Yukiyoshi Kamio

Adaptive modulation system with variable coding rate concatenated code for high quality multi-media communication systems

This paper proposes an adaptive modulation system with a concatenated code (AMS-CC) for land mobile communications to achieve high quality, high bit rate transmission in Rayleigh fading environments. The proposed system adaptively controls the coding rate of the inner convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. The performances in Rayleigh fading environments are evaluated theoretically and by computer simulation. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

Performance of modulation-level-controlled adaptive-modulation under limited transmission delay time for land mobile communications

The performance of an adaptive-modulation/time division duplex (TDD) scheme to support constant-bit-rate services under transmission delay time constraint conditions is evaluated in this paper. According to the received signal conditions, the modulation levels or transmission modes are selected from transmission-off, QPSK, 16QAM, or 64QAM by using the reciprocity of the propagation path characteristics in the TDD systems. Moreover, the transmission delay time is limited to keep data transmission rate constant by the memory buffer. The received signal condition is estimated by using extrapolation of pilot symbol or estimated received signal distortion at the decision stage. The performance is evaluated by computer simulation in case of 32 ksymbol/s transmission and is compared with the performance of conventional trellis-coded (TCM) 32QAM. The results show that the proposed method improves the BER performance and delay spread immunity of a system transmitting data at a constant rate under multipath fading conditions and the performance is better than that of TCM-32QAM in Rayleigh fading conditions with small Doppler frequency.

ARQ schemes with adaptive modulation/TDMA/TDD systems for wireless multimedia communication services

This paper proposes automatic repeat request (ARQ) protocols combined with an adaptive modulation system (AMS) (ARQ/AMS) to achieve high throughput data transmission for wireless multimedia communication services. First, it analyses the cause of the throughput limitation of the conventional fixed modulation ARQ system, and discusses basic strategies to improve the throughput performance by effectively combining ARQ and AMS. Next, it proposes a selective repeat ARQ (SR-ARQ) with AMS (SR-ARQ/AMS), and shows its throughput performance improvement effect. Finally, this paper proposes a type-II hybrid ARQ with a punctured convolutional coding combined with the AMS (type-II hybrid ARQ/AMS) to further improve the throughput performance. Computer simulation confirms that the proposed type-II hybrid ARQ/AMS can achieve higher throughput performance than the conventional selective repeat ARQ with QPSK under any channel conditions.

Adaptive modulation system with punctured convolutional code for high quality personal communication systems

This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. The performance in fading environments is evaluated theoretically and by computer simulation. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

Adaptive modulation/TDMA with a BDDFE for 2 Mbit/s multi-media wireless communication systems

This paper proposes an adaptive modulation/time division multiple access (TDMA) system using a bi-directional decision feedback equalizer (BDDFE) and space diversity to support multi-media wireless communication systems with a bit rate of up to 2 Mbit/s under frequency selective fading conditions. A 7-tap BDDFE and space diversity are employed to cope with a delay time of up to 3-symbol duration. When the maximum delay time (/spl tau//sub max/) is shorter than 3-symbol duration for the full rate, the full rate is employed. When /spl tau//sub max/ is longer than that, the symbol rate is lowered to half-rate, quarter-rate or 1/8 -rate to satisfy the condition that /spl tau//sub max/ is shorter than 3-symbol duration. The modulation level is also selected from 16QAM and QPSK according to the channel conditions to increase spectral efficiency. Computer simulation confirms that the proposed scheme is effective to achieve 2 Mbit/s transmission at /spl tau//sub max/=10 /spl mu/s and 1 Mbit/s at /spl tau//sub max/=20 /spl mu/s.

