FEC (Forward Error Correction) can repair the damage to communication quality due to packet loss. The growing requirement of FEC for high-quality video transmission is inevitable on broadband networks. We have designed and implemented FEC, and integrated it to our developed video transmission system named "mpeg2ts." Our goal is to make it possible to deploy this system on the broadband Internet. However, the problem with constant redundancy of FEC is that weakness to fluctuation of network condition. To resolve this problem, in this paper, we propose and evaluate an efficient FEC method for high-quality video transmission. The proposed mechanisms can provide robustness as well as saving of processing load and optimization of bandwidth consumption. Moreover, we integrate it into a system to deploy it on the real broadband Internet. Transmission experiment demonstrates availability of developed system deployed on the network.

Direct sequence code division multiple access (DS-CDMA) provides flexible data transmission in wide range of data rates by the use of orthogonal multicode multiplexing. In a multipath fading environment, the transmission performance of multicode DS-CDMA degrades as that of single code DS-CDMA does. Chip interleaving is known to improve the bit error rate (BER) performance of the single code transmission by altering the fading channel into severely time selective fading channel. However, this partially destroys orthogonality property among spreading codes and thus, significantly degrades the BER performance of multicode DS-CDMA. In this paper, we propose the joint use of chip interleaving and time-domain minimum mean square error combining (MMSEC) equalization to improve the multicode DS-CDMA transmission performance. It is confirmed by computer simulations that the joint use of chip interleaving and MMSEC equalization significantly improves the BER performance of multicode DS-CDMA and achieves better BER performance compared to the single code DS-CDMA using chip interleaving and maximal ratio combining (MRC).

Multiple access interferecnce (MAI) is a major factor limiting the performance of direct-sequence code-division multiple access (DS-CDMA) systems. Since the amount of MAI is dependent on the correlation among user signals, one way to reduce it is to reduce such correlation. In mobile multiuser communication, each user experiences a different time-varying channel response. This user-dependent characteristic in channel variation can be exploited to assist the separation of different user signals, in addition to the capability provided by the spreading codes. As the correlation among different user channels are expected to decrease with increase in time span, enhanced decorrelation among different users' signals can be effected by spacing out the chips of one modulated symbol in time. Thus we consider chip-interleaving DS-CDMA (CI-DS-CDMA) in this study. We investigate its performance through theoretical analysis and computer simulation. Employing only a slightly modified rake receiver structure, CI-DS-CDMA is shown to attain significant performance gain over conventional DS-CDMA, in multiple access communication over single- and multi-path fading channels, without complicated multiuser detection. CI-DS-CDMA also has a lower demand for short-term power control than conventional DS-CDMA, especially in one-path Rayleigh fading. Results of the theoretical analysis and the computer simulation agree well with each other.

This paper presents a performance comparison of the channel-interleaving method in the frequency domain, i.e., bit interleaving after channel encoding, symbol interleaving after data modulation, and chip interleaving after spreading, for Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) wireless access with frequency domain spreading, in order to reduce the required average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) and achieve the maximum radio link capacity. Simulation results show that, for QPSK data modulation employing turbo coding with the channel coding rate R=3/4, the chip-interleaving method decreases the required average received Es/N0 the most for various radio parameters and propagation model conditions, where the number of code-multiplexing, Cmux, the spreading factor, SF, the r.m.s. delay spread, σ, the number of multipaths, L, and the maximum Doppler frequency, fD, are varied as parameters. For example, when Cmux=12 of SF=16, the improvement in the required average received Es/N0 from the case without interleaving at the average packet error rate (PER) of 10-2, is approximately 0.3, 0.3, and 1.4 dB for the bit, symbol, and chip interleaving, respectively, in a L=12-path exponential decayed Rayleigh fading channel with σ of 0.043 µsec and fD of 20 Hz. This is because the chip interleaving obtains a higher diversity gain by replacing the chip assignment over the entire bandwidth. Meanwhile, in 16QAM data modulation with R=1/2, the performance of the chip interleaving is deteriorated, when Cmux/SF>0.25, due to the inter-code interference caused by different fading variations over the spreading duration since the successive chips during the spreading duration are interleaved to the separated sub-carriers. Thus, bit interleaving exhibits the best performance although the difference between bit interleaving and symbol interleaving is slight. Consequently, we conclude that the bit-interleaving method is the best among the three interleaving methods for reducing the required received Es/N0 considering the tradeoff between the randomization effect of burst errors and the mitigation of inter-code interference assuming the application of adaptive modulation and channel coding scheme in OFCDM employing frequency domain spreading.

