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1. According to one definition of digital signal the modulated signal is a digital signal and according to another definition the modulation is a form of digital to analog conversion In digital wireless communication systems the modulating signal may be represented as a time sequence of symbols or pulses Each symbol represents n bits of information where n log2m bits symbol 10 Advantages of Digital over Analog Greater noise immunity due to its finite process Robustness to channel impairments Easier multiplexing of various forms of information like voice data video Security by using coding techniques to avoid jamming Accommodation of digital error control codes which detect and or correct transmission errors Equalization to improve the performance of over all communication link Supports complex signal conditioning and processing methods 1 4 1 Binary frequency shift keying 2 FSK Frequency shift keying FSK is the most common form of digital modulation in the high frequency radio spectrum and has important applications in telephone circuits BFSK uses a pair of discrete frequencies to transmit binary Os and 1s information The demodulation of a binary FSK signal can be done using very efficient algorithms even on low power microcontrollers Data Carrier Modulated Signal Figure 9 Example of BFSK modulation 11 1 4 2 Minimum shift keying MSK e MSK is a type of continuous phase frequency shift keying th
2. STMicroelectronics Spirit1 Radio Module Overview power consumption and integration POLITECNICO DI TORINO OQU SAL Orse 1 Wa ST Polito 1 5 iY Politecnico Trino Analog and TLC Electronics Prof Dante Del Corso Student Emilio Fazzoletto Emilio Fazzoletto Analog and TLC Electronics 2015 Pag 1 Summary Chapter 1 ST Microelectronics Spirit Module ccccscsccccscsceccccscsceccccscnceccccscscescccecscececcecces 4 1 1 introd ction block GIA CAA cesta seeceese scsi sees nas NEA 4 1 2 Operan gt DECI Ca Ul OS sieci i O E Eai 7 CA LEVITON Gl WIOU CS eas E E E TO 7 M2 2 MVS EVANS ONAR C O e EE E E canaeeenteaee 7 2o Data MOOO eene E A 9 1 3 Power Output Configuration and Supported ModulationS sssssssesseseesesrerserrrresrrressreresrrrrserereserreseeeee 9 1 3 1 Power Output Configuratio sicceceiendsisasiccncsinswvendeosbesedseswssedveet E 9 13 2 SUpport ed Modulation errs A evan dou ees cn Steaceac deen eeeseunenetee ee 10 1 4 Overview ON SUPPOrted MOMUIATIONS cseeccccesseccccesecccceeseccceuececeeeceeeeuseceseunecessugeeessuaecetsegecetsenes 10 1 4 1 Binary frequency shift keying 2 FSK cccccccccssseccccceessecceeeeeeecccceeeesecceeeeeeeceeseeeeeesseteeueeeeessagenes 11 14 2 Minimum shift KEVING MSK srren N N 12 1 4 3 Gaussian frequency shift keying GFSK e sesssssesesssreeesrrrreessrrrrsssrrrreessrrrressereressrrrrressrreressrrereeseens 12 1 4 4 Amplitude shift keyin
3. Standby Mode An further step is to use a deeper sleep mode for the MCU in this case the standby mode for the STM32 was used Using the standby mode the device can achieve much lower level of absorbed current even if it will need a reconfiguration after the wake up and this imply a much longer delay before restart the operation However if the idle time is order of magnitude greater than the activity time the standby mode is undoubtedly a better solution To wake up the MCU the RTC alarm interrupt has been used in this way no external interrupt is necessary all the peripherals can be switched off except the LSI Low Speed Internal oscillator in order to minimize the power consumption Wait for TX Wait for TX Wait for TX l Wait for TX Figure 19 MCU Standby Mode Current Consumption MCU Sleep MCU Standby o al 3 2 System battery life simulation For actual embedded systems one of the most important parameters is the battery life in all that applications which cannot use a different power supply The instantaneous power is not the right parameter to evaluate the battery life the big deal is the energy requested by the system to perform a task The designer s objective is to minimize this energy choosing the best combination between activity time generally inversely proportional to the energy performance level and low power modes If for example the task is to monitor the temperature of a room to regulate radiators is sufficient t
