSI

LAI

MSC

BTS

BSS

BSC

2

4

5

2

6

1

2

4

5

6

3

4TMSI

5

IntraVLR Location Update


123/195

VLR

IMSITMSI

LAI

1

2

3

4

new TMSI

TMSI + old LAI 2

3

42

3TMSI

New TMSI

New LAI

MSC

BTS

BSS

BSC

IMSI not Required

BSS

InterVLR Location Update


124/195

New LAI

newTMSI

TMSI + old LAI

TMSI New TMSI

MSC

BSS

BTS

BSC

1

2

5

7

2

57

2

IMSI,TMSILAI

New VLR

IMSI, TMSIOld LAI

Old VLR

RAND, SRES,Kc

HLR

newVLR id

subscriberdata

3

4

6

6

5

IMSI not Required

RAND, SRES,Kc

IMSI Attach


125/195

MSCBTS

BSS

BSC

VLR

3

4

5

4

6

1 CHANNELREQUEST

2IMMEDIATEASSIGNMENT

LOCATION UPDATINGREQUEST (IMSI Attach)

3

5LOCATION UPDATINGACCEPT (LAC, TMSI)

4AuthenticationProcedure

IMSI Detach


126/195

MSC

BTS

BSS

BSC

VLR

1 CHANNELREQUEST

2IMMEDIATEASSIGNMENT

IMSI DETachINDication

3

4CHANNELRELEASE

IMSI DETachINDication

3


127/195

The GSM DedicatedMode Procedures

Power Control


128/195

BTS commands MS at differentdistances to use different power levelsso that the power arriving at the BTSs Rx isapproximately the same for each TS

- Reduce interference- Longer battery life

Power Control

Handover


129/195

Means to continue a call even a mobile crossesthe border of one cell to anotherProcedure which made the mobile station really

roamHandover causesRxLev (Signal strength , uplink or downlink)RxQual (BER on data)O & M interventionTiming AdvanceTraffic or Load balancing

Handover Types


130/195

Internal Handover (Intra-BSS)

Within same base station - intra cell

Between different base stations - inter cell

External Handover (Inter-BSS) Within same MSC -intra MSC

Between different MSCs - inter-MSC

Handover TypesGMSC


131/195

BSC

BSC

BSC

BSC

MSC

MSC

GMSC

C-1 C-2

C-3

C-4

HO requiredActivate TCH(facch)with HoRef#

HO performed

BSC

Intra BSC handover


132/195

Periodic MeasurementReports (SACCH)

Periodic MeasurementReports

with HoRef#

if1. Check for HO passed2. Channel avail in new BTS

Acknowledges andalloctes TCH (facch)

HO cmd with HoRef#Receives new BTS data(FACCH)

MS tunes into new frequencyand TS and sends HO message tonew BTS (facch)

Periodic MeasurementReports (SACCH)

Release TCH

Cell 1

Cell 2

BTS 1

BTS 2

Frequency plan and importance of BCCH


133/195

B3

B2

B9

B6 B4

B1

Sectored

antennas

MS ( monitoring the

broadcast radio B1 in idle

mode )

F S B B B B .. F S .. .. I

F0 F50F2 F3 F4 F5 F10 F11F1

F,S,B exist in time slot 0 of each frame

B7

B8

B5

B10

B11

B12

BPL frequency plan:

Broadcast frequencies :

15 Broadcast channels = 48-62

15 Hopping channels = 32-46

What information does Broadcast Control channel

(BCCH) contain?


134/195

(BCCH) contain?

Serves as a Beacon for the Cell

Country Code (CC) and the Network Code (NC)

Location Area Identity (LAI)

List of neighboring cells which should be monitored by MS

List of frequencies used in the cell

Cell identity

Back

Location Updates


135/195

Location Updates can be classified into

two:

Periodic Location Updates:

This occurs as per the timer set by the network operator.If the MS does not perform this update the MSC marksthe MS as Detached on the VLR.

Location Update on a handover:This occurs if during a handover the MS is moved into anew Location Area Code (LAC).

