Research On Access Technologes Of Cognitive Radio Ad-Hoc Networks

With rapid growth in service traffic between different networks and different access technologies in wireless communication, the spectrum resource is becoming more scarce. The problems on how to further improve spectrum utilization, system capacity and quality of services need urgent solutions in next-generation wireless communication. Cognitive Radio, which has broad application prospects in the new generation wireless communication network, is a new issue that can utilize the spectrum resource adequately.Ad hoc network is a kind of wireless communication network with self-organization and without fixed infrastructure. At present, Cognitive Radio Ad Hoc Networks (CRAHNs), which combine Cognitive Radio technology and Ad Hoc network technology together, is the research focus in Cognitive Radio area. Combined with existing mobile communication network, CRAHNs can provide broadband wireless multimedia services for users.This dissertation takes the MAC layer and physical layer in CRAHNs access as the research objective, and discusses the key technical issues in CRAHNs design and implementation, here are the main findings:1. Constrained Markov Decision Processes (CMDPs) with Collision probability (between authorized users and cognitive users) constraint and Maximum available channel opportunity are modeled for the CRAHNs with the cluster. The model is abstracted to find optimal policy solution to make channel throughput rate maximum under collision probability constraint. Based on perceived channel state information (including authorized channel busy/idle state, SNR, channel equalization parameters), Adaptively Channel Access Algorithm for Single Cognitive users (ACAAS) and Adaptively Channel Access Algorithm for Multiple Cognitive users (ACAAM) are proposed, corresponding to single transmitting user and N transmitting users in M channels respectively.2. For CRAHNs with multiple services and a cluster, periodic audio service and unperiodic data service mix together. When service traffic in single Cognitive user not large, the problem that how multiple users share the same channel and how more Cognitive users accommodate together in the channel would be faced and vital. In this dissertation, IEEE802.11e HCF hybrid mechanism is introduced to solve the problem with multiple users sharing the same channel. Under the HCF mechanism based on IEEE802.11e, the channel can only accommodate fewer numbers of voice channel, access opportunity to channel for the voice and data services can not be controlled when VoWLAN (VoIP over WLAN) service and data service transmitted together. Contention Free Reservation Queue Channel Access (CFRQCA) mechanism and Adaptively Scheduling Algorithm of Access Opportunities (AOASA) based on traffic monitor are proposed to improve medium access control (MAC) protocol. Theoretical analysis and simulation show that CFRQCA mechanism and AOASA scheduling algorithm can significantly improve the voice channel capacity and meet the application requirement with multiple users sharing a same CR channel and multiple services mixed, including real time audio.3. In physical layer, a mechanism with multiple users sharing a same channel is proposed. In this machanism, OFDM/nQAM modulation technique, the cross-layer control idea, transmitting power and spectrum sub-band adaptively adjustment are used together. While a node communicating simultaneously with multiple nodes, multiple MAC bursts could be aggregated into different sub-bands of the same physical burst. Transmitting power level, modulation mapping mode, channel error-correction idea and number of frequency points are chosen according to burst importance, MAC bursts length and distance between the receiving user and the sending user. Multiple bursts share the same training sequence to save overhead, so the mechanism can improve the channel throughput and save node power consumption. A test-bed is developed and set up based on software defined radio, DSP/FPGA/ADC/DAC baseband circuit board, Radio Frequency Modules and vector signal generators. In this test-bed, OFDM/nQAM modem module, ACAAS algorithm, ACAAM algorithm, CFRQCA mechanism and AOASA scheduling algorithm with multiple users sharing the same channel are realized through program codes under FPGA and DSP developing environment. To the digital down conversion quadrature demodulator in FPGA technique, the improved algorithm is proposed to improve bandwidth and to reduce computational complexity and FPGA resource consumption.