4. T CHT Maa z poA TENTEA DETAN TIN HAEA LEE ACNTINO_T PEN TCS TIMI HYSA MEES ir i UTIN CHASE t_ CI DOLARAIT TA im A _ SCALES AX Ci TAME ESLenic ir WES r af uw EI YESA HEAR jr RREA UTACANTX 4 area tee Figure 23 Dashboard Schematic MCU After that added the CAN transceiver the LCD connector used for the 12C protocol and to supply power to the display the buttons connectors and another one used to read the output of an analog selector used to manage different engine maps 28 Figure 24 Dashboard Schematic CAN and buttons Finally add the radio module and the needed discrete components to adapt the power output of the module with the SMD antenna we used The connections between the radio module and the MCU uses an SPI peripheral and some other GPIO based interrupt lines dedicated to the radio only An additional UHF connector has been added to add the capability to use external antennas with higher gain hi Ao GNO et e et m Det m WE YOO oem Ss EXT TAI mia Hoja E g ja S a la H B ja fo fa u a a u H Figure 25 Dashboard Schematic Spirit1 29 Since we used the OrCAD Capture tool to develop the schematic diagram we rely on another Cadence CAD for the layout of out PCBs OrCAD Allegro PCB designer Here is the layout of the dashboard PCB which measures 140x100 mm Figure 26 Dashboard PCB The datasheet of the antenna describes how to design th
5. The device has an embedded CSMA Carrier Sense Multiple Access which is optionally usable This module is dedicated to manage the multiple access on the channel using the carrier sensing This protocol level MAC of the ISO OSI standard avoid collisions between multiple devices operating on the same physical channel 1 7 3 AGC The AGC algorithm Automatic Gain Control is used to keep the output power level inside the limits specified by the user Using an upper and a lower limits the AGC algorithms will vary the output signal gain in order to track the output power target 1 7 4 Temperature Sensor A temperature sensor is embedded on the chip and its analog voltage signal can be available on the GPIOO When used the sensor increase the absorbed current of about 400uA in Standby Ready and Sleep states 1 7 5 AES Engine The integrated cryptographic coprocessor implements the 128 bitbit AES Advanced Encryption Standard standard This peripheral can be used through 3 128 bit registers e AES _KEY_IN register used to provide to the coprocessor the encryption key e AES _DATA_IN register used to provide input data e AES DATA_OUT read only register it provides the encrypted data The AES engine works on 128 bit data blocks with 128 bit encryption key and provides 4 different operations e Data encryption starting from a given key e Calculus of the decryption key starting from the encryption one e Data decryption starting from a given dec
6. akeup t adio_config tacq_data T CRTC TX tsyn_RTC An additional check has been added during the synchronization phase if the TX node does not find any RX device within a given time then the node goes anyway in standby mode in order to avoid energy wastes In this way is possible to implement a network polling with given frequency in order to check periodically in time if there is the possibility to perform a synchronization Start Data Acquisition Count 0 Are there something in RX Data transmission and sync packet RTC realignement Standby Standby Mode Mode Count Figure 15 flow chart of the implemented firmware This basic algorithm can be utilized to develop more advanced management firmware for WSN applications The purpose of this test was to synchronize two development boards without any constrain about the maximum clock shift between the internal clocks The transmission delay has been neglected too as well as the time needed to process the received packet tg The radio module has been configured as follow 0 5Mbps datarate maximum available in order to reduce the transmission time e Stack packet frames e 64 bit preamble 32 bit synchronization key to evaluate the communication quality using a quality indicator engine e 8 bit CRC Representing the system time with 32 bit the length of the utilized synchronization message was 144 bit With a datarate of 500kbps the minimum achievable o
