(19)
(11)EP 1 492 274 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
25.02.2015 Bulletin 2015/09

(21)Application number: 04011698.0

(22)Date of filing:  17.05.2004
(51)Int. Cl.: 
H04W 92/20  (2009.01)

(54)

Method for providing a mesh network using a plurality of wireless access points (WAPS)

Verfahren zur Bereitstellung eines, mehrere drahtlose Zugangspunkte verwendenden Maschennetzes

Procédé pour fournir un réseau maillé utilisant plusieurs points d'accès sans fil


(84)Designated Contracting States:
DE FR GB

(30)Priority: 26.06.2003 US 606565

(43)Date of publication of application:
29.12.2004 Bulletin 2004/53

(73)Proprietor: Broadcom Corporation
Irvine, CA 92617 (US)

(72)Inventors:
  • Seshadri, Nambi
    Irvine, California 92612 (US)
  • Karaoguz, Jeyhan
    Irvine, California 92606 (US)

(74)Representative: Jehle, Volker Armin et al
Bosch Jehle Patentanwaltsgesellschaft mbH Flüggenstrasse 13
80639 München
80639 München (DE)


(56)References cited: : 
WO-A-94/28645
US-A- 5 659 596
US-A- 6 154 652
WO-A-97/31487
US-A- 6 119 005
US-B1- 6 219 346
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD OF THE INVENTION



    [0001] Embodiments of the present application relate generally to hybrid wired/wireless networking, and more particularly to a method and system for providing a mesh network using a plurality of wireless access points.

    BACKGROUND OF THE INVENTION



    [0002] The Open Systems Interconnection (OSI) model promulgated by the International standards organization (ISO) was developed to establish standardization for linking heterogeneous computer and communication systems. The OSI model describes the flow of information from a software application of a first computer system to a software application of a second computer system through a network medium. FIG. 1a is a block diagram 100 of the OSI model. Referring to FIG. 1a, the OSI model has seven distinct functional layers including layer 7, an application layer 114; layer 6, a presentation layer 112; layer 5, a session layer 110; layer 4, a transport layer 108, layer 3, a network layer 106; layer 2: a data link layer 104; and layer 1, a physical layer 102. The physical layer 102 may further include a physical layer convergence procedure (PLCP) sublayer 102b and a physical media dependent sublayer 102a. The data link layer 104 may also include a Medium access control (MAC) layer 104a.

    [0003] In general, each OSI layer describes certain tasks which are necessary for facilitating the transfer of information through interfacing layers and ultimately through the network. Notwithstanding, the OSI model does not describe any particular implementation of the various layers. OSI layers 1 to 4 generally handle network control and data transmission and reception, generally referred to as end-to-end network services. Layers 5 to 7 handle application issues, generally referred to as application services. Specific functions of each layer may vary depending on factors such as protocol and/or interface requirements or specifications that are necessary for implementation of a particular layer. For example, the Ethernet protocol may provide collision detection and carrier sensing in the physical layer. Layer 1, the physical layer 102, is responsible for handling all electrical, optical, opto-electrical and mechanical requirements for interfacing to the communication media. Notably, the physical layer 102 may facilitate the transfer of electrical signals representing an information bitstream. The physical layer 102 may also provide services such as, encoding, decoding, synchronization, clock data recovery, and transmission and reception of bit streams.

    [0004] The PLCP layer 102b may be configured to adapt and map services provided by the physical layer 102 to the functions provided by the device specific PMD sublayer 102a. Specifically, the PLCP layer 102b may be adapted to map PHY sublayer service data units (PDSUs) into a suitable packet and/or framing format necessary for providing communication services between two or more entities communicating via the physical medium. The PMD layer 102a specifies the actual methodology and/or protocols which may be used for receiving and transmitting via the physical medium. The MAC sublayer 104a may be adapted to provide, for example, any necessary drivers which may be utilized to access the functions and services provided by the PLCP sublayer 102b. Accordingly, higher layer services may be adapted to utilize the services provided by the MAC sublayer 104a with little or no dependence on the PMD sublayer 102a.

    [0005] 802.11 is a suite of specifications promulgated by the Institute of Electrical and Electronics Engineers (IEEE), which provide communication standards for the MAC and physical (PHY) layer of the OSI model. The 801.11 standard also provides communication standards for wired and wireless local area networks (WLANs). More specifically, the 802.11 standard specifies five (5) types of physical layers for WLANs. These include, frequency hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS), infrared (IR) communication, high rate direct sequence spread spectrum spread spectrum (HR-DSS) and orthogonal frequency division multiplexing (OFDM). The 802.11 standard also provides a PLCP frame format for each of the specified PHY layers.

    [0006] Over the past decade, demands for higher data rates to support applications such as streaming audio and streaming video, have seen Ethernet speeds being increased from about 1-2 megabit per second (Mbps), to 10 Mbps, to 100 Mbps, to 1 gigabit per second (Gbps) to 10 Gbps. Currently, there are a number of standards in the in the suite of specifications, namely 802.11 b, 802.11 a and 802.11 g which have been adapted to facilitate the demands for increased data rates. The 802.11g standard for example, provides a maximum data rate of about 54 Mbps at a transmitter/receiver range of 19 meters (m) in a frequency range of 2.4 GHz to 2.4835 GHz. The 802.11 b standard for example, provides a maximum data rate of about 11 Mbps at a transmitter/receiver range of 57 meters (m) in a frequency range of 2.4 GHz to 2.4835 GHz. Finally, the 802.11a standard for example, may be adapted to provide a maximum data rate of about 54 Mbps at a transmitter/receiver range of 12 meters (m) in a 300 MHz segmented bandwidth ranging from 5.150 GHz to 5.350 GHz and from 5.725 GHz to 5.825 GHz.

