Analysis and simulation of a communication system with Quadrature Phase Shift Keying(QPSK) modulation

Analysis and Simulation of a Communication System Using Quadrature Phase Shift Keying (QPSK) [Insert Student Name, ID Number, and Date of Submission] Abstract The concepts being used here for the symbols are referred to as QPSK symbols depending on the constellation diagram of the present technique which forms the treatment of the input bit sequence. A carrier signal with frequency of 1 kHz and the sampling rate of 10 kHz was used to generate the modulation signal. Keywords: QPSK, AWGN, BER, Eb/No, digital modulation. I. Introduction Digital modulation techniques have, over the past few decades, assumed the position of prominence in modern communication systems because of their preferable characteristics of noise tolerance, bandwidth utilization, and, at the same time, facilitating multiplexing. Quadrature Phase Shift Keying (QPSK) is a digital modulation technique that maps four digits per symbol; it happens to be among the most preferred modulation techniques since they are incredibly efficient in bandwidth utilization while, on the other hand, it is highly immune to noise. For this reason, QPSK doubles the efficiency of Binary Phase Shift Keying (BPSK) regarding the spectral density.[For its turn, Quadrature Phase Shift Keying (QPSK), in addition to being characterized as having high tolerance to noises, is recognized for doubling the bandwidth efficiency of BPSK, making of it as especially appropriate for wireless, satellite and broadband applications [1].] This work evaluates and simulates the QPSK-modulated communication system over an AWGN channel. The specific objectives include: 1. Modulating the QPSK signal in the transmitter and receiving the modulated signal in the receiver is simulated, and the time-frequency analysis is plotted. 2. Comparing the BER of QPSK for varying Eb/N0 in an AWGN channel. 3. To evaluate the accuracy of the simulated system and noise immunity, compare the obtained BER results with the expected theoretical values for the binary communication system. This work deals with QPSK communication system with a data rate of 4.8 kbps without considering pulse shaping. In keeping this specific configuration, this evaluation helps to provide insight on the system’s performance at its standard in different levels of noise interference. This performance of QPSK is also expressed in the results obtained; it is a two bits per symbol scheme that optimizes the use of bandwidth in case of interference. Various simulations performed in AWGN surroundings are used to illustrate the behavior of QPSK in different noise conditions. Due to these facts, QPSK is ideal for practical communication system requirements in where it is imperative to provide reliable data over a constrained environment which includes; wireless, satellite and broadband networks [3]. II. System Description Figure 1: Block Diagram of QPSK This block diagram is a representation of the number of distinct phases that are involved in the operation in the QPSK Communication System. Every box describes a procedure (e.g., Bit Generation, QPSK Modulation, AWGN Channel, etc.), and lines indicate the data transport. The diagram covers allankein steps of the system's functioning to facilitate a relatively easy comprehension. A. QPSK Modulation QPSK is a digital modulating technique in which two bits of data are inserted in a single symbol by varying phases of the carrier signal. The modulation process assumes division of the phase plane into four regions, and symbol states = four symbols. Each state is a binary input with two possibilities – 0 or 1, which is input in binary form. The two bits are added, thus have (00, 01, 10, 11). It is possible to define the general expression for the QPSK signal and indicate that it can be represented in the form of below: Here A is the carrier amplitude, FC is the carrier frequency and last but not the least, φ is the phase out of symbol m [4]. This is achieved while using less bandwidth and keeping the envelope constant, the technique is also relatively immune to nonlinearities that may be present in the communication apparatus.[The proximity of the simulated and theoretical BER curves affirms the efficiency of QPSK in AWGN and affirms its applicability in the development of efficient communication systems under the varying noise conditions.] B. Additive White Gaussian Noise (AWGN) The thermal noise is characterized in AWGN as a zero-mean Gaussian random process with a constant power spectral density and is by far the most widely used channel model in digital communication systems. It actually adds some form of noise in the transmitted signal, and the signal received is: C. BER Performance in AWGN The BER for QPSK in an AWGN channel is derived as follows: BERtheoretical = Q(√(2Eb/N0)) Q(x) is the Complementary Gaussian error function, Eb is the energy per bit, and N0 is the noise power spectral density. This equation indicates that QPSK provides better noise tolerance than propositions like Amplitude Shift Keying (ASK) and has the same spectral efficiency. III. Simulation Methodology The simulation was implemented in Matlab with the following steps: A. Signal Generation The concepts being used here for the symbols are referred to as QPSK symbols depending on the constellation diagram of the present technique which forms the treatment of the input bit sequence. A carrier signal with frequency of 1 kHz and the sampling rate of 10 kHz was used to generate the modulation signal. In this paper, QPSK modulation technique is used to represent the time-domain signal as shown in the Figure 1. Figure 1: QPSK Modulated Signal B. Frequency Domain Analysis The periodogram of a power signal was calculated to understand the spectral characteristics of the QPSK-modulated signal. The full spectrum is depicted in Figure 2 below. Figure 2: Power Signal C. AWGN Channel AWGN was added to the QPSK-modulated signal to simulate noise under various Eb/N0 conditions, ranging from 0 to 15 dB. D. BER Evaluation The noise-formed signal was then detected, and the received symbols were remapped to the actual bits sent. The BER was determined by dividing the total number of erroneously received bits by the number of total bits transmitted [5]. The performance of simulated BER has been compared with that of theoretical BER and is presented in Figure 3 below. Figure 3: BER vs.Eb/No for QSPK IV. Results and Analysis A. Time and Frequency Domain Visualization The block diagram of the QPSK-modulated signal is depicted in the following Figure 1, which demonstrates the time domain waveform of the signal. This modulated carrier waveform shows phase shifts related to the input bit pairs. In the time domain, there is fluid interconnection from one phase state to the other, and the steadiness of the envelope of QPSK is emphasized. This differential envelope character is necessary for communication systems since it often enables nonlinear amplifiers, thereby increasing power efficiency. This could result from QPSK being an orthogonal signaling system, and all the symbols shift between phase states without affecting each other. What distinguishes QPSK from other Amplitude Modulation (AM) methods wherein signal power or strength varies and which can easily undergo distortion because QPSK only features constant amplitude strength but whose phase shifts [7]. This feature also makes the QPSK more appealing for satellite and wireless communication, especially those very sensitive to the nonlinearity of amplifier distortion. The duration of the repetitive appearance of similar features in the time domain signal d...