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1x3 Frequency Reuse Technology (V1.0) Public Use
Documentation Center of Radio
Planning and Design Section,
Huawei Technologies
Document No. Product version Confidentiality level
Product name: M900/M1800 24 pages in total
1X3 Frequency Reuse Technology
Guideline
(Public Use)
Drafted by: Topic Research Study Group
Date: 2002-10-22
Reviewed by: Date: yyyy/mm/ddReviewed by: Date: yyyy/mm/ddApproved by: Date: yyyy/mm/dd
Huawei Technologies
All Rights Reserved
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1x3 Frequency Reuse Technology (V1.0) Public Use
Table of Contents
1 General........................................................................................................................................4
1.1 Application background.....................................................................................................4
1.2 Basic concepts..................................................................................................................4
1.3 The advantages and disadvantages of 1*3......................................................................5
1.3.1 Advantages.............................................................................................................5
1.3.2 Disadvantages........................................................................................................6
2 1*3 tight reuse technology...........................................................................................................6
2.1 Layout of sites...................................................................................................................6
2.2 1*3 improve the capacity of network.................................................................................7
2.3 1*3 tight reuse pattern.......................................................................................................8
2.3.1 The basic concepts of frequency hopping..............................................................9
2.3.2 Continuous allocation mode...................................................................................9
2.3.3 Interval allocation mode........................................................................................10
2.3.4 The comparison of two allocation modes.............................................................10
2.4 1*3 probability of ad-frequency collision.........................................................................12
2.4.1 Distribution of ideal meshes.................................................................................12
2.4.2 Irregular network...................................................................................................14
2.5 1*3 reuse technique impact on network quality..............................................................15
2.5.1 Frequency hopping influence on speech quality..................................................15
2.5.2 Impact on 1*3 network performance caused by C/I.............................................16
2.5.3 Impact on 1*3 caused by layout of sites...............................................................17
2.5.4 Impact on 1*3 network performance caused by engineering parameters............17
2.5.5 Impact on 1*3 network capacity cause by handover............................................21
2.5.6 Impact on 1*3 network cause by load handover..................................................23
3 1*3 frequency-hopping data configuration................................................................................24
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1X3 Frequency Reuse Technology Guideline
Key words: Frequency planning, 1*3, 4*3, tight reuse, base transceiver station layout,
ideal mesh, capacity
Abstract: This document combines radio network layout and application experience of
1*3 reuse. It is a guideline to introduce the principles and measures of 1*3 tight
reuse frequency planning.
Reference List
Name Author Code Released
date
Where and
how to
access
Publisher
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1 General
Due to the shortage of frequency resource, in recent years equipment manufactories and
operators have been focusing on improving the efficiency of frequency utilization in GSM
system, and they try to improve network capability in limited frequency resource.
1.1 Application background
At the beginning of GSM network construction with small capacity, 4*3 reuse pattern or
more loose frequency reuse technology are employed. With the increasing of network
capacity, new tight reuse technologies appear, such as 3*3, MRP, 1*3, and 1*1.
It is hard to decide when to use 1*3 tight reuse in actual network planning, because
different operators have much different frequency resource. The maximal site
configurations under different frequency bandwidth and reuse patterns are listed as follows:
Table1 Frequency bandwidth --tight reuse technology--the maximal configuration
Bandwidth 4*3 MRP 1*3
6 MHz S3/2/2 - S4/4/3
7 MHz S3/3/2 S4/4/4 S5/4/4
8 MHz S4/3/3 S5/5/5 S6/5/5
10MHz S4/4/4 S6/6/6 S8/8/8
Notes:
1. Configurations listed above are theoretic values
2. Because the amount of carriers participated in frequency hopping is equal to frequencies
used under the MRP reuse pattern, so for small configuration site, frequency hopping
obtains small gains. Hereby, MRP is not suitable. 1*3 must adopt radio frequency hopping.
The essence of tight reuse technology is bartering capability with quality. The tighter the
frequency reuse is, the worse network quality will be. Therefore, it is better to adopt loose
reuse frequency.
BCCH carrier frequency must adopt 4*3 pattern in an actual frequency planning, BCCH
needs at least 12 frequencies (because of the importance of BCCH, 14 frequencies are
given to BCCH. So real maximal configuration is less than the value in the above table. For
example, if 6MHz bandwidth adopts 1*3, theoretical maximal configuration can only reach
S4/3/3).
