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Spread spectrum techniques
Published in Geoff Lewis, Communications Technology Handbook, 2013
Figure 34.4(a) indicates how the use of a phase lock loop (PLL) and three multipliers are used for BPSK and QPSK demodulation in the Costas loop. This diagram also shows how the mathematical equations develop at each stage and the effects of the low-pass filters in removing the unwanted harmonic components. The output signal ±A/2(cos φ) = ±A/2 when φ = 0 and this represents the bi-polar signal. As shown in this diagram, the Costas loop will also function as an analogue FM demodulator. The main disadvantage of this demodulator is that it does not provide an amplitude output to drive a signal present or in lock detector or a coherent AGC system within the receiver. This problem can be overcome by adding the circuit shown in Fig. 34.4(b) in parallel with the loop. The output signal A2/4[cos(0+2φ)+cos900]=A2/4[cos2φ].
C
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
where T is the transmitted symbol period and is a parameter that is known as the excess bandwidth (0 1). The case = 0 yields the ideal low-pass filter, and the case = 1 yields a filter referred to as the raised cosine filter. cosine transform a transform that consists of a set of basis functions, which are cosine functions. Usually referred to as discrete cosine transform. See discrete cosine transform. cost function a nonnegative scalar function that represents the cost incurred by an inaccurate value of the estimate. Also called penalty function. Costas loop a carrier synchronization loop in a digital communications receiver that uses a quadrature phase detector in place of a conventional square-law device. cotree the complement of a tree in a network.
Development of adaptive optical correction and polarization control modules for 10-km free-space coherent optical communications
Published in Journal of Modern Optics, 2020
In the experiments, heterodyne differential binary phase shift keying (DBPSK) modulation is used to modulate the carrier signals to convey the video information when the signals were transmitted by the transmitting antenna. A Costas loop (phase-locked loop) with frequency estimation was designed at the receiver to estimate the frequency of the IF signals accurately and recover the baseband signals.