User j has a different code x(i) (t), generated as shown in Figure 11.18. As you can see in this figure, the only difference between the code (j) (t) for user j and the code x(k) (t) for user k is the phases that multiply each frequency. User j's code is drawn in the time domain in Figure 11.19. Multiple Access Schemes: Teaching Telecommunications Systems to Share x(k)(t) t=A 10(k) Figure 11.17 The user k's code x(k)(t) (drawn without the cos(wt) terms) ejact user k ejl(wc + Aw)t) jAOGi x(j)(t) ejllwc + (N-1)1w)t) @j(N-1)^0() Figure 11.18 The creation of user j's code (t) in CIMA x(j)(t) ===== Figure 11.19 (t) in the time domain (with cos(wt) not drawn) Chapter Eleven When looked at in the time domain, the only difference between the code of user k and the code of user j is that their pulses occur at different times. In that way, CIMA looks like TDMA-each user sends a pulse with a +1 or -1 on it, and these pulses are separated in time. However, one main difference is this. In TDMA, you always make sure that Equation (11.5) is satisfied; in CIMA, you start out by making sure Equation (11.5) is satisfied. When more users want to use your system, SO many that Equation (11.5) can no longer be satisfied, TDMA tells some users they cannot use the system; CIMA shifts to making sure that Equation (11.7) is satisfied instead (that is, your users shift automatically from being orthogonal to pseudo-orthogonal) and you can now handle all the new users. Not only that, but our current research is showing us that CIMA is able to offer better performance than TDMA. In a very real way, CIMA is a bridge between TDMA and CDMA, and that is a nice thing. 11.7 Conclusion This chapter is all about the "how-to" of sharing a communication channel among many users. We saw the guiding principle behind this idea, then we saw how to share time (TDMA), how to share frequencies (FDMA), and finally, in CDMA, how to share codes. We also proposed a new set of multiple access possibilities when we introduced CIMA, a brand-new multiple access syste