Short synchronization time data modem

• US 6,625,209 B1
• Filed: 03/29/1999
• Issued: 09/23/2003
• Est. Priority Date: 03/29/1999
• Status: Expired due to Fees

• Current Assignee: Telular Corporation (Ametek Incorporated)
• Original Assignee: CSI Wireless Incorporated
• Inventors: Najafi, Hamid
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Bayard, Emmanuel
• Application Number:
  US09/280,400
• Time in Patent Office: 1,639 Days
• Field of Search: 375/219, 375/220, 375/222, 375/316, 375/356, 375/359, 375/373, 375/376, 375/375, 375/294, 375/327, 375/215, 370/278, 370/282, 455/427, 455/13.2, 455/13.1, 455/12.1, 455/265, 342/357.05, 342/357.09, 342/357.1, 342/457, 342/352
• US Class Current: 375/222
• CPC Class Codes: G04G 5/002 brought into action by radio
• CPC Class Codes: H04W 4/02 Services making use of location information

Abstract

A short synchronization time modem comprising a GPS receiver for receiving a broadcasted signal comprising a high precision clock. When a first short synchronization data modem communicates with a second, a PLL in each data modem synchronizes its own local clock to the same high precision clock derived from the same received broadcasted signal. The modems connect for the first time using one of many clock recovery schemes known to the modem designers. Once they disconnect, the modems keep their clocks synchronized using a local GPS receiver and the received broadcasted signal. This prevents the local clock of the modems from drifting, which significantly reduces the time period the modems need to synchronize the next time they connect.

Claims

1. A short synchronization time data modem system, wherein the data modem system comprises a first data modem terminal (terminal A) and a second data modem terminal (terminal B), comprising:

a terminal A further comprising a first antenna for receiving an incoming broadcasted signal comprising a high precision, broadcasted clock signal;

a first modem receiver coupled to the first antenna to receive the incoming broadcasted signal and generating in response a corresponding first digital synchronization clock signal (UTCC1);

a first PLL, the first PLL coupled to the first modem receiver to receive UTCC1 and generating an output first modem clock signal (MCLK1) having a frequency comprising a multiple N of a first locally generated clock signal (CCLK1);

a first phase detector circuit to detect a first phase difference (α

1) between CCLK1 and UTCC1, and activating in response to the detected first phase difference one or more phase control signals provided as input control to a first counter in the first modem receiver for phase adjustment of MCLK1 relative to a detected phase of UTCC1;

a terminal B further comprising;

a second antenna for receiving an incoming broadcasted signal comprising a high precision, broadcasted clock signal;

a second modem receiver coupled to the second antenna to receive the incoming broadcasted signal and generating in response a corresponding second digital synchronization clock signal (UTCC2); and

a second PLL, the second PLL coupled to the second modem receiver to receive UTCC2 and generating an output second modem clock signal (MCLK2) having a frequency comprising a multiple N of a second locally generated clock signal (CCLK2);

wherein the second modem answering a subsequent call from a first modem and waiting m number of seconds before sending a 2100 Hz signal for about 3. 3 sec while synchronizing the MCLK1 in the first modem to an UTCCD1 signal derived from UTCC1;

the first modem transmitting a binary sequence to the second modem, the first modem waiting y number of seconds prior to transmitting actual data to the second modem, the second modem detecting the set of binary sequence with a second modem clock MCLK2 in the second modem, then waiting z number of second prior to actual data transmission.

2. The data modem system of claim 1 wherein the high precision, broadcasted clock signal is a GPS clock signal.

3. A short synchronization time data modem method comprising:

receiving by a first modem receiver a high precision, broadcasted clock signal and generating a corresponding first digital synchronization clock (UTCC1);

generating a first local clock signal (CCLK1) in the first modem receiver having the same frequency as UTCC1 and generating a first modem clock (MCLK1) at a frequency comprising a multiple N of the first local clock; and

detecting a phase difference (α

1) between CCLK1 and UTCC1 and providing in response to the detected first phase difference α

1 one or more phase control signals to a first counter in the first modem receiver to provide synchronization of phase between MCLK1 and UTCC1;

initially connecting to a second modem receiver using a standard training procedure;

answering by the second modem a subsequent call from a first modem and waiting m number of seconds before sending a 2100 Hz signal for about 3. 3 sec;

synchronizing the MCLK1 in the first modem to an UTCCD1 signal derived from UTCC1;

transmitting from the first modem to a second modem a set of binary sequence;

waiting y number of seconds prior to transmitting actual data from the first modem to the second modem; and

detecting by the second modem the set of binary sequence with a second modem clock MCLK2 in the second modem, then waiting z number of second prior to actual data transmission.

4. The short synchronization time data modem method of claim 3 wherein the high precision broadcasted clock signal comprises a GPS clock signal.

5. The short synchronization time data modem method of claim 3 further comprising receiving a location data for determining a physical location of the first modem receiver.

6. The short synchronization time data modem method of claim 3 further comprising executing a shortened training procedure in a subsequent modem connection.

7. The short synchronization time data modem method of claim 3 wherein the step of detecting a phase difference, comprises the steps of:

detecting initially when UTCC1=CCLK1=0; and

detecting when UTCC1≠

CCLK, and activating either a counter adjust up signal or a counter adjust down signal in response to detecting whether UTCC=1.

8. The short synchronization time data modem method of claim 3 further comprising:

providing multiple data transmissions; and

providing a data burst transmission in between the multiple data transmissions.

9. The short synchronization time data modem method of claim 3 wherein the multiple data transmissions comprise voice data.