Feature Tuning, Practical Case study

ICM
Table of Contents
Contents
1 Abstract 3
2 Introduction 3
3 Concept 3
3.1 General description 3
3.2 Main Controlling Parameters 4
3.3 Benefit 5
4 Practical case 6
4.1 Network Information 6
4.2 BSCTIZ1 Serving Area 6
4.3 Cell Data 7
4.4 Setting before implementation 7
4.5 Work procedure 7
5 Test cases evaluation 8
5.1 15224C 8
5.2 15225C 9
5.3 15234A 10
5.4 15633A 11
5.5 15651C 12
5.6 15658A 13
6 Conclusion 14
7 Abbreviation 15
8 Reference 15

1
Abstract
The aim of this report is to find the best parameters setting for ICM feature and knows what is weight of each parameter (LIMIT, SAS,…).
2 Introduction
Idle Channel Measurement is a function that gives the information about the uplink interference on each idle channel (Traffic Channel (TCH) or Stand Alone Dedicated Control Channel (SDCCH)). This information can then be used during channel allocation to select the best suited channel for a connection
It also generates statistics on interference, giving a general picture of the quality of the channels in a cell.
3 Concept
3.1 General description
The quality of a channel depends on the ratio between the signal strength of the carrier and that of interfering signals, C/I. The quality is reduced as interference increases.
Therefore, one way to evaluate the general quality of the channels in a cell is to monitor the signal level of the interferer in these channels.
When the Idle Channel Measurements feature is activated in a cell, The BTS continuously performs uplink signal strength measurements as long as the channel is idle. To determine a value for the interference on a channel, the BTS takes the average of measurements over a number of SACCH periods. This is done once every SACCH period, and the number of SACCH periods to average over is determined by parameter INTAVE. The BTS only reports to the BSC when the interference band for an idle channel has changed. The channel is then moved to the appropriate interference band in the BSC.
Depending on the measured signal level of the interferer each channel is placed in one of the five corresponding interference bands
The interference bands are disjunctive and together cover values in rile units from 0 (low interference) up to 63 (high interference) as shown in the figure below

Figure-1: ICM LIMIT
3.2 Main Controlling Parameters
When a channel becomes idle, the BSC places it in an interference band according to the procedures described in sections Section 3.1
* LIMIT
LIMIT1 is the most important parameter. This parameter divides the idle channels into two main parts, the idle channels in interference band 1, which are used at channel allocation in the first place, and the idle channels in interference bands 2 to 5. Of course, if there are no idle channels in interference band 1, the idle channels in interference bands 2 and then 3 etc. are allocated. The default setting of LIMIT1 to LIMIT4 corresponds to the following interference levels:

Parameter name
Default value

Recommended value

Value range

LIMIT1
2
SSDES+92
0 to 62
LIMIT2
6
SSDES+100
0 to 62
LIMIT3
12
SSDES+108
0 to 62
LIMIT4
22
SSDES+129
0 to 62

F
Table-1: Limit Parameter setting.
* SSDES
The recommended values for LIMIT1 to LIMIT4 are based on how the Dynamic MS Power Control parameter SSDES is set
* INTAVE
Is the number of SACCH periods that the BTS will use measurements from to calculate the average uplink interference value for a channel. The parameter is defined per cell.
* ICMSTATE
Is a state variable in the BSC that sets the idle channel measurements to ACTIVE, PASSIVE or NOALLOC. NOALLOC means that the idle channel measurements are used for statistics only, and not for channel allocation.
3.3 Benefit
The aim with this feature is to enhance the quality for individual calls, by means of “sorting out” idle channels with high interference (idle channels in interference bands 2 to 5), which is performed by the Channel Administration feature (see Reference [1]). This is especially important for connections with low signal strength. A rule of thumb is to set LIMIT1 so that at least 5 to 10 % of the most interfered idle channels are sorted out from interference band 1. In networks with high interference level, it is benefice to distribute the idle channels more evenly between the interference bands.
4
Practical case
4.1 Network Information
Country
Algeria
Operator
Mobilis
City/Region
Tizi Ouzou /Sub center
BSC
BSCTIZ1
Bsc Tizi1 was selected as test environment for ICM tuning, it has 140 site served by frequency band 900[85-124].
4.2 BSCTIZ1 Serving Area
Figure-3 here below shows the geographical served area of BSCTIZ1.
BSCTIZ1 serving area is considered as Suburban area from radio point of view; moreover one of the main characteristics of the area is that it has hilly nature.

Figure-2: BSC TIZI1 serving area.
4.3 Cell Data
The cells chosen for the test case are those which suffering from quality point of view and need new setting of ICM limit.
BSC
Cell Normal
ICMSTATE
BSCTIZ1
15224C
ACTIVE
BSCTIZ1
15225C
ACTIVE
BSCTIZ1
15234A
ACTIVE
BSCTIZ1
15245A
ACTIVE
BSCTIZ1
15604C
ACTIVE
BSCTIZ1
15630C
ACTIVE
BSCTIZ1
15630A
ACTIVE
BSCTIZ1
15630B
ACTIVE
BSCTIZ1
15633A
ACTIVE
BSCTIZ1
15633B
ACTIVE
BSCTIZ1
15651C
ACTIVE
BSCTIZ1
15658A
ACTIVE
Table-2: Selected cells for test case.
4.4 Setting before implementation

Date
SSDESUL
LIMIT1
LIMIT2
LIMIT3
LIMIT4
SAS
Before 4 September
80
2
10
18
39
Quality
Table-3: Old ICM Settings.
4.5 Work procedure
Test cases time Plan.
Date
SSDESUL
LIMIT1
LIMIT2
LIMIT3
LIMIT4
SAS
4-5 September
80
2
6
12
22
MULTI
6-7-8 September
80
12
20
28
49
MULTI
9-10 September
80
12
20
28
49
QUALITY
11-12 September
90
2
6
12
22
MULTI
13-14-15 September
90
2
10
18
39
MULTI
16-17 September
90
2
10
18
39
QUALITY
Table-4: test cases time plan.

1
5 Test cases evaluation
5.1 15224C

Figure-3: Cell 15224C Performance trend
5.2
15225C

Figure-4: Cell 15225C Performance trend.
5.3 15234A

Figure-5: Cell 15234A Performance trend.
5.4
15633A

Figure-6: Cell 15633A Performance trend.
5.5
15651C

Figure-7: Cell 15651C Performance trend.
5.6
15658A

Figure-8: Cell 15658A Performance trend
6 Conclusion
ICM feature was found to be beneficial for Network accessibility, retainablity and integrity. Main function is to help the system to assign the best time slot to subscriber from quality point of view, which reflected on TCH assignment success rate, good SQI, TCH/SDCCH drop call rate.
Best Parameter setting is listed here below:
* SSDESUL=90.
* LIMITS= Recommended value (LIMIT1=2, LIMIT2=10, LIMIT=18, LIMIT=39).
* INTAVE=25.
* SAS= QUALITY means that at channel allocation we use ICM.

7
Abbreviation
BSC Bas Station Controller
BTS Radio Base Station
SACCH Slow Associated Control Channel
SAS Single slot Allocation Strategies
SDCCH Stand alone Dedicated Control Channel