# Channel tracking in an OFDM system

Started by July 28, 2008
Hello,

I am trying to design an adaptive equalizer for an OFDM system which has
an extremely low symbol rate. I have a question regarding this.

The transmitter and the receiver are moving wrt each other. For what
amount of relative motion between them in one OFDM symbol period (as a
fraction of the carrier wavelength) can I assume that the channel is
reasonably correlated across OFDM symbols?

The front end uses an isotropic antenna.

Any help is much appreciated.

Thank you,
Ananth
On Jul 28, 11:20 am, "ananth.rs" <ananth...@gmail.com> wrote:
> Hello, > > I am trying to design an adaptive equalizer for an OFDM system which has > an extremely low symbol rate. I have a question regarding this. > > The transmitter and the receiver are moving wrt each other. For what > amount of relative motion between them in one OFDM symbol period (as a > fraction of the carrier wavelength) can I assume that the channel is > reasonably correlated across OFDM symbols? > > The front end uses an isotropic antenna. > > Any help is much appreciated. > > Thank you, > Ananth
It depends on how much SNR hit you can tolerate. You can try to use a bounding technique based on the triangle inequality in this case. Suppose we take a simple single-carrier with 1-tap channel and equalization. The received signal is: y_n = x_n * h + z_n where h is the channel. For simplicity, let the channel have unit norm ||h|| = 1. Now suppose let's consider an MMSE or zero-forcing equalization, let the equalizer be: g = 1/h Then the equalizer output is: q_n = g * y_n If the channel h changes to h', then the error induced on the equalizer output if the equalizer g is not adapted can be bounded by the triangle inequality. Hope that helps. Julius
>Hello, > >I am trying to design an adaptive equalizer for an OFDM system which has >an extremely low symbol rate. I have a question regarding this. > >The transmitter and the receiver are moving wrt each other. For what >amount of relative motion between them in one OFDM symbol period (as a >fraction of the carrier wavelength) can I assume that the channel is >reasonably correlated across OFDM symbols? > >The front end uses an isotropic antenna. > >Any help is much appreciated. > >Thank you, >Ananth >
You can determine this based on the channel coherence time(depend on the relative speed of motion and wavelength) as relative to the OFDM symbol time. You can check a good reference paper by Prof. Bernard Sklar. The title is something like Fading Channel Characterization. Michael