Features of the SDH line of microwave systems

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.

Manufacturers MRR


  1. Microwave radio relay system SDH «96xx», which includes the following modifications:
    1. LH - system level STM-1 with long inter-station sections;
    2. UH - system level STM-1 for use in an urban environment;
    3. LM - system level OC-1 for use with the access networks;
    4. UM - system level OC-1 for use in urban environments.
  2. The transport relay system "9667 TH» STM-1 level;

ECI: radio-relay systems SDH «SDH-Radio» level STM-1 and STM-4;

NEC: SDH radio relay signaling system level STM-1 signals or PDH E4.


Backbone SDH radio relay link until recently used the STM-1 level. When the need to ensure a large capacity used N STM-1 channels. In posledneevremya in connection with the adoption of new versions of the recommendations of the ITU-T G.7xx an opportunity to use the zero level of SDH - STM-0 (corresponding to the level SONET OC-1). It is no longer known as a new SDH levels, and as a special format of STM-RR synchronous transport module STM transmission rate from 51.840 Mbit / s, which can not be used on cable interfaces SDH network nodes.

Multiplexing scheme when forming SТМ-RR

VC - virtual container
TU - tributary unit
TUG - tributary unit group
AU - an administrative unit

Scheme transition from STM-RR module to module STM-1

Scheme transition from STM-RR module to module STM-1

Types of radio relay stations

Terminal station (OC), intended to enter the MRR multichannel signal on the transmission side and the signal separation on the receiving side.

Terminal station MRR

Intermediate station is designed to receive signals from a previous station, amplify and transmit them towards the next station. The connection at the substation between the transmitter and receiver is carried out at an intermediate frequency, ie, without demodulating the signal in the receiver and no modulation at the transmitter

Intermediate station MRR

Nodal station are designed to extract part of the STA channels and the introduction of a corresponding number of new channels. From CSS often originate new MRR (branch line). The STA trunks on CSS produced demodulation signal from the reception and modulation by the transmission.

Nodal station MRR

Classification of MRR

Two types of radio relay: line of sight and troposphere.

  • By appointment: long-distance backbone, intra-local RRL.
  • Over a range of frequencies allocated bandwidth in the 2, 4, 6, 8, 11 and 13 GHz. Studies are under way to establish radio relay at frequencies of 18 GHz or higher. But on the RF signal is strongly attenuated in the sediments.
  • By the method of sealing and modulation mind: FDM, TDM and analog pulse modulation, digital radio relay.
  • On capacity: RRL ёmkosti- large (more than 100 Mbit / s), medium capacity for zonal-60 ... to 300 (10-100 Mbit / s), low capacity for local and departmental communication.. Use multiple trunks to increase capacity.

Modulation techniques

  • The analog MRR is almost always used the World Cup
  • When AM and single sideband modulation is more difficult to deal with the distortions caused by the nonlinearity of Arts and lower noise immunity to thermal noise.
  • In digital radio relay link to the average bandwidth used Differential Phase Shift Keying (RPM), the phase difference is encoded by two adjacent radio pulses.
  • When FSK changes frequency radioimulsov. Binary FM and AM are used in radio relay with a low bandwidth.
  • Use of AFM provides high bandwidth efficiency. For DRRL high bandwidth AFM 16 and RPM-4.

Reservations MRR

  • In order to increase the reliability of the link works are various ways redundancy. In the frequency bands above 10 GHz DRRL most common are Redundancy 1 + 1, when you have one backup per working trunk.
  • The complex propagation conditions, both the trunk can be used to organize the diversity significantly improves stability of the communication system.
  • Often simple Single-barrel built communication systems without redundancy, considering the high reliability of modern equipment. For example, MTBF DRRL type MINI equipment - LINK E ERICSSON Swedish company reaches (according to advertising) 20 - 30 years.

Frequency Bands

  • Use ranges UHF and santimetr- ovyh waves, where you can get a wide frequency band (30GGts) and where almost no atmospheric and industrial noise.
  • For RRL can use two frequencies when the antenna with a narrow radiation pattern (CMB) circuit as a broken line.
  • For lower frequencies using the four-channel plan for the forward and reverse direction is selected different frequency pairs.
  • For tropospheric RRL allocated frequency bands in the range 1; 2 and 4.5 GHz. Throughput of up to 120 frequency channels, distance 300 ... 400, in some cases up to 600 ... 800 km.
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