ago, the use of Brillouin based distributed fiber sensor systems for structural health monitoring applications has increased rapidly [5; 6], due to their high measurement range up to tens of kilometers. The familiar techniques in time-domain based Brillouin fiber sensors are; Brillouin optical time-domain reflectometry (BOTDR) [7] and Brillouin optical time-domain analysis (BOTDA) [8]. The BOTDR system is implemented using spontaneous Brillouin scattering (SpBS) which requires access to one end of the fiber. The BOTDA system uses stimulated Brillouin scattering (SBS) with counter-propagating continuous probe wave and access to both ends of the fiber is essential. Providing a new fiber infrastructure for a distributed sensing system comes at a huge cost with much complexity, which discourages their widespread use. Therefore, sharing an existing data transmission fiber infrastructure for distributed sensing offers cost-effectiveness and efficiency savings. For example, the railway industry uses a fiber infrastructure installed along the track-side for data transmission. The integration of distributed sensing system with the existing optical cable can be used for real-time condition monitoring of land-slides, track ballast, snowdrifts, flooding and line-side fire detection [9]. The integration of distributed sensing and active data transmission using a single optical fiber is an unexplored area of research.  
In this paper, we demonstrate a proof-of-concept of simultaneous integration of fiber communication system and the BOTDR sensor system using a single optical fiber, demonstrating the performance of both systems experimentally. For the fiber communication system, the error vector magnitude (EVM) is analyzed for three different modulation formats of quadrature phase-shift keying (QPSK), 16-QAM and 64-QAM at different data and sensing system powers using a 25 km single-mode silica fiber. In order to evaluate the BOTDR sensor system performance, the temperature effects have been measured and the temperature errors evaluated. To demonstrate the proof-of-concept, we used a single 25 km fiber spool in the experiments. However, the sensing range can be further improved by in-line erbium-doped fiber amplifier (EDFA) [10] and Raman amplification [11; 12], while choosing the optimized larger wavelength spacing between the data and sensing systems. It is significant to remark on certain previous works, such as [PERSON] et al. [13], which validated a simulation performance based on VPI photonics for phase-sensitive optical time-domain reflectometry (OTDR) into dense wavelength division multiplexing (DWDM) fiber data transmission. In 2017, [PERSON] et al. [14] demonstrated a phase-OTDR system into a dual-polarization QPSK based data system and investigated the Q-factor performance influenced by the phase-OTDR system power. However, in their work, the sensing performance was not investigated in the presence of active data transmission. Therefore, the implementation and purposes of the system proposed in this paper are significantly different. Essentially, the proposed system is based on BOTDR and QAM over OFDM based communication system (aligns to 4G, 5G and beyond implementation [15]), where its performance is experimentally characterized by the simultaneous temperature and communication system EVM measurements.