frquency planning guideline

7/27/2019 Frquency Planning Guideline

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Frequency Planning

Guideline



ZTE Confidential Proprietary /8

Contents Frequency Planning Guideline ........................................................................................... 3

1. Frequency Multiplexing Technology .......................................................................... 3 2. Frequency Planning Principle ..................................................................................... 3 3. 4 x 3 Multiplexing Technology .................................................................................... 4 4. Multiple Multiplexing Pattern (MRP) .......................................................................... 5 5. Frequency Hopping (FH) ............................................................................................. 6




Frequency Planning Guideline

1. Frequency Multip lexing Technology

Frequency multiplexing is a kind of technology commonly used in a GSM network, by which

the same frequency is applied to cover different areas. In addition, there will be a certain

distance, called co-frequency multiplexing distance between these areas using the same

frequency.

If directional antenna is used, it is recommended to adopt 4 x 3 multiplexing method. In certain

areas with heavier traffic, other multiplexing methods can be adopted according to machine

capability, such as 3 x 3 and 2 x 6. No matter which method is adopted, its basic principle is to

meet the requirements of interference protection ratio with a view to different propagation

conditions, different multiplexing methods, and multiple interference factors. They are shown

as follows:

1. Co-frequency protection ratio C/I ≥ 9 dB

2. Adjacent frequency interference protection ratio C/I ≥ -9 dB

3. 400 kHz adjacent frequency interference protection ratio C/I ≥ -41 dB

2. Frequency Planning Principle

When performing frequency planning, frequency distribution is usually achieved according to

geographic areas. Several frequency channels should be reserved for the border area, which

should be kept away from traffic hot spot or complex organizing network area. Usually

planning starts from area densely distributed with sites. For example, planning from the city’s

downtown area, to suburban area with low TRX configuration site (usually choose S111or O1

as border area). Pay attention to the situation where there are lakes or big rivers in the city. In

that case, interference by water surface reflection should be avoided. Due to irregularity of the

sites distribution, it’s hard to guarantee full use of conventional mode such as 4 x 3 or 3 x 3 in

TRX frequency within the same layer, and flexible adjustment needs to be made on basis of

actual situation.

The following rules about frequency planning need to be considered:

1. No co-located channels or adjacent channels should be distributed to one BTS site.




2. It would be better that the frequency interval between BCCH and TCH in one single cell be

more than 400 KHz.

3. When no hopping technology is adopted, it would be better that the TCH frequency

interval in one single cell be more than 400 KHz.

4. Adjacent sites should be avoided to be configured with co-located channel. (Even though

the antenna’s main-lobes are different, strong noise will be caused by side-lobes)

5. Considering antenna height and complex wireless environment, co-located channels and

adjacent channels should be kept away from BTS sites with low inter-site distance.

6. When 1*3 reuse mode is adopted, the number of hopping frequency channels should be

configured at least twice as the hopping TRXs numbers.

7. Focus on co-channel reuse, and avoid configuring the same BCCH and BSIC in close

region.

3. 4 x 3 Multip lexing Technology

There are a variety of frequency multiplexing structures used in GSM, such as 4 x 3, 3 x 3,

and 2 x 6. Usually, regardless of the multiplexing methods adopted, limited frequencies are to

be classified into a certain number of groups. In sequence these groups will form a cluster of

frequency and be assigned to adjacent cell (shown in the following figure). According to GSM

system criteria, 4 x 3 is commonly used in various GSM networks. By this multiplexing method,

frequencies are divided into 12 groups which are assigned to 4 sites in turn. That means 3

frequency groups can be used in each station. As a result of long multiplexing distance

brought about by this frequency multiplexing method, the requirement of co-frequency

protection ratio and adjacent frequency interference protection ratio required by GSM system

can be met reliably. Therefore, it makes GSM network run in fine quality and good security.




By this method, the full band of frequency is divided into two mutually orthogonal bands, that is,

BCCH frequency band and TCH frequency band, which are to be planned by different

multiplexing methods respectively. One method to improve system capacity is to use closer

multiplexing method. BCCH channel plays a decisive role in the process of mobile station

access and switching. Therefore, by using the frequency orthogonal to TCH frequency band,

the following benefits can be enjoyed, which will ensure the quality of BCCH channel :

1. BCCH can use 4 x 3 or higher multiplexing coefficient to ensure the quality of BCCH

channel, while TCH uses relatively close multiplexing method.

2. Separation between each layer of BCCH and TCH frequency band reduces planning

workload. Therefore, planning by layer is feasible. In addition, a section of frequency may

be reserved for micro cell.

3. BSIC decoding has nothing to do with voice channel load. BCCH frequency band and

TCH frequency band are mutually orthogonal. Therefore, the increase in TCH channel

load has little influence on BCCH channel. In addition, it does not have any impact on

BSIC decoding, and thereby improving switching performance.

4. Simplify the configuration of adjacent cell list. Some documents indicate that long

adjacent cell list will weaken switching performance, while this method can simplify

adjacent cell list, and thereby improving switching performance.

