Showing papers on "Continuous phase modulation published in 1996"

Orthogonal frequency division multiplexing

Abstract: In an orthogonal frequency division modulation (OFDM) apparatus and method, a transmitter produces a clock and a reference signal to provide an accurate phase in modulation of a carrier. A receiver is thus able to reproduce the reference signal, even if the signal-to-noise (S/N) ratio of the carrier is poor. The OFDM method includes the steps of AM-modulating a group of digital signals with a plurality of carriers, in which a reference signal is frequency-modulated at a symbol period, combining the AM-modulated carrier and modulating the combined carrier into a main carrier, detecting the main carrier by phase-locking the frequency-modulated reproduced reference signal with the transmitted reference signal and fast-Fourier-transforming the combined carrier to demodulate the digital signal.

Transmitter for encoded data bits

Abstract: Quadrature Amplitude Modulated signals are generated from data bits by using a first Quadrature Phase Shift Keying (QPSK) modulator for encoding a first pair of the data bits into one of four carrier signal phases, thereby producing a first QPSK signal. A second QPSK modulator encodes a second pair of the data bits into one of four carrier signal phases, thereby producing a second QPSK signal. The first QPSK signal is amplified to a first power level, and the second QPSK signal is amplified to a second power level. The first and second amplified signals are then combined to produce a signal in which four data bits are encoded. In another aspect of the invention, a new type of modulation, called Offset Quadrature Phase Shift Keying (OQPSK), is used in place of the first and second QPSK modulators, so that an Offset Quadrature Amplitude Modulation (OQAM) transmitter is formed. An OQPSK modulator encodes data bits by encoding a first sub-group of the data bits into a real part of a complex signal at an odd instant of a clock, and by encoding a second sub-group of the data bits into an imaginary part of the complex signal at an even instant of the clock. OQPSK modulation provides the benefit of having all signal transitions being constrained to trajectories around constant radius circles, thereby producing spectral efficiency.

Designing fully continuous phase screens for tailoring focal-plane irradiance profiles

Abstract: An iterative algorithm for constructing fully continuous phase screens for tailoring far-field intensity profiles is presented. The algorithm is robust, stable, and, if run properly, maintains the continuous nature of the phase throughout the iterative process. The iterative procedure is applied to generate continuous phase screens to produce a 12th-power super-Gaussian far-field intensity profile.

Intrinsic envelope fluctuations and modulation-detection thresholds for narrow-band noise carriers.

Abstract: A model is presented which calculates the intrinsic envelope power of a bandpass noise carrier within the passband of a hypothetical modulation filter tuned to a specific modulation frequency. Model predictions are compared to experimentally obtained amplitude modulation (AM) detection thresholds. In experiment 1, thresholds for modulation rates of 5, 25, and 100 Hz imposed on a bandpass Gaussian noise carrier with a fixed upper cutoff frequency of 6 kHz and a bandwidth in the range from 1 to 6000 Hz were obtained. In experiment 2, three noises with different spectra of the intrinsic fluctuations served as the carrier: Gaussian noise, multiplied noise, and low-noise noise. In each case, the carrier was spectrally centered at 5 kHz and had a bandwidth of 50 Hz. The AM detection thresholds were obtained for modulation frequencies of 10, 20, 30, 50, 70, and 100 Hz. The intrinsic envelope power of the carrier at the output of the modulation filter tuned to the signal modulation frequency appears to provide a good estimate for AM detection threshold. The results are compared with predictions on the basis of the more complex auditory processing model by Dau et al. [J. Acoust. Soc. Am. 99, 3615–3622 (1997)].

Digital continuous phase modulation for a dds-driven phase locked loop

Abstract: A system and method are provided in which a phase modulation generator is used to modulate the output signal of a DDS with a modulation index, h/N. The phase-modulated. DDS output drives a PLL, which is an upconversion stage for a radio transmitter, with the modulated DDS signal as the PLL's reference. The output of the PLL will have a modulation index of h. Consequently, the frequency band of the DDS output is significantly narrower than the frequency band of upconversion stages used in conventional transmitters, and there are significantly less spurious emissions in the transmitted signal. However, a transmitter employing the present phase-modulated DDS-driven PLL topology can still transmit over a relatively wide frequency band.

