Sdcch congestion rate optimization guide

1 When SDCCH are required?
The requests for the SDCCH in GSM are mainly made in the following two procedures:
A. The procedure for requesting the SDCCH for services such as point-to-point calls, location updating (only SDCCH), call re-establishment, or short messages;
B. The procedure of SDCCH handovers (including both the intra-BSC and inter-BSC handovers)

2 Principles of SDCCH Congestion Rate: 
SDCCH congestion rate is one of the important counters that indicate accessibility in circuit service. This counter provides the ratio of failed SDCCH seizures due to busy SDCCH to the total requests for the SDCCH. SDCCH congestion rate indicates the failed requests for the SDCCH for various reasons. SDCCH congestion rate also indicates the status of the SDCCH resource utilization.

3 Definition & Formula of SDCCH Congestion : 
The definition and formula of SDCCH congestion rate are as follows:
• Definition:
Ratio of failed SDCCH seizures due to busy SDCCH to the total requests for the SDCCH
• Formula:
SDCCH congestion rate = Failed SDCCH seizures due to busy SDCCH/Total requests for the SDCCH x 100%

4 Factors of SDCCH Congestion Rate in GSM : 

4.1 Congestion Caused by Faults on Equipment or Transmission : 
The faults on BTS, BSC, and Abis interface, such as broken LAPD link, cause the SDCCH congestion. The alarm "Excessive Loss of E1/T1 Signals in an Hour" also causes the SDCCH congestion.

4.2 Congestion Caused by Insufficient Signaling Resources : 
The heavy traffic and burst traffic cause the SDCCH congestion. Proper setting of the number of SDCCHs and TCHs, and the SDCCH dynamic conversion function can relieve the congestion.

4.3 Congestion Caused by Improper Data Configuration : 
The SDCCH congestion relates to the relevant parameters of the BSC such as SDCCH Availability, LAC and T3101 (the timer used in the immediate assignment procedure), and T3212 (the timer used for periodic updating). If these parameters are set correctly, the SDCCH congestion can be relieved. In addition, if the assignment procedure is set to Late Assignment, the time of the SDCCH being occupied increases, which may lead to congestion.

4.4 Congestion Caused by Interference : 
Interference on the Um interface also causes congestion. For example, if the main BCCH in the serving cell and the TCH in the neighboring cell share the same TRX frequency and BTS BSIC, the handover access on this TCH may be mistaken as random access. As a result, the SDCCH is abnormally allocated and congestion occurs. The excessive receive sensibility can also make the interference signal mistaken as access signal, which leads to congestion.

5 Analysis Procedure of SDCCH Congestion Rate : 
SDCCH congestion rate is classified into BSC-level and cell-level according to the statistic object of the counter. The SDCCH congestion rate of a BSC is composed of the SDCCH congestion rate of a series of cells. Procedure of SDCCH congestion rate analysis is as shown below:



First, determine the level of the SDCCH congestion rate. If the congestion occurs in a large area, check the traffic volume and the setting of T3212. Then, calculate the SDCCH capacity to check whether it meets the system demand and whether the faults exist on system-level equipment or transmission. If congestion occurs in only a few cells, check the hardware, data configuration, and Um interface quality of the cell.

Below given is the analysis & optimization procedure for SDCCH Congestion Rate : 

1 Checking Channel Configuration : 
Query the traffic statistics to see whether the traffic volume on the SDCCH and TCH are higher than the normal value. If the congestion is caused by excessive traffic on the SDCCH, for multi-TRX BTSs, enable SDCCH dynamic allocation function or increase the number of SDCCH channels to relieve the congestion. For cells with only one TRX or without extra channels, enable the very early immediate assignment procedure. In the very early immediate assignment procedure, the TCH channel is immediately assigned when the SDCCH has no available resource during the processing of access request. In this case, a TCH can be used as only one SDCCH, which is a waste of the TCH resources.

All the services such as location updating, MS attach/detach, call setup, short messages are performed on the Schiff a certain service causes burst traffic, the SDCCH congestion may occur.
In this case, check whether the abnormity of Channel Requests, Successful Immediate Assignments or Successful SDCCH Seizures is caused by the service of location updating, MOC, paging, or short message. Note that you should check the history traffic statistics when querying these traffic counters to see whether they fluctuate during a certain period.

