A new iterative algorithm based on the Gauss-Seidel iteration method is proposed to solve the matrix equation in the MoM analysis of the array antennas. In the new algorithm, the impedance matrix is decomposed into a number of sub matrices, which describe the self and mutual impedance between the groups of the array, and each sub matrix is regarded as a basic iteration unit rather than the matrix element in the ordinary Gauss-Seidel iteration method. It is found that the convergence condition of the ordinary Gauss-Seidel iteration scheme is very strict for the practical use, while the convergence characteristics of the present algorithm are greatly improved. The new algorithm can be applied to the sub domain MoM with a fast convergence if the grouping technique is properly used. The computation time for solving the matrix equation is reduced to be almost proportional to the square of the number of the array elements. The present method is effective in MoM analysis of solving large-scale array antennas.

Space-time turbo codes have both advantages of space-time codes and turbo codes, and the space-time turbo code proposed by Su and Geraniotis is known to achieve full coding rate and full antenna diversity. This paper presents some improvements of their space-time turbo code in a two-antenna configuration. We first propose a new condition for full antenna diversity which imposes less constraints on the interleaver. Next, by applying a method used to improve turbo trellis-coded modulation to the space-time turbo code, we propose a new decoding algorithm which utilizes more precise estimates on extrinsic information. Simulation results show that the proposed condition assures full antenna diversity and the new decoding algorithm provides a better performance than that of Su and Geraniotis'.

A unified view of RAKE reception is proposed which models a RAKE receiver as an antenna array. This unified view provides valuable insight to the signal environment under RAKE reception. Based on this view, an optimum combining scheme for RAKE receivers is proposed for the downlink of multi-code W-CDMA systems. In multi-code scenarios, the presence of inter-code interference causes severe performance degradation. The antenna array model suggests that enhancement can be achieved by increasing the receiver's degrees of freedom which is defined as the number of RAKE fingers and employs an appropriate combining scheme. The conventional maximum-ratio combining scheme is excluded since it is not capable of exploiting the increased degrees of freedom. In contrast, the proposed combining scheme provides better interference suppression when the degrees of freedom are increased. Numerical results obtained show that the proposed scheme provides very promising performance.

An adaptive array antenna should be applied for suppression of CCI in the spatial domain. However, the adaptive array antenna has some problems as follows. Because the adaptive array antenna takes a long time to converge to the optimum antenna weights, it's hard to track in case of quick varying channel. On the other hand, processing burden increases with the number of elements in the array antenna. To solve these problems, we propose an adaptive array antenna using array antenna as element antennas, the so-called "Layered array antenna." At the 1st layer, sector area are defined. We can change the sector areas according to the DOA distribution, because the sector areas are defined by the antenna weights. At the 2nd layer, MMSE is performed. Interference that couldn't be suppressed at the 1st layer is suppressed at the 2nd layer. By the proposed system, we confirmed higher convergence speed while relieving processing complexity.

This paper presents an optimum antenna diversity combining method associated with despreading that employs Minimum Mean Square Error (MMSE) combining over the frequency domain in a frequency-selective fading channel for forward link Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access, in order to achieve the maximum radio link capacity. Simulation results considering various propagation channel conditions elucidate that the antenna diversity combining method with Equal Gain Combining (EGC) subsequent to the despreading employing MMSE combining based on pilot symbol-assisted channel estimation and interference power estimation can decrease the required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) the most, taking into account the impact of the inter-code interference. Furthermore, we clarify that the required average received Eb/N0 for the average packet error rate of 10-2 employing the diversity combining scheme with EGC after despreading with MMSE combining is improved by approximately 0.3 dB compared to the diversity combining scheme with EGC before despreading with MMSE combining at the number of code-multiplexing of 24 for the spreading factor of 32 in a 24-path Rayleigh fading channel.

