PSK coherent demodulation has difficulty in achieving high speed carrier extraction and symbol synchronization when implementing to slow FH-SS radio system. On the other hand, implementation to FPGA has the requirement of a small gate size to design because of FPGA cost issue. We developed a QPSK coherent demodulation digital modem for FH-SS radio systems using FPGA by solving problems. The designed modem performs symbol synchronization with no carrier extractions, under the limitation of the small gate size requirement. The modem employs shift arithmetic operation and a comb digital BPF to achieve very good synchronization lock-up performance with small gate size. In this paper, the symbol synchronization and the carrier tracking scheme are mainly discussed. Analysis of its performance and stability are also explained. The achievement of its very good performance is presented by experimental measurement.

This paper proposes a bandwidth division type parallel combinatory (PC) spread spectrum (SS) modulation scheme. In the proposed system, a given system bandwidth for the conventional single-carrier PC-SS system is divided into H subbands, and H PC-SS signals are transmitted in parallel. We evaluate the frame error rate (FER) of the proposed system under the asynchronous CDMA environment. We show that the proposed scheme provides a smaller FER than the single-carrier PC-SS system for a given information bit rate. We also show that the proposed scheme attains a higher information bit rate than the single-carrier PC-SS system for a given FER.

A complete single chip multi-format Phase Shift Keying (PSK) demodulator ULSI for Japanese BS digital broadcasting is reported. The carrier recovery system shows the pull-in range up to +/-5 MHz. The clock recovery system cancels the poor group delay characteristic and the orthogonality degradation caused by the analog front end, and improves the BER performance by 0.2 dB. Thus the requirement to the analog front end is relaxed. A digital PLL ensures minimum program clock reference jitter in the output data stream, which simplifies jitter management in the succeeding MPEG2 system decoder. It integrates two 8-bit 60 MHz ADCs, 58 MHz VCO, 1 Mbit SRAM and the 450 K-gate FEC-demodulator core. Implementation of 1 Mbit de-interleaver RAM facilitates the use of a low cost receiver. The 8.8 milion transistor chip occupies the 72 mm2 in a 0.25 µm triple-metal CMOS technology.

Improvement of direct sequence spread spectrum (DSSS) communication systems' performance using a lattice based adaptive infinite impulse response (IIR) notch filter with a simplified adaptation algorithm is presented. The improvement is shown to be achieved by rejection of a narrowband interference in a received DSSS binary phase shift keying (BPSK) signal. Sources of noise generated by an adaptive IIR notch filter are also studied. Apart from noise associated with input additive white gaussian noise, noise attributed to leakage sinusoids due to fluctuation of steady-state variable coefficient is also analysed. Using statistical properties of notch filter and pseudonoise (PN) correlator outputs, improvement of the performance of a DSSS system gained by the use of interference rejection filter is shown. Computer simulation results are used to confirm analytically derived expressions.

Phase locked loops (PLL's) are well known as a threshold extension demodulator for analogue FM signals. This capability may lead to the low bit error rate demodulation for digital FM signals. A PLL has also its native frequency tracking ability and is suited to the demodulation of the signals having large Doppler shifts, for example signals from Low Earth Orbit (LEO) satellites. In this paper, we study the demodulation scheme of Continuous Phase FSK (CPFSK) and Gaussian filtered MSK (GMSK) signals using a Digital Signal Processing type Digital PLL (DSP DPLL). First we propose a DSP DPLL completely equivalent to an Analog PLL (APLL). Next we adopt the sequence estimation scheme to compensate the Inter-Symbol Interference (ISI) associated with the finite loop bandwidth of the DSP DPLL. Through computer simulations it is clarified that the proposed DSP DPLL with sequence estimator can achieve better BER performance compared with the conventional Limiter Discriminator (LD) detection on the AWGN channel. We have also shown that the DSP DPLL with sequence estimator has excellent BER characteristics on Rician fading channels having actual large Doppler shifts.

The differential 4-quadrature (D4Q) coherent optical system which does not need absolute phase information is proposed. The input information is encoded in the relative position of the present symbol with respect to the reference frame constructed by the previous 3 symbols. The general theory of the system operation including encoding and decoding is presented. This system does not need to track the fluctuation of the states of polarizations which is essential for most other polarization modulation systems. As an example, the 4-symbol D4Q system is described. And the saddle point approximation is applied to estimate the bit error rate performance. The analytic approximation agrees with the simulation results very well.

In this paper we propose a new lattice based second-order adaptive infinite impulse response (IIR) notch filter that uses a simplified adaptation algorithm. Steady-state analysis of the proposed structure is then studied based on the mean-squared error analysis of the steady-state variable coefficient fluctuations. The analysis is used to derive simple analytical expressions for steady-state variable coefficient variance and an upper bound for the step size adaptation constant. The results are shown to be useful in designing an FSK demodulator using the proposed structure. Computer simulation results are shown to confirm derived analytical expressions.

