Time synchronization of packetized radio signals to base stations

• US 6,539,004 B1
• Filed: 09/17/1998
• Issued: 03/25/2003
• Est. Priority Date: 09/17/1998
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Sawyer, Albert Joseph
• Primary Examiner(s): Nguyen, Steven
• Assistant Examiner(s): Nguyen, Phuongchau Ba
• Application Number:
  US09/154,885
• Time in Patent Office: 1,650 Days
• Field of Search: 370/441, 370/333, 370/337, 370/235, 370/236, 370/238, 370/239, 370/253, 370/301, 370/307, 370/235.1, 370/328, 370/331, 370/335, 370/342, 370/350, 370/316, 370/332, 370/395.4, 370/320, 370/902, 370/508, 370/509, 370/510, 370/512, 370/516-519, 370/336, 370/58.3, 370/471, 370/503, 370/473, 455/503, 455/438, 455/69, 455/442, 455/502, 455/439, 455/436, 455/67.6, 455/522, 455/517, 455/13.2, 455/32.1, 375/367
• US Class Current: 370/331
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging

Abstract

Methods and apparatus for transmitting packets from a source of such packets to one or more radio station sites so that the radio station sites can transmit the packets at the correct real time. Each radio site has an independent source of exact time based on the reception of signals derived from satellite inputs. Using the real time calculated by a base station, the base station calculates an offset between the time of arrival of a signal with a specified time marker, and the time that a signal with that specified time marker should have arrived in order to be transmitted in a timely fashion. The offset is sent back to the source of packets, and used by the source of packets to advance, or retard, the transmission of future packets. Advantageously, packets can be transmitted from each base station at the correct time, and if packets are being transmitted for a given call from several base stations, can be transmitted simultaneously, by these base stations.

Claims

1. A method of adjusting the timing of frames for transmission to a radio transmitter site of a cellular wireless communications system, comprising the steps of:

said radio transmitter site receiving signals representing an accurate source of time;

from said signals representing an accurate source of time, deriving timing for a periodic multi-frame timing signal having an indication of the beginning of each frame of the multi-frame signal, and a sequence number within said mutli-frame sequence representing an identity of said each frame within the periodic multi-frame timing signal;

transmitting from a source of a periodic sequence of frames, a first frame with a sequence number and a transmit time for said first frame in said periodic sequence;

at said radio transmitter site, calculating a frame offset and a time offset between an actual time of reception of said first frame and a desired time of reception for a frame having a sequence number received with said first frame;

transmitting said frame offset and said time offset to said source of frames;

at said source of frames, adjusting a sequence number within a multi-frame sequence and a time of transmittal from said source of frames to conform to said frame and said time offset;

whereby subsequent frames are transmitted from said source at a time such that they are received at said radio transmitter site at a desired time of arrival for a specified time of transmission.

2. The method of claim 1, wherein said signals representing an accurate source of time are received from a Global Positioning Satellite System.

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

recognizing a need to add an additional transmitter site for transmitting said frames;

transmitting a second frame with a sequence number of a second transmit time for said second frame to said additional transmitter site;

at said additional transmitter site, calculating a second frame offset and a second tm offset between an actual time of reception of said second frame, and a desired time of reception for a second frame having a second sequence number received with said second frame;

transmitting said second frame offset and said second time offset to said source of frames;

computing a candidate new sequence number of a specified transmit time, and a new time offset for transmittal from said source of frames to conform to said second frame offset and said second time offset;

comparing said candidate new sequence number with said indicator; and

selecting whichever of said sequence number, and said candidate new sequence number will deliver frames on time to the radio transmitter site which requires earliest transmission to arrive at that radio transmitter site.

4. Apparatus adjusting the timing of packets for transmission to a radio transmitter site of a cellular wireless communication system, comprising:

at said radio transmitter site, means for receiving signals representing an accurate source of time;

from said signals representing an accurate source of time, means for deriving timing for a periodic multi-frame timing signal having an indication of the beginning of each frame of the multi-frame signal, and a sequence number within said multi-frame sequence representing an identity of said each frame within the periodic multi-frame timing signal;

means for transmitting from a source of a periodic sequence of frames, a first frame with a sequence number and a transmit time for said first frame in said periodic sequence;

at said radio transmitter site, means for calculating a frame offset and a time offset between an actual time of reception of said first frame and a desired time of reception for a frame having a sequence number received with said first frame;

means for transmitting said frame offset and said time offset to said source of frames;

at said source of frames, means for adjusting a sequence number within a multi-frame sequence, and a time of transmittal from said source of frames to conform to said frame and said time offset;

whereby subsequent frames are transmitted from said source at a time such that they are received at said radio transmitter site at a desired time of arrival for a specified time of transmission.

5. The apparatus of claim 4, wherein said signals representing an accurate source of time are received from a Global Positioning Satellite System.

6. The apparatus of claim 4, further comprising:

means for recognizing a need to add an additional transmitter site for transmitting said frames;

means for transmitting a second frame with a sequence number of a second transmit time for said second frame to said additional transmitter site;

at said additional transmitter site, means for calculating a second frame offset and a second time offset between an actual time of reception of said second frame, and a desired time of reception for a second frame having a second sequence number received with said second frame;

means for transmitting said second frame offset and said second time offset to said source of frames;

means for computing a candidate new sequence number of a specified transmit time, and a new time offset for transmittal from said source of frames to conform to said second frame offset and said second time offset;

means for comparing said candidate new sequence number with said indicator; and

means for selecting whichever of said sequence number, and said candidate new sequence number will deliver frames on time to the radio transmitter site which requires earliest transmission to arrive at that radio transmitter site.