In this paper, as an important technology for the software-defined radio, a novel scheme of adaptive array antenna utilizing bandpass sampling technique is proposed. For adaptive signal processing, it is necessary to convert the radio frequency signal received by the antenna that is given by real number into baseband region, i.e., complex number region. Then, the method for dividing the bandpass sampled signal to in-phase and quadrature components is analyzed. The sampling scheme is called the IQ-division bandpass sampling. An adaptive array antenna based on the IQ-division bandpass sampling is characterized by the signal processing at the bandpass sampled signal stage, namely, intermediate frequency stage, not baseband. Finally, we will confirm the validity of the proposed scheme through an experiment in a radio anechoic chamber.

We provide an efficient transmission scheme which embeds a pilot signal in the data signal for channel state information (CSI) based on the configuration of a multiple-input multiple-output (MIMO) system using space-time block coding (STBC) with an adaptive array (AA). A computer simulation and analysis show that the proposed scheme, which combines the advantage of an Alamouti-like STBC scheme and the pilot-based AA, can suppress the irreducible error due to random FM noise. The proposed scheme using a pilot minimizes the decoding delay, and is highly robust against fast fading. We show that the proposed scheme can significantly increase the data transmission rate by using the transmitter diversity based on STBC, and the accuracy of the proposed technique is exemplified by a computer simulation.

In this paper, we propose a spatio-temporal equalizer for the space-time block coded transmission over the frequency selective fading channels with the presence of co-channel interference (CCI). The proposed equalizer, based on the tapped delay line adaptive array (TDLAA), performs signal equalization and CCI suppression simultaneously using the minimum mean square error (MMSE) method. It is to show that our scheme outperforms the previous two-stage combined adaptive antenna and delayed decision feedback sequence estimator (DDFSE) approach. We also show that performance can be further improved if the synchronization between the preceding and delayed paths is achieved.

Smart or adaptive antennas promise to provide significant space-time communications against fading in wireless communication systems. In this paper, we propose multiple-input multiple-output (MIMO) beamforming for frequency-selective fading channels to maximize the Signal-to-Noise and Interference Ratio (SINR) based on an iterative update algorithm of transmit and receive weight vectors with prior knowledge of the channel state information (CSI) at both the transmitter and receiver. We derive the necessary conditions for an optimum weight vector solution and propose an iterative weight update algorithm for an optimal SINR reception. The Maximum Signal-to-Noise (MSN) method, where noise includes the additive gaussian noise and interference signals, is used as a criterion. The proposed MIMO with M N arrays allows the cancellation of M + N - 2 delayed channels. Computer simulations are presented to verify our analysis. The results show that significant improvements in performance are possible in wireless communication systems.

This paper presents the theoretical analysis of subband adaptive array combining cyclic prefix transmission scheme (SBAA-CP) in multipath fading environment. The exact expressions for optimal weights, array outputs and the output signal to interference plus noise ratio (SINR) are derived. The analysis shows that use of the cyclic prefix data transmission scheme can significantly improve the performance of subband adaptive array (SBAA). An example of implementing SBAA-CP as a software antenna is also presented.

In this paper, we propose a multiple-input multiple-output (MIMO) beamforming scheme for a multiuser system in frequency-selective fading channels. The maximum signal-to-noise and interference ratio (MSINR) is adopted as a criterion to determine the transmit and receive weight vectors. In order to maximize the output SINR over all users, two algorithms for base station are considered: the first algorithm is based on the receive weight vector optimization and the second algorithm is based on an iterative update of both transmit and receive weight vectors. Based on the result of single user MIMO beamforming, we analyze the interference channels cancellation ability of multiuser MIMO system. The first algorithm is a simple method and the second algorithm is a performative solution. Through computer simulations, it is shown that multiuser communication system is achievable using the proposed methods in frequency-selective fading condition.

Diversity transmission using space-time block coding (STBC) shows a degraded performance in frequency selective fading (FSF) channel. In this paper, assuming the CSI is unknown at both transmitter and receiver while a pilot signal is available during the training period, we propose a MIMO transmission scheme using STBC by adopting subband adaptive array (SBAA) processing. The receive signal is converted into the frequency-domain and adaptive processing is done at each subband. A novel construction of SBAA is introduced to process received signal based on STBC. Simulation results demonstrate that the proposed scheme has a better performance compare to conventional STBC, and has a better performance and less computational load compare to STBC-TDLAA.