We present a scalable parallel rasterizer based on our interleaved scanline rasterization. The sorting overhead of a conventional scanline-based parallel rendering approach has been studied and removed by implementing a scanline assignment hardware. All advantages of the scanline-based parallel rendering are kept such that a good scalability and a small memory usage are achieved. Our architecture is evaluated precisely by a discrete event-based simulation, and the rendering performance and utilization are shown for a various number of rasterizers. The simulation results show more than 8 Mtriangles/s of performance with 64 rasterization engines running at 10 MHz.

Channel coding for bandwidth limited channels based on multilevel bit-interleaved channels is discussed in this paper. This coding and decoding structure has the advantage of simplified design, and naturally incorporates flexible and powerful design of unequal error protection (UEP) capabilities, especially over time-varying channels to be often found in mobile radio communications. Multilevel coded modulation with multistage decoding, and bit-interleaved coded modulation are special cases of the proposed general framework. Simulation results verify the usefulness of the system considered.

In this study, we propose a simple multipoint-to-point ABR mechanism that can be implemented easily in existing ATM networks. The proposed scheme can provide fair bandwidth allocation among the sources in multipoint-to-point connection.

In wireless ATM networks, the condition of the transmission channel fluctuates significantly as a result of many causes such as multipath, shadow phasing, and so forth. Several schemes have been proposed to take care of transmission errors. Some schemes are suitable for favorable channel conditions, while others are more suitable for unfavorable channel conditions. Thus, using a fixed error control scheme regardless of channel conditions is destined to be inefficient. This paper presents a dynamic error control scheme that dynamically selects an appropriate error control scheme according to the conditions of the transmission channel. Using this method, we can decrease both errors and the overhead of redundancy.

In this paper, we investigate the bit error rate (BER) performance of Direct Sequence-Code Division Multiple Access (DS-CDMA) systems under impulsive radio noise environments, and propose a novel DS-CDMA receiver which is designed to be robust against impulsive noise. At first, employing the Middleton's Class-A impulsive noise model as a typical model of impulsive radio noise, we discuss the statistical characteristics of impulsive radio noise and demonstrate that the quadrature components of impulsive noise are statistically dependent. Next, based on the computer simulation, we evaluate the BER performance of a conventional DS-CDMA system under a Class-A impulsive noise environment, and illustrate that the performance of the conventional DS-CDMA system is drastically degraded by the effects of the impulsive noise. To deal with this problem, motivated by the statistical dependence between the quadrature components of impulsive radio noise, we propose a new DS-CDMA receiver which can eliminate the effects of the channel impulsive noise. The numerical result shows that the performance of the DS-CDMA system under the impulsive noise environment is significantly improved by using this proposed receiver. Finally, to confirm the effectiveness of this proposed receiver against actual impulsive radio noise, we evaluate the BER performance of the DS-CDMA system employing the proposed receiver under a microwave oven (MWO) noise environment and discuss the robustness of the proposed receiver against MWO noise.

Bit-interleaving can enhance performance of a trellis coded modulation system over a fading channel. A combined system with decision feedback equalization is proposed. In the system, TCM decoded symbols are fed back for equalization. To avoid a bad effect of decoding delay, a deinterleaver is utilized effectively. Information sequence is divided into three subsequences and encoded by three encoders. Among the 3 code vectors from the encoders, bits are interleaved and decoding proceeds in parallel. Simulation results show that the proposed system realizes 0.6 dB more coding gain than a symbol interleaved system. A calculation method of a branch metric for decoding is proposed. Performance with the branch metric is shown to be nearly independent from the desired/undesired power ratio of a intersymbol interference channel. An approximate upper bound is analyzed for the proposed system, and the optimum code is searched.

Three-dimensional (3-D) instrumentation using an image sequence is a promising instrumentation method for intelligent systems in which accurate 3-D information is required. However, real-time instrumentation is difficult since much computation time and a large memory bandwidth are required. In this paper, a 3-D instrumentation VLSI processor with a concurrent memory-access scheme is proposed. To reduce the access time, frequently used data are stored in a cache register array and are concurrently transferred to processing elements using simple interconnections to the 8-nearest neighbor registers. Based on a row and column memory access pattern, we propose a diagonally interleaved frame memory by which pixel values of a row and column are stored across memory modules. Based on the concurrent memory-access scheme, a 40 GOPS vprocessor is designed and the delay time for the instrumentation is estimated to be 42 ms for a 256256 images.

