This paper describes implementation and performance evaluation of simple SDM-COFDM (Space Division Multiplexed-Coded Orthogonal Frequency Division Multiplexing) prototype over fading MIMO (Multi-Input Multi-Output) channel in order to achieve higher frequency utilization efficiency. It employs ZF (Zero Forcing) type detection scheme for SDM transmission to reduce hardware implementation complexity, where ZF type detection scheme needs to only multiply the received data by the estimated inverse propagation coefficient matrix at each OFDM subcarrier. Moreover, in order to improve the performance degradation due to the increase of the transmitted data length per frame in fast fading environments, the inverse matrix tracking using STC (Space-Time Coded) pilot is proposed and implemented in the prototype. Experimental results show that the prototype with 22 antennas achieves about 90% increase of the frequency utilization efficiency compared to the SISO (Single-Input Single-Output) transmission.

A waveguide 2-plane hybrid coupler with two operating bands is proposed. The cross-sectional shape of the coupled region inside the proposed coupler is designed with a two-dimensional arbitrary geometry sorting method. Simulations of the proposed hybrid coupler has a fractional bandwidth (FBW) of 2.17% at the center of 24.99GHz, and at the center of 28.28GHz an FBW of 6.13%. The proposed coupler is analyzed by the mode-matching finite-element hybrid method, and the final result is obtained using a genetic algorithm. The analyzed result of the coupling for the main modes in the coupled region is presented. The design result is confirmed by measurements.

This paper presents a wireless burst modulation/ demodulation method for narrowband ubiquitous communication systems. This method especially suits those systems, whose traffic is especially dominated by short frame bursts. The proposed modulation method provides a preamble-less frame structure with training symbols, which improves both transmission efficiency and burst synchronization performance. Moreover, the proposed demodulation method achieves superior burst synchronization performance in low carrier-to-noise power ratio (CNR) environments by applying a synchronization method that includes symbol timing recovery, slot synchronization, carrier frequency correction and channel tracking. In addition, this paper presents the result of experiments on hardware prototypes of the proposed modulator and demodulator. The basic operation and practical performance of the proposed method is confirmed through testbed studies.

High gain antennas with narrow-beamforming are required to compensate for the high propagation loss expected in high frequency bands such as the millimeter wave and sub-terahertz wave bands, which are promising for achieving extremely high speeds and capacity. However using narrow-beamforming for initial access (IA) beam search in all directions incurs an excessive overhead. Using wide-beamforming can reduce the overhead for IA but it also shrinks the coverage area due to the lower beamforming gain. Here, it is assumed that there are some situations in which the required coverage distance differs depending on the direction from the antenna. For example, the distance to an floor for a ceiling-mounted antenna varies depending on the direction, and the distance to the obstruction becomes the required coverage distance for an antenna installation design that assumes line-of-sight. In this paper, we propose a novel IA beam search scheme with adaptive beam width control based on the distance to shield obstacles in each direction. Simulations and experiments show that the proposed method reduces the overhead by 20%-50% without shrinking the coverage area in shield environments compared to exhaustive beam search with narrow-beamforming.

High-frequency wireless communication is drawing attention because of its potential to actualize huge transmission capacity in the next generation wireless system. The use of high-frequency bands requires dense deployment of access points to compensate for significant distance attenuation and diffraction loss. Dense deployment of access points in a mobility environment triggers an increase in the frequency of handover because the number of candidate access points increases. Therefore, simple handover schemes are needed. High-frequency wireless systems enable station position to be determined using their wideband and highly directional communication signals. Thus, simple handover based on position information estimated using the communication signal is possible. Interruptions caused by handover are also a huge barrier to actualizing stable high-frequency wireless communications. This paper proposes a seamless handover scheme using multiple radio units. This paper evaluates the combination of simple handover and the proposed scheme based on experiments using a formula racing car representing the fastest high-speed mobility environment. Experimental results show that seamless handover and high-speed wireless transmission over 200Mbps are achieved over a 400-m area even at station velocities of greater than 200km/h.

This paper proposes a new multi-task synchronization scheme for packet mode orthogonal frequency division multiplexing (OFDM) signals in multi-input multi-output (MIMO) transmission systems; it targets high-rate wireless LANs that offer over 100 Mbit/s. In addition, this paper introduces a packet format for MIMO-OFDM signals that ensures backward compatibility with IEEE 802.11a. The proposed synchronization scheme has simple open-loop construction and consists of automatic frequency control (AFC), symbol timing detection, MIMO channel estimation, and phase tracking. AFC and symbol timing detection are carried out in the time-domain. After OFDM demodulation, the proposed scheme performs MIMO channel estimation and phase tracking in the frequency-domain. Considering all of the above synchronization tasks, we evaluate the packet error rate (PER) performance using the IEEE 802.11 TGn-defined channel model-D and model-E. In channel model-D with the RMS delay spread = 50 ns, the proposed scheme shows superior performance; it suppress the required Eb/N0 degradation to within 0.4 dB with 1000 byte packets compared to the performance achieved if only MIMO channel estimation is considered. Moreover, in channel model-E with the RMS delay spread = 100 ns, it is found that the proposed scheme degrades the required Eb/N0 only by approximately 1.5 dB compared to the MIMO channel estimation only case, even if the packet length is 1000 bytes with 64QAM and coding-rate = 7/8.