International audienceA new technique known as Hybrid Tone Reservation (HTR) for Peak-to-Average Power Ratio (PAPR) reduction in OFDM systems has been proposed. It is shown that this new technique, based on the inclusion of the Guard Interval (GI) signal into the well-known Tone Reservation using Null-Subcarriers (TRNS) technique can significantly increase the PAPR reduction gain. In this paper, we propose to extend the performance evaluation of the HTR technique over Additive White Gaussian Noise (AWGN) channels in presence of a RF Power Amplifier (PA) model with memory effects. Simulation were carried out under the IEEE 802.11a standard in presence of a commercial 2W class-AB PA from RF Micro Devices. The model parameters of the considered PA were estimated by an experimental based method. The evaluation results in terms of Bit Error Rate (BER), Error Vector Magnitude (EVM) an spectral regrowth show that this new technique allows using the PA at high output level and consequently high power efficiency, while maintaining a good transmission quality compared to the classical TRNS method. These results highlight the performances of this technique in presence of PA nonlinearity
This paper proposes the design of a precoder in MIMO systems dedicated to JPEG Wireless (JPWL) (ISO/IEC 15444-11) image transmission which jointly takes into account the channel noise and the nonlinear distortions due to the high power amplifier (HPA) used in the transmitter. MIMO-OFDM (Orthogonal Frequency Division Multiplexing) systems dedicated to image transmission rely only on the Channel State Information (CSI) and the image content to design their precoding solutions. However, the nonlinear behavior of the HPA used at the front-end is not taken into account when designing the current precoders. In order to ensure the QoS of the transmitted image, a large level back-off is usually applied to avoid the nonlinear distortions generated by the HPA. In addition, the Input Back-off (IBO) value is statically chosen and does not depend on the other parameters of the link such as the instantaneous MIMO channel status, the modulation order and the scalability of the JPWL content. This may reduce both the global energy efficiency and the transmission quality of the Radio-Frequency (RF) link. Therefore, this work proposes a new precoding scheme to allocate the total available power while dynamically adjusting the optimal power IBO value according to the HPA parameters, the instantaneous channel status and the image content to be transmitted. Numerical results using a commercial HPA model under the IEEE 802.11n standard show that the proposed power allocation algorithm improves the visual quality of the received JPWL images compared to the state-of-the-art over a realistic radio channel model.
International audienceAlthough orthogonal frequency division multiplexing is adopted by many standards in wireless communication systems, it generates high peak fluctuations which are affected by radio frequency circuit non-linearities, reducing the power efficiency and the network quality of service. In recent years, tone-reservation using null subcarriers (TRNS) scheme has been proposed to reduce the level of these fluctuations, measured by the peak-to-average power ratio (PAPR). However, TRNS performances only depend on the available number of null subcarriers in the current standards. In this study, a new scheme to improve TRNS performances by including the samples of the guard interval signal within the parameters of the optimisation algorithm is proposed, allowing higher PAPR reduction gain and requiring no side information. Simulations under the wireless local area network IEEE 802.11a standard show that the new method does not violate the specified spectrum mask and achieves a higher PAPR reduction gain compared to TRNS method. Also, the evaluation of bit error rate and error vector magnitude under additive white Gaussian noise and Rayleigh fading channels shows a comparable level of the quality of communication between the two schemes
International audienceThe transmission of highly scalable image and video codestream over error-prone networks can be ensured by using Unequal Power Allocation (UPA) in MIMO-OFDM systems. However, UPA schemes are usually designed without taking into account the High Power Amplifier (HPA) nonlinearity, especially in MIMO-OFDM systems which are known to generate signals with a high Peak-to-Average Power Ratio (PAPR). This paper aims to evaluate the impact of HPA nonlinearity on the transmission of scalable image cotents over a precoded Closed-Loop MIMO-OFDM system when the well-known Content-Based Precoder (CBP) is used for UPA. For PAPR reduction, we have considered the Tone Reservation Using Null Subcarriers (TRNS) technique. Simulations are performed under the IEEE 802.11n standard in a realistic urban environment in presence of a commercial 2W class-AB memoryless HPA from RF Micro Devices. The experimental results in terms of Bit Error Rate (BER) and visual quality show that the error-protection of the most sensitive parts of the codestream against channel distortions achieved using UPA is significantly disturbed in presence of HPA nonlinearity. These results highlight the influence of HPA nonlinearity on the scalable image transmission
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