Out Of Band Radiation Research Articles

Peak to average power ratio reduction in spectrally efficient FDM using repeated clipping and filtering

Multi-carrier transmission may be considered one of the important developments in wireless communications. Spectrally efficient frequency division multiplexing (SEFDM) is a promising multi-carrier modulation which can significantly improve utilization of spectral. The SEFDM has high peak to average power ratio (PAPR) like any multicarrier system. High PAPR reduces the random forest (RF) transmitter power amplifier efficiency, which minimize the use of this technique in limited power supply transmitters. In this work, a repeated clipping and filtering method is introduced to reduce the PAPR in SEFDM with minimum or no out of band radiation. The results of the simulated approach show that the PAPR of the SEFDM was reduced from 16.264 dB to 7.9146 dB with marginal degradation in system performance when the clipping ratio varied from 4 to 2.

Joint Precoder and Window Design for OFDM Sidelobe Suppression

Spectral precoding and windowing are two effective approaches to reduce out-of-band radiation (OBR) in multicarrier systems. Their performance comes at the price of reduced throughput and additional computational complexity, so there is strong motivation for simultaneously using both techniques. We present a novel design that jointly optimizes the precoder and window coefficients to minimize radiated power within a user-selectable frequency region. Results show that the proposed design achieves a better OBR/throughput/complexity tradeoff than either of these individual techniques separately.

Precoded SLM and PTS Scheme for Reduced PAPR in OFDM for Wireless Communications

Orthogonal Frequency Division Multiplexing (OFDM) contribute high data rates in current as well as future wireless communication systems but it aches from high Peak to Average Power Ratio (PAPR). But this high PAPR makes the High-Power Amplifier (HPA) complex which increases the cost of it and leads to the drawbacks like Inter Carrier Interference (ICI) and rise in out of band radiation. Even though many techniques are there to decrease the complexity of HPA by reducing the PAPR, Selected Mapping (SLM) and the Partial Transmit Sequence (PTS) provides less PAPR with low complexity. In this paper, both PTS and SLM are combined with Discrete Sine Transform (DST) and their PAPR and efficiencies are also compared with OFDM signal. The proposed hybrid DST-PTS and DST-SLM provides less PAPR compared to OFDM, SLM and PTS techniques with low complexity. Also, the bit error rate for DST-SLM and DST-PTS techniques are compared for different values of SNR. In future wireless communication systems, these proposed techniques can be used as they provide less bit error rate and less PAPR with low complexity

Performance evaluation of companded localized FDMA for LTE uplink communications

The maximum-to-expected power ratio is critical metric in the current day mobile communications. Single-carrier frequency division multiple access is the most promotional scheme to reduce the peak-to-average power ratio in order to compromise the bit error rate for mobile communications. The proposed companding functions play a vital role in SC-FDMA than in OFDMA for LTE uplink systems. Here, in this paper the nonlinear compandings like μ-law, error, logarithmic, exponential, trapezoidal and airy function are more attractive to solve the problem and analyze PAPR and BER. The μ-companding is not recommended to use because of its average power and outband radiation. This paper proposed a companding functions based on special function to limit power ratio without enhancing the average power. The novel airy function gives suitable trade-off with their power ratio PAPR and error rate BER. The suggested method maintains superior performance with and without decompanding function in SC-FDMA systems at the receiver side without effecting the complexity.

Performance of generalized frequency division multiplexing over gamma gamma free space optical link

Generalized frequency division multiplexing (GFDM) with the free space optical channel can be a desirable option for free space optical communication systems as it has numerous benefits such as high spectral efficiency, flexibility, low out of band radiation and low peak-to-average power ratio. In this paper, the closed form expressions of symbol error and outage probabilities with and without pointing errors are derived for GFDM over gamma–gamma channel model. The theoretical results are verified with the Monte-Carlo simulations. Moreover, the impact of turbulence levels and comparison with orthogonal frequency division multiplexing are also explored.

