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This paper proposes an efficient hybrid modulation scheme for a mixed phase-shift keying and pulse-position modulation (PSK/PPM) for heterogeneous networks employing ultra-wideband impulse radio (UWB-IR). The proposed scheme can support both coherent and noncoherent reception and is compatible with the IEEE 802.15.4a standard. Conventional hybrid modulation schemes for heterogeneous networks are generally constructed with a super-orthogonal coding (SOC) technique with which coherent receivers can get an additional performance improvement by encoding the phase bits. However, with the proposed modulation scheme, a coherent receiver can achieve a performance improvement by displaying its best capability on phase detection through a simple waveform mapping scheme. The proposed scheme requires no extra hardware or power consumption for performance improvement in coherent receivers. Simulations show that the BER of the proposed scheme in a coherent receiver is increased by 2.7dB over the hybrid modulation with no combined phase coding and also comparable to the SOC-combined modulation scheme employed in the IEEEE 802.15.4a. The error performance of the proposed scheme is analyzed, and the numerical results are presented in this paper.

This paper presents a novel method for overlaying an analogue value on top of a digital signal. By adding a phase rotation and a signature sequence to a block of digitally modulated data symbols, this analogue value can be conveyed to a receiver without significant degradation to the underlying digital data. A near-ML estimator is derived which is non-data driven and hence independent of the digital data sequence. It is shown that this method of signalling a value is superior to quantising it and adding it to the digital data stream. We analyse the performance of the analogue and digital methods and also compare them using simulations.

In this paper we present two new Non Data Aided (NDA) phase detectors (PDs) for carrier synchronization Phase Locked Loops (PLLs) in M-ary Phase Shift Keying (M-PSK) receivers. The first structure is a self-normalizing modification of the M-th order nonlinearity detector. We investigate this detector theoretically in order to predict its S-curve, self-noise, squaring-loss, and phase-error variance performance. These theoretical predictions are then verified by computer simulations, and the results are contrasted with results obtained using other NDA and Decision Directed (DD) phase detectors. As those comparisons show, the proposed structure offers improved phase-error variance performance that is robust to Automatic Gain Control (AGC) circuit imperfections. Moreover, the new detector has a compact hardware structure suitable for implementation within an FPGA or ASIC. The second phase detector structure presented is an adaptive detector whose principal novelty is that it dynamically adapts the phase detector's gain to allow the PLL to perform optimally at any input Signal-to-Noise Ratio (SNR) at which it can lock. This detector is also robust vis-a-vis the AGC and has a compact hardware implementation suitable for FPGAs and ASICs.

In this paper we consider hybrid automatic repeat request transmission based on binary phase shift keying modulation. Our objective is to improve the performance of the retransmissions, keeping at the same time the complexity and the performance of the first transmission unaltered. We conclude that the so-called mapping rearrangement (MR) may considerably improve the performance if multi-dimensional modulation is applied. We evaluate the theoretical limits of bit-interleaved coded modulation with MR, verify the functioning of the practical coding scheme, and propose to improve the performance via iterative detection-decoding (BICM-ID) which brings considerable gains. In particular, for high coding rates, a 4 dB SNR gain over transmission without MR may be achieved.

In this paper, we introduce a low-complexity carrier phase estimation algorithm to be integrated into the data decoder of a turbo-coded modem employing a linear modulation. The estimator is based on a pseudo-maximum-likelihood approach and makes iterative use of soft decisions provided by the soft-in/soft-out decoders within the overall turbo-decoding scheme. In doing so, iterative decoding and carrier phase recovery go together iteration after iteration in a "soft decision-directed" mode. This allows performing reliable blind phase estimation and almost ideal coherent detection for values of the signal-to-noise ratio down to a few decibels only, and without the need to resort to narrowband phase-locked loops with large acquisition time. Performance in terms of mean estimated value, root mean-squared estimation error, and overall decoder bit-error rate as derived by simulation are also reported.

Analogous to multiple-symbol differential detection of quadrature phase-shift keying (QPSK), a multiple-bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood considerations together with the representation of differentially encoded offset QPSK as a continuous phase modulation, the proposed scheme is purported to be the most power-efficient scheme for such a modulation and detection method.

