In recent years, labor accidents and a shortage of skilled workers due to an aging population have become significant issues at construction sites in Japan. To address these challenges, we are developing a Cyber-Physical System (CPS) platform called ROS2-TMS for Construction, which aims to improve both the efficiency and safety of earthwork operations. In this study, we propose a task management system for construction machinery using an open platform named OPERA as an additional function of ROS2-TMS for Construction. This task management system controls construction machinery using environmental information stored in a database, which collects and stores data from sensors deployed throughout the construction site, and an extended Behavior Tree. At the end of this study, the results of the initial validation tests of autonomous earthwork operations using an OPERA-compatible backhoe ZX200 are presented.

Recently, LTE high-speed mobile communications have allowed service developers to create various interactive applications using push communications. In a push communication, a paging procedure is required to find the location of the target mobile terminal and to notify the arrival of the pushed data. The Mobility Management Entity (MME) speculatively sends many copies of a paging message to base stations to catch the target mobile terminal. As push-communication applications increase, the workload of MME will increase owing to multiple copies of paging messages sent and this would cause, delay of communication initiation. We propose a lightweight paging method where the MME selects paging areas based on the elapsed time of the last location update in LTE. Compared to ordinary paging (i.e., the paging area is pre-configured) we show through simulation experiments that the workload is reduced in the proposed method.

The behavior of single-carrier frequency-division multiaccess with localized subcarrier assignment (localized SC-FDMA) over doubly selective, that is, frequency and time selective, fading channels has not yet been studied well. In this paper, we study a behavior of the localized SC-FDMA channel called the user channel instability, where the standard linear minimum mean-squared error (MMSE) equalizer fails to work properly due to a few excessively small eigenvalues of the user channel matrix, and show that, although it has a crucial effect on the performance of linear minimum mean-square error (MMSE) equalization, its effect can be alleviated with the use of advanced techniques, such as stepwise decision detection and diversity reception with multiple receive antennas.

In this paper, we propose the use of coded constellation rotated vector OFDM (CRV-OFDM) to alleviate the necessity for a convolutional code with a large free distance dfin coded OFDM. Theoretical analysis indicates that CCRV-OFDM of vector length-M attains diversity order min{P, Mdf} over a length-P Rayleigh fading channel with an appropriately designed interleaver. We employ Almost linear interleaver (ALI) to CCRV-OFDM and introduce a union bit error rate (BER) bound which is used for the purpose of the parameter selection of ALI. The effectiveness of our design and the superiority of CCRV-OFDM on BER over coded OFDM are demonstrated through simulations.

In this paper, we study pairwise error probability (PEP) of a system employing constellation-rotated vector orthogonal frequency-division multiplexing (CRV-OFDM), which is an enhancement of vector OFDM (V-OFDM) with enhanced diversity, over a frequency-selective channel with both carrier frequency offset (CFO) and Doppler frequency spread. First, we extend the work of Rugini and Banelli, which is known to give a good bit-error rate (BER) approximation for the standard OFDM system only with CFO, to PEP evaluation for CRV-OFDM and discuss its limitations. Then, we discuss the conditionally Gaussian characteristi2cs of the Doppler-induced interference and propose a conditionally Gaussian PEP approximation. Confirming a good match of the conditionally Gaussian PEP approximation and with simulation results, we propose a new semianalytical PEP lower bound. The new lower bound is computationally feasible and is shown by simulation to be tight for small to moderate CFO. Finally, a computationally more feasible approximation of the lower bound is also proposed. Our discussion reveals, as a by-product, why the Gaussian assumption for the Doppler-induced interference works for standard OFDM systems although the assumption is actually incorrect.

A new service discovery scheme using mobile agents for mobile ad hoc networks (MANETs) we have proposed are effective for dissemination and collection of service information because mobile agents can migrate among nodes in spite of topology change in MANETs. In the proposed scheme, mobile agents migrate to one of neighboring nodes in which the number of services collected in the predefined time (called service collection time) is the lowest. This paper investigates the property of the proposed mobile agent based scheme for realtime service dissemination and collection in MANETs through simulation experiments. The simulation results show that the service collection time has the impact on the dissemination time of the proposed scheme in imbalanced location of services, and that the proposed scheme can achieve real-time service dissemination and collection by autonomously adjusting the service collection time.

