ese other jammers and to reduce the jammer's effectiveness to that of the baseline broadband noise Basic Concepts and System Models (a) BROAD BAND (b) PARTIAL-BAND Figure 3.2. Noise jammer frequency distribution. jammer case. An effective anti-jam communication system is one that gives performance close to or better than the baseline performance, regardless of the type of jammer waveform used. A partial-band noise jammer, as shown in Figure 3.2(b), spreads noise of total power J evenly over some frequency range of bandwidth W, which is a subset of the total spread bandwidth Wss. We define p as the ratio p-w/s1 (3.10) which is the fraction of the total spread-spectrum band that has noise of power spectral density = N //p. (3.11) Jammer Waveforms 3.3.2 CW and Multitone Jammers A CW jammer has the form J(t) = V2J cos[wt + 0] = (3.12) while the multitone jammers using N equal power tones can be described (3.13) These are shown in the frequency domain in Figures 3.3(a) and 3.3(b). All phases are assumed to be independent and uniformly distributed over [0, 3.3.3 Pulse Jammer Pulse jamming occurs when a jammer transmits with power I peak 11 (3.14) for a fraction p of the time, and nothing for the remaining fraction 1 - p of the time. During the pulse interval, noise or tones can be transmitted while the time-averaged power is J. 3.3.4 Arbitrary Jammer Power Distributions A natural generalization of the broadband and partial-band noise jammers given above is a Gaussian noise jammer with an arbitrary power spectral density of total power J. For most cases of interest, the power spectral density (a) CW: (b) MULTITONE: Figure 3.3. Tone jammer frequency distribution. Basic Concepts and System Models that has the worst impact on the communicator has the simple partial-band form shown in Figure 3.2(b) for some corresponding worst case value of p. We illustrate this point in Part 2, Chapters 1 and 2. An exception to this occurs when the channel is non-uniform in the sense that the actual signal- to-noise ratio varies across the