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.

For reducing bit errors on wireless channels, we have proposed the multiroute coding scheme on multiple routes for wireless multihop networks. In this paper, we introduce ARQ to our multiroute coding scheme. In our multiroute coding scheme, a destination node combines and decodes subpackets which are encoded and divided by a source node. Each intermediate node relays a subpacket, that is, only a part of a packet. Therefore, intermediate nodes cannot detect packet errors, and only a destination node can do so after combining and decoding subpackets. We propose an ARQ scheme between a source node and a destination node. We analyze the proposed ARQ scheme and evaluate the system performance.

Error control codes have extensively been applied to semiconductor memories using high density RAM chips with wide I/O data, e.g., with 8-bit or 16-bit I/O data. Recently, spotty byte errors called s-spotty byte errors are newly defined as t or fewer bits errors in a byte having length b bits, where 1 ≤ t ≤ b. This paper proposes another type of spotty byte errors, i.e., m-spotty byte errors, where more than t bits errors in a byte may occur due to hit by high energetic particles. For these errors, this paper presents generalized m-spotty byte error control codes with minimum m-spotty distance d.

This paper deals with the random number generation problem under the framework of a separate coding system for correlated memoryless sources posed and investigated by Slepian and Wolf. Two correlated data sequences with length n are separately encoded to nR1, nR2 bit messages at each location and those are sent to the information processing center where the encoder wish to generate an approximation of the sequence of independent uniformly distributed random variables with length nR3 from two received random messages. The admissible rate region is defined by the set of all the triples (R1,R2,R3) for which the approximation error goes to zero as n tends to infinity. In this paper we examine the asymptotic behavior of the approximation error inside and outside the admissible rate region. We derive an explicit lower bound of the optimal exponent for the approximation error to vanish and show that it can be attained by the universal codes. Furthermore, we derive an explicit lower bound of the optimal exponent for the approximation error to tend to 2 as n goes to infinity outside the admissible rate region.

In this paper, a non-data aided minimum mean square error (MMSE) receiver with enhanced multiple access interference (MAI) suppression is proposed for direct-sequence code-division multiple-access (DS-CDMA) systems over a multipath fading channel. The design of the proposed receiver is via the following procedure: First, an adaptive correlator is constructed based on the linearly constrained minimum variance (LCMV) criterion to collect each multipath signal and suppress MAI blindly. A maximum ratio combiner is then utilized to coherently combine the correlator outputs. With a set of judicious chosen weight vectors, effective diversity combining can successfully suppress MAI and the desired signals can be effectively retained. Finally, further performance improvement against the finite data sample effect is achieved using a decision-aided scheme in which the channel response is obtained by the decision data and incorporated with the MMSE method to compute the refined weight vector. Performance analysis based on the output signal-to-interference-plus-noise ratio (SINR) is done to examine the efficacy of the proposed non-data aided MMSE receiver, which can offer the similar results as those of the MMSE receiver with the channel estimation correctly obtained beforehand. Computer simulation results then confirm correctness of the analysis results and demonstrate that the proposed blind receiver can successfully resist MAI as well as the finite data sample effect, and significantly outperform than the conventional blind receivers.

In this paper, we derive an upper bound for the average block error probability of a standard irregular low-density parity-check (LDPC) code ensemble under the maximum-likelihood (ML) decoding. Moreover, we show that the upper bound asymptotically decreases polynomially with the code length. Furthermore, when we consider several regular LDPC code ensembles as special cases of standard irregular ones over an additive white Gaussian noise channel, we numerically show that the signal-to-noise ratio (SNR) thresholds at which the proposed bound converges to zero as the code length tends to infinity are smaller than those for a bound provided by Miller et al.. We also give an example of a standard irregular LDPC code ensemble which has a lower SNR threshold than a given regular LDPC code ensemble.

With the rapid progress of electronic and information technology, an expectation for the realization of body area network (BAN) has risen. However, on-body transmission characteristics are greatly dependent on the frequency, and a high-speed transmission is difficult due to the remarkable signal attenuation at higher frequencies. In this study, we proposed a pulse transmission system with the frequencies at dozens of mega-hertzes. The system was based on an impulse radio (IR) scheme with bi-phase modulation. By using the frequency-dependent finite difference time domain (FD2TD) method, we investigated the on-body transmission characteristics and derived a path loss expression. Based on the transmission characteristics, we also investigated the influences of white Gaussian noises and other narrow-band interferences on the communication link budget and bit error rate (BER) performance. The results have shown the feasibility of the proposed on-body IR communication system.

