This paper presents the subjective speech quality evaluation in terms of the Mean Opinion Score (MOS) and the relationship between BER and subjective speech quality in a GSM-based radio system. The results show that in certain environments (hilly terrain and rural areas), a SNR (or C/I) higher than 12 dB is required for acceptable speech quality. For an acceptable speech quality, a BER(c1) better than 10-2 is needed in a GSM-based system.

This paper describes IDDQ testability for bridging faults in a variety of flip-flops. The flip-flop is a basic element of the sequential circuit and there are various structures even for the same type. In this paper, we use five kinds of master-slave D-type flip-flops as the circuit under test. Target faults are two-line resistive bridging faults extracted from a circuit layout. A flip-flop with a deliberately introduced bridging fault is simulated by the SPICE simulator. Simulation results show that IDDQ testing cannot detect faults existing at specific points in some flip-flops, and this problem depends on the flip-flop structure. However, IDDQ testing has high fault coverage ( 98%) compared with traditional logic testing. We also examine performances of fully IDDQ testable flip-flops.

Video on demand is regarded as one of the most important applications in future broadband networks. Although several trial runs in various parts of the world do not bring instant success, its inherent requirements for bandwidth and bounded delay make it a suitable candidate for studying various networks and protocols in real-time applications. Recently, the Hybrid Fiber Coaxial (HFC) networks emerged as network architecture for bringing broadband services to the home. The co-axial cable network uses a tree-like architecture and requires complex protocols for synchronizing and sharing uplink communications among many users. This paper proposes that a dual bus network may be a simpler and cost effective alternative. We implement an interactive VOD (IVOD) system as an example to demonstrate its simplicity and suitability as a community network. The system uses client/server architecture with guaranteed bandwidth and bounded delays. Simulations are conducted to test the network load and response time for different number of users. The results indicate its feasibility and the delay time can be further reduced by releasing bandwidth during the pause operation.

In this paper, to obtain higher spectral efficiency than a conventional M-ary/Spread Spectrum (SS) communication system using an orthogonal code, we propose Double M-ary/SS communication systems in which transmitting sequences are produced by multiplying two sequences obtained from different M-ary/SS systems. First, we estimate the system performance of a Double M-ary/SS in which transmitting sequences are composed of two kinds of sequences which have the same chip duration and the same sequence length in AWGN environment by theoretical analysis and computer simulations using random sequences. And we show that the bit error rate (BER) of the system can be improved, compared to that of the conventional M-ary/SS. Next, we propose two concrete examples of the Double M-ary/SS systems. We investigate the performance of these systems in AWGN environment by computer simulations, and show that the BER and spectral efficiency can be improved by the two systems compared to those of the conventional M-ary/SS. Further, we consider a modified method of the demodulation for one of the examples of Double M-ary/SS systems, and show that we can reduce quantity of calculations by the method.

CDMA unslotted ALOHA system with finite size of queueing buffers is discussed in this paper. We introduce an analytical model in which the system is divided into two Markov chains; one is in the user part, and the other is in the channel part. In the user part, we can model the queueing behavior of the user station as an M/G/1/B queue. In the channel part, we can consider the number of simultaneously transmitted packets as an M1 + M2/D///K queue. We analyze the queueing system by using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, the rejection probability and the average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.

We shall generalize B. S. Clarke and A. R. Barron 's analysis of the Bayes method for the FSMX sources. The FSMX source considered here is specified by the set of all states and its parameter value. At first, we show the asymptotic codelengths of individual sequences of the Bayes codes for the FSMX sources. Secondly, we show the asymptotic expected codelengths. The Bayesian posterior density and the maximum likelihood estimator satisfy asymptotic normality for the finite ergodic Markov source, and this is the key of our analysis.

In this paper, we discuss the error correcting capability of the constant amplitude coding. In orthogonal multi-code CDMA systems, the transmitted signal has large amplitude fluctuation and the amplitude fluctuation causes large nonlinear distortion. In order to avoid the amplitude fluctuation, we have proposed "constant amplitude coding" in our previous study. The constant amplitude coding can achieve constant amplitude transmission by utilizing the redundancy of the coding, i. e. , the coding can have an error correcting effect. In this paper, we examine the effectiveness of the error correcting capability of the constant amplitude coding and show that the constant amplitude coding is very effective against nonlinear distortion under the consideration of the error correcting capability.