7. at was developed in the late 1950s and 1960s e MSK encoding results in a constant modulus signal constant envelope signal e In MSK the difference between the higher and lower frequency is identical to half the bit rate as aresult the modulation index m is 0 5 e Avariant of MSK called GMSK is used in the GSM mobile phone standard I symbol 0 833ms sub carrier 1500Hz VY Data Level gt H MSK signal Y 1200Hz 1800Hz 1200Hz gt abe lt i Figure 10 Example of MSK modulation 1 4 3 Gaussian frequency shift keying GFSK e GFSK is a type of frequency shift keying modulation that uses a Gaussian filter to smooth positive negative frequency deviations which represent a binary 1 or 0 e Itis used by Bluetooth the minimum deviation is 115 kHz e A GFSK modulator is similar to a FSK modulator except that before the baseband waveform levels 1 and 1 goes into the FSK modulator it is passed through a Gaussian filter to make the transitions smoother so to limit its spectral width Frequency Figure 11 Example of GFSK modulation 12 1 4 4 Amplitude shift keying ASK e ASK is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave e ASK uses a finite number of amplitudes each assigned a unique pattern of binary digits Usually each amplitude encodes an equal number of bits Each pattern of bits forms the symbol that is represented by the par
8. ces a standard 4 pin SPI port and 4 programmable GPIO pins The SPI interface can be used to send command to the Spiriti to read write configuration registers and to read write data in the TX RX buffer FIFOs The 4 GPIO pin 4 pin can be used for the interrupt management and to send unbuffered data to the transmitter The interrupt status is available in the IRQ _STATUS 3 0 bits In table 1 there are the supported interrupts which can be generated by the Spirit1 14 Table 1 Spirit1 Interrupts Events group Interrupt event RX data ready RX data discarded upon filtering TX FIFO almost full RX FIFO almost empty Max number of backoff during CCA Valid preamble detected Signal quality related Sync word detected RSSI above threshold carrier sense Wake up timeout in LDCR mode STANDBY state switching in progress RX operation timeout AES end of operation S a _ _ _ E Lf d 1 7 Advanced functionality 1 7 1 Low Duty Cycle Reception Mode LDCR The Spirit1 can operate in a particular functional mode called Low Duty Cycle which allows to use the device with very low power consumption without suspend the transceiver operations In LDCR the Spirit1 controller is configured to use the low frequency internal RC oscillator 34 7kHz instead of the external crystal used in this case for the RF Synthesize only The non used functional blocks are shut down 1 7 2 CSMA CA engine
9. e Current A Time values 0 44348 0 0 052 0 053 0 054 0 055 300 Internal Resistance Ohms Repesting Sequence Output values 0 036275 0 035 0 035 0 050 0 050 0 0017 0 0017 Capacity Ah Nominal Voltage 0 92243 a 4 pi gt ox I Cancel Help Apply Cox Cancel Help Ready Figure 20 Simulink block diagram utilized for the simulation of the battery life Thinking at a system usable to acquire environment temperature the block simulating the device under test has been configured to simulate the transmission of few data every 5 minutes using high power level 10dBm The simulation has been set to provide in output the battery status after few hours of work In order to have a short simulation time the final battery life as be computed starting from the energy consumed in few hours Since the time to simulate is long hours or better days and the operation time where the energy is concentrated is very concentrated few micro seconds the simulation steps have to be very small to have good results making an eventual exhaustive simulation very expensive computationally 4f SR S swe Fak x lt SOC gt Figure 21 Result of the Simulink simulation The simulation results shows that after an hour the battery charge level has a drop of 0 175 With a linear approximation the system in this particular condition would have a 24 days autonomy 26 Chapt
10. e layout and the feeding line and also STMicroelectronics gives advice about how to design the antenna circuit Using the Cross Section tool integrated in Cadence Allegro CAD is possible to calculate the geometrical parameters needed to obtain a characteristic impedence equal to 50 Ohm Ga Layout Cross Secti Subclass Name Type Material Thickness MM Conductivity mho cm Dielectric Constant Width MM Impedance ohm es SURFACE ee SS SURFACE Figura 27 Allegro Cross Section Tool 30 The antenna feeding line was designed in order to respect the design rules given by the antenna manufacturer The SMD passive components needed to couple correctly the antenna with the radio module was placed in order to reduce as much as possible undesired parastitic effects Figura 28 Feeding line layout and in the upper picture the real PCB in the lower one the CAD In the following image the placing of the most important components is shown e in red the microcontroller STM32F103 with the 3 3V and the 5V DC DC e In light blue the LCD connector and the ones for buttons and LEDs e In blue the programming connector and the CAN controller section e in violet the SPIRIT1 radio the antenna is on the top rights corner Figure 29 Dashboard PCB Components layout e In white the power section After the validation of this first PCB which is actually only a prototype another one
