OMF007001 Frequency Planning ISSUE1.4.pdf

8/14/2019 OMF007001 Frequency Planning ISSUE1.4.pdf

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OMF 007001

Frequency Planning

ISSUE1.4

OMF 007001

Frequency Planning

ISSUE1.4

Wireless Training Department


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contentcontent

Frequency planning

Tight frequency reuse

Frequency hopping


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Content of Frequency planningContent of Frequency planning

!Frequency resource of GSM system

!Requirement for interference and carrier-to-

interference ratio

!Signal quality grade coding

!Concept of frequency reuse

!4*3 frequency reuse


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GSM 900 :

GSM 1800 : 1710 1785 1805 1880

Duplex distance : 95 MHz

890 915 935 960

Duplex distance : 45 MHz

Frequency Resource of GSM SystemFrequency Resource of GSM System

GSM consists of GSM900 and GSM1800 according to different system frequency

bands. GSM is a duplex system. According to the GSM protocol, the uplink

frequency band (MS to BTS) of GSM 900 is 890MHz-915MHz, and the downlink

frequency band (BTS to MS) is 935MHz-960MHz, the duplex distance is 45MHz;

the uplink frequency band of GSM1800 is 1710MHz-1785MHz, while the downlink

frequency band is 1805MHz-1880MHz, the duplex spacing is 95 MHz. In different

countries, the specified frequency resource is allocated to different operators, each

operator may only have a part of resources in the entire frequency band. With the

limited resources, frequency planning plays an important role in maximizing the

system capacity and service quality to achieve the goal and thus maximize the

benefit of the operator.


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Frequency Band ConfigurationFrequency Band Configuration

! GSM900:

" BTS receiver (uplink ): f1 (n) =890.2+ (n-1)*0.2 MHz

" BTS transmitter (downlink ): f2 (n) =f1 (n) +45 MHz

! GSM1800:

" BTS receiver (uplink ): f1 (n) =1710.2 + (n-512) * 0.2 MHz

" BTS transmitter (downlink ): f2 (n) =f1 (n) +95 MHz


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All useful signals carrier

All useless signals interference=

GSM standard: C / I >= 9 dB

In practical projects: C / I >= 12dB

Useful signal Noise from environment

Other signals

Requirement for Interference and Carrier-

to-Interference Ratio


to-Interference Ratio

C/I =

GSM is an interference restricted system. Carrier-to-interference ratio (C/I), also

called interference protection ratio, refers to the ratio of all useful signals to all

useless signals. In GSM system, this ratio is relevant to the instantaneous location

and time of MS due to irregular landform, different shape, type and number of

surrounding scatterer, different type, direction and height of antenna, as well as

different number and intensity of interference source, etc. Usually, the interference

signal comes from the following three kinds of sources:

1. Multi-path signal interference of useful signal itself which falls outside the system

delay equalizer

2. Co-channel and adjacent frequency interference generated from frequency reuse

of useful frequency itself


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To-Interference Ratio


To-Interference Ratio

All useful signals carrier

All useless signals interference=

GSM standard: C / I >= 9 dB

In practical projects: C / I >= 12dB

Useful signal Noise from environment

Other signals

C/I =

3. Other signal interferences from outside (radar station, illegal co-channel

equipment, noise from environment, etc.)

According to the signal demodulation requirement of air interface, GSM specifiesthat the co-channel and adjacent frequency protection ratio must comply with the

following requirements:

Co-channel carrier-to-interference rate: C/I 9dB; add 3dB allowance in

engineering, that is, C/I 12dB; C/I refers to the interference from other cells to

service cell when different cells use the same frequency. In a board sense,

certainly the electromagnetic wave energy of all useless signals falling into this

frequency carrier should also be considered.

Adjacent frequency suppression rate: C/A -9dB; add 3dB allowance in

engineering, that is, C/A -6dB; C/A refers to the interference from all adjacent

signals around the service cell (carrier offset 200KHz) to service cell channel under

frequency reuse condition.

The carrier-to-interference ratio requirement under carrier offset 400KHz is:

C/2A -41dB.


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Effect of InterferenceEffect of Interference

! Decrease of signal quality

" Bit error

# Recoverable: channel coding, error correction

# Irrecoverable: phase distortion

" System interference model

# Unbalanced: uplink interference downlink interference

#Asymmetrical: the interference is different at the MS and BTS ends

The influence of interference to the system is reflected on the bit error rate of useful

signals, while the bit error rate directly affects voice quality. Therefore, interference

can exert severe influence upon system service quality. Make sure that related co-

channel and adjacent frequency interference protection ratio complies with the

requirement in frequency planning.

There are two kinds of bit error codes: one is recoverable, using system channel

coding, error correction; the other is irrecoverable, such as phase distortion, etc.

Since GSM system is a frequency reuse system, the co-channel and adjacent

frequency interference in each frequency carrier produced by frequency reuse must

comply with the above requirements in frequency planning. Of course the above

indices can be lowered under the support of other anti-interference technologies,

but finally it is measured with actual system voice quality and network indices.


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RXQUAL Mean BER BER range

class (%) from... to

0 0.14 < 0.2%

1 0.28 0.2 ... 0.4 %

2 0.57 0.4 ... 0.8 %

3 1.13 0.8 ... 1.6 %

4 2.26 1.6 ... 3.2 %

5 4.53 3.2 ... 6.4 %6 9.05 6.4 ... 12.8 %

7 18.1 > 12.8 %

Fairly good

Intolerable

Good

Acceptable

Signal QualitySignal Quality

! Receiving quality (RXQUAL parameter)

! Level of receiving quality (0 ... 7)

" Bit error rate before decoding and error correction

The above figure shows the relationship between system receiving quality

(represented by level 0~7) and bit error rate (before decoding and error correction).

