Coordination of wireless medium among a plurality of base stations

• US 5,068,916 A
• Filed: 10/29/1990
• Issued: 11/26/1991
• Est. Priority Date: 10/29/1990
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Harrison, Colin G., Hortensius, Peter D.
• Primary Examiner(s): KUNTZ, CURTIS A
• Application Number:
  US07/605,628
• Time in Patent Office: 393 Days
• Field of Search: 455/49, 455/51, 455/66, 455/67, 455/601, 455/607, 370/85.1, 370/110.1, 370/100.1, 370/85.3, 375/107
• US Class Current: 455/39
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

Method and apparatus for coordinating a usage of a wireless transmission medium among a plurality of transmission units (12). The transmission medium is of a type that is utilized in accordance with a protocol having a transmission period that is comprised of a plurality of consecutively occurring transmission sub-periods. A method includes the following steps. A data structure (28a) is periodically circulated among the transmission units, the data structure being expressive of an identification of each of the transmission units and also expressive of an identification of an assigned transmission sub-period or sub-periods, if any, during which each of the transmission units is permitted to transmit on the wireless medium. The step of circulating includes the following steps: (a) receiving the data structure from a first transmission unit with a second transmission unit; (b) respsonsive to the receipt of the data structure at the second transmission unit processing the data structure in accordance with an amount, if any, of impending transmission activity to modify the assignments of sub-periods therein; and (c) transmitting the modified data structure to another one of the transmission units. A method of synchronizing the plurality of transmission units to a slotted transmission protocol is also disclosed.

Claims

1. A method of coordinating a usage of a wireless transmission medium amongst a plurality of transmission means, the transmission medium being utilized in accordance with a transmission period that is comprised of a plurality of consecutively occurring transmission sub-periods, comprising the steps of:

periodically circulating amongst the transmission means a data structure, the data structure being expressive of an identification of each of the transmission means and also being expressive of an identification of an assigned transmission sub-period or sub-periods, if any, during which each of the transmission means is permitted to transmit on the wireless medium, the step of periodically circulating including the steps of;

receiving the data structure from a first transmission means with a second transmission means;

responsive to the receipt of the data structure at the second transmission means processing the data structure in accordance with an amount, if any, of impending transmission activity to modify the assignments of sub-periods therein; and

transmitting the modified data structure to another one of the transmission means.

2. A method as set forth in claim 1 wherein the step of processing includes the steps of modifying the data structure so as to (a) relinquish one or more assigned transmission sub-periods or, to (b) assign to the second transmission means one or more unassigned transmission sub-periods.

3. A method as set forth in claim 1 wherein the step of processing includes a step of, responsive to a condition wherein there are no unassigned transmission sub-periods, modifying the data structure to indicate that the second transmission means requires at least one transmission sub-period.

4. A method as set forth in claim 3 wherein the step of processing includes a step of determining from the data structure if another one of the transmission means requires a transmission sub-period;

and if another transmission means is determined to require a transmission sub-period, relinquishing at least one sub-period.

5. A method as set forth in claim 1 wherein the steps of receiving and transmitting each include a step of communicating through a wired network.

6. A method as set forth in claim 1 wherein the step of processing includes a step of storing the modified data structure within the second transmission means for subsequent use and, in response to an external event, the method includes a step of initializing the stored data structure to a default condition.

7. For use in a wireless communications system, apparatus for coordinating a usage of a wireless transmission medium amongst a plurality of transmission means, the transmission medium being utilized in accordance with a transmission period that is comprised of a plurality of consecutively occurring transmission sub-periods, each of the transmission means comprising:

means for periodically circulating amongst the transmission means a data structure, the data structure being expressive of an identification of each of the transmission means and also being expressive of an identification of an assigned transmission sub-period or periods, if any, during which each of the transmission means is permitted to transmit on the wireless medium, the circulating means comprising;

means coupled to a wired network for receiving the data structure from another transmission means;

means, responsive to the receipt of the data structure, for processing the data structure in accordance with an amount, if any, of impending transmission activity to modify the data structure so as to alter the assignments of sub-periods; and

means, coupled to the wired network, for transmitting the modified data structure to another one of the transmission means.

8. Apparatus as set forth in claim 7 wherein each of the transmission means further comprises means for storing the modified data structure for subsequent use.

9. Apparatus as set forth in claim 8 wherein each of the transmission means further includes means for initializing the stored data structure to a default condition.

10. Apparatus as set forth in claim 7 wherein the wireless medium employs infrared energy and wherein each of the transmission means includes means for transmitting and receiving modulated infrared energy that is expressive of data and control information.

11. Apparatus as set forth in claim 10 wherein each of the transmission means includes means for transmitting the data with a first infrared channel at a first bandwidth;

means for transmitting the control information with a second infrared channel at a second bandwidth; and

wherein the first bandwidth is significantly higher than the second bandwidth.

12. Apparatus as set forth in claim 11 wherein the first channel is a line of sight channel and wherein the second channel is a diffuse transmission channel.

13. A method of synchronizing a usage of a wireless transmission medium amongst a plurality of transmission means having a transmission coverage area associated therewith, at least two of the coverage areas having an overlap region therebetween, the transmission medium being utilized in accordance with a transmission period that is comprised of a plurality of consecutively occurring transmission sub-periods, comprising the steps of:

(a) transmitting a message over the wireless transmission medium with only one of the transmission means, the message being repetitively transmitted during each of the transmission sub-periods of at least one of the transmission periods;

(b) receiving the repetitively transmitted messages with one or more transmitter/receiver means disposed within the coverage area associated with the transmitting transmission means;

(c) re-transmitting the received messages with each of the transmitter/receiver means receiving the repetitively transmitted messages, including a transmitter/receiver means, if any, that is disposed within the overlap region;

(d) receiving the re-transmitted messages from the transmitter/receiver within the overlap region with another transmission means; and

responsive to the reception of the re-transmitted messages

(e) synchronizing a timekeeping function of the second transmission means thereto so as to subsequently determine with the timekeeping function a required starting time of a predetermined one of the sub-periods for transmitting or receiving another message therein.

14. A method as set forth in claim 13 wherein the step of transmitting includes an initial step of each of the transmission means communicating over a wired network information that indicates that each of the transmission means is to temporarily suspend use of the wireless medium so that the first transmission means can repetitively transmit the message.

15. A method as set forth in claim 13 wherein the step of synchronizing includes an additional step of communicating over a wired network information that indicates that the second transmission means has synchronized its timekeeping function;

and wherein the step of transmitting includes a step of terminating repetitive transmission of the message in response to the second transmission means having synchronized its timekeeping function.

16. A method as set forth in claim 15 wherein, if there is no transmitter/receiver means within the overlap region, the step of terminating is executed instead in response to a timeout function.

17. A method as set forth in claim 13 wherein steps (a, b, c, d and e) are executed in turn by a plurality of the transmission means until each transmission means having a coverage area that overlaps the coverage area of another transmission means has synchronized an associated timekeeping function.

18. A method as set forth in claim 13 wherein the wireless medium employs infrared energy and wherein each of the transmission means includes means for transmitting and receiving modulated infrared energy that is expressive of data and control information.

19. A method as set forth in claim 18 wherein each of the transmission means transmits the data with a first infrared channel at a first bandwidth;

transmits the control information with a second infrared channel at a second bandwidth;

wherein the first bandwidth is significantly higher than the second bandwidth; and

wherein the repetitively transmitted messages are transmitted with the second infrared channel.

20. A method as set forth in claim 19 wherein the first channel is a line of sight channel and wherein the second channel is a diffuse transmission channel.