UCOM: Exploring the role of Multiple Radios in Short-hop Wireless Networks (2001-03)
Assuming that the cost of RF Transceivers (radios) will continue to plummet,
eventually reaching a price point that is negligible, we argue that two or
more radios working collaboratively to perform the same task, in a
short-hop wireless network improve the performance and functionality of the system dramatically
over traditional single-radio wireless systems that are popular today.
In this context, we re-visit some classical problems in wireless networking,
including energy management, mobility management, channel failure
recovery, capacity enhancement, quality of service, bandwidth
management, and location determination
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We show that a systems approach, grounded on three design
principles: Design for Separation, Design for Choice, and Design for Flexibility,
can alleviate many of the problems prevalent in current Wifi based wireless
networks. We corroborate our assertion with results obtained from a
multi-radio system that we have built. Our experience leads us to take a
position that a multi-radio platform is the right platform to base the
future of local area and personal area wireless networking. Creating such
a platform has serious implications on both hardware and software design as
well as on algorithmic and protocol research. We are exploring some of these
issues in this research.
|
Publications
- P. Bahl, A. Adya, J. Padhye, and A. Wolman,
Reconsidering the Wireless LAN Platform with Multiple Radios,
Microsoft Technical Report, MSR-TR-2003-45, June 2003
(pdf, 500 Kbytes)
- A. Adya, P. Bahl, J. Padhye, A. Wolman, and L. Zhou
A Multi-Radio Unification Protocol for IEEE 802.11 Wireless Networks,
Microsoft Technical Report, MSR-TR-2003-41, June 2003
(pdf, 376 Kbytes)
- E. Shih, P. Bahl, and M. Sinclair,
Wake on Wireless: An Event Driven Energy Saving Strategy for Battery Operated Devices,
Proceedings of ACM MobiCom 2002, Atlanta, GA (September 2002)
(pdf, 1,024 Kbytes)
Presentations
- P. Bahl, SIGCOMM Future Directions in Networking Architecture Workshop, (August, 2003)
- P. Bahl, NSF-COST(EU) Networking Research
Funding Workshop, Invited Talk (June 2003)
Wireless Internet Access in Public Places (1999-2001)
To the best of our knowledge, CHOICE was the first free public area wireless
hot-spot network in the world. We ran the network in Crossroad Mall, Bellevue (CROWN)
for 2 years (1999-2001). This project was then retired. The Crossroad's mall
continues to use our equipment and provide free wireless access. Check it out
here
The Choice Network (Nov. 1999 - Aug. 2001)
The wireless communications revolution is the ability
to connect to the Internet from anywhere at anytime. This revolution is
typified by the 3rd generation or 3G wide-area cellular systems
which are touted as the wave of the future because of their ability to
support data networking at speeds of 2 Mb/sec. But is this sufficient?
Today, local area wireless networks can provide connectivity at up to
11 Mb/sec, and in the near future they will provide access speeds of
up to 54 Mb/sec! Consequently, there is and will continue to be, a large
difference in performance between 3G systems and local area wireless networks.
As we become accustomed to these higher data rates and as the Internet becomes
increasingly multimedia-centric, our appetite for faster connectivity
will most likely increase.
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The CHOICE Network is about providing a choice
to individuals who want to access the Internet from "almost anywhere".
Almost anywhere includes places of congregation or public spaces such
as airports, restaurants, libraries, train-stations etc. The CHOICE
Network is a hardware-agnostic, software-only technology that can
propell the deployment of wireless LANs making them ubiquitous. Thus,
individuals presenting the proper credentials can access the Internet
at speeds that are much greater than 3G speeds from almost anywhere. |
The underlying language of the Choice Network is the
Protocol for Authorization, and
Negotiation of Services, or
PANS. PANS provides authentication, access, charging,
security, compression, and last-hop QoS to users of the Choice
Network.
PANS authentication is global and individual-centric i.e. the user
can be anywhere in the world and PANS can securely authenticate his or her
credential using a globally available server and database. Once this is done, PANS
allows access to the Internet in accordance to a pre-configured policy manager.
Security is robust with per-user, varying-length keys and varying encryption
algorithms valid for a varying amount of time, all of which lead to a system that
is considerably more secure than the Wired Equivalent Privacy
(WEP) security available in today's popular WLAN products. Last-hop QoS
scheduling is based on the Generalized Processor Sharing discipline, combining
centralized class-based scheduling with a propriety distributed weighted fair
scheduling mechanism within classes.
CROWN Deployment
We have deployed the CHOICE network at the Crossroads Shopping Center in Bellevue,
Washington. Dubbed CROWN (for CROssroad's Wireless Network),
this network enables everyone equipped with an IEEE 802.11b wireless network card
to access the Internet after he or she has authenticated themselves to MS Passport.