This paper proposes a phase-rotating phase-shift keying (PSK) modulation and shows that its narrow-band version is suitable for Viterbi equalization. The proposed PSK has the following features: 1) a spectrum shaping of the transmit/receive filters does not need to be restricted to the Nyquist criterion; 2) the transmitted data sequence is rotated for every symbol in order to reduce noise-correlation at the receiver. First, this paper discusses a performance degradation of bit error rate of Viterbi equalizers in the presence of the sampling timing offset or under time-dispersive frequency selective fading. Next, computer simulation confirms that π/2-shifted binary PSK with narrow-band spectrum shaping filter, which includes offset QPSK for its special case, solves the above mentioned performance degradation, keeping good spectrum efficiency equal to M-ary PSK.

Fiber optic subcarrier transmission system using coherence multiplexing techniques for broad-band distribution networks is proposed. This system makes it possible to improve the laser linewidth requirement and also to eliminate the effect of intermodulation distortion (IMD) which is serious problem in subcarrier multiplexed (SCM) system. In the proposed system, the frequency difference, fo, between the reference light and the signal light makes it possible to generate the broadand FM signal after photodetecting. Thus, an increase in the modulation index provides a corresponding increase in receiver sensitivity. We analyze the fundamental performance of the proposed system and derive the signal-to-noise ratio (SNR) at the output of FM demodulator by taking the threshold effect and spike noise into account. The proposed system can achieve the total capacity in excess of 10 GHz, and thus it is attractive for multichannel broad-band distribution networks.

This paper proposes a new simultaneous carrier and bit-timing recovery (CBR) scheme for offset quadrature phase shift keying (O-QPSK) for agile acquisition over satellite communication channels. The proposed simultaneous CBR scheme employs a preamble shared for the carrier and bit-timing recover, which has a specific bit-pattern designed so that its baseband signal alternates between two adjacent decision points at the symbol rate. Using the preamble, the proposed simultaneous CBR scheme estimates the carrier phase and the bit-timing, simultaneously and independently, by open-loop approach. For comparison, this paper also describes the performance and configuration of a joint carrier and bit-timing recovery scheme, which is expanded for O-QPSK from the one conventionally proposed for QPSK. This paper demonstrates with simulation results that the proposed simultaneous CBR scheme significantly improves the agility of acquisition: a mere 30-symbol preamble is sufficient for low-Eb/No channels typical of satellite communication systems. The proposed CBR scheme is also advantageous from the viewpoint of digital implementation: it processes at 2 samples/symbol and eliminates an analog voltage control clock (VCC). The proposed simultaneous CBR scheme is a strong candidate for TDMA systems that require the high data-transmission and frequency utilization efficiency.

This paper proposes a novel Doppler frequency shift compensation technique to achieve terrestrial and low earth orbit (LEO) satellite dual mode DS/CDMA terminals robust to high Doppler shift and multipath fading. In order to satisfy the requirements of wide dynamic range and high accuracy simultaneously, the proposed scheme employs two stage compensation scheme, i.e., coarse compensation to keep dynamic range of about 100 kHz and fine compensation to satisfy its resolution of about 30 Hz, using block demodulation technique. Computer simulation results show that the proposed scheme can sufficiently compensate for the offset frequency up to the range of about 100 kHz at the terrestrial and LEO satellite combined mobile communication systems.

Frequency demodulation of a single side-band signal with a carrier is discussed and a new demodulation method is proposed. Compared with the conventional RZSSB (real zero single-side band) demodulator, there are no even-order distortions in the demodulated output signal of the proposed method and the third-order distortion can be canceled very easily without any Hilbert transformer as is required in the conventional RZSSB demodulator. Since the carrier can be reproduced completely from the input signal by the proposed method, it can be used for not only an RZSSB signal but also a full-carrier SSB signal or a low-carrier SSB signal. Compared with transmitting an RZSSB signal, it more efficiently transmits a low carrier SSB signal since the carrier does not include any useful information. By this means, the transmission efficiency can be greatly improved by adopting the proposed method.

In this paper, we subjects the case that frequency–shift–keying (FSK) modulation and phase locked loop (PLL) demodulator are used in frequency hopped spread spectrum (FH–SS) communication system. So the carrier frequencies of undesired transmitters may come into collision with the carrier frequency of desired transmitter in this communication system, we evaluate the response of PLL by two sinusoidal inputs so as to estimate how the response of PLL demodulator is affected by the collision of carrier frequencies. First, we compute the synchronization diagrams of PLL with two sinusoids. From this, it is indicated that allowable value of amplitude ratio of interference transmitter's signal to disired transmitter's signal decreases with increasing FSK modulation width of desired transmitter. Next, we calculated the output of PLL demodulator with two sinusoids. To this end, it is shown that the allowable value of amplitude ratio is bounded by a constant value even if FSK modulation width is enough small.

This paper reviews recent progress in adaptive signal processing techniques for digital mobile radio communications. In Radio Signal Processing (RSP) , digital signal processing is becoming more important because it makes it relatively easy to develop sophisticated adaptive processing techniques, Adaptive signal processing is especially important for carrier signal processing in RSP. Its main objective is to realize optimal or near-optimal radio signal transmission. Application environments of adaptive signal processing in mobile radio are clarified. Adaptive equalization is discussed in detail with the focus on adaptive MLSE based on the blind algorithm. Demodulation performance examples obtained by simulations and experiments are introduced, which demonstrates the recent advances in this field. Next, new trends in adaptive array processing, interference cancelling, and orthogonalization processing are reviewed. Finally, the three automatic calibration techniques that are based on adaptive signal processing are described for realizing high precision transmission devices.