    [0007] The 802.11 standard forms the basis of the other standards in the suite of specifications, and the 802.11 b, 802.11a and 802.11g standards provide various enhancements and new features to their predecessor standards. Notwithstanding, there are certain elementary building blocks that are common to all the standards in the suite of specifications. For example, all the standards in the suite of specifications utilize the Ethernet protocol and utilize carrier sense multiple access with collision avoidance (CSMA/CA) for distribution coordination function (DCF) and point coordination function (PCF).

    [0008] CSMA/CA utilizes a simple negotiation scheme to permit access to a communication medium. If a transmitting entity wishes to transmit information to a receiving entity, the transmitting entity may sense the communication medium for communication traffic. In a case where the communication medium is busy, the transmitting entity may desist from making a transmission and attempt transmission at a subsequent time. In a case where the communication transmission is not busy, then the transmitting entity may send information over the communication medium. Notwithstanding, there may be a case where two or more transmission entities sense that the communication medium is not busy and attempt transmission at the same instant. To avoid collisions and retransmissions, CSMA/CA or a ready to send (RTS) and clear to send (CTS) messaging scheme may be employed, for example. Accordingly, whenever a transmitting device senses that the communication medium is not busy, then the transmitting device may send a ready to send message to one or more receiving device. Subsequent to the receipt of the ready to send message, the receiving device may send a clear to send message. Upon receipt of the clear to send message by the transmitting device, the transmitting device may initiate transfer of data to the receiving device. Upon receiving packets or frames from the transmitting device, the receiving device may acknowledge the received frames.

    [0009] The 802.11b standard, commonly called Wi-Fi, which represents wireless fidelity, is backward compatible with its predecessor standard 802.11. Although 802.11 utilizes phase-shift keying (PSK) as a modulation scheme, 802.11 b utilizes a hybrid PSK scheme called complementary code keying (CCK). CCK permits higher data rate and particularly less susceptible to interference effects such as multipath-propagation interference, the PSK.

    [0010] The 802.11a standard provides wireless asynchronous transfer mode (ATM) support and is typically utilized in access hubs. 802.11a utilizes orthogonal frequency-division multiplexing (OFDM) modulation/encoding scheme, which provides a maximum data rate 54 Mbps. Orthogonal frequency-division multiplexing is a digital modulation technique which splits a signal into several narrowband channels, with each channel having a different frequency. Each narrowband channel is arranged so as to minimize the effects of crosstalk between the channels and symbols in the data stream.

    [0011] Since equipment designed to provide support for 802.11a operates at frequencies in the ranges 5.150 GHz to 5.350 GHz and from 5.725 GHz to 5.825 GHz, 802.11 a equipment will not interoperate with equipment designed to operate with the 802.11 b standard which defines operation in the 2.4 to 2.4835 GHz frequency band. One major drawback is that companies that have invested in 802.11 b equipment and infrastructure may not readily upgrade their network without significant expenditure.

    [0012] The 802.11g standard was developed as an extension to 802.11b standard. The 802.11 g standard may utilize a similar OFDM modulation scheme as the 802.11a standard and delivers speeds comparable with the 802.11a standard. Since 802.11 g compatible equipment operates in the same portion of the electromagnetic spectrum as 802.11 b compatible equipment, 802.11 g is backwards compatible with existing 802.11 b WLAN infrastructures. Due to backward compatibility of 802.11 g with 802.11 b, it would be desirable to have an 802.11 b compliant radio card capable of interfacing directly with an 802.11 g compliant access point and also an 802:11g compliant radio card capable of interfacing directly with an 802.11 b compliant access point.

    [0013] Furthermore although 802.11g compatible equipment operates in the 2.4 GHz to 2.4835 GHz frequency range, a typical transmitted signal utilizes a bandwidth of approximately 22 MHz, about a third or 30% of the total allocated bandwidth. This limits the number of non-overlapping channels utilized by an 802.11 g access point to three (3). A similar scenario exists with 802.11 b. Accordingly, many of the channel assignment and frequency reuse schemes associated with the 802.11 b standard may be inherent in the 802.11 g.

    [0014] RF interference may pose additional operational problems with 802.11 b and 802.11 g equipment designed to operate in the 2.4 GHz portion of the electromagnetic spectrum. The 2.4 GHz portion of the spectrum is an unlicensed region which has been utilized for some time and is crowded with potential interfering devices. Some of these devices include cordless telephone, microwave ovens, intercom systems and baby monitors. Other potential interfering devices may be Bluetooth devices. Accordingly, interference poses interference problems with the 802.11 b and 802.11 g standards.

    [0015] 802.11a compatible equipment utilizes eight non-overlapping channels, as compared to three non-overlapping channels utilized by 802.11b. Accordingly, 802.11 a access points may be deployed in a more dense manner than, for example 802.11 b compatible equipment. For example, up to twelve access points each having a different assigned frequency may be deployed in a given area without causing cochannel interference. Consequently, 802.11a may be particularly useful in overcoming some of the problems associated with channel assignment, especially in areas that may have a dense user population and where increased throughput may be critical. Notwithstanding, the higher operating frequency of 802.11 a along with its shorter operating range, may significantly increase deployment cost since a larger number of access points are required to service a given service area.

    [0016] In hybrid wired/wireless network systems that may utilize one or more protocols in the 802.11 suite of protocols, the mobility of access devices throughout the network may pose additional challenges for conventional switches and switching equipment. Since access devices are continuously changing their point of access to the network, conventional switches may not have the capability to control other network devices and/or entities to provide seamless communication throughout the network. Allocation and de-allocation of certain network resources can be challenging in a network in which the traffic dynamics are continuously changing. Moreover, particularly in network systems that may handle large volumes of access device traffic, providing adequate coverage while access devices are mobile within the network may be critical.

    [0017] International patent application WO 94/28645 discloses a method and apparatus for supporting mobile communications in asynchronous transfer mode based networks. Distributed call setup and rerouting are realized in a mobile communications network. A connection tree is set up within the network, e.g., upon a mobile user accessing a base station. The connection tree comprises communication routes from a fixed point in the network, the root of the tree, to each base station within a vicintiy of the base station accessed by the mobile user. When the mobile user moves from one cell to another within the connection tree, the call is rerouted to another route within the connection tree.

