The present invention relates to communication networks, for example to wireless local area networks (WLANs) substantially conforming to standards such as IEEE 802.11 including its variants and extensions. Moreover, the invention also relates to mobile stations (MS) and access points (AP) operable in such communication networks. Furthermore, the present invention also relates to methods of communicating data in such communication networks. Additionally, the invention also concerns software executable on computing hardware forming at least a part of such communication networks for implementing the methods, and also to signals adapted for implementing the present invention.
Communication networks are known. Such networks are susceptible to being implemented as wireless local area networks (WLANs) wherein communication nodes included in such networks are operable to exchange data therebetween by wireless communication. Earlier WLAN standards, for example “Bluetooth” and IEEE 802.11, define communication protocols for communicating data at data rates of 1 to 2 Mbps by employing wireless transmissions at a wireless carrier frequency of substantially 2.4 GHz. Extensions to this IEEE 802.11 standard such as IEEE 802.11a are susceptible to enabling data rate approaching 54 Mbps at a wireless carrier frequency of substantially 5 GHz. For convenience, a phrase “IEEE 802.11” utilized herein is to be construed to relate to the IEEE 802.11 and its associated variants and extensions, for example IEEE 802.11a, IEEE 802.11b and IEEE 802.11g.
WLANs are susceptible to being affected by indoor propagation of wireless radiation being non-isotropic, for example due to attenuation and reflection of wireless radiation. Such lack of isotropy can result in a WLAN with regularly spatially distributed network nodes having certain spatial regions which are inadequately served by the nodes. Operation of the WLANs is further complicated when certain of the nodes of the WLANs are implemented as mobile devices, for example as “mobile stations” (MS), which move spatially relative to other nodes of the WLANs.
In contemporary communication networks such as WLANs, it is known that data communication capacity in the networks is operatively greatest when a frequency reuse factor pertaining to the networks is unity, namely that all communication cells of such networks utilize a same wireless radiation carrier frequency and exploit an entire extent of a corresponding communication bandwidth available. Such networks implemented with communication cells therein are conveniently referred to as “virtual cellular networks” (VCNs). VCNs implemented with a frequency reuse factor of substantially unity with full exploitation of a bandwidth available are potentially operable to provide increased reliability against multipath fading.
In known IEEE 802.11 standards, a communication node implemented as a mobile station (MS) is only permitted, at a given time, to associate with a single communication node when implemented as an access point (AP), namely the mobile station (MS) is restricted by the IEEE 802.11 standard to associate with just one access point (AP) at any given instance of time. In an event that the association between the mobile station (MS) and the access point (AP) at the given instance of time is compromised, for example when a quality of wireless reception is poor or degrades, the mobile station (MS) has to de-associate from its present access point (AP) and then associate with an alternative access point (AP) capable of providing improved wireless communication for the mobile station (MS).
Thus, contemporary WLANs conforming to the known IEEE 802.11 standards suffer a first problem that they are not able to best exploit macro-diversity within the WLANs such that the data communication capacity of the WLANs is not fully realized in practice. Moreover, a second problem pertains in that re-association of a mobile station (MS) from a first access point (AP) to another access point (AP) takes time, namely “hand-over” time; this hand-over time is a major limiting factor in providing “Quality of Service” (QoS). Quality of service (QoS) is concerned with guaranteeing constant bit rate channel allocations with constant delay and minimum jitter. Both the aforementioned IEEE 802.11a and IEEE 802.11b standards follow similar Medium Access Control (MAC) layer procedures. The WLAN MAC layer is based on CSMA/CA protocol and targets asynchronous traffic such as client-server data applications. Hence, the WLAN MAC layer lacks quality of service (QoS) considerations which are required for multimedia applications such as voice, video and audio. A third problem in WLANs conforming to the IEEE 802.11 standard is that adjacent cells of the WLAN are required to be configured in operation to employ mutually different wireless channels; such a restriction creates operating difficulties for WLANs conforming to IEEE 802.11b and IEEE 802.11g standards wherein the number of non-overlapping wireless channels permitted is restricted to three channels. In a published United States granted patent no. U.S. Pat. No. 6,799,054, multiple access points (APs), configured to operate at a mutually identical wireless carrier frequency and coupled to a high-speed backbone, for example via an Ethernet connection, are operable to simultaneously receive an uplink data packet transmitted by a mobile station (MS) in communication range of the multiple access points. The access points (APs) are further operable to arbitrate and coordinate their transmission of acknowledgement (ACK) packets to the mobile station (MS) over the high-speed backbone that interconnects them. In the aforesaid granted patent, it is disclosed that transmission of acknowledgement (ACK) packets has to be executed in a timely manner, for example within a time-frame of 10 microseconds. There is thereby provided a low-latency protocol implemented using a communication back-bone, for example Ethernet, which is operable to link multiple access points (APs). In practice, such an approach only adequately works for Ethernet hubs and requires provision of a separate PHY layer or a COMBO layer in associated communication protocols utilized.
