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

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 Review Paper on PAPR Reduction in OFDM using SLM and Adaptive Clipping

Orthogonal Frequency division Multiplexing (OFDM) is an effectual technique of data transmission for high speed communication schemes. However, the main drawback of OFDM system is the high Peak to Average Power Ratio (PAPR) of the communicated signals. OFDM contain of large number of independent subcarriers, as a result of which the amplitude of such a signal can have high peak values. Coding, phase rotation and clipping are between many PAPR reduction schemes that have been proposed to overcome this problem. Here in this paper we survey on two different PAPR reduction methods adaptive clipping and selective mapping (SLM) are used to reduce PAPR. Important reduction in PAPR has been achieved using these techniques