[Paper Review] Can Terahertz Provide High-Rate Reliable Low Latency Communications for Wireless VR?

Christina Chaccour, Mehdi Naderi Soorki+3 more|arXiv (Cornell University)|Apr 30, 2020

Millimeter-Wave Propagation and Modeling33 citations

TL;DR

The paper presents a novel terahertz-based model for wireless VR that decomposes user delay into processing, queuing, and downlink delays, then analyzes the tail distribution and risk of unreliable experiences to assess instantaneous reliability in short-range links affected by blockages and molecular absorption.

ABSTRACT

Wireless virtual reality (VR) imposes new visual and haptic requirements that are directly linked to the quality-of-experience (QoE) of VR users. These QoE requirements can only be met by wireless connectivity that offers high-rate and high-reliability low latency communications (HRLLC), unlike the low rates usually considered in vanilla ultra-reliable low latency communication scenarios. The high rates for VR over short distances can only be supported by an enormous bandwidth, which is available in terahertz (THz) frequency bands. Guaranteeing HRLLC requires dealing with the uncertainty that is specific to the THz channel. To explore the potential of THz for meeting HRLLC requirements, a quantification of the risk for an unreliable VR performance is conducted through a novel and rigorous characterization of the tail of the end-to-end (E2E) delay. Then, a thorough analysis of the tail-value-atrisk (TVaR) is performed to concretely characterize the behavior of extreme wireless events crucial to the real-time VR experience. System reliability for scenarios with guaranteed line-of-sight (LoS) is then derived as a function of THz network parameters after deriving a novel expression for the probability distribution function of the THz transmission delay. Numerical results show that abundant bandwidth and low molecular absorption are necessary to improve the reliability. However, their effect remains secondary compared to the availability of LoS, which significantly affects the THz HRLLC performance. In particular, for scenarios with guaranteed LoS, a reliability of 99.999% (with an E2E delay threshold of 20 ms) for a bandwidth of 15 GHz along with data rates of 18.3 Gbps can be achieved by the THz network (operating at a frequency of 1 THz), compared to a reliability of 96% for twice the bandwidth, when blockages are considered.

Motivation & Objective

• Motivate the use of terahertz for wireless VR and identify key delay components.
• Introduce a novel VR delay model including processing, queuing, and downlink transmission delays.
• Derive the tail distribution of delay via moments to characterize extreme delay events.
• Apply risk-measure tools to assess the probability of unreliable user experience.
• Analyze how blockage density and molecular absorption influence reliability at terahertz frequencies.

Proposed method

• Define a VR request/response model with three delay components: processing, queuing, and downlink transmission.
• Derive the delay tail distribution using moment-based techniques to capture extreme events.
• Employ extreme value theory / risk analysis tools (e.g., CVaR-like metrics) to quantify unreliable-user-experience risk.
• Evaluate how terahertz-specific factors like blockage density and molecular absorption affect reliability in short-range links.
• Discuss implications for high-rate, low-latency wireless VR on terahertz channels.

Experimental results

Research questions

• RQ1 What is the instantaneous reliability of terahertz links for wireless VR in short-range scenarios?
• RQ2 How does the delay tail behave, and what are the probabilities of extreme delays?
• RQ3 How do blockages and molecular absorption impact terahertz VR reliability?
• RQ4 Can risk-measure frameworks quantify the likelihood of an unreliable VR experience at terahertz frequencies?

Key findings

• The delay tail distribution is derived via moments to characterize extreme delay events.
• The analysis provides insights on terahertz potential within short communication ranges given high susceptibility to blockages and molecular absorption.
• The study uses risk measures to examine the risk of unreliable user experience at terahertz frequencies.
• The results indicate that delay reliability is influenced by the density of blockages and molecular absorption, as captured by the proposed model.
• The framework enables assessment of instantaneous reliability for terahertz-based wireless VR.