Extended Reality (XR) enables a plethora of novel interactive shared experiences. Ideally, users are allowed to roam around freely, while audiovisual content is delivered wirelessly to their Head-Mounted Displays (HMDs). Therefore, truly immersive experiences will require massive amounts of data, in the range of tens of gigabits per second, to be delivered reliably at extremely low latencies. We identify Millimeter-Wave (mmWave) communications, at frequencies between 24 and 300 GHz, as a key enabler for such experiences. In this article, we show how the mmWave state of the art does not yet achieve sufficient performance, and identify several key active research directions expected to eventually pave the way for extremely-high-quality mmWave-enabled interactive multi-user XR.

Using Millimeter-Wave (mmWave) wireless communications is often named as the prime enabler for mobile interactive Extended Reality (XR), as it offers multi-gigabit data rates at millisecond-range latency. To achieve this, mmWave nodes must focus their energy towards each other, which is especially challenging in XR scenarios, where the transceiver on the user's XR device may rotate rapidly. To evaluate the feasibility of mmWave XR, we present the first throughput and latency evaluation of state-of-the-art mmWave hardware under rapid rotational motion, for different PHY and MAC-layer parameter configurations. We show that this parameter configuration has a significant impact on performance, and that specialized beamforming approaches for rapid rotational motion may be necessary to enable uninterrupted, high-quality mobile interactive XR experiences.

Achieving extremely high-quality and truly immersive interactive Virtual Reality (VR) is expected to require a wireless link to the cloud, providing multi-gigabit throughput and extremely low latency. A prime candidate for fulfilling these requirements is millimeter-wave (mmWave) communications, operating in the 30 to 300 GHz bands, rather than the traditional sub-6 GHz. Evaluations with first-generation mmWave Wi-Fi hardware, based on the IEEE 802.11ad standard, have so far largely remained limited to lower-layer metrics. In this work, we present the first experimental analysis of the capabilities of mmWave for streaming VR content, using a novel testbed capable of repeatably creating blockage through mobility. Using this testbed, we show that (a) motion may briefly interrupt transmission, (b) a broken line of sight may degrade throughput unpredictably, and (c) TCP-based streaming frameworks need careful tuning to behave well over mmWave.

Millimeter-wave technology provides the necessary improvements in capacity and performance for the next generation of wireless networks. The new IEEE 802.11ay amendment extends IEEE 802.11ad to offer 100 Gbit/s connectivity in the unlicensed 60 GHz band through technical advancements such as Multiple-Input and Multiple-Output (MIMO), channel bonding and aggregation. Additionally, it offers improvements to the Beamforming Training (BFT) process in order to increase its efficiency and accuracy. One new technique defined by IEEE 802.11ay is Group Beamforming, which allows to simultaneously train all stations, and significantly reduces training overhead, especially in very dense networks. In this paper, we provide an implementation of IEEE 802.11ay in ns-3 and perform, to the best of our knowledge, the first detailed system-level evaluation of the performance of the novel IEEE 802.11ay protocol. We specifically study the performance of Group Beamforming and compare it against the legacy 802.11ad BFT. We explore how different BFT approaches scale in large networks, identify the possible problems and evaluate at how the BFT process influences the performance of the network overall. Our analysis shows that Group Beamforming can outperform the legacy approach, resulting in lower overhead and improved network performance. However, we also found that the Access Point (AP) training is quite vulnerable to interference in dense networks, introducing severe limitations to the performance, especially in large rooms where precise BFT is crucial to maintain the communication link. Therefore, we propose several improvements to Group Beamforming that improve performance and provide robust beamforming even in very dense scenarios.

The multi-user multiple-input-multiple-output (MU-MIMO) beamforming training (BFT) enables an access point (AP) and multiple stations (STAs) to determine appropriate directional antenna patterns; to this end, the AP transmits multiple action frames to the STAs during the MU-MIMO BFT. However, if the antenna weight vectors (AWVs) are determined to transmit the action frames inefficiently, this could lead to unnecessary transmissions, which could increase the BFT time. To mitigate the signaling overhead, the schemes used in our previous work employed AWVs, which use multiple beams simultaneously to transmit the action frames. Nevertheless, these existing schemes are still adversely affected by redundant transmissions because these schemes overlook the transmit diversity gain obtained from multi-beam concurrent transmission. Therefore, in this study, we propose a novel transmit antenna configuration scheme that mitigates the signaling overhead by considering the transmit diversity of the inter-symbol interference (ISI) channel incurred when multiple beams are used simultaneously. Our proposed scheme determines each candidate antenna weight vector (AWV) using multiple beams and efficiently identifies the STAs within reach of the corresponding multi-beam concurrent transmission. The numerical and simulation results demonstrate that our proposed scheme shortens the BFT time in comparison with existing schemes.

