Wireless Spectrum Cognitive Theory And Research Of Networking Technology

In the cognitive network, the system focuses on dynamic spectrum access,The network would be operating within a specific spectrum band which is shared with other networks including primary users and secondary use cognitive networks. Secondary use cognitive networks use spectrum white space-bands which are unused at a given time and place on the base of giving no interfere to the primary user which operate on the same spectrum. In general, nodes of the cognitive network coordinate to establish network connectivity. The availability of the white space spectrum depends upon the operation of other networks in the given band, it fluctuate unexpectedly over time. In the field of dynamic spectrum access, there are some challenges of cognitive network coordination which involve the establishment of communication links within a cognitive network and the robust maintenance of the these links under conditions of changing spectrum availability. These challenges need coordinating the cognitive network by use many of ways. One of the method is use of a static common control channel,in other words,it may be a waste to the limiting spectrum and the Secondary user cognitive networks need the approvability of primary user.In the case of opportunistic spectrum use,a static control channel may be not supported by the networks; An alternative approach may be achieved by the uniform data link control,and the availability of spectrum may be considered unchangeable however,the successful creation and maintenance of node clusters involves considerable additional network complexity and overhead.As increasing of number of wireless access user,it is necessary that improving the indentify ability of the network. Many of communication signals in use today contain inherent cyclic stationary features which arise from underlying period within those signals.Thus many of study focuses on this new field, someone study on indent signals by using their uniquely signature, and creating an special cyclic stationary signal through artificially embedding unique cyclic stationary signatures in OFDM-based signal, that means there would be a waste for spectrum band and there would be no sufficiency credibility on this method. The cyclic spectral analysis of empirical signals from blending modulation systems which is based on orthogonal frequency division multiplexing (OFDM) is analyzed and exploited in cognitive radio applications in this thesis. Four kinds of channel states, that is, spectrum vacancy, primary signal transmitting, secondary signal transmitting, and mix signals transmitting, can be distinguished agilely using their distinct cyclic spectrum feature, which help to access to or remove from channels agilely and reliably. The design of transmitter and receiver are simple and need not a static common control channel with the proposed model of cognitive radio, which promise greater spectral-usage efficiency. Simulation results show that the proposed model can improve spectral-usage efficiency and performance in cognitive radio networks.