This paper evaluates the steady-state tracking performance of the soft DTTL symbol synchronizer which is a low SNR approximation of the hyperbolic tangent nonlinearity in the in-phase channel. The normalized s-curve, slope of the s-curve, and normalized noise density are derived and compared to the hard DTTL which is a high SNR approximation of the nonlinearity. Moreover, the symbol SNR region where the steady-state timing jitter of the soft DTTL outperforms that of the hard DTTL is determined.

When signals from a user (fixed or mobile) are received at multiple antennas, the signals can be arrayed to increase the signal-to-noise ratio (SNR) of the received signal. This article describes two maximal ratio combining techniques referred to as full spectrum combining (FSC) and complex symbol combining (CSC), and then compares them in terms of the achievable arraying gain. Although the performance of these techniques is derived for the case of binary phase shift keying (BPSK) signalling in an additive white Gaussian noise channel, the analytical techniques here are applicable to other modulations and channels. The paper also addresses the use of symbol SNR degradation and symbol SNR loss as system performance measures. It is shown that degradation and loss are equal at weak signal levels but degradation is a lower bound for loss when the signal is strong. The telemetry arraying techniques described are applicable to any phase modulated signal. We assess the deep space communication channel performance scenario where the weakest signals ever are detected.

All-digital phase locked loops (DPLLs) have many advantages over analog loops. However, due to digital device limitations and costs, superwide PLLs with front-end bandwidths as high as one gigahertz are commonly implemented using analog parts. This article presents a new architecture that allows an all-digital implementation of superwide PLLs. The problem of operating digital components at high speed is avoided here (without reducing the front-end bandwidths) by inserting a multirate digital filter bank in front of the DPLL. The new design is shown to have steady-state and transient performance that is identical to a conventional DPLL.

Practical M-FSK systems experience a combination of time and frequency offsets (errors). This paper assesses the deleterious effect of these offsets, first individually and then combined, on the average bit error probability performance of the system. Exact expressions for these various error probability performances are derived and evaluated numerically for system parameters of interest. Also presented are upper bounds on average symbol error probability for the case of frequency error alone which are useful in assessing the absolute and relative performance of the system. Both continuous and discontinuous phase M-FSK cases are considered when timing error is present, the latter being much less robust to this type of offset.>

This paper describes the performance of the all digital data transition tracking loop (DTTL) with coherent and noncoherent sampling using nonlinear theory. The effects of few samples per symbol and of non-commensurate sampling and symbol rates are addressed and analyzed for perfectly square pulses as well as filtered pulses. Their impact on the probability density and variance of the phase error are quantified through computer simulations. It is shown that the performance of the all-digital DTTL approaches its analog counterpart when the sampling and symbol rates are noncommensurate (i.e., the number of samples per symbol is irrational). The phase error variance for an even number of samples per symbol is also shown to degrade compared to an odd number of samples per symbol.>

This paper presents a simple technique for the design of a phase-modulated residual carrier communications link to mitigate mutual interferences among the channels for optimum system performance. The emphasis is on two data channels which am operated simultaneously with a ranging signal. The data channels employ PCM/PM and PCM/PSK/PM modulation schemes for high and low data rate channels, respectively. The technique proposed selects the optimum (1) subcarrier frequency to reduce the interference between the two data channels, and (2) modulation indices to suppress the undesired signals in the data channels. Further, this technique also provides an optimum balance of power between the two telemetry data channels and the ranging channel. Although this technique is proposed to optimize the performance degradation for two data channels, generalizations can be made for more than two data channels. To make the generalizations easier, this paper presents an algorithm based on the proposed technique, along with numerical results demonstrating its applicability.>

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.>

Four different arraying schemes applicable to deep space communications are discussed and analyzed. These include symbol stream combining (SSC), baseband combining (BC), carrier arraying (CA) and full spectrum combining (FSC). In addition, sideband aiding (SA) is also included and compared. Moreover, combinations of these schemes are introduced and discussed such as carrier arraying with sideband aiding and baseband combining (CA/SA/BC) or carrier arraying with symbol stream combining (CA/SSC), just to name a few. Complexity versus performance is traded off throughout the paper and benefits to the reception of existing spacecraft signals are discussed.>

