A Framework for Energy- Scalable Communication in High-Density Wireless Networks Telvis Calhoun Wireless Sensor Networks CSC Dr. Li 8/27/2008

Background  Overview  Power Control API  Radio Channel Background  Communication Models  Summary

API  Introduce power control API for wireless sensor nodes.  Trade-off communication for energy savings Latency Reliability Range for energy savings.  Goal is to add energy efficient protocol design.  Scalable sensor networks

Energy vs. Performance  Voltage/Freq Processor effects end-to-end latency scalability in communication  Code[rate] Provides reliability.  Transmit power Range scalability.

Knobs  Range Works with location aware protocol. Set destinations unicast or multicast. Range number or nearest neighbors or distance in meters.

Other Knobs  Latency – set maximum latency (usecs)  Reliability – set min reliability (ber)  Energy - set max energy(ujoules)

Radio Model  Radio Model Parameters Amplification RF and RF Pathloss Forward Error Correction Bit-error rate Receiver thresholds Noise and Interference

Power Amplification [2, 3]  Increases the power and/or amplitude of a signal.  Also called gain.

RF and RF Pathloss [10]  RF is a frequency or rate of oscillation  Attenuation of an electromagnetic wave as it propagates through space.  Influenced by terrain contours, environment (urban or rural, vegetation and foliage), Propagation medium (dry or moist air), Distance between the transmitter and the receiver Height and location of antennas.

Forward Error Correction [5]  Sender adds redundant data to its messages  Allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data. Coderate k/n for every k bits of useful information n bits of data, of which n minus k are redundant. [6]

Bit-error rate [7]  Ratio of the number of bits incorrectly received to the total number of bits sent during a specified time interval.  Mitigated by FEC

Receive Thresholds  RF Sensitivity Threshold Lowest signal strength at which a signal can be detected on the channel.  RF Receive Threshold Lowest signal strength a which a signal can be received as information.

Noise and Interference [8]  Noise Floor Measure of the signal created from the sum of all the noise sources and unwanted signals Includes thermal noise.  Interference Signals from different users to interfere with one another.[9] Mitigated by orthogonal channels and MAC algorithms

Communication Energy Models  Radio Transmission Energy – (PIC). Represent the energies at startup and transmission. Pstart,Tstart represent power and latency or radio at startup PtxElec is active transmission power Pamp is dissipated amplifier power R radio bit rate Rc is convolutional code rate N number of bits before FEC (forward error correction)

Decoding and Receive Energy  Energy required to receive a packet N is energy dissipated by the radio at startup R received coderate Edecbit is the decoding energy per information bit

Modeling Communication  Node-to-Base Station Base station is an energy-unconstrained node  Node-to-Node Sum of receive and transmit energies. Minimum energy policy is enforced by choosing least-energy paremeters to satisfy requirements

Point-to-Point Communication  Code (K) Kc=7=max  Power amplifier (V)  Decoding processor voltage (V, MHz)  N is data bits

Multi-hop Data Aggregation  Vary power parameters to achieve least cost multi-hop route

Summary  Paper provides an API used for adaptive power control  Describes theoretical models  Shows performance impact of various parameters  Reviewed radio parameters  Communication Models

References [1]R. Min and A. Chandrakasan, "A framework for energy-scalable communication in high-density wireless networks," in Proceedings of the 2002 international symposium on Low power electronics and design Monterey, California, USA: ACM, [2]Amplifier, " [3]Electronic_amplifier, " [4]Radio_frequency, " [5]Forward_Error_Correction, " [6]Code_rate, " [7]Bit_error_probability, " [8]Noise_floor, " [9]WiMAX, "Wireless Radio Channel," in channel. channel [10]Pathloss, "