Some of the Contributions of John Costas to Communications
by Donald W. Tufts
As a result of historical development it became an axiom of communications theory and practice that bandwidth was a precious commodity and should not be “wasted” such as in the case of amplitude modulation systems which create a pair of identical side-band terms. In the early fifties the crusade to save bandwidth took special aim at the military and amateur radio services. Conversion from amplitude modulation to single
side band (SSB) modulation was strongly encouraged. One issue of the Proceedings of the IRE in those days devoted itself almost entirely to SSB and became known as the “SSB Issue.” One dissenting paper by John Costas, “Synchronous Communications,” was permitted in that issue. He argued that there were actually many potential advantages to having a pair of identical side bands, especially for military applications. He further argued that the use of additional bandwidth, if properly exploited, could provide significant benefits and that such use should not be classified out of hand as a “waste.”
In that dissenting paper Dr. Costas also described a method for receiver oscillator phase synchronization for use with suppressed-carrier AM, double-side-band (DSB) signals. This synchronization procedure has been widely copied and used world-wide in direct-sequence spread-spectrum systems and has become universally known as the “Costas Loop.” Experts in this field have often remarked that in spite of the longevity and widespread use of the “Costas Loop,” its form remains essentially unchanged from the description in the original paper.
In a later paper in the Dec. 1959 issue ofthe IRE Proceedings, “Poisson, Shannon and the Radio Amateur,” Dr. Costas expanded considerably on the potential advantages of spread-spectrum operation. This paper has become a classic in the intervening years, giving many communications engineering students their first serious exposure to a generalized view of bandwidth utilization. Some professors of electrical engineering have incorporated this paper directly into their communications theory courses. It is interesting to note in Section VII of this paper, “The Question of Channels,” that some of the advantages claimed today for CDMA usage in cell-phone service are clearly detailed in this forty-two-year-old publication. (This paper has been reprinted and appears as the lead paper of a 1992 IEEE Press Book, “Multiple Access Communications-Foundations for Emerging Technologies,” edited by Norman Abramson.)
http://www.engr.uconn.edu/~willett/uasp_booklet_2001.pdf
