SmartCheck50+ Localised Wireless Sensor Network (LWSN) System Requirements Specification (SRS) Version 1.0 1. Purpose of this document This document specifies the functional, technical, performance, quality, safety, regulatory, and operational requirements for the Localised Wireless Sensor Network (LWSN) , principally p roposed to be incorporated into the SmartCheck50+ The LWSN is a non - invasive, low - cost, wireless sensing system intended to collect physiological data from adults aged 50+ in Sub - Saharan Africa (SSA) and transmit this data securely to a remote server for further assessment. This document covers only Phase 1 of SmartCheck50+ development - the LWSN 2. System scope The LWSN shall: • acquire a predefined set of physiological signals, • perform basic signal conditioning and quality checks locally, • transmit validated data wirelessly to a remote gateway or server ( potentially cloud server ) , • operate safely, reliably , and affordably in SSA deployment contexts. 3. Design objectives The LWSN shall be designed to meet the following primary objectives: 1. Low cost and affordability for low - and middle - income SSA settings. 2. Clinical - grade signal quality comparable to standard point - of - care monitors. 3. High reliability and operational robustness in real - world environments. 4. Low power consumption suitable for portable ( potentially wearable ) operation. 5. Scalability to large community deployments. 6. Modularity and upgradeability for Version 2 and future add - ons. 4. High - level system description The Localised Wireless Sensor Network (LWSN) is a portable, point - of - measurement sensing system intended to be temporarily applied to a person for a short measurement session (typically 2 to 5 minutes), after which it is cleaned and prepared to be used on another individual. The LWSN is not designed for continuous monitoring The system is intended to support high - quality physiological measurements comparable to standard point - of - care clinical devices, while enabling low - cost, scalable deployment in resource - constrained settings. The LWSN consists of: • a portable, reusable sensor node (ESP32 - based) that is temporarily attached or applied to the body during a measurement session, • multiple non - invasive biomedical sensing modules , • a microcontroller unit dedicated primarily to sensor control, timing, acquisition, buffering and secure communication (not clinical or diagnostic processing), • a Bluetooth Low Energy (BLE) communication subsystem for low - power local data transfer, • a local data buffering and packetisation subsystem for resilience to connectivity disruptions, • a secure uplink interface to a remote server via a smartphone or local gateway device 5. Intended users and operating environment 5.1 Users • Adults aged 50 years and older • Community health workers • Primary healthcare staff • Research and pilot study participants 5.2 Operating environments • Urban, peri - urban , and rural settings in SSA • Homes, clinics, community centres, mobile outreach points • Ambient temperatures: 5 °C – 45 °C • Relative humidity: up to 90% non - condensing • Intermittent power and intermittent network connectivity 6. Physiological measurements – Version 1 The LWSN shall acquire physiological signals during short, supervised or semi - supervised measurement sessions of typically 2 to 5 minutes per subject. The system shall support repeated use across multiple individuals in a single day. The LWSN shall not assume permanent attachment to a specific individual. The LWSN shall support the following six sensing modalities. Explicit exclusions (V1): • Blood glucose • Activity quality scoring • Potential add - ons : s aliva , stool , sweat , urine , and tear teste rs/sensor s only for TB, cancers , a nd CVD s screening ( locat ion dependant ) 7. Functional requirements 7.1 Sensor acquisition The system shall: • simultaneously or sequentially acquire all supported signals, • support configurable sampling rates per sensor, • timestamp all samples with a common system clock. 7.2 Local signal quality assurance The LWSN shall perform only minimal local signal integrity checks necessary to ensure valid acquisition, including: • sensor connection and placement detection, • saturation or clipping detection, • basic motion artefact indicators. No Modality Notes 1 Heart rate & heart rate variability ( HRV ) From ECG or P PG [ MAX 30102 ] 2 Single - lead ECG ( Primary for HRV ) Diagnostic - quality waveform [ AD8232 ] 3 Peripheral oxygen saturation (SpO ₂ ) Optical PPG - based [ MAX 30102 ] 4 Body temperature Skin or near - core proxy 5 Blood pressure Non - invasive, cuff - based , or validated alternative 6 Motion/posture reference For artefact detection only ( stability ) The LWSN shall not perform clinical interpretation, classification, risk scoring, or screening inference locally 7.3 Measurement session management The LWSN shall: • support an occasional / session - based measurement model (not continuous 24/7 monitoring), • allow configuration of session duration per modality, • support manual or remote session initiation. 7.4 Local processing The device shall perform only minimal local processing necessary to support reliable data capture and transmission , including: • sensor configuration and control, • timing and synchronisation, • signal digitisation, • packetisation, • optional lightweight filtering strictly for transmission quality or signal stabilisation. All statistical or case /ML - based analysis shall be performed on the remote server. 7.5 Wireless communication The LWSN shall use Bluetooth Low Energy (BLE) as the primary wireless communication interface. BLE shall be used to: • transmit acquired physiological data to a nearby smartphone or gateway device, • receive configuration commands, • receive time synchronisation and session control commands. The system shall prioritise: • low power consumption, • robustness to intermittent connectivity, • reliable data transfer rather than high throughput. 7.6 Data transmission target The LWSN shall transmit data to: • a smartphone acting as a primary gateway device, or • a locally deployed gateway device connected to the internet. The LWSN shall not require direct long - range connectivity (cellular, Wi - Fi infrastructure) on the sensor node itself. 7.7 Device configuration The system shall support: • remote configuration of sampling rates, • enabling/disabling of specific sensors, • firmware updates over a wired or wireless interface. 