# TEC and ROTI Measurements from a New GPS Receiver at BOWEN University, Nigeria
## 2 The CASES Hardware Platform  
The CASES GPS receiver was made with the intention of offering a powerful platform with a wide range of peripheral options, as it is inexpensive, compact, and power-efficient. The final configuration consists of three parts, namely: a custom-built dual frequency, a digital signal processor board, and a \"single board computer\" with an ARM microcontroller,Figure 1 depicts a block schematic of the receiver hardware, and Figure 2 shows a photo of a CASES GPS receiver and antenna. The dual-frequency back end generates 2-bit samples at a rate of 5.7 samples/second within a constrained bandwidth of 2.4 MHz that produces one set of 2-bit samples for each of the L1 and L2 GPS frequencies. In addition, the automatic gain-controlled amplification, filtering, mixing to an intermediate frequency, and sampling are all performed by this front end. The back end provides an optional input for attaching an external 10 MHz frequency reference, with the termination of 50 or 1000 Ohms, and can supply a chosen 5-volt DC bias on the antenna input to power active antennas. The board uses about 360 milliamps at 5 volts, excluding any power needed by an active antenna that is connected. Despite the non-negligible changes in the measured carrier phase that a temperature-compensated crystal oscillator (TCXO) introduces [13], both frequencies are sampled concurrently, with the frequency reference provided by an onboard TCXO. A general-purpose digital signal processor handles all processing for the CASES GPS receiver, a software-defined receiver. A Texas Instruments C6457 digital signal processor is housed on a second custom-built board (DSP). The processor contains 4 MB of non-volatile flash memory, 128 MB of off-chip RAM, and a 1 GHz clock speed. It also has 2 MB of on-chip RAM. All acquisition and tracking tasks, as well as the computation of the navigation solution and different observables including pseudo-range, beat carrier phase, and Doppler shift, is carried out by the DSP board. The board outputs the beat carrier phase, timestamps, in-phase and quadrature accumulations, and other data at 10 Hz or less. Approximately 75% of the processor is used when tracking 12 GPS L1 C/A code channels and 4 GPS L2 CL channels, computing the navigation solution, acquiring continuous background  
Figure 1: Block diagram of the CASES receiver hardware. Figure 2: Photo of a CASES GPS receiver. signals, and carrying out all additional overhead. At 5 volts, the DSP board uses about 580 milliamps. A \"single-board computer\" (SBC) running the GNU/Linux operating system makes up the third main reception component. An ARM AT91 SAM9260 microcontroller with a wide range of available peripherals powers the SBC. This board has 128 MB of flash memory for the file system and 32 MB of RAM. Ethernet, a serial peripheral interface, a secure digital card reader, a universal serial bus, ZigBee, Wi-Fi, a 10-bit analog-to-digital converter, and general-purpose I/O pins are among the peripherals that are offered. Images or configuration files are frequently used for communication, along with an RS232 serial port, Ethernet, or Wi-Fi. The SBC also maintains a secure shell server that enables remote log-in for additional tasks that the server application does not provide. At 5 volts, the SBC uses about 260 milliamps. The SBC is equipped with a network-connected server application that enables remote data logging, code image or configuration file upload, and monitoring. It also maintains a secure shell server that enables remote log-in for additional tasks that the server application does not provide. At 5 volts, the SBC uses about 260 milliamps. Detailed descriptions of the CASES GPS receiver can also be found in the works of [14; 15]. This Connected Autonomous Space Environment Sensor (CASES) from ASTRA is a software-defined GPS receiver with the dual frequency of L1 C/A and L2C codes for space-weather monitoring and can be remotely programmed via an internet source.