Patent Publication Number: US-2018039316-A1

Title: Smart security device with status communication mode

Description:
This application relates to U.S. Ser. No. 14/635,248, filed Mar. 2, 2015, which relates to U.S. Ser. No. 14/169,464, filed Jan. 31, 2014, which relates to U.S. Ser. No. 14/103,209, filed Dec. 11, 2013, which relates to U.S. Ser. No. 13/946,414, filed Jul. 19, 2013, now U.S. Pat. No. 8,850,242, which relates to U.S. Ser. No. 13/406,469, filed Feb. 27, 2012, now U.S. Pat. No. 8,516,279, which relates to U.S. Ser. No. 12/472,327, filed May 26, 2009, now U.S. Pat. No. 8,127,158, which relates to U.S. Ser. No. 11/443,668, filed May 30, 2006, now U.S. Pat. No. 7,539,882, which relates to U.S. Provisional Application No. 60/685,976, filed May 30, 2005. U.S. Ser. No. 14/169,464 also relates to U.S. Ser. No. 14/090,099, filed Nov. 26, 2013, now U.S. Pat. No. 9,721,201. Each of the mentioned applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The embodiments disclosed herein relate to power management in self-powered electronic devices, and, in particular, to predictive power management in self-powered electronic devices that include power saving features. 
     BACKGROUND OF THE INVENTION 
     Private and public networks, such as the Internet, continue to grow at an exponential rate. These rapidly expanding networks consume a tremendous amount of power, which is typically supplied from traditional electrical power grids. As such, most networked computers are either tethered to electrical wall outlets or require periodic charging at electrical wall outlets. Many networked computers, however, have benefited tremendously by being self-powered. For example, emergency communication systems, computing devices in rural areas where access to traditional power sources is limited, etc. 
     However, current self-powered devices, such as devices that obtain energy from solar power, typically waste much of their power communicating with other networked computing devices. As such, it would be highly desirable to provide a self-powered device (SPD) that consumes less power when communicating with other devices in a network. 
     Wireless sensor networks have been proposed for a wide range of monitoring applications in various industries, such as health care, energy, transportation, infrastructure, agriculture, security, the environment and many other fields. Billions of active sensors have been installed that can wirelessly connect to networks and capture data. Such an installed base of sensors creates issues such as powering such sensors as well as transporting and storing the data received from the sensors. 
     Various conventional approaches have been developed in response to particular constraints. Microelectronics companies are concerned with creating low power devices with energy harvesting technologies and improved batteries. Communications companies are continuing to build networks with more radio towers, improved data compression and adherence to interference regulations. Cloud computing companies are developing approaches for storing more data with data structures suited for the expected exponential growth in capturing data. Such conventional approaches are unlikely to be sufficient with the grand vision of the “Internet of Things”. The communications bandwidth (and data storage on the Internet to implement such an approach) could include hundreds of times as many sensors as conventional smartphones, potentially consuming the highest amount of energy of the Internet. 
     Most conventional approaches are based on autonomous sensor notes that are always on and capture and transmit large amounts of sensor data to a network that always needs to be listening and recording the transmissions. The network then needs to relay back an acknowledgment to the sensor that the data was accurately received. If scaled to a trillion sensors, a huge number of devices would need to be implemented with batteries that would be unaffordable (or at least inconvenient) to change. A huge amount of traffic on already congested networks would further increase the power needs of each device, since higher antenna output would likely be needed to overcome interference and noise. 
     Different approaches are needed. The motivation of a better approach stems from a more fundamental question—Why do we need all of this data anyway? The data and related power needs of capturing, transmitting and recording data are highly context and application dependent. Most conventional sensors blindly capture and transmit data. Such sensors assume the application needs or knows what to do with that data. Some data inevitably are more important than others. The importance of data can vary with time and with the knowledge embedded in the application. 
     It would be desirable to implement a predictive power management in a wireless sensor network. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a device comprising a processor, an energy source, one or more sensors, a wireless transceiver and a memory. The memory may comprise instructions for selecting one of a plurality of modes of operation. The modes of operation may comprise (i) a low-power mode in which the device consumes less than a pre-determined or an adaptively-determined amount of power and the device has less than full functionality and (ii) a high-power mode in which the device consumes more than the pre-determined or the adaptively-determined amount of power and the device has more functionality than in the low-power mode. The instructions for selecting one of the modes of operation may comprise (i) instructions for conserving power by transitioning from the high-power mode to the low-power mode and (ii) instructions for activating the wireless transceiver to transmit a message with information from the sensors to a remote device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the disclosure herein, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating an embodiment of a system including one or more self-powered devices; 
         FIG. 2  is a block diagram illustrating a context of the invention; 
         FIG. 3  is a block diagram showing an implementation with multiple sensor nodes; 
         FIG. 4  is a block diagram illustrating an embodiment of a self-powered device; 
         FIG. 5  is a more detailed diagram of one of the sensor nodes; 
         FIG. 6  is a block diagram illustrating an embodiment of a photovoltaic collector of  FIG. 4 ; 
         FIG. 7  is a block diagram illustrating an embodiment of a converter and storage system of  FIG. 4 ; 
         FIG. 8  is a block diagram illustrating an embodiment of the current flow from the collector of  FIG. 4 ; 
         FIG. 9  illustrates an embodiment of a software protocol stack for a network interface of  FIG. 4 ; 
         FIG. 10  illustrates periodic enabling of a transceiver of  FIG. 4 ; 
         FIG. 11  illustrates coordinated communication; 
         FIG. 12  is a flow diagram illustrating a low power activation signal monitoring mode cycles; 
         FIG. 13  is a flow diagram showing a power-aware data collection mode cycle; 
         FIG. 14  is a flow diagram showing a power-aware communications mode; 
         FIG. 15  is a context diagram showing wireless signal configurations; 
         FIG. 16A  is a block diagram illustrating a computer network having an MS-Exchange server; 
         FIG. 16B  is a block diagram illustrating a computer network having a web DAV/iCal server; 
         FIG. 16C  is a block diagram illustrating a computer network having an MS-Exchange server; 
         FIG. 16D  is a block diagram illustrating another computer network; and 
         FIG. 17  is a flow chart of a method for managing power consumption. 
     
    
    
