Pseudo-random dynamic scheduler for scheduling communication periods between electronic devices

[0001] This application is related to and claims priority from U.S. patent application Ser. No. 60/272,630 filed Feb. 28, 2001, for “Effective scheduling of inter system communication,” with inventor Daryl Hlasny, which is incorporated herein by reference.

[0002] This invention relates generally to electronic devices, and is more particularly directed toward systems and methods for scheduling communication periods between electronic devices.

[0003] Computer and communication technologies continue to advance at a rapid pace. Indeed, computer and communication technologies are involved in many aspects of a person's day. For example, many devices being used today by consumers have a small computer incorporated within the device. These small computers come in varying sizes and degrees of sophistication. These small computers may vary in sophistication from one microcontroller to a fully-functional complete computer system. For example, small computers may be a one-chip computer, such as a microcontroller, a one-board type of computer, such as a controller, a typical desktop computer, such as an IBM-PC compatible, etc.

[0004] Computers typically have one or more processors. The processor(s) usually are interconnected to different external inputs and outputs and function to manage the particular computer or device. For example, a processor in a thermostat may be connected to buttons used to select the temperature setting, to the furnace or air conditioner to change the temperature, and to temperature sensors to read and display the current temperature on a display.

[0005] Many appliances, devices, etc., include one or more small computers. For example, thermostats, furnaces, air conditioning systems, refrigerators, telephones, typewriters, automobiles, vending machines, and many different types of industrial equipment now typically have small computers, or processors, inside of them. Computer software runs the processors of these computers and tells the processors what to do to carry out certain tasks. For example, the computer software running on a thermostat may cause an air conditioner to stop running when a particular temperature is reached or may cause a heater to turn on when needed.

[0006] These types of small computers that are a part of a device, appliance, tool, etc., are often referred to as embedded systems. The term “embedded system” usually refers to computer hardware and software that is part of a larger system. Embedded systems may not have typical input and output devices such as a keyboard, mouse, and/or monitor. Usually, at the heart of each embedded system is one or more processor(s).

[0007] With the increased use of electronic devices and embedded systems, and with the increased demands for the exchange of information, more devices are now able to detect surrounding devices and establish electronic communications with these devices. The Bluetooth specification defines one standard whereby devices can communicate with each other through short-range radio signals. Many kinds of devices may benefit from being able to connect to other devices without needing user intervention. For example, printers, personal digital assistants, digital cameras, telephones, laptop computers, video monitors, electronic calendars, desktops, fax machines, keyboards, joysticks, etc., may all become part of a short-range radio system to connect to other devices. By enabling this type of communication, a bridge is provided to existing data networks to form small private ad hoc groupings of connected devices away from fixed network infrastructures. Thus, device networks may be formed on-the-fly as devices discover each other. However, as more devices attempt to communicate with one another, inefficiencies may arise that may slow down or otherwise hinder the overall communication of one or more electronic devices. Thus, benefits may be realized if communications by electronic devices were enhanced with additional systems and methods for providing more effective communication techniques.

[0008] An electronic device is disclosed that is adapted to communicate with a first device network and to communicate with a second device that is part of a second device network. The device includes a processor and a communications module in electronic communication with the processor for communications with other devices including the second device and at least one device from the first device network. Memory may also be included in electronic communication with the processor for storing data. The electronic device may also include a pseudo-random scheduler for providing time points defining a schedule for the electronic device to communicate with the other devices. A dynamic scheduler may also be included to modify the schedule. The electronic device may also include an event queue.

[0009] The dynamic scheduler may implement a fair allocation method of dynamically allocating communication bandwidth. The fair allocation method may include extending previous communications periods. The fair allocation method may also include reducing the number of initiation time points in the event queue.

[0010] An opportunistic allocation method may be implemented by the dynamic scheduler to dynamically allocate communication bandwidth. The opportunistic allocation method may include evaluating traffic pending and device availability and modifying the schedule based on the evaluation.

[0011] The pseudo-random scheduler may implement a predetermined synchronized method for generating time points. In addition, the pseudo-random scheduler may implement a predetermined asynchronized method for generating time points. A real-time method may also be used in the pseudo-random scheduler.

[0012] The event queue may include a plurality of initiation time points. A plurality of channel identifications may also be stored in the event queue. Further, the event queue may include a plurality of data pending indicators.

[0013] The electronic device may further include a state machine for scheduling and communicating. The state machine may include an idle state, a data state, a negotiate schedule state and a re-establish state.

[0014] The electronic device may be used in a Bluetooth system. In such an environment, the device may become part of a piconet. If the device becomes part of a piconet, the pseudo-random scheduler may provide time points defining the schedule for the electronic device to communicate with piconets.

[0015] A method is also disclosed for pseudo-randomly and dynamically scheduling communication periods between electronic devices. The method may include the steps of transmitting outbound data from a first electronic device to a first device network and receiving inbound data by the first electronic device from the first device network. The method may also include the steps of discovering a second electronic device of a second device network, providing pseudo-random time points defining a schedule for the first electronic device to communicate with the first device network and with the second electronic device, storing the time points in an event queue, and dynamically modifying the schedule to add additional communication bandwidth to at least one communication channel.

