System and method for dynamic time division access

• US 5,812,547 A
• Filed: 08/22/1996
• Issued: 09/22/1998
• Est. Priority Date: 08/22/1996
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Pace, Richard F., Benzimra, Albert
• Primary Examiner(s): Patel, Ajit
• Application Number:
  US08/701,342
• Time in Patent Office: 761 Days
• Field of Search: 370/337, 370/329, 370/336, 370/345, 370/347, 370/350, 370/442, 370/503, 370/507, 370/509, 370/579, 375/358, 375/371, 375/372, 375/468, 375/349, 375/477, 455/502
• US Class Current: 370/350
• CPC Class Codes: H04L 12/417 with deterministic access, e.g. token passing
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02

Abstract

The present invention is a system and method for providing wireless packet data transmission without dependence on a fixed time slot access method or central timing mechanism. An available radio frequency (RF) channel in a communications network is divided into time frames which are further divided into time slots, wherein corresponding single time slots in each frame define a logical channel for carrying user packet data. The network includes a plurality of nodes divided into at least two time domain groups, wherein the time domain groups are divided into segments. Each of the time domain groups includes an independent timing source for synchronizing the time slots of logical channels within a time domain, wherein communication between nodes is accomplished through a data messaging scheme, such as a token passing scheme. Buffer segments interface between the time domain groups. The buffer segments maintain logical synchronization for communication between interconnected time domains by dynamically reassigning the token from the logical channel of a first time domain to an unused time slot of another logical channel in response to a given offset condition. The logical channel for dynamic reassignment is chosen such that the time slot of a first time domain does not overlap the logical channel used by a second time domain.

Claims

1. A communications network for providing time division wireless data communication across one or more radio frequency (RF) channels, said communications network comprising:

a plurality of nodes divided into at least two time domain groups, wherein said one or more RF channels is divided into a plurality of frames including multiple time slots in each frame, a given time slot in each of said frames comprising a logical channel, wherein each of said time domain groups includes an independent timing source for synchronizing said time slots of a logical channel; and

at least one buffer segment for interfacing between said at least two time domain groups, each includes a plurality of nodes, said buffer segment adapted to maintain logical synchronization for communication between interconnected time domains by dynamically reassigning the logical channel between said time domains to an unused time slot of another logical channel in response to a given offset condition.

2. The network of claim 1, wherein said time domains are divided into a plurality of segments, each of said segments including multiple nodes and using a circulating token to pass messages between said nodes, said plurality of segments including at least one inter-segment device for synchronizing said time slots of adjacent segments and to recirculate said token within a segment.

3. The network of claim 2, wherein said inter-segment device includes a master module and one or more slave modules, said master module adapted to generate a synchronization signal to said slave modules upon receiving a token on its master module, said slave modules adapted to send a token toward a corresponding segment only if said slave modules hold said token after receiving said synchronization signal to thereby provide a periodic logical channel re-synchronization within said segments.

4. The network of claim 3, wherein said independent timing source is a timing master device node, wherein all segments in a time domain are synchronized on a token issued from said timing master device node.

5. The network of claim 2, wherein each of said nodes within said network include a unique node address, said node address including a time domain index, a segment index and a node index, said segment index being unique within a time domain and said node index being unique within a segment.

6. The network of claim 5, when nodes within said buffer segments have addresses corresponding to a lowest addressed time domain to which a buffer segment interfaces.

7. The network of claim 6, wherein a buffer segment interfaces to a time domain through an inter-domain device node, said buffer segment using the timing of an inter-domain device node having a lowest time domain index termed a controlling segment.

8. The network of claim 7, wherein an inter-domain device node coupled to a buffer segment which has a higher domain index is termed a slave segment, said slave segment operable to report a time offset between logical channels of said controlling segment and said slave segment.

9. The network of claim 8, wherein said slave segment is further operable to provide an algebraic rate of clock drift calculated from successive time offsets acquired between reception of two inter time domain tokens.

10. The network of claim 1, wherein the logical channel for dynamic reassignment of said logical channel is chosen such that the time slot of a first time domain does not overlap the logical channel used by a second time domain.