1 The MS is monitoring the BCCH and has all the decoded


136/195

1. The MS is monitoring the BCCH and has all the decodedinformation stored on the SIM ( including the LAC)

2. As soon as the mobile is on a TCH it sends the signalstrength indication on the corresponding SACCH

3. The BSC monitors the signal strengths and on analysis

sends a handoff request on FACCH. The handoffprocess is completed on the FACCH.

4. After the completion of call, the MS starts monitoring theBCCH again. On finding the LAC (stored on SIM) and that

decoded from the BCCH to be different , the MS requestsa Location Update through SDCCH.

MS BSS MSC PSTN

Mobile Originating Call


137/195

ACM = Address Complete MessageANM = ANswer MessageIAM = Initial Address Message

MS BSS MSC

CHANNEL REQUEST1

PSTN

CM SERVICE REQUEST2 CM SERVICE REQUEST2

CALL PROCEEDING7CALL PROCEEDING

7

Assignmentprocedure7

IAM6

IMMEDIATE ASSIGNMENT2

ACM8

VLR

Ring

ANM10

ALERTING9

SETUP (basic) or

EMERGENCY4 SETUP4

CONNECT11

CONNECT ACKnowledge11

Authenticationprocedure3

Cipheringprocedure3

5

Dialing

RingingPath

Established

Ringing

SendingNumber

Mobile Originating Call


138/195

1- The MS originates the call by sending a CHANNEL REQUEST message(onRACH).

2- Immediate assignment: channel allocation with TCH / FACCH or SDCCH.3- The VLR launches authentication (if required) and completes ciphering.

4- The MS initiates call establishment by sending a SETUP message (calledparty number) to the MSC.

5- The MSC in turn checks mobile subscriber capabilities with VLR for desiredservice.

6- If it agrees, the MSC relays the called number over an ISUP Initial AddressMessage.

7- The MSC also sends a CALL PROCEEDING message to the MS (assigningTCH / FACCH EA in case of Early Assignment).

8- Recipient PSTN switch rings the land telephone and returns an ISUP Address

Complete Message to the MSC.9- Upon receiving this message, the MSC alerts the MS with an ALERTING

message.

10-The Called party goes off hook, and the PSTN sends an ISUP ANswerMessage to the MSC. The MSC then connects the MS (assigning a TCH incase of OACSU).

11-The call is accepted (CONNECT/CONNECT ACK) and the conversation

Mobile Terminating Call

1 - Paging Principle


139/195

PSTN

LA1

LA2

BTS11

BTS21

BTS22

BTS31

BTS12

BTS23

HLR

4

3

5

1

2

5

6

6

BSC1

BSC2

BSC3

MSC/VLR

GMSC

1 Paging Principle


1 - Paging Principle


140/195

1 Paging Principle

The main difference with an MO Call procedure is the Paging of theMobile Station.

When the MS is in Idle mode, the network does not know the cell, butonly the Location Area where the MS is located.

Since RR sessions are only established at the request of the MS, therole of the Paging procedure is to trigger that operation.

Principle A call from the fixed network (PSTN) is switched to the Gateway MSC

(GMSC).

The GMSC retrieves from the HLR, the identity of the MSC/VLR (or VisitorMSC) handling the Location Area of the Mobile Station.

The GMSC routes the call to the VMSC.

The VMSC reads the LA where the MS is located into its VLR.

The VMSC sends instructions to one or several BSC (BSC1 and BSC2) topage the MS in the different cells of LA1. BSC1 and BSC2 page the MS in the BTSs of the Location Area LA1.

(BTS11, BTS12, BTS21).

Mobile Terminating Call2 - Detailed Procedure


141/195

VMSCBSS

VLR

Visitor PLMN

GMSC

HLR

Home PLMN

RoutingInformation

(MSRN)

6

IAM : Initial Address MessageMSISDN : Mobile Station Integrated Services Digital

network NumberMSRN : Mobile Station Roaming Number

IMSI : International Mobile Subscriber IdentityGMSC : Gateway MSCVMSC : Visitor MSCTMSI : Temporary Mobile Subscriber Identity

PN

InternationalSS7

ISDNIAM (MSRN)

7IAM

(MSISDN)2

Send

RoutingInformation(MSISDN)

3

Provide Roaming Number

(IMSI)4

PAGE(TMSI + LA)

9

Send infoto I/C(MSRN)

8

Roaming Number

(MSRN)5

PAGINGREQUEST

(TMSI + LA)10

PAGINGREQUEST

(TMSI)

11

MSISDN

1


2 - Detailed Procedure


142/195

2 Detailed Procedure

Procedure1- The calling subscriber accesses the ISDN by dialing an MS-ISDN number.

