@article {TWC_Khalid_19,
	title = {Low-Complexity User Selection Algorithm for Multiuser Transmission in mmWave WLANs},
	journal = {IEEE Trans. on Wireless Communications},
	year = {Submitted},
	publisher = {IEEE},
	abstract = {In this paper, we propose a low-complexity user selection algorithm for an uplink multiuser transmission in millimeter wave (mmWave) WLAN. We first formulate the user selection problem, taking hybrid beamforming (HBF), an NP-hard problem, into consideration. We then develop a three-step HBF algorithm that incorporates user selection. Specifically, users can be selected based on semi-orthogonality instead of collecting perfect channel state information (CSI) from all potential users. We optimize the digital beamforming to mitigate residual interference among the selected users. Furthermore, we provide analytical validation for the proposed user selection algorithm and study the impact of angle correlation, analog beam pattern, and beamwidth on the achievable rate of the selected users. Extensive simulations validate the performance of the proposed overall HBF algorithm when compared with existing solutions.},
	author = {Aldubaikhy, Khalid and Wu, Wen and Ye, Qiang and Shen, Xuemin}
}
@article {WC_Khalid_19,
	title = {MmWave IEEE 802.11ay for 5G Fixed Wireless Access},
	journal = {IEEE Wireless Communications},
	year = {Accepted},
	publisher = {IEEE},
	abstract = {Fixed wireless access (FWA) utilizing both licensed and unlicensed millimeter wave (mmWave) spectrum is considered as a key technology that can lead to the early deployment of the fifth-generation new-radio (5G-NR) networks. The 5G FWA can provide easy installation of network infrastructure and ubiquitous high-speed Internet access at low cost compared to the conventional broadband fixed access networks. In this article, we investigate the mmWave distribution network (mDN) use case that has been standardized recently by the IEEE 802.11ay standard as an alternative 5G FWA solution. Specifically, we provide a comprehensive tutorial view of the considered new protocol specifications and design elements of the mDN. We also highlight some challenging research issues in the field of the mDN. Finally, we provide a case study based on the investigation of the mDN where a low-complexity concurrent transmission protocol is proposed to enhance the network performance while mitigating the interference.},
	author = {Aldubaikhy, Khalid and Wu, Wen and Zhang, Ning and Cheng, Nan and Shen, Xuemin}
}
@article {8632712,
	title = {Beef up mmWave Dense Cellular Networks with D2D-Assisted Cooperative Edge Caching},
	journal = {IEEE Transactions on Vehicular Technology},
	year = {2019},
	pages = {1-1},
	abstract = {Edge caching is emerging as the most promising solution to reduce the content retrieval delay and relieve the huge burden on the backhaul links in the ultra-dense networks by proactive caching popular contents in the small base station (SBS). However, constraint cache resource of individual SBSs significantly throttles the performance of edge caching. In this paper, we propose a device-to-device (D2D) assisted cooperative edge caching (DCEC) policy for millimeter (mmWave) dense networks, which cooperatively utilizes the cache resource of users and SBSs in proximity. In the proposed DCEC policy, a content can be cached in either users{\textquoteright} devices or SBSs according to the content popularity, and a user can retrieve the requested content from neighboring users via D2D links or the neighboring SBSs via cellular links to efficiently exploit the cache diversity. Unlike existing cooperative caching policies in the lower frequency bands that require complex interference management techniques to suppress interference, we take advantage of directional antenna in mmWave systems to ensure high transmission rate whereas mitigating interference footprint. Taking the practical directional antenna model and the network density into consideration, we derive closed-form expressions of the backhaul offloading performance and content retrieval delay based on the stochastic information of network topology. In addition, analytical results indicate that, with the increase of the network density, the content retrieval delay via D2D links increases significantly while that via cellular links increases slightly. Comprehensive simulations validate our theoretical analysis and demonstrate that the proposed policy can achieve higher performance in offloading the backhaul traffic and reducing the content retrieval delay compared with the state-of-the-art most popular caching (MPC) policy.},
