Full-Duplex Wireless for 6G: Progress Brings New Opportunities and Challenges

The use of in-band full-duplex (FD) enables nodes to simultaneously transmit and receive on the same frequency band, which challenges the traditional assumption in wireless network design. The full-duplex capability enhances spectral efficiency and decreases latency, which are two key drivers pushing the performance expectations of next-generation mobile networks. In less than ten years, in-band FD has advanced from being demonstrated in research labs to being implemented in standards and products, presenting new opportunities to utilize its foundational concepts. Some of the most significant opportunities include using FD to enable wireless networks to sense the physical environment, integrate sensing and communication applications, develop integrated access and backhaul solutions, and work with smart signal propagation environments powered by reconfigurable intelligent surfaces. However, these new opportunities also come with new challenges for large-scale commercial deployment of FD technology, such as managing self-interference, combating cross-link interference in multi-cell networks, and coexistence of dynamic time division duplex, subband FD and FD networks.Comment: 21 pages, 15 figures, accepted to an IEEE Journa

Full-Duplex OFDM Radar With LTE and 5G NR Waveforms: Challenges, Solutions, and Measurements

This paper studies the processing principles, implementation challenges, and performance of OFDM-based radars, with particular focus on the fourth-generation Long-Term Evolution (LTE) and fifth-generation (5G) New Radio (NR) mobile networks' base stations and their utilization for radar/sensing purposes. First, we address the problem stemming from the unused subcarriers within the LTE and NR transmit signal passbands, and their impact on frequency-domain radar processing. Particularly, we formulate and adopt a computationally efficient interpolation approach to mitigate the effects of such empty subcarriers in the radar processing. We evaluate the target detection and the corresponding range and velocity estimation performance through computer simulations, and show that high-quality target detection as well as high-precision range and velocity estimation can be achieved. Especially 5G NR waveforms, through their impressive channel bandwidths and configurable subcarrier spacing, are shown to provide very good radar/sensing performance. Then, a fundamental implementation challenge of transmitter-receiver (TX-RX) isolation in OFDM radars is addressed, with specific emphasis on shared-antenna cases, where the TX-RX isolation challenges are the largest. It is confirmed that from the OFDM radar processing perspective, limited TX-RX isolation is primarily a concern in detection of static targets while moving targets are inherently more robust to transmitter self-interference. Properly tailored analog/RF and digital self-interference cancellation solutions for OFDM radars are also described and implemented, and shown through RF measurements to be key technical ingredients for practical deployments, particularly from static and slowly moving targets' point of view.Comment: Paper accepted by IEEE Transactions on Microwave Theory and Technique

Intelli MAC Layer Protocol for Cognitive Radio Networks

According to the FCC (Federal Communications Commission) [11], the utilization of the spectrum has been increasing rapidly over a wide range of frequency bands. There are various reasons that cause this dynamic growth. One reason is increase in network capacity. Another reason is increase in mobile services needed to carry over the spectrum. In order to overcome the shortage of spectrum due to increased usage, Cognitive Radio (CR) technology has been introduced. Cognitive Radios can utilize idle spectrum holes that are not occupied by the Primary Users (PUs) for performing temporary wireless communication tasks. PUs are licensed users which own and have access to certain spectrum bands. Challenging issues that need to be addressed by the CRs are spectrum sensing, spectrum sharing, spectrum management and spectrum mobility. The main contribution of this thesis is to design a new MAC layer protocol in order to determine the behavior of Secondary Users (SUs) based on PUs transmission history while taking into account both PUs and SUs. SUs are non licensed users which transmit only on those spectrum bands that are unutilized by the PUs. SUs usually observe the activity of PUs on spectrum bands. This new protocol allows the CR nodes to sense, share and manage access of the nodes to the spectrum. This protocol prevents any damage caused by SUs to the PUs transmission. Also, the new MAC protocol will negotiate the spectrum by assisting the CRs to identify the underutilized spectrum based on channel conditions such as channel throughput, channel data rate, channel score, channel utilization and packet error rate (PER). The Intelli MAC layer protocol measures transmission time among PUs and reduces channel sensing time for SUs. For managing the entire network, this protocol uses the concept of Harmonious Channel (HC). This protocol uses multiple half duplex transceivers for carrying data communication among users

5G Cellular: Key Enabling Technologies and Research Challenges

The evolving fifth generation (5G) cellular wireless networks are envisioned to provide higher data rates, enhanced end-user quality-of-experience (QoE), reduced end-to-end latency, and lower energy consumption. This article presents several emerging technologies, which will enable and define the 5G mobile communications standards. The major research problems, which these new technologies breed, as well as the measurement and test challenges for 5G systems are also highlighted.Comment: IEEE Instrumentation and Measurement Magazine, to appear in the June 2015 issue. arXiv admin note: text overlap with arXiv:1406.6470 by other author

Wireless body sensor networks for health-monitoring applications

This is an author-created, un-copyedited version of an article accepted for publication in Physiological Measurement. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0967-3334/29/11/R01

Adaptive nonlinear interference suppressor for cognitive radio applications

To utilize the radio frequency spectrum efficiently a Cognitive Radio (CR) can operate as a secondary user in a frequency band which is licensed to a primary user. To this end, the CR must sense the spectrum continuously to find empty frequency channels for its transmission. The transmitted signal by the local transmitter of the CR, however, induces a strong local interference in the local receiver of the CR. Hence a half-duplex transceiver is used where the transmit and sense operations are done in separate time slots. The time-slotted operation though, reduces the throughput of the CR. This paper proposes application of an adaptive Nonlinear Interference Suppressor (NIS) to suppress this strong local interference to enable simultaneous transmit and sense. We present experimental results of a transceiver testbed that uses an implementation of the NIS, fabricated in 140 nm CMOS technology. These experiments show that the NIS can substantially suppress the local interference with low complexity and power consumption

S-Band Transponder Multi-Network Compatibility, Space Environment and Radiation Testing

This paper presents the development and testing of the Software Define Radio (SDR) transceiver to meet the emerging needs for SmallSat communication and navigation. Vulcan Wireless and NASA Goddard Space Flight Center (GSFC) collaborated in testing the Vulcan Wireless S-band SDR engineering model. Apart from testing, communication link analysis was performed for a Low Earth Orbit (LEO) 400 km scenario. The results of the compatibility, radiation, environmental testing, and link analysis are presented. Also, this paper reviews a set of SmallSat missions under development at NASA GSFC