In this letter, we introduce a new adaptive beamforming assisted receiver based on minimizing the approximate negentropy (NEGMIN) of the estimation error. We consider the approximate negentropy by using a nonpolynomial expansion of the estimation error as a new performance criterion to improve the performance of adaptive beamforming receivers based on the minimizing minimum mean squared error (MMSE) criteria. Negentropy includes higher order statistical information and its minimization provides improved converge, performance, and accuracy compared to traditional methods such as MMSE in terms of bit error rate (BER).

In a frequency-selective multiple-input multiple-output (MIMO) channel, the optimum transmission is achieved by beamforming with eigenvectors obtained at each discrete frequency point, i.e., an extension of eigenbeam-space division multiplexing (E-SDM). However, the calculation load of eigenvalue decomposition at the transmitter increases in proportion to the number of frequency points. In addition, frequency-independent eigenvectors increase the delay spread of the effective channel observed at the receiver. In this paper, we propose a pseudo eigenvector scheme for the purpose of mitigating the calculation load and maintaining frequency continuity (or decreasing the delay spread). First, we demonstrate that pseudo eigenvectors reduce the delay spread of the effective channels with low computational complexity. Next, the practical performance of the pseudo E-SDM (PE-SDM) transmission is evaluated. The simulation results show that PE-SDM provides almost the same or better performance compared with E-SDM when the receiver employs a time-windowing-based channel estimation available in the low delay spread cases.

Optical wireless communications is a research topic of extreme interest since it offers high data rate (Gbps data rate), security, and RF interference immunity. However, optical wireless communications places severe restrictions on the communications paths; they must be direct beam connections. To increase the number of users and link robustness, optical wireless communications must be able to operate even when obstacles are placed between transmitters and receivers, so optical micro-cell (OMC) with autonomous beam control can overcome link robustness. In addition, OMC based optical wireless communication yields compact systems. This paper presents the design, an implementation, and a demonstration of a 114 Mbps autonomous beam control optical wireless communication system based on an OMC technique. The robust posture control results optimum downlink alignment and good eye diagram of data transmission.

A method for measuring the luminance distribution of an electron beam spot was described, which is fundamental to evaluate the resolution of a color display tube. First, to achieve high sensitivity and wide dynamic range identical to those of visual inspection, we proposed the use of an ICCD camera for imaging and two levels of sensitivity. With that method, we were able to measure the luminance distribution of an electron beam spot over a range of currents that extends from the extremely weak cathode current region to large current that correspond to the peak luminance. Specifically, we were able to measure the entire distribution shape from the base to the peak for beam spots in the cathode current range from 20 µA to 300 µA, while compensating the absolute luminance level. Second, a reconstruction algorithm of entire beam distribution from the shape of the masked part of the beam was also proposed, in which shift error is compensated to reduce the variance in measurement results caused by jitter noise in the conventional image processing method. That algorithm improves the reproducibility of repeated measurements. Specifically, a function for estimating the actual shift from the first-order moment of the image was incorporated into the spot shape reconstruction algorithm, resulting in a reduction of the standard deviation for repeated measurements of the horizontal beam spot diameter at 5% intensity from 0.02 mm to 0.005 mm.

This paper presents interference suppression using a subband adaptive array (SBAA) for uplink space-time block coding (STBC) code division multiple access (CDMA) under a frequency selective fading (FSF) channel. The proposed scheme utilizes CDMA with STBC and a receive array antenna with SBAA processing at the receiver. The received signal is converted into the frequency domain before despreading and adaptive processing is performed for each subband. A novel SBAA construction is introduced to process CDMA signals based on STBC. To improve the performance of the proposed scheme, we evaluate STBC-SBAA using spreading codes cyclic prefix (CP). Simulation results demonstrate an improved performance of the proposed system for single and multiuser environments compared to competing related techniques.

This paper describes a beam scanning antenna that consists of a movable dielectric plate loaded onto a microstrip comb-line antenna. This type of antenna uses a mechanical system and so offers a simple structure and low cost. The main beam direction of the proposed antenna is changed by moving the dielectric plate. The guide wavelength of the microstrip line was measured at the quasi-millimeter wave band (20 GHz) when moving the dielectric plate to investigate the possibility of beam scanning. The proposed antenna was fabricated to experimentally demonstrate its principle operation. A possible beam scanning angle of 20 degrees was confirmed.

