Tadashi Fujino

A low-noise direct conversion PSK receiver for TDMA land mobile communications

This paper presents a new scheme of direct conversion phase shift keying (PSK) receivers applicable to time division multiple access (TDMA) land mobile communication systems. In the scheme, a matched filter in each I and Q channel is divided into two parts in front and at the back of a baseband amplifier to reduce baseband noise power and improve sensitivity. A rational design method to divide the filter is proposed; the filter cell that has narrowest equivalent noise bandwidth in the filter is chosen as the back part, while the remainder constitutes the front part. Moreover, memories are employed to eliminate DC offset in baseband signals. Experimental results show that, when applied to Personal Handy Phone System (PHS), a receiver employing the scheme achieves sensitivity comparable to that of a super-heterodyne receiver in continuous and burst reception.

A list-output Viterbi equalizer with two kinds of metric criteria

This paper proposes a list-output Viterbi equalizer (LVE) for wide-spread time-dispersive channels, which uses two kinds of metric criteria, in order to achieve a good trade-off between complexity and bit error rate (BER) performance. For the Viterbi equalization employing a state-reduction algorithm, the modified metric proposed by Ungerboeck (1974) is not always equivalent to the squared Euclidean distance. This paper proposes the following two LVEs: (1) to combine two kinds of metric criteria; (2) to select the metric criterion according to the channel impulse response. Finally, computer simulation shows that the proposed scheme improves the BER performance on frequency selective fading channels, even if the proposed scheme has smaller complexity than the conventional one.

A study on bi-orthogonal modulation for W-CDMA higher bit rate transmission

This paper studies a modulation method for a wideband code division multiple access (W-CDMA) system in order to enhance its performance. The modulation method studied here introduce bi-orthogonal modulation instead of multicode transmission in order to suppress the envelope variation which comes from code division multiplexing in multicode transmission. Bi-orthogonal modulation studied here selects a single code in both in-phase and quadrature components, and leads to relaxation of the requirement of HPA linearity. This relaxation enhances the implementation of the mobile station (MS) with smaller size or lower power consumption. Computer simulation results show that the power level of spurious emission in the adjacent channel is reduced by approximately 8 dB with use of bi-orthogonal modulation, while keeping the required E/sub b//I/sub o/ almost the same as multicode transmission.

Performance of a soft-output adaptive equalizer combined with soft-decision metrics generator based on differential detection

This paper proposes a soft-output adaptive equalizer combined with a novel soft-decision metrics generator based on differential detection, and assesses its performance by computer simulation and hardware experiments. The proposed soft-decision metrics generator performs differential detection by using the equalizers soft-decision output and weights its results with the short-term average of squared errors in the equalizer. We confirm that the proposed scheme achieves good performance with lower complexity in generating the soft-decision metrics for Viterbi (1979) decoding compared with the conventional scheme.

A receiver with iterative soft decision and forward error correction

As a receiving method suitable for channels with intersymbol interference such as frequency selective fading, a method is proposed in which the soft decision using the hard decision sequence generated from the data after forward error correction (FEC) is alternated with FEC. In the conventional receiver with a serial configuration of the equalizer, deinverter, and decoder, the performance of the equalizer significantly affects the overall receiver characteristics. Hence, the performance of the equalizer is emphasized. On the other hand, in the proposed method the error generated in the initial equalization can be corrected by repetitive soft decision and FEC. Therefore, the method does not strongly depend on the performance of the equalizer used in the initial equalization. Hence, even if an equalizer requiring a smaller amount of process with a somewhat degraded performance is used in the initial equalization in place of a high-performance equalizer, the amount of process for the entire receiver can be decreased without degrading the characteristics of the proposed method very much. In this paper, the characteristics of the proposed method are evaluated by computer simulation. The following are the confirmed conclusions. (1) The proposed method using the maximum-likelihood sequence estimation (MLSE) as the equalization has superior BER characteristics over the conventional method using a maximum a posteriori (MAP) equalizer and MLSE. (2) In a transmission channel with a large delay spread, the degradation of the BER characteristics of the proposed method using the delayed decision-feedback sequence estimation (DDFSE) in place of MLSE is very slight while the amount of processing can be reduced substantially from that in the conventional method using MLSE.

A Design Of An Adaptive Decision Feedback Equalizer For Digital Mobile Communication Systems

This paper describes a design of an adaptive decision feedback equalizer (DFE) using Kalman filter algorithm and an assessment of its performance by computer simulation over fading multipath channels. The adaptive equalizer consists of a fractionally spaced decision feedback equalizing part and a tap-coefficient-update part. Tap coefficients are updated according to the square-root Kalman filter algorithm, resulting in stable operation in spite of the reduced quantization number of hits in the algorithm. Key design parameters are considered such ns the allowable frame timing offset and input signal level variation and the performance of the bit error probability is evaluated for various fading multipath conditions. I t is shown that the adaptive DFE investigated here is effective over fast timevarying fading multipath channels.

Performance of CDMA mobile packet communication systems under microcell multipath environment

This paper addresses the physical layer performance of CDMA mobile packet communication systems using RAKE under microcell multipath environment in urban areas. The bit error rate (BER) performance versus multipath selection threshold of matched filter based RAKE in a microcell environment is shown.

An adaptive soft-output Viterbi equalizer for fast time-varying frequency-selective fading

In this paper, an adaptive soft-output Viterbi equalizer (SOVE) is proposed for fast time-varying frequency-selective fading. The demodulator can make a symbol-by-symbol or bit-by-bit soft-decision based on a posteriori probabilities. The proposed adaptive SOVE has the following advantages: (1) it has a superior tracking ability for fast time-varying frequency-selective fading, (2) it works in blind if the coding rules are suitably designed, and (3) a good BER is obtained at the output of the decoder by introducing interleaves. In this paper, these advantages are confirmed by computer simulations. In particular, in the presence of frequency-selective fading, we can show that the proposed method is superior to adaptive maximum-likelihood sequence estimation which carries equalizing and decoding simultaneously.

Self-Noise Produced by Quadrupling of Qpsk Signals

Computer simulation results of the self-noise performance of the quadrupling circuit are described. The input waveforms are assumed to admit full and half cosine roll-off spectra, and the class of nonlinearity is assumed to be memoryless vth power law.