Showing papers on "Minimum-shift keying published in 1992"

Automatic classification of communication signals using higher order statistics

Abstract: A method for the automatic classification of digitally modulated communication signals is introduced. Different nonlinearities applied to the complex envelope of the signal under classification are used to exploit differences in the higher-order moment spaces of the time-discrete modulating process. These differences manifest themselves in lines in the spectrum of the transformed signal, associated with the unknown carrier frequency and baud rate. The lines are detected by the periodogram analysis. Their existence, position and amplitude constitute a robust feature for separating 2ASK, 2PSK, 4PSK, MSK and 2FSK. A complete statistical analysis of the classification performance in terms of the probability of detection and the false alarm rate is carried out and compared with simulated data. The obtained results are found to be valid for a wide range of modulation parameters. >

Linewidth requirements for optical synchronous detection systems with nonnegligible loop delay time

Abstract: The spectral spreads of quadrature-phase-shift-keying (QPSK) modulation and minimum shift keying (MSK) modulation are narrower than those of other kinds of modulation with the same bit rate. Therefore, they are attractive for systems limited by electrical bandwidth and available optical frequency. The synchronous demodulation offers better sensitivity than differential demodulation. However, the propagation delay time of the phase locked loop affects the performance of synchronous detection systems. Therefore, linewidth requirements while considering the loop delay time must be considered in designing these systems. The linewidth requirements for BPSK, QPSK, and MSK homodyne/heterodyne detection systems are obtained by applying the Pade approximation in evaluating the receivers' performance. A change in the power penalty with respect to the change in these values is also obtained. >

Differential detection via the Viterbi algorithm for offset modulation and MSK-type signals

Abstract: The differentially coherent reception of two families of constant-envelope signals, the linear offset quaternary phase shift keying and the binary partial response continuous phase modulation with index 0.5, is addressed. When the conventional (PSK-type) differentially coherent detector is used, a large performance degradation, compared with that of coherent receiver, is observed. The reason for this is the presence of an inherent intersymbol interference (ISI) in the signal and also noise enhancement and correlation introduced by the receiver filter. A differential detection strategy which compensates for ISI and avoids noise enhancement is presented. A phase estimate that takes into account the presence of the inherent ISI is derived. This phase estimate is then used in the decision metric of a coherent receiver. The resulting decision rule can be implemented using the Viterbi algorithm. Simple Viterbi receivers with good performance are obtained. Simulation results are given. >

GMSK with frequency-selective Rayleigh fading and cochannel interference

Abstract: The author derives a formula for error probability of partial-response continuous-phase modulation with differential phase detector and limiter discriminator detector in a multipath Rayleigh fading channel, taking into account frequency-selective fading, cochannel interference, Doppler frequency shift, and additive Gaussian noise while the receiver rejects a specified amount of adjacent channel interference. A formula for the error floor is also presented. Numerical results are presented for Gaussian minimum shift keying with a premodulation normalized filter bandwidth of 0.25. Under mild channel conditions and low energy-to-noise ratios, the best detector is an optimized two-bit differential detection; otherwise the best detector is the limiter discriminator detector. >

Noncoherent block demodulation of MSK with inherent and enhanced encoding

Abstract: It is shown that there is a close relation between known noncoherent minimum shift keying (MSK) demodulation structures, such as envelope and differential receivers, and schemes derived from the noncoherent maximum-likelihood block estimation (N-MLBE) principle. When the observation interval is increased, the performance of MSK with N-MLBE tends to that of binary coherently detected orthogonal binary frequency shift keying. A new demodulation strategy, reduced block noncoherent estimation (RBNE), is introduced and shown to improve the performance of noncoherent MSK, beyond that of coherently detected orthogonal FSK. When RBNE is used with MSK and the observation interval is increased, the performance approaches that of antipodal signaling. The key feature of all these structures is multisymbol noncoherent processing with exploitation of the MSK inherent coding properties induced by its phase continuity. The use of binary block codes for MSK with N-MLBE is considered. It is shown that simple binary block codes with low bandwidth expansion that exploit the inherent MSK memory can give significant gains. >

