Power management in a wireless ad hoc network

In a wireless ad hoc network (20) of nodes (22), a method (64) of power management entails monitoring (82) a current traffic load of the network (20), and in response to the current traffic load, selecting (106, 132) a subset (102) of epochs (80) within cyclically repeating time windows (78) for network communication. A message (122) is communicated (120) between the nodes (22) in the network (20). The message (122) identifies the subset (102) of epochs (80) for using in communicating network traffic (32). Following receipt of the message, each of the nodes (22) modifies (124) a transmit capability mode by entering a run state (40) during the epochs (80) within the subset (102) to enable communication of network traffic (32) and by entering a low power consumption idle state (42) during the remaining epochs (80) within the time window (78).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of wireless ad hoc networks. More specifically, the present invention relates to managing power consumption by nodes within a wireless ad hoc network.

BACKGROUND OF THE INVENTION

Over recent years, the market for wireless communications has enjoyed tremendous growth. Wireless technology now reaches or is capable of reaching virtually every location on earth. This rapid growth in wireless communication technology and portable computing platforms has led to significant interest in the design and development of instantly deployable, wireless networks often referred to as “ad hoc networks” for both military and commercial applications.

In a wireless ad hoc network, mobile user nodes are linked within a limited geographical region, and all nodes participating in the ad hoc network operate cooperatively to forward data packets and determine whether the packets were successfully delivered from the original source to the final destination. A wireless ad hoc network has a number of advantages over cellular networks. For example, a wireless ad hoc network does not require infrastructure such as base stations or access points, and it does not require any centralized administration or control. As such, an ad hoc network can be entirely self-organizing between the mobile nodes that form the network. Thus, an ad hoc network can change position and shape in real time (i.e., dynamically) in order to adapt to a changing situational environment, such as a military operation, in times of emergency, such as earthquake, fire, or power interruption, and so forth.

In order to self-organize and operate cooperatively to forward information, all wireless nodes in an ad hoc network must continuously process and forward network information (e.g., data, voice, etc). In addition, all nodes in an ad hoc network must continuously send and receive routing overhead messages in order to maintain network connectivity. To support these operations, battery powered portable networking nodes in an ad hoc network continuously discharge their batteries. Consequently, users of such nodes are compelled to carry additional batteries and/or to use larger batteries to maintain connectivity to the ad hoc network for a given mission duration. Not only is it inconvenient to carry an additional quantity of batteries, it is highly undesirable in situations where mobility, weight reduction, and an individual's load carrying capacity are fundamental to mission success.

Thus, it would be desirable to have a power management scheme in a wireless ad hoc network that reduces power consumption at individual wireless nodes without sacrificing network responsiveness to changes in network traffic activity or network capability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention entail methodology and a system for managing power consumption in a wireless ad hoc network. In particular, the methodology and system extend battery life of wireless mobile nodes within the ad hoc network without sacrificing responsiveness or network capability. Power management is fundamentally achieved by identifying and avoiding wasted power. Thus, time periods are created in which a wireless node can enter a low power consumption state so that power consumption is effectively reduced. The reduction of wasted power in this manner enhances the ability of the wireless mobile nodes to remain in-network performing their assigned role. By reducing wasted power, battery life can be extended. Therefore, savings is achieved in terms of size and weight of the wireless mobile nodes since fewer batteries and/or smaller batteries can be used. Additionally, a reduction in power consumption reduces a node's thermal signature thereby increasing its operating life and making it less detectable to thermal imaging systems.

FIG. 1shows a block diagram of an exemplary wireless ad hoc network20in which an embodiment of the invention may be implemented. Exemplary wireless ad hoc network20includes a plurality of wireless radio devices, referred to herein as nodes22. Nodes22are configured for communication within wireless network20, i.e., intra-network communication, over wireless links24. That is, wireless links24carry network traffic as distinct bitstreams between the particular ones of nodes22and others of nodes22within ad hoc network20in accordance with particular routing solutions. Wireless links24may be implemented using any suitable networking waveform, e.g., a wideband networking waveform (WNW), a soldier radio waveform (SRW), or another developed or upcoming networking waveform solution.

At least one of nodes22may additionally be configured for communication outside of network20, i.e., extra-network communication. This extra-network communication is represented by a wireless channel26between a gateway node28and an extra-network location, represented as a cloud element30. Gateway node28provides ingress and egress into the local domain of nodes22.

