With the rapid growth of mobile data services, the traditional cellular system is unable to meet the demand of future wireless communications. A series of infrastructure-less wireless network architectures have received extensive attentions from both academic and industry fields. Among them, cognitive radio networks, which introduce the cognitive function to nodes, can effectively improve the spectrum utilization and the transmission efficiency. Due to the nature of decentralization and self-organization, Ad Hoc networks are suitable for a variety of applications where the central nodes cannot be relied on. Researchers at the IWCT of SJTU have made the following theoretical advances in the areas of infrastructure-less wireless networks.
Two-way relay channel, where two source nodes exchange information with each other the help of a relay node, is a building block of wireless networks to apply network coding in the physical layer. Compared with traditional one-way relay techniques, two-way relaying is able to achieve much higher spectral efficiency. We have made tremendous progress in two-way relaying as follows.
1) We proposed a novel physical layer network coding scheme, named Superimposed XOR, for asymmetric two-way relay channels. It is superior than existing methods and closely approaches the capacity bound.
2) We studied the effective capacity of two-way relay systems for statistical delay QoS guarantees, and proposed an optimal cross-layer resource optimization algorithm.
3) For LDPC-coded two-way relay fading channels, we introduced pairwise check decoding at the relay to realize joint network-channel coding.
4) When each node is equipped with multiple antennas, we also designed joint source and relay precoding based on MSE criterion.
Dynamic Spectrum Sensing and Cognitive Access
Dynamic spectrum sensing is used to find the idle channel as quickly as possible. Cognition of the transmission link can significantly improve the transmission efficiency, network throughput and energy efficiency. We study the fast algorithms for dynamic spectrum sensing and cognitive access with high efficiency. The main results are as follows.
1) Statistical Analysis in Circle Noise Spectral Domain. We are the first to establish the relationship between the detection threshold of circle spectrum signal and the probability of false alarm. We further propose a fast detection algorithm for circle spectral domain based on the noise statistics characteristics.
2) High Energy-Efficient Cognitive Access Method. We design the optimal Energy-Efficient information sharing method for cognitive network by constructing the energy consumption model for cognitive terminals and optimizing the dynamic spectrum division unit.
Dynamic Spectrum Allocation Mechanism and Capacity of Cognitive Radio Networks
Efficient dynamic spectrum allocation is a key technology in wireless domain waiting for realization. We study the dynamic spectrum allocation mechanism and the capacity improvement of cognitive radio system. The main results obtained are as follows.
1) We proposed cognitive radio dynamic spectrum allocation schemes based on economic theories. Extensive researches include game theory, auction and contract theory, providing reference for practical application of cognitive radio technology in actual network environment.
2) We proposed motion cast mechanism to improve the reuse rate of data. We also established clusters topology model, and solve the optimal connectivity and coverage in heterogeneous networks.