Abstract
Orthogonal Frequency Division Multiplexing (OFDM) is one of the key modulations for current and novel broadband communications standards. For example, Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) is an excellent choice for the ECMA-368 Ultra Wideband (UWB) wireless communication standard. Nevertheless, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals reduces the power efficiency of the key element in mobile devices, the High Power Amplifier (HPA), due to non-linear distortion, known as the non-linear saturation of the HPA. In order to deal with this limiting problem, a new and efficient pre-distorter scheme using a Neural Networks (NN) is proposed and also implemented on Field Programmable Gate Array (FPGA). This solution based on the pre-distortion concept of HPA non-linearities offers a good trade-off between complexity and performance. Some tests and validation have been conducted on the two types of HPA: Travelling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA). The results show that the proposed pre-distorter design presents low complexity and low error rate. Indeed, the implemented architecture uses 10% of DSP (Digital Signal Processing) blocks and 1% of LUTs (Look up Table) in case of SSPA, whereas it only uses 1% of LUTs in case of TWTA. In addition, it allows us to conclude that advanced machine learning techniques can be efficiently implemented in hardware with the adequate design.
Highlights
Ultra Wideband (UWB) technology has been deployed for broadband wired and wireless communications since in February 2002, the implementation of a regulation gave authorization on the use of UWB technology for telecommunications consumer in the United States by the Federal Communications Commission (FCC)
It points out the MB-Orthogonal Frequency Division Multiplexing (OFDM) scheme to transmit information for a wireless personal area network, identically to all OFDM based communications systems, the ECMA-368 undergoes the large Peak to Average Power Ratio (PAPR), this drawback reduces the High Power Amplifier (HPA) efficiency at the transmitter
The Travelling Wave Tube Amplifiers (TWTA) has been used with α|| = 2, β|| = 1, αPM = 4 and βPM = 9 [10], while the Solid State Power Amplifiers (SSPA) used is the NEC GaAs Power Amplifier used for standardization with parameters: g = 19, Asat = 1.4, s = 0.81, α = −48000, β = 0.123, c1 = 3.8 and c2 = 3.7 [10]
Summary
Ultra Wideband (UWB) technology has been deployed for broadband wired and wireless communications since in February 2002, the implementation of a regulation gave authorization on the use of UWB technology for telecommunications consumer in the United States by the Federal Communications Commission (FCC). In the ECMA-368 system, very efficient amplifiers are used, mainly of two different types, namely, Traveling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA) These amplifiers are highly non-linear and in order to avoid the distortion of the signal, large back-offs are needed. Numerous methods have been proposed to overcome the high PAPR problem in OFDM signals [8,9] Among these techniques, the HPA pre-distorter [10] is one of the most promising ones because it avoids the increase on transmit energy, it does not need side information which reduces efficiency, it is only needed to be applied at the transmitter, which eases the implementation, and it does not increase the BER, among other advantages.
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