Abstract:
A method, apparatus, and computer program product are disclosed for wireless communications networks, such as WiMedia networks, to solve problems of channel congestion, searching for candidate channels to select, and achieving reliable channel changes that will be recognized by other devices in the network. A wireless communications device selects a channel finding technique in a first stage, based on whether the device has any active connections in a current channel. The device then performs the selected channel finding technique with a plurality of channels to find a candidate channel. Then the initiating device sends a request to at least one remote device to change its channel from the current channel to the candidate channel during a time slot within a repeating time interval. If the request is successful, the initiating device receives an acceptance of the request from the remote device. Then in a second stage, the initiating device selects a channel changing technique based on whether the device has any active connections in the current channel. The initiating device then executes the selected channel changing technique to change a channel from the current channel to the candidate channel, thereby establishing the desired new connection across the candidate channel with the remote device.

Description:
FIELD OF THE INVENTION 
   The present invention relates to wireless communications. More particularly, the present invention relates to techniques for sharing wireless communications media in wireless network environments. 
   BACKGROUND OF THE INVENTION 
   Short-range wireless proximity networks typically involve devices that have a communications range of one hundred meters or less. To provide communications over long distances, these proximity networks often interface with other networks. For example, short-range networks may interface with cellular networks, wireline telecommunications networks, and the Internet. 
   High rate physical layer (PHY) techniques for short-range proximity networks are quickly emerging. One such technique involves frequency hopping applications of orthogonal frequency division multiplexing (OFDM). This technique involves the transmission of OFDM symbols at various frequencies according to pre-defined codes, such as Time Frequency Codes (TFCs). Time Frequency Codes can be used to spread interleaved information bits across a larger frequency band. 
   The WiMedia Alliance has developed an OFDM physical layer. This physical layer is described in WiMedia Alliance  MultiBand OFDM Physical Layer Specification, Release  1.1, Jan. 14, 2005 (also referred to herein as the WiMedia PHY. This document is incorporated herein by reference in its entirety. 
   The WiMedia Medium Access Control (MAC) group is developing a MAC layer that would be used with an OFDM physical layer, such as the WiMedia PHY. A current version of this MAC is described in O&#39;Conor, Jay; Brown, Ron (ed.),  Distributed Medium Access Control  ( MAC )  for Wireless Networks, WiMedia Technical Specification, Release  1.0, Dec. 8, 2005 (also referred to herein as the WiMedia MAC Specification v. 1.0). This document is incorporated herein by reference in its entirety. 
   This MAC layer involves a group (referred to as a beacon group) of wireless communications devices that are capable of communicating with each other. The timing of beacon groups is based on a repeating pattern of “superframes” in which the devices may be allocated communications resources. These communications resources may be in the form of one or more time slots, referred to as media access slots (MASs). 
   MAC layers govern the exchange among devices of transmissions called frames. A MAC frame may have various portions. Examples of such portions include frame headers and frame bodies. A frame body includes a payload containing data associated with higher protocol layers, such as user applications. Examples of such user applications include web browsers, e-mail applications, messaging applications, and the like. 
   In addition, MAC layers govern the allocation of resources. For instance, each device requires an allocated portion of the available communication bandwidth to transmit frames. The WiMedia MAC provides for the allocation of resources to be performed through communications referred to as beacons. Beacons are transmissions that devices use to convey non-payload information. Each device in a beacon group is assigned a portion of bandwidth to transmit beacons. 
   Such transmissions allow the WiMedia MAC to operate according to a distributed control approach, in which multiple devices share MAC layer responsibilities. Accordingly, the WiMedia MAC Specification v. 1.0 provides various channel access mechanisms that allow devices to allocate portions of the transmission medium for communications traffic. These mechanisms include a protocol called the distributed reservation protocol (DRP) in which reservations for connections are negotiated among devices. These mechanisms also include a protocol called prioritized contention access (PCA). 
   The WiMedia PHY provides for various channels across a frequency range. These channels are referred to as logical channels. Each logical channel employs a different Time Frequency Code (TFC). As discussed above, TFCs specify a repeating time sequence in which various frequency bands within a frequency range are used. Thus, a device employing a TFC transmits at different frequencies at particular times specified by the TFC. Currently, the WiMedia PHY specifies each band having a 528 MHz bandwidth. Also, these bands are within a frequency operating range of between 3.1 and 10.6 GHz. 
   The current WiMedia MAC (WiMedia MAC Specification v. 1.0) is limited to elementary techniques for handling channel changes. Moreover, the current WiMedia MAC fails to provide any tools for device(s) to search for channel candidates after joining a beacon group. If a current WiMedia MAC device decides to change or re-select a beacon group channel, it can send a Channel Change IE notice in its beacon to inform the other devices on that beacon group. However, the current WiMedia MAC provides no guarantee that the other devices in the beacon group will follow the device to another channel. Thus, channel-changing devices are in jeopardy of losing existing connections as well as basic connectivity under the current WiMedia MAC specification. 
   Many situations can occur in which a channel change is desirable (for either a device or to a group of device). One such situation occurs when a currently used channel (i.e. a beacon group) is congested. This congested condition may be attributed to a large number of devices in the beacon group and/or to a lack of available resources for a new application or DRP reservation. The potential for such congested conditions occurring is substantial. One reason for this is because the current WiMedia MAC specification allows even two devices (e.g. two WUSB hosts) to reserve almost a full superframe (224 out of 256 MASs). 