1.2 Basic concepts
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In frequency planning, Frequency Reuse Factor is often used to scale frequency utilization
efficiency or tightness degree of frequency reuse. Frequency Reuse Factor is defined as
below:
K NW/NTRx
K is Frequency Reuse Factor; NW is the number of available frequencies; NTRX is the maximal
amount of carriers in a cell.
When 15 frequencies are used for the carriers participating in frequency hopping and the
number of FH carriers in the cell is 2, Frequency Reuse Factor K = 7.5. When the number
of FH carriers is 3, K = 5.
Figure 1 The overlapped depth of coverage is different in cells
Figure 1 The coverage overlap
Because the different overlapped depth of A and B network, the number of A’s adjacent
cells is less than B’s, so the interference of B is bigger than A’s.
Conclusion: The more adjacent cells are, the bigger the probability of co-frequencies
collision is, and the lower the utilization efficiency is. Therefore, the amount of adjacent cell
should be decreased whichever frequency reuse technology is used.
1.3 The advantages and disadvantages of 1*3
1.3.1 Advantages
1. The 1*3 reuse pattern is tighter than 3*3 and MRP , so capability proportion that can be
improved is higher than the latter.
2. The frequency planning is simple. Only BCCH frequency planning is necessary. During
network optimazation and carrieres expansion, frequency planning needn’t be made again.
3. The technology can improve planning efficiency greatly.
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4. Radio frequency hopping is adopted, frequency hopping gain is higher than baseband
frequency hopping(baseband frequency hopping can’t be used for 1*3 reuse pattern).
1.3.2 Disadvantages
1. Broadband combiner is needed and cavity combiner with the property of frequencies
selection can’t be used on 1*3.
2. Broadband repeater is adopted, because 1*3 has much influence on frequency-selected
repeater.
3. As the reuse distance decreases, interference of ad-frequency and co-frequency will
increase rapidly.
4. Network needs delicate optimizing adjustment. Especially, The overlap of coverage
should be restricted strictly.
It is worthy to point out that most sites configuration can only be S2/2/2 and few of them
can be S3/2/2 while we adopt general 4*3 tight reuse technology and 6MHz band is
available. Otherwise the network performance will be out of control. When 1*3 close reuse
technology is used, the maximal configuration is S4/3/3(but it is a theoretical value, the
actual configuration is S3/3/3 generally). Moreover, the capacity is twice of 3*4 reuse
technology, which can save the invests of operators greatly (the expense of tower,
equipment room, power supply, transmission and other assistant equipment will be higher
than the BTS equipment).
2 1*3 tight reuse technology
As some anti-interference technologies can’t be employed on BCCH carrier, such as
frequency hopping, power control and DTX. Therefore BCCH frequency can only use 4*3
reuse pattern.1*3 tight reuse technology is general used on no-BCCH carriers. How to
make a 1*3 frequency planning is illustrated by an actual planning within 6MHz band.
2.1 Layout of sites
Sites layout is an important work in the prophase of network planning. Whichever frequency
planning technology is used, reasonable distribution of the sites is always concerned, which
is based on the requests of coverage, capacity, network quality and construction invests. In
the premise of meeting coverage and capacity, the urban sites should be distributed in the
ideal meshes in order to absorb the traffic as possible. However due to the constraint of
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landform and tenancy, the actual sites can’t be put on ideal meshes and they are always
distributed irregularly. Comparatively, 4*3, 3*3 and MRP have a more tolerance on irregular
layout of sites, while for 1*3, layout of sites should be as regular as possible. Therefore, we
should decide the technology of Frequency planning according to usable frequency
resource, maximal site configuration which could meet the requisition of capability
nowadays and in the future.
What is ideal mesh? The relative position of ideal meshes must meet some mathematics
relation, the relation of the equilateral triangle.
Figure 2 The allocation of ideal stations
The experience proves that the quality of network and utilization efficiency of frequency will
be best when the sites are based on ideal meshes. In other words, more users will be
contained.
