Coordination of silent periods for dynamic spectrum manager (DSM)

A method for use in a Dynamic Spectrum Manager (DSM) for coordinating asynchronous silent periods in a network, the method comprising detecting a primary user in the network, transmitting a Silent Period Start Control Message to one or more cognitive radio (CR) nodes in the network, wherein the message indicates the start and duration of a silent period and initiates spectrum sensing, receiving a Measurement Report Control Message from the one or more CR nodes in the network indicating results of spectrum sensing, and transmitting a message to the one or more CR nodes, wherein the message instructs the one or more CR nodes to move to a different frequency based on the spectrum sensing results.

BACKGROUND

The need for higher bandwidth efficiency for emerging networking technologies and the fact that today's licensed bandwidth is inefficiently utilized has lead to the development of technologies in cognitive radios (CR). A CR-enabled device is able to communicate on bands licensed to other devices by performing a spectrum sensing operation to find available spectrum at a particular instant and using the available spectrum at times where it may not be occupied by the primary user. In order to ensure that CR networks may coexist with current licensed technologies, CR devices may require a high degree of agility, (ability to quickly detect the presence of a primary user and react to the arrival of a primary user), in order to sense the arrival of a primary user on a band and to move to another available band without causing interference to the primary user.

Cooperative spectrum sensing may be used to decrease the sensitivity requirements of the spectrum sensing algorithm for a CR node which may be in a deep fading environment. In the most traditional form of cooperative spectrum sensing, a set of CR nodes may perform spectrum sensing simultaneously and transmit the individual results to a central node to determine the spectrum availability. This requires a method for coordinating and exchanging the spectrum sensing between users.

The simplest form of spectrum sensing algorithm may be the category of energy detection. This category of algorithms detects the presence or absence of a primary user by a measure of the energy detected on the particular band of interest. The simplicity of this form of spectrum sensing makes it highly attractive for the CR application. For example, the IEEE 802.22 standard for wireless regional area networks (WRANs) made energy detection using white spaces in the TV spectrum one of the accepted spectrum sensing techniques. A major challenge using energy detection for the CR device is to distinguish between a primary user transmission and another CR device transmission when performing the spectrum sensing. In addition, for cost reasons, a CR device may contain only one receiver and may not be able to perform spectrum sensing simultaneously with normal transmit (TX) receive (RX) operations. The resulting scenario where many CR devices form an ad-hoc or CR network and may coexist, spectrum sensing periods for each of these nodes need to be coordinated in time to ensure that the spectrum sensing is performed when no other CR nodes in the vicinity are transmitting. This leads to what is called a silent period for spectrum sensing.

The use of silent measurement periods in a network was explored for wireless access points (AP) needing to perform measurements on an allowable channel set. This previous work does not address the needs of a CR network trying to perform spectrum sensing in an environment with different primary users using differing wireless technologies. For example, the silent measurement period (SMP) requested by an AP may only be initiated when the communication medium becomes available, which may not address the agility requirements of a CR device. The CR device may react to the arrival of a primary user by switching to an unused band in a limited delay not to incur any interference to the primary user.

For example, the IEEE 802.22 draft standard requires an evacuation time of two seconds. This is the time required for a secondary user to leave the currently used band following the arrival of a licensed primary user to that band. Typically, periodic spectrum sensing periods have been considered, which require the CR nodes to perform spectrum sensing at least every two seconds to be able to achieve the required evacuation time. In general, periodic spectrum sensing may result in higher overhead in the CR node due to context switching, maintaining of buffers and real-time traffic during the spectrum sensing times. As a result, short spectrum sensing periods are highly undesirable from an efficiency perspective. Accordingly a method for coordinating silent periods for spectrum sensing in a CR network is needed.

SUMMARY

A method for use in a Dynamic Spectrum Manager (DSM) for coordinating asynchronous silent periods in a network, the method comprising detecting a primary user in the network, transmitting a Silent Period Start Control Message to one or more cognitive radio (CR) nodes in the network, wherein the message indicates the start and duration of a silent period and initiates spectrum sensing, receiving a Measurement Report Control Message from the one or more CR nodes in the network indicating results of spectrum sensing, and transmitting a message to the one or more CR nodes, wherein the message instructs the one or more CR nodes to move to a different frequency based on the spectrum sensing results.

DETAILED DESCRIPTION

The serving gateway144may also be connected to the PDN gateway146, which may provide the WTRUs102a,102b,102cwith access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs102a,102b,102cand IP-enabled devices.

A method for coordinating silent periods for spectrum sensing in a cognitive radio (CR) network may allow for the continuous collection of spectrum utilization information by a centralized management entity. The method may also allow a CR device that is pre-empted by a primary user to quickly move to an unused band of frequencies without causing interference to the primary user arriving on that band. The coordination method may also stress efficiency in the CR node in order to minimize the complexity of context switching and real-time traffic management that may be a consequence of silent periods in the CR nodes.

The CR network includes one or more CR nodes that may communicate over a licensed band of one or more primary users using a wireless link. The CR nodes may be configured to periodically perform spectrum sensing on the licensed bands to detect the presence of a primary user and gain knowledge of the available spectrum for use in direct links between nodes.

In order to perform silent period coordination for the CR nodes, a centralized controller may be used as a Dynamic Spectrum Manager (DSM). The DSM may be configured to dynamically allocate bandwidth from the licensed band to CR nodes for the creation of a direct link. Further, the DSM may be responsible for scheduling the silent periods for spectrum sensing in each of the CR nodes in its management area, and collecting the sensed information in order to determine the available bandwidth that may be used by CR nodes. The DSM may be a specialized node such as an AP, in a Home enhanced-Node B (H(e)NB), or may itself be a CR node that is selected as a cluster or management area head to perform specialized DSM tasks. The DSM and the CR nodes in the CR network may use a licensed band or an unlicensed band for exchange of data and control information.