This paper proposes a novel deterministic inter-leaver, called almost linear interleaver (ALI) as the generalization of block and linear interleavers, and discusses its parameter/depth selection for coded orthogonal frequency division multiplexing (COFDM) system over Rayleigh fading channel. The concept of diversity guard is introduced to guarantee the achievable maximum diversity order with a reasonable complexity. Simulation results shown that the proposed design always outperforms random interleaver (RI) and the block interleaver (BI) adopted by the IEEE 802.11a standard.

We consider improvement of bit error rate (BER) upper bounds, based on the notion of decomposable error vectors (DEVs) introduced by S. Verdu, for downlink multiuser space-time systems over Rayleigh fading channels. Although omission of DEVs and limiting before averaging (LBA) technique are known to improve the standard union bound (UB) considerably, it is mathematically intractable to obtain a bound in a closed-form. In this paper, assuming maximum-likelihood (ML) detection for downlink multiuser space-time spreading (STS) systems, we introduce a new modification of the decomposability of error vectors and propose a new BER upper bound. We prove that the proposed bound is tighter than the standard union bound and the bound based on the overall decomposability. The numerical results show that the proposed bound is also tighter than the bound based on positive-sum-decomposability (PSD) in the scenario of downlink multiuser transmission.

In this paper, we propose the use of constellation rotated vector OFDM (CRV-OFDM) to combat a fast fading channel, which accompanies with carrier frequency offset (CFO) and Doppler frequency spread (DFS). Employing Gaussian approximation of interference, we give pair-wise error probability bounds of CRV-OFDM in terms of the CFO and DFS. The theoretical analysis indicates that robustness of CRV-OFDM against fast fading increases with M, the length of vectorized symbols, and such argument is confirmed by running computer simulations.

In this paper, convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) employing the zero-correlation-zone (ZCZ) code generated from the Chu sequence is proposed as a novel multi-access scheme for fast fading multipath channels. Analysis results demonstrate that the system remains approximately multiuser interference (MUI)-free even when the system is heavily loaded and subject to severe Doppler spreads. An effective channel estimation method based on B-spline approximation is also proposed. Simulation results show, in combination with the Probabilistic Data Association (PDA) equalization, the system significantly outperforms the DS-CDMA system employing Linear Minimum Mean Squared Error (LMMSE) chip-wise equalization and polynomial interpolation-based channel estimation from medium to high user population.

The complete complementary code (CCC) that was proposed by Suehiro and Hatori is a sequence family, that is a set of sequence sets, with ideal correlation sums. Numerous studies in the literature show its applications to direct-spread code-division multiple access (DS-CDMA) systems for interchannel interference (ICI)-free communication with improved spectral efficiency. In this paper, we propose a systematic framework for the construction of CCCs based onN-shift cross-orthogonal sequence families (N-CO-SFs) . We show theoretical bounds on the size ofN-CO-SFs and CCCs and give a set of four algorithms for their generation and extension. The algorithms are optimal in the sense that the size of the resultant sequence families achieves theoretical bounds and, with the algorithms, we can construct an optimal CCC consisting of sequences whose lengths are not only almost arbitrary but even variable between sequence sets. We also discuss the family size, alphabet size, and length of constructible CCCs based on the proposed algorithms.

