Multicarrier TDD systems using channel state feedback information

In this paper we discuss transmission using orthogonal frequency division multiplexing (OFDM) in the context of a TDMA/TDD multiple access scheme based loosely around that used in the Digital European Cordless Communications (DECT) system. The DECT framework makes results more tangible, however the real aim of this work is to highlight novel OFDM techniques. All the proposed systems make use of only a small number of subchannels, the rationale behind this choice is discussed in detail in O´Neill and Lopes (1996) and is briefly reiterated in the present paper. We present three systems, all of which make use of channel state feedback information, which is readily available because of TDD and useful because relative speeds of motion are low in DECT. The first is targeted at improving speech quality by attempting to map speech vocoder output bits to subchannels based on significance. The second uses a reduced set of the available subchannels for transmission in a given timeslot, hence avoiding frequency selective fades and improving overall performance in both speech and data applications. The final system combines transmission on a reduced set of subchannels with base-station diversity