EVALUATIONResources NeededTest SpecificationTransceiverSimulationHardware TestingSoftware TestingMicrocontrollerFirmware TestingPower ModuleSimulationHardware TestingSensor InterfaceIntegration TestingWSN Page 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. Figure 4.1. Hardware block diagram. 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 December 4, 2003WSN 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, 2003WSN 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
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