gsm based cellular_rf level 2

7/27/2019 GSM Based Cellular_RF Level 2

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RF Engineering Level-2

Course Duration : 8 days


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Multi-path propagation Shadowing Terrain

Building Reflection Interference


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Reflections

Strong echoes can cause excessive transmission delay No impact If the delay falls in the equalizer window Cause self-interference if the delay falls out of the equalizer window

direct signalstrong reflected signal

equalizer window 16 s

amplitude

delay time

long echoes, out of equalizer window:self-interference


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Slow fading (Lognormal Fading) Shadowing due to large obstacles on

propagation direction Partially Scattered Field One Dominant Strong Path

Others are comparable and weaker

Fast fading (Rayleigh fading) Serious interference from multi-path

signals Completely Scattered Field No Dominant Direct Path All Paths have comparable Strengths.

+10

0

-10

-20

-300 1 2 3 4 5 m

Level (dB)

920 MHzv = 20 km/h

Fading(1)


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time

power

2 sec 4 sec 6 sec

+20 dB

meanvalue

- 20 dB

lognormalfading

Rayleighfading

Fading(2)


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1. Antenna system

2. Diversity technique

3. Interference and interference reduction


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Capacity can be increased by cell splitting where antenna re-alignment is necessary

Rotate original antennas through 30 o

Add new sites as shown

New siteOld siterotated

New cell


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Lobes Main lobes Side and Back lobes Front-to-Back ratio

Half-power beam-width

Antenna downtilt Polarization Frequency range Antenna impedance Mechanical size


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Down tilt of antennas often used to:

reduce interference adjust cell size direct coverage e.g. into a building

Mechanical tilt: set by operator distorts azimuth (H plane) radiation

pattern Electrical tilt:

set by manufacturer reduces radiation H plane pattern

equally in all directions, withoutdistortion

Omni-directional antenna with electrical down tilt


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-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

No Tilt MechanicalDowntilt

ElectricalDowntilt

Electrical Downtilt +

Mechanical Uptilt


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main lobe

5 .. 10

Horizontal separationSufficient decoupling distance: 5-10 Antenna patterns superimposed if

distance too close

Vertical separationDecoupling distance:1 can provide good RX /TX decoupling

Minimum coupling loss


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Recommended decoupling TX - TX: ~20dB TX - RX: ~40dB

Horizontal decoupling distance depends on Antenna gain Horizontal rad. pattern

Omni-directional antenna Use vertical separation for RX and TX

Use vertical separation (fork) for RX and diversity RX

Vertical decoupling is much more effective

0,2m

Omni-directional.: 5 .. 20mdirectional : 1 ... 3m


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Directional antenna Antenna down tilt

Improve hotspot coverage Reduce interference

5..8 deg


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Feeder parameter Type Diameter 1800MHz 900MHz

(mm) dB/100m dB/100m

3/8 10 14 10

5/8 17 9 6

7/8 25 6 4

1 5/8 47 3 2

Use the short feeder whenever possible


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Leaking feeder Cables with very high loss per length unit distributed antenna

often used for tunnel coverage. This kind of feeder is expensive

Optic fiber distribution system Distribute RF signal radiate from discrete antenna points at

remote locations via (very thin) optic fiber.

50 Ohm

Propagation loss: 4 ... 40 dB/100m

coupling loss: ~ 60 dB (at 1m dist.)


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Repeater type Narrow-band Repeater Wide-band Repeater

The Repeater is used to relay signal into shadowed areaBehind hillInto valleyInto building

Note: The Repeater needs a host celldecoupling ~40 dB needed


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1. Antenna system




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Time diversityCoding, interleaving

Frequency diversityFrequency hopping

Space diversityMultiple antennas

Polarization diversity

Dual-polarized antennas

Multi-path diversityEqualizer

t

f

Diversity reception is a way to improve the quality and strength of the signalarriving at the base station, by receiving it in several independent ways


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Diversity gain depends on environmentAntenna diversity

3dB gainMore path loss acceptable in link budget

Higher coverage range

R

R(div) ~ 1,3 R A 1.7 A70% more coverage per cell

Needs, less cells in total The above case can be satisfiedonly under ideal condition. That isthe environment is infinitely largeand flat


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Two receiving antennas are used at the basestation

If they are far apart, the received signals will be independent of each other

If one has suffered fading, the other may

not A suitable distance is generally about 10wavelengths

GSM 900, 10l = 3 metres

Better isolation between the two signals canalso be obtained by mounting the antennas atdifferent heights on the tower 10


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Plan views of two possible tri-sectored site antenna systems

Transmit antenna isseparate from the receivers

One antenna is used for transmitand receive, using a duplexer in theBTS to direct the signal

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Tx/Rx

Tx/Rx

Tx/Rx


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As the radio signal undergoes multiplereflections and scattering, the plane of

polarisation is rotated randomly

This can be used to provide diversity reception

by designing antennas with dipoles crossed toreceive different components of the polarisation

The preferred method is to cross the dipoles at45o

This gives good coverage of vertical polarisation and strong components of rotatedsignals

Dipolescrossed at 45 o


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Diversity is used when necessary to balance the system.

