SDH technology is not limited to use as a transmission medium, only the fiber-optic cable (FOC) . Also, widespread use of radio for the organization of radio relay line SDH networks. Relay channels have great promise for replacing relay RDN systems, the possibility of more effective interaction with the existing SDH systems, optimization of networks SDH circuits in the complex for laying FOC areas of organization of alternative SDH signal transduction pathways and backup of the existing fiber-optic SDH lines.
RRL manufacturers
Alcatel:
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Microwave radio relay system SDH "96xx", including the following modifications:
- LH - STM-1 level system with long inter-station sections;
- UH - STM-1 level system for work in urban conditions;
- LM - OC-1 level system for working with access networks;
- UM - OC-1 level system for urban operation.
- Transport radio relay system "9667 TH" of STM-1 level;
ECI: SDH "SDH-Radio" radio relay systems of STM-1 and STM-4 levels;
NEC: radio relay system for transmitting SDH signals of STM-1 level or PDH E4 signals.
STM-0
Trunk SDH RRL until recently used the STM-1 level. If it was necessary to provide a large capacity, N STM-1 channels were used. Recently, in connection with the adoption of new versions of ITU-T G.7xx recommendations, it became possible to use the zero SDH level - STM-0 (corresponding to the SONET OS-1 level). It is better known not as a new layer of SDH, but as a special STM-RR format of the STM synchronous transport module with a transmission rate of 51.840 Mbps, which cannot be used on the interfaces of SDH cable network nodes.
Multiplexing scheme when forming STM-RR
VC - virtual container
TU - tributary unit
TUG - tributary unit group
AU - administrative block
Transition diagram from STM-RR module to STM-1 module
Transition diagram from STM-RR module to STM-1 module
Types of radio relay stations
Terminal station (OC), are intended for inputting a multi-channel signal into the RRL on the transmitting side and for extracting this signal on the receiving side.
Terminal station RRL
An intermediate station (SS) is designed to receive signals from the previous station, amplify and transmit them in the direction of the next station. The connection on the SS between the transmitter and the receiver is carried out over an intermediate frequency, i.e. without signal demodulation in the receiver and without modulation in the transmitter
RRL intermediate station
Node stations (CS) are intended to allocate part of the TLF channels and introduce an appropriate number of new channels. New RRL (branch lines) often originate from the US. Signals are demodulated from the receiving side and modulated from the transmitting side in the TLF trunks on the US.
RRL junction station
RRL classification
Two types of RRL: line of sight and tropospheric.
- By appointment: intercity trunk, intrazonal, local radio relay lines.
- By frequency range: frequency bands are allocated in the 2, 4, 6, 8, 11 and 13 GHz regions. Research is underway to create an RRL at frequencies of 18 GHz and higher. But at HF the signal is greatly attenuated in precipitation.
- By the method of compaction and type of modulation: with FDC, with FDC and analog pulse modulation, digital radio relay links.
- In terms of throughput: high-capacity radio relay links (more than 100 Mbit/s), medium capacity for zone communication-60... 300 k. (10-100 Mbit/s), small capacity for local and departmental communications. Multiple barrels are used to increase throughput.
Modulation methods
- In analog PPC, FM is almost always used
- With AM and SSB, it is more difficult to deal with distortions caused by nonlinearity of the AX and lower noise immunity to thermal noise.
- In digital radio relay lines with an average bandwidth, relative phase shift keying (OFM) is used, the phase difference of two adjacent radio pulses is encoded.
- Frequency shift keying changes the radio pulse frequency. Binary FM and AM are used in RRL with low bandwidth.
- Application of AFM provides high bandwidth efficiency. AFM-16 and OFM-4 for high-capacity TsRRL.
RRL reservation
- In order to increase the reliability of the communication line, various redundancy methods are used. In the frequency ranges above 10 GHz, 1 + 1 redundancy systems are most widely used in the RRL, when there is one reserve barrel per working barrel.
- In difficult conditions of radio wave propagation, both trunks can be used to organize diversity reception, which significantly improves the stability of the communication system.
- Often, simple single-barreled communication systems are built without redundancy, given the high reliability of modern equipment. For example, the MTBF of the MINI - LINK E type CRRL equipment of the Swedish company ERICSSON reaches (according to the advertisement) 20 - 30 years.
Frequency bands
- Uses the decimeter and centimeter wave ranges where a wide frequency band (30 GHz) can be obtained and where atmospheric and industrial interference is almost completely absent.
- For RRL, two frequencies can be used if the antennas with a narrow radiation pattern (SMB) have a path in the form of a broken line.
- For lower frequencies a four-frequency plan is used, for forward and reverse directions select different pairs of frequencies.
- Frequency bands are allocated for tropospheric radio relay lines in ranges 1; 2 and 4.5 GHz. Capacity up to 120 PM channels, distance 300 ... 400, in some cases up to 600 ... 800 km.