Additional services such as access to local printers, mall portal site, splash
screen of services, list of upcoming activities/event, in-store buddy list, and
location guidance will also be offered. The pilot is being used to fine tune
PANS and serves as a testbed for research on connectivity and computing in public spaces.
Demos / Coverage
Publications
- A. Balachandran, P. Bahl, and G. Voelker,
Hot-Spot Congestion Relief and Service
Guarantees in Public-Area Wireless Networks, Proceedings of WMCSA 2002,
Callicoon, New York (June 2002) (pdf, 281 Kbytes)
- A. Balachandran, G. Voelker, P. Bahl, and V. Rangan,
Characterizing
User Behavior and Network Performance in a Public Wireless LAN,
Proceedings of ACM SIGMETRICS 2002, Marina Del Rey, California (June 2002)
(pdf, 591 Kbytes)
- P. Bahl, A. Balachandran, A. Miu, W. Russell, G. Voelker and Y.M. Wang,
PAWNs: Satisfying the Need for Ubiquitous Connectivity and Location
Services, to appear in the IEEE Personal Communications Magazine (PCS),
Vol. 6, (October 2001) (pdf, 338 Kbytes)
- P. Bahl, A. Balachandran, and S. Venkatchary,
Secure Wireless Internet Access in Public Places, in
Proceedings of the IEEE
Conference on Communications, Helsinki, Finland (June 2001)
(pdf, 82 Kbytes)
- A. Miu and P. Bahl,
Dynamic Host
Configuration for Managing Mobility between Public and Private Networks,
in The 3rd Usenix Internet
Technical Symposium, San Francisco, California, USA (March 2001)
(pdf, 156 Kbytes)
Presentations
- A. Balachandran,
Secure Wireless Internet Access
in Public Places, IEEE Conference on Communications, Helsinki,
Finland (June 20, 2001)
(pdf, 390 Kbytes)
- A. Balachandran,
Requirements for Internet
Access in Public Places, 50th IETF, Basic User Registration Protocol
(BURP) BOF, Minneapolis, Minnesota, USA (March 20, 2001)
(pdf, 42 Kbytes)
- A. Miu,
Mobility Management between Public
and Private Networks, 3rd Usenix Internet Technical Symposium, San Francisco,
California, USA (March 27th, 2001)
(pdf, 858 Kbytes)
Related Work
- Internet Engineering Task Force (IETF)
- Institute of Electrical and Electronics Engineer (IEEE)
Collaborators
- Victor Bahl
- Srinivasan (Cheenu) Venkatachary (no longer with Microsoft)
- Anand Balachandran (UCSD Intern, Fall 1999)
- Allen Miu (MIT Intern, Summer 2000)
- Stephen Dahl, System Support
- Paul Hoeffer, Web Support
- Pierre De Vries (No longer with Microsoft)
RADAR: Location Determination and Services (1998-2000)
An area of study that has fascinated researchers for close to 10 years
has been one of building systems and services that are location-aware.
Generally speaking, most of the systems developed to-date have required
specialized hardware. The cost of deploying this hardware, usually for the
sole purpose of location determination, has been prohibitive compared to
the perceived benefits of the system. Consequently, wide-scale adoption
of location-aware systems has been limited.
Inspired by the promise of enabling a new class of applications and of adding
value to popular wireless LAN technology, we have built an in-building user
location and tracking system. Our approach is different from most
previous efforts in that we do not require any specialized hardware but
instead our system is built upon an already deployed and fully functional
wireless data network.
 |
RADAR is an in-building location-aware system in which
radio-frequency (RF) wireless LAN enabled mobile nodes compute their location
and use this information to inform other nodes of their location, and to
determine which network resources (e.g., printers, scanners, etc.) are within
close proximity. The system consists of a signal processing front-end and a
directory services, and a service location back-end. |
The front end operates by recording and processing signal strength
information from multiple base stations positioned to provide overlapping
coverage in the area of interest. It combines empirical measurements
and signal propagation modeling with environmental profiling,
mobility modeling, and topographical constraints to locate
and track mobile nodes. The back-end uses the location information to
query a directory server (via
LDAP)
to locate nearby network resources. Where no directory server is available
a service discovery protocol is used.
