Research on QPSK Carrier Synchronization Algorithm Based on Software Defined Radio (2024)

FAQs

What is carrier synchronization in QPSK? ›

In the case of QPSK carrier (phase and frequency) synchronization, implementing the loop filter as a digital P+I (proportional-plus-integrator) filter produces a second order PLL. The controlled oscillator ( Phase Accumulator ) adjusts the angle of the received QPSK signal via a complex rotation.

Carrier synchronization is one of the key technologies of digital wireless communication. As a kind of four phase shift keying modulation method, QPSK has strong anti-interference ability of the suppressed carrier, which is widely used in digital wireless communications.

Literally, QPSK stands for Quadrature Phase Shift Keying (modulation/demodulation). This is a technique of encoding (modulating) data onto a carrier wave by shifting the phase of the carrier by 90 degrees to indicate the data being modulated. This is a much more complicated topic than can be answered in this forum.

QPSK Modulator The mathematical analysis shows that QPSK S n (t)=√(2 s/T)cos(2Πfct+(2n-1)Π/4); for n=1,2,3,4 (1) This yields the four phases π/4 3π/4 5π/4 and 7π/4 as needed. This results in a two-dimensional signal space with unit basis functions.

Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal.

In QPSK modulation schemes, it is necessary to have two carrier signals of equal amplitude at frequency f_c that have a phase difference of 90 degrees (π/2 rad). A circuit that can generate two signals of equal amplitude that are 90 degrees out of phase is depicted in Fig. 9.18.

Two types of synchronization are possible- external synchronization and internal synchronization. In a real time scenario, it is important for the system to be synchronous with each other and with a common external reference time. This is called external synchronization.

There are two types of process synchronization: synchronous or periodic, also called Time-triggered (where a clock transition is the trigger to move information across a communications network) and asynchronous or aperiodic also called Event-triggered, (where specific Event signals act as the triggers to change State).

For quadrature phase-shift keying (QPSK) modulation, four different phase values of constant amplitude signal are used. Figure 3.5b displays the signal constellation for a QAM modulation.

(Quadrature Phase Shift Keying) A phase modulation technique that transmits two bits in four modulation states. See PSK, phase modulation and QAM.

What are the main features of QPSK? ›

QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol, shown in the diagram with Gray coding to minimize the bit error rate (BER) – sometimes misperceived as twice the BER of BPSK.

QPSK has one very large advantage, however, and that is its spectral efficiency. QPSK can transmit approximately 1.4 information bits/Hz of bandwidth, while BPSK can transmit only about 0.7 information bits/Hz of bandwidth.

Symbol rate or Band rate (R _s) is the transmission of the number of symbols per second. Bit rate = (symbol rate) × (number of bits per symbol) Bandwidth of BPSK = 2R _b and Bandwidth of QPSK = R.

Traditionally, QPSK waveform will be generated by multiplying sine and cosine waveforms with odd and even bits from input bit stream as shown in Fig. 1. It uses two balanced modulator each fed with carrier signals generated from local oscillator.

Carrier synchronization is required if processing at the receiver requires a coherent reference, symbol synchronization is required to know when individual symbols start/stop, and frame synchronization is often required to know when frames of data start/stop.

Synchronization is at the heart of telecom, utility, and industrial networks because it helps to enable critical functions (e.g. handovers between cell towers, timestamping of financial transactions, highly accurate monitoring of electrical grids) at distributed nodes that require a precise frequency and time reference ...

Synchronization of an OFDM signal is required to find the symbol timing and carrier frequency offset (CFO). Before demodulation of subcarriers, either from explicit training data or using cyclic prefix of the OFDM signal we can get synchronization at receiver.