The DC component suppressing method, called Guided Scrambling (GS), has been proposed, where a source bit stream within a data block is subjected to several kinds of scrambling and a RLL (Run Length Limited) coding to make the selection set of channel bit streams, then the one having the least DC component is selected. Typically, this technique uses a convolutional operation or GF (Galois field) conversion. A review of their respective symbol error properties has revealed important findings. In the former case, the RS (Reed-Solomon) decoding capability is reduced because error propagation occurs in descrambling. In the latter case, error propagation of a data block length occurs when erroneous conversion data occurs after RS decoding. This paper introduces expressions for determining the decoded symbol error probabilities of the two schemes based on these properties. The paper also discusses the difference in code rates between the two schemes on the basis of the result of calculation using such expressions.

Fitt's law is commonly used to model target selection. But Fitts' law deals with only one kind of selection strategy. Our question is, do changes in target size, distance and direction to a target affect the differences in performance between target selection strategies? We performed the first empirical tests on a pen-based system to evaluate differences in performance between six selection strategies for selecting a target. Three target sizes, eight pen-movement-directions and three pen-movement-distances were applied to all six strategies. The results show that differences between selection strategies are affected by variations in target size but not by the other parameters (distance and direction).

In this paper, a virtual-short circuit which consists of only two MOS transistors operated in the weak-inversion region is proposed. It has the advantages of almost zero power consumption, low voltage operation, small chip area, and no needlessness of bias voltages or currents. The second order effects, such as the device mismatch, the Early effect, and the temperature dependency of the circuit are analyzed in detail. Next, current-controlled and voltage-controlled current sources using the proposed virtual-short circuit are presented as applications. The performance of the proposed circuits is estimated using SPICE simulation with MOSIS 1. 2 µm CMOS device parameters. The results are reported on this paper.

A new numerical procedure called asymptotic periodic waveform evaluation (APWE) for finding the steady state solution of nonlinear circuits driven by one tone periodic input signal is presented. APWE starts by constructing a virtual system which gives the same periodic steady state waveform as the original system's but with a shorter transient duration. Thus the periodic steady state (PSS) response can be obtained by simply performing transient analysis of the newly derived system for a few periods. An efficient method for solving the nonlinear equations occurred during the transient analysis is presented. To improve the convergence rate of PSS waveform, APWE is combined with extrapolation method. Some simulation results are shown.

In GSM High Speed Circuit Switched Data (HSCSD), the data rate can be increased by using multiple time slots instead of single time slot. Multiple time-slot assignment results in high blocking rate. To accommodate more users, flexible resource allocation strategies have been proposed. Since GSM follows TDMA/FDMA, the channels (time slots) in a base station are segmented by frequency carriers. The base station must allocate the channels which belong to the same frequency carrier to individual requests. This Flexible Resource Allocation scheme for GSM (FRA-GSM) is contrastive to the scheme proposed in our previous studies where a base station may arbitrarily allocate idle channels in the base station to incoming requests. We define satisfaction indication SI as the measurement to compare the performance of these schemes. Experiment results indicate that FRA-GSM scheme has good performance when the user mobility is high, or when some cost factors are taken into account.

The stability of slotted ALOHA systems with various types of capture phenomena and multiple packet reception capability is discussed in conjunction with the cusp catastrophe. The slotted ALOHA systems considered are classified into; 1) single packet reception with geometric capture, 2) independent multiple packet reception with geometric capture, 3) single packet reception with M-out-of-N capture (M N), 4) multiple packet reception with M-out-of-N capture, and 5) single packet reception with perfect capture. First, general expressions for the cusp points and the bifurcation sets are derived. Then, we present explicit formula for the stability of slotted ALOHA systems for the five types of capture and multi-packet reception capability and demonstrate how the bistable behavior is mitigated due to capture effect and multi-packet reception capability.