     Like reference numerals refer to the same or similar components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of self-powered systems, devices, and methods are described herein. The self-powered system may include a computing device that selectively communicates with a self-powered device. The self-powered device may include: a circuit to power the self-powered device; memory; a processor; and a program mechanism that is stored in the memory for execution by the processor. The program mechanism may include instructions for selecting one of a plurality of modes of operation, including a first mode of operation in which the self-powered device consumes less than a pre-determined amount of power and a second mode of operation in which self-powered device consumes more than the pre-determined amount of power. (See  FIG. 17 ). 
     Embodiments of the invention provide a context-aware and/or power-aware wireless sensor network system that enables application needs to determine which data is captured, transmitted and/or stored at the edge of the wireless sensor network. Such an implementation may result in lower power usage, lower bandwidth usage, less interference, and/or less storage and/or processing capacity in the cloud. The determination of which data is important may change and may be determined based on context and/or knowledge. The sensor system is highly adaptable. A software application can reprogram the sensor nodes with new instructions as data needs change and/or grow more complex. Additionally, the power management of the sensor nodes is application-driven to prioritize limited power resources according to the application needs. Power resources may be calculated based on available energy, a power budget, predicted future power needs and/or energy harvesting opportunities. 
     The program mechanism may further include instructions for communicating with the computing device when the self-powered device is in the second mode of operation. The self-powered device may conserve power by alternating between the first mode of operation and the second mode of operation such that the self-powered device is in the second mode of operation during pre-determined time intervals. A duty-cycle of the second mode of operation relative to the first mode of operation may be based on a power budget for the self-powered device. 
     The computing device and the self-powered device may be synchronized such that transmit circuits and receive circuits in the computing device and the self-powered device are to communicate signals during one or more of the pre-determined time intervals or adaptively-determined time intervals. In some embodiments, the synchronization includes use of a Network Time Protocol. In some embodiments, the synchronization includes a Wi-Fi periodic beacon signal. 
     The computing device may poll the self-powered device during one or more of the pre-determined or adaptively-determined time intervals. 
     The self-powered device may switch to the second mode of operation prior to one or more of the pre-determined time intervals or adaptively-determined time intervals, and the self-powered device may switch to the first mode of operation after one or more of the pre-determined or adaptively-determined time intervals. 
     In some embodiments, the self-powered device further includes instructions for determining a periodicity of the pre-determined time intervals or adaptively-determined time intervals in accordance with signals provided by the computing device, and the duty-cycle is further determined in accordance with the periodicity. 
     In some embodiments, the self-powered device further includes instructions for combining messages that are to be communicated to the computing device in order to reduce a communication overhead. 
     In some embodiments, the system further includes one or more additional self-powered devices and a coordination element. The coordination element may assign communication priorities to the self-powered device and the one or more additional self-powered devices in accordance with power budgets for these devices. 
     In some embodiments, the self-powered device further includes instructions for providing an acknowledgment message to a sending self-powered device with a higher priority than other types of messages. 
     In some embodiments, a circuit converts an external energy source into signals that power the self-powered device. The external energy source may include light. 
     In some embodiments, the circuit includes a component, such as a photovoltaic cell, a wind energy generator, a thermo-electric energy generator, a kinetic energy generator, a piezoelectric device, a magnetic energy generator, and/or a chemical-to-electricity generator. 
     In some embodiments, the computing device provides control information to the self-powered device. 
     In some embodiments, the self-powered device includes one or more sensors. The sensor may measure a characteristic, such as temperature, humidity, pressure, vibration, light, motion, sound, proximity, flow rate, electrical voltage, and electrical current. In some embodiments, the self-powered device may provide configuration information to one or more output devices in accordance with the measured characteristic, the internal status of the self-powered device, any received message, elapsed time, local and/or remote user interaction, or a local and/or remote automatic process. The output devices may include a switch, a relay, an electromechanical actuator, a heater, a fan, a speaker, a solenoid, a motor, an electric field generator, a magnetic field generator, and an electro-magnetic field generator. 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the subject matter presented herein. However, it will be apparent to one of ordinary skill in the art that the subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
     The following description describes various self-powered devices (“SPDs”), systems that include SPDs, and methods for operating SPDs and the systems that they operate in. SPDs are devices that are configured to operate solely under power sources from external energy sources, such as light, thermal, kinetic, wind, wave or other energy. In some embodiments, the SPDs may also be powered by battery power and/or using a power line at ˜50 or ˜60 Hz. 
     The SPDs may include a variety of features and/or functionality (i.e., hardware and/or software) to conserve power. In particular, the SPDs may use duty-cycle power management in which the SPDs alternate between low and high-power modes of operation based on a power budget. The SPDs may also alternate between many different power-consumption modes. Furthermore, the SPDs may communicate with computing devices during communication windows. This communication may be periodic and may utilize pre-determined time windows. For systems that include multiple SPDs, a communication priority may be assigned to a given SPD based on its power budget, with a higher priority accorded to devices that have a lower power budget. The SPDs may also combine messages in order to reduce communication overhead and/or give higher priority to providing acknowledgment messages over other types of messages. 
       FIG. 1  is a block diagram of a system  100  including one or more self-powered devices  102 . The system  100  may also include other computing devices, such as desktop or stationary computers  104 , laptop computers  106 , personal digital assistants  116 , cellular telephones, or the like. These computing devices may be connected to one another via one or more routers or switches  110 , firewalls  112 , wireless access points  114 , fixed network connections  108 , or other computer networking equipment, such as computers, cables, switches, firewalls, routers, bridges, gateways, or the like. These computing devices are generally located remotely from the SPDs  102 . 
     In some embodiments, the system  100  has a single connection link between a SPD (such as SPD  102 - 1 ) and a remote computing device (such as computing device  104 - 1 ), while in other embodiments there may be many wired and/or wireless links between one or more of the SPDs  102  and the computing devices  104 , such as Universal Serial Bus (USB), Firewire, Ethernet, coaxial cable, copper telephone line, optical fiber, wireless, infra-red, or the like. For example, SPD  102 - 2  may couple to the system  100  via a WiFi (Wireless Fidelity--IEEE 802.11x wireless networking protocol) access point  114 . Also, the system  100  may communicate over private or public networks, such as an intranet and/or the Internet. 
     Referring to  FIG. 2 , a block diagram of a system  150  is shown implementing a context of the present invention. The system is shown comprising a block  170 , a block  172 , a block  174 , and a block  102 . The block  170  may be implemented as a mobile computing device. The block  172  may be implemented as a network data services device. The block  174  may be implemented as a network computing services device. The block  102  may be implemented as a self-powered device, such as a wireless sensor node. In one example, the SPD  102  may be implemented as part of the mobile computing device  170 . The SPD  102  is shown receiving inputs from a number of blocks  160   a - 160   n . The blocks  160   a - 160   n  may be implemented as sensors. The sensors  160   a - 160   n  may also be referenced as sensors A, B, C, etc. The block  160   a  may represent (or capture) a contextual logic signal. Another block (e.g.,  160   b ) may represent (or capture) a beacon signal. The block  160   n  may represent (or capture) a proximity signal. Various other signals may be captured by the sensor node  102 . 
     Referring to  FIG. 3 , a diagram illustrating a plurality of sensor nodes  102   a - 102   n  is shown. The sensor nodes  102   a - 102   n  may be implemented as SPDs. The sensor nodes  102   a - 102   n  are shown connected to a mobile computing device  170   b . However, some of the sensor nodes  102   a - 102   n  may be connected to a mobile computing device  170   a , while others may be connected to the mobile computing device  170   b , while still others may be connected to a mobile computing device  170   n . The particular number of sensor nodes  102   a - 102   n  and wireless computing devices  170   a - 170   n  may be varied to meet the design criteria of a particular implementation. 
     Each of the sensor nodes  102   a - 102   n  may have a power budget based on predicted energy input and/or energy output needs. For example, an energy input need may be a function of past patterns and/or cycles as well as predictable future opportunities to harvest energy from the environment (e.g., weather and/or day/night/seasonal patterns on a photovoltaic device, etc.), at least up to the storage capacity. The predicted energy expenditures may also be based on the predicted power consumed given known upcoming calendar and/or event data as well as other inputs. 
     A context-aware activation signal may be used to wake up the device  102 . The device  102  may begin sensing and/or processing other data, and/or provide power management that is context-aware. A higher priority may be placed on processing certain data. Such data may be data deciding whether to spend more power to transfer the data with less delay and/or more reliability. For example, logic may be implemented to boost radio power based on priority and/or distance from a cellular tower. Such logic may minimize the radio power that may otherwise reduce interference with other sensors. 
     One or more of sensors  160   a - 160   n  may be implemented internally as a beacon signal sensor or as a radiation sensor, a blood glucose sensor, a proximity sensor, chemical/gas sensor, blood pressure sensor, a location sensor, a pollution sensor, a heart rate sensor, a vibration sensor, an air flow sensor, a heart rate variability sensor, an acceleration sensor, a fluid flow sensor, a skin conductance sensor, a position sensor, a direction sensor, a rotation sensor, a weight sensor, a displacement sensor, a machine operations sensor, a fluid retention sensor, a velocity sensor, a leakage sensor, a respiration sensor, a magnetic field, a microphone, an ECG, one or more derived quantities, temperature, image, color, pulse oximetry, physical pressure, odor, drug delivery, air pressure, voltage, container opening, etc. One or more of the sensors  160   a - 160   n , or a combination of the sensors  160   a - 160   n  may be implemented internally as part of the sensor node  102  (e.g., within a sensor node housing), or alternatively may be implemented externally (e.g., as a separate sensing device coupled to the sensor node  102 ). Additionally, the sensors  160   a - 160   n  may transmit data directly to a network, in which case the sensor node  102  may receive data as a network data source. Such network data sources may include, for example, environmental or weather data, location-based data, proximity data, etc. 
     The various sensors  160   a - 160   n  may be configured in one of a number of categories, such as a logical condition, a fluid/gas level, a biological process, etc. The logical conditions may be further configured to receive signals from devices such as a beacon, a proximity sensor, a location sensor, a vibration sensor, an acceleration sensor, a position/direction sensor, a displacement velocity sensor, a magnetic field sensor, a temperature sensor, a physical pressure sensor, an air pressure sensor, a force/strain sensor, a moisture/humidity sensor, etc. The fluid/gas level category of sensors may be implemented to receive signals from devices such as a radiation sensor, a chemical/gas sensor, a pollution sensor, an air flow sensor, a fluid flow sensor, a rotation sensor, a machine operations sensor, a leakage sensor, a microphone, an image/color sensor, an odor sensor, a voltage sensor, an electrical sensor, a current sensor, a gyroscope, etc. The biological process category of sensors may be configured to receive signals from devices such as a blood glucose sensor, a blood pressure sensor, a heart rate sensor, a heart rate variability sensor, a skin conductance sensor, a weight measuring device, a fluid retention sensor, a respiration device, and ecg, a pulse oximetry device, a drug delivery device, a container opening device, a medication dispensing device, a microbial device, etc. 
       FIG. 4  is a block diagram of an embodiment of a self-powered devices  102  shown in  FIG. 1 . SPD  200  contains a plurality of components, such as at least one central processing unit (CPU)  202 , memory  204 , an optional wireless transceiver  206  coupled to a wireless antenna  208 , an energy collector  210 , an energy converter  212  with an optional energy storage device  214 , optional user input and/or output devices  216 , an optional network interface  218 , one or more optional sensors and/or output devices like actuators or one or more sensor/actuator interfaces  220  configured to be coupled to the one or more sensors, and at least one bus  222  that connects the aforementioned components. Different embodiments may include some or all of these components. Also in some embodiments, these components are, at least partially, housed within a housing, where the housing may be configured to withstand direct exposure to the elements, such as sun and rain. 
     The CPU  202  may include programmable or non-programmable circuits, such as ASICs or microcontrollers. This circuitry typically includes non-volatile memory to retain programmed memory  204  functionality, event logs, and/or data, even after a period of power that is insufficient for continued operation. In some embodiments, the data contained in memory  204  may be updated while the SPD is deployed, in response to either local and/or remote instigation, allowing new and/or different capabilities to be added to the functionality. 
     Using the memory  204 , the CPU  202  operates and manages the remainder of the components in the SPD  200 . In some embodiments, some SPDs may also operate and manage other SPDs in the system  100  ( FIG. 1 ). 
     The wireless transceiver  206  includes a transmitter and receiver configured for transmitting and receiving radio signals via the antenna  208 . 
     The energy collector  210  is any suitable mechanism for collecting energy from the surrounding environment in which the SPD is located. For example, the energy collector  210  may include photovoltaic cells that generate electrical energy from light, wind energy generator(s), thermo-electric energy generator(s), kinetic (motion) energy generator(s) (such as piezoelectric devices), magnetic/inductive energy generator(s), chemical-to-electricity generator(s), etc. Furthermore, the energy collector  210  may collect electromagnetic energy from, for example, a system of antenna(s) and rectifying device(s), or other suitable means. In addition, in some embodiments, electrical energy may be collected via signals received through the network interface  218 . In other embodiments, energy may be collected from more than one of these sources at the same time, or at different times. Also in some embodiments, energy collection may be supplemented with more traditional power sources, such as replaceable batteries, AC (line) power, an external DC power supply, Power-over-Ethernet, or the like. 
     In embodiments where the collector  210  generates power from light, the collector may include one or more photovoltaic (PV) cells (also known as “solar cells”). These cells absorb incident radiation (light) and convert that radiation to electrical energy. In addition to the PV cell(s) themselves, the collector may contain any necessary interconnections to form a series and/or parallel array of cells. The properties of the electrical energy generated by a PV cell for a particular intensity of incident light are typically characterized by an open-circuit voltage V OC , a short-circuit current I SC , and a maximum power delivered P MAX , which occurs at a particular output voltage V MAX  (where V MAX ≦V OC ) and output current I MAX  (where I MAX ≦I SC ). (For many PV cells, I SC  and I MAX  are roughly proportional to the intensity of the incident light across several orders of intensity magnitude, whereas V SC  and V MAX  are comparatively constant, perhaps changing by a factor of only 2 or 3 across the same large variation of incident lighting conditions). 
     The PV cells may be based on a number of different technologies, including monocrystalline silicon, multicrystalline silicon, amorphous silicon, thin-film, or other photovoltaic technologies. If the collector  210  uses more than one cell, the cells may be connected together in series to provide a higher voltage than a single cell, in parallel to provide a higher current, or in a hybrid configuration to provide higher current and voltage than a single cell. The cells may be physically arranged at the best possible location to receive incident light, such as above the SPD. In some embodiments, the cells form an integral part of the SPD housing so as to not detract from the appearance of the device. Also in some embodiments, energy collection procedures  236  (described further below) are configured to notify the user of the power output from the collector  210 , such that the user may determine the best physical location of the cells for optimal energy collection. For example, the SPD may display an indication or emit an audible tone that varies and/or is representational of the instantaneous collected power. Since the SPD may have the ability to store excess collected energy, the ability to maximize the collected energy over some extended time may be particularly valuable for some SPD applications. 