Bit error is caused by interference. Different bit error rates correspond to different

signal qualities. Signal quality level shows the situation of signal interference.


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{fi,fj..fk}

{fi,fj..fk} {fi,fj..fk} {fi,fj..fk}.. ..

Macro-cell system

d

Micro-cell system

Concept of Frequency ReuseConcept of Frequency Reuse

The mobile communication network has evolved from macro-cell system to the

micro-cell system, as shown in the above figure. Under macro-cell system, the

traffic is low, frequency resource is relatively rich. So only one BTS is needed with

high transmit power to cover a larger area. Within this area, channel groups {f1, f2,

f3... fn} are used, frequency reuse is unnecessary. When user and traffic increase,

the original channels (f1, f2...fn) are no longer enough, the only way is to reuse

frequency. In network wireless design, the transmit power of BTS is lowered to

reduce the coverage of each BTS. The area originally covered by one BTS is now

covered by several BTS , while the entire network figure resembles a honeycomb.

Frequency reuse means that the channel used by one cell is reused in another cell

after certain distance. If total channel numbers are fixed, it can increase the

channel number in unit area. Frequency reuse is conditioned, since the same

frequency carrier is used repeatedly in different cells, big or small co-channel and

adjacent frequency interferences are unavoidable, depending on the distance andthe intensity of signals. To ensure that the carrier-to-interference ratio in all design

service areas of the system complies with the requirement, different frequency

reuse technologies should be adopted according to different conditions in frequency

planning.


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The Reason of Frequency ReuseThe Reason of Frequency Reuse

! Frequency resource is limited. If there is 8MHz frequency

resource, 8 MHz = 40 channels * 8 timeslots = 320

==> max. 320 users can access the network at the same

time.

It is known that GSM system is a cellular system and the total channel resource is

limited. In this case, the limited channel resources have to be reused in different

cells to expand system capacity. Suppose that a GSM network operator has only

8MHz band, 40 frequency carriers or 320 channels. Even all channels are used for

user communication, only 320 users are allowed to communicate at the same time.

If each frequency carrier is reused for n times, then 320*n users can communicate

at the same time.


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Looser reuse

Higher frequency reuseefficiency, but interference

is serious. More technique

Is needed.

Tighter reuse

0 10 20

Little interference, but frequency

reuse efficiency is low.

Reuse DensityReuse Density

" Reuse density is the number of cells in a basic reuse cluster.

4*3 12

n*m n*m

n: BTS number in a basic reuse cluster

m: Frequency group number in a BTS

Usually, 12 is the boundary. That is, the reuse density smaller than 12 is called tight

reuse, reuse density larger than 12 is called loose reuse, and 12 is the regular

reuse. In specific frequency planning, we usually use the average reuse density to

measure the objective interference in networks. If total frequency resource is 1~n,

the reuse density of carrier i is re-use(i), then the average reuse density will be:

re-use(ave.)=[re-use(1)+...re-use(i)+..re-use(n)]/n


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[fn]

[fn]

D

[fn]

R

Reuse of a frequency causes the co-channel interference

Problem of Frequency ReuseProblem of Frequency Reuse

In a cellular system, since the frequency resource is limited, frequency reuse turns

to be an effective means to improve frequency utility. But frequency reuse will

definitely result in mutual interference, which is called co-channel interference. The

less the distance between two reused frequencies, the higher the frequency usage

and the interference. An interference distribution is illustrated in the above figure.

For the convenience of theoretical analysis, a cell is illustrated as a regular

hexagon. In the above figure, D represents reuse distance, [fn] represents the

frequency reused.


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R

D

This old-fashioned frequency distribution

mode is not recommended

Frequency Reuse PatternsFrequency Reuse Patterns

" Purpose: to minimize the interference in the whole network with

the final frequency allocation plan

" Theoretically

# Regular hexagon cell

# Regular network distribution

# Cell cluster

# Multiplexing distance

D = R *sqrt(3*K)

For the convenience of theoretical analysis and explanation, suppose that cell is a

regular hexagon or other imaginary model. Regular frequency reuse means to

allocate all frequency carriers regularly in a selected cell cluster, each frequency

carrier is allocated once only, and the same principle is used in other same cell

clusters for allocation. In this way, each frequency carrier is used repeatedly in

different cell clusters. According to different cell clusters selection, different

frequency reuse modes or models are adopted.

Note: the theoretical frequency reuse plan is not feasible due to the complexity of

actual environment. Usually the automatic frequency allocation function of

computer is used in stead. But various frequency reuse technologies can provide

guidance and help on automatic frequency allocation, site mode planning and

network capacity planning.


