GSM Radio Network Features Figure 19 - 1 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
Idle Channel Measurements
BTS measures the uplink interference on idle channels
E N / F A D 10 9 001 5
Main Purpose of the Feature
• To provide information to the Channel Administration feature
– Allocate the “most suitable” idle channel for a connection
• Collection of statistics on UL interference
– Quality – Frequency plan
GSM Radio Network Features Figure 19 - 3 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
• Unbalanced frequency plan
– Some frequencies are always disturbed
• Long term variations
– External interferers
• Short term variations
– Channel allocation/release in co/adjacent channels
Interference
E N / F A D 10 9 001 5ICM - the Measurement Function
• Uplink measurements of interference on idle channels (TCHs
and SDCCHs)
• Implemented in the BTS
• The measurements on TCH and SDCCH are made in the
same way as on active channels
GSM Radio Network Features Figure 19 - 5 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
The Measurement Function
• Averaging in the BTS
– One interference sample every SACCH period (~0.5s)
– INTAVE
– length of the running average filter
• Reporting to BSC
– When IB, the Interference Band, for a channel changes – => BTS sends report to BSC in message RF Resource
Indication E N / F A D 10 9 001 5
Idle Channel Measurements
LIMIT4: 22
(-88 dBm)
IB1
IB2
IB3
IB4
IB5
-110dBm -47dBm LIMIT1: 2 (-108 dBm) LIMIT2: 6 (-104 dBm) LIMIT3: 12 (-98 dBm) 0 2 6 12 22 63
IB: Interference Band
HIGH
GSM Radio Network Features Figure 19 - 7 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
Frequency Hopping ?
• Mean value of the the interference on the time slots in the
hopping sequence
• FH => Interference averaging
=> decreased influence of ICM
=> not possible to identify high interfered frequencies
• Interference on time slot basis will still be conquered
• Non-hopping BCCH
E N / F A D 10 9 001 5Channel Release
• Normal release the channel is placed in the same Interference Band as that it was taken from at channel allocation.
• Abnormal release for full rate channels (due to dropped call) ? the channel is placed in the Interference Band immediately above that it was taken from at channel allocation.
• Abnormal release for half rate channels ? the channel is placed in the same Interference Band (as in normal release) if its corresponding half rate channel is idle
After a channel release, the BTS reports the UL i.f. for that channel to the BSC within two SACCH periods.
GSM Radio Network Features Figure 19 - 9 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
Dual Rate Channels
The BTS measures the interference on the channels individually.
When evaluating the interference level for a FR channel composed of two HR channels, the BSC uses the average of the interference bands for the HR channels. E N / F A D 10 9 001 5
Channel Administration by Means of ICM
Which channel in the selected Resource Type In the normal channel selection case, in all traffic cases except Intra-cell handover, the following process is applied:
1. If half rate is requested, select the group of idle channels that have been partly allocated for half rate (in order to save the completely idle TCHs for FR).
2. If no partly allocated channels for half rate were found, select the group of idle channels from the least adaptable TCH capabilities group. 3. Among these channels, select a group of channels according to the status
of the TCH on the BCCH allocation preference parameter, CHALLOC. The value of this parameter is used to determine if an idle non-hopping TCH on the BCCH frequency should be allocated first, last or if there is no preference.
4. Among these channels, the group of TCHs or SDCCHs with the lowest interference band is selected if the Idle Channel Measurement feature is active.
5. Among these channels, the group of TCHs or SDCCHs hopping over as many frequencies as possible is selected.
6. Among these remaining channels, a TCH or SDCCH is allocated in accordance with the first in first out principle.
GSM Radio Network Features Figure 19 - 11 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
GPRS Selection of Packet Data Channels
GPRS Channel Administration can use the ranking of channels into interference bands as helpful information when selecting dedicated and on-demand PDCHs from the circuit switch domain.
When a PDCH is reconfigured to a TCH the channel is placed in the interference band it was in before it was allocated as PDCH. Idle Channel Measurements are not performed on PDCHs.
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Evaluation
• Channel Event Recording (CER)
– Mean number of idle channels per IB per Resource Type – Information of individual logical channels
GSM Radio Network Features Figure 19 - 13 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
Evaluation
E N / F A D 10 9 001 5Evaluation
GSM Radio Network Features Figure 19 - 15 E N / F A D 10 9 001 5 038 13 - EN/LZU 108 3704 Rev A
Main Controlling Parameters
• LIMIT1..LIMIT4
– Threshold limits for defining the different interference bands
• INTAVE
– Running average filter length for the interference measurements
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Parameter Setting
Default parameter setting:
– LIMIT1: 2 – LIMIT2: 6 – LIMIT3: 12 – LIMIT4: 22 – INTAVE = 6 Recommended values SSDES + 92 SSDES + 100 SSDES + 108 SSDES + 129 25