     In some embodiments, the SPD  200  is intended to be used over a wide range of lighting conditions, varying from direct sunlight to low-level indoor fluorescent lighting. In these embodiments, the SPD  200  may efficiently collect and convert the incident light energy to usable electricity. Selection of the appropriate type and size of PV cell(s) to use for a particular embodiment of the SPD  200  is typically determined by the corresponding power required, expected radiant light conditions, and cost constraints for that embodiment of the SPD  200 . 
     The energy converter  212  is electrically coupled to the collector  210  and the optional energy storage device  214 . The converter  212  converts the energy collected by the collector  210  into a form that is usable by the SPD  200 . Typically, this conversion is from one voltage to another, for example from the maximum power voltage (Vmax) of the PV cell(s) to the appropriate supply voltage(s) of the rest of the subsystems in the SPD  200 . The storage device  214 , which may more generally include an energy storage device such as a battery or capacitor, stores the converted energy for later use by the SPD  200 . When excess energy is collected, this excess energy is stored until the battery  214  is fully charged. When there is insufficient energy being collected, the battery  214  provides additional energy until it has discharged or reached a minimum useable level. If the energy from the collector  210  is otherwise deemed adequate for use by the SPD  200 , then the battery  214  of the collector may be minimized or eliminated. 
     For some embodiments, the SPD  200  may need a useful life of many years, and the converter  212  may need to operate over this lifetime without requiring replacement of any internal energy storage device(s), such as the battery  214 . This lifetime may need to be maintained over the expected range of operating temperature and humidity, and also after many charge/discharge cycles, in some cases many of these cycles occur every day. 
     The network interface  218  and/or wireless transceiver  206  may include hardware as well as associated firmware and/or software components. The network interface  218  provides communications connectivity to the remainder of the system  100  ( FIG. 1 ) via wired connections, while the wireless transceiver  206  and antenna  208  provide communications connectivity to the remainder of the system  100  ( FIG. 1 ) via wireless connections. Some embodiments may include both wired and wireless connectivity, while other embodiments may include one or the other. Furthermore, some embodiments may include more than one network interface  218  and/or wireless transceiver  206 . In still other embodiments, no network interface  218  or wireless transceiver  206  is provided, as the SPD  200  does not require connectivity to the system  100  ( FIG. 1 ), such as for stand-alone, sense-and-display or sense-and-control applications. 
     The network interface  218  may be of any suitable type, such as a parallel interface, a serial interface, or the like. These interfaces may be based on a proprietary format or on industry-standard protocols, such as SCSI, printer-style Parallel Port, ESDI, GPIB, PCI, RS-232, Ethernet, I2C, USB, FireWire, Token Ring, DS1, or DS3. For purposes of this discussion, the possible wired connectivity also includes communication through optical fibers. These optical-fiber-based communications protocols may similarly be serial or parallel, and may be based on industry standards (e.g.—Fiber Channel, OC-3, OC-12, etc.) or may be proprietary in nature. 
     Possible wireless connectivity for the wireless transceiver  206  include radio-based protocols, light-based protocols, magnetic-induction-based protocols, or other methods of communicating that do not require some sort of physical connection. Radio-based interfaces may be based on industry standards, such as Wi-Fi (IEEE 802.11-based protocols), BlueTooth, RFID, and other interfaces known to those skilled in the art, or may be proprietary in nature. Light-based protocols may be industry standard (e.g.—IrDA, or other industry-standard protocols) or may be proprietary in nature. 
     The user input and/or output devices  216  may include input devices for controlling the SPD  200 , such as one or more buttons or switches, a keyboard, a touch screen, a proximity sensor, a microphone, and other input functions known to those skilled in the art, or some combination of these. The user input and/or output devices  216  may also include output devices, such as one or more indicators (such as light-emitting diodes, or passive reflective indicators), multi-digit numeric or alpha-numeric displays, an array of pixels (such as bit-mapped LCD screen or another pixeled array of indicators), speakers, or the like. Inputs and outputs may be initialized and/or updated, through an automatic process and/or through user interaction, and coordinated remotely and/or locally at the installed location. 
     A number of techniques can be used to conserve the power of the user input/output devices, including operating the output devices at a lower duty cycle or turning the output devices off when available power is low. Depending on the underlying technology, displays may also be dimmed, or operated at reduced contrast or refresh rate, with different encoding/decoding parameters, and other power-conservation techniques known to those skilled in the art. In addition, various forms of input and output functions may be combined, such as the use of proximity sensors as a “user input” so that the display may activate automatically when sensing a user&#39;s presence. 
     The sensory I/O subsystem  220 , if present, may include input and/or output functionality. For example, the sensors may include input device(s), such as temperature, humidity, pressure, vibration, light, motion, sound, proximity, flow rate, electrical voltage, and/or electrical current sensors; and/or output device(s), such as relays, electromechanical actuators, heaters, fans, speakers, solenoids, motors, electrical and/or magnetic field generators. 
     The memory  204  may comprise Random Access Memory (RAM) and/or Read Only Memory (ROM). The memory  204  may include an operating system  226  that has instructions for communicating, processing, accessing, storing, or searching data. Examples of suitable operating systems include embedded LINUX or a proprietary or scaled-down operating system. In addition, memory  204  may include communication procedures  228 , wireless procedures  230 , power management procedures  232 , sensor procedures  234 , the energy collection procedures  236 , input/output procedures  238 , and other applications, such as applications  240  and  242 . 
     The communication procedures  228  are used for communicating with the remainder of the devices in the system  100  ( FIG. 1 ). The communication procedures  228  may also control power management of the wireless transceiver  206  and/or network interface  218 , protocol implementation and participation (such as with 802.11b, etc.), persistent network interface or wireless operating parameter management, network interface statistics management, bridging/routing functions, encryption and security services, etc. 
     The wireless procedures  230  may work in conjunction with the communication procedures  228  to facilitate wireless communication between other devices in the system  100  ( FIG. 1 ) and the SPD  200 . In some embodiments, the SPD  200  may also include a wireless network adapter, for example, as at least part of a printed circuit board that controls communication at the data link level (OSI layers 1 and 2) between an external computing device and the SPD  200 . 
     For some embodiments of the SPD, conserving power is of utmost importance. In these embodiments, numerous techniques may be used to reduce power consumption. One or more of these techniques may be implemented using hardware and/or software, such as the power management procedures  232 . For example, power consumption may be reduced by maximizing gain of the passive input components; coalescing messages; explicit attention to latencies; access point placement; duty cycling and/or sleep modes; priority ranking based on power levels; static and/or dynamic tokenization of commonly exchanged information blocks; static and/or dynamic distillation of repeated information blocks; periodic (versus continuous) transceiver enable; peer-forwarding based on power disparities; gateway routing based on power disparities; and other power-conservation techniques known to those skilled in the art. 
     Thus, in some embodiments, the power management procedures  232  are used to reduce power consumption by the SPD  200  by (i) initiating a series of prioritized shutdowns of partial or entire subsystems when the available power from the collector  210  and/or battery  214  becomes insufficient to keep the SPD  200  fully powered, and/or (ii) ensuring partial or entire subsystems are powered back on when sufficient power again becomes available to support additional operation usually according to the priority of each function in the subsystem. 
     The sensor procedures  234  are used to measure variables from the sensors and/or communicate with output devices. For example, the procedures may be monitoring the sensors for ambient and/or external stimuli, collecting and formatting the information, and then initiating any appropriate action based on that input information. For the output function(s), these procedures initiate, modify, and/or terminate the operation of the output device(s). In conjunction with the power management procedures  232 , the sensor procedures  234  also manage the power consumption and operating characteristics of the sensors and/or the output devices  220 . 
     The energy collection procedures  236  are used to control and manage energy collection and storage, such as by (i) monitoring the voltage and current produced by the collector  210  and, based on the known properties of the collector  210 , determining the intensity of the input energy (light, heat, motion, etc.) to the collector  210  as well as the overall energy being made available to the SPD  200 , (ii) ensuring that the current drawn from the collector  210  is adjusted to maximize the power extracted from the collector  210 , (iii) ensuring that the storage device  214  (if present) is properly charged, and/or (iv) monitoring and controlling the available energy stored in the battery  214 , etc. 
     The user input/output procedures  238  control and manage the user input/output devices  216 , such as by collecting and formatting (thresholding, debouncing, etc.) the user input, and initiating any appropriate action based on that input. For the output function(s), these procedures are responsible for any necessary formatting/construction of the information to be displayed, as well as updates of that displayed information. In addition to these primary functions, these procedures in conjunction with the power management procedures  232  manage the power consumption of the user input/output devices  216 . 
     Referring to  FIG. 5 , a more detailed diagram of one of the sensor nodes  102   a  is shown as a block (or circuit)  200   a . Each of the self-powered sensor nodes  102   a - 102   n  may include a processor, an RF transceiver, an energy storage unit, one or more sensors and a memory. The memory may store a set of instructions executable by the processor to evaluate and selectively store sensed data in the memory or transmit sensed data based on sensor data values and the stored instructions. The remote computing device  170  may be located separately from the sensor node  102   a . The device  170  may be selectively coupled to one of the sensor nodes  102   a - 102   n  to collect stored data and/or to transmit new instructions to the sensor node. 
     The sensor node  200   a  is shown comprising a block  202   a , a block  204   a , a block  206   a , a block  208   a , a block  210   a , a block  214   a , a block  250   a , a block  252   a , and a block  254   a . The block  202   a  may be implemented as a CPU (or processor) circuit. The block  204   a  may be implemented as a memory. Details of the memory  204   a  are shown by the blocks  270   a - 270   n . The block  206   a  may be implemented as a radio. The block  208   a  may be implemented as an antenna. The antenna  208   a  and the radio  206   a  may form a transceiver. The block  210   a  may be implemented as an energy capture unit (ECU). The block  214   a  may be implemented as an energy storage unit (ESU). The block  250   a  may be implemented as a sensor I/O. The block  252   a  may be implemented as a user I/O circuit. The block  254   a  may be implemented as a clock generation circuit. 
     The output portion of the user I/O  252   a  may be configured to preset one or more signals to a speaker, a display, an LED, a vibrator, an actuator, an electrical field, a magnetic field, etc. The signals presented to the I/O  252   a  may be an electrical signal (such as a DC signal), a data signal, etc. The input portion of the user I/O  252   a  may be configured to receive signals from a microphone, a camera, a light sensor, a motion sensor, a position sensor, a button, a touch screen, a proximity sensor, etc. The signals presented to the I/O  252   a  may be an electrical signal, such as a DC signal, a data signal, etc. 
     In one example, the sensor  102  may implement a learning process and/or predictive modeling on the CPU  202   a  (to be described in more detail in connection with  FIGS. 12-14 ). New rules may be stored in the memory  204   a . In another example, the machine learning process(es) may be run on the mobile computing device  170  and/or the network computing services block  174 . The processing power and energy to implement the learning process(es) may use more aggregated data and/or processing power than the sensor  102  can process efficiently while running on the energy storage unit  214   a . By offloading the processing, the overall energy used by the sensors  102   a - 102   n  may be reduced. 
       FIG. 6  is a block diagram of a photovoltaic collector  300  of a self-powered device, such as the SPD  200  ( FIG. 4 ). As described above, in some embodiments the collector  300  includes one or more PV cells  301  connected together to supply power to the converter  212  ( FIG. 4 ). When illuminated, the interconnected PV cells  301  together produce a current I PV  at a voltage V PV . In other embodiments, other forms of energy collection and generation of electricity from external energy sources may be used. Whether the generator(s) derive their input power from light, heat, motion, chemical energy, vibration, pressure, network interface communications, other electromagnetic radiation, or some other form of energy, or some combination of these external sources, the electricity produced is characterized by an output voltage at some output current. 
     An optimal operating point typically exists where the output voltage at a particular output current yields a maximum power from the available input energy and operation at this optimal operating point may be achieved using the methods described below. Furthermore, more than one of these PV cells  301  may be combined as shown using PV cells of the same or different types. Furthermore, in some embodiments, switching mechanisms are provided so that the presence of one set of PV cells  301  do not adversely affect the operation of another set of PV cells  301 , such as when one set is operating, and another set is not operating. 
       FIG. 7  is a block diagram illustrating an embodiment of a converter  400 , such as the converter  212  ( FIG. 4 ). In some embodiments, the converter  400  includes an input DC-to-DC converter  402 , a storage device  404 , and an output DC-to-DC converter  406 . The input DC-to-DC converter  402  transforms the current coming from the collector at V PV  to the voltage V STORE  of the storage device  404 . The output DC-to-DC converter  406  transforms the current flowing from the storage device  404  to the voltage(s) used by the other subsystems in the SPD, known as V OUT1 , V OUT2 , etc. These output voltages may be the same or different depending on the requirements of the SPD. If present, the storage device  404  includes one or more physical rechargeable storage devices interconnected in series and/or parallel that meet the requirements of that embodiment. One should note that in some embodiments, a storage device may not be required. In these embodiments, all that is required is to convert the input voltage derived from the collector  210  ( FIG. 4 ) to the output voltage required by the rest of the subsystems in the SPD. Additionally, other embodiments do not require the input DC-to-DC converter  406  if the optimal voltage supplied by the collector  210  ( FIG. 4 ) is within a predefined acceptable range. Likewise, some embodiments do not require the output DC-to-DC converter  406  if the rest of the subsystems in the SPD are able to operate using the output voltage from the storage device  404 . 
       FIG. 8  is a block diagram illustrating an embodiment of the current flow  500  from the collector  210  ( FIG. 4 ). In order to maximize the power taken from the collector  210  ( FIG. 4 ), the converter  212  ( FIG. 4 ) attempts to maintain the current flowing from the PV cells  301  ( FIG. 6 ) at about I MAX , which yields a voltage of approximately V MAX . Since the optimal voltage V MAX  of the collector  210  ( FIG. 4 ) may be different from the voltage V STORE  of the storage device  404  ( FIG. 7 ), some embodiments may make use of a DC-to-DC converter (as described above) to make the voltage transformation, preferably with minimal power loss. Suitable DC-to-DC converters operate in a switching mode, which is to say that they periodically draw some current to “charge” an inductor, then “discharge” that current (at a different voltage) into the load. These two operations may then be repeated when more power needs to be transferred. 
     For DC-to-DC converters, the time that the current is being drawn into the converter to charge the inductor may be referred to as T ON , and the time that the DC-to-DC converter is transferring the stored charge to its load (or is otherwise waiting for the next cycle to begin) may be referred to as T OFF . The full cycle time of the converter may be expressed as T ON +T OFF . Similarly, the current drawn into the DC-to-DC converter when it is on may be referred to as I DCON , and the current drawn into it when it is discharging its inductor to the load (or it is otherwise waiting for the next cycle to begin) may be referred to as I DCOFF . In order to maintain the maximum power output from the collector, the time average of these two converter input currents may be kept to about I MAX . 
     For most switching DC-to-DC converters, I DCOFF  is approximately equal to 0, and assuming that the converter is on for only a small fraction of its full cycle time (T ON +T OFF ), the I DCON  usually needs to be greater than I MAX . Unfortunately, for a DC-to-DC converter operating in these conditions connected directly to the collector  210  ( FIG. 4 ), the current drawn alternates between I DCON  during T ON  and approximately 0 during T OFF , neither of which are the optimal current I MAX . Therefore, to maintain the optimal current drawn from the collector at about I MAX , a capacitor  510  or other charge-storage device may be connected across the output of the collector, as shown. With the addition of the capacitor  510 , when the DC-to-DC converter is on, the net current into the capacitor is I PV −I DCON . Since I DCON  is typically greater in magnitude than I PV , the capacitor  510  is therefore discharging during T ON . During T OFF , typically I DCOFF ≈0, so the net current into the capacitor  510  is I PV −I DCOFF ≈I PV , and the capacitor  510  is charging. The average value of the current into the capacitor  510  may be expressed as 
     