If the SDCCH congestion is caused by certain burst services such as location updating and short messages, use the following methods according to the specific configuration of the BTSs.

a. For the BTS with multiple TRXs, enable the SDCCH dynamic allocation function or increase the number of SDCCH channels.

b. For the cell with only one TRX or without extra channels, enable the immediate assignment procedure. In the immediate assignment procedure, the TCH is immediately assigned when the SDCCH has no available resource during the processing of access request.

c. Increase the number of TRXs.
It is difficult to avoid the SDCCH congestion caused by network burst services; however, you can take some relief measures such as increasing the number of SDCCHs or enabling the SDCCH dynamic conversion function.

UMTS Pilot channel failure ,high downlink interference

Symptoms
From the drive test, following symptoms will be observed by using TEMS:
• Received Ec/No of the pilot channel is less than –16dB and
• Received RSCP of the pilot channel is high enough to maintain the connection, e.g. > -100dBm and
• DL RSSI is very high and
• The connection finally drops.

Reason 1 – no dominant cell
There are many overlapping cells at the problem area. The received signal strengths of these pilots are almost the same.



Solution 
The most direct and effective way to solve this problem is to increase the pilot channel power Primary CPICH power of the desired cell.



The drawbacks of this solution are:
• Due to uneven pilot power setting, some UEs might no longer be connected to the “closest” cell with respect to the pathloss. Then they transmit with high UE powers. As a result, the uplink interference level of the carrier is consequently increased. It means uplink is not optimized and this phenomenon is called as uplink near-far problem. It is recommended that

–Reporting Range 1a: threshold for addition window/2 ≤ difference of the pilot power settings of two neighboring cells ≤ Reporting Range 1a: threshold for addition window/2

• In case the pilot power of a cell is increased, the required power for the downlink DPCHs in that cell also increase. Finally, the load of the cell becomes high and then cell blocking may happen.
• The downlink interference level of the carrier will be higher.
• The cell with higher pilot power will absorb more UEs from its adjacent cells. Then the load of the cell will be higher.
• Pilot power changes may lead to uplink coverage and pilot coverage imbalance problems.

Reason 2 – dominant interferer

An undesired cell with very high signal strength is found in the problem area.



Solution 1
The simplest solution to overcome this problem is to include the overshooting cell into the neighboring cell list. This means the interferer now becomes a useful radio link.
The drawbacks of the solution 1 are:
• It creates more unnecessary handovers and excessive numbers of UEs are in soft handover.
• If the overshooting cell is physically far way to the problem area, the handover sequence might be messed up after including it into the neighboring cell list.

Solution 2
An alternative solution is to change the antenna configuration of the overshooting cell, e.g. tilting down the antenna, re-directing the antenna orientation, reducing the antenna height.
With this solution, UL/DL coverage imbalance problem will not occur in the interferer because both UL/DL pathloss is modified simultaneously. Moreover, the interferer probably will cover fewer UEs, and transmit a lower total downlink power. This means that its downlink interference contribution might be further decreased.

The main drawback of the solution 2 is:
• Neighboring cells of the interferer will cover a larger area and will thus absorb additional UEs. The risk of high blocking rate therefore increases in these cells. Moreover, due to transmit high Tx power, they might become interferers if their coverages are not well confined.

Solution 3
The third possible solution is to decrease the pilot power Primary CPICH power of the overshooting cell.
The drawbacks of the solution 3 are:
• Reducing the pilot power, the downlink channel estimation in the UE is affected. This influences the downlink quality. In the end, the UE might request more power from base stations.
• When the pilot power is reduced, the maximum allowed DL DCH power decreases. Then, outage of the downlink DPCH will be higher if the pilot power is reduced too much.

Reason 3 – low best serving PPilot/PTot
The received Ec/No of the best serving pilot channel is very low (near or less than –16dB) even though there is no other cell. It means the pilot power setting is not large enough to fulfill existing downlink load.

Solution 1
The best solution is to add a new site with “good coverage control” at the problematic area.

Solution 2 
The direct but ineffective solution is to increase the pilot channel power Primary CPICH power of the problematic cell. With high pilot power, the common channel powers and the required power for the downlink DPCHs will be increased. At the end, the ratio of the PPilot/PTot does not increase much.

