Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

ESA Wireless Sensor Motes Study

George Prassinos, SSC, University of Surrey

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

EMC/EMI

• Electromagnetic interference can cause undesirable behaviour to the electronic devices of our spacecraft or even damage them completely.

• Motes have no shielding making them even more susceptible to EMI.

• Motes need to be contained in order to be shielded from radiation. • The EMI coupling process is initiated from an EMI Radiating device

which is transmitted even by RF or by conduction to our structure. • For low frequencies the coupling effects are even Capacitive or

Inductive and for high frequency models the effects are Radiative. • If for conduction the coupling is conductive both for low and high

frequency modes.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

EMC/EMI

In space missions there are several sources of radiation caused from natural and manmade systems:

• Sun, • cosmic, • radio stars • the electronic subsystems of the spacecraft

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

EMC/EMI

• Wireless communication data links utilize free-space propagation and are subject to interference and signal disruption from a broad spectrum of sources.

• Wireless communication networks utilize several different frequencies. (MHz to GHz)

• The effects of noise and interference are: – data link connectivity problem,– reliability – data rates of the network.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Glaramara Board

• SSTL has from previous projects a Glaramara Development kit from CompXs.

• The kit provides a way for prototyping and application development based on the 802.15.4/ZigBee protocol.

• PIC18LF452PT microcontroller• 32 KB of Flash program memory, • 1536 bytes of RAM data memory • 256 bytes of EEPROM data memory. • The microcontroller is interfaced to the Radio Module via

its built-in SPI interface as well as some general I/O pins.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Glaramara Board

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Scaffell

• The radio module used on the development kit is Scafell from CompXs

• Scafell implements a Wireless Personal Area Network (WPAN) enabling communication with a wide range of devices over relative short distances.

• compliant with IEEE 802.15.4 • provides inherently duplex synchronous-byte

serial interface between the Network layer and the Media Access Control layer (MAC).

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Scafell

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Scafell

• The radio module is using an FCPG processor which is very susceptible to EMI.

• The development board is likely to suffer performance due to EMI as it has absolutely no shielding.

• FLASH and EPROM modules are used to store software

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Alternative Motes

• An alternative solution to the above mentioned motes is the Intel Mote 2 Platform.

– based on an Intel PXA270 XScale CPU – integrates high performance processing including DSP capabilities, – large amounts of RAM and FLASH memory, – standard and high-speed I/O interfaces as well as an advanced security

subsystem. • The platform provides an on-board IEEE 802.15.4 radio and the option to

add other wireless standards such as Bluetooth and 802.11b via an SDIO Interface.

• based on the 802.15.4 protocol can operate in either – broadcast or – point-to-point link modes

• The platform features a substantially expanded set of I/O interfaces besides the standard ones i.e. UART, SPI, USB.

• The processing core is based on the ARM architecture enabling to use both TinyOS and Linux.

• The mote can run at low frequencies of 13 Mhz up to a few hundred MHz.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Intel Mote 2

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

FHSS

• Because there is no way to predict what interferers at any given time, frequency and time the network must be able to continually sidestep these interferences.

• The operating bands of the motes can be sliced into several discrete frequency ranges from: – 900-928 MHz, – 2.400-2.4835 GHz.

• The slices enable an effective frequency hopping stream spectrum (FHSS) routine which can efficiently sidestep RF interference.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

MICA2

• Another option could be a MICA2 mote from Xbow. • Designed for embedded sensor networks with more than

a year’s lifetime with just a single AA battery cell. • Capability to be used as a router with operational

frequencies of:– 315 Mhz– 433 MHz– or 868/916 MHz.

• Although fixed at these frequencies the radios can easily and quickly switch channels to avoid interferences caused by EMI.

• It also provides a cost effective solution comparing to motes from other manufacturers.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Preferred Motes

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Preferred Motes

• mostly interested in the:– MPR2400 MICA2 mote operating at 2400-2483.5 MHz – MPR2600 mote operating at the same frequency range. – high frequencies

• greater robustness against EMI • faster data rates which are up to 250 kbps for the MPR2400.

– Both motes are using the Atmel ATMega 128L Processor and are compliant with 802.15.4 protocol.

• TelosB MOTES– most recent development in this area and promise excellent performance. – compatible with the IEEE 802.15.4 protocol and offer speeds of up to 250 Kbps. – use the TI MSP430 micro controller which has displayed good EMC in previous tests.– TPR2400 can be easily programmed through a common USB port and have very good

library support for TinyOS.– It is a platform created for research testing and it is recommended to be tested for space

system suitability. • Glaramara Development kit with the Scafell Radio Module will be used for testing as it

has being previously used by SSTL to test the capabilities of Zigbee. • Offers:

– MAC programming implementing a Wireless Personal Area Network (WPAN) enabling communication with several devices in relatively short distances.

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Preferred Motes

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Sensor Boards

Surrey Space Centre, University of Surrey, Guildford, Surrey, GU2 7XH

Requirements

• We want data rates which at minimum exceed the minimum data rate requirements of each subsystem.

• SSTL CAN Bus operates with only 32kbps • MICA2 mote at 433-434.8 MHz

– offer speeds of up to 38.4 Kbps – FSK Frequency Selectable radio receiver.