AbstractsComputer Science

To enable high data rate target applications in a typical ultra-wideband (UWB) dense multipath channel, DS-UWB signaling suffers from a severe inter-symbol-interference (ISI) and multiple access interference (MAI). In an attempt to avoid complexity at the receiver, we tackle these problems from the transmitter side and consider ternary sequence based UWB (TS-UWB) signaling as a unifying descriptor of a number of impulse-based UWB schemes. We propose a technique which employs ternary complementary sets to improve the performance of orthogonal pulse based multi-channel UWB systems. By assigning mutually orthogonal (MO) complementary sets to the users, both MAI and multipath interference can be significantly suppressed. One of the major impediments to deploying such systems is a high peak-to-average power ratio (PAPR). We show that PAPR can be upper bounded by an autocorrelation merit function of column sequences of the corresponding complementary set matrix. Hence, we propose a design of complementary sets satisfying a column correlation constraint. The design algorithm recursively builds a collection of MO complementary set matrices starting from a companion pair of sequences. We relate correlation properties of column sequences to that of the companion pair and illustrate how to select an appropriate companion pair to ensure that a given column correlation constraint is satisfied. To support high-speed and multirate data services, we construct ternary orthogonal variable spreading factor (OVSF) code with a zero-correlation zone (ZCZ). Compared to the conventional Walsh code based OVSF code, the proposed ZCZ-OVSF code maintains its code orthogonality even in a multipath channel or when synchronism is lacking and, thus, is suitable for quasi-synchronous (QS) TS-UWB systems. We further propose an adaptive data rate transmission scheme which maximizes the uplink aggregate throughput of the system by allocating OVSF codes to the active users based on their signal to interference and noise ratios (SINR). Finally, we propose an adaptive transmission approach that suggests selecting a ternary beamforming sequence for a TS-UWB signal based on the signs of the reflection coefficients corresponding to a few strongest paths so that the signal energy at the output of the simple non-adaptive receiver is enhanced.