Air Interface V2

7/29/2019 Air Interface V2

1/29

GSM Air Interface

YLI Sessions

VFE Radio Team

January 2008


2/29

13 September 2013

Presentation title in footer2

Idle mode behaviour

What is idle mode?The MS is said to be in Idle mode when it is powered on but not allocated any dedicatedchannel.

Idle mode activities :PLMN selection CELL selection & reselectionTune to the control channel of the cell, to listen to the system information messagestransmitted in that cell (Camping on the cell)4- It must also be able to register its current location to the network (Location Updating)


3/29

13 September 2013


Idle Mode: PLMN SelectionPLMN selection (Automatic/Manual mode) Automatic mode1- Last registered PLMN

2- Home PLMN3- According to PLMN list stored on SIM4- PLMNs with SS > -85 dBm in random order5- All other PLMNs in order of decreasing SS

Manual mode1- Last registered PLMN2- Home PLMN3- The MS will indicate the user all available PLMNs


4/29

13 September 2013


Idle mode: Cell Selection

Why MS must camp on a cell? The MS can receive system information The MS can initiate a call The system can reach the MSTypes of cell selection:Normal cell selection The MS will search all RF channels in its supported frequency band (124 channels inGSM 900)Stored list cell selection The MS will perform the measurements for only the last BA list BCCH carriers stored

on SIM before it was powered off.


5/29

13 September 2013


Idle mode: Cell Selection

Scan 124 channels and measure signal strength

Tune to the RF channel with the highest

received average signal strength

Determine if it is a BCCH frequency carrier by

searching for frequency correction bursts

Tune to the RF-channel with the

highest signal strength not already

tried

The MS shall attempt to synchronize to this

carrier and read BCCH info

Is it a BCCH carrier

Is it the wanted PLMN ?

Is the cell barred for access ?

Is C1>0 ?

Camp on this cell

No

Yes

No

Yes

No

Yes

Yes

No


6/29

13 September 2013


Idle mode: Cell reselection

Cell reselection:The MS detects that it is more suitable to camp on another cell.Why?The MS at all times try to camp on the cell which has the highest probability ofsuccessful communication on both up and downlinks when accessing the systemWhen?MS performs cell reselection if:

The serving cell becomes barred Downlink signaling failure C1C2(serving) (+CRH) more than 5sec


7/2913 September 2013


Idle mode: Cell reselection

Cell reselection procedures: MS monitors Neighbors BCCH carriers as well as the serving one. MS measure server BCCH at least once every 30s MS measures neighbors BCCH carrier at least once every 5min. MS attempts to decode the BSIC parameter at least once every 30s (for each of the six strongest surrounding cells)




Idle mode: location updating

Location Updating:The location updating is initiated by the MS to keep the network updated by its location.

Types of Location updating :1- Normal: MS listens to the broadcasted system information. It compares the broadcasted LAI with the stored one on the SIM. If it is different , a location updating type normal will be initiated.

2- Periodic registration:Reduces unnecessary paging of MSs which lost coverage or run out of battery. T3212 parameter (1 255) determines how often MS should perform periodic locationupdate.




Idle mode: IMSI attach/detach

When a MS is powered on, an IMSI attach message is sent to the MSC/VLR When a MS is powered off, an IMSI detach message is sent to the MSC/VLR Implicit detach?


10/29

13 September 2013


Normal Location update within same MSC/VLR service area

MSC / VLR

BSC

1

1. The Mobile sends an SDCCH allocation

request message on the RACCH to the BTS

2

2. The BTS responds with the SDCCH allocation

message on the AGCH

3

3

3

3. The mobile sends a location update request

message with its IMSI on the allocated

SDCCH channel to the MSC/VLR

4

4

4

4. The MSC/VLR updates the location

information and sends a Location Update

confirmation message on the SDCCH

channel to the mobile then the SDCCH

channel is released


11/29

13 September 2013


Normal Location update between 2 MSC/VLR service areas

7

7

7

7. The new MSC/VLR sends a locatio

updating confirmation message to

the mobile

HLR

Old MSC

Old BSC

New MSC

New BSC

1

1

1

1. The mobile requests a location update just like the first case

IMSI MGT2

2. The new MSC/VLR receives the IMSI and conclude the MGT

3

3. The MSC/VLR sends a subscriber

information request with the IMSI

to the HLR

4. The HLR stores the address of

the new MSC/VLR

HLR

5

HLR

5. The HLR sends the data to the

new MSC/VLR and it is kept ther

New MSC

6

6. The HLR sends a location

cancellation message to the old

MSC/VLR to remove the data

Old MSC


12/29

13 September 2013


Dedicated Mode: Handover

Handover : Handover is essential to keep continuity of the call when MS roamsalong the network and moving from one cell to another betweendifferent nodes in the network. During a call, the MS is continuously measuring the signal levels ofneighboring cells in addition to servers and reports this results tothe BSC through the BTS. The BSC, being responsible on supervising the cells, is responsibleof handover initiation. Good neighbor relations between cells is an important factor inkeeping the network performance in the accepted level.Types of handover : Intra Cell Intra BSC Handover Inter BSC / Intra MSC Handover Inter MSC Handover

BSC


13/29

13 September 2013


Basic definitions

Basic definitions: Time Slot : TS is the basic radio resource during which the carrier serves one logic channel

MS receives TS by TS and also sends TS by TS. Burst : the contents of each time slot is called a burst. Physical channel : the recurrence of the same physical TS in successive frames. Logical channel : the recurrence of the same TS contents in successive frames.


