pioneerelex
2011-12-12, 09:47 PM
Hi Friends,
Find below the main causes for Handover failures and optimization tips and more:
High handover failures rate will probably be due to one or more of the following reason:
1. High Neighbour Interference
2. No Dominant Server
3. Database Parameters
Optimization Tips :
1. High Neighbour Interference While handling off to the best neighbour the interference on the target cell frequency may result in the hand off failure.
TIPS: When designing the cell frequencies care should be taken that there is proper frequency spacing between the cells to avoid neighbour interference. In most of the cases Ping Pong Handover starts i.e the mobile hand off to a cell for better level and due to interference (Quality issues) hand off again to original cell. A through drive test can determine the “interfering frequencies” which should be eliminated from the frequencies plan.
2. No Dominant Server If cell sites are designed poorly there might be areas where neighbour being received at the same level and some neighbour randomly look good for hand off for a certain amount of time. Such situation is disastrous because handoff decision will be hard and mostly it will end up unsuccessful handovers.
TIPS : Antenna tilts provide the good way to reduce the footprint of the sites. Efforts should be made that a single dominant server should serve the specific area. Timing advance limitation is applied to cell areas where there is multiple servers.
3. Database Parameters Received level, receive quality and power budget algorithm are set in the system information to define the criteria for handover. Improper values for these criteria may result in poor handoff.
TIPS: Enable the “per neighbour” feature which dispalys the successful and unsuccessful handovers on a per cell basis. In optimization, monitor the following stats, which comes under “cell statistic category”.
All those cells can be identified which are problematics in terms of hand off so one can focus only specific cell causing the major contribution towards poor HSSR. Ensure that handover margins are optimised.
Rule of thumb is a 4 dB for adjecent frequencies and 6 dB per cell without adjecent frequencies. The following parameters can be played for defining the threshold for imperative and non-imperative handovers:
a. Defines the lower threshold for uplink quality handovers. ex : Range 0 to 1800 Step size = 0.01 a value of 500 defines the lower threshold value of 5 (BER) for a quality handover to be triggered for uplink. The optimum for this threshold is 500.
b. Defines the lower threshold for downlink quality handovers
c. Defines the lower threshold for received level uplink handovers. Ex : A value of 20 defines the threshold value of -90 dBm for a level handover to be triggered for uplink. Range 0 to 63 Where 0 = -110 dBm 1 = -109 dBm 63 = -47 dBm The optimum value for this threshold is 15 ( – 95 dBm). If the signal level goes below that, a level handover is initiated.
d. Defines the lower threshold for received level downlink handovers.
e. Defines the upper threshold for uplink interference handovers
f. Defines the upper threshold for downlink interference handovers
Find below the main causes for Handover failures and optimization tips and more:
High handover failures rate will probably be due to one or more of the following reason:
1. High Neighbour Interference
2. No Dominant Server
3. Database Parameters
Optimization Tips :
1. High Neighbour Interference While handling off to the best neighbour the interference on the target cell frequency may result in the hand off failure.
TIPS: When designing the cell frequencies care should be taken that there is proper frequency spacing between the cells to avoid neighbour interference. In most of the cases Ping Pong Handover starts i.e the mobile hand off to a cell for better level and due to interference (Quality issues) hand off again to original cell. A through drive test can determine the “interfering frequencies” which should be eliminated from the frequencies plan.
2. No Dominant Server If cell sites are designed poorly there might be areas where neighbour being received at the same level and some neighbour randomly look good for hand off for a certain amount of time. Such situation is disastrous because handoff decision will be hard and mostly it will end up unsuccessful handovers.
TIPS : Antenna tilts provide the good way to reduce the footprint of the sites. Efforts should be made that a single dominant server should serve the specific area. Timing advance limitation is applied to cell areas where there is multiple servers.
3. Database Parameters Received level, receive quality and power budget algorithm are set in the system information to define the criteria for handover. Improper values for these criteria may result in poor handoff.
TIPS: Enable the “per neighbour” feature which dispalys the successful and unsuccessful handovers on a per cell basis. In optimization, monitor the following stats, which comes under “cell statistic category”.
All those cells can be identified which are problematics in terms of hand off so one can focus only specific cell causing the major contribution towards poor HSSR. Ensure that handover margins are optimised.
Rule of thumb is a 4 dB for adjecent frequencies and 6 dB per cell without adjecent frequencies. The following parameters can be played for defining the threshold for imperative and non-imperative handovers:
a. Defines the lower threshold for uplink quality handovers. ex : Range 0 to 1800 Step size = 0.01 a value of 500 defines the lower threshold value of 5 (BER) for a quality handover to be triggered for uplink. The optimum for this threshold is 500.
b. Defines the lower threshold for downlink quality handovers
c. Defines the lower threshold for received level uplink handovers. Ex : A value of 20 defines the threshold value of -90 dBm for a level handover to be triggered for uplink. Range 0 to 63 Where 0 = -110 dBm 1 = -109 dBm 63 = -47 dBm The optimum value for this threshold is 15 ( – 95 dBm). If the signal level goes below that, a level handover is initiated.
d. Defines the lower threshold for received level downlink handovers.
e. Defines the upper threshold for uplink interference handovers
f. Defines the upper threshold for downlink interference handovers