Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-12-08
2004-09-21
Marcelo, Melvin (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S338000, C370S346000, C370S468000
Reexamination Certificate
active
06795418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wireless medium access control (MAC) protocol, and more particularly relates to a hybrid wireless MAC protocol which uses a combination of slot (bandwidth) allocation, a variation on conventional token passing and polling for use in regulating isochronous traffic transmission.
2. Description of Related Art
The wireless communication market has lately enjoyed tremendous growth and is now capable of reaching every place on earth. Hundreds of millions of people exchange information every day using pagers, cellular telephones and other wireless communication products. Wireless communication has broken the harnesses of wireline networks, allowing users to access and share information on a global scale nearly everywhere they venture.
Standard LAN protocols (wireline), such as ETHERNET™, operate on wireline networks using various MAC protocols, e.g., carrier sense multiple access with collision detection (CSMA/CD), at fairly high speeds with inexpensive connection hardware which provides an ability to bring digital networking to practically any computer. Until recently, however, LANs were limited to physical, hard-wired (wireline) infrastructure. Even with phone dial-ups, network nodes were limited to access through wireline connections. Wireline communications, however, have set the stage for wireless communications.
Since the recent development of wireless LANs, many network users, such as mobile users in business, the medical professions, industry, universities, etc., have benefited from the enhanced communication ability of wireless LANs, i.e., increased mobility. Uses for wireless network access are practically unlimited. In addition to increased mobility, wireless LANs offer increased flexibility. Compared to wireline counterparts, however, wireless networks are known to have much less bandwidth, and hence it is highly desirable to utilize the wireless link bandwidth efficiently.
The IEEE standard for wireless LAN protocol is identified as “Standard for Information Technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY),” 1999, which will be referred to hereinafter as IEEE 802.11. IEEE 802.11 specifies parameters of both the physical (PHY) and medium access control (MAC) layers of the network. The PHY network handles transmission of data between nodes by either direct sequence spread spectrum, frequency-hopping spread spectrum, or infrared (IR) pulse position modulation. IEEE 802.11 makes provisions for data rates of either 1 Mbps or 2 Mbps, and calls for operation in the 4.4-2.4835 GHz band (spread spectrum), and 300-428,000 GHz for IR transmission.
In accordance with IEEE 802.11, there are two different ways to configure a network: ad-hoc and infrastructure. An example of an ad-hoc wireless network would include employees in various places using small computers and wireless links to implement an “ad-hoc” wireless network to facilitate the business meeting “on the fly”. Such ad-hoc networks may be brought up and torn down in a very short time as needed, either around the conference table and/or around the world. In order to maintain such networks, algorithms such as the spokesman election algorithm (SEA) have been designed which “elect” one machine as the base station (master) of the ad-hoc wireless network, the remaining network members as slaves.
An example of an “infrastructure” wireless network under IEEE 802.11 uses fixed network access points with which mobile nodes can communicate. These network access points are sometimes connected to landlines to widen the LAN's capability by bridging wireless nodes to other wired nodes. If service areas overlap, handoffs can occur (which operation is very similar to conventional cellular technology). Regardless of the wireless LAN configuration, however, the WLAN still requires a medium access control protocol.
The MAC layer is a set of protocols which is responsible for maintaining order in the use of a shared medium. IEEE 802.11 specifies a carrier sense multiple access with collision avoidance (CSMA/CA) protocol for use as a random access protocol technique. Within such a network, when a node receives a packet to be transmitted, it first listens to ensure that no other node is transmitting. If the channel is clear (i.e., no other node is transmitting), the node then transmits the packet. Otherwise, the node chooses a random backoff factor which determines the amount of time the node must wait until it is allowed to retransmit the packet.
The reader should note, however, that collision detection, as is employed in ETHERNET™, cannot be used for the radio transmissions of IEEE 802.11 because transmitting nodes within the wireless LAN cannot hear any other node in the system (network) which may be transmitting. That is, the transmitting node's own signal is presumably stronger than any other signal arriving at the node. The problem can be analogized to the problem of hearing impairment, that is, some nodes are hearing impaired for any of various reasons.
Under IEEE 802.11, when a mobile wishes to transmit a packet, it may send out a short ready-to-send (RTS) packet containing information on the length of the packet. If the receiving node hears the RTS, it responds with a short clear-to-send (CTS) packet. The transmitting node sends its packet, and, when received successfully by the receiving node, the receiving node sends an acknowledgment (ACK) packet. Problems arise, however, with respect to those receiving nodes which are “hearing impaired”.
Hidden nodes or stations (STAs) prevent efficient use of bandwidth as a result of their hearing impairment to certain transmissions. For example,
FIG. 1
shows an example of a wireless local area network (WLAN) composed of an access point (AP) and a number of stations (STAs). WLAN operation therein is based on the premise that the AP can communicate with all STAs directly over the wireless link while STAs can communicate each other depending on the relative locations due to their limited transmission ranges.
In
FIG. 1
, STA
1
is seen as clearly able to communicate with STA
2
directly (or in one hop), but not with STA
3
. In
FIG. 1
, a circle around each STA (and the AP) represents the corresponding transmission range, where STAs
1
and
3
are called hidden terminals to each other since they cannot know even the existence of each other without the help of the AP in between. Note that the communication between STAs
1
and
3
should be performed via the AP.
Various attempts have been made to utilize unused portions of TDMA time slots assigned to particular nodes within a WLAN, i.e., to implement channel efficiency. For example, Cheng-Shang Chang, et al., GUARENTEED QUALITY-OF-SERVICE WIRELESS ACCESS TO ATM NETWORKS, IEEE Journal on selected Areas In Communications, vol. 15, no. 1, January, 1997, discloses the use of polling in an effort to realize a protocol for non-preemptive priority for constant bit rate (CBR) and variable bit rate (VBR) traffic which supports ATM services.
U.S. Pat. No. 5,684,791 to Raychaudhuri, et al. (Raychaudhuri) discloses data link procedures for wireless ATM network channel access based on dynamic TDMA (time division multiple access)/TDD(time division duplexing) framework. The system provides ATM services such as ABR data and constant/variable (CBR/VBR) voice using wireless specific MAC and data link control (DLC) protocols. However, a reading of Raychaudhuri shows the complexity of its bi-component MAC protocol and operation.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a wireless MAC protocol, and a wireless LAN system using the MAC protocol which overcomes the shortcomings of conventional methods of efficiently utilizing bandwidth.
It is also an object of the invention to provide a wireless MAC protocol for isochronous traffic support which utilizes the prec
Marcelo Melvin
Vodopia John F.
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