What is Concentric in GSM Technology?

The principle of ordinary concentric is that a cell is divided into underlay and overlay, both having the same site and sharing the same TRXs, antenna and BCCH. The coverage of overlay is the same as that of ordinary cell, while the underlay use small transmitting power and thus has smaller coverage. The

frequency reuse factor of overlay differs from that of underlay. The former adopts frequency reuse pattern of 4 ´ 3, while the latter adopts closer pattern of 3 ´ 3, or 2 ´ 3. The BCCH and SDCCH are

used by overlay, in which the call will be set up. As a cell is subdivided into two layers, abrand new switching algorithm should be added. Inter-cell hand-over is conducted in overlay,while overlay-

underlay and intra-underlay is added to intra-cell .

Calculation of C/I

 Where, Pown_cell  is the signal strength of current cell;  Pi_BCCH  is BCCH signal strength of interfering

cell i measured by MS

Directed Retry handover means: SDCCH to TCH

Which kind of Handovers more desired in the Network: Power Budget

Same BCCH-BSIC combination in adjacency will lead to a Massive Handover failur and Call drop.

What is the reason of ping-pong handover: Cable swap No dominant cell coverage Improper handover margin.

Coding Schemes used in GSM- GMSK & QPSK

What is frequency reuse factor.Frequency reuse factor denotes the reuse of certain frequency after count of cells.Like 3/12 reuse means a frequency used in one cell can be used again in after 12 That is 13 cell.This helps in minimizing C/I of network

How to improve network Accessibility? Network accessibility can improved by minimizing congestion (RACH, SDCCH and TCH).

How to resolve indoor customer complaints.Indoor complaints can be resolved by installing indoor boosters, optimizing neighboring cells, using highgain antennas and planning new sites and IBS.

New Site planning criteria. Coverage and Capacity site planning. Knowledge of 3G and 4G.3G or UMTS is evolution over 2G.Data rates are 2Mbps in UL and 14

Mbps in DL.4G is LTE, mobile broadband speeds can be achieved. High Gain antenna uses.On highways mainly. What is Combiner? Hardware which combines two frequencies in one output. Two trxs can be

combined Benefits of TMA

o Provides a gain of 12 dBo Improves System sensitivityo Reduces noise figure of equipmento Increase mobile battery

What are Mobile Originated Call setup basic steps?o RACCH requesto Access granto SDCCH Allocateo Authenticationo Cipheringo Alertingo Call proceedingo Connect

Handover Reasonso Bad Coverageo Bad Qualityo High Distanceo High Powero Traffic based

What is AMR? Adaptive Multi Rate Coding States- Half Rate AMR & Full Rate AMR Code- 12.2 ,10.2,7.95,7.40,6.70,5.90,5.15, 4.7 Kbps

Dropped calls can be caused by either RF environments or incorrect systemparameters.The

following data should be checked to ensure that it has been collected properly. Layer 3 Messages •Neighbour Cell List (BA Table) •RxLEV (Server • & Neighbour) RxQUAL (Server

• & Neighbour) Finally, ensure that the automatic setting for the call length is not shorter than that for the

Timer monitoring for unauthorised call drop-outs. The setting should be a minimum of 30 seconds

Handover ProblemsHandover problems are generally caused by inaccurate settings of the handoverboundary.This can cause ping-ponging, where the server will keep changing, and congestion attheswitch. Check the following.The transceiver antenna is fitted correctly •Collection of Layer 3 Messages •Collection of Neighbour Cell List (BA Table) •Collection of Scanning Information •Collection of Cell Identities •Collection of T.Adv for the Serving Cell •Also, ensure that the collection of data from the new serving cell immediately afterthehandover has occurred (particularly RxLEV and RxQUAL) isnot timed to occur prior to the-synchronisation of thetransceiver itself.If a particular serving cell can be isolated as a potential cause of handoverproblems,slowly drive around the cell in a radius of around 500m- 1km, checking when handovers occur.Blocked Calls / System BusyIf calls are repeatedly classified as blocked, it is recommended that the drive testistemporarily halted in order to try and locate the cause.Check that the number called is fully functional •Check that there is adequate coverage from the expected serving BTS •Check the equipment transceiver is functioning correctly by using an ordinary •mobile to call the officeIf all appears functional, try to place calls through an alternative BTS. If this •succeeds, inform the office immediately and re-suspend the drive test

Radio Link Time-OutEvery time a SACCH message can not be decoded the radio link time-outcounter is decreased by 1. If the message can be decoded the counter isincremented by 2. However, the value can not exceed the initial value. Theinitial value is set by the parameter RLINKT for radio link time-out in themobile station and by RLINKUP for timeout in the BSC. If the mobilemoves out of coverage and no measurement reports are received in theBSC, there will be a radio link time-out and the message Channel Release(cause: abnormal release, unspecified) is sent to the mobile station andthe SACCH is deactivated in the BTS. A Clear Request message is sent tothe MSC. To be sure that the mobile has stopped transmitting, the BSCnow waits RLINKT SACCH periods before the timeslot is released and anew call can be established on the channel.

