本文研究WiFi信号来估计步频计数的问题
*step counting: selecting subcarriers and limb speed
*50volunteers
*two indoor environments
*90.2% and 87.59%, respectively
*device-free
FMCW bandwidth:1.79GHz
WiFi bandwidth:20 or 40MHz
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分为两步：walking detection, step counting
butterworth bandpass filter:带通滤波主要获取一定频率范围内的信号,具体来说就是移除高频的噪音和低频的呼吸以及心跳
收发设备的配置：
transmitter with one directional antenna(这个就是限制啊)
receiver with 3 omni-directional antennal
sampling packet:1000Hz(发包率有点高)
##Considering human activities in traditional indoor environment introduce frequencies of no more than 300Hz in CSI amplitudes(CARM), thus WiStep is configured with a sampling rate of 1000Hz that is larger than the Nyquist sampling rate##
上述图展示了躯干部份与腿部分对信号反射产生的频率不同。
参考的文献：
[1]WifiU: gait recognition using wifi signal, 2016
[2]CARM: understanding and modeling of wifi signal based human activity recognition,2015
evaluation metrics:
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acceleration and deceleration phases:加减速阶段
step counting=count walking steps
accelerometers
gyroscopes
sensory data:感知数据
light condition, power consuming, and personal privacy
stem from
