Showing papers on "Demodulation published in 1987"

Oversampled Sigma-Delta Modulation

Abstract: Oversampled sigma-delta modulation has been proposed as a practical implementation for high rate analog-to-digital conversion because of its simplicity and its robustness against circuit imperfections. To date, mathematical developments of the basic properties of such systems have been based either on simplified continuous-time approximate models or on linearized discrete-time models where the quantizer is replaced by an additive white uniform noise source. In this paper, we rigorously derive several basic properties of a simple discrete-time single integrator loop sigma-delta modulator with an accumulate-and-dump demodulator. The derivation does not require any assumptions on the correlation or distribution of the quantizer error, and hence involves no linearization of the nonlinear system, but it does show that when the input is constant, the state sequence of the integrator in the encoder loop can be modeled exactly as a linear system in an appropriate space. Two basic properties are developed: 1) the behavior of the sigma-delta quantizer when driven by a constant input and its relation to uniform quantization, and 2) the rate-distortion tradeoffs between the oversampling ratio and the average mean-squared quantization error.

Highly Efficient Digital Mobile Communications with a Linear Modulation Method

Abstract: Although linear modulation methods can achieve high spectrum efficiency, very little attention has been directed to their use in mobile radio systems. This is mainly due to the fact that the nonlinearity of the transmitter power amplifier tends to spread the spectrum and thus eliminate any spectrum efficiency advantage gained through the use of linear modulation methods. In this paper, a linear modulation system is proposed, which solves the above difficulty and which gives higher spectrum efficiency than conventional digital FM. The modulation/demodulation method is \pi /4 shift QPSK and phase-shift detection with a limiter-discriminator and an integrate-and-dump filter. By introducing a cartesian coordinate negative feedback control, 35 percent power efficiency at 10 W output power and - 60 dB relative out-of-band radiation are simultaneously achieved with a class "AB" amplifier, owing to the 29 dB feedback gain. The receiver configuration is easy to realize and gives immunity against fast fading through the use of noncoherent detection with limiter-discriminator. By using a novel decision method, bit error rate performances under both nonfading and fading condition are comparable to those obtained by digital FM. These results make it possible for linear modulation methods to achieve higher spectrum efficiency than is possible with conventional digital FM methods in mobile radio communications.

Phase diversity techniques for coherent optical receivers

Abstract: In the present state of the art, coherent optical receivers most often operate in the heterodyne mode. Here a photodiode-amplifier combination having bandwidth greater than twice the bit rate ( B ) is needed: indeed bandwidths considerably greater than 2B are preferably employed to ease design of the bandpass filter needed for noise limitation, and to avoid demodulator penalties in some modulation schemes. For the high bit rate systems now coming into service (560 Mbit/s-2.4 Gbit/s), the optical receiver design requirements become more stringent for coherent heterodyne operation. The various modes of "zero IF" operation, however, require only baseband receiver module bandwidth. The options available are either homodyne (phase locked) operation, or phase diversity (multiport) techniques. In this paper, we compare these options, and show that phase diversity techniques are capable of good performance for high bit rate coherent receivers. In phase diversity operation, not only is phase locking avoided, but also the necessary frequency locking does not have high stability requirements. Furthermore, there are advantages in operating with a small frequency offset from zero (of the order of 1 percent of the bit rate). An experimental receiver has been operated at 320 and 680 Mbit/s, demodulating both amplitude shift keying (ASK) and differential phase shift keying (DPSK). Operation with FSK is also possible. Sensitivities so far achieved of -47.5 dBm (320-Mbit/s ASK) and -42 dBm (680- Mbit/s ASK) with limited local oscillator power are capable of substantial improvement when higher power local oscillators and lower noise receive modules become available. Demodulation of DPSK at 320 Mbit/s has also been achieved and shows a measured receiver sensitivity improvement of over 4 dB over ASK at the same bit rate and local oscillator power. These practical results show clearly that phase diversity is a very realistic option for high bit rate systems.

Optically readable record carrier for recording information, method and apparatus for manufacturing such a record carrier, apparatus for recording information on such a record carrier, and apparatus for reading information recorded on such a record carrier

Abstract: An optical disc record carrier having a radiation-sensitive surface and a spiral or concentric pattern of information tracks thereon. The radial displacement of each track is modulated to produce a periodic radial wobble, the frequency of such periodic displacement being modulated by a position-information signal identifying the relative positions of the tracks. During recording or reading of information on the tracks the track modulation is read by a scanning beam. A clock signal for controlling scanning velocity is recovered from the track displacement modulation, and an FM demodulator recovers the position-information signal from the frequency modulation of such displacement.

