Challenges in Low Power Communication Protocol Design

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Challenges in Low Power Communication Protocol
Design ImplementationA SensiumTM Case Study

• Okundu C. Omeni, Alan CW Wong, Declan McDonagh,
  Alison Burdett
• Toumaz Technology Ltd, UK
• www.toumaz.com
• okundu.omeni_at_toumaz.com

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Talk Outline

• Application area
• Available standard-based solutions motivation
  for a proprietary solution
• Toumazs Sensium communication protocol (NSP)
• Implementation Performance details
• Summary

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Non-Intrusive Wireless Vital Signs BAN
Digital Patch
Life Pebble
SoC miniaturization gives Quality of
life/comfort for patient Critical data for the
physician Ultra low power consumption Non-Intrusiv
e, continuous intelligent
Vital Signs - Temperature - Physical Activity -
Heart Rate - Blood glucose - ECG/EKG -
Pressure - Respiration
Wireless BAN
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Medical Body Area Network Application
Requirements

• Low power
• Low cost
• For some applications (digital patch), devices
  would be disposable
• Robustness
• Reliability
• Security

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Motivation Wearable Batteries Wireless Standards
Increasing Power, Cost, Size
New Proprietary PHY MAC for wireless healthcare
monitoring
WiFi/802.11
UWB/802.15.3
Wibree(ULP BT)/Bluetooth/802.15.1
Zigbee/802.15.4
Existing Proprietary
All current standards compromise power
consumption for generality, data rate/range.
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Sensium Nano Sensor Protocol (NSP) primary
network topology

• Star topology
• Central node is called a Basestation terminal
  (power constrained) nodes targets
• Target nodes can roam between Basestations
• Basestations can communicate

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Main NSP Features Terminologies

• Star topology (Basestation - Target) network
  Architecture
• Network of Basestation and Targets termed a
  cluster
• FDMA/TDMA channel access
• Poll based access mechanism
• LBT if required by regulation
• Acknowledged protocol
• Dynamic Time Slotting
• Wakeup Fallback Time (WFT) increases autonomy
• Cross-Layer optimization

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Additional NSP Features

• Word level hamming error CODEC (15,11)
• Inverse parity bit also included (guarantees bit
  transitions irrespective of data)
• Frame level error detection using CRC16
• MAC Word masking provides data whitening
• Communication post-link establishment is based on
  address recognition
• Support for time-slot enforcement
• Security mechanisms based on AES-128
• Timing Synchronization between Targets
  Basestation

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Sensium NSP Communication modes

• In the next few slides I will go through the
  various communication modes that are supported by
  the NSP
• I would also be highlighting applications which
  could use these modes

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Protocol Handshake Process 1BASESTATION to
TARGET (DEFAULT) Communication
TS1
Basestation (INITIATE MODE)
Target (LISTEN MODE)
BS
BS
TS3
TS2
Request/Command
Response/Data (TACK)
TS4
Response /DATA (BACK)
Time line
T1 T2 T3 T4 BS IDLE/SLEEP T1
Default communication mode. Basestation
establishes links with 1 or more Targets and
assigns them timeslots for future communication.
All target applications start off using this mode.
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Protocol Handshake Process 2TARGET TO
BASESTATION COMMUNICATIONS
Target (INITIATE MODE)
Basestation (LISTEN MODE)
Initiate Command
Reverse Request Command
Response /DATA (TACK)
Response (BACK)
Used for Application ALARM handling and ROAMING.
This mode is unscheduled, so the Basestation
needs to be listening and idle to hear this
communication. The flowchart shows how this could
be used in an application.
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Protocol Handshake Process 3BASESTATION TO
BASESTATION COMMUNICATIONS
BS2
BS1
BS3
BS4
Essentially Peer to Peer communication. This is a
mode that allows communication without the need
to setup a network. It is also unscheduled and
completely under application control. This mode
could also be used to implement complex mesh
based networks.
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Protocol Handshake Process 4TARGET BROADCAST
COMMUNICATION
BS2
BS1
BS2
Target (INITIATE MODE)
Basestation(s) (LISTEN MODE)
BS2
BS2
TS1
TX DATA
BS3
BS4
BS2
This mode can be scheduled or unscheduled. Here
the Target device just transmits its payload to 1
or more Basestations and returns to sleep without
waiting for an acknowledgement. It could be used
for streaming applications as well as broadcast
to multiple Basestations (in fixed locattions)
for tracking the location of a Target device
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Protocol Handshake Process 5BASESTATION
BROADCAST COMMUNICATION
TS1
TS1
Basestation (INITIATE MODE)
Target(s) (LISTEN MODE)
BS
TS1
TX DATA
TS1
This mode is usually for scheduled
communications. Here the a Basestation broadcasts
a message to multiple target devices usually for
application or network management.
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Message Frame Formats
Made up of a message header and body as shown
below
Message Header MHDR
Message Body MBODY
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Link Establishment

