Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/30—TPC using constraints in the total amount of available transmission power
  • H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
  • H04W52/343—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading taking into account loading or congestion level
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/38—TPC being performed in particular situations
  • H04W52/46—TPC being performed in particular situations in multi hop networks, e.g. wireless relay networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/1607—Details of the supervisory signal
  • H04L1/1692—Physical properties of the supervisory signal, e.g. acknowledgement by energy bursts
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L2001/0092—Error control systems characterised by the topology of the transmission link
  • H04L2001/0097—Relays
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W40/00—Communication routing or communication path finding
  • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
  • H04W40/04—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources
  • H04W40/08—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources based on transmission power
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W40/00—Communication routing or communication path finding
  • H04W40/24—Connectivity information management, e.g. connectivity discovery or connectivity update
  • H04W40/248—Connectivity information update
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W40/00—Communication routing or communication path finding
  • H04W40/24—Connectivity information management, e.g. connectivity discovery or connectivity update
  • H04W40/30—Connectivity information management, e.g. connectivity discovery or connectivity update for proactive routing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W40/00—Communication routing or communication path finding
  • H04W40/24—Connectivity information management, e.g. connectivity discovery or connectivity update
  • H04W40/32—Connectivity information management, e.g. connectivity discovery or connectivity update for defining a routing cluster membership
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
  • Y02D30/00—Reducing energy consumption in communication networks
  • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

• This invention relates to power management within the context of wireless ad-hoc networks. More specifically, the invention relates to a power management scheme configured to reduce power consumption and enhance data throughput in wireless ad-hoc networks.
• Wireless communication between mobile nodes has become increasingly popular.
• the first uses existing cellular networks which are essentially systems of repeaters wherein the transmitting or originating node contacts a repeater and the repeater retransmits the signal to allow for reception at the destination node.
• the obvious drawbacks to the cellular systems include significant infrastructure costs and geographic limitations. Because of the significant infrastructure costs it is not practical to have cellular networks in all areas. Furthermore, in times of emergency, such as earthquake, fire, or power interruption the cellular network can become disabled in the precise location where it is needed most.
• the second technique for linking nodes is to form a wireless ad-hoc network among all users within a limited geographical region.
• each user participating in the ad-hoc network should be capable of, and willing to, forward data packets and participate in ascertaining if the packet was delivered from the original source to the final destination.
• the wireless ad-hoc network has a number of advantages over cellular networks.
• the wireless ad-hoc network is more robust, in that it does not depend on a single node, but rather has a number of redundant, fault tolerant, nodes, each of which can replace or augment its nearest neighbor. Additionally, the ad-hoc network can change position and shape in real time.
• It is an object of the present invention is to provide both a method and apparatus configured to reduce power consumption, enhance data throughput, and reduce demand for node resources traditionally allocated for data reception and transmission.
• Power based connectivity provides improved end-to-end network throughput, and simultaneously reduces power consumption.
• the connectivity range also increases, consequently each node in the wireless ad-hoc network would reach almost all other nodes in a single hop.
• higher powers cause higher interference levels, more collisions are likely to occur.
• the interference zones may be significantly reduced.
• the method and apparatus according to the present invention provides a system that dynamically reaches a near-optimal operating power level in a wireless ad-hoc network, such that the end-to-end throughput is optimized.
• the present invention permits a reduction in the total power usage.
• One of the major advantages provided by the present invention is conservation of power. Power is a particularly precious resource in the wireless environment.
• Typical wireless ad-hoc networks that might benefit from power based routing include low mobility wireless ad-hoc networks, including pedestrian networks formed by soldiers relaying situational awareness information on the battlefield, rescue workers and emergency disaster relief workers.
• the invention may also find application in a variety of sensor networks.
• Another object of the present invention is to provide a power management scheme that reduces power consumption, increases transmission range, enhances data throughput, and reduces demand for node resources traditionally allocated for data reception and transmission.
• the wireless ad-hoc network of the present invention uses only the minimum power required to contact a limited number of the nearest nodes, and consequently minimizes power requirements because transmission power requirements are reduced. Furthermore, transmission range can be greater than that found in a network where the signals are not relayed.