A multiple-symbol differential detector is formulated for M-ary differential phase-shift keying modulation where the channel state information is unknown to the receiver. The maximum-likelihood decision statistic is derived for the detector, and its performance is demonstrated by analysis and simulation. Under the Gaussian assumption for the aggregate interference plus noise, an exact expression for the symbol pairwise error probability is developed for M-ary differential phase-shift keying modulation over a diversity, slow-fading Rayleigh channel in the presence of an interference source. A simpler expression of the pairwise error probability is developed for the asymptotic case of large signal-to-noise ratio and small signal-to-interference ratio. It is shown that with an increasing observation interval, the performance of the differential detector over an unknown channel approaches that of optimum combining with known channel.

A fully digital and simple to implement frequency detector for use with high frequency signals is presented. The new frequency detector can detect small phase movements of much less than one cycle, even though the frequency detector is clocked at a low rate. Existing digital techniques can only detect phase movements of more than one cycle, or require clock rates much higher than the frequency of the signal. The operating limits of the new frequency detector are derived. Examples of the application of the new frequency detector are also given.

Noncoherent multiuser detection for nonlinear modulation was previously studied and the idea of phase-independent noncoherent decorrelation was introduced and three post-decorrelative detectors were obtained and analyzed. However, their implementation requires the knowledge of the signature waveforms of all the users, which may be available only for centralized implementation. In this paper, we obtain a blind adaptive noncoherent decorrelative detector for nonlinear modulation that is suitable for distributed implementation with the knowledge of only the normalized signals of the desired user and the additive noise variance. This detector is based on the stochastic approximation method and does not require the overhead of any kind of "training." Two adaptive algorithms are developed, one guided by every signal in the desired user's signal set individually, and the other by the user's entire signal space. While this paper focuses on the particular problem of blind adaptive noncoherent decorrelative detection, it addresses a more general adaptation issue, namely, that of improving the convergence properties of an adaptive scheme by effectively using all the information that is known, and adapting only to the part of the desired solution that is truly unknown. Convergence is shown in the mean squared error sense for both the fixed step-size and time-varying step-size versions of the two algorithms.

It is known that continuous phase modulation (CPM) signals can be optimally detected by using coherent demodulation followed by Viterbi decoding. However, such a receiver is generally complicated, particularly at higher numbers of states, as it requires many correlators and many reference signals in the demodulator. In this study, a much simpler receiver, which employs a soft-decision phase detector followed by a Viterbi decoder, is proposed for the detection of CPM signals. The phase detector makes a decision in favor of one of the preselected phase subregions at the end of every interval, which is then used to calculate metrics for decoding. As in optimal detection, the Viterbi decoder decodes according to the trellis structure of CPM signals. The proposed receiver is analyzed in a narrow-band Gaussian channel with 2REC, 2-h, and trellis-coded continuous-phase frequency-shift keying signals. Numerical results show that the proposed receiver performs close to optimal detection with all types of signals considered in this study. The effect of the number of subregions in the phase detector is examined.

In this letter, a new recursive structure of a decision-feedback (DF) phase-tracking receiver for continuous phase modulation (CPM) is derived. This receiver uses the previously detected symbols to continuously estimate the initial phase in the current symbol and thus makes optimum coherent detection. The theoretical and simulation analyses of the error performance are given. It is shown that the BER performance of binary continuous phase frequency-shift keying (2CPFSK) and raised cosine (2RC) with a small modulation index is very close to the ideal bound, and the BER performance of GMSK is better than any previously known noncoherent detection.

A performance characteristic of M-ary phase shift keying (MPSK) receivers is the variance of the phase error between the received and recovered signal carriers. For binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) loops utilizing integrate and dump filters and operating in the linear region, closed-form solutions for this variance exist (Hinedi and Lindsey 1989; and Yuen 1983). In this paper the variance is found by numerical methods for M>4. For verification and to investigate operation in the nonlinear region, computer simulation and hardware modeling were used (Kopp 1994).

We show that decision-feedback differential phase detection (DFDPD) is equivalent to a technique which generates a phase reference by averaging several primitive phase references. We then modify the DFDPD into a differential phase detection (DPD) technique which generates the phase reference using a simple recursive form. The proposed technique can be easily implemented and has satisfactory error performance.

A formula suitable for numerical evaluation is derived for the mean cycle slip time of a first-order loop with state-dependent spectral density of the loop noise. The formula is applied to a synchronizer with sinusoidal type limiter phase detector. The accuracy of the asymptotic expression due to Moeneclaey (1985) is evaluated. Better cycle slip performance of the considered synchronizer compared to that with multiplier phase detector is reported at the loop signal-to-noise ratio (SNR) /spl alpha/>2.