Receiving circuit for demodulating an angle modulated signal

Abstract: A receiving circuit is designed for an MSK (Minimum Shift Keying) receiver and a QPSK (Quadrature Phase Shift Keying) receiver. The circuit provides a synchronous state determining device and a control voltage sweeping device for sweeping the output of a voltage oscillator. In the asynchronous state, a switch is turned off for interrupting a reproducing phase error signal so that the output of the voltage oscillator may be swept for causing the synchronous state. Then, the sweeping operation is stopped and the switch is turned on for controlling the voltage of the voltage controlled oscillator so that the low-frequency error component is removed from the phase error signal of the demodulating circuit. This results in implementing the simply-arranged demodulating circuit which keeps the proper demodulating performance against the shifted carrier frequency without any degrade and demodulates the input signal stably if the signal has a low C/N ratio. This circuit is capable of stably demodulating an MSK signal from a broadcasting satellite or a communication satellite.

Multipath simulation models for mobile radio channels

Abstract: Several ray models with various delay profiles are analyzed to study their statistical compatibility with natural fading events and evaluated in terms of irreducible BER caused solely by the time delay spread. The results obtained from the analysis and computer simulation suggest that two-ray delay model (American Digital Cellular Standard) yields the worst-case BER performance compared to larger ray models with the same amount of RMS delay spread. For identical signal-to-ISI ratio yields lower irreducible BER. The results were obtained for coherent QPSK modulation. It is also shown that they can be readily applied for BPSK, pi /4-QPSK or GMSK. >

Modeling of intersymbol-interference in a Rayleigh fast fading channel with typical delay power profiles

Abstract: By applying a propagation model which combines Rayleigh fast fading with typical, prescribed delay power profiles, the authors analyze intersymbol interference error performance of a single-bit differential detector. A quadrature modulation with +or- pi /2 phase rotation within one symbol period, which is the case for MSK, is assumed. An analytic expression is derived for the error probability as a function of the ratio of the average energies of the relevant symbol and the preceding interfering symbols. This interference is caused by the channel time dispersion. The error probability lies between an upper and a lower bound with a margin that never exceeds 3 dB. The upper bound error probability turns out to be almost identical to the cochannel interference as calculated by the model of K. Hirade et al. (1979). Using typical delay power profiles of European propagation environments, the authors calculate error probability versus symbol duration. For bad-urban and hilly-terrain cases, in which error bursts may last for a few milliseconds, several tens to several hundreds of successive symbols will be corrupted, unless proper signal recovery measures are taken. >

On the representation of CPM signals by linear superposition of impulses in the bandpass domain

Abstract: A novel signal generation concept for continuous phase modulations (CPMs) with modulation index 1/2 based on real impulses is presented. With this concept, bandpass CPM signals can be generated directly in one step instead of the two consecutive steps, namely, the generation of the complex envelope and the modulation of the carrier by the complex envelope, which are necessary in conventional signal generators. Mathematical expressions for both the real impulses and the bandpass CPM signals are derived and a simple modulator structure is discussed. Examples for the real impulses are given. Among these are the well-known CPM schemes of minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and Gaussian minimum shift keying (GMSK). As an example, the validity of the novel signal generation concept is shown for the latter CPM scheme. >

Multifrequency minimum shift keying

Abstract: A new modulation scheme that produces a constant envelope continuous phase signal set with a compact power spectrum and power efficiency better than that of MSK is proposed. The scheme can be implemented by quadrature-carrier multiplexing of two frequency/phase modulated signals of the type NFSK/2PSK, both with the same frequency in each transmission interval, and with sinusoidal symbol shapes. The generated signal can be viewed in each transmission interval as an MSK signal at one of the N frequencies and is referred to as multifrequency minimum shift keying (MF MSK). Modulation, demodulation, and synchronization circuits are described, and the spectral properties and power efficiency on the AWGN channel are analyzed. Combining a number of attractive attributes such as constant envelope, excellent spectral properties, high power efficiency, and self-synchronization capability, the proposed modulation format lends itself to a variety of applications, one of them being the digital satellite link. >

Heterodyne detection of 310-Mb/s quadriphase-shift keying using fourth-power optical phase-locked loop

Abstract: The authors report an experimental synchronous heterodyne receiver for quadriphase-shift keying based upon a fourth-power optical phase-locked loop. The transmitter and local-oscillator sources are 1.521 mu m external-cavity semiconductor lasers, and the modulation is applied using a series combination of two traveling-wave LiNbO/sub 3/ phase modulators. In detection of 310-Mb/s quadriphase-shift keying (QPSK), a receiver sensitivity of 104 photons/b has been achieved. Using the same receiver, 155-Mb/s binary-phase shift keying (BPSK) with a sensitivity of 65 photons/b has been detected. >