11. een 30 dBm and 11 dBm in 0 5 dB steps Figure 6 Frequency Synthesizer A frequency synthesizers figure 6 generate the feeding signal of the PA The Spirit1 includes a fast startup frequency synthesizer with a settling time of 6 us and the typical frequency resolution is 33Hz A crystal connected to XIN and XOUT is used to provide a clock signal to the frequency synthesizer The allowed clock signal frequency is either 24 26 48 or 52 MHz As an alternative an external clock signal can be used to feed XIN for proper operation 1 2 Operating Specifications 1 2 1 Functional Modes The Spirit1 is equipped with a controller which switches the functional mode between two main ones transmission TX and reception RX There are also other states and the complete FSM finite state machine is shown in figure 7 e a al SHUTDOWN 5 n mpa P AM09259V1 Figure 7 Spirit1 state diagram At the power on the device is in Ready State and starting from it the Spirit1 can reach the Standby Lock or Sleep mode The Lock state is a mandatory transition state to pass through in order to reach the TX RX Standby and Sleep on the other hand allow to reduce by a different amount the power consumption In particular the Sleep mode is suitable for short idle period whereas Standby is much more indicated for long inactivity period it allows the highest reduction in consumption but needs a more complex and l
12. er 4 design of a PCB integrating the Spirit1 module 4 1 Idea The dashboard electric system of the SCXV includes many different subsystems which all together assure the communication between the steering wheel board and the other electronic parts of the car In addition the dashboard manages the 4 3 LCD display as well as some compulsory LEDs and some buttons The goal is to have a system capable to ensure that the driver has all the information he needs with the possibility to tune some key parameters for example the amount of regenerative breaking torque and have a feedback when these changes are applied 4 2 System Block Diagram LCD DISPLAY P PC i BMS LED ower a Supply Protocol H IMD LED CAR SIDE gt START Button CAN BUS O KEY Button Low Voltage Power b RADIO Button A i in DRS Button rT ji Power Bidirectional 4 CAN BUS Wireless wy Gace Supply EMERGENCY STOP Connection Q Y backup STEERING WHEEL Figure 22 CXV Dashboard and Steering System block diagram The electronic system is built around a main PCB called dashboard which you can see in the block diagram above On the electronic board there are the STM32 microcontroller 32 bit based on ARM Cortex M3 architecture the high speed CAN transceiver AMIS 30663 fully compatible with the ISO 11898 2 Standard and all discrete components needed to supply the power to the system using the low voltage battery as source A ser
13. ey e SHN ODN ienr A AE E 25 Chapter 4 design of a PCB integrating the Spirit MOCUIEC cccsccscsceccccscsceccccscscececcscncecees 27 4 1 Idea 4 2 System Block DIAG PANN enai a a a aman entaetsaraeinis 4 3 Schematic and PCB development aisis elas aa aaa ee ke References Chapter 1 ST Microelectronics Spirit1 Module 1 1 Introduction block diagram The Spirit 1 is a low power low datarate RF transceiver capable to operate in sub GHz bands have chosen it as radio module due to its small package low power consumption and high flexibility It matches the tipical WSN wireless sensor network system specifications The available frequency bands start from 150MHz and goes up to 956MHz the supported digital modulations are 6 2 FSK GFSK MSK GMSK OOK e ASK and the datarate goes up to 500kbps In the following chapters there is an overview about the functional modes protocols I O and all main features such as the encryption engine In Figure 1 you can see the Spirit1 block diagram GPIO_0 GPIO_1 J GPIO_2 J GPio 3 RXp RXn CSn SCLK SDI SDO J VR DIG PLL LDO o o o a oS ala i olols oO ale x aio Ols alg d 2 gt 5 2 2 E a 1 0 VCO LDO SDN VDD DIG VDD SMPS SMPS Ext SMPS Ext2 AMO9257V1 Figure 1 Spirit1 Block Diagram In the block diagram is possible to see at least 5 important digital components the LNA Low Noise Amplifier two Mixers t
