Research On Interference Alignment And Spectrum Sharing In Cognitive Wireless Network

Future wireless communication networks have been facing higher data rate and larger transmission capacity. This will be called multimedia communication networks. There will be massive spectrum resource demand. Actually, various spectrum efficiency lifting technology is proposed under the condition that interference free between users. In essence, the spectrum efficiency lifting is to solve the problem of user interference in wireless network. This thesis proposes the interference alignment technique and spectrum sharing auction technique in cognitive network under this context. We expect that combined with the cognitive network and these two technologies can maximize the spectrum efficiency.The main works of this thesis is as follows:1. Research on the opportunistic accessing scheme of cognitive networksCognitive users can only access to the idle bandwidth in traditional cognitive networks, while, they can’t share the same bandwidth with the primary user simultaneously. In order to make full utilization of spectrum, we proposed a capacity optimal opportunistic interference alignment algorithm. On the basis of ensuring the channel capacity of primary user, cognitive users and primary users can share the same bandwidth and cognitive users cause no interference to the primary user. In the proposed algorithm, the hybrid network base station estimates channel state information and calculates channel capacity, then it determines the pre-coding vectors and decoding vectors according to the capacity optimal rule. Cognitive users access to the networks by capacity optimal opportunistic interference alignment when the primary user’s channel capacity almost does not decline and the whole network can also obtain good channel capacity. The simulation results show that the proposed algorithm can obtain more channel capacity and increase the utilization ratio of spectrum than existent other algorithms under the same condition of channel state information.2. Distributed interference alignment and interference cancellation technologyThis thesis proposes one kind of interference alignment algorithm based on transmission delay. This proposed algorithm separates receiving signals by odd time slot and even time slot, thus expected signal and unexpected signal can be separated. The base station equipped with two antennas may support3even4users simultaneously by using our algorithm to access the uplink wireless network. We simulate the performance of uplink network adopting virtual MIMO. Further, we also propose an improved interference alignment algorithm based on transmitting delay and its corresponding network coverage scheme. This algorithm can separate expected signal from interference signal according to different transmitting delay. According to the characteristics of high-speed railway, we propose a distributed space linear interference alignment algorithm which is applied to the inside access system. Analysis results show that the inside access system can obtain totally four degrees of freedom and its performance of bit error rate is better than the system which does not adopt this interference alignment technology. Moreover, its performance of downlink bit error rate is slightly better than the uplink’s. In the back haul system, two sets of train access units can access to the network simultaneously. Its performance of bit error rate is better than the system which does not adopt this interference alignment technology based on transmitting delay.3. Relay interference alignment algorithm in cognitive networksOpportunistic interference alignment applying in cognitive networks can allow the primary users and the cognitive users to transmit information simultaneously by sharing the same frequency band. But the opportunistic interference alignment has high complexity and requires primary user to complete the channel pre-coding. The proposed relay interference alignment algorithm in cognitive network can greatly reduce the burden on the system. Its pre-coding operations are implemented by cognitive users. The primary users do not need to perceive the existence of cognitive users. In addition, the thesis analysis the channel capacity of the relay interference alignment algorithm. Simulation results show that no matter the channel conditions with strong correlation or weak correlation the channel capacities are better than traditional spatial linear interference alignment algorithm and opportunistic spatial orthogonal interference alignment algorithm.4. Research on the scheme of spectrum auction and sharingCognitive radio technology is considered to be an effective solution to allocate spectrum resource, whereas primary users of a network do not fully utilize available frequency bands. Spectrum auction framework has been recognized as an effective way to achieve dynamic spectrum access. From the perspective of spectrum auction, multi-band multi-user auction provides a new challenge for spectrum management. In this thesis, we propose an auction framework based on location information for multi-band multi-user spectrum allocation. The performance of our proposed framework is compared with that of traditional auction framework based on binary interference model as a benchmark. Simulation results show that primary users will obtain more total system revenue by selling their idle frequency bands to secondary users and the spectrum utilization of our proposed framework is more effective and fairer.