Demo / Coverage
Publications
- P. Bahl, V. N. Padmanabhan, and A. Balachandran,
Enhancements to the RADAR User Location and Tracking System,
Microsoft Research
Technical Report: MSR-TR-00-12 (February 2000)
(pdf, 209 Kbytes)
- P. Bahl and V. N. Padmanabhan,
RADAR: An In-Building RF based User Location and Tracking System,
Proceedings of IEEE INFOCOM 2000, Tel-Aviv, Israel (March 2000)
(pdf, 147 Kbytes)
- Yi-Min Wang, P. Bahl, and W. Russell, The SIMBA User Alert Service
Architecture for Dependable Alert Delivery, to appear in
International Conference on Dependable Systems
and Networks, Goteborg, Sweden (July 2000)
T. Liu, P. Bahl and I. Chlamtac,
Mobility Modeling, Location
Tracking, and Trajectory Prediction in Cellular Networks,
in the
IEEE Journal on Special Areas in Communications,
Special Issue on Wireless Access Broadband Networks,
Vol. 16, No. 6, (August 1998):922-936
(pdf, 449 Kbytes)
Presentations
Collaborators
Wireless LAN Programming, Performance, and New Applications (1997-99)
WiLIB (Library for Configuring Wireless Hardware)
(June 1997 to July 1999; Retired)
Radical differences in channel characteristics coupled with end-node mobility
make wireless networking sufficiently different from wireline networking.
Unfortunately, under the current implementation of most operating systems
a local area wireless network is treated as just-another-network and
is generally exposed to the higher layer networking protocols, operating system,
and applications as an Ethernet technology. In our opinion this is
a limited programming paradigm since it makes it difficult for the
system to adapt to the changing channel conditions and prevents software
vendors from developing adaptive and novel applications.
 |
We have enhanced the programming interface exposed by the Network Device
Interface Specification (NDIS) under Windows. With our extensions
the software components are assured of compatibility with all WLAN NICs that
support this interface. Similarly, hardware that provides the specified
interface (via NDIS miniport driver) is assured that software components
are able to locate and access its functionality. This, we feel, will lead to
smarter software that: (1) improves hardware utilization and system performance,
(2) conserves power, (3) improves last-hop quality of service, (4) manages mobility
efficiently, and (5) enables new and exciting network services not possible
on wired networks. |
The need for this project arose out of the frustration and pain we experienced
in porting mobile-aware and wireless-aware applications over hardware from
different vendors. Each vendor had his or her own propriety interface. In
addition to the usual ramp-up time and effort required to learn the interface,
the programming library was generally provided under restrictive terms and agreement
which prevented free and timely publication of research results.
In addition to the NDIS WLAN extensions we are creating WiLIB,
a user-level library, that lets programmers configure wireless hardware dynamically
(e.g. moving between ad hoc and infra-structure mode etc.). Once completed, we
intend to use WiLIB to carry out research on studying the effects of
the RF channel on upper-layer protocols and applications, and on providing
information to the networking stack that lets these protocols adapt to the
changing environmental conditions.
Collaborators
- Victor Bahl
- Gavin Holland (Intern, Summer 1999)
- Josh Broch (Intern, Summer 1998)
- Tom Fout (Windows Networking, Operating Systems Division)
- Stephen Hui (Windows Networking, Operating Systems Division)
Publications
- G. Holland, N. H. Vaidya, and P. Bahl, A Rate-Adaptive MAC Protocol
for Wireless Networks, to appear in the Porceedings of
ACM International
Conference on Mobile Computing and Networking (MobiCom 2001),
Rome, Italy, USA (July 2001)
- P. Bahl, Enhancing
the Windows Device Networking Interface Specification for Wireless Networking,
White Paper
- G. Holland and P. Bahl, NDIS Support for Mobile Wireless
LANs -- Proposed Extensions to the NDIS Standard (Specifications),
Microsoft Internal Publication (July 1999)
- P. Bahl, A Proposal for Enhancing NDIS for Local Area Wireless
Networking, Microsoft Internal Publication, (November 1998)
Fair Scheduling and Quality of Service in wireless LANs
This project looks at issues that are associated with providing quality-of-service
in broadband networks including ad hoc LANs and multi-hop wireless networks. Two
important issues need to be addressed in this context: (a) impact of broadcast
nature of wireless medium on design of QoS mechanisms, and (b) applicability
of traditional "fairness" definitions in the context of ad hoc networks.