FIG. 2illustrates a CR node network200that may be portioned (cellularized) into small localized regions or cells201,202, and203. Each cell coordinates its own localized measurement intervals. However, CR nodes204A not in the middle of a particular cell201will interfere with measurements in adjacent cells221and203.FIG. 2illustrates a need for coordinating quieting intervals locally in a way that a DSM205(for example) can be enabled to coordinate quieting intervals for all CR nodes204and204A that it may interfere with, but without undue interruption to a CR node's204A ability to transmit.

FIG. 3is an example of basic quiet interval scheduling protocols.FIG. 3shows a requestor DSM301and a respondent DSM302. The requestor DSM301may determine that a spectrum management needs to be scheduled and may transmit a quiet interval request to all known neighbors (303). The respondent DSM302may respond to the request with either Accept or Reject in a quiet interval response (304). If the request is accepted by at least a “sufficient” number, percentage, or type of respondent DSMs302, the requestor DSM301may schedule a quiet interval by transmitting a quiet interval confirm message (305). The requestor DSM301may optionally transmit a list of other respondent DSM302who accepted the request. This may allow some of the respondent DSMs302to schedule their own measurements at the same time if they determine that their own spectrum will be sufficiently quiet. The issue of “sufficiency” in the acceptance of respondent DSMs302may be of critical importance.

A state machine may be defined for each respondent DSM302in order to be more responsive to the needs of a respondent DSM302. For example, the state machine may be used to determine whether a respondent DSM302needs to make a measurement, whether a respondent DSM302has been requested to support a particular quieting interval, or whether a respondent DSM's302need to make a measurement has been satisfied, etc.

A CR node may be in one of four (4) states, as shown inFIG. 4, which shows a state transition diagram. In a first state (NO_REQ), the CR node may either not need to make a measurement or its measurement needs may be satisfied and therefore may have made no requests for a measurement. Additionally, the CR node may have received no request for quieting. This is equivalent of an “idle” state in this process. In a second state (REQ_OUT/REQ_IN), the CR node may have an outstanding measurement request and it may have received a request itself. In a third state (REQ_OUT/no_REQ_IN), the CR node may have an outstanding measurement request, however, it may have received no requests itself. In a fourth state (no_REQ_OUT/REQ_IN), the CR node may have no outstanding measurement requests. The CR node may not require a measurement or the CR node may have received a request itself.

FIG. 4provides further detail on additional messaging needed beyond the approach shown inFIG. 3. FromFIG. 4several observations may be made on operation of each requestor DSM301.

When a requestor DSM301receives a request for a quieting, (REQ message), it may transition, (or stay in), either the NO_REQ_OUT/REQ_IN402or REQ_OUT/REQ_IN state401.

Transmission of a negative response to a request (RESP_NACK) or reception of a cancellation of a request (REQ_CANCEL) may result in a transition to NO_REQ403or REQ_OUT/NO_REQ_IN state404.

Acceptance of a request, which results in a transmission of RESP_ACK message, may keep the node in either the NO_REQ_OUT/REQ_IN402or REQ_OUT/REQ_IN401state.

The following transitions, REQ_OUT/NO_REQ_IN404to NO_REQ403and REQ_OUT/REQ_IN401to NO_REQ_OUT/REQ_IN402may indicate a resolution of a request transmitted by a respondent DSM302. This may happen in one of a number of ways. For example, a node may determine to cancel the request, (transmitting a REQ_CANCEL message). This may happen for a number of reasons, such as a reception of a sufficiently large number of NACKs for the request to be declined, a decision to use another quieting interval, (i.e. one initially scheduled by another respondent DSM302), and a time-out of the request. In another example, a node may have received a sufficient number of ACK responses and may have transmitted a REQ_CONFIRM message confirming the measurement period.

Based on the specific demands and configuration of each system, the basic protocol described above may be modified in a number of ways. For example, the protocol described above may result in significant overhead and delay if the number of nodes in a network is large. This may be addressed by adding a Scheduling Service Node (SSN). The SSN node may facilitate communication between the requestor DSM and the one or more respondent DSM in the network. In particular, the basic protocol ofFIG. 3is preserved. However, the Quiet Interval Request message may be transmitted to the SSN first which then forwards the Quiet Interval Request message to the respondent DSM. The respondent DSM may also respond to the SSN which may forward all the responses to the requestor DSM and may then forward the Confirm message back to the respondent DSM.

The SSN, however, may take a more productive role in the process. Instead of just acting as the neighbor database and message relay, it may take on the role of a quiet interval scheduler. The resulting embodiment is shown inFIG. 5.

FIG. 5shows an example of an enhanced protocol with the SSN acting as a scheduler for quiet intervals. In this embodiment, the requestor DSM501transmits a scheduling request to the SSN502(504). The SSN502may transmit a timing request to all of the requestor DSM's neighbors, (respondent DSM503) (505). Such respondent DSM503may accept or reject such request from the SSN502(506). Based on the accept/reject responses, the SSN502may attempt another time-resulting in several rounds of the Quiet Interval Timing Request/Response exchanges between the SSN502and a plurality of respondent DSM503(506) Assuming that a successful quieting time is eventually found, the SSN502may issue a scheduling response to the requestor DSM501(507). At the same time, the SSN502may notify certain respondent DSM503that may also benefit from this quiet interval that a measurement opportunity will be available to them as well (508).

This approach offers a number of benefits over the baseline approach without an SSN. For example, a lower backhaul/side channel communication load, as the scheduling handshakes are now only between an SSN and respondent DSM and not the requestor DSM and respondent DSM. Another benefit is lower processing/memory load on terminals which may no longer need to be aware of network topology, their neighbors, etc. This is especially important in networks where mobility is present. A further benefit is the ability of the SSN to coordinate the scheduling of quiet intervals so that more than one requestor DSM is granted the same interval, thus reducing the overall number of quiet intervals and increasing efficiency of the network.