	keywords = {Cooperative caching, cooperative edge caching, D2D communication, Delays, Device-to-device communication, Directional antennas, Interference, mmWave dense network, Network topology, Stochastic processes},
	issn = {0018-9545},
	doi = {10.1109/TVT.2019.2896906},
	url = {https://ieeexplore.ieee.org/document/8632712},
	author = {W. Wu and N. Zhang and N. Cheng and Y. Tang and K. Aldubaikhy and X. Shen}
}
@mastersthesis {22176,
	title = {Low-Complexity Multi-User MIMO Algorithms for mmWave WLANs},
	year = {2019},
	type = {PhD thesis},
	abstract = {Very high throughput and high-efficiency wireless local area networks (WLANs) have become essential for today{\textquoteright}s significant global Internet traffic and the expected significant global increase of public WiFi hotspots. Total Internet traffic is predicted to expand 3.7-fold from 2017 to 2022. In 2017, 53\% of overall Internet traffic used by WiFi networks, and that number is expected to increase to 56.8\% by 2022. Furthermore, 80\% of overall Internet traffic is expected to be video traffic by 2022, up from 70\% in 2017. WiFi networks are also expected to move towards denser deployment scenarios, such as stadiums, large office buildings, and airports, with very high data rate applications, such as ultra-high definition video wireless streaming. Thus, in order to meet the predicted growth of wireless traffic and the number of WiFi networks in the world, an efficient Internet access solution is required for the current IEEE 802.11 standards.\&nbsp;Millimeter wave (mmWave) communication technology is expected to play a crucial role in future wireless networks with large user populations because of the large spectrum band it can provide. To further improve spectrum efficiency over mmWave bands in WLANs with large numbers of users, the IEEE 802.11ay standard was developed from the traditional IEEE 802.11ad standard, aiming to support multi-user MIMO. Propagation challenges associated with mmWave bands necessitate the use of analog beamforming (BF) technologies that employ directional transmissions to determine the optimal sector beam between a transmitter and a receiver. However, the multi-user MIMO is not exploited, since analog BF is limited to a single-user, single-transmission. The computational complexity of achieving traditional multi-user MIMO BF methods, such as full digital BF, in the mmWave systems becomes significant due to the hardware constraints. Our research focuses on how to effectively and efficiently realize multi-user MIMO transmission to improve spectrum efficiency over the IEEE 802.11ay mmWave band system while also resolving the computational complexity challenges for achieving a multi-user MIMO in mmWave systems. This thesis focuses on MAC protocol algorithms and analysis of the IEEE 802.11ay mmWave WLANs to provide multi-user MIMO support in various scenarios to improve the spectrum efficiency and system throughput. Specifically, from a downlink single-hop scenario perspective, a VG algorithm is proposed to schedule simultaneous downlink transmission links while mitigating the multi-user interference with no additional computational complexity. From a downlink multi-hop scenario perspective, a low-complexity MHVG algorithm is conducted to realize simultaneous transmissions and improve the network performance by taking advantage of the spatial reuse in a dense network. The proposed MHVG algorithm permits simultaneous links scheduling and mitigates both the multi-user interference and co-channel interference based only on analog BF information, without the necessity for feedback overhead, such as channel state information (CSI). From an uplink scenario perspective, a low-complexity user selection algorithm, HBF-VG, incorporates user selection with the HBF algorithm to achieve simultaneous uplink transmissions for IEEE 802.11ay mmWave WLANs. With the HBF-VG algorithm, the users can be selected based on an orthogonality criterion instead of collecting CSI from all potential users. We optimize the digital BF to mitigate the residual interference among selected users. Extensive analytical and simulation evaluations are provided to validate the performance of the proposed algorithms with respect to average throughput per time slot, average network throughput, average sum-rate, energy efficiency, signal-to-interference-plus-noise ratio (SINR), and spatial multiplexing gain.},
	author = {Khalid Aldubaikhy}
}
@conference {wu2018enhance,
	title = {Enhance the edge with beamforming: Performance analysis of beamforming-enabled WLAN},
