Timing signal correction system for use in direct sequence spread signal receiver

• US 4,653,076 A
• Filed: 03/23/1984
• Issued: 03/24/1987
• Est. Priority Date: 03/23/1984
• Status: Expired due to Term

• Current Assignee: Itron Electricity Metering, Inc. (Itron, Inc.)
• Original Assignee: Sangamo Weston, Inc.
• Inventors: Jerrim, John W., Horwitz, Lawrence B.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Huseman, M.
• Application Number:
  US06/592,668
• Time in Patent Office: 1,096 Days
• Field of Search: 375/1, 375/115, 375/107, 375/111, 375/96, 370/18
• US Class Current: 375/367
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713

Abstract

A direct sequence spread spectrum transmitter and receiver can be synchronized when the timing reference frequency is less than or equal to the data sampling rate and the ratio of the data sampling rate to the timing reference is an integer by combining two, four or eight consecutive data samples to yield one data sample point. By combining these data samples, an optimum data sample point may be determined while receiving an alternating sign preamble by comparing the magnitudes of all possible summations and selecting the sample which gives a maximum output. If each sample is assigned to its own synchronization point, then synchronization may be accomplished by locking to the time that gives the maximum output.

Claims

1. In a data receiver adapted to receive a data signal from one of a plurality of transmitters, each transmitting a data signal spread by a common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence and timing signals from a timing source, the receiver including means for establishing initial synchronization between the receiver and a predetermined one of the transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence and means for sampling said data signal at an integral multiple of the frequency of the timing signal source to obtain data samples, and wherein there is a tendency of the receiver and predetermined transmitter to become locked to different signals of said timing signal source and thereby have a reduced data recovery characteristic, a method of locking said receiver and the predetermined transmitter to common timing signals following initial synchronization of said receiver and predetermined transmitter by said synchronization means, comprising the steps of:

(a) combining at least two consecutive data samples to generate data sample points corresponding to particular timing points of said timing signal source;

(b) detecting which one of said data sample points has a maximum value; and

(c) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.

2. In a direct sequence spread spectrum code division multiplex system comprising a timing signal source, a plurality of transmitters synchronized to the timing signal source and each transmitting a data signal spread by common pseudo-random code which is a different assigned shift of a common pseudo-random code sequence, and a receiver normally synchronized to the timing signal source for receiving said transmitted pseudo-random code from a predetermined one of said transmitters having a predetermined assigned code sequence shift, said receiver including means for establishing initial synchronization between the receiver and a predetermined one of the transmitters transmitting a data signal spread by the pseudo-random code having said predetermined assigned code sequence and means for sampling said data signal at an integral multiple of the frequency of the timing signal source to obtain data samples, and wherein there is a tendency of the receiver and predetermined transmitter to become locked to different signals of said timing signal source and thereby have a reduced data recovery characteristic, a method of locking said receiver and predetermined transmitter to common signals of said timing source, following initial synchronization of said receiver and predetermined transmitter by said synchronization means, comprising the steps of:

(a) combining at least two consecutive data samples together to generate data sample points corresponding to particular timing points of said timing signal source;

(b) detecting which one of said data sample points has a maximum value; and

(c) locking the receiver to the timing point of the timing signal source corresponding to said detected maximum value data sample point.