Study On Key Issues About QoS Guarantee In Ad Hoc Networks

Ad hoc network is a self-organizing and self-configuring multihop wireless network without predefined infrastructure where the network topologies, transfer model and channel environment dynamically change with node mobility. Despite the long history of Ad hoc networks, there are still quite a number of problems that are open. With the development of communication and electronics, Ad hoc network faces a new chanllenge. Focusing on the QoS guarantee in Ad hoc networks, this paper studied key issues of QoS guarantee of MAC and physical layers. The BER and transmission rate requirements are ensured by physical layer and the time delay, delay jitter and bandwidth requirements are ensured by MAC layer. Moreover the cross layer design between MAC and physical layers is discussed in this paper. The main research production of this dissertation is as follows:1. A distributed synchronous reservation multiple access control protocol (DSRP) which is based on time division multiple access is proposed in this chapter. The protocol combines the competition mechanism with reservation mechanism, and gives priority to the real-time service. If a real-time service can reserve a time slot successfully, it will occupy the fixed time slot in the following frames until the service burst is end. Thus the bandwidth and time delay requirements are ensured and the delay jitter is avoided. The problems of hidden terminal, exposed terminal and intruded terminal are solved by the reasonable design of frame structure, so that the hidden terminal can receive data and exposed terminal can send data. The channel utilization ratio and average package discarded ratio are derived theoretically, and the analysis results are testified by simulations. The comparision results with IEEE 802.11 DCF and CATA protocol indicate that DSRP protocol has better performance if the networks load is heavy.2. An algorithm to realize unequal error protection by adaptive modulation in OFDM system is proposed in this chapter. Considering the consumer's requirements and the different power coefficients of sub-carriers in OFDM system, the sub-carriers are adaptively classified into groups. The data transmission rate and bit error rate of each sub-carriers group should satisfy the requirements of relevant essentiality data, as well as the total transmission power should be minimized. An adaptive sub-carriers grouping algorithm and an adaptive bit and power assign algorithm in each sub-carriers L team, named MTP AM-UEP, are proposed in chapter. The simulation results indicate that the power of MTP AM-UEP algorithm approaches the theoretics minimum value, and each level's transmission quality requirements are guaranteed. The comparision results with other algorithms show that MTP AM-UEP algorithm has best transmission quality by given power, as well as the minimum power with the same transmission quality.3. Based on the MTP AM-UEP algorithm, the carriers can be grouped into subbands to decrease the complexity of MTP AM-UEP algorithm and reduce the signaling transmission and information feedback. The performance of the subband adaptive modulation algorithm named MTP SAM-UEP under five effective power coefficients schemes is discussed. These schemes are minimum gain, maximum gain, reciprocal average gain, geometric mean gain and arithmetic mean gain. The simulation results show that, considersing IEEE 802.16 SUI-3 channel model, when the geometric mean gain is adopted, the best balance between transmission performance and power consumption is obtained. Even when there are 16 sub-cairriers in a subband, the performance of MTP SAM-UEP is comparable with MTP AM-UEP.4. Based on the OFDM model with data spread, this chapter analyses the model's features and points out that original data symbols have entirely same transmission characteristic. In order to improve transmission quality, the weighting factors of new data symbols can be adjusted, which completely depend on the channel characteristic. Then the specialty of adaptive modulation OFDM system with data spread is analyzed, and average assignment is discovered to be the optimum one. The number of original data symbols should equal to the number of sub-carriers. The problems of capacity maximization and power minimization are investigated, and an adaptive modulation algorithm is given. The data spread technique is further applied to UEP transmission, thus a minimum power data spread adaptive modulation UEP algorithm which targets for users'requirements is proposed. The simulation results indicate that the performance of OFDM system with data spread isn't as good as traditional OFDM system, but it solved several problems of traditional OFDM system, such as complexity is high and modulation parameter to be transmitted is too much. This algorithm can still guarantee the transmission quality requirements and have important application valve.5. The MAC protocol of QoS guarantee and the physical transmission scheme of QoS guarantee are combined effectively in this chapter, and the cross layer design between MAC and physical layers is discussed also. First the PPDU frame structure to support QoS in physical layer is introduced, which is composed of PLCP header, signaling part and data part.The detailed frame and function are described, where two additional signalings are used to realize UEP and adaptive modulation. Then the the MAC protocol to support QoS is introduced, including the parameter definition and process description. The information exchange between MAC layer and physical layer is analysed at last. The cross layer design can use the channel resourse adequately, and also enhance the data transmission quality and ensure the QoS requirements, such as BER, delay, et.al.