OFDM communications system

A method of communication between one or more base stations and a plurality of terminals served by one or more base stations and in which information from the base station(s) is transported to the terminals in the form of symbols in an orthogonal frequency division multiplexed (OFDM) format, the method comprising:

• at each terminal, measuring a channel dispersion associated with multipath signal reception for that terminal and reporting that dispersion measure to the base station, and, at the base station(s), providing for a group of terminals respective symbol and prefix lengths on the basis of the dispersion measurement of that group of terminals.

A method of communication between peers of a communication network such that that transmitter and receiver are both mobile terminals disposed in respective ad-hoc networks, in which the terminals are arranged to perform channel dispersion measurements, the method comprising:

• at each terminal, measuring a channel dispersion associated with multipath signal reception for that terminal, and providing for a group of terminals of similar dispersion measurement respective symbol and prefix lengths on the basis of the dispersion measurement of that group of terminals.

A method of communication between a base station and a set of terminals such that a subset or all of the terminals have formed an ad-hoc network and the same or a different subset are also in communications with one or more base stations, the method comprising:

• at each terminal, measuring a channel dispersion associated with multipath signal reception for that terminal and reporting that dispersion measure to the base station, and, at the base station(s), providing for a group of terminals respective symbol and prefix lengths on the basis of the dispersion measurement of that group of terminals.

A communications system comprising a base station, and a plurality of terminals served by that base station, in which information from the base station is transported to the terminals in the form of symbols in an orthogonal frequency division multiplexed format, in which each terminal has means for measuring a channel dispersion corresponding to multipath signal reception for that terminal and for reporting that dispersion measure to the base station, and, in which the base station is arranged to provide, for a group of terminals respective symbol and prefix lengths on the basis of the dispersion measurement of that group of terminals.

A communications system comprising one or more base stations, and a plurality of terminals served by that one or more base stations, and wherein some of the terminals have formed an ad-hoc network in which information from the base station or other transmitting terminals is transported to the terminals in the form of symbols in an orthogonal frequency division multiplexed format, in which each terminal has means for measuring a channel dispersion and channel phase stability corresponding to multipath signal reception for that terminal and for reporting that dispersion and phase variation measure to the base station or transmitting terminal, and, in which the base station or transmitting terminal is arranged to provide, for a group of terminals respective symbol and prefix lengths on the basis of the dispersion and phase stability measurement of that group of terminals.

A base station for use in a communications system in which information from the base station is transported to the terminals in the form of symbols in an orthogonal frequency division multiplexed format, the base station comprising;

• means for receiving channel dispersion measurements and rate of channel phase variations from terminals served by the base station, and means for providing, for groups of terminals having similar channel dispersion and phase variations, respective symbol and prefix lengths on the basis of the dispersion and phase variation measurements of that group of terminals.

A method of operating a base station in an OFDM (orthogonal frequency division multiplex) communication system comprising a plurality of terminals, some of which may form an ad-hoc network, the method comprising the steps of:

• receiving an indication of channel dispersion and channel phase change rates associated with each terminal;
• and
• for groups of terminals having similar channel dispersion and phase change rate, generating respective symbol and prefix lengths on the basis of the dispersion measurements of that group of terminals.

An OFDM (orthogonal frequency division multiplex) communications signal for use on a channel between a base station and a terminal, said signal comprising a plurality of symbols each having a prefix, and wherein the symbol and prefix lengths are adjusted on the basis of an indication of channel dispersion and the phase stability on that channel.