A T user multiple access collision channel without feedback is considered where the channel inputs are called packets. The packets take values from non-binary input alphabet. It is supposed that at most M users are active, i.e., are communicating simultaneously (2 M T). We are looking for codes and protocol sequences of users of minimum length such that from the output of the channel it can be determined which users were active, what were their synchron positions, and what they sent.

We study asynchronous SSMA communication systems using binary spreading sequences of Markov chains and prove the CLT (central limit theorem) for the empirical distribution of the normalized MAI (multiple-access interference). We also prove that the distribution of the normalized MAI for asynchronous systems can never be Gaussian if chains are irreducible and aperiodic. Based on these results, we propose novel theoretical evaluations of bit error probabilities in such systems based on the CLT and compare these and conventional theoretical estimations based on the SGA (standard Gaussian approximation) with experimental results. Consequently we confirm that the proposed theoretical evaluations based on the CLT agree with the experimental results better than the theoretical evaluations based on the SGA. Accordingly, using the theoretical evaluations based on the CLT, we give the optimum spreading sequences of Markov chains in terms of bit error probabilities.

Although data compression is popularly used, compressed data have a problem that they are very sensitive to errors. This paper proposes a single burst error recovery method for Huffman coding by using the bidirectionally decodable Huffman coding. Computer simulation shows that the proposed method can recover 2.5lburst bits burst error with high probability, where lburst is the maximum length of burst errors which the proposed method is expected to be able to recover.

The recent Internet needs a network structure and traffic engineering that can support various applications requiring differentiated traffic processing and a high quality of service. The extension of the Internet from wired to wireless systems that generate location-dependent and burst errors has made the support of good services more difficult with existing packet scheduling algorithms. Accordingly, this paper proposes a wireless differentiated service packet scheduling (WDSPS) algorithm that can provide reliable and fair services in differentiated wireless internet service networks. As such, the proposed scheduling algorithm solves the HOL blocking problem within a class packet queue that occurs in a wireless network, supports differentiated services for each class defined in a differentiated service network, and facilitates gradual and efficient service compensation not only among classes but also among flows within a class, thereby preventing a monopoly by one class or one flow. Simulations confirmed that the proposed WDSPS scheduling algorithm could provide the required QoS differentiation between classes and enhanced the service throughput under various wireless network conditions.

A novel phase error correction scheme is proposed for the high rate OFDM-based wireless local area networks (WLANs). The proposed scheme makes the system capable of efficiently compensating the whole phase error due to the residual sampling clock offset and frequency offset estimation error after timing and frequency offset compensation, as well as the phase noise.

The linear complexity and its stability of periodic sequences are of fundamental importance as measure indexes on the security of stream ciphers and the k-error linear complexity reveals the stability of the linear complexity properly. The k-error linear complexity of periodic sequences is defined to be the smallest linear complexity that can be obtained by changing k or fewer bits of the sequence per period. For 2pn-periodic binary sequences, where p is an odd prime and 2 is a primitive root modulo p2, we present and prove the unique expression of the linear complexity. Moreover we show a relationship between the linear complexity and the minimum value k for which the k-error linear complexity is strictly less than the linear complexity.

A new simple recovery scheme for transient bit errors in the RAM of a ROM-based embedded system is presented, which exploits the information stored in the ROM. And a new scrubbing technique suitable to the proposed recovery scheme is also presented. With the proposed recovery scheme and scrubbing technique, the reliability of the RAM against transient bit errors can be improved remarkably with no additional extra memory and scrubbing overhead.

This paper considers the problem of finding two-dimensional (2-D) direction of arrivals (DOAs) for coherent cyclostationary signals using a 2-D array with random position errors. To alleviate the performance degradation due to the coherence between the signals of interest (SOIs) and the random perturbation in 2-D array positions, a matrix reconstruction scheme in conjunction with an iterative algorithm is presented to reconstruct the correlation matrices related to the received array data so that the resulting correlation matrices possess the eigenstructures required for finding 2-D DOAs. Then, using the reconstructed matrices, we create a subspace orthogonal to the subspace spanned by the direction vectors of the SOIs. Therefore, the 2-D DOAs of the SOIs can be estimated based on a subspace-fitting concept and the created subspace. Finally, several simulation examples are presented for illustration and comparison.

