## 3 Physiological Signal Monitoring and WBSNs Overall System
### Vital Signs  
Vital signs are those that make possible to evaluate the basic functions of the human being. The vital signs indicate the health condition of a person. The typical vital signs are:  
* Electrocardiography (ECG): An electrical recording of the heart signal to detect anomalies.
* Electroencephalography (EEG): the electrical recording of the brain's activity.
* Pulse: Measurement of the heart rate, that is, the number of times the heart beats during a determined period.
* Respiratory Rate: Inspiration and expiration activity within a specific time interval.
* Blood pressure: Pressure of the heart pushing blood, to distribute it against arteries resistance.
* Temperature: Measure of the body's ability to generate and get rid of heat.
* Oxygen saturation: Measure of the oxygen levels in the blood.  
The testing frequency of the vital signs depends on the health condition of the patient. Inpatients should be checked for long periods of time, for example, a heart attack risk or post-surgery condition patient requires continuous 24-hour monitoring. For injured and stable patients, the test frequency is every hour. A table showing the different signal requirements of body temperature, pulse oxygen, blood glucose, blood pressure, ECG and EEG in a wireless body monitoring system, is presented in [19]. The sampling rates and data bits needed for each sample vary depending on signal characteristics and behavior. The sampling frequencies displayed in the table for body temperature, pulse-oximeters, and glucose are lower than ECG and EEG signals due to their slow change in time. The total transfer time per sample represents the amount of time required for each application to transfer information. Duty cycle comes from calculating the time ratio between active and inactive communication. Other values involved in the transfer of information within a wireless monitoring network as bit error rate (BER) and latency are shown in [20]. BER for vital signal wireless monitoring, is an important issue not at all defined by researchers. To set a BER limit desired for WBSN's is not an easy task; there are important situations that could affect the reliability performance over the network as the distance between sensors and base station, number of sensors in the network, time intervals of each sensor, sampling rate, data packet sizes, body motion, environment surrounding the event, and if sensors are in line of sight (LOS) or not (NLOS). A work done in [21], mentions a BER of 0.002% as a reasonable rate for WBAN when the receiving device of a packet is in the line of sight of the sending node, while for non-line of sight (probably due to body motion) the value is set between 0.01% and 0.02%. The authors in [22] indicate that the BER increases significantly as the number on-body sensor nodes increases and an analysisperformed shows that the number of sensor nodes in the WBAN must be limited to six in order to maintain an acceptable BER of 0.001. Tables shown in [19,20] specify information to choose relevant parameters involved in data monitoring, data collection and data transmission useful to provide feedback for system optimization.