Research On Key Technologies Of HSPA And LTE Heterogeneous Wireless Converged Networks

Due to the development in technology and the increasing service requirement, multi-radio access technologies are co-existing and evolving, which results in a heterogeneous networks situation. Different radio access technologies have their own advantages and disadvantages and can meet different requirements of services and situations. The heterogeneous wireless networks applying multi-radio access technologies can complement each other to extend the coverage area and improve the capacity. Therefore, the convergence of heterogeneous wireless networks is regarded as the key feature of the future wireless networks, and arising highly concerns. Among the diverse wireless networks, High Speed Packet Access (HSPA) and Long Term Evolution (LTE) are the two most widely deployed networks. It is important to solve the problem of their convergence. HSPA adopts Code Division Multiple Access (CDMA) as the radio access technology, while LTE adopts Orthogonal Frequency Division Multiple Access (OFDMA). Both the networks are developed by the3rd Generation Partnership Project (3GPP) as Beyond3rd Generation (B3G) standards. LTE focuses on the use of new technologies, while HSPA pays more attention on the backward compatibility. Both of them keep evolving along their respective directions. Technically they can not replace each other, and they will co-exist for a long while in the future. Although they can be integrated through the evolved core network, it can not satisfy the demand of the future wireless networks. They need to be integrated in the radio access networks.Our research can be composed of the following parts,Firstly, the resource allocation based on joint radio resource management is studied. For the downlink situation, the channel allocation problem is formulated as the linear programming problem with the objective of maximizing the system throughput, considering the amount of resources and the quality of services as constraints. Comparing the feasible regions, it is proved that the converged network adopting joint radio resource management performances better than the heterogeneous network without being integrated. Simulations are carried out to verify the conclusion. For the uplink situation, the power for the networks is provided by the user equipment, so the power allocation is taken into consideration. LTE adopts Single-Carrier Frequency-Division Multiple Access (SC-FDMA) as the radio access technology and the users are assigned different resource blocks. HSPA is interference-limited in uplink, so the power for HSPA has to be allocated appropriately. Therefore, the resource allocation problem for uplink is formulated as the optimization problem with the objective of maximizing the system throughput, considering the bandwidth of LTE, the interference limitation of HSPA and quality of service as constraints. Furthermore, the problem is a convex optimization problem, which can be proved by using Hessian matrix. Then the problem can be solved by using Lagrange functions. A distributed algorithm to allocate radio resources is proposed. The procedure of the algorithm is divided into two parts. One is carried by the user equipment, while the other is carried by the networks. The allocation of bandwidth and power can be optimized through the iterative method.Secondly, traffic splitting and video stream scheduling is studied. Assuming the users can receive data from LTE and HSPA simultaneously, traffic splitting is formulated as the problem with the objective of maximizing the user throughput, considering the amount of packet as constraints. By using the graphic method, the problem is solved. It is found that minimizing the delay between both networks means maximizing the throughput. Furthermore, the conclusion can be extended and applied to the heterogeneous wireless networks with more than two radio access networks. Based on the conclusion, the basic traffic split scheme and the adaptive traffic split scheme are proposed. Then the joint scheduling framework for video stream is studied. The joint scheduling framework implements two functions, traffic split and multi-user scheduling. The former splits the video flow of the user into sub-flows. The later assigns the resources to the users by employing the scheduling algorithm which takes the delay, link rate into consideration.Thirdly, the multi-radio transmission scheme is studied to improve the performance of Transmission Control Protocol (TCP). Based on generic link layer, multi-radio transmission diversity can improve the efficiency and reliability. In wireless networks, TCP degrades due to varying channel condition and high error rate. TCP misinterprets these as network congestion and reduces the transmission rate. Motivated by the character of TCP, the multi-radio transmission diversity scheme is used to improve the performance of TCP. The TCP send rate of two parallel multi-radio transmission diversity schemes is analyzed. One transmits the copy of the same data over both LTE and HSPA at the same time for reliability, while the other one transmits different data via both networks for efficiency. Through developing a cross-layer model, the packet error rate and retransmission in the wireless networks are taken into consideration. By comparing the performance of these schemes, it is proposed the hybrid multi-radio transmission diversity scheme which aims at obtaining good tradeoff between robustness and efficiency to improve TCP performance.Finally, the summary is given at the end, where the further research and related work on the LTE and HSPA wireless converged networks are pointed out.