Method and apparatus for wireless spread spectrum communication with preamble sounding gap

• US 6,317,452 B1
• Filed: 05/07/1999
• Issued: 11/13/2001
• Est. Priority Date: 09/09/1994
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Xircom Incorporated (Intel Corporation)
• Inventors: Burbach, Mark, Durrant, Randolph L.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/307,646
• Time in Patent Office: 921 Days
• Field of Search: 375/141, 375/142, 375/146, 375/147, 375/150, 375/130, 375/133, 375/145, 375/149, 370/320, 370/335, 370/342
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04J 14/005 Optical Code Multiplex
• CPC Class Codes: H04L 27/2014 in which the phase changes in a piecewise linear manner during each symbol period, e.g. minimum shift keying, fast frequency shift keying H04L27/201 takes precedence
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

A wireless spread spectrum communication system comprises a spread spectrum transmitter and spread spectrum receiver which communicate according to an over-the-air protocol. The spread spectrum transmitter transmits a burst comprising a preamble followed by a short gap, followed by a data message. The spread spectrum receiver receives and demodulates the transmitted burst. The receiver detects the preamble using a non-coherent parallel correlator, and from the preamble correlation peak generates a series of integration periods for serial non-coherent correlation. The short gap between the preamble and the data message allows the receiver time to process the preamble and set the timing of the electronics for receiving the data message. The receiver has a plurality of non-coherent correlators operating in parallel to recover the spread spectrum encoded information. For each of M spread spectrum codes, the receiver simultaneously attempts to correlate the non-preamble portion of the received spread spectrum signal by separating the received signal into real and imaginary parts, correlating both real and imaginary parts for I and Q sequences, and combining the real I, real Q, imaginary I, and imaginary Q correlation signals into a unified correlation signal.

Claims

1. A method for spread-spectrum communication between a first transceiver and a second transceiver, the method comprising the steps of:

transmitting, from a spread spectrum transmitter associated with the first transceiver to a spread spectrum receiver associated with the second transceiver, a spread spectrum preamble;

transmitting, from said spread spectrum transmitter to said spread spectrum receiver, a spread spectrum encoded data message immediately following said spread spectrum preamble, said spread spectrum encoded data message separated in time from said spread spectrum preamble by a predefined gap during which the second transceiver does not transmit to the first transceiver;

receiving said spread spectrum preamble at said spread receiver;

generating, at said spread spectrum receiver, a correlation signal in response to said spread spectrum preamble;

receiving said spectrum encoded data message at said spread spectrum receiver; and

despreading said spread spectrum encoded data message at said spread spectrum receiver.

2. The method of claim 1, wherein said predefined gap is of sufficient duration to allow correlation of said spread spectrum preamble by said spread spectrum receiver.

3. The method of claim 1, further comprising the steps of

generating a repeating time frame, and

defining a plurality of equally spaced time offsets relative to a starting boundary of said repeating time frame,

wherein said step of transmitting said spread spectrum preamble comprises the step of transmitting said spread spectrum preamble with reference to one of said time offsets.

4. A spread spectrum communication system, comprising:

a first transceiver having a first spread spectrum transmitter and a first spread spectrum receiver, said first spread spectrum transmitter transmitting a burst comprising a spread spectrum preamble and a spread spectrum encoded data message following said spread spectrum preamble after a preamble sounding gap; and

a second transceiver having a second spread spectrum transmitter and a second spread spectrum receiver, said second spread spectrum receiver comprising circuitry for receiving and correlating to said spread spectrum preamble and circuitry for receiving and processing said spread spectrum encoded data message;

wherein said second spread spectrum transmitter does not transmit to said first spread spectrum receiver during said preamble sounding gap.

5. A spread spectrum communication system, comprising:

a first transceiver comprising a spread spectrum transmitter; and

a second transceiver comprising a spread spectrum receiver;

wherein said spread spectrum transmitter and said spread spectrum receiver communicate using an over-the-air protocol according to which said spread spectrum transmitter transmits, and said spread spectrum receiver receives, a spread spectrum preamble followed after an idle period of predetermined duration by a spread spectrum encoded data message, said idle period being relatively short in comparison to a period of transmitting said spread spectrum encoded data message, no information being transmitted by said spread spectrum transmitter or received by said first transceiver during said idle period.

