Research

Efficient management of multi-dimensional resources has gained new aspects as inevitable results of the overlapping and coexistence of many communication systems. New waveforms approaches exploiting the complementary features of multi-dimensional resources emerge to be a tempting solution to break the bottleneck in the physical layer toward heterogeneous networks. In this context, novel waveform designs to fulfill the requirements of heterogeneous networks constitute our main research interests. Toward this ultimate point, our scope ranges from the fundamental properties of the waveforms (e.g., pulse shapes, orthogonality, nonorthogonality, time-frequency lattice, delay-Doppler-angular resolution) to the frame structures in the transmission. We investigate not only waveform itself in time-frequency in terms of channel adaptation and flexibility, but also cross relations between waveforms like signal separability regarding their suitability to next-generation networks. Moreover, we investigate 2D and 3D modulation domains for waveform design like OTFS (2D).  Additionally, considering practical systems, we focus on their impacts on the other topics in the physical layer (e.g. PAPR, equalization, channel estimation, out-of-band radiation) and MAC layer (e.g. scheduling), since they essentially affect the transmitter and receiver algorithms.

Our current efforts for next-generation wireless technologies:

• Hybrid waveform design for beyond 5G,
• Ultra-flexible and scalable OFDM-based waveform design,
• Waveform design for the robustness to doubly dispersive channels,
• Waveform design for integrated sensing and communication,
• Waveform design for multi-point to multi-point networks.

Integrated sensing and communication (ISAC) is one of the emerging technologies for 5G and beyond networks. With the ever-growing spectrum scarcity and futuristic applications which depends both on sensing and communication, ISAC is becoming an important and crucial technology. The constant evolution of current wireless networks paves the way for cutting edge applications including autonomous driving, air traffic control (ATC), geophysical monitoring, traffic surveillance, and security applications that require sensing in addition to conventional communication. Additionally, these bandwidth-hungry wireless applications require carrier frequencies that are typically reserved for radar systems. Therefore, the scientific community is compelled to revamp classical communication architecture by integrating radar sensing into it. Radar and communication systems operate in fundamentally distinct ways. Radar illuminates the intended target by transmitting a known signal towards it and processes the received echoes to extract useful information about the target such as distance, velocity, height, azimuth, and other physical properties. Contrarily, information exchange takes place between cooperative transceivers in classical communication systems.

Challenges and Opportunities:

1. Waveform design/frame design for ISAC
2. Interference management for radar and communication coexistence
3. Signal processing techniques/algorithms for ISAC
4. THz sensing and communication
5. Machine learning for ISAC
6. Channel models for ISAC

Fifth generation (5G) and beyond wireless systems signaled a paradigm shift in wireless networks by introducing a variety of services satisfying different performance requirements rather than concentrating on increasing the achievable data rates. Given the diverse use cases in 5G and beyond wireless networks, the wireless systems will not only be used for communication but also to acquire information about the environment and/or users using sensing techniques to improve the overall network performance. However, the very fact that radio signals can be used to gain environmental awareness renders them prone to being eavesdropped on, manipulated, jammed, and exploited by malicious nodes/entities. Although commonly utilized, conventional cryptographic security is not designed for networks with the diversity of capabilities as seen in the current (or future) wireless systems since it requires certain computational capabilities at all nodes. As such, these methods are unable to scale well with the decentralized and heterogeneous networks that are becoming more prevalent. On the other hand, physical layer security (PLS) offers a potential supplementary solution to guarantee the confidentiality, integrity, authenticity, and availability of communications by leveraging the dynamic aspects of the wireless environment.

Current Efforts

1. Physical layer security for 5G and beyond
2. Cognitive/Intelligent security
3. Cross-layer and hybrid security
4. Radio environment mapping (REM) security
5. Physical layer authentication
6. Context-aware security frameworks
7. Artificial-intelligent (AI) based security solutions
8. Reconfigurable Intelligent Surfaces (RIS) assisted security solutions

Multiple access is an approach where multiple users use the resources either orthogonally or non-orthogonally in the most effective manner. Different significant approaches to be considered in this area such as how to allocate the resources, what are the most effective scheduling approaches can we use, what is the best mechanism to deal with multi-user interference, and finally how can we achieve a good performance metric. Those approaches can be considered in 6G and beyond networks are called next generation multiple access (NGMA) such as rate splitting multiple access (RSMA).

