Method of accommodating periodic interfering signals in a wireless network

A method is provided for accommodating periodic interfering signals in a wireless network. In this method, a network scans a transmission medium to locate any interfering signals. If it finds interfering signals, the scan determines their period, and the network alters the period of its superframes such that: either the period of the superframes is equal to the period of the interfering signals; the period of the superframes is an integer multiple of the period of the interfering signals; or the period of the interfering signals is an integer multiple of the period of the superframes. The network then alters the position of the superframes relative to the position of the interfering signals to arrange things such that no portion of the interfering signal interferes with a superframe beacon, such that that a maximum amount of contiguous channel time is provided in each superframe, or both.

BACKGROUND OF THE INVENTION

The present invention relates to wireless personal area networks and wireless local area networks. More particularly, the present invention relates to a method for accommodating periodic interfering signals in a wireless network.

The International Standards Organization's (ISO) Open Systems Interconnection (OSI) standard provides a seven-layered hierarchy between an end user and a physical device through which different systems can communicate. Each layer is responsible for different tasks, and the OSI standard specifies the interaction between layers, as well as between devices complying with the standard.

FIG. 1shows the hierarchy of the seven-layered OSI standard. As seen inFIG. 1, the OSI standard100includes a physical layer110, a data link layer120, a network layer130, a transport layer140, a session layer150, a presentation layer160, and an application layer70.

The physical (PHY) layer110conveys the bit stream through the network at the electrical, mechanical, functional, and procedural level. It provides the hardware means of sending and receiving data on a carrier. The data link layer120describes the representation of bits on the physical medium and the format of messages on the medium, sending blocks of data (such as frames) with proper synchronization. The networking layer130handles the routing and forwarding of the data to proper destinations, maintaining and terminating connections. The transport layer140manages the end-to-end control and error checking to ensure complete data transfer. The session layer150sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. The presentation layer160converts incoming and outgoing data from one presentation format to another. The application layer70is where communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified.

The IEEE 802 Committee has developed a three-layer architecture for local networks that roughly corresponds to the physical layer110and the data link layer120of the OSI standard100.FIG. 2shows the IEEE 802 standard200.

As shown inFIG. 2, the IEEE 802 standard200includes a physical (PHY) layer210, a media access control (MAC) layer220, and a logical link control (LLC) layer225. The PHY layer210operates essentially as the PHY layer110in the OSI standard100. The MAC and LLC layers220and225share the functions of the data link layer120in the OSI standard100. The LLC layer225places data into frames that can be communicated at the PHY layer210; and the MAC layer220manages communication over the data link, sending data frames and receiving acknowledgement (ACK) frames. Together the MAC and LLC layers220and225are responsible for error checking as well as retransmission of frames that are not received and acknowledged.

FIG. 3is a block diagram of a wireless network300that could use the IEEE 802 standard200. In a preferred embodiment the network300is a wireless personal area network (WPAN), or piconet. However, it should be understood that the present invention also applies to other settings where bandwidth is to be shared among several users, such as, for example, wireless local area networks (WLAN), or any other appropriate wireless network.

When the term piconet is used, it refers to a network of devices connected in an ad hoc fashion, having one device act as a coordinator (i.e., it functions as a server) while the other devices (sometimes called stations) follow the time allocation instructions of the coordinator (i.e., they function as clients). The coordinator can be a designated device, or simply one of the devices chosen to function as a coordinator. One primary difference between the coordinator and non-coordinator devices is that the coordinator must be able to communicate with all of the devices in the network, while the various non-coordinator devices need not be able to communicate with all of the other non-coordinator devices.

As shown inFIG. 3, the network300includes a coordinator310and a plurality of non-coordinator devices320. The coordinator310serves to control the operation of the network300. As noted above, the system of coordinator310and non-coordinator devices320may be called a piconet, in which case the coordinator310may be referred to as a piconet coordinator (PNC). Each of the non-coordinator devices320must be connected to the coordinator310via primary wireless links330, and may also be connected to one or more other non-coordinator devices320via secondary wireless links340, also called peer-to-peer links.

In addition, althoughFIG. 3shows bi-directional links between devices, they could also be unidirectional. In this case, each bi-directional link330,340could be shown as two unidirectional links, the first going in one direction and the second going in the opposite direction.

In some embodiments the coordinator310may be the same sort of device as any of the non-coordinator devices320, except with the additional functionality for coordinating the system, and the requirement that it communicate with every device320in the network300. In other embodiments the coordinator310may be a separate designated control unit that does not function as one of the devices320.

