WO2008090509A2

WO2008090509A2 - Quiet period management in wirelses networks

Info

Publication number: WO2008090509A2
Application number: PCT/IB2008/050210
Authority: WO
Inventors: Carlos M. Cordeiro; Kiran S. Challapali; Bong-Jun Ko
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-01-26
Filing date: 2008-01-21
Publication date: 2008-07-31
Also published as: TW200843378A; WO2008090509A3

Abstract

Spectrum agile devices use non or under utilized portions of the radio spectrum to communicate. However, when a primary user of the channel starts operation, the spectrum agile device must typically vacate the channel. Thus, spectrum agile devices use quiet periods to sense whether a primary device is present. Quiet Periods can be scheduled or on-demand, and quiet periods can be initiated so that the quiet periods of different channels do not overlap.

Description

QUIET PERIOD MANAGEMENT IN WIRELESS NETWORKS

FIELD OF THE INVENTION

[0001] This disclosure is directed to wireless communications, more particularly, to methods and systems for managing quiet periods of spectrum agile radio systems.

BACKGROUND OF THE INVENTION

[0002] The continual growth in the usage of the radio spectrum has led to initiatives on better managing it. One approach involves the opportunistic usage of unused or under-used licensed radio spectrum, which is also known as spectrum opportunity or opportunity. The identification and use of spectrum opportunity are enabled by Spectrum Agile Radio (SARA) devices, also known as cognitive radios. SARA devices allow the use of vacant spectrum without causing harmful interference to incumbents, such as, for example, TV or cellular signals. Incumbents are also known as primary users. SARA devices, also known as secondary users, can also be used in unlicensed frequency bands, such as, for example frequencies used by cordless phones and/or WiFi. In one embodiment, devices that are not cognitive can be considered higher priority users, and SARA devices can communicate while the higher priority users are not using the spectrum.

[0003] One issue in the deployment of secondary users in frequency bands already occupied by primary radio systems, either licensed or unlicensed, is that primary users may appear on the channel at unpredictable times, at which point the secondary user must vacate the channel. This reliable detection of the presence or absence of the primary user is accomplished through the use of Quiet Periods (QPs). During QPs, all network traffic is suspended and the secondary users sense the channel for primary users. Sensing a channel that is currently being used, or directly impacted (e.g., the adjacent channels), by a secondary device is called in-band sensing, and sensing any other channel is called out-of-band sensing.

[0004] Accordingly, there is a desire to manage quiet periods in order to sense channels for spectrum opportunity and primary users.

SUMMARY OF THE INVENTION

[0005] The invention as described and claimed herein satisfies this and other needs, which will be apparent from the teachings herein. [0006] In one aspect, a method of managing quiet periods comprises, receiving a packet from a first node in a spectrum agile radio network, the packet comprising information associated with a timing of at least one quiet period that will be initiated on at least one channel of the spectrum agile radio network, wherein the quiet period is used to sense for a primary user.

[0007] In one embodiment, the method further comprises scheduling at least one quiet period based on the received information. In one embodiment, the at least one quiet period is scheduled to avoid overlapping quiet periods between other channels. In one embodiment, the scheduled at least one quiet period is periodic and over two or more superframes.

[0008] In one embodiment, the information further comprises at least one of channel information, primary user detection information, hop information, report information and backup channel information.

[0009] In one embodiment, the method further comprises receiving a request to quiet packet, the request to quiet packet comprising information associated with a quiet period to begin at or soon after the reception of the request to quiet packet. In one embodiment, the request to quiet packet is transmitted by a node in response to sensing a signal that might represent a primary user. In one embodiment, the start time and duration for the quiet period is selected that avoids overlapping with quiet periods in one or more channels of the radio spectrum. In one embodiment, the request to quiet packet is broadcast to at least one other node over multiple hops.

[0010] In one embodiment, the method further comprises, starting a quiet period, sensing for a primary user, and transmitting the results of sensing for a primary user onto the network. In one embodiment, the packet is a periodically broadcast control packet.