• FIG. 1 shows a power-controlled ad-hoc network
• FIG. 2 shows the format of a signaling packet
• FIG. 3 depicts the typical format of a data packet
• FIG. 4 shows the typical format of a connectivity table
• FIG. 5 illustrates the average node throughput as a function of connectivity range, N
• FIG. 6 shows the end-to-end network throughput as a function of connectivity range, N
• FIG. 7 shows average power consumption as a function of connectivity range, N
• FIG. 8 shows average node throughput as a function of connectivity range, N;
• FIG. 9 depicts end-to-end network throughput as a function of connectivity range, N;
• FIG. 10 shows average power consumption per user, per slot, in mW as a function of connectivity range, N.
• the present invention provides a method and an apparatus useful for enhancing end-to-end network throughput, while simultaneously reducing power consumption, and may be tailored to a variety of other applications.
• the following description, taken in conjunction with the referenced drawings, is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular applications. Narious modifications, as well as a variety of uses in different applications, will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments. Thus, the present invention is not intended to be limited to the embodiments presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
• Power based connectivity provides improved end-to-end network throughput, and simultaneously reduces power consumption.
• the connectivity range also increases, and consequently each node in the wireless ad-hoc network would reach almost all other nodes in a single hop.
• the present invention provides a method and an apparatus that dynamically reaches a near- optimal operating power level, such that the end-to-end throughput is optimized.
• the present invention permits a reduction in the total power usage, to a level close to the minimum.
• One of the major advantages provided by the present invention is conservation of power. Power is a particularly precious resource in the wireless environment.
• Typical wireless ad-hoc networks that might benefit from power based routing include low mobility wireless ad-hoc networks, including pedestrian networks formed by soldiers relaying situational awareness information on the battlefield, rescue workers and emergency disaster relief workers.
• the invention may also find application in a variety of sensor networks.
• the present invention provides a power management scheme that can be utilized in conjunction with traditional table-driven routing protocols, with possibly minor modifications to the protocols themselves.
• the performance measures are taken to be the end-to-end network throughput and the average power consumption.
• each node transmits at a power level such that only a fixed number of neighboring nodes can distinguish the transmission. For example, a node might transmit with a power such that only its three closest neighbors can hear its transmission. Thus, in FIG. 1, node A transmits with a power such that only its three nearest neighbors i.e., nodes B, C and D can distinguish the transmission. Similarly, node D would transmit with a different power, say, such that only it's three nearest neighbors i.e., nodes A, C and E can hear the transmission.
• the wireless ad-hoc network for the purposes of this invention, will be assumed to be comprised of n nodes, wherein each node has a unique ID denoted by Node ID.
• the number of nodes, n may be dynamically shifting as nodes enter and leave the wireless ad-hoc network.
• the mobile nodes are assumed to have low mobility patterns relative to one another, for instance, nodes traveling in a manner such that changes in inter-nodal reception vary slowly as a function of time. Such a low mobility pattern would result when the network nodes are carried by pedestrians.
• each mobile node has a transmittance power that allows for direct connectivity only to each node's N closest neighbors, where Nmay be adapted dynamically.
• N may be adapted dynamically.
• the type of traffic to be handled is significantly connectionless (datagrams), i.e., routing decisions are made on a packet-by-packet-basis.
• the transmit power of any mobile node is upper bounded by a maximum power level, P ma ⁇ ., where P max is constrained by the limited size and weight inherent in mobile terminals.
• the transmit power of any mobile node has a lower, minimum power, boundary level P m ; n . This constraint is essential as a means of reducing the possibility of partitioning the network into isolated islands.
• MAC schemes are deployed in this system.
• the invention assumes the availability of a reliable reverse channel that, preferably, operates in a different frequency band. This channel is essential for sending acknowledgement, o ⁇ ACK, messages from the receiving node to the transmitting node in order to enable retransmission when required. The determination relating to when retransmission is appropriate can be based on an interval of time when no packets are forthcoming, but one or more was expected.
• Such "time-outs" are set at the transmitting node to detect if packets were involved in collisions or otherwise lost.
• the data packet will reach its destination successfully, and upon successful reception, the destination node is expected to broadcast an acknowledgement message, at optionally the maximum allowable power level, P max , in order to reach the source node directly.
• P max the maximum allowable power level
• This acknowledgement enables each node to periodically compute its end-to-end throughput that is to be optimized. The protocols will use this computation in order to drive the average throughput towards a maximal value.
• Guard bands are crucial in order to keep the nodes in the network time-synchronized.
• the guard band provides a time interval in excess of that required to the receive data.
