Jon W. Mark

Convolutional Codes and Their Performance in Communication Systems

This tutorial paper begins with an elementary presentation of the fundamental properties and structure of convolutional codes and proceeds with the development of the maximum likelihood decoder. The powerful tool of generating function analysis is demonstrated to yield for arbitrary codes both the distance properties and upper bounds on the bit error probability for communication over any memoryless channel. Previous results on code ensemble average error probabilities are also derived and extended by these techniques. Finally, practical considerations concerning finite decoding memory, metric representation, and synchronization are discussed.

Erlang Capacity of a Power Controlled CDMA System

This paper presents an approach to the evaluation of the reverse link capacity of a CDMA cellular voice system which employs power control and a variable rate vocoder based on voice activity. It is shown that the Erlang capacity of CDMA is many times that of conventional analog systems and several times that of other digital multiple access systems.

Tamed Frequency Modulation, A Novel Method to Achieve Spectrum Economy in Digital Transmission

This paper describes a new type of frequency modulation, called Tamed Frequency Modulation (TFM), for digital transmission. The desired constraint of a constant envelope signal is combined with a maximum of spectrum economy which is of great importance, particularly in radio channels. The out-of-band radiation is substantially less as compared with other known constant envelope modulation techniques. With synchronous detection, a penalty of only 1 dB in error performance is encountered as compared with four-phase modulation. The idea behind TFM is the proper control of the frequency of the transmitter oscillator, such that the phase of the modulated signal becomes a smooth function of time with correlative properties. Simple and flexible implementation schemes are described.

Performance of Combined Amplitude and PhaseModulated Communication SystemsReceived by the PGCS, June 6, 1960.

The performance of two types of digital phase-and amplitude-modulated systems is investigated for the high signal-to-noise ratio region. Approximate expressions for the probability of error and channel capacity of the more optimum of these two systems are compared with corresponding expressions for probability of error and channel capacity for a digital phase-modulated system. It is shown that the phase-and amplitude-modulated systems show a definite power advantage over the phase-only system when the information content per transmitted symbol must be greater than 3 bits. From a channel capacity standpoint, the phase-and amplitude-modulated systems make more efficient use of the channel for signal-to-noise ratios greater than 11 db. The more optimum of the two phase and amplitude systems has only a 3-db advantage over the less optimum and is considerably more difficult to instrument.

Physical and Link Layer Aspects of Communications

The Best of the Best: Fifty Years of Communications and Networking Research consists of a group of 50 papers selected as the best published by ComSoc in its various journals in the Society’s 50-year history. The editors of the collection have written an essay to introduce the papers and discuss the historical significance of the collection and how they were selected for the collection. The book divides the papers into two major categories (Communications and Networking) and groups them by decade within these major subdivisions.

Routing and Flow Control in TYMNET

TYMNET uses two mechanisms for moving data: a tree structure for supervisory control of the original network and a virtual circuit approach for everything else. Each mechanism is described. The routing and flow control is contrasted with ideal routing and flow control, and also with conventional packet-switched networks. One of the mechanisms described, the virtual circuit as implemented in TYMNET, is compared to the ideal. This mechanism avoids several inefficiencies found in other packet networks. The tree structure is shown to have several problems which increase roughly with the square of the size of the network.

Cochannel Interference Considerations in Frequency Reuse SmallCoverageArea Radio Systems

Frequency reuse small-coverage-area radio systems having hexagonal and square coverage areas are compared. Comparison is made on the basis of average signal to average interference ( ?>/ ?> ) in the corners of the areas and on the basis of the expected probability of S/I exceeding some system threshold for at least one base station that is eligible to provide service. The difference in performance between square and hexogonal systems is small, smaller than the usual uncertainties in the propagation parameters needed in the performance estimates. Results suggest that, even if the signal strength decreases as slowly as the inverse cube of the distance and the standard deviation of the large scale signal variation is as large as 10 dB, good service probabilities (on the order of 99 percent) can be provided in small-coverage-area radio systems using 30-40 channel sets.

Performance Evaluation for PhaseCoded SpreadSpectrum MultipleAccess CommunicationPart I: System Analysis

An analysis of an asynchronous phase-coded spread-spectrum multiple-access communication system is presented. The results of this analysis reveal which code parameters have the greatest impact on communication performance and provide analytical tools for use in preliminary system design. Emphasis is placed on average performance rather than worst-case performance and on code parameters which can be computed easily.

Routing Procedures in Communications Networks Part I: Random ProceduresReceived September 25, 1962. This work was supported by the U. S. Continental Army Command under Air Force Contract AF 19 (604)5200.

A study is made of possible routing procedures in military communications networks in order to evaluate these procedures in terms of future tactical requirements. In Part I this study is devoted to procedures involving random choices. In such networks each message path is essentially a random walk. Estimates of the average traverse time of each message and average traffic flow through each node are derived by statistical methods under reasonable assumptions on the operating characteristics of the network for various typical random routing procedures. This paper does not purport to present a complete system design. Many design questions, common to all network routing problems??-??response to temporary loss of links or nodes, rules for handling of message priorities, etc.??-??are not considered here. It is shown that random routing procedures are highly inefficient but extremely stable. A comparison of these theoretical results with the results of an extended computer simulation effort lends support to their reliability, discrepancies being accounted for by the simplifying nature of the statistical assumptions. It is suggested that in circumstances where the need for stability outweighs the need for efficiency, this type of network might be advantageously employed.

The SL Undersea Lightguide System

A digital optical fiber undersea cable system targeted for transatlantic service in 1988 is now under development at Bell Laboratories. The system uses single-mode fibers to carry data at a bit rate of 280 Mbits/s. Using digital speech compression techniques, a total system capacity of over 35 000 two-way voice channels can be realized. With laser transmitters at 1.3 ?>m, repeater spacings are expected to exceed 35 km. This paper discusses system parameters, repeaters, fiber and cable design, terminal equipment, and system measurements.