Spread-Spectrum Multiple-Access Performance of Orthogonal Codes: Linear Receivers

Abstract: This paper analyzes a direct-sequence, spread-spectrum, multiple-access (SSMA) communication system which assigns a set of M orthogonal sequences to each user. With all direct sequence SSMA systems, K users share a channel by phase modulating their transmissions with signature sequences. However, the users of our system transmit log_{2}M bits of information/sequence. This contrasts classical SSMA schemes which use a pair of antipodal sequences and transmit 1 bit/sequence. In this paper, we assume that the channel noise is a combination of additive white Gaussian noise (AWGN) and multiple-access interference. We employ the optimum (single-user) demodulator for orthogonal signals in Gaussian noise. The multiple-user performance of this receiver is analyzed. We obtain approximations for the multiuser probability of error by using a Gaussian approximation for the multiple-access interference. We also obtain an upper bound on the exact probability by using characteristic functions. Our SSMA system is Well suited for application at the lower radio frequencies. Therefore, a companion paper describes a realistic model for low-frequency radio noise, modifies the receiver to include a zero-memory nonlinearity, and studies the performance of the nonlinear receiver.

Mobile digital communications via tone calibration

Abstract: A new digital signaling technique that is particularly suited for channels impaired by multipath fading is presented. The proposed modulation scheme employs a continuous-wave (CW) tone to calibrate the mobile channel against the multipath-induced phase uncertainties. This technique is applicable to quaternary phase shift keying as well as to more complicated signal constellations such as M-ary phase shift keyed schemes. The advantages of tone calibration are: 1) robustness of the receiver and 2) elimination of the link dependent error floor. Furthermore, since the CW tone can also be used for coherent signal demodulation, carrier phase acquisition can be achieved within a bit time. This property is particularly attractive when a burst of data with a short burst length has to be detected. This radio technique is useful for both the terrestrial mobile and the newer satellite-aided mobile communication (SAMC) services.

Satellite communications system for medical related images

Abstract: A satellite communications system for transmitting medical related images from a mobile unit to a central headquarters and then sending back diagnostic analysis from the central headquarters to the mobile unit by having a high resolution camera and a video compressor for converting high resolution images into voltage analog signals, a modulator for converting the voltage analog signals into a narrow band width and low frequency signal, a satellite system for transmitting and receiving images and analyses, a demodulator for converting the narrow band width and low frequency signal back into a voltage analog signal, a video expander for converting the voltage analog signal into a digital signal, a buffer for buffering the digital signal, a high resolution monitor for converting the buffered digital signal into a high resolution digitized image.

Device for demodulating a spread spectrum signal

Abstract: Circuitry for receiving and demodulating a spread spectrum signal integrates signal acquisition and tracking functions and also accommodates signal drift. Two data decoding signals are generated which correspond to the pseudo noise code used to modulate the received signal and which are phase-shifted by a half-chip interval. Two correlators use the decoding signals to demodulate the received signal, both during acquisition and tracking, producing two data signals. A summer combines the two data signals to produce a signal whose strength is less dependent on the degree of synchronization of each data decoding signal with the received signal. Tracking error circuitry periodically compares the two demodulated data signals and incrementally phase shifts the two data decoding signals, the magnitude of the increment being one-quarter chip and the polarity being selected to strengthen the weaker of the two data signals. This causes the circuitry to track the received signal despite gradual signal drift. A bank of correlators also demodulate the received signal using test decoding signals having different phase angles. The phase angles of the test decoding signals are periodically adjusted to locate stronger signals. Control circuitry constantly compares the strength of the demodulated test signals and of the two data signals and adjusts the phase of the two data decoding signals to correspond to that phase producing the strongest demodulated signal.

