WO2008001291A2

WO2008001291A2 - Distributed rendezvous channel and frequency channel grouping mechanisms for multi-channel wireless systems

Info

Publication number: WO2008001291A2
Application number: PCT/IB2007/052433
Authority: WO
Inventors: Carlos M. Cordeiro; Stefan Mangold
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2006-06-28
Filing date: 2007-06-22
Publication date: 2008-01-03
Anticipated expiration: 2008-12-28
Also published as: WO2008001291A3; AR061680A1; TW200814683A

Abstract

A wireless system and a method of wireless communication are described. At least one beacon period in at least one rendezvous channel is provided.

Description

Distributed Rendezvous Channel and Frequency Channel Grouping Mechanisms for Multi-Channel Wireless Systems

Background and Summary

Wireless communication technology has significantly advanced making the wireless medium a viable alternative to wired solutions. As such, the use of wireless connectivity in data and voice communications continues to increase. As wireless applications continue to grow, so do the numbers of devices, networks and systems vying for the communications spectrum. Wireless 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 is known, there are dedicated or licensed portions as well as unlicensed portions of the communications spectrum. Because the unlicensed bands of the spectrum (e.g., ISM bands) 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 bands is being used. Thus, much of the unlicensed bands are overcrowded, while a relatively large portion of the licensed bands remains unused. 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.

With the reallocation of certain licensed communication bands for use by unlicensed (secondary) users, channel management is needed to ensure that licensed (primary) users with primary access to the band (often referred to as incumbent devices) are provided this access in an unfettered manner. For example, regulatory bodies (e.g., the

FCC) may require that a secondary user vacate a channel in a relatively short period of time after an incumbent user begins occupation of the channel. Moreover, channel management also must be applied to the unlicensed users in order to afford a certain quality of service (QoS). Therefore, the medium access control (MAC) layer and physical (PHY) layer specifications must include provisions directed to this needed channel management.

One known method of providing service to unlicensed users involves a rendezvous channels (RC). Rendezvous channels may be used as a conduit for unlicensed users in the event that communications in one or more licensed channels is lost to incumbents, for example.

While the use of RCs provides a viable option toward the end of increasing the use of the unused or under-utilized spectrum, there are drawbacks to known device, systems and methods. For example, many known secondary devices require a dedicated radio transceiver for monitoring and communicating in the RC. In addition to other shortcomings, this redundancy increases the cost of devices.

What is needed, therefore, is a method and apparatus that overcomes at least the noted shortcomings described above. In accordance with an illustrative embodiment, a method of wireless communication in a wireless communication network includes: determining a communications channel for use as a rendezvous channel (RC) during a beacon period; transmitting an identity of the RC, the beacon period to at least one wireless station (STA) of the network, wherein the STA includes a single radio transceiver; and during the beacon period and in the RC, exchanging beacons to negotiate communications after the duration. In accordance with another illustrative embodiment, a wireless network includes a rendezvous channel (RC) having a beacon period and at least one wireless station (STA) of the network. The STA includes a single transceiver and is adapted to exchange beacons in the RC during the beacon period.

Brief Description of the Drawings

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. 1 is a simplified schematic diagram of a wireless communication system in accordance with an illustrative embodiment. Fig. 2 is a timing diagram of data transmission in accordance with an illustrative embodiment.

Fig. 3 is a simplified flow-chart of a method of wireless communication in accordance with an illustrative embodiment. Detailed Description

In the following detailed description, for purposes of explanation and not limitation, illustrative 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 illustrative 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 illustrative embodiments. Finally, wherever practical, like reference numerals refer to like features. In accordance with illustrative embodiments, wireless systems, wireless stations

(STAs) and methods are adapted to function in communications channels for incumbent users, which are given first priority access to the channels. Since the radio spectrum availability for the STAs of the illustrative embodiments changes with time, frequency, and location, the radio spectrum environment of the example embodiments is characterized as having one or multiple channels (MCs), as the spectrum occupation by a primary user varies dynamically. These MCs may be used by wireless devices within a network or system. Often referred to as dynamic spectrum access (DSA) wireless networks, these networks may be implemented in dedicated (licensed or unlicensed) portions of the communications spectrum. 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 DSA 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). 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; a Code Division Multiple Access (CDMA) 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. 1 is a simplified schematic diagram of a wireless network 100 in accordance with an illustrative embodiment. The wireless network 100 comprises a plurality of wireless stations (STAs) 101, which also may be referred to as wireless devices or as Customer Premise Equipment (CPE). In an alternative embodiment, the network 100 may be a centralized network with an access point (AP) (not shown) and a plurality of wireless stations.