   Other situations in which a channel change is desirable occur when radio conditions for the current channel are poor (e.g. interference, frame error rate, etc.), the achievable range on the current radio channel is insufficient, and/or a specific device is found operating on another channel. Current WiMedia implementations only require devices to listen to a single channel at a time, thus limiting the choices for channel changes that can be recognized by a device. 
   SUMMARY OF THE INVENTION 
   The problems of channel congestion, searching for candidate channels to select, and achieving reliable channel changes that will be recognized by other devices in the network are overcome by the embodiments of the invention disclosed herein. 
   In an example embodiment of the invention, a wireless communications device selects a channel finding technique in a first stage, based on whether the device has any active connections in a current channel. The device then performs the selected channel finding technique with a plurality of channels to find a candidate channel. Then the initiating device sends a request to at least one remote device to change its channel from the current channel to the candidate channel during a time slot within a repeating time interval. If the request is successful, the initiating device receives an acceptance of the request from the remote device. Then in a second stage, the initiating device selects a channel changing technique based on whether the device has any active connections in the current channel. The initiating device then executes the selected channel changing technique to change a channel from the current channel to the candidate channel, thereby establishing the desired new connection across the candidate channel with the remote device. 
   In one embodiment, the selected channel finding technique broadcasts a beacon transmission that the initiating device will hibernate. The initiating device then proceeds to scan for available channels during hibernation, either to find a best available radio channel or to find a specific target device. 
   In another embodiment, the selected channel finding technique broadcasts a beacon transmission that the initiating device will be unavailable for a predetermined number of superframes. Then the initiating device scans for available channels during the predetermined number of superframes, either to find a best available radio channel or to find a specific target device. 
   In a further embodiment, the selected channel finding technique scans one channel at a time, alternating between broadcasting a beacon transmission in the initiating device&#39;s original channel, then scanning in a first new channel, then returning s to its original channel for at least one superframe in order to continue communications therein, followed by scanning in a second new channel, so that it scans one new channel at a time, either to find a best available radio channel or to find a specific target device. 
   In another embodiment, the selected channel finding technique broadcasts a beacon transmission to inform peer devices in the initiating device&#39;s beacon group that the initiating device is performing ongoing channel selection operations. The peer devices then maintain the initiating device&#39;s reservation and status in the initiating device&#39;s original channel for a predetermined number of superframes, in response to the broadcasting. 
   In still another embodiment, the selected channel finding technique broadcasts a beacon transmission to inform peer devices in the initiating device&#39;s beacon group that the initiating device is performing ongoing channel selection operations for a stated number of superframes. The peer devices then maintain the initiating device&#39;s reservation and status in the initiating device&#39;s original channel for the stated number of superframes, in response to the broadcasting. 
   In a further embodiment, the selected channel finding technique broadcasts a beacon transmission to inform peer devices in the initiating device&#39;s beacon group that the initiating device will be unavailable for a stated number of superframes. The peer devices then maintain the initiating device&#39;s reservation and status in the initiating device&#39;s original channel for the stated number of superframes, in response to the broadcasting. 
   In another embodiment, the selected channel changing technique transmits an information element including a list of identifiers of peer devices in the initiating device&#39;s beacon group, the information element including a request to change channel with the initiating device. The peer devices then respond whether they accept the request. 
   In this manner, the resulting invention solves problems of channel congestion, searching for candidate channels to select, and achieving reliable channel changes that will be recognized by other devices in the network. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number. The present invention will be described with reference to the accompanying drawings, wherein: 
       FIG. 1  is a diagram of an exemplary operational environment; 
       FIGS. 2A and 2B  are diagrams of superframe formats employed in shared transmission media; 
       FIG. 3A  is a flowchart of a channel changing process according to embodiments of the present invention; 
       FIG. 3B  is a more detailed flowchart of an exemplary channel changing process, according to embodiments of the present invention; 
       FIGS. 4-6  are diagrams involving the format of a Distributed Reservation Protocol Information Element; 
       FIG. 7  is a diagram of a device architecture, according to embodiments of the present invention; 
       FIG. 8  is a diagram of a wireless communications device implementation, according to embodiments of the present invention; 
       FIG. 9A  is a diagram of a new Unavailability Information Element; 
       FIG. 9B  is a flow diagram of the channel finding technique using the Unavailability Information Element; 
       FIG. 10A  is a diagram of a modified Channel Change Information Element; 
       FIG. 10B  is a flow diagram of the channel changing technique using the modified Channel Change Information Element; 
       FIG. 11  is a diagram of a new Channel Change Request Information Element; 
       FIG. 12  is a diagram of a new Channel Change Response Information Element; 
       FIG. 13  is a diagram of a Command Frame definition for Channel Change Request and Response; and 
       FIG. 14  is a diagram of a Channel Change Command Frame Type encoding. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   I. Operational Environment 
