OPTIMAL POWER SAVING SCHEDULER
FOR 802.11E APSD
FIELD OF INVENTION
The present invention relates generally to wireless networks and more particularly to systems and methods for saving power in wireless local area networks.
BACKGROUND OF THE INVENTION 10
The Institute of Electrical and Electronics Engineers (IEEE) has produced a series of standards referred to as 802.X, which encompasses LANs (Local Area Networks), MANs (Metropolitan Area Networks) and PANs (Personal 15 Area Networks) such as Bluetooth. The IEEE 802 is confined to standardizing processes and procedures that take place in the bottom two layers of the OSI (Open System Interconnection) reference model—the media access control (MAC) sublayer of the link layer and the physical layer. 20
The original standard that is currently used to establish a wireless local area network (WLAN) is the IEEE 802.11 standard. The IEEE 802.11 standard was published first in 1997 and it was designed to provide data rates up to 2 Mbps (such as a DSL connection) at 2.4 Ghz. The standard 25 includes specifications for Media Access Control (MAC) and physical layer operation. The physical layer standard was designed to use either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). In 1999, 802.11a and 802.11b provided enhancements at the 30 physical layer with higher data rate support up to 54 Mbps in the 5 GHz band and 11 Mbps in the 2.4 GHz band, respectively.
The newly developed 802.lie standard is working to enhance the current 802.11 MAC to expand support for 35 applications with high QoS (Quality Of Service) requirements. Wireless networks fit both business and home environments, that both require the support of multimedia, and the 802.lie standard provides the solution for this need. In both wired and wireless networks, data transmission is 40 susceptible to interruptions caused when packets are present or lost during the transmission process. These interruptions can cause problems for data to be streamed in a contiguous fashion. The 802.lie has created a QoS baseline document that proposes methods for handling time-sensitive traffic. 45
In the WLAN topology, each wireless network requires a radio transceiver and antenna. Components on the wireless network are either stations (STAs) or access points (APs). Typically, a station STA is mobile or portable, and the access point AP may be a permanent structure analogous to a base 50 station tower used in cellular phone networks or to a hub used in a wired network. A basic service set (BSS) is formed when two or more stations have recognized each other and established a network. An extended service set (ESS) is formed when BSSs (each one comprising an AP) are con- 55 nected together.
A standard WLAN according to 802.11 operates in one of two modes—ad-hoc (peer-to-peer) or infrastructure mode. The ad-hoc mode is defined as Independent BSS (IBSS), and the infrastructure mode as a BSS. WLANs may also be 60 classified as distributed (ad-hoc), or as centralized systems (infra-structure based system).
In ad-hoc mode (IBSS), each client communicates directly with the other clients within the network on a peer-to-peer level sharing a given cell coverage area. This 65 mode was designed such that only the clients within transmission range of each other can communicate. If a client in
an ad-hoc network wishes to communicate outside of the range, one of the clients (members) must operate as a gateway and perform routing.
FIG. 1 illustrates the basic service set BSS 1 operating in the infrastructure mode, wherein a wireless network is formed between one or more stations (STA) 2 communicating with an access point (AP) 4 such as a communications tower. The access point acts as an Ethernet bridge and forwards the communications onto the network (e.g., either wired or wireless network). Several such BSS networks communicating together over the infrastructure between APs further form an Extended Service Set (ESS), or a Distribution System (DS).
Before stations and access points can exchange data, they must establish a relationship, or an association. Only if an association is established can the STA and AP exchange data. The association process involves three states:
Unauthenticated and unassociated
Authenticated and unassociated
Authenticated and associated
In the transition between the states, the communicating parties exchange messages called management frames. The APs are designed to transmit a beacon management frame at fixed intervals. To associate with an access point and join the BSS, a station listens for beacon messages to identify the access points within the range. After the station receives a beacon frame (message) it selects the BSS to join. The network names, or service set identifiers (SSID) contained in the beacon frame, permit the user to choose the SSID the user wishes to join. A station can also send a probe request frame to find the associated access point with the desired SSID. After the station identifies the access point, they perform an authentication by exchanging several management frames.
As illustrated in prior art FIG. 2, a wireless transceiver 20, according to the OSI (Open System Interconnection) reference model, comprises in part, a series of protocol layers 23 having a physical layer PHY 24, a data link layer 26, and a NETWORK layer 28. The data link layer 26 further comprises a medium access control MAC 26a sublayer and a logical link control LLC 26b sublayer. The OSI reference model describes networking as a series of protocol layers with a specific set of functions allocated to each layer. Each layer offers specific services to higher layers while shielding these layers from the details of how the services are implemented. A well-defined interface between each pair of adjacent layers defines the services offered by the lower layer to the higher one and how those services are accessed.
The physical layer PHY 24 is involved in the reception and transmission of the unstructured raw bit stream over a physical medium. It describes the electrical/optical, mechanical, and functional interfaces to the physical medium. The PHY 24 layer carries the signals for all the higher layers. The MAC 26a sublayer of the data link layer 26, manages access to the network media, checks frame errors, and manages address recognition of received frames.
The LLC 26b sublayer establishes and terminates logical links, controls frame flow, sequences frames, acknowledges frames, and retransmits unacknowledged frames. The LLC 26b sublayer uses frame acknowledgement and retransmission to provide virtually error-free transmission over the link to the layers above. The NETWORK layer 28 controls the operation of the subnet. It determines the physical path the data should take, based on network conditions, priority of service, and other factors, including routing, traffic control, frame fragmentation and reassembly, logical-to-physical address mapping, and usage accounting.