Method and system for initial synchronization and collision avoidance in device to device communications without network coverage

Patent metadata

Field	Value
Publication number	US-9775187-B2
Application number	US-201615204588-A
Country	US
Kind code	B2
Filing date	Jul 7, 2016
Priority date	Aug 8, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

A method at a first device for enabling a device-to-device wireless link, the method detecting whether a presence signal of a second device is received over a first time period, the presence signal of the second device having a time-slot boundary; and if the presence signal of the second device is not detected, initiating a time-slot boundary by the first device including: transmitting a first presence signal of the first device in a selected time-slot; and checking for an acknowledgment to the first presence signal.

First claim

The invention claimed is:

1. A method at a first device for enabling a device-to-device wireless link, the method comprising:
detecting whether a presence signal of a second device is received over a first time period, the presence signal of the second device having a subframe boundary;
if the presence signal of the second device is not detected, initiating a subframe boundary at the end of the first time period including:
transmitting a first presence signal of the first device in a selected subframe;
wherein the first device transmits the first presence signal in the selected subframe during a subsequent frame and a message comprising a system frame number, wherein a frame comprises an integer number of subframes;
wherein a subframe duration is predetermined.

2. The method of claim 1 , wherein the frame period comprises an integer number of subframe durations.

3. The method of claim 1 , further comprising:
if the presence signal of the second device is detected, aligning a subframe boundary on the first device to the subframe boundary established by the second device; and
after aligning to the subframe boundary established by the second device, determining a subframe to use for transmission by the first device.

4. The method of claim 3 , wherein the determining the subframe comprises:
detecting one or more free subframes;
choosing a free subframe;
transmitting the first presence signal on the chosen free subframe.

5. The method of claim 4 , further comprising:
checking for an acknowledgment to the first presence signal.

6. The method of claim 1 , further comprising sending an acknowledgment to a received presence signal of any device other than the first device.

7. The method of claim 1 , wherein the first presence signal comprises one or more sequences.

8. The method of claim 7 , wherein the first presence signal comprises a primary synchronization signal and a secondary synchronization signal.

9. The method of claim 8 , wherein the primary synchronization signal is used to establish the subframe boundary.

10. The method of claim 7 , wherein one or more of the sequences varies between two consecutive presence signal transmissions.

11. The method of claim 7 , wherein one or more of the sequences stays the same for a plurality of consecutive presence signal transmissions.

12. The method of claim 1 , wherein the selection of the first presence signal is related to an identity of the first device.

13. A method at a first device for enabling a device-to-device wireless link, the method comprising:
listening for a presence signal on a channel, the presence signal comprising at least one sequence; and
upon detection of the presence signal,
aligning to a subframe boundary associated with the presence signal by utilizing the at least one sequence of the presence signal;

wherein the presence signal comprises a primary synchronization signal relating to an identity of a plurality of devices and a secondary synchronization signal relating to an identity of a device that transmits the presence signal.

14. The method of claim 13 , wherein the presence signal comprises a Zadoff-Chu sequence.

15. The method of claim 13 , wherein the first device uses the secondary synchronization signal to identify signal collisions.

Assignees

• Blackberry Ltd

Inventors

• Nguyen Nam
• Blankenship Yufei Wu
• Dhakal Sagar

Classifications

• H04W56/002

  Mutual synchronization · CPC title

• H04W74/085 Primary

  collision avoidance · CPC title

• H04W4/70

  Services for machine-to-machine communication [M2M] or machine type communication [MTC] · CPC title

• H04W56/00

  Synchronisation arrangements · CPC title

• H04W72/02

  Selection of wireless resources by user or terminal · CPC title