In the context of WLAN conforming to the IEEE 802.11 standard, Flextronics Software Systems Ltd. has proposed a stand-by access point (AP). In Flextronics' proposal, a mobile station (MS) serviced from a first access point (AP1) is provided with a second access point (AP2) configured to run in a stand-by mode. The second stand-by mode access point (AP2) is operable to continuously monitor the first access point (AP1) in the same channel as the first access point (AP1). In a situation of the first access point (AP1) failing to respond, the second stand-by access point (AP2) takes over a role of servicing the mobile station (MS). However, hand-over from the first access point (AP1) to the second access point (AP2) involves de-association from the first access point (AP1) and association to the second access point (AP2) which is problematic when maintenance of quality of service (QoS) is desired.
The present invention is thus directed to at least partially address the aforementioned problems and thereby provide communication between access points (APs) and mobile stations (MSs) in communication networks, for example WLANs; however, the present invention is potentially relevant to other types of communication networks other than WLANs.
An object of the present invention is to provide a communication network with an improved reliability and quality of communication therein.
According to a first aspect of the present invention, there is provided a communication network comprising communication nodes operable to communicate data therebetween, wherein said nodes include at least one station operable to cooperate with a plurality of corresponding access points including a first access point operable to provide a first communication route to said at least one station, and at least a second access point operable to sense operation of the first access point, said at least a second access point being operable to provide a second communication route to said at least one station in an event of said first access point ceasing to provide said first communication route, said sensing occurring in operation during slot periods individually assigned to said plurality of access points, said slot periods arising within signals communicated within the network for the access points to acknowledge receipt of messages from or to said at least one station.
The invention is of advantage in that use of the assigned slot periods for communicating individual acknowledgements is capable of enabling more efficient transfer of responsibility for communicating with the at least one station from one access point to another, thereby potentially enhancing reliability and quality of communication to the at least one station.
Optionally, the communication network is implemented such that only one of said plurality of access points is operable to provide the communication route to said at least one station at any given time. Such a manner of operation circumvents conflicts between access points as a sensing access point is effectively subordinate to an access point present providing a communication route to the station. More optionally, the slot periods and operation of said access points are implemented to be a development from contemporary IEEE 802.11 standards, for example the IEEE 802.11e MAC standard.
Optionally, the communication network is implemented such that said at least one station and its corresponding access points are implemented as at least a part of a wireless local area network. The present invention when applied to a WLAN is potentially especially effective as it enables a mobile station roaming within the network to be substantially seamlessly coupled and de-coupled from one access point to another. Such seamless coupling is highly desirable for voice-over-Internet-protocol (VoIP) wherein the station is susceptible to being implemented as a mobile telephone, a personal data assistant (PDA), a portable computer or similar mobile computing hardware. Thus, in the communication network, the at least one station is optionally a mobile station susceptible to moving position spatially within the network relative to its corresponding access points.
Optionally, the communication network is implemented such that said access points for said at least one station are each individually assigned an associated slot period, and each access point is restricted in operation to transmitting an acknowledgement frame in its assigned slot period. More optionally, assignment of the slot periods to corresponding access points is executed over a communication medium provided in the network.
