Method and system for medium access control in communication networks

• US 20090109938A1
• Filed: 10/31/2007
• Published: 04/30/2009
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Singh, Harkirat, Shao, Huai-Rong, Ngo, Chiu
• Granted Patent: US 8,837,435 B2
• Time in Patent Office: Days
• US Class Current: 370/337
• CPC Class Codes: H04L 12/4035 in which slots of a TDMA packet structure are assigned based on a contention resolution carried out at a master unit TDM/TDMA multiplex systems per se H04J3/1694; hybrid switching systems H04L12/64
• CPC Class Codes: H04L 12/413 with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02
• CPC Class Codes: H04W 74/0816 with collision avoidance

Abstract

A method and a system for medium access control among devices in a communication system is provided. One implementation involves selecting a contention-based control period for access to a shared communication medium; dividing the contention-based control period into multiple time slots, wherein each slot has a duration that is a function of one or more of the duration of transmission of a request to send (RTS) frame, the duration of transmission of a clear to send (CTS) frame, and an inter frame space (IFS) duration therebetween; and transmitting an RTS frame in a selected slot for allocating a reservation period for accessing the medium for data transmission.

Claims

1. A method for medium access control among devices in a communication system, comprising:

selecting a contention-based control period for access to a shared communication medium;

dividing the contention-based control period into multiple time slots, wherein each slot has a duration that is a function of one or more of;

the duration of transmission of a request to send (RTS) frame, the duration of transmission of a clear to send (CTS) frame, and an inter frame space (IFS) duration therebetween; and

transmitting an RTS frame in a selected slot for allocating a reservation period for accessing the medium for data transmission.

2. The method of claim 1, wherein the RTS frame includes a duration field indicating the number of slots desired for the reservation period.

3. The method of claim 2 further including allocating a reservation period by receiving the RTS frame, and transmitting a CTS frame in response during said selected slot to indicate successful allocation of the reservation period for accessing the medium.

4. The method of claim 3, wherein the CTS frame includes a duration field indicating the number of slots in the reservation period, the method further including the step of upon successfully receiving the CTS frame, comparing the duration field in the CTS with the duration field in the RTS, and if the two duration fields match, then assuming a successful reservation of the medium and initiating transmission of data via the medium during the reservation period.

5. The method of claim 3 further including updating a timer based on the duration field, and determining if the medium is busy by checking if the timer has a value which is greater than the current time, wherein allocating a reservation period further includes before transmitting the RTS frame, randomly choosing a number with a uniform distribution between 1 and a current backoff window, as a number of backoff slots before transmission of the RTS.

6. The method of claim 5, wherein allocating a reservation period further includes:

before transmitting the RTS, backing off for said number of backoff slots;

checking if the timer is less than the current time, and if so, transmitting the RTS during the selected slot;

determining if the timer is greater than the current time, and if so, then backing off for the difference between the timer and the current time; and

thereafter, determining if the timer is less than the current time, and if so, backing off for a selected number of slots between 1 and the current backoff window, before sending another RTS with a duration field with a value zero, in another slot to release the medium.

7. The method of claim 3, wherein the CTS frame includes a preamble indicating it is in response to the RTS, and the CTS frame does not include a MAC and PHY header, the method further comprising the step of directionally transmitting a data packet and an acknowledgment packet over a shared wireless communication medium, wherein the RTS and CTS transmissions comprise omni-directional transmissions over a shared wireless communication medium.

8. The method of claim 1, wherein the medium comprises a shared 60 GHz wireless channel and the data comprises video information.

9. The method of claim 1, wherein the CTS does not require receiver address information or transmitter address information, and allocating a reservation period further includes adjusting the current backoff window value and broadcasting it over the medium in a beacon for the devices to use the same backoff window value, wherein the current backoff window is a function of the number of inactive devices in the network.

10. The method of claim 1, wherein allocating a reservation period further includes:

randomly choosing a number with a uniform distribution between 1 and a current backoff window, as a number of backoff slots before transmitting data, wherein each slot has a duration based on the time required to transmit an RTS frame;

backing off for the number of backoff slots;

when the medium is not busy, transmitting an RTS frame;

transmitting a data packet over the medium in a slot subsequent to transmission of the RTS frame; and

transmitting an acknowledgment for the data to indicate a successful reception of the data,

wherein the duration field in the RTS frame and/or CTS response is avoided, thereby always a fixed number of slots are allocated for the subsequent data transmission.