[0016] A computer-readable medium for carrying program data is also disclosed. The program data includes executable instructions for implementing a method. The method may include the steps of transmitting outbound data from a first electronic device to a first device network and receiving inbound data by the first electronic device from the first device network. The method may also include the steps of discovering a second electronic device of a second device network, providing pseudo-random time points defining a schedule for the first electronic device to communicate with the first device network and with the second electronic device, storing the time points in an event queue, and dynamically modifying the schedule to add additional communication bandwidth to at least one communication channel.

[0042] It will be readily understood that the components of the embodiments as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of the embodiments of the invention.

[0043] FIG. 1A is a block diagram illustrating two electronic devices 102, 104 that comprise a device pair 106. The device pair 106 may enter into communication 108 with one another. Some examples of an electronic device 102, 104 are a vending machine, a telephone, a door lock, a temperature sensor, a motor, a switch, a light, a printer, a fax machine, a refrigerator, a health monitor, an elevator/escalator, a copier, a scanner, manufacturing equipment, industrial equipment, computer equipment and peripherals, security systems, monitoring equipment, a thermostat, and the like.

[0044] FIG. 1B illustrates a communication period diagram that includes a schedule 110 for a communication period 112 between the two devices 102, 104 of the device pair 106. Typically a schedule 110 is created for each pair 106 of devices that wish to communicate. The schedule 110 may be specific to the device pair 106 and may be known by both devices 102, 104. As shown, the schedule 110 may include time points 114, 116 that signal the initiation and termination of the communication between the device pair 106. The time between the initiation time point 114 and the termination event 116 is called the communication period 112.

[0045] An initiation time point 114 is the typical method used to start communication between two devices 102, 104. Both devices 102, 104 are usually aware of the initiation time point 114 so that they may start communication at this time.

[0046] In the embodiment of FIG. 1A, either device 102, 104 may terminate communication. A device may arbitrarily terminate the communication period 112, but typically the period 112 is terminated by a conflicting time point from another device pair schedule. Termination may be accomplished by signaling between the device pair 106 on a per connection basis. A termination time point 116 may be used to end the communication period 112 but is not essential. Termination time points 116 are created by the schedule negotiation process that is carried out between pairs of devices.

[0047] Typically, initiation time points 114 are determined by a predetermined pseudo random schedule that is unique and random relative to the pseudo random schedule for other interconnected devices pairs. Initiation time points 114 may also be determined by a negotiation between each pair of devices where the negotiated time point is within a valid communication period as determined by the predetermined pseudo random schedule. The negotiation process is performed between device pairs and is used to create free time in the schedule for other purposes.

[0048] A device pair 106 typically consists of one device that has the role of master with respect to the connection and another device that has the role of slave. The master device typically initiates and controls the connection, while the slave responds to the master's commands. The schedule typically uses the time base of the clock of the master device. The slave device may maintain synchronization with this clock. Another time base may be used if available to both devices.

[0049] FIG. 1C is a communication period diagram illustrating a series of communication periods 118, 120, 122 comprised of multiple initiation time points 124, 126, 128 and termination time points 130, 132, 134 and/or terminating events. In many situations, the device pair 106 may continue to communicate with each other over a period of time. These communications may take place in several communication periods 118, 120, 122, rather than one continuous communication period 112.

[0050] Although FIGS. 1A–1C illustrated two devices 102, 104 communicating with one another, in some situations there may be more than two devices communicating with each other. For example, and as shown in FIG. 2A, two device networks 202, 204 may exist. Device A 206, device B 208, device C 210 and device D 212 comprise a first device network 202. The second device network 204 includes device E 214, device F 216, device G 218 and device H 220. FIG. 2A illustrates two separate device networks 202, 204, or, in other words, two distinct systems.

[0051] The first device network 202 includes one master and three slaves. Device A 206 serves as the master, while device B 208, device C 210 and device D 212 serve as slaves. The second device network 204 also includes a master (device E 214) and three slaves (device F 216, device G 218, and device H 220). As shown, intrasystem communication 222 may take place between the devices in the first device network 202 and in the second device network 204.

[0052] One exemplary application of the embodiments herein may be with the Bluetooth standard and the relevant personal area network technology relating to Bluetooth. The Bluetooth standard is described in the Specification of the Bluetooth System, incorporated herein by reference. Depending on the particular communication system type, the application of the schedulers disclosed herein can be extended to what were previously considered internal system links. This may be particularly applicable to a Bluetooth system where a piconet is an independent system. In Bluetooth terms, the device networks 202, 204 may both be piconets. When an interpiconet connection is made, the schedulers disclosed herein may be applied to both the new connection and to the previous intra-piconet connection of that device to its piconet master, if one previously existed.

[0053] Of course, it will be appreciated by those skilled in the art that the embodiments and inventive principles disclosed herein are not limited to personal area network technology and/or to Bluetooth networks. The inventive principles herein may be applied to various types of communications systems that include electronic devices and/or computers that communicate with each other.

[0054] Further to the example shown in FIGS. 2A–2D, there are generally three possible ways of connecting the two networks 202, 204. As stated above, in FIGS. 2A–2D device A 206 and device E 214 serve as masters, while the other devices serve as slaves. Thus, master/slave relationships exist between the masters and slaves of each device network 202, 204.

