Shinjiro Oshita

Multiple-symbol differential detection of APSK based on MAP criterion

The multiple-symbol differential detection scheme based on the MAP criterion is adopted to APSK. The decision rule to estimate the transmitted signals is constructed theoretically which includes the terms of the channel noise power. The symbol error rate (SER) performance of 16APSK under the decision rule is evaluated. It is confirmed that the performance shows good approach to that of the ideal coherent detection on the AWGN channel. We also consider the transmission over the Rayleigh fading channel and confirm the performance through the computer simulation for the star QAM and the (4,12) QAM which are the typical constellations for 16APSK.

Improved distributed genetic algorithm with cooperative-competitive genetic operators

We have presented an empirical model of genetic algorithms (GA) that puts parallel genetic operators in a cooperative-competitive stand with each other. An improved GA (GA-SRM) based on this model remarkably improves the search performance of a single population GA. We extend GA-SRM to distributed GAs in order to improve the performance of multiple population GAs. Simulation results verify that the parallel genetic operators in GA-SRM, CM and SRM, can successfully contribute to improve the search performance of distributed GAs.

Halftone Image Generation with Improved Multiobjective Genetic Algorithm

A halftoning technique that uses a simple GA has proven to be very effective to generate high quality halftone images. Recently, the two major drawbacks of this conventional halftoning technique with GAs, i.e. it uses a substantial amount of computer memory and processing time, have been overcome by using an improved GA (GA-SRM) that applies genetic operators in parallel putting them in a cooperative-competitive stand with each other. The halftoning problem is a true multiobjective optimization problem. However, so far, the GA based halftoning techniques have treated the problem as a single objective optimization problem. In this work, the improved GA-SRM is extended to a multiobjective optimization GA to generate simultaneously halftone images with various combinations of gray level and spatial resolution. Simulation results verify that the proposed scheme can effectively generate several high quality images simultaneously in a single run reducing even further the overall processing time.

Performance of Coherent PSK and DSPK Systems in an Impulsive and Gaussian Noise Environment

General probability of error expressions of coherent PSK and differentially coherent DPSK systems in the presence of both impulsive and Gaussian noise are derived. The presented impulsive and Gaussian channel disturbance is a first-order approximation to operational multichannel satellite and terrestrial microwave systems in which in addition to front-end Gaussian noise, out-of-band intermodulation noise is also present. Our analysis contains an extension of the method developed by Bello and Esposito [1], [2] to include the Gaussian as well as the impulsive noise environment. Computed results are presented for a one-pole bandpass filter and a lognormal impulse amplitude distribution. The numerical results show that a welldefined threshold region exists, above which the effect of the impulsive noise on the system performance is predominant. A comparative study of system performance having integrate-sample-and-dump receivers with sample-only receivers is presented.

Multiple-Symbol Differential Detection for Space-Time Block Codes over Fast Rayleigh Fading Channels

In this paper, multiple-symbol differential detection (MSDD) for space-time block codes (STBC) is considered over fast Rayleigh fading multiple-input multiple-output (MIMO) channels. The decision metric is derived by considering the fading autocorrelation, and the M-algorithm is adopted to reduce the computational complexity of the decision metric. Simulation results demonstrate that MSDD is effective to fill the performance gap between conventional differential detection and coherent detection of differential STBC by extending the observation interval.

Approximate equation of average bit-error rate in DS-CDMA systems over fading channels

The transmission quality in mobile wireless communications is affected not only by additive white Gaussian noise, but also by multipath fading, which drastically changes the amplitudes and phases of wireless signals. It is one of the key themes in direct-sequence code-division multiple-access systems to evaluate average bit error rate (BER) performances as parameters of the Doppler frequency, the delay profile, the number of simultaneous access users, and so on. This paper proposes the approximate equation for easily calculating the average BER over fading channels (multiray fading models). The performance evaluations are carried out in the two-ray model, the IMT2000 model, and the COST207 model. It is confirmed from the coincidence of approximate results with computer simulation results that the proposed approach is applicable to a variety of parameters.

Fuzzy early discard (FED) to improve TCP Reno performance over ATM-UBR

We propose a fuzzy logic-based buffer management scheme called fuzzy early detection (FED) to improve TCP Reno performance over ATM-UBR service. FED employs the strategies of early congestion detection and selective packet discard to achieve its design goals, and adopts EPD to prevent frequent buffer overflows. Its performance is compared to that of pure EPD through simulation. The effects of TCP MSS and propagation delay on their performances are studied. Our simulation results prove that FED is superior to EPD in terms of efficiency and scalability, while its fairness remains comparable with the latter.

Theoretical analysis of BER in DPSK/OFDM systems with postdetection diversity reception

In OFDM systems with differential phase shift keying (DPSK), it is possible to apply differential modulation in either the time or frequency domain, depending on fading channel conditions, such as Doppler frequency shift and delay spread. Meanwhile, postdetection diversity for DPSK is attractive because the cophasing function necessary in predetection combiners is not required. The paper proposes a simple calculation method, that is an approximate closed-form equation of the bit error rate (BER) in DPSK/OFDM systems with postdetection diversity over both time and frequency selective Rayleigh fading channels. The validity of the proposed method is demonstrated by the fact that the BER performances given by the derived equation coincide with those by Monte Carlo simulation.

Approximate equation of bit error rate in OFDM systems over specular multipath fading channels

Orthogonal frequency division multiplexing (OFDM) systems avoid the effect of multipath fading by absorbing delayed waves into guard interval. But as the effect of delayed waves over guard interval becomes stronger, it causes the bit error rate (BER) performance in OFDM systems to be more degraded. This paper proposes the approximate derivation method of the BER in DQPSK/OFDM systems over frequency selective fading channels. In this study, we will derive the approximate equation of the BER with differential coding/differential detection in the time domain. We confirm that the BER derived from the proposed approximate equation coincides with that by computer simulation even when such parameters as the Doppler frequency shift, the delay spread, the Rician factor and so on are varied.

Parallel cooperative-competitive self-adaptive mutation in genetic algorithms

In previous work we have presented a model of genetic algorithm (GA) that applies varying mutations parallel to standard crossover & mutation putting them in a cooperative-competitive standing with each other (Aguirre et al., 1999). An improved GA based on this model (GA-SRM) using an adaptive mechanism for parallel mutation significantly improves the performance of GAs (Aguirre et al., 2001). Now, we introduce a self-adaptive mechanism within the parallel mutation operator of GA-SRM and show that the model is an appropriate framework to effectively use and develop further self-adaptation within GAs.