Through the course if the following disclosure the coordinator310will be considered to be a device just like the non-coordinator devices320. However, alternate embodiments could use a dedicated coordinator310. Furthermore, individual non-coordinator devices320could include the functional elements of a coordinator310, but not use them, functioning as non-coordinator devices. This could be the case where any device is a potential coordinator310, but only one actually serves that function in a given network.

Each device of the network300may be a different wireless device, for example, a digital still camera, a digital video camera, a personal data assistant (PDA), a digital music player, or other personal wireless device.

The various non-coordinator devices320are confined to a usable physical area350, which is set based on the extent to which the coordinator310can successfully communicate with each of the non-coordinator devices320. Any non-coordinator device320that is able to communicate with the coordinator310(and vice versa) is within the usable area350of the network300. As noted, however, it is not necessary for every non-coordinator device320in the network300to communicate with every other non-coordinator device320.

FIG. 4is a block diagram of a device310,320from the network300ofFIG. 3. As shown inFIG. 4, each device (i.e., each coordinator310or non-coordinator device320) includes a physical (PHY) layer410, a media access control (MAC) layer420, a set of upper layers430, and a management entity440.

The PHY layer410communicates with the rest of the network300via a primary or secondary wireless link330or340. It generates and receives data in a transmittable data format and converts it to and from a format usable through the MAC layer420. The MAC layer420serves as an interface between the data formats required by the PHY layer410and those required by the upper layers430. The upper layers430include the functionality of the device310,320. These upper layers430may include a logical link control (LLC) or the like. The upper layers allow the MAC layer420to interface with various protocols, such as TCP/IP, TCP, UDP, RTP, IP, USB, 1394, UDP/IP, ATM, DV2, MPEG, or the like.

Typically, the coordinator310and the non-coordinator devices320in a WPAN share the same bandwidth. Accordingly, the coordinator310coordinates the sharing of that bandwidth. Standards have been developed to establish protocols for sharing bandwidth in a wireless personal area network (WPAN) setting. For example, the IEEE standard 802.15.3 provides a specification for the PHY layer410and the MAC layer420in such a setting where bandwidth is shared using a form of time division multiple access (TDMA). Using this standard, the MAC layer420defines frames and superframes through which the sharing of the bandwidth by the devices310,320is managed by the coordinator310and/or the non-coordinator devices320.

Preferred embodiments of the present invention will be described below. And while the embodiments described herein will be in the context of a WPAN (or piconet), it should be understood that the present invention also applies to other settings where bandwidth is to be shared among several users, such as, for example, wireless local area networks (WLAN), or any other appropriate wireless network.

The present invention provides a method of coordinating devices310,320either operating in a network300or trying to join a network300through the use of cyclic beacons inside superframes that define the data path across the network300.

Device IDs and MAC Addresses

One important aspect of working with devices310,320in a network300is uniquely identifying each of the devices310,320. There are several ways in which this can be accomplished.

Independent of any network it is in, each device310,320has a unique MAC address that can be used to identify it. This MAC address is generally assigned to the device by the manufacturer such that no two devices310,320have the same MAC address. One set of standards that is used in preferred embodiments of the present invention to govern MAC addresses can be found in IEEE Std. 802-1990, “IEEE Standards for Local and Metropolitan Area Networks: Overview and Architecture.”

For ease of operation, the network300can also assign a device ID to each device310,320in the network300to use in addition its unique MAC address. In the preferred embodiments the MAC420uses ad hoc device IDs to identify devices310,320. These device IDs can be used, for example, to route frames within the network300based on the ad hoc device ID of the destination of the frame. The device IDs are generally much smaller than the MAC addresses for each device310,320. In the preferred embodiments the device IDs are 8-bits and the MAC addresses are 48-bits.

Each device310,320should maintain mapping table that maps the correspondence between device IDs and MAC addresses. The table is filled in based on the device ID and MAC address information provided to the non-coordinator devices320by the coordinator310. This allows each device310,320to reference themselves and the other devices in the network300by either device ID or MAC address.

SUMMARY OF THE INVENTION

Consistent with the title of this section, only a brief description of selected features of the present invention is now presented. A more complete description of the present invention is the subject of this entire document.

An object of the present invention is to manage a wireless network such that it can accommodate a periodic interfering signal in a simple manner, allowing for easy data transfer in a manner that avoids the interfering signal.

Another object of the present invention is to implement any required change in system parameters in a manner that allows some devices in a network to enter a sleep mode without missing key system change instructions.

These and other objects are accomplished by way of a method of accommodating periodic interfering signals in a wireless network. This method comprises: scanning in a transmission medium for the interfering signals; determining a period of the interfering signals; and altering a superframe period in the wireless network such that the superframe period is equal to the period of the interfering signals.