Symbol timing estimation with CPM modulation

Abstract: Symbol timing in continuous phase modulated signals is investigated making use of maximum likelihood estimation methods. Nondata-aided algorithms are proposed with a feedforward structure. They are suitable for digital implementation and can be employed with either full or partial response signaling. Multilevel symbol alphabets are allowed and the modulation index may be arbitrary. The performance is assessed by analysis and simulation. It turns out that full response schemes are comparatively easier to synchronize. Difficulties arise with partial response signaling especially with long frequency pulses.

Pilot symbol-assisted detection of CPM schemes operating in fast fading channels

Abstract: We present a coherent detection technique for continuous phase modulation (CPM) operating in the Rayleigh flat fading channel. The technique is based on the idea of inserting periodically data dependent pilot symbols that force the CPM signal to pass through known phase states. This transmission format enables the receiver to extract from the received signal the channel fading gains at regularly spaced instants. When coupled with proper channel estimation filters, very accurate channel state information (CSI) can be estimated at the receiver for fading compensation. Moreover, the accuracy of the CSI can be further refined by adopting a multiple-pass decoding approach. The paper discusses (a) the pilot symbol encoding technique required to force a M-level CPM scheme with a modulation index of p/M, p is an integer, to return periodically to a set of known phase states, (b) the optimal channel estimation filters, (c) a trellis-based precoding technique that can reduce the bit error rate in M-level CPM systems by close to 50%, and (d) a multiple-pass channel estimator/demodulator. Analytical and simulation results are presented for minimum shift keying (MSK), Gaussian MSK, and four-level continuous phase frequency shift keying with a modulation index of 1/4. It is observed that our pilot symbol-assisted CPM schemes exhibit no irreducible error floor even at a channel fade rate of three percent the symbol rate. The implicit phase coding in CPM and the accurate CSI provided by the pilot symbols lead to a diversity effect in the bit error rate curves of these modulation schemes.

Orthogonal modulation scheme

Abstract: The modulation scheme has two versions that can transform two data streams into two mutually orthogonal modulated signals within the same carrier-frequency band. In one embodiment, the modulation scheme is a quadrature-phase shift-keying (QPSK) modulation scheme having an in-phase part and a quadri-phase part. In this embodiment, one version of the QPSK modulation scheme conforms to the IS-95 telecommunications standard. In this version, the in-phase part is applied to a first data stream to generate an in-phase signal that is multiplied by a cosine function of the carrier frequency. In a parallel path, the quadri-phase part is applied to the first data stream to generate a quadri-phase signal that is multiplied by a sine function of the carrier frequency. The resulting signals are combined to generate a conventional IS-95 signal. In this embodiment, the other version of the QPSK modulation scheme is designed to transform a second data stream into a second modulated signal that is orthogonal to the IS-95 signal, even though the second modulated signal is within the same carrier-frequency band and even if the second data stream is encoded using the same Walsh code sequence as the first data stream. In one implementation of the second version, the logical negation of the quadri-phase part of the QPSK modulation scheme is applied to the second data stream to generate an quadri-phase signal that is multiplied by the cosine function of the carrier frequency. In a parallel path, the in-phase part of the QPSK modulation scheme is applied to the second data stream to generate an in-phase signal that is multiplied by the sine function of the carrier frequency. The resulting signals are combined to generate a modulated signal that is orthogonal to the IS-95 signal and which therefore will not interfere with the IS-95 signal, even though the two modulated signals exist within the same carrier-frequency band and may in fact be based on two data streams that were encoded using the same Walsh code sequence. Those skilled in the art will understand that the modulation scheme of the present invention can be implemented in contexts other than the IS-95 standard.

System and method for combining two data streams while maintaining the continuous phase throughout the combined data stream

Abstract: A system and method for a generating a data stream for encoding by combining data from a multiple of sources. In order to maintain a continuous phase in the combined data stream, any phase differentials between the data supplied from the multiple sources are eliminated upon combination of the source data. The phase differential between the data from any two different sources is eliminated by trimming data from one of the sources such that when the trimmed data is combined with the data from the other source the resulting combined stream has a continuous phase.

