# FM-UWB: Towards a Robust, Low-Power Radio for Body Area Networks
## 3 Single-User FM-UWB Communication  
Although different FM-UWB receiver architectures have been explored, most of them (with the exception of [13]) focused on standard 2-FSK sub-carrier modulation, targeting data rates below 100 kb/s. Transmitters proposing higher data rates (1 Mb/s) and more complex M-FSK modulations have been implemented, but the full communication has never been demonstrated with one of the existing receivers. Here, the receiver from [7; 19] was used to demonstrate the feasibility of \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Reference** & [23] & [21] & [22] & [17] & [24] & [13] & [10; 18] \\ \hline Year & 2010 & 2011 & 2011 & 2012 & 2013 & 2014 & 2015 \\ SC Modulation & 2-FSK & 2-FSK & 2-FSK & 2-FSK & 2/4/8-FSK & 2-FSK & 2-FSK \\ Frequency [GHz] & 3.8 & 3.8 & 4 & 3.8 & 3.75 & 8 & 4 \\ RF Bandwidth [MHz] & 600 & 700 & 500 & 560 & 500 & 500 & 500 \\ Power cons. [mW] & 9.6 & 18.2 * & 0.9 & 8.7 & 1.14 & 0.39/3.5 ** & 0.63 \\ Supply [V] & 1.6 & 1.6 & 1 & 1.6 & 1 & 1 & 1 \\ Data rate [kb/s] & 10 & 1000 & 100 & 50 & 750 & 1000 & 100 \\ Out. power [dBm] & \(-14.5\)*** & \(-12.8\) & \(-10.2\) & \(-13.7\) & \(-14\) & \(-11\)*** & \(-10.1\) \\ Energy Efficiency & 960 & 18.2 * & 9 & 174 & 1.5 & 0.39 & 3.1 \\ Tech. node [nm] & 180 & 180 & 90 & 180 & 65 & 65 & 65 \\ \hline \hline \end{tabular}  
* Excluding the output PA;
* With and without duty cycling; *
* Estimated from figure.  
\end{table} 
Table 2: Performance summary of state-of-the-art Frequency Modulated Ultra-Wideband (FM-UWB) transmitters. Figure 5: FM-UWB transmitters and receivers, evolution of power consumption. Type of demodulator used in each receiver is indicated on the graph. communication at higher data rates and using M-FSK without any modification to the wideband FM demodulator. In fact, any of the architectures shown in Figure 3 could be used to accommodate different sub-carrier modulations. Minor modifications would be needed only in the baseband circuitry. As the power consumption of the baseband part is typically negligible compared to the RF part, increasing communication speed up to a certain point would only result in a small increase of the overall consumption. It is therefore expected that higher speed leads to a higher energy efficiency of the entire system. The transmitted signal was generated using two signal generators. A 12 GS/s, 12-bit arbitrary waveform generator M8190A provides the quadrature baseband FM-UWB signal. This generator allows generation of any signal up to 4 GHz of baseband bandwidth and was used to create different transmission scenarios (including the multi-user communication). The quadrature signal is then upconverted to 4 GHz using the PSG signal generator. The whole test setup is shown in Figure 6. Signal power at the receiver is controlled using a variable attenuator. The output data from the FM-UWB receiver is digitized and then processed off-line to obtain the Bit Error Rate (BER). The BER curves for different data rates are shown in Figure 7. In all cases, orthogonal frequencies are used with a modulation index of 0.5. As expected, the sensitivity of the receiver decreases due to increased bandwidth of the sub-carrier signal. Nevertheless, if the distance between nodes is small enough and the channel is sufficiently good, higher communication speeds can be used to decrease latency in the network. In this case, the limitation to data rate comes from the filter following the FM demodulator, which was designed for sub-carrier frequencies from 1-2.5 MHz. Figure 8 shows the test setup that demonstrates over the air communication. The distance between the two antennas is approximately 2 m, roughly corresponding to the distances that are targeted for short range communications in a WBAN (although still simplistic compared to a real use-case scenario). The signal is transmitted at \(-15\) dBm, somewhat lower than the allowed power in the UWB frequency range. Oscilloscope screen shows the spectrum of the demodulated signal (using the FFT). Two cases are presented.