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Wireless Communication Systems
Published in Keshab K. Parhi, Takao Nishitani, Digital Signal Processing for Multimedia Systems, 2018
The advantages of the QPSK versions lie in a greater degree of robustness against a single strong tone interferer or DS/BPSK interferer. In the case of a DS/BPSK system the effect of one of these interferers is dependent on the carrier phase of the interferer with respect to the carrier phase of the signal of interest. In this case if the phase between the carriers of the signal and interferer is zero then depending on the power of the interferer we may have a large bit error probability. On the other hand if the phase between the same two signals is ninety degrees then the bit error probability is zero. In practice the phase between the carriers of two such signals will drift slowly depending on the offset in carrier frequencies and there will be an error pattern that is bursty with the burst length depending on the frequency offset between the two carriers. On the other hand the DS/QPSK scheme of Fig. 8.15(b) is not sensitive to the phase of the carrier of the interferer. This scheme is sometimes referred to as balanced QPSK.
From the Top Down: The Physical Layer–AM OFDM
Published in David P. Maxson, The IBOC Handbook, 2007
Like BPSK, QPSK is constructed of phase shifts, and no information is conveyed in the amplitude of the waveform. QPSK has two phase-states for In-Phase and two for Quadrature components of the signal, netting two bits per symbol. QPSK is employed on the hybrid Tertiary subcarriers riding beneath the analog signal. On the constellation diagram, the four possible data words are 90 degrees apart and share the same amplitude (See Figure 7.4). To obtain more bits per symbol, the number of phase states can be increased, and also the amplitude of the signal can be used to convey information. Without using amplitude, 16-PSK would employ 22.5-degree phase shifts on the circle in Figure 7.4. 64-PSK would employ 5.6-degree phase shifts. In the presence of noise, and with minor imperfections in obtaining a phase reference, symbols with such narrow phase resolutions would be difficult to recover reliably. Conveying information in both phase and amplitude reduces the ambiguity between adjacent states on the constellation, permitting higher-order modulation.
Unmanned Aircraft Systems (UAS) Communications
Published in R. Kurt Barnhart, Douglas M. Marshall, Eric J. Shappee, Introduction to Unmanned Aircraft Systems, 2021
The first step would be to decide the data rate required for the application we have in mind. If we are using off the shelve components, manufacturers will have the specifications about what data rates are manageable. Section 13.4.1 has general rules for establishing data rate requirements for a given application when FSK modulation is used where there were only two levels (M = 2). In other digital modulation schemes, different values of M may need to be used such as M = 2 for binary phase shift keying (BPSK) and M = 4 for quadrature phase shift keying (QPSK). Very briefly, BPSK uses the same frequency and opposite phases to modulate, while QPSK uses the same frequency with four different phases.
Signal fingerprint feature extraction and recognition method for communication satellite
Published in Connection Science, 2022
The communication mode of the current marine environment mainly relies on communication satellite terminals. Among them, the most widely used communication satellite terminal is the Iridium system. The system comprises a satellite constellation, system control station, and gateway station. Users can make voice calls worldwide through the equipped iridium satellite terminal. The satellite constellation of the Iridium system is composed of 66 low-orbit satellites operating in orbit at an altitude of 780 km, which can ensure that the Iridium satellites cover any location on the earth at any time. The iridium communication system mainly transmits the signal to the gateway station through the interstellar link, and the gateway station sends the signal to the ground telephone. This paper will simulate the iridium signal to carry out the fingerprint feature extraction and recognition experiment of communication satellite signals. The iridium star system adopts Quadrature Phase Shift Keying (QPSK) modulation method. QPSK is a digital modulation method. QPSK represents four binary combinations of 01, 00, 10, and 11 according to four initial phases. After the serial-to-parallel conversion of the data stream is performed according to the corresponding trigonometric function, it is divided into two channels, multiplied by cos and sin, respectively, and then superimposed to generate a QPSK signal. QPSK has high modulation efficiency, fast transmission rate, and strong anti-interference ability, so it is especially suitable for satellite channels with serious noise and attenuation.
Mitigation of DME interference in LDACS1-based future air-to-ground (A/G) communications
Published in Cogent Engineering, 2018
L-DACS1 supports two different ways of communication, one A/G communication and a second one for A/A communication. In our work, we mainly focus only on A/G communication. It supports the data communication and also supports the voice communication as optional. The A/G communication assumes star topology between the centralized GS and multiple aircrafts within the LDACS1 cell (i.e. operating range of GS). For the FL, the OFDM is chosen a modulation technique, whereas, in the RL, a combination of orthogonal frequency-division multiple access (OFDMA) and time-division multiple-access (TDMA) is applied. The FL and RL directions are separated by FDD. The LDACS1 and LDACS2 system parameters are depicted in Table 1 and OFDM parameters for LDACS1 are shown in TABLE 2. The large number of different combinations of modulation and coding techniques is used for modern communication system. Utilizing those, the transmission can be continuously adjusted to the channel condition, interference conditions, and user requirements. In LDACS1, the coding comprises of a Reed-Solomon (RS) code linked with a convolutional coding technique. As modulation technique, quadrature phase shift keying (QPSK) is used.
An efficient SLM technique based on chaotic biogeography-based optimization algorithm for PAPR reduction in GFDM waveform
Published in Automatika, 2023
S. Selvin Pradeep Kumar, C. Agees Kumar, R. Jemila Rose
QPSK is an important modulation scheme it allows for higher data rates and spectral efficiencies. It achieves high rate transmission without increasing the bandwidth in wireless communication systems. The PAPR0 [dB] – Pr [PAPR > PAPR0] curve of each approach is derived in Figure 5 to evaluate the PAPR reduction capability of the CBBO–SLM method with the existing procedures. As demonstrated in Figure 5, the proposed method is obviously the best performing technique for lowering the PAPR of the original signal to the lowest values.