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differentiation, however, is no longer valid.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.
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
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
Quadrature Amplitude Modulation
with 16 to 1024 symbols
has become common. A further major technological advance is
which will play a major role in Ethernet transmission systems. In
this case microwave link systems with both Ethernet and E1-interfaces are