Subband adaptive array (SBAA) has been realised as a promising method to perform space-time signal processing in mobile communications. Recently, several schemes of SBAA have been introduced. However, theoretical analysis of SBAA performance has been only limited to case of SBAA without using decimation. In this paper, we introduce a novel method to analyse the performance of SBAA using critical sampling with localised feedback scheme. We first provide a detailed analysis of the SBAA performance in the case of single path and multipath fading environment. The simulation results are then presented to verify the proposed method.

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.

We propose an implementation of the tapped delay line adaptive array (TDLAA) at the base station for improving the BER performance of asynchronous multi-user mobile communication over fast fading channels using multiple antennas. The data of each user at the mobile station, which applies two transmit antennas, are encoded by Space Time Block Code (STBC). The proposed scheme transmits the pilot signal and information data in alternate time slots. We derive performance criteria for designing such a scheme under the assumption that the fading is classified as fast fading. We show that the proposed scheme can suppress co-channel interference (CCI) and defeat Doppler spread effectively.

A baseband transmission scheme for wireless communications has been proposed and examined using a pair of discone antennas for transmission and reception. The wireless baseband transmission scheme radiates a baseband signal stream, such as non-return-to-zero (NRZ), return-to-zero (RZ), or Manchester encoded signals, directly from an antenna. Namely, a carrier in terms of a sinusoidal radio wave or light wave is not used in the transmission. In experiments, baseband pulses generated with a data generator were radiated directly from the discone antenna, and received waveforms were observed with a digital storage oscilloscope. The experiments showed that wireless baseband transmission is realisable when using antennas with a flat amplitude spectrum and a linear phase characteristic, such as discone antennas, over a given band. Manchester encoding is promising for this wireless baseband transmission.

This paper presents an approximation method of statistical distribution of the largest eigenvalue of i.i.d. (independent and identically distributed) MIMO (multiple input multiple output) channel correlation matrices under Nakagami-Rice fading environment. The equation is actually derived for MIMO Nakagami m fading channel which is known as a good approximation of Nakagami-Rice fading, hence it well approximates the curves of the largest eigenvalue distribution of noncentral Wishart matrices. In the proposed approximation method, MIMO MRC (maximal ratio combining) system is ascribed to SIMO space diversity theory with the same number of branches, and the statistical distribution becomes a monomial gamma distribution. As a result, the derived marginal density function does not contain any special functions, and has a simple monomial gamma form which is suitable for various calculations of performance indices. Through computer simulations, it is shown that the proposed approximation formula is effective and has a better precision than conventional method.

MIMO leads to dramatic improvement in channel capacity and/or link reliability of wireless systems. However, a MIMO channel has only one degree of freedom in a keyhole environment. As a result, this environment reduces achievable channel capacity and link quality. This paper proposes a MIMO repeater system, which can realize a multi-stream transmission. Although the averaged channel capacity in the MIMO repeater system is discussed in several published papers, the probability density functions of eigenvalues of correlation matrix are not analyzed. MIMO transmission performance can basically be estimated from eigenvalues of the channel correlation matrix. We derive an approximated formula for the probability density function of all eigenvalues linked to the space diversity. It is shown that the calculated values based on the proposed method agrees very well with the simulated values.

In this paper, we propose an adaptive algorithm based on accumulated signal processing, which could be applicable to Post-FFT-type OFDM adaptive array antennas. Proposed scheme calculates the weight of each element at a particular instant t, by considering both post- and pre-received symbols. Because of the use of additional forthcoming information on channel behavior in the weight calculation scheme, one can expect an improved performance in fast fading conditions by using the proposed adaptive algorithm. This paper also discusses the application of the proposed adaptive algorithm to OFDM adaptive array. In OFDM application, a few subchannels are being used to transmit pilot symbols, and at the receiver, the proposed adaptive algorithm is applied to those pilot subchannels, and interpolates the weights for the data subchannels which are allocated between the pilot subchannels. Finally, the system performance improvement with the application of the proposed adaptive algorithm is verified by computer simulation.

