Gregory S. Sternberg

On the Secrecy Capabilities of ITU Channels

We consider the secrecy inherent in the reciprocal nature of multipath fading channels and present a technique to generate a shared perfectly secret key by two terminals observing a multipath fading channel. Using this technique we quantify the secrecy that can be generated from ITU cellular channels for the 2 GHz frequency range.

Architecture and protocols for LTE-based device to device communication

The evolution of cellular wireless communications has involved the introduction of technologies such as multiple antennas, OFDM, higher spectral efficiency through better modulation, denser deployments and carrier aggregation. A different approach to enhancing the cellular network by using direct communication between UEs is presented in this paper. Direct device-to-device (D2D) communication can be used for several purposes including network traffic offloading, public safety, and social applications such as gaming. The architectural and protocol enhancements required to extend the current 3GPP LTE-Advanced system to incorporate D2D communication are described, including the logical functions of a D2D server in the core network, the procedures for devices to discover each other and obtain D2D services, the steps involved in establishing and maintaining a D2D call and procedures for efficient mobility between a traditional cellular mode and a D2D mode of operation.

System capacity and coverage of a cellular network with D2D mobile relays

It has been predicted that the recent explosive growth in wireless data traffic will continue for the foreseeable future. To date, attempts to address this explosive growth have included increasing base station density through smaller cells, and to a lesser extent, by improving spectral efficiency using close-to-capacity channel coding and MIMO techniques. Providing further capacity and coverage improvements through ever shrinking cells could lead to large infrastructure costs and operating expenses. In this paper we propose a far less expensive alternate solution using a topology which employs mobile User Equipment (UE) nodes as virtual infrastructure to enhance the cellular capacity while also improving network coverage. The improvements in capacity and coverage are achieved by enabling cellular controlled direct Device to Device (D2D) links to carry relayed traffic. Each terminal UE (T-UE) with an active connection could potentially be assigned a Helper UE (H-UE), depending on the network conditions and traffic requirements to improve the system capacity. In addition, T-UEs which are out of coverage can also be assigned a H-UE, which would extend the typical coverage of a base station and lead to improved network coverage. In this paper, we present both coverage enhancement and system capacity results using Monte Carlo simulation techniques for both uplink and downlink communications. Our results indicate that cell edge percent throughput capacity improvements as well as percent throughput coverage improvements of more than 150% may be realized using idle UEs in the system as mobile relays.

System Architecture for a Cellular Network with Cooperative Mobile Relay

This paper describes a comprehensive system architecture that enables mobile-to-mobile communications for the purpose of enhancing the capacity of the cellular network. The architecture is developed using LTE Release-10 as the baseline. The impact on the protocol stack is discussed in detail. Neighbor discovery mechanisms are described to enable users to identify potential helper mobiles to enable a cooperative mobile relay. Resource partitioning for the mobile-to-mobile link is detailed and changes to the design of the HARQ entity structure and timing are discussed.

Uplink system capacity of a cellular network with cooperative mobile relay

This paper studies the performance of a hybrid cellular network with cellular controlled direct radio links between multiple mobile User Equipments (UEs). The main focus is on the uplink of the proposed system with multiple idle UEs acting as relays to assist the communication of any given UE with an active connection. In the presence of multiple UEs as relays, the Base Station (BS) dynamically chooses the best relay to maximize the throughput of each radio link. We present system capacity results using Monte Carlo system simulation techniques. Further, we compare results with and without the use of distributed beam forming techniques. Our results indicate that cell edge capacity could be improved by more than 99% by using idle UEs in the system as mobile relays. The performance improvement at cell edge is achieved while improving the mean cell throughput by more than 50%.

Model-based QoE prediction to enable better user experience for video teleconferencing

The ultimate goal of network resource allocation for video teleconferencing is to optimize the Quality of Experience (QoE) of the video. We consider the IPPP video coding structure with macroblock intra refresh, which is widely used for video teleconferencing. Generally, the loss of a current frame causes error propagation to subsequent frames due to the video coding structure. Therefore, to optimize the QoE, a communication network needs to be able to accurately predict the consequence of each of its resource allocation decisions. We propose a QoE prediction scheme by considering QoE models that use the per-frame PSNR time series as the input, thus reducing the QoE prediction problem to a per-frame PSNR prediction problem. The QoE prediction scheme is jointly implemented by the video sender (orMCU) and the communication network. Simulation results show that the proposed per-frame PSNR prediction method is fairly accurate, with an average error well below 1dB.

User-adaptive mobile video streaming

Summary form only given. We describe the design of a mobile streaming system, which optimizes video delivery based on dynamic analysis of user behavior and viewing conditions, including user proximity, viewing angle, and ambient illuminance.

User-aware DASH over Wi-Fi

Dynamic Adaptive Streaming over HTTP (DASH) is being adopted as a cost effective means for multimedia delivery. User Adaptive Video (UAV) is a new technique that exploits the perceptual limits of the human visual system to modulate a video streams bit rate based on the viewing conditions, such as viewing distance and ambient illuminance, resulting in significant bandwidth reduction without perceived loss of quality to the user. UAV presents an opportunity to significantly improve the efficiency of DASH by not requesting unnecessarily high bit rate video. Due to the random access nature of the Wi-Fi MAC protocol and the intricate interaction among DASH traffic flows, it is not clear whether UAV will manifest its benefits in Wi-Fi networks. We design UAV-enabled DASH (UDASH) and evaluate its performance in Wi-Fi networks. We show that UDASH in a Wi-Fi network has the benefits of not only improving the video streaming performance such as reducing the rebuffering probability, but also enhancing the performance of cross traffic. We also give the conditions under which the benefits can be achieved. Simulation results confirm that the benefits of UDASH are significant.

User adaptive transcoding for video teleconferencing

The human visual system (HVS) cannot perceive spatial frequency components in an image that are above a certain limit, the value of which is affected by factors such as the viewing distance. This has been exploited to improve the video coding efficiency by first filtering out redundant frequency components and then doing conventional video encoding. To facilitate the deployment of this scheme, we propose to implement it in a network entity such as a Multipoint Control Unit (MCU). Specifically, by analyzing the video sent from a client, the MCU infers that clients viewing conditions, which are then used to adapt the encoding of the video destined to that client. The scheme is implemented in a real-world video teleconferencing system. Experimental results show that our approach can result in significant savings in bandwidth without affecting subjective video quality.

Early Packet Loss Feedback for WebRTC-Based Mobile Video Telephony over Wi-Fi

We consider improving the performance of WebRTC-based mobile video telephony over a Wi-Fi link, which is susceptible to channel-caused or congestion-caused packet losses. Existing reactive packet loss mitigation mechanisms rely on end-to-end feedback, which takes about one round-trip time (RTT), causing excessive artifacts or video freeze in the received video in typical network scenarios. To address this problem, we propose early packet loss feedback (EPLF), where the MAC layer of the local Wi-Fi link sends a spoofed NACK to the Realtime Transport Protocol (RTP) layer if and only if the transmission failure is caused by a channel error, and the NACK immediately triggers an RTP layer retransmission. This significantly reduces the loss-feedback delay while improving the effectiveness of the RTP-layer congestion control. Analytic modeling and experimental results show that EPLF almost completely eliminates channel-caused video freezes.