[0011] A spectrum agile device, implemented in accordance with one aspect of the invention comprises, a spectrum agile communication module, the communication module being operable to transmit and receive data over spectrum not being used by a primary user; a processor, the processor being operable to initiate a quiet period on at least one channel of a spectrum agile radio network based on quiet period information received from a packet transmitted on the spectrum agile network; and a sensing module, the sensing module being operable to detect a primary user on at least one channel of the spectrum agile network. [0012] A spectrum agile radio system, implemented in accordance with one aspect of the invention comprises, a primary user; and a spectrum agile user, the spectrum agile user comprising, a spectrum agile communication module, the communication module being operable to transmit and receive data over spectrum not being used by a primary user, a processor, the processor being operable to initiate a quiet period on at least one channel of a spectrum agile radio network based on quiet period information received from a packet transmitted on the spectrum agile network, and a sensing module, the sensing module being operable to detect a primary user on at least one channel of the spectrum agile network. In one embodiment, the primary user is a licensed user of the channel.

[0013] Other objects and features of the invention will become apparent from the following detailed description, considering in conjunction with the accompanying drawing figures. It is understood however, that the drawings are designed solely for the purpose of illustration and not as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0014] The drawing figures are not to scale, are merely illustrative, and like reference numerals depict like elements throughout the several views.

[0015] Fig. 1 illustrates a spectrum agile wireless network implemented in accordance with one embodiment of the invention.

[0016] Fig. 2 illustrates scheduled and on-demand quiet period (QPs) for a channel implemented in accordance with one embodiment of the invention.

[0017] Fig. 3 illustrates a request to quiet packet implemented in accordance with one embodiment of the invention.

[0018] Fig. 4 illustrates a two hop propagation of an RTQ implemented in accordance with one embodiment of the invention.

[0019] Fig. 5 illustrates scheduled and on-demand QPs for a plurality of channels implemented in accordance with one embodiment of the invention.

[0020] Fig. 6 illustrates a method for scheduling QPs implemented in accordance with one embodiment of the invention. [0021] Fig. 7 illustrates a method for initiating an on-demand quiet period implemented in accordance with one embodiment of the invention.

[0022] Fig. 8 illustrates a device implemented in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0023] There will now be shown and described in connection with the attached drawing figures several embodiments of a methods and systems for managing quiet periods (QPs).

[0024] The term packet as used herein, unless otherwise specified expressly or by context, is intended to have a broad non-limiting definition, and refers, without limitation, to a bundle of data that can be transmitted in any manner from one device to another.

[0025] The term node as used herein, unless otherwise specified expressly or by context, is intended to have a broad non-limiting definition, and refers, without limitation, to a device, computer, object and the like coupled to communications network in any manner.

[0026] Fig. 1 illustrates an exemplary communication system 100, implemented in accordance with an embodiment of the invention. Fig. 1 comprises a plurality of nodes, for example, a primary user 106 coupled to a communications antenna 108, and a plurality of secondary users, node one 102 to node N 104. In one embodiment, the primary user is a television broadcaster who has licensed a channel on the radio spectrum and uses that licensed channel to broadcast content to TV viewers (not shown). Some television broadcasters do not broadcast continuously and/or some television channels are completely vacant, thus openings in the radio spectrum are available. The secondary users 102, 104 use these openings, also known as spectrum opportunity, to communicate with each other and/or with a communication base station (not shown) when the primary user 106 is not using the channel. Since secondary users 102, 104 must typically vacate the channel when a primary user 106 is present on the channel, the secondary users 102, 104 use quiet periods (QPs) to sense for a primary user 106. This is also known as in-band sensing. Two methods of in-band sensing, i.e., scheduled and unscheduled, are described in further detail below. In Fig. 1 the primary user is a licensed user of a channel, however, in one embodiment, the primary user can be a higher priority user in an unlicensed channel. In one embodiment, a regulatory body, such as, for example, the FCC in the USA, can determine the priority of channel users. The primary user can be any signal or radiation that would require a secondary user to vacate the channel.

[0027] The radio spectrum comprises a plurality of channels, both licensed and unlicensed, and secondary users 102, 104 can use one or more of those channels for communication. The secondary users 102, 104 illustrated in Fig. 1 may be communicating on separate channels with different users and/or base stations. Additionally, in one embodiment, even though the secondary users 102, 104 are operating in different channels, the secondary users 102, 104 can communicate information, such as, for example, channel conditions, to each other.

[0028] Since secondary users 102, 104 may be forced from one channel into another because of the presence of a primary user 106. In one embodiment, secondary users 102, 104 can sense for primary users 106 in channels in which the secondary users 102, 104 are currently operating, and in channels in which they are not operating, also known as out-of-band sensing. The channel in which a secondary user 102, 104 is operating is also known as the home channel, and all other channels are called foreign channels. In other words, in-band sensing takes place on a secondary user's 102, 104 home channel, while out-of-band sensing occurs on foreign channels.

