Yuji Tohzaka

Pilot Signals for Multiuser Tomlinson-Harashima Precoding in MIMO-OFDM Systems

This paper describes pilot signals in multiuser multiple-input multiple-output orthogonal frequency division multiplexing systems with nonlinear Tomlinson-Harashima precoding (THP). The transmission processing of THP consists of three parts : feedback processing, modulo operation, and feedforward processing. In particular, the increased transmit power in the feedback processing is reduced by the modulo operation. In the conventional linear precoding systems, the same precoding weight is applied for both pilot and data signals at the transmitter for channel estimation at the receiver. If it is directly applied to THP, however, this will lead to significant increase in transmit power since the modulo operation cannot be applied for pilot signals. In our proposal, only the feedforward processing is applied for pilot signals and the interference due to the lack of feedback processing is removed by using orthogonal pilot signals. Simulation results show that the proposed pilot signals significantly improves the packet error rate performance.

A practical and cost-effective cyclic pulse synchronization system using IEEE 802.11 wireless LAN

Timing synchronization is important for collaborating machines. For various reasons concerning practicability, some machines cannot have cables to synchronize them. To synchronize wirelessly connected machines, this paper proposes a practical and cost-effective cyclic pulse synchronization system. The proposed system consists of a master machine with an IEEE 802.11 wireless LAN AP and slave machines with wireless LAN STAs. The master machine outputs a cyclic pulse to the AP. Then the STAs can reproduce synchronized cyclic pulses for the slave machines. Thus the machines can synchronize their work timing using the cyclic pulses. All functions to synchronize the pulses are implemented in a wireless LAN chip as user software applications without additional hardware. We evaluated the pulse synchronization precision of our system in the case of the peak network load. The proposed system achieves approximately 200 μs precision for the maximum pulse edge delay of STA output pulse to AP input pulse.