Low-rate long-range mode for OFDM wireless LAN

• US 7,733,939 B2
• Filed: 11/03/2005
• Issued: 06/08/2010
• Est. Priority Date: 11/03/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Trachewsky, Jason Alexander
• Primary Examiner(s): Ghayour; Mohammad H
• Assistant Examiner(s): Vlahos; Sophia
• Application Number:
  US11/265,134
• Publication Number:
  US 20060104335A1
• Time in Patent Office: 1,678 Days
• Field of Search: 375/141, 375/260, 375/219, 375130-131, 375135-136, 375/295, 375/316
• US Class Current: 375/141
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04K 1/00 Secret communication
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/026 using code division
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: H04W 4/18 Information format or content conversion, e.g. adaptation by the network of the transmitted or received information for the purpose of wireless delivery to users or terminals
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/04 adapted for relaying to or from another terminal or user

Abstract

A system for implementing an orthogonal frequency division multiplexing scheme and providing an improved range extension. The system includes a transmitter for transmitting data to a receiver. The transmitter includes a symbol mapper for generating a symbol for each of a plurality of subcarriers and a spreading module for spreading out the symbol on each of the plurality of subcarriers by using a direct sequence spread spectrum. The symbol on each of the plurality of subcarriers is spread by multiplying the symbol by predefined length sequences. The receiver includes a de-spreader module for de-spreading the symbols on each of the plurality of subcarriers. The de-spreader module includes a simply correlator receiver for obtaining maximum detection. The correlator produces an output sequence of a same length as an input sequence and the de-spreader module uses a point of maximum correlation on the output sequence to obtain a recovered symbol.

Claims

1. A wireless communication device comprising:

a receiver and a transmitter,

wherein the transmitter comprises a symbol mapper and a spreading module,

wherein the symbol mapper is configured to generate, from data, a stream of sub-symbols for each of a plurality of orthogonal frequency division multiplexing (OFDM) subcarriers;

wherein the spreading module is configured to spread out the stream of sub-symbols on each of the plurality of OFDM subcarriers by using direct sequence spread spectrum (DSSS) techniques in which the stream of sub-symbols on each of the plurality of OFDM subcarriers is spread across an OFDM subcarrier bandwidth by multiplying the stream of sub-symbols by spreading code sequences of predefined length, each sub-symbol being expanded into a set of chips, the number of chips in the set being related to the predefined length,

wherein the transmitter appends, to an outgoing signal to be wirelessly transmitted, a number of copies of short training symbols, the number of copies of the short training symbols equaling the number of chips in the set, the copies of the short training symbols being transmitted between a legacy signal and a proprietary signal.

2. The device according to claim 1, wherein the transmitter comprises:

a scrambler configured to scramble bits in the data;

a convolution encoder and puncture module configured to code the data with a coding rate of half, prior to transmitting the data to the symbol mapper;

an Inverse Fast Fourier Transformer configured to convert the OFDM subcarriers output by the spreading module from a frequency domain to a time domain;

a parallel-to-serial converter configured to convert parallel time domain signals to a plurality of serial time domain signals; and

a cyclic prefix insertion module configured to introduce a cyclic prefix as a guard interval to each of the plurality of the OFDM subcarriers.

3. The device according to claim 1, wherein the symbol mapper is further configured to generate a stream of quadrature phase shift keying sub-symbols for each of the plurality of subcarriers.

4. The device according to claim 3, wherein the stream of sub-symbols on each of the plurality of subcarriers is spread over the frequency domain OFDM subcarrier bandwidth.

5. The device according to claim 1, wherein the stream of sub-symbols on each of the plurality of subcarriers is spread using a Constant Amplitude Zero Auto Correlation sequence, wherein when a correlation is performed with itself, a non zero component is present at only one point in time.

6. The device according to claim 1, wherein the stream of sub-symbols on each of the plurality of subcarriers is spread using length Constant Amplitude Zero Auto Correlation sequences, wherein the length is one of four, sixteen or sixty-four.

7. The device according to claim 1, wherein when the length is four the spreading module produces four symbols for each of the plurality of subcarriers.

8. The device according to claim 1, wherein when the length is sixteen the spreading module produces sixteen symbols for each of the plurality of subcarriers.

9. The device according to claim 1, wherein when the length is sixty-four the spreading module produces sixty-four symbols for each of the plurality of subcarriers.

10. The device according to claim 1, wherein each of the chips in the set is mapped to a different OFDM sub-carrier of the plurality of OFDM sub-carriers.