     FIG. 1  is a diagram of a communications environment in which the techniques of the present invention may be employed. This environment includes a beacon group  100  in which multiple communications devices (DEVs)  102  may exchange wireless transmissions. In particular,  FIG. 1  shows a device  102   a  sending a wireless transmission  120  to a device  102   b . Also,  FIG. 1  shows a device  102   d  sending a wireless transmission  122  to a device  102   c.    
   Transmissions  120  and  122  are shown as being point-to-point communications. However, each of devices  102  periodically sends a transmission referred to as a beacon, which is directed (broadcast) to each device in beacon group  100 . For instance,  FIG. 1  shows device  102   a  transmitting a beacon  124 , device  102   b  transmitting a beacon  126 , device  102   c  transmitting a beacon  128  and device  102   d  transmitting beacon  125 . Beacon transmissions are described in greater detail below. 
   II. Superframe 
   Wireless network transmissions in the environment of  FIG. 1 , such as beacons and data communications may be based on a repeating time pattern, such as a superframe. An exemplary superframe format is shown in  FIG. 2A . In particular,  FIG. 2A  shows a frame format having superframes  202   a ,  202   b , and  202   c.    
   Each superframe  202  includes a beacon period  204  and a data transfer period  206 . Beacon periods  204  convey transmissions from each of the active devices in the beaconing group. Accordingly, each beacon period  204  includes multiple beacon slots  207 . Slots  207  each correspond to a particular device in the network. The devices employing beacon slots  207  are referred to as a beaconing group. During these slots, the corresponding device may transmit various overhead or networking information. For WiMedia networks, such information may be in predetermined forms called Information Elements (IEs). 
   For instance, such information may be used to set resource allocations and to communicate management information for the beaconing group. In addition, according to the present invention, data transfer periods  206  may be used to transmit information regarding services and features (e.g., information services, applications, games, topologies, rates, security features, etc.) of devices within the beaconing group. The transmission of such information in beacon periods  204  may be in response to requests from other devices. 
   Data transfer period  206  is used for devices to communicate data according to various transmission schemes. These schemes may include, for example, frequency hopping techniques that employ OFDM and/or time frequency codes (TFCs). For instance, data transfer periods  206  may support data communications across links  120  and  122 . In addition, devices (e.g., DEVs  102   a - d ) may use data transfer periods  206  to transmit control information, such as request messages to other devices. The current WiMedia MAC provides for command and control frames for the transfer of such information. To facilitate the transmission of traffic, each device may be allocated one or more particular time slots within each data transfer period  206 . In the context of the WiMedia MAC, these time slots are referred to as media access slots (MASs). 
   A MAS is a period of time within data transfer period  206  in which two or more devices can exchange data (i.e., communicate). According to the WiMedia MAC, MASs may be allocated by a distributed protocol, called the distributed reservation protocol (DRP). DRP protects the MASs from contention access by devices acknowledging the reservation. Alternatively, the WiMedia MAC provides for resource allocation according to a prioritized contention access (PCA) protocol. Unlike DRP, PCA isn&#39;t constrained to reserving one or more entire MASs. Instead, PCA can be used to allocate any part of the superframe that is not reserved for beaconing or DRP reservations. 
     FIG. 2B  is a diagram of a frame format designated by the WiMedia MAC Specification v. 1.0. Like the frame format of  FIG. 2A , the WiMedia frame format has successive superframes  210 . As shown in  FIG. 2B , the current WiMedia superframe includes 256 MASs and has duration of 65,536 microseconds. Within each WiMedia superframe  210 , a first set of MAS(s) is designated as a beaconing period  212 . The number of MASs in this period is flexible, so it may dynamically change. The remaining portion of the (i.e., non-beaconing period portion) of WiMedia superframe  210  is designated as a data transfer period  214 . 
   III. Channel Change Overview 
   The present invention provides techniques for a device to find best available channel for its needs. Such a channel may be found when the device has already joined a beacon group (and has thus selected a channel). Also, this may occur when the device has connection(s) or other active data transmission(s) with one or more other devices. Embodiments of the present invention involve procedures for finding the best available channel as fast as possible. 
   If the device has already joined a beacon group, finding the best available channel involves scanning the other channels and possibly scanning for other devices. However, given the current WiMedia PHY and WiMedia MAC, such scanning is not currently possible after joining a beacon group on a specific channel. Also, if a device has connections with one or more other devices, it is desirable for the device to find a new channel that meets its needs without losing its existing connections. In addition, it is desirable for the device to ensure that the other device(s) will follow it into the new channel (or at least know which devices are willing to follow it into the new channel) 
   The current WiMedia PHY and WiMedia MAC provide no mechanisms for such channel changes. Thus, the present invention provides solutions for finding a new channel candidate, sharing channel change related information, and executing a channel change. Accordingly,  FIG. 3A  is a flowchart of an exemplary channel changing process, according to embodiments of the present invention. 
   The process of  FIG. 3A  includes a step  302  in which a device finds one or more channel candidates. Step  302  may employ different techniques based on various factors. For instance, certain techniques may be employed when the device has no active connections (e.g., DRP reservations), but may have active PCA data transmissions in the current channel, while other techniques may be employed when the device has one or more active connections (e.g. DRP reservations) in the current channel. 
   In a step  304 , the device shares information with other devices in its network (e.g., beacon group). This information is related to a contemplated or planned channel change. Step  304  may comprise exchanging information through various information elements (IEs) in beacon transmissions. Alternatively, step  304  may include the exchange of control/command frames (which are non-beacon, payload transmissions containing control/command information). 
