Iterative Multiuser Detection for DS-CDMA/MC-CDMA Powerline Communications

The increasing ubiquity of the Internet is creating a rapidly growing demand for larger bandwidth to the home. Currently the narrowband twisted-pair access network from an optical network unit (ONU) or a central office (CO) to a customer’s premises, the socalled “last dirty mile”, is the bottleneck for Internet traffic. The increasing demand for a home/office network further necessitates a flexible broadband network access. Electric power lines, which can be found in essentially all buildings and residences, naturally exhibit potential as a convenient and cheap communication alternative. Also, in rural areas where services from telephone companies or cable companies do not reach, and where radio coverage is poor or very expensive through one-way satellite access, communication through power lines may be the only feasible solution. As to home networking, the powerline is inherently the most attractive medium due to its universal existence in homes, the ubiquity of outlets, and the simplicity of the power plug. In comparison, the phone line/cable suffers from too few connection points, and wireless suffers from congestion and interference in the unlicensed bands. Even though powerline communications is an attractive substitute for broadband Internet access for the last mile and in-home/office networking, many difficulties and challenges exist, as power lines were not originally intended or designed for data communications [1]. To facilitate reliable high-speed communications over low-voltage (LV) power distribution networks, advanced signal processing techniques should be pursued to combat the adverse environment. The dominant sources of impairment for powerline communications are time-varying channel attenuation, multipath frequency-selective fading, multiple-access interference, and impulse noise. These phenomena naturally remind us of the similar impairments and corresponding mitigating techniques used in digital subscriber line (DSL) and wireless communications. Given the similarities among DSL, wireless and powerline channels, techniques developed for the first two types of channels are natural candidates for application in powerline communications. In this study we consider such application. We adopt DSCDMA and MC-CDMA as modulation and multipleaccess methods, based on which powerline communication model is under consideration (see Section II). On forming a serially concatenated system at the transmitter through introducing an interleaver between coding and modulation modules, multiuser detection and turbo decoding are used at the receiver for data detection and decoding, further details of which are given in Section III. Some numerical results are given in Section IV to demonstrate the performance of the proposed signal processing techniques, in comparison with traditional ones. Finally, Section V concludes the paper.