Gautam D. Bhanage

SplitAP: Leveraging Wireless Network Virtualization for Flexible Sharing of WLANs

Providing air-time guarantees across a group of clients forms a fundamental building block in sharing an access point (AP) across different virtual network providers. Though this problem has a relatively simple solution for downlink group scheduling through traffic engineering at the AP, solving this problem for uplink (UL) traffic presents a challenge for fair sharing of wireless hotspots. Among other issues, the mechanism for uplink traffic control has to scale across a large user base, and provide flexible operation irrespective of the client channel conditions and network loads. In this study, we propose the SplitAP architecture that address the problem of sharing uplink airtime across groups of users by extending the idea of network virtualization. Our architecture allows us to deploy different algorithms for enforcing UL airtime fairness across client groups. In this study, we will highlight the design features of the SplitAP architecture, and present results from evaluation on a prototype deployed with: (1) LPFC and (2) LPFC+, two algorithms for controlling UL group fairness. Performance comparisons on the ORBIT testbed show that the proposed algorithms are capable of providing group air-time fairness across wireless clients irrespective of the network volume, and traffic type. The algorithms show up to 40% improvement with a modified Jain fairness index.

GSTAR: generalized storage-aware routing for mobilityfirst in the future mobile internet

The Internet is at a historic inflection point where mobile, wireless devices are becoming so dominant that core architectural changes are necessary to efficiently support them. This paper presents the high-level concepts and design decisions used to realize the key routing component of the MobilityFirst architecture, which is a clean-slate project being conducted as part of the NSF Future Internet Architecture program. In particular, we describe GSTAR, a mobilitycentric generalized storage-aware routing approach based on the following key design principles: separation of names from addresses, late binding of routable addresses, in-network storage, and conditional routing decision space. The GSTAR protocol described is based on hop-by-hop forwarding of large protocol data units (PDUs) between routers with storage. The packet header incorporates both name and address information enabling routers to execute a hybrid forwarding algorithm that uses topological addresses when available and refers back to names (i.e. global identifiers) to deal with dynamically changing points of attachment and disconnection. At a local level, GSTAR utilizes both fine-grain path quality information and DTN-style connectivity information to deal with the many challenges found in mobile environments.

Space Versus Time Separation for Wireless Virtualization on an Indoor Grid

The decreasing cost of wireless hardware and ever increasing number of wireless testbeds has led to a shift in the protocol evaluation paradigm from simulations towards emulation. In addition, with a large number of users demanding experimental resources and lack of space and time for deploying more hardware, fair resource sharing among independent co-existing experiments is important. We study the proposed approaches to wireless virtualization with a focus on schemes conserving wireless channels rather than nodes. Our detailed comparison reveals that while experiments sharing a channel by space separation achieve better efficiency than those relying on time separation of a channel, the isolation between experiments in both cases is comparable. We propose and implement a policy manager to alleviate the isolation problem and suggest scenarios in which either of the schemes would provide a suitable virtualization solution.

VNTS: A Virtual Network Traffic Shaper for Air Time Fairness in 802.16e Systems

The 802.16e standard for broadband wireless access mandates the presence of QoS classes, but does not specify guidelines for the scheduler implementation or mechanisms to ensure air time fairness. Our study demonstrates the feasibility of controlling downlink airtime fairness for slices while running above a proprietary WiMAX basestation (BS) scheduler. We design and implement a virtualized infrastructure that allows users to obtain at least an allocated percentage of BS resources in the presence of saturation and link degradation. Using Kernel virtual machines for creating slices and Click modular router for implementing the virtual network traffic shaping engine we show that it is possible to adaptively control slice usage for downlink traffic on a WiMAX Basestation. The fairness index and coupling coefficient show an improvement of up to 42%, and 73% with preliminary indoor walking mobility experiments. Outdoor vehicular measurements show an improvement of up to 27%, and 70% with the fairness index and coupling coefficient respectively

RollCall : The Design For A Low-Cost And Power Efficient Active RFID Asset Tracking System

One of the most compelling and immediate applications of pervasive computing would be to use RF technology to support low-cost, long-lived and continual tracking of assets. Unfortunately, initial solutions have not yet led to widespread deployment. We believe that meeting the economic and system requirements of this application requires a redesign of the tag, the transmission protocol, and the algorithms used by basestations to identify tags, all with the underlying goal of reducing cost and power consumption through simplification. In this paper, we propose a new inventory tracking system, called RollCall, in which a transmit-only RFID tag will be attached to every item, and these tags will report their presence to the readers periodically by broadcasting the tag IDs so that a missing tag/item can be quickly identified. The power conservation obtained from short transmissions on a very simple MAC layer combined with the hardware cost and size reduction from having a simple radio stack on the tag provides considerable economic, dimensional and tag lifetime benefits. In this paper, we present the design and architecture of the RollCall system, and conduct preliminary studies to examine the feasibility of building such a system by tweaking off-the-shelf signal processing algorithms. Initial studies and simulation results suggest that it is possible to monitor about 5000 tags in a store with networked basestations at a low error rate with an extended tag life time of at least a year based on conservative estimates with non-custom tag radio and micro-controllers.

