To describe joint time- and frequency-selective (doubly-selective) channels in mobile broadband wireless communications, we propose to use the finite parameter model based on the same Bessel functions for each tap (Bessel model). An expression of channel estimation mean squared error (MSE) based on the finite parameter models in Orthogonal Frequency Division Multiplexing (OFDM) systems is derived. Then, our Bessel model is compared with commonly used finite parameter models in terms of the channel estimation MSE. Even if the channel taps have different channel correlations and some of the taps do not coincide with the Bessel function, the channel estimation MSE of the Bessel model is shown to be comparable or outperform existing models as validated by Monte-Carlo simulations over an ensemble of channels in typical urban and suburban environments.

The directional MAC protocols improve spatial reuse, but require the exact location of destination and have the problem of deafness. In this paper, we propose a dual-channel MAC protocol with directional antennas for mobile ad-hoc networks. In the proposed MAC protocol, RTS/CTS are sent omnidirectionally as nodes do not have the exact location of the destination in mobile environments. Omnidirectional transmissions on control channel overcome deafness, but have low spatial reuse. We propose a new blocking algorithm to improve spatial reuse on control channel. We use the negative CTS (NCTS) to solve the exposed terminal problem. We confirm throughput of the proposed MAC protocol by simulations using Qualnet ver. 3.8 simulator.

A blind joint parametric channel estimation and non-coherent data detection algorithm is proposed for the downlink of an orthogonal-frequency-division-multiplexing code-division-multiple-access (OFDM-CDMA) system with multiple-input-multiple-output (MIMO) antenna arrays. To reduce the computational complexity, we first develop a tree-structured algorithm to estimate high dimensional parameters predominantly describing the involved multipath channels by employing several stages of low dimensional parameter estimation algorithms. In the tree structure, to exploit the space-time distribution of the receive multipath signals, spatial beamformers and spectral filters are adopted for clustered-multipath grouping and path isolation. In conjunction with the multiple access interference (MAI) suppression techniques, the proposed tree architecture algorithm jointly estimates the direction of arrivals, propagation delays, carrier frequency offsets and fading amplitudes of the downlink wireless channels in a MIMO OFDM-CDMA system. With the outputs of the tree architecture, the signals of interest can then be naturally detected with a path-wise maximum ratio combining scheme.

This paper describes the experimental evaluation of a testbed with a simple decision-feedback channel tracking scheme for MIMO-OFDM systems. The channel tracking scheme periodically estimates the channel state matrix for each subcarrier from received signals and replicas of the transmitted signal. The estimated channel state matrices, which are obtained at mutually different timings, are combined based on maximum ratio combining and used for MIMO signal detection. The testbed was implemented on field programmable gate arrays (FPGAs) of 1/5 scale, which confirms the implementation feasibility of the channel tracking scheme. The packet error rate (PER) and mobility performance of the testbed were measured. The testbed employed a 22 MIMO channel, zero-forcing algorithm for MIMO signal detection, 16QAM for the subcarrier modulation scheme, and coding rate of 1/2. The proposed scheme suppressed the increase in the required SNR for PER of 10-2 to less than 1 dB when the relative velocity between the transmitter and the receiver was less than 45 km/h assuming 5 GHz band operation. In addition, the proposed scheme offers 6.3% better throughput than the conventional scheme. The experimental results demonstrate that the channel tracking scheme implemented in the testbed effectively tracks the fluctuation of a MIMO channel.

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 an investigation of radio-wave propagation characteristics in the 5 GHz band in a residential two-story house. We investigated the 3-D angular spectra of incident waves when a transmitter and a receiver were situated on the first and second floors, respectively. First of all, correlation in the measured "home environment" containing furniture such as beds, a sofa and tables was determined to confirm a quasi-static environment. Then, 3-D angular spectra measurements were performed by using an eight-element Yagi-Uda antenna as a receiving antenna. Furthermore, the 4-by-4 MIMO channel capacity at each elevation angle was estimated by using elevation angular spectra and the propagation characteristics between the first and second floors were evaluated. The results indicated that the channel capacity in the elevation direction was strongly influenced by the direction of the transmitting antenna.