UE-Analysis-Clasification Tems Analysis

CONTENTS
1 INTRODUCTION
2 SCOPE
3 LONG CALL TEST
3.1 Radio Frequency
3.1.1 Missing neighbour relationship
3.1.2 Poor coverage
3.1.3 Bad Ec/No
3.2 Site/System problem
3.2.1 Unable to add/remove SC to/from the AS
3.2.2 ASU without MR
3.3 Not classified
3.3.1 Ec/No dropping very fast .
3.3.2 UE Tx Power down after RL removal

4 SHORT CALL TEST

4.1 Radio Frequency
4.1.1 Poor coverage
4.1.2 Bad Ec/No
4.2 Site/System problem
4.2.1 CM service reject
4.3 UE Problem
4.3.1 UE freeze
4.3.2 Call attempt to the worst cell
4.3.3 Only one RRC Connection Request.
4.3.4 Best SC removed from the AS
4.3.5 Motorola A835 incorrect sequence number
4.4 Not classified
4.4.1 L1 Synchronization problem
4.4.2 RRC Connection Request with no AICH
4.4.3 RRC Connection Release after Radio Bearer Reconfiguration Complete
4.4.4 Out of synchronization RL
4.5 Other

UE-Analysis-Clasification Tems Analysis -

Lte Frequency

E-UTRA frequency band (36.101)

Band	Name	Bandwidth (MHz)	Downlink (MHz)		Uplink (MHz)		Duplex spacing (MHz)	Equivalent UMTS band
			Low Earfcn	High Earfcn	Low Earfcn	High Earfcn
1	IMT 2.1 GHz	60	2110 0	2170 599	1920 18000	1980 18599	190	1
2	PCS 1900	60	1930 600	1990 1199	1850 18600	1910 19199	80	2
3	DCS 1800	75	1805 1200	1880 1949	1710 19200	1785 19949	95	3
4	AWS	45	2110 1950	2155 2399	1710 19950	1755 20399	400	4
5	850 MHz	25	869 2400	894 2649	824 20400	849 20649	45	5
6	UTRA only	10	875 2650	885 2749	830 20650	840 20749	45	6
7	2.6 GHz	70	2620 2750	2690 3449	2500 20750	2570 21449	120	7
8	900 MHz	35	925 3450	960 3799	880 21450	915 21799	45	8
9	1700 MHz	35	1844.9 3800	1879.9 4149	1749.9 21800	1784.9 22149	95	9
10	Extended AWS	60	2110 4150	2170 4749	1710 22150	1770 22749	400	10
11	1.5 GHz Lower	20	1475.9 4750	1495.9 4949	1427.9 22750	1447.9 22949	48	11
12	700 MHz Lower, A+B+C	17	729 5010	746 5179	699 23010	716 23179	30	12
13	700 MHz Upper	10	746 5180	756 5279	777 23180	787 23279	-31	13
14	Public Safety	10	758 5280	768 5379	788 23280	798 23379	-30	14
17	700 MHz Lower, B+C	12	734 5730	746 5849	704 23730	716 23849	30
18	Japan 800 MHz lower	15	860 5850	875 5999	815 23850	830 23999	45
19	Japan 800 MHz upper	15	875 6000	890 6149	830 24000	845 24149	45	19
20	800 MHz EDD	30	791 6150	821 6449	832 24150	862 24449	-41	20
21	1.5 GHz Upper	15	1495.9 6450	1510.9 6599	1447.9 24450	1462.9 24599	48	21
22	3.5 Ghz	80	3510 6600	3590 7399	3410 24600	3490 25399	100	22
23	2 GHz S-Band	20	2180 7500	2200 7699	2000 25500	2020 25699	180
24	L Band	34	1525 7700	1559 8039	1626.5 25700	1660.5 26039	-101.5
25	PCS 1900 + G Block	65	1930 8040	1995 8689	1850 26040	1915 26689	80	25
26	800 MHz iDEN	35	859 8690	894 9039	814 26690	849 27039	45	26
27	850 MHz lower	17	852 9040	869 9209	807 27040	824 27209	45
28	700 MHz APAC	45	758 9210	803 9659	703 27210	748 27659	55
33	TDD 2000	20	1900 36000	1920 36199			Tdd
34	TDD 2000	15	2010 36200	2025 36349			Tdd
35	TDD 1900	60	1850 36350	1910 36949			Tdd
36	TDD 1900	60	1930 36950	1990 37549			Tdd
37	TDD PCS	20	1910 37550	1930 37749			Tdd
38	TDD 2.6 GHz	50	2570 37750	2620 38249			Tdd
39	China TDD 1.9 GHz	40	1880 38250	1920 38649			Tdd
40	China TDD 2.3 GHz	100	2300 38650	2400 39649			Tdd
41	TDD 2.5 GHz	194	2496 39650	2690 41589			Tdd
42	TDD 3.4 GHz	200	3400 41590	3600 43589			Tdd
43	TDD 3.6 GHz	200	3600 43590	3800 45589			Tdd
44	700 MHz APAC	100	703 45590	803 46589			Tdd

