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-Ideas about a handover algorithm
-======================================================================
-
-This is mostly based on the results presented in Chapter 8 of "Performance
-Enhancements in a Frequency Hopping GSM Network" by Thomas Toftegaard Nielsen
-and Joeroen Wigard.
-
-
-=== Reasons for performing handover ===
-
-Section 2.1.1: Handover used in their CAPACITY simulation:
-
-1) Interference Handover
-
-Average RXLEV is satisfactory high, but average RXQUAL too low indicates
-interference to the channel. Handover should be made.
-
-2) Bad Quality
-
-Averaged RXQUAL is lower than a threshold
-
-3) Low Level / Signal Strength
-
-Average RXLEV is lower than a threshold
-
-4) Distance Handover
-
-MS is too far away from a cell (measured by TA)
-
-5) Power budget / Better Cell
-
-RX Level of neighbor cell is at least "HO Margin dB" dB better than the
-current serving cell.
-
-=== Ideal parameters for HO algorithm ===
-
-Chapter 8, Section 2.2, Table 24:
-
-Window RXLEV averaging: 10 SACCH frames (no weighting)
-Window RXQUAL averaging: 1 SACCH frame (no averaging)
-Level Threashold: 1 of the last 1 AV-RXLEV values < -110dBm
-Quality Threshold: 3 of the last 4 AV-RXQUAL values >= 5
-Interference Threshold: 1 of the last AV-RXLEV > -85 dBm &
- 3 of the last 4 AV-RXQUAL values >= 5
-Power Budget: Level of neighbor cell > 3 dB better
-Power Budget Interval: Every 6 SACCH frames (6 seconds ?!?)
-Distance Handover: Disabled
-Evaluation rule 1: RXLEV of the candidate cell a tleast -104 dBm
-Evaluation rule 2: Level of candidate cell > 3dB better own cell
-Timer Successful HO: 5 SACCH frames
-Timer Unsuccessful HO: 1 SACCH frame
-
-In a non-frequency hopping case, RXQUAL threshold can be decreased to
-RXLEV >= 4
-
-When frequency hopping is enabled, the following additional parameters
-should be introduced:
-
-* No intra-cell handover
-* Use a HO Margin of 2dB
-
-=== Handover Channel Reservation ===
-
-In loaded network, each cell should reserve some channels for handovers,
-rather than using all of them for new call establishment. This reduces the
-need to drop calls due to failing handovers, at the expense of failing new call
-attempts.
-
-=== Dynamic HO Margin ===
-
-The handover margin (hysteresis) should depend on the RXQUAL. Optimal results
-were achieved with the following settings:
-* RXQUAL <= 4: 9 dB
-* RXQUAL == 5: 6 dB
-* RXQUAL >= 6: 1 dB
-
-
-
-== Actual Handover on a protocol level ==
-
-After the BSC has decided a handover shall be done, it has to
-
-# allocate a channel at the new BTS
-# allocate a handover reference
-# activate the channel on the BTS side using RSL CHANNEL ACTIVATION,
- indicating the HO reference
-# BTS responds with CHAN ACT ACK, including GSM frame number
-# BSC sends 04.08 HO CMD to MS using old BTS
-