Detection for the statistically known channel (SKC) is aimed at obtaining good performance in situations where our statistical knowledge of a time-varying channel is good, and where other equalization/detection schemes are either too complex to implement, or their performance is limited due to the rapidity of channel fading, or where we are simply unable to perform channel estimation. By using a statistical characterization of the channel, we develop a new detector that performs maximum-likelihood sequence estimation (MLSE) (given the channel model) on blocks of N symbols. Both symbol-spaced and fractionally spaced samples are used, to obtain two different detectors, that are generalizations of those devised for optimal block schemes on nondispersive channels. The detector that uses fractionally spaced samples is shown to outperform the detector that uses symbol-spaced samples. The performance of both appears to approach that of the corresponding known channel (KC) detector as the block length increases. We also numerically evaluate the SKC detector performance under conditions where the channel parameters (statistics) are incorrectly estimated, and show that the fractionally spaced detector is fairly robust to modeling errors. Finally, we devise a sliding block algorithm, for use when transmitting more than N symbols.

This paper discussed four open-loop frequency acquisition techniques for suppressed-carrier BPSK signals. The techniques, which do not require accurate symbol timing nor a data preamble sequence, employ fast Fourier transforms (FFT's) on the Costas loop phase detector output to detect the Doppler frequency offset. Performance of the full-, half-, and staggered-symbol integration techniques as well as the low-pass filter technique are compared in terms of the error signal output SNR's. Then, the probability of detecting the frequency offset is computed for the special case when the frequency of the tone to be detected coincides with one of the FFT-bin center frequencies. It is shown that the performance of the integration techniques depends strongly on the symbol timing offset. On the other hand, the detection probability for the one-pole arm filter technique depends directly on the filter bandwidth. The staggered integration technique is shown to have comparable performance to the low-pass filter technique for low-to-medium symbol SNR's but the latter is superior at high symbol SNR's. >

In addition to the conventional matched filter, implementation of Gardner's (1990) frequency detector (GFD) based on the maximum-likelihood principle also involves a frequency-matched filter. the present authors give a reduced-complexity frequency detector (RCFD) derived from Gardner's detector through a simple approximation to the frequency-matched filter. They analyze its steady-state jitter properties and frequency acquisition performance and compare it to the original GFD as well as to the well-known balanced quadricorrelator. The results show that performance of the RCFD is close to that of the original GFD and that this detector significantly outperforms the balanced quadricorrelator which involves a similar hardware complexity. Another contribution of the paper is the analysis of GFD and RCFD when their outputs are computed at twice the symbol rate. >

A theory of optimum receiver design for symbol-by-symbol detection of an uncoded digital data sequence received over the Gaussian channel with unknown carrier phase is presented. Linear suppressed-carrier modulation is assumed. The work here aims at laying a conceptual foundation for optimum symbol-by-symbol detection, and rectifies existing approaches to the problem. The optimum receiver structure is obtained explicitly for an arbitrary carrier phase model, but its computational requirements are too heavy in general for any practical implementation. In one important special case, namely, the case in which the carrier phase can be treated as a constant over some K+1 symbol intervals, the optimum receiver can be approximated by a readily implementable decision-feedback structure at high SNR. Simulated error performance results are presented for this latter receiver for PSK modulations, with various carrier phase models. Since a decision-feedback receiver can encounter a "runaway", a variation of this receiver is developed which uses feedforward of tentative decisions concerning future symbols. This modified receiver does not have any "runaway" problem, and has been shown to yield good error performance via simulations. >

A digital PLL bit synchronizer with variable loop bandwidth for rapid acquisition and good tracking performance is proposed, and its performance analyzed using Markov chain techniques. Results are presented for the distributions of acquisition time and time to first bit slip in terms of state transition probabilities. For burst mode data, results for the timing error and bit error rate as a function of the preamble bit number are obtained. All results are evaluated by repeated matrix products and verified by simulation. Comparison of the variable bandwidth DPLL to a fixed bandwidth DPLL shows significantly faster acquisition for a given tracking performance. >

The effect of the signal transition variation, due to the signal transition density, data asymmetry, and sinusoidal modulation, on the performance of the data transition tracking loop (DTTL) symbol synchronizer is addressed. These factors will affect the DTTL performance, such as the clock jitter and the cycle slippage rate, and unnecessary system loss may result if the system parameters are not well selected. Given the background of C. S. Tsang and W. C. Lindsey (1986), this result can serve as an engineering design guideline for the DTTL in the context of the signal transition variation. >

