Cell Selection and Re-selection in GSM

Cell Selection Procedure

• First MS powers-on
• MS starts measuring received power level from all cells in range
• MS calculates average power level received from each cell:
• Stored in RXLEV(n) parameter
• MS calculates C1 parameter for each cell based on RXLEV(n)
• Mobile compares cells which give a positive value of C1 and ‘camps-on’ to the cell with the highest C1 value.
On switch-on, an MS periodically measures the received power level on each of the BCCH frequencies of all cells within range. From these periodic measurements the MS calculates the mean received level value from each cell, stored in the parameter RXLEV (n) where n=neighboring cell number.

Cell Re-selection – GSM Phase 1 Mobiles

For GSM Phase 1 mobiles, cell reselection is achieved by comparing current cell C1 with neighboring C1 cell measurements:
• Between cells within a Location Area:
C1 (new) > C1 (old)         (for more than 5 seconds)

• Between cells on a Location Area boundary:
C1 (new) > C1 (old) + OFFSET      (for more than 5 seconds)

Cell Re-selection – GSM Phase 2 Mobiles

• GSM Phase 2 introduced a separate cell re-selection parameter, C2
• Intended to:
• Prevent multiple handovers for fast-moving mobiles
• Ensure MS camps on to cell with greatest chance of successful communications
• The C2 calculated is:

C2 = C1 + OFFSET – (TEMPORARY_OFFSET x H(PENALTY_TIME –T)

Ericsson 2G OSS Command


Command
Description
RLDHP:CELL=ALL;
CELL DYNAMIC HR ALLOCATION DATA
DBTSP:TAB=AXEPARS;
DATABASE TABLE FILE PRINTOUT STATUS
PLLDP;
PROCESSOR LOAD DATA
RAEPP:ID=ALL;
BSC EXCHANGE PROPERTY DATA
RLCAP;
BSC CIPHERING ALGORITHM DATA
RLDCP;
BSC DIFFERENTIAL CHANNEL ALLOCATION DATA
RLLBP;
BSC LOCATING DATA
RLLSP;
BSC LOAD SHARING STATUS
RLOMP;
BSC BAND OPERATION MODE DATA
RLTYP;
BSC SYSTEM TYPE DATA
RLVAP;
CELL SEIZURE SUPERVISION OF LOGICAL CHANNELS ALARMED OBJECTS DATA
RRGBP;
RADIO TRANSMISSION GB INTERFACE CONFIGURATION DATA
RLHBP;
BSC LOCATING HIERARCHICAL CELL STRUCTURE BAND DATA
ALLIP;
ALARM LIST
SAAEP:SAE=ALL;
SIZE ALTERATION OF DATA FILES INFORMATION
SAACP:SAE=ALL;
SIZE ALTERATION OF DATA FILES CROSS-REFERENCE
RLCPP:CELL=ALL;
CELL CONFIGURATION POWER DATA
RLLOP:CELL=ALL;
CELL LOCATING DATA
RLLOP:CELL=ALL,EXT;
CELL LOCATING DATA FOR EXTERNAL CELLS DEFINED IN THE BSC
RLLHP:CELL=ALL;
CELL LOCATING HIERARCHICAL DATA
RLLLP:CELL=ALL;
SUBCELL LOAD DISTRIBUTION DATA
RLACP:CELL=ALL;
CELL ADAPTIVE LOGICAL CHANNEL CONFIGURATION
RLCHP:CELL=ALL;
CELL CONFIGURATION FREQUENCY HOPPING DATA
RLGAP:CELL=ALL;
CELL CHANNEL GROUP ALLOCATION DATA
RLCXP:CELL=ALL;
CELL CONFIGURATION DTX DOWNLINK DATA
RLDGP:CELL=ALL;
CELL CHANNEL GROUP DATA
RLDTP:CELL=ALL;
CELL TRAINING SEQUENCE CODE DATA
RLDMP:CELL=ALL;
CELL DYNAMIC FR/HR MODE ADAPTATION DATA
RLGRP:CELL=ALL;
CELL GENERAL PACKET RADIO SERVICE RESOURCES DATA
RLGSP:CELL=ALL;
CELL GENERAL PACKET RADIO SERVICE DATA
RLCLP:CELL=ALL;
CELL CHANNEL ALLOCATION DATA
RLHPP:CELL=ALL;
CONNECTION OF CELL TO CHANNEL ALLOCATION PROFILE DATA
RLIHP:CELL=ALL;
CELL LOCATING INTRACELL HANDOVER DATA
RLIMP:CELL=ALL;
CELL IDLE CHANNEL MEASUREMENT DATA
RLLCP:CELL=ALL;
CELL LOAD SHARING DATA
RLLDP:CELL=ALL;
CELL LOCATING DISCONNECT DATA
RLLFP:CELL=ALL;
CELL LOCATING FILTER DATA
RLLPP:CELL=ALL;
CELL LOCATING PENALTY DATA
RLLUP:CELL=ALL;
CELL LOCATING URGENCY DATA
RLOLP:CELL=ALL;
CELL LOCATING OVERLAID SUBCELL DATA
RLPBP:CELL=ALL;
HANDOVER POWER BOOST DATA
RLPRP:PP=ALL;
BSC DIFFERENTIAL CHANNEL ALLOCATION PRIORITY PROFILE RESOURCE TYPE DATA
RLSBP:CELL=ALL;
CELL SYSTEM INFORMATION BCCH DATA
RLSLP:CELL=ALL;
CELL SUPERVISION OF LOGICAL CHANNEL AVAILABILITY DATA
RLSMP:CELL=ALL;
CELL SYSTEM INFORMATION BCCH MESSAGE DISTRIBUTION
RLSSP:CELL=ALL;
CELL SYSTEM INFORMATION SACCH AND BCCH DATA
DTDIP:DIP=ALL;
DIGITAL PATH
DTQUP:DIP=ALL;
DIGITAL PATH QUALITY
DTSTP:DIP=ALL;
DIGITAL PATH STATE
NTCOP:SNT=ALL;
SWITCHING NETWORK TERMINAL CONNECTION DATA
NTSTP:SNT=ALL;
SWITCHING NETWORK TERMINAL STATE
EXEMP:RP=ALL,EM=ALL;
EM DATA
EXRPP:RP=ALL;
RP DATA
STDEP:DEV=RTGPHDV-0&&-700;
DEVICE STATE DETAILS
RXMOP:MOTY=RXOTRX;
RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT DATA
RXMSP:MOTY=RXOTRX;
RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT STATUS
RXMFP:MOTY=RXOTRX;
RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT FAULT INFORMATION
RXAPP:MOTY=RXOTG;
RADIO X-CEIVER ADMINISTRATION ABIS PATH STATUS
RXELP:MOTY=RXOCON;
RADIO X-CEIVER ADMINISTRATION ERROR LOG DATA
RXTCP:MOTY=RXOTG;
RLMTP:ID=ALL,CELL=ALL;
CELL BROADCAST SHORT MESSAGE SERVICE MESSAGE DISTRIBUTION DATA
RLDMP:CELL=ALL;
CELL DYNAMIC FR/HR MODE ADAPTATION DATA
RLAPP:CELL=all;
AMR POWER CONTROL CELL DATA
RLMBP:ID=ALL;
CELL BROADCAST SHORT MESSAGE SERVICE MESSAGE DATA
RLLDC:CELL=CELLNAME,MAXTA=8;
For changing the TA value of the cell





