Digital Microwave Radio Transceiver
Coding, Modulation and Synchronization for Digital Microwave Radio Transceivers for the UMTS Backbone Network
A Feasibility Study on Digital Microwave Radio Transceivers
The ever increasing demand on capacity of mobile Networks (e.g. GSM, IS95, UMTS) also encroaches on the connection of the specific basestations with the core network.
The project therefore focused on the development of an digital microwave radio transceiver, halving its channel bandwidth (channel spacing).
By doing so and with constant transmission capacity (e.g. 155.52Mbit/s),
the bandwith efficiency of the system was doubled.
A a main task of the project was to apply an appropriate coding and modulation scheme
supporting those bandwidth efficiencies.
Another crucial task in every digital receiver implementation is the synchronization, meaning the estimation and compensation of the relevant channel parameters. The concept of estimating those parameters and then using them as if they were the true values is called synchronized detection and is used in virtually every digital receiver implementation. In our case, the necessary channel parameters need to be estimated and tracked throughout the transmission very robustly, because referring to the standards, each day approximately only one biterror may occur .
Issues analyzed throughout the project are
- examination of appropriate inner coding/modulation scheme
trellis coded modulation (TCM)
bit interleaved coded modulation (BICM)
- examination of appropriate outer coding schemes
- constellation shaping schemes
- equalization of the Rummler channel,
- development of a robust phase noise tracking scheme
compensation for time varying operating points
- sampling clock tracking
- frame synchronization
- frequency offset tracking
- floating point model conversion of parts of the transceiver to
a fixpiont representation & design methodology
The results of the project have been highly benefitial for our industrial partner.
An ASIC implementation of the digital portion of the transceiver has been implemented
and meets the very stringent requirements of the ETSI standards.
Volker Simon, Andreas Senst, Meik Dörpinghaus