Although the single antenna vector OFDM (VOFDM) proposed by Xia shows performance robust to channel spectral nulls, it does not necessarily attain full diversity for multi-path fading channels. It is known that the degradation in diversity order is sometimes rescued by the rotation of constellation. A simple application of constellation rotation to the V-OFDM system does not, however, improve its performance. In this paper, we discuss the sub-channel spectral structure of the V-OFDM signal and give upper bounds on its pair-wise error probability over multi-path Rayleigh fading channels and propose a novel constellation-rotated V-OFDM (CRV-OFDM) with improved diversity. To this end, we design rotation angles for sub-channel symbols to minimize upper bounds on BER. Simulation results show that the proposed CRV-OFDM attains diversity order min{M,P} for the vector length M and the number of paths P. As the results, for BER 10¿4, CRV-OFDM improves the performance of V-OFDM by 2 dB for both BPSK and QPSK modulation when M is 2, and, for M = 4, the improvement factor is about 1.3 dB. We also discuss the effects of M on the transmitter and receiver complexities and on the peak-to-averate power ratio. Finally, we compare several methods for rotational angle determination.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath downlink channels with the use of zero correlation zone (ZCZ) codes. However, MUI-free transmission is guaranteed only when the data length D, channel delay L, and ZCZ length Z satisfy Z+1 ≥ D + L. In this paper, we consider the situation that MUI-free transmission is not realized inevitably because of excessive multipath delays or deliberately because of the necessity to get a higher bandwidth efficiency, clarify the structure of MUI in the CS-CDMA/CP system employing M-ZCZ codes, and propose iterative partial multiuser detection (IPMUD). The detection is implemented at symbol-level (after despreading) and the number of users jointly considered can be adjusted flexibly to offer a tradeoff between system performance and receiver complexity. The performance of the proposed scheme is verified numerically by density evolution approach and BER simulations. The CS-CDMA/CP system with IPMUD is shown to be much less complex than the DS-CDMA system with Wang and Poor's turbo MUD receiver and to be less complex and better, in terms of bit error rate (BER) performance, than the DS-CDMA system with iterative chip-wise equalization receivers.

Although the single antenna vector OFDM (V-OFDM) proposed by Xia is robust to channel spectral nulls, it does not necessarily attain full diversity for multi-path fading channels. In this paper, we propose a novel constellation-rotated V-OFDM (CRV-OFDM) system based on modified V-OFDM, and analyze its performance over Rayleigh fading channels. In CRV-OFDM, we design rotation angles for each symbol to minimize upper bounds on bit error rate (BER) with full diversity order. Our simulation results show that, compared with V-OFDM, proposed CRV-OFDM always attains the maximum diversity order determined by the vector length M. As a result, for BER 10-4, CRV-OFDM improves the performance of V-OFDM by 2 dB for both BPSK and QPSK modulation for M = 2, and, for M = 4, the improvement is about 1.3 dB. To verify optimality of the derived angles, we also test, in therms of BER, some other angles including the angles derived from minimum product distance (MPD) criterion and compare with the theoretical union bounds and show that the BERs take the smallest values at our derived optimal angles.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath downlink channels with the use of zero correlation zone (ZCZ) codes. However, MUI-free transmission is guaranteed only when the data length D, channel delay L, and ZCZ length Z satisfy Z + 1 ges D + L, and the user population is constraint to be K les [N/(Z+1)], where N is the code length. In this paper, for the purpose of allowing higher bandwidth efficiency for more active users, we propose an iterative partial multiuser detector for CS-CDMA/CP with M-ZCZ code to allow Z + 1 < D + L. Because the detector is implemented in the symbol-level (after despreading) and only a partion of users are jointly considered, its receiver complexity is expected to be acceptable for a mobile terminal. Comparison with the DS-CDMA system employing chip-equalization receiver shows that the CS-CDMA/CP system employing the proposed receiver offers a better tradeoff between the performance and receiver complexity, which indicates its potential application in future wireless communications.

