A Block-Based Tomlinson-Harashima Precoder for Wireless Uplink

Peak-to-amplitude power ratio (PAPR) has long been a key research topic in telecommunications, especially in orthogonal frequency division multiplexing (OFDM) based communications systems. Time-division duplexing is being more widely exploited in modern and anticipated future wireless communications standards. Consequently, more accurate channel state information is more readily available through the principle of channel reciprocity. There exists an opportunity to develop waveforms that are at once low-PAPR, low-complexity, compatible with block-based (bursty) transmission and simply equalised. Such waveforms would be particularly applicable to cellular wireless uplink. Tomlinson-Harashima precoding (THP) is a classical technique that demonstrates most of the desired qualities, except that it is unsuited to block-based transmission. In this paper, we propose a modification that naturally adapts THP to block-based transmission, while retaining its other advantages. We demonstrate that it arises out of a so-called lattice-based multi-carrier modulation (LBMCM) technique proposed by Clarkson and Collings [1], [2]. The new block-based THP is, in essence, a hybrid of classical THP and LBMCM with near-orthogonal subcarriers. Simulations show dramatic reduction in storage of channel-related coefficients without significantly affecting the operational BER. Comparison with single-carrier frequency-division multiple access (SC-FDMA) is made.