U.S. FCC 700MHz band for commercial services

lte band

U.S. FCC broadband PCS band

PCS band plan

U.S. Advanced Wireless Services (AWS-1) band

AWS band plan

U.S. 2300 MHz Wireless Communications Services (WCS) band

LTE FDD spectrum

LTE FDD spectrum

LTE TDD spectrum

LTE TDD spectrum

cdma2000 bands

Band class (C.S0057-E)

CDMA2000 band class

Band	Name	Bandwidth (MHz)	Downlink (MHz)		Uplink (MHz)		Duplex spacing (MHz)
			Low	High	Low	High
0	800 MHz Cellular	34	860	894	815	849	45
1	PCS 1900	60	1930	1990	1850	1910	80
2	TACS	43	917	960	872	915	45
3	JTACS	38	832	870	887	925	-55
4	Korean PCS	30	1840	1870	1750	1780	90
5	450 MHz	73	420	493	410	483	10
6	2 GHz IMT-2000	60	2110	2170	1920	1980	190
7	700 MHz Upper	12	746	758	776	788	-30
8	1800 MHz	75	1805	1880	1710	1785	95
9	900 MHz	35	925	960	880	915	45
10	Secondary 800 MHz	89	851	940	806	901	45
11	400 MHz European PAMR	73	420	493	410	483	10
12	800 MHz PAMR	6	915	921	870	876	45
13	2.5 GHz IMT-2000 Extension	70	2620	2690	2500	2570	120
14	US PCS 1.9 GHz	65	1930	1995	1850	1925	80
15	AWS	45	2110	2155	1710	1755	400
16	US 2.5 GHz	66	2624	2690	2502	2568	122
18	700 MHz Public Safety	12	757	769	787	799	-30
19	700 MHz Lower	18	728	746	698	716	30
20	L-Band	34	1525	1559	1626.5	1660.5	-101.5
21	S-Band	20	2180	2200	2000	2020	180

CDMA2000 spectrum

cdma spectrum

CDMA channel numbers and corresponding frequencies

Band class 0 / 800 MHz Cellular

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A0	824.025	835.005	869.025	880.005	11
A0+	844.995	846.495	889.995	891.495	2
A1	824.025	835.005	869.025	880.005	11
A1+	844.995	848.985	889.995	893.985	4
A2	824.025	829.995	869.025	874.995	6
A3	815.025	829.995	860.025	874.995	15
B0	835.005	844.995	880.005	889.995	10
B0+	846.495	848.985	891.495	893.985	2
B1	835.005	844.995	880.005	889.995	10

Band class 1 / PCS 1900

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	1850	1865	1930	1945	15
D	1865	1870	1945	1950	5
B	1870	1885	1950	1965	15
E	1885	1890	1965	1970	5
F	1890	1895	1970	1975	5
C	1895	1910	1975	1990	15

Band class 2 / TACS

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	872.0125	879.9875	917.0125	924.9875	8
A+	890.0125	897.4875	935.0125	942.4875	7
A++	905.0125	908.9875	950.0125	953.9875	4
B	880.0125	887.9875	925.0125	932.9875	8
B+	897.5125	904.9875	942.5125	949.9875	7
B++	909.0125	914.9875	954.0125	959.9875	6
ATG	894	895.5	849	850.5	2

Band class 3 / JTACS

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	887.0125	888.9875	832.0125	833.9875	2
A+	893.0125	898	838.0125	843	5
A++	898.0125	900.9875	843.0125	845.9875	3
A+++	915.0125	924.9875	860.0125	869.9875	10

Band class 4 / Korean PCS

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	1750	1760	1840	1850	10
B	1760	1770	1850	1860	10
C	1770	1780	1860	1870	10