Binary and multilevel offset QAM, spectrum efficient modulation schemes for personal communications

Abstract: In personal communications, especially in small cells, high capacity is needed. The modulation scheme utilized must be spectrally efficient. The performance of linear binary and quaternary offset QAM schemes is simulated in indoor cellular environment. The performance and the spectrum efficiency is compared with GMSK, a constant envelope modulation scheme. Binary offset QAM is shown to be 10-35% more spectrum efficient. A comparison is made with conventional 4 QAM. Binary offset QAM is shown to be more robust against power amplifier nonlinearities. The spectrum efficiencies of binary and quaternary offset QAM schemes are compared. Offset QAM schemes are shown to be good candidates for the third-generation mobile radio system. >

Synchronization in M-PSK modems

Abstract: It is economical for a single modem to receive multiple modulation formats. The use of binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8PSK, and 16PSK modulation is considered. The authors address a technique for achieving carrier synchronization for all four of these PSK schemes in a single modem. This is accomplished by using quadrature channel carrier recovery processing and a version of the maximum a posteriori (MAP) estimation phase detector algorithm. A model for the simulation of this tracking process is derived, and results are presented to confirm its functionality. >

Serial MSK spread-spectrum multiple-access communications

Abstract: A serial minimum-shift-keyed (MSK) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system is described and analyzed to obtain the signal-to-noise ratio. The single-channel system generates the same transmitted signals as a corresponding parallel MSK/DS/SSMA system. Hence, the transmitted signals have a constant envelope and desirable spectral properties. However, hardware is required for only one channel, and the multiple-access capability of the system compares favorably with a standard binary DS/SSMA system. >

Baseband pulse shaper for GMSK modulators

Abstract: A system provides and Q baseband analog modulation signals for use in GMSK modulation responsive to serial bits of digital data. The I baseband modulation signal is represented by I(t) = cos [2πf m ∫ g(t)dt] and the Q baseband modulation signal is represented by Q(t) = sin [2πf m ∫g(t)dt], wherein f m is the modulating frequency and g(t) is a filtered version of the serial bits of digital data. The system includes an input for receiving the serial bits of digital data, a memory including addressable memory locations for storing data representing the waveform amplitudes of the I and Q modulation baseband analog signals, and an address generator for addressing selected ones of the memory locations responsive to the serial bits of digital data. The system further includes digital to analog converters coupled to the memory for receiving the data stored at the memory locations addressed by the address generator and for converting the data to the I and Q modulation baseband analog signals.

Error floor mechanisms in indoor digital portable communications

Abstract: By analytical derivation, supported by simulation, the authors develop a closed form theory of the error floor probability of differentially detected MSK in a slowly fading Rayleigh channel with small delay spread. As the major error source they identify the phase jitter generated by group delay bursts coinciding with the frequency deviation of the modulated signal, rather than the timing jitter following the instantaneous mean delay. Such errors turn up in the fades even when the channel is short-term invariant and the receiver is stationary. For experimental verification they apply controlled delay spreads (over the air) in a DECT-like test bed. The results confirm that the error probability is, to first order, a function of the delay spread to bit-length ratio only and varies with the square of this ratio. >

Digital radio modulator

Abstract: A radio modulator/demodulator particularly suitable for TDMA mobile telephone use employs digital techniques for GMSK phase modulation. Phase numbers representative respectively of an intermediate frequency carrier and modulation symbols are combined digitally to combination phase numbers which are subjected to a single folded cosine table to produce a digital trignometric sequence of numbers for modulating the transmitter. Economy of components and memory is achieved and some of the modulator components are used in demodulation which is effected by the single look-up table used in sine and cosine mode alternately.

Error performance of differentially-detected MSK in small delay-spread Rayleigh channel

Abstract: A first order approximation is introduced for the irreducible intersymbol-interference error probability of differentially detected MSK in a Rayleigh fading channel with small delay spread. The error probability is derived from the PDF of the group delay and depends only on the normalised delay spread. DECT-like systems demand receiver synchronisation on the instantaneous mean excess delay.