11. A transmitter for information communication over a shared communication medium, comprising:

a reservation module configured for allocating a reservation period for accessing the medium for data transmission, by transmitting a request to send (RTS) frame in a selected time slot of a contention-based control period that is divided into multiple time slots, wherein each slot has a duration that is a function of one or more of;

the duration of transmission of an RTS frame, the duration of transmission of a clear to send (CTS) frame, and an inter frame space (IFS) duration therebetween.

12. The transmitter of claim 11, wherein the RTS frame includes a duration field indicating the number of slots desired for the reservation period, and the reservation module is further configured for awaiting receipt of a CTS frame in response to the RTS frame for reserving the medium, the transmitter further including a packet communication module configured for initiating transmission of data via the medium during the reservation period.

13. The transmitter of claim 12, wherein the reservation module is further configured for updating a timer based on the duration field, and determining if the medium is busy by checking if the timer has a value which is greater than the current time, such that before transmitting the RTS frame, the reservation module randomly choosing a number with a uniform distribution between 1 and a current backoff window, as a number of backoff slots before transmission of the RTS.

14. The transmitter of claim 13, wherein the reservation module is further configured such that before transmitting the RTS, the transmitter backs off for said number of back-off slots, and checking if the timer is less than the current time, and if so, transmitting the RTS during the selected slot.

15. The transmitter of claim 14, wherein the reservation module is further configured such that before transmitting the RTS, the transmitter backs off for said number of back-off slots, and thereafter, determines if the timer is greater than the current time, and if so, then backs off for the difference between the timer and the current time, and thereafter, determines if the timer is less than the current time, and if so backs off for a selected number of slots between 1 and the current backoff window, before sending another RTS with a duration field with a value zero, in another slot to reserve the medium.

16. The transmitter of claim 12, wherein the reservation module is configured such that upon successfully receiving the CTS, the reservation module compares the duration field in the CTS with the duration field in the RTS, and if the two duration fields match, then assumes a successful reservation of the medium.

17. The transmitter of claim 13, wherein the current back-off window is a function of the number of inactive devices in the network, and a coordinator adjusts the current backoff window value and broadcasts it over the medium in a beacon.

18. The transmitter of claim 11, wherein the medium comprises a shared 60 GHz wireless channel and the data comprises video information.

19. The transmitter of claim 11, wherein the CTS does not require receiver address information or transmitter address information, and the CTS frame includes a preamble indicating it is in response to the RTS and the CTS frame does not include a MAC and PHY header.

20. The transmitter of claim 12 further including a communication module configured for directionally transmitting information over the medium during the reservation period over a shared wireless communication medium, and the RTS and CTS transmissions comprise omni-directional transmissions over a shared wireless communication medium.

21. The transmitter of claim 11, wherein:

each slot has a duration based on the time required to transmit an RTS frame;

the reservation module is further configured for;

randomly choosing a number with a uniform distribution between 1 and a current backoff window, as a number of backoff slots before transmitting data;

backing off for the number of backoff slots; and

when the medium is not busy, transmitting an RTS frame;

the transmitter further including a packet communication module for transmitting a data packet over the medium in a slot subsequent to transmission of the RTS frame.

22. A receiver for information communication over a shared communication medium, comprising:

a reservation module configured for receiving a request to send (RTS) frame during a selected time slot of a contention-based control period and allocating a reservation period by transmitting a clear to send (CTS) frame in response during said selected slot, to indicate successful allocation of the reservation period for accessing the medium;

wherein the contention-based control period is divided into multiple time slots, wherein each slot has a duration that is a function of one or more of;

the duration of transmission of an RTS frame, the duration of transmission of a CTS frame, and an inter frame space (IFS) duration therebetween.

23. The receiver of claim 22, wherein the RTS frame includes a duration field indicating the number of slots desired for the reservation period, and the CTS frame includes a duration field indicating the number of slots in the reservation period.

24. The receiver of claim 23, wherein the CTS does not require receiver address information or transmitter address information, and includes a preamble indicating it is in response to the RTS and the CTS frame does not include a MAC and PHY header.

25. The receiver of claim 24, wherein the medium comprises a shared 60 GHz wireless channel and the data comprises video information.