This paper proposes a new switched-beam eight-sector antenna for multi-gigabit wireless LAN in the 60-GHz band. Our antenna system introduces access-point (AP) and user-terminal (UT) antennas having the same secθ pattern in the elevation plane so that the received signal power at the receiver is kept constant, independent of the position of the UT. For this system, an eight-sector antenna, a single-pole eight-throw (SP8T) switch, and a beam control unit are integrated as the switched-beam eight-sector antenna. The specifications of the antenna are wide bandwidth ( ≥3 GHz), high-gain ( ≥13 dBi at θ =66), and wide coverage area in both azimuth (0 ≤ φ ≤ 180) and elevation planes (0 ≤ θ ≤ 66). The antenna beam is steered within the specified response time (which is short) by the Media Access Control (MAC). In our antenna, both high gain for a wide elevation angle and wide bandwidth are obtained by using the proposed closely spaced waveguide slot array antenna, which is used as each sector of the eight-sector antenna. The SP8T switch with the beam control unit enables 180 beam scan in the azimuth plane. In a component evaluation, the eight-sector antenna achieves a 10-dB return loss bandwidth of 8 GHz with more than 40-dB port-to-port isolation. Radiation characteristics of the eight-sector antenna indicate that it covers 82% of the entire coverage area at the center frequency and that the coverage rate in the operating frequency band is from 78% to 88%. The performance of the SP8T switch and the beam control unit is verified by measuring the insertion loss at all eight ports and the switching response time. In the antenna system evaluation, measurement by using two prototype antennas as the AP and the UT antennas in the usage condition indicates that the measured received signal power meets the specified constant power for the specified wide elevation angle range, independent of the position of the UT. These experimental results verify the effectiveness of our proposed antenna for multi-gigabit WLAN.

An efficient noise reduction algorithm is proposed to improve speech recognition performance for human machine interfaces. In the algorithm, a probabilistic adaptation mode controller (AMC) is designed and adopted to the generalized sidelobe canceller (GSC). To detect target speech intervals, the proposed AMC calculates the inter-channel correlation and estimates speech absence probability (SAP). Based on the SAP, the adaptation mode of the adaptive filter in the GSC is decided. Experimental results show the proposed algorithm significantly improves speech recognition performances and signal-to-noise ratios in real noisy environments.

In conventional preamble based channel estimation in OFDM/offset QAM (OFDM/OQAM) system, both the even index subcarriers and the odd index subcarriers are with identical value selected from { 1 } respectively to avoid inter-carrier interference (ICI), if and only if channel frequency response in neighbor few subcarriers remain invariable. However, it requires larger coherent bandwidth. In this paper, we propose an effective preamble design with ICI cancellation for channel estimation in OFDM/OQAM system. With this structure, we only utilize even (or odd) index of subcarriers as reference signal to avoid ICI, and then the channel information of remaining subcarriers can be estimated by the interpolation approach. Based on the sampling theorem, the mean square error (MSE) performance of the proposed preamble design is analyzed, where channel estimation performance is same for all subcarriers. Simulation and analytical results demonstrate that the proposed preamble design with ICI cancellation method outperforms the conventional one in term of channel estimation accuracy in OFDM/OQAM system.

In this paper, a new handover procedure for OFDM-based multi-hop relay systems is proposed to reduce handover overhead by distinguishing an inter-cell handover event from an intra-cell handover event at the level of the physical layer using a preamble with a hierarchical design. A Subcell ID concept used to identify relay station in a cell is proposed in the hierarchical design that works in conjunction with the existing Cell ID used to identify base station. The proposed handover procedure can simplify the scanning procedure and skip/simplify the network re-entry procedure, resulting in a significant reduction in handover overhead.

OFDM (Orthogonal Frequency Division Multiplexing) is widely used in wideband wireless communication systems due to its excellent performance. One of the most important operations in OFDM receivers is preamble detection. This paper addresses a general form of extended differential detection methods, which is a combination of differential detection and a moving average filter. This paper also presents a filter size determination method that achieves satisfactory performance in various channel environments.

