Interference as a source of green signal energy in wireless communications

Description

Imagine a transmission from a WiFi base station (BS) to an IPod that draws free useful power from the simultaneous transmission from the BS to a laptop also connected to the WiFi network; two wireless links that conventionally are thought of as competing for the same resources. This is an example of the envisaged future of green wireless networks that the present proposal aims at.

The physical layer of wireless communication is a core building block of all wireless networks and the ever-increasing demand for higher quality of service (QoS) directly reflects on the performance requirements of the relevant signal processing techniques.

Conventionally, it is the aim of signal processing to eliminate interference and attain reliable communication. However, the more the existing interference, the more the required power to cancel it. Hence, the goal of higher QoS is closely tied with restrictions on the signal power transmitted from antennas. These restrictions are backed primarily by the public concern on the health repercussions of electromagnetic fields [A1] as well as more tangible limitations such as the battery consumption of mobile devises and the bounded performance of the hardware circuitry [A2]. In addition, there is a growing concern to reduce the global CO2 emission in all fields of communications [A3]. It is therefore desired to constantly improve the reliability and information capacity of wireless links while constraining the transmitted power. While interference has always been regarded as the main obstacle in wireless systems, recent work from the author of this proposal has revealed that, on an instantaneous basis, it can contribute constructively to the useful signal energy seen at the wireless receiver [A4]. This important source of useful energy is currently ignored by the techniques adopted in the communication standards. A special case of communication scenarios is the one where interference is explicitly known a priori at the transmitter [A5]. Practical scenarios of such nature involve downlink cellular communications where a single BS transmits to multiple users [Fig. 1a]. A vast number of signal processing techniques have been developed in the past to eliminate the resulting interference at the transmitter by use of precoding, which are now gradually dominating communication standards. These techniques involve linear and non-linear precoding for multiple-input-multiple-output (MIMO), orthogonal frequency division multiple access (OFDM) and code division multiple access (CDMA) systems amongst others. This project aims to investigate the adaptation of all these techniques to allow the utilization of constructive interference and achieve performance improvements without raising the power of the actual transmitted signal. Moreover, joint precoding techniques that allow the cooperation of multiple BSs in multi-cellular communication scenarios [Figs. 1b,1c] towards cancelling inter-cell interference, are currently being investigated for future generations of communication systems. These provide a new area of exciting research and it is one of the aims of the proposed work to apply the above concept to make use of constructive inter-cell interference. The potential of utilizing this source of green energy that is inherent in all wireless links presents a field of exciting and highly fruitful research. It can provide a breakthrough to the current bottleneck of wireless communications formed by the urge for better performance in conjunction with the scarcity of available resources such as transmit power and frequency spectrum. It is therefore a critical challenge to adapt the existing communications architectures and design novel signal processing techniques that dynamically allow wireless links to interfere when this mutually improves their performance and cancel interference when it mutually degrades reliability. The field of wireless communications is a dynamic and constantly evolving area at the forefront of te