Multichannel coherent optical communications systems

Abstract: Balanced coherent receivers perform substantially better than single-detector receivers in multichannel optical fiber FDM communications systems since the balanced approach eliminates the direct-detection and signal-cross-signal interference. The permissible channel spacing D depends on the intermediate frequency f IF , on the bit rate R b , and on the modulation/demodulation format. In particular, D increases by 2 Hz for every 1-Hz increase of the f IF . The signal-to-interference ratio SIR, as defined in the text, provides a simple measure of the amount of the interference generated by undesired channels. The criterion SIR = 30 dB is selected in this paper and leads to the following minimum channel spacings: for heterodyne systems, 3.8R_{b} for FSK, 9.5R_{b} for ASK, and 12.4R_{b} for PSK; for homodyne systems, 7.5R_{b} for ASK and 10.5R_{b} for PSK. Simultaneous transmission of several channels generates an excess shot noise studied here for the first time. If the local oscillator power is 40 dB above the received signal power and 2000 channels are transmitted without optical prefiltering, the excess shot noise power penalty is less than 1 dB.

Time-domain addressing of remote fiber-optic interferometric sensor arrays

Abstract: This paper describes and analyzes a particular application of high duty-cycle time-division multiplexing to the separation and identification of signals from an interferometric sensor array. Using the method discussed here, the coherence length of the laser is no longer a severe design constraint. Also, the source phase-induced intensity noise which limits some other multiplexing methods may be overcome, leading to a higher sensitivity. The arrays of all-passive remote sensors exhibit minimal crosstalk between sensors, and have downlead insensitivity. A synthetic heterodyne demodulation technique prevents environmentally induced signal fading. Analysis includes coupling ratios for all directional couplers in the system, signal and noise spectra, minimum detectable phase shift, and the effect of ac coupling on noise and crosstalk. An experimental all-fiber implementation of a two sensor array has yielded a measured sensitivity of approximately 10 μrad/ \sqrt{Hz} over a range of signal frequencies, and a crosstalk level of better than 55 dB.

Multiplex signal processing apparatus

Abstract: A multiplex signal processing apparatus in a signal transmitting and receiving system includes at the transmitting side: a first amplitude-modulator for modulating a first carrier by a main signal to obtain a vestigial sideband, amplitude-modulated main signal; a second amplitude-modulator for modulating a second carrier which has the same frequency but differs in phase by 90° from the first carrier by a multiplex signal to obtain a double sideband, amplitude-modulated multiplex signal; an inverse Nyquist filter for filtering this signal to obtain a vestigial sideband, amplitude-modulated multiplex signal; and an adder for adding the vestigial sideband, amplitude-modulated main and multiplex signals to obtain a multiplexed signal. The apparatus at the receiving side includes: a Nyquist filter for filtering the multiplexed signal; a carrier regenerator for regenerating the first and second carriers from the multiplexed signal; a main signal detector for detecting the main signal from the multiplexed signal passed through the Nyquist filter by using the first carrier; a filter for removing quadrature distortion from the multiplexed signal; and a multiplex signal detector for detecting the multiplex signal from the multiplexed signal passed through the filter by using the second carrier. By inverse Nyquist filtering the auxiliary signal in quadrature to the picture carrier, a normal synchronous receiver will produce a conventional television signal without distortion (crosstalk) caused by quadrature distortion of an auxiliary signal containing additional picture information while at the same time allowing relatively simple demodulation of the auxiliary signal in improved receivers without adding distortion.

Measurements and models of a land mobile satellite channel and their applications to MSK signals

Abstract: The fading and shadowing effects observed on land mobile satellite signals are characterized in statistical terms. Models are developed in terms of probability distribution of the signal's envelope and phase as well as its rate of change with time. The multipath fading and shadowing effects modelled are typical of those encountered in a mobile-satellite link in rural and suburban areas. A comparison of the models with experimental data at 870 MHz and 1542 MHz is given. Applications of the models to predict performance of a minimum shift keying (MSK) signal at 2400 bits/s show that large margins are required to compensate for the effects of fading and shadowing. In addition, the results show that conventional coherent demodulation of a MSK signal may not be feasible due to phase variation caused by fading and shadowing. On the other hand, the results show that random FM has negligible effect on the probability of error of the MSK signal at 2400 bits/s when frequency demodulation is used.

