Transcript Modified OSI Architecture for Low

Modified OSI Architecture for
Low-Power Wireless Networks
Jay Bruso
Mike Matranga
Agenda
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Review Thesis
Physical Layer Fundamentals
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Data Link Layer Fundamentals
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Modulation / Demodulation
Front-end circuitry
PLL
Methods of data processing
Proposed solution
Project objectives
Thesis Proposal
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Applying standard OSI model to WSNs
results in poor energy utilization
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Physical Layer lacks knowledge of data being sent
across the channel
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Data Link Layer forced to do work that could be
done in Physical Layer
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Packet Format, Length, Data Type, etc.
Cost of performing work in Data Link Layer will be more
expensive than equivalent function in Physical Layer
For energy optimization
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Physical Layer needs to be smarter
Transceiver Block Diagram
Modulation to the CC2400
Frequency Shift Keying
The CC2400 uses FSK/GFSK
Receiver Front End Review Part 1
MIXER
RF AMP
RF IN
RF IN * A
IF OUT
LO IN
RF amplifier: amplifies a weak RF signal coming out of the antenna.
Mixer: together with the local oscillator downconverts the RF signal
to the IF frequency band.
Receiver Front End Review Part 2
Power Divider
Frequency Synthesizer
0
To
Mixers
N, R
from
TXCR
Control
Logic
90
Control
Logic
SPI from Microcontroller
CLK to Microcontroller
Reference Clock
• Frequency Synthesizer is a PLL
Phase Locked Loop
N and R are programmed by the microcontroller,
and stored into registers in the transceiver.
Receiver Front End Review Part 3
Filter
AGC
ADC
RSSI
CLK
Bandpass Filter: Removes out of band signals
Automatic Gain Control (AGC):
Adjusts the IF amplifier gain according to the signal level
(to keep the average signal amplitude almost constant)
Analog to Digital Converter : Digitizes the analog signal
Demodulation
V1
V2
PLL
FSK Signal In
Tracking Voltage
1
0
This data is digitally filtered & buffered.
Once the signal is recognized, the outputs
CLK, SOM, RXDATA are sent to the Microcontroller
Typical WSN Block Diagram
Sensor
A
SPI
CLOCK
Controller
RXDATA
Transceiver
SOM
Sensor
N
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Controller configures XCVR for receive mode
XCVR notifies controller with SOM signal
Controller processes incoming data
Controller disables XCVR when done
Methods of Data Processing
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Method 1, Polling for Bytes
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Controller continuously checks for new
data received
Checks if message is complete, and if so,
powers off transceiver
Most inefficient because CPU always
running
Methods of Data Processing
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Method 2, Interrupt Driven
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Controller interrupted after every byte is
received
Checks if message is complete, and if so,
powers off transceiver
More inefficient than polling because CPU
can go to sleep (enter low-power) mode in
between receiving data
Methods of Data Processing
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Method 3, DMA
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Controller interrupted after a block of data
is received
More efficient than interrupt because CPU
is woken up less often
More difficult than interrupt because size
of DMA transfer must be predetermined
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Difficult when receiving packets of unknown
length
Usually results in setting DMA transfer size
small (5 bytes, etc)
Data Processing Comparison
Method
Polling
Interrupt
DMA
Response Time Power
Consumption
High
High
High
Low
Med
Med
Where is Power Wasted
RXCLK
RXDATA
EOMDET
Byte N-2
Byte N-1
Byte N, EOM
Tproc
Tpwroff
PWROFF
Twaste
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Finite amount of CPU time required to
process and detect end of message
Finite amount of time required for CPU to
disable power to XCVR
Wasted Power = (Tproc+Tpwroff )*Ireceive
What Can Be Done
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Provide physical layer with intelligence
for detecting EOM condition
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Packet Format
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Message length encoding
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Character frame encoding
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Offset into data stream where to find length
Provide register for escape character (0x80)
Provide register for EOM character (0xFE)
No Data Received Timer
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Automatically powers off if no message
received within programmed time interval
Focus of Project
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Quantify how much power is really
being wasted
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Design and implement a small WSN
Measure power wasted
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Various protocols
Various processing methods
Various data rates
MSP430 as controller
ChipCon CC2400 as transceiver
Focus of Project (cont’d)
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Quantify how much power can be
saved if physical layer were smarter
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Implement proposed solutions in small
CPLD (XPLA3 … XCR3512XL)
Repeat previous tests and measure power
saved
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Various protocols
Various processing methods
Various data rates
Project Model
TXENA
Sensor
A
SPI
RXENA
SOM
RXCLK
Controller
EOM
CPLD
RXDATA
XCVR
TXD
TXCLK
Sensor
N
RXD
TXDATA
SXCR (Smart Transceiver)
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Add DLL functionality into PL using CPLD
Demonstrate improved performance
Quantify energy savings
Report results