2.2 1*3 improve the capacity of network
1*3 tight reuse technology can improve the capacity greatly. Using general frequency reuse
technology, the maximal configuration is S3/2/2 when bandwidth is 6MHz. Nevertheless,
using 1*3 tight reuse technology the maximal configuration is S4/3/3 with the same
bandwidth. The relation of configuration and capacity is listed below:(6MHz bandwidth,
GOS=2%, 0.02 Earl /user)
Table 2 The capacity increasing
Reuse Configuration Cell 1 Cell 2 Cell 3 Site capacity The amount
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patterncapacity
(Erl)capacity
(Erl)capacity
(Erl)(Erl)
of subscribers
4*3 S2/2/2 8.20 8.20 8.20 24.60 1230
1*3 S3/3/3 14.03 14.03 14.03 42.09 2104
S4/3/3 21.00 14.03 14.03 49.06 2453
Notes:The capacity is theoretical values, in actual planning 70~80 percents of theoretical
capacity above is available.
Diagram3: The capability increase
Figure 3 The capacity increasement
Figure 3 The capacity increasing
The capability will increase 99 percents after using 1*3 tight reuse technology under the
condition the quality of network could be accepted.
2.3 1*3 tight reuse pattern
When using 1x3 frequency reuse pattern, three cells of every site will constitute a cluster.
Reuse pattern of frequency will work in every cluster. In other words, the same cell of
different sites will use the same frequency set. It will be shown in the figure below.
Figure 4 1*3 tight reuse pattern
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While adopting 1*3 tight reuse technology, we must use Radio Frequency Hopping. There
are two kinds of allocation mode of MA: continuous allocation mode and interval allocation
mode. Principles of frequency hopping are expressed as follows:
MAI f(MAIO,FN,MA,HSN,N)
f(FN,HSN,N) f(MA,MAIO)
where MAI is mobile allocation index; N is the amount of frequency in MA; FN is frame
number.
When FN, HSN, N of the three cells in the same site are all the same, MAI is only related to
MA and MAIO. It shows that ad-frequencies collision intra-site can be controlled by
planning MA and MAIO carefully. It also shows that ad-frequencies collision inter-site will be
controlled when the amount of the frequencies in MA of the three cells is the same.
NOTICE: It is different from the FH descriptions in GSM Protocol that the cells of intra-site
share the same HSN. The reason is to avoid inter-cell ad-frequencies collision in the site.
It is determined by BTS equipment that FN of different cells in the same site is the same.
When the number of sites with frequency hopping is more than 63, those sites that are far
apart between them can reuse HSN.
2.3.1 The basic concepts of frequency hopping
MA: Mobile Allocation, (in other words, the set of frequency hopping) is referred to the
hopping frequencies in a cell. MA of max 64 frequencies is supported in HUAWEI BSC.
HSN: Hopping Sequence Number, value range: 0~63. When HSN=0, it is circular frequency
hopping; when HSN=1~63, it is pseudo-random frequency hopping.
MAIO: Mobile Allocation Index Offset, value range is 0~(N-1), N is the number of carriers
participating in frequency hopping.
FN: Frame Number, range: 0~(51*26*2048-1). It is decided by BTS.
2.3.2 Continuous allocation mode
The MA and MAIO planning under continuous allocation mode are listed below:
Table 3 Continuous allocation mode
MA0 MA1 MA2 MA3 MA4 MAIO
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CELL 1 96 97 98 99 100 0, 2
CELL 2 101 102 103 104 105 0, 2
CELL 3 106 107 108 109 110 0, 2
In continuous allocation mode, the maximal configuration is S3/3/3 (BCCH carrier without
frequency hopping + 2 TCH carriers with frequency hopping). For bigger site configuration,
the ad-frequencies collision in a cell is unavoidable.
2.3.3 Interval allocation mode
Under interval allocation mode, planning of MA and MAIO is listed below:
Table 4 Frequency hopping aggregation in interval allocation
MA0 MA1 MA2 MA3 MA4 MAIO
CELL 1 96 99 102 105 108 0, 2, 4
CELL 2 97 100 103 106 109 1, 3
CELL 3 98 101 104 107 110 0, 2
In interval allocation, the maximal site configuration is S4/3/3, .For bigger site configuration,
the ad-frequencies collision in a cell is unavoidable.
2.3.4 The comparison of two allocation modes
For those two frequency allocation modes, BCCH carriers of all cells must take 4*3 reuse
pattern. It is proved that BCCH frequencies should be more than 14. TCH carriers with 1*3
tight reuse must adopt radio frequency hopping. If the site configuration is less than S3/3/3,
both of the two allocation modes could avoid ad-frequency collision in the same site.
