WO2007034461A2

WO2007034461A2 - Multi-channel wireless systems having dynamic rendezvous channels

Info

Publication number: WO2007034461A2
Application number: PCT/IB2006/053483
Authority: WO
Inventors: Carlos De Morais Cordeiro; Chun-Ting Chou
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2005-09-26
Filing date: 2006-09-25
Publication date: 2007-03-29
Anticipated expiration: 2008-03-26
Also published as: WO2007034461A3

Abstract

A wireless system and method including a multi-channel (MC) medium access control (MAC) layer are described.

Description

Multi-Channel Wireless Systems Having Dynamic Rendezvous

Channels

The wireless communication bandwidth has significantly increased making the wireless medium a viable alternative to wired and optical fiber solutions . As such, the use of wireless connectivity in data and voice communications continues to increase. These devices include mobile telephones, portable computers in wireless networks (e.g., wireless local area networks (WLANS) , stationary computers in wireless networks, portable handsets, to name only a few. As wireless applications continue to grow, so do the numbers of devices, networks and systems vying for the communications spectrum. As is known, there are dedicated or licensed portions as well as unlicensed portions of the communications spectrum. Because the unlicensed (public) bands of the spectrum may be accessed freely, these bands tend to be heavily populated by users. Contrastingly, recent studies indicate that only a small portion of the licensed band is being used. Thus, much of the public band is unavailable for use, while a relatively large portion of the licensed band remains available for use. This had lead regulatory bodies (e.g., the Federal Communications Commission (FCC) of the U.S.) to an evaluation of current communication band allocations and their use.

One option for reallocation of the communications band involves the use of wireless networks having multiple channels (MCs) that may be used by wireless devices within a network or system. The MC wireless networks may be implemented in dedicated portions of the communications spectrum. For example, the MC wireless network may operate in a spectrum normally dedicated for television transmission and reception. Thereby, certain portions of the communications band may be more fully utilized.

Known MC wireless networks have a dedicated (fixed) channel used for common logic in the network. In operation, the dedicated channel, often referred to as a rendezvous channel (RC) , serves as a meeting channel/conduit for all devices in the network and ensures that network performance meets certain expectations. Moreover, the RC is useful in realizing broadcasting/multicasting within the network. Unfortunately, there are drawbacks and shortcomings associated with known MC networks having a fixed RC. For example, if the MC wireless network were operating in a licensed or dedicated portion of the communications spectrum (e.g., television (TV) bands), and an incumbent device (s) began to broadcast over the channel occupied by the RC, the use of the RC by the devices of the MC wireless network must cease as the incumbent device has priority over the MC wireless network. This can result in a disruption in wireless communication over the network. Accordingly, what is needed is a wireless network and method that overcomes at least the shortcomings of the known networks described above.

In accordance with an example embodiment, a wireless system includes a plurality of wireless devices and a plurality of wireless channels available to the plurality of wireless devices. The wireless system also includes a rendezvous channel selected from among the plurality of wireless channels. Moreover, the wireless system is adapted to change the rendezvous channel to another one of the plurality of wireless channels.

In accordance with another example embodiment, a method of wireless communication includes scanning a plurality of wireless channels and selecting from the plurality of wireless channels a rendezvous channel for devices in a wireless network.

The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion.

Fig. IA is a simplified schematic diagram of neighboring wireless networks in accordance with an example embodiment.

Fig. IB is a simplified schematic of neighboring wireless networks in accordance with an example embodiment.

Fig. 2 is a conceptual diagram of a multi-channel (MC) structure in accordance with an example embodiment. Fig. 3 is a flow-chart of a method of wireless communication in accordance with an example embodiment.

Fig. 4 is a flow-chart of a method of wireless communication in accordance with an example embodiment.

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods, systems and protocols may be omitted so as to not obscure the description of the example embodiments. Nonetheless, such devices, methods, systems and protocols that are within the purview of one of ordinary skill in the art may be used in accordance with the example embodiments . Finally, wherever practical, like reference numerals refer to like features .

