Distributed Constraint Satisfaction Based Wireless Channel Assignment

Wireless cellular networks are a milestone of today's communications systems. As more and more applications, and more and more attractive functions available for cell phones recently, the cellular network has become one of the most profitable mobile communication networks. Therefore, effectively utilizing the limited resources of electromagnetic spectrum and thoroughly maintaining the communication qualities become one of the most important issues in the management system of a cellular network. To address this issue, channel assignment is indispensable.The objective of channel assignment is to assign channels to mobile terminals and base stations such that the network's capacity, in terms of numbers of mobile users and no interference conflicts, is maximal. The capacity is maximal when the call-blocking and hand-over failure probabilities are minimal. Many previous works have been done in reducing the complexity of solving these problems, but for real time traffic, their designs are suffer from a few challenges such as:●Practical deployment of channel assignment in large scale networksSince channel assignment problem (CAP) is NP-complete, few computational intelligence approaches proposed in order to find a channel assignment that satisfies the hard constrains:co-channel constraint, adjacent channel constraint and co-site constraint, which using a minimum number of channels. However they may get an optimal solution in a resource allocation problem, but they are not pursued in the mobile communications in which satisfy all user requests while the voice generates or call arrives in real time. Moreover, many works are proposed to solve in a small scale networks.●Fault-tolerant Channel assignment in case of mobile handoverThe handover is a common problem that arises due to mobility. The handover is the process by which a user in motion crosses over the border between two cells. The increased demand for cellular networks makes this an important subject of study, since it is one of the bottlenecks of the cellular system. Several techniques are used to manage handovers that cope well with the traffic variation. However they have ability to minimize the handover failure probability, but may increase the new call blocking probability. On the other hand, the process of finding the proper channel to be borrowed is usually performed randomly and therefore carries a penalty.●Joint Routing and channel assignment in multi-hop cellular networksMulti-hop cellular networks (MCN) are new important concepts which are widely believed for future generation (4G) wireless systems. But in MCN, the problem of dead spots and hot spots still exit in these networks. Therefore, the optimal channel assignment due to multi-hop relaying and the efficient routing protocols at high mobility are needed. The exiting approaches proposed in the way of separation, which can't maximize the system throughput and solve well the congested problem. Because the channel assignment in MCN determines the network connectivity/topology, which affects the routing decision; and routing determines the amount of traffic on each link, which in turn affects the channel assignment decision.To solve the above problems, we propose Distributed Constraint Satisfaction Problem (DCSP) based channel assignment. Our works are supported in part by the National Natural Science Foundation of China through the grant 60772088 and 60602029, and the Foundation of Hubei Provincial Key Laboratory of Smart Internet Technology under Grant No.HSIT200605. The main contributions of our research are as follows:1. In order to minimize the maximum of channel utilization in which can guarantee an interference free network, we formulize CAP as DCSP. Our DCSP based channel assignment can satisfies all user requests, while voice generates or call arrives and is suitable for a large-scale scene. The result shows that it can achieve much tight lower bounds on the number of required channels with related less computation time and cost.2. In order to continue communicating with base station while mobile hosts move across the congested cells, we propose Fault Tolerant Channel Assignment (FTCA) for handover traffic. FTCA is the ability of a cell to continue communicating with its mobile hosts, even if there is an insufficient number of an available channel. Several techniques such as the influence-based channel reservation technique, technique of channel borrowing with user directions, the directional co-lock channel technique, and reuses available channels more efficiently, are used in our fault tolerant framework. As the result, our scheme greatly minimizes both of the average number of handover failures and new call blocking.3. In order to design for balancing traffic to minimize the total call blocking probability and hand-over failure probability, we propose Joint Routing and Channel Assignment (JRCA) scheme in such a lower bound number of channels and no channel collision. Experimental results show that, our JRCA scheme can reduce in both of the call block rate and the hand-over failure rate, compared to traditional cellular network.