Comparison of two allocation modes:
1. MAIO is different between interval allocation and continuous allocation.
2. MA is different between interval allocation and continuous allocation.
3. Whether interval or continuous allocation mode is adopted, the ad-frequency collision
could be avoided among the three cells in the same site by reasonable planning. The
difference is:
1) Probability of co-frequency collision in cells with the same number in adjacent
BTS is same. There is still ad-frequency collision in continuous allocation mode, but
there is no ad-frequency collision in interval allocation mode.
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2) In interval allocation, ad-frequency collision will happen among different cells of
adjacent BTS. In continuous allocation, ad-frequency collision will happen among
frequencies which locate on two ends of hopping frequencies set (for example, in this
example, 100 in Cell 1,101 and 105 in Cell 2,106 in Cell 3), but collision won’t happen
in other frequency
4. Some testing of existing network proves: in 1*3 tight reuse pattern, continuous allocation
mode is better than interval allocation mode (idle BURST testing). But the final conclusion
needs more testing. Till now interval and continuous allocation modes both work normally
online.
5. When bandwidth is 6MHz, the maximal BTS configuration that continuous allocation
mode supports is S3/3/3(theoretical value) and that supported by interval allocation mode is
S4/3/3.
Figure 5 1*3 Instance of two allocation mode
Notice: In the above allocation, BCCH frequency 111 should be used as less as possible.
Especially, it can’t use in the third cell (the cell contained 110 in MA).
When continuous and interval allocation mode are used in one actual network (idle BURST
send testing), there is no difference in coverage. On the other hand, continuous allocation
mode is better than interval allocation mode in receiving quality and their difference is listed
below:
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Figure 6 1*3 quality difference of two allocation mode
Figure 6 The receiving quality of two allocation modes
2.4 1*3 probability of ad-frequency collision
After using 1*3 tight reuse technology, the probability of co-frequency and ad-frequency
collisions will be increased greatly. The collision probability and impact on network
performance are related to the amount of adjacent cells.
2.4.1 Distribution of ideal meshes
The most perfect assumption: engineering parameters of sites are completely consistent.
Propagation environment is identical too. Sites locate on ideal meshes. Load ratio of each
cell is less than 40 percent. The number of the carriers participating in FH in a cell is 1 or 2,
and the number of the frequencies participating in FH is 5.
Cell Load Ratio is defined below:
Cell Load Ratio = The number of carries participating in FH/ The number of frequencies
participating in FH
Figure 7 1*3 tight reuse technology
In this figure, there are no co-frequency collisions in cell A-3, but there are ad-frequency
collision in A-3 with B-1, D-1, D-2 and C-2. In the figure, the number of ad-frequency
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collision cells is listed below:
Table 5 The number of cells which there are ad-frequency collisions with A-2
Interference area X X1 X2 X3 X4
Interference cells number 2 2 1 2 1
Because it have been assumed that engineering parameters and propagation environment
are all the same, the receiving levels of A-3 and adjacent cells are same at the receiving
points. Because the interference at X, X1 and X3 is maximal, only calculating the probability
at X is enough (The frequencies number in MA is 5):
1. When there is one carrier participating in FH in A-3, D-1, and D-2, the maximal
probability of ad-frequency collision is:
P 15 1
5 15 1
5 225 8%
2. When there are 2 carriers participating in FH in A-3, D-1, and D-2, the maximal
probability of ad-frequency collision is :
P 25 2
5 25 2
5 825 32%
3. When there are 2 carriers participating in FH in A-3, D-1, and D-2, the maximal
probability of ad-frequency collision is :
P 35 3
5 35 3
5 1825 72%
Notes: when three carriers participate in FH and the frequency number in MA is 5,
continuous allocation mode can't avoid ad-frequency collision intra-cell. But interval
allocation mode can avoid ad-frequency collision intra-cell. When the site configuration is
lower than S4/3/3, interval allocation mode can avoid ad-frequency collision between
adjacent cells of the site. When the configuration is higher than S4/3/3, interval allocation
can’t avoid ad-frequency collision between adjacent cells of a site.
The calculation proves that when MA is fixed, probability of ad-frequency collision has
direct ratio with square of carriers participating in FH. In other words, ad-frequency
interference will increase rapidly with increasing of network capability.
It needs to be pointed out that the calculation above is done when network runs under full
load. Actually the network load is lower than the full. One connection in A-3 cell will cause
ad-frequency interference to connections, which locate on the same timeslots in D-1 and D-
2, and there is no ad-frequency interference to the other timeslots. Therefore, ad-frequency
collision of actual network is related to the number of connections.