	booktitle = {Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 2018 16th International Symposium on},
	year = {2018},
	pages = {1{\textendash}6},
	publisher = {IEEE},
	organization = {IEEE},
	abstract = {The ultra-dense edge networks with mmWave and beamforming are envisioned as a potential solution to satisfy the high rate and capacity requirements in 5G networks. In IEEE 802.11 ad, which is the first beamforming-enabled WLAN standard, all stations (STs) contend for beamforming (BF) training opportunities in associated beamforming training (A-BFT) slots. However, due to limited number of A-BFT slots, BF training suffers from a severe collision issue, especially in dense networks, which results in a low channel utilization in the A-BFT stage. To achieve the maximum channel utilization, it is of significance to allocate A-BFT slots efficiently. Therefore, in this paper, we propose an analytical model to analyze IEEE 802.11 ad medium access control (MAC) protocol in BF training stage. In particular, we analyze the successful transmission probability and channel utilization of IEEE 802.11 ad MAC protocol in the dense network. Based on theoretical analysis, we provide the optimal number of A-BFT slots. In addition, theoretical analysis indicates that the maximum channel utilization in the A-BFT stage is barely e<sup>-1</sup>\&nbsp;which is the same as that of slotted ALOHA protocol. Simulation results are provided to validate the accuracy of the analytical model and theoretical analysis.},
	url = {https://ieeexplore.ieee.org/document/8362872},
	author = {Wu, Wen and Shen, Qinghua and Aldubaikhy, Khalid and Cheng, Nan and Zhang, Ning and Shen, Xuemin Sherman}
}
@conference {15170,
	title = {HBF-PDVG: Hybrid beamforming and user selection for UL MU-MIMO mmWave systems},
	booktitle = {IEEE Global Communications Conference (Globecom)},
	year = {2018},
	month = {Dec. 2018},
	pages = {1-6},
	publisher = {IEEE},
	organization = {IEEE},
	abstract = {In this paper, a novel hybrid beamforming (HBF)\&nbsp;design utilizing a pre-defined virtual grouping (PDVG) algorithm\&nbsp;is proposed for the uplink (UL) multi-user (MU) multiple-input\&nbsp;multiple-output (MIMO) millimeter wave (mmWave) systems. The\&nbsp;computational complexity of achieving traditional MU-MIMO\&nbsp;beamforming (BF) methods in the mmWave systems becomes\&nbsp;significant due to the hardware constraints. Thus, the proposed\&nbsp;HBF-PDVG algorithm aims to reduce the feedback overhead\&nbsp;by employing a three-phase algorithm. The essential idea is to\&nbsp;perform the user selection independently from the HBF design\&nbsp;by utilizing the PDVG algorithm after completing the analog\&nbsp;BF training and then mitigating the remaining MU interference\&nbsp;among the selected users using digital BF. Simulation results\&nbsp;demonstrate the significant sum-rate benefits of the HBF-PDVG\&nbsp;algorithm compared with zero-forcing (ZF) and random selection\&nbsp;algorithm methods.},
	url = {https://ieeexplore.ieee.org/document/8644274},
	author = {Khalid Aldubaikhy and Wen Wu and Xuemin Sherman Shen}
}
@booklet {shen2018methods,
	title = {Methods and systems for multi-user beamforming},
	year = {2018},
	note = {US Patent App. 15/360,852},
	publisher = {Google Patents},
	author = {Shen, Xuemin and Wang, Miao and Aldubaikhy, Khalid and Aboul-Magd, Osama and Xin, Yan and Au, Kwok Shum and Sun, Sheng}
}
@conference {aldubaikhy2018simultaneous,
	title = {Simultaneous DL Transmission in mmWave Ultra Dense Networks: Inter-BSS Interference Prospective},
	booktitle = {2018 IEEE International Conference on Communications Workshops (ICC Workshops)},
	year = {2018},
	pages = {1{\textendash}6},
	publisher = {IEEE},
	organization = {IEEE},
	abstract = {In this paper, a novel multi-hop virtual grouping (MHVG) medium access control (MAC) protocol is proposed for ultra dense networks (UDN). The proposed MHVG MAC protocol enables multi-user (MU) downlink (DL) transmission for millimeter wave (mmWave) communications with the goal of enhancing system throughput and mitigating the interference. The proposed MAC permits the scheduling of simultaneous links and the mitigation of the inter- basic service sets (BSS) interference based only on analog beamforming (BF) information, without the necessity for feedback overhead, such as channel state information (CSI). The results of the evaluative simulations conducted demonstrate the superior performance offered by the proposed scheme with respect to average throughput per time slot, signal-to-interference-plus-noise ratio (SINR), and spatial multiplexing gain.},
