# Flexible Wearable Heart Rate Monitoring System and Low-Power Design: A Review
## 6 Design of the Flexible Wearable Heart Rate Signals Transmission and Output Module
### Hardware-Algorithm Co-Design for Flexible Wearable Heart Rate Signal Transmission and Output Module  
In the heart rate signal transmission and output module, hardware-algorithm co-design serves as a crucial element for achieving both module functionality and low-power consumption. This integrated approach combines optimal low-power hardware platforms with compatible communication protocols to enable efficient data transmission. By incorporating CRC verification algorithms [140], it ensures complete and error-free data transfer, thereby realizing more efficient and stable heart rate data transmission. Furthermore, hardware-algorithm co-design demonstrates outstanding performance in optimizing module energy consumption. For example, [PERSON] et al. [62] constructed an IoT-based flexible wearable health monitoring transmission and output module through hardware-algorithm co-design.Specifically, the BLE module on the central board of the system is configured based on data transmission algorithms and MQTT protocol algorithms [141; 142]. Equipped with a built-in ARM Cortex M0 processor, this module can perform preliminary processing on collected physiological data, reducing data volume before transmitting via BLE. This hardware-algorithm co-design approach not only enhances the efficiency of data transmission algorithms but also optimizes power consumption. In terms of power management, the algorithm is tailored to optimize the hardware of the power board. It implements a charging mode of constant current followed by constant voltage through a linear charge controller, while a low-power voltage divider circuit is used to monitor battery voltage. These measures effectively reduce the hardware power consumption of the power board and extend battery life. Furthermore, the system employs a state monitoring and decision algorithm that adjusts parameter configurations according to the current hardware status. This enables hardware components, such as sensors, to switch between working and standby modes, thereby achieving low-power operation of the entire system. The power consumption is 44.57 mW when all sensors are operating; 18.03 mW when only the PPG sensor is active. For another example, [PERSON] et al. [121] developed a flexible wearable ECG signal transmission and output module through hardware-algorithm co-design, with the hardware-algorithm co-design primarily manifested in its transmit (Tx) and receive (Rx) working modes. Specifically, during transmission, the Gaussian Frequency Shift Keying (GFSK) modulation algorithm [143] is adopted to modulate and transmit data from the MCU, while during reception, coherent or non-coherent demodulation algorithms are employed to demodulate the radio frequency signals emitted by the low-power nRF24L01 transceiver. This two-fold approach not only significantly reduces the complexity of system data processing but also enhances energy efficiency through GFSK modulation, thereby lowering the overall system power consumption. Simultaneously, the system ensures transmission accuracy via a Cyclic Redundancy Check (CRC) mechanism, which helps minimize additional power consumption arising from error-induced retransmissions. Furthermore, the integrated design of the system reduces the number of external components, while the Arduino Nano microcontroller coordinates data processing and transmission. Through parameter tuning and mode switching, this microcontroller further optimizes power consumption, resulting in an average system power consumption of approximately 72.6 mW, ensuring that the system achieves high energy efficiency and maintains stable performance under low-power conditions. In summary, both [PERSON] et al. 's IoT module and [PERSON] et al. 's ECG signal transmission module have consistently implemented low-power concepts throughout their hardware-algorithm co-design for heart rate signal transmission and output modules.