OFDM communication channel

Abstract

In an OFDM-based receiver, means for achieving time synchronization comprising: A. means for extracting pilot signals contained in the OFDM received signal; B. means for analyzing the pilot signals in the frequency domain and for issuing a signal indicative of a synchronization error in the received signal; C. means for correcting the synchronization error responsive to the signal indicative of the synchronization error. In an OFDM-based receiver, automatic frequency correction means in a subscriber unit comprising: A. an inner frequency correction loop for generating a LO frequency related to a frequency of a received signal; B. an outer frequency correction loop for correcting the LO frequency according to instructions received from a base station. In an OFDM-based receiver, a channel sounder comprising: A. means for extracting pilot signals contained in the OFDM received signal; B. means for analyzing the pilot signals in the frequency domain and for issuing signals indicative of a distortion in each pilot signal, wherein each of said pilot distortion signals comprises both an amplitude and a phase component; C. means for analyzing the signals indicative of a distortion in each pilot signal and for computing therefrom corrective signals for correcting distortions in the received signal.

Description

[0001] The present application is a divisional from U.S. patent application Ser. No. 09 / 493,662 entitled “OFDM communication channel” filed on 28 Jan. 2000, and claims priority therefrom.FIELD OF THE INVENTION [0002] This invention relates to OFDM communication channels, and more particularly to improvements in channel performance using signal processing of pilot signals in the channel. BACKGROUND OF THE INVENTION [0003] Advanced communications today may use the Orthogonal Frequency Division Multiplex (OFDM) modulation for efficient transmission of digital signals. These signals may include video, voice and / or data. OFDM is a commonly used implementation of Multi-Carrier Modulation (MCM). [0004] The Orthogonal Frequency Division Multiplex (OFDM) is a modern advanced modulation method, that achieves better use of the frequency spectrum. [0005] OFDM has been used in recent years in many applications where robustness against severe multipath and interference conditions is required, or ...

AI Technical Summary

Benefits of technology

[0074] Thus, the system will adapt to varying channel characteristics in real time, to achieve improved communications.

[0080] A second application relates to a channel sounder. Using means for analyzing the received pilot signals, a signal processor can characterize the communication channel. Using the pilots rather than the information or noise in the channel may achieve a better performance system.

[0083] A better correction may be achieved using an interpolation process to correct for phase and amplitude of received signals between any two adjacent pilots. This corrects the distortion of the signal frequency spectrum, to improve the receiver performance.

[0088] Using signal processing applied to the spectral picture (the pilots representation in the frequency domain), each pilot signal can be reconstructed. The changes in the pilots are indicative of the multipath effects in the channel. The information thus derived may be used to correct for multipath. Thus, the interference because of multipath is reduced.

[0089] Moreover, multipath signals may be added to the main path signal, to actually increase the signal power to improve the signal to noise ratio.

Problems solved by technology

A possible problem in the above modulation scheme may be an error in the time synchronization between several signals appearing at the receiver, or between transmitter and receiver.

This effect creates interference within the subchannel.

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