In order to ensure backward compatibility with contemporary communication standards, in the communication network, the slot periods are optionally temporally included between a SIFS period defining commencement of the slot periods and a DIFS period defining termination of the slot periods. DIFS and SIFS are defined in contemporary communication standards, for example in the IEEE 802.11 standards and extensions thereof, for example the IEEE 802.11e MAC standard.
Optionally, the communication network is implemented such that said access points cooperating in operation with said at least one station are operable to perform a clear channel assessment within a period corresponding to not more than substantially 50% of their assigned slot period. The expression “substantially 50%” is to be construed broadly, for example to include a range of 25% to 75%. Such rapid clear channel assessment is susceptible to enabling substantially instantaneous transfer of communication route from one access point to another.
Optionally, the communication network is implemented such that said access points cooperating in operation with said at least one station are operable to utilize a similar wireless communication channel. Utilization of the single channel is susceptible to enhancing data communication capacity of the communication network.
According to a second aspect of the invention, there is provided an access point adapted to provide data communication in a communication network comprising communication nodes operable to communicate data therebetween, said access point being operable to cooperate with said at least one station of the network, said at least one station being served by another cooperating node, said another cooperating node being operable to provide a first communication route to said at least one station, and said access point being operable to sense operation of the cooperating node, said access point being operable to provide a second communication route to said at least one station in an event of said cooperating node ceasing to provide the first communication route, said sensing being arranged to occur during slot periods individually assigned to said access point and said cooperating node, said slot periods arising within signals communicated within the network for the access point and the cooperating node to acknowledge receipt of messages from or to said at least one station.
According to a third aspect of the invention, there is provided a method of communicating data in a communication network comprising communication nodes operable to communicate data therebetween, said nodes including access points operable to provide communication to at least one station of the network, wherein said method includes steps of:
(a) configuring the network so that said at least one station is operable to cooperate with a plurality of corresponding access points;
(b) providing a first communication route between a first access point of said plurality of access points and said at least one station;
(c) applying at least a second access point of said plurality of access points to sense operation of the first access point;
(d) configuring said at least a second access point to provide a second communication route to said at least one station in an event of said first access point ceasing to provide said first communication route;
said sensing being arranged to occur during slot periods individually assigned to said plurality of corresponding access points, said slot periods arising within signals communicated within the network for the access points to acknowledge receipt of messages from or to said at least one station.
Optionally, the method is implemented to include a step of configuring said access points to cooperate in operation with said at least one station so as to perform a clear channel assessment within a period corresponding to not more than substantially 50% of their assigned slot period.
Optionally, the method is implemented to include a step of configuring said access points cooperating in operation with said at least one station to utilize a similar wireless communication channel.
According to a fourth aspect of the invention, there is provided an access point adapted to assist in implementing the method according to the third aspect of the invention.
According to a fifth aspect of the invention, there is provided a mobile station adapted to assist in implementing the method according to the third aspect of the invention.
According to a sixth aspect of the invention, there is provided software conveyed on a data carrier, said software being executable on computing hardware for implementing the method according to the third aspect of the invention. In the context of the present invention, “software” is to be construed to relate to a set of machine instructions susceptible to being sequentially executed on computing hardware for causing the computing hardware in conjunction with associated apparatus to implement a method or algorithm represented by the software. Moreover, in the context of the present invention, “data carrier” is to be construed to be any type of physical medium capable of carrying data, for example a CD ROM, or alternatively a signal capable of conveying data representing the software.
According to a seventh aspect of the invention, there is provided an acknowledgement signal operable to convey information in a communication network comprising a plurality of access points and at least one station, a first of said access points being configurable to provide a first communication route from or to said at least one station, and a second of said access points being operable to provide a second communication route from or to said at least one station in an event to said first access point ceasing to be able to provide said first communication route, said acknowledgement signal including time slots susceptible to being selectively allocated to said plurality of access points for said plurality of access points to selectively acknowledge receipt of communication thereat from said at least one station and said acknowledgement signal being useable in the network for providing the second communication route.