To create a next-generation mobile satellite communication system that offers large communication capacity, the onboard antenna system must be a multi-beam system consisting of a light weight 20-m class reflector and a light weight 100-beam class antenna feed system. We clarify that the antenna gain decrease created by the reflector surface distortion expected in orbit is relatively large. This paper presents a deformed antenna pattern compensation method that minimizes circuit scale. Validity of the proposed method is confirmed by antenna pattern calculations and experiments on a fabricated array-fed reflector antenna.

Multiuser multiple input multiple output (MU-MIMO) systems are attracting attention due to their frequency efficiency. However, in uplink MU-MIMO systems, different frequency offsets among multiple mobile stations (MSs) significantly degrade the transmission quality, especially when orthogonal frequency division multiplexing (OFDM) is used. In this paper, the influence of these frequency offsets is first analyzed in a frequency selective fading environment. Numerical analysis shows that an error floor occurs in the bit error rate and the influence of the frequency offset becomes larger in short delay spread environments. To overcome this problem, a new beamforming method is proposed to compensate for the frequency offset by introducing an auto frequency controller after frequency-space equalization in each data stream. The effect of the proposed method is evaluated in a frequency selective fading environment by computer simulations and measured results.

Multiple input multiple output (MIMO) systems represent a very attractive candidate for future high data rate wireless access systems to increase the channel capacity. To obtain a further increase in the channel capacity, a distributed wireless communication system that has multiple access points (APs) and an access controller (AC), was proposed. This system increases not only the peak transmission rate but also the overall transmission rate in the service area. In this paper, we consider a cooperative multiple AP system where APs are synchronized in terms of time, but not in terms of phase. We propose a transmission method for the cooperative multiple AP system that enables the mobile station to obtain a high achievable bit rate regardless of decoding algorithms. The performance of the multiple AP systems is evaluated in comparison to the conventional single AP system. To evaluate the effectiveness of the proposed method in the cooperative multiple AP system, computer simulations are performed using the i.i.d. channel in Rayleigh and Ricean fading environments. Furthermore, we evaluate the performance of the cooperative multiple AP system using the channel measured in an actual indoor environment.

In this paper, we examine the effectiveness of clock control in protecting stream ciphers from a distinguishing attack, and show that this form of control is effective against such attacks. We model two typical clock-controlled stream ciphers and analyze the increase in computational complexity for these attacks due to clock control. We then analyze parameters for the design of clock-controlled stream ciphers, such as the length of the LFSR used for clock control. By adopting the design criteria described in this paper, a designer can find the optimal length of the clock-control sequence LFSR.

In this letter, we study the impact of feedback error on transmit beamforming systems with finite rate feedback. The feedback channel is modeled as a uniform symmetric channel. The outage probability, bit error rate (BER), diversity gain, and array gain formulas are given. Both analytical and simulation results show that feedback error with small probability will make the system behave badly at high signal-to-noise ratios (SNR).

This paper presents the switched-beam slot antenna over the electromagnetic band-gap (EBG) reflector. This antenna is composed of two slot elements fed with a phase difference and the EBG reflector, which is used in order to realize a low profile structure. The radiation characteristics of this antenna are calculated using the FDTD method. Calculations show that the height of the antenna using the EBG reflector is 60 % lower than that of the antenna using a perfect electric conductor (PEC) reflector. The radiation characteristics at the center of the operating frequency band in the EBG reflector are equivalent to that in the PEC reflector. It is shown that the tilt angle of the main beam in the elevation plane varies with the operating frequency, and the variation in the case of the EBG reflector is caused by its frequency-dependent reflection phase. Moreover, the radiation pattern of the fabricated antenna is measured. The results demonstrate that the low profile design can be achieved by using the EBG reflector, and reveal the influence of the EBG reflector on the antenna efficiency.

We introduce a novel configuration for a multi-user Multiple-Input Multiple-Output (MIMO) system in mobile communication over fast fading channels using space-time block coding (STBC) and adaptive array. The proposed scheme adopts the simultaneous transmission of data and pilot signals which reduces control errors caused by delay of obtaining channel state information (CSI). Data and pilot signals are then encoded using a space-time block code and are transmitted from two transmit antennas. In order to overcome the fast fading problem, implementation of adaptive array using recursive least squares (RLS) algorithms is considered at the base station. Through computer simulation, it is shown that the proposed scheme in this way can overcome Doppler spread in higher frequencies and suppress co-channel interference up to N-1 users for N receiving antennas.