Illustratively, the wireless network 100 may be one of the types of networks noted previously. Moreover, the STAs 101 may be computers, mobile telephones, personal digital assistants (PDA), or similar device that typically operates in such networks. It is contemplated that the STAs 101 may communicate bilaterally, and are adapted to function in frequency channels of a frequency band that requires protection of incumbent users. These incumbent users may be licensed or unlicensed users.

It is noted that only a few STAs 101 are shown; this is merely for simplicity of discussion. It is contemplated that many other STAs 101 may be used. Finally, it is noted that the STAs 101 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 network 100.

The methods and apparati of the DSA MAC layer of the network 100 of the illustrative embodiments may be implemented in dynamic environments where the availability and quality of channels vary over time (e.g., wireless technologies designed for use in existing TV bands). Thus, the network of secondary STAs of the illustrative embodiments beneficially obtain channel availability in a dynamic manner; and beneficially notify other secondary STAs of the occupation or future occupation of a channel by an incumbent STA. Moreover, the DSA MAC layer methods and apparati of the illustrative embodiments foster the notification by the secondary STAs 101 to other secondary STAs 101 that an incumbent device(s) has begun occupying licensed channels or frequency bands, or that the occupation is imminent.

In accordance with the present teachings, the STAs 101 each includes a single (radio) transceiver adapted to function in one frequency channel at a time, or in a set of contiguous frequency channels (e.g., one, two or three contiguous TV channels). This is in contrast to known STAs 101 that include at least two transceivers, with one transceiver continuously monitoring and communication in a selected rendezvous channel. As will be appreciated, the use of one transceiver results in a comparative reduction in the complexity and cost of the STAs 101. The features of the STA 101 MAC layer enabling the function of the network with only one transceiver per STA is described presently.

Fig. 2 is a timing diagram in accordance with an illustrative embodiment. The description of Fig. 2 is more clearly understood when reviewed concurrently with Fig. 1.

The timing diagram conceptually shows, inter alia, the frequency versus time for a plurality of channels of the network. The channels include a rendezvous channel (RC) 201, a second channel 202, a third channel 203 and a fourth channel 204. The number of channels is merely illustrative and it is contemplated that n-channels may be included for use by the network. In certain embodiments n<4, in other embodiments, n>4, and in other embodiments n»4. Moreover, the channels 202-204 may also have different characteristics, including, but not limited to: bandwidth and transmit power limit. In the present embodiments, the function of two of the STAs 101 (designated 'nodes' A and B) is segregated to provide a description of the salient aspects of the present teachings. The methods described may be applied to many additional STAs as noted.

First one or more RCs are selected for use in a superframe. The selection of RCs is carried out by one of a number of known methods. Moreover, the RCs are not necessarily fixed channels. Rather, the RCs may, and in many embodiments will, change in time. For example, if an incumbent device is to occupy the RC 201, another RC must be selected. Illustrative methods for selecting, changing the RC 201 and methods for notifying the STAs 101 are described in U.S. Provisional Patent Applications having application serial numbers (60/733,504; 60/733,519; 60/733,520; and 60/733,503) and sharing a filing date of November 4, 2005. Other methods useful in the selection and changing of the RC 201 and in notifying STAs 101 of the change may be implemented. Such methods are within the purview of one of ordinary skill in the art. Illustrative examples of these methods are described the referenced U.S. Provisional Patent Applications. Furthermore, the use of a backup RC (not shown) is contemplated. This RC would provide the same function as RC 201.

In accordance with an illustrative embodiment, a group of STAs are designated to send and receive beacons in a particular channel in a particular superframe. Such a group of STAs is referred to as a logical network. For example, at a beacon period 205, all STAs that are part of a logical network, including STAs A and B, terminate communication in other channels and switch to the RC 201. The beacon period 205 is selected to have a start time and a duration, which is decidedly dynamic based on a variety of factors such as the number of STAs within the logical network. For example, if the logical network includes ten (10) STAs, in order to provide time for beacons exchange/negotiation between the

STAs, the duration of the beacon period 205 is likely to be larger than if the logical network had only five (5) STAs.

In an embodiment, the start time and duration of the beacon period 205 is provided in beacons from the STAs (or nodes) of the network. Alternatively, each STA MAC layer can send beacons in a distributed fashion and fix the start time and duration of the beacon period. At the selected start time, the STAs engage the RC 201 for the instructed duration.