A code-division multiple access (CDMA) communication system achieves the maximum spectral efficiency over multipath fading channels if employed spreading sequences have ideal correlations, i.e., the ideal auto-correlation that are zero except for zero shift and the ideal cross-correlations that are zero for all shifts. Unfortunately, such sequences are known non-existent and, Suehiro and Hatori proposed a sequence family with ideal correlation sum called the complete complementary code (CCC). For (quasi-) synchronous CDMA systems, the ideal correlation sum of CCC provides an inter-channel interference (ICI)-free communication and CCC based CDMA (CCC-CDMA) improves spectral efficiency significantly. In previous work, we have proposed a general and systematic construction of the optimal CCC. However, in special cases, the proposed construction results in CCCs with extra interesting properties. In this paper, we propose a new type of CCC called the Z-connectable CCC (Z-CCC), which gives a sequence set with zero correlation zone (ZCZ) by connecting codes in its complementary codes. We also present two Z-CCCs which consist of rows of the discrete Fourier transform (DFT) and Hadamard matrices. Due to Z-CCC provides the guard-part reduced sub-packet structure, Z-CCC based CDMA (Z-CCC-CDMA) realizes higher spectral efficiency than the traditional CCC-CDMA and, intimate relationships of the present Z-CCCs and the DFT matrix or Hadamard matrix allows low implementation complexity.

Verdu¿ introduced the notion of indecomposable error vectors (IEVs) and showed that the union bound including IEVs only gives a quite tight bit error rate (BER) upper bound for multiuser detection over an AWGN channel. There have been some efforts to strengthen the notion of IEVs to make them applicable to fading channels, but those efforts only led to bounds still loose at low signal-to-noise power ratios (SNRs). In this paper, we propose a new union bound based on the notion of IEVs and apply it to a space-time spreading (STS) code-division multiple access (CDMA) system over an MIMO Rayleigh fading channel. We calculate a BER upper bound for the ML receiver in a downlink space-time CDMA system and show that the upper bound is tighter than the previously known union bound based on the conventional strengthening of the IEV property and than the well-known limit-before-averaging (LBA) bound more than one transmit antennas.

This paper studies the impact of fast fading on the performance of coded convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) combined with iterative detection, which was originally proposed for multiuser interference-free (MUI-free) downlink transmission over a quasi-static multipath fading channel. We show that the CS-CDMA/CP system in conjunction with a single pilot, with zero-correlation-zone code from an M-sequence (M-ZCZ), and with iterative detection works also well for fast fading, and the impacts of Doppler spreads can be made negligible without bandwidth efficiency loss by the employment of excess channel spread configuration and iterative partial multiuser detection. We compare the proposed system and the standard W-CDMA system for downlink transmission by simulation and show that both systems enjoy time-diversity effects of fast fading and that, although the W-CDMA system performs better for a small number of users, the CS-CDMA/CP system performs much better for the number of users from moderate to as large as processing gain.

In this paper, a coded convolutional spreading codedivision multiaccess with cyclic prefix (CS-CDMA/CP) system in conjunction with iterative receivers is proposed for synchronous downlink transmission over frequency selective fading channels and its performance is compared with the uncoded CS-CDMA/CP employing maximum-likelihood sequence estimation (MLSE) receiver as well as with the conventional coded direct sequence CDMA (DS-CDMA) employing (maximal ratio combining-) MRC-RAKE. Contrary to the uncoded CSCDMA/ CP system which suffers from performance degradation at low signal-to-noise power ratios (SNRs), it is demonstrated that the proposed scheme can attain almost the full path diversity gain over all SNRs with single-user complexity. Compared with the coded DS-CDMA system with single-user receivers, the proposed system is free from multiuser interference (MUI) whenever the multipath delay of the channel does not exceed the designed maximum delay. It is also demonstrated, moreover, that the proposed system shows a robust performance even if the channel length exceed the designed maximum delay slightly. Because of the subblock structure of CS-CDMA/CP, the proposed system can utilize time-diversity effects, when the channel subjects fast fading, and this greatly improves the resultant performance. Finally, it is shown that the receiver complexity of the proposed system is compared quite favorably with the iterative multiuser receivers for coded DS-CDMA systems of comparable performance.

The Shannon rate-distortion function R(D) of a random process provides a lower bound to the minimal average distortion given a constraint on the average rate. When a positive source coding theorem with a fidelity criterion applies, the lower bound is achievable in the limit of large block length and hence R(D) characterizes the optimal performance for source coding or lossy data compression. The source coding theorem for possibly nonstationary Gaussian autoregressive sources was established over three decades ago, but two apparently different formulas for R(D) have appeared in the literature, resulting in long standing confusion about which is correct. There has also been related confusion about the asymptotic eigenvalue distributions of the inverse covariance matrices of such processes. We here establish the equality of the two formulas under fairly general conditions and clarify the confusion regarding asymptotic eigenvalue distributions.

