Cocktail Party on the Mobile Kwan Hong Lee, Andrew Lippman Viral Communications Group MIT Media Lab 20 Ames St. Cambridge, MA 02139 {kwan,lip}@media.mit.edu Thiago Santos Embedded System and Pervasive Computing Lab Federal University of Campina Grande 882 Apr´ ıgio Veloso St. Bodocong´ o, Campina Grande, Brazil thiagoss@embedded.ufcg.edu.br Abstract We present the architecture, user interface and prototype implementation of Fluid Voice, a proximity based mobile group communication system for opportunistic social ex- changes. It is designed for coordinating people in outdoor settings, spreading news during emergency responses and supporting impromptu social exchanges by exploiting the inherent broadcast nature of wireless and mobility of peo- ple. It supports diverse media: live audio, asynchronous audio, text messages, audio messages, audio polls and wish lists. In this paper, we focus on the audio support and the design for intermittent connectivity characteristics of mobile systems with limited range. Users can transition from live to asynchronous audio communication in a fluid manner depending on the wireless environment. When ev- ery node is able to hear each other, the receiver mixes all sources and provides the user with a “push to listen” inter- face to “tune in” to who they want to listen to. When the wireless channel is congested, it transitions to a “push to talk” interface (without taking over the whole channel) to reduce collisions while allowing people to barge in. When nodes cannot hear each other, Fluid Voice caches content for future delivery using a dynamic multi-stream mixer with time shifting (Tivo) functionality. The system was proto- typed on the Nokia N810’s for real world testing and we discuss its technical and social limitations. 1 Introduction In the 1950’s, Hoot and Holler [1] was a party line telecommunication system that wired a community of junk- yards in a local area. When a requested item was not found in a junkyard, the owner could pick up the microphone and reach out to other junkyards to find that missing item. This provided a means to fulfill unusual needs of customers while benefiting the business and the community of junk- yards. The party line evolved as a social utility for curious late night eavesdroppers[6], overzealous gossipers as well as important emergency dispatchers. This genre of communi- cation is defined as emergent multi-party communications. Several of today’s applications fall into this category includ- ing instant messaging chat rooms for teenagers and con- ferencing bridges for corporate businessmen. When a time sensitive information needs to be communicated to a group, the communal party line broadcast system can serve as a means to spread information efficiently. In the 1990s, Family Radio Service (FRS) radios were authorized in the US to allow any user cluster to commu- nicate without infrastructure. Citizen’s Band (CB) radios were used by truck drivers in the 1970s to notify others about road hazards and speed traps[13]. CB radios enabled a cooperative social culture on the highways for friendly conversations in addition to providing road assistance and accident prevention among the drivers. As cell phones and multi-band WiFi enabled cell phones are becoming ubiqui- tous in the 21st century, an exciting opportunity arises for supporting opportunistic social collaboration within a local area. According to In-Stat, by 2011, over 50 million sub- scribers world wide will have WLAN capabilities on their devices[5]. Yet, the main capability of such devices in- volve traditional long haul voice communications and ac- cess point based Internet services. Only a handful of works propose system solutions for decentralized conferencing[2, 12]. As people become more mobile, it becomes more impor- tant to efficiently seek information and spread relevant in- formation using a many-to-many communications system. Current phone systems are inherently designed for point to point communications. In setting up a conference bridge for many-to-many communications, significant effort is needed at a higher layer to setup a many-to-many communications Tenth IEEE International Symposium on Multimedia 978-0-7695-3454-1/08 $25.00 © 2008 IEEE DOI 10.1109/ISM.2008.33 440 Authorized licensed use limited to: MIT Libraries. Downloaded on February 9, 2009 at 14:56 from IEEE Xplore. Restrictions apply.