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2.4.2 Irregular network
The analysis listed above is based on ideal regular network, but the adjacent-cells of one
service cell are very complicated because of the difference of network structure and
propagation environment. When overlap of coverage can’t be controlled well, the adjacent
cells with ad-frequency and co-frequency collision will appear.
Assumption:
1) One cell has j adjacent cells in some interfered area and the receiving signal strength of
different adjacent cells is same.
2) The cell has j-2 adjacent-cells of other BTS, including k adjacent cells have the same
number with the current cell.
3) The number of frequencies participating in FH is N.
1. When there is one carrier participating in FH,
The probability of co-frequency collision:
P 1n 1
n k k/n2
The probability of ad-frequency collision:
P1n 1
n j 2 k j 2 k/n2
2. When there are two carriers participating in FH,
The probability of co-frequency collision:
P 4k/n2
The probability of ad-frequency collision:
P 4j 2 k/n2
3, when there are m carriers taking part in frequency hopping
The probability of co-frequency collision:
P m2k/n2
The probability of ad-frequency collision:
P m2j 2 k/n2
The probability of collision is related to connections in network.
The key points to garanntee network performance:
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1. The layout of the sites locations should be distributed along the regular meshe, and
antennas height should be almost same during the planning and design period.
2. In optimizing period the coverage should be controlled right to aviod the co-frequnecy
adjacent cells with the same number. According to calculation listed above, C/Ia should be
0 in X area, but the actual C/I is much lower than this value because of the coverage
overlap, the fast fading and handover threshold. Therefore, the key works during
optimization are to reduce the depth of overlap coverage and improve the handover
sensitivity.
2.5 1*3 reuse technique impact on network quality
2.5.1 Frequency hopping influence on speech quality
According to subject evaluation of speech quality, FH has much impact on Rx Qual of MS.
Testing result and subject evaluation is listed below:
Table 6 Rx Qual difference between FH and without FH
Rx_Qual
0 1 2 3 4 5 6 7
Subject
evaluation
Without FH A A B B C D D E
FH A A A B B C D E
Table 7 Subject evaluation grade
Subject evaluation grade Evaluation criterion
A Very clear, no noise
B clear, a little noise
C Understood, noise
D Understood after repeating
E Can’t be understood
Testing result proves: Receiving quality and subject speech quality in FH is different from
that in without FH. When FH is not used, Rx_Qual is 0 or 1, subject speech quality is A;
Rx_Qual is below 3, subject speech quality is clear. When FH is used, Rx_Qual is 0,1 and
2, subject speech quality is A; Rx_Qual is below 4, subject speech quality is clear; Rx_Qual
is above 6, there are no difference between FH and without FH.
Subject evaluation and quality grade between FH and without FH is showed below:
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Figure 8 The difference of Subject evaluation and quality grade
Figure 8 Subject evaluation and Rx_Qulity
2.5.2 Impact on 1*3 network performance caused by C/I
The drive test data of idle BURST sending (at this time interference cell send out data
continuously without power control) is analyzed in detail.
The relation of C/I and receiving quality grade from the driver testing data is
shown as follows:
Table 8 C/I and Rx_Qual
Rx_Qual 7 6 5 4
C/I (dB) 1 2 3 10
When C/I of 1*3 network is greater than 10dB, the subject speech quality can reach B
(clear, a little noise). When C/ I is between 3~10dB, subject speech quality is C
(understood, noise). When C/I is less than 3dB, network performance will deteriorate
rapidly.
Testing data proves that interference source in which quality grade is lower than 3 is
caused by ad-frequency collision between different-numbered cells of adjacent sites.
2.5.3 Impact on 1*3 caused by layout of sites
When 1*3 tight reuse is employed in an actual network, the test result shows the conclusion
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that the network performance of regular sites distribution is better than that of irregular sites
distribution.
Figure 9 The comparison of receiving quality ratio between regular cells and irregular cells
The data above is originated from an actual running network, and the conclusion can be
made that the distribution of the sites is very important for 1*3 network.
2.5.4 Impact on 1*3 network performance caused by engineering parameters
Engineering parameters include site location, layout, antenna height, azimuth angle,
downtilt and so on. Once site location and layout are decided and put in practice, they are
difficult to change. Therefore site should locate on the ideal meshes as possible. And the
azimuth angle and downtilt of antennas should be selected properly. When antenna is too
high, the height should be decreased to avoid interference.
