Transmission function:

MS, BTS and BSC are concerned with transmission HLR, VLR or EIR transmit their signaling needs.

RR is a group of functions concerned with administration of channels at Um. Main RR procedures:

Power control Channel quality monitoring Handover Frequency hopping Discontinuous transmission Timing advance.

Enables power adaptation of MS and BTS. Main reasons for power control:

Saving MS battery Power Improve CIR.

Can be enabled or disabled. Performed separately for uplink and DL. Measurements on UL and DL are sent to BSC every 480 ms. Measurements in terms of:

Signal strength in dB. Signal quality in BER.

MS Power (dBm)

Max. transmit power

Power increase step

Signal strength measured at BTS

Upper threshold

Lower threshold

Distance Power control increase command

Distance

Handover Control

Automatic switching of a call from one TCH to another. Can be within the cell or between cells. Handover occurs on TCH when call is in speech stage. Only started if power control is not helpful. Unique feature of mobile network.

Reasons for intra-cell handover 1. reduction of co-channel interference. 2. Maintenance activity 3. Equipment failure

Handover types: Inter cell handover

Involves change of carrier and BTS. Intra-cell handover Involves change of carrier in same cell.

BSC

BSC

MSC-A

BTS

BTS

BTS BTS

BSC

BTS

Inter-MSC HO

Inter-BSC HO Intra-MSC HO

Intra-BSC HO

Intra-cell HO

MSC-B

Handover types

Requirements for Handover

1. Execution speed 2. Reliability

3. Transparent to users (not aware) 4. Service-dependent (voice, data)

• No excessive HO

• No delayed HO

• No early HO

Criteria for Handover

BSC receives measurement data from BTS and MS. The MS measures downlink:

Signal strength (dBm) Signal quality (BER) Signal strength of 6 neighboring BTSs downlink

The BTS measures UL:

Signal strength received from MS. Signal quality received from MS. Distance between BTS and MS.

MSC-A

BTS

BTS

BSC

Handling of Handover

Reserved channel concept Some channels are reserved for HO

1

2

Nc

N

New calls

Handover

N-times retry Multiple request for Handover

Handover queue HO wait for a free channel.

Sub-rating algorithm Full rate TCH is split into 2 half rate TCHs.

Intra-BSC (Inter-cell) HO

Old BTS

1

2

BSC

5

2

6

5

4 3

New BTS

Old BTS 4

New BSC

7

6 5

New BTS

MSC

Old BSC

4

9

1

4

8

2 3

7 4

7

Inter-BSC (Intra-MSC) HO

Old BTS

New BSC

5

8

7 6

New BTS

MSC-A Old BSC

5

8

1

5

3 4

8

5

MSC-B

2

GSM PLMN PSTN

Inter-MSC HO

9 9

Mobility Management (MM)

o Main task of MM is to support mobility.

o MM activities include: 1. IMSI attach and detach. 2. Location update 3. Registration 4. Update HLR/VLR 5. TMSI re-allocation. 6. Authentication of MS.

Location Update in same MSC/VLR

If MS detects a change in LAI, it informs network MSC/VLR check if it is a visitor

BTS

BSC

VLR

HLR

MSC

2

3

4

1

2

3

4

Location Update with New MSC/VLR

When MS enters into new LA, location update. LA may belong to new MSC/VLR.

BTS

BSC

New VLR

HLR

MSC

4

1

5

3

2

Old VLR

4

Periodic Registration

o MS is forced to send registration periodically. o If MS miss registration, the network marks o it as detached. o This occurs if MS is out of area. o This avoids paging. o Periodic registration has Ack. o MS tries until it receives Ack.

IMSI Attach

o When MS is switched on, it performs attach.

BTS

BSC MSC/VLR

3 2

4

1

4

Mobile Terminated Call

8

GMSC

BSC TRAU

5

11

8

7

GSM PLMN PSTN

6

2 HLR

MSC VLR

4 5

11

9

8 8 9

11 10

BTS BTS

Local Exchange

Telephone

1

1

10

BTS

BSC MSC/VLR

2

1

4

3

1

2

3

4 4

Exchange

Telephone

5

GSM PLMN

PSTN

Mobile Originated Call