       
         
           
             
               
                 
                   ( 
                   
                     
                       I 
                       PV 
                     
                     - 
                     
                       I 
                       DCON 
                     
                   
                   ) 
                 
                 · 
                 
                   T 
                   ON 
                 
               
               + 
               
                 
                   ( 
                   
                     I 
                     PV 
                   
                   ) 
                 
                 · 
                 
                   T 
                   OFF 
                 
               
             
             
               
                 T 
                 ON 
               
               + 
               
                 T 
                 OFF 
               
             
           
         
       
     
     which may be set to be approximately I MAX  for efficient operation of the collector  210  ( FIG. 4 ). For large capacitances, the drop in the voltage of the capacitor  510  during T ON  may be very small, and the rise in the voltage during T OFF  may likewise be very small. 
     Since the average current drawn from the collector  210  ( FIG. 4 ), I PV , is now maintained at approximately I MAX , the average voltage on the capacitor  510  (and the collector  210  in  FIG. 4 ) is, therefore, approximately V MAX . The value of the capacitor  510  is chosen such that the variation in voltage is small enough to be acceptably close to V MAX . 
     As previously stated, the maximum power of one of the PV cells  301  ( FIG. 6 ) typically occurs at a certain current I MAX , and at a certain voltage V MAX . However, the actual values of this operating point may change with incident light intensity, operating temperature, and may also vary from device to device due to processing and manufacturing differences. This may make it difficult to predetermine the ideal operating point values for any particular device at any particular light intensity and temperature. In some embodiments, the ideal operating point for the PV cell(s)  301  ( FIG. 6 ) may be determined automatically and, furthermore, may be adjusted automatically as operating conditions change, using the following method. 
     To determine the power being delivered by the converter  212  ( FIG. 4 ), the energy collection procedures  236  ( FIG. 4 ) periodically measure the current I PV  from the collector  210  ( FIG. 4 ), and the voltage V PV  on the collector  210  ( FIG. 4 ), and multiplies these two values together. One way to increase the average current drawn by the input DC-to-DC converter  402 , usually resulting in a reduced V PV , is by increasing the on time of the DC-to-DC converter, T ON . Likewise, by reducing T ON , the average current drawn from the collector  210  ( FIG. 4 ) may be decreased, allowing V PV  to increase. Other means to increase or decrease the average current drawn by the input DC-to DC converter may be used. 
     To maintain the maximum power from the collector  210  ( FIG. 4 ) under varying operating conditions, the energy collection procedures  236  ( FIG. 4 ) (i) measure the power from the collector  210  ( FIG. 4 ), (ii) increase I PV  by a small amount, such as 0.1% to 1% of the full value, (iii) measure the power from the collector  210  ( FIG. 4 ), (iv) if power has increased, go to step (ii) above, otherwise continue, (v) decrease I PV  by a small amount, such as 0.1% to 1% of the full value, (vi) measure the power from the collector  210  ( FIG. 4 ), (vii) if power has increased, go to step (v) above, otherwise go to step (ii) above. Using this process, the controller may continuously “hunt” for the maximum power delivered from the collector  210  ( FIG. 4 ). As the operating conditions vary, this procedure may allow those changes to be tracked by the SPD, allowing the energy collection procedures to continuously adjust the operating point of the collector  210  ( FIG. 4 ) in order to achieve maximum power delivery. 
     To prevent operating at only either the maximum current I SC  or the maximum voltage V OC , which may happen under very low lighting and/or other extreme conditions, when it may be difficult to determine how the power from the collector  210  ( FIG. 4 ) has actually changed, the procedure may be modified to switch the direction of the “hunt” if the change in I PV  value has moved in the same direction for the last 10 or 20 (or other appropriate number of) steps or iterations. This means that under extreme operating conditions, the operating point of the collector  210  ( FIG. 4 ) may be scanned across a wide range of possible operating points to increase the likelihood that the maximum power delivery point is found. In some embodiments, to ensure that the storage device  404  ( FIG. 7 ) in the converter  212  ( FIG. 4 ) is maintained within its safe operating parameters, its voltage and/or current may be continuously monitored by the controller. 
     When the maximum capacity of the battery  214  ( FIG. 4 ) is reached, the controller typically turns off the input DC-to-DC converter. This may be accomplished by setting the on time T ON  of the DC-to-DC converter to approximately zero, or otherwise disabling its operation. 
     When the energy held in the battery  214  ( FIG. 4 ) gets low, and/or is not otherwise being sufficiently recharged from the collector  210  ( FIG. 4 ), the energy collection procedures  236  ( FIG. 4 ) may reduce the power consumption of the other subsystems in the SPD. In some embodiments, the energy collection procedures  236  ( FIG. 4 ) may compare the energy in the battery  214  ( FIG. 4 ) against one or more pre-determined low-energy thresholds, and once the threshold(s) is crossed, the energy collection procedures  236  ( FIG. 4 ) may take one or more action(s) to reduce the energy demand from the battery  214  ( FIG. 4 ), if appropriate. 
     When the remaining energy in the battery  214  ( FIG. 4 ) drops to the lowest threshold, below which proper operation of the SPD may no longer be guaranteed, in some embodiments, the energy collection procedures  236  ( FIG. 4 ) and/or the power management procedures  232  ( FIG. 4 ) initiate a series of controlled shutdowns of any subsystems that remain on, including the majority of the SPD itself. Once this is accomplished, the SPD may be held in a reset condition, through the use of an automatic circuit until sufficient energy is delivered to the battery  214  ( FIG. 4 ) to allow initiation of SPD startup. 
     When the energy level of the battery  214  ( FIG. 4 ) transitions from below the lowest threshold to above that threshold, a subset of the SPD may be automatically brought out of reset and may begin to turn on various subsystems of the SPD, typically in a prioritized sequence, depending upon how much energy is in the battery  214  ( FIG. 4 ), and/or how quickly it is being recharged. As increasing energy becomes available in the battery  214  ( FIG. 4 ) and/or more power is available from the converter  212  ( FIG. 4 ), and the various low-power thresholds are overcome, more and more SPD subsystems may be brought out of any low-power states until eventually the SPD may be returned to its full-power mode. 
     To eliminate unnecessarily repeated or oscillatory transitions between various low-power states, some embodiments may include an appropriate amount of hysteresis to be added to each threshold. This ensures that as a low-power threshold is approached in the decreasing direction, a slightly lower value than the nominal threshold value may be required to be achieved before transitioning the SPD to the next lower-power state. Likewise, when the energy in the battery  214  ( FIG. 4 ) is increasing and that threshold is approached, a slightly higher value than the nominal threshold value may be required to be achieved before transitioning from the previous low-power state. The amount of hysteresis for each threshold level is chosen to minimize oscillatory transitions, yet not make the actual transition points too different from the nominal threshold value. 
     In a given embodiment, there may be zero or more network interfaces, such as the network interface  218  ( FIG. 4 ) of one or more types. The specific type(s) of network interfaces utilized in an SPD do not necessarily imply a specific network behavior, and may include technologies such as, but not limited to, wired interfaces (RS-232, RS-485, USB, Ethernet, FDDI, Fiber Channel, or any other wire or cable-based protocol, standard or proprietary) and wireless interfaces (Bluetooth, Zigbee, IrDA, UWB, Wi-Fi, GPRS, GSM, CDMA, or any other wireless protocol, standard or proprietary). As illustrated in  FIG. 9 , typically each network interface includes the following hardware and software layers, as defined by the classic OSI networking reference model: physical layer  610  (such as RS-232, 100BaseT, T1 and radio), link layer  612  (such as Ethernet, FDDI, Wi-Fi and HDLC), network layer  614  (such as IP, IPX and similar protocols), transport layer  616  (such as TCP, UDP, RTP and SMB). Higher layers, such as session layer  618 , presentation layer  620  and application layer  622 , may be viewed as part of the client software, so are not discussed as part of the network interface itself. 
     In many embodiments, one of the key attributes of the network interface may be its operation on an extremely low power budget. This is discussed further below. 
     Numerous issues may affect power usage in an implementation of the network interface, including range requirements, the amount of power consumed per unit of time, the amount of power consumed per bit conveyed, and any needed networking layer overhead from the associated network interface software stack and its impact on the power consumed in generating, transmitting, receiving, and processing that overhead. 
     In general, the power consumption of a communication subsystem increases with the amount of data communicated and the distance that the communications traverse. Similarly, a low-bit-rate communications system may generally be designed to consume less power per unit of operating time than a high-bit-rate system, but may have a higher cost per bit communicated. Finally, communication subsystems based on newer, specialized, and/or proprietary communications protocols often consume less power for a given transmission distance or bit rate than existing, general-purpose, and/or standardized protocols. 
     Keeping in mind these general characteristics, the design, implementation, and usage of each network interface for a particular embodiment of an SPD may have various constraints including (but not limited to): The need for wireless vs. wired operation. The distance required for data transmission. The volume of data to be transferred for the SPD application. The sensitivity of the application to data stream latency. The frequency of communications needed to meet protocol requirements. Any compatibility requirements with installed network infrastructure. The average power available to the network interface subsystem. The tolerable cost and/or size of the subsystem. 
     Several methods to reduce average power in the network interface subsystem are described here. Embodiments of the SPD may use one, many, all, or none of these methods and strategies. Some strategies outlined are applicable to any network interface technology while others are applicable only to one or some network interface technologies. 
     One class of radio computer network technology is based on the IEEE 802.11 set of standards, commonly referred to as “Wi-Fi”. Versions of this standard support various transmission distances and bit rates, and existing equipment may support more than one version simultaneously. In an exemplary embodiment, therefore, the SPD may be used with one or more IEEE 802.11 “Wi-Fi” Protocols. Implementation in embodiments that support a compatible version of Wi-Fi may typically not require installation of an additional wireless access point(s) in the external computer network. Instead, an existing, i.e., an already-installed, access point(s) may typically be used. In some cases, the access point functionality may already be incorporated into the remote device(s), such as computer devices  104  ( FIG. 1 ), with which the SPD(s)  102  ( FIG. 1 ) communicate. 
     An additional advantage of using a Wi-Fi radio is that the components needed to implement the radio are often readily available, physically small, and relatively inexpensive. The Wi-Fi data rate may also be high enough for most SPD applications. However, the existing component sets may consume relatively large amounts of power, even when not transmitting. Thus, in some embodiments, various schemes to dramatically reduce the power consumption of the Wi-Fi radio may be employed. 
     In some embodiments, the SPD includes sleep modes and/or duty-cycle control. Selectively shutting down or turning off some or all of circuits in the physical-layer networking subsystems may offer the ability to reduce power consumption. These features are typically referred to as “sleep modes”. The duty cycle of such subsystems is the ratio of the time the subsystem spends in the “on” or “awake” state compared with the total time. Assuming the higher-layer protocols and/or applications may tolerate it, adjusting the duty-cycle of the network interface may allow the controller to reduce power consumption of the subsystem without requiring additional external hardware and/or reconfiguration of the device. 
     For some network interface technologies, a high-rate of power consumption when active may be more than offset by the low power consumption from remaining in sleep mode the majority of the time and powering the subsystem for the minimum time necessary to affect communication. Thus, for a given amount of data to be transferred, some implementations of the network interface may have a high power-per-unit-of-time cost but may still be efficient in the cost of the power per bit communicated. 
     This approach accepts a high power draw for short periods of time because it seeks to optimize the power per bit communicated through the network interface. It is possible for such an implementation to consume less average power than an implementation using a low-bit-rate protocol because the network interface may spend substantially less time powered on even though the network interface is drawing more power when it is powered on. 
     Often, it is not known beforehand when a message must be sent from an SPD to a remote device such as one of the computer devices  104  ( FIG. 1 ) and vice-versa. In particular, if the network interface in an embodiment is operated with duty-cycle control (as described above and further below) then its transceiver spends some of its time active, and some of its time disabled in a sleep mode. If a message is to be properly communicated, the transmitting device must be enabled and the receiving device must likewise be enabled in order to detect the message and properly receive it. 
     When there are no power consumption constraints, the transceiver circuits in each device may be left enabled all of the time. In some embodiments, however, there may be power consumption constraints, so it may be desirable to use duty-cycle control as a power management technique. To ensure that message communication may occur reliably under these conditions, the duty cycles between the transmitting and receiving devices need to be aligned such that the transceivers are enabled in each device at the same time. 
     By using periodic communication windows, the duty-cycle alignment may be achieved through synchronization. This assures that the transmitter in the sending device and the receiver in the receiving device are enabled at the same time. This is illustrated in  FIG. 10 , in which (a) transceivers are enabled just prior to the communication time window, (b) communication occurs, often lasting just long enough to initiate a session (see  FIG. 9 ) that will span numerous enable periods, and (c) each SPD shuts down its transceiver as soon as it can, but no later than after some limited period of time. 
