Low complexity PAPR reduction techniques for clipping and quantization noise mitigation in direct-detection O-OFDM systems

Keywords: Fast Hartley transform Optical OFDM Peak to average power ratio Selective mapping Partial transmit sequence Direct-detection a b s t r a c t We present different distortionless peak-to-average power ratio (PAPR) reduction techniques that can be easily applied, without any symmetry restriction, in direct-detection (DD) optical orthogonal frequency division multiplexing (O-OFDM) systems based on the fast Hartley transform (FHT). The performance of DD O-OFDM systems is limited by the constraints on system components such as digital-to-analog converter (DAC), analog-to-digital converter (ADC), the Mach–Zehnder modulator (MZM) and electrical amplifiers. In this paper, in order to relax the constraints on these components, we propose to symmetrically clip the transmitted signal and apply low complexity (LC) distortionless PAPR reduction schemes able to mitigate, at the same time, PAPR, quantization and clipping noise. We demonstrate that, applying LC-selective mapping (SLM) without any additional transform block, the PAPR reduction is 1:5 dB with only one additional FHT block using LC-partial transmit sequence (PTS) with random partitions; up to 3:1 dB reduction is obtained. Moreover, the sensitivity performance and the power efficiency are enhanced. In fact, applying LC PAPR reduction techniques with one additional transform block and a 6 bit DAC resolution, the required receiver power for 8 dB clipping level and for a 10 À3 BER is reduced by 5:1 dB. Orthogonal frequency division multiplexing (OFDM) has been introduced in optical communications systems as it has the capability to provide flexible high-capacity transmission and to cope with dispersion impairments, thanks to the digital signal processing (DSP) at the transceivers and the multicarrier modulation [1,2]. High order modulation formats can be used for increasing the system spectral efficiency and unique scalability to high-speed transmission is achieved, resulting suitable to access, metro and long-haul optical networks. Direct-detection (DD) and coherent detection are two different implementations for receiving the OFDM signal through the optical channel. DD optical OFDM (O-OFDM) is a cost effective solution using simpler transmitter and receiver architectures than coherent schemes at expenses of the spectral efficiency and receiver sensitivity. When real-valued OFDM signals are transmitted, the modulation format is also called discrete multitone (DMT). A typical transmitter configuration uses a Mach–Zehnder modulator (MZM) and a single digital-to-analog converter (DAC). Additionally, in reception the local oscillator is not required and only one photodetector and an analog-to-digital converter (ADC) are needed to recover the signal. The signal processing in the DMT transmitter/receiver is based on …