Even in noiseless optical channels one must take into account the fact that the time resolution available is finite. An optimization scheme under the constraint of a given information rate (in nats/second) and minimum time-slot resolution is presented. It is shown that system efficiencies in excess of tens of nats/phonon will be extremely difficult to achieve due to fundamental time resolution limitations.

In a low-noise environment, a simple inversion circuit can be used for quick-look decoding of a convolutional code. The bit error performance of the raw inversion circuit is improved by a simple pattern-recognition technique operating on the syndrome stream, which is also used to acquire node sync.

The combination of a bandpass limiter and an nthpower tracking loop is considered. It is shown that the performance of the combination does not depend on the form of the nonlinear function used to create the nthharmonic signal as long as some energy in that zone is produced. Furthermore, the order in which the limiter andnpower nonlinearity occur is unimportant so that the results apply equally well to then-phase Costas type of implementations of the nthpower loops. Closed form expressions for the signal suppression factors are obtained, and it is shown that the coherent and noncoherent SNR's out of the nthpower-limiter combination can be expressed in terms of two of these suppression factors. This latter point enables one to estimate the loop SNR of an nthpower-limited phase locked loop by simply calculating the suppression factors for nthand ((2n)^{th}) power loops. Finally,nthpower phase locked loops without limiters are compared with similar loops with limiters where it is shown that the presence of the limiter can actually enhance the output SNR at moderate to large values of input SNR.

This paper presents data and criteria to assess and guide the design of modems for coded noncoherent communication systems subject to practical system constraints of powerS, bandwidthW, noise spectral density N0, coherence time Tc, and number of orthogonal signalsM. Three basic receiver types are analyzed for the noncoherent multifrequency-shift keying (MFSK) additive white Gaussian noise channel: hard decision, unquantized (optimum), and quantized (soft decision). Channel capacity and computational cutoff rate Rcompare computed for each type and presented as functions of the predetection signal-to-noise ratioST/N_{0}and the number of orthogonal signalsM = 2TW. This relates the channel constraints of power, bandwidth, coherence time, and noise power to the optimum choice of signal durationT \leq T_{c}and signal numberM.

This article presents new tighter upper bounds on the rate of Gaussian autoregressive channels with linear feedback. The separation between the upper and lower bounds is small. We have\frac{1}{2} \ln \left( 1 + \rho \left( 1+ \sum_{k=1}^{m} \alpha_{k} x^{- k} \right)^{2} \right) \leq C_{L} \leq \frac{1}{2} \ln \left( 1+ \rho \left( 1+ \sum_{k = 1}^{m} \alpha_{k} / \sqrt{1 + \rho} \right)^{2} \right), \mbox{all \rho}, where\rho = P/N_{0}W, \alpha_{l}, \cdots, \alpha_{m}are regression coefficients,Pis power,Wis bandwidth,N_{0}is the one-sided innovation spectrum, andxis a root of the polynomial(X^{2} - 1)x^{2m} - \rho \left( x^{m} + \sum^{m}_{k=1} \alpha_{k} x^{m - k} \right)^{2} = 0.It is conjectured that the lower bound is the feedback capacity.

This paper describes a new phase-shift-keyed/phasemodulation (PSK/PM) scheme, called Interplex, which improves the performance of multichannel telemetry systems by reducing the cross-modulation loss. In the case of two-channel systems, the improvement in data power efficiency relative to a conventional system can be as much as 3 dB. A major feature of Interplex is that it can be implemented with very minor modification of existing conventional PSK/PM systems.

Although linear feedback is by itself sufficient to achieve capacity of an additive Gaussian white noise (AGWN) channel, it can not, in general, achieve the theoretical minimum mean-squared error for analog Gaussian data. This correspondence gives the necessary and sufficient conditions under which this optimum performance can be achieved.

The well-known technique of detecting binary pulses in white noise and unknown dc drift by means of a high-pass filter followed by a bit-by-bit detector is not theoretically optimum. The optimum procedure is shown to require a rank-ordering operation on the received data.

The feedback coding problem for additive noise systems, in which the noise may be colored, nonstationary, and correlated between channels, is formulated in terms of arbitrary linear operations at the transmitting and receiving points. This rather general linear formulation provides a unified approach for deriving new results, as well as previous results obtained under more restrictive assumptions, in a straightforward manner. Thus the sequential form of the optimum linear feedback code with an average power constraint on the transmitter is derived for noiseless feedback but forward noise of arbitrary covariance. It is shown explicitly that noiseless feedback increases the capacity of a channel with colored noise. The noisy feedback problem is considered and upper and lower bounds on the performance presented.