Cambridge Broadband Networks Limited

Adaptive Broadband Corporation

Malcolm Paul Sellars

John David Porter

Stephen David Greaves

In a fixed wireless access (FWA) communications system comprising an Access Point () and a plurality of Subscriber Units (---N) each Subscriber Unit transmits a concentration word when it wishes to obtain access to transmit data. Each Subscriber Unit () includes a linear precoder () which predistorts the contention word to compensate for the impulse response of the transmission channel between it and Access Point (). The precoder () is optimized specifically for the contention word to be transmitted instead of for general data.

Predistorting of contention signals

A fixed wireless access communications system comprises an access point and a plurality of subscriber units. Each subscriber unit () contends for access to a communications channel to the access point by transmitting a contention word to the access point during a contention time slot. The contention word is predistorted to compensate for the channel impulse response of the transmission channel so that the access point can decode the contention words without using equalisation. A control unit (), which may comprise a microprocessor, loads the predistorted contention word (a) into a memory () and causes the stored predistorted contention word (a) to be applied to a transmitter () during a contention time slot when the subscriber unit () wishes to request a transmission channel to transmit data to the access point.

Precoding of contention words in a fixed wireless access system

A precoding scheme for digital data transmission across multipath channels is described, which improves on existing methods of precoder stability. This precoding scheme uses radial reduction of unstable roots to stabilize the precoder. Furthermore, in a broadband access system in which the preceding scheme is used, all of the precoding and equalization is performed in the subscriber units. This eliminates the problems of equalization and training delays occuring at the base station, thus allowing rapid demodulation of data arriving at the base station for several disparate subscriber terminals units.

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Ely, United Kingdom

Malcolm Paul Sellars