   After this exchange of information, the device may execute a channel change in a step  306 . This change may employ different techniques based on various factors. For instance, certain techniques may be employed when the device has no active connections (e.g., DRP reservations), but may have active PCA data transmissions in the current channel, while other techniques may be employed when the device has one or more active connections (e.g. DRP reservations) in the current channel. In embodiments of the present invention, the other device(s) having connections with the device follow the channel change. 
     FIG. 3B  is a more detailed flowchart of an exemplary channel changing process, according to embodiments of the present invention. The flow diagram of  FIG. 3B  represents a computer program and the steps of the flow diagram represent programmed instructions of the computer program that, when executed by a computer program processor, carry out the functions of the invention. 
   Step  320 : Initially, a wireless communications device selects a channel finding technique in a first stage, based on whether the device has any active connections in a current channel. 
   Step  330 : The device then performs the selected channel finding technique with a plurality of channels to find a candidate channel. 
   Step  340 : Then the initiating device sends a request to at least one remote device to change its channel from the current channel to the candidate channel during a time slot within a repeating time interval. 
   Step  350 : If the request is successful, the initiating device receives an acceptance of the request from the remote device. 
   Step  360 : Then in a second stage, the initiating device selects a channel changing technique based on whether the device has any active connections in the current channel. 
   Step  370 : The initiating device then executes the selected channel changing technique to change a channel from the current channel to the candidate channel. 
   Step  380 : The initiating device then establishes the desired new connection across the candidate channel with the remote device. 
   IV. Finding New Channel Candidates 
   A device may employ various techniques to find a channel candidate. Selection of these techniques is based on whether the device has any connections or active data transmissions. More particularly, certain techniques may be selected when a device has joined a beacon group, but has no active connections (e.g., DRP reservations), but may have active PCA data transmissions. Similarly, certain techniques may be employed when a device has an active connection (e.g., a DRP reservation). 
   A. No Active DRP Reservations 
   When a device has no active connections, but may have active PCA data transmissions, embodiments of the present invention provide two alternative techniques. The first alternative technique involves hibernation. In particular, the device announces (e.g., in a beacon transmission) that it will hibernate. During the device&#39;s hibernation period, the device scans the available channels. This scanning is directed at finding either the best available radio channels or at finding a specific target device. 
   After finding a new candidate channel, the device returns to original channel and wakes up from the hibernation. Thus, this technique does not require any changes to the WiMedia MAC. 
   A second alternative shown in  FIG. 9A  involves the addition of a new information element (IE)  900  to the current WiMedia MAC. This new Unavailability IE  900  includes three fields. A first field  902  is the element&#39;s ID, for example the value  23 . A second field  904  gives the length of the following fields, in this case a length of one octet. The third field  906  gives the unavailability duration in units of superframes. In one embodiment, the number of superframes of unavailability is predetermined. In another embodiment, the number of superframes of unavailability is expressly stated in the field  906 . Thus, the Unavailability IE  900  contains information, which indicates that the device will be unavailable for a predetermined number of superframes (N superframes). During the device&#39;s absence, the other devices in the beacon group still update the device&#39;s status in their own beacons. Also during the device&#39;s absence, the device scans the available channels for either the best available radio channels or a specific target device.  FIG. 9B  is a flow diagram of the channel finding technique using the Unavailability information element (IE)  900 . The initial channel finding Steps  320  and  330  of  FIG. 9B  are the same as those same numbered steps described for  FIG. 3B . In Step  320 : Initially, a wireless communications device selects a channel finding technique in a first stage, based on whether the device has any active connections in a current channel. In Step  330 : The device then performs the selected channel finding technique with a plurality of channels to find a candidate channel. In Step  331 , the selected channel finding technique broadcasts a beacon with the Unavailability information element (IE)  900  indicating that the initiating device will be unavailable (or that the initiating device will hibernate) for a predetermined number of superframes. Then in Step  332 , the initiating device scans for available channels during the predetermined number of superframes, either to find a best available radio channel or to find a specific target device. The following Steps  340  and  350  of  FIG. 9B  are the same as those same numbered steps described for  FIG. 3B . In Step  340 : If a suitable channel is found, then the initiating device sends a request to at least one remote device to change its channel from the current channel to the candidate channel during a time slot within a repeating time interval. In Step  350 : If the request is successful, the initiating device receives an acceptance of the request from the remote device. 
   B. Active DRP Reservations 
   When a device has joined a beacon group and has an active DRP reservation, certain timing delays occur in finding a new channel candidate. For instance, in the context of the current WiMedia MAC, such delays are at least two superframes in duration. More particularly, it may require at least one superframe for the device to synchronize to the new channel and receive needed information from the new channel. In addition, one superframe may be required for the device to synchronize to the old channel again. 
   However, it is undesirable for such delays to extend beyond two superframes. This is because (in the current WiMedia MAC specification) after mMaxLostBeacons, which is currently identified as three superframes in the WiMedia MAC specification, if no beacon is received from a device, all active DRPs are released and device itself is assumed to be lost. To accommodate such constraints, the present invention provides various alternative techniques. 