Wireless networks operating in the 60 GHz band have the potential to provide very high throughput but face a number of challenges (e.g., high attenuation, beam training, and coping with mobility) which are widely accepted but often not well understood in practice. Understanding these challenges, and especially their actual impact on consumer-grade hardware is fundamental to fully exploit the high physical layer rates in the 60 GHz band. To this end, we perform an extensive measurement campaign using two commercial off-the-shelf 60 GHz routers in practical real-world environments. Our study is centered around two fundamental adaptation mechanisms in 60 GHz networks-beam training and rate control-whose interactions are key for performance. Understanding these interactions allows us to revisit a range of issues and provide much deeper insights into the reasons for specific performance compared to prior work on performance characterization. Further, our study goes beyond basic link characterization and explores for the first time practical considerations such as coverage and access point deployment. While some of our observations are expected, we also obtain highly surprising insights that challenge the prevailing wisdom in the community.

The IEEE Task Group ay has recently defined new physical and medium access control specifications to design the next-generation 60 GHz wireless standard IEEE 802.11ay. Built upon the predecessor IEEE 802.11ad, IEEE 802.11ay introduces various technological advancements such as Multiple-Input and Multiple-Output (MIMO) communication, channel bonding/aggregation, and new beamforming techniques to offer unprecedented performance with 100 Gbit/s of throughput and ultra-low latency. Such performance paves the way for new emerging wireless applications such as millimeter-wave distribution networks, data center inter-rack connectivity, mobile offloading, augmented reality/virtual reality, and 8K video streaming. Studying and analyzing these new use-cases is of paramount importance and demands high fidelity network-level simulator due to the scarcity and cost of real IEEE 802.11ay test-beds. In this paper, we present our implementation of the IEEE 802.11ay standard in the network simulator ns-3. Our implementation captures the specifics of IEEE 802.11ay operations such as the 802.11ay frame structure, channel bonding, new beamforming training procedures, quasi-deterministic MIMO channel support, and single-user MIMO and multi-user MIMO beamforming training. We also validate and demonstrate the performance of the aforementioned techniques by simulations. The code for our simulation model is publicly available.

Millimeter-wave (mmWave) communications have emerged as one of the most promising options to vastly increase wireless data rates due to the high bandwidth they offer. Given the high path loss at mmWave frequencies, such systems require directional antennas to achieve a good communication range. Thus, the communicating devices need to align the beam directions of their mmWave antennas. Due to the high penetration loss, the paths between the antennas also need to be free of blocking obstacles. This makes an efficient and reliable operation of mmWave networks in dynamic environments very challenging. At the same time, the directionality reduces interference and allows to scale these networks to much higher access point and device densities. In this paper, we discuss the above-mentioned challenges and present techniques that allow mmWave networks to scale to high-density deployments, to adapt to dynamic and mobile environments, and to consistently achieve high data rates. This includes learning the environment to find different propagation paths, reacting timely to channel impairments such as blockage, and integrating mmWave networks with networks operating at a lower frequency for robustness. A key ingredient to enable these forms of adaptivity is the use of location information. Such mechanisms then turn a collection of very-high-speed but brittle mmWave links into an efficient, low-latency, and reliable network.

Wireless communications in the millimeter-wave band bring unprecedented capabilities to achieve wireline performance in wireless networks and alleviate the congestion problem of current wireless technologies. However, efficient wireless networking in this band is extremely challenging compared to wireless technologies operating in the microwave band. IEEE 802.11ay is the next generation multi-gigabit standard to support wireless networking at 60 GHz. It is envisioned to support extremely high data-rates of up to 300 Gbps, achieved through new complex physical layer techniques including MIMO communication, channel bonding and aggregation, and high order-modulation schemes. Simulating the IEEE 802.11ay standard in a network-level simulator requires accurate abstraction models to incorporate the effects of those techniques. At the time of writing, ns-3, a system-level simulator widely used by the scientific community, still lacks support for MU-MIMO communication. Additionally, it requires generating environment dependent SNR-to-BER look-up tables to accurately simulate SU-MIMO communication. In this paper, we propose a hybrid implementation that includes minimum signal processing blocks to accurately simulate IEEE 802.11ay SU/MU-MIMO communication in ns-3 with high accuracy and reduced computational complexity.