• Basestation finds vacant RF Channel from a list
  using RSSI LBT (depending on regulatory
  requirements)
• Transmits BSEEK message and listens for Target
  response. Repeats this cycle until a response is
  received or it times out.
• Target finds active channel and listens for
  BSEEK. If not found in time window, it moves to
  the next active channel. If found, it responds,
  receives an address and a link is established

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SLEEP/WAKEUP CYCLES

• After Link establishment, a Target goes through
  SLEEP/WAKEUP cycles.
• During SLEEP, sensor data may be acquired (while
  rest of system is powered-down)
• On WAKEUP, this data can be transmitted to the
  Basestation
• The Basestation is usually always active, as it
  services multiple Targets and also listens for
  possible ALARMS

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Sensium SoC Solution

• Requirements
• - Supply voltage 1-1.5V - Max current lt 3mA - BAN
  Range gt 3m
• Small form factor - Min resolution 8 bits - Min
  sensor signal BW 100 Hz
• All parts of the system must be optimised for
  power consumption

Ref A. Wong, D. McDonagh, G. Kathiresan, O.
Omeni, O. El-Jamaly, T. Chan, P. Paddan, A.
Burdett, A 1V, Micropower System-on-Chip for
Vital-Sign Monitoring in Wireless Body Sensor
Networks, Proc. ISSCC, Feb. 2008.
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Power consumption table for Sensium SoC
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Relative Performance
ref O.Omeni, A. Wong, A. Burdett, C. Toumazou,
Energy Efficient Medium Access Protocol
forWireless Medical Body Area Sensor Networks,
Transactions on Biomedical Engineering
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The Sensium Ecosystem
We are creating complete hospital systems for
patient surveillance initially in non-acute
wards - Digital patches, networking components,
software, user interfaces
Sensium Server
Gateway / Bridge (Wall Mounted)
Gateway / Bridge (Wall Mounted)
Hospital Information System
Ethernet or Wi-Fi
Ethernet or Wi-Fi
Sensium
Sensium Wireless link
Ethernet or Wi-Fi
Wi-Fi Bluetooth etc
Nurses Station
Digital Patches
PDA / MCA
Digital Patches
Patients can move and auto-connect to closest
relay station
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IEEE 802.15.6 BAN Standard group

• Formed in 2006 to develop a power efficient
  wireless network protocol for on-body
  applications
• Medical/Healthcare applications are the main
  target for this standard
• Toumaz is part of a consortium MedWiN formed with
  3 other companies TI, GE Philips Research to
  propose a solution for this standard which meets
  the low power and other requirements of the
  medical applications outlined earlier
• The standard development process is currently at
  the baseline selection process and hopefully this
  phase would be completed by the end of the year
• We are cautiously hopeful that the final standard
  that comes out of this process would be at least
  as power efficient as Toumazs solution

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Thanks for listening Any questions Okundu.omeni
_at_toumaz.com