Possible Direction areas

1. NGMA to achieve the fundamental limits of wireless networks.
2. NGMA for multiuser/multi cell multi antenna networks.
3. NGMA based robust interference management.
4. NGMA in MU MIMO, CoMP, massive MIMO, millimetre wave MIMO, relay, cognitive radio, coded caching, physical layer security, cooperative communications.
5. Coding and Modulation for NGMA.
6. Cross layer design, optimization, and performance analysis of NGMA.
7. Implementation and standardization of NGMA.
8. NGMA in B5G services and applications such as enhanced eMBB enhanced URLLC, enhanced MTC, massive MTC, massive IoT, V2X, cellular, UAV and satellite networks, wireless powered communications, integrated communications, and sensing, etc.
9. Radio resource management for green wireless systems.
10. Radio resource management in heterogeneous and small-cell networks.
11. Quality-of-service and resource management.

Interference is the fundamental nature of the wireless communication systems due to the existence of multiple transmissions over a common propagation medium (air, in this context). As the wireless networks become more heterogeneous in nature due to the inclusion of varieties of scenarios and use cases stemming from societal needs, the interference problem gets more serious and imposes a primary challenge on the realization of reliable and spectrally efficient wireless systems. In most existing wireless systems, interference has been dealt with by coordinating users to orthogonalize their transmissions in time, frequency, or code or by increasing the transmission power and treating each other’s interference as noise. Sophisticated receiver designs, such as multiuser detection, have been also considered for interference suppression under various settings. Apart from interference arising from transmissions of other users, self-interference due to undesirable propagation channel condition is becoming increasingly critical as well. In this regard, waveform design-based approaches have been widely studied. In recent years, a paradigm shift on dealing with the interference problem has been observed. In addition to the traditional approaches, there is also a focus on how to intelligently exploit the knowledge and/or the structure of interference to improve the reliability, throughput, spectral, and energy efficiency of wireless communication systems.

Our Focus

• Interference analysis and modeling
• Interference mitigation and cancellation techniques
• Interference exploitation
• Interference-free coexistence mechanisms

Terahertz (THz) Frequency Bands

The issue of spectrum scarcity in 4G cellular communication systems has pushed 5G towards using millimeter-wave frequency bands. Moreover, applications such as virtual/augmented reality (AR/VR), personal assistance, digital twins, autonomous vehicles, internet of things (IoT), etc., that require high-rate communication and high-resolution sensing demand migration towards even higher carrier frequencies such as terahertz (THz). However, these higher frequencies have their own challenges compared to low frequencies. High frequencies particularly THz frequencies inherently suffer from short communication ranges owing to high path loss which is justified by Friis free space power equation. Other factors such as reflection losses, intermittent availability of LOS paths, and molecular absorption effect also contribute to the short communication range at high frequencies. To extend the small footprint offered by THz frequencies, attenuation losses are countered by concentrating the transmitted signal energy in high-power, highly directional narrow beams. However, these directional point-to-point THz links are susceptible to blockages and can easily be disrupted by micro-movement caused by a user or any object in the environment. Therefore, sophisticated mechanisms must be developed to counter blockages at these frequencies. Furthermore, the potential of certain phenomena peculiar to higher frequencies such as reflection and molecular absorption losses must be investigated to be used for sensing.

Our Focus

• Advanced signal processing algorithms for integrated sensing and communications (ISAC) at mm-Wave/THz frequency bands.
• Non-Line-of-sight communication and sensing at sub-THz frequency bands.
• Waveform design and modulation techniques for beyond 5G communication systems.
• MIMO/beamforming techniques/challenges at higher carrier frequencies.
• Channel Modelling and parameter estimation at sub-THz frequencies.