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Page WSN 1 of 23 4. EVALUATION Evaluation of the system will be executed through simulation and testing. Fundamental communications and circuit design principles implemented in the system will be evaluated in a simulation environment. The realization of these principles will require testing. 4.1. Resources Needed CC1010 Dev. Kit: Provides the antenna circuitry and will be used to program the processor. Oscilloscope: For signal analysis on the mote. Spectrum Analyzer: To determine frequency characteristics of the mote. Function Generator: To supply test tones. DC Power Supply: To supply a regulated voltage to the mote. Digital Multimeter: To measure DC voltage and current of the components. MFJ Box: To test the digital I/O. Resistance Box: For variable load testing. Potentiometer: To test for correct voltage of the analog I/O. PSPICE: To simulate antenna and power circuitry. SystemView: To model the communications between the motes. Thermal Chamber: To test the temperature constraint of the mote. 4.2. Test Specification The test specifications explain the procedures used to verify that the system conforms to the specified design constraints. The system is divided into four modules: the transceiver, the processor, the power module, and the sensor interface (Figure 4.1). Each module will be tested to verify that it performs in accordance with the design constraints. Each test specifies the design constraint that will be tested and outlines the procedure to be performed. Where appropriate, evaluation of each module is divided into three stages: simulation, hardware testing, and software testing. 4.2.1. Transceiver The decision to operate the transceiver at a frequency of 433 MHz rather than 916 MHz was based on the idea that less attenuation would occur at the lower frequency. We imposed a design constraint of transmitting data a distance of 300 ft with bit error rate of 10-6. ECE 4512: Design I Figure 4.1. Hardware block diagram. December 4, 2003 WSN Page 2 of 23 4.2.1.1 Simulation RF Frequency: We will simulate the system using SystemView. This software will allow us to determine the attenuation characteristics of our transceiver. The block diagram for the FSK transceiver can be seen in Figure 4.2: FSK Transceiver Block Diagram. Figure 4.2: FSK Transceiver Block Diagram 4.2.1.2 Hardware Testing Transmission Distance: We will test transmission distance both indoors and outdoors. The Drill Field on the Mississippi State University campus will serve as the outdoor testing stage. With the motes separated by a given distance, a program utilizing the mote s received signal strength indicator (RSSI) pin will detect the strength of the signal. This distance will be incremented in steps of 10 ft. When the received signal strength falls below a certain threshold, the maximum useful distance will be obtained. To test the indoor transmission distance, a similar test will be performed in the Simrall Engineering building. Each of these environments has its own multipath characteristics. Test Procedure: 1. Ensure that a voltage ranging from 2.7V 3.3V is applied. 2. Program the microcontroller of a module to record signal strength. 3. Place a module on the base station. 4. Vary the distance between the programmed module and the base station s module in increments of 10 ft. Verify that the two modules are communicating properly at each 10ft. increment. 5. Perform this procedure both indoors and outdoors. Bit Error Rate: We will perform a similar test to determine the bit error rate. This time, an 8-bit counting sequence will be transmitted. The receiving mote will compare the received bits to a stored counting signal bit stream. The differences will serve as a metric for the bit error rate. Test Procedure 1. Ensure that a voltage ranging from 2.7V 3.3V is applied. 2. Program the microcontroller of a module to record the Bit Error Rate. ECE 4512: Design I December 4, 2003 WSN Page 3 of 23 3. Place a module on the base station. 4. Vary the distance between the programmed module and the base station s module in increments of 10 ft. Compare the record of the Bit Error Rate at each 10ft increment. 5. Perform this procedure on the Drill Field and in Simrall. 4.2.1.3 Software Testing Transceiver Functionality: The CC1000 transceiver uses registers to interface sent and received data to the microcontroller. To test this functionality, we will read and write data to these registers. A receiving mote will verify that the data have been sent correctly. This straightforward test is crucial to the system's success, as it involves the operation of all layers, from physical (the medium) to application (the operation of the chip). 4.2.2. Microcontroller The microcontroller is responsible for the interpreting data and maintaining the overall network architecture. In particular, our system will introduce channel coding to the WSN network stack. This feature should improve reliability and overall power efficiency. Testing of this module will be done entirely in firmware. 