Code Selected M-ary DS-BPAM UWB Communication System Zhiquan Bai 1,2 , Dongfeng Yuan 2 , Senior Member, IEEE, Yingji Zhong 1 , Hohwan Park 1 and Kyungsup Kwak 1 , Member, IEEE 1 UWB Wireless Communications Research Center (INHA UWB-ITRC), Graduate School of Information Technology and Telecommunications, Inha University, Incheon, Korea 2 School of Information Science and Engineering, Shandong University, Jinan, Shandong, P.R. China Abstract—In this paper, a novel code selected M-ary direct sequence ultra wideband communication system is introduced. The objective is to get a high data rate UWB system by using the M-ary coded selected direct sequence bipolar pulse amplitude modulation (MCSDS-BPAM) scheme. In this system, a particular DS code sequence can be selected by the log 2 (M/2) bits from the DS code set. This scheme can obtain high data rate without increasing the system bandwidth or changing the pulse shape. With the increase of the modulation level M, the system bit error rate (BER) will be improved for the same signal energy per bit. The simulation results are provided in the condition of AWGN channel and correlation receivers. ∗ Keywords—Direct sequence spread spectrum (DSSS), Ultra wideband (UWB), Bipolar Pulse amplitude modulation (BPAM) I. INTRODUCTION Ultra Wideband time-hopping spread spectrum communication system had been proposed in [1] [2]. In UWB system, data bit is transmitted using sub-nanosecond baseband pulses without the need for mixers, and the occupied frequency band is from near direct current to several gigahertzes. UWB technology has attracted much attention in indoor high rate communications for its significant characteristics. Because of the large bandwidth, UWB technology can achieve high throughput and is robust to co-channel interference and narrowband jammers and has a greater ability in realizing spectrum sharing. High capacity can be achieved with much lower transmission power levels. In the modern wireless communications, high data rate and high transmission quality are the two key system requirements. In this paper, without changing the pulse shape and the transmission bandwidth, a new M-ary bipolar pulse amplitude modulation (BPAM) scheme based on the selection of direct sequence code is proposed, which can achieve a higher data rate compared with traditional DS-BPAM UWB system. This proposed scheme can additionally transmit 2 log 2 M data bits by selecting one of the 2 M DS codes. In This research was supported by University IT Research Center Project (INHA UWB-ITRC) of Korea and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry the Fund of Chinese Ministry of Education the receiver end, the transmitted signal is detected by using 2 M correlators and the template signals of the receiver are generated according to the 2 M DS codes. Hence, the receiver complexity will be increased by a factor 2 log 2 M compared to the conventional DS-BPAM system. After doing the correlation, we select the maximum value of the correlator outputs to get the selected coded sequence and then the additional data bits can be obtained. The commonly used M-ary modulation scheme in UWB system is M-ary PPM which is proposed in [5]. In this modulation format, M-ary PPM is used to transmit 2 log M data bits, such that the data rate is improved at the expense of bandwidth expansion and the receiver is composed of M correlators. M-ary Biorthogonal pulse shape modulation (BPSM) for UWB system is introduced in [4][6]. This method can be seen as another M-ary modulation UWB system constituted by the selection of biorthogonal pulse shapes. These two M-ary modulation schemes increase the system complexity or the bandwidth expansion. Compared with the above M-ary schemes, the proposed MCSDS-BPAM scheme does neither expand the transmission bandwidth nor change the pulse shape. The proposed scheme can achieve better performance than the conventional DS-BPAM with the feasible improvement of the system complexity under higher modulation level M. The organization of this paper is as follows. In Section II, an overview of the proposed M-ary code-selected DS UWB system using bipolar pulse amplitude modulation is provided and the performance evaluation algorithm is given. Section III obtains the simulation results and gives interpretations. Finally, conclusions are presented in Section IV. II. PROPOSED MCSDS-BPAM UWB SYSTEM In this section, we present the MCSDS-BPAM modulation scheme as shown in Fig.1. Here, we will consider a DS code set composed of { } 0 1 21 , ,..., M − c c c , where ( ) { } ,0 ,0 , 1 , ,..., c l l l l N c c c − = c . While one bit is transmitted using BPAM, additional 2 log 2 M data bits select a particular DS code sequence from the DS code set. Compared with the DS-BPAM UWB system, we can increase the data rate by a factor of ( ) 2 1 log 2 M + . Assuming the data rate of the ISBN 978-89-5519-136-3 -883- Feb. 17-20, 2008 ICACT 2008