Currently deployed mobile networks including High Speed Downlink Packet Access (HSDPA) offer only best-effort Quality of Service (QoS). In wireless best effort networks, the bandwidth variation is a critical problem, especially, for mobile devices with small buffers. This is because the bandwidth variation leads to packet losses caused by buffer overflow as well as picture freezing due to high transmission delay or buffer underflow. In this paper, in order to provide seamless video streaming over HSDPA, we propose an efficient real-time video streaming method that consists of the available bandwidth (AB) estimation for the HSDPA network and the transmission rate control to prevent buffer overflows/underflows. In the proposed method, the client estimates the AB and the estimated AB is fed back to the server through real-time transport control protocol (RTCP) packets. Then, the server adaptively adjusts the transmission rate according to the estimated AB and the buffer state obtained from the RTCP feedback information. Experimental results show that the proposed method achieves seamless video streaming over the HSDPA network providing higher video quality and lower transmission delay.

Infrastructure wireless mesh network has been attracting much attention due to the wide range of its application such as public wireless access, sensor network, etc. In recent years, researchers have shown that significant network throughput gain can be achieved by employing network coding in a wireless environment. For further improvement of network throughput in one dimensional (1D) topology, Ono et al. proposed to use multiple antenna technique combined with network coding. In this paper, being inspired by MIMO network coding in 1D topology, the authors establish a novel MIMO network coding algorithm for a 2D topology consisting of two crossing routes. In this algorithm, multiple network coded flows are spatially multiplexed. Owing to the efficient usage of radio resource of network coding and co-channel interference cancellation ability of MIMO, the proposed algorithm shows an 8-fold gain in network capacity compared to conventional methods in the best-case scenario.

Proxy Mobile IPv6 (PMIPv6) has been proposed in order to overcome the limitations of host-based mobility management in IPv6 networks. However, packet losses during doing handover are still a problem. To solve this issue, several schemes have been developed, and can be classified into two approaches: predictive and reactive handover. Both approaches commonly use bi-directional tunnel between mobile access gateways (MAGs). In predictive schemes especially, mobility support for a mobile node (MN) is triggered by simplified link signal strength. Thereafter, the MN sends handover notification to its serving MAG, and is then able to initiate packet forwarding. Therefore, if the MN moves toward an unexpected MAG that does not have any pre-established tunnel with the serving MAG, it may lead to packet losses. In this paper, we define this problem as Early Packet Forwarding (EPF). As a solution, we propose an enhanced PMIPv6 scheme using two-phase tunnel control based on the IEEE 802.21 Media Independent Handover (MIH).

Bloom filters are widely used for various network applications. Because of the limited size of on-chip memory and the large volume of network traffic, Bloom filters are often required to update their contents incrementally. Two techniques have been used for this purpose: cold cache and double buffering. Cold cache outperforms double buffering in terms of the average cache ratio. However, double buffering works much better than cold cache for the worst-case cache hit ratio. In this paper, we propose a new updating scheme for Bloom filters, which updates the contents of Bloom filter incrementally while the assigned memory space is fully utilized. The proposed scheme works better than cold cache in terms of the average cache hit ratio. At the same time, it outperforms double buffering for the worst-case cache hit ratio.

Multiple-input-multiple-output (MIMO) wireless systems can not always have full spatial multiplexing gain due to the channel correlation problem caused by various factors such as the coupled antenna elements, and the key-hole effect of the propagation environment. In this paper, we proposed a channel reconfiguration technique to combat the rank deficiency problem of the involved MIMO wireless channels that can not afford high-order multiplexing gains. In the proposed approach, each mobile station can simultaneously receive several independent data streams from multiple base stations through a set of MMSE-based receive beamformers to suppress the multiple access interferences. Making use of the receive beamforming, which virtually produce the effect of a single antenna at each receive mobile, makes the transmit base station possible to reconfigure the MIMO downlink channel and then pre-cancel the co-channel interferences. The proposed signal processing mechanism that iteratively optimized the MMSE receive weights and the transmit precoders, which brings the reconfigured MIMO system about the high data throughput seen only with indoor MIMO systems having rich wireless channels. It is shown that as compared to the conventional MIMO system, the M4 system can achieve a significantly higher capacity which is proportional to the number of the linked base stations.

A multiuser beamforming algorithm using codebook is proposed in this letter to reduce inter-user interference and improve the throughput of the downlink of multiuser MIMO systems. Basing on the minimal leakage criterion, we combine the codebook selection, limited feedforward and MMSE detection method in the new proposed algorithm. It not only improves the performance of systems, but also reduces the computational complexity at transmitter. Simulation results shows that the proposed algorithm has better performance than conventional beamforming methods.

