Bit error rate analysis of different digital modulation schemes in orthogonal frequency division multiplexing systems

This study presents the design of an orthogonal frequency division multiplexing (OFDM) system and analyses the performance of the different digital modulation techniques employed in the system. The OFDM system was modelled and different modulation schemes: M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) were employed over two different channels: additive white Gaussian noise (AWGN), and Rayleigh multipath fading channels. Bit error rate (BER) analysis was carried out for the different digital modulation schemes over the two channels, and the number of fast Fourier transform (FFT) points used during the transmission was examined. Generally, results showed that over both AWGN and Rayleigh fading channels, lower order modulation schemes perform better than the higher order schemes. This comes at the detriment of the data rate, as lower order schemes have lower data rates compared with their higher order counterparts. In addition, it was observed that the system performed better over AWGN channel than Rayleigh fading channel for all modulation schemes used. On the number of FFT points used during the transmission, findings revealed that the performance of the system is more or less not really affected by the number of FFT points employed during transmission.Key words: Digital modulation, bit error rate, orthogonal frequency division multiplexing, additive white Gaussian noise, modulation schemes, fast Fourier transform

Performance of MiMo-OFDM Systems in Rayleigh Channel

Along with the development of wireless communication makes the increasing demand for obtaining quality services and better range, bandwidth-efficient and reliable system. OFDM is a multicarrier transmission technique to overcome multipath fading, which may result in intersymbol interference (ISI). On the other hand there is the antenna system with the use of multiple antennas at the transmitter and receiver that can also be overcome multipath fading,ie Multiple Input Multiple Output (MIMO) to increase channel capacity and diversity gain. MIMO techniques used in this Final adaldah Space Time Block Code. Simulation aims to simulate and analyze the MIMO OFDM technique using space-time block code against the influence of the number of subcarriers and influence user speed in AWGN channel and Rayleigh. The simulation results based on the number of subcarriers in AWGN channel, the best performance is obtained by subcarrier number 256. With BPSK and QPSK modulation obtained BER = 6 10-4 when SNR 4 dB. Simulation based on Rayleigh channel obtained when BER = 9.7 10-5 with BPSK modulation. Based on the comparison of the greater frequency doppler given doppler frequency, resulting in BER generated even greater, because the state of the canal will be getting worse

Improved Spatial Modulation Techniques for Wireless Communications

Transmission and reception methods with multiple antennas have been demonstrated to be very useful in providing high data rates and improving reliability in wireless communications. In particular, spatial modulation (SM) has recently emerged as an attractive transmission method for multiple-antennas systems due to its better energy efficiency and lower system complexity. This thesis is concerned with developing transmission techniques to improve the spectral efficiency of SM where antenna/subcarrier index involves in conveying information bits. In the first part of the thesis, new transmission techniques are developed for SM over frequency-flat fading channels. The first proposed scheme is based on a high-rate space-time block code instead of using the classical Alamouti STBC, which helps to increase the spectral efficiency and achieve a transmit diversity order of two. A simplified maximum likelihood detection is also developed for this proposed scheme. Analysis of coding gains and simulation results demonstrate that the proposed scheme outperforms previously-proposed SM schemes at high data transmission rates. Then, a new space-shift keying (SSK) modulation scheme is proposed which requires a smaller number of transmit antennas than that required in the bi-space shift keying (BiSSK). Such a proposed SSK-based scheme is obtained by multiplexing two in-phase and quadrature generalized SSK streams and optimizing the carrier signals transmitted by the activated antennas. Performance of the proposed scheme is compared with other SSK-based schemes via minimum Euclidean distance analysis and computer simulation. The third scheme proposed in this part is an improved version of quadrature SM (QSM). The main feature of this proposed scheme is to send a second constellation symbol over the in-phase and quadrature antenna dimensions. A significant performance advantage of the proposed scheme is realized at the cost of a slight increase in the number of radio-frequency (RF) chains. Performance comparisons with the most recent SM schemes confirm the advantage of the proposed scheme. The last contribution of the first part is an optimal constellation design for QSM to minimize the average probability of error. It is shown that, the error performance of QSM not only depends on the Euclidean distances between the amplitude phase modulation (APM) symbols and the energies of APM symbols, but also on the in-phase and quadrature components of the QSM symbols. The analysis of the union bound of the average error probability reveals that at a very large number of transmit antennas, the optimal constellations for QSM converge to a quadrature phase shift keying (QPSK) constellation. Simulation results demonstrate the performance superiority of the obtained constellations over other modulation schemes. In the second part of the thesis, the applications of SM in frequency-selective fading channels are studied. First, a new transmission scheme that employs SM for each group of subcarriers in orthogonal frequency-division multiplexing (OFDM) transmission is investigated. Specifically, OFDM symbols in each group are passed through a precoder to maximize the diversity and coding gains, while SM is applied in each group to convey more information bits by antenna indices. Performance analysis and simulation results are carried out to demonstrate the superiority of the proposed scheme over a previously-proposed combination of SM and OFDM. Next, the performance of OFDM based on index modulation and a flexible version of OFDM, knows as OFDM with multiple constellations, is compared for both case of "no precoding'' and "with precoding'' of data symbols. It is shown that the precoded OFDM with multiple constellations outperforms precoded-IM based OFDM systems over frequency-selective fading channels. The last part of the thesis investigates a multiuser downlink transmission system based on in-phase and quadrature space-shift keying modulation and precoding to reduce the minimum number of transmit antennas while keeping the complexity of the receiver low. In addition to the maximum likelihood (ML) detection, the low complexity zero forcing (ZF) receiver is also studied. Theoretical upper bounds for the error probabilities of both ML and ZF receivers are obtained and corroborated with simulation results

Bit Error Rate and Signal to Noise Ratio Performance Evaluation of OFDM System with QPSK and QAM M-array Modulation Scheme in Rayleigh, Rician and AWGN Channel Using MATLAB/Simulink

The Orthogonal Frequency Division Multiplexing (OFDM) is a practical application of both amplitude and phase modulation scheme and has taking its place in Multiplexing Techniques where a number of independent message signal are at the same time transmitted over a single channel. OFDM is beneficial in transmission with high data rate and better performance. High data rates are achieved by the use of multiple carriers and performance improvement. This paper is based on the QPSK and QAM of Different Modulation order. The performance Evaluation is done using the Bit Error Rate (BER) Against the Signal to Noise Ratio (SNR) parameters which shows a low BER to High SNR.  At the end of the work, it was found out that the QPSK has more better performance in OFDM system than the QAM. QPSK has lower BER than the QAM in AWGN, Rayleigh and Rician channel. The performance of QPSK in OFDM is better than the QAM in the OFDM system. The simulation was done using MATLAB/SIMULINK. Keywords: Orthogonal Frequency Division Multiplexing, Quadrature Phase Shift Keying, Quadrature Amplitude Modulation, Bit Error Rate, Signal to Noise Ratio

Performance Analysis of BER in CDMA using Various Coding & Simulation Techniques

Wireless Communication is the most important part of our life in today’s time. CDMA system has made it more secure system to communicate within the system. CDMA system has been developed enough to improve various problems like multipath fading, interference, cross talk etc. This paper inculcated various approaches to improve BER in CDMA system with different Coding & Simulation Techniques. This also represents various advantages and limitations of different evaluation/analysis methodology used to evaluate BER