It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompany claims.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:
In overview, embodiments of the present invention are concerned with providing reliable and efficient communication from a first access point (AP) of a communication network, for example a wireless local area network (WLAN) generally conforming to the IEEE 802.11 standard including its various extensions, to a mobile station (MS). The embodiments include one or more additional access points (APs) which are operable to assume responsibility for providing a communication path to the mobile station (MS) in an event of communication between the first access point (AP) and the mobile station (MS) deteriorating or becoming unavailable. Management of the first access point (AP) in relation to the one or more additional access points (APs) is performed by utilizing a plurality of timing slot allocations for conveying acknowledgement messages (ACK) from the access points involved (APs).
In order to set the present invention in context with regard to a communication network, reference is made to
The network 20 also comprises a primary access point (AP1) denoted by 70 coupled in the network 10 between a communication node 20a of the network 10 and a mobile station (MS) denoted by 80. Bi-direction data communication is provided by the network 10 between the mobile station (MS) 80 via the primary access point (AP1) 70 to the communication node 20a and therefrom to other communication nodes 20 of the network 10. When implementing the present invention, the network 10 further includes a secondary access point (AP2) 90 also in communication with the communication node 20a. On account of limitations of the IEEE 802.11 standard generally employed when implementing the network 10, the mobile station (MS) 80 is not permitted to communicate concurrently through both access points (AP1, AP2) 70, 90, but only through the primary access point (AP1) 70. The secondary access point (AP2) 90 is operable, as will be elucidated in greater detail later with reference to
In order to further elucidate operation of the communication network 10,
In operation, a mobile station (MS), for example the mobile station (MS) 80, with data frames 120 to transmit, senses wireless transmissions for a period denoted by 160; the period is known as a DIFS period or DCF inter-frame space. The mobile station (MS) 80 senses the wireless transmissions, to ensure that no other mobile stations (MS) are transmitting. This period 160 has a duration which is a sum of:
(a) a SIFS period 140; and
(b) an acknowledgement period 150; the acknowledgement period 150 is itself of a duration corresponding to twice a slot period.
A back off (BO) period 170 temporally separates an end of the DIFS and SIFS periods 140, 160 and commencement of transmission of a subsequent data frame 120. Actual values of the SIFS (Short IFS) period and the aforesaid slot period are determined by a physical layer used to implement the network 10, the physical layer being arranged to be generally in conformity with the IEEE 802.11 standard and its extensions.
In operation, if the wireless medium is not available, namely not “free”, for example because other devices are transmitting wireless radiation, the mobile station (MS) 80 backs off for a period of time and then proceeds to re-sense the wireless medium. Conversely, if the wireless medium is sensed to be available, namely “free”, a data frame 120 is transmitted by the mobile station (MS) 80. The access point (AP) 70 waits for a time period of SIFS and proceeds to respond by sending an acknowledgement (ACK) frame 130.
As elucidated in the foregoing, the contemporary standard IEEE 802.11 and its extensions only permit one access point (AP) to be associated with a mobile station (MS). Thus, according to the standard IEE 802.11, the secondary access point (AP2) 90 cannot concurrently function with the primary access point (AP1) 90 in servicing the mobile station (MS) 80; however, the present invention enables the secondary access point (AP2) to monitor communication between the primary access point (AP1) 70 and the mobile station (MS) 80 and to intervene to assume a role of the primary access point (AP1) 70 in an event of the primary access point (AP1) 70 ceasing to support communication to the mobile station 80, for example caused by the primary access point (AP1) 70 becoming non-operational. Moreover, the DCF presented in
Operation of the present invention will now be further described with reference to
In order to substantially comply with the contemporary IEEE 802.11 standard and yet enable alternative access point (APs) to assume a role of supporting communication to a mobile station (MS), the present invention concerns a slotted acknowledgement mechanism. This slotted acknowledgement mechanism is susceptible to being implemented to fall substantially within the IEEE 802.11 standard, although other implementations are possible with in connection with other standards. The IEEE 802.11 standard defines two mechanisms for sharing access to a radio resource, namely wireless communication channels; the two mechanisms concern a Distributed Coordination Function (DCF) and a Point Coordination Function (PCF). The slotted acknowledgement mechanism of the present invention is pertinent to both PCF and PCF functions. When further describing the present invention, utilization of the mechanism in connection with DCF will be especially described.
