This letter shows the results of a series of link level simulations conducted to evaluate the performances of spatial and temporal equalizers (S/T-equalizers) using field measurement data. The configuration of the spatial and temporal equalizer discussed in this letter can be expressed as a cascade of an adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of channel delay profile. Bit error rate (BER) performances of the S/T-equalizers are presented, and performance sensitivity to symbol timing offset is investigated.

In SDMA, a spatial domain interference canceller applying a multistage processing concept to the MMSE multibeam adaptive array has an attractive feature. Weak power signals strongly interfered can be detected in the succeeded stages after removing other strong power signals which are already detected. This idea can be enhanced to the reference timing estimation required in the MMSE algorithm. In this paper, the spatial domain interference canceller introducing multistage timing estimation is proposed and its performance is evaluated by computer simulations. The results show that the timing estimation performance highly improved.

In this paper, we present a new transmit diversity scheme with power control by using two transmit antennas in which the power control unit is added to adaptively suit the channel fading variation. Compared to the transmit diversity scheme (STD, one space time coding scheme) proposed by Alamouti and the traditional maximal ratio combining (MRC) diversity scheme employed at the receiver, simulation results indicate that the new scheme has considerable performance gain. We also discuss the effects of the imperfect channel parameter estimation on the performance of the system. Simulation results show that the new system is more robust to the estimation error of channel fading parameters than the STD. As the signal to noise ratio is relatively high, the diversity scheme with power control is more sensitive to the channel estimation error compared to the MRC. But when the channel estimation accuracy is relatively high, the diversity scheme with power control still has better performance than the ideal MRC as the BER is about 1 10-3.

In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) especially from high rate users. This paper proposes a fast and accurate two-step beam tracking algorithm implemented in a pilot symbol-assisted coherent adaptive antenna array diversity (CAAAD) receiver and evaluates its performance both by computer simulation and laboratory experiments. In the proposed scheme, the receiver antenna weights are updated by using both the signal-to-interference power ratio (SIR) measurements employing multiple sets of antenna weights (MSAW) and an adaptive algorithm based on the minimum mean square error (MMSE) criterion, in which other sets except for a original set of antenna weights are simply generated by a original set. Computer simulation results show that antenna weights of a four-antenna CAAAD receiver using the proposed beam tracking algorithm tracks changes in the direction of arrival (DOA) of the desired user at up to 34.3 degrees/sec, which corresponds to 215 km/h at 100 m from a base station. We also confirm based on the experiments in a radio anechoic room that the generated antenna weights track the DOA changes up to 12.3 degrees/sec.

Constant Modulus Algorithm (CMA) is a method that has been widely known as blind adaptive beamforming because it requires no knowledge about the signal except that the transmitted signal waveform has a constant envelope. Although CMA has the merit of this blind operation, it possesses problems in its convergence property. In this paper, problems that are inherent to this algorithm is resolved using a combination of CMA and another major adaptive algorithm SMI (Sample Matrix Inversion). The idea is to use SMI to determine the initial weights for CMA operation. Although the benefit of CMA being a blind algorithm is not fully taken advantage of, good aspects of both SMI and CMA can be introduced. By using this approach, two major problems in convergence properties of CMA can be solved. One of these problems is the reliability and this relates to the convergence performance in certain cases. When the interfering signal is stronger than the desired signal, the algorithm tends to come up with the wrong solution by capturing the interfering signal which has the stronger power. Also, the convergence time of this algorithm is slow, limiting its application in dynamic environment, although the slow convergence time of CMA has been studied previously and several methods have been proposed to overcome this defect. Using the proposed method, the deterioration due to both of these problems can be mitigated. Simulation results are shown to confirm the theory. Furthermore, evaluations are done concerning the fading characteristics. It is also confirmed from the simulation that the tracking performance of this method can be regarded as sufficient in personal mobile communication.

Precise and quick multi-beam forming including null control will be one of the key technologies for the future satellite communication systems utilizing SDMA (Space Division Multiple Access) and DOA (Direction of Arrival) estimation. In order to realize the precise multi-beam forming, calibration procedure is indispensable since there are several unavoidable factors that degrade the multi-beam patterns of the array. Particularly amplitude and phase imbalance between RF circuits needs to be calibrated frequently and quickly when the array system exists in changeable environment since the imbalance easily occurs due to thermal characteristics of each RF circuit. This paper proposes a simple and high-speed remote calibration scheme compensating for amplitude and phase imbalance among RF circuits of a transmitting adaptive array antenna onboard satellite. This calibration is conducted at a remote station such as a gateway station on the ground in the satellite communication system, by utilizing the received signal including the temporally multiplexed orthogonal codes transmitted from the array antenna onboard satellite. Since the calibration factors for all the antenna elements can be simultaneously obtained by the parallel digital signal processing, calibration time can be drastically reduced. The accuracy of this calibration is estimated by simulation. Simulation results show that the amplitude imbalance among RF circuits can be suppressed within the range from -0.5 dB to +0.25 dB for the initial imbalance ranging from -2 dB to +3.5 dB, phase imbalance can be suppressed within the range of -3 deg. to +3 deg. for the initial imbalance ranging from -120 or +180 deg. by this method. The amplitude and phase deviations among the elements can be suppressed within 0.36 dB and 2.5 degrees, respectively, in 80% of probability. Simulation results also show that this calibration method is valid under the relatively bad carrier-to-noise conditions such as -10 dB at the receiver. Good improvement of the multi-beam patterns by this calibration is shown under the low carrier-to-noise ratio condition.

