S. Amir Hosseini

Directional Cell Discovery in Millimeter Wave Cellular Networks

The acute disparity between increasing bandwidth demand and available spectrum has brought millimeter wave (mmWave) bands to the forefront of candidate solutions for the next-generation cellular networks. Highly directional transmissions are essential for cellular communication in these frequencies to compensate for higher isotropic path loss. This reliance on directional beamforming, however, complicates initial cell search since mobiles and base stations must jointly search over a potentially large angular directional space to locate a suitable path to initiate communication. To address this problem, this paper proposes a directional cell discovery procedure where base stations periodically transmit synchronization signals, potentially in time-varying random directions, to scan the angular space. Detectors for these signals are derived based on a Generalized Likelihood Ratio Test (GLRT) under various signal and receiver assumptions. The detectors are then simulated under realistic design parameters and channels based on actual experimental measurements at 28 GHz in New York City. The study reveals two key findings: 1) digital beamforming can significantly outperform analog beamforming even when digital beamforming uses very low quantization to compensate for the additional power requirements and 2) omnidirectional transmissions of the synchronization signals from the base station generally outperform random directional scanning.

Directional cell search for millimeter wave cellular systems

Millimeter wave (mmW) bands between 30 and 300 GHz are considered a promising candidate for next-generation cellular networks to relieve spectral congestion in conventional cellular frequencies. However, cellular communication at these frequencies will likely require highly directional transmissions to achieve suitable signal range. This reliance on directional beamforming complicates initial cell search since the mobile and base station must jointly search over a potentially large angular directional space to locate a suitable path to initiate communication. This paper proposes a directional cell search procedure where each base station periodically transmits synchronization signals in randomly varying directions. Detectors are derived for this synchronization signal based on a Generalized Likelihood Ratio Test (GLRT) for the case where (i) the mobile has only analog beamforming (where the mobile can “look” in only direction at a time) and (ii) digital beamforming where the mobile has access to digital samples from all antennas. Simulations under realistic parameters demonstrate that mobiles may not be able to achieve suitable detection performance with analog beamforming alone. In contrast, digital beamforming offers dramatically better performance. We argue that the additional power consumption cost of digital beamforming can be offset by using very low quantization rates with minimal performance loss, thus arguing that low-rate fully digital front-ends may be a better design choice for directional cell search.

Initial Access in Millimeter Wave Cellular Systems

Millimeter wave (mmWave) bands have attracted considerable recent interest for next-generation cellular systems due to the massive available spectrum at these frequencies. However, a key challenge in designing mmWave cellular systems is initial access-the procedure by which a mobile device establishes an initial link-layer connection to a cell. MmWave communication relies on highly directional transmissions and the initial access procedure must thus provide a mechanism by which initial transmission directions can be searched in a potentially large angular space. Design options are compared considering different scanning and signaling procedures to evaluate access delay and system overhead. The channel structure and multiple access issues are also considered. The results of our analysis demonstrate significant benefits of low-resolution fully digital architectures in comparison with single stream analog beamforming.

Directional initial access for millimeter wave cellular systems

Communication in millimeter (mmWave) bands seems an evermore promising prospect for new generation cellular systems. However, due to high isotropic pathloss at these frequencies the use of directional antennas becomes mandatory. Directivity complicates many system design issues that are trivial in current cellular implementations. One such issue is initial access, i.e., the establishment of a link-layer connection between a UE and a base station. Based on different combinations of beamforming architectures and transmission modes, we present a series of design options for initial access in mmWave and compare them in terms of delay performance. We show that the use of digital beamforming for initial access will expedite the whole process significantly. Also, we argue that low quantization digital beamforming can more than compensate for high power consumption.

Not) yet another policy for scalable video delivery to mobile users

In this work, we provide a methodology to analyze optimal adaptation policies for scalable video delivery in mobile environments. Typically, download policies for adaptive video are tuned to very specific system settings. The aim of this work is not to propose a new policy, but instead to understand how the optimal policy changes according to the operating environment and the system characteristics of a mobile video client. Armed with this insight, we can design or adapt policies for SVC adaptive video delivery for a broader range of settings. Using a semi-Markov decision process (SMDP), we find optimal video retrieval policies for a single user, subject to different limits on buffer capacity and different wireless environments. We apply a decision tree classifier to the output of the SMDP to derive simple approximate policies for 55 scenarios and use these to derive high-level rules on the relationship between optimal download policy and the underlying channel settings. For example, we show that the optimal policy is more conservative in slowly varying channels, and becomes more greedy in fast changing channels, and that instantaneous channel state is relevant to the decision-making process only in a setting with a very limited buffer capacity and slow-varying channel.