     In some embodiments, therefore, periodic transceiver enabling is used. Different network interface protocols may support such enabling. For example, a sparsely populated Wi-Fi network may be used in conjunction with a periodic beacon signal having an appropriate rate. The periodic beacon signal may be adjustable. The periodic beacon signal notifies some or all radio NICs (the Wi-Fi nomenclature for a remote node versus an access point) of its presence, timestamp, supported rates, capabilities, and an indication of any traffic waiting to be transmitted (TIM). In concert with the beacon signal, a Wi-Fi NIC may be kept in sleep mode for an interval just short of the beacon signal interval, and then be automatically woken-up in time to receive the beacon signal. The NIC may then determine if there is any traffic queued up for it to receive, and then receive the traffic (if any). It may then send the pending items it has queued for transmission (if any) and then go to sleep again until the next beacon signal interval. 
     In some embodiments, to reduce the power consumed by a Wi-Fi radio subsystem that uses commercially-available chip sets, yet still maintain an adequate communications bit-rate, the radio may be kept in a low-power “off” or “standby” mode as much as possible. In some embodiments, the standby mode may be used the majority of the time. One way to do this is to take advantage of Wi-Fi&#39;s beacon feature, described above, whereby the Wi-Fi access point associated with an SPD periodically polls the SPD (and any other associated remote Wi-Fi devices the access point is aware of) at regular pre-set intervals. The beacon signal interval may often be set at once per 100 ms (although a different interval may instead be configured in the access point). By monitoring the beacon signal activity, the SPD determines the beacon signal period. Thus, the SPD knows when the next beacon signal will occur, thus when it must awaken to receive the next beacon signal. 
     By placing the SPD&#39;s radio in a low-power “off” or “standby” mode until just before the beacon signal arrives, the SPD&#39;s controller may ensure that the SPD radio is active during the beacon signal time so as to transfer any data to or from the access point, and then return the radio to its low-power state as soon as the data transfer is complete. Assuming the beacon signal interval is not set to be unreasonably short, this strategy may allow the SPD radio to spend the large majority of its time in a very low power state yet still maintain sufficiently low transmission latencies and adequate data throughput to support typical SPD operation. 
     Some techniques used to reduce power consumption in the network may benefit from having an SPD synchronized in some way with one or more other nodes and/or access points in the network. If all nodes and/or access points participating in the communications exchange are synchronized then they will know when to enable their transceivers for periodic communications. 
     In one embodiment, synchronization may be achieved using the Network Time Protocol (NTP) that is typically available in computer networks that adhere to the Internet Protocol (IP) set of standards. By utilizing the NTP facilities available in the network, an SPD and other nodes may accurately determine the time of day and, from this information, facilitate their periodic communications. 
     In another embodiment, synchronization may be achieved by leaving the SPD&#39;s network interface receiver enabled long enough to receive several periodic transmissions. By observing the periodicity of the transmissions, the SPD may then enter a sleep state between the periodic transmissions, gradually increasing the length of the intervening sleep states until the duty cycle of the network interface is low enough to achieve the desired power savings but high enough to ensure sufficient probability of being awake during the periodic transmissions. 
     Moreover, standardized communications between computers typically operate in layers. However, additional layers increase overhead costs that negatively impact efficiency, as measured in terms of payload data communicated per unit of energy and/or power consumed. Coalescing messages is a systems approach to efficiency, and allows for communications to be optimized by having additional knowledge about the communicating devices and/or the protocols they are using to communicate. 
     In a typical embodiment, messages for various purposes flow between the SPD and one or more remote device(s). In the event that more than one such message is going to the same remote device, it may be possible to examine the pending messages destined for that remote device and combine the messages into a form of multi-block message so that layering overheads are minimized. 
     Combining or coalescing messages may be combined with periodic transceiver enabling and duty-cycle control to create a natural collection or “queuing” point in time where opportunities for combining the messages prior to communication may be found. 
     Most messages to and from an SPD may be categorized into various classes. Attention messages include a message from a client node on the network requesting information or service from a server node. Information messages include a message to or from an SPD containing information. This message may be in response to an Attention Message and/or may contain unsolicited information. Ack/Nak Messages include a message to or from an SPD indicating that a previous message is being acknowledged, or negatively acknowledged. 
     In an exemplary embodiment of coalescing, an information block consisting of 1000 bytes in total of data is to be sent from a remote device to an SPD. Even though the 1000 bytes are to be sent from the same remote device to the same SPD, because of the way the information block is typically created using modern software methods, it is often sent as a series of smaller messages, each consisting of 50 to 100 bytes of payload data. Each message, if sent individually over Ethernet, typically may have a wrapper that includes the UDP header, the IP header, and the 802.3 header, plus the preamble. In total, this may double the number of bits transmitted in each message, as compared with just the bits in the payload data. Therefore, coalescing these messages into a multi-block message may require a frame to indicate the coalescing behavior (perhaps 4 bytes) and an additional approximately 2 bytes per block of data to demarcate each sub-block for later extraction. This multi-block message may still have the UDP header, the IP header, the 802.3 header, and the preamble, but only one for each of these, thus requiring approximately one tenth the overhead necessary as compared with no coalescing of the information. 
     Communicating a message from one computer to another generally involves some form of acknowledgment (positive or negative) that the message was seen, acted on, or otherwise processed. When an SPD sends a message to a remote device, the time that the SPD spends waiting for acknowledgment to return from the remote device may often be time that the SPD is waiting with its network interface and/or other subsystems powered on. Minimizing the time waiting for the return Ack/Nak Message minimizes the overall time that the SPD subsystems remain powered on, thus reducing the average power consumption of the SPD. 
     There are a variety of ways such latency may be reduced or minimized, including: Arrange for the remote device to acknowledge a message immediately upon its receipt by the remote device, and not to wait for the message to be fully processed and/or any message-requested action to be completed. Arrange for the remote device to acknowledge a message as a high-priority task in its internal task-scheduling algorithm. Allow the remote device to coalesce the Ack/Nak Messages it needs to return to an SPD and then let the SPD “decoalesce” them upon receipt for distribution to the SPD&#39;s internal sending entities. The coalescing of Ack/Nak Messages by the remote device may be performed separately for each SPD that is communicating with the remote device. Process the messages where the sender is awaiting a response preferentially over other message types. Some, all, or none of the above methods may be used in an SPD and/or remote device implementation in order to reduce the power consumption and/or otherwise increase the operating efficiency of an SPD. 
     In applications where a remote server is handling information for multiple requesting SPDs, there may arise cases where some SPDs have a lower average power budget than others. In such cases, the scheduling of resources when dealing with multiple SPDs simultaneously may favor those with lower power budgets to minimize the impact of latency on their power budgets. 
     In the case of multiple SPDs requesting communication in an environment using periodic transceiver enabling, one technique to optimize power consumption includes a coordinating element (such as the server handling the requests) giving preferential permission to communicate to the energy-poor SPD(s) ahead of the energy-rich SPD(s) during the period of permitted communication. The energy-poor SPD(s) may then disable their network interfaces(s) and/or other subsystems sooner, better conserving their less-abundant power than the energy-rich SPDs. This approach is illustrated in  FIG. 11 , in which (d) transceivers are enabled just prior to the communication time window, (e) numerous SPDs vie for the ability to communicate so that a coordinating element (such as a server) utilizes a token scheme to control which SPDs communicate thereby allowing energy-poor nodes to communicate preferentially in order to allow them to disable their transceivers sooner and save power, and (f) each SPD shuts down its transceiver as soon as it can, but no later than after some predetermined and limited period of time. 
     In the case of multiple SPDs requesting service from a remote device, another technique to optimize power consumption includes the server preferentially servicing the power-poor SPD(s) ahead of the energy-rich SPD(s) if requests from more than one SPD are pending completion at the server. Minimizing the response time to the energy-poor SPDs may help them conserve their less-abundant power by allowing them to place their network interface(s) and/or other subsystems in a sleep mode sooner at the expense of more energy-rich SPDs. 
     As a refinement on the ideas of periodic transceiver enable and duty-cycle power management, pseudo-time slot allocation may be used. This technique recognizes that multiple SPDs operating in a network or ecosystem may experience contention in communicating, especially to a central point such as a Wi-Fi access point and/or a server. This technique allows each client SPD to attempt to exercise its periodic communications during the same periodic interval but each in a time slot that occurs at a different, pre-assigned phase within the periodic interval. Just prior to the periodic communications interval, the master/server node may queue up time slot assignment messages, one destined to each client SPD, indicating when the SPD may exercise its right to communicate within the periodic interval. Alternatively, another method of assigning time slots may be used as long as only one client SPD is assigned a particular time slot or as long as there is an effective way to handle time-slot conflict issues. 
     At the beginning of the periodic interval, all SPDs accept one (or a small number of) message(s) to allow the time slot assignment message to be received. Alternatively, this part of the protocol may be eliminated if the time slots have already been assigned through some other method. If the assigned time slot for an SPD has not yet arrived, the SPD may place its network interface and/or other subsystems in a sleep state (if they are not already in such a state) and reawaken them just before the time slot arrives. When the assigned time slot does arrive, the appropriate SPD may then transfer any pending messages with the master/server node. 
     The method(s) used to assign the order of the time slots may use any number of algorithms or procedures, such as pseudo-random, round-robin, fairness, and other algorithms known to those skilled in the art, and may also offer the most energy-poor SPD in the ecosystem the first right to communicate, followed by the next-most-energy-poor SPD, and so on in an orderly progression. The scheduling algorithms may take advantage of information such as the energy available to the SPD, the estimated energy it may need to communicate, its communications bandwidth and/or latency requirements, how often it has communicated in the past, and/or other relevant information. 
     In a communications system between computers that implement an application having a predefined function, blocks of information are typically communicated repeatedly, and the contents of some of the blocks may often be known beforehand. For a communications subsystem where every communicated bit represents another reduction in the available power, replacing large blocks of this type with reference tags may reduce the number of bits that must be exchanged to accomplish a given functionality. Receipt of a particular reference tag may indicate to the receiving device that it may replace the reference tag with the associated block of information. 
     In an exemplary embodiment, an SPD is used to display a calendar. A calendar view may be represented by a series of visual “planes”. Each plane may represent something either new to a day&#39;s calendar entry or something that does not change from one day to the next. The unchanging elements may be considered background planes that may be stored in the SPD memory and referenced by a symbolic name (a reference tag) that is shorter than the image they represent. Typically, when displaying a calendar, the elements that must change regularly from one day&#39;s view to the next are few and are generally the label for each block of allocated time. All other items may effectively be referred to by the reference tag, effectively reducing the number of bits that must be transmitted to display the calendar view. 
     An enhancement to traditional static distillation (as described further below) is a process of dynamic distillation of repeated blocks. In this dynamic process, a server (either an SPD or a remote device) may associate a block of information represented by a reference tag “on the fly”. After establishing the meaning of the reference tag with the client (either a remote device or an SPD), the server thereafter utilizes the tag to communicate the intended information in a more cost-effective manner than communicating the information itself. 
     In an exemplary embodiment, an SPD is used to display a calendar. Consider a block of time on the calendar with a label describing that block of time. If the total calendar time was 8 hours and the label applied to a 30 minute interval, the label describing that time frame may typically be transmitted to the SPD, in full, approximately 16 times. Conversely, sending a single message to define the label image along with its reference tag may allow use of just the tag in all subsequent communications, thus reducing the amount of information transmitted (and possibly stored). 
     As discussed previously, it is often the case that proprietary and/or shorter range communication protocols may operate on less power than standard and/or longer-range protocols. In addition, it is possible for the different SPDs in a network or ecosystem to have vastly different power budgets due to available energy conditions, opportunity for wired operations, or other factors. In such cases, a gateway/peer-forwarding behavior may be implemented that utilizes SPD power reserves as a link-cost metric. Combined with routing behaviors among SPDs in an ecosystem, such a routing algorithm may provide the optimal communications path by allowing the energy-rich SPD or SPDs to operate as gateway nodes to other parts of the network. 
     In an exemplary embodiment, a Wi-Fi transceiver and a very-low-power radio transceiver are provided as network interfaces in each of several SPDs in a network. The SPDs communicate with each other and with a non-SPD remote device. The Wi-Fi network interface has a power-per-bit-communicated cost of transceiver operation that is many times what the same bit costs to communicate over the very-low-power radio link. Furthermore, at least one of the SPDs may have an abundant energy source. In such a case, the SPD that has abundant energy may be selected to communicate through its Wi-Fi network interface to the remote device, forwarding messages to and from the other SPDs through its very-low-power radio link. The other SPDs, which may have relatively scarce energy sources, may therefore communicate through their very-low-power radio links, and, therefore, reduce the power consumed for communications. 
     In addition, some embodiments of the SPD contain software and/or hardware mechanisms to aid in the placement of an entire SPD and/or access point. These mechanisms may be utilized in order to maximize the quality of the wireless networking signal in order to improve communications bandwidth, to reduce the communications error rate, and/or to reduce the power consumed for communications. For example, in some embodiments, the SPD includes a mechanism that displays an indication or emits an audible tone that varies proportionally with and/or is representative of the quality of the communications signals to aid in the placement of the SPD and/or access point. 