The effect of carrier frequency offset on the performance of band limited single carrier and OFDM signals

Abstract: In this contribution, the bit error rate (BER) degradation caused by a carrier frequency offset between the transmitter and receiver carrier oscillator is investigated for single carrier (SC) and multi carrier (OFDM) signaling. For both modulation formats a carrier frequency offset results in a rotation and an attenuation of the transmitted symbols. In addition, this impairment gives rise to inter-symbol interference (ISI) and destroys the orthogonality between the carriers of the multi carrier signal which yields inter-carrier interference (ICI). The analysis shows that for SC transmission the BER degradation is dominated by the reduction of the useful signal component, provided that the carrier frequency offset is small with respect to the SC symbol rate. For OFDM transmission, a comparison of the different interferences reveals that the BER degradation is determined by the ICI.

Noncoherently detected trellis-coded partial response CPM on mobile radio channels

Abstract: A noncoherent receiver is proposed for partial response trellis-coded continuous phase modulation (TC-CPM) on interleaved flat Rician-fading channels. By using a multiple-symbol observation interval and a simple metric calculator, the power efficiency is improved over a receiver that uses a single-symbol observation interval. Performance bounds on the bit error probability are derived by defining a set of characteristic distances for CPM signals, and showing that TC-CPM is equivalent to a TCM scheme. Our results show that, with the same observation length, the proposed receiver is less than 0.5 dB inferior to a coherent receiver for which perfect channel information is needed. We also conclude that in terms of joint power-bandwidth complexity, 2RC is the best candidate for rate-1/2 TCM codes.

Synchronous polarization and phase modulation using a periodic waveform with complex harmonics for improved perfomance of optical transmission systems

Abstract: A method and apparatus is provided that yields improved performance by modulating the optical phase and polarization of an optical signal with a periodic waveform having harmonic content that is more complex than that associated with a simple sinusoidal waveform. A phase modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The phase modulator modulates the phase of the optical signal in a continuous manner with the periodic waveform with complex harmonics where the fundamental phase modulation frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. In another illustrative embodiment of the invention, a polarization modulator further processes the optical signal by modulating the state-of-polarization of the signal in a continuous fashion with the periodic waveform with complex harmonics where the fundamental polarization modulation frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. In addition to being continuously modulated, the polarization modulation is performed so that the average value of the state of polarization over each modulation cycle is substantially equal to zero.

Selection of an optimal modulation scheme for digital communications over low voltage power lines

Abstract: There is an ever increasing demand for environmental management of buildings, office automation, security monitoring or remote control of customer appliances and remote meter reading. The AC low voltage power line would be an ideal communications medium for digital data. Several systems for power line communications (PLC) were presented. The reliability of PLC is strongly influenced by time-variant and frequency-selective attenuation and interference on the power line channel. Various experiments were made to evaluate different PLC systems and set up a channel model. This paper gives a short summary of typical transfer characteristics and interference to be observed at power line networks. It is shown that at transmission over a single phase of the power supply system the maximum phase jitter of the time-variant transfer function is in most cases below 90/spl deg/. In the second part important modulation schemes are evaluated for applicability to power line communications. This evaluation considers chirp modulation, direct sequencing phase shift keying modulation (PN/PSK) and hopping techniques with spectral redundancy given by carriers with M different frequencies. The selection of the optimal modulation technique considers the European standard EN 50065, which restricts both the frequency range and the maximum signal amplitude. This paper deals with modulation schemes, using M frequencies, namely classic frequency hopping modulation (MFH) and the multifrequency,phase modulation (MFH/PSK and MF/PSK). Significant advantages of M frequency phase modulation in comparison with classic frequency hopping are pointed out.

Disk-growing algorithm for phase-map unwrapping: application to speckle interferograms

Abstract: Interferometric techniques combined with phase shifting allow computation of the phase that is linked to the displacement of the object under study. The phases before and after displacement are computed from three or more interferograms (called specklegrams when speckle is used as the information carrier). Subtraction of these two phase patterns leads to a raw phase map. Phase unwrapping restores the 2π discontinuities and gives a continuous phase map. The disk-growing algorithm presented allows the inner and the outer propagation of the unwrapping from a growing disk and so avoids the main problem of anisotropic error propagation for noisy phase maps. It works successfully in speckle interferometry.

