Nonlinear transform approach to the reduction of peak-to-average power ratio in orthogonal frequency division multiplexing (OFDM) systems




Dursun, Serkan

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The design of modulation technique for wireless data communications in mobile radio channels is important implementation issue due the dispersive and time-variant nature of the channel. In recent years, the interest in multicarrier modulation for wireless transmission has been increased. In general multicarrier schemes, the transmitted data is split into a number of parallel data streams, each one used to modulate a separate subcarrier. An attractive approach to multicarrier modulation is Orthogonal Frequency Division Multiplexing (OFDM). OFDM offers advantages in transmission over (severe) multipath channels so that there is an increased interest in applying OFDM in high-data rate mobile or portable data transmission.

The transmit signal in OFDMsystem has a high Peak-to-Average Power Ratio (PAPR) and therefore both the Digital-to-Analog Converter (DAC) and the Power Amplifier (PA) require high dynamic range to perform accurately, otherwise the signal is distorted and hence Bit Error Rate (BER) performance degradation occurs. On the other hand, the battery life in mobile communication is an important key concept in the system design. The PA is driven at high bias voltage levels in order to achieve power efficiency, therefore, it is the main part which requires the most energy as far as the power consumption is concerned. Besides, for signals with large PAPR as in OFDM system, BER performance can be severely degraded by the nonlinear distortion of the PA. As a result, the reduction in PAPR in OFDM system is desirable in order to obtain power efficiency and increase BER performance.

In this research, a novel nonlinear sliding norm transforms (SNTs) are developed to reduce the PAPR of the OFDM transmit signal. These are Absolute Norm Sliding Transform, Maximum Norm Sliding Transform, and L 2-by-3 Norm Transform. The simulation results showed that the proposed transforms provide different PAPR reduction based on different modulation levels of QAM. The SNTs exploit the sliding norm of the signal to reduce PAPR. It is shown that the proposed method reduces PAPR of the OFDM signal and thus increases efficiency of power amplifier, increases system performance by reducing in-band and out-of-band distortions. The key novelty of the transforms can briefly be summarized that they are nonlinear, reversible and fast transforms, applicable independently of the signal constellation and mapping on subcarriers, and reduce PAPR at low computational complexity. The transforms can adjust the PAPR reduction by only changing value of parameter alpha and this value can be used by transmitter and receiver as a convention; it does not have to be transmitted.

Theoretical and performance analysis of the proposed SNTs in terms of PAPR reduction and BER are given for different values of the parameter alpha of the proposed SNTs. In the simulation, the system is IEEE 802.11a Wireless LAN PHY Layer with Memoryless Rapp Model Power Amplifier with different IBO (Input Backoff). The proposed transforms are suitable for OFDM based wireless communication systems such as IEEE 802.11a, g, 802.16e, Multi-band OFDM, DVB/DAB, and HiperLAN/2.


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Nonlinear Transforms, OFDM, Peak-to-Average Power Ratio, Power Amplifier, Wireless LAN



Electrical and Computer Engineering