     In addition to (or instead of) optimizing the placement of SPD nodes and/or access points, the existing placements may be utilized along with a mechanism to additionally take advantage of the nodes and/or access points with better placements. As an extension to the concept of gateway operations for wireless networks (described further below), the SPD may dynamically or statically select which SPD and/or access point is to be used as the gateway for the others based on a combination of SPD energy reserves and/or communications signal strength. 
     In an exemplary embodiment, obstructions may sometimes severely influence the signal strength seen by a wireless node on a network. Moving the antenna, emitter and/or detector for an access point or SPD by a few feet may make dramatic differences in signal strength. Treatment of a group of SPDs as a system and selecting the SPD(s) with the best signal strength to operate as the gateways for the group of SPDs may allow for higher communications quality and/or lower communications power. 
     In some embodiments, another method to reduce the power consumption of an SPD wireless radio subsystem is to turn the radio on briefly after a period of “off” time, such as once every 10 or 100 seconds. Assuming the “on” time during this period is kept to 10 or a few 10s of milliseconds (or less), this may result in a sufficiently low average power such that even low-cost, readily-available wireless protocol (such as Wi-Fi) chip sets may be used in SPDs with extremely tight power constraints. The ratio of “on” time to “off” time and the corresponding ratio of “on” power to “off” power determines the average power consumption of the SPD&#39;s communications subsystem. Thus, the “off” time may be chosen to achieve a particular low average power consumption given a minimum “on” time to complete the wireless protocol steps needed to send and/or receive a complete message, the “off” time may be chosen to be appropriately long. 
     One difficulty with this approach may be in keeping the access point (or other centralized wireless protocol device) from concluding that the remote wireless protocol device (in this case, the SPD) has left the wireless network. If the access point has concluded that the SPD has left the network and then subsequently the SPD attempts to reestablish communications with the access point, this may require the SPD to go through a complete wireless protocol “rejoin” procedure each time the SPD wanted to have data wirelessly transferred. By convincing the access point that the SPD has been subject to a temporary interference with its transmission signal, the communications may be reestablished without requiring the more involved, time-consuming, and power-consuming “rejoin” procedure. Various schemes known to those skilled in the art may be used to convince the access point that the SPD has not left the wireless network, even if the SPD has not communicated for many seconds. 
     Some embodiments may have a minimum amount of user input/output (I/O) functionality for setting basic operating parameters. In some embodiments, even this minimum amount of user I/O functionality may be unnecessary for normal operation and this I/O may be made inaccessible after initial deployment of the device. 
     In some embodiments, one or more SPDs may include a single-indicator display. A variety of power-saving techniques may be applied to a single-indicator display. These include (but are not limited to): Applying intermittent power to the indicator at a high-enough frequency such that it appears to be on continuously when viewed by the human eye. This frequency may be in the range of 60 cycles per second or greater. In concert with intermittently powering the single indicator, adjust the duty cycle of the power circuit for the indicator such that the indicator is powered for substantially less than 100% of each cycle. This technique relies on the human eye&#39;s propensity to integrate the light that it receives in such a way that a rapidly-pulsing indicator may appear to be on continuously if the frequency of pulsation is high enough, and also that the eye will tend to overestimate the width of the pulses such that the indicator will appear brighter than the duty cycle may otherwise suggest. 
     Also in some embodiments, one or more SPDs may include a simple numeric or alpha-numeric display. A variety of power saving techniques, such as those described above, may be used with these types of displays. 
     In some embodiments, one or more SPDs may include a pixeled display. A variety of power-saving techniques may be applied to pixeled displays. These include (but are not limited to): Application of sleep modes based on scheduled “night” periods. Leaving the display in sleep mode until user proximity is automatically detected and/or the user otherwise triggers active operation of the display. Requiring an explicit user trigger for high-power-drain items such as backlights. 
     Depending on the application being served by the SPD, numerous forms of sensors may be utilized in an SPD embodiment. Sensors with implications for power management or other unique purposes are described below, but any form of sensor operable within the SPD&#39;s power budget, size restrictions, product cost, and/or other constraints may be supported. 
     In some embodiments, one or more SPDs may include a passive infra-red (PIR) device or some other mechanism to effect proximity detection of personnel. Their application in an SPD embodiment for display of information may alter the behavior of the SPD to minimize power consumption. For example, driving or updating an LCD display consumes power that may be reduced or eliminated by suppressing updates to the display and/or shutting down the display if no one is present to observe the content of the display. 
     In some embodiments, one or more SPDs may include a photo-detector, since the presence of light may be an indicator of current or pending activity. In one embodiment, to display information, the absence of light may also indicate it may be prudent to enter a power-down state. The SPD may also inform a central monitoring point that insufficient light is present in an area that is intended to be lit for security, safety, aesthetic, or other reasons. 
     A variety of methods and strategies may be used to reduce power in the controller. Some embodiments of the SPD may use one, many, all, or none of these methods and strategies. 
     In some embodiments, operating power is reduced during periods of inactivity. Often times the controller&#39;s periodic tasks may be arranged such that they are completed in a burst of activity followed by a period of inactivity until the periodic tasks again need to be performed. As long as these periods of activity and inactivity are kept relatively short and frequent, it may appear to the rest of the SPD that the controller is performing these tasks continuously, albeit at a slower rate. 
     In some embodiments, the controller may be designed to “sleep” during the periods of inactivity, and “wake up” in response to some stimulus, change of state, and/or elapsed time. This may be useful when the power consumption of the controller during sleep is lower than when it is awake. The average power consumption for the controller operating in this way may be less than if it were awake all of the time. 
     Some techniques to reduce power in the controller during periods of inactivity include running the controller&#39;s internal circuitry at a lower frequency and/or lower voltage than when it is fully awake, executing fewer instructions per unit time than when it is fully awake, and selectively disabling some or all of the functions within the controller. 
     In some embodiments, operating power may be reduced during periods of reduced activity. For example, the controller may have several different reduced-power modes of operation, as compared with its full-power, full-operation mode. Often, only a subset of the full capabilities of the controller is needed at any particular time. In this case, some of the functions of the controller may be unused except during specific times and may be disabled the rest of the time to reduce average power consumption. Additionally, some of the functions within the controller may be needed but only at a slower operating rate so operating them at a lower frequency may reduce average power consumption. Continuously adjusting the operating frequency of one or more subsystems to better match the needed performance at any particular time may also reduce the controller&#39;s average power consumption. By automatically selecting the appropriate low-power operating mode appropriate for the tasks it needs to perform at any particular period of time, the controller may reduce its average power consumption while still allowing the SPD to operate acceptably well. 
     In some embodiments, operating power is reduced by running at a lower or lowest voltage. Often, the circuitry that may be used to implement a particular controller embodiment is specified to operate properly over a range of voltages. Typically, the lowest power consumption is achieved at the lowest supply voltage. In some embodiments, the maximum frequency of guaranteed operation is reduced when the supply voltage is reduced, even if the supply voltage remains within the specified operating range. Also, in some embodiments, certain functions of the controller may be guaranteed to operate only at a higher minimum voltage than the minimum voltage required by other functions. 
     By allowing the operating voltage of the controller to be varied, some embodiments may have the controller select its operating voltage based on the frequency at which it needs to operate and/or which functions it needs to use during any particular period of time. Using this technique, the average power consumption of the controller may be lower than if the controller were to be operated at the highest minimum guaranteed operating voltage of all of its frequencies and functions. 
     In some embodiments of the SPD, updating the controller&#39;s non-volatile program and/or data memory may allow the controller to maintain the contents of its memory after a loss of power. In some cases, these non-volatile memory circuits require a higher operating voltage during update operations than during read operations. Allowing the controller to adjust the operating voltage of the non-volatile memory subsystem, such that it is operated at the higher voltage only during update operations, and operated at the lower voltage during read operations, may reduce the average power consumption of some embodiments of the SPD. 
     In some embodiments, the total extra power consumption needed in the controller when the higher voltage is used for writing to non-volatile memory circuits may be further reduced by grouping together the non-volatile-memory update operations. The “overhead” time spent raising and lowering the voltage may, therefore, be shared among multiple update operations. This means that for a given set of update operations, the time (and excess power) spent on most of the “overhead” may be eliminated. 
     A variety of methods may be used to initialize the SPD operating parameters. One method that may be used is through the inclusion of a USB port or similar serial interface for initial configuration and/or initial power charge of the SPD and to use a laptop or computer that is able to directly operate at the MAC layer of the Wi-Fi protocol to set up the higher layer operations. In many environments where the SPD is operating, the DHCP protocol is often available, so the IP address(es) may be obtained automatically. In environments where the DHCP protocol is not available or is otherwise inappropriate to be used, the IP address(es) and other relevant operating parameters may be allocated manually. 
     Some embodiments include a button on the back of the SPD that invokes the display of the IP address momentarily. With the IP address known, a configuration utility downloadable from a web site or other convenient location may be used to configure the operating behaviors of the SPD. Alternatively, for embodiments in which the SPD includes touch-screen capability, triggering a configuration mode may lead to a series of menu queries that may adequately drive initial configurations. 
     For some of SPD applications, compromise of the host network by the SPD is typically not possible due to the limited network interface power budget and/or lack of standard higher-layer protocols that will be present on the device. For example, in many SPD embodiments, there will not typically be support for TCP operations. The SPD functional behaviors, therefore, will be governed by an entirely proprietary message set. In some embodiments, however, passwords and/or other means may be used to limit access to the SPD to authorized personnel and/or designated remote device(s). 
     Referring to  FIG. 12 , a method (or process)  700  is shown. The method  700  illustrates an example of a low power activation signal monitoring process. The method  700  generally comprises a step (or state)  702 , a step (or state)  704 , a decision step (or state)  706 , a step (or state)  708 , a step (or state)  710 , a step (or state)  712 , a decision step (or state)  714 , and a step (or state)  716 . The step  702  may start a low power mode cycle (or process). Next, the step  704  may collect and store energy. Next, the step  706  may determine the amount of energy needed for the predicted power usage. If there is not enough energy stored, the method  700  moves to the step  708 . To reduce power usage, the step  708  may slow down an internal clock to the CPU  202   a  and/or may lower the operating voltage. If there is enough energy for the predicted power needs, the method  700  moves to the step  710 . The step  710  senses one or more activation signals. If an activation signal is present, such as a signal received from the step  712 , the decision step  714  determines if an activation condition has been met. If not, the method  700  moves back to the step  702 . If an activation condition has been met, the method  700  moves to the step  716 . The step  716  starts a data collection mode (to be described in more detail in connection with  FIG. 13 ). 
     Referring to  FIG. 13 , a method (or process)  800  is shown. The method  800  illustrates an example of a power-aware data collection process. The method  800  comprises a step (or state)  802 , a step (or state)  804 , a decision step (or state)  806 , a step (or state)  808 , a step (or state)  810 , a step (or state)  812 , a step (or state)  814 , a step (or state)  816 , and a step (or state)  818 . The step  802  starts the data collection mode cycle. Next, the step  804  collects and stores energy. Next, the step  806  determines if enough energy has been stored to perform a minimum predicted operation based on the predicted power needs. If not, the method  800  moves to the step  808 . The step  808  may perform a number of prioritization rules based on a power budget. For example, the step  808  may activate/deactivate one or more components, adjust the duty cycle and/or timing interval, adjust a voltage on the components or other power saving parameters (or rules). If there is enough energy stored for the predicted power needs, the method  800  moves to the state  810 . The decision state  810  determines if the conditions are still met to remain in the data collection mode. If not, the method  800  moves to the state  812 , which returns to the lower power mode. If the conditions are still met, the method  800  moves to the state  814 . The state  814  stores and processes sensor data. Next, the decision state  816  determines if the communication conditions have been met. If not, the method  800  moves back to the state  802 . If the communication conditions have been met, the method  800  moves to the state  818 . The state  818  starts the communication mode (to be described in more detail in connection with  FIG. 14 ). 
