[Paper Review] A Comparative Study of Unipolar OFDM Schemes in Gaussian Optical Intensity Channel

Jing Zhou, Wenyi Zhang|arXiv (Cornell University)|Jul 14, 2017

Optical Network Technologies4 citations

TL;DR

This paper presents a comparative analysis of unipolar OFDM schemes in Gaussian optical intensity channels with average optical power constraints. Using i.i.d. Gaussian codebooks and nearest-neighbor decoding, it derives information rates, establishes equivalence among certain schemes, and demonstrates that component-multiplexing schemes with optimized power allocation achieve rates within 0.07 bits of the high-SNR capacity.

ABSTRACT

We study the information rates of unipolar orthogonal frequency division multiplexing (OFDM) in discrete-time optical intensity channels (OIC) with Gaussian noise under average optical power constraint. Several single-, double-, and multicomponent unipolar OFDM schemes are considered under the assumption that independent and identically distributed (i.i.d.) Gaussian or complex Gaussian codebook ensemble and nearest neighbor decoding (minimum Euclidean distance decoding) are used. We obtain an array of information rate result. These results validate existing signal-to-noise-and-distortion-ratio (SNDR) based rate analysis, establish the equivalence of information rates of certain schemes, and demonstrate the evident benefits of using component-multiplexing at high signal-to-noise-ratio (SNR). For double- and multi-component schemes, the component power allocation strategies that maximize the information rates are investigated. In particular, by utilizing a power allocation strategy, we prove that several multi-component schemes approach the high SNR capacity of the discrete-time Gaussian OIC under average power constraint to within 0.07 bits.

Motivation & Objective

• To evaluate and compare the information rates of various unipolar OFDM schemes under average optical power constraints.
• To investigate the impact of component-multiplexing on spectral efficiency and information rate in optical intensity channels.
• To determine optimal power allocation strategies for double- and multi-component unipolar OFDM schemes to maximize information rate.
• To validate SNDR-based rate analysis and establish equivalence in performance among specific unipolar OFDM schemes.
• To demonstrate that multi-component schemes can approach the high-SNR capacity of the discrete-time Gaussian optical intensity channel.

Proposed method

• Analyzes discrete-time optical intensity channels with additive Gaussian noise under average optical power constraints.
• Employs i.i.d. Gaussian or complex Gaussian codebook ensembles for signal generation.
• Applies nearest-neighbor decoding (minimum Euclidean distance) to estimate achievable information rates.
• Derives the generalized mutual information (GMI) for channels with transceiver distortions using a general framework for complex-valued vector channels.
• Uses the GMI expression ${\cal I}_{\textrm{GMI}}=N\log\left(1+\frac{\Delta}{1-\Delta}\right)$ with $\Delta$ defined via expectations of input and distorted signals.
• Optimizes the decoding scaling parameter $a_{\textrm{opt}}$ to maximize the GMI and achieve the highest information rate.

Experimental results

Research questions

• RQ1 How do different unipolar OFDM schemes compare in terms of achievable information rate under average optical power constraints?
• RQ2 What is the impact of component-multiplexing on the information rate of unipolar OFDM in optical intensity channels?
• RQ3 Which power allocation strategies maximize the information rate in double- and multi-component unipolar OFDM schemes?
• RQ4 To what extent can multi-component unipolar OFDM schemes approach the high-SNR capacity of the discrete-time Gaussian optical intensity channel?
• RQ5 Are there performance equivalences between certain unipolar OFDM schemes under the same decoding and power constraints?

Key findings

• Component-multiplexing in double- and multi-component unipolar OFDM schemes provides significant performance gains at high SNR.
• The information rates of certain unipolar OFDM schemes, such as ADO-OFDM and HACO-OFDM, are shown to be equivalent under the same decoding and power constraints.
• By using an optimized power allocation strategy, multi-component schemes approach the high-SNR capacity of the discrete-time Gaussian OIC to within 0.07 bits.
• The GMI-based rate analysis is validated and shown to be consistent with existing SNDR-based rate models.
• The DoF efficiency of multi-component schemes such as FDM-UOFDM and eU-OFDM is $1-2^{-L}$, which increases with the number of components $L$.
• The derived GMI framework with optimal decoding scaling $a_{\textrm{opt}}$ enables accurate estimation of achievable rates under transceiver distortions.