14/29

13 September 2013


Basic definitions

Physical Channels

CH 1 54321 6 70 0 1Time

CH 3 54321 6 70 0 1

CH 2 54321 6 70 0 1

CH 12454321 6 70 0 1

GSM band is divided into 124 RF channels, and each channel is divided into 8 time

slots using TDMA. These time slots are called physical channels.


15/29

13 September 2013Presentation title in footer15

Logical Channels

Synchronization ChannelBroadcast Control Channel

Frequency Correction Control Channelaging Channel

Random Access ChannelAccess Grant Channel

Standalone Dedicated Control ChSlow Associated Control Ch

Fast Associated Control ChCell Broadcast Control Ch

BroadcastommonDedicated

Logical Channels

Control ChannelsTraffic Channels

Half Rate Full Rate


16/29


Traffic Channels

TCH is allocated to the MS when it is in dedicated mode. TCH is intended to carry two types of bi-directional user information : Encoded speech

and data . Two types of traffic channels are defined

TCH/F: Full rate uses one physical channel TCH/H: Half rate shares one physical channel with another TCH/H

Channel rate:Full Rate (22,8 kbps gross bit rate on air interface)Half Rate (11,4 kbps gross bit rate)

Speech versionsFR SPV 1 = normal Full Rate (FR) 13 Kbps (speech coding rateFR SPV 2 = enhanced Full Rate (EFR) 12.2 Kbps (speech coding rate)FR SPV 3 = AMR Full Rate (AMR-FR) ACS (Active Codec Set)HR SPV 1 = normal Half Rate (HR) 5.6 Kbps (speech coding rHR SPV 3 = AMR Half Rate (AMR-HR) ACS (Active Codec Set)


17/29


Broadcast Channels

Frequency Correction Channel (FCCH): The 1st Burst that MS looks for just after switching on It is the repetition of frequency correction bursts Bursts containing only zeros are transmitted Make sure that this is the BCCH carrier Allow the MS to synchronize to the frequency Only transmitted DL , TS0


18/29


Broadcast Channels

Synchronization Channel (SCH): Used to provide synchronization information between MS & BTS in the time domain. Repetition of synchronization bursts Transmitted DL only. Base Station Identity Code (BSIC) TDMA Frame Number (RFN)


19/29


Broadcast Channels

Broadcast Control Channel (BCCH): When a mobile is turned on, it scans the GSM spectrum to find an available BTS. It is a permanent channel to be scanned, providing network information (called

system information) Transmitted DL only. Contains; cell description, cell identity, location area identity, network identity, BCCH

of neighboring cells.


20/29


Common Control Channels

Paging Channel (PCH) : When the network wants to initiate a communication with the MS, it looks for the

mobile by sending a paging request. Incoming call or incoming short message. Mobile Identity parameter (IMSI) or (TMSI). Transmitted DL only.

Access Grant Channel (AGCH) : Inform about the SDCCH or TCH allocated. Transmitted DL only. Channel description, Timing advance.


21/29


Common Control Channels

Random Access Channel (RACH) : When the MS requests allocation of signaling channel by sending a Channel Request Answering to paging, network contact Only transmitted UL


22/29


Dedicated Control Channels

Slow Associated Control Channel (SACCH) : When an SDCCH or a TCH is allocated, an associated channel is used by MS &

Network in Order to exchange general information Transmitted both UL and DL Up-Link: Measurement report Down-Link: System information, MS power level, timing advance

Fast Associated Control Channel (FACCH) : During a hand over, both MS and Network need to send a fast message to the other Works in stealing mode Transmitted both UL and DL


23/29


Dedicated Control Channels

Standalone Dedicated Control Channel (SDCCH) : MS and network need to exchange information before initializing communication. Used in authentication, ciphering, setup and assignment procedures Transmitted both UL and DL Transmission of SMS in idle mode.

Cell Broadcast Control Channel (CBCCH) It displays general information (weather, addresses, traffic..) . It uses one of the SDCCH channels MS must be configured to receive this channel

.


24/29


Normal Burst Structure

.

GSM Overview

Technical Session

TailBits

Encrypted Bits Training Sequence Encrypted BitsTailBits

GuardPeriod

3 57 1 26 1 57 3 8.25

0 1 2 3 4 5 6 7

TDMA Frame

156.25 bits in 577 m Sec


25/29


Mapping of logical channels (DL)

CBBBBSF

F S F S F S F S F S IB C C C C C C C C C

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

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7


26/29


Mapping of logical channels (UL)

RRRRRRR

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

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

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7


27/29


Post installation cycle

Site integration

Site testing

Site optimization


28/29


Drive-test Sample


29/29

Questions

Thanks

Air Interface V2

Documents

Transcript of Air Interface V2