There are multiple usable open-source LTE handset software implementations. They work with a suitable SDR like e.g. a LimeSDR or similar. AFAIK not even a single open-source UMTS software implementation works well enough for practical, day-to-day use. More than one of the LTE implementations archived that reliability. They all guzzle power though, IIRC. But that's the easy part (offload ping detection and FEC (de-)coding to an FPGA).