The method may comprise altering a superframe position relative to an interfering signal position. The step of altering a superframe position relative to an interfering signal position may be performed such that no portion of the interfering signal interferes with any superframe beacon. The step of altering a superframe position relative to an interfering signal position may also be performed such that a maximum amount of contiguous channel time that is not interfered with by the interfering signals is provided in each superframe

The method may further comprise assigning to a network coordinator all channel time in each superframe that is interfered with by the interfering signals.

The periodic interfering signals may be radar signals. The wireless network may be an ultrawide bandwidth network.

An alternate method is also provided of accommodating periodic interfering signals in a wireless network. This method comprises: scanning in a transmission medium for the interfering signals; determining a period of the interfering signals; and altering a superframe period in the wireless network such that the superframe period is equal to n times the period of the interfering signals, where n is an integer greater than 0.

The method may further comprise: altering a superframe position relative to an interfering signal position. The step of altering a superframe position relative to an interfering signal position may be performed such that no portion of the interfering signal interferes with any superframe beacon. The step of altering a superframe position relative to an interfering signal position may also be performed such that a maximum amount of contiguous channel time that is not interfered with by the interfering signals is provided in each superframe

The method may further comprise assigning to a network coordinator all channel time in each superframe that is interfered with by the interfering signals.

The periodic interfering signals may be radar signals. The wireless network may be an ultrawide bandwidth network.

Another alternate method is also provided of accommodating periodic interfering signals in a wireless network, comprising: scanning in a transmission medium for the interfering signals; determining a period of the interfering signals; and altering a superframe period in the wireless network such that the superframe period is equal to 1/n times the period of the interfering signals, where n is an integer greater than 0.

The method may further comprise: altering a superframe position relative to an interfering signal position. The step of altering a superframe position relative to an interfering signal position may be performed such that no portion of the interfering signal interferes with any superframe beacon. The step of altering a superframe position relative to an interfering signal position may be performed such that a maximum amount of contiguous channel time that is not interfered with by the interfering signals is provided in each superframe

The method may further comprise assigning to a network coordinator all channel time in each superframe that is interfered with by the interfering signals.

The periodic interfering signals may be radar signals. The wireless network may be an ultrawide bandwidth network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the drawings. Throughout the several views, like reference numerals designate identical or corresponding parts.

The available bandwidth in a given network300is split up in time by the coordinator310into a series of repeated superframes. These superframes define how the available transmission time is split up among various tasks. Individual frames of data are then transferred within these superframes in accordance with the timing set forth in the superframe.

FIG. 5is a block diagram of a superframe according to preferred embodiments of the present invention. As shown inFIG. 5, each superframe500may include a beacon period510, a contention access period (CAP)520, and a contention free period (CFP)530.

The beacon period510is set aside for the coordinator310to send a beacon frame out to the non-coordinator devices320in the network300. Such a beacon frame will include information for organizing the operation of devices within the superframe. Each non-coordinator device320knows how to recognize a beacon510prior to joining the network300, and uses the beacon510both to identify an existing network300and to coordinate communication within the network300.

The CAP520is used to transmit commands or asynchronous data across the network. The CAP520may be eliminated in many embodiments and the system would then pass commands solely during the CFP530.

The CFP530includes a plurality of time slots540. These time slots540are assigned by the coordinator310to a single transmitting device310,320and one or more receiving devices310,320for transmission of information between them. Generally each time slot540is assigned to a specific transmitter-receiver pair, though in some cases a single transmitter will transmit to multiple receivers at the same time. Exemplary types of time slots are: management time slots (MTS) and guaranteed time slots (GTS).

An MTS is a time slot that is used for transmitting administrative information between the coordinator310and one of the non-coordinator devices320. As such it must have the coordinator310be one member of the transmission pair. An MTS may be further defined as an uplink MTS (UMTS) if the coordinator310is the receiving device, or a downlink MTS (DMTS) if the coordinator310is the transmitting device.

A GTS is a time slot that is used for transmitting isochronous non-administrative data between devices310,320in the network300. This can include data transmitted between two non-coordinator devices320, or non-administrative data transmitted between the coordinator310and a non-coordinator device320.

As used in this application, a stream is a communication between a source device and one or more destination devices. The source and destination devices can be any devices310,320in the network300. For streams to multiple destinations, the destination devices can be all or some of the devices310,320in the network300.

