TABLE OF CONTENTS The receiver is responsible for downconverting, demodulating, decoding, and unformatting the data that is received over the link with the required sensitivity and bit error rate according to the link budget analysis of Chapter 1. The receiver provides the dynamic range to cover the expected range and power variations as well as the sensitivity for low level signals and prevent saturation from larger power inputs. In addition, the receiver detects and synchronizes the incoming signals to retrieve the data that was sent by the transmitter. The receiver section is also responsible for despreading the signal when spread spectrum signals are used.
The main function of the receiver is to take the smallest input signal, i.e., the minimum discernable signal (MDS) at the input of the receiver and amplify that signal to the minimum discernable signal at the A/D converter while maintaining a maximum possible S/N ratio (SNR). A typical block diagram of a receiver is shown in Figure 3-1. Most receivers are referred to as superheterodyne receivers which means that they use a common inter-mediate frequency (IF) and two stages to downconvert the signal to base-band, as shown in Figure 3-1.
This type of receiver is used for the following reasons:
A common IF can be used to reduce cost of parts and simplify design for different RF operating ranges.
Easy to filter image frequency since the image frequency is by two times the IF frequency.
Easy to filter...
