The link budget provides a means to design a transceiver and to perform the necessary analysis to ensure that the design is optimal for the given set of requirements. The link budget provides a way to easily make system trade-offs and to ensure that the transceiver operates properly over the required range. Once known or specified parameters are entered, the link budget is used to solve for the unknown parameters. If there is more than one unknown parameter, then the trade-offs need to be considered. The link budget is continually reworked, including the trade-offs, to obtain the best system design for the link. Generally a spreadsheet is used for ease of changing the values of the parameters and monitoring the effects of the change.

The receiver is an important element in the transceiver design. The receiver accepts the signal in space from the transmitter and amplifies the signal to a level necessary for detection. The LNA is the main contributor to the NF of the system. The superheterodyne is the most used receiver type and provides the most versatility by being able to apply a common IF. Saturation, compression, sensitivity, DR, reduction in unwanted spurious signals, and maximization of the SNR are the main concerns in designing the receiver. Mixers perform the downconversion process using spur analysis and selecting the correct mixer for the application. Two types of DR include amplitude, which is the most common way to express DR, and frequency DR, related to the two-tone third-order intercept point. Group delay plays an important role in digital communications and careful consideration in the design will help reduce dispersion and ISI. Digital receivers perform most of the detection in data links today, and the ADC is used to translate an analog signal into the digital domain. The sooner the signal is in the digital domain, the better the receiver can optimize the detection process.

The demodulation process is an important aspect in the design of the transceiver. Proper design of the demodulation section can enhance the sensitivity and performance of data detection. Two types of demodulation can be used to despread and recover the data. The matched filter approach simply delays and correlates each delay segment of the signal to produce the demodulated output. This process includes the use of PPM to encode and decode the actual data. Another demodulation process uses a coherent sliding correlator to despread the data. This process requires alignment of the codes in the receiver, which is generally accomplished by a short acquisition code. Tracking loops, such as the early/late gate, align the code for the dispreading process. Carrier recovery loops, such as the squaring loop, Costas loop, and modified Costas loop, provide a means for the demodulator to strip off the carrier. A symbol synchronizer is required to sample the data at the proper time in the eye pattern in order to minimize the effects of ISI. Finally, receivers designed for intercepting transmissions of other transmitters use various means of detection depending on the type of phase modulation utilized.

Multipath affects the desired signal by distorting both the phase and the amplitude. This can result in a lost signal or a distortion in the TOA of the desired signal. Multipath is divided into two categories: specular and diffuse. Specular multipath generally affects the system the most, resulting in more errors. Diffuse multipath is more noise-like and is generally much lower in power. The Rayleigh criterion is used to determine if the diffuse multipath needs to be included in the analysis. The curvature of the earth can affect the analysis for very long-distance multipath. One of the ways to reduce the effects of multipath is to use leading edge tracking so that most of the multipath is ignored. Some approaches for determining multipath effects include vector analysis and power summation. Several methods of multipath mitigation were discussed, including using multiple antennas for antenna diversity.

The last few years there has been increased interest in the commercialization of the Global Navigation Satellite System (GNSS) which is often referred to as the Global Positioning System (GPS) in various applications. A GPS system uses spread spectrum signals-binary phaseshift keying (BPSK)-emitted from satellites in space for position and time determinations. Until recently, the use of GPS was essentially reserved for military use. Now there is great interest in using GPS for navigation of commercial aircraft. The U.S. Federal Aviation Administration (FAA) is looking into the possibility of using a wide area augmentation system (WAAS) to cover the whole United States with one system. There are also applications in the automotive industry, surveying, and personal and recreational uses. Due to the increase in popularity of GPS, and since it is a spread spectrum communication system using BPSK, a brief introduction is included in this text.

Broadband and home networking will shape the future, although at this time it is unknown which of the three distribution methods will be favored or if, perhaps, a combination of all three of them will be used. New standards are being reviewed as new technologies are developed and as the data rates increase. With several incoming signals to a home, such as voice, data, and video, there is a need to provide optimal distribution throughout the home to allow for easy access. Networking is becoming important on the military battlefield and JTRS and Link 16 play important roles in the interoperability of communication devices. The development of these technologies and other new technologies will provide the military with a network for all communication devices in the future.

This chapter provides the answers to the questions posed at the end of each of the previous chapters.

This appendix explains True North calculations and Phase Ambiguities.

This appendices explains the Earth's Radius Compensation for elevation angle calculation.