In an approximately synchronous CDMA (ASCDMA) system, zero correlation zone (ZCZ) sequences are known as the sequences to eliminate co-channel and multi-path interferences. Therefore, numerous constructions of zero correlation zone (ZCZ) sequences have been introduced e.g. based on perfect sequences, m-sequences and complete complementary codes etc.. However, the previous construction method which based on complete complementary code is lacking for merit figure. In this paper, a new construction method of ZCZ sequences based on complete complementary codes is proposed. By proposed method, the ZCZ sequences with greater than 1/2 merit figure are constructable.

Source coding theorems and Shannon rate-distortion functions were studied for the discrete-time Wiener process by Berger and generalized to nonstationary Gaussian autoregressive processes by Gray and by Hashimoto and Arimoto. Hashimoto and Arimoto provided an example apparently contradicting the methods used in Gray, implied that Gray's rate-distortion evaluation was not correct in the nonstationary case, and derived a new formula that agreed with previous results for the stationary case and held in the nonstationary case. In this correspondence it is shown that the rate-distortion formulas of Gray and Hashimoto and Arimoto are in fact consistent and that the example of Hashimoto and Arimoto does not form a counterexample to the methods or results of the earlier paper. Their results do provide an alternative, but equivalent, formula for the rate-distortion function in the nonstationary case and they provide a concrete example that the classic Kolmogorov formula differs from the autoregressive formula when the autoregressive source is not stationary. Some observations are offered on the equality of the asymptotic distributions of the eigenvalues of the sequence of inverse autocorrelation matrices of possibly nonstationary autoregressive processes and of their Toeplitz approximations.

We propose a transmit diversity CDMA scheme which is a combination of convolutional spreading (CS) and space-time spreading (STS) over multiple-input single-output (MISO) multipath Rayleigh fading channels. With our scheme, multiuser detection over an MISO multipath channel is transformed to single-user detection over a single-input single-output (SISO) multipath channel as the scheme by Petre et al. Because of its simple configuration, it is immediate to see that our scheme realizes full transmit- and path-diversity for two transmit antennas. We extend the system to four transmit antennas employing quasi-orthogonal construction and show a necessary and sufficient condition for full transmit- and path-diversity to be realized. The proposed scheme requires less hardware complexity and less latency than the one by Petre et al.

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath channels with the use of zero correlation zone (ZCZ) codes. In our previous work, we proposed application of a class of binary ZCZ codes generated from an M- sequence, the M-ZCZ code, which has larger user capacity than known binary ZCZ codes and high robustness against transmitter nonlinearity. CS-CDMA/CP guarantees MUI-free transmission only when the data length D, multipath channel length L, and the ZCZ length Z satisfy Z ges D + L - 1, and, for a long spread multipath channel of length Le> L, CS-CDMA/CP suffers from MUI. In this paper we discuss the effect of MUI over the CS-CDMA/CP system employing an M-ZCZ code and propose MUI cancellation schemes for channels with excess spreads, D + Le- 1 > Z. Some simulation results show that the proposed schemes show good BER performance and, more importantly, allows increased user population, compared to the fully MUI- free case with a graceful performance degradation.

N-shift cross-orthogonal sequences are powerful materials for constructing complete complementary codes. In this paper, we present six theorems concerning general construction and expansion methods with the least upper bounds for N-shift cross-orthogonal sequences and complete complementary codes. Applying the theorems that about construction and expansion method of N-shift cross-orthogonal sequences, many types of N-shift cross orthogonal sequences are constructed systematically. Those include the sequence sets consisting of different lengths and include previous classes as special cases. Based on the generated N-shift cross orthogonal sequences, a complete complementary code are constructed by the theorem of construction method of complete complementary code. The last theorem which is about expansion method of complete complementary code are given for increase the number of sequence sets.

