Research On The Key Techniques In Future Wireless Communication Systems

As the people’s requirements of the speed and quality of wireless communication systems, the key techniques in future wireless communication systems has got increasing attention, which includes: MIMO technology, cognitive radio technology, OFDM technology, signal processing technology and network protocols. This paper focuses on the spectrum allocation technology of cognitive radio, MIMO based signal processing technology in cognitive radio and the retransmission technology in WLAN network. In cognitive radio networks, for the second user, there are two kinds of access method:one is zero interference access, in which the second user can access only when the first user does not exist; the other one is interference limited access, in that the second user can access even in presence of the first user, but its interference has to be limited below a certain threshold. Studies have shown that if a plurality of second users can simultaneously access the same frequency, the spectral efficiency can be further improved. At the same time, zero interference access in presence of the first user can be achieved using MIMO diversity technologies, through rational designing the precoding vectors and receive filter vectors. In wireless local area networks, multicast communication has catches more and more people’s attention. However, due to the instability of the radio channel’s quality and the mobility of the wireless terminals, the phenomenon of packet loss is very serious, but the vast majority of multicast communication need to be reliable transmission, so the wireless multicast network packet loss retransmission technology has become very important. This thesis focuses on spectrum allocation in cognitive radio networks and packet loss retransmission techniques in wireless multicast network. The main work is as follows:1, In cognitive radio networks, that multiple users can access the same primary user’s band, in the presence of interference with each other, a new power allocation algorithms named Pseudo Water-filling power allocation algorithm is proposed, based the idea of water-filling algorithm. Then, using this algorithm, a new spectrum allocation scheme is designed, that makes the system performance become higher than traditional algorithms.2, In cognitive radio networks based on MIMO diversity techniques, the traditional precoding vectors and receive filtering vector designing method uses only its own channel information, but the information of the first systems’ traditional precoding vectors and receive filtering vector is not used. To solve this problem, A new algorithm is proposed which uses the information of both the channel and the precoding vector and receiving vector of the primary system, this algorithm can carry out spectrum sharing under the condition that no idle spectrum resource is available. In the end, all algorithms are extended to muti-user scenario.3, In WLAN multicast packet loss and retransmission scenarios, due to the problems of the traditional algorithm, that includes high computational complexity and large number of retransmission packet, retransmission scheme is designed using the concept of full rank of binary matrix. In this scheme, the retransmission packet is generated through the XOR operation of the original packet. Simulation results show that using the proposed scheme, the number of retransmission packets reach the limit value.