Closed-form BER (bit error rate) expressions are derived for Gray-encoded QPSK (quadrature phase shift keying) and 8-PSK schemes using coherent detection in a slow Rayleigh fading narrowband channel with fading cochannel interference. Earlier work has been limited to deriving the approximate BER using the canonical Stein (1961) receiver concept. The symbol error rate (SER) for the QPSK scheme is also derived. The desired signal and the cochannel interferer are both PSK signals, modulated by different baseband pulses with identical signaling rate. >

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. >

The error performance of multiple-symbol differential detection of uncoded QPSK signals transmitted over correlated Rayleigh fading channels is studied. The optimal detector is presented, along with an exact expression for the corresponding pairwise error event probability. It is shown that multiple-symbol differential detection is a very effective strategy for eliminating the irreducible error floor associated with a conventional differential detector. In all of the cases investigated, a detector with an observation interval as small as two symbols is sufficient for this purpose. It is also found that the error performance of a multiple-symbol differential detector is not sensitive to the mismatch between the decoding metric and the channel fading statistics. >

A decision-directed, digitally implemented carrier synchronizer for channels with both frequency and phase uncertainty is presented. This combined algorithm and its derivatives are analyzed with respect to the achievable carrier acquisition time and the resulting bit error probability. For certain data rates (approximately 50 MSps or less), this algorithm can be implemented using CMOS gate array technology. As examples BPSK and QPSK modulation formats are studied herein and compared to their differentially coherent counterparts of DPSK and DQPSK. >

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. >

A variety of schemes for performing differential detection in environments characterized by frequency offset are discussed. All of the schemes involve encoding the input phase information as a second-order difference and performing an analogous second-order differential detection at the receiver. Because of the back-to-back differential detection operations at the receiver, The performance of most of the schemes is considerably degraded relative to that of first-order differential detection schemes. However, the latter are quite sensitive to frequency offset and, in many instances, cannot be used at all. It is demonstrated that via a simple enhancement of using a 2 T s (instead of T s) delay in the second stage of the encoder and first stage of the decoder, the performance degradation can be significantly reduced. This result is significant in view of the fact that it comes without any penalty in implementation complexity. >

A digital phase-locked loop (DPLL) consisting of a modified 9-gate phase detector, a frequency multiplier, and a loop filter is described. All the components are implemented in digital hardware. The Z-transform is employed to deduce the system function, and some simple properties of the DPLL are inferred by examining the mathematical model. The advantages of the proposed DPLL are: high lock-in speed, no steady-state frequency tracking error even for period ramp input signals; and ease of integration into a single chip. The use of the DPLL to realize the pitch synchronous analysis of voiced speech is reported. >

Transparent tone-in-band (TTIB) creates a spectral gap by splitting a signal into frequency bands, which are then separated by modulation. Phase locked transparent-tone-in-band (PLTTIB), in its original form, contained an unacceptably high level of self-noise in the coherent band recombination process. A performance analysis of PLTTIB with symmetric phase detection is given. Several new results are highlighted including the effect of recombination phase error on bit-error rate, the mean-square phase error, the probability density function of phase error, and the pull-in time of the phase tracker. Although the detailed results are obtained only for static channels, a qualitative assessment of the effect of fading is given. >

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems. >

An expression is derived for the error probability of M-ary frequency shift keying with a limiter-discriminator-integrator detector and a narrowband receiver filter in the satellite mobile channel. This channel contains, as special cases, the Gaussian and Rayleigh (land mobile) channels. The error probability is computed as a function of various system parameters for M=2, 4, 8 symbols and a third-order Butterworth receiver filter. >

A communication scheme based on continuous-phase modulated (CPM) signals used in conjunction with trellis-coded modulation (TCM) is considered. To keep the complexity manageable, a detection scheme based on differential detection of CPM signals is used. Methods that estimate the Doppler-induced frequency shift from the receiver signal are studied. Since differential detection transforms a frequency shift into a phase shift, the phase estimation problem is examined first. Three Doppler frequency estimation schemes that are based on open-loop structures and that are designed to achieve different ranges of Doppler frequencies that can be estimated are introduced. These estimators show different degrees of complexity and (at least for high signal-to-noise ratios) significantly different estimation errors. Their performance is compared by using a simulation approach. >