It helps the uplink but not the downlink. Diversity allows the BTS to operate at higher power whilst

maintaining link balance.

Hence it allows greater coverage to be achieved .

Uplink limitDownlink limit

Unbalanced system

Uplink limitDownlink limit

Balanced system


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1. Antenna system




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Signal quality =sum of all expected signals carrier (C ) sum of all unexpected signal interference (I)=

Notes: GSM specification : C / I >= 9 dB (Co-Channel)

expected signalatmosphericnoise

other signals


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Affect signal quality Cause bit error

Repairable errors : channel coding, error correction Irreducible errors : phase distortions

Interference situation is Non- reciprocal : uplink downlink Unsymmetrical : different situation at MS and BTS

C/I Co-Channel C/I : 9dB Adjacent Channel C/I : -12dB


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RX QualityRXQUAL class : 0 ... 7

RXQUAL Mean BER BER rangeclass (%) from... to0 0.14 < 0.2%1 0.28 0.2 ... 0.4 %2 0.57 0.4 ... 0.8 %3 1.13 0.8 ... 1.6 %4 2.26 1.6 ... 3.2 %

5 4.53 3.2 ... 6.4 %6 9.05 6.4 ... 12.8 %7 18.1 > 12.8 %

usable signal

unusablesignal

good

acceptable


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Multi-path (long echoes) Frequency reuse External interference

Note : Interference has the same effect as poor coverage.

Reduce the interference as possible.


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Frequency planning Suitable site location Antenna azimuth, downtilt and height

good location

bad location


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Directional pattern of sectoredantennas reduces response tointerference

Increases C/I significantly Allows greater frequency re-use, i.e.

smaller cells If cells A and B use the same carrier:

B will cause co-channel interference inA

A will cause very little co-channelinterference in B

Interference is no longer mutual

A

B


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Frequency hopping A diversity technique, frequency diversity

include:

Less fading loss De-coding gain Interference averaging

Power control based on quality Evaluate signal level and quality

DTX Silent transmission in speech pauses


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Diversity technique Frequency diversity can reduce fast fading effects Useful for static or slow-moving mobiles

Cyclic base-band hopping TRX hops cyclic between its allocated frequencies

RF hopping Either cyclic or random hopping Needs wideband combiner

Can use any frequency included in the MA


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Save battery life-time Minimize interference

GSM : 15 steps and 2 dB for each

Use power control in both uplink and downlink triggered bylevel or quality

time

signallevel target level

e.g. -85 dm

Power control isnt allowed on BCCH


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E=A+B+C-D


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1.1.1: Signaling Protocol & Networks


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1.1.1: Signaling Protocol & Networks

Radio Interface


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Page 75

Another MSC

HLR/AUC/LR

SMC

PSTNISDN

OMC

MS

MS

Um

Um

A-bis

interface

BSC

A interface

MAP interface

BTS

MSC

There are three dominant interfaces, namely, an interface between MSC and the Base Station Controller (BSC), an A-bis interface between BSC and the Base Transceiver Station (BTS), and an Urn interface between the BTS and MS.

Hierarchical Structure of Um Interface


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Page 76

Communication management (CM)

Radio resources management (RR)

Mobility and security management(MM)

Integrated management

TCH0 TCH1 TCH2 SACCH TCH23 IDL

Multi-framePhysical link layer (L1)

Data link layer (L2)

Network application layer (L3)

RACH BCCH AGCH/PCH SDCCH SACCH TCH FACCH


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The physical layer of the A-interface is 120-ohm symmetrical twisted pair or 75-ohm coaxial cablewhose rate is 2 Mbit/s. The physical layer of A-interface has the following features:

The 2 Mbit/s transfer rate complies with G.703.Frame structure, synchronization and timing comply with G.705.Fault management complies with G.732.CRC4 complies with G.704.


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The main function of MTP is to ensure reliable signaling message transfer in thesignaling network. In case of system and signaling network faults, it takes measures

to avoid or reduce the loss of messages, repeated messages and out-of-sequencepackets. MTP comprises three functional levels:1. signaling data link function2. signaling link function3. signaling network function

1) Signal ing da ta l ink fun ct ion

Signaling data link (layer 1) is the channel used for signaling transmission. Itcomprises two data channels of the same data rate but two opposite workingdirections. The data rate is 64kbit/s. Generally, the signaling data link occupiestimeslot 16 of a trunk cable. The specific timeslot is to be determined by negotiationbetween BSC and MSC. By data configuration, the timeslot can be used to establisha semi-permanent connection.The signaling data link is the information bearer of SS7. One of its importantfeatures is that the signaling link is transparent, i.e. the data transferred on it cannotbe changed. Therefore, equipment such as echo canceller, digital attenuator, A/urate converter, cannot be connected to this link.


