# Bluetooth Communication Leveraging Ultra-Low Power Radio Design
## 4 Conclusions and Future Work  
BLE, as a well-established protocol, is utilized for short-range communications in a wide spectrum of applications, ranging from audio streaming to wireless sensors nodes. It offers a low power solution that can support connectivity between heterogeneous IoT devices and access points in personal area networks. Several efforts have been devoted \begin{table}
\begin{tabular}{c c c c c c} \hline  & [59] & [53] & [6] & [53] & [41] & [51] \\  & **JSSC’21** & **ISSCC’19** & **JSSC’19** & **JSSC’19** & **ISSCC’18** & **JSSC’16** \\ \hline
**Technology** & 40 nm & 65 nm & 28 nm & 40 nm & 65 nm & 28 nm \\ \hline
**Supply Voltage** & 0.6/1.0 V & 1.2 V & 0.2 V & 0.6/0.9 V & 1.0 V & 0.5/1.0 V \\ \hline
**Transmission** & Closed loop & \multirow{2}{*}{Open Loop} & Closed loop & Closed loop & Closed loop & Closed loop \\
**Scheme** & (RO-based) & & & (Type-I) & (RO-based) & (ADPLL) & (PLL) \\ \hline
**PLL Locking Time** & 50 \(\upmu\)s & 15 \(\upmu\)s & N/A & 0.4 \(\upmu\)s & Not reported & 15 \(\upmu\)s \\ \hline
**Power** & \multirow{2}{*}{1.1 mW} & \multirow{2}{*}{0.61 mW} & \multirow{2}{*}{4 mW} & \multirow{2}{*}{1.55 mW} & \multirow{2}{*}{3.1 mW} & \multirow{2}{*}{6.3 mW} \\
**Consumption** & & & & & & \\ \hline
**TX Output Power** & Not reported & \(-\)8.4 dBm & 0 dBm & \(-\)3.3 dBm & \(-\)3 dBm & 3 dBm \\ \hline
**Overall efficiency** & Not reported & 23.6\% & 25\% & 30.17\% & 16.13\% & 32\% \\ \hline
**Die Area** & 1.33 mm\({}^{2}\) & 0.494 mm\({}^{2}\) & 0.53 mm\({}^{2}\) & 0.0166 mm\({}^{2}\) & 1.64 mm\({}^{2}\)\({}^{*}\) & 0.65 mm\({}^{2}\) \\ \hline \end{tabular}  
* Transmitter and receiver area.  
\end{table} 
Table 2: Comparison table for the state-of-the-art Bluetooth-Low Energy transmitters. to reducing the power consumption of the RF radios to empower scaling IoT devices and enable self-powered operation. Efficient and complete solutions can be realized in both the network and physical layers. In the network layer, back-channel communication is presented where the back-channel message is embedded in a standard compliant BLE packets which is an attractive solution to design ULP radios while able to connect with the already-deployed infrastructure. Back-channel communication can be implemented in a packet-level fashion within an advertisement event or within a packet based on the latency requirements. This approach allows the main radios to stay in a deep sleep-mode, while the ULP wakeup/BC receivers continuously monitors the spectrum for wakeup/BC signaling from the access points or other fully functioning devices. We presented a comprehensive survey for fully compliant BLE transceivers as well as back-channel receivers. In receive mode, fully compliant BLE receivers consume mWs of power to meet the stringent requirements on the data rate, sensitivity level at 0.1% BER and adjacent channel interference rejection. On the other hand, different backchannel receiver architectures were proposed to limit the power consumption to 10 s or 100 s of \(\upmu\)Ws. Mixer-first architectures, in an open-loop transmission scheme, accompanied with RF passive gain provide a decent performance at low power budget. BLE transmitters utilizing linear/switched power amplifiers suffer from low overall efficiency which led to a power consumption of several mWs to achieve high output power levels. Ring oscillator PLL-based architectures are proven to decrease the power budget to 100 s of \(\upmu\)Ws while satisfying the BLE requirements in terms of phase noise and frequency stability. Alternatively, open loop transmission utilizing LC-based oscillators can be utilized to eliminate the extra power of PLLs and PAs leading to a significant reduction in power consumption. Extensive research efforts from industry and academia are still ongoing to create more energy-efficient wireless connectivity and low-power radio design architectures. These efforts extend beyond the BLE standard to cover the entire connectivity landscape of IoT devices.