Transmission types

• Asynchronous transmission
• Plesiochronous transmission
• Synchronous transmission

Asynchronous transmission
Asynchronous transmission is transmission of data in which time intervals between transmitted characters may be of unequal length. Transmission is controlled by start and stop bits at the beginning and end of each character. Transition of signals do not occur at the same nominal rate Generally free running quartz oscillators derive the clock, there is no timing pulses sent from transmitter to receiver

Plesiochronous transmission
Plesiochronous is a Greek word meaning Almost Synchronous, but not fully synchronous. The digital transitions in the signals occur at almost the same rate. There may be a phase difference between the transitions of the two signals, and this would lie on specified limits.

Synchronous transmission

The digital transitions in the signals occur at exactly the same rate. There will be no phase difference between the transitions of the two signals, and this would lie on specified limits. In a synchronous network, all the clocks are traceable to one primary reference clock (PRC). The accuracy of the PRC is better than 0.1 in 1011 and is derived from a cesium atomic standard.

Multiplexing

It is the process of combining a number of individual channels into a common frequency band or into a common bit stream for transmission.

Different multiplexing techniques are:
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Wavelength Division Multiplexing (WDM)

Frequency Division Multiplexing
FDM is a process in which the bandwidth is divided in frequency domain, or in other words each of the input signals is transmitted at a different frequency (Carrier) but simultaneously (or in the same time slot).  FDM is a multiplexing technique used for analog signals.

Time division multiplexing
TDM is a type of multiplexing in which different signals are multiplexed in different time slots. In TDM each time slots is fixed for different signals sequentially. TDM uses full bandwidth for every channel, but not at the same time so that every channel gets its time slot in the shared line.

Wavelength division multiplexing
It is a type of multiplexing in which different signals are multiplexed at different wavelengths for full time slots. When each wavelength is multiplexed from different TDM signals then the multiplexing is called TDM over WDM. WDM is widely used for the following reasons:

• Better utilization of fiber
• Low unit cost of bandwidth in high capacity systems

• Easily integrated with existing equipment in the network

Network Management Subsystem (NMS)

The Network Management Subsystem (NMS) is the third subsystem of the GSM network in addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS), which we have already discussed. The purpose of the NMS is to monitor various functions and elements of the network.
The functions of the NMS can be divided into three categories:
·                Fault management
·                Configuration management
·                Performance management

These functions cover the whole of the GSM network elements from the level of individual BTSs, up to MSCs and HLRs.

Fault management
The purpose of fault management is to ensure the smooth operation of the network and rapid correction of any kind of problems that are detected. Fault management provides the network operator with information about the current status of alarm events and maintains a history database of alarms.
The alarms are stored in the NMS database and this database can be searched according to criteria specified by the network operator.


Configuration management
The purpose of configuration management is to maintain up-to-date information about the operation and configuration status of network elements. Specific configuration functions include the  management of the radio network, software and hardware management of the network elements, time synchronization, and security operations.

Performance management
In performance management, the NMS collects measurement data from individual network elements and stores it in a database. On the basis of these data, the network operator is able to compare the actual performance of the network with the planned performance and detect both good and bad performance areas within the network.