OVERHEAR-BASED TRANSMITTING CONTROL SYSTEM IN WLANS

• US 20080181101A1
• Filed: 02/16/2007
• Published: 07/31/2008
• Est. Priority Date: 01/31/2007
• Status: Active Grant

• Current Assignee: Seoul National University Industry Foundation (Seoul National University)
• Original Assignee: Seoul National University Industry Foundation (Seoul National University)
• Inventors: OH, Ha-young, Kim, Chong-kwon, Yoon, Sung-ro, Yoo, Ki-baek
• Granted Patent: US 7,746,837 B2
• Time in Patent Office: Days
• US Class Current: 370/218
• CPC Class Codes: H04L 1/1887 Scheduling and prioritising arrangements
• CPC Class Codes: H04L 2001/0097 Relays
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 74/00 Wireless channel access
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 84/22 with access to wired networks

Abstract

We propose overhear-based transmitting control system in WLANs to improve performance of 802.11 wireless LANs. The main idea of this scheme is that when the transmission of a node fails, one of neighboring nodes with better channel quality retransmits the lost frame in substitution. To do so, every node should maintain overhear table to buffer the transmitted packets that is not yet acknowledged. We also present algorithms to retransmit lost packets, to maintain the overhear table and to compensate for the retransmission of packets of other nodes. The performance of this scheme is evaluated via simulations in terms of MPDU size and average path loss. It shows that in environments where the packet is likely to be lost more, the throughput gain of our proposed scheme performs better.

Claims

1. A system for controlling overhear-based packet transmission over a Wireless Local Area Network (WLAN) comprising:

at least one station for overhearing data of other stations, collecting/transmitting its own transmission data and data of the other stations if it is determined that a data transmission failure occurs, compensating for channel access opportunities of the other stations if it is determined that the transmission data of the at least one station is transmitted from the other stations; and

an access point (AP) for communicating with the at least one station over the WLAN, and equally assigning the channel access opportunity to the at least one station.

2. The overhear-based packet transmission control system according to claim 1, wherein the station manages an overhear table, determines the presence or absence of a data transmission failure of the other stations, and stores a packet of the data transmission failure of the other stations in the overhear table if the presence of the data transmission failure of the other stations is determined.

3. The overhear-based packet transmission control system according to claim 1, wherein the station includes a transmission table for managing its own transmission data.

4. The overhear-based packet transmission control system according to claim 1, wherein the station compares its own reception (Rx) signal intensity with a reception (Rx) signal intensity of a transmission-failure station, determines whether the Rx signal strength of the station is higher than the Rx signal intensity of the transmission-failure station, determines whether a MAC Service Data Unit (MSDU) equal to the sum of the transmission data of the station and overhear data of the transmission-failure station is larger than a maximum MSDU, performs fragmentation of the MSDU if it is determined that the Rx signal strength of the station is higher than the Rx signal intensity of the transmission-failure station and the MSDU is larger than the maximum MSDU, and transmits the fragmented MSDU several times.

5. The overhear-based packet transmission control system according to claim 1, wherein the station, if it has the channel access opportunity and has to compensate the other stations for the channel access opportunity of the station, generates a modified RTS including address information of the compensation-object station, and transmits the modified RTS including the address information to the access point (AP).

6. The overhear-based packet transmission control system according to claim 1, wherein the at least one station, upon receiving an acknowledgement (ACK) message indicating successful transmission completion from the access point (AP) acting as a destination, deletes a list of data to be transmitted to the destination from its own overhear table.

7. The overhear-based packet transmission control system according to claim 1, wherein the access point (AP), upon receiving a modified RTS including address information of a compensation-object station from the station, transmits a CTR to the compensation-object station, and assigns a data transmission opportunity to the compensation-object station.

8. The overhear-based packet transmission control system according to claim 7, wherein the compensation-object station, upon receiving the channel access opportunity acquired by the compensation of the at least one station, does not re-compensate for the acquired channel access opportunity although there is a debt to the other stations, and uses the acquired channel access opportunity for the compensation-object station itself.

