## 4 Case Studies
### Case Study of COTS System: TEMPO  
TEMPO 3.2 is the latest version of the TEMPO platform which has been designed for a range of BSN applications and illustrates the aforementioned tradeoffs between flexibility and efficiency in a COTS based system platform. Specifically, TEMPO was designed to meet requirements for human motion analysis: a broad category that can contain many specific applications. With this application area in mind, a low power non-invasive device is needed that is still flexible enough to address applications that vary from gait analysis to tremor assessment and activity detection. TEMPO 3.2 uses MEMS accelerometers and gyroscopes to perform inertial sensing to measure and study human motion and wirelessly transmit this data to central aggregator such as a smart phone or PDA. Accelerometers and gyroscopes were chosen for inertial measurement because they are small in size, self contained, and inexpensive when compared with other technologies like optical motion capture or magnetic localization. In order to enable communication to PDAs and smart phones while still keeping power consumption as low as possible, Bluetooth was selected as the communication protocol. While Bluetooth and other standard protocols allow for interoperability, they are not the optimal choice for BSNs, and a networking protocol tailored to these types of systems may be necessary if systems are to be effective and energy efficient. However, standard protocols such as Bluetooth enable quick prototyping for initial data collection which can be beneficial for showing the value of new and emerging BSN technologies. Also, since the devices need to be a small form factor and wearable, TEMPO 3.2 was created in the form of a large wristwatch. This enables it to be wearable and flexible from design perspective, but puts other significant limitations on the system. The size of the device not only puts restrictions on the size of the electronics, but also has a significant impact on the size and capacity of the battery that powers the device. Therefore, efficiency becomes a large concern for TEMPO 3.2 as it is required to have a runtime of several hours up to several days. In order to meet the runtime constraints mentioned above, TEMPO 3.2 uses the ultra-low power TI MSP430 microcontroller that still provides the ability to program and load a wide range of functions and digital signal processing techniques. The microprocessor gives the ability to optimize power consumption of the system by compressing data or performing the digital signal processing techniques that let us transmit less data over the radio (the main consumer of power). However, as is common with many systems, there is a desire to be able to adapt as new technology emerges and as application requirements change. TEMPO 3.2 remains flexible by including a daughter board connector that allows the addition of another sensor for addressing a wider range of applications. Likewise, radio technology is a constantly changing field as newer and lower power technologies are being developed. So TEMPO 3.2 includes the option of taking out the Bluetooth radio and replacing it with a different radio that communicates over the UART or SPI protocols. This leaves TEMPO 3.2 as a general platform that can address a wide range of applications, but does not address a specific application as power and size efficiently as custom hardware could. In summary, this platform utilizes the advantages of COTS based systems such as hardware expandability and interoperability with other commercial devices. Hardware capabilities may be swapped out with pin-compatible ICs and daughter boards to facilitate application reuse along with changing technology standards and software functionality is easily modified and tested which can be beneficial for applications in which the processing requirements are still unknown. These advantages are typical of COTS platforms.