In some embodiments the uplink MTS may be positioned at the front of the CFP530and the downlink MTS positioned at the end of the CFP530to give the coordinator310a chance to respond to an uplink MTS in the in the downlink MTS of the same superframe500. However, it is not required that the coordinator310respond to a request in the same superframe500. The coordinator310may instead respond in another downlink MTS assigned to that non-coordinator device320in a later superframe500.

The superframe500is a fixed time construct that is repeated in time. The specific duration of the superframe500is described in the beacon510. In fact, the beacon510generally includes information regarding how often the beacon510is repeated, which effectively corresponds to the duration of the superframe500. The beacon510also contains information regarding the network300, such as the identity of the transmitter and receiver of each time slot540, and the identity of the coordinator310.

The system clock for the network300is preferably synchronized through the generation and reception of the beacons510. Each non-coordinator device320will store a synchronization point time upon successful reception of a valid beacon510, and will then use this synchronization point time to adjust its own timing.

Although not shown inFIG. 5, there are preferably guard times interspersed between time slots540in a CFP530. Guard times are used in TDMA systems to prevent two transmissions from overlapping in time because of inevitable errors in clock accuracies and differences in propagation times based on spatial positions.

In a WPAN, the propagation time will generally be insignificant compared to the clock accuracy. Thus the amount of guard time required is preferably based primarily on the clock accuracy and the duration since the previous synchronization event. Such a synchronizing event will generally occur when a non-coordinator device320successfully receives a beacon frame from the coordinator310.

For simplicity, a single guard time value may be used for the entire superframe. The guard time will preferably be placed at the end of each beacon frame, GTS, and MTS.

The exact design of a superframe500can vary according to implementation.FIG. 6shows an example of a specific superframe design. As shown inFIG. 6, the transmission scheme600involves dividing the available transmission time into a plurality of superframes610. Each individual superframe610includes a beacon frame620, an uplink MTS630, a plurality of GTS640, and a downlink MTS650. This exemplary superframe includes no contention access period.

The beacon frame620indicates by association ID (known as a device ID in the IEEE 802.15.3 draft standard) a non-coordinator device320that is assigned to the current superframe610. It also indicates via a receive-transmit table the transmitter/receiver assignments for the individual GTS640.

In the exemplary superframe structure shown inFIG. 6, the uplink MTS630is set aside for the non-coordinator device320assigned to the current superframe610to upload signals to the coordinator310. All other non-coordinator devices320remain silent on the current channel during this time slot. In alternate embodiments that use multiple channels, all other stations on that channel must remain silent during an uplink MTS630, though they may still transmit on alternate channels.

The plurality of GTS640are the time slots set aside for each of the devices310,320to allow communication between devices. They do so in accordance with the information set forth in the receive-transmit table in the beacon620. Each GTS640is preferably large enough to transmit one or more data frames. When a transmitter-receiver set is assigned multiple GTS640, they are preferably contiguous.

The downlink MTS650is set aside for the coordinator310to download signals to the non-coordinator device320assigned to the current superframe610. All other non-coordinator devices320may ignore all transmissions during this time slot.

The lengths of the uplink and downlink MTS630and650must be chosen to handle the largest possible management frame, an immediate acknowledgement (ACK) frame, and the receiver-transmitter turnaround time. The GTS640, the length and number must be chosen to accommodate the specific requirements of frames to be transmitted, e.g., short MPEG frames, large frames of the maximum allowable length, and the ACK policy used.

Although the disclosed embodiment uses one uplink MTS630placed before a plurality of GTS640, and one downlink MTS650placed after a plurality of GTS640, the number, distribution, and placement of MTS630,650and GTS640may be varied in alternate embodiments.

However, such a TDMA protocol in general has no support for asynchronous data. A system is forced to use a static stream connection for the passing of asynchronous data, which leads to a large signal overhead, or to provide an asynchronous period (e.g., a CAP520) that uses a contention access protocol like carrier sense multiple access/collision avoidance (CSMA/CA), which leads to performance degradation and to power usage increase The power consumption is increased because every device310,320must remain powered up during the CAP520(i.e., none of the devices310,320can enter a power-saving sleep mode). The performance is degraded because there is less certainty of a given data frame being transmitted at any given time.

Channel Time Allocations

Each device310,320that desires to send data will be assigned one or more time slots540to pass that information. This time slot assignment can be referred to as a channel time allocation (CTA), since it represents the amount of time in the available wireless channel that the device310,320is provided.

This CTA may require a device310,320to be assigned a time slot540in each superframe500,610, or it may only require that the device310,320be assigned a time slot540at some fixed or valuable periodic rate.