Band class 5 / 450 MHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	452.5	457.475	462.5	467.475	5
B	452	456.475	462	466.475	4
C	450	454.8	460	464.8	5
D	411.675	415.85	421.675	425.85	4
E	415.5	419.975	425.5	429.975	4
F	479	483.48	489	493.48	4
G	455.23	459.99	465.23	469.99	5
H	451.31	455.73	461.31	465.73	4
I	451.325	455.725	461.325	465.725	4
J	455.25	459.975	465.25	469.975	5
K	479	483.475	489	493.475	4
L	410	414.975	420	424.975	5
M	450	457.475	461.25	469.975	7 / 9
N	450	457.475	460	469.975	7 / 10

Band class 6 / 2 GHz IMT-2000

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
Low, not valid	1920	1922.45	2110	2112.45	2
SR1	1922.5	1977.5	2112.5	2167.5	55
High, not valid	1977.55	1979.95	2167.55	2169.95	2

Band class 7 / 700 MHz Upper

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
C	776	787	746	757	11
A	787	788	757	758	1

Band class 8 / 1800 MHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
Low, not valid	1710	1711.2	1805	1806.2	1
SR1	1711.25	1783.75	1806.25	1878.75	73
High, not valid	1783.8	1784.95	1878.8	1879.95	1

Band class 9 / 900 MHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
Low, not valid	880	881.2	925	926.2	1
SR1	881.25	913.75	926.25	958.75	33
High, not valid	913.8	914.95	958.8	959.95	1

Band class 10 / Secondary 800 MHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	806	810.975	851	855.975	5
B	811	815.975	856	860.975	5
C	816	820.975	861	865.975	5
D	821	823.975	866	868.975	3
E	896	900.975	935	939.975	5

Band class 11 / 400 MHz European PAMR

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	452.5	457.475	462.5	467.475	5
B	452	456.475	462	466.475	4
C	450	454.8	460	464.8	5
D	411.675	415.85	421.675	425.85	4
E	415.5	419.975	425.5	429.975	4
I	451.325	455.725	461.325	465.725	4
J	455.25	459.975	465.25	469.975	5
K	479	483.475	489	493.475	4
L	410	414.975	420	424.975	5

Band class 12 / 800 MHz PAMR

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A,C	870.0125	875.9875	915.0125	920.9875	6
B	871.5125	874.4875	916.5125	919.4875	3

Band class 13 / 2.5 GHz IMT-2000 Extension

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	2500	2505	2620	2625	5
B	2505	2510	2625	2630	5
C	2510	2515	2630	2635	5
D	2515	2520	2635	2640	5
E	2520	2525	2640	2645	5
F	2525	2530	2645	2650	5
G	2530	2535	2650	2655	5
H	2535	2540	2655	2660	5
I	2540	2545	2660	2665	5
J	2545	2550	2665	2670	5
K	2550	2555	2670	2675	5
L	2555	2560	2675	2680	5
M	2560	2565	2680	2685	5
N	2565	2570	2685	2690	5

Band class 14 / US PCS 1.9 GHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	1850	1865	1930	1945	15
D	1865	1870	1945	1950	5
B	1870	1885	1950	1965	15
E	1885	1890	1965	1970	5
F	1890	1895	1970	1975	5
C	1895	1910	1975	1990	15
G	1910	1915	1990	1995	5

Band class 15 / AWS

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	1710	1720	2110	2120	10
B	1720	1730	2120	2130	10
C	1730	1735	2130	2135	5
D	1735	1740	2135	2140	5
E	1740	1745	2140	2145	5
F	1745	1755	2145	2155	10

Band class 16 / US 2.5 GHz

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	2502	2518.5	2624	2640.5	17
B	2518.5	2535	2640.5	2657	17
C	2535	2551.5	2657	2673.5	17
D	2551.5	2568	2673.5	2690	17

Band class 18 / 700 MHz Public Safety

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	787	788	757	758	1
D	788	793	758	763	5
Public Safety Broadband	793	798	763	768	5
Public Safety Guard band	798	799	768	769	1

Band class 19 / 700 MHz Lower

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	698	704	728	734	6
B	704	710	734	740	6
C	710	716	740	746	6

Band class 20 / L-Band

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
Low, not valid	1626.5	1627.1	1525	1525.6	1
SR1	1627.15	1659.85	1525.65	1558.35	33
High, not valid	1659.9	1660.5	1558.4	1559	1

Band class 21 / S-Band

Block	Transmit frequency band (MHz)				Top
	Mobile Station		Base Station		Bandwidth UL / DL
A	2000	2010	2190	2200	10
B	2010	2020	2180	2190	10