     Referring to  FIG. 14 , a method (or process)  900  is shown. The method illustrates a power-aware communications mode. The method  900  generally comprises a step (or state)  902 , a step (or state)  904 , a step (or state)  906 , a step (or state)  908 , a decision step (or state)  910 , a decision step (or state)  912 , a step (or state)  914 , a step (or state)  916 , and a step (or state)  918 . The state  902  starts the communication mode. Next, the state  904  activates the radio (or wireless transceiver). Next, the state  906  adjusts the broadcast power of the radio based on a power budget, interference levels, and/or communication prioritization rules. Next, the method  900  moves to the state  908 . The state  908  sends collected data. Next, the decision state  910  determines if an acknowledgment has been received. If not, the method  900  moves to the decision state  912 . The decision state  912  determines if the data received is priority data. Priority data may be considered data that may break low power operation rules. If so, the method  900  moves back to the state  906 . If the data is not priority data, the method  900  moves to the state  914 . In the decision state  910 , if an acknowledgment has been received, the method  900  moves to the state  914 . In the state  914 , the method  900  receives instructions related to predicted power needs, activation condition rules, and/or communication rules. Next, the method  900  moves to the state  916 , which sends an acknowledgment. Next the state  918  returns to the data collection mode (e.g., the process  800 ). 
     The controller in the SPD may maintain the physical and logical address of the SPD. A default set of these addresses may be pre-programmed when the SPD is manufactured. If necessary, some or all of these addresses may be set or changed when the SPD is initially deployed and/or changed while the SPD is operational. 
     In the event that the SPD is deployed in a network that does not broadcast its security information, the network interface access codes will need to be entered as part of the initial configuration of the SPD. 
     The issues of privacy and encryption are of concern when there is a need for protection of information communicated across an open network interface. This need may be addressed in a number of ways with respect to SPD communications with a remote device, including: Information communicated across the external computer network may be sent in a proprietary format, minimizing the risk of casual observance through the use of a network “sniffer” or similar device. Standard encryption techniques may be applied to communications across the external computer network for even more robust privacy and protection against unauthorized observation. 
     In embodiments that include communication with the remote device(s), this communication typically takes place through the external computer network. Some embodiments of the SPD may contain one or more network interfaces that implement a wireless communications protocol. The wireless protocol may be a standard, commonly-deployed technology, such as “Wi-Fi” (IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, etc.), or the protocol may be a specialized one particularly tailored to the low-power transmission distance, and/or other needs of the SPD and/or its application. Combinations of different network interface types are also possible, allowing for gateway operations where applicable. 
     Regardless of the type of wireless protocol, one (or more) devices in the external computer network typically provide the wireless connection to the overall external computer network. Whether the external computer network is inherently wireless or a hybrid of wired and wireless networking technologies, the device that operates as the intermediary to provide the connection is often referred to as a wireless access point. In some cases, the wireless access point may be built into a node on the network, and/or may be part of one or more remote device(s). In some cases, the wireless access point may be a device dedicated to bridging the wireless network to a wired network. In some cases, the remote device may use a built-in wireless interface to directly communicate to the SPD (in Wi-Fi nomenclature, this is known as “ad-hoc” operation mode). 
     The wireless access point used by the SPD may be a standard commercially-available device that is typically used with other standard wireless products or the access point may be a specialized device whose wireless port may be used only with the SPD. The access point may be configured to support one or more SPDs, one or more other commercially-available wireless products, or any combination of these. In most cases, the function of the access point for the SPD may be to convert the wireless messages from the SPD to the wired networking protocol used by the external computer network and vice-versa. 
     A role of the external computer network when used with the SPD is typically to transfer messages from the SPD to the remote device(s) and vice-versa. In many cases, it is expected that standard, already-installed computer networks may be used for this function. Therefore, the SPD may typically be operated such that its messages may be easily converted by the existing wireless access point(s) for carriage across the computer network. 
     Typically, the SPD does not require any protocol changes in the wired part of the external computer network and in some cases, requires no special protocol changes for the wireless portion either. SPD messages may therefore be constructed, formatted, and addressed for easy transport across the external computer network to the remote device(s), and vice-versa. 
     In cases where proprietary communication methods are used between SPDs, a gateway function may exist either among the SPDs or in a special-purpose device co-located with the SPDs but connected to the external computer network via a standards-oriented wired or wireless means. 
     Once the network connectivity has been established between the SPD and the remote device(s), they may typically communicate with each other using the standard messaging format and protocol(s) used in the external computer network. Each SPD may have a unique network address, or other means to be addressed uniquely, and likewise, each remote device may have a unique network address, or a means to be addressed uniquely. Properly-addressed messages may be sent across the external computer network by both the SPD(s) and the remote device(s) using the existing networking mechanisms. 
     Referring to  FIG. 15 , a context diagram of a system  1000  showing wireless signal configurations is shown. The memory  204   a  may contain instructions outlining a set of threshold conditions for storing sensed data (e.g., the process  800 ). The memory  204   a  may also contain instructions outlining a set of threshold conditions for transmitting sensed data (e.g., the process  900 ). The instructions for storing and/or transmitting data may be based on a power budget and/or available power. The instructions may contain computational logic for computing a threshold condition based on one or more types of sensed data and/or one or more data points over time. A beacon  1002  is shown connected between the network computing services block  174  and the wireless sensing device  102 . The beacon  1002  may be used to send a signal from the network computing device  174  to the sensor node  102 . The beacon  1002  may send a signal to wake up the node  102 , or to prepare the node  102  to receive new instructions, etc. A software agent block  1010   a  is shown in the mobile computing device  170   a . Similarly, a software agent block  1010   n  is shown in the computing device  170   n . A software agent block  1020  is shown in the network computing services block  174 . The software processing may be distributed between the mobile computing devices  170   a - 170   n  and the network computing services block  174 . A network data services block  1040  is shown connected to the network computing services block  174 . The network data services block shows a number of classifications of network data services  1050   a - 1050   n.    
     In one example, the computational logic may include a cascade (e.g., one or more) of threshold conditions that may be used to determine when additional features of the sensor node  102  will be powered on or powered off. For example, when the sensor node  102  determines that one of the sensors (e.g., a sensor A) detects a signal over a determined threshold, then one or more other sensors (e.g., a sensor B and/or a sensor C) may be activated. In another example, when the sensor node  102  determines that the sensor B in combination with the node C are below a threshold, then the sensors B and C may be turned off. In such an example, one of the sensors  160   a - 160   n  may be awake (or operational) continuously. Other sensors  160   a - 160   n  may only be powered on when the sensor node  102  determines that monitoring is needed (e.g., by the continuously operated one of the sensors  160   a - 160   n ). Other input parameters may be uploaded by the mobile computing device  170  to the sensor node  102 . Such parameters may include a schedule of when sensor data should be captured and/or stored. 
     The computational logic cascade may implement a power-aware prioritization of sensor data capture and/or communications information. For example, when power stored in the ESU circuit  214   a  is low, the duty cycle of the sensor node  102  may be changed less frequently. In one example, the logic may only receive signals from the sensors  160   a - 160   b  when power is sufficient. 
     The computational logic may include logic for coalescing data, such as only recording changes to a base state or expected state. A computationally efficient process may be implemented. For example, a process that only records the average value of one or more of the sensors  160   a - 160   n  over a period of time may be used. The sensor  102  may begin to record events if a measurement received from the sensors  160   a - 160   n  is significantly above average. 
     Since the sensor nodes  102   a - 102   n  are self-powered (through the energy storage unit  214   a ), the power budget of the sensor nodes  102   a - 102   n  is generally kept small. By capturing additional energy with the ECU  214   a , the nodes  102   a - 102   n  may operate for long periods of time on a single battery. The energy storage unit  214   a  may be implemented as a battery or other storage device. The energy capture unit  214   a  may store energy through various sources, such as energy created through harvesting of light, vibration, thermal variation, thermal gradient, infrared, chemical, RF sources or some combination. 
     The computational logic for determining the threshold conditions for storing and/or transmitting data may be based on currently available power, predicted future energy harvesting opportunities (e.g., based on forecasting the future environment), and/or predicted energy consumption (e.g., based on applying the threshold rules to the forecast environment). 
     A machine learning process that optimizes the predictive model may be set up as a series of energy input functions and/or energy consumption functions with scaling factors that are optimized based on historical data for the sensor nodes  102   a - 102   n . Based on prior patterns, the model may operate with techniques of machine learning optimization including, but not limited to, a least square minimization of the difference between model predictions and actual historical data, various gradient descent techniques, etc. 
     In order to adapt the duty cycle, the sensor sampling rates, the adaptive and conditional powering of additional sensors based on a set of initial sensors, the data storage and data transmission policies of the sensor node  102 , each energy use in the system  150  may be characterized as an energy cost function. For example, energy harvesting may be a negative cost, or energy contribution. Each data captured may be characterized as a utility or benefit function. An optimization may be performed to maximize the utility within a set of cost parameters. Alternatively, optimization may be performed to maximize utility per unit of cost. 
     In one example, the remote computing device  170  may be a local device on the edge of the network. For example, the remote computing device  170  may be implemented as a smartphone, or personal digital assistant (PDA) type device, which in turn is connected to the central data storage and computing facility  174 . In such an implementation, some or all of the computational logic for determining the threshold conditions and/or rules may be implemented on the devices  170   a - 170   n . In such an example, only the threshold values (or simplified rules) may need to be transmitted to the sensor nodes  102   a - 102   n . In one example, a subset of the processing is done on the sensor nodes  102   a - 102   n . If power is not an issue, the devices  170   a - 170   n  may capture a more complete stream of data from the local sensor nodes. The data may then be processed and/or be evaluated locally before being sent to a central server on the computers facility  174 . Such an implementation may reduce network traffic and/or storage needed at the central data center  174 . The central data center  174  may send program instructions to one or more of the smartphones  170   a - 170   n  for computing threshold conditions. The program instructions may in turn be sent to one of the sensor nodes  102   a - 102   n.    
     Various sources of data may be used to generate energy consumption and/or harvesting predictions. Such sources may include (i) a schedule of upcoming calendar events in the neighborhood of the sensor, (ii) the proximity to or presence of nearby people, objects, buildings, vehicles, (iii) security or threat conditions that increase the importance of sensing, (iv) location-based data (such as features of the location of the sensor), (v) weather forecasts and/or other environmental conditions, (vi) scheduled or location-based energy harvesting opportunities, (vii) presence of increased ambient or directed RF power, (viii) known or observed cycles including day, week, month, season, and/or (ix) other patterns in prior data. 
     Various energy harvesting technologies may be used in the energy capture unit  214   a . Examples of such technologies include piezoelectric effects of stress and/or strain, vibration, thermal gradient, thermal variation, solar photovoltaic, ambient light photovoltaic, infrared, radio frequency, chemical energy, air or fluid flow, and electromagnetic fields. Many of these effects are context dependent and may vary with location, time, proximity to other devices or environmental features and other factors. Being able to predict future energy inputs based on the context of the sensor node  102  may help to determine the current power budget. 
     In addition to the environmental context, the predicted power inputs and predicted power consumption may take into account various application rules encoded in the control logic of the memory  204   a . Such inputs may be used to determine the duty cycle sensor node  102 , the sampling rate of the sensor, the conditional powering of different components, as well as the data storage and/or data transmission policies. 
     In an example of a security application used to detect intruders, the sensor node  102  may have a very different predicted power need than the same presence or proximity sensor node  102  used to optimize lighting and heating based on building or room usage. The security application may consume power when an office is closed. The lighting and heating application may need to be active during the scheduled office hours. The energy harvesting opportunities may also be different. The security application may need to store enough power during the day to last throughout the night. The office energy application may be able to harvest enough energy during the day to meet most needs. The transmission policies for the security application may be immediate during non-office hours. The transmission policy for the energy application may be daily or weekly. In another example, a seismic vibration sensor might have a high sampling rate after an initial threshold event, while a temperature sensor might be needed less frequently. For many applications, a diminishing return on the value of the data occurs at higher sampling rates. The particular value depends on the application. 
     The predicted power needs and/or harvesting opportunities may be computed through machine learning techniques in which the contribution of environmental features to energy harvesting and energy consumption are learned based on prior observations. For example, consider an application where during a time interval t i , and at location  1 , energy contribution or cost is expressed as a linear relationship between a set of environmental features f and energy the contribution by the following equation: 
       Δ e ( t   i   ,l )= a   1   f   1 ( t   i   ,l )+ a   2   f   2 ( t   i   ,l )+ a   3   f   3 ( t   i   ,l )+ a   4   f   4 ( t   i   ,l )
 
