R&D
Reconfigurable Smart Surfaces
Reconfigurable intelligent surface (RIS) is one of the promising candidate for the next generation wireless communication networks. While theoretical and simulation studies of the RIS-assisted wireless communication systems have revealed the RIS’s potential, implementation and demonstration of the RIS in practical communication scenarios are essential to validate the RIS’s benefits and applicability for the next generation communication systems. Therefore, our main focus on the RIS studies is practical implentation of the RIS into various application of beyond 5G scenarios as well as theoretical and simulation studies of the RIS. Our RIS infrastructure contains two different RIS prototypes. The first RIS prototype operating at 5 GHz frequency band consists of 76 reflecting elements whose have binary phase shift adjustment as 0 and 180 degree. The second RIS prototype operates around 28 GHz frequency band and contains 1600 reflecting elements with binary phase shift adjustment. Moreover, we are collobareting with TÜBİTAK MAM to develop an RIS prototype operating at the 5G FR1 frequency in order to enhance our RIS infrastructure.
Here are some of the practical demonstrations we have realized using RIS prototypes:
Measurement-Based Characterization of Physical Layer Security for RIS-Enabled Wireless Systems
This paper presents a measurement-based characterization of RISs to provide physical layer security. The transmitter (Alice), the target user (Bob) and the listener (Eve) are placed in an indoor environment. Each user is equipped with a software-defined radio connected to a horn antenna. The phase shifts of the reflective elements are software-controlled to determine the received signal strength at the positions where Bob and Eve are located, aiming to maximize the stealth capacity. Consisting of 76 passive reflective elements, an iterative method is used to control the Greenerwave RIS prototype. Computer simulation and measurement results show that a RIS can be an effective tool to significantly increase the privacy capacity between Bob and Eve.
This paper was awarded the "Best Paper Award" at the IEEE VTC2023-Spring Conference.
Performance Demonstration of RIS Control Algorithms Using srsRAN
In this demonstration, the performance of a RIS-enabled wireless communication system is shown in a closed environment. For this demonstration, the Greenerwave sub-6GHz RIS prototype and an open source 4G/5G emulator (srsRAN) running on a Linux-based PC integrated with Software Defined Radio (SDR) will be used as base station (BS) and user equipment (UE). Real-time video will be transmitted from the BS to the UE over a RIS-enabled wireless link. Then, optimization of the RIS configuration using iterative and codebook-based algorithms will be demonstrated. The results show that RIS provides more than 15 dB increase in RSRP when using horn antennas, resulting in higher modulation and data rate.
This demonstration has been accepted for presentation at the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2023 in Toronto, Canada.
Indoor Measurements for RIS-Enabled Communications: Practical Phase Shift Optimization, Coverage Extension and Physical Layer Security
In this work, we present practical measurements to demonstrate RIS capabilities to increase signal coverage and provide physical layer security (PLS) in a closed environment. First, extensive measurements are performed in a single-user setup using iterative, grouping and codebook-based phase shift optimization methods. With careful adjustments of the RIS phase configurations when the receiver is placed in different locations, the iterative method achieves a performance improvement of about 10 dB in received signal strength. The grouping method reduces the training time required to find a suitable RIS configuration, losing only a few dB in received signal power. Another experiment was conducted to demonstrate PLS in a multi-user setup where the RIS is divided into two zones serving intended and unintended users. The results show that the codebook method can effectively increase the on-the-go privacy capacity without using feedback other than the users' locations during the phase shift optimization process, whereas the iterative method requires a continuous feedback channel for the received signal strengths.
This paper has been invited for publication in the Special Issue of Selected Best Papers of IEEE International Conference on Communications (ICC) of the IEEE Open Journal of the Communications Society.
Indoor Measurements of Reconfigurable Smart Surfaces in 5G Millimeter Wave Networks
This study presents the experimental results of RIS, one of the leading technologies for sixth generation (6G) networks, in the Turkcell 5G millimeter wave testbed. In this study, a RIS with 1,600 reflective elements is used to establish non-line-of-sight links between a mmWave base station (BS) and customer premise equipment (CPE) transmitting the 5G new radio (NR) waveform. The impact of the RIS on the performance metrics received by the CPE is demonstrated.
