| OFDM combines the advantages of high performance and relatively low implementation complexity. The OFDM transmission scheme has been already employed in several recent mobile broadband wireless standard (e.g. WiMAX, LTE, DVB-H). These systems suffer from different types of interferences which can be primarily contributed to the mobile broadband wireless channel itself. In such doubly selective channel scenarios, for reliable coherent detection of the input signal, the OFDM receiver needs accurate channel estimation more than ever not only to detect the signal but also to mitigate the interferences from adjacent sub-carriers. When the channel exhibits fast time variation , channel estimation at the receiver becomes quite challenging for two main reasons 1) the receiver needs to perform this estimation more frequently and 2) channel time-variations introduce inter-carrier interference among the OFDM sub-carriers which can degrade the performance of conventional channel estimation algorithms significantly. In this proposal, we present a new pilot-aided algorithm for the estimation of fast time-varying channels in OFDM transmission and propose some future works for interference suppression in OFDM systems. Unlike many existing OFDM channel estimation algorithms in the literature, we propose to perform channel estimation in the frequency domain, to make a collective use of the constraints on the channel response (such as frequency and time correlations and bandedness) and perform most of the computations offline resulting in high performance at substantial complexity reductions. Given a fixed number and total power of the pilot subcarriers, we show that the MMSE-optimum pilot design for the proposed channel estimation algorithm consists of identical equally-spaced clusters where each cluster is zero-correlation-zone sequence.;We also investigate computationally efficient reliable OFDM downlink signal detection algorithm in presence of relatively strong co-channel interference (CCI) from adjacent interfering base transceiver station (BTS). We propose and compare the performance of several per-subcarrier based CCI cancellation algorithms considering 1 and 2 receive antennas at the user terminal. |
