Research On Cross-Layer Design In Next Generation Wireless Networks

Under the action of technology progress, market competition and demand expansion, wireless communication networks have been developing tremendously in service quality, network capacity, transmission rate, etc. The traditional cellular mobile communication system is experiencing the generational evolution, and in the meantime, various new radio access technologies (RATs) come forth. Wireless communication networks is evolving towards diversification of access method, high speed of data transmission, universal mobility and all IP (Internet protocol) integration, and will become an all inclusive, ubiquitous and omnipotent next generation wireless networks. The next generation wireless networks integrate different type of mobile networks and Internet, provide the seamless handover and roaming between heterogeneous networks, support multi-hop self-organizing access and cooperative relaying technology, and provide all kinds of IP-based services. However, since the wireless resource is scarce and precious, the wireless channels are dynamic and time-varying, and the wireless media is shared and competed by users, there are many challenges to implement efficient reliable secure next generation wireless networks, such as, how to coordinate the management of the radio resources controlled by different RATs, how to keep user always best connected, how to achieve seamless and smooth handover, how to select the optimal relay node, how to establish a high data-rate route, etc. This paper investigates the applications of cross-layer design scheme in next generation wireless networks, and the coordination of different layers of the protocal stacks to improve the system performance and efficiency. Based on cross-layer design scheme, the paper proposed the cooperative radio resource management of heterogeneous wireless networks, the optimal relay selection policy in cooperative relaying networks, and high data-rate routing protocal in multi-hop self-organizing networks. The contribution of the paper is as follows:This paper summarized the development and evolution of wireless networks, and carefully investigated the characteristic, challenges and related work of the next generation wireless networks. This paper also investigated the idea and approaches of cross-layer design of different layers of the transmission control protocol/Internet protocol (TCP/IP) protocal stacks, and analyzed the principle of cross-layer design and the methods to improve system performance.This paper proposed the concept of cooperative radio resource management (Co-RRM), which operates from a common perspective that take into account the overall amount of resources in the available RATs. Co-RRM refers to the set of functions that are devoted to ensure an efficient use of the available radio resources by means of joint access control and data scheduling. The proposed policy-based radio resource allocation algorithm provides a flexible approach for operators and network providers to deploy and correlate business strategies with the overall network actions. This paper introduced the analytic hierarchy process into the network selection mechanism to derive the weights of different decision factors including user's preference, service application and network condition, with the objective of keeping mobile users always best connected in any environment. This paper investigated the cooperative transmission and data scheduling, which allocate wireless interfaces to packets from different services according to the transmission capability of an interface provided by physical layer and quality of service (QoS) requirement demanded by application layer. The adaptive vertical handover scheme based on layer-2 trigger is proposed, which improves the vertical handover process through utilizing parameters passed up from physical layer, and sets the state variables of TCP according to the bandwidth information provided by link-layer in order to utilize the network resource after vertical handover effectively.This paper proposed an energy efficient optimal relay selection algorithm, which models the optimal relay selection problem in mobile time-varying networks as a restless multi-armed bandit system in stochastic control theory. In this algorithm, the wireless channels are modeled as first-order finite-state Markov channels (FSMCs), the residual energy of nodes in wireless networks is partitioned into different levels and the transition of the energy levels is modeled as the Markov chain, adaptive modulation and coding (AMC) is applied by each node in order to increase the spectral efficiency in fading channels, two approaches are adopted to maximize network lifetime:minimizing the energy consumption required to deliver data packets by selecting the relay with better channel state and balancing energy usage among the relays by selecting the relay with high residual energy. This algorithm sets one statistically optimal relay to be active in each time-slot according to the current observed channel and energy state and state transition probabilities. Simulation results show that the proposed scheme can mitigate error propagation, increase spectral efficiency and maximize network lifetime.In this paper, we investigate the end-to-end TCP throughput in cooperative relaying networks and take cross-layer design approach when selecting a relay and adjusting link-layer parameters to optimize the TCP throughput. We formulate the cross-layer TCP throughput optimization problem as a restless bandit system, which is a powerful stochastic control modeling framework. The optimal relay selection policy can be obtained by solving restless bandit problem with linear programming relaxation and primal-dual index heuristic algorithm. The obtained relay selection policy has an indexability property and the optimal selection policy is to simply choose the relay with the lowest index. The priority-indices can be computed and stored into a table off-line before transmission, which dramatically reduces the computation and implementation complexity of the relay selection policy. The proposed scheme is fully distributed and scalable. There is no need for a centralized control point, and relays can join and leave from the set of relay candidates freely. Simulation results show that both physical layer and link-layer design parameters have significantly impact on the TCP throughput, and the TCP throughput can be improved substantially with the proposed cross-layer design scheme.This paper proposed a high data-rate route selection scheme based on power control. The cross-layer design technique is adopted, and the physical layer data-rate is used as the performance metric when establishing the route. When establishing a route, the node first discovers route within the transmission range of the highest rate, and increases the transmission range to that of a lower rate if it fails to find the path, until it gets to the lowest rate. Because the transmission range is determined by the transmit power level, so we simply adjust the transmit power to the corresponding data-rate level. Simulation results show that the proposed scheme increases the network throughput, decreases end-to-end delay and minimizes the power consumption. This paper also proposed a high data-rate route selection scheme based on MAC (Medium Access Control) transmission time (MTT), which uses MTT as the performance metric when establishing the route. The method of MTT metric minimizes the total medium access time consumed for sending a packet from a source to a destination, and results in an increase in total network throughput. For the simplicity of incorporating the MTT metric into existing ad hoc routing protocols, this paper presents the weight scheme which assigns a weight to each link in the network that is proportional to the amount of medium access time occupied by sending a packet on that link. Simulation results show that this method is capable of establishing a high data-rate, low delay and robust route.