    [0018] US patent 6,119,005 discloses a system for automated determination of a handoff neighbor list for cellular communication systems. Said automated determination system uses the data collected from mobile subscriber units to automatically update the handoff neighbor list. The mobile subscriber unit produces Pilot Strength Measurement (PSM) data that is indicative of the relative signal strength measured at the mobile subscriber unit from a plurality of pilot channels. The mobile subscriber unit transmits this data, along with a list of viable pilot channel candidates as determined by the mobile subscriber unit, to the base station serving the existing call. The system for automated determination of the handoff neighbor list maintains a data structure that stores data indicative of the number of instances that a pilot channel is recommended, the sum of power levels that were measured by the various mobile subscriber units for these instances. This data is processed to determine a metric for each data structure in the list, with the metric being a function of the number of occurrences multiplied by a weighting factor summed with the sum of power levels.

    [0019] According to the invention, there is provided a method as defined in claim 1, a machine-readable storage as defined in claim 7, and a system as defined in claim 8. Further advantageous features of the invention are defined in the dependent claims.

    [0020] According to another aspect of the invention, a method for providing a mesh network using a plurality of access points, the method comprises: coupling a first access point located in a first cell to at least a second access point located in a second cell; providing service initially to at least one of a plurality of access devices by said at least a first access point located in said first cell; and servicing said at least one of a plurality of access devices by said at least a second access point located in said second cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.

    [0021] Advantageously, said at least a second cell is a neighboring cell located adjacent to said first cell.

    [0022] Advantageously, the method further comprises transmitting a first signal from a first beamforming antenna coupled to said first access point, to said at least a second access point.

    [0023] Advantageously, the method further comprises transmitting a second signal from a second beamforming antenna coupled to said at least a second access point, to said first access point.

    [0024] Advantageously, a path for facilitating said transmitting said first signal between said first beamforming antenna and said second beamforming antenna is an uplink channel.

    [0025] Advantageously, a path for facilitating said transmitting of said second signal between said second beamforming antenna and said first beamforming antenna is a downlink channel.

    [0026] Advantageously, said uplink and said downlink channel is a backhaul channel.

    [0027] Advantageously, the method further comprises coupling said first access point located in a first cell to at least a third access point located in said first cell.
    Advantageously, the method further comprises servicing said at least one of a plurality of access devices by said at least a third access point located in said first cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.
    Advantageously, at least one of said first access point and said at least one of a plurality of access devices determines when said signal for said at least one of a plurality of access devices falls below a specified threshold.
    According to another aspect of the invention, a machine-readable storage, having stored thereon a computer program having at least one code section for facilitating communication in a mesh network using a plurality of access points, the at least one code section being executable by a machine for causing the machine to perform the steps comprises: coupling a first access point located in a first cell to at least a second access point located in a second cell; providing service initially to at least one of a plurality of access devices by said at least a first access point located in said first cell; and servicing said at least one of a plurality of access devices by said at least a second access point located in said second cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.
    Advantageously, said at least a second cell is a neighboring cell located adjacent to said first cell.
    Advantageously, the machine-readable storage further comprises code for transmitting a first signal from a first beamforming antenna coupled to said first access point, to said at least a second access point.
    Advantageously, the machine-readable storage further comprises code for transmitting a second signal from a second beamforming antenna coupled to said at least a second access point, to said first access point.
    Advantageously, a path for facilitating said transmitting of said first signal between said first beamforming antenna and said second beamforming antenna is an uplink channel.
    Advantageously, a path for facilitating said transmitting of said second signal between said second beamforming antenna and said first beamforming antenna is a downlink channel.
    Advantageously, said uplink channel and said downlink channel is a backhaul channel.
    Advantageously, the machine-readable storage further comprises code for connecting said first access point located in a first cell to at least a third access point located in said first cell.
    Advantageously, the machine-readable storage further comprises code for servicing said at least one of a plurality of access devices by said at least a third access point located in said first cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.
    Advantageously, at least one of said first access point and said at least one of a plurality of access devices comprises code for determining when said signal for said at least one of a plurality of access devices falls below a specified threshold.
    According to another aspect of the invention, a system for providing a mesh network using a plurality of access points, the system comprises: means for coupling a first access point located in a first cell to at least a second access point located in a second cell; means for providing service initially to at least one of a plurality of access devices by said at least a first access point located in said first cell; and means for servicing said at least one of a plurality of access devices by said at least a second access point located in said second cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.
    Advantageously, said at least a second cell is a neighboring cell located adjacent to said first cell.
    Advantageously, the system comprises a first beamforming antenna coupled to said first access point for transmitting a first signal from said first access point to said at least a second access point.
    Advantageously, the system comprises a second beamforming antenna coupled to said at least a second access point for transmitting a second signal from said at least a second access point to said first access point.
    Advantageously, a path for facilitating said transmitting between said first beamforming antenna and said second beamforming antenna is an uplink channel.
    Advantageously, a path for facilitating said transmitting between said second beamforming antenna and said first beamforming antenna is a downlink channel.
    Advantageously, said uplink channel and said downlink channel is a backhaul channel.
    Advantageously, the system further comprises coupling said first access point located in a first cell to at least a third access point located in said first cell.
    Advantageously, the system further comprises servicing said at least one of a plurality of access devices by said at least a third access point located in said first cell whenever a signal for said at least one of a plurality of access devices falls below a specified threshold.
    Advantageously, at least one of said first access point and said at least one of a plurality of access devices determines when said signal for said at least one of a plurality of access devices falls below a specified threshold.

    [0028] Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.