We propose a transmit diversity CDMA scheme which is a combination of convolutional spreading (CS) and space-time block coding over multiple input single output (MISO) multipath Rayleigh fading channels. Using orthogonal space-time block coded CS, we can reduce the communication problem over the multiple-input and multiuser channel to relatively simple communication problem over a single-antenna and single-user system. Similar to the scheme in [5], full transmit diversity gain is achieved, and path diversity gain is achieved as well. For quasiorthogonal space-time block coded CS, we also show that signal-constellation rotation is adopted [16] to achieved the full transmit diversity and path diversity gain.

Orthogonal frequency division multiplexing (OFDM) systems for mobile applications suffer from inter-carrier-interference (ICI) due to frequency offset and to time-variation of the channels and from high peak-to-average-power ratio (PAPR). In this paper, we revisit symmetric cancellation coding (SCC) proposed by Sathananthan et al. and compare the effectiveness of SCC employing a fixed subtraction combining with the well-known polynomial cancellation coding (PCC) over Rayleigh fading channels with Doppler spread in terms of the signal-to-interference plus noise power ratio (SINR) and bit-error-rate (BER). We also compare our SCC employing subtraction combining with SCC of Sathananthan et al. employing maximum ratio combining (MRC). Our results show that, our SCC-OFDM gives higher SINR than PCC-OFDM over the flat Rayleigh fading channel, and that this superiority is not maintained under multi-path induced frequency-selective fading unless diversity combining is used. However, we show that, for frequency-selective fading channels, our SCC-OFDM in conjunction with differential modulation in frequency domain shows better performance than PCC-OFDM and normal OFDM for a certain range of Doppler spread. Finally, we also demonstrate that the SCC-OFDM signal has less PAPR compared to the normal OFDM and PCC-OFDM.

For synchronous downlink direct-sequence code-division multiple access (DS-CDMA), we introduce a cyclic-prefix (CP)-based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes, which gives a class of multiuser interference (MUI)-free CDMA schemes, including Suehiro's CDMA and block spreading (BS) CDMA as special cases. We show that CS-CDMA/CP employing appropriately selected binary and ternary ZCZ codes have good user capacity, peak-to-average power ratio (PAPR), and transmission power loss, compared with previously proposed BS-CDMA schemes. By simulation, we show the effect of PAPR to its bit-error rate (BER) performance when nonlinear amplifiers are used, and also compare its BER performance with the conventional DS-CDMA scheme employing a RAKE receiver

In synchronous DS-CDMA systems the multi-user interference (MUI) caused by multipath propagation degrades the system performance. To overcome this, MUI-free schemes, such as Suehiro's CDMA in N. Suehori (1994) and H.H. Chen et al. (2001) and CIBS-CDMA in S. Zhou et al. (2002) are introduced. In this paper a new class of cyclic prefix (CP) based convolutional spreading CDMA (CS-CDMA/CP) scheme employing zero correlation zone (ZCZ) codes [P.Z. Fan et al., May 1999] is proposed. We show that above two MUI-free schemes are special cases of CS-CDMA/CP and they only difference comes from the particular employed ZCZ code. A comparison in terms of PAPR and transmission power loss for the CS-CDMA schemes is given. We consider a pilot aided downlink CS-CDMA/CP employing equalizers, and compare its performance with the conventional DS-CDMA system employing RAKE receivers via simulation. Our simulation results show that, CS-CDMA/CP performs better than DS-CDMA when system has many users.

Although sequential decoding of convolutional codes gives a very small decoding error probability, the overall reliability is limited by the probability PGof deficient decoding, the term introduced by Jelinek to refer to decoding failures caused mainly by buffer overflow. The number of computational efforts in sequential decoding has the Pareto distribution and it is this "heavy tailed" distribution that characterizes PG. The heavy tailed distribution appears in many fields and buffer overflow is a typical example of the behaviors in which the heavy tailed distribution plays an important role. In this paper, we give a new bound on a probability in the tail of the heavy tailed distribution and, using the bound, prove the long-standing conjecture on PG, that is, PGap constanttimes1/(sigmarhoNrho-1) for a large speed factor sigma of the decoder and for a large receive buffer size N whenever the coding rate R and rho satisfy E(rho)=rhoR for 0 les rho les 1

We consider two schemes for an overloaded space-time spreading system. One is to realize tradeoffs between the number of users and the diversity gain with constant signal amplitudes. Another is to achieve great diversity order by varying user signal amplitudes. For each scheme we give some simulation results.