14. ffset between two devices given by the chosen algorithm and hardware is 288 us Taking into account this delay is possible to slightly improve the system performance since this is an always present offset Chapter 3 Power Consumption Characterization This chapter provide an overview over different low power technique both for the Spirit1 radio module and the STM32 uC utilized in the test platform The different results are shown in order to provide at the user a general idea about the capability of modern wireless communication devices Figure 16 iNemo M1 System on Board with the STM32 uC To simulate the typical scenario for a small WSN the test device has been programmed to transmit small data packets periodically in time between two transmission different option of low power modes has been explored The power consumption of the entire system has been measured the voltage drop ona small resistor 1Ohm connected in series at the power supply cable The first two measures has been taken without using any power consumption technique Both the uC and the Spirit1 was configured to operate at the maximum allowed frequency 72 and 52Mhz respectively The radio output power level was set to OdBm TRIGGER Tipo sorgente Pendenza ries oe Pee soe ee PORE Be et 8 ees ese Eo GS e Ea ie eee Wait for TX Lock Tx OdBm Tx Wait for next TX CH1 100m CH2 2 00 Figure 17 Power consumption with no low power techniques implemen
15. g ASK ccccsscsssssssrscsscssarscstecscarsenseaueauseuseusearsensauseurcansauserseateassersenteaues 13 14 5 Omoff OVI IS OOK carheccaea decane sate toc srsee deaeciowane bee E 13 1 5 Packets management engine sciiienscecscccesnadancdstecossaenateleahsevacteanoudaueddecssnaepestuaddediunteedoniauedecsaeeraeiaeabderooecs 14 1 6 Interfacing With a micro controller sesiseeiisinsseniseniianata rasa Ea E A 14 L Advanced UNC UOMA y pee E EE E 16 1 7 1 Low Duty Cycle Reception Mode LDCR cccccccccssseccceeeesseccecceeeecceeeeeeeeceeseueneccesseeeeceseeagenees 16 LAC MN 2a gg ee Ore ac ee 16 MT BP E OES EE A A E aaa N E A S E sana eee odessa aoa 16 t7 A Temperature SENSON eer A ecieeatraersnsevnincctaaeneaaciuasaes boaseccadinacteaananaeenes 16 EZS AES ENEN nern E E E 16 1 7 7 Data encoding and integrity CHECK evesctesesvnencsa cosacetasnnecuss aenedsaaienesssd voneausaunnauuseaioagietetusaancteapsauseanaanets 17 Mes Enk Layer Proloco eniran arr E E E 17 Chapter 2 iNemo M1 Spirit1 Real Time Clock Synchronization sesessssesecesesescececesessesecesese 18 PMN ane s Tu 1e 1 geste E EPE ENAP ETNE E E N EE E E EE E 18 2 2 implementat Oseere EE EE EE 18 Chapter 3 Power Consumption Characterization ccscscsccccscsccccccscsccccccscsceccccscnceccccecscecess 21 3 1 MCU in Standby Mode scivccsacadesatainunidincacwsaiecinasadsanadesnGodoonediweasenatodourageassdeunTesinentdueensonssedsowedsannieaCanqunadins 24 32 SYST Da
16. gister of the Spirit1 In particular using two registers TXSOURCE and PCKTCTRL1 is possible to select one of the following data treatment options e O normal mode 1 direct through FIFO data packets have to be written by the external MCU the Micro Controller Unit which is using the Spirit1 directly in the TX FIFO no processing will be automatically performed the user is responsible for the data coding e 2 direct through GPIO o direct mode the data are reading in real time using a GPIO specially programmed for this function Data are transmitted without any processing The transmission is synchronized using a clock which has to be transmitter on a second GPIO e 3 PN9 mode an internal generator create a pseudo random binary sequence this mode is suitable for test purpose only The TX FIFO register as well as the RX FIFO has 96 byte This two FIFO registers has 2 programmable thresholds usable to have information about the filling status of the registers 1 3 Power Output Configuration and Supported Modulations 1 3 1 Power Output Configuration The power output level can be modified using the 8 bit PA_LEVEL register The user can save up to 8 different power levels in order to obtain ascending and descending power ramps in order to for example model the symbols of an ASK Amplitude Shift Keying modulation The maximum output power is 11 dBm 16 in TX boost mode using additional external hardware in addition a