Circularly pulse‐shaped orthogonal time frequency space modulation

Orthogonal time-frequency space (OTFS) modulation is a recently proposed waveform for efficient data transfer in high-speed vehicular scenario. Use of rectangular pulse shape in OTFS results in high out of band (OoB) radiation, which is undesirable for multi-user scenarios. In this work, the authors present a circular pulse shaped framework for OTFS for reducing the OoB. The authors also design a low complexity transmitter for such a system. They argue in favour of orthogonal transmission for low complexity transceiver structure. The authors establish that frequency-localised circulant Dirichlet pulse is one of the possible pulses having this desirable unitary property, which can reduce OoB radiation significantly (by around 50 dB) without any loss in BER. They also show that the proposed pulse-shaped OTFS has a lower peak to average power ratio than conventional OTFS system.

Blind Algorithm Development for Peak to Average Power Ratio Reduction in OFDM Systems under Frequency Selective Channels

One major drawback of orthogonal frequency division multiplexing (OFDM) system is peak to average power ratio (PAPR). This effect causes high power amplifier (HPA) to introduce intermodulation and out of band radiation as the signal goes through, thus degrades the performance of OFDM systems. This paper proposes blind algorithms which takes advantage of signal transformation technique and signal distortion technique. Simulation results show that at complementary cumulative distribution function (CCDF) level of 10-3 , the proposed algorithm achieved 3.2 dB PAPR improvement compared to discrete Fourier transform with interleaved frequency division multiple access (DFT-IFDMA) based algorithm. The bit error rate (BER) performance has degraded by 2 dB compared to the original OFDM signal with no distortion under frequency selective channel (FCS) at BER of 10-4 . These presented results, mark this algorithm as a better candidate for PAPR reduction algorithm in long term evolution (LTE) network. Under AWGN channels, the proposed algorithm performs better both in low and high signal power values. Under frequency selective channels, the existing and proposed algorithm converges after 10 dB of signal to noise power values. The low BER transmissions at low signal power values signify energy efficiency, ideal for portable wireless devices with limited battery power.

Performance analysis of UFMC waveform in graded index fiber for 5G communications and beyond

For the first time, we demonstrate in this paper an intensity-modulation direct-detection (IMDD) universal filtered multi-carrier (UFMC) system through several hundred meters of multimode fiber (MMF) that can be adopted for 5G communications and beyond. The proposed system is simulated and evaluated in terms of bit error rate (BER), Q factor, out of band (OOB) emission and Peak-to-Average Power Ratio (PAPR), at a data rate of 10 Gb/s. It is shown that filtering used with UFMC reduces the OOB radiation by 40 dB compared to orthogonal frequency division multiplexing (OFDM). Moreover, we prove that UFMC gives lower values of BER than OFDM, and even if the PAPR ratio of UFMC is higher than OFDM, the gap remains small. The results also show that using a Volterra equalizer with increasing taps enables to obtain acceptable performance through the MMF in terms of BER, even with high number of excited mode groups.

On preambles with low out of band radiation for channel estimation

We investigate preamble designs for channel estimation that jointly address the estimation efficiency and the out of band (OOB) radiation of the transmit preambles. Accordingly, we provide two novel techniques for obtaining preambles for a single carrier system. Furthermore, we give a juxtaposition based method to extend their application to multi-carrier systems. The obtained preambles have 10 dB to 35 dB lower OOB radiation than the existing preamble based estimation techniques in literature. We also bring out the fundamental trade-off that exists between the estimation efficiency and the OOB radiation power, and highlight that the improved OOB performance comes at a cost of increased estimation error. Finally, as a case study, we study the performance of the obtained preambles in a multiple input multiple output (MIMO) Generalized Frequency Division Multiplexing (GFDM) system, aimed for transmit diversity.

Bit error rate analysis of generalised frequency division multiplexing with weighted‐type fractional Fourier transform precoding

Generalised frequency division multiplexing (GFDM) as a non-orthogonal waveform candidate is posed to reduce the high out of band radiation of orthogonal frequency division multiplexing system via pulse shaping. In this study, an analytical model of introduced interference from neighbouring subcarriers caused by pulse shaping is firstly proposed. Signal-to-interference-plus-noise ratio (SINR) is calculated according to related GFDM models with different weighted-type fractional Fourier transform (WFRFT) precoding orders. Approximated bit error rate (BER) expressions are derived for the low complexity GFDM system over additive white Gaussian noise and fading channels based on the analysis of SINR. Particularly, the BER superiority of WFRFT precoding is highlighted over the fading channels. Furthermore, peak-to-average power ratio and out of band power suppression performances are simulated at different WFRFT orders to illustrate the advantages of WFRFT precoding.