This paper proposes a receiver antenna weight-updating algorithm using I/Q-code multiplexed pilot and decision feedback data symbols after channel decoding for both reference signal generation of the mean squared error (MSE) calculation and channel estimation (also for Rake combining) in the coherent adaptive antenna array diversity (CAAAD) receiver and investigates its performance, in order to decrease further the transmit power of a mobie station, thereby increasing system capacity in the wideband direct sequence code division multiple access (W-CDMA) reverse link. Experimental results show that the required transmit Eb/N0 for the average BER of 10-3 with the CAAAD receiver using pilot and decision feedback data symbols after channel decoding both for reference signal generation and for channel estimation can be decreased by approximately 0.8 dB compared to when using only pilot symbols with convolutional coding or turbo coding, when the ratio of the target Eb/I0 for fast transmit power control of the desired to interfering users is Δ Eb/I0 = -12 dB. The results also elucidate that the required transmit Eb/N0 at the average BER of 10-6 with turbo coding using the proposed decision feedback antenna weight-updating and channel estimation is smaller by approximately 0.5 dB than that using convolutional coding when the channel interleaving length is 20 msec for Δ Eb/I0 = -12 dB.

An AGC Applebaum array, which is a modified Applebaum array employing an automatic gain controller (AGC), is proposed. When the eigenvalues of the input covariance matrix of an array system are spread by orders of magnitude, conventional adaptive arrays are unable to remove all the interference signals quickly. The proposed array increases the cross-correlation between the low-power interference signals at the array input and output through the use of an AGC block in the feedback loop. As a result, the weight vector is adapted for the removal of both low-power and high-power interference signals. Computer simulations were performed to demonstrate that the proposed array can produce high output signal to interference plus noise ratio (SINR) with a fast convergence speed.

We describe a simplified receiver structure having several receiving antennas (i.e., an adaptive array antenna system) and using time-division-multiplexing (TDM) signal processing. Three simplified receiver structures were investigated for use in the antenna system. To confirm the feasibility of using a TDM receiver, both a TDM receiver and a conventional adaptive array receiver were constructed for testing. In our proposed system, several repetitions of the constant modulus algorithm (CMA) are used to reduce co-channel interference (CCI). The frame format used for both receivers was the same as that of the personal handy phone system in Japan. The laboratory testing was done using a fading simulator to enable measurement of the bit error rate. The results are very promising and show the feasibility of the TDM receiver.

The uniform switching system is the family of non-linear n m binary arrays constrained such that all columns are from the constant weight k vectors and all rows have weights divisible by p > 0. For this system, we present a cardinality formula and an enumerative algorithm.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

We propose a novel optical add/drop multiplexer (OADM) utilizing free spectral range (FSR) periodicity of an arrayed-waveguide multiplexer (AWG). In this OADM, wavelength-division multiplex (WDM) signal is multiplexed and/or de-multiplexed in two steps. Power penalty due to coherent crosstalk is drastically reduced compared with that of conventional OADM where AWG multiplexers are opposite to each other. The calculated power penalty due to the coherent crosstalk is about 0.7 dB after the 16 OADMs in the case of 128 wavelengths. It was confirmed through a computer simulation that more than one hundred channels at 10 Gbps data rate could be accommodated in an OADM network with 16 nodes. These results show that the OADM network with over 1 Tbps capacity and 16 nodes could be constructed.

In order that speech recognition system may have a high recognition rate in a noisy environment, a wide-band sharp directional microphone system is required at the input for securing a high S/N ratio. The authors have already reported the realization of a wide-band uni-directional microphone system by three-microphone integration method. In this paper, we intend to describe the derivation of a sharp directivity function and the realization of its microphone system. First, setting the shape of the characteristic function to bring a sharp directional pattern and then expanding it into the Fourier series, we derive a new directivity function. Next, on the basis of this directivity function, we will present a sharp directional microphone system with only three non-directional microphones and the subsequent analog signal processing. And also, the directional pattern acquired by the proposed method and the effect of the dispersion in the sensitivity of the constituent microphones on the directivity are discussed in detail.

This paper describes a new method for estimating the direction of arrival (DOA) using a nonlinear microphone array system based on complementary beamforming. Complementary beamforming is based on two types of beamformers designed to obtain complementary directivity patterns with respect to each other. In this system, since the resultant directivity pattern is proportional to the product of these directivity patterns, the proposed method can be used to estimate DOAs of 2(K-1) sound sources with K-element microphone array. First, DOA-estimation experiments are performed using both computer simulation and actual devices in real acoustic environments. The results clarify that DOA estimation for two sound sources can be accomplished by the proposed method with two microphones. Also, by comparing the resolutions of DOA estimation by the proposed method and by the conventional minimum variance method, we can show that the performance of the proposed method is superior to that of the minimum variance method under all reverberant conditions.