[0029] In one embodiment, secondary users 102, 104 can coordinate the usage of the multiple channels. For example, in one embodiment, information associated with quiet periods of different channels is disseminated across two or more secondary devices 102, 104. Using this disseminated information, quiet periods can be scheduled so that quiet periods on different channels do not overlap. One advantage of non-overlapping QPs is that a secondary device can perform out-of-band sensing of another channel during that channel's QP without having to sacrifice a quiet period on its own channel.

[0030] In one embodiment, coordination between secondary users 102, 104 is performed through multiple channel medium access control (MC-MAC) protocols. Properly designed MC- MAC protocols allow devices in the same neighborhood to communicate concurrently in different channels without interfering with each other. However, the methods and systems described herein are not limited to a MC-MAC protocol and, in various embodiments can be implemented at different communication layers using other protocols. [0031] Fig. 2 illustrates three superframes (i, i+1, i+2) of a single channel, C₁. Time in a channel can be divided into reoccurring superframes. The superframes comprise scheduled QPs and on-demand QPs. In one embodiment, scheduled QPs are scheduled by secondary users 102, 104 beforehand. Secondary users 102, 104 on the same home channel know about the existence of these scheduled QPs before they take place, and the scheduled QPs have a known start time and duration. During this time the secondary users 102, 104 suspend their transmission and perform in-band sensing. These scheduled QPs can be periodic and can occur over multiple superframes.

[0032] In one embodiment, scheduled QPs are communicated in regularly transmitted control packets. For example, in one embodiment, scheduled QPs are communicated in beacon packets, which are supported in many existing wireless networks, such as, IEEE 802.11, WiMedia UWB MAC, IEEE 802.15, and other wireless protocols. In these networks, beacon packets, also referred to as beacons, are broadcast periodically and are used to convey network control information, thus beacons are good candidates for carrying information regarding scheduled QPs.

[0033] On-demand QPs are initiated during a superframe by a secondary user 102, 104 that detects an urgent situation that requires a QP. For example, a possible primary user 106 is sensed on the channel. In urgent situations, the secondary users can't wait for a scheduled QP and must enter a QP immediately. An on-demand QP can be initiated by a single secondary user and does not have to have the same periodicity as a scheduled QP. In one embodiment (not shown), an on-demand QP can overlap and take the place of a scheduled QP. Similar to scheduled QPs, secondary users 102, 104 on the same home channel suspend transmissions and perform in-band sensing during an on-demand QP.

[0034] Since on-demand QPs are initiated randomly, beacon packets may not be ideal for initiating an on-demand QP. Thus, in one embodiment, a network 100 can define a special control packet that is broadcast to nodes, potentially over multiple hops, and that would initiate a quiet period for one or more channels. In this manner, a quiet period region is formed around the node that initiated the on-demand QP. One exemplary control packet that can initiate an on- demand QP is a request-to-quiet (RTQ) control packet. [0035] Fig. 3 illustrates an RTQ 300 packet implemented in accordance with one embodiment of the invention. Various embodiments of the invention can use RTQs with more or less information depending on a standard and/or the needs of a particular network. In one embodiment, an RTQ can be a signal that triggers a device to immediately enter a QP once the signal is received. The RTQ illustrated in Fig. 3 comprises a channel element 302, a duration element 304, primary detection information element 306, information associated with the number of hops the RTQ should be propagated element 308, instructions associated with reporting back information element 310, a backup channel element 314 that a device can switch to if a primary user is detected, a threshold .

[0036] As a result of receiving an RTQ, nodes initiate a QP and sense for a primary user.

The channel information element 302 tells a node which channel to initiate the QP on. In one embodiment, the RTQ may omit channel information and a node can initiate a QP on its home channel. The duration information element 304, tells a node when to start the QP and the length of time the QP should last. This information can be transmitted in a plurality of different forms. For example, in one embodiment, the RTQ 300 can comprise a QP start time and a QP finish time. In one embodiment, the RTQ can comprise a QP start time and a duration, such as, for example, 10 milliseconds.

