System Design of Cooperative Wireless Networks
With the prediction that the number of wireless devices will reach tens of billions by 2020, wireless networks that exist today will have to be reengineered to support the increase in the number of users and the required capacity. Cooperation among terminals is envisioned as an enabling technique that can benefit from the increased number of connected devices and boost the network capacity beyond what is possible with today's network architectures, which rely on direct source-destination transmissions. While most of the work in this area focuses on designing relaying schemes that can achieve the promised capacity increase, little has been done in terms of implementing practical cooperative systems. To implement cooperation among terminals, a number of practical challenges need to be addressed across several layers of the communication system. This work focuses on the design aspects of physical and MAC communication layers, by suggesting low-complexity signal processing algorithms for multi- device cooperation and designing digital baseband hardware that showcases cooperation between two wireless devices.
We use the quantize-map-and-forward (QMF) relaying scheme, which has been shown to have good theoretical performance with multiple relays. System design of a cooperative communication link with half-duplex QMF relays is presented in three steps. First, we perform a theoretical analysis of the achievable rate and propose a local relay scheduling algorithm that performs close to the optimal relay scheduling algorithm. This local scheduling algorithm, as well as the system design approach in general, is based on the premise that relay terminals can be oblivious to other relays in the network. We show that spectral efficiency scaling with the number of relays achieved with this approach is close to optimal for both slow and fast- fading channel environments. The performance of a physical layer system design procedure for a QMF link is demonstrated by an example in which the spectral efficiency of a direct link is doubled by cooperating with three relays close to the source, as predicted by the theoretical analysis. Finally, we design the main baseband blocks for the three cooperating terminals in hardware and implement them on FPGAs. We show that the complexity of the cooperative receiver's baseband increases by 40% compared to a direct-link receiver.