Digital radio modulator/demodulator

Abstract: of EP0545546A radio modulator/demodulator particularly suitable for TDMA mobile telephone use employs digital techniques for GMSK phase modulation. Phase numbers representative respectively of an intermediate frequency carrier and modulation symbols are combined digitally to combination phase numbers which are subjected to a single folded cosine table to produce a digital trignometric sequence of numbers for modulating the transmitter. Economy of components and memory is achieved and some of the modulator components are used in demodulation which is effected by the single look-up table used in sine and cosine mode alternately.

Phase-independent continuous phase modulation for bandwidth efficient multiple-access communication

Abstract: A class of spread-spectrum multiple-access systems with continuous phase modulation is defined. The signals are unique in that the information bits and spreading chips affect the phase separately. The signal allows shaping of the lower spectral density, via the spreading phase, with little impact on receiver complexity. Receiver complexity is driven by the information phase modulation method. A specific subclass that uses a serial MSK receiver is examined. >

Differentially detected GMSK signals in CCI channels for mobile cellular telecommunication systems

Abstract: The performance of conventional and decision-feedback differential detection receivers for GMSK signals transmitted in the presence of co-channel interference (CCI) and additive white Gaussian noise (AWGN) is evaluated. For the interference, the authors adopt a model which includes N statistically independent static as well as faded CCI. Various bit error rate (BER) performance evaluation results have indicated that the receiver under investigation performs better as compared to other more conventional receiver structures. Especially significant BER improvements have been obtained for the static CCI channel. For example, it was found that with a carrier-to-interference (C/I) ratio of 14 dB, the performance of a 2-bit decision feedback differential receiver outperforms a conventional 2-bit differential detector by more than 14 dB (at a BER=10/sup -3/) For the faded CCI, the improvement is less. It was also found that for a given C/I the performance of the former would depend on the number of interferers whereas this is not the case for the latter. >

Performance improvement methods for DECT and other non-coherent GMSK systems

Abstract: A simple and low cost configuration, fourth-order premodulation Gaussian LPF (GLPF) paired with fourth-order postdiscriminator Butterworth LPF (BLPF), is demonstrated to yield robust performance in GMSK systems. Frequency drift of voltage-controlled oscillator (VCO) and IC-type mismatch will cause DC-offset during noncoherent demodulation. A DC-offset compensation technique based on the decision detection concept is investigated. By using this method, 40% and 80% of DC-offset is compensated within 0.5 dB of BER performance degradation. The use of a pseudo error monitor for DC-offset compensation is also proposed. >

A robust MSK demodulator through DSP

Abstract: A minimum shift keying or fast frequency shift keying coherent demodulating algorithm is discussed. Both carrier synchronisation and optimal symbol correlation are done within two decision switched Costas loops, each operating at one of the reference signal frequencies. Simulation shows the demodulator to be robust against phase distortion and frequency drift in the received signal. The receiver is relatively simple and well suited to a DSP or digital implementation. >

Design of switched-capacitor FIR filters with application to a low-power MFSK receiver

Abstract: Finite impulse response (FIR) switched-capacitor (SC) filters for minimum frequency-shift keying (MFSK) demodulation techniques have been developed and are discussed. The proposed filters comprise combinations of the following building blocks: sample-and-hold circuits, even-odd delay circuits, Gillingham delay circuits, recharge memory elements, Lee-Martin summer circuits, recharge summer circuits, and rotator switches. These are described in the paper. Furthermore, composite SC filter structures are derived using a morphological approach. The FIR SC filter structures are compared and evaluated with respect to the required chip area when implemented in 3 μm CMOS technology, and, by computer simulation, with regard to bit error probability when used in an MFSK receiver. It is shown that the receiver performance is independent of the FIR filter structure used. Furthermore, using the FIR filters, and for a given bit error probability, the required signal-to-noise ratio (SNR) is actually 3 dB lower than for a typical commercial MFSK receiver (e.g. an MB87002).

