SYNCHRONIZATION FOR FH COMMUNICATION

• US 20090135887A1
• Filed: 11/20/2008
• Published: 05/28/2009
• Est. Priority Date: 11/23/2007
• Status: Active Grant

• Current Assignee: Saab AB
• Original Assignee: Saab AB
• Inventors: Andersson, Morgan, Numminen, Michael
• Granted Patent: US 8,295,323 B2
• Time in Patent Office: Days
• US Class Current: 375/134
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04B 2001/71563 Acquisition

Abstract

A method for synchronization of transmitted and received signals in frequency hopping communications systems. A synchronization unit is arranged for synchronization of transmitted and received signals in frequency hopping communication systems and a frequency hopping communication system including a synchronization unit.

Claims

1. A method for synchronization of transmitted and received signals in frequency hopping communication systems where data is transmitted in frames comprising a preamble and a data block, the frequency hopping communication system comprising a transmitter and a receiver, two PN-generators, one located at a transmitting end and one located at a receiving end, both generating a same predefined frequency pattern causing the transmitter and the receiver to hop in frequency according to the same pattern, the receiver and the PN-generator at the receiving end being part also of a synchronization unit wherein the clock rate in the receiver is slowed down compared to the clock rate of the transmitter, thus causing a characteristic pattern and a reversed characteristic pattern both patterns resulting from interference between the predefined frequency patternof the transmitted signal and the slowed down predefined frequency pattern used in the receiver, the slowed down predefined frequency pattern being controlled by the slower clock rate in the receiver and used in the receiver during synchronization, the time elapsed from start of synchronization represented by a starting point, the synchronization being initiated by a start sync signal, until obtaining the characteristic patterns being a measure of the delay between the transmitted and received signal which is used to synchronize the receiver to the transmitted signals.

2. The method for synchronization according to claim 1, wherein the frequency hopping communication system uses one bit per symbol and wherein a frequency hop is made at each bit.

3. The method for synchronization according to claim 1, wherein more than one frequency hop is performed at each bit.

4. The method for synchronization according to claim 1, wherein the transmitter is stationary and wherein the receiver is moving away from the transmitter.

5. The method for synchronization according to claim 1, wherein both the transmitter and the receiver are stationary.

6. The method for synchronization according to claim 1, wherein:

an Rx-timer in the synchronization unit sends time stamps deciding the speed of the predefined frequency pattern generated by the PN-generator and used in the receiver during synchronization and defining the positions in the predefined frequency pattern,

a Tx-timer in the synchronization unit being identical to a Tx-timer in the transmitter communicates the Tx-time to the Rx-timer through a bus link at start of the start sync signal,

the Tx-timer is continuously adjusted against a reference, the Tx-timer generates the start sync signal to the Rx-timer at regular intervals equal to a frame interval, and

the start sync signal initiates the clock rate in the Rx-timer to slow down causing the rate of the time stamps to decrease and the predefined frequency pattern used in the receiver during synchronization to be generated at a slower speed.

7. The method for synchronization according to claim 1, wherein an interference pattern is generated by interference between the predefined frequency pattern of the transmitter, and the predefined frequency pattern used in the receiver during synchronization and running at a slower speed, and wherein when the two predefined frequency patterns have the same frequency at the same time, the characteristic patterns will be generated and the receiver will be able to receive the transmitted signal and the output signal from the receiver will include the received signal.

8. The method for synchronization according to claim 1, wherein the output signal is fed to a symbol detector through a first path and a correlator through a second path, both being located in the synchronization unit, the output signal being correlated in the correlator with the characteristic pattern and the reversed characteristic pattern being stored in the correlator and the correlator generating an out signal when there is a correlation between the output signal and the characteristic patterns stored in the correlator.

9. The method for synchronization according to claim 1, wherein the maximum of the out signal is detected in a peak detector which generates a trigger signal to a calculation delay unit, the peak detector and the calculation delay unit both being located in the synchronization unit.

10. The method for synchronization according to claim 1, wherein the calculation delay unit receives:

a trigger signal,

a Tx-time from the Tx-timer,

an Rx-time from the Rx-timer,

based on this information the calculation delay unit;

calculates a delay from the start sync signal to reception of the trigger signal corresponding to the delay between the transmitted and received signal and

sends an offset value to the Rx-timer informing the Rx-timer of the delay and at the same time, trigger the Rx-timer to change the clock rate to the clock rate of the Tx-timer.

