te in bits/second. It is easily verified from (1.18) that process- ing gain and energy gain are identical when Rb = KSD/2Ts, e.g., for binary orthogonal signalling (D = 2) with no diversity (Ks = 1). Two key assumptions were made in showing that the pure SS strategy is best: (1) The channel is ideal and propagates all signals equally well, and (2) the proper performance measure is the total effective jamming energy. If either of the above assumptions is not acceptable, then the jammer's strat- egy may influence the performance measure, and the optimum diversity fac- tor Ks may be greater than one. Indeed, in later chapters it is shown that the use of bit-error rate (BER) as a performance measure implies that the opti- mum diversity factor can exceed unity. Let's summarize the requirements characteristic of a digital spread-spec- trum communication system in a jamming environment: 1. The bandwidth (or equivalently the link's signal-space dimension D) required to transmit the data in the absence of jamming is much less than the bandwidth W (or equivalently the system's signal space dimension 2TWss) available for use. 2. The receiver uses inner product operations (or their equivalent) to con- fine its operation to the link's D-dimensional signal space, to demodu- late the signal, and thereby to reject orthogonal jamming waveform components. 3. The waveforms used for communication are randomly or pseudoran- domly selected, and equally likely to be anywhere in the available band- Spread-Spectrum System Configurations and Components width (or equivalently, anywhere in the system's 2TWSS SS dimensional sig- nal space). The term pseudorandom is used specifically to mean random in appearance but reproducible by deterministic means. We will now review a sampling of the wide variety of communication sys- tem designs which possess SS characteristics. 1.3 SPREAD-SPECTRUM SYSTEM CONFIGURATIONS AND COMPONENTS A pure spread-spectrum strategy, employing only a single link at any time, can be mechanized more efficiently than the s