   In a first technique, the device sends a beacon in its old channel and changes to new channel. Then the device scans the new channel and returns to the original (old) channel for one or two superframes in order to continue its DRP reservations (as well as to send or receive possible data). Thus, the device scans one channel at a time. This technique does not require changes to the current WiMedia MAC Specification. 
   A second technique requires changes to the current WiMedia MAC specification. This technique adds a new field (e.g., a 1-bit field) to the DRP IE. This new field informs peer devices (devices in the beacon group) of the original channel that the device is performing ongoing channel selection operations by including the corresponding field in the DRP IE in its beacon. Upon receiving a DRP IE having this field, the peer device(s) maintain the device&#39;s reservation and status in the original channel for a predetermined number (N) superframes (e.g., N=[2, 2*(# of channels−1)], in the current WiMedia PHY specification 30 channels are defined. Thus, N=[2, 58]). Although this technique requires changes to the WiMedia MAC specification, the current DRP IE has room to accommodate this new field (e.g. in 3-bit Reserved field in DRP Control Field). 
   A third technique also requires changes to the current WiMedia MAC specification. In this technique, a new field (e.g., a 3-bit field) is added to the DRP IE. This new field informs peer devices (devices in the beacon group) of the original channel that the device is performing ongoing channel selection operations for a certain number of superframes indicated by this new field. For example, when a three bit field is employed such channel selection operations may occur for 1 to 7 superframes. In embodiments, a zero value indicates no ongoing channel selection operations. 
   During this indicated number of superframes, the peer device(s) keeps up the device&#39;s reservation and status in the original channel by including the corresponding DRP IE in its beacon. As with the second technique, this technique requires changes to the current WiMedia MAC specification. However, the current DRP IE has room to accommodate this new field (e.g. the 3-bit Reserved field in DRP Control Field). 
   According to a fourth technique, the Reservation Status bit of the DRP IE is changed to zero with a new Reason Code called “Channel Selection Ongoing”. Upon receiving such a DRP IE, the peer device(s) maintain by including the corresponding DRP IE in its beacon the device&#39;s reservation and status in the original channel for a predetermined number (N) superframes (e.g. N=[2, 2*(# of channels−1)], in the current WiMedia PHY specification 30 channels are defined. Thus, N=[2, 58]). This technique requires changes to the WiMedia MAC specification. 
   A fifth technique modifies the current WiMedia MAC specification by adding a new IE for beacon transmissions shown in  FIG. 9A . This new IE contains information that the device will be unavailable for a certain number (N) of superframes. Upon receipt of this IE, the peer devices for the DRP reservations maintain (keep up) the device&#39;s reservation and the peer devices still update the device status in their own beacons during this period of unavailability. 
   V. Information Sharing 
   Unlike the aforementioned techniques for finding candidate channels, information sharing is independent of any active data transmission. The current WiMedia MAC specification allows a device to inform other devices that it is changing its channel by using the Channel Change IE. However, other devices are not required to follow the device to the new channel. 
   To overcome this shortcoming, the present invention provides various techniques. For example, a first technique expands the existing Channel Change IE by adding a new list element. The modified Channel Change Information Element  1000  of  FIG. 10A  includes the following fields. A first field  1002  is the element ID, for example “18”. The second field  1004  is the length of the remaining fields, in this case it is two octets for fields  1006  and  1008  plus two additional octets for each of N device addresses listed in fields  1012  through  1014  to  1016  of the list element  1010 . Field  1006  is the channel change countdown and field  1008  is the new channel number being requested by the IE  1000 . This new list element  1010  contains device identifiers (DEV IDs) of the peer devices that are requested to change channel with the device originating the modified Channel Change IE  1000 . This list  1010  may specify a group of devices that, for example, belong to the same context (e.g. a person&#39;s data storage and data display). The Channel Change information element (IE)  1000  shown in  FIG. 10A  may include a new channel indicator and a countdown timer.  FIG. 10B  is a flow diagram of the channel changing technique using the Modified Channel Change IE  1000 . The channel finding Steps  320 - 350  and the initial channel changing Step  360  of  FIG. 9B  are the same as those same numbered steps described for  FIG. 3B . In Step  361 , the selected channel changing technique transmits a beacon including the Modified Channel Change IE  1000  that includes the list  1010  of identifiers of peer devices in the initiating device&#39;s beacon group, the information element  1000  including a request to change channel with the initiating device to a new channel number in field  1008 . 
   Upon receiving such an IE, each device in the list responds with its own Channel Change IE to accept the request. This IE contains the initiator&#39;s DEV ID as well as the same channel and countdown time as in the initiator&#39;s message. In Step  362  of  FIG. 10B , the peer devices are shown responding whether they accept the request. Then in Step  370 , the initiating device executes the selected channel changing technique to change a channel from the current channel to the candidate channel. 
   A second technique for sharing channel change information involves modifying the current WiMedia MAC to include a new Channel Change Request IE  1100  shown in  FIG. 11  and a Channel Change Response IE  1200  shown in  FIG. 12 . The Channel Change Request Information Element  1100  of  FIG. 11  includes the following fields. A first field  1102  is the element ID, for example “24”. The second field  1104  is the length of the remaining fields, in this case it is two octets for fields  1106  and  1108  plus two additional octets for each of N device addresses listed in fields  1112  through  1114  to  1116  of the list element  1110 . Field  1106  is the channel change countdown and field  1108  is the new channel number being requested by the IE  1100 . In embodiments of the present invention, the Channel Change Request IE  1100  contains a list  1110  of DEV IDs of peer devices that are requested to change channel with the device transmitting this IE  1100 . In addition, the Channel Change Request IE  1100  includes a new channel identifier in field  1108  and a countdown timer in field  1106 . 