11. The network of claim 1, wherein said given offset is Δ

t, and for a decreasing offset, Δ

t, if Δ

t≧

1 slot and the token is received timely, and alternatively if Δ

t≧

T_ch1 >

1 slot and the token has not been received, where T_ch1 represents a threshold value being monitored, the logical channel will not be reassigned.

12. The network of claim 1, wherein said given offset is Δ

t, and for an increasing offset, if Δ

t≦

1 slot and the token is received timely, and alternatively if Δ

t≦

T_ch2 where (2 slots<

T_ch2 <

3 slots), where T_ch2 represents a threshold value being monitored, the logical channel will not be reassigned.

13. A method for providing time division data communication in a wireless communications network across one or more radio frequency (RF) channels, said communications network including a plurality of nodes adapted to communicate with one another, said method comprising the steps of:

dividing said plurality of nodes into at least two time domain groups, wherein said one or more RF channels is divided into a plurality of frames including multiple time slots in each frame, a given time slot in each of said frames comprising a logical channel;

maintaining an independent timing source in each of said time domain groups for synchronizing said time slots of a logical channel;

monitoring a time offset between logical channels of said at least two time domain groups; and

dynamically reassigning the logical channel between time domains to an unused time slot of another logical channel in response to a given time offset condition, thereby maintaining logical synchronization for communication between interconnected time domains.

14. The method of claim 13, wherein said step of reassigning includes the step of assigning user data transmitted between said time domains to a logical channel that increases the time offset in response to said given time offset being below a predetermined threshold.

15. The method of claim 13, wherein said step of reassigning includes the step of assigning user data transmitted between said time domains to a logical channel that decreases the time offset in response to said given time offset being above a predetermined threshold.

16. The method of claim 13, wherein said nodes are adapted to communicate with one another by means of a token passing scheme and said step of reassigning is accomplished by assigning a token to said unused slot.

17. The method of claim 13, wherein said time domains are divided into a plurality of segments, each of said segments including multiple nodes and using a circulating token to pass messages between said nodes, said plurality of segments including at least one inter-segment device, further including the step of synchronizing said time slots of adjacent segments and recirculating said token within a segment by means of said inter-segment device.

18. The method of claim 17, wherein said inter-segment device includes a master module and one or more slave modules, wherein said step of synchronizing includes the step of generating a synchronization signal from said master module to said slave modules upon receiving a token on said master module, said slave modules adapted to send a token toward a corresponding segment only if said slave modules hold said token after receiving said synchronization signal to thereby provide a periodic logical channel re-synchronization within said segments.

19. The method of claim 17, wherein each of said nodes within said network include a unique node address, said node address including a time domain index, a segment index and a node index, said segment index being unique within a time domain and said node index being unique within a segment.

20. The method of claim 19, when said time domains interface with one another through buffer segments and nodes within said buffer segments have addresses corresponding to a lowest addressed time domain to which a buffer segment interfaces.

21. The method of claim 20, wherein said buffer segments interface to a time domain through an inter domain device node, and said buffer segments use the timing of an inter-domain device node having a lowest time domain index termed a controlling segment.

22. The method of claim 21, wherein an inter-domain device node coupled to a buffer segment which has a higher domain index is termed a slave segment, further including the step of reporting a time offset between logical channels of said controlling segment and said slave segment to said controlling segment.

23. The method of claim 22, wherein said slave segment is further operable to provide an algebraic rate of clock drift calculated from successive time offsets acquired between reception of two inter time domain tokens.

24. The network of claim 13, wherein the logical channel for dynamic reassignment of said token is chosen such that the time slot of a first time domain does not overlap the logical channel used by a second time domain.

25. The method of claim 13, wherein said given offset is Δ

t, and for a decreasing offset, Δ

t, if Δ

t≧

1 slot and the token is received timely, and alternatively if Δ

t≧

T_ch1 >

1 slot and the token has not been received, where T_ch1 represents a threshold value being monitored, the logical channel will not be reassigned.

26. The method of claim 13, wherein said given offset is Δ

t, and for an increasing offset, Δ

t, if Δ

t≦

1 slot and the token is received timely, and alternatively if Δ

t≦

T_ch2 where (2 slots<

T_ch2 <

3 slots), where T_ch2 represents a threshold value being monitored, the logical channel will not be reassigned.

27. The method of claim 17, wherein a time frame includes n times slots and a node waits n-1 times slots before propagating said token.