Today, communication enters our daily lives in so many different ways that it is very easy to overlook the multitude of its facets. The telephones at our hands, the radios and televisions in our living rooms, the computer terminals with access to the Internet in our offices and homes, and our newspapers are all capable of providing rapid communications from every corner of the globe. Communication provides the senses for ships on the high seas,aircraft in flight, and rockets and satellites in space. Communication through a wireless telephone keeps a car driver in touch with the office or home miles away. Communication keeps a weather forecaster informed of conditions measured by a multitude of sensors.Indeed, the list of applications involving the use of communication in one way or another is almost endless.In the most fundamental of sense, communication involves implicitly the transmission of information from one point to another through a succession of processes,as described here:

1. The generation of a message signal: voice,music, picture, or computer data.

2.The description of that message signal with a certain measure of precision, by a set of symbols: electrical, aural, or visual.

3. The encoding of these symbols in a form that is suitable for transmission over a physical medium of interest.

4. The transmission of the encoded symbols to the desired destination

5. The decoding and reproduction of the original symbols.

6. The re-creation of the original message signal, with a definable degradation in quality; the degradation is caused by imperfections in the system.There are, of course, many other forms of communication that do not directly involve the human mind in real time. For example, in computer communications involving communication between two or more computers, human decisions may enter only in setting up the programs or commands for the computer, or in monitoring the results.

Irrespective of the form of communication process being considered, there are three basic elements to every communication system, namely, transmitter, channel, and receiver,as depicted in Figure 1. The transmitter is located at one point in space, the receiver is located at some other point separate from the transmitter, and the channel is the physical medium that connects them. The purpose of the transmitter is to convert the message signal produced by the source of information into a form suitable for transmission over the channel. However, as the transmitted signal propagates along the channel, it is distorted due to channel imperfections. Moreover, noise and interfering signals (originating from other sources) are added to the channel output, with the result that the received signal is a corrupted version of the transmitted signal.The receiver has the task of operating on signal so as to reconstruct a recognizable foam of the original message signal for a user.

There are two basic modes of communication:

1. Broadcasting, which involves the use of a single powerful transmitter and numerous receivers that are relatively inexpensive to build. Here information-bearing signals flow only in one direction.

2. Point-to-point communication, in which the communication process takes place over a link between a single transmitter and a receiver. In this case, there is usually a bidirectional flow of information-bearing signals, which requires the use of a transmitter and receiver at each end of the link.

The broadcasting mode of communication is exemplified by radio and television, and the ubiquitous telephone provides the means for one form of point-to-point communication.

Another example of point-to-point communication is the link between an Earth station and a robot navigating the surface of a distant planet.

All these different communication systems as well as others not mentioned here share a common feature: The underlying communication process in each and every one of them is statistical in nature. Indeed, it is for this important reason that much of this book is devoted to the statistical underpinnings of communication systems. In so doing, we develop an exposition of the fundamental issues involved in the study of different communication methodologies and thereby provide a natural forum for their comparative evaluations.

Primary communication resources

In a communication system, two primary resources are employed: transmitted power and channel bandwidth. The transmitted power is the average power of the transmitted signal The channel bandwidth is defined as the band of frequencies allocated for the transmission of the message signal. A general system design objective is to use these two resources as efficiently as possible. In most communication channels, one resource may be considered more important than the other. We may therefore classify communication channels as power limited or band limited. For example, the telephone circuit is a typical band-limited channel, whereas a space communication link or satellite channel is typically power limited.

When the spectrum of a message `signal extends down to zero or low frequencies, we define the bandwidth of the signal as that upper frequency above which the spectral content of the signal is negligible and therefore unnecessary for transmitting information. For example, the average voice spectrum extends we1T beyond 10 kHz, though most of the average power is concentrated in the range of 100 to 600 Hz, and a band from 300 to

3100 Hz gives good articulation. Accordingly, we find that telephone circuits that respond well to this latter range of frequencies give quite satisfactory commercial telephone service.

