WO2007083202A1

WO2007083202A1 - Detection and avoid (daa) method for the protection of lower power devices

Info

Publication number: WO2007083202A1
Application number: PCT/IB2006/054752
Authority: WO
Inventors: Carlos M. Cordeiro
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-01-17
Filing date: 2006-12-11
Publication date: 2007-07-26
Also published as: TW200737787A; AR058952A1

Abstract

A wireless system (100) and method of wireless communication comprising a primary wireless station (STA) (103) that transmits and receives at a first range ; a beacon STA (104) that transmits and receives at least at a second range, wherein the second range is greater than the first range; and a secondary STA (101, 102) that transmits and receives at the second range, wherein the beacon STA is adapted to transmit a beacon to the secondary STA informing the secondary STA of the occupation of a channel by the primary STA.

Description

Detection and Avoid (DAA) Method for the Protection of

Lower Power Devices

This application claims the benefit of U.S. provisional application number 60/759,522, filed January 17, 2006, which is incorporated herein in whole by reference .

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. 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 bands of the spectrum (e.g., the industrial, scientific and medical (ISM) radio 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 band is being efficiently used. Thus, much of the unlicensed band is overcrowded, while a relatively large portion of the licensed band is allocated but 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.

One option for reallocation of the communications band involves the use of wireless networks adapted to dynamically access the communications spectrum. For example, dynamic spectrum access (DSA) wireless networks may be implemented in dedicated (licensed) portions of the communications spectrum. Illustratively, DSA wireless networks may operate in a spectrum normally dedicated for television transmission and reception. Thereby, certain portions of the communications band may be more fully utilized.

With the reallocation of certain communication bands for use by unlicensed (secondary) users, spectrum management is needed to ensure that licensed (primary or incumbent) users with priority access to the band 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. Therefore, the medium access control (MAC) layer and physical (PHY) layer specifications must include provisions directed to this needed spectrum management.

As can be appreciated, in order for a secondary device to vacate a channel when an incumbent device begins occupying the channel, the secondary device must be provided notice of the need to vacate the channel. In certain scenarios, the licensed users transmit at comparatively high power levels, and thus over a comparatively long ranges. For example, a primary user may transmit at power levels on the order of one kilowatt (kW) and thus over a range of, for example, 100 km. By contrast secondary users may transmit at power levels of milliwatts (mW) and thus over a range of, for example, 1 km. In such a scenario, because of the comparatively large range of the primary user transmission, secondary users are more readily able to sense the presence of a primary user(s) and vacate channels as needed.

In other scenarios, the primary user may be transmitting at a comparatively low power and the secondary user at a comparatively high power. In this case, the detection of primary users by known sensing methods can be problematic. For instance, because the range of the primary user is comparatively small, there may be no secondary users in range for detection of the primary user. However, the secondary user can transmit over a much greater range. Thus, the secondary user may be transmitting interfering signals in the primary user' s channel, without knowledge of the presence of the primary.

There is a need, therefore, for a method and system that overcomes at least the shortcomings described above.

Summary

In accordance with an illustrative embodiment, a wireless system includes a primary wireless station (STA) that transmits and receives at a first range. The system also includes a beacon STA that transmits and receives at least at a second range, wherein the second range is greater than the first range; and a secondary STA that transmits and receives at the second range. The beacon STA is adapted to transmit a beacon to the secondary STA informing the secondary STA of the occupation of a channel by the primary STA.

In accordance with yet another illustrative embodiment, a method of wireless communication includes providing a primary wireless station (STA) that transmits and receives at a first range; providing a beacon STA that transmits and receives at least at a second range, wherein the second range is greater than the first range; providing a secondary STA that transmits and receives at the second range; and transmitting a beacon to the secondary STA informing the secondary STA of the occupation of a channel by the primary STA.

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. Wherever practical, like reference numerals refer to like elements in the drawing figures.

Fig. 1 is a simplified schematic diagram of a wireless communication system in accordance with a representative embodiment .