A second-order DPLL with time-varying loop gains is applied to the symbol synchronization of burst mode data signals. An algorithm to control the DPLL loop gains is derived from adaptive Kalman filtering theory. Simulation results for the variable gain DPLL compared to a fixed gain DPLL demonstrate the improved acquisition performance. >

In burst digital transmission using PSK (phase shift keying) modulation with coherent detection, the recovery of the carrier reference phase and the symbol clock is a key aspect. If all users have a common clock synchronization, symbol timing needs not to be recovered in each burst. A digital processor for carrier recovery without preambles, in the presence of frequency offset, is considered. As an example, a 2 Mb/s QPSK transmission system is considered in which E/sub b//N/sub o/=10 dB, and the burst and estimation interval length L=15. Using the algorithm described and averaging eight successive estimated frequency offsets, in order to eliminate anomalous errors, the BER (bit error rate) degradation is equal to 0.14 dB when Delta f=20 kHz. >

We propose computationally inexpensive and efficient solutions for signal activity detection of phase-shift keying (PSK) signals in additive white Gaussian noise. We consider the complex amplitude of the signal as well as the information sequence as the unknown parameters. In addition, the noise variance is assumed unknown. We derive the generalized likelihood ratio test (GLRT) and suggest a computationally efficient implementation thereof. Furthermore, we develop a new inexpensive detector for binary PSK signals, which we will refer to as the generalized energy detector. To evaluate the performance of these detectors, we attempt to derive a uniformly most powerful invariant test (UMPI) as an optimal detector. It turns out that the UMPI test exists only if the signal-to-noise ratio is known. We use this UMPI test in order to obtain an upper-bound performance for the evaluation of invariant detectors, such as the above-mentioned GLRT. Simulation results illustrate and compare the performance and the efficiency of the proposed signal activity detectors.

Hamamoto (see ibid., vol.44, no. 8, p.959-66, 1996) presented a detection technique for differential phase-shift keying (DPSK) with improved performance over conventional differential coherent detection. Leib (see ibid., vol.43, no.2/3/4, p.722-25, 1995) comments that this technique had been introduced much earlier. As correctly stated by Hamamoto the essence of the "new DPSK detection scheme" is based on a technique introduced by Leib and Pasupathy (1988). Differential coherent detection can be viewed as a scheme that uses the previous data symbol as a phase reference. The problem is that this phase reference suffers from the channel noise in very much the same way as the data symbol does and, therefore, it results in a performance degradation.

In many signal processing satellite applications, it is necessary to pack as many bit-time unsynchronized, power imbalanced digital FDM users as possible into the available bandwidth. In certain important cases the on-board demodulator (which simultaneously detects each user bit-stream individually) is not able to maintain phase reference. Phase comparison sinusoidal frequency shift keying (PCSFSK), a phase incoherent demodulation method with low adjacent-channel crosstalk properties, has been proposed as one way of meeting the requirements mentioned above. This paper describes a mathematical model and computer simulation which have been used to analyze the effects of adjacent-channel crosstalk on bit-error rates for a PCSFSK demodulator. Both the model and the simulation are flexible enough to incorporate many users of various strengths and center frequency separations and may be modified to yield results for any phase comparison MSK-type modulation. The results of this work show very close agreement between the model's prediction and the simulation. User scenarios of interest involve from two to eight users both with and without additive white Gaussian channel noise. Of particular interest is the performance of one weak user among many stronger users. A typical example involves eight users, seven of which are 20-dB stronger in power than the user whose probability of error was monitored. In this case, a bit-error rate of 10-3requires that adjacent users be separated in frequency by two times the data rate. If, however, all users are of equal strength, the minimum frequency separation need only be equal to the data rate. The above results indicate that close packing of signals is possible when incoherent detection (PCSFSK) is used, and that optimum user spacings can be determined if the relative power ratio between users is known.

Suboptimum SSB-PM envelope and phase detectors are considered and their performances above threshold are evaluated and compared. The results show a slight superiority of the phase SSB-PM over the envelope SSB-PM demodulator. Both detectors show poor performance for high index modulation. A lower bound on the MMSE of an optimum SSB-PM demodulator is computed and it is shown to be slightly higher than the corresponding bound for PM for small index modulation and that it deteriorates (becomes much larger) for high index modulation.

