## 2 Related Work  
There are different common types of wearable motion measurement sensors and systems which help in diagnosing and detecting neurological diseases that affect human gait such as Parkinson's disease wirelessly. These sensors include accelerometers, gyroscopes, magnetometers, electromagnetic tracking systems (ETS), force sensors, and surface electromyography (EMG) [11]. All these sensors can be used together or separately as deemed to help in various analysis applications. For instance, an accelerometer is a sensor that measures linear acceleration and is suitable for measuring the locomotion status in human gait [12]. On the other hand, a gyroscope is an angular velocity sensor that can be used for measuring the posture and motion of the patient in gait analysis by measuring the segments' angular rate of the patient's body [12]. Whereas, electromyography (EMG) is used for measuring the action and the activity of the muscles, as an indirect measurement of muscle activity by using surface or wire electrodes [13]. Even though electrocardiogram (ECG) measures the electrical activity of the heart using an outer body surface electrodes placed on the skin, it has also been proposed in some cases of gait monitoring [11]. Among the sensors used for the detection and assessment of neurological diseases, accelerometers have been widely used in most studies, either solely or in combination with other types of sensors, as they provide insightful information about the movement of body limbs being tested, which directly affects gait parameters [14]. There are a number of medical uses for accelerometers that can greatly impact the quantitative measurement of PD. The following is some studies which included accelerometers in their tests. [PERSON] et al. [15] conducted a research was including twelve test subjects with age ranges from 46 to 75 years to diagnose idiopathic PD. Three accelerometers were used in total to detect FOG and to measure three-dimensional (3D) acceleration. Two of the sensors were attached to the patients' legs at the shank slightly above the ankle and on the thigh right above the knee. The third 3D accelerometer was positioned on the lower back of the patient on a belt [15]. Typically, the number and position of sensors vary according to the target gait parameter being tested, and the anticipated accuracy of results. Another approach was proposed by [PERSON] et al. [16], in which seven patients diagnosed with PD were recruited (six males; 62.7 \(\pm\) 10 years). Eight accelerometers (based on the Shimmer platform) have been placed on the upper and lower arms and legs of test subjects to monitor them while they were asked to do specific sets of motor tasks. Several studies employed wireless wearable accelerometers and smartphones for the assessment of PD tremor and simulated tremor, e.g., the study conducted by [PERSON] et al. [17]. Other research suggested the use of accelerometers, gyroscopes and magnetometers together to increase the rate of success in diagnosing PD. [PERSON] et al. [18] collected their data by using tri-axial wearable sensors, namely accelerometer, magnetometer and gyroscope for the classification of patients with PD from healthy controls. The wearable sensors were attached to both wrists and limbs of each test subject to capture movement data while performing certain motor tests. The output signals were passed through a low-pass filter with a cutoff frequency of 4 Hz. [PERSON] et al. [8] proposed a newer approach to diagnose PD, in which they combined accelerometer sensors and EMG sensors. More specifically, they used sEMG electrodes to measure the data from the EMG electrodes that were placed on the belly of the biceps with an inter electrode spacing of 3 cm. The neutral electrode was positioned 6-7 cm from the recording electrode. They also used accelerometers that were placed on the Palmer sides of each patient's wrists.