Subsystems:

Inputs- Body vitals of the patient (Heart rate, Breath rate)

Outputs- Application-specific message passing

Interfaces-

• Interface between the sensors and the forehead of the user of the VR headset.
• Interface between the device and the VR headset
• Interface between the total VR app and applications that use heart rate and breathing rate either directly or indirectly

Requirements:

1. L0: The device shall measure heart rate in beats per minute. (Functional and measurable requirement, Sensor subsystem) L1.1: The upper bound of the heart rate shall be 300 beats per minute. L1.2: The lower bound of the heart rate shall be 30 beats per minute. L1.3: The accuracy should be ±3 beats per minute. L1.4: The heart rate measurements should be made every one second.
2. L0: The device shall measure breath rate in breaths per minute. (Functional and measurable requirement, Sensor subsystem) L1.1: The upper bound of the breath rate shall be 70 breaths per minute. L1.2: The lower bound of the breath rate shall be 5 breaths per minute. L1.3: The accuracy should be ±1 breath per minute. L1.4: The breath rate measurements should be made every one second.
3. L0: The interface of the device with the body shall be made of skin-friendly texture. (Interface and observable requirement, Sensor subsystem) L1.1: The interface with the skin shall be made of soft, hypoallergenic materials. L1.2: The interface with the skin shall be made of non-abrasive and non-corroding materials.
4. L0: The device should sustain rough handling by the user. (Constraint and observable requirement, Microcontroller subsystem, Sensor subsystem) L1.1: The device should sustain drops from a height of four meters. L1.2: The device should make measurements below the tolerance range up to a height of four meters above sea level.
5. L0: The device shall follow all the federal standards in all countries. (Safety and observable requirement, Microcontroller subsystem, Sensor subsystem, Application-specific subsystem) L1.1: The device shall conform to the Food and Drugs Administration (FDA) rules in the US and similar agencies in other countries. L1.2: The device shall be compliant with the Federal Communications Commission (FCC) in the US and similar agencies in other countries. L1.3: The device shall be following the HIPAA rules and protect the sensitive health information from being disclosed without the consent or knowledge of the user.
6. L0: The device shall not be affected by extreme temperature and weather conditions. (Constraint and observable requirement, Sensor subsystem, Microcontroller subsystem) L1.1: The device should not suffer any physical damage within the temperature range of -40°F to 122°F. L1.2: The device should make measurements within the tolerance range in temperatures between 4°F and 104°F.
7. The device shall be universally compatible. (Constraint and observable requirement, Communication subsystem, Application-specific subsystem) L1.1: The device shall be interfaceable with all models of virtual reality headsets.
8. L0: The communication latency between the device and VR headset shall be less than 100 milliseconds. (Performance and measurable requirement, Microcontroller subsystem, Communication subsystem) L1.1: The tolerance shall be 50 milliseconds.
9. L0: The device shall be durable. (Performance and observable requirement, Sensor subsystem, Microcontroller subsystem) L1.1: The components used should last for at least three years.
10. L0: The device shall be easily portable. (Constraint and observable requirement, Microcontroller subsystem, Sensor subsystem) L1.0: The weight of the bio-feedback device should be less than 50g (1.7637 oz). L1.1: The device dimensions should be at most 0.8x0.8x0.1 inches.
11. L0: The device should use a low power system. (Constraint and measurable requirement, Microcontroller subsystem) L1.1: The device should be run on a 500maH battery. L1.2: The device should have entirely on-board processing.