Multiple symbol trellis coding of CPFSK

Abstract: This paper describes a technique related to the design of a trellis encoder, combined with the full response M-ary continuous phase frequency shift keying (CPFSK) with modulation index 1/M. A new representation of CPFSK waveforms in N signaling intervals, is proposed as a function of an (N+1)-D vector. We also decompose the generation of the proposed CPFSK waveform into two stages, an N-consecutive continuous phase encoder (NCPE) and a memoryless modulator (MM). This decomposition makes it possible to design binary convolutional encoders with various code rates, cascaded to the NCPE. Specific optimal outer convolutional encoders of two and three-consecutive full response four-ary CPFSK with modulation index 1/4 are designed following Ungerboeck's (1982) set partitioning approach. These codes achieve asymptotic coding gains up to 4.77 dB for the two consecutive case with code rate 3/4, and asymptotic coding gains up to 5.45 dB for the three-consecutive case with code rate 5/6.

Optimum bandwidth-distance performance in partial response CPM systems

Abstract: The problem of optimizing the baseband pulse shape in order to obtain the minimum effective bandwidth for a prescribed value of minimum Euclidean distance is treated for partial response CPM. Some comparisons with standard pulses are performed and the results are presented in the form of bandwidth-distance and spectral density plots.

Constant envelope continuous phase frequency shift key modulation apparatus and method at radio frequencies

Abstract: Constant envelope angle modulation apparatus comprises a frequency synthesizer for outputting a stepped output waveform having a selectable precise output frequency. The output of the synthesizer provides an input to a mixer for O-QPSK modulating a received information signal. The O-QPSK modulated signal is then hard-limited (315), for example, via a series of hard-limiting amplifier (326) and filter circuits (318, 322) and a divider circuit (316). Preferably, a data stream for modulation may be filtered via a filter (375) having an approximately 70-100 % roll-off characteristic, such as a root raised cosine filter. A hard-limited, constant envelope angle modulated signal results that is easily frequency converted to, for example, microwave frequencies for landline or satellite applications via a simple multiplier circuit. The multiplier circuit preferably comprises a series of stage-filtered multipliers and band pass filters to achieve the desired output microwave frequency.

All-digital reverse modulation architecture based carrier recovery implementation for GMSK and compatible FQPSK

Abstract: A carrier recovery circuit implementation with an all-digital reverse modulation approach for coherent detection in the GSM/GMSK system as well as the GMSK compatible improved efficiency cross-correlated FQPSK system is presented. The proposed carrier recovery implementation utilizes all-digital reverse modulation circuit in a feedback loop to remove the modulated signal from the received intermediate frequency (IF) signal and to estimate the phase error of this carrier signal using a phase-locked loop (PLL). The digital reverse modulation approach avoids the multipliers required in an analog reverse modulation design, so that it can be implemented in a single chip FPGA. Hardware implementation of the coherent detection demonstrates that cross-correlated FQPSK is completely compatible with GMSK in the system performance and the receiver structure for GSM. Experimental performance evaluations show that the proposed carrier recovery circuit provides a Bit Error Rate (BER) performance within 0.3 dB in a non-linearly amplified channel corrupted by additive white Gaussian noise (AWCN) as compared with the simulated performance of the GSM/GMSK system.

Phase plate technology for laser marking of magnetic discs

Abstract: An advanced design for a phase plate enables the distribution of spots in arbitrarily shaped patterns with very high uniformity and with a continuously or near-continuously varying phase pattern. A continuous phase pattern eliminates large phase jumps typically expected in a grating that provides arbitrary shapes. Large phase jumps increase scattered light outside of the desired pattern, reduce efficiency and can make the grating difficult to manufacture. When manufacturing capabilities preclude producing a fully continuous grating, the present design can be easily adapted to minimize manufacturing errors and maintain high efficiencies. This continuous grating is significantly more efficient than previously described Dammann gratings, offers much more flexibility in generating spot patterns and is easier to manufacture and replicate than a multi-level phase grating.

Continuous-Phase Modulations for CDMA Radio Communications: Modem Architecture and Performance

Abstract: In this paper we analyze the structure and the performance of a digital modem for band-limited spread-spectrum signals to be employed in a radio communication network with asynchronous code-division multiple access and constant-envelope continuous-phase modulation. After a description of the modem structure and the evaluation of its bit error rate in the presence of co-channel interference, we tackle the key point of code synchronization. In particular, we present a detailed analysis of the code acquisition strategy, assessing its performance in terms of false alarm probability, missed detection probability and mean acquisition time. Furthermore, we address the problem of code chip timing recovery, describing the performance of three different code tracking loops in terms of the steady-state RMS chip timing error jitter. The analytical approach we present can be applied to any Continuous Phase Modulation (CPM) format that can be approximated by an Offset-QAM signal, such as Gaussian-filtered Minimum-Shift Keying (GMSK).

