128 research outputs found
Proactive Received Power Prediction Using Machine Learning and Depth Images for mmWave Networks
This study demonstrates the feasibility of the proactive received power
prediction by leveraging spatiotemporal visual sensing information toward the
reliable millimeter-wave (mmWave) networks. Since the received power on a
mmWave link can attenuate aperiodically due to a human blockage, the long-term
series of the future received power cannot be predicted by analyzing the
received signals before the blockage occurs. We propose a novel mechanism that
predicts a time series of the received power from the next moment to even
several hundred milliseconds ahead. The key idea is to leverage the camera
imagery and machine learning (ML). The time-sequential images can involve the
spatial geometry and the mobility of obstacles representing the mmWave signal
propagation. ML is used to build the prediction model from the dataset of
sequential images labeled with the received power in several hundred
milliseconds ahead of when each image is obtained. The simulation and
experimental evaluations using IEEE 802.11ad devices and a depth camera show
that the proposed mechanism employing convolutional LSTM predicted a time
series of the received power in up to 500 ms ahead at an inference time of less
than 3 ms with a root-mean-square error of 3.5 dB
A Survey of Beam Management for mmWave and THz Communications Towards 6G
Communication in millimeter wave (mmWave) and even terahertz (THz) frequency
bands is ushering in a new era of wireless communications. Beam management,
namely initial access and beam tracking, has been recognized as an essential
technique to ensure robust mmWave/THz communications, especially for mobile
scenarios. However, narrow beams at higher carrier frequency lead to huge beam
measurement overhead, which has a negative impact on beam acquisition and
tracking. In addition, the beam management process is further complicated by
the fluctuation of mmWave/THz channels, the random movement patterns of users,
and the dynamic changes in the environment. For mmWave and THz communications
toward 6G, we have witnessed a substantial increase in research and industrial
attention on artificial intelligence (AI), reconfigurable intelligent surface
(RIS), and integrated sensing and communications (ISAC). The introduction of
these enabling technologies presents both open opportunities and unique
challenges for beam management. In this paper, we present a comprehensive
survey on mmWave and THz beam management. Further, we give some insights on
technical challenges and future research directions in this promising area.Comment: accepted by IEEE Communications Surveys & Tutorial
Location, Location, Location: Maximizing mmWave LAN Performance through Intelligent Wireless Networking Strategies
The main objective of this dissertation is to design and evaluate intelligent techniques to maximize mmWave wireless local-area network (WLAN) performance. To meet the ever-increasing data demand of various bandwidth-hungry applications, we propose techniques to enable consistently ultra-high-rate mmWave communication in the wireless environment. However, the weak diffraction of mmWave signals makes them extremely sensitive to blockage effects caused by real-world obstacles, and this is a primary challenge to overcome for the feasibility of mmWave communications. To this end, we exploit location sensitivity to explore robust mmWave WLAN designs that expedite the full realization of ubiquitous mmWave wireless connectivity. The techniques investigated to exploit location sensitivity are the use of multiple access points (APs), controlled mobility, AP-user association mechanisms, and environment-aware prediction We first develop optimal multi-AP planning approaches to maximize line-of-sight connectivity and aggregate throughput in mmWave WLANs, and then study multi-AP association mechanisms to achieve low-overhead and blockage-robust mmWave wireless communications among multiple users and multiple APs. Furthermore, we explore the potential benefits achievable from AP mobility technology, which yields insights on the best configurations of mobile APs. We also develop an environment-aware link-quality predictor to accurately derive dynamic mmWave link quality due to static blockages and small changes in device locations, which provides a basis for the development of anticipatory networking with proactive resource-allocation schemes. In a complementary direction for evaluating the performance of mmWave networks, we develop and implement advanced features for dense wireless networks that increasingly characterize many mmWave scenarios of interest in the widely-used network simulator ns-3, including a sparse cluster-based wireless channel model that statistically models multi-path components in mmWave WLANs.Ph.D
Experimental Investigations of Millimeter Wave Beamforming