Ad hoc network20may be composed of multiple domains of nodes22, each deployed in a hierarchical relationship. Nodes22within any domain of ad hoc network20can be a mixture of vehicle based and portable battery powered nodes, and network traffic can include sensor data, voice, position data, and the like. Each of nodes22participates in network20by transporting network traffic, represented by packets32communicated within network20via wireless links24. Network traffic32entails both network overhead traffic and user data including, for example, voice and position information.

In certain operational scenarios, such as in a military application, nodes22may be lightly loaded (i.e., have a low volume of network traffic32) a majority of the time. However, there may be bursts of higher activity (i.e., a high volume of network traffic32) interspersed within the given period of time. Wireless ad hoc network20may be defined and organized to provide bandwidth, also referred to herein as network capacity, sufficient to support the bursts of higher activity. However, these bursts of higher activity may occur occasionally. Thus, full bandwidth capacity may only be utilized infrequently. Accordingly, while it may be critical to mission success to have a given network capacity to support network communication, power consumption by nodes22to maintain this capacity may be undesirably high when the network capacity isn't fully being utilized.

FIG. 2shows a state diagram34for a wireless node22that may be utilized within the ad hoc network20. A number of strategies have been developed to reduce power consumption at wireless nodes22by periodically placing nodes22in a lower power mode, such as an idle state or a sleep state. By way of example, as illustrated inFIG. 2, each of nodes22may be capable of functioning in either of two fundamental modes. These two fundamental modes can be an operational mode36and a sleep mode38. In operational mode36, node22is capable of operation within network20in which network traffic32(FIG. 1) can be passed between nodes22.

In an exemplary scenario, operational mode36can include a run state40and an idle state42, where run state40can further be subdivided into a transmit state44and a receive state46. When node22enters idle state42, it neither receives nor transmits network traffic32(e.g., overhead messages or user data). Whereas, when node22enters run state40, it is instantaneously capable of receiving and/or transmitting network traffic32. Power consumption by node22in idle state42is typically much lower than when node22is in run state40since node22neither receives nor transmits network traffic32in idle state42.

Like idle state42, sleep mode38also refers to a low power consumption mode for node22. However, in sleep mode38, certain elements (e.g., oscillator, voltage regulator, transceiver, etc.) of node22may be turned off so that node22enters a sleep state47in order to minimize power consumption. Accordingly, power consumption by node22in sleep mode38can be significantly less than power consumption by node22in idle state42.

Aside from power consumption, a notable difference between idle state42and sleep mode38is that of latency, i.e., the time delay experienced by node22to either enter or exit run state40. In wireless ad hoc network20, this time delay can affect whether node22remains “in-network” (i.e., is recognized as a member of ad hoc network20) or whether node22becomes “extra-network” (i.e. node22is no longer recognized as a member of ad hoc network20).

In idle state42, node22is neither transmitting nor receiving, but since multiple elements of node22are not powered down in idle state42, an interrupt can result in transition from idle state42to run state38with a very short transition delay. Thus, in idle state42, node22can maintain network connectivity with the remainder of nodes22in ad hoc network20. That is, node22in idle state42can remain “in-network,” and will be recognized as such by the remainder of nodes22.

In contrast, when node22is in sleep mode38, node22may lose network connectivity with remaining nodes22in ad hoc network20. A transition from sleep state47to run state40may occur as a result of a realtime clock alarm, i.e., a search wakeup alarm48. In response to search wakeup alarm48, node22may be compelled to enter a search state50to power up various components that were powered down and to send overhead messages in order to reestablish network connectivity with nodes22of ad hoc network20. Consequently, the transition from sleep mode38to run state40can be many times longer than the transition from idle state42to run state40.

Typical networking waveforms use a time slotted structure of, for example, Time Domain Multiple Access (TDMA) and/or Carrier Sense Multiple Access (CSMA). Such a scheme allows each node22within ad hoc network20a great deal of flexibility to access the radiofrequency (RF) medium, i.e. wireless links24(FIG. 1), during the time slots. Time slot access is generally available on a scheduled basis or a contention access basis, such as CSMA. The unpredictability of contention based access to wireless links24makes power management particular challenging. Power management is difficult because all nodes22within network20need to constantly “listen” for network traffic in order to allow the network traffic to be sent on any time slot with little or no a-priori knowledge. As such, wireless network nodes22must continually be in receive state46during mission critical time periods, thereby consuming power. Moreover nodes22must be in receive state46, even when nodes22are not currently receiving or transmitting network traffic32(FIG. 1).