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2) Signaling link functionSignaling link function (layer 2) regulates the functions and procedures to send the

signaling to the data link, and together with layer 1, it implements reliable signalingmessage transfer between two directly-connected signaling points. Due tolong-distance transmission, a certain rate of bit errors may be caused on the data linkbetween two adjacent signaling points. However, no error is allowed in CCS7signaling message codes.

The purpose of layer 2 is to guarantee error-free transmission of message codes in the casethat there exist bit errors on layer 1.

Functions of layer 2 include:1. signaling unit delimitation,2. signaling unit alignment,3. error detection,

4. error correction,5. initial alignment,6. processor fault,7. level-2 flow control, and8. signaling link error rate monitoring.


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3) Signaling network functionBy controlling the route and performance of the signaling network, signaling network function(level 3) guarantees that signaling information can be reliably transferred to the user part,

whether the signaling network is in normal state or not.. Signaling network functions include1. signaling message processing2. signaling network management.

Signaling message processing function sends signaling messages to the corresponding signalinglinks or user parts. The user part in BSS only contains SCCP. Signaling message processing functionscomprise three parts: message routing (MRT), message discrimination (MDC) and messagedistribution (MDT),

Signaling network management is to re-construct the signaling network and to keep andrecover the normal transfer ability of the signaling unitwhen the signaling network fails. Signaling network

management includes three parts: signaling trafficmanagement, signaling ink management and signalingroute management.


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The purpose of SCCP is to provide complete network layer functions with the help of MTP. Network layer provides

connectionless services andconnection-oriented services.

The connectionless service means that MS does not establish a signaling connectionin advance, and uses the routing functions of SCCP and MTP to directly transfer datainformation in the signaling network. It is applicable to the transfer of a small quantityof data.

The connection-oriented service means that a signaling connection is established inadvance, and data are directly transferred on the signaling link, instead of using theroute selection function of SCCP. It is applicable to the transfer of large quantities of data, and effectively shortens the transmission delay of batch data.


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1) Protocol overviewThe BSSAP protocol, which serves as A-interface specification, describes two kindsof messages, BSSMAP and DTAP message. BSSMAP messages are used for trafficflow control, and are to be processed by the internal functional module of thecorresponding A interface. For DTAP messages, A interface is merely equivalent to atransport channel, On BSS side, DTAP messages are directly transferred to radiochannels. On MSC subsystem side, DTAP messages are transferred to thecorresponding functional processing unit.

2) Typical message contentsa) DTA P m es s ag es : The DTAP messages can be divided into Mobile Management

(MM) messages and Call Control (CC) messages.

The MM messages consist of messages related to authentication, CM servicerequest, identification request, IMSI detach, location update, MM state, TMSIre-allocation, etc.

The call control messages consist of alerting, call proceeding, connection, setup,modification, release, disconnection, notification, state query, DTMF startupmessages, etc.


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b) BSSMAP messages The BSSMAP messages can be divided into connectionless andconnection-oriented messages.

1. The connectionless messages consist of Block/Unblock, Handover, Resource,Reset, Paging messages, etc.

2.The connection-oriented messages include Assignment, Handover, Clear andCipher messages.

c) BSSAP protocol functionality The BSSAP protocol can deliver its own functions inconnection-oriented mode and connectionless mode of SCCP. When MS needs to

exchange service-related messages over radio resources with the network side while thereis no MS-related SCCP connection between MSC and BSS, a new connection will beestablished. A new connection shall also be set up for external handover. There are twokinds of connection setup:

While MS sends the Access Request message on the RACH, BSS allocates adedicated radio resource (DCCH or TCH) to MS. After the L2 connection is setupon the SDCCH (or FACCH) where resources are allocated, BSS starts theconnection setup.

When MSC decides to execute an external handover (the target BSS might bethe original BSS), it must reserve a new DCCH or TCH from the target BSS. In thisscenario, MSC starts the connection setup.


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Layer 1 of the Abis interface is a physical link which receives data from and transmits datato the transport layer based on the bottom layer driver of the hardware.

The layer 2 protocol of the Abis interface is based on the LAPD. LAPD addresses TRX (orBCF) through TEI, and uses different logical links for message transfer. RSL is to transfertraffic management messages. OML is to transfer network management messages. L2MLis to transfer L2 management messages.