• the guard bands provide a margin of safety against time domain variations in sequential operations. More specifically, the slot duration is intentionally made larger than packet duration by a time interval equal to a guard band.
• each mobile node has two buffers.
• First is a Medium Access Control, MAC, Buffer, which is configured to store packets arriving during a time slot until the beginning of the next time slot. When the MAC Buffer is full, packets are dropped and they are treated as lost packets.
• Second is a Retransmission Buffer that temporarily stores transmitted packets, until the Retransmission Buffer receives a message from the next node. If it receives an acknowledge, ACK, message, meaning that the packet was successfully delivered, then the retransmission buffer discards the packet. Alternatively, if the ACK message is not forthcoming before the buffer times out, the buffer concludes that the packet was lost, and the packet is retransmitted after a period of time.
• MAC Medium Access Control
• one embodiment includes the use of a classical shortest-path routing algorithm well known in the art as the Bellman Ford algorithm.
• the algorithm is slightly modified to comport with the unique characteristics inherent in the novel link cost calculations.
• the link costs are chosen to be the transmitted powers. Therefore, the objective is to route the packet from the source to the destination through the minimum power path.
• Other embodiments may compute link costs using an optimal combination of transmitted powers and other factors.
• Each node in the wireless ad-hoc network is equipped with a squelch circuit, wherein the squelch circuit requires that the received signal power be greater than a minimum power level, MinRecvPower.
• the squelch circuit is configured to suppress spurious noise and excessively weak signals. Such a circuit is helpful as a means for guaranteeing reliable communication between the transmitter and the receiver.
• the value of MinRecvPower helps determine the power level at which a mobile node has to transmit in order to directly reach a neighboring node.
• the Signaling Packet format is shown in FIG. 2, wherein the Node ID is the identifier for the node broadcasting the signaling packet; and wherein the Neighbor ID is the identifier for a direct neighbor to which the node is broadcasting the signaling packet; and wherein the Transmit Power Level is the minimum power level needed to reach that neighbor.
• the Data Packet format is shown in FIG. 3, and the following definitions hold; the "Source ID” is the identifier of the node that generated the packet, and the “Destination ID” is the identifier of the packet's destination node.
• the "Current Node ID” is the identifier of the relay node at which the packet is currently stored on its path to the destination.
• the "Next Node ID” Identifies of the next relay node to which the packet is to be transmitted on its path to the destination.
• the "# Re-Transmissions” represent the total number of re-transmission attempts performed on that packet. Retransmission will be necessary whenever a packet encounters a collision or otherwise must be retransmitted.
• the Connectivity Table, for the wireless ad-hoc network shown in FIG. 1, will have the format shown in FIG. 4.
• Node Throughput is defined as the percentage of successful transmission attempts and End-to-End Network Throughput is defined as the percentage of packets that reach their destinations successfully and is denoted by ⁇ .
• the Average Power Consumption is defined as the average transmitted power/node/slot and is denoted by P .
• the channel model includes only path loss and shadowing effects.
• the second model includes a wireless ad-hoc network, consisting of n nodes, each with a connectivity range of N, where 2 ⁇ N ⁇ n-l.
• Each mobile node has a direct link to the closest N nodes out of (n-1) mobile nodes.
• N the mobile node adjusts its power to reach, at most the farthest node within its cluster.
• the advantages of this approach are lower power consumption per transmission.
• a node's transmission will cause lower interference to other simultaneous transmissions when compared to the previous case.
• the drawbacks are that a higher number of hops might have to be traversed in order to reach a destination, and there exists the possibility of having isolated clusters.
• link costs calculated in terms of transmitted powers are generally different depending on the radius of each cluster. Accordingly, incorporating the minimum power routing algorithm is crucial to. limit power consumption.
• the limitation of this model relates to the absence of power adaptation within a cluster. Because of this lack of power adaptation it is possible that a mobile node communicates with a node within its cluster using a power level higher than the minimum required power to communicate with that node, and thereby possibly introduces more interference than that incurred in the case to be discussed in conjunction with the third model.
• the third model pertains to a wireless ad-hoc network with each node having a connectivity of N , where 2 ⁇ N ⁇ n-l. Again, each mobile node has a direct link to the closest N (out of (n-Vj) mobile nodes.
• N out of (n-Vj) mobile nodes.