[0037] In one embodiment, in order to assist a node in sensing a primary user, an RTQ

300 can also comprise primary detection information element 306. This information element 306 can comprise threshold(s) that determine whether a channel is being used, probabilities of detection and false alarm and/or any other information that would help determine whether a primary user has entered the channel. In one embodiment, a node senses for any energy during a quiet period, since the SARA devices are not transmitting during a quiet period, if the node senses a predetermined level of energy, it can assume a primary user is present and will vacate the channel. In one embodiment, a node can perform one or more refined tests during a quiet period such as, for example, looking for particular signatures of the signal instead of simple energy detection. The tests can be different tests or the same test and can have different thresholds and/or other parameters. In one embodiment, the primary detection information element 306 comprises information associated with the type and quantity of tests performed. [0038] As mentioned above, an RTQ can be propagated over any number of hops. Fig. 4 illustrates a communication network 400, comprising nodes A-O, in which an RTQ transmitted by node S is propagated over 2 hops with each arrow corresponding to a hop. In one embodiment, an RTQ can comprise a counter which is decreased with every transmission after the first transmission. A node that receives an RTQ with a zero counter does not retransmit the RTQ. Counters and/or other hop information can be transmitted through hop information field element 308 of RTQ 300.

[0039] In one embodiment, a node can report information obtained during a quiet period to other nodes, such as, for example, the originating node. The reporting information can tell other nodes to switch channels because of a primary user, tell other nodes that no primary was detected, the reporting information can comprise raw test results, channel frequency, the effective duration of the sensing (a full QP may not be necessary if a primary user is immediately detected), a type of the user detected, a signal level detected and other information about a user and/or the channel. Nodes receiving this reporting information can use it make measurements and determinations regarding the channel. In one embodiment, report information element 310 of RTQ 300 can comprise a flag indicating whether information associated with the QP tests should be transmitted to other nodes. In one embodiment, the report information element 310 can comprise an identifier for the node who sent the RTQ, so that the receiving node knows who to transmit information back to. In one embodiment, the report information element 310 can comprise time slots in which the node should broadcasts its results. In one embodiment, a node does not have to report after every quiet period. Instead, a node can transmit reporting data every other quiet period, periodically, randomly or according to any other algorithm. The contents of the report can comprises the results of the latest sensing during the latest quiet period and/or the contents can comprises any combination of results from any previous quiet periods.

[0040] If a primary user is detected, secondary users must typically vacate the channel.

Thus, in one embodiment, RTQ 300 can comprise backup channel information element 314. The back up channel information element 314 can be used by a node when switching channels to avoid a primary user. In one embodiment, the backup channel information element 314 comprises more than one channel so that many nodes do not try to switch to the same channel after detecting a primary user. In addition, in one embodiment, a node can change backup channel information element 314 before retransmitting to a next hop.

[0041] Some or all of the information in an RTQ can also be in a control packet used to manage scheduled QPs such as, for example, the beacon packet.

[0042] In one embodiment, RTQs are handled with high priority and are forwarded to a next hop with a short enough time to meet the required QP timing announced in the corresponding RTQ. In one embodiment, the header field of packets transmitted by nodes comprise a special flag that informs other nodes of a potential primary user. In one embodiment, this field can be called an Urgent Coexistence Situation (UCS) field. When the USC field is set, nodes can perform a predefined operation to support quicker propagation of subsequent RTQs. For example, nodes can slow down on-going transmission or refrain from transmitting normal packets for a predefined amount of time.

[0043] Fig. 5 illustrates a multi-channel embodiment (Ci and C₂), where QPs across channels do not overlap in time. While Fig. 5 illustrates only 2 channels, a multi-channel QP management can be scaled to any number of channels. As illustrated in Fig. 5 by the broken arrows, the scheduled QPs in Ci do not overlap in time with the scheduled QPs of C₂. Since QPs are not overlapping, a node that uses Ci as its home channel can perform spectrum sensing in channel C₂ during C₂ 's QP without having to miss an in-band sensing opportunity during a QP of its home channel C₁. The same applies to nodes with C₂ as their home channel. Thus, the efficacy of out-of-band sensing can be considerably improved if information regarding in-band QPs is communicated between nodes in a similar neighborhood.

[0044] Since on-demand QPs, normally occur when an urgent situation arises, a node may not be able to avoid overlapping QPs with another channel because of the urgency of the situation. Thus, two on-demand QPs may overlap, such as, for example, the two on-demand QPs in superfames i and j of channels Ci and C₂, respectively. In one embodiment, an on- demand QP may overlap with a scheduled QP of another or the same channel. In one embodiment, nodes can delay the start time of on demand QPs to avoid overlapping between an on-demand QP and any scheduled QPs. [0045] The QP management system and methods described herein can be used in, for purposes of example and not limitation, IEEE 802.22, WiMedia UWB, IEEE 802.11, IEEE 802.15 and other wireless systems.