The SSN may also assume the role of quiet interval controller, whereby it may periodically attempt to schedule quiet intervals autonomously, (e.g. without a request), for the benefit of a group of terminals which are then provided measurement opportunities. In this case, the SSN-respondent DSM exchange described inFIG. 5is used, but the messaging between the requestor DSM and the SSN may no longer be needed.

There are several information elements that may need to be present in the messages. The following messages have been previously defined: REQ, (request for a quiet interval for messages), RESP_ACK, (response to a request acknowledging the request, for example agreeing to it), RESP_NACK, (response to a request declining it), REQ_CANCEL, (cancellation of a request), and REQ_CONFIRM, (confirmation that a request is being “locked”). Each one of these messages may contain the following elements which are used for identification, synchronization, and decision making, such as requestor DSM/respondent DSM ID, request ID, (to differentiate different requests), request/response network time, requestor DSM/respondent DSM geo-location, and respondent DSM maximal transmit power.

A request for quieting requires a sufficient number of positive acknowledgement (ACK) responses for the requestor DSM to schedule a quiet interval. The central issue is how many ACK responses are sufficient. The goal of quieting is to eliminate emissions from primary users to a level sufficiently below the required sensing threshold so that sensing can be performed. In a network where the number and location of non-primary users is fairly well-known, a first approach for determining sufficiency may be done by counting the number of responses. Counting the number of responses can be performed most efficiently by the SSN.

A different approach may be to ignore all the NACK responses from respondent DSM whose location and transmit power are such that their emissions are below the sensing threshold. Thus, the respondent DSM's maximal transmit power and geo-location, may enable this approach. Conversely, the requestor DSM's geo-location may allow a device to decline a request without causing disruption because it knows that its transmit power is too low to impact the measurement. Finally, this may support partial quieting, where devices, having accepted a request (ACK'ed it) reduce their transmit power below the level it impacts the measurement at the requestor DSM, while maintaining some connectivity.

FIG. 6illustrates an example scenario for silent period coordination within a particular cell. The system may consist of a set of CR nodes601which want to establish direct links between each other. The set of CR nodes601may employ the bandwidth allocated by the centralized DSM602, which is also responsible for coordinating the silent periods required for spectrum sensing on the bands actively used by the direct links.

In the example shown inFIG. 6, although the links between the DSM and the CR nodes, as well as the direct links between CR nodes are shown to utilize 802.11-based MAC/PHY, the methods described herein are independent of the MAC/PHY used for this connection. Therefore, this connection could potentially use a different MAC/PHY such as for a cellular system.

Several, or all, of the CR nodes may first perform spectrum sensing simultaneously during periodically occurring silent periods. The DSM may be responsible for configuring the length and frequency of the periodic silent periods, and the band over which each CR node may perform spectrum sensing during each silent period. Periodic silent periods may be scheduled at a frequency in which maximum quality of service for the CR nodes may be maintained. The use of periodic silent periods may also allow the DSM to maintain a dynamic map of the licensed bandwidth which may be currently utilized or free at a particular period of time. As a result, the CR network may maintain a minimum level of knowledge concerning the available bands and some degree of agility to the arrival of primary users on the bands that may be occupied by CR nodes.

In addition to periodic silent periods, the DSM may schedule asynchronous silent periods to perform immediate spectrum sensing, thus improving the network's agility. The silent periods may be triggered by either the DSM itself, based on information about a primary user that may be available from other networks, or by an event triggered by any of the CR nodes that may be currently using a licensed band. The use of asynchronous silent periods may give the CR network the agility to have CR nodes vacate the licensed bands within a shorter amount of time than with periodic silent periods. Further, the asynchronous silent periods may allow the CR network to make use of information about the primary user in a more timely fashion. Information about the primary user may be in the form of a change in the environment or a priori information about the primary user. The change in the environment may be detected by any of the CR nodes. The DSM may have available the priori information from the primary user network itself.

In the case where the arrival of a primary user on a specific band may be sensed by a change in the environment, one or more of the CR nodes may be actively using the band in question and may be able to sense the change in the environment through a local change in current key parameters associated with the active link. The parameters may be, but are not limited to, the channel quality, link throughput, number of retransmissions, and the like.

Although a change in any of the parameters may indicate the arrival of a primary user, an asynchronous silent period for spectrum sensing may be triggered to immediately determine whether a primary user may be present, and may have accurate, up to date information about the available bands following this change in environment. An asynchronous silent period may also be extended by the DSM in the case where the reliability of the decision obtained from spectrum sensing a single silent period is insufficient to determine the presence of a primary user and to suggest moving the primary user to alternate bands being pre-empted by the CR node.

A change in the environment may include using interference cancellation or any other means for the actual transmitted signal to detect a change in the environment. The sensor for the change in environment may be part of the same node that does the transmission. The sensor may also be a separate entity, protocol layer, or algorithm which communicates with the spectrum sensing entity.

The scheduling of silent periods may be enabled through the use of a thin DSM protocol layer. This protocol layer may be an L2.5 or L3 entity that is independent of the RAT or PHY used by the network. The use of the thin DSM protocol layer allows for a DSM protocol layer on a network with devices having different RATs.FIGS. 7 and 8illustrate the placement of this DSM layer in an 802.11-based network (FIG. 7) and a cellular-based network (FIG. 8).