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A1C1

B1D1

A2

A3B2

B3

C2

C3D2

D3

A1C1

B1D1

A2

A3B2

B3

C2

C3D2

D3

A1C1

B1D1

A2

A3B2

B3

C2

C3D2

D3 A1C1

B1D1

A2

A3B2

B3

C2

C3D2

D3

A1C1

B1 D1

A2

A3B2

B3

C2

C3

D2D3

A1C1

B1D1

A2

A3B2

B3

C2

C3D2

D3

4*3 Frequency Reuse4*3 Frequency Reuse

The basic frequency reuse mode of GSM is 4*3 frequency reuse. It is the basic of

other frequency reuse modes, we also call it regular frequency reuse model. "4"

represents 4 sites, "3" represents 3 cells in each site. Totally 12 cells become a

basic frequency reuse cluster. Different cells in the same cluster have different

frequencies. The above figure shows a cell cluster of 4*3 frequency reuse mode,

while those inside the bold black line is a basic cell cluster model, including 4 BTS

which have 3 frequency reuse group, there are 12 cells totally. In a specific

allocation, all frequencies are allocated to each cell according to certain principle

and same as other cell clusters. In this way, each frequency carrier is reused in

different cell cluster time and time again.

Certainly, other reuse model n*m means that each basic reuse cell cluster contains

n BTS, and each BTS includes m frequency reuse group. All frequency carriers in

this cell cluster are allocated to respective cells according to certain principle, and

by analogy for other surrounding cells.


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A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3

34 34 35 36 37 38 39

40 41 42 43 44 45 46 47 48 49 50 51

52 53 54 55 56 57 58 59 60 61 62 63

64 65 66 67 68 69 70 71 72 73 74 75

76 77 78 79 80 81 82 83 84 85 86 87

88 89 90 91 92 93 94 95

Illustration of Frequency Allocation of 4*3

Frequency Reuse

Illustration of Frequency Allocation of 4*3

Frequency Reuse

Suppose that available bandwidth is 12.2MHz, channel number from 34 to 95, the

above table illustrates the frequency carrier distribution of 4*3 frequency reuse of

12 cells in a basic cell cluster. From which cell to start the allocation of beginning

frequency carrier 34 is not restricted. As seen from the table, 5 frequency carriers

can be allocated to most cells, some cells even have 6 frequency carriers.

Therefore, average largest site mode is S5/5/5 under 12.2MHz condition. Under the

above regular allocation mode, it's impossible to have co-channel or adjacent

channel in the same cell or adjacent cells.


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OutlineOutline

Frequency planning


Frequency hopping


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Tight Frequency Reuse TechnologyTight Frequency Reuse Technology

! Multi-layer reuse pattern

! Underlaid and overlaid cell

! 1*3

! 1*1

Usually, system capacity can be increased by applying some special technologies.

There are following popular technologies at present: Multi-layer frequency reuse

technology, 1*3 and 1*1 reuse technology. Multi-layer frequency reuse needs no

special equipment function support, while Underlaid/Overlaid reuse pattern, 1*3

and 1*1 technology require corresponding support function to be added in

supplier's equipment. Huawei supports Multi-layer reuse pattern, 1*3, 1*1 and

Underlaid/Overlaid frequency reuse technology.

Note: Multi-layer reuse pattern, 1*3 and 1*1 frequency reuse are frequency

planning allocation models instead of technologies. That they are referred to as

"technologies here, is based on the consideration that to make the frequency

allocation plan from above frequency allocation model feasible, corresponding

support functions must be supplied by the network, such as frequency hopping,

power control and DTX, etc.

With close reuse technology, the channels number in a unit area can be increased

under certain bandwidth conditions.


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BCCH: n1

TCH1: n2

TCH2: n3

TCHm-1: nm

n1 n2 n3 n4 ...... nm

And n1+n2+...+nm=n

Multi-layer Reuse PatternMulti-layer Reuse Pattern

Multi-layer reuse technology requires equipment which supports baseband

frequency hopping or radio frequency hopping. It is created on the idea of carrier

layering (in fact, single frequency reuse model is the exception of Multi-layer reuse

pattern and it can be regarded as layered reuse with same carriers on each layer).

That is to divide all available frequency carriers into several groups, each group

serves as a carrier layer (frequency subgroup). Suppose that the whole frequency

resource consists of n frequency carriers which falls into m groups, the carrier

resource allocated to each group is shown in the above figure.


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Multi-layer Reuse Pattern Frequency AllocationMulti-layer Reuse Pattern Frequency Allocation

! Suppose that the available frequency carrier is 10MHZ,

channel number is 46 94, the Multi-layer reuse pattern

should be:

RC typeAllocatedfrequencies

Number ofavailable

frequencies

BCCH 46~57 12

TCH1 58~66 9

TCH2 67~74 8

TCH3 75~82 8

TCH4 83~88 6

TCH5 89~94 6

The planning of BCCH and TCH carrier layer can use consecutive grouping mode.

In the consecutive grouping mode, BCCH allocates 12 frequency carriers for

regular frequency reuse. Because BCCH frequency carriers are used to transfer

system information and signaling, they are very important to the system and should

enjoy special protection to minimize the interference on them. Therefore, BCCH is

regarded as a special layer and allocated to 12 frequency carriers. In specific

planning, usually 1~2 extra frequency carriers are added to allocate 12~14

frequency carriers in planning. If a micro cell is to be constructed in the network,

some frequency carriers are usually reserved for it, or the microcell frequency

carriers are made a separate carrier layer.

As shown above, the whole frequency carrier resource is divided into 6 groups, the

carrier layer where broadcast channel (BCCH) locates 12 frequency carriers for

reuse, the traffic channels are divided into 5 groups of carrier layers as

TCH1~TCH5, each group is allocated with different number of frequency carriers

for reuse.

In this way, BTS configuration can be S6/6/6 under 10MHz bandwidth. In traditional

4*3 reuse mode, the maximum configuration of BTS can only achieve S4/4/4.