[0055] FIG. 2B illustrates an intersystem communication link 224 between device D 212 and device F 216. The scheduling apparatus and methods disclosed herein may be used with the intersystem communication link 224. As shown, the links between device A 206 and device D 212 and between device E 214 and device F 216 may also be treated as intersystem links 224. Thus, the original connection between each slave and its master may now be treated as an intersystem link because the slave devices may not be available to the master at all times with the additional link. Communications between device A 206 and device D 212 and between device E 214 and device F 216 may be rescheduled because the capacity of the slaves (device D 212 and device F 216) is now being shared between two connections rather than just one connection.

[0056] FIG. 2C illustrates an intersystem communication link 224 between the two master devices 206, 214. FIG. 2D illustrates an intersystem communication link 224 between a master (device A 206) and a slave (device F 216). If the embodiments of FIGS. 2A–2D were implemented and used in a Bluetooth environment, the two systems 202, 204 and the intersystem communication 224 may be referred to as a scatternet. As stated, the embodiments and inventive principles herein are not limited to a Bluetooth environment but have broad application. The embodiments herein provide solutions to the scheduling issues for devices that wish to have an arbitrary number of connections. Further, the embodiments shown herein allow arbitrary topologies of devices to communicate effectively when the connections are treated as intersystem connections.

[0057] FIG. 3A illustrates a simple system topology consisting of a device (electronic device B 302) that communicates with two other devices (device A 304 and device C 306). Electronic device A 304 and device B 302 make up a device pair 308. Similarly, device B 302 and device C 306 make up a device pair 310.

[0058] For each pair 308, 310 of communicating devices, there is a schedule for communication indicating the initiation time points as shown in FIG. 3B. Communication periods 314, 316, 318 between device B 302 and device A 304 are started through communication A-B initiation time points 320, 322, 324. The initiation time points 320, 322, 324 start a communication period 314, 316, 318 for the corresponding pair 308 of devices 304, 302. Communication periods 326, 328, 330 between device B 302 and device C 306 are started through communication B-C initiation time points 332, 334, 336. These initiation time points 332, 334, 336 start communication periods 326, 328, 330 for the B-C pair 310 of devices 302, 306. As illustrated, each initiation time point becomes the terminating event for the preceding communication period. The end of the communication period is signaled to the other device when another initiation time point occurs that conflicts with the current active communication period. For example, initiation time point 320 starts a communication period 314 between device A 304 and device B 302. This period 314 continues until an initiation time point 332 occurs to signal the beginning of a communication period 326 between device B 302 and device C 306. FIG. 3B illustrates the typical operation for the embodiment shown in FIG. 3A.

[0059] FIG. 4 illustrates a device network topology generalization. A communication link 402 exists between device A 404 and device B 406. Multiple devices X₁ to X_n are in electronic communication with device A 404. Similarly, multiple devices Y₁ to Y_m are in electronic communication with device B 406. The performance of the system provides fair distribution of capacity. This performance may be generalized in the case where all links are fully utilized. The relationship is given by the equation below for the generalized system that is diagrammed in FIG. 4. The capacity available to link A–B 402 is inversely proportional to the total number of other intersystem links that both device A 404 and device B 406 participate in. The equation below does not take into consideration the overhead due to switching between connections or other signaling overhead needed for system operation. The Cap_A-B number indicates the relative capacity available to a connection. It shows the relative amount of time that is utilized for communication between the device pair. This relation is applicable to a system where the density of time points is equal for all intersystem links and each link has a random distribution with respect to the others.

[0060] ${\mathrm{Cap}}_{A-B}=\frac{1}{1+n+m}$

[0061] FIG. 5 is block diagram illustrating the major hardware components typically utilized in an electronic/embedded device 500. An electronic device 500 typically includes a processor 502 in electronic communication with input components or devices 504 and/or output components or devices 506. The processor 502 is operably connected to input 504 and/or output devices 506 capable of electronic communication with the processor 502, or, in other words, to devices capable of input and/or output in the form of an electrical signal. Embodiments of devices 500 may include the inputs 504, outputs 506 and the processor 502 within the same physical structure or in separate housings or structures.

[0062] The electronic device 500 may also include memory 508. The memory 508 may be a separate component from the processor 502, or it may be on-board memory 508 included in the same part as the processor 502. For example, microcontrollers often include a certain amount of on-board memory.

[0063] The processor 502 is also in electronic communication with a communication module 510. The communication module 510 may be used for communications with other devices. Thus, the communication modules 510 of the various devices may be designed to communicate with each other to send signals or messages between the electronic devices 500.

[0064] The electronic device 500 may also include other communication ports 512. In addition, other components 514 may also be included in the electronic device 500.

[0065] Of course, those skilled in the art will appreciate the many kinds of different devices that may be used with embodiments herein. Accordingly, the block diagram of FIG. 5 is only meant to illustrate typical components of an embedded device 102, 500 and is not meant to limit the scope of embodiments disclosed herein.

[0066] FIG. 6 is a block diagram illustrating software modules that may be used with the electronic device 600. An embedded application 602 may be used to operate the electronic device 600. The embedded application 602 may include the functionality needed for operation of the electronic device 600. An input/output module 604 may be used for receiving data from the input(s) 504 and for sending data to the output(s) 506. Depending on the type of electronic device 600, the particular functionality of the input/output module 604 may vary.

[0067] A device communications module 606 may be included with functionality to handle incoming and outgoing messages. For example, the device communications module 606 may include the instructions necessary to send and receive communications using the communications module 510. The device communications module 606 may send or transmit outbound data 608 and may receive inbound data 610.