5. BCCH independently uses a segment of frequency (12 frequency points in 4 x 3 method),

and thus the adjacent cell list (composed of BCCH frequency points) can be greatly

shortened.

6. Give full play to immunity technologies to interference, such as power control and DTX.

BCCH cannot use dynamic power control and DTX and it has been transmitting signal in

the highest transmission power. Therefore, BCCH and TCH will influence the effect of

these anti-interference technologies by using the same frequency band.

7. Each layer in BCCH and TCH is comparatively independent, which is conducive to

maintenance and expansion by layer. Increasing or deleting sites or TRX in cells will not

impact pre-existing BCCH frequency planning and thus facilitating network maintenance.

5. Frequency Hopping (FH)

Frequency hopping is one kind of spread spectrum communication. It is applied to cell mobile

communication system to improve system’s countering capacity against multipath fading. In

addition, it can curb co-frequency interference on communication quality. Especially,

nowadays when spectrum resource is more and more insufficient, frequency hopping

becomes one of the most effective methods to improve spectrum utilization rate.




GSM supports baseband frequency hopping and RF frequency hopping (also called

Synthesized Frequency Hopping). Baseband frequency hopping means that many transmitters

work on their own fixed frequency points, while on baseband signals from different channels

switched to different transmitters are sent according to frequency sequence. Baseband

frequency hopping can be easily realized. However, there are only a few frequency hopping

points as a result of the limited TRX. Frequency hopping artificial system established by ZTE

mainly supports RF frequency hopping. Baseband frequency hopping is only regarded as an

exception to RF frequency hopping (that is, the number of frequency points equals to that of

TRXs). The advantage brought by frequency hopping is mainly about the effect of Frequency

Diversity and Interference Diversity. Frequency diversity actually improves network coverage

scale, and Interference diversity increases network capacity.

The number of available frequency hopping in baseband frequency hopping is equal to that of

TRX. Therefore, it can only bring frequency diversity gain. However, now GSM operators are

more concerned about capacity as coverage is no longer a problem in most cities. RF

frequency hopping is a very effective method to solve capacity problem.

RF frequency hopping is more and more frequently applied to network planning. Frequency

diversity means its immunity ability to Rayleigh fading. Since Rayleigh fading on different

carriers is definitely irrelevance (the more frequency differential is, the less irrelevance is),

then burst distributed on different carriers will not be influenced by the same Rayleigh fading. It

counts a lot to the still and moving-at-low-speed mobile station. It is supposed to provide a

gain value of 6.5dB. However, MS moving at high speed and two successive burst in the same

channel are different in terms of timing position, which means that they are irrelevant to

Rayleigh fading. They are seldom influenced by the fading when frequency diversity provided

by low-speed frequency hopping is very little.

Under the condition that MS moves at a high speed, frequency points assigned to cells have

little impact on frequency hopping performance. While under the condition without frequency

hopping, there is frequency diversity gain of about 1 dB to 2dB. When MS moves at a low

speed (TU3), because of frequency diversity effect, the number of frequency points assigned

has significant influence on system performance. Frequency points increased by a time will

obtain gain value of about 0.2~1dB, and load rate can be increased by 10% or so.




Interference diversity means that capability of interfering signals in other co-frequency

multiplexing cell will be curbed, that is, frequency hopping and interfering differential on the

transmission path will be provided in order to improve interference under the harshest

conditions. It enables all users to enjoy good communication quality, which is very important

for the mobile communication system with lots of users, especially critical to increase

communication traffic through augmenting frequency multiplexing rate. Usually interference

diversity effect should be provided, and the number of frequency hopping points should be no

less than 3.

If co-frequency point is 10 MHz, frequency hopping planning and capacity analysis without

frequency hopping are as follows:

The multiplexing method of BCCH is 4X3, and the multiplexing method of traffic channel is

3X3. 10 MHz has 50 frequency points. Except 1 protection frequency point and 12 BCCH

frequency points, there are 37 frequency points left. Thus, each cell can be assigned with 4

traffic frequency points ((37-1)/9), and only one frequency point is left. Then its maximum

configuration should be 5+5+5. Each cell can provide 37 channels

(1BCCH+2SDCCH+37TCH).

When RF frequency hopping technology is adopted, traffic channel can adopt 1X3 multiplexing.

In case of 50% load, each cell can provide 6 service logic frequency points. The reason why it

is called logic frequency point is that they all adopt the same 12 frequency hopping collection

((37-1)/3). Only HSN is different from MAIO, and one frequency point is left. The maximum

configuration becomes 7+7+7. It can provide 53 service traffic channels

(1BCCH+2SDCCH+53TCH) with an increase on capacity by 43%. At this time the C/I value in

more than 90% of areas will be 9dB. When DTX and distinctive ZTE fast power control

algorithm are adopted at the same time, system capacity can be improved much better. If

intelligence traffic control technology is adopted, GSM can acquire soft capacity, and gain

more system capacity by sacrificing certain voice quality in hot traffic areas.

frquency planning guideline

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