   Upon receiving a Channel Change Request IE  1100 , each device in the list responds with its own Channel Change Response IE  1200  shown in  FIG. 12 . The Channel Change Response Information Element  1200  of  FIG. 12  includes the following fields. A first field  1202  is the element ID, for example “25”. The second field  1204  is the length of the remaining fields, in this case it is five octets for fields  1206 ,  1208 ,  1210 , and  1212 . In embodiments, this IE  1200  contains either a positive confirmation or a rejection in field  1206  of the channel change requested in the Channel Change Request IE  1100 . Field  1208  is the channel change countdown and field  1210  is the new channel number that the responding device is agreeing to change to, as was requested in the IE  1100 . The flow diagram of  FIG. 10B  also applies to the channel changing technique using the Channel Change Request IE  1100  of  FIG. 11  and the Channel Change Response IE  1200  of  FIG. 12 . 
   A third technique for sharing channel change information involves providing new control/command frames. Thus, this technique requires changes to the current WiMedia MAC specification. For instance, embodiments of the present invention add a new command/control frame, Channel Change Request and Response command frame  1300  shown in  FIG. 13 , which is identified by a Frame Type value in field  1302 . An example of Channel Change Command Frame Type Encoding  1400  shown in  FIG. 14 , with the Frame Type value  1402  indicating the type of Channel Change Command Frame Payload  1404 . Command Frames are sent as MAC payload, with the payload occupying N octets in field  1308 . A Frame Type  1402  with a first value of “zero” can identify that a Channel Change Request (with information similar to the Channel Change Request Information Element  1100  of  FIG. 11 ) is in the payload in field  1308 . A Frame Type  1402  with a second value of “one” can identify that a Channel Change Response (with information similar to the information in the Channel Change Response Information Element  1200  of  FIG. 12 ) is in the payload in field  1308 . The frame  1300  contains a list of DEV IDs in payload field  1308  for a Channel Change Request, which identifies devices that are requested to change their channel along with the device transmitting this control frame. In addition, this control frame  1300  for a Channel Change Request provides a new channel identifier and a countdown timer in payload field  1308 , similar to the information in the Channel Change Request Information Element  1100  of  FIG. 11 . 
   Devices included in the device list of the Channel Change Request frame respond with a Channel Change Response frame having information in payload field  1308  similar to the information in the Channel Change Response Information Element  1200  of  FIG. 12 . This Channel Change Response frame contains either a positive confirmation or a rejection of the requested channel change in payload field  1308 , similar to the Channel Change Response Information Element  1200 . However, in alternate embodiments, a rejection may instead be made with an additional Channel Change Reject message. For high security devices, command/control frames can be sent in a secure manner. 
   VI. Channel Change Execution 
   In embodiments of the present invention, channel change execution is based on whether the changing device has active DRP reservations. If the device has no active DRP reservations, the changing device changes to the new channel according to channel change information using MAC procedures. Once the channel change has occurred, the device selects a new beacon slot in the new channel and resumes normal mode of operation. 
   In embodiments of the present invention, when a device changes its channel, other device(s) having DRP reservations with the device follow the channel change as agreed on information sharing phase. Accordingly, if the device has active DRP reservations, the device (and its associated channel changing devices) change to the new channel according to channel change information using MAC procedures. Once the channel change has occurred, each device selects a new beacon slot in the new channel. In embodiments, all existing DRPs from the old channel are renegotiated in the new channel. 
   Moreover, in embodiments of the present invention, after changing channels, a device may be precluded from changing its channel again within a certain time (e.g., 50 superframes). This feature advantageously prevents continuous channel changes (so called “ping-pong” effect) 
   VII. Information Elements 
   In embodiments of the present invention, various information elements (IEs) are transmitted to carry out the aforementioned techniques. Such IEs include for example DRP IEs and Channel Change IEs. These IEs are described below with reference to  FIGS. 4-12 . 
   DRP IEs are described with reference to  FIGS. 4-6 . These IEs are used to negotiate a reservation for certain MASs. In addition, DRP IEs are used to announce the reserved MASs.  FIG. 4  is a diagram of a DRP IE format according to the current WiMedia MAC standard. The DRP IE shown in  FIG. 4  includes an Element ID field  402 , a Length field  404 , a DRP Control field  406 , a Target/Owner DevAddr field  408 , and one or more DRP Allocation fields  410 . 
   Fields  402  and  404  identify the IE as a DRP IE and indicate its length.  FIG. 5  is a diagram showing the format of DRP Control Field  406 . As shown in  FIG. 5 , this field includes a reserved field  502 , an unsafe field  504 , a conflict tie-breaker field  506 , an owner field  508 , a reservation status field  510 , a reason code field  512 , a stream index field  514 , and a reservation type field  516   
   Unsafe field  504  indicates whether any of the MASs identified in DRP Allocation Fields  410  are considered unsafe because they exceed one or more specified reservation limit(s). Such an indication exists when unsafe field  504  is set to “1”. 
   Owner field  508  is set to “1” if the transmitting device is the owner of the reservation. Otherwise this field is set to “0” when the transmitting device is the target. 
   Reservation status field  510  indicates the status of the DRP negotiation process. For instance, this field is set to “0” when the corresponding reservation is under negotiation or in conflict. In contrast, this field is set to “1” when the transmitting device is confirming a reservation or maintaining an established reservation. 
   Reason code field  512  is used by a reservation target. This field indicates whether a DRP reservation request was successful and whether a reservation has been modified. The encoding scheme of this field is provided below in Table 1. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Reason Code Field Encoding 
             