11. The device according to claim 1, wherein the wireless communications device is a cellular phone.

12. A method that provides for orthogonal frequency division multiplexing (OFDM) communications in a wireless communications device, the method comprising:

generating, by a transmitter of the wireless communications device, a stream of sub-symbols for each of a plurality of OFDM subcarriers from a stream of data bits;

spreading out, by the transmitter of the wireless communications device, the stream of sub-symbols on each of the plurality of OFDM subcarriers by using direct sequence spread spectrum (DSSS) techniques, wherein the symbol on each of the plurality of OFDM subcarriers is spread by multiplying the stream of sub-symbols by spreading code sequences of predefined length, each sub-symbol being expanded into a set of chips, the number of chips in the set being related to the predefined length; and

appending, by the transmitter of the wireless communications device, to an outgoing signal to be wirelessly transmitted, a number of copies of short training symbols, the number of copies of the short training symbols equaling the number of chips in the set, the copies of the short training symbols being transmitted between a legacy signal and a proprietary signal.

13. The method according to claim 12, wherein the transmitter of the wireless communications device performs at least the following:

scrambling bits in an incoming data portion;

coding the data with a coding rate of half prior to the generating of the stream of sub-symbols;

converting OFDM subcarriers from a frequency domain to a time domain, after the spreading out the stream of sub-symbols;

converting parallel time domain signals to a plurality of serial time signals; and

introducing a cyclic prefix as a guard interval to each of the plurality of OFDM subcarriers.

14. The method according to claim 12, wherein the generating of the stream of sub-symbols further comprises generating a stream of quadrature phase shift keying sub-symbols for each of the plurality of OFDM subcarriers.

15. The method according to claim 12, wherein the spreading out of the stream of sub-symbols further comprises spreading the stream of sub-symbols on each of the plurality of OFDM subcarriers over the frequency domain OFDM subcarrier bandwidth.

16. The method according to claim 12, wherein the spreading out of the stream of sub-symbols further comprises spreading the stream of sub-symbols on each of the plurality of OFDM subcarriers using a Constant Amplitude Zero Auto Correlation sequence, wherein when a correlation is performed with itself, a non zero component is present at only one point in time.

17. The method according to claim 12, wherein the spreading out of the stream of sub-symbols further comprises spreading the symbol on each of the plurality of OFDM subcarriers using length Constant Amplitude Zero Auto Correlation sequences, wherein the length is one of four, sixteen or sixty-four.

18. The method according to claim 17, wherein the spreading out of the stream of sub-symbols further comprises producing four sub-symbols for each of the plurality of OFDM subcarriers when the length is four.

19. The method according to claim 17, wherein the spreading of the stream of sub-symbols further comprises producing sixteen sub-symbols for each of the plurality of OFDM subcarriers when the length is sixteen.

20. The method according to claim 17, wherein the spreading of the stream of sub-symbols further comprises producing sixty-four sub-symbols for each of the plurality of OFDM subcarriers when the length is sixty-four.

21. The method according to claim 12, wherein each of the chips in the set is mapped to a different OFDM sub-carrier of the plurality of OFDM sub-carriers.

22. The method according to claim 12, wherein the wireless communications device is a cellular phone.

23. A wireless communication device that supports orthogonal frequency division multiplexing communications comprising:

a transmitter that comprises

a symbol mapper configured to generate a stream of quadrature amplitude modulation (QAM) sub-symbols for each of a plurality of orthogonal frequency division multiplexing (OFDM) subcarriers, and

a spreading module configured to spread out the stream of QAM sub-symbols on each of the plurality of subcarriers by using direct sequence spread spectrum (DSSS) techniques, wherein the stream of QAM sub-symbols on each of the plurality of subcarriers is spread by multiplying the stream of QAM sub-symbols by DSSS spreading code sequences of predefined length, each QAM sub-symbol being expanded into a set of chips, the number of chips in the set being related to the predefined length; and

a receiver that comprises a cyclic prefix removal module that is coupled to a Fast Fourier Transformer that is coupled to a frequency domain module that applies a weighting factor on each frequency domain signal, the frequency domain module being coupled to a de-spreader that is coupled to a QAM symbol demapper that is coupled to a parallel-to-serial converter that is coupled to a decoder that is coupled to a de-scrambler,

wherein the de-spreader module comprises a correlator,

wherein the de-spreader module is configured to detect a maximum correlator output from a plurality of correlator outputs, the number of correlator outputs being related to the predefined length, and

wherein transmitter appends, to an outgoing signal to be wirelessly transmitted, a number of copies of short training symbols, the number of copies of the short training symbols equaling the number of chips in the set, the copies of the short training symbols being transmitted between a legacy signal and a proprietary signal.

24. The device according to claim 23, wherein the correlator comprises a matched filter.

25. The device according to claim 23, wherein each of the chips in the set is mapped to a different OFDM sub-carrier of the plurality of OFDM sub-carriers.

26. The device according to claim 23, wherein the wireless communications device is a cellular phone.