Phase Shift Keying (PSK)
In phase shift keying (PSK), the phase of the carrier changes in discrete levels in accordance with the input digital signal, while the amplitude of the carrier remains the same. In this chapter, the PSK modulation will be presented, along with the respec
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Phase Shift Keying (PSK)
Topics • • • • • • •
Introduction Binary Phase Shift Keying (BPSK) Modulation QPSK Modulation 8PSK Modulation 16PSK Modulation PSK spectrum and Bandwidth SSB Spectrum and Bandwidth
6.1
Introduction
In phase shift keying (PSK), the phase of the carrier changes in discrete levels in accordance with the input digital signal, while the amplitude of the carrier remains the same. This is shown in Fig. 6.1, where • m(t) is the input modulating digital signal, • C(t) is the carrier frequency, and • S(t) is the PSK-modulated carrier frequency. As shown in the figure, the digital binary signal changes the phase of the carrier on two discrete levels. This enables the receiver to extract the digital signal by demodulation. Notice that the phase of the carrier changes in accordance with the input signal, while the amplitude of the carrier does not change after modulation. However, it can be shown that the modulated carrier S(t) contains several spectral components, requiring frequency domain analysis. In the following sections, the above disciplines in PSK modulation will be presented, along with the respective spectrum and bandwidth. These materials have been augmented by diagrams and associated waveforms to make them easier for readers to grasp. © The Author(s) 2017 S. Faruque, Radio Frequency Modulation Made Easy, SpringerBriefs in Electrical and Computer Engineering, DOI 10.1007/978-3-319-41202-3_6
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6 Phase Shift Keying (PSK)
Fig. 6.1 Binary PSK (BPSK) waveforms. The phase of the carrier changes in accordance with the input digital signal. The amplitude of the carrier remains the same
6.2 6.2.1
Binary Phase Shift Keying (BPSK) BPSK Modulation
Phase shift keying (PSK) is a method of digital modulation that utilizes phase shifting of the relative phase content of the signal [1–3]. The signal to be modulated and transmitted is binary, which is encoded before modulation. This is an indispensable task in digital communications, where redundant bits are added with the raw data that enable the receiver to detect and correct bit errors, if they occur during transmission [4–16]. While there are many error-coding schemes available, we will use a simple coding technique, known as “Block Coding” to illustrate the concept. Figure 6.2 shows an encoded BPSK modulation scheme using (15, 8) block code where an 8-bit data block is formed as M-rows and N-columns (M = 4, N = 2). The product MN = k = 8 is the dimension of the information bits before coding. Next, a horizontal parity PH is appended to each row and a vertical parity PV is appended to each column. The resulting augmented dimension is given by the product (M + 1) (N + 1) = n = 15, which is then PSK modulated and transmitted row by row. The rate of this coding scheme is given by
6.2 Binary Phase Shift Keying (BPSK)
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Fig. 6.2 Binary phase shift keying (BPSK) modulation. The input encoded data block is transmitted row by row. The phase of the carrier changes in accordance with the input digital signal
Code Rate : r ¼ ðMNÞ=½ðM þ 1ÞðN þ 1
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