At the start time of the beacon period 205, all STAs belonging to the logical network including STAs A and B terminate communications in other channels and commence communications in the RC 201. In an embodiment, all STAs transmit beacons in their assigned time slots. Through these beacons, the STAs negotiate channel(s) to use for data communication, the start time of the communication and duration of the communication. For example, STAs A and B, may transmit beacons to one another to negotiate the selection of channels, times to commence communications in the selected channels, and the duration of the communications. Thus, the RC 201 provides the conduit for the nodes/STAs to negotiate and select multiple contiguous data channels.

The beacon exchange/negotiation may be carried out according to one of a variety of known protocols, such as the WiMedia distributed Ultra- wideband MAC protocol which employs a beacon period for the purpose of beacon exchange amongst STAs 101. As such, further details are not provided to avoid obscuring the description of the present embodiments. After the beacon period 205 terminates, the STAs A and B continue to function in one or more channels until their negotiated time of communication begins.

In an embodiment, STAs A and B negotiate through the beacon exchange performed over the RC during the beacon period 205, a set of contiguous channels to be grouped or bonded for transmission. Illustratively, in optical frequency domain multiplexing (OFDM) technology, bonding of contiguous channels may be achieved by increasing the Fast Fourier Transform (FFT) size, while keeping the symbol size constant. Another option is to use the same FFT size, but to change the symbol size to reflect a change in the inter-carrier spacing needed to accommodate a desired larger bandwidth. In accordance with certain illustrative embodiments, channel bonding is dynamic. That is, channels are bonded based on their availability (e.g., can only bond channels that are not being used by an incumbent users) and also based on the communication needs of the devices. In the present example, STAs A and B, through the beacon exchange process, inform each other of the channels to bond, when the bonding is to take place and the duration of the channel bonding.

Beneficially, the bonding of the channels provides a greater bandwidth to the STAs A and B for communication. In the present illustrative embodiment, the contiguous channels are the second channel 202 and third channel 203 and in time window 206. After the contiguous channels are selected for bonding during the beacon period 205, the STAs A and B switch their respective transceivers to communicate in the bonded channels and carry out their transmission. Once the communication in the time window 206 is completed, the STAs may return to the RC 201 , or may communicate in another RC such as described herein. Once in the (next) selected RC the STAs negotiate again with each other or other devices to set the usage of other frequency channels for future periods. Alternatively, the STAs A and B may continue to function according to one or more MC-MAC protocols, or may enter a sleep-mode until the next designate period in the RC 201.

In accordance with other embodiments, more than one beacon period may be used in a superframe, or more than one RC may be used in a superframe, or both. Illustratively, the second channel 202 may include a second beacon period 207, and thus function as a second RC. In this embodiment, the second beacon period 207 is substantially concurrent with beacon period 205. In an alternative embodiment, the third channel 203 may include a third beacon period 208, and thus function as a third RC. The third beacon period 208 begins after the termination of the beacon period 205, the second beacon period 207, or both. It is contemplated that the third beacon period 208 commences substantially simultaneously with the termination of the first beacon period 205, or the second beacon period 207, or both. Finally, it is contemplated that various permutations and combinations of the scheduled beacon periods are effected. For example, the second beacon period 207 may be foregone, leaving the third beacon 208 period to follow the first beacon period 205. Furthermore, the present teachings contemplate that the RCs function as both communications channels and RCs, albeit not concurrently. For example, consider that the time duration of Fig. 2 represents a superframe having a duration of 100 ms, and the beacon period 205 has a duration of 5 ms. In an example embodiment, after the termination of the beacon period 205, the RC functions merely as another communication channel (i.e., a first channel 201).

The use of more than one beacon period and/or RC channel provides certain benefits. Some of these benefits are specifically mentioned, and others will become apparent to one of ordinary skill in the art upon review of the present disclosure.

To understand one benefit, consider the use of two beacon periods, first beacon period 205 and third beacon period 208 in separate RCs. A first logical network comprising certain STAs may be assigned to RC 101 during beacon period 205 in a previous beacon transmission. A second logical network comprising other STAs may be assigned channel 202 during third beacon period 208. In this manner, a larger group of STAs may be serviced in essentially the same time period.

