New techniques developed to improve wireless systems
Researchers, led by a team from the UK wireless company Rinicom, have succeeded in improving advanced signal processing and coding techniques to boost the performance of wireless systems, as exemplified by the current Wimax (worldwide interoperability for microwave access) system. Wimax is an international standard for wireless broadband access network with a cellular structure consisting of base-stations and fixed or mobile user terminals. One of the main goals of the 'Next generation wireless broadband access systems and advanced coding techniques' (Wi-coding) project was to develop new coding techniques. The research team used an entirely new coding method called 'polar coding', a class of codes with low-complexity encoding and decoding algorithms, to achieve this. They investigated how to take polar coding from a theoretical idea and turn it into practice. Their initial work in this area included a critical assessment of polar codes as a potential competitor to the existing coding schemes used in the Wimax system. With 'encouraging' results, the researchers will continue to work on designing coding, modulation, and space-time coding schemes based on the polar coding paradigm. Another project target was the development of a pre-distortion algorithm to correct amplifier non-linearities. Orthogonal frequency division multiplexing (OFDM) is a means of allowing multiple users to share a common communication electromagnetic spectrum. It has become the air-interface of choice for modern wireless systems, but it suffers from a 'peak to average power ratio (PAPR)' problem which makes OFDM systems costly to implement. In OFDM systems, the PAPR of transmitted signals tends to be high which prevents the OFDM transmitter's high-power amplifier from operating efficiently. The Wi-coding research team developed a novel hybrid pre-distortion algorithm for OFDM systems and prepared a prototype of the pre-distorter, which will compensate for the non-linear behaviour of the power amplifier when it is saturated by a strong input signal. To balance the academic and practical aspects of the project, the novel ideas were all developed and tested in the context of emerging next-generation wireless standards, such as Wimax.