Hybrid time division multiple access (TDMA) and carrier sense multiple access (CSMA) for interference avoidance method therefor

1. A method for interference avoidance when transmitting a message in a wireless system comprising:

dividing a frame into a plurality of time slots, wherein a first plurality of time slots allocated as Time Division Multiple Access (TDMA) time slots and a second plurality of time slots allocated as contention slots;

transmitting the message in a designated TDMA time slot by a corresponding wireless node assigned to the designated TDMA time slot if the designated TDMA time slot is idle;

relabeling a contention slot as the designated TDMA time slot for the corresponding wireless node when the designated TDMA time slot for the corresponding wireless node remains busy;

relabeling the designated TDMA time slot as the contention slot; and

transmitting the message in the contention slot relabeled as the designated TDMA time slot for the corresponding wireless node.

2. The method of claim 1 , comprising relabeling simultaneously the contention slot as the designated TDMA time slot for the corresponding wireless node when the designated TDMA time slot for the corresponding wireless node remains busy during a contention period and the designated TDMA time slot as the contention slot.

3. The method of claim 1 , comprising verifying the designated TDMA time slot is idle.

4. The method of claim 1 , comprising verifying the designated TDMA time slot is idle by carrier sensing.

5. The method of claim 1 , comprising:

waiting for a predetermined timeframe if the designated TDMA time slot is busy; and

transmitting the message in a designated TDMA time slot by the corresponding wireless node if the designated TDMA time slot is idle after waiting for the predetermined timeframe.

6. The method of claim 5 , comprising operating under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe.

7. The method of claim 6 , wherein under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe comprises:

continuously checking the designated TDMA time slot to see if the designated TDMA time slot is busy;

calculating a probability P A , wherein

P

A

=

(

1

-

1

N

)

N

-

1

and N is the number of wireless nodes connected to a shared channel;

transmitting the message in the designated TDMA time slot if the value of P A is less than 1; and

waiting until the designated TDMA time slot is idle if the value of P A is more than 1.

8. The method of claim 1 , comprising:

finding an idle contention slot if the designated TDMA time slot is busy;

transmitting the message in the idle contention slot if the designated TDMA time slot is busy.

9. The method of claim 1 , comprising updating a TDMA slot-table of the corresponding wireless node.

10. The method of claim 9 , comprising sending a message with the TDMA slot-table updated to another wireless node.

11. A method for interference avoidance when transmitting a message in a wireless system comprising:

dividing a frame into a plurality of time slots, wherein a first plurality of time slots allocated as Time Division Multiple Access (TDMA) time slots and a second plurality of time slots allocated as contention slots;

verifying the designated TDMA time slot is idle;

transmitting the message in a designated TDMA time slot by a corresponding wireless node assigned to the designated TDMA time slot if the designated TDMA time slot is idle;

waiting for a predetermined timeframe if the designated TDMA time slot is busy;

transmitting the message in a designated TDMA time slot by the corresponding wireless node if the designated TDMA time slot is idle after waiting for the predetermined timeframe;

finding an idle contention slot if the designated TDMA time slot is busy;

relabeling the idle contention slot as the designated TDMA time slot for the corresponding wireless node when the designated TDMA time slot for the corresponding wireless node remains busy;

relabeling the designated TDMA time slot as the idle contention slot; and

transmitting the message in the idle contention slot relabeled as the designated TDMA time slot for the corresponding wireless node.

12. The method of claim 11 , comprising:

relabeling simultaneously the idle contention slot as the designated TDMA time slot for the corresponding wireless node and the designated TDMA time slot as the idle contention slot during a contention period.

13. The method of claim 12 , comprising updating a TDMA slot-table of the corresponding wireless node.

14. The method of claim 13 , comprising sending a message with the TDMA slot-table updated to another wireless node.

15. The method of claim 11 , comprising verifying the designated TDMA time slot is idle by carrier sensing.

16. The method of claim 11 , comprising operating under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe.

17. The method of claim 16 , wherein under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe comprises:

continuously checking the designated TDMA time slot to see if the designated TDMA time slot is busy;

calculating a probability P A , wherein

P

A

=

(

1

-

1

N

)

N

-

1

and N is the number of wireless nodes connected to a shared channel;

transmitting the message in the designated TDMA time slot if the value of P A is less than 1; and

waiting until the designated TDMA time slot is idle if the value of P A is more than 1.

18. A method for interference avoidance when transmitting a message in a wireless system comprising:

dividing a frame into a plurality of time slots, wherein a first plurality of time slots allocated as Time Division Multiple Access (TDMA) time slots and a second plurality of time slots allocated as contention slots;

verifying the designated TDMA time slot is idle by carrier sensing;

transmitting the message in a designated TDMA time slot by a corresponding wireless node assigned to the designated TDMA time slot if the designated TDMA time slot is idle;

waiting for a predetermined timeframe if the designated TDMA time slot is busy;

transmitting the message in a designated TDMA time slot by the corresponding wireless node if the designated TDMA time slot is idle after waiting for the predetermined timeframe;

finding an idle contention slot if the designated TDMA time slot is busy;

relabeling the idle contention slot as the designated TDMA time slot for the corresponding wireless node when the designated TDMA time slot for the corresponding wireless node remains busy;

relabeling the designated TDMA time slot as the idle contention slot;

transmitting the message in the idle contention slot relabeled as the designated TDMA time slot for the corresponding wireless node if the designated TDMA time slot is busy;

updating a TDMA slot-table of the corresponding wireless node; and

sending a message with the TDMA slot-table updated to another wireless node.

19. The method of claim 18 , comprising operating under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe.

20. The method of claim 19 , wherein under p-persistent CSMA if the designated TDMA time slot is busy after waiting for the predetermined timeframe comprises:

continuously checking the designated TDMA time slot to see if the designated TDMA time slot is busy;

calculating a probability P A , wherein

P

A

=

(

1

-

1

N

)

N

-

1

and N is the number of wireless nodes connected to a shared channel;

transmitting the message in the designated TDMA time slot if the value of P A is less than 1; and

waiting until the designated TDMA time slot is idle if the value of P A is more than 1.