Fig. 2 is a simplified flow-chart of a method of wireless communication in accordance with a representative embodiment . Fig. 3 is a timing diagram of data communication in accordance with a representative embodiment.

Fig. 4 is a conceptual representation of a beacon information element in accordance with a representative embodiment .

Fig. 5 is a conceptual representation of an acknowledge information element in accordance with a representative embodiment.

Defined Terminology

As used herein the term Restricted frequency channel' or Restricted channel' means a frequency channel dedicated for use by primary users. The restricted channels may be portions of the communications spectrum that is licensed by a regulatory body such as the FCC, or that are accessed on a priority basis by certain users. For example, the television channels in the United States are licensed frequency channels. However, certain device such as wireless microphones (e.g., operating according to Part 74 of the FCC rules) may access the network with priority over other users, even though the wireless microphones are not expressly licensed primary users for use of the television spectrum but rather licensed secondary users.

As used herein, the terms ^λa' and ^λan' mean one or more; and the term ^λplurality' means two or more.

Detailed Description In the following detailed description, for purposes of explanation and not limitation, representative 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, hardware, software, firmware, methods, systems and protocols may be omitted so as to not obscure the description of the representative 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 representative 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 DSA Medium Access (MAC) layer, such as to be defined under IEEE 802.22, or as defined under the ECMA 368 standard, IEEE 802.16, IEEE 802.11, or IEEE 802.15. The disclosures of the specifications of the referenced IEEE or EDMA standards are specifically incorporated herein by reference in their entirety.

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 view of a wireless system 100 in accordance with an illustrative embodiment. The wireless system 100 may comprise a centralized network and include an access point (AP) , which is also referred to as a base station (BS) . The wireless system 100 further comprises a plurality of wireless stations, which also may be referred to as wireless stations (STAs) or Customer Premise Equipment (CPE) . Notably, the present teachings may be generalized to distributed wireless networks.

The wireless system 100 includes a plurality of primary STAs and at least one secondary STA. For example, the primary STAs may be part of the group of STAs 105. The group of STAs includes primary STAs 103 and a beacon STA 104.

The system 100 also includes secondary STAs 101, 102. One or both of the secondary STAs 101, 102 may be APs of secondary networks or may be STAs joined to another AP (not shown) of secondary networks. As such, in certain embodiments, the secondary STAs 101, 102 may transmit beacons and perform other tasks normally carried out by APs. In representative embodiments, the primary STAs transmit, or receive, or both, at a first range; and the secondary STAs transmit, or receive, or both, at a second range, which is greater than the first range. In representative embodiments, the beacon STA 104 is adapted to transmit, or receive, or both over a range that is at least equal to if not greater than the transmission range of the secondary STAs 101, 102. As will be appreciated, this improves the likelihood that secondary STAs 101, 102 are made aware of the presence of a primary STA 103. Finally, the noted ranges are generally indicative of the power of the STAs, with the primary STAs being of lower power compared to the secondary and beacon STAs.

Illustratively, the wireless system 100 may comprise one of the types of networks noted previously. Moreover, the STAs may be computers, mobile telephones, personal digital assistants (PDAs) , or similar device that typically operates in such networks. In a specific embodiment, at least one of the STAs is stationary. It is contemplated that the STAs are adapted to function in restricted frequency channels of a frequency band that requires protection of incumbent users. Often, for simplicity restricted frequency channels and restricted channels may be referred to as ^λchannels.'

It is noted that only a few primary and secondary STAs are shown; this is merely for simplicity of discussion. Clearly, many other STAs may be used. Moreover, it is noted that the primary and secondary STAs are not necessarily the same. In fact, a plethora of different types of both primary and secondary STAs adapted to function under the chosen protocol may be used within the networks of the system 100.