The present invention is concerned with enabling multiple access point (APs) to respond by each sending an acknowledgement (ACK) to an uplink transmission from a single mobile station (MS) or similar single client. When implementing the present invention, transmission of an acknowledgement (ACK) frame has to be commenced before the mobile station (MS) or client considers its uplink transmission to be failure. When conforming substantially to the aforementioned IEEE 802.11 and IEEE 802.11e MAC standards, a period of time for transmitting an acknowledgement (ACK) potentially exists between aforesaid SIFS 140 and DIFS 160, see
In order to avoid communication collisions when multiple access points (APs) respond with their respective acknowledgements, a period 150 between SIFS 140 and DIFS 160 is sub-divided into temporally-punctuated acknowledgement slots (ACK-slots) as illustrated in a time graph indicated generally by 300 in
As elucidated in the foregoing, the IEEE 802.11 standard only permits a mobile station (MS), namely a mobile client, to communicate with a single access point (AP). To ensure substantial compatibility when implementing the present invention, for example in the network 10, the mobile station (MS) must remain under an impression that it is only communicating via one access point (AP) at any given moment. Such a constraint results in a concept of primary and secondary access points (AP1, AP2) within a slotted mechanism as depicted in
The present invention provides an opportunity for multiple access points (APs) to receive uplink data and respond by way of a corresponding acknowledgements (ACK) communicated by way of the acknowledgement slots (ACL-slots) associated with the multiple access points (APs). More robust communication of data to mobile stations (MS) is thereby possible. By configuring the access points 70, 90220 to utilize a similar wireless channel frequency and to exploit a full associated wireless communication bandwidth at any given spatial location within the network 10, it is potentially feasible to arrange the network 10 to operate so that aggregate communication capacity of the network 10 is substantially optimized, namely maximized.
Operation of aforementioned primary and secondary access points (AP1, AP2) will now be further elucidated with reference to a flow chart indicated generally by 400 in
The flow chart 400 will now be further elucidated with reference to Table 1 in conjunction with
Thus, in overview, in a sequence of steps represented by the flow chart 400, during Clear Channel Assessment (CCA), the secondary access point (AP2) 90 is operable to sense, namely “listen”, to determine whether or not the wireless channel is free. Only in a situation wherein the channel is free during a whole acknowledgement slot, for example during the acknowledgement slot 310, the secondary access point (AP2) 90 is operable to transmit an acknowledgement frame. In practice, a Clear Channel Assessment (CCA), namely the step 610, takes substantially in an order of half the slot period 320, 340 or less; there is thereby sufficient temporal tolerance to accommodate and thereby overcome temporal synchronization errors. In order to further elucidate the present invention, a state model of a given one of the access points (AP1, AP2) 70, 90 is provided in
In
The state model 700 follows in operation a sequence of events as illustrated by way of interconnection topology in
Although the state model 700 is shown pertaining only to the primary and secondary access points (AP1, AP2), it will be appreciated that the state model 700 can be adapted to describe a situation wherein the primary access point (AP1) is monitored for correct operation by the secondary access point (AP2), and, in turn, the secondary access point (AP2) is monitored by the tertiary access point (AP3) for correct operation. If required, more than three access points (AP2) can optionally be utilized. The network 10 is thereby capable of being provided with multiple levels of backup in its access points (APs) for ensuring more reliable communication to mobile stations (MS) or similar coupled to the network 10.
Referring to
In operation, when functioning to provide a first communication path to the mobile station 80, the first access point (AP1) 70 is operable to commence sending its acknowledgement signal 1020 within a predetermined first temporal delay 1050. The secondary access point (AP2) 90 is operable to monitor operation of the first access point (AP1) 70 and determine whether or not the first access point (AP1) 70 has sent its acknowledgement signal 1030 by an end of a second temporal delay 1060 as illustrated. In an event that the first access point (AP1) 70 has not sent its acknowledgement signal 1030 by the end of the second temporal delay 1060, namely the first access point (AP1) 70 is not able to provide the first communication route, the second access point (AP2) 90 is operable to send its acknowledgement signal 1040 commencing before the end of the second temporal delay 1060. However, the second access point (AP2) 90 is configured so that it does not commence sending its acknowledgement signal 1040 before the end of the first temporal delay 1050. The node 20a is thereby provided with information regarding which of the access points (AP1, AP2) 70, 90 is capable of providing communication routes therethrough to the mobile station (MS) 80 without signal conflicts arising between the primary and secondary access point (AP1, AP2) 70, 90.