MIMO systems using a space division multiplexing (SDM) technique in which each transmit antenna sends an independent signal substream have been studied as one of the successful applications to increase data rates in wireless communications. The throughput of a MIMO channel can be maximized by using an eigenbeam-SDM (E-SDM) technique, and this paper investigates the practical performance of 22 and 44 MIMO E-SDM based on indoor measurements. The channel capacity and bit error rate obtained in various uniform linear array configurations are evaluated and are compared with the corresponding values for conventional SDM. Analysis results show that the bit error rate performance of E-SDM is better than that of SDM and that E-SDM gives better performance in line-of-sight (LOS) conditions than in non-LOS ones. They also show that the performance of E-SDM in LOS conditions depends very much on the array configuration.

In this paper, a weighted element-wise block adaptive frequency-domain equalization (WEB-FDE) is proposed for a single-carrier system with the cyclic-prefix. In the WEB-FDE, the one-tap equalizer corresponding to a frequency-bin first preserves input DFT elements (element-wise block). Its coefficient in each block is then calculated by minimizing a weighted squared norm of the a posteriori error. Simulation results in a time-varying typical urban (TU) channel show that the bit-error-rate (BER) performance of the WEB-FDE outperform that of the normalized least-mean-square (NLMS)-FDE and recursive-least-square (RLS)-FDE.

This paper describes a new criterion for speech recognition using an integrated confidence measure to minimize the word error rate (WER). The conventional criteria for WER minimization obtain the expected WER of a sentence hypothesis merely by comparing it with other hypotheses in an n-best list. The proposed criterion estimates the expected WER by using an integrated confidence measure with word posterior probabilities for a given acoustic input. The integrated confidence measure, which is implemented as a classifier based on maximum entropy (ME) modeling or support vector machines (SVMs), is used to acquire probabilities reflecting whether the word hypotheses are correct. The classifier is comprised of a variety of confidence measures and can deal with a temporal sequence of them to attain a more reliable confidence. Our proposed criterion for minimizing WER achieved a WER of 9.8% and a 3.9% reduction, relative to conventional n-best rescoring methods in transcribing Japanese broadcast news in various environments such as under noisy field and spontaneous speech conditions.

The quantization error of phase delay in an ultrasonic annular arrays imaging system is analyzed which impairs image resolution, and proper sampling rate is considered to reduce system complexity.

In this paper, a method of feeding point analysis is proposed for microstrip antenna that is based on the probe current compensation (PCC) method and the overlapping-grid technique (OGT) in FDTD. Generally, in the Maxwell and Ampere's differential curl equation-based FDTD, calculated error occurs in computation of the feeding point current. By applying the PCC method, the current of the feeding point can be compensated. This paper also analyzes the proposed feeding point model with cylindrical shape. When feeding point model is analyzed by rectangular coordinate, contour path error occurs. Therefore, the OGT is proposed to solve the contour path error. In the OGT, the cylindrical coordinate is applied for modeling of feeding point. In the case of using the PCC method and the OGT, the calculated error and contour path error are reduced and improved.

This paper proposes a novel signal estimation method that uses a tensor product expansion. When a bivariable function, which is expressed by two-dimensional matrix, is subjected to conventional tensor product expansion, two single variable functions are calculated by minimizing the mean square error between the input vector and its outer product. A tensor product expansion is useful for feature extraction and signal compression, however, it is difficult to separate global noise from other signals. This paper shows that global noise, which is observed in almost all input signals, can be estimated by using a tensor product expansion where absolute error is used as the error function.

Spatial multiplexing (SM) offers a linear increase in transmission rate without bandwidth expansion or power increase. In SM systems, the LMMSE receiver establishes a good tradeoff between the complexity and performance. The performance of the LMMSE receiver would be degraded by MIMO channel estimation errors. This letter focus on obtaining the asymptotic convergence of output interference power and SIR performance for the LMMSE receiver with channel uncertainty. Exactly matched simulation results verify the validity of analysis in the large-system assumption. Furthermore, we find that the analytical results are also valid in the sense of average results for limited-scale system in spite of the asymptotic assumption used in derivation.