The traffic statistic indexes will be compared between the 4*3 network, 1*3 network without
engineering parameters optimization and 1*3 network with engineering parameters
optimization. The comparison is listed as follows:
Table 9 The comparison of traffic statistics indexes
SDCCH call
drop rate
SDCCH
congestion rate
TCH call
drop rate
TCH congestion
rate
Traffic
(Erl)
Handover
success rate
4*3 0.25% 0% 0.92% 1.22% 166.79 93.02%
1*3 without 0.3% 0.3% 0.79% 1.19% 172.93 92.33%
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optimization
1*3 with
optimization0.22% 0.01% 0.66% 1.13% 178.87 93.45%
According to data above, after 4*3 reuse network is changed to 1*3 and before
optimization, SDCCH congestion rate deteriorate greatly, handover success rate drop,
SDCCH call drop rate and TCH congestion rate change little and traffic increase a little.
After optimization 1*3 network, each index is improved. Compared with index before
optimization, five key indexes (SDCCH congestion rate, SCCH call drop rate, TCH call drop
rate, TCH congestion rate and handover success rate) have exceeded or reached indexes
before optimization.
Figure 10 The traffic statistics indexes contrast
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Figure 11 The traffic statistics indexes contrast
Table 10 Other traffic statistics indexes contrast
Traffic Interf.B
and 3
Interf.
Band 4
Interf.
Band 5
HO
Requests of
BQ
HO
Requests
Call set
up
Average HO
times per
connection
4*3 166.79 2.41 0.15 0.16 859 9985 10362 0.96
1*3 before
optimization172.93 2.40 0.28 1.56 2433 12716 11190 1.14
1*3 after
optimization178.87 4.00 0.40 0.11 1832 11895 11935 0.99
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Figure 12 Other traffic statistics indexes contrast
The number of idle channels falling into interference band 5 is much lower than that of
before 1*3 optimization.
Figure 13 Other traffic statistics indexes contrast
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Figure 14 Other traffic statistics indexes contrast
Comparing 1*3 FH network before optimization with 4*3 no FH network, handover times
increased by about 2700 times and total Bad Quality handovers increased by about 1600
times. Comparing 1*3 FH network after optimization with 4*3 no FH network, handover
times increased by about 1900 times and Bad Quality handovers increased by about 1000
times. Compare increase of Call set up times with increase of traffic, the conclusion can be
made that traffic increasing is natural. The increase of handover times makes little
contribution on traffic increasing, and it will be explained in next section.
The increasing proportion of total bad quality handovers is much higher than that of traffic.
On one hand, it is due to the closer reuse frequency and the irregularity of real
experimental network causes interference in some area; on the other hand, interference
handover threshold (50) in 4*3 reuse is equal to 1*3 tight reuse threshold. The subject
speech quality of frequency hopping whose Rx_Qual is equal to 5 is as good as that of no
frequency hopping network whose Rx_Qual is equal to 4(explained in 2.5.1 impact on
network quality caused by frequency hopping). The difference of subject voice-quality
standard is the main cause of the increase of bad quality handovers.
2.5.5 Impact on 1*3 network capacity cause by handover
When MS handover from a cell to another cell in the same BSC, TCH channel of the old
cell won't be released after the target cell TCH channel is activated, until BSC receives HO
Complete message from the new cell. During Channel Activation and RF Chan Release
Ack, TCHs of the old and new cell are occupied by the same connection. In this period,
traffic statistics will repeat to count TCH seizure time. The contribution on traffic caused by
handover will be analyzed.
In order to prove whether handover will increase traffic, The test of synchronous and
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asynchronous handover have been made on GSM1800 network that haven’t been in use
commercially. Signaling time from the new cell's CHANNEL ACTIVATION (caused by
handover) to the old cell's RF CHAN RELEASE ACK is gotten by testing. Synchronous
handover counts 20 times and asynchronous handover counts 11 times. The result is listed
below:
Table 11 The time of two channels are occupied by one connection during HO (1800M)
Average time(ms) Shortest time(ms) Longest time(ms)
Synchronous
handover348 339 420
Asynchronous
handover408 398 450
The test of handover period is done in GSM900 network with large traffic, and handover
times are 18.
