Orthogonal frequency division multiplexing (OFDM) is an efficient multi-carrier modulation technique for wireless communication. However, one of the main drawbacks encountered in implementing it is its resultant high peakto- average power ratio (PAPR). Many techniques have been proposed in the literature to substantially decrease the peaks in the OFDM signal. The problem with these, however, is that their effects on other parameters are not always positive. These effects include a decrease in the bit error rate (BER), an increase in complexity, or a reduction in the bit rate. The objective of this paper is to describe the PAPR problem in a bid to reduce the peaks in the OFDM signal. The paper proposes a classification, performance evaluation and optimization of PAPR reduction techniques for commercial, public safety and tactical applications. In the taxonomy proposed herein, we also include a new category, namely, hybrid techniques. Furthermore, we compare the principal characteristics through a complementary cumulative distribution function (CCDF) and BER evaluation, and conclude on the importance of hybrid techniques when the goal is to both improve the BER and reduce the PAPR.

One main disadvantage of the multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system is that the signals transmitted on each antenna may experience high peak-to-average-power ratio (PAPR). We will present a new hybrid PAPR reduction technique that combines and optimizes three methods, namely convolutional code, successive suboptimal cross-antenna rotation and inversion (SS-CARI), and iterative modified companding and filtering. The results for the hybrid PAPR reduction technique show that this scheme significantly reduces the PAPR compared with SS-CARI alone; it can improve the bit error rate to levels better than what obtains with the space-time block coding MIMO-OFDM system, and the spectral splatter due to companding is also controlled by the use of frequency-domain filtering. In addition, it is a flexible technique in which the net gain can be optimized based on the requirements of scheme parameters, such as the code rate, the constraint length of the convolutional code, the number of subblocks for SS-CARI, and the companding parameters.

Orthogonal frequency division multiplexing (OFDM) is a modulation and multiplexing technique widely used in communication systems since it guarantees reliable communications on noisy wireless channels. However, OFDM implementation is a very challenging task due to the high peak-to-average power ratio (PAPR) value. In this work, a PAPR reduction technique is applied, namely clipping technique. This technique is evaluated in a real OFDM system, which is implemented in software defined radio (SDR). We present and demonstrate that is possible to increase the range and coverage through the efficient use of the transmission power when the PAPR reduction technique is applied in the SDR technology. The results show that when a clipping technique with a threshold of 60% is used, the power required is reduced in 33.75%. Additionally, the reduction percentage could be transformed into 9.58% of increase in range and 63.07% in coverage.

Coded orthogonal frequency division multiplexing (COFDM) is a popular modulation technique for wireless communication that guarantees reliable transmission of data over noisy wireless channels. However, a major disadvantage in implementing it is its resulting high peak to average power ratio (PAPR). Including forward error correction (FEC) in the orthogonal frequency division multiplexing (OFDM) system enables the avoidance of transmission errors. Nevertheless, the selected code may impact the value of PAPR. The objective of this paper is to analyze the impact of FEC on the PAPR for the COFDM system based on the autocorrelation of the signal, before the inverse fast Fourier transform (IFFT) block in the COFDM system, the evaluation of the complementary cumulative distribution function (CCDF) of PAPR, and the bit error rate (BER). The autocorrelation of the COFDM system is calculated based on a Markov Chain Model. From the results, we can reach a conclusion on the characteristics we need to consider in order to choose the codes relating to the PAPR performance in the COFDM system.

Propagation is an essential factor ensuring good coverage of wireless communications systems. Propagation models are used to predict losses in the path between transmitter and receiver nodes. They are usually defined for general conditions. Therefore, their results are not always adapted to the behavior of real signals in a specific environment. The main goal of this work is to propose a new model adjusting the loss coefficients based on empirical data, which can be applied in an indoor university campus environment. The Oneslope, Log-distance and ITU models are described to provide a mathematical base. An extensive measurement campaign is performed based on a strict methodology considering different cases in typical indoor scenarios. New loss parameter values are defined to adjust the mathematical model to the behavior of real signals in the campus environment. The experimental results show that the model proposed offers an attenuation average error of 2.5% with respect to the losses measured. In addition, comparison of the proposed model with existing solutions shows that it decreases the average error significantly for all scenarios under evaluation.