Patent Application
20060133394
The present invention relates generally to wireless communication systems and in particular to the field of wireless backhaul in wireless local area networks.
In a wireless local area network (WLAN), wireless backhaul comprises access points (APs) necessary to transport communications from a client served by a coverage access point (CAP) through to an access point (AP) that is directly connected to a fixed network infrastructure, as termed a “wired” AP. In a WLAN, typically the clients are endpoints of a communication path, and the APs are typically stationary and the intermediaries by which a communication path to a client may be established or maintained. To reduce the number of wired APs required to provide coverage for a given area, a layer of intermediate APs is placed between the CAPs and the wired APs. This layer of intermediate APs, the associated CAPs, and the wired APs are all in communication wirelessly and are collectively termed “wireless backhaul.” The communications in the wireless backhaul take place on a communications channel that is a shared radio frequency (RF) frequency where the APs utilizing the communications channel must share the time that they use it.
Each AP, whether intermediate, coverage, or wired, needs to handle communications in two directions. The first direction is from the client through the wireless backhaul to a wired AP and is termed “upstream.” The second direction is from the wired AP through the wireless backhaul to the client and is termed “downstream.” Because the communications channel is shared, each AP needs to effectively manage its access to the communications channel for both the upstream and downstream directions and manage its access in a manner that does not interfere with another AP's access to the communications channel.
Accordingly, there exists a need for an improved method of wireless backhaul in a wireless local area network.
A preferred embodiment of the invention is now described, by way of example only, with reference to the accompanying figures in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to each other. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate identical elements.
An embodiment of the present invention is described with reference to
The distinction between coverage APs and tiered APs, e.g. tier 1 AP or tier 2 AP, is that a coverage AP interfaces with the clients of the multi-tier WLAN and the tiered APs are the intermediaries of a communication between the clients in the multi-tier WLAN. In an alternate embodiment, the functionality provided by a tiered AP may be combined into a coverage AP, and vice versa, so one AP, whether tiered or coverage, may provide both functions.
In one embodiment, each AP in the multi-tier WLAN implements the IEEE 802.11 PCF protocol where an AP sends a poll message to a client and the client responds. In an alternative embodiment, each AP in the multi-tier WLAN implements the IEEE 802.11E protocol where the AP implements quality of service enhancements. In another alternative embodiment, a contention based protocol may be used to provide each AP with access to the communications channel. In an illustrative embodiment, each access point has a polling list that comprises information about APs that would like to be serviced. The polling list includes information such as MAC address and a channel number for the communication. Alternatively, the polling list may also include information such as signal strength. The process of populating the polling list is performed by a number of network protocols, such as beacon transmissions (also termed “beacons”), explicit requests by clients, distance vector routing, and other similar protocols, and is beyond the scope of this disclosure.
On the client side of the multi-tier WLAN communications hierarchy, a client 138 communicates directly with a single coverage AP to provide access to the wired network (not shown) or to the rest of the wireless multi-tier WLAN communications hierarchy. Although there is only one client 138 shown in
As will be appreciated by those of skill in the art, the clients may be any suitable type of wireless communications device capable of communicating within a wireless network, such as computers, personal data assistants (PDAs), fixed mounted devices, vehicular mounted devices, or handheld devices, as well as others. Certain of the clients may also be connected to a fixed communications infrastructure, if desired.
Communications in the multi-tier WLAN occur in one of two directions, namely upstream and downstream. Upstream communications occur between an AP and its neighboring AP which is closer to the MBU in the multi-tier WLAN. For example, an upstream communication occurs when a CAP sends a communication to an IBU. Downstream communications occur between an AP and its neighboring AP which is closer to the client in the multi-tier WLAN. For example, a downstream communication occurs when an IBU sends a communication to a CAP. Further, in one embodiment, both upstream and downstream communications in any single AP use a single RF frequency. For example, AP 1 may use a communications channel having a frequency of 4.9475 GHz for both upstream and downstream communications whereas AP 4 may use a communications channel having a frequency of 4.9725 GHz for both upstream and downstream communications.
An AP functions as a “parent” when it sends communications in a downstream direction and/or receives communications from an upstream direction. In contrast, an AP functions as a child when it sends communications in an upstream direction and/or receives communications from a downstream direction. Because each AP in the wireless backhaul is able to send and receive communications in both the upstream and downstream directions, each AP in the wireless backhaul functions as both as a parent and a child. However, each AP can not indefinitely function as either a parent or a child, so the AP must divide its time between the time that it spends functioning as a parent and the time that it spends functioning as a child. In one embodiment, the time that an AP spends as a parent and the time that the AP spends as a child is predetermined and triggered by a timer. For example, the AP may spend 25 msec as a child and may follow that with 25 msec as a parent.
Referring to
Referring to
Having described the functionality performed by an AP behaving as a parent and as a child, shown in
In general, beacons are defined as packets transmitted by an AP which has information about the multi-tier WLAN such as timing synchronization, traffic queues, and the capabilities of the sender, e.g. the AP. In such an embodiment and as known in the IEEE 802.11 art, beacons transmitted by an AP are transmitted once every beacon interval where a beacon interval is defined as the time between consecutive beacons transmitted by a tier 1 AP, e.g. 300, 301 as shown in
As mentioned above, an AP behaving as a child may request suspension from service from its parent by sending a communication to its parent. In one embodiment, the communication is a standard IEEE 802.11 packet comprising an information element. In such an embodiment, the information element may have fields such as a) an identification of the child, e.g. a MAC address, b) an action to be performed, e.g. place the child on the polling list, remove the child from the polling list, and request additional service time, and c) the duration of the action. Likewise, a parent may respond to requests for service by sending a communication to a child. In one embodiment, the communication is a standard IEEE 802.11 packet comprising an information element. In such an embodiment, the information element may have fields such as a) an identification of the parent, e.g. a MAC address, b) an action to be performed, e.g. accept child's request, conditionally accept child's request, and reject child's request, and c) the duration of the action.
While the invention has been described in conjunction with specific embodiments thereof, additional advantages and modifications will readily occur to those skilled in the art. The invention, in its broader aspects, is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. For example, the subscriber unit and/or the base radio may comprise a storage medium having stored thereon a set of instructions which, when loaded into a hardware device (e.g., a microprocessor), causes the hardware device to perform the following functions of the present invention. The present invention can be implemented in at least one of hardware, firmware and/or software. Various alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Thus, it should be understood that the invention is not limited by the foregoing description, but embraces all such alterations, modifications and variations in accordance with the spirit and scope of the appended claims.
It should be noted that the terms “a” or “an”, as used herein, are defined as one or more than one. The term “plurality”, as used herein, is defined as two or more than two. The term “another”, as used herein, is defmed as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language).