In this paper, we propose a new error feedback (EF) structure for 2-D separable-denominator digital filters described by a rational transfer function. In implementing two-dimensional separable-denominator digital filters, the minimum delay elements structures are common. In the proposed structure, the filter feedback-loop corresponding to denominator polynomial is placed at a different location compared to the commonly used structures. The proposed structure can minimize the roundoff noise more than the previous structure though the number of multipliers is less than that of previous one. Finally, we present a numerical example by designing the EF on the proposed structure and demonstrate the effectiveness of the proposed method.

In this paper, we propose a statistical model for detecting article errors, which Japanese learners of English often make in English writing. It is based on the three head words--the verb head, the preposition, and the noun head. To overcome the data sparseness problem, we apply the backed-off estimate to it. Experiments show that its performance (F-measure=0.70) is better than that of other methods. Apart from the performance, it has two advantages: (i) Rules for detecting article errors are automatically generated as conditional probabilities once a corpus is given; (ii) Its recall and precision rates are adjustable.

The technological development of wireless environment has made real-time multimedia communications possible in wireless networks. Many studies have been done on real-time communications in wireless networks in order to overcome a higher bit error rate in wireless channels. However, none of work deals with firm real-time communications which can be applied to multimedia communications. In this paper, we propose an adaptive error correcting scheme for firm real-time multimedia communications in wireless networks in order to maximize the expected net profit. The proposed scheme adaptively selects an error correcting code under the current air state and the message state of a message stream. Throughout simulation results, we show that the suggested scheme provides more profit than single error-correcting code schemes.

Taking the uplink and downlink cochannel interference and noise into account, we determine the error probability in detecting a binary phase-shift keying (BPSK) signal transmitted over a satellite system containing two high power amplifiers (HPA). The first one is the constituent part of the transmitting ground station and the second one is the constituent part of the satellite station. The emphasis is placed on determining the system performance degradation imposed by the influence of the nonlinear characteristic of the HPA at the transmitting ground station in combination with the negative influences of the uplink and downlink cochannel interference, as well as the nonlinear characteristic of HPA at the satellite station.

Orthogonal modulation provides low probability of bit error, however its bandwidth efficiency is very low. Biorthogonal code may double the bandwidth efficiency, but its required bandwidth grows exponentially with the number of input bits as in orthogonal modulation. In this paper, we propose a multi-code biorthogonal code keying (MBCK) scheme that significantly reduces the signal bandwidth with the benefit from orthogonal waveform coding maintained. The system consists of multiple waveform coding blocks, and the sum of output codewords is transmitted. A problem with MBCK is that output signal is multi-level, which requires amplifier with high linearity. So it may not be an appropriate scheme for portable unit where power efficiency is highly important. We also propose a modified MBCK scheme that guarantees constant amplitude output. The transmitter of the proposed scheme contains a redundant waveform coder whose input is generated by encoding the information bits. Adding the codewords from all constituent waveform coding blocks, the composite signal has constant amplitude. It is also shown that the redundant bits are not only used to make constant amplitude signal but also used to improve the BER performance at the receiver.

In this paper, we present an MPEG-4 decoding scheme based on reversible variable length code. The scheme is purely decoder based and compliance with the standard is fully maintained. Moreover, the data recovery scheme suggested in MPEG-4 can still be used as the default scheme. Simulation results show that the proposed scheme achieves better data recovery, both in terms of PSNR and perceptual quality, from error propagation region of a corrupted video packet, as compared to existing MPEG-4 scheme.

In this paper, a new error concealment algorithm for MPEG-4 object-based video is presented. The algorithm consists of a feature matching step to identify temporally corresponding features between video frames and an affine parameter estimation step to find the motion of the feature points. In the feature matching step, an efficient cross-radial search (CRS) method is developed to find the best matching points. In the affine parameter estimation step, a non-iterative least squares estimation algorithm is developed to estimate the affine parameters. An attractive feature of the algorithm is that the shape data and texture data are handled by the same method. Unlike previous methods, this unified approach works for the case where the video object undergoes a drastic movement, such as a sharp turn. Experimental results show that the proposed algorithm performs much better than previous approaches by about 0.3-2.8 dB for shape data and 1.6-5.0 dB for texture data.

