Analysis and Design of Communication Techniques in Spectrally Efficient Wireless Relaying Systems

This project deals with the analysis and design of communication techniques in MIMO relaying systems, especially in MIMO two-way relaying systems. The analysis of the considered system is based on information theoretical performance limits, such as capacity and achievable rates. For the design of communication techniques, we propose practical transmission strategies and show their performance results based on practical performance measures.

Firstly, we verify that relay communication can extend the coverage of wireless networks, and propose a quantitative analysis framework for determining the coverage extension by us- ing decode-and-forward (DF) relays in cellular wireless systems. We define the coverage of cellular relaying networks based on the achievable rates, and provide theoretical calculations as well as simulations to show the improvement of coverage in cellular relaying systems.

Secondly, information-theoretic performance analysis on MIMO two-way relaying systems are proposed. For MIMO two-way DF relaying systems, two data-combining schemes, i.e., the superposition coding (SPC) scheme and the network coding scheme, are studies in detail. When the transmit channel knowledge is available at the relay, we propose the optimum transmission strategies at the multi-antenna relay from the information-theoretic perspective for the two data combining schemes. Furthermore, we propose the methods to find the optimum time-division (TD) strategies between the multiple access (MAC) phase and the broadcast (BRC) phase in two-way DF relaying systems, considering both peak and average power constraints.

Next, we consider the design of practical transmission schemes in MIMO two-way relay- ing systems. We propose a novel channel estimation method for the BRC phase of MIMO two-way DF relaying systems when the SPC scheme is applied. The self-interference (SI), which contains the known data at the receivers in two-way relaying systems, is utilized to estimate the channel. Since the SI is inherent in the received signals in two-way relaying systems, it does not consume additional system resources as pilots do. On the other hand, the SI can also be used together with pilots to offer superior channel estimation performances than the purely pilot-aided channel estimation scheme. Furthermore, we quantify the spec- tral efficiency improvement of the BRC phase channel with SI-aided channel estimation by deriving its achievable rates using different codebooks.

Finally, we propose a novel method to exploit the bit-level SI so that asymmetric data rates can be transmitted in the BRC phase of two-way DF relaying systems when the network cod- ing scheme is applied. Since the network coding scheme combines the data on the bit level, the major problem faced by the network coding scheme is how to transmit with asymmetric data rates to the user stations according to their individual link qualities in the BRC phase. In the proposed scheme, the weaker link receiver exploits the a priori bit information in each received data symbol, so that it only needs to decode on a subset of the signal constellation. Subject to the same bit error rate constraint, the weaker link receiver can decode at lower signal-to-noise ratio (SNR) compared to the stronger link.