Comments on "GMSK with differential phase detection in the satellite mobile channel

Abstract: The error probability results shown by I. Korn (see ibid., vol.38, no.11, p.1980-6, 1990) indicate that the error floor is higher for systems with decision feedback (DF). It was concluded that DF gives a lower error probability only for smaller values of the normalized bandwidth B/sub t/T of the premodulation Gaussian filter, higher values of the ratio of powers in the direct and diffuse signal components K, and a lower range of signal-to-noise ratio. It is shown that this conclusion is not correct by theoretically analyzing the case of the land mobile channel where K=0 (or - infinity dB) and deriving a simple closed-form expression for the error probability for 1 bit differential detection with DF. It is shown that DF reduces the error probability for all values of B/sub t/T and signal-to-noise ratios. The formula derived can be easily evaluated not only for Gaussian minimum shift keying (GMSK) but for all partial-response continuous-phase-modulation (PRCPM) signals. >

MSK performance under various fading conditions in the presence of worst-case CW interference

Abstract: The author analyzes the flat-fading-channel performance of coherent MSK (minimum shift keying) matched filter demodulation in the presence of cochannel interference. It is shown that the most deleterious interference is CW (continuous wave) at center frequency. Bit error rate (BER) performance is first characterized for nonfading signal and interference typical of a terrestrial line-of-sight scenario. Subsequent analyses address fading signal vs. nonfading interference (typical of a long skywave or scintillation communication path and local interference), fading signal vs. fading interference (typical of satellite communication performance in ionospheric fading and remote interference), and nonfading signal vs. fading interference. The performance under fading-signal conditions, regardless of whether the interference is constant (short range) or fading (long range), is extremely poor; to be usable, such channels will require the use of diversity techniques. >

Rotative quadrature phase-shift keying

Abstract: A rotative quadrature phase-shift keying (RQPSK) modulation scheme is proposed. By rotating the QPSK signal constellation by pi/2, either clockwise or anticlockwise, during a symbol duration, the conventional QPSK scheme can be modified to transmit 3 bits per symbol to achieve both power and bandwidth efficiency.

GMSK with Frequency -Selective Rayleigh Fading and Cochannel Interference

Abstract: We derive a formula for error probability of par- tection (N-DPD) and limiter discriminator detection (LDD) in the presence of FSF, CCI, and ~~~~l~~ fie- quency shift in addition to additive white Gaussian noise. We take into account AC1 by limiting the bandwidth of the receiver filter. The channel model is composed Of K paths with independent Rayleigh fading. In the numer- ical we consider only GMSK and a two-path no- tation for narrowband signals, impulse responses, and random processes. Thus, tial-response continuous-phase modulation with differential phase detector and limiter discriminator detector in a multi- path Rayleigh fading channel taking into account frequency- selective fading, cochannel interference, Doppler frequency shift, and additive Gaussian noise while the receiver rejects a specified amount of adjacent channel interference. A formula for the error floor is also presented. Numerical results are pre- sented for Gaussian minimum shift keying with a premodula- conditions and low energy-to-noise ratios, the best detector is an optimized two-hit differential detection, otherwise the best detector is the limiter discriminator detector. tion normalized filter bandwidth of 0.25. Under mild channel In deriving the equations, we On the Of (16)-(18). We adopt the has real part (inphase) xr(t), imaginary part (quadrature phase) xe(t), envelope A, (t), phase 4, (t) , and its Fourier transform is X(f). If x(t) is a random process, its auto- correlation and power are: mobile radio communication through power and bandwidth-limited fading channels with nonlinear am- plifiers and adjacent channel interference (ACI), it is im- portant to select a constant envelope and spectrally-effi- I"

Performance evaluation of Rayleigh and log-normal GMSK signals in the presence of cochannel interference

Abstract: The paper presents the results of a software study of multiple cochannel interferers in a digital system, employing Gaussian minimum shift keying (GMSK) modulation with a bandwidth data rate product BbT = 0.3. The bit-error rate (BER) performance was determined in a Rayleigh and log-normal fading environment typically encountered in mobile radio systems. It has been shown that the error rate is independent of the number of interferers present when the total S/I ratio of up to 6 interferers are considered. Additional performance measures were investigated such as block-error rates, the probability, P(m,n) of having m errors in a block of length n, burst and gap-length distributions. These measures have shown that the interference causes errors to occur in a more bursty manner than Gaussian noise.

An integrated circuit for GSM mobile communications

Abstract: An integrated circuit for the Pan European GSM mobile communications system is described which performs GMSK digital modulation and front-end functions for both base and mobile stations. The circuit includes, as main functional blocks, a 10-bit D/A converter, a 13-MHz switched-capacitor interpolating filter, and a power buffer. A fully differential approach was used. The circuit has been fabricated using a 2-μm CMOS process. The chip size is 6.7×5.3 mm2. The overall circuit performance fully meets GSM specifications.