Addressing the hidden terminal problem in MU-MIMO WLANs with relaxed zero-forcing approach

Shrestha, Sanjeeb

Addressing the hidden terminal problem in MU-MIMO WLANs with relaxed zero-forcing approach

Shrestha, Sanjeeb

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Publication Type:: Thesis
Issue Date:: 2017

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Field	Value	Language
dc.contributor.author	Shrestha, Sanjeeb
dc.date.accessioned	2017-09-11T23:22:20Z
dc.date.available	2017-09-11T23:22:20Z
dc.date.issued	2017
dc.identifier.uri	http://hdl.handle.net/10453/116766
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_AU
dc.description.abstract	An ever-increasing data rate demand, mainly due to the proliferation of numerous smart devices, enterprises’ mission critical networks, and industry automation, has mounted tremendous pressure on today’s Wireless Local Area Networks (WLANs). Several avenues such as bandwidth, constellation density, the Multiple Input Multiple Output (MIMO) technique, etc., have been explored, e.g., IEEE802.11n/ac standards, to keep up with the demand. Future WLAN standard, e.g., IEEE802.11ax, with potential technologies such as uplink Multi-User (MU)-MIMO, full duplex transmission, etc., is anticipated by 2019. Having said that, there has been a strong emphasis on solving the technical issues with WLANs along with the addition of new frontiers in order to cope with the data rate demanded. One such appending decade-long issue is the inevitable Hidden Terminal (HT) problem in a distributive, decentralised and densely deployed WLANs, which fundamentally arises because of the transmission time overlaps between different transmitters operating at a particular frequency. The consequence is that it causes collisions of signals, which sharply reduces the system throughput. In the context of MU-MIMO based WLANs, several designs for a general network scenario, without the consideration of the HT problem, have been proposed, bringing efficiency by avoiding the collision of signals. However, a dedicated design, which could effectively address the HT problem in MU-MIMO WLANs and also become interoperable (with legacy standards) and feasible with existing hardware, is lacking to the best of our knowledge. In this thesis, we propose a solution for the HT problem which has three fundamental attributes. First, a) at the Physical (PHY) layer, the Zero-forcing (ZF) transmission strategy with fairness and throughput aware precoding is proposed, b) a hybrid scheduling scheme, combining the packet position-based First In First Out (FIFO) and channel quality-based scheme, namely the Best of the Two Choices, is designed, c) at the Medium Access Control (MAC) layer, Degrees-of-Freedom (DoF) based Transmission Opportunity (TXOP) for Access Points (APs) is developed which is backed by an extended Point Coordination Function (PCF), d) an explicit channel acquisition framework is proposed for ZF which has a reduced signaling time overhead of 98.6740 μs compared to IEEE802.11ac. e) performance evaluation methodologies are: i) hardware testbed results of the PHY strategy, which shows a received SNR gain of about 6 dB on average, and about 10 dB in comparison to the HT scenario, ii) simulation results of the MAC design, which shows a constant throughput gain of 4 − 5 times w.r.t. the popular Request to Send/Clear to Send (RTS/CTS) solution. Second, to address the interoperability issue, we purposefully use the standard frame format except for some required logical changes. Notably, the transition mechanism of our design, and for any MAC that uses standard frame formats, is investigated meticulously. The transition condition, transition steps and transition frame formats are detailed. Third, to address a practical constraint of an imperfect Channel State Information (CSI) at APs, a) we incorporate the Finite Rate Feedback (FRF) model in our solution. The effects on system parameters such as quantisation error bounds, throughput loss w.r.t. perfect CSI, etc., are discussed with closed-form analytical expressions, b) instead of an ideal ZF technique, a Relaxed ZF (RZF) framework is considered, in which the interference and power constraints of the optimisation problem are relaxed to the interference upper bound and to the maximum transmit power respectively. Our results lead to a distributive algorithm for calculating the optimal ZF precoding vector which suits the distributive, decentralised and uncoordinated nature of MU-MIMO WLANs.	en_AU
dc.format	Thesis (PhD)
dc.language.iso	en_AU	en_AU
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/116766/2/02whole.pdf
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	au.edu.uts.lib/ppc
dc.rights	info:eu-repo/semantics/openAccess
dc.source	Optimal ZF precoding vector .	en
dc.subject	Wireless Local Area Networks (WLANs)	en
dc.subject	IEEE802.11n/ac standards.	en
dc.subject	Future IEEE802.11ax standards.	en
dc.subject	Uplink Multi-User (MU)-MIMO.	en
dc.subject	Collisions of signals.	en
dc.subject	ZF technique.	en
dc.subject	Relaxed ZF (RZF) framework.	en
dc.title	Addressing the hidden terminal problem in MU-MIMO WLANs with relaxed zero-forcing approach	en_AU
dc.type	Thesis	en_AU
utslib.copyright.status	open_access

