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a wide band sequentially in time. This is accomplished by randomly hopping the carrier from

one frequency to the next. In direct sequence, the signal power is instantaneously over a wider

bandwidth. SESS is based off of direct sequence due to the ease of simulating in digital

communications, but both direct sequence and frequency hopping techniques benefit from being

able to use many different types of modulation techniques [7].

There are many different types of modulation schemes that can be used in conjunction

with spreading techniques. The three main digital modulation methods are Amplitude-shift

keying (ASK), Frequency-shift keying (FSK), and Phase-shift keying (PSK). ASK is a form of

modulation that represents digital data as variations in the amplitude of a carrier wave. The

amplitude of an analog carrier signal varies in accordance with the bit stream (modulating

signal), keeping frequency and phase constant. The level of amplitude can be used to represent

binary logic 0s and 1s.The ASK technique is also commonly used as the basic system behind

digital data transmitted over optical fiber (light pulses). In FSK digital information is transmitted

through discrete frequency changes of a carrier wave. An example of the simplest FSK would be

binary FSK (BFSK). BFSK uses a couple of discrete frequencies to transmit binary information.

Multiple frequency-shift keying (MFSK) is a more advanced form of FSK, and is used for VHF

& UHF communications (radio and over the air television). PSK conveys data by changing, or

modulating, the phase of a reference signal. Although frequency modulation and phase

modulation are very similar, in practical signals, phase modulation is often considered superior

[9]. As with any digital modulation scheme, it uses distinct signals to represent digital data. In

PSK a finite number of phases are each assigned a unique pattern of binary bits. The

demodulator determines the phase of the received signal and maps it back to the symbol it

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