Implication of MAC Frame Aggregation on Empirical Wireless Experimentation

Wireless network emulator testbeds have become increasingly important for realistic, at-scale experimental evaluation of new network architectures and protocols. Typically, wireless network performance measurements are made at multiple layers of the wireless protocol stack, i.e. link layer, MAC layer and network layer. This study highlights the impact of layer 2 frame aggregation that is enabled by default in the software drivers for commodity wireless 802.11 devices while it is still not a part of the core 802.11 standard. Using experimental measurements, it is shown that this feature has an impact across a diverse set of wireless experiments and should be considered while comparing results. Measurements on the ORBIT testbed show that throughput measurements can vary up to a startling 25% for certain packet sizes and the variance in receiver side inter-frame delays can almost double if MAC aggregation and preset transmission opportunities are not taken into consideration. Further results for VoIP traffic show a deterioration in jitter of up to 8 times when coupled with MAC layer aggregation in 802.11.

Facilitating an Active Transmit-only RFID System Through Receiver-based Processing

Many asset tracking applications demand long-lived, low-cost, and continuous monitoring of a large number of items, which has posed a significant challenge to todays RFID design. In order to satisfy these requirements, we propose to adopt transmit-only tags without a receiver, which can offer both low power and low cost. In spite of their great potential, such a platform faces many challenges since it cannot sense the channel, causing the collisions among tag transmissions to be high. It is thus crucial to employ effective multi-user detection schemes at the tag reader to extract valid information from collided signals. Traditional detection schemes, such as successive cancellation, cannot be directly applied to the targeted system. Firstly, due to the simplicity of receiver-less transmit-only tags, there is no mechanism for feedback to the tags that is traditionally needed for accurate multi-user detection. More importantly, these schemes impose serious processing and memory requirements on the underlying system, which makes real-time tracking impossible. In this study, we address these challenges by performing a statistical estimation of the signal amplitude, and by dividing the received signal sequence (from all the tags) and assigning each block to one reader. We also adopt an online learning mechanism so that readers can anticipate the tags that belong to them. We show that the proposed detection algorithm can achieve low detection error under realistic system conditions.

Relay MAC: A Collision Free And Power Efficient Reading Protocol For Active RFID Tags

A promising application for RFID tags is to trace valuable assets in an inventory. In such systems, the key challenge is to achieve reliable and energy-efficient tag reads. This paper proposes a novel tag reading protocol, Relay-MAC, which aims at reducing the information sent over the network and the energy spent in collision detection and handling by introducing deliberate sequencing at runtime. This paper provides an in-depth study of the design issues one may face in implementing such a protocol on RFID tags, and validates its feasibility using simulation studies. These studies clearly demonstrate that Relay- MAC can yield much better throughput and energy conservation when compared to a conventional select-and-read protocol.

A virtualization architecture for mobile WiMAX networks

Systems virtualization offers convenient means for sharing networking infrastructure while improving its utilization. This study addresses the challenges of virtualizing a commercial off-the-shelf 4G mobileWiMAX basestation. We highlight additions and modifications needed in theWiMAX network architecture for supporting multiple simultaneous virtual basestations on a single physical basestation. The most prominent features provided by the proposed virtual basestation framework include the capability to perform all frame switching at layer-2, and control mechanisms to provide isolation across slices needed to ensure experiment repeatability. By prototyping on a commercial WiMAX radio, this paper shows the usage of the virtual basestation system for housing mobile virtual network operators and testbeds alike. A use case is shown where the virtual basestation design is used to evaluate mobile handoff schemes. Another usage case is shown for optimizing a video delivery on the edge. The video delivery use case is used to show performance improvements of up to 5dB in the PSNR. Evaluation of prototype shows a significant improvement in the slice isolation, with aggregate throughput improvements of up to 192% achievable through fair resource allocation.

Fast track article: Backlogged queue based MAC frame aggregation

Frame aggregation is a wireless link optimization mechanism that aims to reduce transmission overheads by sending multiple frames as the payload of a single MAC frame. Aggregation mechanisms need to address two main performance concerns. Naive aggregation schemes can wait to aggregate until enough data for pre-decided aggregated frame lengths is available, which can result in delay penalties due to variations in traffic type or load levels. The second possible performance side effect is that the increase in the aggregated frame length may result in an increased packet error rate in noisy environments. Adaptive aggregation methods have previously been proposed to deal with the above problems independently. In this study, a backlogged queue (BQ) aggregation approach is proposed that considers both these aspects, and also ensures inter-operability with other WLAN devices that are not capable of frame aggregation. The length of the backlogged queue is used as an indicator for delay-optimal framing, and, using modeling, the study shows that it is always beneficial to perform BQ frame aggregation up to the wireless MTU even in the presence of noise. Performance evaluation of the proposed algorithm on the ORBIT testbed shows throughput improvements of up to 56% in the presence of channel noise and 25% in scenarios with high contention over using a simple 802.11e based TxOP. An experimental case study shows improvement in FTP file transfer times of up to 11% while preserving performance for real-time traffic.