6. The spread spectrum communication system of claim 5, wherein said spread spectrum transmitter transmits a non-informational fill code during said idle period.

7. A multiple-access spread spectrum communication system, comprising:

a base station, said base station comprising a base station transmitter and a base station receiver; and

a plurality of user stations, each of said user stations comprising a user station transmitter and a user station receiver;

wherein each of said user stations transmits on an assigned channel a burst with reference to one of a plurality of time slots of a repeating time frame during which burst the user station does not receive information from the base station on the same channel, each burst comprising a spread spectrum preamble, a preamble sounding gap following said spread spectrum preamble, and a spread spectrum encoded data message following said spread spectrum preamble, said preamble sounding gap being shorter in duration than said spread spectrum encoded data message; and

wherein, for each burst, said base station receives said spread spectrum preamble, correlates said spread spectrum preamble during said preamble sounding gap, and despreads said spread spectrum encoded data message thereafter based upon the correlation of said spread spectrum preamble.

8. The multiple-access spread spectrum communication system of claim 7, wherein said spread spectrum preamble is the same for each of said user stations communicating with said base station.

9. The multiple-access spread spectrum communication system of claim 8, wherein said base station is located in a cell within a cellular communication system, wherein said spread spectrum preamble comprises a spread spectrum code selected from a set of spread spectrum codes available to each user station, and wherein each user station transmits a second spread spectrum preamble to a second base station located in a different cell from said base station, said second spread spectrum preamble comprising a different spread spectrum code than said first spread spectrum preamble.

10. The multiple-access spread spectrum communication system of claim 7, wherein said spread spectrum encoded data message comprises a sequence of M-ary spread spectrum codes of predefined length, and wherein said base station receiver comprises

means for dividing a received signal into a real signal and an imaginary signal;

a non-coherent parallel correlator for correlating to said spread spectrum preamble, said non-coherent parallel correlator receiving as inputs said real signal and said imaginary signal and generating, during the preamble sounding gap following receipt of said spread spectrum preamble, a correlation signal of variable width upon recognizing said spread spectrum preamble;

a center-seeking circuit for identifying the center of correlation signal and synchronizing a correlation clock thereby during said preamble sounding gap;

a bank of serial correlators, each of said serial correlators configured to recognize a different one of said M-ary spread spectrum codes and generate a correlation signal upon recognizing its respective M-ary spread spectrum code, said serial correlators each comprising an integrator responsive to said correlation clock and each receiving as inputs said real signal and said imaginary signal; and

a best-of-M magnitude comparator and data extractor connected to the output correlation signal from each of said serial correlators.

11. A method for multiple-access spread spectrum communication, comprising the steps of:

transmitting, from each of a plurality of user stations, a spread spectrum preamble;

transmitting, from each of said user stations, a spread spectrum encoded data message following the respective spread spectrum preamble transmitted by a user station, said spread spectrum encoded data message lagging said spread spectrum preamble by a preamble sounding gap during which the user station does not receive a data message, said preamble sounding gap shorter in duration than said spread spectrum preamble;

receiving said spread spectrum preambles at a receiver;

generating a correlation signal at said receiver in response to each spread spectrum preamble received at said receiver;

receiving said spread spectrum encoded data messages at said receiver, each spread spectrum encoded data message received following arrival of its respective spread spectrum preamble;

despreading each spread spectrum encoded data message at said receiver.

12. The method of claim 11, further comprising the steps of

generating, a plurality of time frames, and

defining a plurality of equally spaced time offsets relative to a starting boundary of each of said time frames,

wherein said step of transmitting, from each of said plurality of user stations, said spread spectrum preamble comprises the step of transmitting, from each of said plurality of user stations, said spread spectrum preamble with reference to one of said time offsets.