The first and second temporal delays 1050, 1060 are selected so that the primary and secondary access points (AP1, AP2) 70, 90 are potentially operable to provide their acknowledgement frame signals 1030, 1040 before any timing-out occurs. Moreover, sensing in the access points (AP1, AP2) 70, 90 is performed in the temporal slots 310, 330. The first and second temporal delays 1050, 1060 also determine a hierarchical order in which, for example, the access points (AP1, AP2, AP3) 70, 90, 220 assume responsibility for ensuring that communication in ensured to and from the mobile station (MS) 80 to the node 20a.
It is to be noted that the temporal slots 310, 330 are included before corresponding message data and not embedded within such message data, for example as depicted schematically in
In an example implementation of the network 10, the primary access points (AP1, AP2) 70, 90 can be configured so that, in an event of the primary access point (AP1) 70 failing in operation to provide a communication route therethrough and the secondary access point (AP2) 90 then assuming responsibility for providing a communication path, the primary access point (AP1) 70 in returning to operation again can monitor the secondary access point (AP2) 90 and re-assume responsibility for communicating with the mobile station (MS) 80 in an event of the secondary access point (AP2) 90 subsequently failing to provide a communication route therethrough or becoming otherwise non-operative. The primary and second access points (AP1, AP2) 70, 90 are therefore capable of being configured to be mutually supportive to ensure a more reliable communication route therethrough. Such mutual support is susceptible to being extended to more than two access points (AP1, AP2) 70, 90, for example also to include the tertiary access point (AP3) 220.
Thus, it is difficult to provide wireless communication coverage using contemporary WLAN installations, wherein data communication capacity is sacrificed to provide increased spatial coverage. Conventionally, adding even a single additional conventional access point (AP) can require careful planning and a site survey. Moreover, such an additional conventional access point (AP) can provide one or more of the following problems:
(a) limited additional spatial range at high data communication rates for additional access points added;
(b) edge users where addition access points are added are potentially susceptible to clogging up wireless air-time within the network 10 itself when implemented in a conventional manner;
(c) dramatically reduced data communication throughput caused by multiple users;
(d) data-rate adaptation may be required to enable the network 10 when implemented in a conventional manner to perform adequately; and
(e) large collision domains and co-channel interference within the network 10 when implemented in a conventional manner caused by re-use of wireless frequencies.
The present invention is capable of addressing one of more of the problems (a) to (e) associated with contemporary WLAN implementations. Access points (APs) provided with temporally-slotted acknowledgement capabilities as depicted, for example, in
WLANs implemented pursuant to the present invention are potentially especially well suited for medical and industrial WLANs which are required to function to a high degree of reliability and provide extensive spatial coverage, for example in hospitals, in chemical plants, in nuclear plants, in naval vessels such as container carriers. Moreover, such WLANs pursuant to the present invention are also potentially operable to provide high-density service areas whereat conventionally co-channel interference and “hot-spots” of communication congestion can often arise. WLANs implemented pursuant to the present invention are potentially useable in domestic wireless networks, namely “home networks”, as well as for implementing zero-handover-latency networks for supporting voice-over-Internet protocol (VoIP).
The nodes 20, 20a of the communication network 10, together with its access points (APs) 40, 70, 90 and its mobile stations (MS) 60, 80 are susceptible to being implemented using digital hardware, for example using application-specific integrated circuits (ASICs). Alternatively, their functionality can also be provided by using digital computing hardware operable to execute software instructions. Thus, appropriate generation of data messages for transmission and temporally-slotted acknowledgement messages as depicted in
Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims.
Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural and vice versa.
Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.
Number | Date | Country | Kind |
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05110105.3 | Oct 2005 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2006/053839 | 10/18/2006 | WO | 00 | 4/25/2008 |