The millimeter wave (mmW) band, commonly referred to as the frequency band between 30 GHz and 300 GHz, is seen as a possible candidate to increase achievable rates for mobile applications due to the existence of free spectrum. However, the high path loss necessitates the use of highly directional antennas. Furthermore, impairments and power constraints make it difficult to provide full digital beamforming systems. In this thesis, we approach this problem by proposing effective beam alignment and beam tracking algorithms for low-complex analog beamforming (ABF) systems, showing their applicability by experimental demonstration. After taking a closer look at particular features of the mmW channel properties and introducing the beamforming as a spatial filter, we begin our investigations with the application of detection theory for the non-convex beam alignment problem. Based on an M-ary hypothesis test, we derive algorithms for defining the length of the training signal efficiently. Using the concept of black-box optimization algorithms, which allow optimization of non-convex algorithms, we propose a beam alignment algorithm for codebook-based ABF based systems, which is shown to reduce the training overhead significantly. As a low-complex alternative, we propose a two-staged gradient-based beam alignment algorithm that uses convex optimization strategies after finding a subregion of the beam alignment function in which the function can be regarded convex. This algorithm is implemented in a real-time prototype system and shows its superiority over the exhaustive search approach in simulations and experiments. Finally, we propose a beam tracking algorithm for supporting mobility. Experiments and comparisons with a ray-tracing channel model show that it can be used efficiently in line of sight (LoS) and non line of sight (NLoS) scenarios for walking-speed movements
Network Management and Control for mmWave Communications
Millimeter-wave (mmWave) is one of the key technologies that enables the next wireless
generation. mmWave offers a much higher bandwidth than sub-6GHz communications
which allows multi-gigabit-per-second rates. This also alleviates the scarcity of spectrum
at lower frequencies, where most devices connect through sub-6GHz bands. However new
techniques are necessary to overcome the challenges associated with such high frequencies.
Most of these challenges come from the high spatial attenuation at the mmWave band,
which requires new paradigms that differ from sub-6GHz communications. Most notably
mmWave telecommunications are characterized by the need to be directional in order to
extend the operational range. This is achieved by using electronically steerable antenna
arrays, that focus the energy towards the desired direction by combining each antenna
element constructively or destructively. Additionally, most of the energy comes from
the Line Of Sight (LOS) component which gives mmWave a quasi-optical behaviour
where signals can reflect off walls and still be used for communication. Some other
challenges that directional communications bring are mobility tracking, blockages and
misalignments due to device rotation. The IEEE 802.11ad amendment introduced wireless
telecommunications in the unlicensed 60 GHz band. It is the first standard to address
the limitations of mmWave. It does so by introducing new mechanisms at the Medium
Access Control (MAC) and Physical (PHY) layers. It introduces multi-band operation,
relay operation mode, hybrid channel access scheme, beam tracking and beam forming
among others.
In this thesis we present a series of works that aim to improve mmWave
telecommunications. First we give an overview of the intrinsic challenges of mmWave
telecommunications, by explaining the modifications to the MAC and PHY layers. This
sets the base for the rest of the thesis. Then do a comprehensive study on how mmWave
behaves with existing technologies, namely TCP. TCP is unable to distinguish losses
caused by congestion or by transmission errors caused by channel degradation. Since
mmWave is affected by blockages more than sub-6GHz technologies, we propose a set
of parameters that improve the channel quality even for mobile scenarios. The next job
focuses on reducing the initial access overhead of mmWave by using sub-6GHz information
to steer towards the desired direction. We start this work by doing a comprehensive High Frequency (HF) and Low Frequency (LF) correlation, analyzing the similarity of
the existing paths between the two selected frequencies. Then we propose a beam
steering algorithm that reduces the overhead to one third of the original time. Once
we have studied how to reduce the initial access overhead, we propose a mechanism
to reduce the beam tracking overhead. For this we propose an open platform based
on a Field Programmable Gate Arrays (FPGA) where we implement an algorithm that
completely removes the need to train on the Station (STA) side. This is achieved by
changing beam patterns on the STA side while the Access Point (AP) is sending the
preamble. We can change up to 10 beam patterns without losing connection and we reduce
the overhead by a factor of 8.8 with respect to the IEEE 802.11ad standard. Finally
we present a dual band location system based on Commercial-Off-The-Shelve (COTS)
devices. Locating the STA can improve the quality of the channel significantly, since the
AP can predict and react to possible blockages. First we reverse engineer existing 60
GHz enabled COTS devices to extract Channel State Information (CSI) and Fine Timing
Measurements (FTM) measurements, from which we can estimate angle and distance.