Receiver for bandspread signals

Abstract: An improved receiver for modulated bandspread carrier signals is disclosed. The invention includes an antenna for intercepting a plurality of modulated carrier signals bandspread at a first clock rate; a radio frequency section in communication with the antenna for selecting a received signal from the plurality of signals; and an intermediate frequency section in communication with the radio frequency section for converting the received signal to an intermediate frequency signal. The intermediate frequency signal is digitized and multiplied by a pseudo-random code stored in a first memory for demodulation. Successive demodulation products are added, stored and used to provide in-phase (I) and quadrature (Q) signals. Means are provided to for utilizing the I and Q signals to control the rate and the timing of the multiplication of the digitized signal with the pseudo-random code stored in the first memory.

Automatic data/voice sending/receiving mode switching device

Abstract: A terminal device (1) sends/receives data and voice signals through a low speed circuit (7) to/from another device (2), while switching automatically data and voice signals. The terminal device (1) comprises a data sender/receiver (3), a voice sender/receiver (9), a modulator/demodulator (4), and an automatic mode switch (8). The automatic mode switch (8) includes a circuit (811) disposed between the data sender/receiver (3) and the modulator/demodulator (4) for detecting special data such as flags from received data coming from the modulator/demodulator (4), a circuit (812) for making a logical product of the output of this detecting circuit (811) and a detection signal of the received carrier and means for separating the voice sender/receiver from the circuit and transmitting a sending request for data sending/receiving use. Further switching over from the voice sending/receiving mode to the data sending/receiving mode is effected by key operations, etc.

Multiplexing of interferometric sensors using phase carrier techniques

Abstract: This paper demonstrates the multiplexing of fiber-optic interferometric sensors using a CW phase generated carrier technique. The technique employs modulated diode laser sources at different carrier frequencies, nearly balanced interferometers (∼4-cm path difference), and phase generated carrier demultiplexing demodulation. This approach leads to a simple all-passive sensor array which has intrinsically low crosstalk. The system is analyzed in terms of shot noise performance and crosstalk. An experimental all optical implementation of a four sensor array was demonstrated; both the single sensor and multisensor arrays were limited by the laser phase noise to a sensitivity of \sim 18 \mu rad/ \sqrt{Hz} . Crosstalk between individual channels was better than -60 dB and crosstalk between three sensors and the test sensor was better than -55 dB. In the absence of laser phase noise the demodulator/demultiplexer demonstrated \sim 2-\mu rad performance with both single sensor and four element array operation.

Isolation amplifier including precision voltage-to-duty-cycle converter and low ripple, high bandwidth charge balance demodulator

Abstract: An isolation amplifier includes a voltage-to-duty-cycle modulator, a non-galvanic isolation barrier, and a demodulator converting a duty-cycle-modulated signal transmitted across the isolation barrier to an analog voltage replica of the analog input voltage. The modulator circuit includes a first current switching means which produces a first current that is switched between positive and negative values in response to an output from a comparator that can be referenced to a noise-synchronized signal. The first current is summed with an input current and the difference is integrated and input to the comparator, the output of which produces the duty-cycle-modulated signal. The demodulator includes a second current switching circuit for producing a second current that is switched between positive and negative levels in response to the duty-cycle-modulated signal received across the isolation barrier and includes circuitry for algebraically summing the input current with the second current and integrating the result to produce the analog output voltage. The modulator circuit and demodulator circuits are fabricated on a single semiconductor area to produce the close matching between components of the first and second current switching circuits. The area is cut in half to produce two chips, which are connected to two isolation barrier capacitors. In the demodulator, a sample and hold circuit synchronized with the duty-cycle-modulated signal transmitted across the isolation barrier samples the output of the integrator.

Time-division multiplexing of interferometric fiber sensors using passive phase-generated carrier interrogation.

Abstract: The multiplexing and demodulation of interferometric sensors using a time-division/phase-generated carrier approach is described. The scheme uses slightly unbalanced interferometers and laser frequency modulation to effect the interrogation of the sensors, while the time-division multiplexing allows individual sensors to be addressed. Phase sensitivities of ∼20μrad/Hz and cross-talk levels of <−47 dB are demonstrated for a three-sensor network.

Clipped Diversity Combining for Channels with Partial-Band Interference--Part I: Clipped-Linear Combining

Abstract: Clipped-linear diversity combining is analyzed for receivers without side information. Communication systems with noncoherent demodulation, binary and M -ary orthogonal signaling, and diversity transmission are considered. The main source of interference is additive Gaussian partial-band interference, but a nonzero quiescent noise level is also included in the analysis to account for wide-band noise sources. Some of the results apply to general (non-Gaussian) interference. The numerical results demonstrate that clipped-linear combining can perform well in terms of both narrow-band interference rejection capability and maximum signal-to-interference ratio requirement. A practical disadvantage of clipped-linear combining is that it relies on measurements of the signal output voltage.