[0046] Fig. 6 illustrates a method 600 for scheduling QPs implemented in accordance with one embodiment of the invention. Method 600 starts in step 602. In step 604, the node listens and/or requests for QP management information. In one embodiment, a node desiring to communicate on a channel can broadcast a request for QP management information. In one embodiment, a node desiring to communicate on a channel can listen for QP management information that is periodically broadcast over the channel. In one embodiment, if a node does not hear broadcasted information after a predetermined amount of time, the node can transmit a request for QP management information.

[0047] In step 606, if no QP management information is received, method 600 proceeds to step 608, where the node schedules at least one QP, based on a set of predetermined parameters. Returning to step 606, if QP management information is received, method 600 proceeds to step 610, where the node schedules at least one QP based on the received QP management information. QP management information can come from nodes using the home channel and/or from nodes using foreign channels. In one embodiment, the node's QPs are scheduled so that they do not overlap quiet periods of foreign channels. Method 600 ends in step 612.

[0048] Fig. 7 illustrates a method 700 for initiating an on-demand QP, implemented in accordance with one embodiment of the invention. Method 700 starts in step 702. In step 704, a first node senses an urgent situation, for example, there is a strong likelihood that a primary user has entered the channel. Then, in step 706, the first node transmits a control packet comprising at least some information to initiate a QP. In one embodiment, the first node sends an RTQ as described with respect to Fig. 3.

[0049] In step 708, other nodes in the vicinity of the first node receive the control packet.

In one embodiment, method 700 proceeds to step 710, however in other embodiments step 710 may be omitted. In step 710, nodes that received the control packet can examine a hop information field 308 to determine whether the receiving node should retransmit the control packet. If the field indicates that the node should transmit a control packet, the node updates the hop information field 308 and transmits its own control packet to neighboring nodes.

[0050] Following step 710, method 700 proceeds to step 712 where a node that receives the control packet initiates a QP based on the received QP information. In one embodiment, the node receives a start time and an end time for an on-demand QP. Once the start time arrives, the node goes silent and senses for primary users. In one embodiment, method 700 ends in step 716

[0051] In one embodiment, method 700 proceeds from step 712 to optional step 714.

Nodes in a QP region can benefit from the sensing results of other nodes in the same region. Thus, in one embodiment, each node can transmit the results of its QP sensing to neighboring nodes. In one embodiment, the information is returned to the node that initiated the on-demand QP. Then method 700 ends in step 716.

[0052] Unless otherwise stated the order and/or omission of the steps in any of the methods described herein are not limited to the described embodiments. Furthermore, additional steps may be added without limitation to any of the methods described herein.

[0053] Fig. 8 illustrates a device 800 implemented in accordance with one embodiment of the invention. Device 800 comprises a processing module 804, a communication module 808, a sensing module 806 and memory 802 coupled together by bus 810. The modules of device 800 can be implemented as any combination of hardware, software, hardware emulating software and reprogrammable hardware. The bus 810 need not be a single bus, but rather, illustrates the interoperability of the different modules of the device 800. In one embodiment, there may be multiple busses. In one embodiment, some modules are directly coupled instead of coupled via a bus 800. Device 800 may be implemented as a desktop, a notebook computer, a Personal Digital Assistant (PDA), a handheld device, a wireless base station, a wireless phone or any other computing device or item known or hereafter developed that is capable of implementing the features, and/or performing functions, as described herein.

[0054] In one embodiment, the processing module 804 can be implemented as, one or more Central Processing Units (CPUs), Field-Programmable Gate Arrays (FPGA), or any other component capable of executing computer applications. Communication module 808 comprises one or more I/O components used by the device 800 to communicate with users and other devices. For example, components such as a monitor, a keyboard, a mouse and a disk drive, can be used by a user to input and output information to and from the device 800.

[0055] In addition, the communication module 808 facilitates communication between the device 800 and other devices or systems. Components such as an antenna, a modem, a network interface card (NIC), a wireless adapter, a Universal Serial Bus (USB) adapter, etc., can be used by the device 800 to communicate with a network and/or with other devices. Communication between the device 800 and the network may also be accomplished wirelessly or via wired connection.