A structure of neural network suitable for clustering and deinterleaving radar pulses is proposed. The proposed structure consists of two networks, one for intrinsic features of pluses and the other for PRIs (pulse repetition intervals). The unsupervised learning method which adjusts the number of nodes for clusters adaptively is adopted for these two networks to learn patterns. These two networks are connected by a set of links. According to the weights of these links, the clusters categorized by the network for features can be refined further by merging or partitioning. The main defect of the unsupervised network with an adaptive number of nodes for clusters is that the result of classification closely depends on the learning sequence of patterns. This defect can be improved by the proposed refinement algorithm. In addition to the proposed structure and learning algorithms, simulation results have also been discussed.

Recently two interesting conjectures on the linear complexity of binary complementary sequences of length 2nN0 were given by Karkkainen and Leppanen when those sequences are considered as periodic sequences with period 2nN0, where those sequences are constructed by successive concatenations or successive interleavings from a pair of kernel complementary sequences of length N0. Their conjectures were derived from numerical examples and suggest that those sequences have very large linear complexities. In this paper we give the exact formula of characteristic polynomials for those complementary sequences and show that their conjectures are true.

In this paper, we evaluate the bit error rate (BER) performance of a coordinate interleaved trellis coded QPSK with T-algorithm. We employ a coordinate interleaving which breaks up burst errors, caused by fading, more effectively than symbol interleaving. We employ a rate-1/2 convolutional codes and the performance is evaluated on Rayleigh fading channels in terms of bit error rate (BER) by analysis and computer simulation. We consider using of the code which having a long effective code length (ECL). For this reason, we employ a decoder based on T-algorithm instead of Viterbi algorithm to avoid the complexity in the decoding. As the results, we achieve satisfactory BER performance with a slight computation in the decoding algorithm and the finite interleaving size.

In high-speed digital land mobile radio communication, communication quality is degraded by frequency selective fading that has intersymbol interference. It causes increase of bit error rate (BER). To decrease BER in the channel, this paper proposes a system with combined multilevel coding and adaptive equalization using interleaving. By using interleaving, the proposed system obtains time diversity effect. Furthermore the system realizes a type of decision feedback adaptive equalizer where signal after multilevel decoder is fed back. These features of the system cause decrease of BER. The proposed system is compared with a similar system with a feedback signal before multilevel decoder. The average bit error rate of the proposed system is less than 1/100 with that of the compared system at average Eb/No = 22 [dB] in a case of fading channel with one intersymbol interference.

In this work, we present an 8-state trellis code for bit interleaved 16-QAM and the BER performance on Rayleigh fading channel is evaluated. We analyze the BER and show that the effective code length and minimum productive distance are also important criterion for code design on bit interleaved system. We design the code by considering not only minimum Hamming distance but also the effective code length and minimum productive distance. As a result, we found that the scheme employing the code achieves good BER performance on Rayleigh fading channel even with the finite interleaving size.

Future digital land mobile communication, for a moving picture, requires more transmission speed and less bit error rate than the existing system does for speech. In the system, the intersymbol interference may not be ignored, because of higher transmission speed. An adaptive equalizer is necessary to cancel intersymbol interference. To achieve low bit error rate performance on the mobile radio channel, trellis-coded modulation with interleaving is necessary. This paper proposes an interleaved trellis-coded modulation scheme combined with a decision feedback type adaptive equalizer of high performance. The reliable symbol reconstructed in the trellis decoder is used as the feedback signal. To make equalizer be free from decoding delay, deinterleaving is effectively utilized. The branch metric, for trellis-coded modulation decoding, is calculated as terms of squared errors between a received signal and an expected signal by taking the reconstructed symbol and the impulse response estimated by the recursive least squares algorithm into account. The metric is constructed to have good discrimination performance to incorrect symbols even in non-minimum phase and to realize path diversity effect in a frequency selective fading channel. Computer simulation results are shown for several channel models. On a frequency selective fading channel, average bit error rate is less than 1/100 of that of the RLS-MLSE equalizer for fdTs=1/1000 at average Eb/N0 beyond 15dB. Performance degradation due to equalization error is less than 1.8dB. Performance is greatly improved by the effect of the reconstructed symbol feedback.

This paper presents improvement of data error rate against burst noise by using both chip interleaving and hard limiter in direct sequence spread spectrum (DS/SS) communication systems. Chip interleaving, which is a unique method of DS/SS systems, is effective when burst noise power is small. However, when the burst noise power is large, date error rate is degraded. While, though hard limiter suppresses burst noise power, it gives little effectiveness when the burst noise length is long. Using chip interleaving and hard limiter together, as they work complementary, stable and considerable improvement of data error rate is achieved.

Two types of multicast error control protocols based on a product code structure with or without interleaving are considered. The performances of these protocols are analyzed on burst error channels modeled by Gilbert's two-state Markov chain. The numerical results reveal that the interleaving does not always succeed in improving the performance of the protocol proposed in Part .