Table 2. Performance comparison with related work. (unit: meter).

Technology	S.E	Outdoor	Indoor
GPS	3.08	2.65	N/A
WiFi[7]	3.90	7.24	5.82
WiFi+accelerometer [12]	2~6		2~6
WiFi+GSM+GPS+PDR[7]	2.73	20.1	3.11