[0068] The electronic device 600 typically includes software to accomplish various tasks including communications, input/output and the monitoring or controlling of the device 600. The device communications module 606 represents the computer program routines or instructions that handle the communications through the communications module 510 or through the communications port(s) 512. The input/output module 604 represents the computer program routines or instructions that handle the input to the device 600 and the output from the device 600. For example, if there were buttons (not shown) on the device 600, the input/output module 604 includes the code necessary to process the inputs from the buttons (not shown). The application 602 controls the device 600 and acts as the main program to carry out tasks of the device 600. Those skilled in the art will appreciate that the software blocks are only examples and the configuration of blocks shown are not necessary to practice the present embodiments. As explained earlier, many different types of devices 102, 500, 600 are available and can be used with embodiments herein. These devices usually already have the necessary software loaded to run the device 600. Embodiments herein can be used with almost all electronic devices 102, 500, 600 that are capable of electronic communications and have some processing capability.

[0069] The device may also include a pseudorandom scheduler 612 and a dynamic allocation scheduler 614. Both the pseudorandom scheduler 612 and the dynamic allocation scheduler 614 will be discussed below. As will be discussed, the dynamic scheduler 614 may include a fair allocation component 616 and an opportunistic allocation component 618.

[0070] An event queue 620 may also be included. The event queue 620 includes one or more queue items 622. Each queue item 622 may correspond to a particular communication channel. Each queue item 622 may include communication time points 624, a channel identifier 626, data pending 628, as well as other information, such as state information 630, status information 632, and other information 634. The data that may be stored in the event queue 620 will be more fully discussed below.

[0071] A method is disclosed and provided herein to dynamically allocate capacity between intersystem connections in the case where the scheduled allocation is not used by a device pair. A decentralized algorithm is used to distribute this capacity to the intersystem links where traffic is available. The unused capacity is allocated first on a fair basis and then the capacity may be opportunistically allocated where communication is possible. The algorithm attempts to maximize the utilization of communication capacity for each device.

[0072] The principle employed to implement fair allocation is to effectively remove an intersystem connection from a device when there is no traffic without actually disconnecting. This causes the inherent fairness of the pseudo random scheduler 612 to reallocate the unused capacity to links that have traffic. In the embodiments herein, two mechanisms are used to achieve fair reallocation of unused capacity: initiation time point reduction and extension of previous communication period.

[0073] In the initiation time point reduction method, a device monitors its internal event queue 620 and traffic on the link. If there is no traffic, the schedule is modified by removal of initiation time points. The schedule is modified so that there is only a fraction of the original time points remaining. For example, in one possible implementation initiation time points may be removed so that only every fourth of the original time points are used. This effectively removes the connection to a device for a short intervals and allows its capacity to be used by other intersystem links. A negotiation process between a device pair is used to modify the schedule and remove time points.

[0074] In the method where previous communication periods are extended, a device will re-establish communication with the device that it previously communicated with when the current communication period is terminated early (i.e., terminations that occur before the next initiation time point). In this way it extends the previous communication period and effectively removes the device that has not fully used its scheduled capacity.

[0075] In principle, opportunistic allocation attempts to maximize the number of parallel communication transfers. To achieve opportunistic allocation, additional processes are performed. In this process a device 102 monitors the traffic pending for each link and the likelihood that a device is available to establish communication. This information may be derived from the signaling that occurred when the previous communication period was terminated for each of its intersystem links. The device 102 may then attempt to establish communication with another device that both has data pending to transfer and is likely to be available. If more that one device meets the criteria, the last one communicated with may be selected. These rules improve the likelihood that both devices will attempt to establish a connection with each other.

[0076] Some applications have very rigid communication requirements that may not be met with the pseudo random intersystem scheduler 612. These requirements are typically expressed in terms of fixed data bit rate and maximum latency. Furthermore, the application will typically negotiate the capability needed when establishing a channel for the service. The service will only be provided if sufficient capacity is available.

[0077] To accommodate more rigid requirements, a method to support resource reserved channels (RRC) is provided. The resource reserved channel type may be implemented as scheduled communication with a fixed period and duty cycle. Traffic for a resource reserved channel has higher priority than the pseudo random scheduled (PRS) channel so that it replaces the PRS traffic when a schedule conflict occurs. The PRS schedule is modified to accommodate any RRC traffic. In current design, resource reserved channels are negotiated such that they do not conflict with each other.

[0078] Because of the periodic characteristic of the resource reserved channel, in many cases it will use a fixed capacity of the communication link. Because of the periodic characteristic, the capacity taken from the PRS traffic is randomly distributed among all links. As a result, the intersystem traffic that is scheduled by the PRS method is still fairly allocated between intersystem connections although reduced by the RRC.

[0079] FIG. 7 illustrates an embodiment of a state machine for the scheduler of a device 102. Each device 102 may implement this state machine to implement a scheduler and to support other related functions. The system description as it relates to the state machine may apply to a MAC/baseband entity responsible for managing the intersystem traffic for the device 102. The information is equally applicable to both devices of the device pair unless otherwise stated. The protocol is based largely on master/slave access mechanisms. The Bluetooth standards use master/slave relationships. For clarity and to illustrate an example of how the state machine may be used, the protocol is described in master/slave and sometimes Bluetooth terminology. Of course, it will be appreciated by those skilled in the art that the inventive principles and embodiments herein may be applied to a wide range of electronic devices 102 configured for electronic communications with other devices.

