Superimposed sequence channel estimation and pilot aided channel estimation: a throughput comparison

Many wireless standards adopted orthogonal frequency division multiplexing (OFDM) modulation technique with training values allocated in empty slots or multiplexed with data (pilots) to estimate the channel, e.g. IEEE 802.11, HIPERLAN/2, IEEE 802.16, HIPERMAN, terrestrial digital video broadcasting (DVB-T). The pilot insertion clearly causes a waste of bandwidth efficiency. In this paper we consider an alternative estimation scheme with a lower computational complexity at a comparable efficiency loss. We address the simple and effective correlation method as time domain superimposed training based channel estimation technique. As a mean of comparison, the classical OFDM estimation technique derived by a windowed least squared (LS) approach is also studied. For both techniques, we derive an analytical expression of the mean square estimation error as a function of the information signal, noise and superimposed sequence powers. Then, we perform a capacity comparison in a realistic OFDM environment yielded by DVB-T standard specifications. We will show that the superimposed scheme allows the same performance as the windowed LS for 8k operational mode up to a signal to noise ratio (SNR) of 15 dB with a much lower complexity.