In multiple input multiple output (MIMO) communication systems, eigenvalues of channel correlation matrices play an essential role for the performance analysis, and particularly the investigation about their behavior under time-variant environment ruled by a certain statistics is an important problem. This paper first gives the theoretical expressions for the marginal distributions of all the ordered eigenvalues of MIMO correlation matrices under i.i.d. (independent and identically distributed) Rayleigh fading environment. Then, an approximation method of those marginal distributions is presented: We show that the theory of SIMO space diversity using maximal ratio combining (MRC) is applicable to the approximation of statistical distributions of all eigenvalues in MIMO systems with the same number of diversity branches. The derived approximation has a monomial form suitable for the calculation of various performance measures utilized in MIMO systems. Through computer simulations, the effectiveness of the proposed method is demonstrated.

Massive multiple input multiple output (MIMO) communication system offers high rate transmission and/or support of a large number of users by invoking the power of a large array antenna, but one of its problem is the heavy computational burden required for the design and signal processing. Assuming the utilization of a large array in the transmitter side and much fewer users than the maximum possible value, this paper first presents a subarray based design approach of MIMO system with a low computational load taking into account efficient subarray grouping for the realization of higher performance; a large transmit array is first divided into subarrays based on channel gain or channel correlation, then block diagonalization is applied to each of them, and finally a large array weight is reconstructed by maximal ratio combining (MRC). In addition, the extension of the proposed method to two-stage design is studied in order to support a larger number of users; in the process of reconstruction to a large array, subarrays are again divided into groups, and block diagonalization is applied to those subarray groups. Through computer simulations, it is shown that the both channel gain and correlation based grouping strategies are effective under certain conditions, and that the number of supported users can be increased by two-stage design if certain level of performance degradation is acceptable.

This paper gives statistical analysis of double fading channels which are typically found in keyhole MIMO(multiple input multiple output) models. First, to investigate the potential of identically distributed double Nakagami-Rice MIMO keyhole channels including LOS(line of sight) environment, the density function of SNR(signal to noise ratio) which corresponds to the only one non-zero eigenvalue of channel correlation matrix is presented. In addition to the exact expression with an infinite series form, an approximation formula with a simple monomial form derived by substituting Nakagami m formula for Rician distribution is also considered. Next, similar equations are introduced for double Rayleigh channels which have correlated branches in both the transmitter and receiver sides(independent but nonidentical case is included here). Through computer simulations, the effectiveness of the proposed formulae is verified, and in double Nakagami-Rice fading case, the advantage of the approximated formula particularly for large array size and/or large Rician factor is demonstrated.

This paper introduces a novel MIMO (Multiple Input Multiple Output) communication system having orthogonal dual polarization diversity branches. We have designed a dual polarized circular patch antenna which has two orthogonal polarization ports such as vertical polarization (V) and horizontal polarization (H) on its metal surface. This design makes it works as two independent antennas in multipath environments. By using two dual polarized antennas at both the transmitter and receiver, we designed a dual-polarization 44 MIMO experiment system. This system can be used to investigate the performance of various MIMO transmission methods as well as the performance of adaptive algorithms in indoor multipath environments. To investigate the performance of our experiment system, we carried out a number of MIMO transmission experiments such as space-time-coded transmission having two parallel streams and MIMO eigenmode transmission. We will show the results of those experiments and discuss the advantages of using polarization diversity in MIMO communication system for next generation broadband wireless communication.

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 presents a mathematically simple method of maximum SINR (Signal to Interference plus Noise Ratio) design of broadband MIMO (Multiple Input Multiple Output) communication systems adopting TDL (Tapped Delay Line) structure for spatio-temporal processing in both transmitter and receiver sides. The weight vectors in both ends are determined alternately, optimizing one side by fixing the other, and this operation is repeated until the SINR converges. The performance of MIMO systems using the proposed approach is investigated through computer simulations, and it is demonstrated that, though it requires high computational cost, the TDL structure brings high ability to mitigate the influence of frequency selective fading, particularly when the duration of the delay profile is long. Moreover, experimental results show that the equable distribution of the resources (weights and delay units) to both arrays is better choice than the concentration of them to one side of the transmitter or receiver.