Performance evaluation of MIMO DFT-Spread WR-OFDM system for spectrum efficiency and power efficiency

Cognitive radio (CR) is considered nowadays as a strong candidate solution for the spectrum scarcity problem. On standards level, many cognitive radio standards have chosen Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) as their modulation scheme. Similar to OFDM, NC-OFDM suffers from the problem of having a high Peak to Average Power Ratio (PAPR). If not solved, either the transmitted signal will be distorted, which will cause interference to primary (licensed) users, or the effeciency of the power amplifier will be seriously degraded. The effect of the PAPR problem in NC-OFDM based cognitive radio networks is worse than normal OFDM systems. In this paper, we propose enhanced techniques to reduce the PAPR in NC-OFDM systems. We start by showing that combining two standard PAPR reduction techniques (interleaver-based and selective mapping) results in a lower PAPR than using them individually. Then, an “adaptive number of interleavers” will be proposed that achieves the same performance of conventional interleaver-based PAPR reduction while reducing the CPU time by 41.3%. Finally, adaptive joint interleaver with selective mapping is presented, and we show that it gives the same performance as conventional interleaver-based technique, with reduction in CPU time by a factor of 50.1%.

Main disadvantage of a multicarrier communication system is high peak to average power ratio (PAPR) of the transmitted signal. The high PAPR causes the performance degradation due to nonlinear distortion in the high power amplifier (HPA). PAPR value is closely depends on transmitted power and correlation properties of the user’s spreading code. High peak and low average value of the transmitted power increases the PAPR. On the other side high auto correlation function (ACF) value and low cross correlation function (CCF) value of the spreading code also increases the PAPR. But to eliminate the multiple access interference (MAI) in receiver end, ACF should be peak and CCF should be posses zero for all time shifts. So, there is a conflicting nature of PAPR and bit error rate (BER). That’s why an exhaustive effort has been made in this paper for proper distribution of transmitted power within an acceptable range of peak transmitted power and evaluates the new spreading codes using Genetic Algorithms (GA). In general, to obtain optimum PAPR reduction using GA, total searching time to find out the proper amplitude and phase parameters must be accomplished. Simulation results show that PAPR and BER performance using this proposed technique is better than conventional network.

Multicarrier modulation technique also known as Orthogonal Frequency Division Multiplexing (OFDM) is considered to be the most rapidly growing technique for 4th Generation wireless communication system. Due to its high speed data rate and its ability of multipath fading channel robustness. OFDM becomes an attractive technique and it is widely adopted in many wireless communications system. OFDM signal carries its major drawback of high Peak to Average Power Ratio (PAPR) problem. Out of band radiation and in band distortion produced due to its high PAPR. Mobile phone communication suffer severe drawback during its amplification. When OFDM employed a non linear Power Amplifier (PA), it produces the fluctuation in amplitude of OFDM signal. This paper discusses the method to overcome PAPR in terms of its performance by using improved clipping technique for PAPR reduction. This method is easy to implement and reduces the amount of PAPR by clipping the peak of the maximum power signal. We present an improved method for PARR reduction for reducing peak magnitude of OFDM signal. This scheme simultaneously minimizes the peak magnitude of PAPR in OFDM signal.

Long Term Evolution (LTE) chose Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink communications due to lower signal envelope changes in SC-FDMA signal. This enables low peak to average power ratio (PAPR) in SC-FDMA in contrast to Orthogonal Frequency Division Multiple Access (OFDMA). High PAPR cannot be ignored as it reduces energy efficiency due to the requirement of large range linear power amplifiers. As the mobile devices are power restricted, there is a requirement to mitigate PAPR in the uplink SC-FDMA systems, especially for higher order modulations. Companding is an attractive technique to mitigate PAPR without any bandwidth extension. This paper suggests a companding transform using exponential function to mitigate PAPR in SC-FDMA systems. The suggested transform maintains the average signal power contrary to $\mu$ law companding. Simulation results demonstrate that exponential companding technique without any decompanding operation reduces PAPR by a significant value by maintaining the average signal power and BER performance.

One of the major drawbacks of OFDM system is the high peak-to-average power ratio (PAPR). This high PAPR causes nonlinear distortion of the high power amplifier (HPA). Among the studies for PAPR reduction, the partial transmit sequence (PTS) is an attractive technique to prevent nonlinear distortion. However, it causes high computational complexity. Moreover, although the random sub-block partition method can obtain the optimum PAPR reduction, it is difficult to design the random sub-block partition method in a systematic manner. In this paper, we propose a new systematic sub-block partition method which shows low computational complexity and effective PAPR reduction. Simulation results show that the PAPR performance of the proposed PTS is closely similar to the random partitioning PTS, while it has low computational complexity.