Then we develop an algorithm that is able to choose between HF and LF in order to
improve the overall accuracy of the system. We achieve less than 17 cm of median error
in indoor environments, even when some areas are Non Line Of Sight (NLOS).This work has been supported by IMDEA Networks Institute.Programa de Doctorado en IngenierĂa Telemática por la Universidad Carlos III de MadridPresidente: Matthias Hollick.- Secretario: Vincenzo Mancuso.- Vocal: Paolo Casar
A Detailed Characterization of 60 GHz Wi-Fi (IEEE 802.11ad)
The emergence of wireless local area network (WLAN) standards and the global system of mobile communication (GSM) in the early 1990s incited tremendous growth in the demand for wireless connectivity. Iterative technological enhancements to cellular and WLAN improved wireless capacity and created a breadth of new mobile applications. The continued increase in display resolutions and image quality combined with streaming displacing satellite/cable has created unprecedented demands on wireless infrastructure. Data-caps on cellular networks deter over consumption and increasingly shift the growing burden to Wi-Fi networks. The traditional 2.4/5 GHz Wi-Fi bands have become overloaded and the increasing number of wireless devices in the home, public, and workplace create difficult challenges to deliver quality service to large numbers of client stations. In dense urban areas, the wireless medium is subjected to increased interference due to overlapping networks and other devices communicating in the same frequency bands. Improvements to conventional Wi-Fi are approaching their theoretical limits and higher order enhancements require idealized conditions which are seldom attainable in practice.
In an effort to supplant to scaling capacity requirements a very high frequency WLAN amendment has been proposed (IEEE 802.11ad). IEEE 802.11ad, also referred to as Wireless Gigabit (WiGig), operates in the globally unlicensed 60 GHz band and offers channel bandwidths nearly 100x as wide as 802.11n. The higher bandwidth facilitates multi-Gbps throughput even with the use of lower complexity modulation coding schemes (MCS). IEEE 802.11ad relies heavily on rate adaptation and high beamforming gain to mitigate interference and fading as signals in the 60 GHz band suffer from higher atmospheric ab- sorption and free space path loss (FSPL). Due to the unique nature of 60 GHz wireless there have been numerous research efforts. Many studies have been directed at simulation and modeling of the 60 GHz channel. However modeling the channel is difficult as real- world environments are highly dynamic with varying link quality and conditions which cannot be accurately predicted by conventional techniques. Some research is focused on medium access control (MAC) enhancements to improve overall capacity by coordinating concurrent links or reducing communication overhead for example. Lastly, there has been a limited amount of real world testing of 802.11ad due to lack of availability of commercial platforms and measurement instrumentation. Some researchers tested early generation devices in certain use cases such as in vehicles for media streaming, in data centers to augment the wired network, or in basic indoor and outdoor environments.
This research contains two main components. In the first study, analytical models are applied to estimate line of sight (LOS) 802.11ad performance for realistic antenna param- eters. The second part contains a comprehensive evaluation of performance and reliability of early generation 802.11ad hardware. This characterization emphasizes environmen- tal performance (e.g. conference room, cubical farm, open office), multiple-client testing (multiclient), multiple network interference (spatial re-use), and stability in the presence of station mobility, physical obstructions, and antenna misalignment. In order to evaluate 802.11ad, early generation platforms from technology vendors were used in extensive test suites. The hardware tested included docks for wireless personal area networking (WPAN) applications, client laptop stations, and reference design access points (APs). Finally, a customized proof-of-concept (PoC) platform was engineered which allowed finer control over front end antenna configuration parameters such as: topology, placement and orienta- tion. The PoC also served as a suitable means to identify practical limitations and system design engineering challenges associated with supporting directional multi-Gbps (DMG) communication in the 60 GHz band
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