## 2 Image Sensor: System Description
### Hardware Design  
Sensor nodes typically capture scalar data values like temperature, pressure, humidity, _etc._, but in our case the captured data is represented by an image, so the device complexity is an issue here: each  
Figure 2: An example of one RPW trap, a snapshot of trap contents, and our wireless image sensor prototype. sensor node should contain a camera, a radio transceiver and a microcontroller with enough computing power to manage image capture and transfer processes. Although there are a bunch of devices that can be used for our target application, we have designed and developed a low-power sensor node based on the CC1110F32 SoC from Texas Instruments [13]. The CC1110F32 is a true low-power sub-1 GHz system-on-chip (SoC) designed for low-power wireless applications. It combines the excellent performance of the state-of-the-art RF transceiver CC1101 with an industry-standard enhanced 8051 MCU, with 32 KB of in-system programmable flash memory and 4 KB of RAM, and many other powerful features. The small 6 \(\times\) 6 mm package makes it very suited for applications with size limitations. The CC1110F32 is highly suited for systems where very low power consumption is required. This is ensured by several advanced low-power operating modes what provides a very promising feature for our long-life pest monitoring system. In Figure 3(a) we show the main components of the wireless sensor architecture, where we can find the CC1110F32 SoC that includes a 8051 enhanced microcontroller unit (MCU), the CC1101 radio transceiver module, and a set of peripherals such as 128-bit AES security coprocessor, one USB 2.0 interface, two USARTs (working also in SPI mode), one I\({}^{2}\)S interface, three 8 bit timers, one 16 bit timer, 7-12 bits ADC, and 21 GPIO pins. The CC1101 radio transceiver was configured to work in the 868 MHz band. There are different modulations available that allows data rates up to 500 Kbps. The effective radio coverage may change  
Figure 3: Image sensor design: (**a**) wireless sensor board based on CC1110F32 SoC, and (**b**) camera module connected to sensor board through USART I/O ports. depending on (1) several parameters that directly depend on the trap location, as terrain profile, radio wave obstacles, noise interference levels at the selected transmission channel and trap location (at ground level or fixed at the palm tree at an specific elevation over the ground), (2) the transmission power level of CC1101 radio (up to 10 dBm), and (3) the antenna type employed [13]. We have performed some outdoor experiments to determine the radio coverage of our image sensor in Line Of Sight (LOS) environments similar to the one shown in Figure 1. At the highest data rate (250 Kbps), with the standard antenna and the maximum available transmission power (10 dBm) we have established point-to-point communications over distances of up to 500 m. We have fixed the maximum point-to-point communications distance in 300 m, where the received signal strength is about -81 dBm, just 10 dB above CC1101 radio receiver sensitivity threshold [12] and the observed average packet error rate was around 1%. Reducing the transmission power to the default value (0 dBm), the one used in all of our experiments, the maximum distance is reduced to 140 m.  
As mentioned above, our study assumes a single-hop communication scenario where every node should be in the coverage area of control station. So, all sensor nodes should be up to 140 m away from the control station location, which roughly represents a 10,000 m\({}^{2}\) monitoring area. As future work, we plan to evaluate other network scenarios (multi-hop, relay based, _etc._) to increase the overall area coverage of our pest monitoring proposal. The choice of the camera was also critical. It should have high resolution, low cost and low power consumption. We have chosen a low-cost C328-7640 color camera from Comedia [14], shown at Figure 3(b).