Interference with Superframes

Unfortunately, the wireless network300may not be the only thing transmitting over the local wireless channel. Other instruments might also transmit signals, e.g., other data signals, radar signals, noise signals, etc. In one situation, an adjacent network could broadcast over the same frequencies as a local wireless network300. In another situation, a radar array might provide a periodic burst of interference that overwhelms the ability of the network300to transmit or receive. Any number of interfering signals could exist. In fact, a network300could be exposed to multiple interference sources. In such a case, however, all interference signals could be lumped together into one conceptual interference signal having multiple parts.

Interfering signals can disrupt the successful transmission of data across the network300by causing a receiver to be unable to properly receive a transmitted signal, e.g., if the power of the interfering signal is too great that a receiving device310,320cannot decipher an intended signal that collides with the interfering signal.

Quite often interfering signals will be periodic in nature. In other words, they will repeat at a given interval. For example, if the interfering signal is a radar system, it might have a sweep time over which it repeats the same transmission. Even if the interfering signal is made up of multiple individual signals, it may still have a period during which it repeats, if each individual component of the interfering signal is periodic.

FIG. 7shows one example of a signal interfering with signals from a wireless network300. As shown inFIG. 7, a network300is transmitting a series of superframes710having a set superframe length. At the same time, a periodic interference signal720is being transmitted by an external source (e.g. a radar transmitter) over the same wireless channel.

InFIG. 7, both the superframes710and the interfering signals720are periodic, although their periods are not related. As a result, the interfering signals720will interfere with a different part of each of the series of superframes710. One interfering signal720collides with the beginning of a superframe720; another interfering signal720collides with the end of a superframe720; yet another collides with the middle of a superframe710; and still another straddles two superframes720, colliding with the end of one and the beginning of the other. In a worst case, the pattern of interference will only repeat at a period equal to the product of the periods of the superframes710and the interfering signals720. As a result, it may be extremely difficult to predict which portions of any given superframe710will collide with the interfering signals720and be unreadable. This can be seen inFIG. 7where the initial series of superframes710will suffer interference from the periodic interfering signals720at different points in each superframe710.

In a preferred embodiment, the network300should use some kind of a scan mode to determine the existence of interfering signals720, as well as their period and position relative to the superframes710. This could be a scan mode performed by the network coordinator310, a scan mode performed by a non-coordinator device320, or any other sort of scan that the network has implemented.

In addition, as noted above, although inFIG. 7the interfering signals720are shown as one signal that repeats at a given interval, in other instances it could be more complicated than that. For example, the periodic interfering signals720could be a collection of signals, separate from each other, but that repeat over a set period. What is important is that over a set period, the pattern of the interfering signals repeats itself predictably.

Alteration of Superframe Size and Position

One way to accommodate an interfering signal720is to alter the size of the superframes710such that either (1) the period of the superframes710is the same as the period of the interfering signals720, (2) the period of the superframes710is an integer multiple of the period of the interfering signals720, or (3) the period of the interfering signals720is an integer multiple of the period of the superframes710. Examples of these three cases are shown inFIGS. 8A-8C.FIG. 8Ais a diagram showing a superframe having the same period as an interfering signal;FIG. 8Bis a diagram showing a superframe having twice the period of an interfering signal; andFIG. 8Cis a diagram showing a superframe having half the period of an interfering signal.

As shown inFIG. 8A, the original superframes710are changed in size to first modified superframes830athat have the same period as the interfering signals720. As a result, each of the interfering signals720will interfere with the same portion of a corresponding first modified superframe830a. This allows the network300to more easily predict when within each first modified superframe830aan interfering signal720will appear. The network coordinator310can then make channel time allocations such that nothing is transmitted for the duration of each interfering signal720.

One way to accomplish this channel time allocation is to designate a time slot540of a length and position equal to the interfering signal720and assign that time slot540to the network coordinator310(since the source of interference does not have a device ID). The coordinator310knows to avoid any transmissions during this time slot540, and no other device can transmit because the time slot540is assigned to the coordinator310. Another way to accomplish this channel time allocation is to have the coordinator310simply not assign any time slots540during the period of interference.

Regardless of how channel time allocation is performed, once the period of the original superframes710is brought into accord with the period of the interfering signals720(by forming first modified superframes830a), CTA will be easier. Once the two periods are the same, the network coordinator310need not consider any information about the period of the interference signals720. All it need know is at what point during each of the first modified superframes830athe interfering signal720will occur. (Or at what points, if the interfering signal is made up of multiple parts.) Since both have the same period, the portion of each of the first modified superframes830athat coincides with the interfering signals720remains the same for each first modified superframe830a.

