A low‐complexity adaptive receiver for DS‐CDMA systems in unknown code delay environment

Abstract

In direct-sequence code division multiple access (DS/CDMA) multiuser communication systems in multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) must be considered. The multipath channel characterizes the propagation effects including the timing offset and delays, etc. Traditionally, we use the delay-locked loop (DLL) code tracking loop to recover the timing delay. But DLL cannot work well in multipath environment. In this paper, we propose a low-complexity adaptive receiver to suppress ISI/MAI and solve the timing offset problems without using conventional DLL code tracking loop. The proposed receiver employs an adaptive filter whose weights are adapted using a block least-mean square error algorithm with fractional sampling. Simulations confirm the good performance, including learning curves and theoretical analysis of minimum mean-square error, of the proposed receiver. Copyright (C) 2010 John Wiley & Sons, Ltd

Performance analyses of adaptive noncoherent receivers for MC‐CDMA communications

“…For Q-tap noncoherent receiver, from (9), the generation of qOEk requires Q 2 C Q multiplications (FrOEn requires Q 2 multiplications and w H OEkx requires Q multiplications). From (10 ) and (12), the generations of error signal and weight update require 1 and 3 multiplications, respectively. Therefore, the Q-tap noncoherent receiver totally requires about Q 2 C Q C 4 multiplications.…”

“…In addition, MC-CDMA capacity is limited by the intercarrier interference due to the use of multi-carrier modulation. Because the MC-CDMA systems involve the property of DS-CDMA schemes, the single-user detection techniques also need to be performed with some form of adaptation [3][4][5][6][7][8][9][10][11][12][13][14][15]. Besides, coherent receivers require exact knowledge of the channel phase for optimum performance.…”

Experimental Measurement of Fiber-Wireless Transmission via Multimode-Locked Solitons From a Ring Laser EDF Cavity

“…Mode-locked fiber lasers have been shown as the most inexpensive optical light sources for practical generation of ultrashort pulses, with actively harmonic mode-locked erbium-doped fiber (EDF) lasers capable of producing transform-limited narrow Gaussian pulses with adjustable multi-GHz bit rates and variable pulsewidths in the picosecond range. Such systems are especially suitable for high speed, long distance WDM transmission [15]- [18]. A main application of the multiple soliton transmission system containing ring laser EDF cavities is high-data rate transmission for short and long distance communication.…”

Multiple access interference and multipath interference analysis of orthogonal complementary code‐based ultra‐wideband systems over multipath channels

“…Typical low complexity direct‐sequence (DS) spread spectrum system design over multipath fading channels can be seen in , which aims to alleviate the influence of the multiple access interference (MAI) and multipath interference (MPI). In UWB system, MAI and MPI are also important factors that significantly affect the system performance over indoor and multi‐user environments .…”