• intra-cluster power adaptation reduces the power consumed on various routes.
• a node would use the minimum power that guarantees reliable communication with that node. Note that this approach would minimize the interference caused by a transmission.
• the advantages and drawbacks are the same as in the second model. This model achieves higher throughput than the previous models at the expense of higher complexity.
• the minimum power routing is once again the candidate routing algorithm.
• P is the average power consumption and is defined as the average transmitted power/node/slot
• P m ⁇ n is the minimum power boundary, below which no node can transmit
• P tl is the transmitted power of node i
• P max is the maximum power boundary, above which no node can transmit.
• ⁇ is equivalent to the ⁇ parameter and has a one-to-one correspondence to ⁇ .
• each mobile node is responsible for keeping track of its closest neighbors. This is done by measuring signal strength, or alternatively the attenuation of P max transmissions.
• Each mobile node updates its local connectivity tables according to the signal strength of its nearest neighbors. Location updates have to be frequently exchanged so as to accurately track topology changes. Briefly the functions performed at each mobile node as follows:
• Each mobile node is assigned a dedicated signaling time slot of a global signaling channel. In this slot, the node is allowed to broadcast a beacon packet, using the power level P max , to all other nodes in the area of interest. Note that the MAC protocol employed for signaling supports contention-free communications, and hence no collisions occur in this phase. 2. In slot i, all other nodes obtain the beacon signal of node i. Accordingly, they record the received power level and store it in a data structure along with the transmitting mobile node's ID. This functionality is simulated in a model using the Power Measurement procedure described herein. Using a set consisting of the latest, predetermined number of received power level measurements, an average is computed. Note that average power measurements are used, rather than instantaneous power measurements. This is motivated by the fact that average power measurements smooth out variations due to fast multi-path fading, which is not compensated for by this scheme.
• mobile node /, 1 ⁇ i ⁇ n is expected to have a ranking of all other nodes and this ranking is based on the average received power levels from those nodes. Based on this ranking, node i picks its N closest nodes, specifically those having highest average received power levels at this node's site, as its direct neighbors. Subsequently, node i updates its local connectivity table by adding the mobile node IDs of its direct neighbors.
• Each node then adapts its transmit power level in order to achieve the required connectivity, i.e., direct links are established only to the closest N nodes.
• Node i updates its local connectivity table to reflect the link costs to the direct neighbors.
• the link cost in this protocol is taken to be the transmit power level.
• Each node then broadcasts a Signaling Packet containing its local connectivity table information in the signaling channel.
• each mobile node obtains and then stores the global network topology information. This information is then used in forming its local routing table.
• a global topological view is essential for the functioning of the table- driven routing algorithms. For large networks, it is not feasible for each node to store the entire global topological information due to the heavy communication overhead incurred and also due to memory constraints. Accordingly, this scheme supports small to mid-size wireless ad-hoc networks or sub-networks of a large ad-hoc network.
• the present invention provides a procedure that emulates the operation of mobile node capturing the beacon signal transmitted by node i during node i's allocated signaling slot, where l ⁇ i,j ⁇ n and i is not equal toj.
• the received signal strength depends solely on the transmitted power level, which is assumed to be P max during this phase, the current positions of nodes i andy, and the effect of the log-normal shadowing.
• the received power level is computed by using the following formula:
• the present invention provides two approaches to power management in mobile ad-hoc networks; the first provides no power adjustment within a cluster while the second does provide for power adjustment within a cluster.
• the basic difference between the two schemes is that in the former scheme, the power needed to communicate with the farthest node in the cluster is also used to communicate with any closer node in the cluster.
• the latter scheme suggests communicating with each node using the minimum power it needs for reliable communication. This introduces less interference to simultaneous transmissions of other nodes.
• the objective of defining a cluster is to reduce collisions and interference and thereby improve the end-to-end network throughput. Assume a minimum required level of received power, denoted MinRecvPower, which is necessary to guarantee a maximum acceptable bit error rate.
• MinRecvPower a minimum required level of received power
• P tj . power transmitted by node i such that the transmission range does not exceed beyond nodej's coordinates.
• P r .. power received by nodey when node i transmits at P max for the given configuration.
• the Minimum Power Routing (MPR) algorithm is a hop- by-hop shortest path routing mechanism where the link costs are the transmitted power levels.
• the routing algorithm then goes through the following steps:
• the power management based routing is recommended for networks characterized by low mobility patterns, especially nodes having movement patterns approximating those of pedestrians.
