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1. SACCH Multi-Frames This parameter determines whether an uplink radio link isfaulty. Each time the BTS fails to decode the measurement report on the SACCH from the MS, the counter decreases by 1. Each time the BTS successfully decodes the measurement report on the SACCH, the counter increases by 2. When the value ofthis counter is 0, the BTS regards the radio link as faulty. In the traffic measurement, if there are many call drops (M3101A) related to radio link failure, you can infer that the radio propagation conditions are poor. In this case, you can set this parameter to a greater value.2. Radio Link Timeout This parameter determines whether a downlink radio link isfaulty. Each time the BTS fails to decode the measurement report sent over theSACCH by the MS, the counter decreases by 1. Each time the BTS successfully decodes the measurement report sent over the SACCH, the counter increases by 2. Whenthe value of this parameter is 0, the BTS regards the radio link as faulty. Inthe traffic measurement, if there are many call drops (M3101A) related to radiolink failure, you can infer that the radio propagation conditions are poor. In this case, you can set this parameter to a greater value.3. RXLEV_ACCESS_MIN This parameter specifies the minimum receive level of an MSto access the BSS. If this parameter is set to a too small value, some MSs withlow receive levels may access the network and call drops are likely to occur. You can set this parameter to a great value to reduce the TCH call drop rate. Thecounters such as call setup success rate and the counters related to traffic volume, however, are accordingly affected.4. RACH Min.Access Level This parameter determines whether an MS can access thenetwork over the RACH. If this parameter is set to a too small value, some MSs w

ith low signal levels may access the network and call drops are likely to occur.You can set this parameter to a great value to reduce the TCH call drop rate. The counters such as call setup success rate and paging success rate, however, are affected.5. Min DL Power on HO Candidate Cell and Min Access Level Offset The sum of thevalues of the two parameters specifies the minimum downlink receive level of a candidate neighboring cell for a handover. If this parameter is set to a too great value, some desired cells may be excluded from the candidate cells; if this parameter is set to a too small value, an unwanted cell may become the candidate cell. Both conditions may lead to the increase of calldrops.6. Timer T3103 series Timer T3101 series consists of T3103A, T3103C, and T8. These timers are started to wait for a handover complete message. If the lengths of

the timers are set to small values, probably no message is received when timerT3103 series expires. In this case, the BSC considers that the radio link in theoriginating cell is faulty. Then, the BSC releases the channel in the originating cell. Thus, call drops occur. In the traffic measurement, if many call dropsare related to handovers (CM331: Call Drops on Radio Interface in Handover State), you can set this parameter to a greater value. If this parameter is set to atoo great value, channel resources are wasted and TCH congestion occurs.7. Timer T3109 This parameter specifies the period for waiting for a Release Indication message after the BSC sends a Channel Release message to the BTS. If this parameter is set to a too small value, the link may be released before the Release Indication message is received. As a result, a call drop occurs. You can set this parameter to a greater value to reduce the TCH call drop rate. It is recommended that timer T3109 be set to 12 seconds longer than timer Radio Link Timeou

t.8. Timer T3111 This parameter specifies the interval between the time that the main signaling link is disconnected and the time that a channel is deactivated. The purpose is to reserve a period of time for repeated link disconnections. If this timer is set to a too small value, a channel may be deactivated too early. Thus, call drops increase.9. Timers T305 and T308 Timers T305 and T308 are used on the MSC side. Timer T305 specifies the period during which the MSC monitors the on-hook procedure. Timer T308 specifies the period during which the MSC monitors the resource release procedure. You should set the two parameters when adding BSC data. Note that the

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modification of the data in the timer table does not take effect. If timers T305and T308 are set to invalid or great values, the MSC clears the call a long time after the MS hangs up. After the T3103 and Radio Link Timeout timers expire, the number of call drops is increased and thus the TCH call drop rate is significantly affected.10. TCH Traffic Busy Threshold If the current channel seizure ratio exceeds thevalue of this parameter, the BSC preferentially assigns a half-rate channel to adualrate-enabled call. Otherwise, the BSC assigns a full-rate channel to the dualrate-enabled call. Compared with a full-rate channel, a half-rate channel hasweak antiinterference capabilities. Therefore, if a large number of half-rate channels are assigned, the TCH call drop rate increases. It is recommended that this parameter should not be set to a too small value if congestion is unlikely tooccur.11. Call Reestablishment Forbidden This parameter specifies whether to allow call reestablishment. In case of burst interference or radio link failure due to blind areas caused by high buildings, call drops occur. In this case, MSs can initiate the call reestablishment procedure to restore communication. To reduce theTCH call drop rate, you can set this parameter to No to allow call reestablishment. In certain conditions, allowing call reestablishment greatly reduces the TCHcall drop rate. Call reestablishment lasts for a long time, and therefore somesubscribers cannot wait and hang up. This affects user experience.12. Parameters related to edge handover When the receive level drops greatly, anedge handover cannot be performed in time in any of the following conditions: The parameter Edge HO UL RX_LEV Threshold or Edge HO DL RX_LEV Threshold is set t

o a small value; the parameter Inter-cell HO Hysteresis is set to a great value;the parameters Edge HO Watch Time and Edge HO AdjCell Watch Timeare set to great values; the parameters Edge HO Valid Time and Edge HO AdjCell Valid Time are set to great values. As a result, a call drop occurs. To reduce the TCH call drop rate, you can appropriately set these parameters so that edge handovers can be performed in time to avoid call drops.13. Parameters related to BQ handover When the signal quality deteriorates, a BQhandover cannot be performed in time in any of the following conditions: The parameters ULQuaLimitAMRFR, ULQuaLimitAMRHR, UL Qual. Threshold, DLQuaLimitAMRFR,DLQuaLimitAMRHR, and DL Qual. Threshold are set to great values; the parameter BQ HO Margin is set to a small value; the parameter Inter-cell HO Hysteresis is set to a great value. As a result, call drops occur. To reduce the TCH call droprate, you should appropriately set these parameters so that BQ handovers can be

performed in time to avoid call drops.14. Parameters related to interference handover If the parameters RXQUAL1 to RXQUAL12 are set to great values or if the RXLEVOff parameter is set to a great value, strong interference may occur. In this case, if interference handovers are not performed in time, call drops occur. To reduce the TCH call drop rate, you can appropriately set these parameters so that interference handovers can be performed in time to avoid call drops. If the parameters RXQUAL1 to RXQUAL12 are setto small values, the number of handovers due to other causes increases greatly,thus affecting the handover success rate.15. Parameters related to concentric cell handover A call at the edge of the overlaid subcell cannot be handed over to the underlaid subcell in any of the following conditions: In the case of a normal concentric cell, the parameters RX_LEVThreshold and RX_LEV Hysteresis are set to great values; in the case of an enhan

ced concentric cell, the parameter OtoU HO Received Level Threshold is set to agreat value. As a result, a call drop is likely to occur. If the Call Drop Ratioon TCH on the TRX in the OverLaid Subcell (RM330a) is high, you can appropriately set these parameters so that calls at the edge of the overlaid subcell can behanded over to the underlaid subcell in time. When a call in the underlaid subcell has interference, the call cannot be handed over to the overlaid subcell ifthe RX_QUAL for UO HO Allowed parameter is set to Yes and the RX_QUAL Thresholdparameter is set to a great value. Thus, a call drop occurs. If the Call Drop Ratio on TCH on the TRX in the Underlaid Subcell (RM330) is high, you can set these parameters properly so that the call can be handed over to the overlaid subcel

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l at the earliest.