    [0029] Aspects of the invention provide a system and method for providing a mesh network using a plurality of access points. A method for providing a mesh network using a plurality of access points may include the step of coupling a first access point located in a first cell to at least a second access point located in a second cell. Service may be initially provided to an access device by a first access point located in the first cell. The access device may be serviced by a second access point located in a second cell whenever a signal for the access device falls below a specified threshold level. The second cell may be a neighboring cell, which may be located adjacent to the first cell.

    [0030] A first signal may be transmitted from a first beamforming antenna to the second access point. The first beamforming antenna may be coupled to the first access point. Similarly, a second signal may be transmitted from a second beamforming antenna to the first access point. The second beamforming antenna may be coupled to the second access point. A path for facilitating transmission of the first signal between the first beamforming antenna and the second beamforming antenna may be an uplink channel. Also, a path for facilitating transmission of the second signal between the second beamforming antenna and the first beamforming antenna may be a downlink channel. The uplink channel and the downlink channel may be a backhaul channel.

    [0031] The first access point located in a first cell may be coupled to a third access point located in the first cell. Accordingly, an access device may be serviced by a third access point located in the first cell whenever a signal level of the access device falls below a specified threshold level. Either of the first access point and the access device may be configured to determine when the signal of an access device falls below a specified threshold level.

    [0032] Another embodiment of the invention may provide a machine-readable storage, having stored thereon a computer program having at least one code section adapted to facilitate communication in a mesh network using a plurality of access devices, the at least one code section being executable by a machine for causing the machine to perform the steps described above.

    [0033] In another embodiment of the invention, a mesh network using a plurality of access points is provided. The system may include means for coupling a first access point located in a first cell to at least a second access point located in a second cell and means for providing service initially to at least one of a plurality of access devices by the a first access point located in the first cell. The invention provides a means for servicing an access device by a second access point located in the second cell whenever a signal for the access device falls below a specified threshold. In this regard, the second cell may be a neighboring cell located adjacent to the first cell.

    [0034] The system may further include a first beamforming antenna coupled to the first access point for transmitting a first signal from the first access point to the second access point. A second beamforming antenna coupled to the second access point may be adapted to transmitting a second signal from a second access point to the first access point. A path for facilitating transmission between a first beamforming antenna and the second beamforming antenna may be an uplink channel. Similarly, a path for facilitating transmission between the second beamforming antenna and the first beamforming antenna may be a downlink channel. The uplink channel and the downlink channel may be a backhaul channel. The system may further include means for coupling the first access point located in a first cell to at least a third access point located in the first cell.

    [0035] The system may further include means for servicing an access device by a third access point located in the first cell whenever a signal level corresponding to the access device falls below a specified threshold. Either of the first access point and/or an access device may include means for determining when a signal level corresponding to the access device falls below a specified threshold.

    [0036] These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.

    BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS



    [0037] FIG. 1a is a block diagram of the OSI model.

    [0038] FIG. 1b is a block diagram illustrating a general PLCP frame as defined by 802.11.

    [0039] FIG. 1c is a block diagram illustrating a PLCP frame utilized by frequency hopping spread spectrum as defined by 802.11.

    [0040] FIG. 1d is a block diagram illustrating a PLCP frame for direct sequence spread spectrum and high rate direct sequence spread spectrum as defined by 802.11.

    [0041] FIG. 1e is a block diagram illustrating a PLCP frame for orthogonal frequency division multiplexing as defined by 802.11.

    [0042] FIG. 2 is a block diagram of system for providing a mesh network using a plurality of wireless access points in accordance with an embodiment of the invention.

    [0043] FIG. 3 is a block diagram of a inter-mesh network handoff in accordance with an embodiment of the invention.

    [0044] FIG. 4 is a block diagram of an intra-mesh network handoff in accordance with an embodiment of the invention.

    [0045] FIG. 5 is a block diagram of an exemplary system that utilizes beam forming in accordance with an embodiment of the invention.

    DETAILED DESCRIPTION OF THE INVENTION



    [0046] Aspects of the invention provide a system and method for providing a mesh network using a plurality of access points. A method for providing a mesh network using a plurality of access points may include the step of coupling a first access point located in a first cell to at least a second access point located in a second cell. Service may be initially provided to an access device by a first access point located in the first cell. The access device may be serviced by a second access point located in a second cell whenever a signal for the access device falls below a specified threshold level. The second cell may be a neighboring cell, which may be located adjacent to the first cell.

    [0047] FIG. 1b is a block diagram 120 illustrating a general PLCP frame as defined by 802.11. Referring to FIG. 1b, there is shown preamble 122, PLCP header 124, MAC data 126, and CRC 128. Preamble 122 may include synchronization (SYNC) data 122a and synchronization delimiter 122b. The PLCP header 124 may include, for example PLCP signal field (PSF) 124a, service data 124b, length 124c and other fields. The preamble 122 may be dependent on the PHY. The SYNC data 122a may include a unique bit stream that may be adapted to signal timing parameters such as the start of a frame. The SYNC data 122a is used for bit synchronization and demodulation. The SYNC delimiter 122b provides frame timing information and may be adapted to delimit the end of synchronization information. The PLCP header 124 may be adapted to contain information used for decoding the frame. For example, the PSF 124a may be adapted to include communication data rate information. The service data 124b is generally reserved, but may be utilized to provide application specific functionality. The length 124c may be adapted to indicate the length of the MAC data 126. In this regard, the length 124c may be expressed in terms of the time required to transmit the MAC data 126.

    [0048] FIG. 1c is a block diagram 130 illustrating a PLCP frame utilized by frequency hopping spread spectrum as defined by 802.11. Referring to FIG. 1c, there is shown a SYNC data 132, PLCP header 134 and PSDU 136. The PLCP header 134 may include, for example, PSDU length word (PLW) 134a, PLCP signaling field (PSF) 134b, header error check field or CRC 134c and other fields. The PLW 134a may specify the number of octets contained in the PSDU 136. The PSF 134 be may be 4-bits in length and may be used to denote the communication data rate.