According to the average reuse density, the average reuse density value in this

example is lowered to 50/6=8.3. The lower of the average reuse density value

shows the rise of interference which must be overcome by frequency hopping.

Under the above consecutive grouping mode, co-channel/adjacent frequency

interference may exist in BTS frequency layer, while interference between BTS

frequency layers appear on frequency demultiplexing point.


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BCCH TCH1 TCH2 TCH3 TCH4

{f1,f3,f5...f23}

{f1,f2,f3,f4,f5...f40}

{f2,f4..f22,f24...f40}

Multi-layer Reuse Pattern Frequency AllocationMulti-layer Reuse Pattern Frequency Allocation

Suppose that the frequencies available for distribution are f1, f2... f40, 12 frequency

carriers for BCCH, others for TCH1, THC2, THC3 and TCH4. Frequencies in each

layer are distributed at an interval. The adjacent frequency interference exists

between layers instead of in layers, and this mode helps to reduce network

interferences while the traffic is not very heavy.


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$Capacity increase when reuse density is multiplied:# Supposing there are 300 cells

# Bandwidth: 8 MHz (40 frequency)

$Normal 4*3 reuse: reuse density=12

# ==> network capacity = 40/12 * 300 = 1000TRX

$Multiple reuse:

# BCCH layer: re-use =14, (14 frq.)

# Normal TCH layer: re-use =10, (20 frq.)

#Aggressive TCH layer:re-use = 6, (6 frq.)

# ==> Network capacity = (1 +2 +1)* 300 =

1200 TRX

cap N BW

re use

i

i

.=

Advantages of Multi-layer Reuse PatternAdvantages of Multi-layer Reuse Pattern

If there are 40 frequency carriers, main site mode is s3/3/3 when using regular

reuse. With Multi-layer reuse pattern, site mode is divided into 3 layers ( 4 layers

actually, but two layers have the same number of carriers) as shown in the figure

above. The site mode can be s4/4/4. BCCH frequency carrier reuse density is 14

(loose reuse) in each cell. The longer co-channel distance in the network ensures

that the frequency carrier interference complies with the requirement. There are

two frequency carriers with reuse density 10 in each cell, the co-channel reuse

distance is shorter than BCCH frequency carrier and certain interferences exist,

thus it is very hard to maintain good communication quality. The remaining

frequency carrier has a reuse density 6 and short co-channel reuse distance,

severe interferences can make these frequency carriers unavailable for

communication at all. To solve this problem, baseband frequency hopping is

adopted in the network. The voice of same channel is transmitted by different

frequency carriers, so the frequency carrier with severe interferences (reusedensity is 6) only affects the fragmentary timeslot of a communication. With the

error correction and detection function of the system, the entire communication

quality can be guaranteed and the system is able to work normally.


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$Capacity increases when reuse density is multiplied:# Supposing there are 300 cells

# Bandwidth: 8 MHz (40 frequency)

$Normal 4*3 reuse: reuse density=12

# ==> network capacity = 40/12 * 300 = 1000TRX

$Multiple reuse:

# BCCH layer: re-use =14, (14 frq.)

# Normal TCH layer: re-use =10, (20 frq.)

#Aggressive TCH layer:re-use = 6, (6 frq.)

# ==> Network capacity = (1 +2 +1)* 300 =

1200 TRX

cap N BW

re use

i

i

.=

Advantages of Multi-layer Reuse PatternAdvantages of Multi-layer Reuse Pattern

The main reason that Multi-layer reuse pattern technology can realize close

frequency reuse layer by layer to add TRX is: though the interference on specific

frequency carrier is increased in the cell, the frequency carriers with slight

interference and the frequency carriers with severe interference are mixed together

by using frequency hopping technology, the same information flow is transmitted

through different frequency carriers, and the interferences are averaged. The bit

error rate is very high when transmitting from the frequency carrier with more

interferences, but it only lasts a short time, the Viterbi decoder still can demodulate

correctly. For better performance of frequency hopping, at least three carriers are

needed for baseband frequency hopping. Usually, BCCH is not involved in

frequency hopping. It's obvious that layered close frequency reuse poses certain

requirement on site mode, the minimum configuration of the site mode should be

s4/4/4. In practical application, the average reuse density is about 7.5~8 at least

(varying with network condition, environment, traffic and distribution, etc.). Taking 8as an example, there must be more than 32 total frequency resources available.


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The inner circle covers a smaller area, and the

frequency can be reused more tightly.

Underlaid/Overlaid Frequency AllocationUnderlaid/Overlaid Frequency Allocation

Overlaid-cellUnderlaid-cell

In the Overlaid/Underlaid technology, all frequency carriers in the cell are divided

into two parts, of which the TRX power of some frequency carriers is lowered, then

two Overlaid/Underlaid with different coverage appear, as shown in the above

figure. The frequency carriers used by the inner circle can be planned in a more

close mode than outer circle frequency carriers due to its small coverage.

This technology is quite simple and requires no special software and hardware, just

modify parameters. It should be noticed that there is less traffic on original edge

area of the cell and handover may happen in the cell, inner circle and outer circle

handover is required for corresponding cell.