BTSM: Base Transceiver Station ManagementLAPD: Link Access Procedure on the D ChannelLAPDm: Link Access Procedure on the Dm ChannelSCCP: Signaling Connection Control PartMTP: Message Transfer PartBSSAP: Base Station Subsystem Application Part RR: RadioResource


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RR (Radio Resource Management) messages are mapped onto the BSSAP(BSS Application Part) in BSC. In BTS, most of RR messages are handled astransparent messages. However, some of them have to be interpreted andexecuted by BTS (for example, cipher, random access, paging and assignment),these messages are processed by the BTSM (BTS Management) entities in BSC and BTS.BSC and BTS do not interpret CM (Connection Management) and MM (MobilityManagement) messages. These messages are transferred over the A-interface by DTAP(Direct Transfer Application Part). At the Abis interface, DTAPmessages are transferred as transparent messages.


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The Abis interface can support threedifferent internal BTS configurations

1. Single TRX.2. Multiple TRXs are connected with

the BSC via a common physicalconnection.

3. Multiple TRXs are connected with

the BSC via different physicalconnections.

TRX (Transceiver) is the functional entity that supports 8 physical channels that belong to thesame TDMA frame, which is defined in the PLMN.

The BCF (Base Control Function) is the functional entity that performs common control functionsincluding BTS initialization, software loading, channel configuration, operation and maintenance.

F i Th f LAPD i li li bl d d i f i f


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Function : The purpose of LAPD is to realize reliable end-to-end information transfer between layer 3 entities through the user-network interface by using the D-channel. To bespecific, LAPD supports:

Multiple terminal equipment between subscriber and interface,Multiple L3 entities.

Functions of LAPD includes:Establishes one or several data links on the D channel.Delimits, locates and transmits transparently frames so that a string of bits

transmitted on the D channel in the form of frames can be identified.Implements sequence control to keep the order of the frames that pass the

data link connections.Checks the transmission errors, format errors and operation errors in the

data link connections.

Makes recovery based on the detected transmission errors, format errorsand operation errors.Notifies the management layer entities of the unrecoverable errors.Flow control.


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The function of Traffic Management are1. Realizing the interworking of the MS and BSS/NSS on the Um interface.2. Implementing part of the radio resource management functions under the

control of BSC.

The traffic management messages can be divided into four groups in terms of functions, which are:

1. Radio link layer management message, used for the management of thedata link layer on the radio channel.

2. Dedicated channel management message used for the management of dedicated channels (SDCCH and TCH).

3. Common control channel management message used for themanagement of common control channels.4. TRX management message used for TRX management.

Radio link layer management procedures


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Radio link layer management procedures

Link establishment indication procedure: BTS uses this procedure to indicate to BSC the success of setting upmulti-frame link originated by the subscriber. BSC establishes a link from MSC to SCCP through the indication.Link establishment request procedure: This procedure is used by BSC to request the establishment of a linklayer connection in multi-frame mode on the radio channel.Link release indication procedure: This procedure is used by BTS to indicate to BSC that a link layer connectionon the radio channel has been released at the initiative of an MS.Link release request procedure: This procedure is used by BSC to request the release of a link layer connectionon the radio channel.Transmission of a transparent L3-message on the Um interface in acknowledged mode: This procedure is usedby BSC to request the sending of a transparent L3 message to MS on the Um interface in acknowledged mode.

Reception of a transparent L3-message on the Um interface in acknowledged mode: This procedure is used byBTS to indicate the reception of a transparent L3 message on the Um interface in acknowledged mode.Transmission of a transparent L3-message on the Um interface in unacknowledged mode: This procedure isused by BSC to request the sending of a transparent L3 message to MS on the Um interface in unacknowledgedmode.Reception of a transparent L3-message on the Um interface in unacknowledgedmode: This procedure is used by BTS to indicate the reception of a transparent L3 message in unacknowledgedmode.Link error indication procedure: Through this procedure BTS indicates BSC incase of any abnormality in theradio link layer.

Dedicated channel management procedures


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Dedicated channel management procedures

Channel activation procedure: This procedure is used to activate a channel at BTS for an MS which later will be commanded tothis channel by an Immediate Assignment, an Assignment Command, an Additional Assignment or a Handover Command message.

Channel mode modification procedure: This procedure is used by BSC to request a change of the channel mode of an active

channel.Handover detection procedure: This procedure is used between the target BTS and BSC to detect the accessing of the MS beinghanded over.

Start of encryption procedure: This procedure is used to start encryption according to the procedure defined in TechnicalSpecification GSM 04.08.

Measurement report procedure: It includes the necessary basic measurement report procedure and measurement reportpreprocessing procedure. BTS reports all parameters related to handover decision to the BSC through this procedure.

Deactivate SACCH procedure: This procedure is used by BSC to deactivate the SACCH at BTS according to the Channel Releaseprocedure defined in Technical Specification GSM 04.08.