It is noted that in the illustrative embodiments described herein, the network may be a wireless network with a centralized architecture or a decentralized architecture. Illustratively, the network may be one which functions under a MC Medium Access (MAC) layer, such as to be defined under IEEE 802.22, or as defined under IEEE 802.16, IEEE 802.11, or IEEE 802.15. Moreover, the network may be a cellular network; a wireless local area network (WLAN) ; a wireless personal area network (WPAN) ; or a wireless regional area network (WRAN) protocols . Furthermore, the MAC protocol may be a time division multiple access (TDMA) protocol; a carrier sense multiple access (CSMA) protocol; a CSMA with collision avoidance (CSMA/CA) protocol; or a frequency division multiple access (FDMA) protocol. It is emphasized that the noted networks and protocols are merely illustrative and that networks and protocols other than those specifically mentioned may be used without departing from the present teachings .

Fig. IA is a schematic view of a first wireless network 101 and a second (neighboring) wireless network 102 in accordance with an illustrative embodiment. The first and second wireless networks 101, 102 are centralized networks. The first wireless network 101 includes a first access point (AP) 103 and the second wireless network 102 includes a second AP 105. The first wireless network 101 further comprises a plurality of wireless stations (STAs) 104, which also may be referred to as wireless devices. Similarly, the second wireless network 102 includes a plurality of STAs (devices) 106.

Illustratively, the first and second networks 101, 102 each may be one of the type of networks noted previously. Moreover, the STAs 104, 106 may be computers, mobile telephones, personal digital assistants (PDA) , or similar device that typically operates in such networks. As indicated by the two-way arrows, the STAs 104,106 may communicate bilaterally; and the APs 103,105 and respective devices 104,106 may communicate bilaterally.

It is noted that only a few STAs 104,106 are shown; this is merely for simplicity of discussion. Clearly, many other STAs 104,106 may be used. Finally, it is noted that the STAs 104,106 are not necessarily the same. In fact, a plethora of different types of STAs adapted to function under the chosen protocol may be used within the networks 101, 102.

In example embodiments, the MAC layers of the first and second networks 101, 102 are MC MAC layers. To this end, each of the STAs 104, 106 and each of the APs 103,105 may communicate in one of a plurality channels 201-204, which are shown in Fig. 2. Notably, the first network 101 operates in a first set of N (N=integer) channels, and the second network 102 operates in a second (different) set of M (M=integer) channels. In a specific embodiment, the N-channels and the

M-channels may be licensed or dedicated channels, for example as administered by the FCC of the U.S.A. In this case, devices that are licensed to function in the plurality of channels (referred to as incumbent devices) have priority over the STAs 104, 106 and the APs 103, 105. That is, the incumbent devices can reclaim the licensed channels at any time, for example by initiating transmissions in these channels. Therefore, the STAs 104,106 and APs 103,105 are adapted to sense and detect the presence of incumbent devices and vacate the reclaimed channels in a timely fashion.

In another specific embodiment, the N-channels and the M-channels may be unlicensed channels that may have priority access provisions, whereby certain (incumbent) devices have priority over other devices; notably the STAs 104, 106 and APs 103, 105.

Regardless of whether the channels are in licensed or unlicensed bands, after the incumbent device (s) vacate the RC, and this vacancy is detected by the STAs 104, 106, or the APs 103,105, or both, the RC may again be occupied by the STAs 104,106 and the APs 103,105.

As described in further detail herein, at any given time, one of the channels 201-204 is selected to be the RC by the AP 103. Similarly, at any given point in time, the second AP 105 selects one of the M channels to be the RC of the second network 102. Moreover, in specific embodiments, the APs 103, 105 may select another of their respective plurality of channels to be a backup RC to its respective RC. Among other functions, the RC serves as a control channel for the STAs of a network. In fact, in the example embodiments described herein a network is defined as one or more STAs that share a common RC.

During superframes, the APs 103, 105 and the STAs 104,106 are adapted to communicate via respective channels of their networks. The APs 103, 105 will transmit beacon frames having an RC field indicating which channel is the RC of its respective network and thus which channels is used as a coordination channel of the STAs 104,106. Moreover, as described more fully herein, the APs 103, 105 will transmit beacons when the RC channel is going to change or has changed.