We have demonstrated a dynamically stable polarization operation of GaInAs/GaAs vertical-cavity surface-emitting laser (VCSEL) array grown on a GaAs (311)B substrate. A fabricated 3 3 VCSEL array consists of devices with an oxide aperture of 3.4 µm 3.4 µm. The threshold current was 0.61 0.05 mA and the threshold voltage was 1.79 0.03 V. All of the devices exhibited single-transverse mode operation with an injection current up to three times the threshold. The side-mode suppression ratio (SMSR) is larger than 30 dB. The array also exhibited stable-polarization operation with an orthogonal polarization suppression ratio (OPSR) of over 25 dB. We measured the time-resolved OPSR under square-wave direct modulation. It was found that the orthogonal non-lasing mode was suppressed even at the first peak of relaxation oscillation with OPSR > 17 dB. In an experiment of 5 Gb/s non-return-to-zero (NRZ) pseudo-random bit sequence (PRBS) modulation, the OPSR was maintained being greater than 27 dB. These observed stable and single polarization characteristics were originated from the anisotropic optical gain of strained GaInAs/GaAs quantum wells formed on (311)B substrate. We also carried out an intensity noise measurement under single-transverse and stable polarization operation for the first time. The relative intensity noise (RIN) of -140 dB/Hz was obtained. In addition, we achieved 2.5 Gb/s data transmission through a 100 m multi-mode fiber. No error floor was observed at -20 dBm of received power level. The minimum received power is determined by the thermal noise.

This paper evaluates through laboratory and field experiments the combined effect of the coherent adaptive antenna array diversity (CAAAD) receiver and signal-to-interference plus background noise ratio (SINR)-based fast transmit power control (TPC) in order to improve performance beyond that of space diversity (SD) with maximal ratio combining (MRC) in all low-to-high signal-to-interference power ratio (SIR) channels in the W-CDMA reverse link. Although the previously proposed CAAAD receiver comprising an adaptive antenna array based on the minimum mean square error (MMSE) criterion and a coherent Rake combiner was very effective in suppressing interference in low SIR (interference is severe) channels, SD employing MRC in noise limited channels (high SIR) outperformed the CAAAD because of its uncorrelated reception of fading variation due to its large antenna separation. The laboratory experimental results showed that the required average transmit signal energy per bit-to-background noise spectrum density (Eb/N0) with the CAAAD receiver using fast TPC is lower than that with an SD receiver over a wide range of maximum Doppler frequency values from fD = 5 Hz to 500 Hz in a low-to-high SIR channel. The results of the field experiments also showed that combining CAAAD and fast TPC is a powerful means to reduce severe multiple access interference (MAI) from high rate users in a low-to-high SIR environment and is more effective than using the SD receiver with the same number of antennas, i.e., the measured BER was improved by approximately one order of magnitude, when the relative transmit power of the desired user was 8 dB with two antennas at the average received SIR at the antenna input of -12 dB.

The ring-like systolic array architecture described in this paper, based on a conventional one-dimensional systolic array architecture, was created through operator rescheduling based on the symmetry of data flow. This eliminated high-latency delay due to the stuffing of the array pipeline in the conventional architecture. The new architecture requires a memory bandwidth no greater than the conventional architecture does, but increases throughput and processor utilization while reducing power consumption.

It is difficult for an adaptive array to reduce interference signals efficiently from received signals when the interference signals and desired signal are closely located. This is a problem for a spatial division multiple access (SDMA) system using the multibeam adaptive array as a multiuser detector. In this paper, we propose a space domain multistage interference canceller (SD-MIC) for the SDMA system. Its performance is evaluated by computer simulations, assuming Japanese personal handy phone system (PHS) uplink environments. The results show remarkable improvement in high spatial correlation situations.

This paper proposes a new adaptation-mode control (AMC) for a robust adaptive microphone array with an adaptive blocking matrix (RAMA-ABM). The proposed AMC is based on cross correlations of two microphone signals and uses a state machine for controlling the adaptation to avoid target-signal cancellation. Evaluation with sound data obtained in different acoustic environments demonstrates that the noise reduction by the proposed AMC is 3 dB better than that by the AMC based on the SNR estimate. Subjective listening tests show that the quality of the output signal by the proposed AMC is comparable to or even better than those by the conventional AMCs.

This paper presents efficient time slot assignment algorithms applicable to the uplink of SDMA system. A frame consists of one control time slot and multiple communication time slots where terminals in different angular positions share the same time slot. In the proposed algorithms, a time slot is assigned to a new terminal considering not only the signal quality of the new terminal but also the signal quality of active terminals. Simple calculation method for estimated signal-to-interference plus noise ratio (SINR) is employed to decrease the computational complexity. The performance of the proposed algorithms is evaluated by computer simulation and compared with sectorized systems to show the validity of the proposed algorithms.