ceivers detect errors by sending a waveform Getting It from Here to There: Modulators and Demodulators where some waveshapes are Receiver not allowed. A picture will help, picks up: SO take a look at Figure 5.12. if 1 sent There, an RZ-AMI modulator is used, and the receiver sees the Impossible: must be either if O sent waveform shown in Figure 5.12. You know from having looked at Figure 5.12 Erroneous recemption in RZ-AMI the RZ-AMI modulator that the waveform in Figure 5.12 could not be the one sent, SO the receiver can easily spot a transmission error. (4) BW compression: In most communication systems, you'd like to send your signal with as small a bandwidth as possible. Take a look at Figure 5.13(a). For every signal sent of duration T6, the BW is proportional to 1/ Tb So, consider NRZ-L and bipolar-RZ (Figure 5.13 (b), (c)). In NRZ-L, the waveform is twice as long as in bipolar-RZ, SO the bandwidth of NRZ-L is half that of bipolar-RZ. Most of the frequency components are in this range -1/Tb NRZ-L signal -2/Tb Bipolar RZ Figure 5.13 Bandwidth considerations Chapter Five (5) Inversion Insensitive: Most people don't like insensitive, but in this case, insensitive is a good thing. Sometimes, when you send your waveform across the channel, it gets turned upside-down along the way (+V becomes -V and -V becomes +V). Inversion insensitive means that even when everything is turned upside-down, the receiver can still figure out (correctly) which bit is a 0 and which is a 1. For example, NRZ-L is not inversion insensitive, because if things get turned upside-down, the waveform for bit 0 becomes the waveform for bit 1, and the receiver will make mistakes. (6) Noise immunity: This should come as no surprise-people want modulators that are relatively immune to noise on the channel. Even when the channel adds noise, it should still be easy for the receiver to tell the difference between the waveform for bit 0 and the waveform for bit 1. For example, NRZ-L is considered more noise immune than unipolar-RZ because, simply put