[0080] The idle state 702 is illustrated in FIG. 7. In the idle state 702, there is no PRS intersystem traffic. The device 102 is free to communicate with other devices in its system or network. The device 102 may be designed to avoid communication that may extend into a PRS scheduled intersystem communication period. For a Bluetooth system, this can occur if a long packet is received that extends past a scheduled time point.

[0081] The data state 704 is also illustrated in FIG. 7. In the data state 704, data is exchanged between intersystem devices. Communication continues until a termination event occurs.

[0082] FIG. 7 also illustrates the negotiate schedule state 706. This state 706 is used to modify the schedule. Either device may initiate this process 706 or state 706. This state 706 is effectively a sub-state of the data state 704 because an active communication period is needed to support the exchange of messages needed for the negotiation of schedule.

[0083] The re-establish state 708 is also illustrated in FIG. 7. The re-establish state 708 implements a procedure for establishing communication during periods when there is no scheduled communication. This mechanism is used to distribute unused capacity to intersystem channels that have data available for exchange.

[0084] FIG. 7 also illustrates events that may cause a transition from one state to another or that may cause the device 102 to stay in the same state. The intersystem schedule manager (not shown) maintains a list of communication events for each intersystem channel in the event queue 620. The event list will consist of an ordered list of scheduled time points 624 and corresponding channel identifiers 626. The scheduled event occurs when the current time matches the scheduled time. When an initiation time point occurs the device 102 will enter the data state 704 and begin communication with the corresponding device. If the device was currently active with another communication channel it will perform the forced termination process on that channel before entering the data state 704.

[0085] There are a number of different types of termination events that may occur. A forced termination occurs when there is a data exchange pending but one of the devices wishes to terminate the current communication period. A device may wish to do this because of another scheduled intersystem communication (or an interpiconet communication in a Bluetooth network) or for other reasons. The device terminates the communication period by asserting an indication of this event in a message to the other device.

[0086] Another type of termination event is a scheduled termination. If the negotiate schedule process 706 or state 706 was successfully completed, a termination time point was agreed upon for the current communication period. A scheduled termination event occurs when this time point occurs.

[0087] A data depleted event is another type of termination event. This event occurs when all the available data has been transferred by both devices. This is signaled to the other device by a message indicating this event. A master device signals to the other device that it has no data to transmit by transmitting a Poll Packet. The slave indicates that it has no data by transmission of a null packet. Thus, the data depleted termination event occurs when both devices indicate that they have no data to transfer.

[0088] Another type of termination event is a non-responsive termination event. A non-responsive termination event occurs when communication is scheduled but does not happen. A device may wait for communication for a fixed period. If no data is received, the communication period may be terminated. If the device is a master, the non-responsive termination event occurs when it does not receive a response to any packets transmitted to the slave device. If the device is a slave, the non-responsive termination event occurs when it does not receive any packets from the master. If the embodiment is being used with a Bluetooth network, this situation may occur when there is a scatternet scheduling violation. It can also occur when a device has a higher priority activity and cannot meet its agreed schedule. This will occur typically for processes that have indeterminate duration (e.g., page response, inquiry response).

[0089] Other types of events are also shown in FIG. 7 and further illustrate other events that may cause a change in state. A negotiate request event is used by a device to initiate a negotiatie schedule process 706. This occurs during the active communication period between the two devices.

[0090] The pending data event or status is an indication of the composite status of all the intersystem links as seen by a device. If any of the links were left in a state where data is remaining to be transferred this indicator may be true. The state is known from the way in which a communication period is terminated. For a link where the data depleted event occurs this indicator may be false. For a link where a forced termination or a non-responsive termination occurs this indicator is true.

[0091] The no pending data event or status is also an indication of the composite status of all the intersystem links as seen by a device. This indicates that none of a device's intersystem links have data pending.

[0092] The communication re-established event is also illustrated in FIG. 7. This event occurs when a poll response sequence has been completed validating that a communication channel has been established. The failure to re-establish event indicates that the device was not able to establish communication in the re-establishment process 708.

[0093] As stated above, the idle state 702 is entered whenever there is no active PRS intersystem communication. The amount of time spent in the idle state 702 is dependent on intersystem traffic load and on any modification made to the pseudo randomly determined interpiconet (more generally intersystem) schedule. A device may modify the intersystem schedule to free time for the idle state 702 if needed for in-system links or other activities. The idle state 702 may imply that the device is idle with respect to PRS intersystem traffic, but the device may be active with other in-system communication activities.

[0094] While a device is in the idle state 702, it typically monitors the intersystem schedule and changes states when defined by the schedule. All other communication activities should be scheduled so that they will not conflict with the intersystem schedule.

[0095] Referring to the data state 704 as shown in FIG. 7, intersystem communication starts when a scheduled initiation event occurs or when the re-establishment procedure 708 has been successful. The scheduled initiation event is typically a time point defined by the pseudo-random scheduler or may be another initiation time point that was previously negotiated between the devices. A communication period consists of the exchange of data between a device pair until a termination event.

[0096] In the data state 704 the master transmits packets to the slave. Data packets are sent if available, otherwise poll packets are sent. This may be done until a termination event occurs. The slave may listen for the master transmitted packets. If packets from the master are received the slave transmits data packets if available and null packets otherwise.