Of course, this also means that the same portions of each of the first modified superframes830awill be free of interferences. As a result, devices310,320in the network300can be given the same time slots540(i.e., time slots540with the same position and duration) within successive superframes830a, if desired. This simplifies the CTA, since devices310,320can be assigned the same CTA in successive superframes830a.

Regardless, by knowing when in each first modified superframe830athe interfering signal will appear, the network coordinator310can better allocate channel time (e.g., time slots) to accommodate the interference.

Although inFIG. 8Athe interfering signal720is shown as being a contiguous signal, in alternate situations, the signal could be broken up into multiple parts. In this case the network coordinator310will have to keep track of each individual segment of the interfering signal720. However, because the period of the superframe710is the same as the period of the interfering signal720, the placement of these interfering signal segments will be the same in each superframe830aand so the network controller310need only remember the interference pattern for a single superframe830a.

In alternate embodiments, the period of the superframe710can be modified not to conform exactly with the period of the interfering signal720, but rather such that one of the superframe710or the interfering signal720have a period that is an integer multiple of the other.

FIG. 8Bis a diagram showing a superframe having twice the period of an interfering signal. As shown inFIG. 8B, the original superframes710are changed in size to first modified superframes840athat have the twice the period of the interfering signals720. As a result, two repetitions of the interfering signals720will interfere with each of the first modified superframes840a. However, since the period of the first modified superframe840ais twice that of the period of the interfering signal720, the interference points caused by the two instances of interfering signals720will be at the same place in each of the first modified superframes840a.

Since the interference pattern that each superframe840awill experience will be identical, the network coordinator310need only remember this one interference pattern. This allows the network coordinator310to more easily predict where the interfering signal720will appear in each of the first modified superframes840a, and so allows it to make channel time allocations such that nothing is transmitted for the duration of each interfering signal720. This can be done in a manner analogous to the methods described above with reference toFIG. 8A.

More generally, the period of the first modified superframe840acan be n times the period of the interfering signal720, where n is an integer greater than 0. Although n is equal to 2 for the embodiment shown inFIG. 8B, n could vary in alternate embodiments. In this more general case, n repetitions of the interfering signal will occur in each superframe. However, because the period of the first modified superframe840ais an integer times the period of the interfering signal720, the these interference points will be at the same place in each of the first modified superframes840a.

Although inFIG. 8Bthe interfering signal720is shown as being a contiguous signal, in alternate situations, the signal could be broken up into multiple parts. In this case the network coordinator310will have to keep track of each individual segment of the interfering signal720. However, because the period of the superframe710is an integer times the period of the interfering signal720, the placement of these interfering signal segments will be the same in each superframe840a, and so the network controller310need only remember the interference pattern of n repeated interfering signals720as they appear in a single superframe840a.

FIG. 8Cis a diagram showing a superframe having half the period of an interfering signal. As shown inFIG. 8C, the original superframes710are changed in size to first modified superframes850athat have half the period of the interfering signals720. As a result, an interfering signal720will only interfere with every other one of the first modified superframes850a. And, since the period of the first modified superframe850ais half that of the period of the interfering signal720, these interference points will appear at the same place in each pair of the first modified superframes840a.

Since the interference pattern that each interfered superframe850a(or superframe pair, since one repetition of the interfering signal720takes place over two superframes850a) will experience will be identical, the network coordinator310need only remember one interference pattern for each pair of superframes850a. This allows the network coordinator310to more easily predict where the interfering signal720will appear in each of the first modified superframes850a, and so allows it to make channel time allocations such that nothing is transmitted for the duration of each interfering signal720.

More generally, the period of the first modified superframe850acan be 1/n times the period of the interfering signal720, where n is an integer greater than 0. Although n equals 2 for the embodiment shown inFIG. 8B, n could vary in alternate embodiments. In this case, the network coordinator310would have to remember the pattern of interference for n superframes, not just two.

Although inFIG. 8Cthe interfering signal720is shown as being a contiguous signal, in alternate situations, the signal could be broken up into multiple parts. In this case the network coordinator310will have to keep track of each individual segment of the interfering signal720. However, because the period of the interfering signal720is an integer times the period of the superframe710, the placement of these interfering signal segments will be the same in each repetition of n superframes850aand so the network controller310need only remember the interference pattern for n repeated superframes850a.