We give a new variable-rate and variable-distortion coding scheme and show a coding theorem for time-discrete stationary sources with abstract alphabets and a single-letter fidelity criterion without assuming reference letters. The approach used to prove the coding theorem is then specialized to maximum-distortion coding and to fixed-rate coding and the corresponding coding theorems are proved for stationary sources. We also consider the possibility of extending the results to time-continuous sources. We still need a reference letter for fixed-rate coding.

The system capacity of the reverse link of a wireless multimedia CDMA system with processing gain control is analyzed in the asymptotic regime, when the processing gain G/spl rarr//spl infin/ for receivers with and without co-channel interference (CCI) cancellers. A new scheme for processing gain control with an optimized power allocation is proposed and its system capacity is compared with the conventional processing gain control scheme as well as the previously discussed power control scheme. It is shown that the proposed scheme has a certain advantage over other schemes.

We present a unified approach to the construction of multidimensional trellis codes that have small constellation expansion ratio (CER) and small peak-to-average power ratio (PAR) and hence are of high bandwidth efficiency. In the approach, we extend Wei's (1987) construction to dimensionalities other than a power of two and propose a low-complexity encoder. We also present a general partition technique that gives geometrically uniform partitions with a good distance profile. The proposed method can generate many good codes including previously reported Ungerboeck codes, Gallager-Calderbank-Sloane codes, and Wei codes with quadrature amplitude modulation signals. Some newly discovered six-dimensional trellis codes are compared with these known codes on their CER, PAR, effective coding gain, and encoder/decoder complexities.

Threshold decision is a decision rule for errors and erasures decoding such that the decoder accepts the decoded codeword if its likelihood is larger than a given threshold value. This decision rule involves a parameter that needs to be optimized. We propose a nonparametric version of threshold decision and show that this nonparametric threshold decision allows us to extend some results on decision rules known only for restricted cases: the relationship between the threshold decision and the rule based on error detection coding and the attainability of Forney's (1968, 1981) exponent by the likelihood-ratio test. These results are derived from a covering theorem which is closely related to the nonparametric threshold decision.

For decoding with erasures, Forney's scheme is known to be optimal in the sense that no other scheme can make the erasure probability P/sub ers/ and undetected error probability P/sub uer/ simultaneously smaller. We propose a scheme for erasure decision which tests the likelihood ratio as well as the likelihood itself and show that the attainable upper bounds on P/sub ers/ and P/sub uer/ are the same as those proved for the optimal scheme up to a constant factor. We also show that the scheme gives, when applied to convolutional codes, a bound which is related to the block-coding bound via Forney's inverse concatenation construction. We show that this bound is the same as the one which naturally arises when we apply Raghavan and Baum's (1998) optimal scheme to convolutional code.

We study the performance of two schemes for decoding with erasures: threshold decision and decision by explicit error detection. We show that the latter scheme based on error-detection coding and maximum-likelihood decoding is at least as good as the former scheme, at least for binary symmetric channels.