8. Performance and accuracy requirements 8.1 ECG • Bandwidth: minimum 0.05 – 150 Hz • Input - referred noise: ≤ 30 μV RMS • CMRR: ≥ 80 dB • Sampling rate: ≥ 250 Hz (minimum) • Resolution: ≥ 12 bits effective 8.2 Heart rate and HRV • HR error: ≤ ±2 bpm compared to reference ECG monitor • HRV metrics error: ≤ 5% relative error compared to reference system 8.3 SpO ₂ • Accuracy: ±2% SpO ₂ in the range 70 – 100% • Update rate: ≥ 1 Hz 8.4 Body temperature • Accuracy: ±0.2 °C in the range 35 – 42 °C 8.5 Blood pressure • Systolic and diastolic error: o mean error ≤ 5 mmHg o standard deviation ≤ 8 mmHg • Must be validated against a clinically approved sphygmomanometer. 8.6 Motion sensing • Minimum 3 - axis accelerometer • Used solely for artefact detection and posture tagging 9. Reliability and stability requirements The LWSN shall: • support reliable operation under intermittent or unstable gateway connectivity, • store all acquired session data locally until positive confirmation of successful upload is received, • resume interrupted data transfers automatically without user intervention, • ensure that no session data is lost due to a temporary lack of internet access at the gateway or smartphone 10. Power and energy requirements The LWSN shall be designed for operation in environments with: • unreliable access to mains electricity, • limited charging opportunities. The system shall therefore: • use BLE as the primary communication mechanism to minimise energy consumption, • support charging via commonly available USB power sources, • allow multiple days of field operation when used only for short measurement sessions, • support clear battery - status indication prior to starting a measurement session. 11. Hardware architecture requirements 11.1 Core processing The ESP32 - class microcontroller shall be used primarily for: • sensor control and synchronisation, • signal acquisition, • temporary data storage, • packet formation, • secure BLE communication. The microcontroller shall not be required to execute clinical algorithms, disease classification or risk models. 11.2 Sensor interfacing The system shall support: • I²C peripherals • SPI peripherals • UART peripherals • ADC inputs • GPIO - based control lines 11.3 Expandability The hardware shall: • expose expansion headers for future sensors, • support Version 2 add - ons without redesigning the full platform. 12. Mechanical and wearable requirements The system shall: • be safe for direct skin contact, • use biocompatible materials at contact points, • support a v ariety of potential configurations , includin g portab le device, wearable or semi - wearable form factor (patch, band or light vest), • support easy disinfection and cleaning ( where individual s com e into direct contact with sensor s ) , • allow sensor replacement without full device replacement. 13. Cost requirements The target bill of materials (BOM) for the LWSN sensor node shall be: • ≤ USD 12 0 (excluding gateway device), • designed for further reduction to ≤ USD 8 0 at moderate production volume. 14. Data handling and integrity The LWSN shall: • buffer all session data locally in non - volatile or protected volatile memory until successful transfer is confirmed, • support store - and - forward operation to enable use in locations with poor or unavailable internet connectivity, • allow multiple completed sessions to be stored locally before upload, • ensure data integrity across power loss and communication interruption events. 15. Security requirements (device side) The LWSN shall secure all BLE communications using authenticated and encrypted connections suitable for transmission of personal health data . Ideally , it shall : • use encrypted wireless communication, • use device - unique identifiers and credentials, • prevent unauthorised firmware installation, • support secure boot where feasible. 16. Interoperability requirements The LWSN shall: • expose a documented data interface for server integration, • use structured, machine - readable data formats, • support backward - compatible firmware updates. 17. Maintainability and support The system shall: • support remote access and diagnostics, • expose device health parameters (battery, sensor faults, memory usage), • support modular firmware updates. 18. Regulatory and clinical readiness requirements The LWSN shall be designed for short - duration measurement sessions and shall: • support rapid placement and removal of sensors, • provide clear visual or audible feedback when a valid measurement session is completed, • clearly indicate when the device is ready for the next patient. 19. Human factors and usability The LWSN shall: • require no specialist training to attach and operate, • provide clear user feedback for: o correct sensor placement, o active measurement, o errors and warnings, • minimise user interaction during measurement. 20. Environmental and durability requirements The LWSN shall: • withstand repeated handling and transportation, • survive accidental drops from 1 m onto hard surfaces, • resist sweat and light rain ingress. 21. Verification and validation requirements The LWSN shall be designed to operate effectively in environments characterised by: • unstable or intermittent internet connectivity, • unstable access to mains power. The system shall therefore support: • offline operation during measurement, • delayed synchronisation of collected data, • safe handling of incomplete or interrupted uploads, • repeated retry mechanisms without user intervention. 22. Deliverables for Phase 1 The engineering team shall deliver: 1. A fully functional LWSN prototype (hardware and firmware). 2. Sensor validation reports. 3. Power and battery performance reports. 4. Wireless performance and reliability reports. 5. Firmware documentation. 6. Hardware design documentation. 7. Risk and safety analysis report. 23. Explicit design constraints • The system must remain non - invasive. • The system must support intermittent connectivity. • The system must be suitable for future clinical trials. • The system must support integration into a larger , future SmartCheck50+ platform. 24. Road - mapping requirement The LWSN architecture shall explicitly support: • addition of biochemical and non - contact sensors in Version 2, • higher - level edge processing in future versions, • integration of alternative wireless backhauls.