Mw frequency planning

Microwave Network Planning and Design--Frequency Planning

Microwave Frequency Planning

Purpose of frequency planning:

Make reasonable use of the frequency resources so that the new microwave links and existing ones do not interfere with each other and the system availability of the microwave network can be ensured. In the process of planning for the microwave network, appropriate frequency bands and channels should be selected and interference avoidance should also be taken into account.

Microwave frequency bands suggested by ITU-R for common use:Frequency

Band

4 GHz L6 GHz U6 GHz 7 GHz 8 GHz 11 GHz 13 GHz 15 GHz 18 GHz 23 GHz 26 GHz 38 GHz

Range 3.6-4.2 5.9-6.4 6.4-7.1 7.1-7.7 7.7-8.5 10.7-11.7 12.7-13.2 14.5-15.3 17.7-19.7 21.1-23.6 24.5-26.5 37.0-39.5

Microwave Frequency PlanningDivision of microwave frequency bands:

LF MF HF VHF UHF SHF EHF

Microwave

� 10 Km 1 Km 100 m 10 m 1 m 10 cm 1 cm 1 mm

f 30 KHz 300 KHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz

Infrared rays

Visible light

Microwave Frequency PlanningPrinciples of selecting proper frequency bands:

1. Select proper frequency bands according to the frequency resources (licenses) owned by the carriers and the stipulations of local radio management committees.

2. Select proper frequency bands according to the characteristics of the designed networks and routes. For example, high-frequency bands are generally used for mobile networks and MANs because quite a few channels available at high-frequency bands.

3. Select proper frequency bands according to their characteristics.

● Low-frequency bands (L6G/U6G/7G/8G/11G) are suitable for long-distance links and high-frequency bands (13G/15G/18G/23G/26G/38G) are suitable for short-distance links.

● Due to the limited number of channels existing at low-frequency bands, interference tends to arise in the long-distance transmission.

● High-frequency bands are suitable for high-speed data transmission and interference sustainable because there are many channels with broad bandwidth.

● High-frequency antennas feature high gains. Compared with low-frequency bands, high-frequency bands require small clearance. Towers with these antennas properly used can be lower than others.


Illustration of the selection of microwave frequency bands:

85432 10 201 30 40 50

1.5 2.5LAN/PCS

Long-distance backbone networks

Area, local, and edge networks

28

34Mbit/s

34140155

Mbit/s

28

34140155

Mbit/s

3.3 11 GHz

GHz

Microwave Frequency PlanningDivision of microwave frequency bands:

Frequency Shift Frequencies (MHz) (T-R Spacing) Use

4-7 GHz 161, 154, 245 Long-distance network

backbones

8 GHz 126, 161, 154. 199, 266, 311 Long-distance network

backbones

11-13 GHz 266 Short and medium distance

15 GHz 308, 420, 490, 315. 720, 728 Short and medium distance

18 GHz 340, 1092.5, 1008, 1010, 1560 Short and medium distance

23 GHz 600, 1050, 1232, 1008, 1200, Short distance in urban areas

26 GHz 855, 1008 Short distance in urban areas

28 GHz 1008 Short distance in urban areas

32 GHz 812 Short distance in urban areas

38 GHz 700, 1260 Short distance in urban areas


Figure 1 for configuring microwave radio frequency channels:

Channel number

Frequency

F3

F1F2

Fo

1 2 n 1' n'

Lower half band Upper half band

Center frequency

Fo: center frequency

2'


Figure 2 for configuring microwave radio frequency channels:

Each channel consists of a pair of transmission and receiving frequencies.

Tx

Rx

Tx

Rx

Channel Channel

1

1'

n

n'

1

1'

n

n'

High site Low site

The site which the receiving frequency higher than transmitting frequency is called a high site.

The site which the receiving frequency is lower than the transmitting frequency is called a low site.

Microwave Frequency PlanningPrinciples of selecting proper bandwidth of microwave channels:

The bandwidth of a microwave channel is decided by the signal rate and radio modulation scheme.

The most commonly used ways are the quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM).

● 2 x E1 requires 3.5 MHz (QPSK)● 4 x E1 requires 7 MHZ (QPSK)● 8 x E1 requires 14 MHz (QPSK)● 16 x E1 requires 28 MHz (QPSK)● STM-1 requires 28 MHz (128QAM)

The more advanced modulation is, the smaller the bandwidth is required. The 16E1 signal subject to QPSK requires the same bandwidth (28 MHz) as the STM-1 signal subject to 128 QAM does.

Microwave Frequency PlanningPrinciples of selecting proper microwave

channels:1. Try not to select the special frequency resources (licensed) used by other carriers even if these frequency bands are not used in some areas (in case they may be used in the future).

2. If the planned microwave link features the same routing or parallel routing as another microwave link, it is recommended that the frequency band/channels different from those of the existing link are used. A different polarization mode should be configured even if the same channel is adopted as a result of the little interference and big margin proved by the calculation and analysis.