    [0049] FIG. 1d is a block diagram 140 illustrating a PLCP frame for direct sequence spread spectrum and high rate direct sequence spread spectrum (HR-DSS) as defined by 802.11. Referring to FIG. 1d, there is shown preamble 142, PLCP header 144 and MPDU 146. Preamble 142 may include synchronization (SYNC) data 142a and synchronization delimiter 142b. The PLCP header 144 may include PLCP signal field (PSF) 144a, service data 144b, length 144c, and CRC field 144d. The SYNC data 142a may be 128 bits as compared to 8 bits for SYNC data 132a for frequency hopping spread spectrum. The CRC 144d is 16 bits, which is similar to CRC 134c for frequency hopping spread spectrum.

    [0050] FIG. 1e is a block diagram 150 illustrating a PLCP frame for orthogonal frequency division multiplexing as defined by 802.11. Referring to FIG. 1e, there is shown preamble 152, PLCP header 154 and PSDU 156, tail 158 and pad 160. Preamble 152 may include synchronization (SYNC) data 152a and synchronization delimiter 152b. The PLCP header 154 may include length 154a, PLCP signal field (PSF) 154b, reserved field 154c, parity 154d, tail 154e and service 154f. The length 154a is a 12-bit field that may be adapted to indicate the length of the frame. The PSF 154b is a 4-bit field that may indicate a modulation scheme utilized and its associated coding rate of the PSDU. For example, the specification utilizes binary 1011 to represent 6 Mbps, 1111 to represent 9 Mbps, 1010 to represent 12 Mbps, 1110 to represent 18 Mbps, 1001 to represent 24 Mbps, 1011 to represent 36 Mbps, 1000 to represent 48 Mbps and finally, 1100 to represent the maximum standardized rate if 54 Mbps. The reserved field 154c is a 1 bit field that is reserved for future use and may be adapted for application specific use. The parity field 154d may indicate odd or even parity. The tail field 154e is a 6-bit field. The service field 154f is a 16-bit field that may be adapted to indicate the type of service.

    [0051] FIG. 2 is a block diagram of system 200 for providing a mesh network using a plurality of wireless access points (WAPs) in accordance with an embodiment of the invention. Referring to FIG. 2, there is illustrated a plurality of cells 202, 204, 206, 208, 210, 212, 214, 216, 218, 220, 222, 224, with each cell containing an access point (AP) 202a, 204a, 206a, 208a, 210a, 212a, 214a, 216a, 218a, 220a, 222a, 224a, respectively. It should be recognized that although each cell is illustrated as a hexagon, the actual shape of a cell may be dependent on various propagation and interference characteristics, and also geographical topology. Accordingly, the invention is not limited in this regard.

    [0052] Each cell may represent a separate mesh network. For example, cell 220 may represent a first mesh network and cell 214 may represent a second mesh network. Within each cell or mesh network, there may be at least one access point which may be adapted to provide WLAN service within the cell. For example, access point 202a may be adapted to provide WLAN service within a coverage area indicated by cell 202. Similarly, access point 214a may be adapted to provide WLAN service within a coverage area indicated by cell 214.

    [0053] In one embodiment of the invention, the range of an access point located within and serving a particular cell may be extended by interconnecting or coupling neighboring and surrounding cells. Cell 202, for example, has six (6) neighboring cells, namely 204, 206, 214, 216, 218, 224. Each of the access points 204a, 206a, 214a, 216a, 218a, 224a located in the cells 204, 206, 214, 216, 218, 224 respectively, may be adapted to provide WLAN service within a coverage area indicated by cell 204, 206, 214, 216, 218, 224, respectively. In accordance with an embodiment of the invention, the coverage area of access point 202 may be extended into any portion of any one or more of the neighboring cells 204, 206, 214, 216, 218, 224 by coupling the access points 204a, 206a, 214a, 216a, 218a, and 224a, to access point 202a. In a case where the access point 202a may be coupled to each one of access points 204a, 206a, 214a, 216a, 218a, 224a, then an access device located in any one of cells 202, 204, 206, 214, 216, 218, 224 may communicate with a device located in any one of the cells 202, 204, 206, 214, 216, 218, 224. For example, an access device located in cell 214 serviced by access point 214a may communicate with an access device located in cell 202 which may be serviced by access point 202a. Similarly, an access device located in cell 216 serviced by access point 216a may communicate with an access device located in cell 224 which may be serviced by access point 224a.

    [0054] In another aspect of the invention, a mobile access device may actively roam from a first mesh network to a second mesh network. For example, an access device may move from a first mesh network represented by cell 216 into second mesh network represented by cell 202.

    [0055] In accordance with another aspect of the invention, intra-mesh network and inter-mesh network hand-off may be provided. In the case of inter-mesh network handoff, an access device moving from a first cell representing a first mesh network may be handed off to a second cell representing a second mesh network. In the case of intra-mesh network handoff, an access device being serviced by a first access point located within a particular cell may be handed off to a second access point located within the same particular cell.

    [0056] FIG. 3 is a block diagram 300 of a inter-mesh network handoff in accordance with an embodiment of the invention. Referring to FIG. 3, there is shown a first cell 302 corresponding to a first mesh network having an access point AP1 302a and a second cell 304 corresponding to a second mesh network having an access point AP2 304a. Located in the first cell is an access device 306. Inter-mesh handoff may involve handoff from a first serving access point, for example access point 302a, to a second access point, for example access point 304a, both access points being located within different cells or on different mesh networks. For example, an inter-mesh network handoff may occur from access point 302a to 304a.