In one embodiment, the beacon STA 104 is adapted to function according to the protocol of the secondary STAs 101, 102. For example, in certain applications, the secondary devices 101,102 function according to the 802.22 protocol referenced above. Accordingly, the beacon STA 104 is adapted to function according to this protocol and may be an STA of the network of secondary STAs. In such embodiments, the beacon STA 104 readily communicates with the secondary STAs 101,102. However, and as will be described more fully herein, it is not essential that the beacon STA 104 functions according to the protocol of the secondary STAs 101, 102. Rather, the beacon STA 104 may merely transmit beacons for reception by the secondary STAs 101, 102.

In embodiments in which the beacon STA 104 is adapted to communicate with the secondary STAs 101, 102, beacons may be transmitted to the secondary STAs 101, 102 in a dedicated channel, and at dedicated periods of time. A method and beacon transmission according to such an embodiment is described in connection with Figs. 2 and 3.

Initially, the beacon STA 104 is tuned to the desired frequency channel (s) where the primary STAs 103 may desire to operate. The beacon STA 104 scans the desired channel (s) in search for beacon packets transmitted by APs of the secondary STAs 101,102. In case no AP beacons are received for a specified amount of time, the beacon STA 104 assumes that no secondary (higher power) system is operating in the channel. Notably, the beacon STA 104 continues to scans the desired channel (s) in search for AP beacon transmissions as an AP may erroneously attempt to initiate transmission in this channel at any time.

At step 201, the quiet period (s) of one or more secondary STAs 101, 102 are determined. Notably, each of the STAs 101, 102 may comprise a AP (or BS) of a centralized network, and thus may transmit beacons that include information of, inter alia, quiet periods (QPs) . The beacon STA 104 of the present embodiment is adapted to receive the beacons from the STAs 101,102 and from this determine the QPs for each STA 101, 102. Alternatively, if the STAs 101, 102 comprise a secondary network with certain STAs 101, 102 not being APs, then only beacons from those STAs 101, 102 that function as APs are received.

After receiving the beacons from the STAs 101, 102, the beacon STA 104 reconstructs a ^λQP map' that includes the QPs for each of the STAs 103 that function as APs. A conceptual illustration of such a QP map is shown in Fig. 3. Illustratively, a first BS (BSl) includes first QPs 301; a second BS (BS2) includes second QPs 302; a third BS (BS3) includes QPs 303, etc.

Once the beacon STA 104 determines the various QPs 301-303, at step 202 of Fig. 2, the beacon STA 104 may selectively broadcast beacons informing the secondary STAs 101, 102 of the presence of a primary STA 103 and the need to vacate a particular channel. In a representative embodiment, the beacons are transmitted in a dedicated channel for reception by the secondary STAs 101, 102. Notably, the identity of the dedicated channel in which beacons are transmitted may be transmitted to the secondary STAs 101, 102 in a previous beacon transmission.

The transmission of the beacons in the QPs does not require the beacon STA 104 to join the network of the secondary STAs 101, 102; however, this is not precluded. Moreover, the beacons are usefully transmitted in a repeated manner in the QPs in order to improve the likelihood that all secondary STAs 101, 102 receive the beacons. This is particularly useful in case one or more STAs 101, 102 may be hidden from the STA 104 or subject to interference. Repeated transmissions in the QPs further ensure that the STAs 101, 102 each receive the notification of the presence of the primary STAs 103. Notably, and as described more fully herein, an acknowledgement (ACK) may be sent from the STAs 101, 102. Upon receipt of the ACK, transmission to the sending secondary STAs 101, 102 can be terminated.

At step 203, if necessary, the secondary STAs 101, 102 switch communications to another channel that is currently not in use by the primary STAs 103. As will be appreciated, by embedding the beacon STA 104 to communicate with the secondary STAs 101, 102, the detection of use by primary STAs is enhanced, particularly when the primary STAs 103 transmit/receive at a comparatively lower range than the secondary STAs 101, 102.