Each of the STAs 104,106 operates in one of the respective channels of its network and transmits a beacon in the channel in which it is operating. The STAs 104, 106 also scan the channels and to make measurements of the quality of service (QoS) of other channels, as well as to determine if STAs of neighboring networks are present. The scanning can be periodic with a period being determined by channel dynamics. Alternatively, the scanning may be sporadic with the STAs only scanning the channels when the QoS of its current channel falls below a predetermined threshold. In addition, the time an STA scans a particular channel also varies and depends on the ongoing activity in that channel.

As detailed herein, based on the scanning, the STAs 104,106 may change to a different channel, which provides a better QoS. Notably, the STAs 104, 106 may change to channels of neighboring networks. In addition, based on scanning, a set of STAs may choose to switch to another RC. This set of STAs may effect the switch if, as a result of the switch, interference levels will decrease and the overall performance of the network will improve. In a specific embodiment, the STAs may switch to another RC if there are fewer STAs detected in the other RC. Illustratively, the number of devices present in an RC may be gathered by monitoring the periodic beacon transmissions in the RC.

Fig. IB is a schematic diagram of a first wireless network 107 and a second (neighboring) wireless network 109 in accordance with an example embodiment. The first and second networks 107, 109 are distributed wireless networks, which do not include an AP. The first wireless network 107 includes a plurality of STAs 108 and the second network 109 includes a second plurality of STAs 110. The STAs may be of the types described in connection with the networks of Fig. IA. Furthermore, there may be more or fewer STAs than shown in Fig. IB and the STAs are not necessarily the same.

Like the centralized networks of the example embodiment of Fig. IA, the first and second distributed networks 107,

109 each have a MC MAC layer. As such, the STAs 108, 110 of each network 107, 109 may communicate with one another via one of a plurality of wireless channels. Moreover, the plurality of wireless channels over which the STAs 108, 110 may communicate may be licensed or unlicensed and may the subjected to priority access by incumbent devices as noted previously. The distributed networks 107,109 of Fig. IB have RCs that are used as control channels for respective networks, among other functions. As described in detail herein, an STA 108 may be operating in a channel (^Λk') and periodically transmits a beacon indicating this operation. If the STA has selected channel k to be the RC by methods described herein, it will include this in an RC field in a transmitted beacon frame .

The STAs 108,110 of the first and second networks 107,109, respectively, scan the respective plurality of channels in their network. This scanning gathers information of channel quality and beacon frames from other STAs . Based on this information, each STA 108,110 of the distributed networks 107, 109 can determine the presence of RCs used by other STAs as well as the QoS of the RCs. As described previously, the determination of RCs may be carried out based on interference level, number of devices, and similar information .

Fig. 3 is a flow-chart of a method of operation of wireless network having a centralized MC MAC in accordance with an example embodiment. Illustratively, the method of Fig. 3 may be applied to the centralized networks of the example embodiment shown in Fig. IA.

At step 301, the AP selects the RC. This initially occurs at network start-up when the AP has no associated devices. The AP scans the available channels and selects a channel that will provide suitable, if not optimal QoS.

At step 302, the AP transmits a beacon frame including an RC field. The RC field indicates the RC and the time that the AP will begin transmitting and receiving via the RC. Notably, the AP may transmit the beacon frame at the beginning of a superframe and may intermittently transmit the beacon frame during the superframe to alert new STAs of the RC or dormant STAs of the RC as they awake.

