## Category Archives: OFDM

### Signal Statistics for OFDM

Here is something that recently piqued my interest (and kept me busy for the better part of last week). It could be (marginally) interesting for people which work on OFDM or Nyquist WDM and – as far as I know – no one has looked at this in more detail…

### Nature Photonics

After what seems (to me) to have been several eons worth of experimenting, writing, re-writing, re-experimenting, more re-writing and then some more re-writing (all of which mostly by others), the all-optical FFT idea that was used at the IPQ department at KIT finally made it into Nature Photonics. When I got there in late ’09, […]

### optical OFDM – Odds and Ends

This is probably gonna be the last of the OFDM posts around here, since I’m no longer working on OFDM-related topics. The next post was supposed to be about reception of optical OFDM signals, and the one after that maybe about the various impediments that can occur in specific types of receivers (e.g. optical beat […]

### Grand Unified Theory

Bridging the worlds of OFDM (on which I spent the last year) and XPolM (on which I spent the three years before that), I thought it might be interesting to see what an OFDM channel does to an XPolM probe. This is an extension of all the stuff that was written in this post, in […]

### Optical OFDM – Blessings and Curses

Due to the time-distributed nature of the subchannel symbols and the unique algorithm used to demultiplex the compound signal, the influence of various transmission impairments on the subchannel signals is very different from what it is in single-channel systems. As we will see, this makes OFDM much easier to analyze and predict its performance, but […]

### Optical OFDM – Generation

Before we go further into the signal processing topics that started with the cyclic prefix, we shall take a look at how we can generate OFDM signals ready for transmission and then, next, how to get them into the fiber. By now you should have a firm grasp on what an OFDM signal is. If […]

### Optical OFDM – Cyclic Prefix

One of the most common misunderstandings about OFDM that keeps coming in most discussions on the topic is if subchannels are still orthogonal when there is a cyclic prefix involved. But let’s start at the beginning… Dispersion We have seen in this post that the DFT can be used at the receiver to demultiplex the […]

### Optical OFDM – Spectrum

We have seen in this post that the DFT spectrum of a single OFDM symbol is a line spectrum with one line for each subchannel $k$ which carries the modulated data $c_{k}$. Within a single symbol there is no spectral overlap, which is the reason why OFDM works. What’s also interesting is the long-time (more […]

### Optical OFDM – OFDM Basics

This post continues the introduction to optical OFDM that I started here. In this post, we’ll discuss what an OFDM symbol looks like and show, starting from the orthogonality condition, that the discrete Fourier transform can be used to demultiplex an OFDM channel into its subchannels. Using the Fourier transform, we also take a look […]

### Optical OFDM – Orthogonality

And now for something completely different… This will be the first of (hopefully) a series of posts that will be an introduction to optical OFDM (or what I have learned in the past half year or so about it). Optical OFDM has been somewhat of a hot topic in recent years in the community, but […]