This letter proposes a sliding window method with iterative tuning for channel estimation of UWB signals. The iterative tuning scheme, which is based on multiple iterations of least mean square (LMS) algorithm, is utilized for modifying the output of the conventional sliding window channel estimator. By using this, the proposed method is more flexible due to the tradeoff between the processing time and accuracy, which makes it more suitable for practical UWB wireless communications. Simulations are also provided for demonstrating the validation of the proposed method.

A multi-input erasure channel is defined as the J(J+1) discrete memoryless channel, for which we study a capacity formula, through the method by Muroga. We first give a simpler capacity formula for the multi-input erasure channel with no cross probability. Next we give an upper bound to the capacity for the general case. Finally we remark that the upper bound is actually the capacity when the cross probability is small.

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.

The effect of wall and indoor scatterers on the indoor multiple input multiple output (MIMO) communication system is investigated by using the hybrid technique of finite difference time domain (FDTD) method and method of moments (MoM). MIMO channel capacity with the wall reflection is investigated with consideration of the eigenvalue of channel covariance matrix, the received power and the effective multipaths of MIMO system. It is found that the stronger side wall reflection can lead to the higher MIMO channel capacity. MIMO system with indoor scatterers is also analyzed and compared with the line of sight (LOS) indoor MIMO system. It is found that the scatterer material has different effect on the received power and the effective multipaths of MIMO system.

This paper reviews our recent antennas and propagation studies for MIMO systems. First we introduce a MIMO propagation channel model in which an interesting nature can be found in eigenvalue statistics from a practical viewpoint. Then we introduce multi-keyhole model which is an efficient tool for designing a MIMO repeater systems, or MIMO radio-relay systems. For realization of compact MIMO antenna systems, effectiveness of using multiple polarizations such as dual polarizations and triple polarizations is demonstrated in multipath-rich propagation environments. With application of MIMO to OFDM systems, we focus our analysis on relation between propagation and digital transmission characteristics under a severe multipath-rich environment where the delay profile exceeds the guard interval. Finally, we discuss transmission characteristics of MIMO-OFDM with maximal ratio combining (MRC) diversity in the environment.

Space-time block coding is an attractive solution for improving quality in wireless links. In general, the multiple-input multiple-output (MIMO) channel is correlated by an amount that depends on the propagation environment as well as the polarization of the antenna elements and the spacing between them. In this paper, asymptotic performance and exact symbol error probability (SEP) of orthogonal space-time block code (STBC) are considered in spatially correlated Rayleigh fading MIMO channel. We derive the moment generating function (MGF) of effective signal-to-noise ration (SNR) after combining scheme at the receiver. Using the MGF of effective SNR, we calculate the probability density function (pdf) of the effective SNR and derive exact closed-form SEP expressions of PAM/PSK/QAM with M-ary signaling. We prove that the diversity order is given by the product of the rank of the transmit and receive correlation matrix. Moreover, we quantify the loss in coding gain due to the spatial correlation. Simulation results demonstrate that our analysis provides accuracy.

This paper generalizes parallel error correcting codes proposed by Ahlswede et al. over a new type of multiple access channel called parallel error channel. The generalized parallel error correcting codes can handle with more errors compared with the original ones. We show construction methods of independent and non-independent parallel error correcting codes and decoding methods. We derive some bounds about the size of respective parallel error correcting codes. The obtained results imply a single parallel error correcting code can be constructed by two or more kinds of error correcting codes with distinct error correcting capabilities.

In this letter, we design an optimal superimposed training scheme for orthogonal frequency division multiplexing (OFDM) systems. A linear least square (LS) channel estimator is developed, and optimal pilot symbols are proposed with respect to the channel estimate's mean square error (MSE). The optimal power allocation between training and data is derived by maximizing the averaged channel capacity lower bound. Simulation results validate our optimum design.