[0097] A device detects a non-responsive condition by monitoring communication activity. If there is no communication for a non-responsive timeout period slots, the device may terminate communication. For the master device, it may transmit packets continuously to the slave device until the non-responsive timeout period expires. For the slave device, it may listen continuously for packets from the master. If the slave has not received any packets for the non-responsive timeout period, it may terminate the connection.

[0098] A device may terminate an active communication period at any time. Typically, a device will terminate the communication because it needs to perform another scheduled event. For example, the device may need to be available for an initiation time point for another link, it may need to communicate with a slave on an in-system link, etc.

[0099] A forced termination may be signaled by a device through a variety of ways. Depending upon the types of devices, systems, protocols, etc., that are being used, different techniques may be implemented by a device to signal a forced termination. Generally, a device may send a forced termination message to other devices to communicate a forced termination. Those skilled in the art will appreciate the many different ways in which this message may be communicated. For example, in a Bluetooth system, the forced termination may be signaled by a device with the flow bit of the packet header. The flow bit is normally enabled (FLOW=1) during the exchange of data. The device may clear it (FLOW=0) to force the termination of the current communication period.

[0100] A forced termination may also be preceded by a negotiate schedule process 706. If used, it may indicate that the device that initiated the new schedule is not available until the new negotiated time. This may imply that this device is not available on this link for any reestablishment. The negotiate schedule state 706 or process 706 may be used by the device that is terminating the active communication and is aware that it will be busy in the near future. If the forced termination is not used, it may imply that the device is likely to be free for re-establishment of this link.

[0101] A data depleted termination occurs when both devices have no data to exchange. This happens when both devices empty their data queues. Similar to a forced termination, a data depleted termination may be signaled by a device through a variety of ways depending upon the types of devices, systems, protocols, etc., that are being used. Generally, a device may send a data depleted termination message to other devices to communicate a data depleted termination.

[0102] Those skilled in the art will appreciate the many different ways in which the data depleted termination message may be communicated. For example, in a Bluetooth system, this event may be signaled when the slave transmits a Null packet and the master transmits a Poll or Null packet. The termination slot is determined based on the last device to signal that is has no data to transmit. The sequence Poll-Null-Poll with the ACKN=0 may be used when the master is the last to run out of data. The last slot used is the Poll packet sent by the master. The sequence Null-Poll-Null with ACKN=0 may be used when the slave is the last device to run out of data. In this case the Null packet from the slave is the last slot to be used.

[0103] The schedule termination may occur if a negotiate schedule process 706 was completed during the current active communication period. As part of this process, the beginning of the hold period (hold instant) was negotiated. The hold instant defines the last slave slot during this communication period.

[0104] As stated above, the negotiate schedule state 706 or process 706 is used to modify the schedule. A device may choose to modify the schedule for any number of reasons (e.g. conflict avoidance, etc). The device modifies its schedule to avoid wasting bandwidth by informing the other device that it cannot meet the obligation of current schedule. A new schedule is then negotiated that is acceptable to both devices.

[0105] The negotiate schedule state 706 or process 706 may be used in several situations. The negotiate schedule state 706 may be used when there are initiation time point event conflicts. In this situation, a device may look ahead at the next time point for the current active communication link, if the next time point conflicts with a time point for another intersystem link and the other link has a higher priority, the negotiate schedule process 706 may be used to negotiate a new time point.

[0106] The negotiate schedule state 706 may be used when there is a communication termination with no opportunity for re-establishment. This may happen if the communication period is going to be terminated by the local device and the link has pending traffic. The local device may look ahead at its predicted availability. If the device is expected to be busy, it may use this procedure to indicate that it is not available by asserting the initiation time point. This information is used by the re-establishment process 708 of the peer device in its selection of communication links.

[0107] The negotiate schedule state 706 may be used when other events occur. For example, if the communication capability of the device is needed for other purposes, the device may make itself available by negotiating inactive periods in the intersystem schedule. This may be done for each intersystem link.

[0108] The negotiate schedule state 706 or process 706 may be initiated by the device that wishes to modify the current schedule. Different techniques may be used by a device to initiate a negotiate schedule process. Generally, a device may send a negotiate schedule initiation message to other devices to initiate a negotiate schedule process 706. Those skilled in the art will appreciate the many different ways in which this message may be communicated. For example, in a Bluetooth system, the state may begin by transmission of an LMP_hold_req message where the hold instant parameter is set to equal the last slot of the communication period as determined by the initiation time point for any other connections. The hold time parameter may be set to correspond to the proposed next initiation time point for the connection. The receiving device may compare the requested hold instant to the next time point event that it has in its scheduled and accept it if it is less. Otherwise the device may request a new hold instant that corresponds to its next scheduled event. In current design, the embodiments are configured to attempt to agree on the shorter of the two periods. The receiving device may also inspect the hold time parameter and accept this parameter if it is able to meet that time. If not, it can propose the next initiation time point for the channel. If both parameters are acceptable, it may send an LMP_Accepted. Otherwise it may transmit an LMP_hold_req with alternate requests. The receiving device may perform similar checks and respond in the same way. After the negotiation is complete, the state may return to the Data state 704 and continue exchange of information until the termination event occurs.