11. The method for synchronization according to claim 1, wherein the Rx-timer after having received the offset value:

initiates a data start signal informing the frequency hopping communication system that valid data now can be received, and

sends a symbol clock signal to the symbol detector to define a sample position of a symbol.

12. A synchronization unit arranged for synchronization of transmitted and received signals in frequency hopping communication systems where data is arranged to be transmitted in frames comprising a preamble and a data block, the frequency hopping communication system comprising

a transmitter,

a receiver, and

two PN-generators, one located at a transmitting end and one located at a receiving end, both PN-generators arranged to generate a same predefined frequency pattern causing the transmitter and the receiver to hop in frequency according to the same pattern, the receiver and the PN-generator at the receiving end being part also of the synchronization unit, wherein a clock rate in the receiver is arranged to be slowed down compared to a clock rate of the transmitter, thus causing a characteristic pattern and a reversed characteristic pattern both patterns resulting from interference between the predefined frequency pattern of the transmitted signal and the slowed down predefined frequency pattern used in the receiver, the slowed down predefined frequency pattern arranged to be controlled by the slower clock rate in the receiver and to be used in the receiver during synchronization, the time elapsed from start of synchronization represented by a starting point, the synchronization being arranged to be initiated by a start sync signal, until obtaining the characteristic patterns being a measure of the delay between the transmitted and received signal which is used to synchronize the receiver to the transmitted signals.

13. The synchronization unit according to claim 12, wherein the frequency hopping communication system is arranged to use one bit per symbol and that a frequency hop is made at each bit.

14. The synchronization unit arranged for synchronization according to claim 12, wherein the frequency hopping communication system is arranged to perform more than one frequency hop at each bit.

15. The synchronization unit according to claim 12, wherein the transmitter is stationary and wherein the receiver is arranged to be moved away from the transmitter.

16. The synchronization unit according to claim 12, wherein both the transmitter and the receiver are arranged to be stationary.

17. The synchronization unit according to claim 12, wherein:

an Rx-timer in the synchronization unit arranged to send time stamps deciding the speed of the predefined frequency pattern generated by the PN-generator and used in the receiver during synchronization and defining the positions in the predefined frequency pattern,

a Tx-timer in the synchronization unit being identical to a Tx-timer in the transmitter arranged to communicate the Tx-time to the Rx-timer through a bus link at start of the start sync signal,

the Tx-timer arranged to be continuously adjusted against a reference,

the Tx-timer arranged to generate the start sync signal to the Rx-timer at regular intervals equal to a frame interval, and

the start sync signal arranged to initiate the clock rate in the Rx-timer to slow down causing the rate of the time stamps to decrease and the predefined frequency pattern used in the receiver during synchronization to be generated at a slower speed.

18. The synchronization unit according to claim 12, wherein the predefined frequency pattern of the transmitter, and the predefined frequency pattern running at a slower speed and used in the receiver during synchronization are arranged to generate an interference pattern and when the two predefined frequency patterns have the same frequency at the same time the receiver is arranged to receive the transmitted signal and the output signal from the receiver will include the received signal.

19. The synchronization unit according to claim 12, wherein the output signal is arranged to be fed to a symbol detector through a first path and a correlator through a second path, both being located in the synchronization unit, the output signal being arranged to be correlated in the correlator with the characteristic pattern and the reversed characteristic pattern arranged to be stored in the correlator and the correlator is arranged to generate an out signal when there is a correlation between the output signal and the characteristic patterns stored in the correlator.

20. The synchronization unit according to claim 12, wherein the maximum of the out signal is arranged to be detected in a peak detector which is arranged to generate a trigger signal to a calculation delay unit the peak detector and the calculation delay unit both being located in the synchronization unit.

21. The synchronization unit according to claim 12, wherein the calculation delay unit is arranged to receive:

a trigger signal,

a Tx-time from the Tx-timer,

an Rx-time from the Rx-timer,

based on this information the calculation delay unit is arranged to;

calculate a delay from the start sync signal to reception of the trigger signal corresponding to the delay between the transmitted and received signal and

send an offset value to the Rx-timer informing the Rx-timer of the delay and at the same time trigger the Rx-timer to change the clock rate to the clock rate of the Tx-timer.

22. The synchronization unit according to claim 12, wherein the Rx-timer is arranged such that after having received the offset value Rx-timer is arranged to:

initiate a data start signal informing the frequency hopping communication system that valid data now can be received, and

send a symbol clock signal to the symbol detector to define a sample position of a symbol.

23. A frequency hopping communication system, comprising:

a synchronization unit according to claim 12.