This work describes the breadboard advanced receiver (called ARX) that is currently being built for use in NASA's deep space network (DSN). This receiver has unique requirements in having to operate with very weak signals from deep space probes and provide high-quality telemetry and tracking data. The hybrid analog/digital receiver performs multiple functions, including carrier, subcarrier, and symbol synchronization. Tracking can be achieved for either residual, suppressed or hybrid carriers and for both sinusoidal and square wave subcarriers. System requirements are specified, and a functional description of the ARX is presented. The various digital signal processing (DSP) algorithms used are illustrated with block diagrams. Other functions, such as time tagged Doppler extraction and monitor/control, are also discussed, including acquisition algorithms and lock detection schemes.>

The performance of a QPSK (quadrature phase-shift keying) lock detector is described, taking into account the degradation due to carrier phase jitter. Such an analysis is necessary for accurate performance prediction purposes in scenarios where both the loop SNR is low and the estimation period is short. The derived formulas are applicable to several QPSK loops and are verified using computer simulations.>

The frequency and phase acquisition performance of three quadrature phase shift keying (QPSK) carrier tracking loops, the MAP estimation loop, the Costas crossover loop, and the generalized Costas loop, is described. Acquisition time and probability of acquisition as a function of both loop signal-to-noise ratio and frequency offset to loop bandwidth ratio are obtained via computer simulations for type II and III loops. It is shown that the MAP loop, which results in the smallest squaring loss for all signal-to-noise ratios, is sometimes outperformed by the other two loops in terms of acquisition time and acquisition probability.>

Previous analyses of lock detector algorithms for Costas loops have ignored the effects of the inherent correlation between samples of the phase error process. In this work, analysis and simulations are used to quantify the effects of phase correlation on lock detection for the 'square law' and 'absolute value' type detectors. Results which depict the lock detection probability as a function of loop signal-to-noise ratio for a given false alarm rate are obtained. It is shown that the square law detector experiences less degradation due to phase jitter than the absolute value detector and that the degradation in detector signal-to-noise ratio is more pronounced for squarewave than for sinewave signals.>

The tracking performance of three conventional carrier tracking loops in the presence of intersymbol interference (ISI) is analyzed. The closed-form expressions for the squaring losses of BPSK (binary phase-shift-keyed) low-SNR (signal-to-noise ratio), BPSK high-SNR, and QPSK (quaternary phase-shift-keyed) low-SNR loops are derived. ISI is shown to affect the BPSK high-SNR loop as much as the I-Q loop despite the nonlinear effect of the hard-limiter. For the QPSK carrier tracking loop, the degradation is shown to be greater due to the modulation of both components of the carrier. In this case, ISI, in addition to modifying the coefficients in the squaring loss, adds a new term not present in wideband channels. In all cases, a unity squaring loss could not be achieved because of the irreducible error due to pattern noise. This noise is only present in band-limited channels and is dependent on the data model used.>

An analysis is presented of a frequency-noncoherent, two-lag autocorrelation statistic for the wideband detection of random binary phase-shift keying (BPSK) signals in noise plus random multitone interference. It is shown that this detector is quite robust to the presence or absence of interference and its specific parameter values contrary to an energy detector. The rule assumes knowledge of the data rate and the active scenario under H/sub 0/. The purpose of the paper is to promote the real-time autocorrelation domain and its samples (lags) as a viable approach for detecting random signals in dense environments.>

Quadrature amplitude-shift keying (QASK) is often used for transmitting two digital data streams in bandwidth-constrained communication systems. Previous analyses of the tracking performance of a decision-feedback carrier tracking loop, which can be used to provide a carrier reference for a QASK signal set, have neglected the effects of the self-noise in the derivation of the loop resonance. The authors incorporate the effects of the self-noise will only result in a conservative assessment of the system's performance, contrary to what might be expected. All results obtained are in closed form and can easily be evaluated numerically for performance prediction purposes.>