Archan Misra

Minimum energy paths for reliable communication in multi-hop wireless networks

Current algorithms for minimum-energy routing in wireless networks typically select minimum-cost multi-hop paths. In scenarios where the transmission power is fixed, each link has the same cost and the minimum-hop path is selected. In situations where the transmission power can be varied with the distance of the link, the link cost is higher for longer hops; the energy-aware routing algorithms select a path with a large number of small-distance hops. In this paper, we argue that such a formulation based solely on the energy spent in a single transmission is misleading --- the proper metric should include the total energy (including that expended for any retransmissions necessary) spent in reliably delivering the packet to its final destination.We first study how link error rates affect this retransmission-aware metric, and how it leads to an efficient choice between a path with a large number of short-distance hops and another with a smaller number of large-distance hops. Such studies motivate the definition of a link cost that is a function of both the energy required for a single transmission attempt across the link and the link error rate. This cost function captures the cumulative energy expended in reliable data transfer, for both reliable and unreliable link layers. Finally, through detailed simulations, we show that our schemes can lead to upto 30-70% energy savings over best known current schemes, under realistic environments.

TeleMIP: telecommunications-enhanced mobile IP architecture for fast intradomain mobility

This article first surveys existing protocols for supporting IP mobility and then proposes an extension to the mobile IP architecture, called TeleMIP. Our architecture attempts to achieve smaller handoff latency by localizing the scope of most location update messages within an administrative domain or a geographical region. TeleMIP is intended for use in evolving third-generation wireless networks, and introduces a new logical entity, called the mobility agent, which provides a mobile node with a stable point of attachment in a foreign network. While the MA is functionally similar to conventional foreign agents, it is located at a higher level in the network hierarchy than the subnet-specific FAs. Location updates for intradomain mobility are localized only up to the MA; transmission of global location updates are necessary only when the mobile changes administrative domains and/or geographical regions. By permitting the use of private or locally scoped addresses for handling intradomain mobility, TeleMIP allows efficient use of public address space. Also, by reducing the frequency of global update messages, our architecture overcomes several drawbacks of existing protocols, such as large latencies in location updates, higher likelihood of loss of binding update messages, and loss of inflight packets, and thus provides better mobility support for real-time services and applications. The dynamic creation of mobility agents (in TeleMLP) permits the use of load balancing schemes for the efficient management of network resources.

MACA-P: a MAC for concurrent transmissions in multi-hop wireless networks

This paper presents the initial design and performance study of MACA-P, a RTS/CTS based MAC protocol that enables simultaneous transmissions in multihop ad-hoc wireless networks. Providing such low-cost multihop and high performance wireless access networks is an important enabler of pervasive computing. MACA-P is a set of enhancements to the 802.11 DCF that allows parallel transmissions in many situations when two neighboring nodes are either both receivers or both transmitters, but a receiver and a transmitter are not neighbors. Like 802.11, MACA-P contains a contention-based reservation phase prior to data transmission. However, the data transmission is delayed by a control phase interval, which allows multiple sender-receiver pairs to synchronize their data transfers, thereby avoiding collisions and improving system throughput.

Minimum energy reliable paths using unreliable wireless links

We address the problem of energy-efficient reliable wireless communication in the presence of unreliable or lossy wireless link layers in multi-hop wireless networks. Prior work [1] has provided an optimal energy efficient solution to this problem for the case where link layers implement perfect reliability. However, a more common scenario --- a link layer that is not perfectly reliable, was left as an open problem. In this paper we first present two centralized algorithms, BAMER and GAMER, that optimally solve the minimum energy reliable communication problem in presence of unreliable links. Subsequently we present a distributed algorithm, DAMER, that approximates the performance of the centralized algorithm and leads to significant performance improvement over existing single-path or multi-path based techniques.

IDMP-based fast handoffs and paging in IP-based 4G mobile networks

We consider the use of our previously proposed Intra-Domain Mobility Management Protocol (IDMP) in fourth-generation mobile networks. On evaluating the heterogeneous access technologies, cellular layouts, and application characteristics of 4G environments, we realize a need to reduce both handoff latency and the frequency of mobility-related signaling. We first present IDMPs fast intradomain handoff mechanism that uses a duration-limited proactive packet multicasting solution. We quantify the expected buffering requirements of our proposed multicasting scheme for typical 4G network characteristics and compare it with alternative IP-based fast handoff solutions. We also present a paging scheme under IDMP that replicates the current cellular paging structure. Our paging mechanism supports generic paging strategies and can significantly reduce the mobility-related IP signaling load.

Autoconfiguration, registration, and mobility management for pervasive computing

In the vision of pervasive computing, users will exchange information and control their environments from anywhere using various wireline/wireless networks and computing devices. We believe that current protocols, such as DHCP, PPP, and Mobile IP, must be enhanced to support pervasive network access. In particular, this article identifies three fundamental functions: autoconfiguration, registration, and mobility management, that need such enhancements. Realizing that the IP autoconfiguration capabilities must be extended to configure routers and large dynamic networks, we first describe our autoconfiguration solution based on the dynamic configuration and distribution protocol (DCDP). Second, we discuss why providing user-specific services over a common infrastructure needs a uniform registration protocol, independent of the mobility and configuration mechanisms. We present an initial version of the basic user registration protocol (BURP), which provides secure client-network registration and interfaces to AAA protocols such as Diameter. Finally, we discuss the dynamic mobility agent (DMA) architecture, which provides a hierarchical and scalable mobility management framework. The DMA approach allows individual users to customize their own mobility-related features, such as paging, fast handoffs, and QoS support, over a common access infrastructure and to select multiple global binding protocols as appropriate.

IDMP: an intradomain mobility management protocol for next-generation wireless networks

This article describes a lightweight intradomain mobility management protocol (IDMP) for managing mobility within a domain, commonly known as micromobility management, for next-generation wireless networks. IDMP is modular and simple because it leverages existing protocols, such as Mobile IP or SIP as global mobility management, for locating roaming nodes. Unlike other proposed intradomain mobility management schemes, IDMP uses two dynamically auto-configured care-of addresses for routing the packets destined to mobile nodes. The global care-of address is relatively stable and identifies the mobile nodes attachment to the current domain, while the local care-of address changes every time the mobile changes subnets and identifies the mobiles attachment to the subnet level granularity. After describing the lightweight base protocol, we discuss possible enhancements to reduce the latency of intradomain updates during handoffs, which are critical for real-time applications both for wide area cellular networks and enterprise wireless LANs. We also discuss mechanisms to incorporate paging support in IDMP and hence reduce the mobility-related signaling load on a mobile node. Detailed implementation and performance results from experiments on our testbed are also presented.

Barometric phone sensors: more hype than hope!

The inclusion of the barometer sensor in smartphones signaled an opportunity for aiding indoor localization efforts. In this paper, we therefore investigate a possible use of the barometer sensor for detecting vertically oriented activities. We start by showing the accuracies of various commodity measurement devices and the challenges they bring forth. We then show how to use the barometer values to build a predictor that can detect floor changes and the mode (elevator, escalator, or stairs) used to change floors with nearly 100% accuracy. We validate these properties with data collected using 3 different measurement devices from 7 different buildings. Our investigation reveals that while the barometer sensor has potential, there is still a lot left to be desired.

The window distribution of idealized TCP congestion avoidance with variable packet loss

This paper analyzes the stationary behavior of the TCP congestion window performing ideal congestion avoidance when the packet loss probability is not constant, but varies as a function of the window size. By neglecting the detailed window behavior during fast recovery, we are able to derive a Markov process that is then approximated by a continuous-time, continuous state space process. The stationary distribution of this process is analyzed and derived numerically and then extrapolated to obtain the stationary distribution of the TCP window. This numerical analysis enables us to predict the behavior of the TCP congestion window when interacting with a router port performing early random drop (or random early detection) where the loss probability varies with the queue occupancy.

A label-switching packet forwarding architecture for multi-hop wireless LANs

A router in wired network typically requires multiple network interfaces to act as a router or a forwarding node. In an ad-hoc multi-hop wireless network on the other hand, any node with a wireless network interface card can operate as a router or a forwarding node, since it can receive a packet from a neighboring node, do a route lookup based on the packets destination IP address, and then transmit the packet to another neighboring node using the same wireless interface. This paper investigates a combined medium access and next-hop address lookup based on fixed length labels (instead of IP addresses), which allows the entire packet forwarding operation to be executed within the wireless NIC without the intervention of the host protocol stack. Medium access schemes to date, such as IEEE 802.11, have been designed implicitly for either receiving or transmitting a packet, but not for a forwarding operation, i.e. receiving a packet from an upstream node and then immediately transmitting the packet to a downstream node as an atomic channel access operation. This paper proposes a MAC protocol for packet forwarding in multi-hop wireless networks. The proposed protocol builds on the IEEE 802.11 DCF MAC using RTS/CTS and uses MPLS like labels in the control packets (RTS/CTS) to allow the forwarding node to determine the next hop node while contending for the channel. The throughput of this protocol is compared with 802.11 DCF MAC through simulation.