Radio channel release procedure: This procedure is used by BSC to release a radio channel that is no longer needed.MS power control procedure: This procedure is used by BSS to set the MS power level or the parameters required by TRX. MS

power control decision must be implemented in BSC, and as an optional procedure in BTS.BTS Transmission power control procedure: This procedure used between BSC and BTS to set the TRX transmission power level

or the parameters required by TRX. The BTS transmission power control decision should be implemented in BSC, or in BTS.Connection failure procedure: This procedure is used by BTS to indicate to BSC that an active connection has been broken.Physical context request procedure: This is an optional procedure which allows the BSC to obtain information on the "physical

context" of a radio channel just prior to a channel change.SACCH information modification procedure: BSC uses this procedure to instruct BTS to change the information (system

information) filled in a specific SACCH channel.


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Common channel management procedures

Channel request by MS procedure: The procedure is initiated by TRX upon detection of a random accessfrom an MS (Channel Request message from MS).

Paging principle procedure: It is used to page an MS on the specified paging sub-channel. The paging of an MS is initiated by BSC sending a Paging Command message to BTS. BSC determines the paging group to beused according to the IMSI of the called MS. The value of this paging group together with the identity of themobile station is sent to BTS.

Immediate assignment procedure: When a mobile station accesses BTS, BSC uses this procedure to assigna dedicated channel for the mobile station immediately.

Delete indication procedure: This procedure is used by BTS to indicate that due to overload on the AGCH,an Immediate Assign Command has been deleted.

CCCH load indication procedure: This procedure is used by BTS to inform BSC the load on a designateCCCH. Indication period is also set by OM.

Broadcast information modification procedure: This procedure is used by BSC to indicate to BTS the newinformation to be broadcast on BCCH.

Short message cell broadcast procedure: Short Message Service Cell Broadcast messages are sent to BTSas SMS Broadcast Request messages.

TRX management procedures


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TRX management procedures

SACCH filling information modify procedure: This procedure is used by BSC to indicate to BTS the newinformation to be used as filling information on SACCHs.

Radio resources indication procedure: This procedure is used to inform BSC on the interference levels on idlechannels of a TRX.

Flow control procedure: This procedure is defined to give some degree of flow control. It can be used for TRX

processor overload, downlink CCCH overload and AGCH overload.

Error reporting procedure: This procedure is used by BTS to report detected downlink message errors, whichcannot be reported by any other procedure.


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Basic structure of Management Object

Managed objects : There are four types of management objects: site, cell, carrier and channel

Object addressing:Addressing of network management messages isrealized by means of managed object types andcases. For each object case in BTS there is a completeL2 connection description. The setup of the firstconnection uses one (semi-) permanentdefault TEI. Subsequent connections use the TEIsprovided when setting up TEI procedures. Objectcases can also use layer 3 addresses. The mixed useof layer 2 and layer 3 addressing enables one BTS siteto have one or multiple physical links.

Managed object state


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Managed object stateManagement status include management status, operation status and availability status.

Management State Description

Locked

BSC has disconnected all calls through this managed object,and no new calls can be connected to this object.

Shut downNew services can not be connected to this managed object,but those existing calls will be maintained.

Unlocked New calls can be connected to this managed object.

Operation State Description

DisabledResources are completely unavailable, and can no longerprovide services to the users.

Enabled All or part of resources are available and can be used.


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Avavilability State Description

Locked The resource is being tested. Its operational state is disabled.

Shut down The source/object is not working due to some internal error.Its operational state is disabled.

UnlockedThe resource needs power supply. Its operational state isdisabled.

Off lineThe resource needs manual or automatic operations. Itsoperational state is disabled.

DependencyServices provided by this resource are degraded in a certainsense, such as rate or operational capacity. Its operationalstate is disabled.

Degraded

Services provided by this resource are degraded in a certain

sense, such as rate or operational capacity. Its operationalstate is enabled.

Not InstalledHardware or software of the managed objects is not installed.Its operational state is disabled.

For a specific object, if a certain basic procedure is not completed, the system will not start its


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For a specific object, if a certain basic procedure is not completed, the system will not start itssubsequent basic procedures. When there is no response to the formatted operation andmaintenance message from the peer layer 3 before L3 timeout, the basic procedure is regarded asnot completed .

When the previous basic procedure has not received any response (ACK or NACK) before layer 3timeout, then no subsequent basic procedure is sent to this object case. The default timeout forlayer 3 is 10s. If part of an original message is not understood or supported, the whole message isdiscarded. A ACK message returned by the object indicates affirm response, it is used to notify themessage sender that the command has been executed or will be executed. A NACK messagereturned by the object indicates disaffirm response, it is used to notify the message sender thatthe command executed unsuccessfully and the corresponding failure cause.

Software loading management procedureAbis interface management procedureTransmission management procedureAir interface management procedureTest management procedureState management and event reporting procedureEquipment state management procedureOther procedure


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The first layer(L1) is the physical layer at the bottom. It defines the radio accesscapabilities of GSM, and provides basic radio channels for information transfer onhigher layer.

The layer 2 is the data link layer using the LAPDm protocol. It defines various datatransmission structures, and controls data transmission.The layer 3 is the highest layer. It includes various messages and programs, and

controls services. It includes 3 sub-layers, which are Radio Resources management (RR),Mobility Management (MM), and Connection Management (CM).

