A simple nonlinear companding transform for nonlinear compensation of direct-detection optical OFDM systems

In direct-detection OFDM systems, the nonlinear effects caused by optical modulation and fiber transmission can degrade the system performance severely. In this study, we propose a new nonlinear companding transform to improve the performance of direct detection optical OFDM transmission systems. The demonstration is realized by Monte-Carlo simulation of the intensity modulation and direct-detection DCO-OFDM optical transmission system at 40 Gbps over a 80 km of standard single mode fiber link. The influence of the companding parameters on the performance of system in different nonlinear transmission conditions has been investigated via simulation

A new technique for reducing size of a wpt system using two-loop strongly-resonant inductors

Mid-range resonant coupling-based high efficient wireless power transfer (WPT) techniques have gained substantial research interest due to the number of potential applications in many industries. This paper presents a novel design of a resonant two-loop WPT technique including the design, fabrication and preliminary results of this proposal. This new design employs a compensation inductor which is combined with the transmitter and receiver loops in order to significantly scale down the size of the transmitter and receiver coils. This can improve the portability of the WPT transmitters in practical systems. Moreover, the benefits of the system enhancement are not only limited to the lessened magnitude of the TX & RX, simultaneously both the weight and the bill of materials are also minimised. The proposed system also demonstrates compatibility with the conventional electronic components such as capacitors hence the development of the TX & RX is simplified. The proposed system performance has been validated using the similarities between the experimental and simulation results. The power efficiency of the prototype circuit is found to be 93%, which is close to the efficiency reached by the conventional design. However, the weight of the transmitter and receiver inductors is now reduced by 78%, while the length of these inductors is reduced by 80%

Hybrid clipping and companding techniques based peak to average power ratio reduction in orthogonal frequency division multiplexing based differential chaos shift keying system

In this paper, a hybrid approach using clipping and companding techniques is introduced to reduce the peak to average power ratio (PAPR) of orthogonal frequency division multiplexing based differential chaos shift keying (OFDM-DCSK), which is the major drawback of the OFDM-DCSK. The hybrid function is processed at the end of the transmitter before transmitting the signal. However, there is no need for an inverse function at the receiver, which decreases the system complexity. Several techniques have been proposed in the literature for decreasing the PAPR value. Clipping and companding are active methods in terms of reducing the PAPR. Finally, the PAPR reduction and bit error rate (BER) performances are evaluated. The simulation results show that this technique gives better performance as compared with the clipping and companding techniques

A New Approach to Peak Threshold Estimation for Impulsive Noise Reduction Over Power Line Fading Channels

Impulsive noise (IN) is a major component that degrades signal integrity in power line communication (PLC) systems. PLC systems driven by orthogonal frequency-division multiplexing (OFDM) have Rayleigh distributed amplitudes. Based on the dynamic nature of each OFDM symbol, peak amplitude of the symbol was recently shown to be a suitable threshold for detecting IN, and this technique outperforms the conventional optimal blanking (COB) scheme. In this study, we improve the dynamic peak-based threshold estimation (DPTE) scheme that relies on the OFDM Rayleigh distributed amplitudes by converting the default Rayleigh distribution to uniform distribution to unveil IN with power levels below that of the conventional peak signal. Then, we perform nonlinear mitigation processing on the received signals, whose amplitudes exceed the uniformly distributed amplitude using blanking, a scheme we will refer to as uniformly distributed DPTE (U-DPTE). Our results (based on U-DPTE) significantly outperform the DPTE scheme by up to 4-dB gain in terms of output signal-to-noise ratio (SNR). Additionally and unlike earlier DPTE studies, we propose a novel threshold criterion that compensates the Gaussian noise power-level amplification (after equalization) for achieving the optimal SNR over a log-normal multipath fading channel. The results further reveal the suboptimality of the DPTE scheme over COB

