Non-optimal receiver for space time spreading across a Time Hopping over Ultra Wideband PPM

A novel non-optimal chip based technique is proposed to use two antennas to transmit data across a direct sequence time hopping ultra wideband dual antenna wireless communication system to a single receiver. The spread data is sent over the independent channels using the space time spreading technique to encode the chips which are sent on each antenna simultaneously. A hard decision is made at each chip of the spreading code received based on the known channel state information which pulse position modulated signal was received from each antenna. The paper shows that by adapting the space time spreading technique to use three pulse positions in a dual input single output system one can transmit data at a lower bit error rate for high Eb/No. Three receive techniques are considered; the use of the first arriving rays, the first set of useful arriving rays and the best set of arriving rays for each symbol period. The proposed receiver is less complex than that of the optimal system where a maximum ratio combiner is used across the entire spread signal space (per symbol rather than per chip), requiring more memory storage in the receiver. In addition, symbols are transmitted during the period of one symbol period for a single antenna system. This is achieved at the expense of a higher measured BER compared to single antenna systems.