Multipair Two-Way DF Relaying with Cell-Free Massive MIMO

TL;DR

This work considers a two-way half-duplex decode-and-forward relaying system with multiple pairs of single-antenna users assisted by a cell-free (CF) massive multiple-input multiple-output (mMIMO) architecture with multiple-antennas access points (APs).

Abstract

We consider a two-way half-duplex decode-and-forward (DF) relaying system with multiple pairs of single-antenna users assisted by a cell-free (CF) massive multiple-input multiple-output (mMIMO) architecture with multiple-antenna access points (APs). Under the practical constraint of imperfect channel state information (CSI), we derive the achievable sum spectral efficiency (SE) for a finite number of APs with maximum ratio (MR) linear processing for both reception and transmission in closed-form. Notably, the proposed CF mMIMO relaying architecture, exploiting the spatial diversity, and providing better coverage, outperforms the conventional collocated mMIMO deployment. Moreover, we shed light on the power-scaling laws maintaining a specific SE as the number of APs grows. A thorough examination of the interplay between the transmit powers per pilot symbol and user/APs takes place, and useful conclusions are extracted. Finally, differently to the common approach for power control in CF mMIMO systems, we design a power allocation scheme maximizing the sum SE.

Figures (8)

• Figure 1: A multipair two-way CF mMIMO relaying network with $M$ multi-antenna APs and $W$ user pairs.
• Figure 2: Sum SE per versus the uplink transmit power $p_{\mathrm{p}} =p_{\mathrm{u}}$ for varying number of APs $M$ with validation by Monte-Carlo simulations ($N=3$, $W=5$, and $p_{\mathrm{r}}=2 W p_{\mathrm{u}}$).
• Figure 3: Sum SE versus the number of APs $M$ for different scenarios ($N=3$, $p_{\mathrm{p}}= p_{\mathrm{u}}$, and $p_{\mathrm{r}}=2 W p_{\mathrm{u}}$), when (a) $W=5$ and (b) $W=20$ user pairs.
• Figure 4: Sum SE versus the number of APs $M$ by means of asymptotic (Scenario A) and exact analysis (Theorem \ref{['theoremTotalSE']}) for $N=3$, $W=5$, $p_{\mathrm{p}}= {E_{\mathrm{p}}}/{M^{\alpha} }$ with $E_{\mathrm{p}}= 10~\mathrm{dB}$.
• Figure 5: Sum SE versus the number of APs $M$ by means of asymptotic (Scenario B) and exact analysis (Theorem \ref{['theoremTotalSE']}) for $N=3$, $W=5$, $p_{\mathrm{u}}= {E_{\mathrm{u}}}/{M^{\beta} }$ with $E_{\mathrm{u}}= 10~\mathrm{dB}$, and $p_{\mathrm{r}}= {E_{\mathrm{r}}}/{M^{\gamma} }$ with $E_{\mathrm{r}}= 10~\mathrm{dB}$ (finite limits).

Theorems & Definitions (12)

• Theorem 1
• proof
• Proposition 1
• Proposition 2
• Corollary 1
• Corollary 2
• Corollary 3
• Proposition 3
• Corollary 4
• Corollary 5