Visit Out Forum For moreOptimization Tips2. Layer 2 Time-OutIf the BTS never get an acknowledge on a Layer 2 message after the timeT200XN200, the BTS will send Error Indication (cause: T200 expired) tothe BSC, which will send Channel Release (cause: abnormal release,timer expired) to the mobile station and a Clear Request to the MSC. TheSACCH is deactivated and the BSC waits RLINKT SACCH periods beforethe timeslot is released and a new call can use the channel. This is onlyvalid if the call is in steady state, i.e. not during handover or assignment

Assignment to TCHBefore sending an Assignment Command from the BSC at TCHassignment, the following two criterion have to be fulfilled:a. There must be a TCH channel available, i.e. no congestionb. The locating algorithm must have received at least one validmeasurement report.If either of the criterion is not fulfilled, Assignment Command will not besent and a Channel Release (cause: abnormal release, unspecified) will besent to the mobile station and a Clear Request to the MSC.

TCH Drop reason (1)The classification of TCH Drop Reasons are arranged in the order of priority:1.Excessive Timing Advance2.Low Signal Strength3.Bad Quality4.Sudden Loss of Connection5.Other Reasons

Excessive Timing AdvanceThe TCH Drop counters due to Excessive Timing Advance will peggedwhen the during the time of disconnection, the last Timing Advance valuerecorded was higher than the TALIM Parameter. This drop reason iscommonly apparent to isolated or island sites with a wide coverage area.Action:Check if the cell parameter TALIM is < "63"

Solution:Set TALIM to a value close to 63.Tilt antenna/reduce antenna height/output power, etc. for co-channel cells

TCH Drop Reasons (2)Low Signal Strength on Down or Uplink or Both LinksThe drops counters due to Low Signal Strength will be pegged when theSignal Strength during the last Measurement Report before the calldropped is below the LOWSSDL and/or LOWSSUL Thresholds.LOWSSDL and LOWSSUL are BSC Exchange Property parameters whichis used only for statistics purposes and does not affect the behavior of calls. If both UL and DL Signal Strength are below the thresholds, onlyDrop due to Low SS BL will pegged. Normally a call is dropped at theborder of large rural cell with insufficient coverage. Bad tunnel coveragecause many dropped calls as well as so called coverage holes. Bad indoor coverage will result in dropped calls. Building shadowing could be another reason.

Action: Check coverage plots.Check output power. Check power balance and link budget. Check if Omni site.

Check antenna configuration & type. Check antenna installation. Perform drive tests & site survey. Check TRX/TS with high CONERRCNT

Solution:Add a repeater to increase coverage in for example a tunnel. Change to a better antenna (with higher gain) for the base station.Add a new base station if there are large coverage holes.Block/Deblock TRX

TCH Drop Reasons (3)Poor Quality on Down or Uplink or Both LinksThe drops counters due to Bad Quality will be pegged when the SignalStrength during the last Measurement Report before the call dropped isabove the BADQDL and/or BADQUL Thresholds. BADQDL and BADQUL(expressed in DTQU) are BSC Exchange Property parameters which isused only for statistics purposes and does not affect the behavior of calls.If both UL and DL Quality are above the thresholds, only Drop due to BADQuality BL will pegged.Problem on Bad Quality is usually associated with Co-channel Interferenceon BCCH or TCH. Faulty MAIO assignment can cause frequency collisionson co-sited cells especially on 1x1 Reuse. External interference is also onepossible cause of problem on quality.

Action:Check C/I and C/A plots.Check Frequency Plan (Co-BCCH or Co-BSIC Problem).Check MAIO, HOP, HSN parameters.Check FHOP if correctly configured (BB or SY).Check for External Interference.Perform drive tests.

Solution: Change BCCH frequency. Change BSIC. Change MAIO, HOP, HSN. Change FHOP. Record RIR or on-site Frequency Scanning to identify source of interference. Use available radio features

TCH Drop Reasons (4)Sudden Loss of ConnectionDrops due to Sudden Loss are drops that have not been registered as lowsignal strength, excessive timing advance, bad quality or hardware (other)reasons, and the locating procedure indicates missing measurementresults from the MS.There are some common scenarios that could lead to Sudden Loss of connections such as very sudden and severe drops in signal strength,such as when subscribers enter into buildings, elevators, parking garages,etc., very sudden and severe occurrence of interference, MS runs out of battery during conversation, Handover Lost, BTS HW faults,Synchronization or A-bis link fault (transmission faults), andMS Faults.

Action:

Check BTS Error Logs, Alarms and Fault Codes.Check CONERRCNT per TRX and TS.Check Transmission Link (A-bis).Check for DIP Slips.Check LAPD Congestion.Correlate Handover Lost to Drops due to Sudden LossSolution:Fix Hardware Faults and Alarms.Reset TRX with high CONERRCNT.Ensure that Synchronization and A-bis Link are stable.Change RBLT with high DIP Slips.Change CONFACT or increase Transmission CapacityInvestigate HO Lost Problem

TCH Drop Reasons (5)TCH Drops due to Other ReasonsTCH drops due to Other Reasons are computed by subtracting the sum of drops due to Excessive TA, Low SS, Bad Quality and Sudden Loss fromthe Total TCH Drop Counts. Drops due to Other Reasons are generallyassociated with hardware problems, transmission link problems on A-bis,Ater or Ainterfaces, and sometimes Handover Lost.Action:Check BTS Error Logs.Check Alarms and Fault Codes.Check CONERRCNT per TRX and TS.Check Transmission Link (A-bis).Check for DIP Slips.Correlate Handover Lost to Drops due to Other ReasonsSolution:Fix Hardware Faults and Alarms.Reset TRX with high CONERRCNT.Ensure that Synchronization and A-bis Link are stable.Change RBLT with high DIP Slips.Investigate HO Lost Problem