that when the communicators use the strat- egy described above, (1.17) is the average total effective jamming energy for any arbitrary distribution of jamming energy. This idealized situation leads one to conclude, based on (1.17), that the receiver can minimize the jammer's effectiveness energy-wise by not using diversity, i.e., by using Ks = 1. Furthermore, the multiplicity K of the orthogonal communication system complex should be made as large as pos- sible to reduce EJeff, i.e., the complex should be designed to use all of the available bandwidth. The energy-optimal communication strategy (Ks = 1) using a single one of the K available communication links, is called a pure spread-spectrum strategy. This strategy, with its accompanying threat to use A Spread-Spectrum Overview any of K orthogonal links, increases the total signal-to-jamming ratio from EE at each receiving antenna's terminals to KEE at the output of the designated receiver, and therefore qualifies as an anti-jam (AJ) modulation technique. The improvement EjEJeff in signal-to-jamming ratio will be called the energy gain EG of the signalling strategy played on the orthogonal com- munication system complex. (1.18) Hence, the energy gain for a pure SS strategy is the multiplicity factor of the complex. In this fundamental form (1.18), the energy gain is the ratio of the signal space dimension 2TWSs perceived by the jammer for potential com- munication use to the total dimension KSD of the Ks links' D-dimensional signal spaces which the receiver must observe. For a fixed T&Wss product, this definition of energy gain makes no distinction between diversity and SS strategies using the same signal space dimension KSD. The reader may rec- ognize the fact that the quantity called the multiplicity factor, or energy gain in this chapter, is sometimes referred to as the processing gain of the SS sys- tem. This nomenclature is by no means universally accepted, and we will instead identify the term processing gain PG with the ratio WSIR, where Rb is the data ra