1. IEEE transactions on information technology in biomedicine 2010
An EMI-aware prioritized wireless access scheme for e-health applications in hospital environments
Phond Phunchongharn
Dusit Niyato, Ekram hossain, Sergio Camorlinga
IEEE transactions on information technology in biomedicine 2010

2. Motivation & Problem
The RF transmission can cause electromagnetic interference (EMI) to biomedical devices
The different types of electronic health (e-Health) applications require different quality of service (QoS)

3. How to solve?
They proposed EMI-aware prioritized wireless access protocol - EMI problem: EMI-aware handshaking protocol - QoS problem: prioritization of the channel access (high, low user)

4. System overview
Electronic medical devices - Passive: do not transmit any radio signal for communications (e.g., ECG monitors, blood pressure monitors, infusion pumps, and defibrillators) - Active: can transmit radio signals (e.g., telemetry monitors, wireless holter monitors, and wireless ECG monitors)
Wireless holter monitor >> ambulatory electrocardiography device

5. System overview
Users - High-priority - Low-priority: utilize the radio resources only when the high-priority users are not present - Protected: do not be interfered by EMI
Channels (under unlicensed bands) - Control channel - Data channel

6. System architecture
A healthcare scenario in a cardiac department, which consists of active medical devices, passive medical devices, and their EMI-aware prioritized wireless access system

7. System architecture
Inventory system: is used to gather information about all electronic medical devices in the hospital (e.g., ON-OFF status, locations, EMI immunity levels, and SINR thresholds)

8. System architecture
Radio Access Controller (RAC): defines safe transmission parameters (i.e., transmit power), performs effective channel allocation, and controls wireless access of the clients using proposed scheme

9. System architecture
Clients: are wireless nonmedical devices using high-priority and low-priority e-Health applications.
EMR >> electronic medical record

10. EMI-aware prioritized wireless access scheme for uplink
Pctrl: is the maximum transmit power for transmitting either RTS or CTS message by a client on the control channel
Each devices have its EMI immunity level
Using equation , RAC can calculates power

11. EMI-aware prioritized wireless access scheme for uplink
If a high-priority user suffers collision, it will wait for a random time based on a constant backoff window, while a low-priority user will wait for a random time based on exponential backoff window
Once the RTS message is successfully received by the RAC, it calculates the upper bound of transmit power for the user on the data channel in the same way as Pctrl

12. EMI-aware prioritized wireless access scheme for uplink
If RAC cannot find a feasible transmit power (the EMI constraints of the medical devices and the minimum QoS requirements of the user), the request for data transmission of the user will be dropped
In this case, the transmission of the user will be dropped due to the EMI effect with probabilities and

13. EMI-aware prioritized wireless access scheme for uplink
In addition, to avoid congestion, the RAC will randomly drop the transmission requests with probabilities and for high-priority and low-priority users, respectively

14. Prediction of blocking probability due to congestion
A two-stage optimization problem Queuing model, Discrete-time Markov chain model
The RAC calculates the blocking probability due to EMI
The average transmission delay of high-priority users
The loss probability of low-priority users

15. Prediction of blocking probability due to congestion
Exponential moving average (EMA) filter >> - a is a constant smoothing factor between 0 and 1
Normalized mean square error (NMSE) -
The accuracy of EMA depends on the smoothing factor a.
We can define the appropriate value of a to minimize the least normalized mean square error.
The NMSE (Normalized Mean Square Error) is an estimator of the overall deviations between predicted and measured values

16. EMI-aware prioritized wireless access scheme for uplink
the RAC will transmit a CTS message with the maximum allowable transmit power
The user can adaptively tune its transmit power on the data channel accordingly

17. Performance
They consider a service section over in a cardiac department of hospital including: - one operating room (OP) - two examination rooms - two patient rooms - an administration room - a physician room - a hall way
They consider: - one life-supporting medical device - four non-life-supporting medical devices - one active medical receiver with five active medical transmitters
The location of RAC, passive medical devices, and active medical receiver are fixed, while the locations of active medical transmitters and the users of high-priority and low-priority applications are uniformly random.
Application requirements - average delay: 300ms - loss probability: 0.01

18. Performance
The average interference probabilities are 81.96%, 43.73%, and 25.50%

19. Performance
The outage probability is the probability that the received signal strength at the RAC is less than -94dBm.
The average outage probability for the traditional protocol with transmit power of 0dBm and -5dBm is 1.01% and 33.51%, while that due to the EMI-aware protocol is 18.71%

20. Performance
As Pd1 increases, average transmission delay of high-priority users decrease but Pd2 does not affect the performance of high-priority users.
As Pd1 increases, low priority users have higher probability to transmit their data. Therefore, PL decreases as Pd1 increases.

21. Comparison with other schemes
First-Come-First-Served (FCFS)
Earliest Due Date (EDD)
The proposed scheme can improve the average delay by 70.08% and 84.90% compared to EDD and FCFS
While the loss probability increases by 2.52% and 6% compared to EDD and FCFS

22. Comparison with other schemes
The proposed scheme can serve more high-priority users which have the shorter transmission lengths than low-priority users.
The proposed scheme can improve the overall throughput by 0.95% and 1.11% compared to EDD and FCFS.

23. Summary
They proposed EMI-aware prioritized wireless access protocol - protect biomedical devices from the harmful interference - can service different types of e-Health applications - satisfies the different QoS requirements
The proposed protocol outperforms the other centralized scheduling schemes (e.g., FCFS and EDD schemes) - reduce the average transmission delay of high-priority users - improve the overall network utilization