Transmit diversity, a key technique derived against multi-path mitigation in wireless communication system, is examined and discussed. Especially, we present an approach to investigate perfect/imperfect channel detection when the maximal ratio receiver combined scheme (MRRC) and a simple transmit diversity scheme (STD) are used in the wireless systems, which provide remarkable schemes for diversity transmission over Rayleigh-fading channels using multiple antennas. In order to effectively make use of the transmit diversity techniques, the same approach is extended to process the situation of one transmit antennas and N receive antennas in MRRC scheme (1 N MRRC) and two transmit antennas and N receive antennas in STD scheme (2 N STD). The effects of perfect/imperfect channel detection and the diversity reception with independent and correlated Rayleigh-fading signals are evaluated and compared carefully.

Microstrip antennas with meshed ground planes are suitable for radiation elements of large satellite phased array antennas. Although they have some mechanical advantages such as the possibility of antenna weight reduction, they also cause electrical problems such as the resonant frequency shift and F/B ratio degradation. The first purpose of this paper is the analytical understanding of the resonant frequency shift, for which two perturbational methods are proposed. One has a closed form expression that provides some useful design data. The other is to solve the integral equations by using the periodicity of the meshed ground plane, which gives more accurate results. The second purpose of this paper is to investigate the backward radiation from the meshed ground plane analytically, for which we derive an analysis method from the calculated results of the resonant frequency shift. The proposed methods are verified with the measured ones.

Active integrated antennas are a maturing topic. Many novel configurations have been described and system designers are how investigating how the advantages of compactness and increased functionality can be exploited in applications. In this paper, the various types of integrated antennas are discussed together with possible ways of exploiting the technology. New configurations of direct conversion integrated antennas are then described in detail, which illustrate some of the possibilities inherent in the technology.

A DS-CDMA mobile communication system accommodating multi-class users is considered. The number of supportable users depends on the distributions of data rate and required communication quality among users. Simple expressions for the reverse link capacity with transmit power control, antenna diversity, and rake combining, are derived for a single-cell system and a multi-cell system.

A new type of triple-band antenna is introduced by combing a tab monopole antenna (TMA) and a planar inverted F antenna (PIFA). The antenna configuration is shown to operate at three discrete frequencies: GSM 900, GSM 1800 (DCS) and GSM 1900 (PCS). The performance of an antenna is presented as well as the results of the computer simulations with a software package based on the Finite Element Method. The simulated results with the real antenna's experimental results. The advantage of the design suggested in this paper is its simplicity of manufacturing and low cost.

In order to clarify the receiver sensitivity of remote keyless entry systems operating at 314 MHz, the radiation characteristics of a cabin antennas must be studied. For this purpose, electromagnetic simulations are very useful but the multiple reflected waves present in the cabin must be accurately estimated. No prior study examined the radiation characteristics of cabin antennas. This paper introduces an accurate simulation method. A MM (Method of Moments) simulator is selected because it can simulate multiple reflected waves. Initial studies are being performed to find the calculation requirements and ensuring convergence of multiple reflected wave structures. Next, calculation requirements for car analyses such as convergence parameters and computer abilities are studied. The calculation time is 11 hours by a personal computer. 1.1 GB of RAM is also needed. Many calculated results such as three-dimensional radiation patterns and induced currents on the car's body are obtained. The radiation pattern varies with antenna position, and polarization changes are shown. In order to ensure that the results are accurate, measurements are made on a one seventh scale model of a car. The good agreement of measured and calculated results verifies the validity of the simulation method. The influence of multiple reflected waves on the radiation patterns is also experimentally studied. The conclusion is that the MM method is shown to be useful in estimating the radiation pattern of cabin antennas. Interesting calculation results are also shown.

In this paper, we propose a new coded orthogonal frequency division multiplex (COFDM)-based ubiquitous antenna system, which is composed of multiple radio base stations (RBSs) deployed over the service area and Radio-on-Fiber (RoF) link that connects RBSs to the central control station (CCS). The proposed system is capable of receiving multiple mobile terminals simultaneously operating at the same frequency by making effective use of joint detection. However, the propagation delay due to the RoF link could be a major problem for realizing the ubiquitous antenna system. In order to overcome this delay problem, we assume that the guard interval of COFDM is longer than the delay difference. Furthermore, in order to improve BER performance in a multipath Rayleigh fading channel, we also propose the MSE normalization scheme followed by the use of an MMSE-based joint detector. Computer simulation results show that the proposed system can improve the frequency utilization efficiency of the broadband wireless access system.