In addition, all nodes22within wireless ad hoc network20continually participate in the network overhead that maintains connectivity among these dynamic, physically moving network nodes22. As nodes22move about, they exchange messages with each of their neighboring nodes22to track the most favorable wireless links24in order to maintain constant contact to their local neighbor nodes22. Likewise, these local wireless links24allow network20to compute routing solutions between all neighboring nodes22and gateway nodes28which provide ingress and egress to the local domain of the wireless ad hoc network20. The constant requirement to participate in maintaining the network routing solution further complicates power management because the individual nodes22need to continually be in run state40(FIG. 2) in order to send and receive overhead messages.

Consequently, it is undesirable and impractical for nodes22to enter sleep mode38during mission critical periods due at least in part to loss of network connectivity and undesirably long latencies to wake up, reestablish connectivity, and enter run state40. Conversely, it is also undesirable to remain constantly in run state40due to excessive power consumption concerns.

As discussed in detail below, embodiments of the invention fundamentally achieve efficient power management by creating more periods of time for nodes22to be in idle state42so as to reduce power consumption at nodes22. By reducing power consumption, battery life can be extended thereby resulting in a reduction in size and weight of wireless mobile nodes22, due to a reduction in a quantity or physical size of the batteries needed to power nodes22. However, by creating more time that nodes22are in idle state42(as opposed to sleep state47), nodes22can remain in-network performing their role. Moreover, nodes22can rapidly transition to run state40as traffic load in ad hoc network20dictates.

FIG. 3shows a block diagram of one of wireless nodes22(FIG. 1) operable within wireless ad hoc network20(FIG. 1). Node22may be a software definable radio system that includes, for example, a transceiver52configured for intra-network communication over wireless link24. A processor section54is in communication with transceiver52and a computer-readable storage medium56. Likewise, processor section54may be in communication with an input section58(e.g., keypad, touchscreen, microphone, sensor, and the like) and a display60.

Computer-readable storage medium56may contain communication algorithms62executable by processor54that define channel modulation waveforms; modulation techniques; wideband analog-to-digital and digital-to-analog conversion; the implementation of intermediate frequency, baseband, and bitstream processing functions; and so forth. Through the execution of communication algorithms62, processor54controls the transfer of signals, i.e., network traffic32, to and from node22. That is, processor54enables forwarding of network traffic32as distinct bitstreams over wireless links24between node22and one or more other nodes22of wireless ad hoc network20.

In accordance with an embodiment, computer-readable storage medium56further contains a power management algorithm64executable by processor54. Processor54executes power management algorithm64, referred to hereinafter as a power management process64, to control when the transfer of signals, i.e., network traffic32, to and from node22will take place. More particularly, through the execution of power management process64, processor54dynamically scales the needed bandwidth of wireless links24in accordance with a current traffic load of wireless ad hoc network20. This scaling of bandwidth is accomplished in order to create more periods of time that node22is in the lower power consumption idle state42(FIG. 2), while rapidly increasing the bandwidth as the network traffic load and/or network mobility dictates.

FIG. 4shows an exemplary time-frequency graph66of communication resources68that may be accessible by wireless nodes22and utilized within wireless ad hoc network20(FIG. 1). In this exemplary embodiment, communication resources68may include multiple frequency channels70which may be utilized for control, data, and voice transmission in accordance with known and developing networking waveform methodologies.

In some embodiments, frequency channels70may be divided into fixed intervals in time, known as frames72, illustrated in conjunction with one of frequency channels70. Frames72may be divided into one or more timeslots74(illustrated in conjunction with one of frames72) in accordance with a particular time slotted structure implemented within the networking waveform technique for wireless ad hoc network20. Timeslots74, each of which accommodates a single burst of information, may be utilized for network traffic32(FIG. 1), such as overhead messages and/or user data.

Network traffic32may include network access data, configuration information of timeslots74, forwarding acknowledgements, user communications from nodes22, such as voice, status information, position data, sensor data, and so forth.