	url = {https://ieeexplore.ieee.org/document/8403509},
	author = {Aldubaikhy, Khalid and Shen, Xuemin}
}
@proceedings {aldubaikhymac,
	title = {MAC Layer Design for Concurrent Transmissions in Millimeter Wave WLANs},
	journal = {IEEE/CIC International Conference on Communications in China (ICCC)},
	year = {2017},
	pages = {1-6},
	abstract = {High frequency and very high throughput wireless local area networks have turned to be an essential need due to the likely substantial world increase of the WiFi public hotspots and the existing internet traffic. Due to the these challenges, an efficient solution is required for the current IEEE 802.11 standards to meet the predicted growth of wireless traffic and the number of WiFi networks in the world. In this paper, practical and efficient concurrent downlink transmission medium access control (MAC) layer design is proposed for the millimeter wave wireless local area networks (WLANs) based on both the IEEE 802.11ad system and spatial multiplexing technique. Particularly, a pre-defined virtual grouping (PDVG) scheduling approach is designed to schedule concurrent downlink links based on the analog beamforming information of the IEEE 802.11ad. The PDVG approach can attain and select concurrent stations (STNs) with no additional computational overhead. We demonstrate via simulations that the proposed algorithm can enhance the throughput and save the available time of the service period (SP) for the IEEE 802.11ad, without adding extra feedback overhead to the beamforming operation time in the system.},
	url = {https://ieeexplore.ieee.org/document/8330449},
	author = {Aldubaikhy, Khalid and Shen, Qinghua and Wang, Miao and Wu, Wen and Shen, Xuemin Sherman and Aboul-Magd, Osama and Xin, Yan and Sun, Rob and AU, Edward}
}
@conference {alsharif2016link,
	title = {Link duration estimation using neural networks based mobility prediction in vehicular networks},
	booktitle = {Electrical and Computer Engineering (CCECE), 2016 IEEE Canadian Conference on},
	year = {2016},
	pages = {1{\textendash}4},
	publisher = {IEEE},
	organization = {IEEE},
	abstract = {The knowledge of Inter-vehicle link duration is an important parameter in Vehicular Ad hoc Networks (VANETs), as it is useful for vehicles to delay their information transmission if link breakage is anticipated before completing the transmission. In addition, it plays a pivotal role in routing, as it allows proactive construction of long-life paths, and optimizing next-hop selection in position-based routing (PBR). However, due to the high mobility of vehicles and the complicated vehicular mobility patterns in urban areas, the estimation of link duration in urban VANETs is still an open research issue. Different from other complex link duration estimation methods, we introduce a lightweight neural networks (NNs) based mobility prediction scheme which allows vehicles to autonomously predict their future mobility speed for a certain time window. Then, the expected speed is used in an urban area mobility prediction model to estimate link duration between neighbouring vehicles. Extensive simulation results are given to demonstrate the validity of the proposed methods.},
	url = {https://ieeexplore.ieee.org/document/7726793},
	author = {Alsharif, Nizar and Aldubaikhy, Khalid and Shen, Xuemin Sherman}
}
@mastersthesis {aldubaikhy2012differential,
	title = {Differential code-shifted reference impulse-radio ultra-wideband receiver: timing recovery and digital implementation},
	year = {2012},
	abstract = {Ultra-wideband (UWB) is a wireless system which transmits signals across a much wider frequency spectrum than traditional wireless systems. The impulse radio (IR) UWB technique uses ultra-short duration pulses of nanoseconds or less. The objective of this thesis is to provide the design, implementation and testing of the timing recovery between the transmitter and receiver of the recently emerging differential code-shifted reference (DCSR) Impulse radio (IR) ultra-wideband (UWB) system. A new non-coherent energy detection based technique and its algorithm are proposed for timing recovery by means of a phase-locked loop (PLL) circuit. Simulations are presented first to verify the proposed algorithm. Then, it is implemented and tested in the Lattice ECP2 field-programmable gate array (FPGA) evaluation board with VHDL codes (a VHSIC hardware description language). The simulation and implementation results show that the proposed timing recovery scheme can be effectively achieved without much error.},
	url = {http://hdl.handle.net/10222/15244},
	author = {Aldubaikhy, Khalid}
}