2- Transmission of the MS-ISDN number to the GMSC through IAM (InitialAddress Message).

3- Transmission of the MS-ISDN number to the HLR through SRI (Send RoutingInformation).

4- The HLR interrogates the VLR (Visitor MSC) that is currently serving the user.

5- The VLR returns a routing number (MSRN) to the HLR, which passes it backto the GMSC.

6- The MSRN is transmitted to the GMSC (address of appropriate VMSC).

7- The GMSC calls the VMSC through an IAM (with MSRN).

8- The MSC asks the VLR to establish where the called party is located.9- The VLR gives location information (LA) to the MSC with a PAGE message.

10- The VMSC alerts all BSCs in charge of cells belonging to this LA,with aPAGING REQUEST message.

11- All the BTSs page the MS over a PCH; depending upon the pagingtypemessage, up to four different TMSI may be contained in the page command.


3 - End to End Procedure


143/195

MS BSS VMSC

CHANNEL REQUEST

(LAC, Cell ID)5

PSTN

IMMEDIATE ASSIGNMENT

(SDCCH or TCH)

6

PAGING REQUEST4

PAGING REQUEST

(TMSI or IMSI, LA)3

GMSC

IAM

(MSISDN) 1IAM(MSRN) 2

CM SERVICE REQUEST

(Paging Response)7 PAGING RESPONSE(TMSI or IMSI, LA)

7

Authenticationprocedure8

Cipheringprocedure9

Address Complete Message11

ANswer Message12

Setup, Assignment, Alerting10

CONNECT12

Dialing

Ringing

Path

Established


3 - End to End Procedure


144/195

3 End to End Procedure

Procedure

1- PSTN sends an IAM (with the MSISDN) to the GMSC.

2- GMSC sends an IAM (with the MSRN) to the VMSC.

3- The VMSC sends a PAGING REQUEST MM message to the BSS.

4- The BSS sends a PAGING REQUEST (with IMSI or TMSI) to the MS.

5- The MS must request a channel (CHANNEL REQUEST message with pagingcause) over the RACH, within 0.5 second.

6- The BSS complies and assigns a dedicated channel (on AGCH) to the MSwith IMMEDIATE ASSIGNMENT message.

7- The MS sends a PAGING RESPONSE to the VMSC via the BSS.

8/9-Authenticationand Cipheringprocedures (if required).

10- Setup, Assignment, Alertingprocedures (see MS Originating Call).

11- Alerting is sent to the PSTN with an ACM (ISUPmessage).

12- CONNECT and ANM messages are sent to the PSTN. The call is completed.

Call Release

1 - Mobile Initiated


145/195

MS BSS MSC

Call in progress1

RELEASE COMPLETE4

PSTN

DISCONNECT2 DISCONNECT

2

RELEASE3RELEASE

3

RF Channel Releaseprocedure 8

Release5

RELEASE INDICATION7

CHANNEL RELEASE6

Release

tone9

Call Release

1 - Mobile Initiated


146/195

d

Call release can be initiated by either the PSTN user or the mobile user.The BSC is responsible for BSS resources, and the MSC is responsible for the NSS andPSTN connection.

Procedure

1- The call is currently in progress.

2- The MS initiates the release of a call by sending a DISCONNECT message to the MSC.

3- The MSC returns a RELEASE message to the MS.

4- The MS acknowledges with a RELEASE COMPLETE message.

5- The MSC can send the Release message to the PSTN without waiting for the RELEASECOMPLETE MM message from the MS.

6- The BSC requests the MS to return to Idlemode with CHANNELRELEASE message.

7- The BTS informs the BSC with RELEASE INDICATION that the signaling link isdisconnected.