• the position of each node is updated periodically, with a predetermined period. The new position is determined using the current position coordinates, the speed of the mobile node, and the direction of motion.
• the speed of the mobile node is drawn from a random variable, uniformly distributed between minimum and maximum values.
• the direction of motion is assumed to be uniformly distributed in [ ⁇ ,2 ⁇ r] .
• SIMULATION RESULTS Data from simulation models for a wireless ad-hoc network that consists of 25 nodes is presented herein.
• the value of P max was selected such that the transmission range of any node using P max spans at least 15 out of the 25 nodes in the network. Therefore, the connectivity range N was limited to take values between 2 and 15 as reflected in Table 1.
• the threshold MinRecvPower is 1 milliwatt. This is sufficient to guarantee a minimum acceptable bit error rate at the receiver. Note from Table 1 that the mobility model parameters reflect the low mobility pattern being considered.
• the data in this section illustrates the impact of manipulating the Connectivity Range N on the end-to-end network throughput and on the average power consumption.
• the maximum end-to-end throughput is achieved for values of N less than 15, which corresponds to the no power management case. This implies that including a transmit power control/management scheme in a wireless ad-hoc environment improves the network throughput.
• the average power consumption is plotted versus N for different network loads. The average power consumption increases monotonically as N increases. Again, this can be explained due to the aforementioned opposing factors affecting the average node throughput. As in the case of the node throughput, as N increases, the first factor dominates the average power consumption behavior.
• each node can communicate with any other node if the power at the receiving node is larger than the minimum received power needed for reliable communication. Therefore, this approach is expected to reduce the interference and hence improve the average node throughput as shown in FIG. 8.
• FIG. 8 shows the similarity of the trends in average node throughput under both approaches of power management.
• FIG. 9 shows the end-to-end network throughput under the two proposed approaches for power management. It is evident that the trends are substantially similar for both approaches.
• the second power management approach outperforms the first in terms of power savings and end- to-end throughput. Note that at the optimal operating point, in terms of end-to-end throughput, the second power management scheme offers an average power saving of 60 mW. The consumed power in the second scheme is 15 mW as opposed to 75 mW in the case of the first scheme.
• Possible protocol implementations include at least two protocols that enable each node to dynamically adapt the connectivity range parameter N in order to achieve a near-optimal operating point.
• the first such protocol is a Periodic Update Protocol, this protocol follows the following steps: 1. Initially, each node independently chooses its connectivity range to be the minimum i.e., the range N is set to 2.
• the node operates for a pre-specified number of frames (k) with this chosen value of ⁇ .
• the performance measure namely the end-to-end throughput of this node.
• each node broadcasts its end-to-end throughput on the reverse channel. This is essential for each node to compute the average end-to-end network throughput. This value is then stored in a data structure denoted by T
• the connectivity range is then increased by one, i.e. N is increased by one.
• the ad-hoc system is expected to operate using this connectivity range for the next k frames.
• the second possible protocol is a Quasi-Periodic Update Protocol.
• This protocol is identical to the Periodic Update Protocol except that, when the network achieves maximum end-to-end throughput, the algorithm less frequently attempts to test if the current connectivity range is the optimal.
• the algorithm takes advantage of the fact that the network under consideration consists of nodes of low mobility, i.e. the network topology changes slowly. Therefore, once the system reaches an operating point wherein the throughput is at a maximum, the algorithm expects the throughput to stay at the maximum or at a value very close to the maximum until the topology changes drastically. Therefore, this algorithm trades simplicity for performance. It is much simpler than the Periodic Update protocol, but there is a possible degradation in the end-to-end network throughput.
• This invention provides a method and apparatus for power management in wireless ad-hoc networks.
• the objective is maximize throughput while minimizing the average power consumption.
• a node adapts its transmit power so as to establish connectivity with only a limited number of neighborhood nodes.
• the node might wish to adapt power to communicate with different nodes, or it might use the same power to communicate with all nodes within the cluster.
• the former scheme performs better in terms of achieving a lower average power consumption and a higher end to end throughput. Simulations further show that both schemes help improve performance in terms of reducing average power consumption and end to end throughput.
• a network with a power management scheme implemented will have better performance than a network without such a scheme. It is envisioned that the invention has application wherein each mobile node has a different connectivity range.

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