# Bluetooth Communication Leveraging Ultra-Low Power Radio Design
## 3 BLE Radio Design Trends and Considerations  
### Receiver Design Trends  
In this section, we will present a survey of low power receivers that have been published in top journals and conferences since 2005 [13]. The survey summarizes the state-of-the-art receiver specifications, helps identify the research directions and trends and gives a deep understanding of radio design trade-offs and limitations [21]. Figure 6a shows the power trend of published receivers over years. It can be seen that the first sub-\(\mu\)W receiver was introduced in 2012 [22] and, since then, a number of sub-\(\mu\)W wakeup receivers have been published for IoT applications. Figure 5: Structure of a BLE advertising event. An important figure of merit (FoM) in receivers design is based on the product of power consumption and the achieved sensitivity. Lower FoM implies an energy-efficient radio design. However, since different radios target different data rate requirements, a normalized sensitivity on data rate is mandatory for a fair comparison and consistent FoM. Figure 6b shows the well known tradeoff between sensitivity and active power  
Figure 6: ULP (ultra-low power) receivers’ survey showing different design trade-offs. (**a**) Power trend of published receivers over years; (**b**) power consumption versus sensitivity; (**c**) power consumption versus normalized sensitivity; (**d**) power versus signal-to-interference ratio (SIR); (**e**) power versus sensitivity at different frequency ranges; and (**f**) power versus sensitivity for different modulation schemes. consumption in radios. With the exception of sub-\(\upmu\)W receivers, a Pareto optimal line with a slope of \(-10\times/20\) dB can be observed bounding the power-sensitivity design space. The slope indicates that for every 20 dB improvement in sensitivity (or a \(10\times\) increase in the transmission range in free-space), you would expect \(10\times\) increase in the power. Therefore, in order to achieve a lower power operation, sensitivity shall be sacrificed. Normalizing the sensitivity to data rate for each point, as shown in Figure 6c, results in a clearer observation for the power-sensitivity trade-off since sub-\(\upmu\)W receivers typically operate at fairly low data-rates. The signal-to-interference ratio (SIR) is another performance metric which resembles another challenge to achieve robust operation at a limited power budget. Figure 6d clearly shows the aforementioned trade-off. Another important observation is that few papers report the SIR performance with a modulated interferer and the majority of these ULP radios have power consumption of 100 s of \(\upmu\)Ws. The reason is that in order to achieve good rejection at adjacent channels, frequency translation and cascaded signal filter stages are required which translates to higher power consumption. An alternative approach to improve the frequency selectivity of the receiver is based on exploiting high-Q off-chip RF MEMS filters, as in [23, 24]. However, it lowers the system integration level and increases the module's cost. In addition, it requires multiple devices to cover the wide bandwidth required in many standards. Network level solutions such as frequency-hopping can effectively improve interference tolerance as proposed in [16]. The distribution of ULP receivers across different frequency bands is shown in Figure 6e. As can be seen, sub-10 \(\upmu\)W receivers operate at sub-3 GHz frequency range. Lower frequencies provide wider coverage at the expense of data rates which is attractive in numerous IoT applications. Several low power and low voltage techniques can be utilized at low frequencies like subthreshold analog and digital logic to reach \(<\)1 \(\upmu\)W power budget [20]. Complexity of the modulation is another critical factor which limits the power consumption of the receivers [25] as depicted in in Figure 6f. Coherent modulation schemes (e.g., BPSK, OFDM, QAM) require the phase information of the received signal for proper demodulation and hence high-performance PLLs are used.