Cochannel interference reduction and path-diversity reception technique using CMA adaptive array antenna in digital land mobile communications

This paper describes a cochannel interference (CCI) reduction and path-diversity reception technique using a constant modulus algorithm (CMA) adaptive array antenna in digital land mobile communications. In this technique, the incident signals are individually recovered by using a multistage constant modulus (CM) array that consists of a multistage cascade of signal recovering and canceling processes. The recovered signals are sorted into the desired signal and CCI signal, and then the desired signals are combined in order to obtain the path-diversity gain, Performance is evaluated for a Gaussian filtered minimum shift keying signal and /spl pi//4-shifted quadrature phase-shift keying signal. Each signal processing is carried out using block demodulation (e.g., CMA adaptive signal recovering process and signal canceling process). Computer simulation results show that CCI can be reduced efficiently for a high-bit-rate time-division multiple-access system for quasi-static and fading channel conditions and that the bit error rate (BER) performance is improved by combining the desired signals. The extent of the improvement in BER performance indicates the difference in diversity gain between maximal ratio combining and selective combining. This suggests that a CMA adaptive array antenna is equivalent to selective combining diversity reception.

Performance of reduced complexity DFE using bidirectional equalizing in land mobile communications

A reduced-complexity decision feedback equalizer (DFE) that uses interpolation and bidirectional equalizing with a center tap position detector is presented. DFE tap gains during information symbols are estimated using an interpolation technique to reduce the number of calculations. Moreover, a bidirectional DFE is used to reduce the number of forward taps keeping good performance. To improve bidirectional DFE performance, the center tap position is determined by estimating the impulse response. Performance is evaluated by computer simulation for the case of 512 k symbols/s 16 QAM transmission, assuming a maximum delay of 10 mu s sec. The proposed method is confirmed to be effective and simple for high-speed data transmission in land mobile communications.<<ETX>>

A Channel Estimation Method for a Highly Mobile OFDM Wireless Access System

Pilot-symbol-aided (PSA) channel estimation for OFDM wireless access systems enables the periodic estimation of channel frequency response by generating reference data from the received OFDM signals. The accuracy of this channel estimation can be improved through the average over a certain time period in each subcarrier-channel. However, the accuracy of the channel estimates by the average degrades as the Doppler shift is large due to a decrease in the average section size according to the Doppler shift for the tracking of the time-varying channel. This paper proposes a novel PSA channel estimation method to mitigate the influence of the noises and interferences. This method detects the channel estimates affected by the noises and interferences, and then removes them before the arithmetic or harmonic averaging to avoid propagating the influence of the noises and interferences. This paper also evaluated the proposed channel estimation method by clipping log-likelihood ratio (LLR) data to inspect the influence of the channel estimation on the LLR calculation by computer simulation.

Complexity reduction and performance improvement of a decision feedback equalizer for 16QAM in land mobile communications

This paper proposes a complexity-reduced decision feedback equalizer (DFE) for 16-ary quadrature amplitude modulation (16QAM) using tap gain interpolation, bi-directional equalizing (BDE) and space diversity combining (SDC) to achieve high spectral efficiency and high quality data transmission over frequency-selective fading channels in land mobile communications. To reduce the amount of computation required for BDE and SDC, we propose a tap gain interpolation scheme and pre-decision schemes for both processes. Computer simulation of a (16QAM/TDMA system) confirms that the proposed scheme improves frequency-selective fading compensation performance by 6 dB or more while using only 27% of the computation of conventional single branch DFE receivers. >

Superimposed Frequency Symbol Based Adaptive Downlink OFDM with Frequency Spreading and Equalization

In AMS/OFDM systems, a base station controls the modulation level of each subcarrier with feedback information (FBI), and then, adaptive modulated packets are transmitted from the base station to the mobile station. In this case, the mobile station requires modulation level information (MLI) to demodulate the received packet. The MLI is generally transmitted as a data symbol, so the throughput is degraded. To overcome this problem and increase the total throughput, in this paper, we propose frequency symbol spreading and MMSEC equalization based on an adaptive downlink OFDM system. In the proposed system, each S/P transformed signal is spread by orthogonal spreading codes and combined. This means that each subcarrier holds several superimposed S/P transformed signals with the same power rate. In this case, the frequency-selective faded subcarriers obtain the same power rate for each S/P transformed signal. Therefore, the detected signals also obtain the same SINR, and as a result, we can assign the same modulation level for each frequency symbol spreading block. Hence, the proposed system requires only one piece of FBI and MLI for each frequency symbol spreading block, as compared with conventional adaptive OFDM