FIG. 7shows an example of a DSM layer in an 802.11-based protocol stack. InFIG. 7, the DSM layer702is shown adjacent to the MAC sublayer703in the 802.11 protocol stack701.FIG. 8illustrates an example of a DSM layer in a cellular-based protocol. InFIG. 8, the functionality of the DSM layer802may also be incorporated into an existing management layer803in a cellular-based protocol stack801as well. Examples of existing management layers which could incorporate this functionality is 802.11 or 802.16 management frames, Zigbee (for management of 802.15.4 MAC/PHY devices), or RRC (for cellular networks). The main functions of the DSM layer may be to create and interpret Silent Period and Sensing Control Messages in order to coordinate silent periods used for measurement and detection of potential primary users on the licensed band being utilized by the DSM-managed network, to determine the appropriate times to trigger silent periods, and to configure the appropriate spectrum sensing operations by the PHY and notify the PHY when spectrum sensing may take place.

The thin DSM protocol layer defines a set of control messages which may be used to enable silent period handling. There are four control messages: Silent Period Start Control Message, Silent Period Trigger Control Message, Measurement Report Control Message, and Sensing Configuration Control Message.

The Silent Period Start Control Message may be transmitted by the DSM node to one or more CR nodes in the network. This message may be addressed to a subset of nodes under the management of the DSM based on the location of these nodes. This location information may be maintained by the DSM entity through appropriate MAC-layer procedures.

The Silent Period Trigger Control Message may be transmitted by any CR node in the network that is communicating with the DSM. The message may be addressed to the DSM to which the particular CR node is registered.

The Measurement Report Control Message may be transmitted by the CR that has been instructed to perform spectrum sensing during the silent period. This message may be transmitted to the DSM, which may make a decision concerning the presence or absence of another network or primary user based on the measurement results.

The Sensing Configuration Control Messages may be transmitted by the DSM to configure spectrum sensing to be performed by each CR node.

These messages may be carried by the underlying MAC layer with a higher priority than normal data. These messages may also be transmitted using MAC layer management frames. The DSM may periodically transmit a Silent Period Coordination Message to all of the CR nodes to trigger a system-wide silent period during which spectrum sensing may be performed. In steady state operation, silent periods may occur periodically or sporadically. Further the silent periods may be interspaced with periods where the CR nodes perform regular TX (transmit) and RX (receive) operations. The duration and frequency of the silent periods may be controlled by the DSM and communicated to all the CR nodes using the Silent Period Start Control Message. As a result, depending on the current use in the system of the utilized channels, the DSM may determine the frequency associated with the Silent Period Start Control Message.

Silent Period Control Messages may also be transmitted to a subset of CR nodes which are located in a certain location or which are utilizing a certain bandwidth, illustrated inFIGS. 9 and 10.FIG. 9shows an example of localized multicast silent period start messages for a first case. InFIG. 9, CR nodes902and903are outside of the range of CR nodes904and905. The DSM901may transmit a Silent Period Start Control Message907addressed only to nodes904and905. When nodes904and905receive this message, the nodes904and905immediately stop transmitting and instruct their PHY layer to perform spectrum sensing of the bandwidth that the nodes904and905are currently using. Transmission906from nodes902and903occurring on the same frequency as the spectrum sensing do not affect the spectrum sensing results, as these nodes are outside the range of nodes904and905.

FIG. 10shows an example of localized multicast silent period start messages for a second case. InFIG. 10, nodes1002and1003are transmitting1008on a frequency that is different than nodes1004and1005. At time t1, the DSM1001transmits a Silent Period Start Control Message1006to nodes1004and1005to start spectrum sensing on the frequency currently utilized by these two nodes. At time t2, the DSM1001transmits a Silent Period Start Control Message1007to nodes1002and1003. These silent periods are repeated periodically with the period determined by the DSM1001.

Asynchronous silent periods may be triggered in two ways to enable a better response to a change of environment. In a first case, an external network may notify the DSM of the presence of a primary user, or other information, such as history, which may be used by the DSM to predict the possible presence of a primary user on a specific band. In this case, the DSM itself may schedule an asynchronous silent period without the inputs of any of the CR nodes.

Asynchronous silent periods may also be triggered by an event created in any of the CR nodes actively using a link on one of the licensed bands. This event may result from a change in the environment on that link. Asynchronous silent periods triggered by an external network, or by the DSM itself, are treated in the same fashion as those triggered by a CR node event.

The procedure for a CR node triggering the asynchronous silent period may include a CR node in the network detecting a change in environment. This change may be detected at the CR node by the PHY or MAC layers, or may be an event that is specific to the DSM layer itself, (e.g. the detection of a new node which joins the network). After this occurs, the CR node may transmit a Silent Period Trigger Message to the DSM. The Silent Period Trigger Message may contain the cause or reason for the event trigger.

The DSM may determine the necessity of triggering an immediate asynchronous silent period based on the CR node from which the Silent Period Trigger Message was received, as well as the information associated with this message. The DSM may then determine which CR nodes may be silenced during the silent period. This decision may be based on the frequency band on which spectrum sensing may be performed, and the nodes which are in close proximity of the CR node that generated the Silent Period Trigger Message. The DSM may make use of position information, which it stores in a local position database, in order to determine the interference range of each of the CR nodes, and from that, the nodes which may receive the Silent Period Start Control Message.

A CR node that generates a Silent Period Trigger Message may continue normal TX/RX operations until it receives a Silent Period Start Control Message. The Silent Period Start Control Message may indicate the starting time and the duration of the silent period. During the silent period, all nodes which have been addressed by the Silent Period Start Control Message may interrupt any transmission which was ongoing. In addition, messages which were scheduled for transmission may be buffered by these CR nodes until the end of the silent period.

During the silent period, spectrum sensing may be performed by the nodes associated as spectrum sensing nodes for a particular spectrum sensing entity. A spectrum sensing entity may be created or modified using a Sensing Configuration Control Message. The control message may be transmitted to the CR node which may be asked to perform spectrum sensing on a particular frequency, and may inform the CR node of the spectrum sensing entity identifier that it is associated with. A CR node may be associated with multiple spectrum sensing entities, in which case it may be called on as the node to perform spectrum sensing on multiple frequencies, for instance. In addition, multiple CR nodes may be associated with the same spectrum sensing entity identifier, which enables having the same DSM collect spectrum sensing results from multiple nodes to enable sensor fusion.