Digital delay FM demodulator with filtered noise dither

Abstract: Audio beat notes produced by sampling a square wave in a digital quadrature FM demodulator are reduced by adding filtered random noise, or dither, to the signal to be demodulated to randomly vary the width of successive pulses in the square wave. Filtration of the random noise prevents feedthrough of noise which would degrade the demodulated signal.

Coherent Lightwave Communications

Abstract: In this talk we will present fundamental theoretical considerations affecting the performance of coherent lightwave communication systems. These systems include a single-mode laser and a modulator at the source and a coherent receiver which is the optical onalog of a superheterodyne radio set. Instead of detecting photons directly, the coherent receiver first converts the incoming signal from the optical regime down to the radio regime, and then uses conventional electronic circuitry to perform various signal processing operations, such as amplification and demodulation. In principle, this technique can yield large increases (~ 20 dB) in receiver sensitivity compared with direct detection using avalanche photodiodes. One of the prime causes of this degradation has been identified as laser phase noise, a phenomenon that is known to be particularly serious in semiconductor devices.

Scanning radio receiver

Abstract: A high-speed, multi-band scanning radio receiver. A frequency synthesizer loaded with a digital code read from memory performs band switching and supplies tracking signals and a local oscillator signal to multi-band RF amplifier and mixer circuitry. An output of an FM detector in the receiver is connected to a squelch circuit which includes a high-pass filter network and a diode detector, with the diode detector output being connected to an internal A/D converter of a microprocessor which converts multiple samples of the incoming signal to digital values and generates a mute signal when the average value of the converted samples is below a predetermined squelch level. An output line from the FM detector to audio output circuitry in the receiver is grounded in response to the mute signal. The microprocessor is also programmed to control receiver tuning during SEARCH mode such that searching continues until the demodulator output signal for an active channel is substantially in the center of the demodulator S curve, as detected by a window detector.

Sub-band speech analyzing and synthesizing device

Abstract: In a sub-band speech analyzing and synthesizing apparatus, a low-pass filter comprises a nonrecursive filter. The center frequency and bandwidth of each channel are selected so that the decimated sampling period of that channel is an integer multiple of the period of the modulating signal or the demodulating signal of the channel. Modulation or demodulation is performed simultaneously with the low-pass filtering by the nonrecursive filter.

Method and circuit arrangement for controlling the phase angle between a generated code and a received code contained in a received spread-spectrum signal

Abstract: In this method, in which the code is generated at several different phase angles and is supplied to mixers, the output signals of which, after band limiting and envelope-curved demodulation, are heterodyned, m codes are generated which are in each case phase-shifted by one bit period with respect to one another, m being greater than 2. The greater the deviation of the code generated in each case from a mean phase angle of the generated codes, the higher the weighting of the output signals during the heterodyning.

FM stereo receiver

Abstract: An FM stereo receiver includes a level detecting circuit for detecting the received electric field intensity and a pseudo stereo circuit for changing the phase of an entered signal and outputting two signals different in phase When the level detecting circuit detects a received electric field intensity below a threshold level, monaural signals produced from outputs of a stereo demodulator are applied to the pseudo stereo circuit to produce pseudo stereo signals

Coded FH/SS Communications in the Presence of Combined Partial-Band Noise Jamming, Rician Nonselective Fading, and Multiuser Interference

Abstract: In this paper we address the problem of combatting combined interference in spread-spectrum communication links. We consider frequency-hopped spread-spectrum systems with M -ary FSK modulation and noncoherent demodulation which employ forward-error-control coding. The interference consists of partial-band noise jamming, nonselective Rician fading, other-user interference, and thermal noise. The coding schemes which we analyze include: ReedSolomon codes (with or without diversity and error-only, erasure-only, or parallel erasure/error decoding), binary, nonbinary, and dual- k convolutional codes with and without side information (information about the state of the channel), and concatenated schemes (Reed-Solomon outer codes with either inner detection-only block codes or inner convolutional codes). In all cases we derive 1) the minimum signal-to-jammer energy ratio required to guarantee a desirable bit error rate as a function of ρ, the fraction of the band which is jammed, when the number of interfering users is fixed; and 2) the maximum number of users that can be supported by the system as a function of ρ, when the signal-to-jammer energy ratio is fixed.