New Hybrid Schemes for PAPR Reduction in OFDM Systems

الـ 3GPP قدمت مشروع LTE لتلبية الطلبات المتزايدة لخدمات الاتصالات ذات السرعة العالية والجودة العالية. يستخدم نظام الـ LTE تقنية مضاعفة تقسيم التردد المتعامد (OFDM) في شكل (OFDMA) في الوصلة الهابطة (Downlink) وشكل الـ (SCFDMA) في الوصلة الصاعدة (Uplink) مجتمعة مع تقنية الـ MIMO لتقديم معدل بيانات عالي، قدرة عالية، وحصانة ضد القنوات متعددة المسارات. ومع ذلك لا يزال ارتفاع نسبة القدرة العظمة إلى المتوسط (PAPR) لإشارة الـ LTE المرسلة هي المشكلة الرئيسية التي تعمل على تدهور كفاءة النظام بشك عام وإمكانية استهلاك الطاقة. لذلك كرست الكثير من البحوث للحد من تدهور الأداء بسبب مشكلة الـ PAPR في أنظمة LTE-OFDM. تعتبر طرق ضغط الإشارة (Companding Methods) جزءاً من الطرق المعروفة والتي تعتبر سهلة ومنخفضة التعقيد، وبلا قيود على شكل التضمين وحجم عدد الحوامل (Subcarrier Size)، ولها خصائص طيفية جيدة، ومع ذلك فإن هذه الطرق تقلل الـ PAPR بمقدار ضئيل. وقد اقترح هذا البحث سبعة طرق هجينة جديدة على أساس مزيج من Zaddoff Chu Matrix Transform (ZCT) مع ست أساليب مختلفة من طرق ضغط الإشارة وهي Rooting Companding (RCT)، New Error Function Companding (NERF)، Absolute Exponential Companding (AEXP)، Logarithmic Rooting Companding (LogR)، Cosine Companding (COS)، وTangent Rooting Companding (TanhR). بالإضافة إلى ذلك تم تطوير الطريقة الهجينة السابعة وتجمع الـ Zaddoff Chu Matrix Transform (ZCT) مع طريقة جديدة مقترحة تسمى Advanced AEXP (AAEXP). أظهرت النتائج أن هذه الطرق المتطورة تجمع بين خصائص طريقة الـ ZCT مع خصائص طرق ضغط الإشارة، وتحقق أداء أمثل وانخفاضاً أفضل من حيث PAPR وBER. كما حققت طريقة الـ ZCT+AAEXP أفضل النتائج مقارنة بالطرق الأخرى.The 3rd Generation Partnership Project (3GPP) introduced LTE to meet increasingly demands for communication services with high speed and quality. LTE uses OFDM in the form of OFDMA in the downlink and SCFDMA in the uplink combined with MIMO offering high data rate, high capacity and immunity against multipath channels. However, still the high PAPR of the LTE transmitted signal is the major problem affecting overall system performance degradation and power efficiency. A plenty of research has been devoted to reduce the performance degradation due to the PAPR problem inherent to LTE OFDM systems. A portion of the current techniques such companding methods have low-complexity, no constraint on modulation format and subcarrier size, good distortion and spectral properties; however, they have limited PAPR reduction capabilities. This paper proposes seven new hybrid schemes including Zaddoff Chu Matrix Transform (ZCT) precoding and six modern companding methods; Rooting Companding (RCT), New Error Function Companding (NERF), Absolute Exponential Companding (AEXP), Logarithmic Rooting Companding (LogR), Cosine Companding (COS) and Tangent Rooting Companding (TanhR) companding. Furthermore, the seventh proposed hybrid scheme has been added incorporating ZCT precoding with new proposed companding called Advanced AEXP (AAEXP) companding. The developed methods are combining properties of both ZCT & Compandings, and achieving superior PAPR performance and optimal BER. Simulations results illustrate that the new seven proposed hybrid schemes can achieve better PAPR reduction, and BER performance and the best achievement has been achieved by ZCT+AAEXP scheme

PAPR reduction in OFDM system using combined MCS and DHMT precoding

Orthogonal Frequency Division Multiplexing (OFDM) has become a preferable scheme for most high data rate wireless communication standards. However, the non-linear power amplifier effect experienced in the OFDM system has increases the peak-to-average power ratio (PAPR). This paper proposed a Median Codeword Shift (MCS) as a new solution to alleviate the effect of high PAPR. MCS takes advantage of the codeword structure and bit position changes through the manipulation of the codeword structure and permutation process to achieve a low PAPR value. Additionally, the enhanced version of MCS is also being proposed by merging MCS with the Discrete Hartley matrix transform (DHMT) precoding method to boost the PAPR reduction. Simulation results show that MCS is capable of minimizing PAPR of conventional OFDM with 24% improvement and at the same time outperform Selective Codeword Shift (SCS) with a 0.5 dB gap. A remarkable result was also achieved by MCS-DHMT with a 15.1% improvement without facing any bit error rate (BER) degradation

Performance Analysis of OFDM with Peak Cancellation Under EVM and ACLR Restrictions

This paper presents performance analysis of an adaptive peak cancellation method to reduce the high peak-toaverage power ratio (PAPR) for OFDM systems, while keeping the out-of-band (OoB) power leakage as well as an in-band distortion power below the pre-determined level. In this work, the increase of adjacent leakage power ratio (ACLR) and error vector magnitude (EVM) are estimated recursively using the detected peak amplitude. We present analytical framework for OFDM-based systems with theoretical bit error rate (BER) representations and detection of optimum peak threshold based on predefined EVM and ACLR requirements. Moreover, the optimum peak detection threshold is selected based on the oretical design to maintain the predefined distortion level. Thus, their degradations are automatically restricted below the pre-defined levels which correspond to target OoB radiation. We also discuss the practical design of peak-cancellation (PC) signal with target OoB radiation and in-band distortion through optimizing the windowing size of the PC signal. Numerical results show the improvements with respect to both achievable bit error rate (BER) and PAPR with the PC method in eigen-beam space division multiplexing (E-SDM) systems under restriction of OoB power radiation. It can also be seen that the theoretical BER shows good agreements with simulation results

Boosted PTS Method with Mu-Law Companding Techniques for PAPR Reduction in OFDM Systems

This paper proposes an enhanced PAPR reduction technique which combines an enhanced PTS method with Mu-Law companding. The enhanced PTS method improves performances in both the partitioning and phase rotation steps. Enhancement in partitioning is achieved through a judicious incorporation of AP-PTS scheme into the IP-PTS. As for phase rotation, an optimal set of rotation vectors is derived based on the correlation properties of candidate signals. The PAPR reduction of this enhanced PTS method is further improved by annexing Mu-Law companding at the end of the enhanced PTS. This application of Mu-Law characteristic in the time domain of OFDM signal significantly improves the PAPR reduction capability of the approach. Simulation results show that the PAPR performance of the enhanced PTS method with Mu-Law companding technique on various scenarios with different modulation schemes is better than that of the PRP-PTS. This approach can be considered as a very attractive candidate for achieving a significant reduction of PAPR, while maintaining a low computational complexity