Layered Structure of Um Interface

Introduction: Um interface (air interface or radiointerface) is defined as the communication interfacebetween MS and BSS. It is for the communicationbetween MS and the fixed part of GSM. Its physicallink is the radio link. The information transmitted viathis interface include radio resource management,

mobility management and connection management.


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The physical layer provides the following services:Access capability : the physical layer provides a series of limited logical channels for

transmission service. The logical channel is multiplexed on the physical channel. There exist 8physical channels on each TRX. Through data configuration, logical channels are mapped to

physical channels Error code detection: Physical layer provides error protection transmission, including errordetection and correction.

Ciphering: Use the selected encrypt algorithm to transmit bit sequence encrypted.


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The purpose of the data link layer is to establish reliable dedicated data links between MS andBTS. The link layer protocol used by the GSM system at the radio interface is the LAPDm protocol

which has evolved from the LAPD protocol.

LAPDm receives the service from the physical layer and provides service to L3.

The data link Service Access Point (SAP) is the node that provides services for layer 3.SAP is identified through SAPI.

Each SAP is associated with one or multiple Data Link Connection End Points (DLCEP).

Currently, two SAPI values are defined in the LAPDm protocol, 0 (main signaling) and 3(short messages).


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LAPDm Function

The provision of one or more data link connections on a Dm channel. Discriminationbetween the data link connections is by means of a data link connection identifier (DLCI).

Allows for frame type identification.Allows L3 message units to be transmitted transparently between L3s.Exercises sequence control to maintain the order of frames that pass DLC.Check on the format and operation errors on the data links.

Flow control.Contention resolution when establishing a data link after an access request has

been made on the RACH.

LAPDm Operation Types


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p ypTwo types of operation of the data link layer are defined for layer 3 information transfer:unacknowledged operation and acknowledged (multiple frame) operation . Theymay co-exist on a Dm channel.

1. Unacknowledged mode: layer 3 information is transmitted in Unnumbered Information (UI) frames At the data link layer, the UI frames are not acknowledged. Flow control mechanisms and error recovery mechanisms are not defined. It is applicable to different types of control channels except for RACH.

2. Acknowledged mode: layer 3 information is transmitted in Unnumbered Information (UI) frames. The data link layer acknowledges the transmitted I frame. Error recovery procedures based on retransmission of unacknowledgedframes are specified. Flow control procedures are also defined. In case of errors, which cannot be corrected by the data link layer, a report

is issued to the layer 3 entity.

LAPDm Information Transfer Mode


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Information transfer on the BCCH: Information transfer on the PCH + AGCH: Information transfer on the DCCHs:

LAPDm Release of Data LinksMultiple frame operation may be released in the following ways:

Normal release by exchange of commands/responses. Local end release, i.e. without exchange of commands/responses, initiated andcontrolled by layer 3.


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L3 Introduction : The signaling layer 3 of the Um interface provides the functions to establish,maintain and terminate circuit-switched connections across a GSM PLMN and other networks to

which the GSM PLMN is connected.

The objectives of the layer 3 are to provide the means for:The establishment, operation and release of a dedicated radio channel connection (RR).For location updating, authentication and TMSI reallocation (MM).For establishment, maintaining and termination of circuit-switched calls (CC).Supplementary services support (SS).Short messages service support (SMS).

Layer 3 consists of 3 sub-layers including Connection Management (CM), Mobility Management(MM) and Radio Resource management (RR).

RRM MM CM

CC

SS

SMS

Layer 3

L3 Structure:


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L3 Structure:

Radio Resources (RR) management handles the establishment, maintenance, and release of physical channels and logical channels, as well as cross-cell transfer on the request of CM sub-

layer.Mobility Management (MM) deals with the all necessary functions of mobile features to

support mobile subscribers. It notifies the network when the mobile station is activated anddeactivated, or the location area is changed. It is also responsible for the security of activatedradio channels.

CC deals with all necessary functions to establish or release the circuit-switched connections.SS deals with all necessary functions to support GSM supplementary services.SMS performs all necessary functions to support point-to-point short message services.

L3 Services:


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L3 Services:

On MS Side 1. Registration services, i.e., IMSI attach and detach operations.

2. Call Control services, including MS originating normal call establishment, MSoriginating emergency call establishment, call hold, call termination, and callrelated Supplementary Services Support.

3. Call independent Supplementary Services Support.4. Short Message Services Support.

On Network Side 1. Call Control Services, including call establishment, call maintaining, call

termination and call related supplementary service support.2. Call independent Supplementary Services Support.3. Short Message Services Support

In ter-layer services b etween th e mo bi le s ta t ion and network s ide Services provided by Radio Resource Management entity . These services are

provided to MM via RR-SAP. They are used for establishing control channelconnections, establishing traffic channel connections, ciphering mode indication,releasing control channel connections, and control-data transfer.Services provided by mobility management entities (MM). These servicessupport call control, supplementary services and short messages services of connection management entities.