    [0057] In operation, access point 302a may initially provide service to access device 306 which may be mobile within the cell 302. However, as access device 306 migrates to the fringe of the cell 302, a signal received from access point 302a may fade until it reaches, for example, a handover threshold. In one aspect of the invention, the handover threshold may be dependent on one or more signal parameters such as the signal strength received from one or more of access point 302a and access point 302b. The access device 306 may dynamically keep a record of the frequency and corresponding signal strength of any received channel it encounters. For example, the access device 306 may be adapted to actively scan a list of frequencies for available channels. The record of the frequency and corresponding signal strength of any received channel may serve as a handoff candidate list. The access device 306 may be adapted to select the best candidate for a handoff from the candidate list based on, for example, a channel having the strongest signal strength. In a case where the access device 306 determines that the best access point for a handoff is access point 304a, then the access device may tune it transceiver to an available transmit and/or receive channel corresponding to the access point 304a. At this point, the access point 304a provides service to the access device 306.

    [0058] FIG. 4 is a block diagram 400 of an intra-mesh network handoff in accordance with an embodiment of the invention. Referring to FIG. 4, there is shown cell 402 corresponding to a mesh network having a first access point AP1 402a and a second access point AP2 402b. Located in cell 402 is an access device 406. Intra-mesh handoff may include handoff from a first serving access point to a second access point, both access points being located within the same cell or on the same mesh network. For example, an intra-mesh network handoff may occur from access point 402a to 402b which may both be located in the same mesh network or cell.

    [0059] In operation, access point 402a may initially provide service to access device 406 which may be mobile within cell 402. However, as access device 406 migrates away from access point 402a and towards access point 402b, a signal received from access point 402a may fade until it reaches, for example, a handover threshold. Simultaneous with the fading of the signal received from access point 402a, a signal having increasing signal strength may be received from access point 402b. The access device 406 may dynamically keep a record of the frequency and corresponding signal strength of any received channel it encounters including the frequencies and signal strength for available channels of access point 402b in its handoff candidate list. The access device 406 may be adapted to select the best candidate for a handoff from the candidate list based on, for example, a channel having the strongest signal strength. In a case where the access device 406 determines that the best access point for a handoff is access point 402b, then the access device 406 may tune its transceiver to an available transmit and/or receive channel corresponding to the access point 402b. At this point, the access point 402b provides service to the access device 406.

    [0060] A client or access device may initiate dissociation when signal strength drops below a threshold level. The client may initiate re-association when a signal strength of the new access point is above a threshold level. The new access point may send a message to the current access point informing the switch of a possible association of the client with the new access point. The current access point may send a response to the new access point to handover session context data. The current access point may send, for example, a security block to the new access point. The new access point may acknowledge the receipt of the security block. The new access point may identify the new switch serving the access point of the move. The new switch may notify the current switch of the re-association. The current switch may respond to the new switch with switch filtering information.

    [0061] An access device may initiate disassociation when signal strength falls below a specified threshold. The access device may initiate re-association when signal strength of a new access point is above a certain threshold. The new access point may send a message to the current AP to announce its re-association. The current access point may send a response to the new access point to handover session context data. The session data may be, for example, encryption data which may prevent re-authentication. The current access point may send a security block to the new access point. The new access point may acknowledge receipt. The new access point may notify a switch of the move. The switch may transfer filtering information from one port to another.

    [0062] In order to minimize the effects of interference, a beam forming technique may be utilized to provide communication between two or more access points co-located within the same cell or located within different cells or mesh networks. FIG. 5 is a block diagram of an exemplary system 500 that utilizes beam forming in accordance with an embodiment of the invention. Referring to FIG. 5, there is shown a first cell 502 having an access point 502a and an access device 502b located therein. A second cell 504 may have an access point 504a and an access device 504b located therein.

    [0063] In an embodiment of the invention, a beam forming antenna associated with access point 502a may be adapted to provide communication with an access point 504b. In this regard, one or more transmit and receive frequencies may be assigned as communication channels to provide communication between access point 502a and access point 504a using the beam forming antenna path. The assigned channels may constitute a backbone channel 506. In one aspect of the invention, the backbone channel 506 may be adapted to utilize an 802.11b standard, while a mesh network 502 associated with access point 502a and a mesh network 504 associated with access point 504a may utilize an 802.11b or 802.1g standard. Accordingly, the backbone channel may provide a communication path that may reduce interference with other channels in a particular cell, thereby increasing .transmission throughput. A plurality of access devices located in cell 502, for example access device 502b, may utilize channels other than those assigned to the backbone channel. Similarly, a plurality of access devices located in cell 504, for example access device 504b, may utilize channels other than those assigned to the backbone channel.

    [0064] FIG. 6 is a block diagram of a system for providing a mesh network in accordance with an embodiment of the invention. Referring to FIG. 6, there is shown a processor 604, a transmitter 606, an application block 608, a database 610 and a receiver 612. Processor 604, transmitter 606, application block 608, database 610 and receiver 612 may be variously coupled to processor 604. The processor 604, transmitter 606 and receiver 612 may contain suitable logic and/or software that may be adapted to facilitate communication in a mesh network in accordance with the invention. FIG. 6 may also include a beamforming antenna 614. The beamforming antenna 614 may include a plurality of receiver antenna elements and transmitter antenna elements. Accordingly, each of the plurality of receiver antenna elements and transmitter elements may be adapted to function as a beamforming antenna. Database 610 may store applications and/or data that may be utilized by processor 606.

    [0065] Processor 604, under control of one or more applications such as application 608, may be adapted to control transmitter 606 and receiver 608 to facilitate communication in a mesh network in accordance with an embodiment of the invention. Processor 604 may be adapted to control communication over a first access point located in a first cell, which may be coupled to a second access point located in a second cell. The processor 604 may be adapted to control receiver 612 and transmitter 606 to initially provide service to an access device by the first access point. The processor 604 may be configured to determine when a signal level of an access device falls below a specified threshold level. A second processor similar to processor 604, which may be associated with a second access point located within a second neighboring cell, may be configured to provide service to the access device. Accordingly, processor 604 may be adapted to terminate or discontinue serving the access device once the second processor starts to provide service to the access device.

