Comparison of Orthogonal vs. Union of Subspace Based Pilots for Multi-Cell Massive MIMO Systems

Chowdhury, Anubhab; Sasmal, Pradip; Murthy, Chandra R.

doi:10.1109/spawc48557.2020.9154341

Cited by 4 publications

(5 citation statements)

References 10 publications

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“…We can now estimate the channel f mk using ẏp,m . We have the following result from [29]. The linear minimum mean squared error (LMMSE) estimate of f mk , denoted as fmk , can be evaluated as…”

Section: Signaling Model and Channel Estimationmentioning

confidence: 99%

“…The problem of pilot allocation in a CF-mMIMO system is fundamentally different from similar problems encountered in the cellular version. In cellular mMIMO systems, we can avoid intra-cell pilot contamination by allotting orthogonal pilots to all the UEs within each cell [29]. Also, in cellular systems, only the serving BS estimates the channel for each UE.…”

Section: Pilot Allocationmentioning

confidence: 99%

“…The first term in (29) equates to (12b). The second term together with the nth UE's beamforming uncertainty corresponds to (12a), and (12c) follows from E g nk 2 = nk .…”

Section: Appendix a Proof Of Theoremmentioning

confidence: 99%

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Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Chowdhury

Chopra

Murthy

2022

IEEE Trans. Commun.

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We consider a dynamic time division duplex (DTDD) enabled cell-free massive multiple-input multipleoutput (CF-mMIMO) system, where each half-duplex (HD) access point (AP) is scheduled to operate in the uplink (UL) or downlink (DL) mode based on the data demands of the user equipments (UEs), with the goal of maximizing the sum UL-DL spectral efficiency (SE). We develop a new, low complexity, greedy algorithm for the combinatorial AP scheduling problem, with an optimality guarantee theoretically established via showing that a lower bound of the sum UL-DL SE is sub-modular.We also consider pilot sequence reuse among the UEs to limit the channel estimation overhead. In CF systems, all the APs estimate the channel from every UE, making pilot allocation problem different from the cellular case. We develop a novel algorithm that iteratively minimizes the maximum pilot contamination across the UEs. We compare the performance of our solutions, both theoretically and via simulations, against a full duplex (FD) multi-cell mMIMO system. Our results show that, due to the joint processing of the signals at the central processing unit, CF-mMIMO with dynamic HD AP-scheduling significantly outperforms cellular FD-mMIMO in terms of the sum SE and 90% likely SE. Thus, DTDD enabled HD CF-mMIMO is a promising alternative to cellular FD-mMIMO, without the cost of hardware for self-interference suppression.

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Section: Signaling Model and Channel Estimationmentioning

confidence: 99%

Section: Pilot Allocationmentioning

confidence: 99%

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Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Chowdhury

Chopra

Murthy

2022

IEEE Trans. Commun.

Self Cite

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show abstract

“…We can now estimate the channel f mk using ẏp,m . We have the following result from [23], [24]. The linear minimum mean squared error (LMMSE) estimate of f mk , denoted as fmk , can be evaluated as…”

Section: Signaling Model and Channel Estimationmentioning

confidence: 99%

Section: Pilot Allocationmentioning

confidence: 99%

Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Chowdhury¹,

Chopra²,

Murthy³

2021

Preprint

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We consider a dynamic time division duplex (DTDD) enabled cell-free massive multiple-input multiple-output (CF-mMIMO) system, where each half-duplex (HD) access point (AP) is scheduled to operate in the uplink (UL) or downlink (DL) mode based on the data demands of the user equipments (UEs). The goal is to maximize the sum UL-DL spectral efficiency (SE). We theoretically establish the sub-modularity of the sum SE, which allows us to develop a new, low complexity, greedy algorithm for the combinatorial AP scheduling problem, with guaranteed optimality properties. We also consider pilot sequence reuse among the UEs to limit the channel estimation overhead. In CF systems, all the APs estimate the channel from every UE, making pilot allocation problem different from the cellular case. We develop a novel algorithm that iteratively minimizes the maximum pilot contamination across the UEs.We compare our solutions, both theoretically and via simulations, against a full duplex (FD) multi-cell mMIMO system. Our results show that, due to the joint processing of the signals at the central processing unit, CF-mMIMO with dynamic HD AP-scheduling significantly outperforms cellular FD-mMIMO in terms of the sum SE and 90% likely SE. Thus, DTDD enabled HD CF-mMIMO is a promising alternative to cellular FD-mMIMO, without the cost of hardware for self-interference suppression.

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Dynamic TDD Enabled Distributed Antenna Array Massive MIMO System

Chowdhury

Murthy

Chopra

2022

2022 IEEE 12th Sensor Array and Multichannel Signal Processing Workshop (SAM)

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Comparison of Orthogonal vs. Union of Subspace Based Pilots for Multi-Cell Massive MIMO Systems

Cited by 4 publications

References 10 publications

Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

Dynamic TDD Enabled Distributed Antenna Array Massive MIMO System

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