Improved Hybrid Blind PAPR Reduction Algorithm for OFDM Systems

The ever growing demand for high data rate communication services resulted into the development of long-term evolution (LTE) technology. LTE uses orthogonal frequency division multiplexing (OFDM) as a transmission technology in its PHY layer for down-link (DL) communications. OFDM is spectrally efficient multicarrier modulation technique ideal for high data transmissions over highly time and frequency varying channels. However, the transmitted signal in OFDM can have high peak values in the time domain due to inverse fast Fourier transform (IFFT) operation. This creates high peak-to-average power ratio (PAPR) when compared to single carrier systems. PAPR drives the power amplifiers to saturation degrading its efficiency by consuming more power. In this paper a hybrid blind PAPR reduction algorithm for OFDM systems is proposed, which is a combination of distortion technique (Clipping) and distortionless technique (DFT spreading). The DFT spreading is done prior to clipping reducing significantly the probability of having higher peaks in the composite signal prior to transmission. Simulation results show that the proposed algorithm outperforms unprocessed conventional OFDM transmission by 9 dB. Comparison with existing blind algorithms shows 7 dB improvement at error rate 10–3 and 3 dB improvement at error rate 10–1 when operating in flat fading and doubly dispersive channels, respectively.Keywords:    LTE Systems; OFDM; Peak to Average Power Ratio; DFT spreading; Signal to Noise Power Ratio

Impact of Adaptive Modulation and Coding Schemes on Bit Error Rate for System Performance in the Uplink LTE System

Long Term Evolution (LTE) is a cellular network technology aims to render enriched data services to users at lower latency and higher (multi-megabit) throughput. The higher system throughput with more reliable transmission is achieved by the support of Adaptive Modulation and Coding (AMC) schemes, scheduling algorithms, multi-antenna techniques etc. The AMC schemes substantially increases the system throughput by reducing the Bit Error Rates (BER) and by adjusting the transmission parameters based on the link quality. The scheduling algorithms also enhance the throughput of individual users, as well as the cell throughput by allocating the resources among the active users. Hence in this paper, an attempt has been made to study and evaluate the effects of AMC schemes such as QPSK, 16-QAM and 64-QAM on uplink LTE system performance for Proportional Fair (PF) and Round Robin (RR) scheduling algorithms using QualNet 7.1 network simulator. The performance metrics considered for the simulation studies are BER, cell throughput, average delay and average jitte