A horizontal x-axis76of time-frequency graph66provided inFIG. 4represents time divided into successive cyclically repeating time windows78. For example, time window78repeats each second. Typically, networks, such as wireless ad hoc network20(FIG. 1), break up these time windows78in shorter blocks of time referred to as epochs80. In this example, each of time windows78is one second in duration, and there are ten epochs80in each time window78. Network20communicates network traffic32(FIG. 1) using timeslots74within frequency channels70during time periods defined by epochs80. Although time-frequency graph66shows each of the one second time windows78being divided into ten epochs, it should be understood that there may be a different number of epochs80per time window78(for example, one hundred epochs per second).

When ad hoc network20is fully loaded, network traffic32is communicated via frequency channels70during all epochs80, thus providing one hundred percent network capacity, or bandwidth. Bandwidth refers to the maximum amount of information (e.g., bits/second) that can be transmitted via communication resources68). However, when ad hoc network20is lightly loaded, communication of network traffic32within network20may take place during only a few epochs80per second. Indeed, when ad hoc network20is very lightly loaded, ninety to ninety-nine percent of the time, subdivided into epochs80, no network communication may take place. That is, frequency channels70may be unused. Accordingly, in time of reduced network activity, correspondingly reduced network capacity, or bandwidth, may be used.

Network traffic32is communicated within ad hoc network20via frequency channels70. However, in accordance with the execution of power management process64(FIG. 3), network traffic32is communicated via frequency channels70over established wireless links24(FIG. 1) during specified predetermined periods of time, i.e., during a subset of epochs80within each successive time window78. Any remaining unused epochs80within time window78can then be made available for power savings, discussed below.

Referring now toFIG. 5,FIG. 5shows a flowchart of power management process64. Power management process64is executed to determine a current traffic load of wireless ad hoc network20(FIG. 1) and to select a subset of epochs80within successive time windows78during which network traffic32may be communicated via frequency channels70. As such, network capacity, i.e., the bandwidth, can be increased or decreased to accommodate the current traffic load of network20.

The power management function of process64may be implemented in a centralized manner or in a more distributed manner. For example, in a centralized implementation, power management process64may be executed by only one of nodes22serving as a network manager. The network manager node22responds to conditions of changing traffic loads by sending out a message to all other nodes22in network20to change the number of active epochs80(FIG. 4). The terms “active epoch” or “active epochs” used herein refers to those epochs80during which network traffic32(FIG. 1) may be communicated. Conversely, “inactive epoch” or “inactive epochs” refers to the remaining epochs80within time window78during which network traffic32is not communicated. These inactive epochs80are time periods during which power savings techniques may be implemented.

In a distributed implementation, power management process64may be executed by each of nodes22. Coordination of epoch adjustment may be performed as a voting action among nodes22. Decisions regarding a change in the number of active epochs80may call for unanimous consent, near unanimous consent, or consent within domains, islands, or subnets of nodes22. For simplicity of description, power management process64will be discussed in connection with its execution at one of nodes22within ad hoc network20. However, the generalized operations of power management process64apply equivalently to both of the centralized and distributed implementation scenarios mentioned above.

Power management process64begins with a task82. At task82, node22monitors a current traffic load of wireless ad hoc network20. The current traffic load may be monitored by acquiring knowledge, through messaging, of queue utilization of network traffic32(FIG. 1) at various nodes22. For example, queue analysis may include queue fill depth versus time.

In addition, to queue analysis, the monitoring of the current traffic load and traffic load analysis may further take into account quality of service considerations (QOS) and/or network mobility. Regarding QOS considerations, the adjustment of a quantity of epochs80(FIG. 4) for communicating network traffic32can take into account the priority of network traffic32so as to optimize the quantity of epochs80used for communicating network traffic32when high priority network traffic32or network traffic32sensitive to latency is to be communicated. Latency sensitive network traffic32includes, for example, voice traffic. Lower priority network traffic32as represented, for example, in an IP packet QOS marking, can tolerate higher latencies and the longer queuing time that could result when a quantity of epochs80available for communicating network traffic32is reduced.

Regarding network mobility, the adjustment of a quantity of epochs80(FIG. 4) for communicating network traffic32can also take into account knowledge of the mobility of nodes22within wireless ad hoc network20(FIG. 1). When network traffic32demand is moderate or low, and nodes22are geographically immobile, the quantity of epochs80available for communicating network traffic32can be maintained low or can be reduced because the need for network topology adjustments is reduced. As nodes22begin to geographically move about, their rate of movement can increase the need for more frequent network maintenance. This rate of change may be used within traffic load analysis of task82to influence an increase in the quantity of epochs80available for communicating network traffic32.

