In this paper, a significantly efficient time-domain algorithm is presented to analyze a transmission line, loaded by a nonlinear component and driven by an arbitrary modulated signal. The proposed method provides the envelope of the solution and removes the redundancy of the calculations. The efficiency of this method is achieved in two major steps. First, an unconditionally stable algorithm for the nonlinear circuit is introduced; The derived equations are generated based on the finite-difference time-domain technique and the results are confirmed by those of the Leapfrog method. As the circuit is excited by a modulated signal, decreasing the computational time by using the unconditionally stable algorithm alone, is not practical. Therefore, in the second step, a new time-domain approach is presented and utilized simultaneously, based on separating the high and low frequency behavior of the modulated signal, which enables the advantage of unconditionally stable algorithm effectively. The accuracy of the presented method is confirmed by the Leapfrog algorithm. The comparisons from the given examples indicate that almost 99.97% of the CPU time is decreased by using the proposed method.

In this study, the authors propose a low‐complexity method for symbol synchronisation in the third generation partnership project long term evolution (LTE) downlink system. The authors introduce the lowest sampling frequency of a receiver for synchronisation purposes. Using a low sampling frequency at the receiver means that the digital signal is decimated and a lower number of processing samples is needed. This results in reducing the computational complexity. It is also shown that this advantage comes at the cost of signal‐to‐noise ratio degradation and insertion of a systematic error in synchronisation that can be avoided by choosing a proper decimation factor. A thorough analysis is also conducted for all possible sampling frequencies that reduce the computational complexity of LTE cell search. To show the validity of the authors’ method, they implemented an LTE primary synchroniser in C++ using GNU Radio libraries and prepared a software‐based radio modem, tested in different conditions. Some Monte‐Carlo simulations are carried out to compare the proposed method with other low‐complexity methods. These comparisons show the suggested method is faster than available techniques in literatures.

A simple and accurate statistical model (SASM) for a high‐power amplifier (HPA) with memory in multi‐input multi‐output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is proposed. This model is statistically equivalent to the more complex generalised memory polynomial (GMP) model, which is one of the most accurate models. The HPA distortion is modelled using stationary white Gaussian noise sources that pass through finite impulse response (FIR) filters. The filter coefficients and the variance of noise sources are derived analytically from the GMP model parameters by spectral decomposition of the GMP noise power spectrum. The number of FIR filters is equal to the memory length of the GMP model. The HPA effect on the OFDM signal, considered as frequency‐dependent attenuation coefficients, is modelled using another FIR filter. These FIR filters with small lengths make the model computationally inexpensive and mathematically tractable. The main characteristics of this model are identical bit error rate (BER) and error vector magnitude of subcarriers with those in the GMP model. The proposed model is the simplest representation of a HPA with memory effects. An excellent agreement between the simulation results of the SASM and GMP model is observed. This verifies the accuracy and efficiency of the proposed method.

The interference to the primary receiver (PR) is a critical issue in the resource allocation of cognitive radio (CR) networks. For instance, the nonlinearity of the power amplifier (PA) causes nonlinear interference to the PRs. This paper studies the power allocation in cognitive radio networks by considering the nonlinear effects of the PA on the received signal-to-noise ratio (SNR) at the secondary receiver (SR) and the adjacent channel interference (ACI) to the PRs. A nonlinear PA with limited dynamic range and a lower limit on the transmit power is assumed for the secondary transmitter (ST). To control the resulting ACI from the ST to the PRs, the PA needs to be turned off in some fading blocks. To investigate the throughput, an analytical expression for the probability of data transmission between the secondary users is derived as a function of the interference temperature limits of the PRs. All analyses are performed for both peak and average ACI power constraints. Through theoretical analysis and simulation studies, maximum achievable average SNR at the SR is investigated. Moreover, the throughput degradation is studied and it is observed that the average ACI power constraints result in the better performance than the peak ones.

In this paper, the effects of nonlinear High Power Amplifier (HPA) with memory on Multi-Input Multi-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system are analyzed and a theoretical framework is proposed. The memory effects are represented by Generalized Memory Polynomial (GMP) model. Moreover, we derive an analytical formulation with infinite nonlinearity order and infinite memory length. The channel is assumed MIMO frequency selective and it is modeled as a linear dispersive channel with uniform power profile. We show that the decision variables of the nonlinearity distortion can be modeled by the complex attenuation and zero mean additive noise model. The analytical expressions for complex attenuation, mean and variance of nonlinear noise are derived and SER of MIMO-OFDM system using HPA with memory is presented. Excellent agreement between the analytical results and numerical simulations is observed that verifies the accuracy and efficiency of the proposed method.

This study presents an exact analysis of circuit non-linearity and phase noise effects on orthogonal frequency division multiplexing (OFDM) communication systems. Using an analytical approach, the degradation effects of these impairments on the performance of OFDM systems are studied. A truncated power series is used to represent the third-order non-linear behaviour of a radio frequency circuit. The phase noise is modelled with Lorentzian power density function. Then, by use of an expression for interferences and intermodulation terms, a closed-form signal-to-noise degradation relation is theoretically extracted. The analytical results are compared with simulation outcomes. The comparison shows that bit error rate of the analytical results closely matches with simulation results of the OFDM system.

The effects of phase noise on the adaptive modulation multiple-input multiple-output (MIMO) wireless system are investigated. A variable-rate variable-power adaptive modulation (AM) technique with perfect channel state information (P-CSI) at both transmitter and receiver is considered. Phase noise (PN) is modeled as a zero-mean, stationary, finite-power random process. The analytical results are extracted and the simulation studies are performed. These studies show the performance degradation of MIMO wireless systems due to phase noise effects. The degradation values are obtained based on phase noise variances in adaptive modulation MIMO systems. Moreover, the experimental studies to evaluate the accuracy of analytical and simulation results are conducted using a MIMO test bed. The excellent agreements among these results are obtained. These results can effectively be used to design and to performance study of practical MIMO wireless systems with adaptive modulation, e.g. IEEE802.16, and Wimax.