Showing papers by "Shivendra S. Panwar published in 2022"
TL;DR: It is shown that low fronthaul capacity reduces the number of users each AP can support, and the cell-free system, consequently, becomes user-centric and the utility of the WSEE metric to incorporate heterogeneous EE requirements of users is demonstrated.
Abstract: Cell-free (CF) massive multiple-input-multiple-output (mMIMO) deployments are usually investigated with half-duplex nodes and high-capacity fronthaul links. To leverage the possible gains in throughput and energy efficiency (EE) of full-duplex (FD) communications, we consider a FD CF mMIMO system with practical limited-capacity fronthaul links. We derive closed-form spectral efficiency (SE) lower bounds for this system with maximum-ratio combining/maximum-ratio transmission processing and optimal uniform quantization. We then optimize the weighted sum EE (WSEE) via downlink and uplink power control by using a two-layered approach: the first layer formulates the optimization as a generalized convex program, while the second layer solves the optimization decentrally using the alternating direction method of multipliers. We analytically show that the proposed two-layered formulation yields a Karush-Kuhn-Tucker point of the original WSEE optimization. We numerically show the influence of weights on the individual EE of the users, which demonstrates the utility of the WSEE metric to incorporate heterogeneous EE requirements of users. We show that low fronthaul capacity reduces the number of users each AP can support, and the cell-free system, consequently, becomes user-centric.
15 citations
01 Jun 2022
TL;DR: System level simulations in NR V2X highway scenarios show significant performance improvement of the proposed scheme over conventional solutions like omnidirectional or directional transmission/reception of SL control information, which helps eliminate hidden node interference while avoiding too many exposed nodes.
Abstract: Device-to-device (D2D) communication using 5G New Radio (NR) sidelink (SL) is envisioned to be a key enabler of high speed, low latency applications, with automated driving being the prime use case. To meet the high data rate requirements, it is essential for SL devices to be able to operate in mmWave/sub-THz frequencies where bandwidth is abundant. Consequently, several enhancements will be needed to the current version of NR SL, which is mainly designed for sub-6 GHz frequencies. Beamforming based highly directional transmission/reception used at high carrier frequencies result in directional deafness in other directions. For SL UE autonomous resource allocation, termed as Mode 2 of NR SL in 3GPP, this results in a UE’s inability to detect transmissions not aligned to its primary direction of reception, which leads to high packet errors. In this paper, we focus on system wide performance of 3GPP based NR SL Mode 2 resource allocation for directional systems at mmWave/sub-THz frequencies. We propose a composite strategy that comprises paired SL control transmission and sensing, whereby SL UEs transmit and receive the SL control information in an additional “paired” direction, directly opposite to their intended direction of transmission. This helps eliminate hidden node interference while avoiding too many exposed nodes. System level simulations in NR V2X highway scenarios show significant performance improvement of the proposed scheme over conventional solutions like omnidirectional or directional transmission/reception of SL control information.
1 citations
04 Dec 2022
TL;DR: Fast Wireless Backhaul (FWB) as discussed by the authors is a new wireless backhaul solution that takes advantage of the multi-connectivity of UEs and the high-capacity low-cost wireless Backhaul promised by IAB.
Abstract: Next generation cellular networks will rely heavily on mmWave and THz spectrum for the abundantly available bandwidth. However, these frequencies suffer from high path and penetration losses. One way to improve the performance is network densification which comes with higher operational cost. To reduce the operational cost of Base Station (BS) deployment, the 3GPP has proposed the Integrated Access and Backhaul (IAB) architecture. Nonetheless, when a handover does occur in IAB networks, even with minimal handover time, the traffic that is already en route to the UE is delayed, as the new serving BS must retrieve the packets from either the previous serving BS or the core. To address these challenges, we propose Fast Wireless Backhaul (FWB), a new wireless backhaul solution. FWB takes advantage of the multi-connectivity of UEs and the high-capacity low-cost wireless backhaul promised by IAB to reduce latency and increase reliability in case of unexpected blockages on the wireless signal path. In FWB, the BSs serving the UE participate in a multicast tree, and receive all packets designated for the UE, but only one BS transmits packets to the UE. In the event of a link failure between the UE and the serving BS, another BS takes over to maintain the data plane connection, without first having to retrieve undelivered downlink packets. We believe our architecture can enable mission critical applications with stringent latency and reliability requirements.
