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Exploiting Semantic Communication for Non-Orthogonal Multiple Access

Xidong Mu, Yuanwei Liu

TL;DR

This work investigates a semantics-empowered two-user uplink NOMA system in which a primary near user uses BitCom and a secondary far user uses SemCom. It characterizes the SvB rate region and demonstrates that SemCom can boost the secondary user’s performance at low transmit power while incurring limits at high power, motivating an opportunistic scheme over fading channels. The scheme dynamically selects SemCom or BitCom per fading state and optimizes power and time allocation under a primary user rate constraint, using Lagrangian duality to derive optimal policies in two scenarios (on-off and continuous resource management). Numerical results show the proposed scheme outperforms solely SemCom or BitCom baselines, especially when the primary user has stringent rate requirements, and highlight the importance of continuous power control over time scheduling for fading channels.

Abstract

A novel semantics-empowered two-user uplink non-orthogonal multiple access (NOMA) framework is proposed for resource efficiency enhancement. More particularly, a secondary far user (F-user) employs the semantic communication (SemCom) while a primary near user (N-user) employs the conventional bit-based communication (BitCom). The fundamental performance limit, namely semantic-versus-bit (SvB) rate region, of the proposed semantics-empowered NOMA framework is characterized. The equivalent SvB rate region achieved by the conventional BitCom-based NOMA is provided as the baseline scheme. It unveils that, compared to BitCom, SemCom can significantly improve the F-user's performance when its permitted transmit power is strictly capped, but may perform worse when its permitted transmit power is high. Guided by this result, the proposed semantics-empowered NOMA framework is investigated over fading channels. An opportunistic SemCom and BitCom scheme is proposed, which enables the secondary F-user to participate in NOMA via the most suitable communication method at each fading state, thus striking a good tradeoff between its own achieved performance and the interference imposed to the primary N-user. Two scenarios are considered for employing the opportunistic scheme, namely on-off resource management and continuous resource management. For each scenario, the optimal communication policy over fading channels is derived for maximizing the ergodic semantic rate achieved at the secondary F-user, subject to the minimum ergodic bit rate constraint of the primary N-user. Numerical results show that the proposed opportunistic scheme in both scenarios can achieve higher communication performance for NOMA than the baseline schemes merely employing SemCom or BitCom.

Exploiting Semantic Communication for Non-Orthogonal Multiple Access

TL;DR

This work investigates a semantics-empowered two-user uplink NOMA system in which a primary near user uses BitCom and a secondary far user uses SemCom. It characterizes the SvB rate region and demonstrates that SemCom can boost the secondary user’s performance at low transmit power while incurring limits at high power, motivating an opportunistic scheme over fading channels. The scheme dynamically selects SemCom or BitCom per fading state and optimizes power and time allocation under a primary user rate constraint, using Lagrangian duality to derive optimal policies in two scenarios (on-off and continuous resource management). Numerical results show the proposed scheme outperforms solely SemCom or BitCom baselines, especially when the primary user has stringent rate requirements, and highlight the importance of continuous power control over time scheduling for fading channels.

Abstract

A novel semantics-empowered two-user uplink non-orthogonal multiple access (NOMA) framework is proposed for resource efficiency enhancement. More particularly, a secondary far user (F-user) employs the semantic communication (SemCom) while a primary near user (N-user) employs the conventional bit-based communication (BitCom). The fundamental performance limit, namely semantic-versus-bit (SvB) rate region, of the proposed semantics-empowered NOMA framework is characterized. The equivalent SvB rate region achieved by the conventional BitCom-based NOMA is provided as the baseline scheme. It unveils that, compared to BitCom, SemCom can significantly improve the F-user's performance when its permitted transmit power is strictly capped, but may perform worse when its permitted transmit power is high. Guided by this result, the proposed semantics-empowered NOMA framework is investigated over fading channels. An opportunistic SemCom and BitCom scheme is proposed, which enables the secondary F-user to participate in NOMA via the most suitable communication method at each fading state, thus striking a good tradeoff between its own achieved performance and the interference imposed to the primary N-user. Two scenarios are considered for employing the opportunistic scheme, namely on-off resource management and continuous resource management. For each scenario, the optimal communication policy over fading channels is derived for maximizing the ergodic semantic rate achieved at the secondary F-user, subject to the minimum ergodic bit rate constraint of the primary N-user. Numerical results show that the proposed opportunistic scheme in both scenarios can achieve higher communication performance for NOMA than the baseline schemes merely employing SemCom or BitCom.
Paper Structure (33 sections, 40 equations, 10 figures, 1 algorithm)

This paper contains 33 sections, 40 equations, 10 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Motivations and Contributions
  4. Organization
  5. Semantics-empowered NOMA: Potentials and Limits
  6. System Model
  7. Achieved bit rate at the N-user
  8. Achieved semantic rate at the F-user
  9. Achieved semantic-versus-bit rate region
  10. Performance Comparison
  11. SemCom v.s. BitCom
  12. Numerical Examples
  13. An Opportunistic SemCom and BitCom Scheme over Fading Channels
  14. Communication Model
  15. BitCom at the N-user
  16. ...and 18 more sections

Figures (10)

  • Figure 1: The illustration of the proposed semantics-empowered two-user uplink NOMA framework, where the primary N-user employs BitCom for uploading information and the secondary F-user tries to reuse the N-user's resource block to upload information with the aid of SemCom.
  • Figure 2: SvB rate region comparison of the proposed semantics-empowered NOMA and conventional BitCom-based NOMA.
  • Figure 3: The semantics-empowered two-user uplink NOMA over the fading channel, where the secondary F-user employs an opportunistic SemCom and BitCom scheme for each fading state.
  • Figure 4: The proposed opportunistic SemCom and BitCom scheme in two scenarios.
  • Figure 5: The achieved ergodic semantic rate of the F-user versus $\overline R$ in Scenario I.
  • ...and 5 more figures