Prioritized Buffer Control in Two-tier 360 Video Streaming

360 degree video compression and streaming is one of the key components of Virtual Reality (VR) applications. In 360 video streaming, a user may freely navigate through the captured 3D environment by changing her desired viewing direction. Only a small portion of the entire 360 degree video is watched at any time. Streaming the entire 360 degree raw video is therefore unnecessary and bandwidth-consuming. One the other hand, only streaming the video in the predicted users view direction will introduce streaming discontinuity whenever the the prediction is wrong. In this work, a two-tier 360 video streaming framework with prioritized buffer control is proposed to effectively accommodate the dynamics in both network bandwidth and viewing direction. Through simulations driven by real network bandwidth and viewing direction traces, we demonstrate that the proposed framework can significantly outperform the conventional 360 video streaming solutions.

SVC-Based Multi-User Streamloading for Wireless Networks

In this paper, we present an approach for joint rate allocation and quality selection for a novel video streaming scheme called streamloading. Streamloading is a recently developed method for delivering high-quality video without violating copyright enforced restrictions on content access for video streaming. In regular streaming services, content providers restrict the amount of viewable video that users can download prior to playback. This approach can cause inferior user experience due to bandwidth variations, especially in mobile networks with varying capacity. In streamloading, the video is encoded using scalable video coding, and users are allowed to pre-fetch enhancement layers and store them on the device, while base layers are streamed in a near real-time fashion ensuring that buffering constraints on viewable content are met. We begin by formulating the offline problem of jointly optimizing rate allocation and quality selection for streamloading in a wireless network. This motivates our proposed online algorithms for joint scheduling at the base station and segment quality selection at receivers. The results indicate that streamloading outperforms the state-of-the-art streaming schemes in terms of the number of additional streams we can admit for a given video quality. Furthermore, the quality adaptation mechanism of our proposed algorithm achieves a higher performance than baseline algorithms with no (or limited) video-centric optimization of the base stations allocation of resources, e.g., proportional fairness.

More bars, more bang for the buck: Channel-dependent pricing for video delivery to mobile users

A great deal of research energy has been focused on the challenge of delivering high-quality video content to mobile users. In many over-the-top video services, however, the scheduler responsible for channel resource allocation is not aware of content characteristics or playback schedules at end user devices. Therefore, it cannot allocate physical resources in a way that maximizes video quality. For example, it cannot prioritize the transmission of a video frame that is to be displayed within seconds over one whose playback deadline is minutes away. Furthermore, for content that is to be viewed immediately, previous pricing structures that incentivize delaying network use to off-peak hours or WiFi offloading do not apply. To address this issue, we introduce a tiered link quality-dependent data pricing scheme for use together with usage-based pricing in wireless networks. Our pricing model encourages selfish users to prefetch video content during short intervals of good link quality, and use minimal resources when they have a poor link quality. This offers an economic incentive to video consumers to use physical resources more efficiently even with an oblivious scheduler, and leads to better overall video quality for all users in a wireless cell, as well as increased revenue for the wireless service provider.

Under a cloud of uncertainty: legal questions affecting internet storage and transmission of copyright-protected video content

The rapid growth of multimedia consumption has triggered technical, economic, and business innovations that improve the quality and accessibility of content. It has also opened new markets, promising large revenues for industry players. However, new technologies also pose new questions regarding the legal aspects of content delivery, which are often resolved through litigation between copyright owners and content distributors. The precedents set by these cases will act as a game changer in the content delivery industry, and will shape the existing offerings in the market in terms of how new technologies can be deployed and what kind of pricing strategies can be associated with them. In this article, we offer a tutorial on key copyright and communications laws and decisions related to storage and transmission of video content over the Internet. We summarize legal limitations on the deployment of new technologies and pricing mechanisms, and explain the implications of recent lawsuits. Understanding these concerns is essential for engineers engaged in designing the technical and economic aspects of video delivery systems.