17. has been developed with a better components placing an improved design of the radio circuit and with more available external connectors all this in a slightly smaller size vom T ee TR Sie Ue ft Figure 30 Dashboard PCB Version 2 References STM32F103xE Datasheet Doc ID 14611 Rev 7 2009 STM32F103xx Reference Manual Doc ID 13902 Rev 14 2011 Spiritl Low data rate low power sub 1GHZ transceiver Datasheet DoclID022758 Rev 5 2013 Mihail L Sichitiu and Chanchai Veerarittiphan Simple Accurate Time Synchronization for Wireless Sensor Networks IEEE Wireless Communication and Networking 2003 vol 2 pp 1266 1273 INEMO system on board Datasheet DoclID023268 Rev 1 2013 How to achieve the lowest current consumption with STM32F2xx Application Note Doc ID 019009 Rev 1 2011 Using the STM32 hardware real time clock RTC Application Note Doc ID 018624 Rev 2 2011 Dae cheol You Young Si Hwang Young Ho Ahn Ki Seok Chung Energy Consumption Prediction Technique for Embedded Mobile Device by Using Battery Discharging Pattern Network Infrastructure and Digital Content IEEE International Conference 2010 STM32 Nucleo boards User Manual DoclD025833 Rev 2 2014 STM32L151xE and STM32L152xE Datasheet DoclID025433 Rev 3 2014 Some images by www wikipedia org
18. ies of Molex Microfit connectors are used to connect the electronic board to LEDs and buttons on the dashboard just in front of the driver The connection with the LCD display is implemented using the I2C protocol using one of the two I2C peripheral of the STM32 Finally the connection with the steering wheel electronic board is ensured by a Sub GHz radio module a STMicroelectronics Spirit1 which allows a transfer rate up to 1Mb s A wired CAN bus connections is available as radio backup together with an optional cabled power supply 27 4 3 Schematic and PCB development The schematic development began implementing the necessary components to made the MCU Micro Controller Unit usable which are the DC DC converters required to obtain the 3 3V and the 5V supply voltages and the programmer circuit needed to download firmware inside the MCU using an external programmer such as the ST Link V2 0 we used x seis JP LAT CT oo UNTIL LH LETA 5 Aiai ppa a ee FLH T PAD EAA 2 TAS NNT O ae aa epi penne pencil O_O m PSE LME e E PAREA SORAD PARTAN EDN oe A _ r PATERN LAOSA T_T ied Ler PLA I TIA LANTO Za Pa ean TET DE 0 m e a r Oo Ea i Lee FOTIL bam a CANT pr Pe Saar roan eT 1 OHEA a i ra g PL ATACANTE TIIA ETAn a oe y Pa eo Pa eA _ r Vi date TOENN Pati LEMN LE PATOTOO COH ETASAN L_ES imar STIAS THIN FoTo PEON eo ae POUCA e Se HST SAC SM oo HAST pe PEYADCI JNE TINO CANTINI OHN a PAPAN NANTINO HETIM LOHN Soe Toc cH bee a Pa e
19. ion the time synchronization is also critical to assure that when a device returns active there will be at least another node ready to communicate avoiding dead time waiting for a receiver node About this purpose is fundamental that the RTCs Real Time Clocks of the WSN devices are synchronized in order to program synchronized sleep and wake up of the entire network 2 2 Implementation In order to test a simply sleep and wake up loop synchronized between two nodes a test firmware has been developed it implements fuctionality to transmit the RTC actual value to an RX node between two test devices using two iNemo M1 based on an STM32 uC equipped with the Spirit1 radio module This test firmware search for an RX node and when it founds it the RTC data are transmitted in order to synchronize the two clocks After the synchronization the two devices goes in standby mode setting a common alarm in order to wake up after the same time using the RTC alarm interrupt event available in the STM32 uC After each wake up events the two nodes are programmed to redo the synchronization before enter the low power mode again Message from TX device gt Ack from RX device Receiver Synchronized Wake Up Transmitter Data Acg Data Acq TX Request Figure 14 Implemented synchronization example 18 The time duration of each active cycle is calculated as follow lactive tw
20. o acquire few data every 10 minutes using a deep low power state during the idle time To obtain a correct prediction of the system battery life is important to use simulations based on a system characterization which provide the trend of the adsorbed power during the task of interest In this chapter the previous studies on the current consumption has been used to estimate the system autonomy using a 3 7V 1020mAh Li lon battery The simulation has been developed using the Simulink environment and a custom block has used to simulate a load with the same characteristic of the test system File Edit D ew Simulation Format Tools Help Implements a generic battery that model most popular 1 F iii Deh amp gt heoo Nomai oF S pame battery types Uncheck the Use parameters based on Battery type and nominal values parameter to edit the discharge characteristics powergui Parameters View Discharge Characteristics Batte Battery type Lithium Ion Nominal Voltage V 3 7 Rated Capacity Ah 1 020 Initial State Of Charge 100 F v Use parameters based on Battery type and nominal valu WE Source Block Parameters Repeating Sequence 28 Maximum Capacity Ah Repeating table mask link in Output a repeating sequence of numbers specified in a table of time value pairs Values of time should be monotonically increasing Fully Charged Voltage V 4 3068 Parameters Nominal Discharg