Once the secondary STAs 101, 102 switch to a vacant channel as to free up the channel for the primary STA 103, the APs of the network of the secondary STA 101, 102 continues to append the beacon acknowledgement IE to all of its routine beacon transmissions. This IE shall be appended for at least the duration of time that the lower power system is in operation in the channel. The retransmission of the ACK usefully notifies any newly joined or hidden secondary STAs 101, 102, which are not aware of the ongoing primary STAs 103 (i.e., lower power or lower range system) operating in the desired channel, to not attempt to transmit in that channel. Therefore, a more effective protection of lower power services can be achieved.

In the embodiments described above, the beacon STA 104 is adapted to communicate with the secondary STAs 101, 102 in order to convey the information regarding the presence of primary STAs 103. In alternative embodiments, the beacon STA 104 may not be adapted to so communicate. To this end, the secondary STAs 101, 102 may operate according to one of a variety of different protocols. In this case, the beacon STA 104 may transmit the information regarding the primary STAs 103 in a continual manner for receipt by the disparate STAs 101, 102 as no information regarding the QPs of these STAs 101, 102 is available and ACK reception by the beacon STA 104 is not possible. Additionally, in the presently described embodiment, the secondary STAs 101, 102 must employ periodic quiet periods in order to be able to detect and decode the beacons transmitted by the beacon STA 104. The duration of the quiet period of the secondary STAs 101, 102 is usefully at least twice the transmission duration of the beacon transmission from the beacon STA 104. This improves the likelihood that the secondary STAs 101, 102 can receive and decode the beacon transmission from the beacon STA 104, if any such beacon exists. Fig. 4 is a conceptual representation of a beacon information element (BIE) in accordance with a representative embodiment. The BIE is transmitted by the beacon STA 104 according to the embodiments described previously. While the BIE includes a number of fields, certain fields are self-explanatory and are not described in great detail.

Notably, the system type (ST) field provides the type of primary system operating in the band. In addition, the BIE includes a TX ID field and a Transaction ID field. These fields allow the secondary STAs 101, 102 of the higher power/higher range system to authenticate the beacon, and hence prevent any misuse of this functionality. It is also possible that the secondary STAs 101, 102 possess pre-programmed security keys that will provide enhanced security by distinguishing unauthorized beacon STAs from authorized ones. These illustrative security measures could be established in a secure manner among the lower power (primary) and higher power (secondary) system operators prior to communication therebetween. A field for such an exchange is provided in the BIE as shown.

The BIE also includes a start time (ST) field and a duration field. The ST and duration field provide with certainty the time and the duration of time that the secondary STAs 101, 102 must vacate the channel (s) to be occupied by the primary STAs 103. Moreover, the BIE may include a field that includes the geographic location of the primary STAs. As will be appreciated, these fields beneficially allow the secondary STAs 101, 102 to adjust as needed for the time allocated to the primary STAs 103 and the location thereof. Notably, the location information can allow a secondary STA 101, 102 to move to (join) another network that is outside the range of the primary STAs 103.

Fig. 5 is a conceptual representation of an acknowledge information element (AIE) in accordance with a representative embodiment. The AIE is used by the primary STA 101,102 to signal the beacon STA 104 that the BIE was successfully received and that the secondary STA will comply with the primary STA request. In case the beacon STA 104 does not receive such acknowledgement, the notification procedure is repeated. This may be done indefinitely until all secondary STAs 101,102 acknowledge receipt of the beacon .

Once all previously secondary STAs 101, 102 indicate the successful reception of the beacons from the beacon STA 104, the beacon STA 104 returns to scanning channels for beacons from primary STAs.

As secondary STAs 101, 102 move to other channels, the interference level in the desired channel decreases, and so increase the chances that other secondary STA systems, which were not detected in the previous scanning phase (e.g., due to interference), now become detectable. If this procedure is repeated, there is a greater probability that the desired channel becomes free of any secondary (high power system) operation. In particular, the DSA MAC layer methods and apparati of the representative 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) . Thus, the network of secondary STAs of the representative embodiments beneficially obtain channel availability in a dynamic manner; and beneficially notify other secondary STAs and the AP of the occupation or future occupation of a channel by an primary STA. Further details of the DSA MAC layer is described in the IEEE 802.22 specification and progeny thereof, and are not included to avoid obscuring the description of the illustrative embodiments.

