A Proposal of Received Response Code Sequence in DS/UWB

Abstract

The demand for a large capacity, high-reliability and high-quality has recently increased in communication systems such as wireless LAN. As a system for this demand, Spread Spectrum (SS) system and Orthogonal Frequency Division Multiplexing (OFDM) system have been studied [1], [2]. Various communication systems are used by the usage for a wireless communication and Ultra Wideband (UWB) has attracted much attention as an indoor short range high-speed wireless communication in the next-generation. Frequency band used of UWB communication is larger than that of a conventional SS communication, and the UWB communication system has high-speed transmission rate [3], [4]. UWB communication has high resolution for multipath to use nano-order pulses, assuming a lot of paths delayed by walls and obstacles in an indoor environment. Furthermore, due to a long delay-path exists, it has known to cause Inter-Symbol Interference (ISI) that influences a next demodulated signal, and the performance of receiver is degraded. In UWB communications, there is a DS/UWB system applied Direct Sequence (DS) method as one of SS modulated methods. When a binary sequence such as M sequence is adopted as a code sequence, its sequence may cause complicated ISI by a multipath environment. Then, to improve Signal-to-Noise Ratio (SNR), a selective RAKE reception method is adopted at a receiver. A selective RAKE reception method can gather peaks of scattered various signals for one peak [5]-[7]. However, when an interference is too large by a multipath environment, it is difficult to gather receive energy efficiently. In this chapter, to resolve the ISI problem caused by a multipath environment, a novel Received Response (RR) sequence that has better properties than a M sequence is proposed, and its generation method is shown. The RR sequence is generated by using estimated channel information at a transmitter. Furthermore, the properties of the RR sequence are evaluated for the number of pulses of the RR sequence and the number of RAKE fingers in UWB system, and the effectiveness of RR sequence is shown. The main contents of this chapter are presented in the below Sections. The explanation of the DS/UWB system and the RR sequence is presented in Section 2. The explanation of the generation method of the RR sequence will be explained in Section 3. In Section 4, simulation conditions and results are shown and discussed. Conclusion of this chapter is presented in Section 5. Refferences are added in Section 6.