4.2.2.1 Firmware Testing Channel Coding/Decoding: Our channel coding and decoding algorithms will be added to the link layer in the network stack. This will add reliability to our channel. A more reliable channel will reduce transmissions thus increasing power efficiency. These algorithms will give the motes the ability to recover from and detect errors introduced in the transmitted message by interference in the medium. This interference can be simulated by randomly changing bits in the message. This can be tested in software. Test Procedure 1. Create a test message. 2. Code the message using the coding algorithm. 3. Insert interference into the message by randomly changing bits. 4. Decode the message using the decoding algorithm. 5. Check to see if the decoder successfully detected and/or corrected the introduced errors. 6. Steps 1-5 will be repeated with many data sets including a randomly generated message and a message formatted similarly to those that will be sent in our system. The errors introduced will include single bit errors and burst errors (errors effective multiple bits in close proximity). Channel Coding Efficiency and Power Savings: Our channel coding algorithm will reduce power consumption by reducing retransmissions. In order to test this against the power consumption of the uncoded channel a software simulation can be run. Test Procedure 1. Create a test message. 2. Code the message using the coding algorithm. 3. Insert interference into the message. ECE 4512: Design I December 4, 2003 WSN Page 4 of 23 4. Decode the message using the decoding algorithm. 5. Check to see if the decoder successfully corrected the introduced errors. 6. Request a retransmission and repeat steps 3-6 if necessary. 7. Take the same message, this time leaving it uncoded. 8. Insert the same interference as in step 3. 9. Request a retransmission and repeat step 8 if necessary. 10. Calculate the ratio of bits sent for the coded and uncoded channels. 11. Steps 1-10 will be repeated with many data sets including a randomly generated message and a message formatted similarly to those that will be sent in our system. The errors introduced will include single bit errors and burst errors (errors effective multiple bits in close proximity). 4.2.3. Power Module The power supply will be simulated using The PSPICE. simulations will be examined to see if the projected voltage regulation level of 3.3Vdc is obtained. MATLAB models will also be created to determine the battery life of the power system. 4.2.3.1 Simulation DC Converter: The process of simulating the power supply for the module will be handled by P-Spice. P-Spice will allow us to construct our actual circuit and verify that our desired output voltage is achieved. We will simulate a circuit with an input voltage of 3 volts. This input voltage will be constructed of (2) 1.5 volt AA batteries connected in series. A DC-DC boost converter (Maxim 1676) will be attached to the power supply in an effort to step up the voltage. Various loads ranging from 0 to 41.25 will be connected to the circuit to ensure that an output voltage of 3.3 V is achieved. The current across the load will also be tabulated. 4.2.3.2 Hardware Testing DC Converter: We will construct the power supply circuit on a breadboard. A resistance box will serve as the load for our power supply. A digital multimeter and an ammeter will be used to measure the voltage and current, respectively. The impedance produced by the resistance box will be varied and the voltage and current will be measured and the different settings. Test Procedure 1. Construct the power supply circuit on a breadboard 2. Attach a load to the power supply by using a resistance box 3. Set the resistance box to 0 4. Measure the output voltage and current 5. Vary the load in increments of 5 6. Measure the output voltage and current at each setting ECE 4512: Design I December 4, 2003 WSN Page 5 of 23 4.2.4. Sensor Interface The system will be compatible with the current MICA2DOT family of sensor boards. The module s sensor interface will be a 21 pin circular interface that contains the following components: 6 Digital I/O, 6 Analog I/O, 6 UART, 2 GND, 1 Power. 4.2.4.1 Hardware Testing The digital I/O will be tested using the MFJ test box. The I/O pins will be connected to the inputs of the box where they will then be tested for correct logic display. The analog I/O will be tested by hooking each of the pins to a potentiometer, and then by measuring the correct voltage with a voltmeter. The UART circuit will be tested for correct serial communications. The power and ground will be checked with a volt meter to ensure that the correct voltage of 3V is being supplied to the sensor board. Test Procedure: 1. Power up the module and verify proper serial communication. 