Tsuguhide Aoki

Suitable MIMO-OFDM Decoders to Compensate IQ Imbalance

Imperfections in analog circuits are a serious obstacle to the realization of high data rate transmission for MIMO-OFDM systems. IQ imbalance is one such imperfection. The paper proposed a compensation scheme using a cascaded connection of MMSE and MLD, which applies MIMO decoding and compensation of IQ imbalance simultaneously. Computer simulations show that the proposed scheme can achieve almost the same performance as the conventional compensation scheme even though the computational complexity is reduced to about 1/3 of that of the conventional compensation scheme.

Preamble Structure for MIMO-OFDM Wlan Systems Based on IEEE 802.11A

This paper proposes a preamble structure for a next-generation high-throughput Wireless LAN physical layer using MIMO-OFDM. The proposed preamble is based on two important criteria as well as those which have already been widely discussed in the literature. One criterion is backward compatibility with legacy devices. The other is accurate AGC for MIMO data payload of the packet. Computer simulations demonstrate that the proposed preamble is superior to the other preambles with respect to these two important criteria

Pilot Design for Frequency Offset Tracking in MIMO OFDM Systems

This paper analyses the estimation of residual frequency offset in MIMO OFDM systems using pilot subcarriers. A closed-form expression for the MSE is derived and this is used to study the pilot design problem. An orthogonal design is proposed and simulation results show that this is superior to using the same pilots on all pilot subcarriers

Novel reduced complexity algorithm based on group detection in multiple antenna systems

Group detection (GD), the combination of maximum likelihood (ML) decoding and linear processing for multiple antenna systems, has been shown to attain reasonable performance and practical complexity. However, the diversity gain of conventional GD degrades since the degrees of freedom at the receive antennas are exploited for the linear processing before the local ML search. This paper proposes a novel GD with overlapped grouping. The proposed GD employs selection diversity within the overlapped signals by using the likelihood value, after the local ML search. Therefore, the proposed GD can achieve higher diversity gain compared with the conventional GD.

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.

Frame length optimization for in-band full-duplex wireless LANs

This paper proposes frame length optimization for wireless local area networks (WLANs) using an in-band full-duplex system that enables a WLAN access point and stations to transmit and receive frames at the same time on the same frequency channel. In in-band full-duplex WLANs, a primary sender which captures the channel transmits a frame to the intended receiver called a secondary sender and then the secondary sender transmits a frame reacting to the primary senders transmission. The difference of time length of frames transmitted by the primary sender and the secondary sender wastes the frequency channel where more frames could be transmitted. The wasted time decreases the system throughput performance of the in-band full-duplex system. In order to solve this problem, we propose a scheme where the secondary sender adjusts the length of its frame to the length of the primary senders frame by selecting frames used for frame aggregation properly. We evaluate the average delay, the average wasted time and the system throughput performance by computer simulations. The simulation results show that the proposed optimization reduces the delay by 49%, reduces the wasted time by 99.9% and improves the system throughput performance by 15% when the traffic is saturated.

Time Domain Loop Interference Channel Estimation and Cancellation for Mobile MIMO Wireless Relays

This paper presents a novel Time Domain (TD) based Multiple-Input Multiple Output (MIMO) implementation of the Expectation-Maximization (EM) algorithm. The algorithm is able to achieve Maximum Likelihood (ML) performance with reduced complexity. Results show how performance superior to the Recursive Least Square (RLS) algorithm, in terms of both convergence and residual Mean Squared Error (MSE), can be achieved with comparable complexity. The channel estimation technique is combined with a new TD based MIMO loop interference cancellation system for wireless relays. Performance results for a 2×2 Downlink (DL) Long Term Evolution (LTE) system are provided for both single-stream transmission with Maximal Ratio Combining (MRC) and dual-stream transmission with Spatial Multiplexing (SM). Results are shown at both low mobility and high mobility, with our EM algorithm showing up to a 2dB improvement in the Error Vector Magnitude (EVM) in the MRC case at 60kmph compared to the RLS.

Performance improvement of CMA based FM multipath cancelling system in automobile application

Constant Modulus Algorithm (CMA) is widely applied to improve distorted transmitting radio signal at the receiver. FM radio is still very popular equipment for in-car entertainment. Therefore, correcting FM multipath distortion on conventional FM radio system is one of the greatly expected applications of CMA technique. In this paper, we discuss performance and improvement of the CMA based FM multipath cancelling system in automobile application by demonstrating influence of impulse noise, which is very common in vehicle environment. Impulse noise, which is received at antenna, will not be corrected at all before it goes into CMA based multipath canceling system as the input. the impulse noise on CMA input will make the system unstable so easily. Proposing limit error signal CMA, we can successfully achieve to avoid influence of the impulse noise.