CMPE 257 Wireless and Mobile Networking Spring 2005 Topology Power Management II CMPE 257 Spring 2005 1 Announcements Homework 1 Midterm on 05 10 MAC Unicast routing Multicast routing CMPE 257 Spring 2005 2 Today Topology and power management Topology management as power management strategy CMPE 257 Spring 2005 3 Where to place power management Hardware based solutions turn off display slow down disk etc Software based solutions Different layers MAC power controlled transmissions idle time management Routing finding energy efficient routes Transport idle time management Power management interface to application Application is able to control trade off between power savings and performance related requirements delay CMPE 257 Spring 2005 4 Power Controlled MAC Monks01 Goal Power control for better channel utilization Focus Multi hop wireless networks CSMA CA based protocols CMPE 257 Spring 2005 5 Contention Based CA Sender receiver acquire floor before data transmission RTS CTS carrier sensing Node transmits only if does not sense carrier and is not deferring Multiple concurrent transmissions in neighborhood not allowed CMPE 257 Spring 2005 6 Spatial reuse One approach nodes acquire only a minimum area sufficient for correct data transmission Problem nodes need to use fixed power for symmetry i e a node s RTS CTS must reach every node whose transmission may cause collision at that node node must assume worst case transmission power from other nodes Even if power is controlled for data transmission for power savings for channel reuse it s like using fixed power CMPE 257 Spring 2005 7 Proposed approach Adaptive floor acquisition Use signal strength of received control packet to bound transmission power Transmitter including hidden terminals bounds transmission power as a function of received CTS strength CMPE 257 Spring 2005 8 PCMA protocol Power Controlled Multiple Access Bounded power model Request power to send RPTS acceptable powerto send APTS Determine minimum transmission power for successful reception Exchange sequence RPTS APTS DATA ACK Busy tone periodically pulsed by receiver on busy tone channel maximum noise tolerance Indicates upper bound on transmit power for other transmitters CMPE 257 Spring 2005 9 More on PCMA Idle node monitors busy tone channel to determine its power bound Power bound maximum power received on busy tone channel When node has data to send sends RPTS at its power bound on DATA channel RPTS contains transmission and noise power at source When destination receives RPTS it measures receive power and computes channel gain using information in the packet CMPE 257 Spring 2005 10 PCMA cont d Receiver computes power level for APTS and data packet which it includes in the APTS On receiving APTS source sends data packet at power specified in APTS if it times out before receiving APTS backs off an starts over Receiver starts sending busy tones on busy tone channel as it starts receiving data busy tone s power is such as to prevent nearby nodes from transmitting but not nodes farther away CMPE 257 Spring 2005 11 PCMA cont d When node senses busy tone it computes its transmit power for that node accordingly transmit power at node defined by most sensitive receiver least transmission power tolerance Narrow busy tones to avoid busy tone collisions After successful data reception receiver sends ACK If ACK goes through source resets backoff timer and back to idle otherwise increases backoff and starts over CMPE 257 Spring 2005 12 Evaluation Single hop network Comparison with 802 11 and ideal protocol global knowledge of link gains noise transmission power bounds PCMA shows improvement in channel utilization 2 times 802 11 s aggregate bandwidth in dense networks Overhead Multi hop Mobility CMPE 257 Spring 2005 13 Topology Control CMPE 257 Spring 2005 14 What s topology control When nodes are deployed how do they organize into a network Neighbor discovery protocol If neighborhood is sparse use all neighbors What if neighborhood is dense Use a subset of neighbors How CMPE 257 Spring 2005 15 Approaches to topology control Adjust transmit power Turn nodes on off CMPE 257 Spring 2005 16 Geography Informed Energy Conservation for Routing Xu01 Motivation Ad hoc network nodes are typically energy constrained Radio in overhearing listening or idle consumes reasonable amount of energy CMPE 257 Spring 2005 17 GAF Geographical Adaptive Fidelity Designed to operate in concert with routing protocols Energy conservation by turning off redundant nodes Assumes nodes know their location Use node equivalence to turn off radios CMPE 257 Spring 2005 18 Node equivalence Routing fidelity uninterrupted connectivity between communicating nodes Nodes are equivalent if a subset of them can be turned off without changing network connectivity 1 3 2 4 CMPE 257 Spring 2005 19 Node equivalence cont d 1 2 3 4 5 R Node equivalence varies with communication end points Example for 1 4 2 and 3 are equivalent for 1 5 only 3 CMPE 257 Spring 2005 20 Virtual Grids Area where nodes are distributed divided into virtual grids Given 2 adjacent grids all nodes in one grid can communicate with all nodes in the other Hence all nodes in each grid are equivalent CMPE 257 Spring 2005 21 Sizing Virtual Grids 2 4 1 R 3 5 2 4 1 3 r 5 CMPE 257 Spring 2005 Maximum distance between nodes R or r2 2r 2 R2 or r R 5 1 2 22 GAF Operation Nodes in sleeping discovery and active states Nodes start in discovery radio on find other nodes within grid Nodes exchange node id grid id timer Node uses its location and grid size to determine grid id Timer Td determines when node sends out discovery message and switches to active CMPE 257 Spring 2005 23 GAF cont d In active mode nodes periodically broadcast discovery message While in active timer Ta determines when node goes back to discovery While in discovery or active node can sleep if it finds equivalent nodes Timer Ts determines when node wakes up and enters discovery CMPE 257 Spring 2005 24 Tuning GAF Ideally only one node active per grid Node ranking Who handles routing Active node ranked higher that discovery node Nodes with longer lifetime are ranked higher Discovery interval can also be influenced by node s lifetime rank Highly ranked nodes suppressing others Sleep interval can be set to current active interval CMPE 257 Spring 2005 25 GAF and Routing GAF runs atop MANET routing It decides nodes duty cycle and routing needs to adjust accordingly Routing could be informed a priori