Table 12 The time of two channels are occupied by one connection during HO (900M)
Average time(ms) Shortest time (ms) Longest
time(ms)
Handover
time
745 584 1675
Testing of traffic statistics is done in laboratory. Statistic period is 15 minutes and MS
handover between cell A to cell B. During testing period, there are no other subscribers
using the two cells and another MS seizures cell C all the time as the terminated. Testing
results are listed below:
Table 13 Lab tests
Statistic time(min) Handover times Statistic traffic(Erl)
Cell A 15 9 0.1400
Cell B 15 9 0.1125
Add up 15 18 0.2525
Cell C 15 0 0.2500
Only one subscriber occupied the channel in cell A or B during 15 minutes testing period, If
no handover occurs, the traffic should be same between them. But the total traffic of Cell A
and B is 0.2525Erl, and the traffic of cell C is 0.25Erl. The excessive 0.0025Erl traffic is due
to handover, and the average crossed-time every handover is 0.5 seconds. Notice:
because the shortest interval of traffic statistics is 480 ms, handover crossed-time
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calculated by traffic statistics has a certain error.
Comparing network with large traffic and low traffic, handover crossed time increases
greatly while traffic become high. It is assumed average handover crossed-time is 0.78s,
and the increasing traffic is 2Erl every 10000 handover (0.75*10000/3600).
Comparing the handover increase of 1*3 network before optimization with that after
optimization, suppositional added traffic is about 0.4Erl caused by 2000 handovers. So
12Erl traffic increasing is natural.
Conclusion: Suppositional added traffic is about 2Erl when 10000 handovers are made.
Impact on traffic caused by suppositional added traffic should be considered when
handover times are extremely high. On the other hand, data above proves that handover
speed is related to traffic (the more traffic, the longer handover time).
2.5.6 Impact on 1*3 network cause by load handover
Table 14 Traffic statistics indexes contrast between enable and disable load handover
Load
handoverDate
Traffic
Erl
TCH call
drop rate %
TCH
Congestion rate %
Handover
success rate %
Handover
failure rate
Enable
16 th, 1 182.98 1.01 0.8 95.59 567
17 th, 1 166.39 0.89 0.44 96.29 412
18 th, 1 171.9 0.93 0.45 96.13 427
Disable
23 rd, 1 180.35 0.54 0.4 96.09 467
24 th, 1 181.8 0.55 0.28 / /
25 th, 1 174.47 0.43 0.49 96.71 385
Comparing traffic statistics indexes between enabling and disabling load handover, TCH
congestion rate is not high, but it hasn’t been lowered greatly after enabling load handover
and call drop rate increases distinctly.
Conclusion: Load handover can’t be employed in 1*3 network. For example the bandwidth
of load handover is 25dB and the connections meet the load HO conditions, they will
handover to second best cell and seize FH channels with serious interference, and call
drop rate will increase distinctly. In order to ensure that MS camp in cells with strongest
signal, cell selection and reselection parameters should be consistent with each other in
1*3 network.
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3 1*3 frequency-hopping data configuration
1*3 configuration data related to frequency hopping is same with other frequency hopping.
Table is shown as bellows:
Table 15 1*3 data configuration related to frequency hopping
Menu name Table name Parameter Value Annotation
Local office
Radio Channel
Configuration
Table
FH index No. 0~1023
Index to frequency- hopping data
table. And the value of the FH TRX
carriers in a cell should be same.
MAIO0~N-1
Mobile Allocation Index Offset. In
this case, the same MAIO is
recommended for all channels of a
TRX and different MAIO for
different TRX in the same cell.
Frequency
Hopping Data
Table
FH index No. 0~1023Correspond to item in Radio
channel configuration table
HSN1~63
Hopping Sequence Number. HSN
in different cells of the same site is
the same
TSC0~7
Training Serial Code, Same with
BCC.
ARFCN 1~
ARFCN N
Available
frequency
Frequencies in MA participating in
FH
Site
Carrier
Configuration
Table
ARFCN 1~
ARFCN N
Available
frequency
BCCH frequency and frequencies
in MA participating in FH
Static TRX
Power class
0~10,
unit:2dB
Power class "0" shows that power
is in its maximum. Each class is
2dB less than its former class.
Cell Cell
Configuration
Data Table
FH mode Radio
frequency
hopping
FH mode should be RF FH for 1*3
frequency reuse pattern
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Cell Allocation
Table
ARFCN 1~
ARFCN N
Available
frequency
BCCH frequency and frequencies
in MA participating in FH
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