The DSM may become aware of the spectrum sensing capabilities of each device during the device's initial association. At any time, for example following association of a node or following the start of a high bandwidth link between two CR nodes, the DSM can create a spectrum sensing entity and attach a set of sensory nodes to it. A separate spectrum sensing configure message, containing the unique identifier of the spectrum sensing entity, may be transmitted to each of the nodes attached to a spectrum sensing entity. The Sensing Configuration Message may also contain configuration that is specific to the CR node in question with regards to the spectrum sensing. When a Silent Period Start Control Message is transmitted, it may contain the unique identifiers of the spectrum sensing configuration entities that may be activated within the coming silent period. The CR nodes receiving the Silent Period Start Control Message, which have been asked to perform spectrum sensing associated with the spectrum sensing entity identifier contained in the Silent Period Start Control Message, may be responsible for performing spectrum sensing and transmitting the results to the DSM at the end of the silent period.

FIGS. 11A and 11Billustrate an example of the procedure described above, (a call flow for asynchronous silent periods), and each of the actions involved in triggering an asynchronous silent period.

In this example, the silent period may be triggered locally between CR node1102and CR node1103due to interference, range, or frequency use. A direct link between nodes1102(Node A) and1103(Node B) and between nodes1104(Node C) and1105(Node D) may have been previously established (1106). The DSM1101may determine from position database or frequency use to create localized silent periods for nodes1102and1103and nodes1104and1105(1107). A Sensing Configuration Control message may be transmitted from the DSM1101to node1102with an identification of i (1108). A Sensing Configuration Control message may be transmitted from the DSM1101to node1104with an identification of j (1109). A Silent Period Trigger Control Message may be transmitted from node1103to the DSM1101(1110). The DSM1101may examine cause and location and determine to start an asynchronous silent period (1111). A Silent Period Start Control Message may be transmitted from the DSM1101to node1102and from node1102to node1103with an identification of i and a duration of t (1112). Node1102may only be configured for spectrum sensing on an entity with an identification of1(1113), may perform spectrum sensing on frequency range1(1114), and may perform spectrum sensing on frequency range N (1115); all of which occur during the silent period duration t. Node1102may transmit a Measurement Report Control Message to the DSM1101(1116). The DSM1101may instruct nodes1102and1103to reconfigure link on a different frequency based on spectrum sensing results (1117). The DSM1101may begin the next planned period silent period for nodes1102and1103(1118). A Silent Period Start Control Message may be transmitted from the DSM1101to node1102and from node1102to node1103(1119).

The occurrence of an asynchronous silent period may move the timing of a normal periodic silent period. For example, if an asynchronous silent period eliminates the need for a scheduled or immediately upcoming periodic silent period, the DSM may choose to cancel the upcoming silent period or reschedule the timing of the periodic silent period accordingly.

In another embodiment, the DSM Silent Period Control Messages use 802.11 Management Frames, where the DSM layer may lie above the MAC sublayer in the protocol stack ofFIG. 7.FIG. 12shows the format of an 802.11 management frame. The frame body1201may contain an identifier1202for the type of frame, (Silent Period Start Control Message, Silent Period Trigger Control Message, Measurement Report Control Message, or Sensing Configuration Control Message), as well as the information needed for each message.

FIG. 13illustrates each of the sensing configuration message management frames described above. Each message is identified with a unique control code field. As inFIG. 12, the frame body1301may contain an identifier1302for the type of frame. The Silent Period Start Control Message1303may contain a field for the duration1304, in number of beacon periods, of the silent period and the spectrum sensing entity IDs1305for each spectrum sensing operation to be performed during the silent period. When a node was previously configured to perform spectrum sensing for the spectrum sensing entity associated with an ID received in this message, the node may perform spectrum sensing during this silent period. Since multiple spectrum sensing operations may be performed on a specific silent period, for example over different frequency ranges, the Silent Period Start Control Message1303may activate multiple spectrum sensing entity IDs1305. The Silent Period Trigger Control Message1306may contain a field for the reason in which the silent period was triggered1307. This field may identify the protocol layer or mechanism that caused the message to be transmitted by the CR node in question. An example where a Silent Period Trigger Control Message is transmitted as a result of a PHY/MAC measurement exceeding a specific value is described below. Finally, the Measurement Report Control Message1308and the Sensing Configuration Control Message1309may both be associated with a particular Sensing Entity identifier1310and contain this identifier as a field in the management frame. Each spectrum sensing entity may be associated with one or more contiguous or non-contiguous frequency ranges to be sensed. The type of spectrum sensing to be performed on each frequency range, as well as the parameters for this spectrum sensing1312, may be transmitted using the corresponding field in the Sensing Configuration Control Message1309. The format for the spectrum sensing results of each frequency range1311may be specified in a separate field in the Measurement Report Control Message1308.

Asynchronous silent periods may also be triggered by CR nodes based on their traffic utilization over a particular frequency. If a node involved in a direct link may be in a sleep or dormant mode for a particular amount of time, or the direct link has no data to transmit for a fixed period of time, the CR node may notify the DSM using a Silent Period Trigger Control Message with the Trigger Reason set to ‘sleep’. The DSM may observe the messages received by each CR node and determine whether an opportunity exists to perform spectrum sensing. This same procedure may be used when a node detects a lower than normal amount of traffic occurring for a fixed amount of time on the direct link in question. In either case, the result may be the scheduling of a silent measurement period at a strategic time which maximizes efficiency. The presence of these asynchronous silent periods may then allow the DSM to reduce the frequency of periodic silent periods.