[0109] The re-establishment state 708 attempts to opportunistically establish communication during periods that are not being used. The algorithm is presently designed to initially fairly distribute unused capacity between devices when possible and to then opportunistically distribute communication capacity where possible.

[0110] A device may enter into the re-establishment state 708 when the current communication has been terminated and there is data pending on any of its intersystem communication links. The device may attempt to re-establish communications on the previous active connection that has data transmission pending where the remote device has indicated that it may be available. If the device is a master, this may consist of the transmission of packets (Poll or data) until a response is received or another initiation time point occurs. If a slave, it may listen until another initiation time point occurs. If a response is received the device may transition into the data state.

[0111] In the case where the device that terminated the communication period signaled that it will be busy, the free device may attempt to establish communication with another device that is likely to be available.

[0112] Each device may maintain an event queue 620 and state information 630 for each intersystem communication channel. The event queue 620 may consist of an ordered list of time points. Each time point may be generated from the pseudo random sequence for the corresponding connection plus any negotiated modifications or additions. The device may combine the lists to determine which connections are scheduled at any point in time.

[0113] For each intersystem link status information 630 may be maintained. This information may be derived from the termination event plus any internal data queue knowledge.

[0114] Each device may include link status information. The link status information may include data pending 628 information, such as pending/no pending data. This may indicate if there is any pending transmission on the link. This is set if there is any data pending transmission in the local queue or if the previous communication period was terminated with a data transmission pending event.

[0115] A device may also include a remote capacity indicator (not shown). This may indicate whether the remote device on a link is currently busy or free. This indicator may be set to free if the previous communication period was not terminated with a negotiate schedule event. Using the negotiate schedule process implies that the remote device is busy until the new negotiated time.

[0116] Link schedule information (not shown) may also be stored on the device. Link schedule information may include pseudo random time points. These time points may be automatically generated based on an algorithm that defines their position relative to the clock of the master device on the link. These time points may also define the initiation of communication.

[0117] Scheduled time points may also be stored. These time points may be created through a negotiation process between the two devices connected by this link. These time points define the initiation of communication. A device may also store termination time points. These are time points that define when communication should be terminated. They are created in the negotiate schedule process 706.

[0118] Because initiation time points are typically generated pseudo randomly, conflicting time points may occur for devices that have two or more intersystem links. The occurrence may be random with a rate dependent on the density of time points. In embodiments disclosed herein, a device detects the conflicting time points and adjusts the schedule to eliminate them. The device may use the negotiate schedule state 706 or process 706 to move or skip conflicting time points when possible. When it is not possible to reschedule conflicting initiation time points, the device should select communication with the device with the longest inactive period over other devices. This assures a fair allocation of bandwidth and minimizes inactive periods.

[0119] A pseudo random generator may be used to create the initiation time points that make up the schedule. Time points may be defined with reference to the clock of the master device of the device pair that make-up the intersystem connection. In current design, both devices are able to independently create the schedule and both have knowledge of the clock needed to utilize the schedule. Given that each schedule may be unique and random with respect to other intersystem schedules, a unique but shared piece of information may be used as input to the generator. For example, if the devices were part of a Bluetooth network, this shared piece of information may be the Bluetooth device address (BD_ADDR) of the master and active member address (AM_ADDR) of the slave.

[0120] One characteristic of the generator is its density, which defines the average time between time points. Other temporal relations may also be imposed on the generation function to achieve particular operating characteristics. Three possible methods and related characteristics are described below. The following methods may be used but each has its own unique system limitations and performance tradeoffs. Those skilled in the art will appreciate that other methods may also be used with embodiments of devices and device software to effect scheduling of communication periods.

[0121] FIG. 8A illustrates a predetermined synchronized method for generating time points. As shown, in the predetermined synchronized time method time points are generated by first breaking the schedule into fixed period intervals (A). The duration of the intervals corresponds to the density of time points desired. A single time point is placed within the interval at a random location. Following is an equation that described how a time point is generated using this method.
TP_N=A×N+Rand(0 . . . A)

[0122] In the foregoing equation, A defines the interval size, and N is the interval number and index to the time point. The function Rand ( ) provides a random number in the range of 0 to A. A unique random number is generated for each time point.

[0123] This predetermined synchronized method has the advantage that the range of communication period lengths can be influenced by the distribution of the time point positions. Different distributions of random numbers can be used to control the statistical characteristics of the communication period length. Typically a uniform distribution of random number would be used. But, for example, to achieve a communication period duration more narrowly distributed around the mean a normal distribution of random numbers centered at A/2 may be used. This would reduce the variation in communication period length but increase the probability of collisions when compared to a uniform distribution.

[0124] This method is primarily applicable to systems where the interval is synchronized between intersystem links. It has the advantage of providing a tighter bound on the maximum delay between communication periods and may better control the statistical distribution of the communication period duration.

[0125] FIG. 8B illustrates a predetermined asynchronized method for generating time points. As shown, in this method of generation time point positions are determined by random number generation over an arbitrary long time. This period is typically many times greater than the density. Typically, this should be 10 to 100 times greater that the average period between time points. Time points are generated randomly with uniform distribution in this period. The time points are then sorted into ascending order for usage by the scheduler.
TP_0..M=Rand(0..A*N)
TP_0..N=Sort(TP_0.M)

[0126] In the foregoing equation, TP_{0 N} is the ordered list of time points used by the scheduler. The Rand( ) function generates time points that are uniformly distributed over the period defined by the density (A) and number of time points needed (N). The total duration that the random numbers are uniformly generated in is determined by the product of the density (A) required and the number of time points (N).

