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Current state-of-the-art

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Information on the current state-of-the-art

Currently the main area of application of microwave links is “the last mile” and for distances of up to a maximum of around 20 km. For this the telecommunications industry provides customised equipment for almost every individual application. The equipment is compact, practically maintenance-free, extremely reliable, and can be installed almost anywhere without high construction costs. Above all, as an alternative to expensive leased lines, microwave links are unbeatable from the cost point of view too.

Until recently, microwave links were considered to belong to either the PDH or the SDH versions of the multiplex process. This method of differentiation, however, is no longer valid. Nowadays the user can as a rule adjust the transmission capacity by changing the RF-bandwidth and modulation scheme through software settings.
On the local side various interfaces of n x E1 up to STM1 or Ethernet with varying data transmission rates are available, which can be flexibly allocated to the proprietary base band on the radio side via an integrated electronic switching matrix (multiplexer) by mouse click.

The scope of the currently common microwave link transmission capacity extends from 8 to 155 Mbit/s per system. In several frequency bands there are in addition RF-channels with 56 MHz bandwidth available. With XPIC, up to 1000 Mbit/s can be transmitted to both of the polarisation planes of a frequency channel of this type (CCDP = co-channel dual polarized).

Above all, in developed countries unallocated microwave frequencies are becoming rarer. To use the limited frequency resources as efficiently as possible, modern microwave link systems have an Automatic Transmit Power Control (ATPC). In this way one and the same frequency can be used in a particular geographical area a far greater number of times than would be possible without ATPC.
Another possibility of the efficient use of the limited number of frequencies is the use of highly complex modulation scheme. In microwave link transmission the
Quadrature Amplitude Modulation with 16 to 1024 symbols has become common. A further major technological advance is Adaptive Modulation, which will play a major role in Ethernet transmission systems. In this case microwave link systems with both Ethernet and E1-interfaces are currently available.

For expanding please click on the images

The indoor unit of this transmission system is characterised by remarkable compactness and high complexity (Huawei). The displayed sub rack covers 2 units of height only and is equipped with IF-boards for two SDH-links and one hybrid link (≈ 120 Mbit/s) plus interface boards for 6 x Ethernet (thereof 2 x GigE) and 16 x E1. The alternative assembly with STM1-interfaces is possible as well. Furthermore this system includes two redundant configured power modules and one add-drop-multiplexer to interconnect the entire traffic.
The indoor unit of this microwave link system with XPIC is remarkable compact designed (SIAE microelettronica). It is able to transmit 4 x STM1, needs 1 unit of height only and is characterised by low power consumption.
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