FIG. 14is an example event triggering presented based on a MAC-layer channel quality indication (CQI). The MAC-layer CQI may be defined as the number of packet retransmission or MAC-layer errors observed on a particular channel. Event configurations and event reports are handled by the DSM Layer of the DSM and the CR node respectively, with help of the MAC layer to provide the measurement associated with the event. The DSM Layer of the DSM node1401may transmit an event configuration message1403to each of the CR nodes1402to configure the event to be monitored by the CR node1402during its active link with another CR node1402. This event configuration message can be encapsulated in the Sensing Configuration Control Message described above. Events may also be monitored by CR nodes1402which are not actively in a link connection, depending on the type of measurement associated with the event. The Sensing Configuration Control Message may be transmitted through the distinct control channel to each CR node1402involved in event monitoring. The MAC layer of the CR node may then be instructed to monitor the CQI of the channel1404as defined above. The MAC layer of all CR nodes in an active link connection that may have received the event configuration message may periodically transmit channel quality measurements1405to its DSM Layer which may further process or filter them based on event configuration.

Filtering may be performed in order to avoid frequent event triggering and unnecessary spectrum sensing periods. This may be achieved by the introduction of a Time-to-Trigger (TTT), in which the channel quality may be below a certain amount for a minimum amount of time (the TTT) in order for the event to be triggered by the DSM Layer filtering logic. Once the even is triggered, the DSM Layer of the CR node1402may transmit an event report1406via the Silent Period Trigger Control Message to notify the DSM1401of the occurrence of the event and the CR node1002where the event occurred.

FIG. 14illustrates the DSM-Layer signaling and DSM-MAC layer interaction required for configuring and reporting a DSM-related event in the case of a generic protocol stack with a MAC, LLC, and DSM layer. This same message flow may apply to an 802-based system, where the DSM layer may be incorporated into the 802-based management frames, and may also be applied to a cellular protocol stack, where the messages could be transmitted at the RRC layer. Without loss of generality, Event A is triggered where the measured channel quality of a link between two CR nodes drops by a certain amount relative to its long-term average, and the measurements transmitted from the MAC to the DSM entity may be the channel quality indicator (CQI) measurements.

The arrival of a primary user on a licensed band currently being used by a CR node may result in a large amount of interference on this band, which may be detected immediately by a CR node due to a change in the number of MAC-layer errors or retransmissions. In addition, if a primary user begins to use a neighboring band, a certain amount of interference may be detectable in the band currently used by the CR node in question through a drop in the CQI. In either case, the DSM may have knowledge of the presence of the primary user in order to update its database of available frequencies and to reallocate CR users that were occupying the licensed band of interest to a different band.

FIG. 15shows the DSM filtering of CQI measurements received from the MAC layer. The CR node may notify the DSM of a detected change in the environment. Each CR node may maintain the average CQI (CQIAVG) measured on a particular link over a time span W in the recent past, and the instantaneous CQI (CQIINST) measured using the reference signals over the last time span of M. If the drop in CQI (CQIAVG-CQIINST) remains larger than some threshold D for a particular time to trigger (TTT), the CR node may generate an Event A.

The values of D, M, TTT, and W may be entirely dictated by the DSM through the Event A configuration (RRC) message. This message, which may be transmitted in a unicast fashion on the distinct control channel prior to and during link establishment, may carry these parameters and allow the DSM to dynamically change them in order to optimize the spectrum utilization. In particular, the DSM could change these values based on the following probability requirements, which are easily monitored using past statistical results.

The first probability requirement is the probability of triggering Event A when a primary user arrives on a band currently utilized by a CR node and should be greater than x %. The second requirement is the probability of triggering Event A when a primary user arrives on a band neighboring the band utilized by a CR node and should be greater than y %. The third is the false alarm probability of triggering Event A when no primary user arrival occurs and should be below z %.

The value of x should be selected as close to 100% as possible, while the value of z may be as close as possible to 0%. The value of y may depend on the frequency of periodic spectrum sensing periods used by the DSM. For instance, a low frequency periodic spectrum sensing period may require y to be relatively large so that available spectrum opportunities, in bands other than those currently utilized by the CR node under the DSM management area, may be tracked by the DSM using asynchronous silent periods. The number of CR nodes in the management area may also be a factor that may determine the value of y.

Triggered Event A's may be transmitted to the DSM through the distinct control channel via event reports. Once the DSM receives an Event A from a CR node within its management area, it may transmit out a Silent Period Start Control Message on the distinct control channel to schedule an asynchronous silent period.

In order to improve the robustness of the system and reduce the latency in signaling of the silent period, the control messages could be transmitted on a control channel which may be on a distinct frequency from the normal data that is transmitted between the DSM and the CR nodes. The control channel consists of wireless channels residing on a dedicated frequency utilized by the CR network. This frequency may be reserved for the CR network, or may be shared with other primary users. In the later case, multiple possible frequencies can be defined for the control channels and an underlay approach, where control channel information is transmitted at low power, may be used if all possible frequencies are occupied.

As an example, the DSM functionality may reside in an 802.11 AP with multiple frequency channel functionality. The distinct control channel may continue to use an 802.11-based MAC/PHY, but for transmission of only management frames and data required for Silent Period Control Messages and other spectrum sensing related information. An upper MAC layer introduced on top of the MAC sublayer may be introduced in order to route Silent Period Control Messages onto the 802.11-based control channel, while any other messages from the upper layer are routed over the data channel.

Another option for the distinct control channel may be where the control messages described are replaced by a PHY-layer control channel instead. This assumes the presence of a synchronization channel which may synchronize all CR nodes to a common time base. A downlink channel may be used for communicating control information from the DSM to the CR nodes. An uplink control channel may be used for transmitting spectrum sensing results and events from the CR nodes to the DSM.

