Interference on Idle Channel

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Idle Channel Measurements

BTS measures the uplink interference on idle channels

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038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 1

GSM Radio Network Features

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

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038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 2

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GSM Radio Network Features

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Microsoft PowerPoint - 03810_19_A(idlech)

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Interference • Unbalanced frequency plan – Some frequencies are always disturbed

• Long term variations – External interferers

• Short term variations – Channel allocation/release in co/adjacent channels 5

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Figure 19 - 3

GSM Radio Network Features

ICM - 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

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038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 4

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GSM Radio Network Features

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Microsoft PowerPoint - 03810_19_A(idlech)

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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

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GSM Radio Network Features

Figure 19 - 5

Idle Channel Measurements IB: Interference Band

-110dBm

IB1

IB2

IB3

IB4

IB5

LOW 0

HIGH 2

LIMIT1: 2 (-108 dBm)

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22

RXLEV 63

LIMIT3: 12 (-98 dBm) LIMIT2: 6 (-104 dBm)

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LIMIT4: 22 (-88 dBm) Figure 19 - 6

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GSM Radio Network Features

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Microsoft PowerPoint - 03810_19_A(idlech)

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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 5

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Figure 19 - 7

GSM Radio Network Features

Channel Release •

Normal release the channel is placed in the same Interference Band as that it was taken from at channel allocation.

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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.

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? the Abnormal release for half rate channels channel is placed in the same Interference Band (as in normal release) if its corresponding half rate channel is idle

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After a channel release, the BTS reports the UL i.f. for that channel to the BSC within two SACCH periods. 038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 8

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GSM Radio Network Features

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Microsoft PowerPoint - 03810_19_A(idlech)

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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.

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038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 9

GSM Radio Network Features

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 5

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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.

038 13 - EN/LZU 108 3704 Rev A

Figure 19 - 10

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GSM Radio Network Features

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Microsoft PowerPoint - 03810_19_A(idlech)

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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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Figure 19 - 11

GSM Radio Network Features

Evaluation • Channel Event Recording (CER) – Mean number of idle channels per IB per Resource Type – Information of individual logical channels – IB statistics per logical channel

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Microsoft PowerPoint - 03810_19_A(idlech)

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Evaluation

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Figure 19 - 13

GSM Radio Network Features

Figure 19 - 14

GSM Radio Network Features

Evaluation

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038 13 - EN/LZU 108 3704 Rev A

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Microsoft PowerPoint - 03810_19_A(idlech)

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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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GSM Radio Network Features

Figure 19 - 15

Parameter Setting Default parameter setting:

Recommended values

– LIMIT1: 2

SSDES + 92

– LIMIT2: 6

SSDES + 100

– LIMIT3: 12

SSDES + 108

– LIMIT4: 22

SSDES + 129 25

– INTAVE = 6

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Figure 19 - 16

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GSM Radio Network Features

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