point in passing on V3, r4 , and SO on, because they just contain noise terms, and these noise terms are independent of all the other noises. And I don't see any use in passing noise to the rest of the receiver." And so, wisely, the receiver front end only provides the rest of the receiver with the parts of r that contain a signal term. In the case of 4-PSK, that is r and V2 In the case of ASK or BPSK, its easy to show that it would simply be . Building the Receiver Front End Now that the receiver front end has decided to give the rest of the receiver the part of r containing the signal terms, this section is all about building a receiver front end. There are many different ways to build a receiver front end, SO that it can do its job and do it well. The receiver front end presented here is called the correlator receiver front end. Glance at Figure 5.26, and you'll see what the correlator receiver front end looks like. Looking at Figure 5.26, you see that the incoming signal is r(t). It's well known that if you want r1, all you have to do is the integral r1 = r(t)q,(t). dt In Figure 5.26 , you can see that the receiver front end does this on its top branch. If the receiver front end also wants to provide r'n (and it will if there's a signal component in rn), then it just computes the integral rN = And that's just what the bottom branch of Figure 5.26 does. And, voila-the receiver front end. Life is good. (i+1)T (i+1)T ON(t) Figure 5.26 Correlator receiver front end Chapter Five Example 5.4 Describe the receiver front end in a BPSK receiver. Solution: Turning back the pages to section 5.3.2, you'll find that there we discovered the orthonormal basis for a BPSK signal is simply (E5.14) Now, all that the receiver front end does is map the received signal r(t) to its value along the orthonormal basis, V1. For the BPSK case, two ways of doing this are shown in Figure E5.6. 2/T cos act (i+1)T r (t) r (t) Figure E5.6 The receiver front end for BPSK-two implementations 5.4.4 The Rest of the Demodulator, Part II-The Decis