21. ong re configuration before starting the operation 1 2 2 Transmission and Reception The Spirit1 is a radio module capable of both transmission and reception it allows a bidirectional communication The module can stay in TX and RX for different time periods depending on some dedicated registers which programmed by the user determine the behavior of the device In the following lists are reviewed the available management modes for both TX and RX The device continues to stay in TX mode e Until the transmission of the current packet ends e Until the TX buffer TXFIFO is not empy if the selected mode is Direct Mode e Until e SABORT Spirit Abort instruction State reached after the transmission e TX if Persistent TX is selected e Protocol if the automatic retransmission is selected e Ready State if no protocol is acitve and the TX ends successfully The device continue to stay in RX mode e Until the reception of the current packet ends e Until the RX timeout is reached e While Direct Mode is active until a SABORT instruction or until the RXFIFO is full State reached after the reception e RX if Persistent RX is active e Protocol if the auto acknoledgement is active e Ready if the RX end successfully and the Low Duty Cycle Mode Reception LDCR is not active e Sleep in case of LDCR 1 2 3 Data Modes In Direct Mode is possible to bypass the data framing deframing and also the data buffering normally used on the I O re
22. ryption key e Data decryption using a given encryption key 1 7 7 Data encoding and integrity check The device has error detection and correction capabilities which can be activated by the user depending on the security level requested by the application The CRC protocol is available with a 8 16 or 24 bit checksum Taking about the error correction capabilities there is a FEC Forward Error Correction engine with a soft Viterbi coding with a ratio equal to 0 5 and k 4 1 7 8 Link Layer Protocol About link layer protocols the user can configure the device in order to use the auto ACK and auto retransmission functionalities if the selected packet framing is STack To improve the transmission efficiency is also possible to use the auto ACK with Piggybacking 17 Chapter 2 iNemo M1 Spirit1 Real Time Clock Synchronization 2 1 Introduction In a wireless sensor network is very important to acquire and transmit not only data but their time stamps too In order to obtain a set of data correctly correlated is necessary that the all the devices on the field are synchronized and it is really important also to power on the interested devices only when necessary increasing their battery life Typical WSN devices are very often cheap and with limited calculus capabilities The only power source is almost everytime a small integrated battery and in order to maximize the autonomy devices have to use low power modes when they are not active In addit
23. t the standard configuration the minimum is 34dBm The PA_RAMP_ENABLE register enables the power ramping It is possible to configure both the steps number and the steps width In figure 8 a power ramping example is showed there are two different ramps in black and in blue WO PA _LEVEL_7 PA_LEVEL_6 PA LEVEL 5 The PA uses this setting steady state level Settings PA_LEVEL_0 to PA_LEVEL_5 are used during ramp up at start of transmission and ramp down at end of transmission and for ASK modulation also PA_LEVEL_MAX_INDEX PA_RAMP_STEP_WIDTH Output Power Levels PA_LEVEL_7 PA_LEVEL 6 PA_LEVEL 5 PA_LEVEL 4 PA_LEVEL 3 PA_LEVEL_ 2 PA_LEVEL_1 PA_LEVEL_0 Time Start TX Stop TX ns PA_LEVEL_MAX_INDEX 7 PA_RAMP_STEP_WIDTH 1 PA_LEVEL_MAX_INDEX 3 PA_RAMP_STEP_WIDTH 3 AMO9263V1 Figure 8 Power ramping example 1 3 2 Supported Modulations Using the MOD_TYPE field of the MODO register is possible to choose between 5 different digital modulations MOD_TYPE 00 gt 2 FSK 01 gt GFSK 10 gt ASK OOK 11 gt MSK If MOD_TYPE 10 the choice between ASK and OOK depends on the configuration of the PA POWER register if the power ramping is activated then the ASK modulation will be used The MODO register together with MOD1 determines in addition the transmission datarate 1 4 Overview on supported modulations In digital modulation an analog carrier signal is modulated by a discrete signal
