Performance of impulse radio direct sequence ultra-wideband system with variable-length spreading sequences

An adaptive transmission scheme using variable-length spreading sequences (VLSS) is proposed. The system is based on an impulse direct sequence ultra-wideband (DS-UWB) approach for wireless communication where the number of active users is variable. In contrast to the conventional DS-UWB system, which employs a fixed length spreading code, the proposed system changes the length of spreading code according to the system load adaptively, which is proven to be able to reduce the inter-chip interference, inter-symbol interference and multiple-access interference and thus improve the system performance in terms of bit error rate. The proposed system is simulated in multipath channels with a high level of multipath fragments, modelled by the standard IEEE 802.15.3a indoor channel model 1 (CM1) and channel model 2 (CM2). Numerical results demonstrate that when RAKE receivers are employed, the proposed VLSS DS-UWB system outperforms the conventional system by appropriately allocating the spreading sequences.