In the embodiments shown inFIGS. 8A and 8B, the interfering signals720(or segments of interfering signals720) could appear at any point in the superframes830a,840a: appearing in the front of a superframe830a,840a, in the back of a superframe830a,840a, in the middle of a superframe830a,840a, or even straddling across two superframes830a,840a. In this latter case where an interfering signal720(or individual segments of an interfering signal720) straddle two superframes, the one superframe830a,840awill have a portion of an interfering signal720at the beginning of the superframe830a,840a, and a corresponding portion of the interfering signal720at the end of the superframe830a,840a. Nevertheless, the total amount and position of channel time interfered with will remain constant for each superframe830a,840a, and so the interference pattern can be predicted and the channel time can more easily be allocated.

In the embodiment shown inFIG. 8C, the interfering signals720(or segments of interfering signals720) could cover two or more superframes850a. In fact, it is possible that the interference pattern of the interfering signals720could cause interference in all n superframes850a. In this case two or more superframes850aout of every n superframe will have interference. However, each will have less channel time interfered with, and the pattern of interference among n sequential superframes850awill be predictable. Thus, the interference pattern can be predicted and the channel time within these n superframes850acan still be easily allocated.

However, although the straddling of superframes830a,840a,850acan be predicted and accommodated regardless of where it appears, it is preferable to expert some control over where the interference signals720will collide with the superframes830a,840a,850a. And since the interference signals720cannot be changed, this involves altering the first modified superframes once more830a,840a,850a.

A preferred way to accomplish this is to realign the superframe position once the superframe period is altered. After the period of the superframes710is matched with that of the interfering signals720to form a first modified superframes830a,840a,850a(either directly or with one being an integer multiple of the other), it is also desirable to realign the position of the first modified superframes830a,840a,850a. By realigning the first modified superframes830a,840a,850a, the relative location of the interfering signals720to the superframes830a,840a,850ais altered, which allows the superframes830a,840a,850ato be placed such that their non-interfered portions are in the most convenient position for system operation.

As shown inFIGS. 8A and 8C, according to preferred embodiments of the present invention, the first modified superframes830a,850aare aligned to form second modified superframes830b,850bin which the interfering signals720are coincident with the ending portion of each second modified superframe830b,850bin which they appear.

As shown inFIG. 8B, according to a preferred embodiment of the present invention, the first modified superframes840aare aligned to form second modified superframes840bin which the a series of interfering signals720are arranged such that the last interfering signal720in the series is coincident with the ending portion of each second modified superframe840b.

This particular positioning serves several purposes. First, by keeping the interfering signals720from the beginning of the second modified superframes830b,840b,850b, the network300eliminates the possibility that the interfering signal720will block a beacon (which appears at the beginning of a superframe).

Second, by arranging the second modified superframes830b,840b,850bsuch that the interfering signals720are placed at the end of the second modified superframe830b,840b,850b, the network300provides the largest possible uninterrupted channel time in each second modified superframe830b,840b,850b.

As shown inFIGS. 8A-8C, if the interfering signals710were not at the end portion of the superframe (i.e., as they are in first modified superframes830a,840a,850aofFIGS. 8A-8C), they would serve to split up the available channel time in a given superframe into two or more smaller channel time portions. These smaller channel time portions could limit the maximum allowable channel time allocation for any given device, which would thereby limit the network to using smaller channel time allocations.

Third, by positioning the second modified superframes830b,840b,850bsuch that the interfering signals720occur at the end of each second modified superframe830b,840b,850b, the network300can eliminate the possibility that an interfering signal720will straddle two superframes, thus simplifying the channel time allocation and further eliminating the possibility of interference during beacon transmittal.

Although in the preferred embodiments disclosed inFIGS. 8A-8C, the second modified superframes830b,840b,850bare aligned such that the interfering signal appears at the end of the superframe830b,840b,850b, alternate embodiments could position the superframes830b,840b,850banywhere desirable. For example, it might be desirable to arrange the superframes such that the interfering signal720was placed a certain length of time before the end of the superframe830b,840b,850bto account for minor variations in the duration of the interfering signals720. Other variations are also possible.

In addition, in some embodiments the interfering signal720may actually be made up of multiple individual segments spread out across the superframe duration. In this case, the alignment of the second modified superframes830b,840b,850bmay be more complicated. The network controller310will preferably align the second modified superframes830b,840b,850bsuch that no beacon is interfered with by a segment of the interfering signal720, and to allow the largest possible contiguous channel times for allocation. As noted above, however, other alignment criteria could be used.

It should be noted that in some instances it is possible that the starting superframe period for a network300will happen to be to be an integer multiple or an integer fraction of the interfering signal720. In this case, no alteration of the superframe period will be necessary. In addition, it is also possible that the superframe position will be such that when the period is appropriate, the interfering signals720are positioned at a desirable location. In this case, no alteration of the superframe position will be necessary.