24. ted 21 The upper signal shows the current absorbed by the TX nodes the lower on has been used to trigger the oscilloscope The figure shows very clearly that when the radio module starts the transmission operation Lock TX the power absorbed rise significantly and then go down a bit during the transmission thanks to the low level used for the output When the development device is in idle the current absorbed is appreciably lower Table 2 Power consumption with no low power modes 0dBm TX Current Time Consumption Duration OdBm Tx The next step has been to shut down the power module when not in transmission the Spirit1 has been switched off the the microcontroller has been configured in sleep mode a very light low power mode which allows a fast switch to the active one As you can see in the following images using low power techniques impact significantly on the power consumption especially when the device is in idle Note starting from this test the transmission power level has been risen since the system was much more efficient thanks to the power saved during the time spent in idle 10dBm Tx with Spirit1 Standby Enabled Idle Current Consumption 34mA 10dB Tx with Spirit1 Stanby MCU Sleep Idle Current Consumption 15mA Figure 18 STM32 Sleep Mode Spirit1 Standby implementation The current absorbed during idle has dropped from 34 to only 15mA for the entire system i S 3 1 MCU in
25. ticular amplitude e Like AM ASK is also linear and sensitive to atmospheric noise distortions propagation conditions on different routes I ev Ge Oo Ft p a WH i Amplitude shift keying ASK Amp V 1 0 i Figure 12 Example of ASK modulation 1 4 5 On off keying OOK e OOK denotes the simplest form of ASK modulation that represents digital data as the presence or absence of a carrier wave e OOK is more spectrally efficient than frequency shift keying but more sensitive to noise e On off keying is most commonly used to transmit Morse code over radio frequencies Input data signal 16d 26d Bd 46d 5Bd 66d fad SBa ASK modulated signal 1Bd 2Bd 26d 47d 56d 66d fad abd Figure 13 Example of OOK modulation 13 1 5 Packets management engine Before the transmission data can be interested in a framing operation The Spirit1 allows a high flexibility in order to customize the data packet structure Using dedicated register is possible to chose between three standard options Stack with auto acknowledge WMBus Wireless Meter Bus and Basic A really important feature is the Automatic Packet Filtering There are 4 different filter criteria supported e CRC Cyclic Redundancy Check Filtering e Destination Address Filtering e Source Address Filtering e Control Field Filtering 1 6 Interfacing with a micro controller The Spiritl module is equipped with two main interfa
26. wo ADCs a Power Amplifier and a Frequency Synthesizer Figure 2 LNA In figure 2 the Low Noise Amplifier it is the first block of the reception chain apart the antenna The effect of noise from subsequent stages in the receiver signal chain is reduced by the gain of LNA while the noise of LNA itself is directly injected into the received signal Thus it is imperative for LNA to boost signal power while adding as little noise and distortion as possible Figure 3 Mixers In figure 3 there are 2 mixers used by the Spirit1 The mixer brings down the received RF signal to IF signal for ease in further processing like filtering amplification and digitization Two mixers are necessary to realize a QA quadrature amplitude demodulator Figure 4 ADCs In figure 4 you can see the two ADCs placed at the end of the analog receiving chain in order to digitalize the information stream The digitalized data can subsequently can be sent to an external processing unit No data are provided by STMicroelectronics about the ADCs used in the Spirit1 module TX GND PA Figure 5 Power Amplifier In the transmitting chain a power amplifier PA in figure 5 converts a low power radio frequency signal into a larger signal of significant power in order to drive the antenna the Spirit1 uses only 1 antenna both for transmission and reception The input is generated by the RF synthesizer while the output level can be configured betw

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