8- BSC requests the BTS to de-activate the RF Channel (TCH): Channel Release.9- The PSTN informs the land terminal with the appropriate tone.

Abnormal termination is monitored by a set of timers (operator configurable) to ensure thatresources are not unused/unavailable.

Call Release

2 - PSTN Initiated


147/195

PSTN

On hook

Purpose:informs the mobilethen releases radio

and network resources.

REL

RLC

MSC

BTS

BSS

BSC

1

1 1

12

33

4

55

4

6

2

Call Release

2 - PSTN Initiated


148/195

Procedure The call is in progress.

The release process starts with an ISUP Releasemessage from the land network.

Upon receiving this message, the MSC initiates therelease of the call by sending a DISCONNECT messageto the MS.

The MS replies by sending a RELEASE CHANNELmessage to the MSC.

The MSC in turn, sends a RELEASE COMPLETEmessage back to the MS and sends a ReleaseComplete message to the PSTN.


149/195

Mobile Originated Call


150/195

Request for Service Authentication

Ciphering

Equipment Validation

Call Setup Handovers

Call Release

Mobile Terminated Call


151/195

Paging Authentication

Ciphering

Equipment Validation

Call Setup Handovers

Call Release


152/195

The GPRS/EDGE AirInterface

GPRS


153/195

Generalities Based on the existing GSM infrastructure

Packet switching functionality

Better data transfer rates Statistical multiplexing

Traffic based billing

Migration Path to 3G Networks

Service Types


154/195

Point-to-Point Internet access by user

Point-to-Multipoint Delivery of information (e.g. news) to multiple

locations or interactive conference applications

In GSM


155/195

A channel is allocated to user for duration ofconnection

Inefficient use of resources

Time-based billing Suitable to real-time applications

In GPRS


156/195

Resources are allocated to user only for thetime it takes to send each packet

A channel may be shared by many users

User pays by the packet Ideal for data traffic

TDMA Frames


157/195

Multislot Operation


158/195

GPRS allows a mobile to transmit data in upto 8 PDCHs

Eight-slot operation

3-bit USF at beginning of each radioblock in downlink points to next uplink radioblock

Comparison with single-slot GSM

Higher delay at higher load Low blocking rate

Improved Throughput

Air Interface


159/195

GPRS ChannelsBroadcast of packet dataDL


160/195

PBCCH

Signalling

and Control

Packet Traffic

Channels

PCCCH

PPCH

PRACH MS initiates uplink transfer

PAGCH Resource assignment to an MS

PNCH Notifying PTM Packet Transfer

Broadcast of packet data

specific information

PDTCH Packet Data Transfer (multislot)

PACCH

DL

UP

DL

DL

DL

DL&UP

PTCH Signalling: Resource ass. / reass.Acknowledgement, PWRC info.

Paging MSs for packet dataand circuit switched services

PTCCH/U, PTCCH/D

Broadcast channels

PBCCH


161/195

PBCCHPacket Broadcast Control Channel

GSM BCCH can also be used

Broadcasts packet data specificsystem Information messages

MS continuously monitors this

channel

Common Control channelsPCH (Packet Paging Channel)


162/195

GSM PCH can also be used.

PRACH (Packet Random Access Channel)

GSM RACH can also be used.

PAGCH (Packet Access Grant Channel)

Used for resource assignment during packet transfer establishment

phase.

GSM AGCH can also be used.

PNCH (Packet Notification Channel)

Downlink only channel used for PTM-M notifications to a group ofMS before PTM-M packet transfer.

Dedicated channels


163/195

PACCH (Packet Associated ControlChannel)

Bi-directional dedicated channel for transferringACK./power control or resource assignment/re-assignmentmessages.

PDTCH (Packet Data Traffic Channel)

Bi-directional. Corresponds to the resource allocated to asingle MS on one physical channel for user data

transmission.

Dedicated channels (cont.)


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PTCCH (Packet Timing Advance ControlChannel)

Uplink dedicated (for transmission of random

access bursts).Downlink common (for transmission of timingadvance information to several MSs).

MS Class CLASS A:

S t i lt tt h i lt ti ti


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Supports simultaneous attach, simultaneous activation,

simultaneous monitor, simultaneous invocation, andsimultaneous traffic.