A query task84is performed in connection with task82. At query task84, a determination is made as to whether the traffic load analysis performed at task82indicates that the current traffic load exceeds a high traffic load threshold.

Referring toFIGS. 6 and 7in connection with task84,FIG. 6shows an exemplary graph86of a current traffic load parameter88relative to time90, andFIG. 7shows an exemplary graph92of time window78indicating those epochs80which are currently available for communication of network traffic32(FIG. 1) within wireless ad hoc network20(FIG. 1).

In response to traffic load monitoring and analysis at task82(FIG. 5), current traffic load parameter88represents the current traffic load within network20, and taking into account quality of service considerations and network mobility. At a first instant in time94, labeled T1, traffic load parameter88falls within a traffic load window96delineated by a high traffic load threshold98and a low traffic load threshold100.

At first instant in time94, node22may have selected two of epochs80to be a subset102of epochs80during which network traffic32(FIG. 1) is to be communicated via wireless links24(FIG. 1) using frequency channels70(FIG. 7). That is, subset102defines a duration within successive time windows78during which nodes22within wireless ad hoc network20are in run state40. Nodes22may enter the lower power consumption idle state42during the remaining epochs80within time window78, in which nodes22abstain from communicating network traffic32.

Thus, power savings is achieved in the example shown inFIG. 7by placing nodes22in idle state42approximately eighty percent of the duration of time window78. Time window78is one of cyclically repeating time windows, as illustrated inFIG. 4. Accordingly, the same subset102of epochs80will remain available for communication of network traffic32until the quantity of epochs80per time window78are increased or decreased in accordance with the execution of power management process64. Although one power savings technique is represented by placing nodes22in idle state42, different or additional power savings techniques may alternatively be implemented.

At query task84(FIG. 5), at a second instant in time104, labeled T2, a determination is made that current traffic load parameter88exceeds high traffic threshold window98. Accordingly, power management process64proceeds to a task106.

At task106, subset102of epochs80is adjusted or otherwise selected to accommodate the increasing traffic load. That is, a quantity of epochs80(FIG. 4) per successive time windows78(FIG. 4) that are available for communicating network traffic32is increased.

Referring toFIG. 8in connection with task106,FIG. 8shows another exemplary graph108of time window78of epochs80selected for communication in response to increased network traffic32. In response to task106, a second subset110of epochs80within time window78is formed in response to current traffic load parameter88(FIG. 6) at second instant in time104(FIG. 6). In this example, second subset110of epochs80includes all epochs80within time window78, and successive ones of the cyclically repeating time windows78. Since communication of network traffic32can occur during all epochs80, wireless ad hoc network20can utilize one hundred percent of its network capacity, i.e., bandwidth. However, during the time when communication can occur during all epochs80, as specified in second subset110, nodes22will not enter idle state42(FIG. 2) and no power savings will be achieved.

With reference back to power management process64(FIG. 5), a task112is performed in connection with task106. At task112, node22sets a timing policy for increasing the quantity of epochs80from first subset102(FIG. 7) to second subset110(FIG. 8) of epochs80. In an embodiment, the rate of increase in epochs80to second subset110can be tailored for each implementation. By way of example, in critical applications, responding to an increased traffic load may require that network20return to one hundred percent capacity as rapidly possible.

Referring toFIG. 9in connection with task112,FIG. 9shows a graph114exemplifying a timing policy116in which a rapid increase characteristic118is implemented for increasing a quantity of epochs80during which network traffic32may occur. As shown, timing policy116entails an aggressive recovery policy to enable network communication during second subset110(FIG. 8) of epochs80(FIG. 8) as quickly as possible. In this exemplary instance, the adjustment from two epochs80per second, as specified in first subset102(FIG. 7) of epochs80, to all ten epochs80per second, as specified in second subset110(FIG. 8) of epochs80should be enabled in less than one second.

With reference back to power management process64(FIG. 5), following the execution of tasks106and112, process64continues with a task120.

At task120, node22communicates management messages122as network traffic32to all nodes22within wireless ad hoc network20. Management messages122can provide nodes22with information regarding second subset110(FIG. 8) of epochs80, such as quantity of epochs80and the particular epochs (80), as well as timing policy116(FIG. 9).