At step 303, the STAs scan the channels of the network seeking the rendezvous channel field from the beacon frame of the AP. Notably, step 303 may commence before step 302 and may continue after step 302 is completed. The scanning begins when devices move into the network, or when the devices wake-up after a dormant period, or both. If a particular STA detects the beacon frame including the RC field (e.g., transmitted per step 302), the scanning of the channels may terminate and the STA then functions according to the protocol set forth by the AP. It is noted that the scanning of the channels may resume at a later time. In a specific embodiment, the scanning may resume at a later time to allow an STA to identify APs with better signal quality, due to mobility, frequency of operation, and similar factors. In another specific embodiment, there may be APs from neighboring networks that overlap. In this case, an STA may detect more than one beacon frame. During scanning, the STA exacts measurements from each channel. As noted previously, the measurements include, but are not limited to: the frequency of operation; the received signal strength and the list of available channels. Based on the results of the measurements, the STA chooses the RC and AP. This may result in the STA' s joining another RC and thus another network. For example, one or more of the STAs 106 may receive better signal quality from AP 103 than from AP 105, and selects the RC of AP 103. In this case, the particular STA 106 will select the RC of AP 103 and thus join the first wireless network 101 and leave the second wireless network 102. In step 303, the STAs may continue to scan the channels of its network or, if neighboring networks are present, the channels of the neighboring network, or both. This scanning may be continually or continuously done after the RC has been identified. Through this scanning, the STAs continues to garner information on the QoS of the scanned channels. Notably, this scanning may be effected autonomously by the STAs or via instructions from the AP via the RC, for example. The information gathered may be reported back to the AP, or used by the STAs to determine whether to switch to another channel for communication, or both. Additionally, the STAs may switch to another AP and RC as a result of this scanning.

As noted previously, the AP of a centralized wireless network may need to change the RC of its network. This decision may result from measurements taken during scans performed by the AP, or performed by the STAs in the network. Alternatively, an incumbent device may begin to transmit in the RC channel. This preemption by an incumbent device may occur with or without notice. At step 304, the AP transmits a beacon frame with an RC beacon field indicating that a new RC has been chosen. The beacon frame may be sent in the beginning of a superframe or periodically during a superframe, or both, and includes the new RC and the time at which the AP will commence using the new RC. At step 305, the STAs switch to the new RC.

In a specific embodiment, based on measurements taken during scanning, the AP may determine that the QoS of the present RC is below a set standard, or that another channel provides better QoS, or both. In this case, the AP transmits the beacon frame providing a new RC and an appointed time to switch to the new RC. At step 305 some or all of the network STAs may switch to the new RC. Alternatively, an incumbent device (such as a TV station) may provide warning that it will commence transmission at the RC at a certain time. The AP will then provide the beacon frame with the new RC and time of the change to the new RC. Again, at the appointed time, some or all of the STAs may switch to the new RC. It may be the case that a beacon frame is not or cannot be sent informing the STAs of a switch to another RC in the future. For example, the incumbent signal may require termination of the use of the RC before such a beacon frame can be sent. In this case, at step 304, after the AP has switched to the new RC, the beacon frame is sent by the AP including the RC field with the new RC. During scanning and after the previous RC is no longer available, the STAs will receive the beacon frame including the new RC. Upon receiving the beacon frame, the STAs will switch to the new RC at step 305.

Alternatively, a backup RC may be sent in the beacon field of the beacon frame by the AP. This backup RC is identified in case a sudden switch to another RC is required or because the primary RC is unavailable for other reasons. Upon recognizing that the primary RC is no longer available (e.g., via channel scanning), the STAs will switch to the backup RC. Of course, the AP may then scan the available channels and select another backup channel in case the present RC becomes unavailable. In a subsequent beacon frame, the AP designates the backup RC in the RC field.

At the termination of step 305, steps 302-305 may be repeated as needed.

It is emphasized that not all of the STAs necessarily switch to the new RC at step 305. Alternatively, one or more STA may switch to another network, or take no action. In the former instance, for example, one or more STA may have scanned channels of a neighboring network and based on these measurements, switched to the neighboring AP and RC. Illustratively, one or more STAs 104 may switch to AP 105 and its RC based on the QoS data garnered in the scans.

As described, STAs of neighboring networks may elect to switch to the RC of the AP of the other network. Additionally, the AP of one network may transmit a beacon field indicating that a switch to the RC of the neighboring network is mandated. In this case, the AP and the STAs of one network, join the neighboring network. Notably, the AP joining the neighboring network becomes an STA of that network upon the switch.

For example, if AP 103 gathers information from its own scanning or the scanning of STAs 104 that indicates that the RC of AP 105 provides a better QoS, the AP 103 may send a beacon frame to some or all of the STAs that they should switch to the RC of AP 105 and thus join that network. If one some of the STAs 104 are switched, the AP 103 continues to function as described in connection with Figs. IA, 2 and 3. However, if all of the STAs 104 and the AP 103 join the second wireless network 102, the first wireless network ceases to exist.

