Direct-sequence spread-spectrum digital signal acquisition and tracking system and method therefor

A method of acquiring and tracking direct-sequence spread-spectrum frames of digital information, said method comprising the steps of:

• (a) spreading at a first location digital acquisition data in an assigned acquisition time slot in each frame of said digital information with a direct-sequence acquisition spreading code, each frame having a predetermined number of time slots,
• (b) spreading at the first location digital communication data in the remaining time slots of each frame with a direct-sequence communication code,
• (c) acquiring synchronization at a second location with the spread direct-sequence acquisition spreading code by measuring the signal strength in each time slot in a given number of successive frames until the assigned time slot having the largest signal strength is located,
• (d) tracking synchronization of the received digital communication data by selecting the largest signal strength in a header field provided in each remaining time slot of each successive frame after acquisition so as to compensate for drift between the first and second locations,
• (e) despreading at the second location the digital communication data in the remaining time slots in each frame with the direct-sequence communication spreading code.

A method of acquiring direct-sequence spread-spectrum frames of digital information, said method comprising the steps of:

• (a) spreading at a first location digital acquisition data in an assigned acquisition time slot in each frame of said digital information with a direct-sequence acquisition spreading code, each frame having a predetermined number of time slots,
• (b) spreading at the first location digital communication data in the remaining time slots of each frame with a direct-sequence communication code,
• (c) acquiring synchronization at a second location with the spread direct-sequence acquisition spreading code by measuring the signal strength in each time slot in a given number of successive frames until the assigned time slot having the largest signal strength is located, and
• (d) despreading after the steps of acquiring and tracking at the second location the digital communication data in the remaining time slots in each frame with the direct-sequence communication spreading code.

A method of tracking direct-sequence spread-spectrum frames of digital information, said method comprising the steps of:

• (a) spreading at a first location said digital information with a direct-sequence acquisition spreading code, each frame having a predetermined number of time slots with each time slot having header bytes,
• (b) acquiring synchronization at a second location with the spread direct-sequence acquisition spreading code,
• (c) tracking synchronization by selecting the largest signal strength in the header field provided in a given time slot of each successive frame after acquisition so as to compensate for drift between the first and second locations,
• (d) despreading after the step of tracking at the second location the digital information in each frame with the direct-sequence communication spreading code.

A spread-spectrum communication system for transferring digital information from a transmitter to a receiver, said system comprising:

• said transmitter comprising:
• (a) means (40) for providing a plurality of frames of digital data, each frame having a predetermined number of time slots, one of said time slots in each frame being assigned to carry acquisition digital data, the time slots in each frame being assigned to carry communication digital data, each of said time slots having a header field containing tracking digital information,
• (b) means (10, 20) for generating first and second direct-sequence spreading digital codes having a higher frequency than the frequency of said digital data,
• (c) means (30, 50) connected to said providing means and to said generating means for spreading said frames of digital data, said acquisition digital data in said one time slot being spread by said first direct-sequence spreading digital code and said communication digital data in said remaining time slots being spread by said second direct-sequence spreading digital code,
• said receiver having:
• (a) means (320) for generating said first and second direct-sequence spreading digital codes,
• (b) means (310, 350) receptive of said spread frames of digital data and connected to said receiver generating means for despreading said spread frames of digital data,
• (c) means (340, 360, 370) connected to said receiver generating means and to said despreading means for adjusting said generating means until said receiver generated first and second direct-sequence spreading digital codes are in synchronization with said first and second transmitter generated direct-sequence codes used to spread said frames of digital data, said adjusting means acquiring synchronization with said acquisition digital data in said one time slot in each of said spread frames;
• after acquiring synchronization said adjusting means tracking synchronization with the tracking digital information in each of said remaining time slots in each of said spread frames.

A spread-spectrum communication system for despreading digital information, said system comprising:

• said transmitter comprising:
• (a) means (40) for providing a plurality of frames of digital data, each frame having a predetermined number of time slots, one of said time slots in each frame being assigned to carry acquisition digital data, the time slots in each frame being assigned to carry communication digital data, each of said time slots having a header field containing tracking digital information,
• (b) means (10, 20, 30, 50) connected to said providing means and to said generating means for spreading said frames of digital data,
• said receiver having:
• (a) means (310, 320, 350) receptive of said spread frames of digital data and connected to said receiver generating means for despreading said spread frames of digital data,
• (b) means (340, 360, 370) connected to said despreading means for adjusting said generating means until said receiver acquires said spread frames by determining the location of said time slot carrying said acquisition data, said adjusting means acquiring synchronization with said acquisition digital data in said one time slot in each of said spread frames;
• after acquiring synchronization said adjusting means tracking synchronization by further adjusting said despreading means only during the presence of the tracking digital information in each of said remaining time slots in each of said spread frames.

A spread-spectrum communication system for transferring digital information from a plurality of transmitters to a receiver, said system comprising:

• each of said transmitters comprising:
• (a) means (40) for providing a plurality of frames of digital data, each frame having a predetermined number of time slots, one of said time slots in each frame being assigned to carry acquisition digital data,
• (b) means (10, 20) for generating a direct-sequence spreading digital acquisition code having a higher frequency than the frequency of said digital data,
• (c) means (30, 50) connected to said providing means and to said generating means for spreading said frames of digital data, said acquisition digital data in said one time slot being spread by said direct-sequence spreading digital acquisition code,
• said receiver having:
• (a) means (320) for generating said direct-sequence spreading digital acquisition code,
• (b) means (310, 350) receptive of said spread frames of digital data from each of said transmitters and connected to said receiver generating means for despreading said spread frames of digital data from each of said transmitters,
• (c) means (340, 360, 370) connected to said receiver generating means and to said despreading means for adjusting said generating means until said receiver generated direct-sequence spreading digital acquisition code is in synchronization with said generated direct-sequence code used to spread said frames of digital data from each of said transmitter, said adjusting means acquiring synchronization with the acquisition digital data in said one time slot in each of said spread frames from the transmitter providing the highest signal strength.