    [0066] Processor 604 may be adapted to control transmitter 606 to transmit a first signal from, for example, a first antenna element or sector of beamforming antenna 614. Similarly, processor 604 may be adapted to control receiver 612 to receive a second signal that may be transmitted from a second beamforming antenna coupled to the second access point. Alternatively, processor 604 may be adapted to control transmitter 606 to transmit a first signal via a wired connection coupling the first and second access points. Similarly, processor 604 may be adapted to control receiver 612 to receive a second signal that may be transmitted from the second access point to the first access point via a wired connection.

    [0067] In accordance with various embodiments of the invention, dependent on the modulation scheme utilized, one or more of the PLCP frames illustrated in FIG. 1b, FIG. 1c, FIG. 1d and FIG. 1e may be adapted to contain information which may be utilized for providing communication between the plurality of access points in one or more mesh networks in accordance the embodiments of the invention. Additionally, the PLCP frames may be adapted to convey information for any one or more of the 801.11a, 802.11 band 802.11g modes of operation utilized by access points and/or access devices in accordance the embodiments of the invention.

    [0068] A method for providing a mesh network using a plurality of access points may include the step of coupling a first access point located in a first cell to at least a second access point located in a second cell. Service may be initially provided to an access device by a first access point located in the first cell. The access device may be serviced by a second access point located in a second cell whenever a signal for the access device falls below a specified threshold level. The second cell may be a neighboring cell, which may be located adjacent to the first cell.

    [0069] A first signal may be transmitted from a first beamforming antenna to the second access point. The first beamforming antenna may be coupled to the first access point. Similarly, a second signal may be transmitted from a second beamforming antenna to the first access point. The second beamforming antenna may be coupled to the second access point. A path for facilitating transmission of the first signal between the first beamforming antenna and the second beamforming antenna may be an uplink channel. Also, a path for facilitating transmission of the second signal between the second beamforming antenna and the first beamforming antenna may be a downlink channel. The uplink channel and the downlink channel may be a backhaul channel. A backhaul link or channel between mesh network access points may be utilize a higher data rate protocol than the individual mesh networks or cells. In this regard, the backhaul link or channel may utilize 802.11a while the individual cell may utilize 802.11b or 802.11g. Additionally, the backhaul channel or link may utilize long distance type wireless standards such as 802.16.

    [0070] The first access point located in a first cell may be coupled to a third access point located in the first cell. Accordingly, an access device may be serviced by a third access point located in the first cell whenever a signal level of the access device falls below a specified threshold level. Either of the first access point and the access device may be configured to determine when the signal of an access device falls below a specified threshold level.

    [0071] Accordingly, the present invention may be realized in hardware, software, or a combination of hardware and software. The present invention may be realized in a centralized fashion in one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.

    [0072] The present invention also may be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.

    [0073] While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.


    Claims

    1. A method for providing a mesh network (200) using a plurality of access points (AP), the method comprising:

    coupling a first access point (200) located in a first cell to a second access point (200) located in a second cell;

    initially providing a service to an access device by said first access point located in said first cell;

    servicing said access device by said second access point located in said second cell whenever a signal for said access device falls below a specified threshold; wherein said second cell is a neighboring cell located adjacent to said first cell; and

    characterized by the step of

    further comprising the step of transmitting a first signal from a first beam forming antenna coupled to said first access point, to said second access point.


     
    2. The method according to claim 1, further comprising transmitting a second signal from a second beam forming antenna coupled to said second access point, to said first access point.
     
    3. The method according to claim 2, wherein a path for facilitating said transmitting said first signal between said first beam forming antenna and said second beam forming antenna is an uplink channel.
     
    4. The method according to claim 3, wherein a path for facilitating said transmitting of said second signal between said second beam forming antenna and said first beam forming antenna is a downlink channel.
     
    5. The method according to claim 4, wherein said uplink and said downlink channel is a backhaul channel.
     
    6. The method according to claim 1, further comprising coupling said first access point located in said first cell to a third access point located in said first cell.
     
    7. A machine-readable storage, having stored thereon a computer program having at least one code section for facilitating communication in a mesh network using a plurality of access points, the at least-one code section being executable by a machine for causing the machine to perform the method for providing a mesh network according to claim 1.
     
    8. A system for providing a mesh network using a plurality of access points, the system comprising:

    means for coupling a first access point located in a first cell to a second access point located in a second cell;

    means for initially providing a service to an access device by said first access point located in said first cell;

    means for servicing said access device by said second access point located in said second cell whenever a signal for said access device falls below a specified threshold; wherein said second cell is a neighboring cell located adjacent to said first cell; and

    characterized by

    further comprising means for transmitting a first signal from a first beam forming antenna coupled to said first access point, to said second access point.


     


    Ansprüche

    1. Verfahren zum Bereitstellen eines Maschennetzes (200), das eine Vielzahl von Zugangspunkten (access points; AP) verwendet, wobei das Verfahren umfasst:

    Koppeln eines ersten Zugangspunkts (200), der sich in einer ersten Zelle befindet, an einen zweiten Zugangspunkt (200), der sich in einer zweiten Zelle befindet;

    anfängliches Bereitstellen eines Dienstes für eine Zugangsvorrichtung durch den ersten Zugangspunkt, der sich in der ersten Zelle befi ndet;

    Bedienen der Zugangsvorrichtung durch den zweiten Zugangspunkt, der sich in der zweiten Zelle befindet, wenn ein Signal für die Zugangsvorrichtung unter eine vorgegebene Schwelle fällt; wobei die zweite Zelle eine benachbarte Zelle ist, die sich nahe der ersten Zelle befindet; und

    gekennzeichnet durch den Schritt,

    dass das Verfahren des Weiteren den Schritt des Übertragens eines ersten Signals von einer ersten Richtantenne, die mit dem ersten Zugangspunkt verbunden ist, an den zweiten Zugangspunkt umfasst.