           
        
         
             
               Value 
               Code 
               Meaning 
             
             
                 
             
             
               0 
               Accepted 
               The DRP reservation request is successful 
             
             
               1 
               Conflict 
               The DRP reservation request or existing 
             
             
                 
                 
               reservation is in conflict with one or more 
             
             
                 
                 
               existing DRP reservations 
             
             
               2 
               Pending 
               The DRP reservation request is being 
             
             
                 
                 
               processed 
             
             
               3 
               Denied 
               The DRP reservation request is rejected or 
             
             
                 
                 
               existing DRP reservation can no longer be 
             
             
                 
                 
               accepted 
             
             
               4 
               Modified 
               The DRP reservation is still maintained but 
             
             
                 
                 
               has been reduced in size or multiple DRP 
             
             
                 
                 
               IEs for the same reservation have been 
             
             
                 
                 
               combined 
             
             
               5-7 
               Reserved 
               Reserved 
             
             
                 
             
           
        
       
     
   
   Stream index field  514  identifies the stream of data to be sent in the reservation. Conflict tie breaker field  506  contains a randomly generated bit value. 
   Reservation type field  516  indicates the type of reservation. The encoding scheme for this field is provided below in Table 2. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Reservation Type Field Encoding 
             
           
        
         
             
                 
               Value 
               Reservation Type 
             
             
                 
                 
             
             
                 
               0 
               Alien BP 
             
             
                 
               1 
               Hard 
             
             
                 
               2 
               Soft 
             
             
                 
               3 
               Private 
             
             
                 
               4 
               PCA 
             
             
                 
               5-7 
               Reserved 
             
             
                 
                 
             
           
        
       
     
