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OTFS-MDMA: An Elastic Multi-Domain Resource Utilization Mechanism for High Mobility Scenarios

Jie Chen, Xianbin Wang, Lajos Hanzo

TL;DR

This work conceive an elastic multi-domain resource utilization mechanism for a novel multi-user OTFS-MDMA system by leveraging user-specific channel characteristics across the DD, power, and spatial resource domains and develops a dynamic programming and monotonic optimization (DPMO) method to find the globally optimal solution.

Abstract

By harnessing the delay-Doppler (DD) resource domain, orthogonal time-frequency space (OTFS) substantially improves the communication performance under high-mobility scenarios by maintaining quasi-time-invariant channel characteristics. However, conventional multiple access (MA) techniques fail to efficiently support OTFS in the face of diverse communication requirements. Recently, multi-dimensional MA (MDMA) has emerged as a flexible channel access technique by elastically exploiting multi-domain resources for tailored service provision. Therefore, we conceive an elastic multi-domain resource utilization mechanism for a novel multi-user OTFS-MDMA system by leveraging user-specific channel characteristics across the DD, power, and spatial resource domains. Specifically, we divide all DD resource bins into separate subregions called DD resource slots (RSs), each of which supports a fraction of users, thus reducing the multi-user interference. Then, the most suitable MA, including orthogonal, non-orthogonal, or spatial division MA (OMA/ NOMA/ SDMA), will be selected with each RS based on the interference levels in the power and spatial domains, thus enhancing the spectrum efficiency. Then, we jointly optimize the user assignment, access scheme selection, and power allocation in all DD RSs to maximize the weighted sum-rate subject to their minimum rate and various practical constraints. Since this results in a non-convex problem, we develop a dynamic programming and monotonic optimization (DPMO) method to find the globally optimal solution in the special case of disregarding rate constraints. Subsequently, we apply a low-complexity algorithm to find sub-optimal solutions in general cases.

OTFS-MDMA: An Elastic Multi-Domain Resource Utilization Mechanism for High Mobility Scenarios

TL;DR

This work conceive an elastic multi-domain resource utilization mechanism for a novel multi-user OTFS-MDMA system by leveraging user-specific channel characteristics across the DD, power, and spatial resource domains and develops a dynamic programming and monotonic optimization (DPMO) method to find the globally optimal solution.

Abstract

By harnessing the delay-Doppler (DD) resource domain, orthogonal time-frequency space (OTFS) substantially improves the communication performance under high-mobility scenarios by maintaining quasi-time-invariant channel characteristics. However, conventional multiple access (MA) techniques fail to efficiently support OTFS in the face of diverse communication requirements. Recently, multi-dimensional MA (MDMA) has emerged as a flexible channel access technique by elastically exploiting multi-domain resources for tailored service provision. Therefore, we conceive an elastic multi-domain resource utilization mechanism for a novel multi-user OTFS-MDMA system by leveraging user-specific channel characteristics across the DD, power, and spatial resource domains. Specifically, we divide all DD resource bins into separate subregions called DD resource slots (RSs), each of which supports a fraction of users, thus reducing the multi-user interference. Then, the most suitable MA, including orthogonal, non-orthogonal, or spatial division MA (OMA/ NOMA/ SDMA), will be selected with each RS based on the interference levels in the power and spatial domains, thus enhancing the spectrum efficiency. Then, we jointly optimize the user assignment, access scheme selection, and power allocation in all DD RSs to maximize the weighted sum-rate subject to their minimum rate and various practical constraints. Since this results in a non-convex problem, we develop a dynamic programming and monotonic optimization (DPMO) method to find the globally optimal solution in the special case of disregarding rate constraints. Subsequently, we apply a low-complexity algorithm to find sub-optimal solutions in general cases.
Paper Structure (28 sections, 1 theorem, 57 equations, 12 figures, 1 table, 3 algorithms)

This paper contains 28 sections, 1 theorem, 57 equations, 12 figures, 1 table, 3 algorithms.

Table of Contents

  1. Introduction
  2. System Model
  3. DD Domain User Accommodation
  4. OTFS Transmission Signal Model
  5. Channel Model
  6. OTFS Reception Signal Model
  7. Problem Formulation: Weighted Sum-Rate Maximization
  8. Communication Performance Derivations
  9. Transmission Rate by NOMA
  10. Transmission Rate by SDMA/OMA
  11. Weighted Sum-Rate in Each RS
  12. Weighted Sum-Rate Maximization
  13. Optimal Solution to The Special Case: Without Rate Constraints
  14. Dynamic Programming Recursion Framework
  15. Preliminaries of MO and Problem Transformation
  16. ...and 13 more sections

Key Result

Lemma 1

raviteja2018practical: Let ${\bf{G}} = {\rm{circ}}\left[ {{{\bf{G}}_0},{{\bf{G}}_1}, \cdots {{\bf{G}}_{N - 1}}} \right]\in{\mathbb C}^{NM\times NM}$ be a block circulant matrix, where ${\bf G}_n\in{\mathbb C}^{M\times M}$ for $0\le n\le N-1$. Then, ${\bf{G}}$ can be re-expressed by a block diagonal where ${{{\bm \Theta} _i} = \sum\limits_{n = 0}^{N - 1} {{{\bf{G}}_n}{e^{ - {\rm{j2}}\pi \frac{{ni}

Figures (12)

  • Figure 1: DD domain user accommodation by MDMA
  • Figure 2: DD domain division with $R=9$ resource slots (RSs), each of which includes ${\left| {{{{\cal R}}_r}} \right|}=\delta_M\delta_N=4$ resource bins
  • Figure 4: Steps in one iteration
  • Figure 5: Box refinement in each iteration
  • Figure 7: The weighted sum-rate of all users versus transmission power without considering QoS constraint: $Q=3$, $D=10$, $M=2$, $N=4$, $\delta_M=1$, and $\delta_N=2$.
  • ...and 7 more figures

Theorems & Definitions (2)

  • Remark 1
  • Lemma 1