In digital transmission and storage systems, sequences must have attributes that comply with the physical characteristics of the channel. These channel constraints can often be satisfied through constrained sequence coding techniques which avoid use of sequences that violate the given channel constraints. In the design of a constrained code, it is usually helpful to consider the PSD of the encoded sequence in order to ensure that PSD requirements are met, and to obtain an indication of bandwidth, response at dc, average power peaks, and other spectral characteristics of interest. In this paper, we introduce an approach for the construction of finite-state sequential machine (FSSM) modeled encoders to satisfy spectral requirements. This approach involves construction of either a Mealy or a Moore FSSM to represent the encoder, and evaluation of the state transition probabilities and codeword values such that the PSD of the designed code meets a predefined spectral shape. Examples in this paper demonstrate the usefulness of this approach.

The average bit erasure probability of a binary linear code ensemble under maximum a-posteriori probability (MAP) decoding over binary erasure channel (BEC) can be calculated with the average support weight distribution of the ensemble via the EXIT function and the shortened information function. In this paper, we formulate the relationship between the average bit erasure probability under MAP decoding over BEC and the average support weight distribution for a binary linear code ensemble. Then, we formulate the average support weight distribution and the average bit erasure probability under MAP decoding over BEC for regular LDPC code ensembles.

The performance of a MIMO-OFDM system significantly depends upon the accuracy of the channel impulse response (CIR) estimates. In the presence of correlation between the CIRs of the transmit or receive antennas, it is desirable to exploit this correlation to improve the performance of CIR estimation. In this letter, we propose a low-complexity channel estimation filter composed of four concatenated one-dimensional Wiener filters which are optimized to the channel characteristics in the time and frequency domains, and the transmit and receiver antenna front ends, respectively. Finally, the performance of the proposed scheme is verified.

This paper proposes pilot-based channel quality reporting for orthogonal frequency division multiple access/time division duplex (OFDMA/TDD) systems with cochannel interference. In the proposed method, a terminal reports his channel quality in multiple subbands to base station (BS) using channel reciprocity of TDD systems. The terminal transmits uplink pilot signals in the subbands with different transmit power which is inversely proportional to the subband-based interference power. The BS can obtain knowledge of the terminal's received signal-to-interference-plus-noise power ratio on subband basis, measuring the pilot signal power. In performance evaluation, accuracy of channel quality reporting and amount of uplink signalling are examined. From numerical results, it is found that the proposed method becomes effective as the number of subbands and terminals for channel quality reporting increases.

In this paper, a sparse multipath channel estimation algorithm is proposed for multiple-input multiple-output (MIMO) single-carrier systems with frequency-domain decision feedback equalizer (FD-DFE). This algorithm exploits the orthogonality of an optimal MIMO preamble based on repeated, phase-rotated, Chu (RPC) sequences, leading to a dramatic reduction in computation. Furthermore, the proposed algorithm employs an improved non-iterative procedure utilizing the Generalized AIC criterion (GAIC), resulting in further computational saving and performance improvement. The proposed scheme is simulated for 802.16d SCa-PHY and SUI-5 sparse channel model under a 22 spatial multiplexing scenario, with the MIMO FD-DFE as the receiver. The result shows that the channel estimation accuracy is significantly improved, and the performance loss compared to the known channel case is only 0.7 dB at the BER of 10-3.

Recently, space-time block codes (STBCs) obtained from coordinate interleaved orthogonal designs (CIODs) have attracted considerable attention, due to the advantages of full-diversity transmission and single-symbol decodability. In this letter, we design a novel STBC from CIOD for two transmit antennas. The proposed code guarantees full-diversity and full-rate along with low peak-to-minimum power ratio (PMPR). Furthermore, in contrast to the existing Alamouti code, the performance of the proposed code is not degraded even in severely time-selective fading channels.