In steady state operation, silent periods occur periodically and sporadically and are interspaced with periods where the CR nodes may perform regular TX and RX operations. The duration and frequency of occurrence of the silent periods may be controlled by the DSM and communicated to all the CR nodes using a special field in the downlink control channel periodic spectrum sensing control message (PSCM). All CR nodes may know when to read the downlink control channel to receive PSCM, as the timing of messages on the downlink control channel for all CR nodes is established through the synchronization channel. The following quantities may be read from the PSCM as illustrated inFIG. 16: TP, TS, TO, TD1, and TD2. TPis the repetition period in frames of the silent period pattern. TSis the starting frame, relative to frame0in a mod N frame numbering scheme, of the first silent period of the silent period patter. To is the offset between the first and second silent period in the silent period pattern. TD1and TD2are the duration of the silent periods1601in the pattern. The remaining time1602the CR nodes may perform regular TX/RX operations.

For a cellular-type system, (and similarly for a WiFi-based system), event configurations and event reports may be handled by the RRC layers of the DSM1701and the CR node1702respectively, with help of the PHY layer to provide the measurement associated with the event as illustrated inFIG. 17. The RRC-DSM1701may transmit an event configuration message1703to each of the RRC-CR1702to configure the event to be monitored by the CR node1702during its active link with another CR node1702. Events can also be monitored by CR nodes1702which are not actively in a link connection, depending on the type of measurement associated with the event. The event configuration message may be transmitted through the downlink control channel to each CR node1702involved in event monitoring. The PHY layer of the CR node1702will then be instructed to monitor the PHY layer quantity1704related to the configured event using a measurement message, between RRC and PHY on the CR node1702. The event configuration message requests monitoring of the channel quality associated with a link. The PHY layer of all CR nodes1702in an active link connection that may have received the event configuration message may periodically transmit channel quality measurements1705to its RRC-CR which may further process or filter them based on event configuration. Filtering is performed in order to avoid frequent event triggering and unnecessary spectrum sensing periods. This may be achieved by the introduction of a Time-to-Trigger (TTT), in which the channel quality may be below a certain amount for a minimum amount of time (TTT) in order for the event to be triggered by the RRC filtering logic. Once the event is triggered, the RRC-CR1702transmits an event report1706to the RRC-DSM1701to notify the DSM1701of the occurrence of the event and the CR node1702where the event occurred. This is shown inFIG. 17, where the measurements in this case are PHY-layer CQI measurements.

FIG. 17illustrates the RRC signaling and RRC-PHY layer interaction required for configuring and reporting a DSM-related event in the case where PHY-layer measurements are being made for channel quality. Without loss of generality, Event A is triggered where the measured channel quality of a link between two CR nodes drops by a certain amount relative to its long-term average, and the measurements transmitted from the PHY to the RRC entity may be PHY-layer channel quality indicator (CQI) measurements.

Considering the direct link or channel between two communicating CR nodes, for the purposes of CQI measurement, each transmitting CR node may embed known fixed power reference signals into the data channel. The receiving CR node may use these known reference signals to determine the CQI of the data link used by the transmitting CR node. This same set of reference signals may be transmitted by every CR node that has an active link with another node, thus giving the CR node network as a whole the knowledge of the channel quality of all licensed bands actively used by CR nodes. A different reference signal may be possible for other PHY, such as CDMA (Code Division Multiple Access), etc.

InFIG. 18, triggered Event A's may be transmitted to the DSM1801through the uplink control channel via event reports (1803). Once the DSM1801receives an Event A from a CR node1802within its management area, it may transmit out a silent period message on the downlink control channel to schedule an asynchronous silent period at a specific time and for a specific duration, specified in the message itself (1804). The start of the silent period may occur after any of the following delays: t1, t2, t3. A propagation delay (t1) to the furthest node in the management area of the DSM may be determined through messaging on the downlink and uplink control channels. A required delay (t2) for a CR node to become quiet may include the delay required to clear PHY buffers. A quieting period (t3) for a data transmission may be transmitted by a CR node just prior to receiving the silent period message.

The start of the silent time may be scheduled at least t1+t2+t3after the transmitting of the silent period message (1805). In addition to this information, the silent period message may contain a field which indicates the behavior that the CR nodes1802may take after they transmit their spectrum sensing results. The CR node1802may perform spectrum sensing over the required silent time (1807). The CR node1802may transmit spectrum sensing results, through the uplink control channel, to the DSM1801(1808). The DSM1801may evaluate the reliability of the spectrum sensing results (1809). The DSM1801may transmit a PHY reconfiguration or silent period message on the downlink control channel (1810). Two possible behaviors may be expected (1811). First, the CR nodes1802may be asked to continue spectrum sensing in order to further refine the results transmitted to the DSM1801, in which case the silent period may be implicitly extended until the next message is received by the DSM1801. Second, the CR node1802may be asked to continue the previously interrupted TX/RX operation until the DSM1801commands another silent period, or reconfigures any CR nodes1802to a different frequency based on the spectrum sensing results.

The system under consideration may be a widely distributed set of CR nodes in a centralized network with multiple central controllers. Every CR node may be associated with one central controller. In such a network, it may be reasonable to assume a dedicated synchronization channel may ensure that all nodes may be slot synchronized with the central controller similar to any slotted Aloha system. It may be assumed that all nodes may be slot synchronized, but may not necessarily be frame synchronized. Additionally, it may be assumed that any pair of nodes actively communicating with each other, called an active pair, may be necessarily frame synchronized.

Moreover, all active pairs may have synchronized quiet periods, that is, both nodes of the active pair may use exactly the same slot(s) within a frame to remain quiet and sense the spectrum. But if there may be N such active pairs, the quiet slot(s) for all the pairs may overlap in time since they are not frame synchronized. Random quiet period within each frame may be used to address the need for having all active pairs of nodes remain quiet simultaneously. A DSM may have knowledge of the quiet period schedule of every active pair in the system. Therefore, a synchronized quiet period may be established with a probability of Pquietnet across the whole network.

