Robust Cooperative Networking and Interference Management in Next-Generation Wireless Networks

Cooperative wireless communication techniques provide the spatial diversity gain over wireless channels by recruiting relay stations that overhear other transmissions to jointly forward information to the intended destination, thereby yielding higher reliability and throughput than direct transmission. While conventional single-relay and distributed spacetime coding (DSTC) based multi-relay cooperative schemes have been employed in various wireless networks, they suffer from performance degradation in a mobile environment due to their inability to track relays. A novel DSTC, called randomized distributed space-time coding (R-DSTC), is able to solve the problems introduced by mobility and is superior to the direct transmission scheme as well as other cooperative schemes. As a fully decentralized cooperative scheme, R-DSTC requires simpler relay selection and much less channel information to operate than all cooperative schemes.;While R-DSTC is well studied in the physical (PHY) layer, in order to realize its performance benefits in upper layers, we developed medium access control (MAC) protocols for the IEEE 802.11WiFi and IEEE 802.16WiMAX networks, called STiCMAC and CoopMAX, respectively. We design a cooperative PHY/MAC cross-layer framework that fully exploits the opportunistic diversity gain of multiple relays. New signaling messages are provided in support of the protocol operation. We developed efficient rate adaptation algorithms that optimize the transmission parameters, such as data rates and space-time code dimension, for these new protocols. Our proposed protocols minimize the signaling cost and maximize the end-to-end throughput for each source/destination pair while maintaining an acceptable end-to-end packet error probability. The system performance of STiCMAC and CoopMAX is evaluated in both a stationary and mobile scenario. These new R-DSTC based protocols are shown to greatly outperform all other direct and cooperative schemes in terms of throughput, delay and interference reduction. In particular, our R-DSTC based cooperative protocols provide robust relaying and undergo the minimal performance loss in a mobile environment.;In this work, we also study the inter-cell interference management problem in the uplink of a multi-cell orthogonal frequency division multiple access (OFDMA) based wireless cellular network. A fully distributed frequency planning scheme is developed to improve the performance of the edge users at the boundary of a cell. Our scheme splits each cell into seven sectors and minimizes the inter-cell interference to the edge sectors of each cell. The user performance is measured in terms of signal-to-interference-plus-noise ratio (SINR). We compared our scheme with standard interference control schemes, i.e., Fractional Frequency Reuse (FFR), employed in current OFDMA based cellular systems, i.e. WiMAX and LTE, showing that a higher SINR gain can be achieved by our new scheme for the edge users under full frequency reuse.