A multicarrier modulation called orthogonal frequency division multiplex (OFDM) is attracting attention as a transmission scheme which is robust against multipath propagation. A major disadvantage of OFDM is that it is sensitive to nonlinear distortion due to its wide transmission amplitude range. The scope of this study is to cope with the nonlinear problem. We propose a nonlinear distortion compensation scheme using an iterative method which has been applied to an image signal restoration.

Unequal error protection (UEP) is a very promising coding technique for satellite broadcasting, as it gradually reduces the transmission rate. From the viewpoint of bandwidth efficiency, UEP should be achieved in the context of multilevel coded modulation. However, the conventional mapping between encoded bits and modulation signals, usually realized for multilevel block modulation codes and multistage decoding, is not very compatible with UEP coding because of the large number of resulting nearest neighbor codewords. In this paper, new coded modulation schemes for UEP based on unconventional partitioning are proposed. A linear operation referred to as interlevel combination is introduced. This operation generalizes previous partitioning proposed for UEP applications and provides additional flexibility with respect to UEP capabilities. The error performance of the proposed codes are evaluated both by computer simulations and a theoretical analysis. The obtained results show that the proposed codes achieve good tradeoff between the proportion and the error performance of each error protection level.

In this paper the performance of the Block Sorting algorithm proposed by Burrows and Wheeler is evaluated theoretically. It is proved that the Block Sorting algorithm is asymptotically optimal for stationary ergodic finite order Markov sources. Our proof is based on the facts that symbols with the same Markov state (or context) in an original data sequence are grouped together in the output sequence obtained by Burrows-Wheeler transform, and the codeword length of each group can be bounded by a function described with the frequencies of symbols included in the group.

Recently, Garcia and Stichtenoth proposed sequences of algebraic function fields with finite constant fields such that their sequences attain the Drinfeld-Vl bound. In the sequences, the third algebraic function fields are Artin-Schreier extensions of Hermitian function fields. On the other hand, Miura presented powerful tools to construct one-point algebraic geometric (AG) codes from algebraic function fields. In this paper, we clarify rational functions of the third algebraic function fields which correspond to generators of semigroup of nongaps at a specific place of degree one. Consequently, we show generator matrices of the one-point AG codes with respect to the third algebraic function fields for any dimension by using rational functions of monomial type and rational points.

In this paper, we study unequal error protection (UEP) capabilities of punctured convolutional codes. For constructing the good UEP convolutional codes, the conditional weight distributions of UEP convolutional codes are defined and evaluated. The conditional weight distributions are computed by using the transfer functions of time-varying trellis structures of punctured convolutional codes. The best UEP convolutional codes from the viewpoint of the weight distributions are listed.

This paper proposes and investigates a coding and decoding scheme to achieve adaptive unequal error protection (UEP) using several convolutional codes which have different error-correcting capabilities. An appropriate encoder is selected to unequally protect each frame of information sequence according to the importance of the frame. Since the supplemental information of selected encoder is not sent for the sake of reducing redundancy, we assume that the decoder does not know which encoder was used, and the decoder has to estimate the used encoder. In order to estimate which encoder was used, the method using biased metric in Viterbi decoding is proposed. In decoding, however, there is a problem of Decoder-Selection-Error (DSE), which is an error that the decoder selected in a receiver does not correspond to the encoder used in a transmitter. An upper bound of DSE rate in decoding is derived. The proposed decoding scheme using the biased metric in a trellis can improve DSE rate and BER performance, because transition probability of encoders is taken into account in calculating likelihood by means of making branch or path metric biased. Computer simulation is employed to evaluate the BER performance and DSE rate of the proposed scheme. The performance is compared with a conventional equal error protection scheme and a UEP with the supplemental information on the used encoder. It is found that the proposed scheme can achieve better performance than them in case N=2.

In this paper, we give lower bounds for the generalize Hamming weights of linear codes constructed on affine algebraic varieties. By introducing a number g*, which is determined by a given affine variety, we show that when the order t of generalized Hamming weights is greater than g*, the proposed lower bound agrees with their true generalize Hamming weights. Moreover, if we use the notion of well-behaving, we can obtain a more precise bound. Finally, we compare the proposed bound and the conventional one for algebraic geometric code on the curve Cab.