It is noted that this switch from one network to a neighboring network is random in nature. As such, this minimizes the event that the first wireless network 101 and the second wireless network 102 switch simultaneously to each other RCs. While this does not disrupt the system operation, it would likely delay the joining of the two networks.

Fig. 4 is a flow-chart of a method of operation of wireless network having a distributed MC MAC in accordance with an example embodiment. Illustratively, the method of Fig. 4 may be applied to the distributed networks of the example embodiments shown in Fig. IB.

At step 401, each STA of the distributed network scans the available plurality of channels, collects measurements and seeks beacon frames. In specific embodiments, the measurements may be: the received signal strength; the profile of the transmitter; the number of transmitters; and the interference and noise level. If an STA receives a beacon frame including an RC field from one or more neighboring

STAs, the STA determines the optimal RC from the measurements from each RC channel detected from the various beacon frames . At step 402, the STA(s) select the best RC.

Alternatively, in step 403 if the STA does not receive a beacon frame with an RC field in a predetermined scanning period, or if none of the RCs available are of a suitable QoS, the STA can select an RC from the plurality of available channels based on QoS data garnered during scanning.

At step 404, the STAs continue scanning available channels and collect measurements of the QoS of these channels. As such, if a channel becomes available that provide a higher QoS, the STA may select this channel as the RC channel and then switch to this channel subsequently. Moreover, during this scanning, the STA (s) may detect beacon frames with RC fields sent by STAs of the same network or of a neighboring network. For example, during scanning, one of the STAs 108 of the first distributed wireless network 107 may receive a beacon frame from another STA 108 indicating in an RC field that another RC is being used by that STA. Alternatively, an STA 108 of the first distributed wireless network 107 may receive a beacon frame from an STA 110 of the second distributed wireless network 109 indicating the RC being used by that network. If no beacon frame with an RC field is obtained during this scanning, no action is taken and the scanning continues.

However, if during the scanning an STA detects the presence of another rendezvous channel (s) and the QoS of one of these channels mandates that a switch to this RC be effected, the STA returns to its primary RC and sends an RC switch announcement in the primary RC. The announcement is carried out in step 405 and includes the new RC channel information and the time of the switch. All STAs using the primary RC record this information and at the expiration of a timer, they switch to the new RC. Upon completion of this switch, the method repeats beginning at step 401.

Notably, the switch from one RC to another may be within a distributed network or may be a switch of one or more STAs from one network to a neighboring network. In either case, the switch is relatively random and thus it is highly improbable that different sets of STAs having different RCs will switch simultaneously. For example, if STAs 110 elect to switch to the RC of STAs 108, it is highly unlikely that STAs 108 will elect to switch to the RC of STAs 110 at the same time. As such, after a finite period of time all STAs in the same neighborhood will likely converge to the same RC. Thereafter, beacons are sent by each STA indicating the RC thereby preventing the switching of STAs back and forth to different RCs .

Finally, step 405 may be carried out because an incumbent signal elects to occupy the RC being used. If this occurs, the STA designating the RC will scan for other available channels per step 401 and will select another RC. After this selection the beacon frame with the RC fields are sent per steps 402-404. Like the centralized network, the beacon frame may be transmitted before the switch, indicating the appointed time of the switch; or may be transmitted after the switch, if the switch is sudden. In the former case, some or all of the STAs will switch to the new RC at the appointed time. In the latter case, the STAs continue scanning and will receive the beacon frame with the RC field. Alternatively, a backup RC may be provided in previous RC fields and the STAs switch to the backup RC.

Beneficially, the MC-MAC methods and apparati of the example embodiment enable STAs in the same area to communicate concurrently in different channels without significantly interfering with each another. This characteristic is very desirable especially in high load scenarios and for QoS sensitive traffic.

The MC-MAC methods and apparati of the example embodiments may be implemented in dynamic environments where the availability and quality of channels vary over time (e.g., new wireless technologies designed for the TV bands) . Other added benefits include the availability of a rendezvous channel for nodes in the same neighborhood allows for effective broadcast/multicast support, interference mitigation and channel bonding.

