The Study Of Cognitive User's Throughput Based On OFDMA

Cognitive Radio(CR) technology enables the secondary user(SU) to access primary users'(PU) licensed idle spectrum at a particular time and specific geographic lacation, on the precondition that it should not disrupt PUs'activities. It can improve the spectrum's utility greatly, thus is regarded as the best resolution to the problem that available frequency is becoming scarce. CR is a complex project composing of several huge modules, which has not been applied currently.The SU's throughput is studied when using the OFDMA modulation technology to access PUs'idle channels. At first how the PU utilizes its allocated channels is discussed, and the exponential distribution model of the channel's state duration is established. Then the OFDMA's sub-channel modulation scheme is introduced. All these work induces the issue that how the number of channels SU occupied and its transmission duration length affect its throughput, while SU has to scan the spectrum holes and transmit the data periodcally. The analytical expressions and Monte Carlo simulation figures for SU's throughtput are presentd. Further more, the performances of SU's two channel selection strategies are compared and the conclusion is work out that these two strategies have their own advantage depending on the number of occupied channels. Finally the interference measurement ---- Secondary Inierference Time Ratio(SITR) is advanced, also related simulations are devised. SITR's constraint could mitigate SU's interference to PUs while making SU's own throughput decreased badly.