Types of Handover in GSM

Power Budget Handover:

When signal strength difference between serving cell and neighbor cell exceeds Power Budget Handover margin which is set in Handover parameters, the call is handed over to the neighboring cell. This margin is usually set to 3 to 6 dB. In case of ping–pong handovers between the same two cells, power budget handover margin between the two could be increased to reduce number of handovers. Margin should be decreased if faster handover decision is wanted.

Level Handover:

If downlink level is worse then HO Thresholds Lev DL parameter, then an immediate level handover takes place. This parameter is set to –95dBm as default. If uplink level is worse then HO Thresholds Lev UL parameter, then an immediate level handover takes place. This parameter is set to –105dBm as default.

Quality Handover:

If downlink quality is worse then HO Thresholds Qual DL parameter, then an immediate quality handover takes place. If uplink quality is worse then HO Thresholds Qual UL parameter, then an immediate quality handover takes place.

Interference Handover:

Any quality problem when downlink signal level is higher then HO Threshold Interference DL causes a handover. This level is generally set to –80dBm. Any quality problem when uplink signal level is higher then HO Threshold Interference UL causes a handover. This level is usually set to –80dBm.

Intra–cell Handover:

The Intra–cell Handover feature aims to maintain good quality of a connection by performing a handover to a new channel within the same cell when bad quality is detected. If the signal strength is very high, the interference is probably lower on another channel within the same cell. Intra–cell Handover aims at improving the carrier–to–interference ratio, C/I, for a connection when the bit error rate estimation, RXQUAL, has indicated poor quality, and the received signal strength at the same time is high. This is done by changing the channel within the cell, a so called intra–cell handover. The intra–cell handover can be triggered from bad quality in the uplink, as well as the downlink. Intra–cell handover decision is given when serving cell is the best cell and quality is worse then 4 and signal strength is lower then –85dBm. Intra–cell handover can solve temporary co– and adjacent channel interference as well as intermodulation problems, but permanent interference and time dispersion cannot be solved.

Directed Retry Handover:

When no TCH is available in the serving cell, TCH can be allocated in an adjacent cell regardless of mobile originated or mobile terminated call. It is basically handover from SDCCH to TCH.

MS Distance Handover:

MS Distance HO Threshold parameter MS Range Max should be set to desired value. If an overshooting site is needed to hand its traffic after some distance from its origin, MS Range Max value could be adjusted to limit the serving area of the site.

Umbrella Handover:

Macro site which is defined as umbrella will shift all the TCH traffic to small sites until signal level of small site becomes worse than HO Level Umbrella RX Level parameter. This parameter could be set from –80 to –90dBm.