Analysis of the Performance of IEEE for Medical Sensor Body Area Networking ECE 5900 Computer Engineering Seminar Instructor: Dr. Chigan Huaming Li

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

Introduction One promising kind of sensor network: Wireless Body Area Network (WPAN)  Medical sensing and control  Wearable computing  Location awareness and identification  Implanted medical sensors (Focus)  Coronary care  Diabetes  Optical aids  Drug delivery

Introduction (Cont) Implanted medical sensors (Focus)  Advantages  Spread the memory load, processing load and improving the access to data  Pains  Power! (battery lifetime)  Replacing or charging batteries means a serious medical procedure

Introduction (Cont) Implanted medical sensors (Main concern)  Objective Make Batteries work years  Method Ensure that all sensors are powered down or in sleep mode when not in active use  Tradeoff Battery life VS. latency

Introduction (Cont) Market Name Standard GPRS/GSM 1xRTT/CDMA Wi-Fi ™ b Bluetooth ™ ZigBee ™ Application Focus Wide Area Voice & Data Web, , Video Cable Replacement Monitoring & Control System Resources 16MB+1MB+250KB+4KB - 32KB Battery Life (days) ,000+ Network Size / 65,000 Bandwidth (KB/s) , Transmission Range (meters) 1, Success Metrics Reach, Quality Speed, Flexibility Cost, Convenience Reliability, Power, Cost Our options

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

(LR-WPAN) Overview IEEE MAC Upper Layers IEEE LLC Other LLC IEEE MHz PHY IEEE /915 MHz PHY Architecture Physical Medium

(LR-WPAN) Overview Physical Layer (use 2.4G here)

(LR-WPAN) Overview MAC Layer (use star topology here) Why star topology here?

(LR-WPAN) Overview  Coordinator is external to the body  PDA, mobile phone or bedside monitor station  Easy to replace of charge batteries  Easy to communicate with other networks  Coordinator defines the start and end of a superframe and is charge of the association and disassociation of the other nodes Why star topology here?

(LR-WPAN) Overview IEEE superframe structure

(LR-WPAN) Overview Two Communication methods  Beacon mode  Pros: Coordinator can communicate at will  Cons: Listeners have to keep awake  Non-beacon mode  Pros: Nodes can sleep more  Cons: Communication latency

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

Analysis Assumptions  Sensor specification  Hardware assumption  Implanted sensor link budget  Description of network

Analysis Assumptions  Sensor specification

Analysis Assumptions  Hardware assumption Transceiver parameters (Chipcon CC2420) Microcontroller: Motorola MC9508RE8 4.5uA 700nA Battery: Lithium 560mAh at 3.0V

Analysis Assumptions  Description of network  A star network consists of the coordinator and 10 body implanted sensors  Steady state network (no consideration about association or disassociation) to or from network  Implanted sensor link budget  A 0 dBm 2.45 GHz transmitter will operate with a 5.6 dB margin

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

Average transmission time with CSMA/CA  Three variables maintained by each node for each transmission attempt (CSMA/CA): NB: Number of back-offs permitted before declaring channel access failure (0-5); CW: contention window length, only used in slotted CSMA/CA (Set to 2) BE: back-off exponent, back-off periods in the range 0 to (0-5) If BE is set to 0, CSMA/CA is switched off

Average transmission time with CSMA/CA Back-off periods The average number of back-off periods for each range is

Average transmission time with CSMA/CA The total transmission time The average number of back-off periods for each range is

Average transmission time with CSMA/CA The total transmission time The average number of back-off periods for each range is P is the probability of a clear channel after the first back-off interval (n sensors) Q is the probability of a sensor transmits in a CCA period

Average transmission time with CSMA/CA The total transmission time The average number of back-off periods for each range is How to calculate For example when R=2.5 The average back-off time for each back-off interval

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

Network scenarios and power analysis Sensor power consumption with beacon reception  Problem: The sensor devices within a beacon network have to wake up to receive the beacon from the coordinator (Power consuming) Timebase Tolerances Warm-up time

Network scenarios and power analysis Data Transfer Mechanisms (Beacon)  Data transfer to a coordinator (upload) Is the upload period

Network scenarios and power analysis Data Transfer Mechanisms (Beacon)  Data transfer from a coordinator (download) Is the download period

Network scenarios and power analysis Data Transfer Mechanisms (Non-beacon)  Data transfer to a coordinator (upload) Is the upload period

Network scenarios and power analysis Data Transfer Mechanisms (Non-beacon)  Data transfer from a coordinator (upload)

Results

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

Results Average Back-off

Results Average Back-off

Results Average Back-off With a small number of sensors that are effectively off most of the time, the probability of a channel being free is greater than 99 %. Therefore, for the relatively small number of sensors used in the WBAN networks explored here, it would be more economical to keep the CSMA/CA switched off. This is to ensure that the automatic initial back-off is avoided.

Results Node Lifetime in Beacon Networks

Results Node Lifetime in Beacon Networks

Results Node Lifetime in Beacon Networks  15-year lifetime may only be obtained for very low upload rates.  It is under very limited data rate conditions and a tight tolerance crystal, which typically must be better than 25 ppm.

Results GTS Option

Results GTS Option  The main drawback of using GTS is that the receiver in the sensor remains on for the duration of the timeslot regardless of the size of the data packet.

Results Non-Beacon Networks

Results Non-Beacon Networks

Outline Introduction Overview Analysis assumptions Average transmission time with csma/ca Network scenarios and power analysis Results Conclusion

 As a solution to the challenge of the body area network, the IEEE standard would provide a limited answer in its non- beacon form.  Sensors that do not have large amounts of data to transfer could be used, i.e., small packets of data several times per hour.

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