Design and Field Test of a 256-QAM DIV Modem

Abstract: The increasing demand for digital transmission facilities has led to the development of modems which allow the transmission of T1 (1.544 Mbit/s) data streams over the existing analog FM and AM/SSB links. The DTS model 2001 data in voice (DIV) modem uses 256-QAM modulation to transmit a T1 data stream in a single supergroup. This paper describes the technical requirements and design of the modem. A number of particularly interesting aspects of the design are discussed in more detail. These items are 1) the extensive use of digital signal processing in the implementation; 2) the techniques used in the demodulator control loops; 3) the use of a low-rate error correction codec and interleaver for random and burst error correction; and 4) the use of signaling constellation customization as a design tool.

Digital demodulator for frequency-division-multiplexed signals

Abstract: An improved digital demodulator capable of demodulating a frequency multiplexed input signal is disclosed. The frequency division multiplexed input signal is sampled in an analog-to-digital converter. The samples are translated by mixing with base band frequency signals to yield real and imaginary values corresponding to phase information in the original modulation signals. After translation, the translated samples are filtered in real and imaginary digital filters. After filtering, the original modulation information is recovered by analysis of the position of vectors in the complex plane represented by the real and imaginary values. In the preferred embodiment, a successive approximation technique is used to determine the angle of the vectors to the real axis. Low pass output filtering may be employed after recovery of the modulation signal for improvements in signal to noise ratio. In the preferred embodiment, the translation is performed by multiplying the input samples by digital values corresponding to sine and cosine values of local oscillator signals at base band frequencies. Preselect filtering may be employed prior to translation to decimate the input samples where possible to reduce subsequent processing requirements. In the preferred embodiment, the unit is operated in a first initialization mode in which a microprocessor supplies appropriate filter coefficients corresponding to the frequencies of the channels to be demodulated. Thereafter, the microprocessor does not directly control supply of samples or coefficients to the filters for evaluation. Very high data rates are thus made possible.

Method and circuit for receiving radio wave, especially multi-antenna diversity reception and apparatus

Abstract: For diversity reception from a plurality of antennas, particularly in an automotive vehicle (FIG 4), the respectively received signals are mixed with a local oscillator signal to form a plurality of IF signals (u 1 u n ) The respective IF signals are weighted with a weighting coefficient which is derived from a sum circuit of all the IF signals, and the respective IF signal, which weighting circuit includes an integrator to minimize temporal variations in the amplitude of the sum signal The sum signal forms the actual IF signal, for further processing, and demodulating to derive an audio signal Preferably, the signals from the antennas are branched, and the branch signals phase-shifted 90°, which, again, are weighted by similarly generated weighting coefficients, and the weighted, phase-shifted signals are combined in the adding or summing circuit (70) to form said eventual IF signal for demodulation

Polarization insensitive coherent lightwave detector

Abstract: A coherent lightwave demodulator is disclosed which is insensitive to the polarization state (S) of the incoming message signal. The demodulator includes a pair of optical hybrids (12,14) aligned to the polarization state of the local oscillator and a pair of optical balanced receivers (16,24). A squaring arrangement, for example a delay demodulator (30), responsive to the output from the pair of optical balanced receivers eliminates the polarization-dependent component of the message signal and allows the recovery of the message signal regardless of the polarization state of the incoming message signal.

A PSK Group Modem for Satellite Communications

Abstract: A PSK group modem which modulates and demodulates multiple PSK signals en bloc will play an important role in realizing a cost-effective satellite communications system based on the narrowband multicarrier PSK/FDMA technique. This paper briefly discusses its possible applications, and presents a developed PSK group modem including its algorithm, hardware design, and implementation. In the algorithm, filtering of respective PSK signals is effectively carried out by digital signal processing techniques applied to the digital transmultiplexer. Furthermore, in order to compensate for the difference between the operation timing of the PSK group modem and the symbol timing of each input/output data signal, digital signal processings based on a table-look-up method using ROM and a rate-conversion filter with adaptive weighting are proposed for the modulator and demodulator, respectively. An experimental 4-phase PSK group modem has been developed, and experiments have been conducted under various conditions. The measured performance of the developed hardware is also demonstrated.