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Super fn

Regular fm Regular fm

Regular fm

Super fn

BCCH 15f Regular 24f Super 12f

BCCH Reuse density: 15

R TCH TRX reuse density: 12

S TCH TRX reuse density: 6

Overlaid/Underlaid Frequency ConfigurationOverlaid/Underlaid Frequency Configuration

Super fn

As shown in the figure above, the idea of Overlaid/Underlaid is to divide BTS

frequencies into two parts (or two layers), one layer is called "REGULAR layer", the

other layer is called "SUPER layer". "REGULAR layer" has longer frequency reuse

distance with loose frequency reuse mode; "SUPER layer" has shorter frequency

reuse distance with close reuse mode. Supposing there are 51 frequency carriers,

15 of them are used by BCCH in 4*3 reuse mode, and each cell is allocated with

one carrier. REGULAR layer uses 24 frequency carriers in the same 4*3 reuse

mode, and each cell is allocated with 2 frequency carriers. SUPER layer uses 12

frequency carriers in 2*3 reuse mode, each cell is allocated with 2 frequency

carriers. Thus, each cell is allocated with 5 frequency carriers in total, the largest

site mode is S5/5/5 when using Overlaid/Underlaid technology. If 4*3 reuse mode is

used alone, the largest site mode can only be S4/4/4.

When using Overlaid/Underlaid technology, the transmitting power of the inner

circle should be adjusted to an appropriate level according to the reuse density and

actual interference. Attention should be paid to the traffic distribution of the overlaid

circle and underlaid circle to make sure there is no congestion in the underlaid

circle.


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BCCH14+TCH36

1BCCH+3TCH

1BCCH+3TCH 1BCCH+3TCH

1BCCH+12 TCH

1BCCH+12 TCH 1BCCH+12 TCH

1*3 1*1

1*3 and 1*1 Reuse Patterns1*3 and 1*1 Reuse Patterns

Isolated reuse technology refers to 1*3 or 1*1 reuse with short reuse distance and

severe interferences, radio frequency hopping technology has to be adopted. The

aggregate of hopping frequencies needs to be far more larger than the number of

TRX (more than twice), MA, HSN and MAIO parameter are used to avoid

frequency conflict. Let's explain the feature of isolated reuse technology with an

example. As shown in the figure, supposing there are 50 frequency carriers with

10MHz bandwidth, 14 of them are occupied by BCCH, 36 of them are used by TCH.

Planning with 4*3 reuse mode, each cell is allocated with 3 frequency carriers, the

site mode is S4/4/4. With 1*3 isolated reuse, each cell is allocated with 12

frequency carriers. The actual frequency carriers available for the cell depend on

isolated reuse rate (RE-LOAD: TRX of frequency hopping/total frequency carriers

allocated by frequency hopping). To be specific, RF-LOAD can be up to 50% in

theory, at this time:

TRX=12*50%=6

The 6 TRX will use radio frequency hopping and can only be realized through radio

frequency hopping technology, which means all these 6 TRX work on the 12

frequency carriers. By setting relevant parameters, make sure they won't have co-

channel conflict due to working on the same frequency carrier at the same time.

When RF-LOAD is 50%, the largest site mode is S7/7/7 when using 1*3 frequency

reuse technology.


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TRX1 TRX2 ... TRX7

TRX8 TRX9... TRX14TRX15 TRX16...TRX21

TRX1 TRX2 ... TRX7

TRX8 TRX9... TRX14 TRX15 TRX16...TRX21

The red items are BCCH RCs

Illustration of 1*3 TCH Frequency AllocationIllustration of 1*3 TCH Frequency Allocation

For the frequency carriers allocated to one cell, TRX1 uses 1 of the 14 BCCH

carriers, TRX2, TRX3, TRX4, TRX5, TRX6 and TRX7 work on 1 of the 12 carriers

allocated to this cell in 1*3 mode respectively at certain time. All TRXs (2~7) have

the same MA and HSN but different MAIO to make sure different carrier boards in

the same cell won't work on the same frequency carrier.


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An example network in a specific place, BTS are densely located.The topography is plain. The maximum BTS configuration is S3/3/2.

$Initial planning:

Example of Frequency PlanningExample of Frequency Planning

Consecutive layering is used to separate BCCH and TCH, of which No. 96~109

frequency carriers are allocated to BCCH, No. 110~124 frequency carriers are

allocated to TCH. In the cell planning process, neighboring cells with Co-channel

and adjacent-channel transmitting towards each other are avoided as much as

possible, but there are many cases where sites separated by other sites in between

have co-channel cells facing each other.

In this plan, there are 4 pairs of co-channel face-to-face cells in different BTS and

they are all BCCH frequency carriers. When engineering parameters of cell and

transmitting power are fixed, interference is only relevant with BTS interval , no

matter whether there are other BTS between two cells. After actual deployment, the

result of this frequency plan is: many complaints from urban subscribers about poor

voice quality and frequent drop.


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$Final frequency planning:

Example of Frequency PlanningExample of Frequency Planning

In whole frequency carrier BCCH and TCH mix up distribution principle, the

frequency plan avoids co-channel opposite cell in different BTS, but adjacent BTS

have more adjacent frequency cell, co-channel frequencies appear in back-to-back

cells. (Using the principle of mixed allocation of BCCH and TCH in the whole

frequency carrier, the frequency plan avoided co-channel frequency cells in

different BTS, with more adjacent-channel cells in neighboring BTS, and the co-

channels cells were transmitting in opposite direction to each other.

At the same time, the downtilt of antenna has been adjusted and PBGT handover

has been enabled, the PBGT handover threshold is adjusted to 70 (equal to 6dB).

The complaints from urban subscribers are reduced, and the TCH drop rate in

traffic statistic index is lowered by about 1%.