2. Power down the mote and hook up digital I/O pins to MFJ test box. 3. Power up the mote and verify correct binary display according to the program installed on the chip. 4. Power down the mote and connect each analog I/O pin to a 10k potentiometer. 5. Power up the mote and use a voltmeter to measure the voltage across the potentiometer as it is varied from 0 to 10k . 6. Measure the Power and Ground pins for 3V. 4.2.4.2 Software Testing The sensor board will interface with the microcontroller through I/O pins. If the sensor is an analog sensor then it will interface through the 6 analog I/O pins. If the sensor is a digital sensor, then it will interface through the 6 digital I/O pins. The interface will be tested for proper functionality by programming the microcontroller to read input data from the sensor board. 4.2.5. Integration Testing In testing each module of the system, our goal is to satisfy the design constraints set forth in Section 2 of this document. Table Table 1: Design Constraints and Tests: shows each constraint along with which test is intended to verify our meeting that goal. In addition to modular testing, we will test the system s high-level functionality. It is also necessary to determine the system s overall efficiency. Functionality: In order to test the entire system, we will run a series of tests to simulate actual operating conditions. These are designed to test the high-level functionality of the system. This functionality includes the sensor module s ability to communicate with other modules, read the attached sensor, and transfer data to the base station. The base station should display the data that is received from the sensor modules. Test Procedure 1. Several modules are distributed at reasonable distances from the base station location. This will be less than the maximum transmission distance of 1000ft. and even smaller if the test is done indoors. 2. A module will be connected to the base station to serve a conduit between the base station and ECE 4512: Design I December 4, 2003 WSN Page 6 of 23 surrounding network. 3. The base station is hooked up to a PC running the base station software. 4. The base station software is initialized. 5. The modules are then powered on. 6. Observe the network information on the base station to confirm that the network self configured properly (all modules appear in the network representation on the PC). 7. Data from the modules should now be periodically transmitted back to the base station. This can be verified by viewing the data transmitted to the base station. 8. In order to verify that the sensor interface is working properly, each module should be stimulated. For example when a temperature sensor is being used, a finger or other warm object can be placed on the sensor to alter the value it is sensing. This change should be visible on the base station. Modules are periodically removed from the network to verify its adaptability. Efficiency: In order to test that a voltage in the range of 2.7V to 3.3V will be supplied to the power supply we will connect 2 coin cell batteries in parallel. This parallel connection will be tied to a DC-DC boost converter. Test Procedure 1. 2. 3. 4. 5. 6. 7. 8. 9. Measure each coin cell battery to get an accurate voltage reading. Connect the test circuit with (2) 3V coin cell batteries in parallel. Apply a load to the test circuit via a resistance box. Vary the load to mimic the 60-70 mA full load. Measure and Record the input voltage and current. Measure and Record the output voltage and current. Vary the load to mimic the 100 200 A at light loading. Measure and Record the input voltage and current. Measure and Record the output voltage and current. 10. Divide the output power by the input power to determine the efficiency. Current Draw: The total current drain of the power supply will be measured with an ammeter. The readings will be used to determine the current of each respective component of the module. These currents will be added allowing us to compare our calculated current consumption values to the realistic ones. So, measuring whether or not the system is using more current than (60-70 mA) specified in the design document will be validated by this test. These readings will also help to determine whether the battery will meet the expected life calculations. The voltage will be checked at the output of the regulator to determine that 3.3Vdc is being supplied to the processor. Table 1: Design Constraints and Tests: Design Constraint RF Frequency Test SystemView Pass/Fail ECE 4512: Design I December 4, 2003 WSN Page 7 of 23 Efficiency Transmission Distance / BER MCU Frequency Software Power Cost Size Reliability Temperature FCC/UL Regulations P-Spice System View N/A C P-Spice N/A N/A N/A Thermal Chamber N/A ECE 4512: Design I December 4, 2003

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