Digital transmission using multimode phase-continuous chirp signals

Abstract: In a spread-spectrum system the transmitted signal is spread over a wide frequency band, often much wider than the minimum bandwidth needed for the information to be conveyed. The concept of varying the modulation index of a continuous phase FSK (i.e. CPFSK) waveform is applied to digital transmission using chirp signals. These multimode chirp waveforms are described and their ability to perform over the coherent Gaussian channel is examined. It is shown that the dual-mode phase-continuous chirp signals out perform monomode signals by nearly 0.8 dB, when corresponding high-SNR 5-bit optimum minimum-bit-error-probability receivers are employed. A low-complexity suboptimum average matched filter receiver for multimode chirp signals is examined and explicit expressions for its performance are given

Ambiguity resolution in SAR interferometry by use of three phase centers

Abstract: In a typical interferometric synthetic aperture radar (IFSAR) system employed for terrain elevation mapping, terrain height is estimated from phase difference data obtained from two phase centers separated spatially in the cross-track direction. In this paper we show how the judicious design of a three phase center IFSAR renders phase unwrapping, i.e., the process of estimating true continuous phases from principal values of phase, a much simpler process that inherent in traditional algorithms. With three phase centers, one IFSAR baseline fan be chosen to be relatively small so that all of the scene's terrain relief causes less than one cycle of phase difference. This allows computation of a coarse height map without use of any form of phase unwrapping. The cycle number ambiguities in the phase data derived from the other baseline, chosen to be relatively large, can then be resolved by reference to the heights computed from the small baseline data. This basic concept of combining phase data from one small and one large baseline to accomplish phase unwrapping has been previously employed in other interferometric problems. The new algorithm is shown to possess a certain form of immunity to corrupted interferometric phase data that is not inherent in traditional 2D path-following phase unwrappers. This is because path-following algorithms must estimate, either implicitly or explicitly, those portions of the IFSAR fringe data where discontinuities in phase occur. Such discontinuities typically arise form noisy phase measurements derived from low radar return areas of the SAR imagery. When wrong estimates are made as to where these phase discontinuities occur, errors in the unwrapped phase values can appear due to the resulting erroneous unwrapping paths. This implies that entire regions of the scene can be reconstructed with incorrect terrain heights. By contrast, since the new method estimates the continuous phase at each point in the image by a straightforward combination of only the measured phases from the small and large baseline, phase estimation errors are confined to that point. We derive quantitative expressions for the new algorithm that relate the probability of selecting the wrong phase cycle to parameters of the interferometer. We then demonstrate that use of median filtering can very effectively mitigate those cycle errors that do occur. By use of computer simulations, we show how the new algorithm is used to robustly construct terrain elevation maps.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Bit error and outage probability for digital cellular systems with a small number of interferers

Abstract: This paper proposes a semi-analytical approach to characterise the performance of digital cellular systems when cochannel interference is determined by a small number of interferers. Linearly modulated signals (such as BPSK, QPSK, M-ASK, M-QAM, MSK, O-QPSK, etc.) with linear receivers are investigated by considering the probability density function of the interference at the input of the decision device. Non-linear (continuous phase) modulation signals (such as GMSK) and non-coherent detection are also investigated by means of simulation. As a consequence, a general approach to outage probability definition considering the protection ratio as a function of the interferers number and useful signal-to-noise ratio is introduced.

Reduced complexity symbol-by-symbol soft output algorithms

Abstract: This paper presents and characterizes the performance of complexity reduction techniques applied to optimum soft output demodulation algorithms for a general modulation model. The optimum soft output algorithm (OSA) recursively computes the posterior probability mass function (PMF) of the modulation state and each information symbol conditioned on the modulation state up to a decoding lag of K. The recursion has complexity O(/spl par//spl sigma//sub k//spl par/M/sup 2/K) where /spl par//spl sigma//sub k//spl par/ is the cardinality of the modulation state and M is the cardinality of the information symbols. This paper focuses on two complexity reduction techniques: (1) retaining states in the OSA recursion only if their PMF is above a threshold (T-OSA) and (2) a reduced state version of OSA (RSSOA) where demodulation occurs assuming a modulation state of lower cardinality than the true modulation state. These algorithms greatly reduce the complexity of OSA while in many cases retaining near optimum performance. Examples are considered for known intersymbol interference channels, concatenated convolution codes, and continuous phase modulation.

