## 2 Indoor Positioning System in 433 MHz ISM Band
### Up-Converting Receiver  
The up-converting receiver subsystem is comprised of the RF blocks and supporting blocks, which are presented in Table 2.  
Figure 4: Implemented GPS down-converting repeater subsystem excluding the antennas. Figure 5: Modelled directional GPS antenna (**a**,**b**), fabricated directional GPS antenna (**c**), modelled 433 MHz dipole antenna (**d**), fabricated 433 MHz dipole antenna (**e**). The up-converting receiver is implemented using the listed components and blocks in Table 2 and is presented in Figure 6. The aforementioned 433 MHz dipole antenna in Figure 5e is also used as the receiver indoor antenna. The RF blocks of the up-converting receiver are (a) a 433 MHz indoor dipole antenna, (b) a signal power conditioner block where a 433 MHz band pass filter, (c) an LNA, (d) a variable attenuator, (e) a second, cascaded LNA, (f) an I/Q power divider, (g) bias tees that provide the required DC to I/Q inputs of the up-converter, (h) a 433 to 1575.42 MHz up-converter, and (i) an off-the-shelf GPS receiver (u-Blox LEA-6T(r)). The controller over Wi-Fi provides interfaces between RF blocks and the user. Moreover, a voltage regulator is designed to provide the required DC voltage to the RF blocks. In this subsystem, the controller is also connected to the custom GPS receiver, and the raw data from the GPS receiver can be sent over Wi-Fi to a remote computer. The retransmitted 433 MHz positioning signals are picked up by the 433 MHz indoor dipole antennas. In the receiver subsystem, the received signals are first filtered and then amplified. Similar to the repeater subsystem, the amplification levels are adjusted by changing the attenuation of the digital step attenuator, which is able to attenuate the signal \begin{table}
\begin{tabular}{c c c} \hline \hline
**Blocks** & **Components** & **Block Properties** \\ \hline
433 MHz Dipole & 433 MHz dipole on FR4 & 2.1 dB gain, \\  & & 80 degree 3 dB beam width on both sides \\ Signal Power Conditioner & DBP433.T.A.30 band pass filter at 433 MHz & 1.7 dB insertion loss at 433 MHz, 19 MHz 3 dB \\  & bandwidth \\ Signal Power Conditioner & LHA-13 LN + low noise amplifier & 22.43 dB gain \\  & & 0.9 dB noise figure \\ Signal Power Conditioner & DAT-31R5A-SP + digital step attenuator & 0 to 31.5 dB adjustable attenuation by 0.5 dB step \\  & (variable attenuator) & size and can be adjusted from controller \\ Signal Power Conditioner & LHA-13 LN + the second low noise amplifier & 22.43 dB gain \\  & amplifier & 0.9 dB noise figure \\ Up-Converter & I/Q power divider, bias tees & Provides I/Q inputs and required DC levels to \\  & & ADRF6720-27 \\ Up-Converter & ADRF6720-27 quadrature modulator & 1.2 dB block loss \\  & & Programmable over SPI from controller block \\ Off-the-shelf GPS Receiver & LEA-6T chipset & \\ Supporting Blocks & Voltage Regulator & Provides DC to system components and blocks \\ Supporting Blocks & Controller with Wi-Fi for programming & Wi-Fi connection to remote PC, SPI connection to \\  & attenuator and down-converter & ADRF6820, and attenuator \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Receiver subsystem and its components. Figure 6: Implemented up-converting receiver excluding the antenna. from 0 to 31.5 dB. By adjusting the attenuation value of the attenuator, the gain of the overall up-converter subsystem may be set to different values. The subsystem also utilizes a second amplifier to further amplify the signal. These up-converted GPS signals then propagate to the off-the-shelf GPS receiver, which is integrated within the up-converting receiver subsystem. As mentioned previously, for further flexibility, the up-converting repeater attenuation levels can be set to different values from a remote computer using a Wi-Fi connection. Using a remote computer with an internet connection, where the ephemeris data of GPS satellites are available, the estimation of the indoor position starts when the raw data are sent from the receiver.