9. The overhear-based packet transmission control system according to claim 1, wherein the station includes:

a Radio Frequency (RF) communication unit for communicating with the access point (AP), and/or overhearing the other stations;

an overhear-data extractor for extracting overhear data of the other stations in conjunction with the RF communication unit;

a controller for managing the overhear data extracted from the overhear-data extractor, controlling management of the transmission data of the station, considering a reception (Rx) signal intensity of the station and a Rx signal intensity of a transmission-failure station from among the other stations during a data transmission time, collecting the transmission data of the station and the overhear data, and controlling a data transmission using the collected data;

a data transmitter for transmitting the collected data to the access point (AP) over the RF communication unit upon receiving a control signal from the controller;

a transmission-table manager for storing the transmission data of the station in a transmission table, and managing the data stored in the transmission table;

an overhear-table manager for storing the overhear data in an overhear table, and managing the overhear data stored in the overhear table; and

a data transmission compensator associated with the controller, if it has the channel access opportunity and has to compensate the other stations for the channel access opportunity of the station, generating a modified RTS including address information of a compensation-object station, and transmitting the modified RTS including the address information of the compensation-object station to the controller, thereby compensating for the data transmission.

10. A method for controlling overhear-based packet transmission over a Wireless Local Area Network (WLAN) in an overhear-based packet transmission control system, which includes at least one station for overhearing data of other stations, collecting/transmitting its own transmission data and data of the other stations if it is determined that a data transmission failure occurs, compensating for channel access opportunities of the other stations if it is determined that the transmission data of the at least one station is transmitted from the other stations;

and an access point (AP) for communicating with the at least one station over the WLAN, and equally assigning the channel access opportunity to the at least one station, the method comprising;

a) if the at least one station can access a channel, allowing one of the other stations to acquire the channel;

b) overhearing packets of neighboring stations of the remaining stations other than the channel-acquisition station;

c) allowing the channel-acquisition station to determine the presence or absence of its own MAC Service Data Unit (MSDU), and determining the presence or absence of an overhear table if the presence of the MSDU is determined;

d) configuring a transmission packet composed of the MSDU and overhear data if the presence of the overhear table is determined, and transmitting the configured transmission packet to the access point (AP); and

e) allowing a corresponding station to delete an acknowledgement (ACK) message and an overhear packet from the overhear table, if successful transmission completion of the transmission packet is determined.

11. The overhear-based packet transmission control method according to claim 10, wherein the channel-acquisition station transmits only its own MDSU to the access point (AP) if the absence of the overhear table is determined.

12. The overhear-based packet transmission control method according to claim 10, wherein the station manages the overhear table, determines the presence or absence of a data transmission failure of the other stations, and stores a transmission-failure packet of the other stations in the overhear table.

13. The overhear-based packet transmission control method according to claim 10, wherein the channel-acquisition station compares its own reception (Rx) signal intensity with a reception (Rx) signal intensity of a transmission-failure station, determines whether the Rx signal strength of the station is higher than the Rx signal intensity of the transmission-failure station, determines whether a MAC Service Data Unit (MSDU) equal to the sum of the transmission data of the station and overhear data of the transmission-failure station is larger than a maximum MSDU, performs fragmentation of the MSDU if it is determined that the Rx signal strength of the station is higher than the Rx signal intensity of the transmission-failure station and the MSDU is larger than the maximum MSDU, and transmits the fragmented MSDU several times.

14. The overhear-based packet transmission control method according to claim 10, wherein the station, if it has the channel access opportunity and has to compensate the other stations for the channel access opportunity of the station, generates a modified RTS including address information of the compensation-object station, and transmits the modified RTS including the address information to the access point (AP).

15. The overhear-based packet transmission control method according to claim 10, wherein the at least one station, upon receiving an acknowledgement (ACK) message indicating successful transmission completion from the access point (AP) acting as a destination, deletes a list of data to be transmitted to the destination from its own overhear table.

16. The overhear-based packet transmission control method according to claim 10, wherein the access point (AP), upon receiving a modified RTS including address information of a compensation-object station from the station, transmits a CTR to the compensation-object station, and assigns a data transmission opportunity to the compensation-object station.

17. The overhear-based packet transmission control method according to claim 10, wherein the compensation-object station, upon receiving the channel access opportunity acquired by the compensation of the at least one station, does not re-compensate for the acquired channel access opportunity although there is a debt to the other stations, and uses the acquired channel access opportunity for the compensation-object station itself.