In view of this disclosure it is noted that the various methods and devices described herein can be implemented in hardware and software. Further, the various methods and parameters are included by way of example only and not in any limiting sense. In view of this disclosure, those skilled in the art can implement the present teachings in determining their own techniques and needed equipment to effect these techniques, while remaining within the scope of the appended claims .

Claims

Claims :

1. A wireless system, comprising: a plurality of wireless devices (103,104,105,106,108,110); a plurality of wireless channels (201 , 202, 203, 204 ) available to the plurality of wireless devices; and a rendezvous channel selected from among the plurality of wireless channels, wherein the wireless system is adapted to dynamically change the rendezvous channel (RC) to another one of the plurality of wireless channels.

2. A wireless system as recited in claim 1, wherein the wireless system is adapted to change the rendezvous channel upon detection of an occupation of the RC by an incumbent device.

3. A wireless system as recited in claim 2, wherein the wireless system is adapted to switch back to the RC upon detection of a vacancy of the RC by the incumbent device.

4. A wireless system as recited in claim 2, wherein the wireless system comprises a centralized wireless network

(101, 102) and one of the plurality of wireless devices is an access point (AP) (103,105).

5. A wireless system as recited in claim 2, wherein the wireless system comprises a distributed wireless network

(107,109) .

6. A wireless system as recited in claim 4, wherein the AP transmits a beacon indicating the change of the rendezvous channel .

7. A wireless system as recited in claim 4, wherein the plurality of devices, excepting the AP, scan for the rendezvous channel after the change.

8. A wireless system as recited in claim 5, wherein one of the plurality of devices transmits a beacon indicating the change of the rendezvous channel.

9. A wireless system as recited in claim 1, further comprising another plurality of wireless devices at least one of which is adapted to switch to the rendezvous channel of the wireless system.

10. A wireless system as recited in claim 9, wherein the another plurality of wireless devices is adapted to select another rendezvous channel and at least one of the plurality of wireless devices is adapted to switch to the another rendezvous channel .

11. A wireless system as recited in claim 1, wherein at least one of the plurality of wireless devices is adapted to scan the plurality of wireless channels and to select the rendezvous channel or to change the rendezvous based on the scanning .

12. A method of wireless communication, the method comprising : scanning a plurality of wireless channels; selecting from the plurality of wireless channels (201,202,203,204) a rendezvous channel (RC) for wireless devices in a wireless network.

13. A method as recited in claim 12, wherein the scanning continues after the selecting from the plurality of wireless channels, and the method further comprises: selecting another rendezvous channel from among the plurality of wireless channels.

14. A method as recited in claim 12, the method further comprising providing an access point (AP) (103,105) and at least one other wireless device (104,106), wherein the AP effects the scanning.

15. A method as recited in claim 12, the method further comprising providing a plurality of wireless devices (103,104,105,106,108,110) and each of the wireless devices is adapted to effect the scanning.

16. A method as recited in claim 15, the method further comprising, after the scanning, providing a beacon from one of the plurality of wireless devices, wherein the beacon identifies the rendezvous channel and a time to switch to the rendezvous channel .

17. A method as recited in claim 12, further comprising: providing a plurality of wireless devices each of which is associated with another rendezvous channel, wherein at least one of the plurality of devices scans the plurality of channels; and based on the scanning, switching to the rendezvous channel .

18. A method as recited in claim 17, wherein the another rendezvous channel is not one of the plurality of wireless channels .

19. A method as recited in claim 18, wherein before the switching, the rendezvous channel is accessed by wireless devices of a first wireless network and the plurality of wireless devices are associated with a second wireless network.

20. A method as recited in claim 12, further comprising: providing a plurality of wireless devices each of which is associated with the rendezvous channel, wherein at least one of the plurality of wireless devices scans a plurality of channels of a neighboring wireless network; and based on the scanning, switching to another rendezvous channel associated with the neighboring wireless network.

21. A method as recited in claim 13, wherein the selecting the another RC further comprises detecting an occupation of the RC by an incumbent device.

22. A method as recited in claim 21, further comprising: switching back from the another RC to the RC after detecting a vacancy of the RC by the incumbent device.