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Enhanced Tracking and Beamforming Codebook Design for Wideband Terahertz Massive MIMO System

Xu Shi, Jintao Wang, Jian Song

Abstract

True-time-delay (TTD) lines are recently applied inside Terahertz (THz) hybrid-precoding transceiver to acquire high beamforming gain against beam squint effect. However, beam tracking turns into a challenging puzzle where enormous potential beam directions bring about unacceptable overhead consumption. Frequency-scanning-based beam tracking is initially explored but still imperfect in previous studies. In this paper, based on TTD-aided hybrid precoding structure, we give an enhanced frequency-scanning-based tracking scheme. Multiple beams are generated and utilized simultaneously via several subcarriers for tracking at one timeslot. The squint beams' angular coverage at all subcarriers can be flexibly controlled by two different subcarrier-angular mapping policies, named forward-pairing and backward-pairing. Then multiple physical directions can be simultaneously searched in one timeslot for lower overhead consumption. Besides, closed-form searching radius bound, parameter configuration and interferences are theoretically analyzed. Furthermore, we provide the coupled codebook design for TTDs and phase shifters (PSs), with joint consideration of both beamforming and tracking. Analytical and numerical results demonstrate the superiority of the new frequency-scanning-based tracking scheme and beamforming codebook.

Enhanced Tracking and Beamforming Codebook Design for Wideband Terahertz Massive MIMO System

Abstract

True-time-delay (TTD) lines are recently applied inside Terahertz (THz) hybrid-precoding transceiver to acquire high beamforming gain against beam squint effect. However, beam tracking turns into a challenging puzzle where enormous potential beam directions bring about unacceptable overhead consumption. Frequency-scanning-based beam tracking is initially explored but still imperfect in previous studies. In this paper, based on TTD-aided hybrid precoding structure, we give an enhanced frequency-scanning-based tracking scheme. Multiple beams are generated and utilized simultaneously via several subcarriers for tracking at one timeslot. The squint beams' angular coverage at all subcarriers can be flexibly controlled by two different subcarrier-angular mapping policies, named forward-pairing and backward-pairing. Then multiple physical directions can be simultaneously searched in one timeslot for lower overhead consumption. Besides, closed-form searching radius bound, parameter configuration and interferences are theoretically analyzed. Furthermore, we provide the coupled codebook design for TTDs and phase shifters (PSs), with joint consideration of both beamforming and tracking. Analytical and numerical results demonstrate the superiority of the new frequency-scanning-based tracking scheme and beamforming codebook.
Paper Structure (15 sections, 2 theorems, 57 equations, 9 figures, 2 algorithms)

This paper contains 15 sections, 2 theorems, 57 equations, 9 figures, 2 algorithms.

Table of Contents

  1. Introduction
  2. System Model
  3. Codebook Design for TTD-aided Model
  4. Enhanced Tracking
  5. Drawback of previous frequency-scanned tracking
  6. Enhanced Tracking Design
  7. Power Leakage Elimination
  8. Searching Radius Enhancement
  9. Forward-mapping tracking zooming_tracking (as comparison)
  10. Forward-Backward-Pairing Tracking (Algorithm 1)
  11. Finite-Codebook-based Tracking
  12. Simulation Results
  13. Conclusion
  14. Proof of Lemma \ref{['lemma1']}
  15. Proof of Theorem \ref{['theorem1']}

Key Result

Lemma 1

The periodic sidelobes Notice that the definitions of sidelobe and mainlobe here don't depend on the beam amplitudes but the locations in (inner_beam_property). The exact location of $\theta_{c,m}^{(2)}$ in (inner_beam_property) is defined as mainlobe while the peak location with periodic shifting i

Figures (9)

  • Figure 1: Block diagram of TTD-aided beamforming model.
  • Figure 2: The beam patterns of $\Xi_P(\cdot)$, $\Xi_{N_\text{TTD}}(\cdot)$ and final beam $\mathcal{G}$ under single subcarrier $f_{-M}$.
  • Figure 3: The tracking procedures of forward and backward pairings between subcarriers and angular values.
  • Figure 4: The beam pattern comparison of conventional forward mapping and forward-backward pairing schemes with overall $128$ subcarriers, where the central angle $\theta_0=0.8$ and searching radius $\alpha=0.08$.
  • Figure 5: The beam patterns of forward-backward pairing scheme under different searching ranges $\alpha$.
  • ...and 4 more figures

Theorems & Definitions (3)

  • Remark 1
  • Lemma 1
  • Theorem 1