Pulse or digital communications – Spread spectrum
Reexamination Certificate
1997-06-23
2001-07-17
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
C375S140000, C375S142000, C375S143000, C375S150000
Reexamination Certificate
active
06263009
ABSTRACT:
RELATED APPLICATIONS
This application is related to the following co-pending applications, all filed on the same day and naming the same inventors as this application: “Processing a Spread Spectrum Signal in a Frequency Adjustable System”; “Bandpass Correlation of a Spread Spectrum Signal”; “Bandpass Processing of a Spread Spectrum Signal”; and “Receiving a Spread Spectrum Signal”.
BACKGROUND OF THE INVENTION
The invention relates to processing a spread spectrum signal.
In wireless systems, information typically is transmitted by modulating the information onto carrier waves having frequencies that lie within preassigned frequency bands. Radio frequency (RF) receivers demodulate the carrier waves to recover the transmitted information.
Spread spectrum communication systems spread transmitted signals over bandwidths much larger than those actually required to transmit the information. Spreading a signal over a wide spectrum has several advantages, including reducing the effects of narrow band noise on the signal and, in many situations, providing increased protection against interception by unwanted third parties. In a direct sequence spread spectrum (DSSS) system, the bandwidth of a transmitted signal is increased by modulating the signal onto a known pseudo-noise (PN) signal before modulating onto the carrier wave. The PN signal typically is a digital signal having an approximately equal number of high and low bits (or “chips”), which maximizes the spectrum over which the signal is spread. A typical implementation of a DSSS receiver recovers the transmitted information by demodulating the carrier wave and then multiplying the resulting signal with a local replica of the PN signal to eliminate the PN signal. The DSSS technique offers heightened security because the receiver must know the PN sequence used in the transmission to recover the transmitted information efficiently. Other spread spectrum techniques include frequency hopped spread spectrum (FHSS).
SUMMARY OF THE INVENTION
In one aspect, the invention features detecting a spread spectrum signal at an unknown spreading signal phase. A despreading function is performed on a signal sampled from the spread spectrum signal at a selected sampling rate. The despreading function uses multiple reference signals, each of which represents one of multiple search phases of the spreading signal. Accumulation outputs then are produced by combining a despreading output with a phase-shifted version of the corresponding accumulation output.
Advantages of the invention may include one or more of the following. Implementation efficient correlators may be used to reduce the costs of DSSS acquisition circuits and to increase the capabilities of such acquisition circuits. Inexpensive correlators allow the use of many correlators in an acquisition circuit, possibly even more correlators than there are possible code phases of the spreading signal used to generate the DSSS signal. Using many correlators allows a more rapid search over a wider frequency range.
Other advantages of the invention will become apparent from the description and from the claims.
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Froelich Robert K.
Fulton Forrest F.
Ramberg Erik A.
CellNet Data Systems, Inc.
Chin Stephen
Fish & Richardson P.C.
Liu Shuwang
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