Collaborators
Publications
- A. Dugar, N. H. Vaidya, and P. Bahl,
Priority and Fair Scheduling in a Wireless LAN,
to appear in the Proceedings of IEEE
Conference on Military Communications (MILCOM 2001),
McLean, VA (October, 2001)
- G. Holland, N. H. Vaidya, and P. Bahl,
A Rate-Adaptive MAC Protocol for Wireless Networks, in the
Proceedings of ACM International
Conference on Mobile Computing and Networking (MobiCom 2001), Rome, Italy, USA (July 2001)
- N. H. Vaidya, P. Bahl, and S. Gupta,
Distributed Fair Scheduling in a Wireless LAN, in the Proceedings of
ACM
International Conference on Mobile Computing and Networking
(MobiCom 2000), Boston, Massachusetts, USA (August 2000)
(pdf, 247 Kbytes)
- N. H. Vaidya, and P. Bahl,
Fair Scheduling in Broadcast Environments,
Microsoft Research
Technical Report: MSR-TR-99-61 (August 1999)
(pdf, 178 Kbytes)
- P. Bahl,
ARMAP - An Energy Conserving Protocol for Wireless Multimedia
Communications, in the IEEE International Symposium on
Personal, Indoor and Mobile Radio Communications, Boston,
Massachusetts, USA (September 1998) (pdf, 48.3 Kbytes)
- P. Bahl,
Supporting Digital Video in a Managed Wireless Network, in
the
IEEE Communications Magazine, Special Issue on Wireless Video,
Vol. 36, No. 6, (June 1998):94-102
(pdf, 134 Kbytes)
- P. Bahl, I. Chlamtac, and A. Farago,
Resource Assignment For Integrated Services in Wireless Networks, in the
International Journal of Communication Systems,
Special issue on Personal Communication Systems, John
Wiley, (April 1998):29-41 (Invited Paper)
(pdf, 162 Kbytes)
Power Aware Ad Hoc Sensor Communications
Networking
We have developed software that allows wireless nodes to create ad hoc
local area networks automatically. This software is being experimented
with in public places where we are building and deploying services that
exploit this functionality. Examples include: proximity networking, buddy-lists etc.
Global Hailing Channel
With the proliferation of numerous wireless devices in the market, certain frequency
bands are getting congested and noisy. This is specially true in the
case of the 2.4 GHz ISM band which is available all over the world and
consequently is highly popular among wireless hardware manufacturers. A substantial
percentage of the local-area and personal-area wireless data networking standards
are being built on the same frequency band, for example: IEEE 802.11, IEEE 802.11b,
HomeRF, Bluetooth, IEEE 802.15, and OpenAir are MAC and PHY standards for
wireless devices operating in the 2.4 GHz band. For the past several years there
has been a steady increase in equipment and users in this band. If the current
popularity of wireless networking continues to explode, it is only inevitable that
the spectrum efficienty and system performance of these devices will degrade
significantly. This in turn, may result in higher user frustration
with wireless devices, which potential could slow the rapid growth of the
overall wireless LAN-PAN market that we see today.
During a summer retreat on
Invisible Computing, we proposed the idea of creating a
Global Hailing Channel. Our proposal is
focussed on improving the radio signal congestion problem, while simultaneously
providing a universal discovery and negotiation channel and a PHY Protocol,
available to devices all over the world. Multi-modal radios use this
channel to exchange connectivity and capability information. A white paper
on this subject will be available shortly.
Collaborators
- Victor Bahl,
Microsoft Research, Redmond, Washington
-
William Kaiser, University of California, Los Angeles
- Robert Mayo
, Western Research Lab, Compaq Research
Publications
- L Li, J. Y. Halpern, P. Bahl, Yi-Min Wang, and R. Wattenhofer,
Analysis of a Cone-Based Topology
Control Algorithm for Wireless Multi-Hop Networks, in the
ACM Symposium on Principles of
Distributed Computing (PODC 2001), Newport, Rhode Island (August 2001)
(pdf, 416 Kbytes)
- R. Wattenhofer, L. Li, P. Bahl, Yi-Min Wang,
Distributed Topology Control for Wireless Multihop Ad-hoc Networks,
in the Proceedings of IEEE INFOCOM 2001, Fairbanks, Alaska, USA (April 2001)
(pdf, 253 Kbytes)
RF Standards
We realize that in order for wireless technologies to succeed it is important
for the different hardware and software manufacturers to agree on a common
(protocol) language. We are therefore actively involved in standards-setting
organizations. Our primary interest is in wireless local area networking
which includes enterprise networking, home networking, and personal area networking
Collaborators
Publications
- J. Lansford and P. Bahl,
The Design and Implementation of HomeRF: A Radio-Frequency Wireless
Networking Standard for the Connected Home, in the
The Proceedings of the IEEE (October 2000): 1662-2676
(pdf, 542 Kbytes)
- P. Bahl,
A Report on the IEEE Wireless Standards Activities,
Mobile Computing and Communications Review, Vol. 4, No. 1 (January 2000)
- J. Redi, and P. Bahl,
Mobile IP: A Solution for Transparent Seamless Mobile Computer
Communications,
Fuji-Keizai's
Report on Upcoming Trends in Mobile Computing and Communications,
(July 1998) (Invited article)
(pdf, 147 Kbytes)