A q-ary (n, k) linear code is said to be proper if, as an error-detection code, the probability of undetectable error P/sub ud/ satisfies P/sub ud//spl les/q/sup -(n-k)/ for completely symmetric channels. We show that a proper code, as an error-correction code, satisfies the expurgated bound on the decoding error probability for a class of channels with the associated Bhattacharyya distance being completely symmetric. Known results on the undetectable error probability then immediately imply that the expurgated exponent is satisfied exactly by, for example, all the binary perfect codes, binary first-order Reed-Muller codes, binary (extended) Hamming code, binary 2-error correcting primitive BCH code, and all the maximum distance separable (MDS) codes, and asymptotically by some class of the binary t-error-correcting primitive BCH codes.>

Forney's (1968) exponent is effectively the best one for the block-coded automatic repeat-request systems (ARQ) and it has been conjectured that a counterpart of Forney's exponent is attainable by convolutional codes with reasonable decoder complexity. In the paper, it is show that the scheme of Yamamoto and Itoh (1980), which is known to be one of the simplest convolutionally coded ARQ schemes, actually gives a better performance than ever expected and that it has an error exponent quite close to the conjectured counterpart of Forney's exponent at relatively low rates. It is further shown that the likelihood ratio test used by Yamamoto and Itoh gives Forney's exponent in the case of block-coded ARQ.>

A coded automatic repeat request (ARQ) scheme based on a generalized Viterbi decoding algorithm is proposed. The scheme utilizes the error propagation, which is commonly observed in reduced-complexity decoding, as a means of error detection. It is shown that a small undetectable error probability is obtained with a small retransmission probability for a discrete memoryless channel, contrary to the conventional convolutionally coded ARQ schemes with Viterbi decoding where a compromise between the retransmission probability and the undetectable error probability must be reached.>

It has been pointed out to the author of the above-tilted paper (see ibid., vol.IT-29, p.785-92 Nov. 1983) that a crucial inequality does not hold in general. He presents a modification of this work that remedies the defect.>

The Viterbi algorithm (VA), an optimum decoding rule for aQ-ary trellis code of constraint lengthK, operates by taking the best survivor from each ofQ^{K-1}lists of candidates at each decoding step. A generalized VA (GVA) is proposed that makes comparisons on the basis of a label of lengthL(L\leq K). It selects, incorporating the notion of list decoding, theSbest survivors from each ofQ^{L-1}lists of candidates at each decoding step. Coding theorems for a discrete memoryless channel are proved for GVA decoding and shown to be natural generalizations of those for VA decoding. An example of intersymbol interference removal is given to illustrate the practical benefits that the GVA can provide.

Tree source coding theorems with a single letter fidelity criterion are proved for stationary ergodic sources using tree codes with a fixed branch length. The higher-than-exponential convergence of distortions is shown for binary symmetric sources and Hamming distortion measure when an excess in rate is allowed.

Although variable-length codes are known to be an efficient class of codes in noiseless coding, little is known about these codes for sources subjected to a fidelity constraint. Variable-length source coding theorems with a fidelity criterion are proved and variable-length coding is shown to be applicable to sources without any regularity requirements such as stationarity. Also, unlike fixed-length coding, it is shown that the convergence of average performances to the distortion-rate function does not depend on the sample path properties of the source.

Channel block codes are shown to have a fine hierarchical structure with respect to the expurgated exponent. Another hierarchy with respect to the random coding exponent is also discussed.

A new proof is presented for the existence of block codes whose error probability under maximum likelihood decoding is bounded asymptotically by the random coding bound universally over all discrete memoryless channels. On the basis of this result, the existence of convolutional codes with universally optimum performance is shown. Furthermore the existence of block codes which attain the expurgated bound universally over all discrete memoryless channels is proved under the use of maximum likelihood decoding.

A general form for the rate-distortion function is presented for the nonstationary Gaussian autoregressive (AR) process and is shown to differ from the well-known form for the asymptotically stationary process in a term corresponding to the log rate of the variance growth if the process has exponentially growing variance.

The long standing conjecture is established that, for a discrete memoryless channel, there exists a linear convolutional code with infinite constraint length such that the\rhoth(\rho \geq 1)moment of the number ofF-hypotheses in the Fano sequential decoding algorithm is bounded, provided that the transmission rateRis less thanE_{0}( \rho,r)/ \rho, wherer(x)is a distribution over the channel input alphabet. A new concept of independence for a finite set of message sequences plays an essential role in averaging a product of likelihood ratios over an ensemble of code sequences in a code tree. A simpler version of the method can be applied to the proof of the conjecture for general tree codes.