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Example of 1*3 Frequency ReuseExample of 1*3 Frequency Reuse

! Suppose 900 band: 96 124

! BTS configuration: S3/3/3

! BCCH layer: 96 109 reuse pattern: 4*3

! TCH layer: 110 124 reuse pattern: 1*3

The frequency planning of TCH layer frequency hopping can be in two modes:

consecutive allocation and interval allocation.


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Group 1 (MA1): 110 111 112 113 114 Cell1

Group 2 (MA2): 115 116 117 118 119 Cell2

Group 3 (MA3): 120 121 122 123 124 Cell3

TCH Consecutive Allocation SchemeTCH Consecutive Allocation Scheme

TCH are grouped by order. The three cells of the same BTS use the same HSN

while different BTS use different HSN and all same layer carriers within the network

use the same MAIO. The HSN of BTS A is 1, the MAIO of two carriers TCH1 and

TCH2 in each cell are 0 and 2 respectively, the HSN of BTS B is 2, the MAIO of two

carriers TCH1 and TCH2 of each cell are 0 and 2 respectively, and so on. In this

way, adjacent frequency is avoided between the three different cells of the same

BTS, the possibility of adjacent frequency conflict between opposite cells of

different BTS is reduced in comparison with TCH interval grouping . But there is an

extra possibility of adjacent frequency conflict between cells of different BTS in

parallel direction in comparison with TCH interval grouping.


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TCH Interval Allocation SchemeTCH Interval Allocation Scheme

Group 1 (MA1): 110 113 116 119 122 Cell1

Group 2 (MA2): 111 114 117 120 123 Cell2

Group 3 (MA3): 112 115 118 121 124 Cell3

In TCH interval grouping , the three cells of the same BTS use the same HSN while

different BTS use different HSN, and different MAIO are used by carriers in the

same layer of the same BTS. The HSN of BTS A is 1, the MAIO of two carriers

TCH1 and TCH2 in Group 1 cell are 0 and 1 respectively, the MAIO of two carriers

TCH1 and TCH2 of Group 2 cell are 2 and 3 respectively, the MAIO of two carriers

TCH1 and TCH2 of Group 3 cell are 4 and 0 respectively, the HSN of BTS B is 2,

and so on. In this way, adjacent frequency is avoided between the three different

cells of the same BTS, the possibility of adjacent frequency conflict between

opposite cells of different BTS is reduced in comparison with TCH consecutive

grouping , but there is an extra possibility of adjacent frequency conflict between

cells of different BTS on parallel direction in comparison with TCH consecutive

grouping.

As to which TCH grouping mode produces less 1*3 frequency hopping

interferences, both consecutive and interval grouping modes have their

disadvantages. For the downtown with dense BTS distribution, adjacent frequency

influence from opposite cell is more than that from adjacent cells on parallel

direction, which makes consecutive grouping more appropriate. But in sub-urban

areas, interval grouping helps to average out the interferences due to the irregular

distribution of BTS. Therefore, actual local situation should be considered when

choosing grouping mode. After the new channel distribution arithmetic under close

reuse has been realized, it is recommended to adopt consecutive grouping scheme

to ensure better service quality over the whole network.


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Comparison Between Multi-layer reuse and 1*3Comparison Between Multi-layer reuse and 1*3

! For Multi-layer reuse pattern, either Base band hopping or RF

hopping can be used. But for 1x3 reuse, only RF hopping can be

used.

! Multi-layer reuse pattern is a gradual process for TCH frequency

planning. In other words, the reuse is rather loose in TCH1 layer and

it is quite close in the last TCH layer (such as TCH5). The reason for

this pattern is that base band hopping is used in the Multi-layer reuse

pattern. When there are rather few frequency carriers, the hopping

gain is small. Therefore, more frequency carriers should be allocated

for the layer with small TCH and then the reuse coefficient is

relatively large. When RF hopping is used in the Multi-layer reuse

pattern and there are a large number of frequency carriers, the

hopping gain is high and the reuse coefficient can be very small. In

addition, the Multi-layer reuse pattern is of a free pattern. It is

different from base band hopping, in which the reuse must be loose

in the first TCH layer and more close in inner layers.


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Comparison Between Example of Frequency

Planning and 1*3

Comparison Between Example of Frequency

Planning and 1*3

! The frequency planning for the 1x3 mode is simple and it is

easy to plan the frequency for new added BTS.

! 1x3 mode requires a rather regular BTS location distribution.

! For the cells with fixed number of TRX, when the traffic is

heavy, the 1x3 provides higher service quality than that of

Multi-layer reuse pattern.

! TRX can be easily added to the 1x3 network, but TRX number

of hopping should not exceed the product of the allocatedhopping frequency number and the max RF load ratio.

! BCCH of Multi-layer reuse pattern can take part in the

frequency hopping, while BCCH in 1x3 mode can not.


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OverviewOverview

Frequency planning


Frequency hopping


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Content of Frequency HoppingContent of Frequency Hopping

!Class of hopping

!Advantages of hopping

!Parameter of hopping

!Collocation of hopping data


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Frequency HoppingFrequency Hopping

When using close frequency reuse technique, system interference is the most

important factor for frequency reuse ratio. Usually, power control and discontinuous

transmission technologies are adopted to lower system interference. To prevent

interference and improve system communication quality under the same

interference condition, frequency hopping technology is used.