Linear Precoding for PAPR Reduction of GFDMA

Similar to the widely used orthogonal frequency division multiplexing systems, generalized frequency division multiplexing suffers from a high peak-to-average power ratio (PAPR). In this letter, we propose a data-independent precoder to minimize the variance of the instantaneous power (IP), subject to the constraint of unchanged average IP as a means for PAPR reduction. Simulation results show that the proposed precoder can reduce PAPR without any increase in out of band radiation or bit error rate degradation. Compared with the existing solutions, the proposed technique provides an improved PAPR performance. Furthermore, an efficient implementation of the proposed precoding technique is introduced. A thorough computational complexity analysis of different PAPR reduction methods is also presented in this letter.

Performance Evaluation of AIC Technique for Single and Multiple Primary Bands in OFDM based Cognitive Radios

Cognitive radio has emerged as an efficient approach to address the problem of spectrum under-utilization. OFDM has been proposed as a potential candidate for the physical layer of cognitive radios due to its inherent characteristics of spectrum shaping, spectrum analysis and robustness to frequency selective fading. One of the major problems of OFDM is high Out Of Band Radiation (OOBR). This is an undesired phenomenon especially if the nearby band is occupied by primary (or licensed) user. Among the proposed techniques to overcome this problem, Active Interference Cancellation (AIC) is considered to be one of the efficient techniques. In this paper, we evaluate the performance of this technique for single and multiple primary bands in OFDM based cognitive radios. For the case of single primary band, it is shown through simulations that narrower primary bands and use of more number of cancellation carriers increases the OOBR reduction in the desired band. For the case of multiple primary bands, the AIC technique is shown to provide better OOBR reduction for larger inter primary band spacing, lesser number of primary bands and more number of cancellation carriers. We also evaluate the bandwidth efficiency for single and multiple primary bands. The bandwidth efficiency shows a linear decrease with the increase in number of cancellation carriers. Multiple primary band system has more bandwidth efficiency degradation than the single primary band system.

A phase trajectories optimization method for CPM signal based on Pan-function model

The continuous phase modulation (CPM) signal has the characteristics of continuous phase, excellent spectral properties, less out-band radiation, and constant envelope. Thus, CPM technology is widely used in communication systems. The shape of frequency pulse can influence the bandwidth occupancy of CPM, and smoother phase trajectories are obtained by using smoother frequency pulses. In this paper, a mathematical Pan-function model of the optimized frequency pulse is established and solved by introducing Fourier series, which can provide smooth phase trajectories of CPM signal. The simulations of the CPM signal quadrature modulation and coherent demodulation are performed using the MATLAB software. Moreover, the spectral characteristics of the obtained optimized CPM signal were analyzed and compared with the minimum shift keying (MSK) signal and other CPM signals with smooth frequency pulses. The simulation results indicate that the proposed method provides an excellent bandwidth efficiency compared to other existing methods discussed in this paper. The whole system has been successfully downloaded to field programmable gate array (FPGA) devices. The operating results are consistent with expected results, verifying the correctness of this method.

A High-Accuracy Metric for Predicting the Power De-Rating of RF Power Amplifiers

Cubic metric (CM) is being recognized as a better alternative to determine the power de-rating of radio frequency power amplifiers (PAs) than peak-to-average power ratio (PAPR). However, in this letter our analysis shows that actually the CM is still inaccurate to predict the required PA power de-rating that satisfies the out-of-band radiation (OBR) requirement of a communication system. Further, by investigating the effect of the third-order nonlinearity of PA on the OBR, we propose a novel metric. Compared with PAPR and CM, the proposed metric has a strong correlation with the OBR, and thus it provides much higher accuracy in determining the required power de-rating of PAs, which is verified by extensive experimental results.

Peak-to-Average Power Ratio Reduction Techniques for OFDM Signals

Orthogonal frequency division multiplexing (OFDM) has been adopted as a standard for many modern wireless applications requiring high data rate due to bandwidth efficiency, resistance to frequency selective fading and simple digital realization using IFFT/FFT operations. However, physical implementation of the OFDM system suffers from several difficulties. One of the major limitations of OFDM is that it suffers from high peak-to-average power ratio (PAPR), which results in inter-carrier interference (ICI), high out-ofband radiation, and degradation of bit error rate performance. In this paper, different OFDM PAPR reduction techniques are reviewed and analyzed based on their computational complexity, bandwidth requirement and error performance.