In this paper, we propose a novel hybrid multiplicative-additive technique to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. This technique consists of two inverse fast Fourier transform (IFFT) blocks. The input symbols of the first IFFT are the mapped symbols, whereas the input symbols of the second IFFT are the summations of the absolute value of the real part of the outer signal constellation points and zeros symbols. First, the output of the two IFFT blocks is partitioned into four subblocks, which are subsequently used to rearrange the subblocks with padding zeros in a specific manner. Then, a new optimization scheme is introduced, in which only a single two-phase sequence and four iterations needs to be applied. Numerical analysis shows that the hybrid proposed technique achieves better bit error rate (BER) and PAPR reduction performance than partial transmit sequences (PTS) multiplicative technique and tone reservation (TR) additive PAPR technique. The other salient feature of this scheme is that no side information (SI) is needed which increases transmission efficiency.

Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for Ultra Wideband (UWB) wireless communication applications. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the Solid State Power Amplifier (SSPA) due to nonlinear distortion caused by high PAPR. Hence, it is necessary to reduce the PAPR of MB-OFDM UWB signals. In this paper, we used a tunable Pre-Distorter (PD) based on the High Power Amplifier (HPA) characteristics for PAPR reduction of MB-OFDM UWB signals. The PD configuration is self-tuning, i.e., it can automatically readjust itself by tracking changes in the HPA characteristics with very few (typically two) training symbols. Through Computer simulations, the performance of the predistorter is evaluated in comparison with filtering after clipping, and clipping with turbo coding for PAPR reduction. The Bit-Error Rate (BER) is used as performance measure in this evaluation.

In this paper, we proposed a new PAPR reduction technique using selective mapping (SLM) cascade with adaptive peak power reduction (APPR) methods. This technique is used in a system based on Orthogonal Frequency Division Multiplexing (OFDM). OFDM has many orthogonally modulated sub-carriers which unexpectedly produce high peak to average power ratio (PAPR). The high PAPR will occasionally reach the amplifier saturation region and therefore result in signal distortion, which causes bit error rate (BER) degradation. The proposed method, a sequence of input data is rearranged by SLM for the reduction of PAPR and then fed into the APPR process in the proposed system. The APPR method controls the peak levels of the modulation signal by an adaptive algorithm. It reduces modulation signals over a predefined range. The parameter for simulation used standard WLAN in IEEE 802.11a system. In simulation results, the proposed method shows the improvement on PAPR, power spectrum density (PSD) and high performance BER compared with conventional APPR.

One of the major drawbacks of OFDM systems is the high peak-to-average power ratio (PAPR). This high PAPR likely causes performance degradation due to nonlinear distortion in the high power amplifier (HPA). In this paper, a new PAPR reduction method is proposed that can achieve a low complexity, low BER degradation and high PAPR reduction for OFDM systems. Although the proposed method is basically similar to the selective mapping (SLM), it generates code sequences that have a low auto correlation coefficient and a low cross correlation coefficient. Moreover, it is needless to transmit the side information. Simulation results of the proposed method are compared with SLM. From the simulation results, the proposed method can overcome some disadvantages of SLM.

Single carrier frequency division multiple access (SC-FDMA) which utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver is a technique that has similar performance and essentially the same overall structure as those of an OFDMA system. One prominent advantage over OFDMA is that the SC-FDMA signal has lower peak-to-average power ratio (PAPR). SC-FDMA has drawn great attention as an attractive alternative to OFDMA, especially in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of the transmit power efficiency. SC-FDMA is currently a working assumption for the uplink multiple access scheme in 3GPP Long Term Evolution (LTE). To achieve low PAPR, a novel scheme, SC-OFDMA with super frame using intermediate mapping (SF-IFDMA), is proposed in this paper. In our proposed scheme, B frames with N subcarriers will be combined into one super frame, then SC-OFDM technique is applied to reduce the PAPR of the super frame, the super frame with lowered PAPR will finally be divided into B OFDM frames for the transmission. The combining and dividing process is equivalent to the concatenation process. The proposed scheme requires no side information and can significantly reduce PAPR while maintaining small number of subcarriers.

High PAPR of the transmitted signal is a major drawback in the OFDM systems. In this paper, coding schemes are proposed to reduce high PAPR One is using parity check coding scheme, and the other is using selected mapping (SLM) applied scheme. With parity check coding scheme, the parity information is used to expand the signal space. Mapping from original source information to the corresponding message sequence with a low PAPR the PAPR of transmitted signal can be reduced. In the SLM applied scheme, a coding scheme with data position permutation and phase rotation is used. For the practical application to IEEE 802.11g, the performance of PAPR reduction is given. The simulation results show PAPR definitely can be greatly reduced with applying the SLM applied coding scheme in the OFDM system.