Therefore, frequency hopping is a very important technology for reducing GSM

system interference and improving frequency reuse ratio. According to GSM

standard recommendations, slow frequency hopping can be used in GSM

communication system. Frequency hopping refers to the regular hopping of carrier

frequency within certain range. The frequency hopping function of the channel

group in each cell can be enabled or disabled separately. Since BCCH is the

broadcast channel, it does not participate in frequency hopping while TCH and

SDCCH channel can utilize frequency hopping. There are two kinds of frequency

hopping modes used by BTS, I.e. base-band hopping and radio frequency hopping.

The mechanisms of implementation of them are not the same.


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Class of HoppingClass of Hopping

! Hopping can be implemented in two ways

" Base-band hopping

" RF hopping

! Class according to the min hopping time

unit

" Timeslot hopping

" Frame hopping


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Base Band Hopping PrincipleBase Band Hopping Principle

There are a number of relatively independent base band processing units and

carrier processing units in the system. The working frequency carrier of each

carrier processing unit is fixed, the service information of each communication path

is processed by fixed base band unit, and then the processed information is

transferred to carrier units of different frequency carriers for processing and

transmitting through bus structure according to time sequence and specific

frequency hopping principles. This hopping mode is called "base band hopping". In

base band hopping, each transmitter works at a fixed frequency, the bursts of the

same voice channel are sent into respective transmitters under control for switching

based on base band signal. Since the frequency of each transceiver is fixed, no

change is needed on the combiner, while both broadband combiner and cavity

combiner can be used. The maximum number of hopping frequencies are limited

by the number of TRX. The problem of base band hopping is that if one TRX board

failed, the corresponding code will be lost and the communication performance willbe affected.


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RF Hopping PrincipleRF Hopping Principle

In this mode, each route of service information is processed by fixed base band unit

and and carrier frequency processing unit, while the working frequency carrier of

carrier frequency processing unit is provided by frequency synthesizer. Under the

control of the control unit, frequency carrier can be changed according to certain

rules. This mode is called "carrier frequency hopping" or "RF hopping". In RF

hopping, one transmitter processes the frequency carriers used by all bursts of one

communication, which is realized through the change of synthesizer frequency

instead of the switching of base band signal. The number of TRX depends on cell

traffic instead of restricted by carrier. Because of the change of synthesizer, the

combiner should be changes, only broadband combiner can be used. This kind of

synthesizer has a insertion loss of about 3db. The cascade connection of multiple

combiners has large insertion loss, so the actual application is restricted. But once

fault occurs to certain TRX, the troubleshooting function of the system will shut

down this TRX.

GSM specifications do not specify that GSM BTS must use "base band hopping" or

band hopping, while the hopping mode used by BTS equipment is specified by

the equipment supplier. As to mobile terminals, since each terminal has only one

carrier unit, it's bound to use carrier frequency hopping.


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Class of HoppingClass of Hopping

! Frame hopping

" Frequency changes every TDMA frame. The different channel

of one TRX uses the same MAIO.

! Timeslot hopping

" Frequency changes every timeslot. The different channel of one

TRX uses the different MAIO.


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Smoothen and average the interference

Interference Diversity of HoppingInterference Diversity of Hopping

In GSM system, the interference strength and distribution on each frequency carrier

in cell are different, the carrier variation of the bursts of the same communication

low the interference on signal, the radio wave interference on communication is

equalized. If no hopping is used, the mobile station will always work on fixed

frequency carrier, each burst during the entire communication may receive fixed

strong interference. In others words, hopping technology disperses the interference

on different carriers with burst, this is called "interference equalization" or

"interference diversity". As shown in the figure, bursts B1, B2... are spread on

frequencies f1, f2, f3... Co-channel interference exists in the cellular network

because of frequency reuse, hopping makes the signal interference discontinuous

to improve radio wave environment. The interference varies from burst to burst,

which improves the communication quality. Otherwise, the entire communication

will suffer from strong interference. That is to say the interference is dispersed on

different carriers with burst. Of course, the frequency conflict from hopping canresult in strong instant interference, which can be solved by defining different MAIO.

In frequency hopping, the more frequency carriers in use, the less likely the

frequency conflict can occur, and the higher the hopping gain. But frequency

availability will be lowered when there are more hopping frequency carriers.


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Description Hopping ParametersDescription Hopping Parameters

!At the Um interface, the ARFCN on a specific burst is an

element in MA set. MAI is used for indication, referring to a

specific element in the MA set.

! When 0< MAI


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Description Hopping ParametersDescription Hopping Parameters

!At the air interface, the RC number on a specific burst is an

element in MA set. MAI is used for indication, referring to a

specific element in the MA set.

!When 0< MAI


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Description of Hopping ParametersDescription of Hopping Parameters

! HSN hopping sequence number 0 63 .

! HSN=0 cycle hopping.

! HSN 0 random hopping. Every sequence number

corresponds a pseudo random sequence.


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Hopping ParametersHopping Parameters

! Hopping mode: the mode used by the BTS system, including

three options: not hopping, base band hopping and RF

hopping.

" Location: in Cell Configuration Table

! CA (Cell Allocation Table): refer to all available frequency

carriers in the cell. The allocation should be consecutive

starting from the effective frequency carrier 0. There should be

no empty data item. The frequency carrier configuration

should be in an ascending order.

" Location: in Cell Allocation Table .


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Hopping ParametersHopping Parameters

! MAIO (Mobile Allocation Index Offset): used to define the initial

frequency of the hopping.

! The MAIO of all channels of one hopping TRX must be identical. The

MAIO of channels of different hopping TRX in the same cell must be

different.

" Location: in frequency hopping table .

