Direct link protocol in wireless local area networks

Details Direct link protocol in wireless local area networks Direct link protocol in wireless local area networks

2003-01-29

2004-09-14

Duong, Frank (Department: 2666)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S311000, C370S346000

Reexamination Certificate

active

06791962

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to telecommunications in general, and, more particularly, to an IEEE 802.11 wireless local area network.
BACKGROUND OF THE INVENTION
FIG. 1
depicts a schematic diagram of a portion of wireless telecommunication system
100
in the prior art, which comprises stations
101
-
1
through
101
-
5
and access point
102
. Stations
101
-
1
through
101
-
5
and access point
102
can communicate with each other within shared communications network
103
and with wired backbone network
104
via access point
102
. Stations
101
-
1
through
101
-
5
and access point
102
constitute an IEEE 802.11(a) or 802.11(b) wireless local area network (hereinafter also called a “WLAN”). An IEEE 802.11(b) network is also known as a “Wi-Fi” network.
Stations
101
-
1
through
101
-
5
are computing devices capable of communicating with each other using wireless network interfaces and, together, constitute a basic service set (hereinafter also called a “BSS”). A basic service set can be regarded as a building block for an 802.11-based network. Access point
102
enables stations
101
-
1
through
101
-
5
to communicate with the rest of the world via wired backbone network
104
. Stations
101
-
1
through
101
-
5
and access point
102
communicate with each other through a wireless medium, which is depicted as shared communications network
103
.
Wireless telecommunication system
100
is classified as an infrastructure BSS because it comprises an access point. An infrastructure BSS is contrasted with an independent BSS, or IBSS, which does not comprise an access point. In wireless telecommunication system
100
, access point
102
is involved in all communications, including those in which two stations (e.g., stations
101
-
1
and
101
-
5
, etc.) communicate with each other. This is because the infrastructure BSS has a logical star topology, and, therefore, access point
102
relays all communications between stations in the BSS.
Referring to
FIG. 2A
, if station
101
-
1
wishes to send, for example, a data frame to station
101
-
5
, station
101
-
1
first sends data frame
201
to access point
102
. Access point
102
then attempts to relay data frame
201
to access point
102
. To accomplish this, access point
102
first checks to see if station
101
-
5
is in active mode, and, therefore, is ready to receive the relayed frame. Station
101
-
5
might, however, be in power save mode, and, therefore, not ready to receive the relayed frame.
When a station is in power save mode, the station has placed its transmitter and receiver in a low power state to conserve power, and, therefore cannot transmit or receive. In accordance with a predictable schedule, a station in power save mode powers up its receiver periodically to determine if the access point has any frames waiting for it. The access point knows when the stations in its BSS wake up from power save mode and initiates a message transaction. Referring again to
FIG. 2A
, in message transaction
202
, access point
102
transmits a beacon frame that comprises a traffic indication map. Station
101
-
5
then transmits a PS-Poll frame, requesting that the frame be sent. Access point
102
then forwards the data frame to station
101
-
5
. Additional frames from station
101
-
1
through access point
102
can follow.
Similarly, station
101
-
5
might have one or more data frames to send back to station
101
-
1
, which is depicted in FIG.
2
B. Station
101
-
5
transmits data frame
203
. Access point
102
then initiates message transaction
204
with station
101
-
1
, and delivers the data frames.
Direct communication between stations
101
-
1
and
101
-
5
is often desirable, but it is problematic because a transmitting station would not know if an intended receiving station were in power save mode and, therefore, unable to receive frames.
SUMMARY OF THE INVENTION
The present invention provides a technique that enables a first 802.11 enhanced station to communicate with a second 802.11 enhanced station directly, even when the second station periodically or sporadically enters power save mode. Furthermore, enhanced stations such as those in the illustrative embodiment are backwards compatible, and, therefore, can operate in a basic service set comprising legacy stations.
In accordance with the illustrative embodiment of the present invention, an enhanced station, hereinafter called a Q-station, requests a direct link with another Q-station (i.e., the targeted Q-station) by first transmitting a direct_link_protocol_request frame to an access point. The access point and not the requesting Q-station then determines if the targeted Q-station is in power save mode. If the targeted Q-station is in power save mode, the access point “wakes” the Q-station by transmitting a beacon frame that comprises a traffic indication map. This wakes the targeted Q-station and causes it to respond by transmitting back to the access point a PS-Poll frame. When the access point receives the PS-Poll frame, the access point responds by forwarding the direct_link_protocol_request frame from the requesting Q-station to the targeted Q-station.
The targeted Q-station then responds by transmitting back a direct_link_protocol_response frame to the requesting Q-station, either through the access point or directly. The targeted Q-station then knows to expect a frame directly from the requesting Q-station. That frame might be, for example, a direct_link_protocol_probe frame to test the suitability of the direct link or a data frame.
The illustrative embodiment of the present invention comprises: receiving at an access point from a first Q-station a direct_link_protocol_request frame that indicates a second Q-station as the destination of the direct_link_protocol_request frame; transmitting from the access point a traffic indication map that indicates that traffic is available for the second Q-station; receiving at the access point, in response to the transmission of the traffic indication map, a PS-Poll frame from the second Q-station; and forwarding from the access point, in response to the reception of the PS-Poll frame, the direct_link_protocol_request frame to the second Q-station.


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patent: 5371734 (1994-12-01), Fischer
patent: 5487069 (1996-01-01), O'Sullivan
patent: 5636220 (1997-06-01), Vook
patent: 5768531 (1998-06-01), Lin
patent: 5991287 (1999-11-01), Diepstraten et al.
patent: 5995849 (1999-11-01), Williams
patent: 6047178 (2000-04-01), Frlan
ANSI/IEEE Std 802.11, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, pp. 1-513, 1999.*
ETSI TR 101 683 V1.1.1, Broadband Radio Access Networks; HIPERLAN Type 2; System Overview, pp. 1-19, 2000.*
Kamerman et al, WaveLan-II: A High-Performance Wireless LAN for the Unlicensed Band, Bell Labs Technical Journal, pp. 118-133, 1997.

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