In this paper, we propose the code orthogonalizing filter (COF) based adaptive array antenna using sample matrix inversion with common correlation matrix (CCM-SMI) of time domain signals for multicarrier DS/CDMA systems. The conventional array antenna system calculates the weight using the correlation matrix of individual subcarrier's signals. On the other hand, our proposed system calculates the weight using the correlation matrix of time domain signals before FFT operation, so it can reduce the calculation time and the complexity of weight calculation than the conventional scheme, to maintain the system performance. Moreover, we consider the code orthogonalizing filter to reduce the demerit of adaptive array antenna system using sample matrix inversion algorithm with common correlation matrix that requires heavy computational complexity while the signal environment frequently changes. Our proposed system obtains more accurate channel response vector using COF than that of the conventional CCM-SMI based on the matched filter, without increasing the matrix size. The performance is evaluated in term of bit error probability. From the analysis and simulation results, it is shown that our proposed scheme achieves better BER performance than that of the conventional system.

This paper proposes adaptive antenna array transmit diversity (AAA-TD) in the W-CDMA forward link with frequency division duplexing (FDD), based on adaptively-generated receiver antenna weights in the reverse link, which only track the changes in the average signal-to-interference power ratio (SIR) and direction of arrival (DOA) but with the calibration of the phase/amplitude variations of the parallel RF receiver/transmitter circuits corresponding to the number of array antennas. The laboratory and field experimental results exploiting AAA-TD are presented to show the strong multipath interference (MPI) suppression effect especially from high-rate users with large transmission power. Laboratory experiments elucidate that by using AAA-TD with four antennas, the required transmitted SIR before multiplying the transmitter antenna weights at the average BER of 10-3 is decreased by approximately 13 dB compared to that with one omni-directional antenna transmitter. Field experiments also show that although an error floor above 10-2 is observed with one omni-directional antenna transmitter when the transmitted SIR is -12 dB due to severe MPI, no error floor is observed when employing 4-antenna AAA-TD and the loss of the required received signal power at the average BER of 10-3 from the single-user case is suppressed to below approximately 5 dB. Therefore, we show that AAA-TD is very effective in suppressing severe MPI especially from high rate users with large transmission power due to its adaptive main lobe and null steering.

In a wireless home network, shadowing is frequently caused by human bodies or furniture. Therefore, relay transmission function is considered for the hub station in Wireless Homelink when the direct communication of terminals is obstructed. However, in relaying high rate isochronous data such as video streams, the bandwidth resource of Wireless Homelink may be crammed with those data. In this paper, we propose an efficient relay scheme--"Pipeline Repeater" for Wireless Homelink. The proposed scheme spatially multiplexes the relay transfer of the isochronous data using antenna directivity. The Pipeline Repeater can relay the isochronous packets as an efficient use of the limited frequency band, and it can be achieved to repeat the high rate data with delay of only one frame. To verify the proposed scheme, we conduct measurements in some actual home environments, and perform the numerical analyses and computer simulations based on the measurements. Our results confirm the efficiency of the Pipeline Repeater scheme.