Performance evaluation of a continuous-phase CDMA modem operating over the 60 GHz mobile radio channel

Abstract: This paper (1) describes the structure and the performance of a band-limited spread-spectrum transmission system suited for short-range terrestrial inter-vehicle or vehicle-to-beacon radio links that features Generalized MSK as modulation format and asynchronous direct-sequence code-division multiple access. The Bit Error Rate (BER) performance of such a system is evaluated over a recently proposed 60 GHz short-range mobile radio channel model. In particular, the sensitivity to a number of relevant link parameters (such as the distance between transmit and receive antennas and the receiver speed) is investigated, and the impact of code tracking errors and of differential encoding/detection of the spreading code chips on system performance is also discussed.

Digital frequency synthesizer/modulator for continuous phase modulations with slow frequency hopping

Abstract: This paper gives a description of a modulator for burst-by-burst carrier frequency hopping in TDMA systems. The architecture consists of a digital frequency synthesizer/modulator for a broad class of continuous phase modulations (CPMs) and a fast frequency settling RF synthesizer consisting of one phase-locked-loop (PLL). The performance of the digital frequency synthesizer/CPM modulator has been analyzed theoretically and simulated by a computer program. The analyses show that the proposed digital frequency synthesizer/CPM modulator achieves lower power consumption and spurious levels than the fast frequency hopping systems synthesizing digitally a full frequency band. In the computer simulations the effect of the digital frequency synthesizer/CPM modulator parameters on the power spectrum and the phase error is investigated.

Method and apparatus for correlating a continuous phase modulated spread spectrum signal

Abstract: A technique for modulating and demodulating continuous phase modulation (CPM) spread spectrum signals and variations thereof. A transmitter encodes M data bits using a selected spread spectrum code, divides the spread spectrum code into a plurality of chip codes (such as even chips and odd chips), independently modulates the even and odd chips with orthogonal carrier signals using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal, divides the spread spectrum signal into duplicate signals, separately demodulates the duplicate signals into an odd chip signal and an even chip signal, simultaneously attempts to correlate the odd chip signal with a locally generated odd chip sequence and the even chip signal with a locally generated even chip sequence, and interleaves the correlation signals into a unified correlation signal. The unified correlation signal may be compared against other correlation signals to determine the content of the transmitted data.

A low complexity digital encoder-modulator for high data rate satellite BISDN applications

Abstract: The development of a low complexity, flexible digital encoder-modulator (DEM) for medium to high data rate RF communication links is discussed. The DEM is intended for use in data downlinks from communications satellites or near-Earth science platforms. The present configuration supports throughput rates up to 280 Mbps using several pulse shaped quadrature modulation schemes. This includes BPSK and QPSK as well as higher order schemes such as 8PSK and 16QAM. Through software modifications the DEM can also support binary CPM schemes (such as GMSK) and multiboard configurations can support higher order CPM schemes. In addition to higher order modulation schemes, combined modulation and forward-error correction coding is used to improve the efficiency of conveying information through power and bandwidth limited channels that are characteristic of space-borne systems. The baseline configuration supports the B-ISDN OC-3 rate of 155.52 Mbps in 80 MHz of null-to-null bandwidth. Test results show less than a 0.2 dB of degradation from theory in the range of operation. The DEM uses approximately 15 watts of DC power, is constructed on a standard VME card (6U/spl times/160 mm) and has a mass of 0.38 kg.

Carrier slip compensation method for coherent detection

Abstract: In the communication system using the binary phase shift keying (BPSK) modulation method, an erroneous data that might be caused by a carrier slip of carrier wave generated during coherent detection can be compensated. The modulation unit of the transmitter transmits identical data at differentiated timing through BPSK modulation, and the coherent detector circuit of the demodulation unit of the receiver detects waves upon receiving signals. The compensating circuit makes time differences in transmitted data equal and compares them to detect mismatch in order to compensate carrier slip found in the received signal and then the combination circuit realizes the combination.