Process64continues with a task124. Following receipt of management messages122, each of nodes22modifies its transmit capability mode by entering run state40(FIG. 2) to enable network communication during epochs80within the adjusted subset of epochs (e.g., second subset110illustrated inFIG. 8) and by entering a non-communication state, such as idle state42(FIG. 2) during the remaining ones of epochs80(if there are any) within the cyclically repeating time window78.

Following task124, power management process64continues with a query task126. At query task126, a determination is made as to whether power management process64is to continue. Process64may continue for an entire duration of a mission operation being carried out by members of wireless ad hoc network20(FIG. 1), and may end following that particular mission operation. Under such a circumstance, following a particular mission operation, when a determination is made at query task126that the execution of process64is to be discontinued, process64ends. Alternatively, when a determination is made at query task126that the execution of process64is to continue, program control loops back to task82to continue monitoring the current traffic load, and increase or decrease epochs80available for network communication in response to the current traffic load for network20.

As discussed above, tasks106,112,120, and124are performed when current traffic load parameter88(FIG. 6) is greater than high traffic load threshold98so as to increase a quantity of epochs80during which network communication can take place. However, referring back to query task84of process64, when a determination is made that current traffic load parameter (FIG. 6) is not greater than high traffic load threshold98(FIG. 6), process64continues with a query task128.

At query task128, a determination is made as to whether the traffic load analysis performed at task82indicates that the current traffic load is less than a low traffic load threshold.

Referring back toFIG. 6, following second instant in time104and the adjustment of transmit capability to second subset110of epochs80, traffic load window96has shifted so that high and low traffic thresholds98and100, respectively, are commensurately shifted. At a third instant in time130, labeled T3, current traffic load parameter88is now less than this reset low traffic load threshold96. When current traffic load parameter88is less than low traffic load threshold96, power management process64continues with a task132.

At task132, subset110(FIG. 8) of epochs80is adjusted to accommodate the decreasing traffic load. That is, a quantity of epochs80(FIG. 4) per successive time windows78(FIG. 4) that are available for communicating network traffic32is decreased.

Referring toFIG. 10in connection with task132,FIG. 10shows another exemplary graph134of time window78of epochs80selected for communication in response to decreased network traffic32.

In response to task132, a third subset136of epochs80within time window78is formed in response to current traffic load parameter88(FIG. 6) at third instant in time130(FIG. 6). In this example, third subset136of epochs80includes only one epoch80within time window78and successive ones of the cyclically repeating time windows78. Since communication of network traffic32can occur only during one epoch80per time window78, ninety percent of the duration of time window78(i.e., nine epochs per second) is available for power savings techniques.

As shown in graph134, ad hoc network20(FIG. 1) is lightly loaded. That is, there is only minimal network traffic32currently being communicated via wireless links24(FIG. 1). In this example, this single epoch80within third subset136is available for network communication that includes, at least, overhead messaging and bandwidth management messages122. In an embodiment, the same epoch80in each time window78(FIG. 4), i.e., the same period of time, may be available for network communication to carry overhead messages, bandwidth management messages122, and the like in order to maintain nodes (FIG. 1) in-network and to maintain, or establish, routing solutions.

With reference back to power management process64(FIG. 5), a task138is performed in connection with task132. At task138, node22sets a timing policy for decreasing the quantity of epochs80from, for example, second subset110(FIG. 8) to third subset136(FIG. 10) of epochs80. That is, the rate of decrease of epochs80to the single epoch80of third subset136can be tailored for each implementation. For example, response to a decreased traffic load may occur gradually.

Referring toFIG. 11in connection with task138,FIG. 11shows a graph140exemplifying a timing policy142in which a gradual decrease characteristic144is implemented for decreasing a quantity of epochs80during which network traffic32may occur. As shown, timing policy142entails a gradual decay policy to enable network communication during epochs80within third subset136(FIG. 10) of epochs80(FIG. 8). In this exemplary instance, the adjustment from ten epochs80per second, as specified in second subset110(FIG. 8) of epochs80, to only one epoch80per second, as specified in third subset136(FIG. 10) of epochs80can be enabled in approximately five seconds.