The tanlock modification of the phase detector characteristics of a phase-lock loop can be used to increase the linear range of operation of the S-curve of an analog loop, hence increasing the tracking and acquisition ranges without increasing the loop gain. The phase-shift-keying tanlock loop is a realization of this modification for the coherent demodulation and tracking of a PSK suppressed carrier signal. In this paper we consider the PSK-TLL loop performance in the presence of additive noise. The equivalent noise source used with the baseband model of the loop is derived. Both linear and quasi-linear approximations are considered for evaluation of the phase error variance (mean-square tracking error) of the loop. The false-lock performance of the PSK-TLL due to distortion of the digital data caused by the limited bandwidth of the arm filters is also considered. Results are obtained for both NRZ and Manchester encoded data symbols.

Synchronization of narrow-band data signals is plagued by self-noise arising from the randomness of the data stream. The disturbance can be resolved into in-phase and quadrature components with respect to the recovered carrier or clock. Only the quadrature component necessarily contributes to phase jitter of the recovered reference. Spectrum of the quadrature component, in many cases, vanishes at the reference frequency. Circuit precautions are needed to avoid cross coupling the in-phase disturbance into phase jitter.

The paper presents a description of a synchronization system suitable for among others, multi-exchange local networks. It includes mathematical formulation and analysis, hardware design, and computer simulation of network operation. The mathematical model is formulated within a framework of a specific control system design that employs digital techniques. A perstation control loop takes the form of a multiple-input PLL with an up-down counter operating as noncyclic phase comparator common to all of the incoming lines. The digital control system is mainly "single ended" mutual synchronization for which the problems of initial phase differences and effects of sampling are minimized, and the problem of "wrong-mode operation" is avoided. Central to the design is the generation of signals, denoted by "beats", upon which simple processing is performed to provide for the different subfunctions of the equipment.A combined discrete-event and continuous simulation model, based on hardware implementation of the bit-by-bit method, has been deve1oped to study the dynamic behavior of the system over long time periods. Factors such as transmission delays, delay variation, jitter, oscillator drift and various control strategies have been taken into account in the simulation.

Two algorithms are presented for optimum timing recovery in digitally implemented equalizers. The first one is a polarity-type algorithm based on the conventional minimum mean-square error criterion. A theoretical analysis is made to characterize the algorithm phase detector and evaluate its steady-state phase jitter variance. Influence of various channel and system design parameters on the algorithm performance is illustrated using phase jitter probability densities obtained by means of computer simulations. Interaction of the algorithm with decision-directed carrier recovery is also examined. It is shown that interaction with carrier recovery may considerably degrade the timing acquisition performance, and a second algorithm is then presented which eliminates this interaction. The second algorithm is based on the minimization of a modified mean-square error criterion which provides a measure of the intersymbol interference, independently of the carrier phase. Decision-directed timing and carrier recoveries are thus decoupled and the system startup period is considerably reduced. Phase detector characteristic and steady-state jitter performance of the second algorithm are evaluated by analytical means and computer simulations, as in the first algorithm.

By using a quasi-stationary approximation a closed form expression is derived for the acquisition time of a third-order swept tracking system, with an arbitrary phase-detector characteristic and with nonideal as well as with ideal integrating filter, optimized for tracking or demodulation in the absence of noise with large initial detuning (relative to the noise bandwidth). For sinusoidal phase detector with ideal or nonideal filters, exact solutions confirm theoretical predictions.

A Costas loop for tracking a BPSK signal does not acquire when the initial frequency error is comparable to the loop bandwidth. This paper describes methods for deriving control proportional to frequency error so as to improve the frequency acquisition capability by an AFC augmentation. A composite AFC/Costas loop is realized by combining the individual loops. Pull-in from a frequency error much greater than the Costas loop bandwidth is now feasible. The increase in phase error due to the AFC capability is evaluated by a linearized analysis. If the bandwidth of the AFC portion is sufficiently narrow, the degradation is negligible. Improved frequency acquisition can also be realized by a simple modification of the Costas loop to remove the low-pass filter on the quadrature phase detector channel, with negligible degradation to phase tracking.

