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`VOLTSERVER EXHIBIT 1032
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`2
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`INTRODUCTION
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`Figure 1.1
`Some examples
`0F communi
`cations syse
`terns.
`
`_
`Wireless
`
`computers
`
` ; Wireless access
`
`point
`
`Wire—line
`network
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`merely learning the operations: of those existing systems they have studied; More impor-
`tantly, they can acquire the basic knowledge needed to design and analyze new systems never
`encountered in a textbook. To begin, it is essential to establish a typical communication sys-
`tem model as shown in Fig. 1.2. The key components of a communication system are as
`follows.
`The source originates a message. such as a human voice, a television picture, an e—mail
`message, or data. If the data is nonelectric (e.g., human voice, e-mail text, television video).
`it must be converted by an input transducer into an electric waveform referred to as the
`baseband signal or message signal through physical devices such as a microphone, a computer
`keyboard, or a CCD camera.
`The transmitter modifies the baseband signal for efficient transmission. The transmitter
`may consist of one or more subsystems: an AID converter, an encoder, and a modulator.
`Similarly, the receiver may consist of a demodulator, a decoder, and a DIA converter.
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`fl
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`4
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`INTRODUCTION
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`steady regardless of the distance from the transmitter. Thus, the signal quality is continuously
`worsening along the length of the channel. Amplification of the received signal to make up for
`the attenuation is to no avail because the noise will be amplified by the same proportion, and
`the quality remains, at best, unchanged.* These are the key challenges that we must face in
`designing modern communication systems.
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`I .2 ANALOG AND DIGITAL MESSAGES
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`Messages are digital or analog. Digital messages are ordered combinations of finite symbols or
`codewords. Forexample, printed English consists of 26 letters, 10 numbers, a space, and several
`punctuation marks. Thus, a text document written in English is a digital message constructed
`from the ASCII keyboard of [28 symbols. Human speech is also a digital message, because it is
`made up from a finite vocabulary in a language.i Music notes are also digital, even though the
`music sound itself is analog. Similarly, a Morse—Eoded telegraph message is a digital message
`constructed from a set of only two symbols—clash and dot. It is therefore a binary message.
`implying only two symbols. A digital message constructed with M symbols is called an M -ary
`message.
`
`Analog messages, on the other hand, are characterized by data whose values vary over a
`continuous range and are defined for a continuous range of time. For example. the temperature
`or the atmospheric pressure of a certain location overtime can vary over a continuous range and
`can assume an (uncountable) infinite number of possible values. A piece of music recorded by
`a pianist is also an analog signal. Similarly, a particular speech waveform has amplitudes that
`vary over acontinuous range. Over a given time interval, an infinite number of possible different
`speech waveforms exist, in contrast to only a finite number of possible digital messages.
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`I.2.I Noise Immunity oi Digi’rol Signals
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`It is no secret to even a casual observer that every time one looks at the latest electronic
`communication products, newer and better “digital technology" is replacing the old analog
`technology. Within the past decade, cellular phones have completed their transformation from
`the first~gencration analog AMPS to the current second-generation (cg, GSM, CDMA] and
`third-generation (e.g., WCDMA) digital offspring. More visibly in every household, digital
`video technology (DVD) has made the analog VHS cassette systems almost obsolete. Digital
`television continues the digital assault on analog video technology by driving out the last
`analog holdout of color television. There is every reason to ask: Why are digital technologies
`better? The answer has to do with both economics and quality. The case for economics is
`made by noting the ease of adopting versatile, powerful. and inexpensive high-speed digital
`microprocessors. But more importantly at the quality level, one prominent feature of digital
`communications is the enhanced immunity of digital signals to noise and interferences.
`Digital messages are transmitted as a finite set of electrical waveforms. In other words,
`a digital message is generated from a finite alphabet, while each character in the alphabet
`can be represented by one waveform or a sequential combination of such waveforms. For
`example,
`in sending messages via Morse code. a dash can be transmitted by an electri-
`cal pulse of amplitude A/ 2 and a dot can be transmitted by a pulse of negative amplitude
`
`* Actually. amplification may further deteriorate the signal because of additional amplifier noise.
`T Here we imply the information contained in the speech rather than its details such as the pronunciation of words
`and varying inflections. pitch. and emphasis. The speech signal from a microphone contains all these details and is
`therefore an analog signal. and its information contem is more than a thousand times greater than the information
`accessible from the wrillen text of the same speech.
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`W‘t
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`l.2 Analog ond Digital Messages
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`5
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`Figure 1.3
`[o] Transmitted
`signal.
`{bl Received
`distorted signal
`{without noise].
`[c] Received
`distorted signal
`[with noise}.
`[cl] Regeneroled
`signal ldeloyed}.
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`(C)
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`(d)
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`—A12 (Fig 1.3a). In an M ~ary case, M distinct electrical pulses (or waveforms) are used;
`each of the M pulses represents one of the M possible symbols. Once transmitted,
`the
`receivor must extract the message from a distorted and noisy signal at the channel output.
`Message extraction is often easier from digital signals than from analog signals because
`the digital decision must belong to the finitc~sized alphabet. Consider a binary case: two
`symbols are encoded as rectangular pulses of amplitudes Af2 and -—A/2. The only deci—
`sion at the receiver is to select between two possible pulses received; the fine details of
`the pulse shape are not an issue. A finite alphabet leads to noise and interference immu-
`nity. The receiver’s decision can be made with reasonable certainty even if the pulses
`have suffered modest distortion and noise (Fig. 1.3). The digital message in Fig. 1.321 is dis—
`
`needed infonnation, and even a slight distortion or interference in the waveform will show up
`in the received signal. Clearly, a digital cortununication system is more rugged than an analog
`communication system in the sense that it can better withstand noise and distortion (as long
`as they are within a limit).
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`l.2.2 Viability oliilDistortionless Regenerative Repeaters
`One main reason for the superior quality of digital systems over analog ones is the viability
`of regenerative repeaters and network nodes in the former. Repeater stations are placed along
`the communication path of a digital system at distances short enough to ensure that noise
`and distortion remain within a limit. This allows pulse detection with high accuracy. At each
`repeaterstation, or network node, the incoming pulses are detected such that new. “clean" pulses
`are retransmitted to the next repeater station or node. This process prevents the accumulation
`of noise and distortion along the path by cleaning the pulses at regular repeater intervals.
`We can thus transmit messages over longer distances with greater accuracy. There has been
`widespread application ofdistortionless regeneration by repeaters in long-haul communication
`systems and by nodes in a large (possibly heterogeneous) network.
`For analog systems. signals and noise within the same bandwidth cannot be separated.
`Repeaters in analog systems are basically filters plus amplifiers and are not “regenerative.”
`
`—- am“
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