Adaptive Zero-Padding OFDM over Frequency-Selective Multipath Channels
- PDF / 999,986 Bytes
- 11 Pages / 600 x 792 pts Page_size
- 82 Downloads / 185 Views
Adaptive Zero-Padding OFDM over Frequency-Selective Multipath Channels Neng Wang Department of Electrical and Computer Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6 Email: [email protected]
Steven D. Blostein Department of Electrical and Computer Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6 Email: [email protected] Received 28 February 2003; Revised 22 August 2003 We present a novel bandwidth (BW) efficient orthogonal frequency division multiplexing (OFDM) scheme with adaptive zeropadding (AZP-OFDM) for wireless transmission. Redundancy issues in OFDM based on cyclic prefix (CP), zero-padding (ZP), as well as no guard interval (NGI) systems are analyzed. A novel system design criterion based on the channel matrix condition is studied and applied to the design of an AZP-OFDM system. Simulation results have shown that the proposed AZP-OFDM offers performance similar to that of CP-OFDM, complexity similar to that of ZP-OFDM, with BW efficiency higher than that of both CP- and ZP-OFDM in channels with small to moderate delay spread. In channels with large delay spread, AZP scheme adaptively maintains high performance at the expense of BW efficiency. Essentially, AZP-OFDM offers a more flexible tradeoff between symbol recovery, BW efficiency, and complexity. Keywords and phrases: bandwidth efficiency, cyclic prefix, equalization, multipath channels, orthogonal frequency division multiplexing (OFDM), zero-padding.
1.
INTRODUCTION
Orthogonal frequency division multiplexing (OFDM) has been receiving growing interest in recent years and has been adopted in many standards. For example, OFDM has been chosen as a solution for digital audio and video broadcasting (DAB and DVB) in Europe, and applied for high-speed digital subscriber line (DSL) modems over twisted pairs (ADSL, HDSL, and VDSL). Recently, it has also been proposed for digital cable television systems and adopted in new standards for wireless local area networks (wireless LAN) in North America (IEEE 802.11a), in Europe (HIPERLAN/2), and in Asia (MMAC) [1]. All standard OFDM systems are based on a cyclic prefix (CP) to eliminate interblock interference (IBI) between successive blocks. A CP of length no less than the channel order is inserted per transmitted block. Discarding the CP at the receiver not only suppresses IBI, but also converts the linear channel convolution into a circular one, which facilitates the diagonalization of the channel matrix, and makes single-tap equalization using scalar division possible [1]. An obvious problem in CP-OFDM systems is that the transmitted symbols cannot be recovered when some channel zeros
are located on subcarriers. Recently, it has been proposed in [1, 2] to replace CP insertion by zero-padding (ZP) at the end of the block of symbols to be transmitted. The padded zeros deterministically suppress the IBI but lead to a larger number of observed samples. That way, the transmitted symbols can always be retrieved regardless of the channel zero locations [1]. Note that since the number of zeros
Data Loading...
