Transmit Diversity

To enhance system performance, the DRM+ channel coding offers the possibility to take advantage of the channel diversity. With frequencies around 100 MHz and slow receiver velocities however the diversity offered by the channel is not enough. Destructive interferences can produce channel attenuation over the whole signal bandwidth for a time period which exceeds the ability of the interleaver and the Viterbi decoder to recover the data. A possibility to avoid this is the implementation of transmitter delay diversity via an additional antenna which transmits the same signal with a delay of some sample times.

 

As delay diversity improves the performance significantly in the Rayleigh fading channel, for line-of-sight propagation it yields to performance loss. With soft delay diversity the power distribution between the multiple transmit antennas can be varied according to the propagation properties.

Transmit diversity has thus the following advantages:

  • Reduction of fading
  • Improved reception in urban and peripheral areas
  • Increased indoor reception