Channel Estimation for Nonlinear OFDM System Using Diagonal Scattered Pilots

The next generation wireless communications require wideband information transmission with high data rates. Orthogonal frequency division multiplexing (OFDM) is recognized as a promising technique which can efficently overcome the multipath effect and inter symbol interference (ISI) of wideband wireless channels [1]. A dynamic estimation of channel is necessary before the demodulation of OFDM signals since the radio channel is frequency selective and timevarying for wideband mobile communication systems. Some approaches have been proposed for the channel estimation of OFDM communication systems. In [2] and [3], the channel estimators are employing time and frequency domain filtering. A single-value decomposition based channel estimator is presented in [4]. Pilot symbol aided channel estimation and tracking technique recently has attracted widespread attention. The comparison of the performance of some pilotaided channel estimation schemes is presented in [5]. The channel estimation can be performed by either inserting pilot tones into all of the subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. The first one, block type pilot channel estimation, has been developed under the assumption of slow fading channel. The latter, the comb-type pilot channel estimation, has been introduced to satisfy the need for equalizing when the channel changes even in one OFDM block. The comb-type pilot channel estimation consists of algorithms to estimate the channel at pilot frequencies and to interpolate the channel. The major drawback of the OFDM technique is its large signal dynamic caused by the high (several hundreds) number of subcarriers with random phase and amplitude, which are summed in the modulator. It results in that OFDM technique is sensitive to nonlinear distortions caused by high power amplifier (HPA). The first obvious solution is to use a very linear HPA, but this solution is expensive and consumes too much power for portable systems. In this paper, we propose a new channel estimation technique that uses diagonal scattered piBinary data Map S/P