Announcements CMPE 257 Wireless and Mobile Networking n n n Project status update 2 Graded exams Project report Spring 2003 Lecture 18 CMPE 257 Spring 2003 1 Today n n CMPE 257 Spring 2003 2 Location Management Location Management Power Management n Approaches n Wide area cellular networks Akyildz96 Jannink97 Prakash96 n n n In building wireless networks Ward97 Bahl00 n n CMPE 257 Spring 2003 3 Reactive approaches MH initiated Proactive approaches Network initiated CMPE 257 Spring 2003 4 RADAR Bahl et al n n Testbed Similar to the Ward97 paper Provide indoor location service n RF Use received signal strength triangulation Low cost Off the shelf hardware n n n n n CMPE 257 Spring 2003 n n n n 5 Functionality n n CMPE 257 Spring 2003 n Off line derive and validate accurate signal propagation models Real time user location 6 7 Signal strength in dBm n n s Watts 10 log10 s 001 dBm Signal to noise ratio SNR in dB n n CMPE 257 Spring 2003 2 Mbps 1 2 ms one way delay 200m and 25m range open close environments What is being collected Off line and real time functions n Single floor 10500 sq ft with 50 rooms 3 base stations covering entire floor Lucent WaveLAN RF technology SNR dB 10 log 10 s n dB For each received packet SS recorded CMPE 257 Spring 2003 8 Data collection process n n More on data collection Mobile broadcasts beacons periodically Base stations record SS and SNR n n n n n n Different than the ORL system Scalability Path asymmetry All clocks synchronized Mobile broadcasts packets 4 pkt sec BS records t bs ss n n n In off line phase collected SS in all 4 directions at 70 different floor locations n CMPE 257 Spring 2003 n n n n Signal strengths from 3 BSs Compare to floor layout energy map Pick location that minimizes Euclidian distance between measured and recorded set of ss s CMPE 257 Spring 2003 CMPE 257 Spring 2003 10 Results Off line data used to build signal propagation model Validation of assumption that from signal strength location can be inferred How is location determined n For each x y d 20 ss samples 9 Processing data n Off line mobile also provides its location by using a floor map Orientation is important LoS obstruction etc 11 n Empirical method performs better than random and strongest BS n Taking k nearest neighbors shows some improvement Analysis of impact orientation number of data points and number of samples User tracking n n n Error approx size of a room CMPE 257 Spring 2003 12 Radio propagation model cont d Radio propagation model n Model of indoor signal propagation n n Adaptation of existing model to single floor n Signal strength varies with distance AND number and type of obstacles Empirical characterization of wall attenuation Use corrected empirical data and linear regression to determine other parameters n No need for empirical data Indoor propagation n n Reflection diffraction scattering Multipath effect n n n n n n Receiver gets signal from multiple paths Distorted signal n Challenges dependency on layout material obstacles number and type etc CMPE 257 Spring 2003 13 n Consider effects of walls Similar values for different BSs location surroundings etc Less accurate results than empirical model but more practical CMPE 257 Spring 2003 14 Why power management Power Management CMPE 257 Spring 2003 15 CMPE 257 Spring 2003 16 Where to place power management n n Power Controlled MAC Monks01 Hardware based solutions turn off display slow down disk etc Software based solutions n n n n Different layers n n n MAC power controlled transmissions idle time management Routing finding energy efficient routes Transport idle time management n n n n 17 Contention Based CA n n Power control for better channel utilization Focus Multi hop wireless networks CSMA CA based protocols Power management interface to application Application is able to control trade off between power savings and performance related requirements delay CMPE 257 Spring 2003 n Goal 18 Spatial reuse Sender receiver acquire floor before data transmission Physical virtual RTS CTS carrier sensing Multiple concurrent transmissions in neighborhood not allowed CMPE 257 Spring 2003 CMPE 257 Spring 2003 n One approach nodes acquire only a minimum area sufficient for correct data transmission n n 19 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 worstcase 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 2003 20 Proposed approach n n PCMA protocol Adaptive floor acquisition Use signal strength of received control packet to bound transmission power n n n n n Determine minimum transmission power for successful transmission Busy tone periodically pulsed by receiver on busy tone channel maximum noise tolerance n Indicates upper bound on transmit power for other transmitters CMPE 257 Spring 2003 22 PCMA Cont d n 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 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 2003 Request power to send RPTS acceptable powerto send APTS n n 21 More on PCMA n n Power Controlled Multiple Access Traditional CA on off model Bounded power model Power conserving each station transmits at minimum power level for successful transmission Cooperation no station changes its transmission power to disrupt others CMPE 257 Spring 2003 n n Transmitter including hidden terminals bounds transmission power as a function of received CTS strength Plus 2 principles n n n 23 n n 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 2003 24 PCMA Cont d n n n n Evaluation 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