[0056] In one embodiment, sensing module 806 can be implemented as an antenna and a signal processing module that can sense for energy or any particular feature of the primary signal on a channel. In case of energy detection, since SARA devices are silent during a quiet period, if a SARA device senses a threshold level of energy during a quiet period, it is likely that a primary user is present on the channel, and the SARA device should vacate the channel.

[0057] In one embodiment, memory 802 provides electronic data storage using a combination of main memory (e.g., RAM) and drive storage. Any type of appropriate electronic memory can be used, including, without limitation, RAM, ROM, drive storage (hard, floppy, optical, etc.), non-volatile memory (e.g., flash) or any other memory that can store data. Memory 802 can also function to store packets before they are transmitted via the communication module 808.

[0058] While the modules of device 800 are illustrated as single boxes, the modules can comprise one, two or more different modules. In addition, any one module of device 800 can be part of another module, such as, for example, sensing module 806 can be a part of communication module 808, and/or processing module 804 can comprise some memory 802.

[0059] While there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and detail of the disclosed invention may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims hereto appended.

Claims

CLAIMSWhat is claimed:

1. A method of managing quiet periods comprising: receiving a packet from a first node in a spectrum agile radio network, the packet comprising information associated with a timing of at least one quiet period that will be initiated on at least one channel of the spectrum agile radio network, wherein the quiet period is used to sense for a primary user.

2. The method of claim 1 further comprising scheduling at least one quiet period based on the received information.

3. The method of claim 2, wherein the at least one quiet period is scheduled to avoid overlapping quiet periods between other channels.

4. The method of claim 2, wherein the scheduled at least one quiet period is periodic and over two or more superframes.

5. The method of claim 1 wherein the information further comprises at least one of channel information, primary user detection information, hop information, report information and backup channel information.

6. The method of claim 1 wherein the packet is a request to quiet packet, the request to quiet packet comprising information associated with a quiet period to begin at or soon after the reception of the request to quiet packet.

7. The method of claim 6, wherein the request to quiet packet is transmitted by a node in response to sensing a signal that might represent a primary user.

8. The method of claim 6 further wherein the start time and duration for the quiet period avoids overlapping with quiet periods in one or more channels of the radio spectrum.

9. The method of claim 6, wherein the request to quiet packet is broadcast to at least one other node over multiple hops.

10. The method of claim 1 further comprising: starting a quiet period; sensing for a primary user; and transmitting results of sensing for a primary user onto the network.

11. The method of claim 10 wherein the results comprises the results of the sensing of at least one quiet period.

12. The method of claim 1, wherein the packet is a periodically broadcast control packet.

13. A spectrum agile device comprising: a spectrum agile communication module, the communication module being operable to transmit and receive data over spectrum not being used by a primary user; a processor, the processor being operable to initiate a quiet period on at least one channel of a spectrum agile radio network based on quiet period information received from a packet transmitted on the spectrum agile network; and a sensing module, the sensing module being operable to detect a primary user on at least one channel of the spectrum agile network.

14. The device of claim 12 wherein the processor is further operable to schedule at least one quiet period based on the quiet period information.

15. The device of claim 13, wherein the device schedules its at least one quiet period to avoid overlapping quiet periods between other channels.

16. The device of claim 12 wherein the device can detect a situation requiring a quiet period, and in response to the detection, wherein the packet is a request to quiet packet, the request to quiet packet comprising a duration of a quiet period to begin at or soon after the reception of the request to quiet packet.

17. A spectrum agile radio system comprising: a primary user; and a spectrum agile user, the spectrum agile user comprising, a spectrum agile communication module, the communication module being operable to transmit and receive data over spectrum not being used by a primary user, a processor, the processor being operable to initiate a quiet period on at least one channel of a spectrum agile radio network based on quiet period information received from a packet transmitted on the spectrum agile network, and a sensing module, the sensing module being operable to detect a primary user on at least one channel of the spectrum agile network.

18. The system of claim 16 wherein the processor is further operable to schedule at least one quiet period based on the quiet period information.

19. The system of claim 16, wherein the spectrum agile user schedules its at least one quiet period to avoid overlapping quiet periods between other channels.

20. The system of claim 16 wherein the spectrum agile user can detect a situation requiring a quiet period, and in response to the detection, wherein the packet is a request to quiet packet, the request to quiet packet comprising a duration of a quiet period to begin at or soon after the reception of the request to quiet packet.