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The MM routing function route the messages of the CM entities and the messages of the MM


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g g gentity of its own sublayer towards the service access point of RR, and multiplex them in case of parallel transactions. The routing function of Radio Resource Management shall distribute themessages to be sent according to their protocol discriminator (PD) and the actual channel

configuration.

The messages provided at the different service access points of layer 2 are split by the RRrouting function according to the protocol discriminator (PD). If PD equals to RR, this messagewill be transferred to RR at the local sub-layer. Other messages are provided to MM via theaccess point RR-SAP. The routing function of MM passes the messages according to the protocoldiscriminator (PD) and the transaction identifier (TI) towards the MM entity or towards the CMentities via the various MM-SAP's.

The RR sub-layer at the bottom receives services provided by layer 2 through variousservice access points (i.e., various types of channels) of layer 2, and provides services via RR-SAPto the MM sub-layer. The MM sub-layer provides services to the three entities (CC, SS and SMS)on the CM sub-layer through different service access points MMCC-SAP, MMSS-SAP and MMSMS-

SAP respectively, provides register services to the higher layer through MMREG-SAP serviceaccess points. The 3 independent entities on the CM sub-layer provide services to higher layersthrough MNCC-SAP, MNSS-SAP and MNSMS-SAP respectively.


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1. MS sends a CHANNEL REQUEST message to BTS on theaccess channel (RACH) of Um interface. The messagecontains the cause value "MOC

2. BTS sends a CHANNEL REQUIRED message to BSC.3. Upon receipt of the CHANNEL REQUIRED message, BSC

allocates a signaling channel and sends a CHANNELACTIVATION message to BTS.

4. If the channel type is correct, upon receipt of theCHANNEL ACTIVATION message, BTS opens the poweramplifier on the specified channel, and sends a CHANNEL

ACTIVATION ACKNOWLEDGE message to BSC.5. BSC sends an IMMEDIATE ASSIGNMENT COMMANDmessage to MS via BTS. The message is sent on AGCH onUm interface.

6. MS sends an SABM frame on SDCCH to BTS to access thenetwork.

7. BTS returns a UA frame on SDCCH for acknowledgement.

8. BTS sends an ESTABLISHMENT INDICATION message to BSC (This message contains the accurate causes forMS' F l diff t l i di t d i th bil igi ti g ll t bli h t


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MS's access. For example, different cause values are indicated in the mobile originating call establishmentprocedure and IMSI detach procedure). This message contains the contents of the CM SERVICE REQUESTmessage.

9. BSC establishes the SCCP link connection on A interface, and sends a CM SERVICE REQUEST message to MSC.

10. MSC returns a message to BSC to acknowledge the link connection.11. MSC sends a CM SERVICE ACCEPTED message to MS. The message is sent on SDCCH on Um interface.12. The calling MS sends a SETUP message on SDCCH.13. MSC sends a CALL PROCEEDING message to the calling MS. The message is sent on SDCCH on Um interface.14. MSC sends an ASSIGNMENT REQUEST message to BSC, which contains the CIC allocated to A interface.15. BSC allocates a TCH, and sends a CHANNEL ACTIVATION message to BTS.16. If the channel type is correct, upon receipt of the CHANNEL ACTIVATION message, BTS opens the power

amplifier on the specified channel, starts to receive the uplink information and sends a CHANNELACTIVATION ACKNOWLEDGE message to BSC.

17. BSC sends an ASSIGNMENT COMMAND message to MS via BTS on SDCCH.18. MS sends an SABM frame to BTS, to access the network on FACCH indicated in the ASSIGNMENT COMMAND

message.19. BTS sends a UA frame for acknowledgement on FACCH.20. BTS sends an ESTABLISHMENT INDICATION message to BSC.21. After accessing the TCH, MS sends an ASSIGNMENT COMPLETE message to BSC on FACCH.

22. After the radio traffic channel and terrestrial circuit are both successfully connected, BSC sends anASSIGNMENT COMPLETE message to MSC, and regards this call in session state.


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23. MSC sends an ALTERING message to the calling MS. The calling MS will hear the ringback. The message issent on FACCH on Um interface.

24. MSC sends a CONNECT message to MS. The message is sent on FACCH on Um interface.25. The calling MS returns a CONNECT ACKNOWLEDGE message on FACCH to MSC.26. The calling MS and called MS enters the session state.27. After the conversation is over, the calling MS hangs up and sends a DISCONNECT message on FACCH.28. MSC sends a RELEASE message to MS. The message is sent on FACCH on Um interface.29. MS returns a RELEASE COMPLETE message. The message is sent on FACCH on Um interface.30. MSC sends a CLEAR COMMAND message to BSC. Upon receipt of the message, BSC initiates the release

procedure.31. BSC sends a CHANNEL RELEASE message to MS through BTS, The message is sent on FACCH on Um

interface.32. MS sends DISC frame on FACCH.33. BTS returns UA frame on FACCH.