3. If the angle between two interleaving routes is comparatively small (for example, smaller than 30 degrees), a different channel should be selected. If the angle is quite large (for example, larger than 60 degrees), the same channel can be used provided a different polarization mode is configured. The same channel with the same polarization mode can be used only when the angle is larger than 90 degrees. This is a generally adopted principle for microwave frequency planning. For different equipment, antenna configuration, or capacity, analysis should be made on the link accordingly.

4. In the design, the microwave link should be as far from the scatter communication station and the satellite communications earth station as possible. When the antenna of the microwave station is directed to the satellite orbit with a tolerance of ±2 degrees, the frequency band of the communication satellite cannot be used.

Microwave Frequency PlanningExample for the microwave frequency planning:

In frequency planning, reusing of frequency resources should be taken into account, the internal and external interference should be avoided, and the link quality should be enhanced. Polarization should alternate every other hop for the decrease of overreach interference. The polarization configured alternate every hop is conducive to the decrease of front-back interference upon the antenna.

1H 1H1V

1V2H

1HOverreach interference

Front-back interference

Microwave Frequency PlanningTwo-frequency system and quadruple-frequency system used

in microwave frequency planning:

For the 1+1 system or 2+0 system of the frequency diversity, the use of the two-frequency system can save the frequency resources, while the use of the quadruple-frequency system can decrease the internal and external interference and enhance the link quality. Whether to select the two-frequency system or the quadruple-frequency system depends on the interference within the planned microwave network system and the mutual interference between the microwave links to be established and the links existing in the system.

Case 1: When the link to be established interleaves with an existing one, the two-frequency system can be used for the former provided the same system is used for the existing link, and a different channel should be selected in this case.

Existing link

Link to be established

1,3

1,3

2,4

2,4

Microwave Frequency PlanningTwo-frequency system and quadruple-frequency system used in

microwave frequency planning:

Case 2: When the link to be established interleaves with an existing one, the quadruple-frequency system can be used for the former provided the same system is used for the existing link. In this case, the neighboring links should have different channels.

Existing link

Link to be established1,3

2,4

2,4

1,3

Case 3: When the link to be established has a branch, the quadruple-frequency system should also be used for this branch.

1,3

2,4

1,3

Microwave Frequency PlanningTwo-frequency system and quadruple-frequency system

used in microwave frequency planning:

Case 4: When the link to be established forms a loop-line with quite small angles, the quadruple-frequency system should be selected.

1,3

2,4

2,4

Case 5: When the routing deflection angles are too great, but the angles of La and Lb are quite small, for example, smaller than 15 degrees, comparatively great overreach interference may occur if the two-frequency system is selected for Site A and Site D. Therefore, the quadruple-frequency system should also be used in this case.

1,3

1,3

1,3

AB

C

D

2,4

La

Lb

Case 6: The quadruple-frequency system should also be selected in such circumstances as the front-back ratio difference of the antenna is smaller than 60dB, the SWR(Standing Wave Ratio) of the antenna feeder is large, and the equipment has weak immunity to interference.

Microwave Frequency PlanningSelection of proper frequency diversity channels:

When the microwave link is designed to adopt the frequency diversity protection, attention should be paid to the selection of channel spacing between the master channel and diversity channel. The formula to calculate the improvement in the frequency diversity is as follows:

where: frequency diversity improvement: frequency spacing between the master channel and diversity channel: Radio center frequency: flat fade margin: transmission section length

From the formula, we can find that the improvement in the frequency diversity is proportional to the channel spacing. Generally, the channel spacing should be at least 2 times of the radio frequency bandwidth. For a greater improvement in the diversity, the channel spacing should be as large as possible.

Case Study for Microwave Frequency Planning

Case study purpose: to be familiar with the preceding rules for microwave frequency

planning and apply them to practice.Project area: Mauritius in the Eastern Hemisphere and Southern Hemisphere

Requirement of the longitude

and latitude of the site:

Frequency resource: assigned by the user, 7G/28M: 2 chs; 8G/7M: 4 chs

Contents of planning:

● Channel

planning● High and low sites configuration

● Configuration of the polarization mode for the channel

GSM Network frequency planning in Mauritius:


Legend:

Complete the routing and capacity planning by referring to the

right map:

STM-1

8E1

4E1

New relay stations

Service hub

BTS


Proper channels of different bandwidths should be selected according to the capacity of

the microwave link and frequency resource the user owns.Frequency resource owned by the user:

Channel selection 1:

Channel No. Frequency Channel No. Frequency

1h

7610

1l 7442

3h

7666

3l 7498

7G: 7.4-7.7; number of channels: 2; channel spacing: 28 MHz


Proper channels of different bandwidths should be selected according to the capacity

of the microwave link and frequency resource the user owns.Frequency resource owned by the user:



Channel No. Frequency Channel No. Frequency

1h

8178

1l 79122

h8192

2l 7926



of the microwave link and frequency resource the user owns.Frequency resource owned by the user:



Channel No. Frequency Channel No. Frequency 1h

8178

1l 79122

h8185

2l 79193

h8192

3l 79264

h8199

4l 7933



of the microwave link and frequency resource the user owns.The following channels are selected according to the capacity of the link:


For STM-1, select f1 and f3 channels (7425-7725) with 28 MHz bandwidth.

