Indoor location for emergency responders using LTE D2D communications waveform

It is well known that GPS signals are very weak so they cannot be received indoors. Without GPS, indoor location is a difficult problem, especially for emergency first responders since a pre-installed WiFi or beacon transmitter infrastructure may no longer be available in an emergency situation. On the other hand, emergency first responders must carry radios for critical communication needs in emergency response missions. In this work, we use the LTE Proximity Services (ProSe) mode for Device-to-Device (D2D) direct communications and the system information resource blocks of the LTE sidelink communication signals to measure time of arrivals (TOAs) among a few such D2D communication devices that form an ad hoc wireless network, thereby providing indoor location service that uses no infrastructure, no additional hardware device, and uses very little communications payload bandwidth. This concept is tested by simulation and by implementation on a software defined radio (SDR) network which is demonstrated in a real-world indoor setting.