Abstract:

An ever-increasing data rate demand, mainly due to the proliferation of numerous smart devices, enterprises’ mission critical networks, and industry automation, has mounted tremendous pressure on today’s Wireless Local Area Networks (WLANs). Several avenues such as bandwidth, constellation density, the Multiple Input Multiple Output (MIMO) technique, etc., have been explored, e.g., IEEE802.11n/ac standards, to keep up with the demand. Future WLAN standard, e.g., IEEE802.11ax, with potential technologies such as uplink Multi-User (MU)-MIMO, full duplex transmission, etc., is anticipated by 2019. Having said that, there has been a strong emphasis on solving the technical issues with WLANs along with the addition of new frontiers in order to cope with the data rate demanded. One such appending decade-long issue is the inevitable Hidden Terminal (HT) problem in a distributive, decentralised and densely deployed WLANs, which fundamentally arises because of the transmission time overlaps between different transmitters operating at a particular frequency. The consequence is that it causes collisions of signals, which sharply reduces the system throughput. In the context of MU-MIMO based WLANs, several designs for a general network scenario, without the consideration of the HT problem, have been proposed, bringing efficiency by avoiding the collision of signals. However, a dedicated design, which could effectively address the HT problem in MU-MIMO WLANs and also become interoperable (with legacy standards) and feasible with existing hardware, is lacking to the best of our knowledge. In this thesis, we propose a solution for the HT problem which has three fundamental attributes. First, a) at the Physical (PHY) layer, the Zero-forcing (ZF) transmission strategy with fairness and throughput aware precoding is proposed, b) a hybrid scheduling scheme, combining the packet position-based First In First Out (FIFO) and channel quality-based scheme, namely the Best of the Two Choices, is designed, c) at the Medium Access Control (MAC) layer, Degrees-of-Freedom (DoF) based Transmission Opportunity (TXOP) for Access Points (APs) is developed which is backed by an extended Point Coordination Function (PCF), d) an explicit channel acquisition framework is proposed for ZF which has a reduced signaling time overhead of 98.6740 μs compared to IEEE802.11ac. e) performance evaluation methodologies are: i) hardware testbed results of the PHY strategy, which shows a received SNR gain of about 6 dB on average, and about 10 dB in comparison to the HT scenario, ii) simulation results of the MAC design, which shows a constant throughput gain of 4 − 5 times w.r.t. the popular Request to Send/Clear to Send (RTS/CTS) solution. Second, to address the interoperability issue, we purposefully use the standard frame format except for some required logical changes. Notably, the transition mechanism of our design, and for any MAC that uses standard frame formats, is investigated meticulously. The transition condition, transition steps and transition frame formats are detailed. Third, to address a practical constraint of an imperfect Channel State Information (CSI) at APs, a) we incorporate the Finite Rate Feedback (FRF) model in our solution. The effects on system parameters such as quantisation error bounds, throughput loss w.r.t. perfect CSI, etc., are discussed with closed-form analytical expressions, b) instead of an ideal ZF technique, a Relaxed ZF (RZF) framework is considered, in which the interference and power constraints of the optimisation problem are relaxed to the interference upper bound and to the maximum transmit power respectively. Our results lead to a distributive algorithm for calculating the optimal ZF precoding vector which suits the distributive, decentralised and uncoordinated nature of MU-MIMO WLANs.

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