It should be understood that graph114(FIG. 9) and graph140(FIG. 11) show only two, of many, possible responses to increased network traffic32and/or decreased network traffic32). Those skilled in the art will recognize that a particular timing policy for increasing and/or decreasing epochs80available for network communication can be varied in accordance with particular wireless ad hoc network implementations taking into account, for example, the criticality of communication, quality of service considerations, latency, network mobility, and so forth.

Returning to power management process64(FIG. 5), following task138, program control continues with tasks120and124in which bandwidth management messages122are communicated to all nodes22within wireless ad hoc network20with information regarding third subset134(FIG. 10) of epochs80, followed by each node22modifying its transmit capability in accordance with third subset136. Subsequent to the execution of tasks120and124, continuation query task126may be performed, as discussed above.

Now returning to query tasks84and128, when a determination is made at query task84that the current traffic load is not greater than high traffic load threshold98(FIG. 6) and a determination is made at query task128that the current traffic load is not less than low traffic load threshold100(FIG. 6), power management process64continues with a task146. At task146, the current subset of epochs80available for network communication is maintained unchanged. That is, negative responses to each of tasks84and128indicates that the current traffic load, represented by current traffic load parameter88(FIG. 6), falls within traffic load window96supportable by the subset of epochs80available for network communication. Therefore, the quantity of epochs80within time window78(FIG. 4) that are available for network communication need not change.

Following task146, process64may simply proceed to continuation task126, as discussed above. In addition, or alternatively, as illustrated inFIG. 5, tasks120and124may be performed, as needed, to communicate management messages122regarding the current subset of epochs80(e.g., first subset102(FIG. 7) available for network communication so that each of nodes122can verify that its transmit capability has been modified in accordance with the appropriate subset of epochs specified in management messages122. Subsequently, continuation query task126may be performed as discussed above.

FIG. 12shows yet another exemplary graph148of time window78of epochs80selected for communication of network traffic32(FIG. 1). As shown in graph148, epochs80selected for inclusion in a subset150of epochs80are approximately uniformly distributed within time window78.

Under some conditions, all epochs80within each time window78need not be selected to support network traffic32. That is, full bandwidth is not required. However, quality of service (QOS) characteristics of network traffic32may call for reduced latency. Through an appropriate selection of epochs to form subset150, latency can be kept short while still making some epochs80available for power savings.

Conversely, graph92(FIG. 7) illustrates a condition in which immediately adjacent epochs80within time window78are selected for inclusion in subset102(FIG. 7). Such a condition is advantageous for power savings in that elements within nodes22can power up, i.e., become active, in order to enter run state40(FIG. 2) and stay active until no longer needed during each time window78, thereby reducing the number of power up and power down cycles.

Consequently, epochs80within subset150are selected to minimize latency with some sacrifice in power savings. Whereas, epochs80within subset102are selected to maximize power savings with some adverse impact to the latency characteristics. Thus, it should be apparent that various epoch selection schemes may be implemented in accordance with particular wireless ad hoc network implementations taking into account, for example, the tradeoff between power savings and latency.

In summary, the present invention entails methodology and a system for managing power consumption in a wireless ad hoc network by dynamically varying network capacity in favor of using less power in response to demand. In particular, a power management scheme is implemented in which time periods are formed during which a network node can enter a low power, non-communication state. These time periods are formed based on current traffic loads, and these time periods can rapidly change as a result of network traffic or mobility demands. The time spent in these lower power states can vary from one epoch in ten to as many as nine epochs in ten. This allows the network nodes to be in a lower power consumption state ten to ninety percent of the time. However, since the nodes are still sending and receiving network routing overhead messages at least one epoch per second, the nodes remain in-network and do not have to reacquire the network when network traffic increases. This avoids a significant time penalty as compared to power management techniques where a node leaves the network for periods of time.

The reduction of wasted power enhances the ability of the wireless mobile nodes to remain in-network performing their assigned role. By reducing wasted power, battery life can be extended. Therefore, savings is achieved in terms of size and weight of the wireless mobile nodes since less batteries and/or smaller batteries can be used. Additionally, a reduction in power consumption reduces a node's thermal signature thereby increasing its operating life and making it less detectable to thermal imaging systems.

Although the preferred embodiments of the invention have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. For example, the order of tasks can be varied greatly from that which was presented. In addition, the particular bandwidth management messages can be varied in accordance with the characteristics of a particular wireless ad hoc network.