Forward collision resolution-a technique for random multiple-accessto the adder channel

Consider M-Choose-T communications: T users or less, out of M potential users, are chosen at random to simultaneously transmit binary data over a common channel. A method for constructing codes that achieve error-free M-Choose-T communication over the noiseless adder channel (AC), at a nominal rate of 1/T bits per channel symbol per active user, is described and an efficient decoding procedure is presented. The use of such codes is referred to as forward collision resolution (FCR), as it enables correct decoding of collided messages without retransmissions. For any given T a code is available that yields a stable throughput arbitrarily close to 1 message/slot. Furthermore, if the occurrence of collisions is made known to the transmitters, such a throughput can be maintained for arbitrary T,T⩽M as well. If such feedback is not available, and T is random, the probability of an unresolved collision is significantly smaller than the probability of a collision in an uncoded system, at comparable message-arrival and information rates     

On FM threshold extension by click noise elimination

The validity of the click noise method of S.O. Rice (1963) for describing the performance of an analog threshold-extending receiver is established within the scope of a simulated environment. The significance of the received signal envelope for enhancing the detection of clicks is examined, and it is shown that a reliable click detector must make use of signal memory. A `genie-aided' errorless click detector could lower the FM threshold by at least 6 dB. Threshold extension of 2.75 dB is observed under simulated conditions, with a realizable, clicks-cancelling receiver at a modulation index of five     

Mutual Tracking in Phase and Delay of Randomly Modulated Signals

A two-parameter tracking loop that mutually locks the phases and delays of two noise-contaminated replicas of a randomly phase-modulated signal, received via different channels, is analyzed. It is shown that, at high SNR, i.e., small tracking errors, the twoparameter loop can be considered as two uncoupled single parameter loops, provided the signals are beaten down to zero center frequency. Special emphasis is put on the delay error variance; it is found that, in general, the broadening of the phase loop bandwidth (provided for more rapid acquisition) induces larger delay-tracking errors. Also, such broadening decreases the expected time to loss of delay lock; the influence of the location of the absorbing boundaries for this problem is investigated. Quantitative results for a typical configuration are presented in Figs. 1-9.     

Design Criteria for Noncoherent Gaussian Channels with MFSK Signaling and Coding

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.     

Upper bounds on capacity for a constrained Gaussian channel

A low-pass and a bandpass additive white Gaussian noise channel with a peak-power constraint imposed on otherwise arbitrary input signals are considered. Upper bounds on the capacity of such channels are derived. They are strictly less than the capacity of the channel when the peak-power constrain is removed and replaced by the average-power constraint, for which the Gaussian inputs are optimum. This provides the answer to an often-posed question: peak-power limiting in the case of bandlimited channels does reduce capacity, whereas in infinite bandwidth channels it does not, as is well known. For an ideal low-pass filter of bandwidth B, the upper bound is Blog 0.934P/(N₀B) for P/( N₀B)≫1, where P is the peak power of the input signal and N₀/2 is the double-sided power spectral density of the additive white Gaussian noise     

Incremental frequency, amplitude and phase tracker (IFAPT) forcoherent demodulation over fast flat fading channels

The incremental frequency amplitude and phase tracker (IFAPT) is a recursive algorithm that estimates the parameters of piecewise-linear approximation to assumed continuous narrow-band signals. The parameters are amplitude, phase, and their respective slopes. The simple, recursive nature of IFAPT enables its direct interaction with recursive algorithms, such as the Viterbi and the BCJR in the APP SISO module, used for iteratively decoding concatenated codes. An augmented APP (A ²P²)-module, containing IFAPT and BCJR algorithms, is here applied to iterative decoding serial concatenated convolutional codes under Rayleigh fading conditions with diversity reception. The bit-error rate under Rayleigh fading with dual diversity reception at E _bT/N₀=6 dB and f_dT_s=10^-2 is 10^-4, where E _bT is the total mean energy per bit in both diversity branches, f_d is the Doppler frequency, and T_s the symbol time     

On dual optical detection: homodyne and transmitted-referenceheterodyne reception

The authors provide mathematical justification, using classical detection theory, for the observed superior performance of coherent dual optical detection over single-diode detection and establish a rationale for determining the intensity of the local oscillator. Viewing the dual detector as an optical channel with one input and two outputs, they show that in the limit of large local oscillator intensity, the optimal processor uses the difference of the two detector outputs, and consequently no bias subtraction needs to be carried out. Since phase is a major problem in applications of coherent optical communication, the authors propose modulation and detection formats that can possibly trade the effects of phase noise for the often less objectionable additive noise     

Limitations of the capacity of the M-user binary adder channel dueto physical considerations

The capacity of the M-user binary adder channel, subjected to various restrictions of physical nature, is investigated. The underlying propagation media considered are (i) fiber-optic, with lossless coupling and Poisson statistics, (ii) radio, under Rayleigh fading, and (iii) radio with constant amplitudes and random phases. Whereas the capacity of the unrestricted (ideal) model for the binary adder channel is known to increase without limit with the number of users, it is shown in the present paper that, for each of these cases, the total capacity is upper-bounded by a constant independent of the number of users: in case (i) by 1.7Q_T bits per channel use, where Q_T is the parameter of the Poisson process, in case (ii) by 4.33 bits per channel use, and in case (iii) by 4.27 bits per channel use     

On the Rice model of noise in FM receivers

The so-called click-and-Gaussian-noise model for the output of a limiter-discriminator receiver for frequency-modulated signals, first proposed by S.O. Rice in 1963, is reviewed. A short survey is presented of the subsequent research that it generated and of some practical applications that it motivated. A more detailed analysis of parameters encountered in the Rice model is carried out with emphasis on their pertinence to click detection. These results are applied to the understanding of the limitations and to the interpretation of the performance of several noise threshold extension techniques for analog modulations and of error reduction techniques for digital modulations that depend on click detection and elimination     

A lower bound on the cutoff rate for Gaussian channels withpeak-limited inputs

A lower bound on the cutoff rate R_O of a dispersive Gaussian channel with peak- rather than average-power-limited input is evaluated and compared to the lower bound on capacity under the same input constraints. It is assumed that the input symbols are independent and uniformly distributed. Both bounds exhibit the same behavior as a function of an appropriately defined signal-to-noise ratio (SNR), with a discrepancy of 1.68 dB to the disadvantage of R_O, at high SNRs. The lower bound on R_O is evaluated for peak- and slope-limited signals that model magnetic recording systems and is compared to the lower bound on capacity