# Hybrid Multi-Antenna Techniques for V2X Communications--Prototyping and Experimentation
## 5 Conclusions  
This article presents a novel methodology that can be used to implement a hybrid diversity scheme suitable for V2X communications. The scheme was designed, implemented, and integrated on a T2T communication testbed. The hybrid diversity is built upon novel compact and re-configurable ESPAR antennas exploiting their beamshaping capabilities. The final integrated technique proved to be resilient and robust as it managed to provide an average of 12 dB SNR gain compared to SISO solutions. The diversity engine is compatible with existing V2X standards, and in addition can support the heterogeneity of ITS applications and services provided by 5G. During the field tests, various KPIs were measured, for example, capacity and coverage probability, that showcased the benefits of the implemented diversity engine. Figure 14: Packet error rate using the diversity engine vs. SISO-OMNI (visualization with Grafana tool). Figure 13: Bit error rate using the diversity engine vs. SISO-OMNI (visualization with Grafana tool). Figure 15: Latency (Physical Layer) of the diversity engine vs. SISO-OMNI (visualization with Grafana tool). In the future, as far as the ESPAR antenna design is concerned, there are two main optimization approaches that will be investigated. The first one involves the fabrication of the 5-element ESPAR antenna with four parasitic wire elements in a circular arrangement in order to expand the diversity capability of the array and increase the number of the produced radiation patterns (from three to nine), achieving at the same time full azimuthal coverage. However, minimization of the array sizes must be achieved. Secondly, additional degrees of freedom can be obtained by employing varactors instead of PIN diodes and increasing this way the number of the antenna operating states. As far as the diversity engine is concerned, the future steps include integration of diversity algorithms that rely on MRC with log likelihood ratio (LLR) scaling or soft bit MRC; transformation of the developed system to a complete beamforming-diversity engine as the standards evolve, and include feedback channels as well as transmit diversity schemes. Conceptualization, K.M., L.M., P.S.B., and A.G.K. ; methodology, K.M., L.M., P.S.B., and A.G.K. ; software, K.M. and L.M. ; validation, K.M. and L.M. ; investigation, K.M., L.M., and P.S.B. ; writing--original draft preparation, K.M., L.M., and P.S.B. ; writing--review and editing, K.M., L.M., P.S.B., and A.G.K. ; visualization, K.M. and L.M. ; supervision, A.G.K. All authors have read and agreed to the published version of the manuscript. This research was funded by Horizon 2020 project ROADART. The research of [PERSON] is funded by Greece and the European Union (European Social Fund- ESF) through the Operational Programme <<Human Resources Development, Education and Lifelong Learning>> in the context of the project \"Reinforcement of Postdoctoral Researchers--2 nd Cycle\" (MIS-5033021), implemented by the State Scholarships Foundation (IKY). This research has received funding from the European Union's Horizon 2020 research and innovation programme under ROADART Grant Agreement No. 636565. The research of [PERSON] is supported by Greece and the European Union (European Social Fund- ESF) through the Operational Programme <<Human Resources Development, Education and Lifelong Learning>> in the context of the project \"Reinforcement of Postdoctoral Researchers--2 nd Cycle\" (MIS-5033021), implemented by the State Scholarships Foundation (IKY). The authors declare no conflict of interest. The following abbreviations are used in this manuscript: