Lochan Verma

Wifi on steroids: 802.11AC and 802.11AD

The advent of bandwidth-hungry wireless applications such as large file transfer, high definition video streaming, wireless display, and cellular data offload highlight the impending need for larger bandwidth and super speed WiFi links exceeding 1 Gb/s. This article introduces two emerging standards likely to shake the wireless world, namely IEEE 802.11ac and IEEE 802.11ad, and identifies the challenges in the path of multi-gigabit WiFi. We study the suitability of these standards for the new usage models enlisted in this article.

Green operation of multi-band wireless LAN in 60 GHz and 2.4/5 GHz

IEEE 802.11ad Task Group is currently defining a standard for multi-gigabits per second data rate WLAN connections in the 60 GHz band with a target completion date of 2012. The 802.11n, which operates in 2.4/5 GHz band, guarantees data rate of at least 108 Mbps and coverage of about 50 meters, with a maximum data rate of 600Mbps over relatively short distances. In comparison, 60 GHz band can support multi-gigabit data-rates (up to 6 Gbps), but the typical coverage is limited to around 10 meters due to significantly higher propagation loss. Therefore, the two wireless bands provide widely different, yet complementary, characteristics in terms of range and throughput. However, there is a greater need for an efficient multi-band operation that enables selecting the optimum interface based on the communicating stations physical proximity and multi-band channel conditions. In this paper, we present techniques that facilitate green multi-band IEEE 802.11ad for portable devices. We performed a detailed simulation study and the results indicate that the proposed techniques reduce energy consumption of the multi-band Wi-Fi devices as they are at least 40% more power efficient.

Reliable, Low Overhead Link Quality Estimation for 802.11 Wireless Mesh Networks

We propose QUEST (QUality ESTimation), a new method that accurately estimates IEEE 802.11 wireless link quality with no in-band signaling overhead. Existing link quality estimation methods either are based on hello exchanges by fixing or varying transmission rates or rely on the history (e.g., delivery ratio) of previously sent data packets in a per-rate/-neighbor manner. QUEST on the other hand, is based on a delivery ratio vs. SNR (Signal to Noise Ratio) relation, called profile, that is managed offline. QUEST estimates the target link quality in terms of delivery ratio by performing profile lookup for any incoming messages including broadcast hello, beacon, data packets, etc. Therefore, it does not depend on a designated protocol to obtain the delivery ratio. Instead, in QUEST, the per-rate/-neighbor management of link quality is achieved by profile lookup. We perform testbed experiments to achieve the profile and also unravel two major bugs in MadWifi driver, widely employed by many researchers to build an 802.11-based system. Utilizing the large database of transmitter and receiver traces with an indigenously developed tool, we study the impact of altering the averaging time period on the profile for different transmission rates.

Collision-Aware Rate Adaptation in multi-rate WLANs: Design and implementation

Many rate adaptation algorithms have been proposed for IEEE 802.11 Wireless LAN devices and most of them operate in an open-loop manner, i.e., the transmitter adapts its transmission rate without using the feedback from the receiver. A key problem with such transmitter-based rate adaptation schemes is that they do not consider the collision effect. Accordingly, they often result in severe throughput degradation when many transmission failures are due to frame collisions. In this paper, we present a transmitter-based rate adaptation scheme, called CARA (Collision-Aware Rate Adaptation), and its MadWifi-based implementation. The key idea of CARA is that the transmitter combines adaptively the RTS/CTS (Request-to-Send/Clear-to-Send) exchange with the CCA (Clear Channel Assessment) functionality in order to differentiate frame collisions from transmission failures due to channel errors. The effectiveness of CARA schemes is evaluated via extensive ns-2 simulations and testbed experimentations.

Backhaul need for speed: 60 GHz is the solution

The availability of 7–9 GHz of unlicensed spectrum at 60 GHz, advances in low-cost silicon technology, and high interference rejection due to atmospheric loss make 60 GHz an ideal solution for future 4G/5G small-cell backhaul links, where multi-gigabit rates are required. In this article, we review the 60 GHz propagation properties, the practical technology limits, and the regulatory and regional environmental impacts to present a framework for the 60 GHz backhaul link design that translates the link requirements to the essential transmitter and receiver system parameters. This approach includes a preliminary design that generates the input data set for an optimization problem. Two physical front-end architectures are discussed in this work: single-input single-output antenna for point-to-point applications and phased arrays for the future 4G/5G self-organizing backhaul networks. It is shown that selecting the proper channel bandwidth can increase the interference rejection. Furthermore, we calculate the physical data rates for the proposed modulation and coding schemes. When phased array is used, the backhaul link design can be defined as an optimization problem to find the optimum number of antennas and the gain per antenna.

Multi-band Wi-Fi systems: A new direction in personal and community connectivity

Strong use cases driven by the need for personal and community connectivity creates market segment for devices with multi-band Wi-Fi systems. We present usage models for such Wi-Fi systems and articulate design and implementation choices.

Proliferation of Wi-Fi: Opportunities in CE ecosystem

With the rapid proliferation of bandwidth intensive content, a newer technology is essential as 802.11 a/b/g cannot satisfy the requirements, like higher bandwidth. The latest generation, 802.11n, is the answer and helps accelerate the uptake of Wi-Fi integration in CE (Consumer Electronic) devices. Nowadays, most of CE devices are Wi-Fi-enabled and the unprecedented growth causes a dearth of bandwidth for Wi-Fi operation. We present the various standardization activities in progress by industry alliances and international standard organizations to assuage the bandwidth paucity problem by defining protocols for Wi-Fi operation in the available license-exempt spectrum in VHF/UHF (Very High Frequency/Ultra High Frequency) and 60 GHz band. The expansion of Wi-Fi to CE coupled with the new standardization initiatives creates new usage models like P2P (Peer-to-Peer) communication, Wireless Display, Smart Grid applications, etc., that are also articulated in this work.

Wireless networking in TV white space leveraging Wi-Fi

Recently, many standardization activities are in progress to extend Wi-Fi operation to the available unlicensed TV spectrum, i.e., 54–698 MHz. TV channel scanning for incumbent detection is crucial for operation in the TV band and we propose IEs (Information Element) that assist an AP (Access Point) in delegating channel scanning operation to the associated STAs (STAtion) so that it is always available for remedial action if an incumbent arrives on the channel on which the BSS (Basic Service Set) is operational. Also, TV channels are of 6 MHz width and we propose IEs that assist in channel bonding negotiations between two Wi-Fi devices operating in the TV spectrum. The proposed IEs are transmitted by the Wi-Fi devices using the Action frames defined in the IEEE 802.11 standard.

Wireless display: An unmet need in CE ecosystem

The trend nowadays is for the consumers to be able to view their multimedia content on a bigger/better display like HDTV instead of gathering around small displays like a laptop screen. Wireless Display is a method of transferring the multimedia content from the source device to the sink device- wirelessly. In this paper we evaluate the various wireless technologies available for Wireless Display function and narrow down on Wi-Fi as the most suitable wireless technology. We identify key technical challenges for a Wi-Fi based Wireless Display and provide insights in to some possible solutions to the identified challenges.

AGILE Rate Control for IEEE 802.11 Networks

We present a transmission rate adaptation algorithm called AGILE (ACK-Guided Immediate Link rate Estimation) for IEEE 802.11 networks. The key idea of AGILE is that the transmitter adjusts the transmission rate by means of measuring the SNR (Signal-to-Noise Ratio) during any frame reception including the ACK (Acknowledgment) frame, and estimating the corresponding maximum achievable throughput using a profile , which is materialized by extensive off-line measurement. AGILE is equipped with an advanced RTS (Request-To-Send)/CTS (Clear-To-Send) activation algorithm, eRTS filter that intelligently switches on/off RTS frame transmission to enhance the achievable throughput depending upon the existence of multiple contending (or even hidden) stations. The effectiveness of AGILE is evaluated in our MadWifi-based testbed implementation and we compare its performance with different rate adaptation schemes in various scenarios.