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1. When the paged MS is located in the serving areaof MSC, MSC sends a PAGING message to BSC,

which contains a paged cell list, TMSI and IMSI.2. BSC sends a PAGING COMMAND message to thepaged cells, which contains the relevant pagingsubchannel Nos. and the occupied timeslot Nos.

3. Upon receipt of the PAGING COMMAND messagefrom BSC, BTS sends a PAGING REQUEST messageon the paging subchannel (PCH subchannel) that

belongs to the paging group. This message containsthe IMSI or TMSI of the paged MS.

4. MS sends a CHANNEL REQUEST message on RACHif it finds itself paged after decoding the pagingmessage.

5. MS sends a CHANNEL REQUEST message to BTS onthe access channel (RACH) of Um interface

6. BTS sends a CHANNEL REQUIRED message to BSC.7. Upon receipt of the CHANNEL REQUIRED message, BSC allocates a signaling channel and sends a CHANNEL


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ACTIVATION message to BTS.8. If the channel type is correct, upon receipt of the CHANNEL ACTIVATION message, BTS opens the power

amplifier on the specified channel, and sends a CHANNEL ACTIVATION ACKNOWLEDGE message to BSC.9. BSC sends an IMMEDIATE ASSIGNMENT COMMAND message to MS via BTS. The message is sent on AGCH

on Um interface.10. MS sends an SABM frame on SDCCH to BTS to access the network.11. BTS returns a UA frame on SDCCH for acknowledgement.12. BTS sends an ESTABLISHMENT INDICATION message to BSC (This message contains the accurate causes for

MS's access. For example, different cause values are indicated in the mobile originating call establishmentprocedure and IMSI detach procedure). This message contains the contents of the CM SERVICE REQUESTmessage.

13. BSC establishes the SCCP link connection on A interface, and sends a CM SERVICE REQUEST message toMSC.

14. MSC returns a message to BSC to acknowledge the link connection.15. MSC sends a CM SERVICE ACCEPTED message to MS. The message is sent on SDCCH on Um interface.16. The calling MS sends a SETUP message on SDCCH.17. MSC sends a CALL PROCEEDING message to the calling MS. The message is sent on SDCCH on Um interface.18. MSC sends an ASSIGNMENT REQUEST message to BSC, which contains the CIC allocated to A interface.19. BSC allocates a TCH, and sends a CHANNEL ACTIVATION message to BTS.20. If the channel type is correct, upon receipt of the CHANNEL ACTIVATION message, BTS opens the power

amplifier on the specified channel, starts to receive the uplink information and sends a CHANNELACTIVATION ACKNOWLEDGE message to BSC.

21. BSC sends an ASSIGNMENT COMMAND message to MS via BTS on SDCCH.22. MS sends an SABM frame to BTS, to access the network on FACCH indicated in the ASSIGNMENT


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COMMAND message.23. BTS sends a UA frame for acknowledgement on FACCH.24. BTS sends an ESTABLISHMENT INDICATION message to BSC.25. After accessing the TCH, MS sends an ASSIGNMENT COMPLETE message to BSC on FACCH.26. After the radio traffic channel and terrestrial circuit are both successfully connected, BSC sends an

ASSIGNMENT COMPLETE message to MSC, and regards this call in session state.27. BTS sends a UA frame for acknowledgement on FACCH.28. BTS sends an ESTABLISHMENT INDICATION message to BSC.29. After accessing the TCH, MS sends an ASSIGNMENT COMPLETE message to BSC on FACCH.30. After the radio traffic channel and terrestrial circuit are both successfully connected, BSC sends an

ASSIGNMENT COMPLETE message to MSC, and regards this call in session state.

31. MSC sends an ALTERING message to the calling MS. The calling MS will hear the ringback. The message issent on FACCH on Um interface.

32. MSC sends a CONNECT message to MS. The message is sent on FACCH on Um interface.33. The calling MS returns a CONNECT ACKNOWLEDGE message on FACCH to MSC.34. The calling MS and called MS enters the session state.35. After the conversation is over, the calling MS hangs up and sends a DISCONNECT message on FACCH.36. MSC sends a RELEASE message to MS. The message is sent on FACCH on Um interface.37. MS returns a RELEASE COMPLETE message. The message is sent on FACCH on Um interface.38. MSC sends a CLEAR COMMAND message to BSC. Upon receipt of the message, BSC initiates the release

procedure.39. BSC sends a CHANNEL RELEASE message to MS through BTS, The message is sent on FACCH on Um

interface.40. MS sends DISC frame on FACCH.41. BTS returns UA frame on FACCH.


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gsm based cellular_rf level 2

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