This paper investigates the optimum adaptive antenna array beam forming (AAA-BF) configuration considering the diversity effect provided by transmit diversity (TD) in a multipath fading channel in the W-CDMA forward link. Computer simulation results show that the required transmit signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) at the average block error rate (BLER) of 10-2 using AAA-BF coupled with TD is decreased by approximately 1.0 dB compared to that of AAA-BF assuming the identical number of total antennas when the capacity, i.e., the number of simultaneously accommodated users with the transmission power proportional to the symbol rate, normalized by processing gain, Pg, is below approximately 20%. However, we find that in an interference-limited channel, when the capacity normalized by Pg is above approximately 30%, AAA-BF employing all antennas accommodates a larger capacity compared to AAA-BF coupled with TD because of a sufficient interference suppression effect due to a much narrower beam width despite the absence of the antenna diversity effect. This paper also elucidates in a multi-cell model that AAA-BF employing all antennas can accommodate approximately 1.5 times more users with the average BLER of 10-2 and with the outage probability of 5%, compared to the case with AAA-BF coupled with TD, when the total number of antennas is 8.

We design a four-reflector offset antenna satisfying the cross-polarization elimination condition and the broadband characteristics condition which consists of one primary horn, three subreflectors and one main reflector. The cross-polarization elimination condition for the four-reflector offset antennas is expressed by the equations of hyperbolas with the coordinate axes of the reciprocal of equivalent focal lengths. The configurations of the reflector system are derived simply from the graphical representation because four-reflector offset antennas satisfying these relationships exist on the hyperbolas with the coordinate axes of the reciprocal of equivalent focal lengths. Furthermore, we clarified that the derived condition for having planar phase front applying the broadband characteristics condition is independent of frequency. An actual design example for the four-reflector offset antennas satisfying the cross-polarization elimination condition and the condition for having planar phase front, both of which are independent of frequency is shown. The design method using the graphical representation is simpler than that of the tri-reflector offset antennas.

Reactive near field reflection characteristics of commercial RF absorbers are investigated to determine the minimum size of a reactive-field anechoic box necessary for measuring the reactive near field of an ESPAR antenna. The reflectivity of the absorber placed in close proximity to an antenna is inversely proportional to the distance between the antenna and the absorber. For carbon filled urethane foam tapered absorbers, we find that the backscattered reflection characteristics mainly depend on their tapered height rather than the thickness of absorber base. As a result, we show that carbon filled urethane foam pyramidal and wave surface shaped absorbers can be used to make reactive-field anechoic boxes. A prototype of a reactive-field anechoic box is presented and the distance from the absorber to the antenna is reduced to a wavelength. The prototype is verified by comparing its performance with that obtained from a large anechoic chamber.

Transmit beamforming is a promising way to increase the downlink capacity of wireless networks. Since all users are coupled via their radiation patterns, the beamforming vectors must be optimized along with power control. It is necessary to balance the signal-to-interference levels according to individual QoS requirements. This problem leads back to the minimization of the infinity-norm of a certain vector and has first been studied by Gerlach and Paulraj in [1]. It has been assumed that the optimum solution can be obtained by minimizing the 1-norm instead, thereby leading to a new problem, which is generally easier to handle. The analytical and numerical results in this paper, however, indicate that this conjecture is generally not valid. We characterize the case where the 1-norm solution also solves the infinity-norm problem. In particular, it is shown that for the special case of a 2-user scenario, both optimization problems are indeed equivalent and a closed-form solution can be given. The analytical results provide new insights into the problem of coupled downlink beamforming and offer a useful approach to the design of efficient and reliable algorithms.

In this paper, the efficient signal enhancement scheme for an adaptive antenna array under the Nakagami fading channel is proposed. The proposed signal enhancement scheme is the modified linear signal estimator with Toeplitz Matrix Approximation (TMA) method. The underlying principle of the proposed signal enhancement scheme is to reduce a noise component using not only the Lagrangian method of the constrained minimization but also a signal-plus-noise subspace method. TMA is also used to have the theoretical property of noise-free signal. These functions greatly enhance the performance of an adaptive antenna array by removing the all undesired noise effects from the post-correlation received signal. The proposed signal enhancement scheme is applied at the Wiener Maximal Ratio Combining (MRC) method which has been widely used as the conventional adaptive antenna array. Also, we investigated the effect of the power control error (PCE) for the proposed scheme over the Nakagami multipath fading channel. Several computer simulation examples are provided for illustrating the effectiveness of the proposed scheme.