Another benefit of multiple beacon periods/multiple RCs includes efficiency within a superframe. For example, suppose an STA of the second logical network needs to communicate with an STA of the first logical network and attempts to transmit a beacon to an STA of the first logical network during beacon period 207. As will be appreciated, the STA in the first logical network will not be receiving at the frequency band of the second channel 202 and will not receive the beacon. Under many protocols, the STA of the second logical network will have to wait at least until the next superframe to attempt to transmit the beacon to the STA in the first logical network. However, in accordance with an embodiment, the logical networks may have changed so that at the third beacon period 208, both STAs are in the same logical network and are communicating in the same channel (second channel 202). Thus, the requisite beacons can be exchanged with a delay of less than the duration of a superframe.

Fig. 3 is a simplified flow-diagram of a method of wireless communication 300 in accordance with an illustrative embodiment. The method includes many features described in connection with the embodiments and teachings surrounding Figs. 2 and 3. These features may not be repeated in order to avoid obscuring the description of the present embodiments.

The method 300 begins at step 301 with the selection of a rendezvous channel. The selection of the channel, as noted previously, may be carried out by one of a variety of known methods. At step 302, information including the selected RC, the starting time and the duration of the window of time (e.g., beacon period 205) is transmitted. This transmission is generally effected by standard beacon transmissions or other known methods.

At step 303, the process of exchanging beacons between STAs/nodes is carried out. These exchanges occur during the selected beacon period in the RC. The identification of channels or bonded channels, the start time and duration of the communications between two STAs is negotiated in step 303. After the completion of step 303, the communications occur at the designated time, in the designated channels and by the STAs/nodes that exchanged beacons in the window of time of the RC. Concurrently or consecutively, the method 300 can commence again. Moreover, variations of the method 300 including the use of multiple beacon periods, or multiple RCs, or both, in keeping with descriptions above are contemplated.

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. In a wireless communication network, a method of wireless communication, comprising: determining a communications channel for use as a rendezvous channel (RC) during a beacon period; transmitting an identity of the RC and the beacon period to at least one wireless station (STA) of the network, wherein the STA includes a single radio transceiver; and during the beacon period and in the RC, exchanging beacons to negotiate communications after the beacon period.

2. A method as recited in claim 1, wherein the network is a centralized network having an access point (AP) adapted to determine the RC and to transmit the identification of the RC and beacon period.

3. A method as recited in claim 1, further comprising a plurality of STAs, wherein each of the STAs is adapted to perform the exchanging of beacons to negotiate communications with at least one other of the plurality of STAs.

4. A method as recited in claim 1, further comprising after the beacon period, communicating in at least one channel other than the RC.

5. A method as recited in claim 3, wherein the plurality of STAs further comprises a first STA and a second STA, wherein the first and second STAs perform the exchanging, and after the beacon period, the first and second STAs communicate within at least two contiguous bonded channels.

6. A method as recited in claim 1, further comprising, after the exchanging, determining at least one other RC, and at least one other beacon period.

7. A method as recited in claim 1, further comprising determining a plurality of beacon periods in one or more RCs in a superframe.

8. A method as recited in claim 7, wherein two of the plurality of beacon periods are sequential and in different communications channels.

9. A method as recited in claim 7, wherein two of the plurality of RCs are substantially concurrent and in different RCs.

10. A wireless network, comprising: a rendezvous channel (RC) having a beacon period; at least one wireless station (STA) of the network, which includes a single transceiver and is adapted to exchange beacons in the RC during the beacon period; and at least one other channel.

11. A wireless network as recited in claim 10, wherein the network is a centralized network having an access point (AP) adapted to determine the RC and to transmit an identity of the RC and the beacon period.

12. A wireless network as recited in claim 10, further comprising a plurality of STAs, wherein each of the STAs is adapted to exchange beacons to negotiate communications with at least one other of the plurality of STAs.

13. A wireless network as recited in claim 10, wherein the at least one STA is adapted to communicate the at least one least one channel.

14. A wireless network as recited in claim 12, wherein the plurality of STAs further comprises a first STA and a second STA, wherein the first and second STAs are adapted to exchange the beacons, and after the beacon period, the first and second STAs are adapted to communicate within at least two contiguous bonded channels.

15. A wireless network as recited in claim 11, wherein the AP is adapted to determine another RC after the beacon period.

16. A wireless network as recited in claim 10, further comprising a plurality of RCs in a superframe.

17. A wireless network as recited in claim 16, wherein two of the plurality of RCs are sequential and in different communications channels.

18. A wireless network as recited in claim 16, wherein two of the plurality of RCs are substantially concurrent and in different communication channels.

19. A wireless network as recited in claim 10, wherein the at least one other channel is adapted to function as a communication channel and as another RC.