On The Key Technologies Of Future Wireless Relay Networks

Wireless communications have been going through a tremendous advancement in recent years. The system capacity and transmission reliability is greatly increased. And there are various new ideas and novel techniques created by both industrial and academia, and they have facilitated the standardization and commercial utilization. However, this kind of great development also leads to degraded wireless transmission environment and shrunk radio resources, which make a huge challenge against new gerneration of communication and people's increasing demands on mobile data services. From Turbo code and MIMO transmission to OFDM processing, we have witnessed each milestone's establishment in wireless communications. Right now, we are witnessing a new concept called cooperative relay transmission stepping onto the stage and showing off its potential capactiy.Cooperative relay coomunication firstly introduce the Relay technique, which forwards its receiving signal after processing to help the transmission between source and destination. Relay can extend the wireless coverage and also strengthens the transmission link. To be generalized, each idle user in wireless network can be considered as a relay node for others. Here comes the concept of cooperative coomunications. As a node belongs to a network, a user tends to devote all its available resources to facilitate the whole network's maximum flow rate rather than only receiving or sending its own information. From individual's point of view, cooperation costs extra resources. Actually, the resource of whole system is saved; that is to say average cost of each user is decreased. This gets along well with the global popular concept such as low-carbon and green environmental protection.This dissetation focus on PHY transmission techniques of wireless cooperative relay communications, and it includes existing relaying modes analysis and optimization, relay signal processing, novel cooperative schemes, etc. Several algorethms and schemes that improve the system are also proposed. The content and achievements are as follows:An adaptive relaying mode selection scheme jointly by destination and relay is proposed. This scheme alters the signal forwarding mode at the relay station. It adaptively chooses among Amplify-and-Forward, Decode-and-Forward and direct transmission mode according to CRC detection both at relay and destination. The simulation results demonstrate that this scheme significantly outperforms other existing relaying mode selection schemes.A novel relaying mode for wireless relay networks is proposed. It is called estimate-and-forward and based on estimating soft symbols and corresponding noise variance. Besides, a simplified approach by establishing and solving linear equation set as implementation is proposed. There is also analysis on features and advantages of this novel relaying mode. Finally, simulations of the three modes' comparison in two cooperative scenarios are provided. As shown in the results, the proposed estimate-and-forward scheme outperforms other relaying modes in terms of BER and FER.A cooperative coding scheme is proposed for cellular OFDM system. In this scheme, source reorganizes and recombines the bits stream, and destination station combines the signals from the two independent paths that are direct and relay links; at the relay, signals are redesigned for orthogonalization. Furthermore, a supplementary strategy of sub-carrier re-allocation is proposed to further enhance the system.