OFDM (Orthogonal Frequency Division Multiplexing) es una tecnología de comunicacióninalámbrica que tiene ventajas como alta eficiencia espectral, alta tasa de transmisión y es robusta a la propagación por mulitrayecto. Sin embargo, su principal desventaja es que tienealta PAPR (Peak-to-Average Power Ratio).Este artículo presenta la evaluaciónde la técnica OPS (Orthogonal Pilot Sequence) para la reducción de la PAPR en un sistema OFDM con canal multitrayecto. Para la evaluación se consideran dos tipos de canalesmultitrayecto selectivos en frecuencia, con y sin línea de vista. Se evalúa la técnica OPS obteniendola gráfica del BER (Bit Error Rate)vs Eb/No (energy per bit to noise power spectral density ratio) y la gráfica de la CCDF (Cumulative Complementary Distribution Function) para distintos parámetros. Losresultados muestran una reducción de la PAPR cuando se utiliza la técnica OPS y una mejora en el BER.

Orthogonal frequency division multiplexing (OFDM) is a strong candidate for 4G wireless networks, due to its high data rate and ability to combat frequency selective fading. OFDM may be combined with multiple-input multiple-output (MIMO) to increase the diversity gain and system capacity over the time-variant frequency-selective channels. However, a major drawback of MIMO-OFDM system is that the transmitted signals on different antennas might exhibit high peak-to-average power ratio (PAPR). The high PAPR leads to nonlinear distortion of the high-power-amplifier (HPA) and results in inter-carrier-interference (ICI) plus out-of-band radiation. In this paper, we present a Zadoff-Chu matrix transform (ZCMT) based space-time-block-coded (STBC) MIMO-OFDM system with reduced PAPR. Extensive simulations have been performed to analyze the PAPR of the proposed system with root-raised-cosine (RRC) pulse shaping. Simulation results show that, ZCMT precoded STBC MIMO-OFDM system has low PAPR when compared to both the Walsh-Hadamard transform (WHT) precoded STBC MIMO-OFDM systems and the conventional STBC MIMO-OFDM systems.

5th generation systems (5G) will be based on Orthogonal Frequency Division Multiplexing (OFDM) multicarrier modulation technique. This modulation has a very high Peak to Average Power Ratio (PAPR). This high PAPR is a drawback when nonlinear Power Amplifiers (PA) are operated near the saturation region, for energy efficiency purposes, due to in-band and out-of-band impairments. In this paper, a new PAPR reduction technique called Iterative Dichotomy PAPR (IDP) is proposed. This method is suited for any multicarrier modulation and is studied here using realistic PA model. For evaluating the signal distortions, two main metrics have been considered to evaluate the performance of IDP technique: bit error rate (BER) and power spectrum density (PSD). The analytical expressions of the IDP technique for any dichotomy order $M$ is firstly described and subsequently the energy efficiency for different $M$ values is compared. We have shown that the proposed IDP method reduces the PAPR by $2.2dB$ for $M=2$ and $4dB$ for $M=4$ . Regarding the energy efficiency, for the same Error Vector Magnitude (EVM) and the same PA power consumption, the output signal power obtained with the IDP based technique outperforms classical OFDM by 20%, 50% and 80% for $M=2$ , $M=3$ and $M=4$ , respectively.

In this paper, we consider the high peak-to-average power ratio (PAPR) problem of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) signals in cognitive radio systems. A high PAPR can lead to saturation in the power amplifier (PA) of secondary users (SUs) and consequently increase spectral spreading, and cause interference to adjacent primary users (PUs). To overcome this problem, existing PAPR reduction techniques for OFDM systems can be applied to NC-OFDM, but they should provide a low PAPR with no side information and relatively low complexity. We consider NC-OFDM with blockwise-subcarrier activation and show that it can intrinsically employ tone reservation (TR) as a PAPR reduction technique. The proposed TR reserves subcarriers within inactive subblocks that are not used by the primary and secondary users. This eliminates data rate loss due to reserved peak reduction tones (PRTs). Further, dynamic PRT allocation in NC-OFDM typically requires side information about the PRT locations to be sent to the receiver. Since we choose PRTs from inactive subblocks, they are simply discarded at the receiver without any side information. The power spectral density (PSD) and bit error rate (BER) are evaluated at the output of the nonlinear PAs to provide a realistic performance comparison.