Wireless communication system and method for synchronization

• US 6,487,252 B1
• Filed: 01/29/1999
• Issued: 11/26/2002
• Est. Priority Date: 01/29/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Humphrey, Michael Eugene, Kleider, John Eric, Bergstrom, Chad Scott, Chuprun, Jeffery Scott, Tarver, Byron L.
• Primary Examiner(s): Corrielus, Jean
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/240,944
• Time in Patent Office: 1,397 Days
• Field of Search: 375/142, 375/145, 375/146, 375/149, 375/240.28, 375/240.18, 375/260, 375/296, 375/326, 375/327, 375/330, 375/342, 375/343, 375/355, 375/362, 375/364, 375/365, 375/367, 370/319-320, 370/324, 370/330, 370/344, 370/342, 370/350, 370/465, 370/480, 370/481, 370/482, 370/503, 370/509, 370/510, 370/513, 370/515
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

An orthogonal frequency division multiplexed wideband communication system provides improved time and frequency synchronization by inserting an unevenly spaced pilot sequence within the constellation data. A receive correlates the received data using the unevenly spaced pilot sequence. The pilot sequence is generated with a maximum length pseudo random noise code and inserted into frequency bins having prime numbers.

Claims

1. A wireless communication system comprising:

a transmitter and a receiver coupled by an communication link, the transmitter comprising;

a modulator element for converting digital data to symbols, said symbols being assigned to frequency bins of a set of frequency bins;

a pilot tone generator for generating a sequence of pilot tones, each pilot tone being associated with frequency bins not assigned to symbols from said modulator element, the frequency bins assigned to said pilot tones being unevenly spaced therebetween;

a polyphase filter for performing an inverse fast Fourier transform (FFT) on the symbols assigned to said set frequency bins and providing a plurality of output samples;

a transmitting portion for transmitting the plurality of output samples over the communication link;

the receiver comprises a correlator for correlating the plurality of output samples received over the communication link with a reference for use in retrieving said digital data, said reference comprising said sequence of pilot tones associated with the unassigned frequency bins; and

the pilot tone generator includes a pilot tone location assignment table identifying said frequency bins assigned to each pilot tone.

2. A system as claimed in claim 1 wherein the pilot tone generator generates said sequence of pilot tones based on a pseudo-noise (PN) sequence having a sequence length, said sequence length corresponding to a number pilot tones of said sequence of pilot tone.

3. A system as claimed in claim 1 wherein said pilot tone location assignment table identifies frequency bins, at least some having locations associated with prime numbered bins of said set of frequency bins.

4. A system as claimed in claim 3 wherein said receiver further comprises a receiver pilot tone generator for generating said sequence of pilot tones for said reference.

5. A system as claimed in claim 3 wherein said receiver further comprises a memory for storing said sequence of pilot tones and said pilot tone location assignment table.

6. A system as claimed in claim 1 wherein the correlator further comprises:

means for adding a stepped frequency offset said reference producing a frequency offset reference;

means for correlating the plurality of output samples received over the communication link with each stepped frequency offset reference for use in retrieving said digital data.

7. A system as claimed in claim 1 wherein the correlator further comprises:

a first FFT element for performing a course Fourier transform on the plurality of output samples received over the communication link, the first FFT element providing a time delay;

a delay element for delaying the plurality of output samples received over the communication link by said time delay;

a second FFT element for performing a fine Fourier Transform on the delayed plurality of output samples; and

means for correlating the delayed plurality of output samples received over the communication link with said reference to retrieve said digital data.

8. A system as claimed in claim 7 wherein the fine Fourier transform is the substantially the same resolution as the inverse FFT performed by the polyphase filter, the course Fourier transform having less resolution than said fine Fourier transform.

9. A system as claimed in claim 1 wherein the receiver further comprises:

a FFT element for performing a Fourier transform on correlated data provided by said correlator and providing channelized data;

a demodulator for operating on the channelized data, the channelized data substantially corresponding with said parallel digital data converted by said modulator.

10. A system as claimed in claim 1 wherein the modulator element comprises a plurality of modulators, at least a one modulator of the plurality being of a first type for operating on voice data, and at least one other modulator of the plurality being of a second type for operating on video data, the voice and video data being present in the digital data, each modulator of the plurality providing said symbols to said polyphase filter.

11. A system as claimed in claim 1 wherein the transmitter further comprises:

a serial to parallel converter for converting sequential digital data from sequential to parallel digital data, and providing said parallel digital data to said modulator element;

a parallel to serial converter for converting the plurality of output samples provided by said polyphase filter to serial digital data, said transmitting portion transmitting said serial digital data; and

a multi-path formatter for adding a cyclic extension to said serial digital data prior to transmission by said transmitting portion.

12. A system as claimed in claim 1 wherein:

the transmitter further comprises a differential encoder for differentially encoding the plurality of output samples provided by the polyphase filter, and

the receiver further comprises a differential decoder for differentially decoding the serial digital data received over the communication link and providing differentially decoded data, said differentially decoded data being corrected for frequency offset associated with said serial digital data received over the communication link.

13. A method of communicating comprising the steps of:

converting digital data to symbols, said symbols being assigned to frequency bins of a set of frequency bins;

generating a sequence of pilot tones, each pilot tone being associated with frequency bins not assigned to symbols from said modulator element, the frequency bins assigned to said pilot tones being unevenly spaced therebetween;

performing an inverse fast Fourier transfer (FFT) on the symbols assigned to said set frequency bins and providing a plurality of output samples; and

transmitting the plurality of output samples over a communication link;

correlating the plurality of output samples received over the communication link with a reference for use in retrieving said digital data, said reference comprising said sequence of pilot tones associated with unassigned frequency bins; and

the generating step includes the step of reading a pilot tone location assignment table identifying said frequency bins assigned to each pilot tone.

14. A method as claimed in claim 13 wherein the generating step includes the step of generating said sequence of pilot tones based on a pseudo-noise (PN) sequence having a sequence length, said sequence length corresponding to a number pilot tones of said sequence of pilot tones.

15. A method as claimed in claim 13 wherein the reading step, said pilot tone location assignment table identifies frequency bins, at least some having locations associated with prime numbered bins of said set of frequency bins.

16. A method as claimed in claim 15 further comprising the step of generating said sequence of pilot tones for said reference.

17. A method as claimed in claim 15 further comprising the step of storing said sequence of pilot tones and said pilot tone location assignment table.

18. A method as claimed in claim 13 further comprising the steps of:

adding a stepped frequency offset said reference producing a frequency offset reference;

correlating the plurality of output samples received over the communication link with each stepped frequency offset reference for use in retrieving said digital data.

19. A method as claimed in claim 13 wherein the correlating step further comprises:

performing a course Fourier transform on the plurality of output samples received over the communication link to provide a time delay;

delaying the plurality of output samples received over the communication link by said time delay;

performing a fine Fourier Transform on the delayed plurality of output samples; and

correlating the delayed plurality of output samples received over the communication link with said reference to retrieve said digital data.