Tim A. Wilkinson

Performance of Reed-Muller codes and a maximum-likelihood decoding algorithm for OFDM

The performance of Reed-Muller encoding and a maximum-likelihood decoding algorithm for orthogonal frequency-division multiplexing is presented. The example codes have a tightly bounded peak-to-mean envelope power ratio, while simultaneously enabling powerful error correction. We present a maximum-likelihood decoder that makes use of a distance-preserving map and multiple fast Hadamard transforms. Its operation is described in detail and its performance is assessed under realistic channel conditions.

On suitable codes for frame synchronisation in packet radio LANs

Standardisation bodies in Europe and North America are currently developing standards for high data rate packet radio LANs. Radio LANs will have two main applications: wired LAN replacement and ad-hoc networking. In contrast to wired LAN replacement, ad-hoc networks will operate without control from a central node. As a consequence, no central synchronisation is provided and nodes must have the capability of acquiring all synchronisation from a received packet. This synchronisation can be achieved by matched filtering synchronisation codes inserted into each data packet. This paper discusses these synchronisation requirements and outlines synchronisation sequence selection criteria.<<ETX>>

An experimental study of OFDM at 5.25 GHz in an office environment

Orthogonal frequency-division multiplexing (OFDM) has received considerable interest as a means for delivering broadband data in highly dispersive wireless channels. Here we present the design, implementation, and performance of an OFDM system operating at 5.25 GHz, which provides 20 Mbits/s in an office environment. From propagation measurements, we describe a design methodology for determining the key parameters of the OFDM system, such as the number of subcarriers and the size of the guard period. The performance of the system is evaluated using experimental data obtained from a typical large open-plan office. Using a transmit power of +7 dBm, the OFDM system is capable of operating in a highly cluttered environment, providing usable error rates up to a range of 20 m. The importance of error control coding is shown, and we empirically derive the degree of correctability required to achieve packet failure rates of <1% from the cumulative distribution of errors per packet.