High Altitude Platform Stations (HAPS) are recently considered as a green infrastructure to provide high speed multimedia services. The critical issue of HAPS is frequency sharing with satellite systems. Regulating antenna beam pattern using adaptive antenna schemes is one of means to facilitate the sharing with a space receiver for fixed satellite services on the uplink of a HAPS system operating in U bands. In this letter, we investigate antenna beam pattern characteristics of HAPS user terminals with various values of scan angles of main beam, null position angles, and null width.

With the increasing deployment of mobile devices and the advent of broadband wireless access systems such as WiBro, mWiMAX, and HSDPA, an efficient IP mobility management protocol becomes one of the most important technical issues for the successful deployment of the broadband wireless data networking service. IETF has proposed the Mobile IPv6 as the basic mobility management protocol for IPv6 networks. To enhance the performance of the basic MIPv6, researchers have been actively working on HMIPv6 and FMIPv6 protocols. In this paper, we propose a new mobility management protocol, HIMIPv6 (Highly Integrated MIPv6), which tightly integrates the hierarchical mobility management mechanism of the HMIPv6 and the proactive handover support of the FMIPv6 to enhance the handover performance especially for the cellular networking environment with high frequent handover activities. We have performed extensive simulation study using ns2 and the results show that the proposed HIMIPv6 outperforms FMIPv6 and HMIPv6. There is no packet loss and consequent service interruption caused by IP handover in HIMIP.

A new random access channel (RACH) preamble detection scheme using variable coherent correlation intervals (CCIs) is proposed. It is shown first that it is enough to employ two CCIs for supporting a user equipment (UE) velocity of 300 km/h, and then a CCI selection criterion is proposed. Computer simulation results indicate that the proposed scheme can provide a robust detection performance in time-varying fading channel environments.

Bessel beams are a family of diffraction-free beams. They have many unique properties and prospective applications. Much attention has been focused to this subject in optics. Recently, the studies of such beams at mm- and submm- wavebands have been carried out in our group. The investigation results, including their theories, generation, propagation and potential applications, are presented in this paper.

The beamforming weights which can suppress the interfering signal toward out-of-cell mobile stations in downlink are designed for a time division duplexing based OFDMA system when the channel information is not perfect. The derived beamforming weights do not improve the average SINR performance monotonously with the increased transmit SNR if the inverse of the transmit SNR is used as the regularization factor of the beamforming weights and the channel information obtained by the BS to design the BF weights is not perfect. Therefore, we suggest a simple scheme to select the regularization factor. The proposed beamforming weights improve the performance monotonously with the increased transmit SNR and achieve near-optimal performance. The performance achieved by applying the beamforming weights used in uplink to downlink beamforming is also investigated.

In this paper, we propose a predicate indexing method which handles equality and inequality tests separately. Our method uses a hash table for the equality test and a balanced binary search tree for the inequality test. Such a separate structure reduces a height of the search tree and the number of comparisons per tree node, as well as the cost for tree rebalancing. We compared our method with the IBS-tree which is one of the popular indexing methods suitable for data stream processing. Our experimental results show that the proposed method provides better insertion and search performances than the IBS-tree.

This letter presents beam tilting characteristics of a slot antenna element with reactance loading. It is found that the beam tilt is obtained by controlling aperture electric field distributions with a loaded reactance on the slot. A large beam tilt angle is obtained when an inductive reactance element is loaded.

This letter presents an adaptive beamformer robust to random steering errors, based on the projection of received signals onto the orthogonal complement of the interference subspace. In the presence of random steering errors, to prevent the suppression of the desired signal, the proposed beamformer effectively finds basis vectors for the estimation of the interference subspace.

Blind beamforming plays an important role in multiple-input multiple-output (MIMO) Systems, radar, cognitive radio, and system identification. In this paper, we propose a new algorithm for multiple blind beamforming algorithm based on the least square constant modulus algorithm (LSCMA). The new method consists of the following three parts: (a) beamforming of one signal with LSCMA. (b) direction-of-arrival (DOA) estimation of the remaining signals by rooting the weight vector polynomial. (c) beamforming of the remaining signals with linear constraints minimum variance (LCMV) method. After the convergence of LSCMA, one signal is captured and the arrival angles of the remaining signals can be obtained by rooting the weight vector polynomial. Therefore, beamforming can be quickly established for the remaining signals using LCMV method. Simultaneously the DOA of the signals can also be obtained. Simulation results show the performance of the presented method.