Next generation wireless local area networks are envisioned to serve a high number of devices with heterogeneous capabilities and service requirements. Millimeter-wave technology is expected to be able to satisfy these demands and complement the highly congested wireless networks operating in the sub-6 GHz band. However, real-world experimentation with millimeter-wave communications is not always feasible due to the significant amount of resources required and its associated costs. For these reasons, researchers resort to high fidelity system-level simulators which provide a high degree of flexibility to test complex network deployments with a reasonable level of abstraction at the physical layer. The ns-3 IEEE 802.11ad model allows researchers to study large-scale wireless networks operating in the 60 GHz band, taking into account all of the essential features supported by the standard. However, the beamforming capabilities in the current implementation still lack both the flexibility and the agility that commercial of-the-shelf devices offer. Additionally, the model relies on a simplified channel model that does not accurately reflect the characteristics of a millimeter-wave channel. In this paper, we augment our ns-3 IEEE 802.11ad model with novel features that enhance its fidelity and provide the user fine grained control over physical and MAC layer aspects of 802.11ad devices. These features include beam codebooks, multi-antenna beamforming training, beam refinement and beam tracking capabilities, and a quasi-deterministic channel model. Our work paves the way for a future implementation of the next generation wireless gigabit standard, IEEE 802.11ay.

Future millimeter-wave networks will support very high densities of devices and access points. This vastly increases the overhead required for access point selection and beam training. Fortunately, the quasi-optical properties of millimeter wave channels make location-based network optimization a highly promising technique to reduce control overhead in such millimeter-wave WLANs. In this paper, we extract channel state information from off-the-shelf routers, we use it to design a high accuracy location system, and then show how location information enables the optimization of network operations. The resulting scheme, named LEAP, can predict blockage, optimize access point association, and select the most suitable antenna beam patterns while significantly reducing the beam training overhead. We show that compared to standard state-of-the-art 802.11ad systems, LEAP's location driven management greatly improves network performance and link stability.

Supporting high data-rates and a large number of connected devices has always been challenging for wireless technologies operating in the microwave band. Wireless communication in the millimeter band is a promising solution to address this challenge and deliver gigabit throughput and very low latency. However, efficient communication in this band poses a great challenge in terms of radio resource allocation and requires adequate network planning and efficient design of wireless networking protocols. Despite the availability of commercial devices utilizing the IEEE 802.11ad protocol, these devices provide only limited access to the operations of the lower layers of the protocol stack, which hinders in-depth analysis and development of innovative solutions. For these reasons, researchers rely on high-fidelity system-level simulators to understand the interactions and behavior of millimeter-wave communication devices. In this paper, we demonstrate the capabilities of the IEEE 802.11ad model in ns-3. This model allows researchers to study the performance of the IEEE 802.11ad protocol for various deployment settings with high fidelity, using realistic phased antenna arrays and quasi-deterministic channel models. More particularly, we look at the impact of LOS blockage and the use of NLOS paths on link performance. In addition, we show the benefits of deploying multiple access points per room to guarantee gigabit throughput per user. Finally, we evaluate the performance of the IEEE 802.11ad protocol in a typical high-density scenario consisting of a single access point and ten stations.

The use of directional antennas in millimeter-wave communication promises high spatial reuse at multi-gigabit-per-second data rates in dense wireless networks. Existing work studies such networks using commercial hardware but is limited to individual links. Moreover, such hardware typically allows for little or no control of the lower layers of the protocol stack. In this paper, We study the performance of dense millimeterwave deployments featuring up to eight stations. To this end, we use a practical IEEE 802.11ad millimeter-wave testbed that allows access to the lower layer parameters of each station. This enables us to analyze the impact of these parameters on upper layer performance. We study, for first time to our best knowledge, issues such as the impact of channel contention on the buffer size at the transport layer, the effect of frame aggregation, and the efficiency of spatial sharing. Our results show that using large buffer sizes with TCP is harmful due to channel contention despite the multi-gigabit-per-second data rates. Further, frame aggregation is only beneficial up to a certain level due to higher error rates for large frames. Finally, we also study delay, showing that the regular beacon transmission time can degrade performance.

Millimeter-wave technology is one of the main pillars of the future wireless networks. The main reason lies in the quantum leap of capacity it provides with respect to wireless networks operating in the sub 6-GHz band. Nevertheless, efficient and reliable communication in this band demands novel techniques to tackle all the associated barriers related to wireless propagation in those bands. In this paper, we present the extension of our ns-3 IEEE 802.11ad model and provide design and implementation details of the new techniques, including dynamic and static channel access schemes, decentralized clustering, beamformed link maintenance, spatial sharing, and half-duplex relay operation as defined in the IEEE 802.11ad amendment. We show how these techniques can boost and enhance wireless networking operation in the 60 GHz band. Our work is the first to implement these techniques in a networking simulator and make the implementation publicly available.