Irregular LDPC codes can achieve better error rate performance than regular LDPC codes. However, irregular LDPC codes have higher error floors than regular LDPC codes. The Ordered Statistic Decoding (OSD) algorithm achieves approximate Maximum Likelihood (ML) decoding. ML decoding is effective to lower error floors. However, the OSD estimates satisfy the parity check equation of the LDPC code even the estimates are wrong. Hybrid decoder combining LLR-BP decoding algorithm and the OSD algorithm cannot also lower error floors, because wrong estimates also satisfy the LDPC parity check equation. We proposed the concatenated code constructed with an inner irregular LDPC code and an outer Cyclic Redundancy Check (CRC). Owing to CRC, we can detect wrong codewords from OSD estimates. Our CRC-LDPC code with hybrid decoder can lower error floors in an AWGN channel. In wireless communications, we cannot neglect the effects of the channel. The OSD algorithm needs the ordering of each bit based on the reliability. The Channel State Information (CSI) is used for deciding reliability of each bit. In this paper, we evaluate the Block Error Rate (BLER) of the CRC-LDPC code with hybrid decoder in a fast fading channel with perfect and imperfect CSIs where 'imperfect CSI' means that the distribution of channel and those statistical average of the fading amplitudes are known at the receiver. By computer simulation, we show that the CRC-LDPC code with hybrid decoder can lower error floors than the conventional LDPC code with hybrid decoder in the fast fading channel with perfect and imperfect CSIs. We also show that combining error detection with the OSD algorithm is effective not only for lowering the error floor but also for reducing computational complexity of the OSD algorithm.

In this paper, we present a design method for fixed-width squarer that receives an n-bit input and produces an n-bit squared product. To efficiently compensate for the truncation error, modified Booth-folding encoder signals are used for the generation of error compensation bias. The truncated bits are divided into two groups (major and minor) depending upon their effects on the truncation error. Then, different error compensation methods are applied to each group. By simulations, it is shown that the proposed fixed-width squarers have lower error than other fixed-width squarers and are cost-effective.

Digital watermarking is a technique that aims at hiding a message signal in a multimedia signal for copyright claim, authentication, device control, or broadcast monitoring, etc. In this paper, we focus on embedding watermarks into still images, where the watermarks themselves can be binary sequences or grayscale images. We propose to scramble the watermark bits with pseudo-noise (PN) or orthogonal codes before they are embedded into an image. We also try to incorporate error correction coding (ECC) into the watermarking scheme, anticipating reduction of the watermark bit error rate (WBER). Due to the similarity between the PN/orthogonal-coded watermarking and the spread spectrum communication, it is natural that, following similar derivations regarding data BER in digital communications, we derive certain explicit quantitative relationships regarding the tradeoff between the WBER, the watermark capacity (i.e. the number of watermark bits) and the distortion suffered by the original image, which is measured in terms of the embedded image's signal-to-noise ratio (abbreviated as ISNR). These quantitative relationships are compactly summarized into a so-called tradeoff triangle, which constitutes the major contribution of this paper. For the embedding of grayscale watermarks, an unequal error protection (UEP) scheme is proposed to provide different degrees of robustness for watermark bits of different degrees of significance. In this UEP scheme, optimal strength factors for embedding different watermark bits are sought so that the mean squared error suffered by the extracted watermark, which is by itself a grayscale image, is minimized while a specified ISNR is maintained.

JPEG2000 compression standard considers a block of wavelet coefficients, called codeblock, as the smallest coding unit that being independently entropy-coded. In this paper, we propose a codeblock-based concealment technique for JPEG2000 images to mitigate missing codeblock due to packet loss in network transmission. The proposed method creates a single JPEG2000 codestream from an image that composed of several subsampled versions of the original image and transmit the codestream over a single channel.The technique then substitutes the affected codeblock in a subsampled image with a copy of the corresponding codeblock obtained from other subsampled images. Thus, it does not require an iterative processing, which is time consuming, to construct an estimated version of the lost data. Moreover, it is applicable for a large codeblock size and can be implemented either in wavelet or codestream domain. Simulation results confirm the effectiveness of the proposed method.

We propose reallocating the power resource among the code symbols in such a way to minimize the post decoding error probability of turbo code. We consider several power reallocation policies and investigate their performance in slowly-varying Rayleigh flat fading channel. We show that the proposed scheme can reduce the post decoding error probability by two orders of magnitude and provide a power gain of 0.86 dB at BER=10-6 over the traditional equal power allocation among all code symbols. We also propose applying different power levels and cut-off thresholds on systematic and parity check bits depending on the channel gain, and investigate the effect of channel gain estimation error.

In this paper, the performance of IEEE 802.11b WLAN under the interference of IEEE 802.15.4 WPAN is analyzed. An analytic model for the coexistence of IEEE 802.15.4 and IEEE 802.11b is presented. Packet error rate, average transmission time, and throughput are evaluated.