Many image and video compression algorithms work by splitting the image into blocks and producing variable-length code bits for each block data. If variable-length code data are transmitted consecutively over error-prone channel without any error protection technique, the receiving decoder cannot decode the stream properly. So the standard image and video compression algorithms insert some redundant information into the stream to provide some protection against channel errors. One of such redundancy is resynchronization marker, which enables the decoder to restart the decoding process from a known state in the event of transmission errors, but its frequent use should be restricted not to consume bandwidth too much. The Error Resilient Entropy Code (EREC) is well known method which can regain synchronization without any redundant information. It can work with the overall prefix codes, which many image compression methods use. This paper proposes an improvement to FEREC (Fast Error-Resilient Entropy Coding). It first calculates initial searching position according to bit lengths of consecutive blocks. Second, initial offset is decided using statistical distribution of long and short blocks, and initial offset is adjusted to insure all possible offset value can be examined. The proposed algorithm can speed up the construction of EREC slots, and can preserve compressed image quality in the event of transmission errors. The simulation result shows that the quality of transmitted image is enhanced about 0.3-3.5 dB compared with the existing FEREC when random channel error happens.

In this paper, a new tracking method for Code Shift Keying Spread Spectrum (CSK/SS) is proposed. In the CSK/SS systems, since the transmitted sequences vary at every frame, synchronization is difficult. In the proposed method, a pair consists of the Manchester-coded PN sequence and the non-Manchester-coded PN sequence as the synchronizing sequence. The cross-correlation characteristic of the pair is used instead of the S-curve of delay lock loop (DLL). The receiver can track the signal timing by using the characteristic. The proposed method is applied to the external synchronization system whose structure is simple. The following performance in channel with the Additive White Gaussian Noise (AWGN) is analyzed and evaluated; (1) the tracking error (jitter) performance and (2) the bit error rate (BER) performance that takes the jitter into account. As a result, the jitter of the proposed system is better than those of the conventional DLL systems as Eb/N0 increases. The jitter of the proposed system has less degradation than those of the conventional systems, even if the number of users increases. Moreover, BER of the proposed system is similar to that of the 1Δ-DLL system and superior to that of the 2Δ-DLL system.

This paper presents a closed form expression of an exact average bit error rate (BER) for a time-division duplex (TDD) transmit diversity scheme employing maximal ratio combining (MRC) over time selective flat Rayleigh fading channels. In the proposed analysis, the feed back delay which degrades the BER performance is taken into account. The results are generally applicable to an arbitrary modulation scheme, as well as an arbitrary number of transmitting branches. To confirm the validity of the proposed analysis, the theoretical results are compared with the simulated ones.

The rapid growth of multimedia applications has increased interest in the compression of video data. This paper presents a new method for improving the compression ratio of video data, which can be easily used in a multilayer environment for error resilience applications as well. Data of four luminance blocks in a macroblock are processed and arranged in such a way that important macroblock data is compressed in one block(A), while the rest of the three remaining data blocks(H,V,D) are given difference values in the horizontal, vertical and diagonal directions. This results in a reduced bitstream size because of the low-valued data present in the three blocks(H,V,D), giving better compression at low bitrates. In an error resilient environment, the important data block in a macroblock is transmitted in a secure channel while the remaining three blocks with difference data are sent via a lossy channel. If error occurs in the lossy channel, picture can still be reconstructed with reasonably good quality using only the block data that is transmitted in the secure channel.

The history of forward error correction in optical communications is reviewed. The various types of FEC are classified as belonging to three generations. The first generation FEC represents the first to be successful in submarine systems, when the use of RS(255, 239) became widespread as ITU-T G.975, and also as G.709 for terrestrial systems. As WDM systems matured, a quest began for a stronger second generation FEC. Several types of concatenated code were proposed for this, and were installed in commercial systems. The advent of third-generation FEC opened up new vistas for the next generation of optical communication systems. Thanks to soft decision decoding and block turbo codes, a net coding gain of 10.1 dB has been demonstrated experimentally. That brought us a number of positive impacts on existing systems. Each new generation of FEC was compared in terms of the ultimate coding gain. The Shannon limit was discussed for hard or soft decision decoding. Several functionalities employing the FEC framing were introduced, such as overall wrapping by the FEC frame enabling the asynchronous multiplexing of different clients' data. Fast polarization scrambling with FEC was effective in mitigating polarization mode dispersion, and the error monitor function proved useful for the adaptive equalization of both chromatic dispersion and PMD.