CLASS B:Simultaneous traffic shall is not supported. The mobile usercan make and/or receive calls on either of the two services

sequentially but not simultaneously. The selection of theappropriate service is performed automatically

CLASS C:Supports only non-simultaneous attach. Alternate use only.

The status of the service which has not been selected isdetached,that is, not reachable.

GPRS Channel Coding Schemes


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GPRS Channel Coding Schemes


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GPRS can also increase the data rate in a single timeslot. The coding

schemes listed above are based on the current scheme used for GSMsignaling channels (notice a single slot rate of 9.05 in CS1 as opposedto the TCH data rate of 9.6 in GSM).

To increase the data rate, some of the error detection and correctionbits are removed from the burst. So CS2 has less C&D bits than CS1,and CS4 has no error protection at all. The consequences of this are

that to maintain a call in CS4 it is necessary to have excellent signalquality. This can only be achieved at positions closer to the BTS.Therefore, the cell radius is greatly reduced when using CS3 and CS4.

The BSS automatically upgrades and downgrades the connectionamong the coding schemes based on the number of erroneous packetsit receives.

In the first release of GPRS, only CS1 and CS2 are implemented. This

is because CS3 and CS4 require structural changes to the Abisinterface. These data rates will not fit into a 16kbit/s channel.

Mobility Management StateGPRS

Attach/ Detach


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Idle

Standby

Ready

PacketTX/RXSTANDBY

Timer Expiry

READYTimer Expiry

MS location known toSGSN level.

MS is capable of receivingPoint-to-Multipoint dataand being paged forPoint-to-Point data

MS location

not known.Subscriber is notreachable by the

GPRS NW.

MS location known tocell level.

MS is transmitting or has

just been transmitting.MS is capable of receivingPoint-to-Point data andPoint-to-Multipoint data.

Routing Area


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RAI =MCC+MNC+LAC+RAC

Modulation


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EDGE 8-Phase Shift Keying


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GSM/ EDGE Comparison


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Wideband CDMA(W-CDMA)

CDMA - Direct Sequence Spread

Spectrum

UMTS Technology Overview


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Spectrumfrequency

time

code

Frame Period (we may still needframes/timeslots for signaling)

CDMA SpreadingEssentially Spreading involves changing the symbol rate on the air interface

Spreading D di



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Identica

l codes

Tx Bit Stream

P

f

Code Chip Stream

Spreading

P

f

Channel

Air InterfaceChip Stream

P

f

Code Chip Stream

Despreading

P

f

Rx Bit Stream

P

f

Spreading and Despreading

1



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Rx Bit Stream


Tx Bit Stream1

-1

Code Chip Stream

XSpreading

Code Chip Stream

XDespreading

Spreading and Despreading with

code Y1


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Tx Bit Stream1

-1

Code Chip Stream

XSpreading

XDespreadingCode Chip Stream Y

Rx Bit Stream

Spreading

If the Bit Rate is Rb the Chip Rate is R the energy


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If the Bit Rate is Rb, the Chip Rate is Rc, the energy

per bit Eb and the energy per chip Ec then

We say the Processing Gain Gp is equal to:

Commonly the processing gain is referred to as theSpreading Factor

b

c

cb

R

REE

b

cp

R

RG

Spreading in noiseTx Signal

P

Rx Signal (= Tx Signal + Noise)

P


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The gain due to Despreading of the signalover wideband noise is the ProcessingGain

Signal

P

f

Spreading Code

f f

P

Channel

Wideband Noise/Interference

P

f

Spreading Code Signal

P

f

Visualising the Processing Gain

W/Hz W/Hz W/Hz


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Signal

Intra-cell Noise

Inter-cell Noise

BeforeSpreading

f

AfterSpreading

f

Ec

IoWith Noise

f

W/Hz

After

Despreading/Correlation

f

W/HzEb

No

Post

FilteringOrthog = 0

f

dBW/Hz

EbNo

Eb/No

f

Eb

No

W/Hz

PostFilteringOrthog > 0

f

EbNo

Eb/NodBW/Hz

f


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UMTS Codes

Spreading process in WCDMA

3 840 Kcps


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1st Step: Channelization

Variable Rate Spreading ( According to user data

rate)

2nd Step: Scrambling Code

Fixed Rate Spreading (3,840 Kchips)

S

ChannelizationCode

ScramblingCode

3,840 KcpsCoding&

Interleaving

Spreading process in WCDMA Downlink (NodeB to UE )

S bli C d Id ifi ll ( )


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Scrambling Code:Identifies cell (sector). Channelization Code:Identifies user channels in cell (Sector).