01 Jun 2022
TL;DR: A set of data-driven codebook design algorithms are proposed to solve the optimization problem for the beam-codebook design to maximize the coverage probability, which is a quadratically-constrained mixed-integer problem.
Abstract: In 5G systems, a predefined codebook with a limited number of beams is used during the initial access and beam management procedures to establish and maintain the connection between the users and the network. At 5G mmimeter wave (mmWave) frequencies, due to the very narrow and directional beams obtained by beamforming, intelligently designing a codebook with a limited number of beams is crucial to avoid coverage holes. We formulate an optimization problem for the beam-codebook design to maximize the coverage probability, which is a quadratically-constrained mixed-integer problem. We propose a set of data-driven codebook design algorithms to solve the optimization problem, which, for a given codebook size constraint, adapts the codebook to the deployment scenario using the provided input channel data. For a sample deployment scenario, we show that as the codebook size increases, the proposed algorithms converge to the upper bound in terms of the coverage probability much faster than several benchmark algorithms. Hence, the proposed algorithms can achieve the coverage levels of benchmark algorithms with a much smaller codebook size. This can significantly reduce the initial access, beam management, and handover delays, which in turn provide higher data rates, lower latency, and lower interruption times.
TL;DR: This paper uses a Markov Chain based analytical model as well as MATLAB based system level simulations to show how user rotation can significantly increase the outage duration under various deployment configurations and propose enhancements to enable faster HO under user rotations.
Abstract: The high data rates required for next generation applications necessitate the use of millimeter wave and terahertz bands where bandwidth is abundant. Due to high path loss in these bands, antenna arrays (AAs) are needed to focus the signal in highly directional beams in the desired directions. However, highly directional communication links in these bands are vulnerable to misalignment and blockages due to mobility. Thus, both mobile blockers and user equipment (UE) rotations can significantly increase the handover (HO) frequency, while HO delays and HO failures jeopardize system latency and reliability. Furthermore, the scanning angle of each AA is limited by the orientation of the device, the mounting angle of the AA, the element spacing and the grating sidelobes formed during beamforming, which is referred as Field-of-View (FoV). In scenarios with UE rotational mobility, limited FoV may lead to loss of connection with the source next-generation NodeB (gNB). In this paper, we analyze current HO and radio link monitoring protocols in scenarios with UE rotational mobility and mobile blockers. We use a Markov Chain based analytical model as well as MATLAB based system level simulations to show how user rotation can significantly increase the outage duration under various deployment configurations. We propose enhancements to enable faster HO under user rotations and demonstrate significant performance improvements using simulations.
DOI•
13 Sep 2022
TL;DR: This work implements a selection of the coexistence techniques described in the literature, and evaluates them in a set of controlled experiments designed to showcase the benefits and limitations of each approach.
Abstract: With the emergence of delay-sensitive applications like cloud gaming, remote driving, and virtual/augmented reality (VR/AR), there has been renewed research interest in the development of low latency congestion control protocols. However, these efforts have been impeded by the difficulty associated with designing an end-to-end protocol that reacts to delay signals, but that also shares a link effectively (i.e., without causing harm to other flows and without being starved by other flows). This is a critical requirement for use in the public internet. To help protocol designers, we summarize the literature on coexistence of delay-based congestion controls. We implement a selection of the coexistence techniques described in the literature, and evaluate them in a set of controlled experiments designed to showcase the benefits and limitations of each approach. Through our experimental analysis, we highlight coexistence-related pitfalls of delay as a congestion signal. We hope that this work will help inform the design of new low latency congestion control protocols or improvements to existing protocols.