Effecting Change in Superframe Period and Position

As noted above, it is desirable to alter the period and position of the periodic superframes500,710to better accommodate the presence of an interfering signal720. To accomplish this, the network controller310preferably sends new superframe timing information through instructions in the beacons510of the superframes500,710. In alternate situations, of course, other information can be sent from the coordinator310to all of the non-coordinator devices320, e.g., information regarding switching channels, handing over to new coordinator310, shutting down the network300, etc. Although the disclosed embodiments relate to the passing of superframe timing information, the methods disclosed are equally applicable to any transfer of important information between the coordinator310and non-coordinator devices320.

One difficulty in transferring information from the coordinator310to the non-coordinator devices320is that not every non-coordinator device320listens to every superframe500,710. In some implementations individual devices320will go into a power-saving sleep mode during any time that they either are not instructed to listen, or have no need to listen for an extended period of time. Devices320that are asleep in a network300will not hear every beacon510, and so would not be able to find out when the network coordinator310is changing the period or position of the superframes500,710, if such information were included in a single beacon510.

It is therefore desirable to provide a way to send relevant beacon information in a manner that ensures that all devices320will receive it, but which also allows non-coordinator devices320to enter a sleep mode. A preferred method of accomplishing this is to provide certain “system wake” beacons that all devices must listen to, regardless of whether they are in a sleep mode or not.

These system wake beacons can be defined in any of a variety of ways. In one embodiment they could simply be a periodic beacon510, i.e., every mthbeacon510(where m is an integer greater than 0). Each device would be required to listen to each mthbeacon,510regardless of whether it was in a sleep mode or not.

In other embodiments it could be a specific beacon that is counted down to in each beacon. So long as the countdown time is no shorter than the longest allowed sleep time (i.e., the longest time a device320is allowed to stay in a sleep mode before it listens to a beacon510), every non-coordinator device320is guaranteed to learn about the system wake beacon before the countdown is complete. Individual devices320would have to listen periodically to a beacon510, but all the devices320need not be coordinated to the same beacon510. Once a device learns that a system wake beacon is coming, it will know from the countdown which other beacon510it must listen for.

In yet other embodiments, the beacons510could be identified by an absolute numbering system, and the system wake beacons could be dynamically set. In this case, each system wake bacon would include information regarding the beacon number of the next system wake beacon. Intermediate beacons could also include this information to account for the chance that a device320will accidentally miss a system wake beacon. All of the devices320would have to listen during each system wake beacon, and they will be able to tell from the present system wake beacon when the next system wake beacon will be.

The relevant information relating to system changes (e.g., alteration of superframe period or position) is preferably contained in the system wake beacon. And as noted above, there are numerous methods to insure that every non-coordinator device320will listen to every system wake beacon.

Absent some method to make certain that each non-coordinator device320listens to every system wake beacon, a sleeping device320might wake up into a situation where its coordinator310has changed, its superframe structure has been altered, etc. In such a case the device320will not be able to find its coordinator310, and will thus be unable to continue its participation in the network300.

In some embodiments, the network coordinator310can provide an indicator that a system change is in progress, which can warn the non-coordinator devices320in the network300that they need to stay awake and listen for that information in the current beacon510. For example, a system change bit can be included at the beginning of the beacon510. If the system change bit is set, then a change is being made to system parameters and sleeping devices should listen to the entire beacon510. If the system change bit is not set, then no change will be made to system parameters, and a sleeping device may return to a sleep mode without interpreting the rest of the beacon510.

In some of these embodiments all participating devices320will echo the system change bit in their own frames. Thus, if a device320missed a beacon510including the system change information, but does successfully receive another frame with the system change bit set, the device320knows to stay awake and listen to the next beacon510.

This method saves power by allowing devices to remain sleeping as long and as often as possible. It also enables synchronized change throughout the network by arranging a set time that changes will occur. This is essential in some circumstances, such as when it is necessary to switch channels.

CONCLUSION

The present invention can be used with the IEEE 803.15.3 standard for high-rate WPANs, which is currently under development by the IEEE 802.15 WPAN™ Task Group 3 (TG3). The details of the current draft 802.15.3 standard, including archives of the 802.15.3 working group can be found at: http://www.ieee802.org/15/pub/TG3.html. Nothing in this disclosure should be considered to be incompatible with the draft 802.15.3 standard, as set forth on the IEEE 802 LAN/MAN Standards Committee web page.

Thus, one preferred embodiment of the present invention is used in an ultrawide bandwidth network. However, it is applicable to other sorts of networks as well.