Millimeter-wave devices must use highly directional antennas to achieve GBit/s data rates over reasonable distances due to the high path loss. As a consequence, it is important to precisely align the antenna beams between sender and receiver. Even minor movement or rotation of a device can result in beam misalignment and thus a strong performance degradation. Existing work as well as standards such as IEEE 802.11ad tackle this issue by means of antenna sector probing. This comes at the expense of a significant overhead, which may significantly reduce the performance of millimeter-wave communication, particularly in mobile scenarios. In this paper, we present a mechanism that can track both movement and rotation of 60 GHz mobile devices with zero overhead. To this end, we transmit part of the preamble of each packet using a multi-lobe beampattern. Our approach does not require any additional control messages and is backward compatible with 802.11ad. We implement our scheme on a 60 GHz testbed using phased antenna arrays, and show that we reduce the angle error to less than 5° in most cases. We also perform simulations to validate our approach in a wide range of scenarios, achieving up to 2x throughput gain.

Millimeter-wave technology is one of the main pillars of the future wireless networks. The main reason lies in the quantum leap of capacity it provides with respect to wireless networks operating in the sub 6-GHz band. Nevertheless, efficient and reliable communication in this band demands novel techniques to tackle all the associated barriers related to wireless propagation in those bands. In this paper, we present the extension of our ns-3 IEEE 802.11ad model and provide design and implementation details of the new techniques, including dynamic and static channel access schemes, decentralized clustering, beamformed link maintenance, spatial sharing, and half-duplex relay operation as defined in the IEEE 802.11ad amendment. We show how these techniques can boost and enhance wireless networking operation in the 60 GHz band. Our work is the first to implement these techniques in a networking simulator and make the implementation publicly available.

This work conducts one of the first experimental studies of Multipath TCP (MPTCP) in dual-band 60 GHz/5 GHz WLANs using off-the-shelf hardware. We consider both uncoupled and different coupled congestion control algorithms, compare their performance and their potential to improve throughput over single path TCP, and uncover their limitations. In contrast to a recent study that reports reduced throughput with MPTCP compared to single path TCP over 60 GHz, our results show that significant performance improvements are possible, especially in the case of uncoupled congestion control. On the other hand, performance gains with coupled congestion control are lower as these algorithms often fail to fully utilize the capacity of both paths simultaneously. We also observe a pathological case that can lead to significantly reduced throughput with MPTCP regardless of the congestion control algorithm.

The IEEE 802.11ad amendment to the 802.11 standard for multi-gigabit communication at 60 GHz was published several years ago, but to date, no precise simulation model for networking in this band is available. In this paper, we present a model for IEEE 802.11ad implemented in the network simulator ns-3. We model new techniques that are essential for IEEE 802.11ad operation such as beamforming training and steering, relay support, and fast session transfer. We then evaluate by simulation the performance of IEEE 802.11ad as well as the gains obtained through the aforementioned techniques. The code for our simulation model is publicly available.

The impact of frame aggregation on wireless network performance increases dramatically with higher data rates. The key problem is that the transmission time of packets decreases while the medium access, preamble and packet header overhead remain the same. Recent 802.11 standards address this issue using frame aggregation, i.e., grouping multiple data frames in a single transmission to reduce the overhead. This already provides substantial efficiency gains in networks operating in the 2.4 GHz and 5 GHz bands, and for future 60 GHz networks such as 802.11ad, gains are even more pronounced due to the order-of-magnitude higher data rates. In 802.11ad, frame aggregation becomes crucial to achieve the multi-gbps data rates that are possible in theory, since medium access overhead can be 20x larger than the time required to transmit a single packet. While frame aggregation is essential, it very much depends on the traffic patterns present in the wireless network, and a node may not always have enough packets in the transmit queue to achieve a sufficiently large aggregated frame size. In this paper, we investigate in which case nodes should wait to construct a larger aggregated packet before starting the channel access procedure. We present a simple waiting policy for the uplink case that either waits for a minimum number of packets or for a maximum amount of time, whichever comes first. For the downlink case, we utilize a maximum weight scheduling policy with a maximum waiting time. Our results show that both policies significantly improve medium utilization, thus increasing throughput and reducing end-to-end delay.