Phase-locked loops have been used in various parts of telecommunication systems because of their wide applicability to bit synchronization and FM- and PM-demodulation, etc. Several types of digital phase-locked loops (DPLL's) have also been studied due to the increased reliability and decreased cost of integrated digital circuitry. DPLL's of the type employing binary quantized phase detection and discrete phase adjustments have been utilized for detection of a binary signal or suppression of phase jitter in data-transmission techniques. Unfortunately the width of the locking-range and the ability to suppress phase jitter are contrary to each other, and furthermore, the capacity for jitter suppression rapidly lowers as the frequency of input signal deviates from a free-running frequency of the loop. To improve these vicious properties, a DPLL employing a new type of sequential loop filter is proposed in this paper. The sequential filter controls the properties of itself asymmetrically, depending on the input and output phase distributions to keep the output phase at the center of input phase distribution. The loop performance is analyzed theoretically, experimentally, and by computer simulation in the presence of random Gaussian phase jitter. It is shown that the loop has satisfactory performance as a DPLL used for phase jitter suppression.

An open-loop technique is presented for estimating and correcting Doppler frequency shift in an M-ary differential phase-shift-keyed (MDPSK) receiver. The novelty of the scheme is based on the observation that whereas the change in phase of the received signal over a full symbol contains the sum of the data (phase) and the Doppler-induced phase shift, the same change in phase over half a symbol (within a given symbol interval) contains only the Doppler-induced phase shift. Thus, by proper processing, the latter can be estimated and removed from the former. Analytical and simulation results are given for the variance of the above estimator, and the error probability performance of the MDPSK receiver is evaluated in the presence of the Doppler correction. Next, the practical considerations associated with the application of this technique on bandlimited Nyquist channels are discussed and incorporated into the final design. It is shown that the receiver can, in the absence of timing jitter, be designed to allow combined Doppler correction and data detection with no penalty due to intersymbol interference (ISI). The effects of ISI due to timing jitter are assessed by computer simulation. >

Most practical synchronizers operating on a PAM waveform corrupted by additive noise can be analyzed by means of the theory of the phase-locked loop (PLL). In this paper, we present a class of synchronizers for which the equivalent phase detector characteristic is such that the timing instants generated by the voltage controlled clock (VCC) are unbiased with respect to the ideal sampling instants to be used in the data reconstruction path. As a consequence of this, the VCC output signal can directly activate the sampler in the data reconstruction path, without being properly delayed for bias compensation.

Two extended-range phase detectors (PDs), including the tanlock PD, are derived from the iterated extended Kalman filter. Fast converging recursion and concise initialization equations are given. Simulations of a Wiener phase process and a first-order Markov FM process show slightly reduced mean-square error near threshold and faster phase acquisition than a sinusoidal PD. >

Synchronous demodulation of Phase-shift-keyed transmissions requires the recovery of carrier and clock timing signals. Envelope detection of the 70 MHz IF signal is used to recover clock, and baseband processing is used to recover carrier for an 8 PSK digital radio with a data rate of 90 Mbits/s in the 11 GHz band. A sequential phase detector is used in a high noise application. Two versions of the carrier recovery circuit are presented. The first one employs hot carrier diode quads to form a compound Costas loop. The second one employs ECL exclusive-OR gates. Emphasis is placed on providing high performance while conserving energy, space, and manufacturing cost.

Approximate results are derived from a new expression for the mean time-to-first-slip for a first-order loop with arbitrary periodic equivalent phase detector characteristic in the presence of frequency detuning. They are accurate for loop signal-to-noise ratios greater than 3 dB or less than 0 dB. The approximations found serve to provide insight into the mean first slip time dependence on the shape of the equivalent phase detector characteristic and the frequency detuning, and dependence on loop parameters. The new expression itself is also of theoretical interest, since it allows one to explicitly express the stationary phase error probability density function and probability current in terms of the mean first slip time. This sheds further light on the interconnections between the conventional modulo-2π approach and the renewal theory approach to the Fokker-Planck method. Extensions to nonperidic equivalent phase detector characteristics are also considered.

A significant problem in phase-locked loop (PLL) timing and carrier extraction is the initial acquisition. Very narrow loop bandwidths are generally required to control phase jitter, and acquisition may depend on an extremely accurate initial VCO frequency (VCXO) or sweeping. We describe two simply implemented frequency detectors which, when added to the traditional phase detector, can effect acquisition even with very small loop bandwidths and large initial frequency offsets. The first is the quadricorrelator, previously applied to timing recovery by Bellisio, while the second is new, and called a rotational frequency detector. The latter, while limited to lower frequencies and higher signal-to-noise ratios, is suitable for many applications and can be implemented with simpler circuitry.