Approach for determining the optimum pilot placement in orthogonal frequency division multiplexing systems

One of the major concerns in wireless communications is multipath fading that causes some adverse effects and significantly limits the performance of a system. To overcome these effects in orthogonal frequency division multiplexing, system channel estimation must be performed. Pilot arrangement is very crucial in pilot aided channel estimation. There is an inevitable trade-off between the number of pilot symbols used in channel estimation, the accuracy of such estimation, and spectral efficiency. In this study, the analytical formulation of the channel estimation mean squared error based on a channel´s sampled power density is presented. A novel mathematical rule for the optimum pilot symbol interval and a novel adaptive pilot placement are proposed to improve channel estimation quality and bandwidth efficiency. The optimum pilot symbol intervals which are related to channels´ coherence times and coherence bandwidths can be calculated easily with the use of the proposed method. As the proposed method effectively reduces the number of searches for the optimum pilot symbol interval, it gives rise to simply constructing adaptive pilot placement in real-time systems. Compared with fixed pilot placement, the proposed adaptive placement shows obvious improvement up to 6% in bandwidth efficiency while maintaining the bit error rate performance.