For the method of operation, let M denote the number of slots in each frame, and K denote the number of quiet slots per frame where these K slots may be used to sense the spectrum. It is assumed that the K out of M slots may be chosen randomly in every frame in 1 out of CKMways. However, every active pair of nodes may choose the same K quiet slots and hop to a different pattern every frame in a synchronized fashion. The K quiet slots may be different between any two different active pairs.

Now, there may be a finite probability Pquietfor all active nodes to be quiet simultaneously in at least one slot in a frame. This may occur randomly in any frame. For example, if Pquiet=0.3, it may mean that all active nodes remain quiet simultaneously for at least one slot in 3 out of 10 frames on an average. Thus for a given N active pairs at any time instant, the parameters M and K may be chosen such that the nodes remain quiet for a predefined Pquiet>x % of the time.

Referring toFIGS. 19 and 20, all the nodes in the network are commonly aware of such boundaries at which dotted vertical lines indicate slot boundaries. The double-headed arrows indicate the frame duration and the frame number. A high in the square wave indicates a quiet period while the low in the square wave indicates transmit/receive activity. In the examples, K=1, M=6 and N=3. InFIG. 19, every active pair of nodes may remain quiet periodically at the same slot number in each frame. That is, active pair A may remain quiet in the third slot of each frame while active pair B may remain quiet in the second slot of each frame. Since the active pairs may not be frame synchronized with each other, the quiet periods of all active pairs may not overlap simultaneously.

In the example shown inFIG. 20, each active pair synchronously may change the quiet time slot randomly to a different location in every frame, That is, active pair A may have a quiet slot at slot #3of frame #N, at slot #2on frame #N+1, slot #1at frame #N. Active pair B may have a quiet slot at slot #2of frame #N, at slot #4on frame #N+1, slot #2at frame #N. Active pair C may have a quiet slot at slot #5of frame #N, at slot #1on frame #N+1, slot #3at frame #N. Due to the random jump of the quiet period from one frame to another, there may be a finite probability of all active nodes to be quiet in the same slot.

Although the examples use K=1 for random quite intervals, one quiet slot may be used in each frame. Increasing the number of quiet slots in a frame may increase the probability of having all nodes being quiet simultaneously over a span of time. But increasing K may reduce the time for communication. Thus, parameters may be chosen appropriately to ensure an optimal tradeoff between spectrum sensing duration and time for communication.

Embodiments

1. A method for use in a Dynamic Spectrum Manager (DSM) for coordinating periodic silent periods in a network, the method comprising:monitoring bandwidth usage during a predetermined time period

2. The method as embodiment 1, further comprising:configuring a length and a frequency of a periodic silent period; andscheduling the periodic silent period at the configured frequency, wherein
the periodic silent period maintains a maximum quality of service (QoS) for a cognitive radio (CR) node in the network.

3. The method as in any one of embodiments 1-2 wherein the DSM is found in an access point (AP).

4. The method as in any one of embodiments 1-2 wherein the DSM is found in a home enhanced Node-B (H(e)NB).

5. A method for use in a Dynamic Spectrum Manager (DSM) for coordinating asynchronous silent periods in a network, the method comprising:detecting a primary user in the network.

6. The method as in embodiment 5, further comprising:transmitting a Silent Period Start Control Message to one or more cognitive radio (CR) nodes in the network, wherein the message indicates the start and duration of a silent period and initiates spectrum sensing.

7. The method as in embodiment 6, further comprising:receiving a Measurement Report Control Message from the one or more
CR nodes in the network indicating results of spectrum sensing; andtransmitting a message to the one or more CR nodes, wherein the message instructs the one or more CR nodes to move to a different frequency based on the spectrum sensing results.

8. The method as in any one of embodiments 5-7 wherein the DSM is found in an access point (AP).

9. The method as in any one of embodiments 5-7 wherein the DSM is found in a Home enhanced-Node B (H(e)NBB.

10. The method as in any one of embodiments 8-9 wherein the detecting a primary user in the network is based on a channel quality indicator (CQI) measurement.

11. The method as in embodiment 10 wherein the CQI measurement is a measured channel quality of a link between two CR nodes.

12. A method for use in one or more Cognitive Radio (CR) node for coordinating asynchronous silent periods, the method comprising:transmitting a Silent Period Trigger Control Message.

13. The method as in embodiment 12, further comprising:receiving a Silent Period Start Control Message, wherein the message
indicates the start and duration of a silent period and initiates spectrum sensing.

14. The method as in embodiment 13, further comprising:transmitting a Measurement Report Control Message indicating results of
spectrum sensing; andreceiving a message from the DSM, wherein the message instructs the
one or more CR nodes to move to a different frequency based on the spectrum sensing results.

15. The method as in any one of embodiments 12-14 wherein transmitting the Silent Period Trigger Control Message is based on a change in an environment detected by the CR node.

16. The method as in embodiment 15 wherein the change in the environment is detected by the CR node through a local change in key parameters associated with an active link.

17. The method as in embodiment 16 wherein the key parameters include a channel quality, a link throughput, and a number of retransmissions.

18. The method as in any one of embodiments 13-17 wherein the spectrum sensing is extended for a period of time on a condition that the results of the spectrum sensing fail to detect the primary user.

19. A method for use in a Dynamic Spectrum Manager (DSM) for basic quiet interval scheduling in a Cognitive Radio (CR) node network, the method comprising:transmitting a quiet interval request to one or more DSMs in the CR node
network.

20. The method as in embodiment 19, further comprising:receiving a quiet interval response from the one or more DSMs in the
CR node network, wherein the quiet interval request is accepted by a number of the one or more DSMs;transmitting a quiet interval confirm message to the one or more DSMs in the CR node network.