New Tone Reservation Technique for Peak to Average Power Ratio Reduction

AbstractIn Orthogonal Frequency Division Multiplexing (OFDM) the transmit signals have a highly fluctuating, non-constant envelope which is a technical challenge for the High Power Amplifier (HPA). Without any signal processing procedures the amplitude peaks of the transmit signal will be clipped by the HPA resulting in out-ofband radiation and in bit error rate (BER) performance degradation. The classical Tone Reservation (TR) technique calculates a correction signal in an iterative way to reduce the amplitude peaks. However this step leads to a high computational complexity. Therefore, in this paper an alternative TR technique is proposed. In this case a predefined signal pattern is shifted to any peak position inside the transmit signal and reduces thereby all amplitude peaks. This new procedure is able to outperform the classical TR technique and has a much lower computational complexity.

A Pan-Function Model for the Utilization of Bandwidth Improvement and PAPR Reduction

Aiming at the digital quadrature modulation system, a mathematical Pan-function model of the optimized baseband symbol signals with a symbol length of4Twas established in accordance with the minimum out-band energy radiation criterion. The intersymbol interference (ISI), symbol-correlated characteristics, and attenuation factor were introduced to establish the mathematical Pan-function model. The Pan-function was added to the constraints of boundary conditions, energy of a single baseband symbol signal, and constant-envelope conditions. Baseband symbol signals with the optimum efficient spectrum were obtained by introducing Fourier series and minimizing the Pan-function. The characteristics of the spectrum and peak-to-average power ratio (PAPR) of the obtained signals were analyzed and compared with the minimum shift keying (MSK) and quadrature phase-shift keying (QPSK) signals. The obtained signals have the characteristics of a higher spectral roll-off rate, less out-band radiation, and quasi-constant envelope. We simulated the performance of the obtained signals, and the simulation results demonstrate that the method is feasible.

Examine the impact of Modulation Order and Sub-bands on PAPR Reduction Techniques using Various Modulator in 802. 11a/b/g

In the modern era of communication Orthogonal Frequency Division Multiplexing (OFDM) technique is the most widely used in wireless technology. With some advantage come few issues such as Peak to Average Power Ratio (PAPR) that leads High Power Amplifiers (HPA) to be worked in nonlinear region which causes inter-modulation distortion and out of band radiation. To overcome with this problem, several techniques were used. Whereas, this paper uses most efficient signal scrambling technique, Partial Transmit Sequence (PTS) and Selected Mapping (SLM) to be worked with various modulators such as Orthogonal Quadrature Phase Shift Key (OQPSK) and Quadrature Amplitude Modulator (QAM) and Binary Phase Shift Key (BPSK) . Under different modulator and different parameters like Sub-Band, Modulation factor, these techniques were analyzed and compared.

Reduction of the Clipping Noise for OFDM/OQAM System

Orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) has been proven to be a promising multi-carrier modulation (MCM) technique for the transmission of signals over multipath fading channels. However, OFDM/OQAM has also the intrinsic disadvantage of high peak-to-average-power ratio (PAPR) that should be alleviated. This paper focuses on the reduction of the clipping noise and out-of band radiation caused by the clipping process. The basic principle is to estimate the clipping noise and then eliminate it from the received signal. Analysis and simulation results show that, with one time iteration, the proposed method can effectively improve the bit error ratio (BER) performance.

Sidelobe Suppression in CR-OFDM system by Adding Extended Data Carriers

Out-band radiation is a severe problem for Cognitive Radio with OFDM system (CR-OFDM) which is caused by the sidelobe of OFDM signals. Lots of studies have been done on suppressing the sidelobe power and numerous methods have been proposed. In this paper, we propose a novel method to minimize the sidelobe by adding extended data carrier so called EDC to the original data carriers so as to protect primary user (PU) spectrum. Unlike the methods before, the EDCs are deployed within the secondary user (SU) data frequency spectrum to fully use the spectrum. Moreover, we derive the linear least squares problem to get the optimal weighting factors of EDCs to minimize the sidelobe power which is subject to an original data interference constraint. By simulation, we find that EDC is more capable in sidelobe suppression than method of Cancellation Carrier (CC) while EDC has only a small loss in BER performance.