This paper presents design of an alternating-phase fed single-layer slotted waveguide array for a sector shaped beam in the E-plane radiation pattern. A sector beam pattern is very effective for radar applications for detecting obstacles in a certain angular range without mechanical or electronic scanning. The sector shaped beam with 13 degree beam width is synthesized by a cascade of T-junctions in the feed waveguide which excite the radiating waveguides with a longitudinal shunt slot array. In order to realize the required excitation distribution of the radiating waveguides for the sector shaped beam, 30 T-junctions with symmetrical arrangement are designed by tuning a width of the coupling window, an offset of the window, and a width of the feed waveguide cascaded to the subsequent T-junction, respectively. Design and measurement are performed in 60 GHz band. The prototype antenna assembles easily; the slotted plate is just tacked on the groove feed structure and is fixed by screws at the periphery, which is the key advantage of the alternating-phase fed arrays. The measured sector pattern with low sidelobe level agrees well with the predicted one. Validity of the sector beam design as well as the performance of the alternating-phase fed array is confirmed by the measurement.

Channel state information (CSI) at transmitter plays an important role for multiuser MIMO broadcast channels, but full CSI at transmitter is not available for many practical systems. Previous work has proposed orthonormal random beamforming (ORBF) [16] for MIMO broadcast channels with partial channel state information (CSI) feedback, and shown that ORBF achieves the optimal sum-rate capacity for a large number of users. However, for cellular systems with moderate number of users, i.e., no more than 64, ORBF only achieves slight performance gain. Therefore, we analyze the performance of ORBF with moderate number of users and total transmit power constraint and show that ORBF scheme is more efficient under low SNR. Then we propose an adaptive ORBF scheme that selects the number of random beams for simultaneous transmission according to the average signal-to-noise ratio (SNR). Moreover, a multi-beam selection (MBS) scheme that jointly selects the number and the subset of the multiple beams is proposed to further improve the system performance for low SNR cases. The simulation results show that the proposed schemes achieve significant performance improvement when the number of users is moderate.

In order to realize a higher density version of the conventional optical disk, shorter wavelength laser and narrower track pitch have been put to practical use. However, using narrow track pitch can cause the increase of the crosstalk from the adjacent tracks. Moreover, the use of narrow pitch and short wavelength can also give rise to the increase of deterioration of the detected signal characteristics due to the microscopic roughness of disk surface. In this paper, in order to estimate the effect of surface roughness theoretically, we try to analyze the light-beam scattering and detected signal characteristics of a blue laser optical disk model with random rough surfaces by the Finite Difference Time Domain (FDTD) method.

The minimum mean square error (MMSE) multiple antenna transmission scheme for a code division multiple access (CDMA) system was recently developed by Choi and Perreau [1]. In this paper, we first show that the zero-forcing (ZF) transmit beamformer for multiple antenna CDMA system has the same form as the MMSE beamformer given by Choi and Perreau. We then develop an analytical method to obtain a closed-form expression of the bit error rate (BER) of the ZF transmit beamformer when there are channel estimation errors. The analytical and simulation results show good agreement, and confirm the importance of accurate channel state information (CSI) at the transmitter when using the ZF transmit beamformer.

Traditional load shedding algorithms for data stream systems calculate current operator selectivity over several run periods and use them to determine where to shed load during the next run period. In this paper, we show that the current selectivity may change due to the implementation of load shedding. Our algorithm, called RLS, determines the optimum drop location by these changed selectivity rather than those pre-calculated values. Simulation results demonstrate that RLS achieves higher accuracy than traditional algorithms.

In order to improve the antenna gain, a composite right/left-handed (CRLH) leaky-wave (LW) antenna composed of symmetrical unit cells with short stubs terminated by vertical vias is designed. The use of symmetrical unit cells suppresses the cross-polarization of radiation to less than 23 dB. By comparing the measured radiation characteristics to that of a conventional CRLH LW antenna without short stub in the X-band, it is shown that the presented CRLH LW antenna with 51 unit cells offers a narrower beam and the antenna gain improves 4.1, 2.2 and 3.1 dB in the backward, broadside and forward directions of radiation, respectively.

Since Smart Antenna technology has powerful spatial processing ability; it is regarded as a promising approach to enhancing the data rates and capacity of wireless LAN systems. In this paper, a small size, practical switched-beam antenna system, well suited for domestic in-home networking in the 2.4 GHz band, is designed and tested. The system has the configuration of regular nine-prism, and nine 1/4 wavelength rectangular patches are symmetrically distributed on the nine sides of the prism. The switching process is based on control of the microstrip used to feed the patch radiators, by placing PIN diodes at the microstrip feeding lines. The antenna array can generate nine beams with a gain of 11 dB. All the beams generated by the system are cophasal excited and have a 40°beamwidth. Compared to the uniform array, the system can guarantee the consistency of every beam and is preferable in shape.