Pilot Design Based On Minimum Power For NC-OFDM System

With the rapid development of wireless communication spectrum scarcity hasbecame a key element that limits the development of mobile communication. Sodynamic spectrum access technology is born. Non-contiguous orthogonal frequencydivision(NC-OFDM) is a kind of orthogonal frequency division, which isdeformation of traditional OFDM. NC-OFDM uses the non-contiguous subcarriers.So it can put together the narrow-banded and scattered spectral shard and therebyimproves the spectrum utilization.Channel estimation with pilots is one of the key technologies in NC-OFDMsystem. Equal spaced and equal powered pilot tones are the best when subcarriers arecontiguous. However,in NC-OFDM system the available spectrum is non-contiguousand dynamic so pilot subcarriers may locate in the spectrum of the primary users andinterferes its communication. Therefore in NC-OFDM system a new pilot designmethod is needed.This thesis presents the research done in the design of NC-OFDM pilot.Summary of contents and contributions include:1) Pilot position design is a kind of combinatorial optimization, which can beseen as conversion of0-1knapsack problem. So we can improve the algorithm thatsolve0-1knapsack and then use it to design pilot position. In the existing literaturethere are many algorithms to solve0-1knapsack problem. We select the discreteparticle swarm optimization for the reason that it is easy to implement,need fewerparameters to adjust and we can set parameters according to our experiment. Thismethod has low complexity and when the parameters in NC-OFDM system changewe only change the number of active subcarriers and the number of total subcarriersin the program. So this kind of design method has stronger versatility.Simulationshows this method could achieve good channel Minimum Mean Square Error(MSE)performance and bitter error rate performance.2) The existing literatures design pilot tones for NC-OFDM system based on channel MSE under the condition of limited power and do not consider the totalpower of pilot subcarriers. As well as we know if subcarriers power is certain thechannel estimation is better when the pilot power is higher. However it reduces thepower of data subcarriers, thereby effects the system performance of datatransmission.This paper, based on minimum power of pilots, proposes a method todesign pilots for NC-OFDM system. Comparing with traditional method, it requiressmaller power under the condition of the given MSE.Therefore it increasesavailability of power. This also responds the popular energy-saving and emissionreduction.Simulation proves it.