Another-important point that we have to keep in mind is the unavoidable presence of noise in a communication system. Noise refers to unwanted waves that tend to disturb the transmission and processing of message signals in a communication syste

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Today, communication enters our daily lives in so many different ways that it is very easy to overlook the multitude of its facets. The telephones at our hands, the radios and televisions in our living rooms, the computer terminals with access to the Internet in our offices and homes, and our newspapers are all capable of providing rapid communications from every corner of the globe. Communication provides the senses for ships on the high seas,aircraft in flight, and rockets and satellites in space. Communication through a wireless telephone keeps a car driver in touch with the office or home miles away. Communication keeps a weather forecaster informed of conditions measured by a multitude of sensors.Indeed, the list of applications involving the use of communication in one way or another is almost endless.In the most fundamental of sense, communication involves implicitly the transmission of information from one point to another through a succession of processes,as described here:

1. The generation of a message signal: voice,music, picture, or computer data.

2.The description of that message signal with a certain measure of precision, by a set of symbols: electrical, aural, or visual.

3. The encoding of these symbols in a form that is suitable for transmission over a physical medium of interest.

4. The transmission of the encoded symbols to the desired destination

5. The decoding and reproduction of the original symbols.

6. The re-creation of the original message signal, with a definable degradation in quality; the degradation is caused by imperfections in the system.There are, of course, many other forms of communication that do not directly involve the human mind in real time. For example, in computer communications involving communication between two or more computers, human decisions may enter only in setting up the programs or commands for the computer, or in monitoring the results.

Irrespective of the form of communication process being considered, there are three basic elements to every communication system, namely, transmitter, channel, and receiver,as depicted in Figure 1. The transmitter is located at one point in space, the receiver is located at some other point separate from the transmitter, and the channel is the physical medium that connects them. The purpose of the transmitter is to convert the message signal produced by the source of information into a form suitable for transmission over the channel. However, as the transmitted signal propagates along the channel, it is distorted due to channel imperfections. Moreover, noise and interfering signals (originating from other sources) are added to the channel output, with the result that the received signal is a corrupted version of the transmitted signal.The receiver has the task of operating on signal so as to reconstruct a recognizable foam of the original message signal for a user.

There are two basic modes of communication:

1. Broadcasting, which involves the use of a single powerful transmitter and numerous receivers that are relatively inexpensive to build. Here information-bearing signals flow only in one direction.

2. Point-to-point communication, in which the communication process takes place over a link between a single transmitter and a receiver. In this case, there is usually a bidirectional flow of information-bearing signals, which requires the use of a transmitter and receiver at each end of the link.

The broadcasting mode of communication is exemplified by radio and television, and the ubiquitous telephone provides the means for one form of point-to-point communication.

Another example of point-to-point communication is the link between an Earth station and a robot navigating the surface of a distant planet.

All these different communication systems as well as others not mentioned here share a common feature: The underlying communication process in each and every one of them is statistical in nature. Indeed, it is for this important reason that much of this book is devoted to the statistical underpinnings of communication systems. In so doing, we develop an exposition of the fundamental issues involved in the study of different communication methodologies and thereby provide a natural forum for their comparative evaluations.

Primary communication resources

In a communication system, two primary resources are employed: transmitted power and channel bandwidth. The transmitted power is the average power of the transmitted signal The channel bandwidth is defined as the band of frequencies allocated for the transmission of the message signal. A general system design objective is to use these two resources as efficiently as possible. In most communication channels, one resource may be considered more important than the other. We may therefore classify communication channels as power limited or band limited. For example, the telephone circuit is a typical band-limited channel, whereas a space communication link or satellite channel is typically power limited.

When the spectrum of a message `signal extends down to zero or low frequencies, we define the bandwidth of the signal as that upper frequency above which the spectral content of the signal is negligible and therefore unnecessary for transmitting information. For example, the average voice spectrum extends we1T beyond 10 kHz, though most of the average power is concentrated in the range of 100 to 600 Hz, and a band from 300 to

3100 Hz gives good articulation. Accordingly, we find that telephone circuits that respond well to this latter range of frequencies give quite satisfactory commercial telephone service.

Another-important point that we have to keep in mind is the unavoidable presence of noise in a communication system. Noise refers to unwanted waves that tend to disturb the transmission and processing of message signals in a communication syste

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