! TSC (Training Sequence Code): used for delay equalization at the

receiver end. TSC must be the same as the BTS color code. When

an MS or BTS receives signals, delay equalization is started with thespecified TSC. But for the co-channel signals with different TSC,

delay equalization is impossible, so that demodulation can not be

received. In this way, erroneous receiving is prevented effectively

and then co-channel interference is prevented.

" Location: in Radio Channel Configuration Table .


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Note: means absolutely same; means absolutely different;

# means uncertain.

Hopping Data Configuration RulesHopping Data Configuration Rules

TSC CA MA HSN MAIO

The same RCin the cell

Different RCin the cell

Co-channelcell

#

1. No hopping for BCCH frequency carrier. Allocate only one frequency carrier for

BCCH carrier in [Carrier Configuration Table].

2. The mobile allocation set MA must be the subset of corresponding cell allocationtable CA, which means all frequency carriers used by certain carrier hopping in cell

must appear in the corresponding records in [Cell Allocation Table].

3. For certain hopping channel, since the anti-interference effect of hopping will be

better when there are more available hopping frequency carriers, usually the mobile

allocation set MA of certain carrier is all CA other than BCCH frequency carrier, in

other words, all available frequency carriers within cell other than BCCH frequency

carrier participate hopping.

4. In the same cell, MA, CA, TSC, HSN, MAIO of all channels on the same carrier

are the same, which means the hopping rules of all channels on the same carrier

are completely the same.

5. MA, CA, TSC, and HSN of different carriers are the same in the same cell, but

MAIO is different. Only the beginning frequency carrier of hopping is different for

different carriers. TSC is the same as the BTS color code of local cell which can be

obtained from [BSC Cell Table].

6. In the adjacent cells (co-channel adjacent cell) using the same frequency group

(CA), if the mobile allocation set MA is also the same, usually the two cells must

use different hopping sequence number HSN.


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Description of Cell Allocation TableDescription of Cell Allocation Table

Field name Meaning Value range Suggestion

Module ID Module ID is the number of the modulecontaining the cell

0~255

Cell ID Cell ID is the index value of the cell 0~65535

Cell name It is just a prompt 30 bit

ARFCN 0~63 It is used to configure the absolute RC numberin the cell using frequency bands; each cell canbe configured with at most 64 frequency bands.The number of frequency bands to be used inpractice is usually determined in networkplanning.When there are less than 64 frequency bands,the invalid field need no configuration. Forexample, if only 6 bands are used, effective

bands 0~5 should be configured and thesubsequent effective bands 6~63 should not beconfigured.

M900:

1~124;

M1800:

512~885

Configureas

necessary


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Field Name Meaning Value range Suggestion

Module ID Module ID is the number of the modulecontaining the cell

0~255

Cell ID Cell ID is the index value of the cell 0~65535

HW-IUOproperty

Indicating whether TRX should be configuredas OverLaid or UnderLaid subcell.

equipmentgroup ID

The number of the equipment group at thesite. One site supports at most 3 equipmentgroups; It is usually configured as 0 atpresent.

0~2 0

ARFCN

Configure the frequency that the RC unitoccupies. Configure one frequency when thereis no hopping. If hopping is necessary,configure 3~64 bands. These effective RCsmust be the subset of the effective RCs in thecell distribution table.

The subsetof the

effective RC

in Cell

Allocation

Table

Static TRXPower classl

Static transmitting power level of the RC. 0corresponds to the static power 46dBm, i.e.40W. The static power is lowered by 2dB withthe level goes up by 1.

0~13 Subject toactualconditionand the

equipmentcapacity

Description of RC Configuration TableDescription of RC Configuration Table


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Fieldname

Meaning Value range Suggestion

FH indexnumber

The index number of all sorts of hopping

status, providing index value for Radio

Channel Configuration Table . The numbers

are in a sequence starting from 0.

0~255

HSN

HSN, indicating the sequence rule of thehopping. Usually, there is only one HSN in

the same cell and the HSN in the co-channelcell must be different. The above-mentioned

rules must be observed.

0~63

TSC

Decide the parameters of the self-adaptiveequalization filter in the receiving processing

filter. It is the same as the correspondingbase color code (BCC).

0~7

FHARFCN

Number of frequency in the hopping serial.According to hopping algorithm, at least 3

frequencies are required for hopping gain. Ifthis field is left blank, it is invalid.

Correspondingparticipant hopping

frequency in CellConfiguration Data

Table

Configure as

necessary

Description of Hopping Data TableDescription of Hopping Data Table


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Domain name Meaning Value range Suggestion

TRX ID The number of TRX unit in an BS 0~24

Channel ID Number of physical timeslot in TRX 0~7

Ch type Logic channel type of timeslots, includingTCH Full Rate, TCH Half Rate 01, TCHHalf Rate 0, SDCCH8, Master BCCH,Composite BCCH, BCH, BCCH + CBCH,SDCCH + CBCH, etc.

9 channelgroupings

FH indexnumber

It is used to index to corresponding record in

Hopping Data Table .

0~255

MAIO MAIO, used to decide initial frequency offsetof the hopping.

Less thanthe numberof hoppingfrequency

Sub-ch ID One timeslot is divided into 2 sub-channel 0,1at half rate. It is all 0 at full rate.

0~1

circuit number Number of trunk circuit at Abis interfaceoccupied by the corresponding physicaltimeslot.

0~65535

Description of Radio Channel Configuration TableDescription of Radio Channel Configuration Table


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