University of Bristol

British Technology Group Limited

National Research Development Corporation

Unique Wireless Developments, L.l.c.

Peter Blakeborough Kenington

Joseph P McGeehan

Mark Anthony Beach

Andrew Bateman

Ross James Wilkinson

Andrew Robert Nix

Wycliffe Timothy Slingsby

Richard M Bennett

A Cartesian loop transmitter for transmitting baseband signals is disclosed. The disclosed Cartesian loop includes a forward path having a first input for receiving the baseband signals and a second input and a feedback path having an input from the forward path. The forward path including an upconverter to upconvert the input signals to a signal to be transmitted, an attenuator having selectable attenuation and a plurality of power amplifier stages. The feedback path including a pin diode attenuator having selectable attenuation and a downconverter to downconvert the input from the forward path. The feedback path provides an error signal indicative of the non-linearity of the forward path to the second input of the forward path.

Cartesian loop transmitter

A full-duplex radio transceiver, in which cancellation of transmission signals in the receive path is achieved by sampling the transmission signals, and controllably adjusting the gain and phase of the sampled signal, before subtracting the adjusted signal from the received signals in order to minimise the component of the transmission signals appearing in the received signals. Processing is done in a DSP at or near baseband.

Full-duplex radio transmitter/receiver

Image-reject mixers

A system for creating multiple subchannels in a single two-way radio channel and a power control system for a mobile radio transmitter are described. Each subchannel in the system is capable of carrying voice or data. Each subchannel is split into an upper and a lower band with the upper band placed in a particular frequency range above the center of the channel and the lower band is placed in a corresponding frequency range below the center of the channel. Either one or two pilot tones placed at or adjacent to the center of the channel are used to provide a reference for all of the subchannels to allow for correction of distortions when the signal is received. The system includes base station with a transmitter and receiver and a plurality of mobile units each with a transmitter and a receiver. The base station transmits a signal which is the sum of all the subchannels. The mobile unit receives the signal, separates and processes the particular subchannel for that mobile unit. The mobile unit transmits only the desired subchannel or subchannels with a pilot tone located adjacent to one of the bands of the subchannel. Two or more subchannels can be used in conjunction to achieve faster data rates or higher quality voice transmissions. The mobile transmitter power control system for the mobile transmitter allows the mobile unit to monitor the pilot tone from the base station and to calculate a transmission power based on a desired signal strength. Additionally, the transmission power may be altered during transmission as commanded by the base station, or if the mobile unit measures a change in the strength of the pilot tone from the base station.

Method and apparatus for creating multiple subchannels in a single

Method and apparatus for signal processing using reference signals

Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of the amplifier 4 by comparison in a subtractor 11 with its input and the error signal is combined in a coupler 17 with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by means of components 24 and 25 in a multi-channel input and in the error signal by means of components 13 and 14. These components receive control signals from feedback networks 18' and 20' which each process two of three input signals from: couplers 34, 36 before the subtractor 11, a coupler 22 which passes the error signal and a coupler 21 after the coupler 17. Preferably the two input signals used by a feedback network are used to form in-phase and quadrature signals by a 90.degree. phase shifter 41 and mixers 42 and 43. These signals are each amplified 46, 47 and integrated 48, 49 to provide the control signals. The input signals from the feedback networks may be reduced in frequency and applied to a DSP which then provides the control signals.

Apparatus and method for reducing distortion in amplification

Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of an amplifier by comparison in a subtractor with its input and the error signal is combined in a coupler with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by two groups of adjustment means, one group in a multi-channel input path and one group in the error signal path. These groups receive control signals from respective feedback networks which each process two of three input signals from: couplers before the subtractor, a coupler which passes the error signal and a coupler situated after the coupler which combines the amplifier output signal and the error signal. Preferably the two input signals used by a feedback network are used to form in-phase and quadrature signals using a 90.degree. phase shifter and two mixers. These signals are each amplified and integrated to provide the control signals. The input signals from the feedback networks may be reduced in frequency and applied to a DSP which then provides the control signals.

Growing community of inventors

Bristol, United Kingdom

Peter Blakeborough Kenington