Scrambling Code A

Scrambling Code B

Scrambling Code C

Channelization

Code 1

Channelization

Code 2 Channelization

Code 3

Channelization

Code 1ChannelizationCode 2

Channelization

Code 2

Channelization

Code 1

Spreading process in WCDMA Up Link (UE to NodeB )

Scrambling Code: Identifies user terminal


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Scrambling Code:Identifies user terminal.

Channelization Code:Identifies channels in user terminal.

Scrambling Code A

Scrambling Code B

Scrambling Code C

Channelization

Code 1

Channelization

Code 2

Channelization

Code 1

Channelization

Code 1


Orthogonal Variable Spreading Factor [OVSF]


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g p g

codes are the channelization codes used forsignal spreading in the uplink and downlink


The code used for scrambling of the uplink Channels may


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The code used for scrambling of the uplink Channels may

be of either long or short type, There are 224

long and 224

short uplink scrambling codes. Uplink scrambling codesare assigned by higher layers.

For downlink physical channels, a total of 218-1 = 262,143

scrambling codes can be generated. Only scramblingcodes k = 0, 1, , 8191 are used.

In the downlink direction 512 of scrambling codes areused to identify the cells in the downlink so downlink

planning is required


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UMTS Proceduresand Techniques

The Radio Channel


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Multi-path propagation Time dispersion

h(t)

t0 t1 t2 t3

t0t1

t2 t3

Direct Signal

Composite Signal


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Direct Signal

Reflected Signal

Combined Signal

Time between fades is related to

Multipath Fading


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Fast (Rayleigh) Fading

time (mSec)

Composite

Received

Signal

Strength

RF frequency

Geometry of multipath vectors

Vehicle speed:

Up to 2 fades/sec per kilometer/hour

Deep fade caused by destructive summation

of two or more multipath reflections

msec

Rake receiverRAKE Receiver

Finger Circuit


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RX

Searcher

Combiner

Calculation

Combined

Signal

Electric PowerElectricPower

Delay Profile

Delay Time

Multiple Signal 1

Multiple Signal 2

Multiple Signal 3

Delay Time

Finger Circuit

Finger Circuit

Finger Circuit

Output Power

Power Control Combats fast fading


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RX power

t

RX power

t

TX power

t

Without power control

TX power

t

With power control

CDMA Power Control


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BLER = Block Error Rate

SIR = Signal to Interference Ratio

TPC = Transmit Power Control

P(Startvalue)

Open loop

P(SIR-Target,UL)

P(SIR-Target, DL)

Inner loop

DL-TPC UL-TPC

SIR-Target,DL

BLER-Measured,DL

DL-Outer loop

RNC

SIR-Target,UL

SIR-Error,UL

UL-Outer loop

Inter-System Handover

Handover from a CDMA system to an Analog or TDMA system

Traffic and Control Channels are Disconnected and must be

Handover


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Traffic and Control Channels are Disconnected and must be

Reconnected Hard Handover

When the MS must change CDMA carrier frequency during theHandover

Traffic and Control Channels are Disconnected and must beReconnected

Soft Handover

Unique to CDMA

During Handover, the MS has concurrent traffic connections with twoBSs

Handover should be less noticeable

Softer Handover

Similar to Soft Handover, but between two sectors of the same cell

Handover is simplified since sectors have identical timing

CDMA Soft Handover


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One finger of the RAKE receiver is constantlyscanning neighboring Pilot Channels.

When a neighboring Pilot Channel reaches thet_add threshold, the new BS is added to theactive set

Monitor Neighbor BS Pilots Add Destination BS Drop Originating BS

Module 9 Advanced Radio Systems

Documents