Harashima Precoding Research Articles

Lattice-reduction-aided Tomlinson–Harashima precoding for point-to-multipoint transmission

A new version of Tomlinson–Harashima Precoding (THP) for multiple-input/multiple-output (MIMO) channels with decentralised receivers employing lattice reduction is introduced. The proposed method clearly outperforms linear equalisation and conventional THP and in particular shows full diversity order.

Tomlinson–Harashima Precoding With Partial Channel Knowledge

We consider minimum mean-square error Tomlinson-Harashima (MMSE-TH) precoding for time-varying frequency-selective channels. We assume that the receiver estimates the channel and sends the channel state information (CSI) estimate to the transmitter through a lossless feedback channel that introduces a certain delay. Thus, the CSI mismatch at the receiver is due to estimation errors, while the CSI mismatch at the transmitter is due to both estimation errors and channel time variations. We exploit a priori statistical channel knowledge, and we derive an optimal TH precoder, adopting a Bayesian approach. We use simulations to compare the performance of the so-derived TH precoder with that of the same-complexity MMSE decision-feedback equalizer (DFE). We observe that for low signal-to-noise ratios (SNRs) and sufficiently slow channel time variations, the optimal TH precoder outperforms the DFE, while at high SNR, the opposite happens.

Performance Analysis of M-PAM Signaling With Tomlinson–Harashima Precoding Over ISI Channels

An analytical method is developed to evaluate the symbol error probability of multilevel pulse amplitude modulation system using Tomlinson-Harashima precoding over inter-symbol interference channels. Analytical and simulation results are in an excellent agreement for different values of M.

Transmitter-Based Equalization for Wireless LAN's

In a high-speed mobile communications network, it is desirable to off-load as much hardware complexity as possible from mobile terminals to the base station. A system architecture is presented where all equalization-related computations, requiring most hardware resources, can be performed at the base station. A conventional decision-feedback equalizer (DFE) is used to equalize the received transmissions, and a modified Tomlinson–Harashima precoding method (Tx-THP) is applied to pre-equalize the transmitted data sequence. The Tx-THP scheme can also be extended to differentially coherent detection, to suit the systems where perfect frequency synchronization is not available. A modified DQPSK receiver is presented to process the extended constellations. To avoid the side effect of severe noise multiplication, an alternative receiver structure is developed, incorporating a discrete-time phase tracker to allow the reduction of the constellation size prior to the correlation operation. With a 2nd-order estimator filter, this receiver approaches the performance of coherent detection for Tx-THP.