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Patent for Sale:

Wireless LAN (WiFi) Patent Porfolio    

Three U.S. patents deal with the question of equalization and estimation of an OFDM signal


The technology covers a method for channel estimation, this is particularly suited for applications in wireless networks with rapid channel variations that can be caused for example by user mobility. It is aimed at situations when reflector velocities are in the range of 60 – 200 km/h (doubly-selective channels with high Doppler spreads). In terms of operations and memory it scales linearithmic (operations) and linear (memory) with the number of the channel taps compared to quadratic scaling of the previously known methods.

The portfolio also includes a method for channel equalizaiton for a wireless communication channel that is given in terms of its basis expansion model coefficients this technology is up-to-date the fastest way for equalization. Due to its low complexity (linearithmically, in subcarrier number, many operations is needed for each iteration) for the OFDM type of transmission signals it is especially suited for situations when receiver moves at a high velocity.

Lastly the porfolio includes a method of equalizing an OFDM signal, this technology represents a robust (especially against inter-carrier interference) low complexity method for equalizing a received OFDM signal. The method gains in performance by using more than one orthogonal tapers for windowing.

Primary Application of the Technology


The Problem Solved by the Technology

The invention devises a method for estimating the BEM coefficients of the channel taps in an OFDM system with less computational and less memory requirements than the state of the art, in particular when scaling with the number of OFDM subcarriers.

The invention devises a method of equalizing a signal received over a transmission channel defined by BEM coefficients with less computational and less memory requirements for a given accuracy than the state of the art.

This technology solves the complexity problem of the equalization method in the OFDM transmissions
over doubly selective channels.

How the Technology Solves the Problem

The channel estimation solution is provided by
a) subsampling a received OFDM symbol in the frequency domain into a set of subsequences
b) inverse Fourier transfünning each subsequence into a transfonned subsequence
c) estimating Fourier coefficients of a truncated Fourier series expansion model of the channel taps from
the set of transformed subsequences.
d) calculating said BEM coefficients from said estimated Fourier coefficients.

The channel equalization method effectively approximates the BEM coefficients by utilizing a diagonal matrix which is derived from the circulant matrix via a similarity transformation with a descrete fourier transform matrix.

The diagonal matrix is computed directly from a discrete fourier transform of the mth BEM coefficients of all channel taps, zero-padded up to the signal length.

The inverse of the first circulant matrix for the zero order BEM coefficients is used as a preconditioner in the iterative method.

Said iterative method is the GMRES algorithm or the LSQR algorithm.

The equalizing of an OFDM signal uses at least two different tapers to window the received signal. Consequently, no part ofthe receive signal is attenuated in the same way by all the windows, and conditioning of the equalization improves dramatically.

Competitive Advantage

There are several advantages these technologies offer. Most attracting features are the low memory use and the robustness.

More concrete:

Mitigation of the Doppler shift
Compensation of the CFO
Synchronized with reception
Uses standard pilot arrangement
Based on FFT
Applicability in low SNRs
Energy efficiency
Can be used with any symbol constellation (4QAM, 16QAM, 64QAM)
Can be combined with any error correcting codes and any decision feedback mechanism

The seller may consider selling these patents individually.

Patent Summary

U.S. Patent Classes & Classifications Covered in this listing:

Class 375: Pulse Or Digital Communications

This is the generic class for pulse or digital communication systems using electrical or electromagnetic signals. Such communication includes transmitting an intelligence bearing signal from one point to another in the form of discrete variations in some parameter of the electrical or electromagnetic signal.

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