In the representative embodiments described herein, a wireless method and system provide access to secondary STAs and networks in restricted channels, while improving the robustness of primary STA and network access. As will be appreciated by one of ordinary skill in the art, many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. These and other variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.

Claims

Claims :

1. A wireless system, comprising: a primary wireless station (STA) (103) that transmits and receives at a first range; a beacon STA (104) that transmits and receives at least at a second range, wherein the second range is greater than the first range; and a secondary STA (101, 102) that transmits and receives at the second range, wherein the beacon STA is adapted to transmit a beacon to the secondary STA informing the secondary STA of the occupation of a channel by the primary STA.

2. A wireless system (100) as claimed in claim 1, wherein the beacon STA (104) transmits the beacon in a dedicated channel .

3. A wireless system (100) as claimed in claim 1, wherein the beacon STA (104) transmits the beacon continually over a channel.

4. A wireless system (100) as claimed in claim 1, wherein the beacon STA (104) and the secondary STA (101,102) function under a same communication protocol.

5. A wireless system (100) as claimed in claim 1, further comprising a plurality of primary STAs (103) .

6. A wireless system (100) as claimed in claim 1, further comprising a plurality of primary STAs (103), each of which is adapted to transmit a respective beacon.

7. A wireless system (100) as claimed in claim 1, further comprising a plurality of beacon STAs (104), wherein each of the plurality of beacon STAs (104) is adapted to transmit information of primary STAs (103) to a dedicated one of the beacon STAs (104), which is adapted to transmit a beacon with an aggregation of the information of the plurality of beacon STAs (104) .

8. A wireless system (100) as claimed in claim 1, wherein the beacon STA (104) is adapted to monitor the secondary STA (101,102) and based on the monitoring, is adapted to determine one or more quiet periods (301-304) of the secondary STA (101,102).

9. A wireless system (100) as claimed in claim 1, wherein the beacon STA (104) is adapted to transmit the beacon during the one or more quiet periods (301-304) .

10. A wireless system (100) as claimed in claim 9, wherein the secondary STA (101,102) is adapted to transmit an acknowledgement of receipt of the beacon.

11. A wireless system (100) as claimed in claim 9, wherein the beacon includes one or more of: a location of the primary STA (103); a duration time during which a channel is to be occupied by the primary STA.

12. A wireless system (100) as claimed in claim 1, wherein the secondary STA (101, 102) has a quiet period (301-304) having a duration at least twice a duration of the beacon.

13. A wireless system (100) as claimed in claim 1, wherein a security key is communicated between the beacon STA (104) and the secondary STA (101, 102) .

14. A method of wireless communication , the method comprising: providing a primary station (STA) (103) that transmits and receives at a first range; providing a beacon STA (104) that transmits and receives at least at a second range, wherein the second range is greater than the first range; providing a secondary STA (101,102) that transmits and receives at the second range; and transmitting a beacon to the secondary STA (101, 102) informing the secondary STA of the occupation of a channel by the primary STA.

15. A method as claimed in claim 14, further comprising transmitting the beacon through a dedicated channel.

16. A method as claimed in claim 14, further comprising mitting the beacon continually.

17. A method as claimed in claim 14, further comprising monitoring the secondary STA (101, 102) and based on the monitoring, determining one or more quiet periods (301-304) of the secondary STA.

17. A method as claimed in claim 17, wherein the transmitting is effected during the one or more quiet periods (301-304) .

18. A method as claimed in claim 14, wherein the secondary STA (101,102) transmits an acknowledgement to the beacon STA (104) .

19. A method as claimed in claim 14, further comprising providing quiet periods (301-304) for the secondary STAs

(101,102) having a duration at least twice a duration of the beacon.

20. A method as claimed in claim 14, further comprising communicating a security key between the beacon STA (104) and the secondary STA (101,102).