s can be viewed as an orthogonal code. Alternatively the entire L bit sequence of BPSK waveforms can be consid- ered to be a single M-ary waveform. The set of waveforms form M orthog- onal signals which can be demodulated coherently or non-coherently. These M-ary waveforms can be regarded as basic signals for an M-ary input mod- ulation. In some applications DS/BPSK spread-spectrum signals are con- verted to these M-ary modulations where demodulation is done non-coherently. In the next chapter we examine M-ary orthogonal signals that are non- coherently demodulated. There the orthogonal signals consist of CW carri- ers of different frequencies referred to as frequency-shift-keying (FSK) modulation. Many of the results there apply to the M-ary waveforms Coherent Direct-Sequence Systems described above which consist of orthogonal binary sequences modulated onto BPSK waveforms. 1.10 REFERENCES [1] Proceedings of the 1973 Symposium on Spread Spectrum Communications, Naval Electronics Laboratory Center, San Diego, CA, March 13-16, 1973. [2] Spread Spectrum Communications, Lecture Series No. 58, Advisory Group for Aerospace Research and Development, North Atlantic Treaty Organization, July 1973 (AD 766914). [3] R. C. Dixon, ed., Spread Spectrum Techniques, New York: IEEE Press, 1976. [4] R. C. Dixon, Spread Spectrum Systems, New York: John Wiley, 1976. [5] L. A. Gerhardt and R. C. Dixon, Special Issue on Spread Spectrum Communications, IEEE Trans. Commun., COM-25, August 1977. [6] D. J. Torrieri, Principles of Military Communication Systems, Dedham, MA: Artech House, 1981. C.E. Cook, F. W. Ellersick, L. B. Milstein, and D.L. Schilling, eds., Special Issue on Spread Spectrum Communications, IEEE Trans. Commun., COM-30, May 1982. [8] J.K. Holmes, Coherent Spread Spectrum Systems, New York: John Wiley, 1982. [9] G. C. Clark, Jr., and J. B. Cain, Error-Correction Coding for Digital Communications, New York: Plenum Press, 1981. [10] MILCOM Conference Record, 1982 IEEE Military Communications Conference, Boston, MA, October 