   
     FIG. 6  provides the format of a DRP Allocation field  410 . As shown in  FIG. 6 , a DRP Allocation field  410  includes a Zone Bitmap  602  and a MAS Bitmap  604 . Zone Bitmap field  602  identifies particular zones containing reserved MASs. If a bit in the field is set to one, the corresponding zone contains reserved MASs. However, if a bit is set to zero, there are no reserved MASs in the corresponding zone. MAS Bitmap  604  indicates which MASs in the zones identified by Zone Bitmap field  602  are part of the reservation. If a bit in field  604  is set to one, the corresponding MAS within each zone identified by the Zone Bitmap is included. 
   VIII. Wireless Communications Device 
     FIG. 7  is a diagram of an exemplary wireless communications device  700 , according to embodiments of the present invention. This device may operate according to the techniques of the present invention. This device may be used in various communications environments, such as the environment of  FIG. 1 . As shown in  FIG. 7 , device  700  includes a physical layer (PHY) controller  702 , a media access controller (MAC)  703 , transceiver  704 , upper protocol layer(s)  705 , and an antenna  710 . 
   MAC controller  703  generates frames (data transmissions) and beacons for wireless transmission. In addition, MAC controller  703  receives and processes frames and beacon transmissions that are originated from remote devices. MAC controller  703  exchanges these frames and beacon transmissions with PHY controller  702 . In turn, PHY controller  702  exchanges frames and beacon transmissions with transceiver  704 . Moreover, in embodiments employing WiMedia, MAC controller  703  performs operations involving the exchange of IEs. For instance, MAC controller  703  is responsible for the processing and generation of IEs, Control/Command frames, and DRP negotiations. 
     FIG. 7  shows that transceiver  704  includes a receiver portion  750  and a transmitter portion  760 . In embodiments of the present invention, transceiver  704  may transmit and receive OFDM signals. Accordingly, in such embodiments, transmitter portion  760  may include components, such as an inverse fast Fourier transform (IFFT) module, a zero padding module, an upconverter, and a transmit amplifier. To receive OFDM signals, receiver portion  750  may include components, such as a downconverter, a receive amplifier, and a fast Fourier transform (FFT) module. 
   As shown in  FIG. 7 , device  700  further includes one or more upper protocol layers  705 . These layers may involve, for example, user applications. Accordingly, upper layers  705  may exchange information with remote devices. This involves layer(s)  705  exchanging protocol data units with MAC controller  703 . In turn, MAC controller  703  operates with PHY controller  702  and transceiver  704  to transmit and receive corresponding wireless signals. 
   The device of  FIG. 7  may be implemented in hardware, software, firmware, or any combination thereof. For instance, the components of portions  750  and  760  may include electronics, such as amplifiers, mixers, and filters. Moreover, implementations of device  700  may include digital signal processor(s) (DSPs) to implement various modules, such as components of receiver portion  750  and transmitter portion  760 . Moreover, in embodiments of the present invention, processor(s), such as microprocessors, executing instructions (i.e., software) that are stored in memory (not shown) may be used to control the operation of various components in device  700 . For instance, components, such as PHY controller  702  and MAC controller  703 , may be primarily implemented through software operating on one or more processors. 
   One such implementation of the  FIG. 7  architecture, according to an embodiment of the present invention, is shown in  FIG. 8 . This diagram illustrates the terminal device implemented according to one embodiment of the present invention. As shown in  FIG. 8 , this implementation includes a processor  810 , a memory  812 , and a user interface  814 . In addition, the implementation of  FIG. 8  includes transceiver  704  and antenna  710 . These components may be implemented as described above with reference to  FIG. 7 . However, the implementation of  FIG. 8  may be modified to include different transceivers that support other wireless technologies. 
   Processor  810  controls device operation. As shown in  FIG. 8 , processor  810  is coupled to transceiver  704 . Processor  810  may be implemented with one or more microprocessors that are each capable of executing software instructions stored in memory  812 , for example, as a computer system. 
   Memory  812  includes random access memory (RAM), read only memory (ROM), and/or flash memory, and stores information in the form of data and software components (also referred to herein as modules). These software components include instructions that can be executed by processor  810 . Various types of software components may be stored in memory  812 . For instance, memory  812  may store software components that control the operation of transceiver  704 . Also, memory  812  may store software components that provide for the functionality of PHY controller  702 , MAC controller  703 , and upper protocol layer(s)  705 . 
   Moreover, memory  812  may store software components that control the exchange of information through user interface  814 . As shown in  FIG. 8 , user interface  814  is also coupled to processor  810 . User interface  814  facilitates the exchange of information with a user.  FIG. 8  shows that user interface  814  includes a user input portion  816  and a user output portion  818 . 
   User input portion  816  may include one or more devices that allow a user to input information. Examples of such devices include keypads, touch screens, and microphones. User output portion  818  allows a user to receive information from the device. Thus, user output portion  818  may include various devices, such as a display, and one or more audio speakers (e.g., stereo speakers) and a audio processor and/or amplifier to drive the speakers. Exemplary displays include color liquid crystal displays (LCDs), and color video displays. 
   The elements shown in  FIG. 8  may be coupled according to various techniques. One such technique involves coupling transceiver  704 , processor  810 , memory  812 , and user interface  814  through one or more bus interfaces. In addition, each of these components is coupled to a power source, such as a removable and/or rechargeable battery pack (not shown). 
   IX. CONCLUSION 
   While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not in limitation. For instance, the features described herein may be employed in networks other than WiMedia networks. 
   Accordingly, it will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.