[0127] The predetermined asynchronized method has the advantage that there is no synchronization needed between clocks of different intersystem links. Its primary disadvantage when compared to the predetermined synchronized method is that the characteristics of the communication period are not bounded. The communication period length and time between communication periods is more variable.

[0128] FIG. 8C illustrates a real-time method for generating time points. In the real-time method, time points are generated relative to previous time points. This is primarily applicable to the case where it is desirable to generate the schedule in real-time although it can also be used to predetermine a schedule. To perform the real-time method, a device may generate a random number with uniform distribution in the range between 0 and 2 times the density. This number is added to the previous initiation time point to determine the next initiation time point. This information to transferred to the other device. This process is carried out by one of the devices in the device pair, typically the master. This method is particularly applicable to Hold mode in the Bluetooth System.

[0129] The intersystem scheduler allows Resource Reserved Channel (RRC) traffic to coexist with Pseudo Random Scheduled (PRS) intersystem traffic. The embodiments described herein allow this coexistence while maintaining the fair performance characteristics of the best effort channel (BEC) provided by the pseudo random scheduler. Two mechanisms are defined to manage the coexistence of the RRC channel types on top of the BEC channel: the traffic overlay method and the dynamic schedule modification method.

[0130] The traffic overlay method is used when the active period of the Resource Reserved traffic is relatively short compared to the PRS average communication period. If the active period is less than the non-responsive termination event timeout threshold, a device is allowed to provide this channel without modifying the intersystem schedule. In this case, the device will simply transmit the RRC traffic in place on the PRS traffic. After completion it will return to the PRS scheduled traffic. If the device is nearing the end of the communication period it will terminate the communication early and then proceed with the RRC traffic.

[0131] The schedule modification method is used when the active period of the RRC traffic is long relative to the average communication period length or if it is longer than the non-responsive termination event threshold of the PRS scheduled traffic. In this case, the PRS schedule is modified to free time for this traffic. This occurs in the communication period prior to the period for the RRC traffic.

[0132] To accommodate in-system data traffic a device must have time available to service it. This free time corresponds to the idle state 702 in the intersystem state machine. A device may use the free time that naturally occurs in the intersystem scheduled traffic or choose to modify the intersystem schedule to make free time available. In the latter case the device can make free time in the intersystem traffic by re-negotiating the intersystem schedule. This is equivalent to the process that is used to manage resource reserved channels. Typically this would be done periodically to meet requirements for in-system communication.

[0133] A device may also choose to treat an in-system link as if it is an intersystem link. In this case it may use a PRS schedule for the in-system link and get the same performance characteristics as an intersystem link. The method used may be dependent on the timing requirements of the in-system communication.

[0134] FIGS. 9A and 9B illustrate a device network configuration and the unique pseudo-random schedule generated for each connection. As shown in FIG. 9A, the device network includes three masters 902, 904, 906 and one slave 908. In a Bluetooth system, the configuration shown in FIG. 9A makes up three piconets (one master for each piconet).

[0135] The communication periods diagram of FIG. 9B illustrates several intervals. As shown, the density used enables an average of one communication period per interval. As discussed above, a communication period starts with an initiation time point and it ends when a conflicting time point occurs or with a termination time point.

[0136] FIGS. 10A and 10B illustrate a device network configuration including four piconets. As shown in FIG. 9A, the device network includes three masters 1002, 1004, 1006, one slave 1008, and one master/slave 1010. The communication periods diagram of FIG. 10B illustrates a minimum capacity allocated to each connection. As discussed herein, dynamic allocation may be used to recover unused capacity.

[0137] FIGS. 11A and 11B illustrate fair allocation of unused capacity by a device network. In this example, there was no traffic between device A 1102 and device D 1104. As a result, the original communication periods for the device A 1102–device D 1104 pair were unused capacity. For the example of FIGS. 11A and 11B, also assume that full capacity was being used between devices B 1106 and D 1104 and between devices C 1108 and D 1104. In fair allocation, the unused capacity of the device A 1102–device D 1104 pair is randomly used by either the device B 1106–device D 1104 pair or by the device C 1108–device D 1104 pair. In a Bluetooth system, this would effectively make device A 1102 appear to be absent from the scatternet.

[0138] FIGS. 12A and 12B illustrate opportunistic and fair allocation of unused capacity by a device network. In this example, there was no traffic between device A 1202 and device D 1204. As a result, the original communication periods for the device A 1202–device D 1204 pair were unused capacity. For the example of FIGS. 12A and 12B, also assume that full capacity was being used between devices B 1206 and D 1204, between devices C 1208 and D 1204, and between devices E 1210 and C 1208. With fair allocation, a terminating event caused by a device that is not active causes the free device to remain on the same channel and to attempt reestablishment. With opportunistic allocation, a terminating event caused by an active busy channel causes the free device to switch to an alternate channel. Thus, opportunistic allocation allows more parallel exchange of data. As shown in the communication periods diagram of FIG. 12B, the unused capacity of the device A 1202–D 1204 pair is fairly allocated and opportunistically allocated to other channels to use the capacity.

[0139] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.