For 8E1 PDH, select f1 and f2 channels (7900-8400) with 14 MHz bandwidth.

For 4E1 PDH, select f1, f2, f3, and f4 channels (7900-8400) with 7MHz bandwidth.


Implement the frequency planning in Pathloss by using the preceding rules flexibly.

Points to be noted in frequency planning:

Frequency planning in Pathloss:

1. All microwave sites must clearly mark the CALL SIGN, which cannot be the

same and will be used in the later interference calculation.

2. Two-frequency system. To prevent the co-channel interference, a site should

use different channels for multi-directions.

3. Deploy the sites in such a way as high sites and low ones alternate. Check the

interference calculation report to see whether this principle is observed.

4. Configure the sites with two polarization modes as required.


Example for frequency planning in Pathloss:


1. Access the PL4.0 program.

2. Log in to the network module.

3. Open the completed routing file.

4. Take the link between Site 5 and Site 21 for instance. Set the CH parameters

after setting the parameters for Radio and Antennas.

5. Click CH. The TX Channels dialog box is displayed, as shown in the next page.


Click CH. The TX

Channels dialog box

is displayed, as

shown in the figure

on the right side :



Click Lookup. In

the File dialog box

that is displayed,

click Open and

select the

corresponding

frequency planning

file from Freqplan,

as shown in the

figure on the right

side.



Open the target

frequency planning

file, as shown in

the figure on the

right side :



SDH adopts the hot

backup system. Select

f1 channel with 7 GHz

bandwidth as required,

and then select the

proper frequency for

use, site 1 as the high

site, and the vertical

polarization mode

before returning to the

previous page and

finally click OK, as

shown in the figure on

the right side :



According to the

two-frequency

system, the

frequency planning

for the SDH

backbone ring is

completed, as

shown in the figure

on the right side:



According to the two-frequency

system, the frequency planning

for the SDH backbone ring is

completed, as shown in the

figure on the right side.

Note that a site (Site 5) in the

ring has both high and low

stations due to the odd number

of the BTSs. In frequency

planning processes, this

should be avoided.


3l 7498 H 7666 3h

3l 7498 V 7666 3h1h 7610 V 7442 1l

3h 7666 H 7498 3l

1l 7442 V 7610 1h

1h 7610 H 7442 1l

3h 7666 V 7498 3l

Site 5/2

Site 21/1

Site 25/1

Site 44/1

Site 35/1

ADD1

ADD2


Statistics about the

frequency planning

for the SDH

backbone ring:


Site Name 1 Site Name 2Frequency/Polarization

Mode

Site 5 (high) Site 21 (low) 1/V

Site 21 (low) Site 35 (high) 3/V

Site 35 (high) Site 44 (low) 1/H

Site 44 (low) Site 25 (high) 3/H

Site 25 (high) ADD 2 (low) 1/V

ADD 2 (low) ADD 1 (high) 3/V

ADD 1 (high) Site 5 (low) 3/H


Take Site 21 for

instance. In Pathloss,

implement the

frequency planning for

the link of 8E1. Select

the 1+1 hot backup

mode, f1 channel in 8

GHz bandwidth, and

vertical polarization,

as shown in the figure

on the right side:



Take Site 21 for

instance. The result

of the frequency

planning for the link

of 8E1 is shown in

the figure on the

right side:


8E1 frequency configuration


Take Site 21 for

instance. The result

of the frequency

planning for the link

of 4E1 is shown in

the figure on the

right side:



The 2-hop SDH link, 1-hop 8E1 link,

and 3-hop 4E1 link converge at Site

21. As 4E1 has quite a few links, try

to select different channels in the

direction of 8E1 links to reduce the

interference. In this case, f1, f3, and

f4 channels with 8 GHz bandwidth

are selected and a different

polarization mode is adopted. The

statistics about the frequency

planning for Site 21 are listed in the

table on the right side:


Site

Names 1

Site

Names 2

Equipment Planned

Frequency

T R

Site 21

(low)

Site 8

(high)

4E1 4H 7933 8199

Site 21

(low)

Site 38

(high)

4E1 3V 7926 8192

Site 21

(low)

Site 39

(high)

4E1 1H 7912 8178


The result of the

frequency

planning for Site

21 is shown in

the figure on the

right side:


Site 5

Site 21

Site 351h 7610 V 7442 1l 3l 7498 V 7666 3h

3h 8192 V 7926 3l

1h 8178 V 7912 1l 8E1-4PSK

1h 8178 H 7912 1l

4h 8199 H 7933 4l

Site 8

Site 38

Site 39


The reference result of

the frequency planning

is shown in figure on

the right side.


Note:

H---F1 V---L

H/L indicates the high/low site.

F1 indicates the SDH frequency; f1 indicates the PDH frequency; V indicates the polarization mode.


Complete all frequency planning for the microwave network according to

the relevant principles and output the design result. The frequency

configuration in the software will be used for the future interference

analysis.


Mw frequency planning

Technology

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