     
    2. Verfahren nach Anspruch 1, das des Weiteren das Übertragen eines zweiten Signals von einer zweiten Richtantenne, die mit dem zweiten Zugangspunkt verbunden ist, an den ersten Zugangspunkt umfasst.
     
    3. Verfahren nach Anspruch 2, wobei ein Pfad zum Erleichtern des Übertragens des ersten Signals zwischen der ersten Richtantenne und der zweiten Richtantenne ein Uplink-Kanal ist.
     
    4. Verfahren nach Anspruch 3, wobei ein Pfad zum Erleichtern des Übertragens des zweiten Signals zwischen der zweiten Richtantenne und der ersten Richtantenne ein Downlink-Kanal ist.
     
    5. Verfahren nach Anspruch 4, wobei der Uplink-Kanal und der Downlink-Kanal ein Rücktransport-Kanal ist.
     
    6. Verfahren nach Anspruch 1, das des Weiteren das Koppeln des ersten Zugangspunkts, der sich in der ersten Zelle befindet, an einen dritten Zusatzpunkt umfasst, der sich in der ersten Zelle befindet.
     
    7. Maschinenlesbarer Speicher, auf dem ein Computerprogramm gespeichert ist, das wenigstens einen Codeabschnitt zum Erleichtern der Kommunikation in einem Maschennetz hat, das eine Vielzahl von Zugangspunkten verwendet, wobei der wenigstens eine Codeabschnitt von einer Maschine ausführbar ist, um zu veranlassen, dass die Maschine das Verfahren zum Bereitstellen eines Maschennetzes nach Anspruch 1 durchführt.
     
    8. System zum Bereitstellen eines Maschennetzes, das eine Vielzahl von Zugangspunkten verwendet, wobei das System aufweist:

    Mittel zum Koppeln eines ersten Zugangspunkts, der sich in einer ersten Zelle befindet, an einen zweiten Zugangspunkt, der sich in einer zweiten Zelle befindet;

    Mittel zum anfänglichen Bereitstellen eines Dienstes für eine Zugangsvorrichtung durch den ersten Zugangspunkt, der sich in der ersten Zelle befindet;

    Mittel zum Bedienen der Zugangsvorrichtung durch den zweiten Zugangspunkt, der sich in der zweiten Zelle befindet, wenn ein Signal für die Zugangsvorrichtung unter eine vorgegebene Schwelle fällt; wobei die zweite Zelle eine benachbarte Zelle ist, die sich nahe der ersten Zelle befindet; und

    dadurch gekennzeichnet, dass

    es des Weiteren ein Mittel zum Übertragen eines ersten Signals von einer ersten Richtantenne, die mit dem ersten Zugangspunkt verbunden ist, an den zweiten Zugangspunkt aufweist.


     


    Revendications

    1. Procédé de fourniture d'un réseau maillé (200) utilisant une pluralité de points d'accès (AP), le procédé comprenant :

    le couplage d'un premier point d'accès (200) situé dans une première cellule à un deuxième point d'accès (200) situé dans une deuxième cellule ;

    la fourniture initiale d'un service à un dispositif d'accès par ledit premier point d'accès situé dans ladite première cellule ;

    la desserte dudit dispositif d'accès par ledit deuxième point d'accès situé dans ladite deuxième cellule à chaque fois qu'un signal pour ledit dispositif d'accès chute en-dessous d'un seuil spécifié ; dans lequel ladite deuxième cellule est une cellule voisine située adjacente à ladite première cellule ; et

    caractérisé par l'étape consistant à

    comprendre en outre l'étape de transmission d'un premier signal d'une première antenne de formation de faisceau couplée audit premier point d'accès, audit deuxième point d'accès.


     
    2. Procédé selon la revendication 1, comprenant en outre la transmission d'un deuxième signal d'une deuxième antenne de formation de faisceau couplée audit deuxième point d'accès, audit premier point d'accès.
     
    3. Procédé selon la revendication 2, dans lequel un chemin pour faciliter ladite transmission dudit premier signal entre ladite première antenne de formation de faisceau et ladite deuxième antenne de formation de faisceau est un canal en voie montante.
     
    4. Procédé selon la revendication 3, dans lequel un chemin pour faciliter ladite transmission dudit deuxième signal entre ladite deuxième antenne de formation de faisceau et ladite première antenne de formation de faisceau est un canal en voie descendante.
     
    5. Procédé selon la revendication 4, dans lequel ledit canal en voie montante et ledit canal en voie descendante est un canal de raccordement.
     
    6. Procédé selon la revendication 1, comprenant en outre le couplage dudit premier point d'accès situé dans ladite première cellule à un troisième point d'accès situé dans ladite première cellule.
     
    7. Stockage lisible par une machine, ayant, stocké sur celui-ci, un programme informatique ayant au moins une section de code pour faciliter une communication dans un réseau maillé utilisant une pluralité de points d'accès, l'au moins une section de code étant exécutable par une machine pour faire en sorte que la machine mette en oeuvre le procédé de fourniture d'un réseau maillé selon la revendication 1.
     
    8. Système de fourniture d'un réseau maillé utilisant une pluralité de points d'accès, le système comprenant :

    un moyen pour coupler un premier point d'accès situé dans une première cellule à un deuxième point d'accès situé dans une deuxième celfule ;

    un moyen pour fournir initialement un service à un dispositif d'accès par ledit premier point d'accès situé dans ladite première cellule ;

    un moyen pour desservir ledit dispositif d'accès par ledit deuxième point d'accès situé dans ladite deuxième cellule à chaque fois qu'un signal pour ledit dispositif d'accès chute en-dessous d'un seuil spécifié ; dans lequel ladite deuxième cellule est une cellule voisine située adjacente à ladite première cellule ; et

    caractérisé par

    comprenant en outre un moyen pour transmettre un premier signal d'une première antenne de formation de faisceau couplée audit premier point d'accès, audit deuxième point d'accès.


     




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    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description