Timing synchronization in OFDM communications receivers

• US 6,754,170 B1
• Filed: 09/29/2000
• Issued: 06/22/2004
• Est. Priority Date: 09/29/2000
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Ward, Robert
• Primary Examiner(s): Patel, Ajit
• Application Number:
  US09/675,955
• Time in Patent Office: 1,362 Days
• Field of Search: 370/480, 370/208, 370/203, 370/343, 370/514, 370/484, 370/210, 370/206, 370/503, 370/509, 370/510, 370/511, 370/512, 370/513, 375/260, 375/219, 375/346, 375/222, 375/231, 375/232, 375/340, 375/348, 375/354, 375/356, 375/365, 375/366, 375/368
• US Class Current: 370/208
• CPC Class Codes: H04B 7/0811 during preamble or gap period
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2685 Speed of convergence

Abstract

An orthogonal frequency division multiplexing (OFDM) receiver is synchronized to a received signal during one of the short symbols of the preamble of the OFDM signal, using a timing synchronizing circuit that derives timing information from timing components generated by a constellation processing circuit which generates the timing components from frequency domain components obtained by performing a Fourier transform on the OFDM signal.

Claims

1. A method of synchronizing a receiver to a received orthogonal frequency division multiplexing (OFDM) signal having a preamble with short and long duration symbols, comprising the steps of:

a) converting the received OFDM signal by Fourier transform to frequency domain components;

b) processing the frequency domain components to timing components;

c) deriving timing information from the timing components;

d) applying the timing information to the received OFDM signal to synchronize the receiver; and

e) all of said steps being performed during one of the short symbols.

2. The method of claim 1;

and further comprising the step of buffering the received OFDM signal during another of the short symbols to obtain a buffered signal.

3. The method of claim 2;

and further comprising the step of automatically controlling the gain of the received OFDM signal during still another of the short symbols.

4. The method of claim 3;

and further comprising the step of selecting an antenna for the receiver during three of the short symbols.

5. The method of claim 2, wherein the applying step is performed by applying the timing information to the buffered signal.

6. The method of claim 5, wherein the deriving step is performed by generating fractional timing information from the timing components, and wherein the applying step is performed by applying the fractional timing information to the frequency domain components.

7. A method of antenna selection in a dual antenna receiver for receiving an orthogonal frequency division multiplexing (OFDM) signal having a preamble with short and long duration symbols, comprising the steps of:

a) converting an OFDM signal received by a first antenna by Fourier transform to frequency domain components;

b) processing the frequency domain components to timing components;

c) deriving timing information from the timing components;

d) applying the timing information to the received OFDM signal to synchronize the receiver;

e) analyzing a signal-to-noise ratio (SNR) of the OFDM signal received by the first antenna of the synchronized receiver during one of the short symbols;

f) repeating steps a) through e) for a second antenna during another of the short symbols; and

g) selecting the antenna which has a higher SNR during another of the short symbols.

8. The method of claim 7, wherein the step of selecting the antenna with the higher SNR is performed in no more than six of the short symbols.

9. An arrangement for synchronizing a receiver to a received orthogonal frequency division multiplexing (OFDM) signal having a preamble with short and long duration symbols, comprising:

a) a Fourier transform (FT) circuit for converting the received OFDM signal to frequency domain components;

b) a constellation processing (CP) circuit connected to the FT circuit, for processing the frequency domain components to timing components; and

c) a timing synchronizing circuit connected to the CP circuit, and operative for deriving timing information from the timing components, and for applying the timing information to the received OFDM signal to synchronize the receiver during one of the short symbols.

10. The arrangement of claim 9;

and further comprising an automatic gain control circuit for controlling the gain of the received OFDM signal during another of the short symbols.

11. The arrangement of claim 10;

and further comprising a buffer circuit connected to the gain control circuit, for buffering the received OFDM signal.

12. The arrangement of claim 11, wherein the timing synchronizing circuit is connected to the buffer circuit, for applying the timing information to the buffer circuit.

13. The arrangement of claim 12, wherein the timing synchronizing circuit is operative for generating and applying fractional timing information to a multiplier connected between the FT and CP circuits.