In digital microwave concept ready introduces to frequency band in the microwave spectrum. This post continues to show Frequency Band Choice and RF Channel Arrangements in Microwave.
Frequency bands frequently used in microwave transmission include 7G/8G/11G/13G/15G/18G/23G/26G/32G/38G (defined by Rec. ITU-R). Each frequency band is used as follows:
Radio resources are restricted by the administrations but the optical cable is not. Microwave frequency needs to be applied for but it does not need to be applied for in a certain period. In the past, 1.8G and 2.4G are used as spreading frequencies such as microwave oven, Bluetooth. 1.8 G and 2.4 G can be transmitted in the noise, but now the interference is too heavy and 2.4 G cannot be randomly used.
In each frequency band, various frequency ranges, transmitting and receiving (T/R) spacing and channel spacing are defined. The channel spacing is equal to channel bandwidth. In using a certain frequency band, there are specifications for the center frequency, T/R spacing and channel spacing. And the specification can be looked up in relevant frequency specifications.
After deciding the microwave frequency band, configure the RF channels. To configure RF channels is to subdivide the specific frequency band, to make the bands adapt to frequency spectrum that the transmitter needs. Those subdivided frequency bands are called “channel”. Normally, any channel is expressed by the center frequency it is configured and an ordinal number. The width of the channel is decided by the spectrum of the signals transmitted, that is, the capacity and the modulation mode adopted.
In configuring RF channel, following factors should be considered:
ITU-R F.746-3 “Radio-Frequency Channel Arrangements for Radio-Relay Systems” recommends that homogeneous patterns are preferred as the basis for radio-frequency channel arrangements. Normally, the basic channel spacing is 2.5 MHz and 3.5 MHz. Digital microwave systems that adopt such channel spacing support the bit rate of both North America and Europe. In the pattern of 3.5 MHz, it may be subdivided into 1.75 MHz spacing to meet the transmission requirement of 1E1 and 2E1 in the low capacity mobile coverage.
Also read Concepts of Digital Microwave in Wireless Communication
Frequency bands frequently used in microwave transmission include 7G/8G/11G/13G/15G/18G/23G/26G/32G/38G (defined by Rec. ITU-R). Each frequency band is used as follows:
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| The use of common frequency band |
- For long-distance PDH microwave circuit (more than 15 km), use 8 GHz frequency band. If the distance is not more than 25 km, use 11 GHz. Choose specific frequency band based on the local weather condition and microwave transmission cross section.
- For short-distance PDN microwave circuit (normally used in the access layer, within 10 km), consider using 11 GHz, 13 GHz, 14 GHz, 15 GHz and 18 GHz.
- For long-distance SDH microwave circuit (normally exceeding 15 km), use 5 GHz, 6 GHz, 7 GHz and 8 GHz. If the distance is not more than 20 km, consider using 11 GHz. Choose specific frequency band based on the local weather condition and microwave transmission cross section.
Radio resources are restricted by the administrations but the optical cable is not. Microwave frequency needs to be applied for but it does not need to be applied for in a certain period. In the past, 1.8G and 2.4G are used as spreading frequencies such as microwave oven, Bluetooth. 1.8 G and 2.4 G can be transmitted in the noise, but now the interference is too heavy and 2.4 G cannot be randomly used.
In each frequency band, various frequency ranges, transmitting and receiving (T/R) spacing and channel spacing are defined. The channel spacing is equal to channel bandwidth. In using a certain frequency band, there are specifications for the center frequency, T/R spacing and channel spacing. And the specification can be looked up in relevant frequency specifications.
Concepts of microwave frequency band arrangements
After deciding the microwave frequency band, configure the RF channels. To configure RF channels is to subdivide the specific frequency band, to make the bands adapt to frequency spectrum that the transmitter needs. Those subdivided frequency bands are called “channel”. Normally, any channel is expressed by the center frequency it is configured and an ordinal number. The width of the channel is decided by the spectrum of the signals transmitted, that is, the capacity and the modulation mode adopted.
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| Simple concepts of microwave frequency band arrangements |
In configuring RF channel, following factors should be considered:
- Utmost economy and efficiency of the RF frequency
- Enough spacing between transmitting frequency and receiving frequency in a microwave station to avoid serious interference generated by transmitter to receiver
- In multi-channel working system, adjacent channels must have enough frequency spacing to avoid interference generated by each other
- Enough guard bands should be reserved at the edge of the distributed frequency band to avoid generating interference with the system working on the adjacent frequency band
- Most RF channel arrangements are based on the homogeneous patterns
ITU-R F.746-3 “Radio-Frequency Channel Arrangements for Radio-Relay Systems” recommends that homogeneous patterns are preferred as the basis for radio-frequency channel arrangements. Normally, the basic channel spacing is 2.5 MHz and 3.5 MHz. Digital microwave systems that adopt such channel spacing support the bit rate of both North America and Europe. In the pattern of 3.5 MHz, it may be subdivided into 1.75 MHz spacing to meet the transmission requirement of 1E1 and 2E1 in the low capacity mobile coverage.
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