etween itself and the CW tone. If this Fortunately, because the desired carrier is a CDMA image falls directly on top of a desired CDMA carrier, it signal, it will pass through a despreading circuit. This has is possible that if the chipping sequence is not orthogonal a side benefit-the decorrelation of the undesired spu- to that of the desired carrier, then the blocking signal rious term. After decorrelating, the CW signal will re- could be received instead of the desired signal. More semble white noise, as shown in the right half of the likely, however, is that the unde-sired signal will simply drawing, while the desired CDMA signal will be ren- increase the effective thermal noise. As shown in the dered as a narrowband and easily filtered and processed. right half of Figure 2.3-17, as with the CDMA2000 ex- Since the spurious signal becomes pseudorandom noise, ample, the desired signal is correlated and the undesired it adds to the effective thermal noise at a density of -174 signal is spread. If the data rate is high enough into the dBm/Hz (kT noise). Furthermore, the mobile power is despreading device, the original wideband in- allowed to increase by 3 dB during this test indicating termodulation product will become doubly spread as it is that the noise generated by the spurious signal is allowed convolved with the orthogonal despreading code. How- to equal that of the thermal noise. If it is assumed that ever, most often the over-sampling ratio into the the spurious products are generated in the ADC, then despreading function is only 2 or 4, potentially causing the noise figure may be added to the thermal noise before much of the doubly spread energy to alias back into the determining how large the spurious signal can be. band of interest, thus causing insignificant decrease in Reflecting all the spurious signal to the antenna, the ef- the spectral density of the noise. As with CDMA2000, fective thermal noise including the NF of the entire signal the mobile is allowed to increase its power by 3 dB, chain pro