     For environmental factors that cost energy, the scaling factors are negative. For environmental conditions that add to energy harvesting, the factor is positive. The change in energy does not go over the storage capacity of the node. The charge does not generally fall under a threshold without shutting down the sensor node  102 . 
     For a time series over all the time intervals, an expression with F being a matrix (where each row is a time interval and each column is a feature) may result in a total energy contribution or drain from environmental factors of 
     
       
      
       E= 
       
       × 
       
         
      
     
     The time intervals before the current time, the actual features and/or energy needs or contributions have already been measured and may be considered the ground truth or training set for a predictive model. The scaling factors may be fit using well known machine learning techniques. The functions describing dependence of the change in energy and features of the environment may first be estimated with known relationships (e.g., such as solar radiation and the contribution to a photovoltaic) so that the machine learning is focused on scaling the relationship to the particular sensor node rather than discovering the relationship in the first place. The sensor node  102  may be implemented with known components. The energy inputs and/or cost functions of such known components should be related to the technology used. The scaling factors are normally related to the context and/or application. 
     In order to create the most efficient power management in a wireless sensor network, the machine learning techniques may be trained with data collected on a subset of the sensor nodes and/or for a subset of time. The power budget and/or power predictions may be calculated at a central computer in the network computing services block  174  for larger calculations. For calculations with fewer features, the power budget may be calculated on the remote computing device  170 . The results of the optimization of the model may be communicated to the sensor node  102  in the form of program instructions and/or thresholds. 
     The optimization of the scaling factors of the predictive model may also take into account the effect of the control logic and the rules currently in use to adapt the duty cycle sensor of the node  102 , the sensor sampling rate, as well as the data recording and/or transmission policies. The functions that express the relationship between a predicted feature of the environment or context to power consumption can include the rules in the calculation so that the optimization is application-specific. 
     In some SPD applications, the software agent(s)  1010   a - 1010   n  running on the remote device(s)  170   a - 170   n  may be used to communicate with the SPD through the external computer network. In some embodiments, the communication may be automatic, with each interaction triggered by some change of status in the remote device, the SPD, or both. In some embodiments, the communication may be manually initiated by a user of the remote device, such as to change the configuration or other state of the SPD. In some embodiments, both initiation modes may be supported. 
     Note that in some embodiments, the user directly interacts with the remote device(s), such as with a keyboard and/or mouse and/or display/monitor. In some embodiments, the user interacts indirectly with the remote device(s), such as across a computer network and/or additional communications link. 
     In some embodiments, communication is automatically initiated by the remote device. Some examples of uses of automatic communication initiated by the remote device may include: The SPD displays a subset of database information: a software agent running on the remote device periodically searches a database resident in the remote device and/or in a computer reachable through the external computer network. The results of the search, possibly along with other relevant information, are formatted by the software agent and are sent to the SPD, especially when those results have changed since the previous update. The SPD displays meeting room information: a software agent running on the remote device monitors the reservations for the meeting room to which the SPD is attached. The software agent may periodically interrogate the networked calendar and/or reservation system (such as Microsoft Outlook, IBM/Lotus Notes, etc.) and send the reservation information, possibly along with other relevant information, to the SPD for display. This application may be useful for general businesses, as well as businesses making rooms available to third parties, such as hotels, convention centers, etc. The SPD displays examination room information in a hospital or doctor&#39;s office. A software agent running on the remote device monitors the patient reservations for the room to which the SPD is attached. The information may allow the medical personnel to know who is in the room without having to enter the room and disturb the patient, and without having to find the reservation clerk and ask him/her about the status of the room. The SPD displays news, advertising, and/or market information: a software agent running on the remote device gathers various news, advertising, stock quotes, headlines, or other relevant information from internal and/or external sources (such as from the Internet). The software agent may format the information and periodically sends the formatted information to the SPD for display. The SPD displays pricing or other product status information: the SPD (or a set of SPDs) may be positioned adjacent to its (their) corresponding retail product(s). Each SPD may be used to display up-to-date pricing and/or other product status information in a supermarket, retail store, warehouse, or other locations. The software agent running on the remote device may gather data to be displayed on each SPD from a database or other computer system, and/or from direct user input at the remote device. The SPD is used as a personal display for each employee/user/customer: an SPD may be attached to each employee&#39;s cubicle or office, and may be used to display personal information, such as where the employee is presently, if the employee is on vacation, if the employee is available for drop-in conferences, or other employee circumstances. The employee may update the display by sending messages through the software agent running on the remote device, and this information may be sent to the SPD, possibly along with other relevant information, such as scheduling derived from other sources. The SPD displays room status information: an SPD may be placed in a room used by many people, such as an area with several cubicles, a ball room, an auditorium, or other locations. The software agent running on the remote device may gather any messages relevant to that room, such as general notices, announcements, or other messages, and may merge that with relevant local data, such as time, date, the current temperature in the room, and may send the formatted information to the SPD for display. The SPD is used as an annunciator: the SPD may be used to display important real-time information needed by people in the room where the SPD is located. For example, in a technical support or telephone call-center application, the SPD may display the average wait for customers on hold, the number of customers presently being served, whether the wait time is increasing, or other relevant information. The software agent running on the remote device may collect real-time information from the telephone switch and combine that information with other relevant information, such as time of day, recent history, or up time, to generate formatted data to send to the SPD for display. The SPD is used as an actuator: the SPD may contain one or more motors, actuators, electrical contacts, or other similar components which may be used to move or position some external mechanical or electrical apparatus. The SPD may receive a message from the remote device requesting that the mechanical or electrical apparatus be moved, repositioned, turned on, turned off, or otherwise adjusted. Alternatively, the SPD may receive a message requesting the status of the mechanical or electrical apparatus, and the SPD may respond with a message reporting that status. 
     In some embodiments, communication is automatically initiated by the SPD. Some examples of uses of automatic communication initiated by the SPD may include: The SPD used as a security sensor: the SPD may contains sensors to detect various environmental states, such as temperature, humidity, lighting, motion, vibration, noise, shock, pressure, or other environmental states. For example, in a security application, a small SPD may be attached to a window and used to detect if the window has been opened or broken. If such a stimulus is detected, the SPD may send a message to the remote device for further processing. The SPD may also send non-urgent messages periodically to confirm its continued correct operation and/or that the communication link is still functional. SPD reports its own health status: the SPD may send messages to the remote device to indicate that the SPD continues to operate correctly and/or the communication link is still intact. When the SPD detects an internal problem, such as insufficient input power and/or internal energy storage to continue operation, the SPD may send a message to the remote device to request maintenance service or other appropriate action. When the remote device does not receive a periodic health status message from the SPD, the remote device may conclude that the communications link and/or the SPD have failed, and the remote device may then take an appropriate action. SPD used as a HVAC sensor: the SPD may be used in a heating/ventilation/air-conditioning application, and may sense temperature, humidity, lighting, or other environmental states. The information may be sent to the remote device for further processing with data from other sensors, and the state of the HVAC system may then be sent to the SPD for display, along with current time, date, local temperature, or other relevant information. SPD used as an intercom: the SPD may contain a microphone and speaker, and perhaps “doorbell” and “talk” buttons. The SPD may send a message to the remote device when the “doorbell” button is pushed, and may digitize/decode voice signals for use with the internal microphone and speaker. The digitized voice data may be sent to and from the remote device, or another computer interconnected with the external computer network. 
     The software agent (SA) running on the remote device(s) may perform a variety of tasks, depending upon the embodiment (s) of the SPD(s) with which it communicates and the intended functionality of the SA and its embodiment(s). SA embodiments typically contain combinations of subprograms which each perform a specific task or set of tasks. For example, some subprograms may be responsible for reading information from a database while other subprograms write to a database. Some subprograms may perform both tasks. SAs that contain both readers and writers may have complex interactions with their corresponding database(s) as well as when communicating with the associated SPD(s). 
     An example SA application and associated environments that may be used with SPD(s) are described below. Actual embodiments of SAs may implement one, some, all, or none of the following examples. 
     In an exemplary embodiment, the SA may implement a calendar. This application allows an SPD (or set of SPDs) to be used for resource management, such as for reservation management of a conference room. The SPD(s) used for this application may typically contain a display of some sort that may show resource scheduling information. The SPD(s) may communicate with the remote device(s) running the calendar SA(s), and the calendar SA(s) may typically interact with a separate calendar management program/database, such as Microsoft Outlook or IBM Lotus Notes. Through the interaction with the separate calendar management program/database, the SA(s) may gather the necessary data to send to the SPD(s) for appropriate display of scheduling information, and/or gather the necessary data from the SPD(s) to appropriately update the separate calendar management program/database. 
     The calendar application may be implemented in a variety of environments. Exemplary environments include small offices using off-site hosted MS-Exchange services, small offices using off-site hosted World Wide Web Distributed Authoring and Versioning or WebDAV services (a set of extensions to the Hypertext Transfer Protocol (HTTP) that allows users to collaboratively edit and manage files on remote web servers), medium-to-large offices using MS-Exchange, and medium-to-large offices using local WebDAV. 
     For small offices using off-site hosted MS-Exchange,  FIG. 16A  illustrates an expected environment for a small office using a hosted MS-Exchange server for their mail services. In this example, company A may have 3 conference rooms, and computer  2  may be an administrative computer that is running Outlook and the SPD A Software Agent (SA). Note that in this example, multiple companies share a single MS-Exchange server, accessing the server via their internet connection perhaps over SSL or VPN connections through a firewall. Routers, hubs, etc. are assumed to be in the LAN cloud but are omitted for clarity. 
     The configuration illustrated in  FIG. 16A  poses several challenges: Installation/operational simplicity: Small offices often operate with little to no information technology staff available for applications training, management or installation. Exchange server modification avoidance: hosting companies providing MS-Exchange services often resist extensions to shared server platforms. Additional outlook license avoidance: MS-Outlook seat license costs are often high for small offices. As a consequence, they typically have less volume discount and purchasing leverage. Minimizing communications hops: Offsite hosting often creates large, variable latencies in communications to the MS-Exchange server. A variety of software architectures may be used to address these challenges. These are described below. 
     In some embodiments, installation and operational simplicity are linked as an issue but may be accomplished in several only somewhat-related ways as follows: Software Agents (SAs) may be designed to be installed only on client workstations. 
     In this way, access to a server machine by an SPD administrator may not be necessary. Two software elements may be used to fulfill the SA behaviors in each of two client workstations: one is an Outlook VBA extension (a version of Visual Basic that is embedded in Outlook) and the other is a separate supporting service. Both software elements may be installed in the same process. As a consequence, decisions about which is needed under what conditions may not be necessary. Delegation may be “hooked” so that the notification of delegate status for a resource managed with an SPD may be provided to the (potentially new) delegate with the option of installing the necessary components to manage the resource. Standard Outlook resource management may be used for creation and management (i.e., delegation) of the resource as a mailbox. This may allow meeting organizers, even for those individuals who are not administrators of the rooms, to use the source when scheduling meetings. Standard Outlook resource management may be used to avoid data collisions or conflicts in accepting resource booking requests. Installation of VBA elements may be largely invisible. To all appearances there may be an additional tool available to manage the SPDs and client software but otherwise it is just standard Outlook for handling the resource. The supporting service may be “fed” information by the Outlook VBA extension in the background on an event-driven basis. This may provide display updates to the SPD, such that no user intervention may be necessary. The supporting service may be a member of a cooperating group of services running on the machines of all resources owners and delegates. SPD communication may be performed only by the currently elected master whose role may be constantly negotiated behind the scenes without administrator input. 
     In some embodiments, utilization of the Outlook VBA mechanism and a local high-priority software service may allow scheduling and creation of resources without changes to the MS-Exchange server. 
     In some embodiments, utilization of the Outlook VBA mechanism and the creation of the resources as a resource mailbox may avoid any need for an additional Outlook license. 
     In some embodiments, utilizing the locally-located workstation of the administrator(s) reduces the latency and communications delays to a best case path over the LAN versus the uncertain path to the MS-Exchange server, thereby minimizing communication hops. 
     For small offices using off-site hosted WebDAV,  FIG. 16B  illustrates an environment for a small office using an offsite hosted iCalendar (a calendar application developed by Apple Computer). In this example, company A may have 3 conference rooms, and computers  1  and  2  may be running the SPD management utilities and Software Agent (SA). Note that the server is accessed via an Internet connection, such as over SSL or VPN connections through a firewall. Routers, hubs, etc. are assumed in the LAN bubble above but are omitted for clarity. 
     The configuration illustrated in  FIG. 16B  poses several challenges: Installation/operational simplicity: Small offices often operate with little to no information technology staff available for applications training, management or installation. The generic nature of WebDAV/iCal services: No calendar behaviors really exist within a WebDAV/iCal service. Instead, the application provides a web-based transactional-based information storage service on which a group calendaring system may be built. Minimizing communications hops: Offsite hosting creates large, variable latencies during communication with the WebDAV server. A variety of software architectures may be used to address these challenges. These are described below. 
     In some embodiments, installation and operational simplicity are linked as an issue but are accomplished in several only somewhat related ways as follows: Installation of software may be limited to client workstations such that no administrator access to any form of server machine is necessary. Two software elements may be used to fulfill the SA behaviors in each of two client workstations. One of these may be an SPD management utility to fulfill the same purpose as the Outlook VBA application. The other may be a separate supporting service. Both software elements may be installed in the same process. In this way, no decisions regarding which one is needed under what conditions may be necessary. Delegation may be handled using an email notification that indicates the delegation status for the resource to be managed. An attached executable file, which is generated and pre-configured for the WebDAV options necessary, may be optionally installed to install the components necessary to manage the resource. 
     For medium-to-large offices using MS Exchange,  FIG. 16C  illustrates a local MS-Exchange server for their mail services. In this example, Company A may have 3 conference rooms, and computers  1  and  2  may be running Outlook and the SPD Software Agent (SA). Note the more direct connections between the system components. Once again, routers, hubs, etc are assumed in the LAN bubble above but are omitted for clarity. 
     For medium-to-large offices using off-site hosted WebDAV,  FIG. 16D  illustrates a local WebDAV server for iCalendar services. In this example, company A may have 3 conference rooms, and computers  1  and  2  may be running SPD management utilities and Software Agent (SA). Note the more direct connections between the system components. Once again, routers, hubs, etc are assumed in the LAN bubble above but are omitted for clarity. 
     In other embodiments (not shown), the SPDs may be used in systems that implement or use Microsoft Outlook and/or Lotus Notes (an application offered by IBM). 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other specific forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and not limited to the foregoing description. 
     The functions performed by the diagrams of  FIGS. 12-14  may be implemented using one or more of a conventional general purpose processor, digital computer, microprocessor, microcontroller, RISC (reduced instruction set computer) processor, CISC (complex instruction set computer) processor, SIMD (single instruction multiple data) processor, signal processor, central processing unit (CPU), arithmetic logic unit (ALU), video digital signal processor (VDSP) and/or similar computational machines, programmed according to the teachings of the specification, as will be apparent to those skilled in the relevant art(s). Appropriate software, firmware, coding, routines, instructions, opcodes, microcode, and/or program modules may readily be prepared by skilled programmers based on the teachings of the disclosure, as will also be apparent to those skilled in the relevant art(s). The software is generally executed from a medium or several media by one or more of the processors of the machine implementation. 
     The invention may also be implemented by the preparation of ASICs (application specific integrated circuits), Platform ASICs, FPGAs (field programmable gate arrays), PLDs (programmable logic devices), CPLDs (complex programmable logic devices), sea-of-gates, RFICs (radio frequency integrated circuits), ASSPs (application specific standard products), one or more monolithic integrated circuits, one or more chips or die arranged as flip-chip modules and/or multi-chip modules or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s). 
     The invention thus may also include a computer product which may be a storage medium or media and/or a transmission medium or media including instructions which may be used to program a machine to perform one or more processes or methods in accordance with the invention. Execution of instructions contained in the computer product by the machine, along with operations of surrounding circuitry, may transform input data into one or more files on the storage medium and/or one or more output signals representative of a physical object or substance, such as an audio and/or visual depiction. The storage medium may include, but is not limited to, any type of disk including floppy disk, hard drive, magnetic disk, optical disk, CD-ROM, DVD and magneto-optical disks and circuits such as ROMs (read-only memories), RAMs (random access memories), EPROMs (erasable programmable ROMs), EEPROMs (electrically erasable programmable ROMs), UVPROM (ultra-violet erasable programmable ROMs), Flash memory, magnetic cards, optical cards, and/or any type of media suitable for storing electronic instructions. 
     The elements of the invention may form part or all of one or more devices, units, components, systems, machines and/or apparatuses. The devices may include, but are not limited to, servers, workstations, storage array controllers, storage systems, personal computers, laptop computers, notebook computers, palm computers, personal digital assistants, portable electronic devices, battery powered devices, set-top boxes, encoders, decoders, transcoders, compressors, decompressors, pre-processors, post-processors, transmitters, receivers, transceivers, cipher circuits, cellular telephones, digital cameras, positioning and/or navigation systems, medical equipment, heads-up displays, wireless devices, audio recording, audio storage and/or audio playback devices, video recording, video storage and/or video playback devices, game platforms, peripherals and/or multi-chip modules. Those skilled in the relevant art(s) would understand that the elements of the invention may be implemented in other types of devices to meet the criteria of a particular application. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention.