MICHELLE EFFROS:

APPLICATIONS

The World Wide Web

With advances in communications media and technologies come corresponding needs for communication techniques that take full advantage of the capabilities particular to those technologies. A prime example of such an area of growth is the medium of internet communications. With the growth of internet communications comes an increased need for techniques whereby a single user can simultaneously communicate the same information to a wide array of other users with vastly varying bandwidth resources, computational capabilities, and performance requirements. Along with a variety of other factors, this need has helped inspire a surge in interest in multi-resolution or progressive transmission source coding as well as source-independent or universal multi-resolution source coding.

Wireless Communications:

Wireless communications systems suffer a number of difficulties caused by the great system uncertainties to which they are subjected. For example, the noise characteristics of a wireless communication channel can vary widely and unpredictably. As a user travels through space and time, the interference, distance to base station, and competing network traffic experienced by the wireless unit may all vary enormously. Devising channel coding strategies to deal with these changing channel characteristics presents a wide array of new challenges. For example, as the channel characteristics change, so too does the maximal rate at which information can be reliably communicated across the channel. Thus good channel codes for wireless communications systems must be adaptive, or at least robust, to channel variations.

Yet developing good channel codes for wireless communications systems, may have consequences not only for channel code design but also for source coding design, leading to a variety of joint-source channel coding issues. For example, if the channel coding rate is allowed to vary over time, then the source coding rate must also vary to make maximum use of the available channel coding rate. Multiple resolution source codes are particularly well-suited to this application, since they allow for varying rate but achieve that varying rate with a single source code, rather than a family of source codes, as would otherwise be required.

An alternative example of the interaction between source and channel codes in wireless communications systems may be seen in wireless data communication systems. Wireless data systems are typically implemented as packet-based networks in order to allow for more users to simultaneously use the same bandwidth. In packet-based networks, information is broken into small pieces or "packets", each of which is carefully labelled and independently sent over the wireless link. Due to network congestion or interference, some of the packets may be lost in transmission, and designing source codes for which data can be reconstructed appropriately even when some subset of the packets is never received (or received too late) at the decoder requires a special form of source codes, known as multiple description source codes.

Speech Recognition: Current relevant projects include universal coding.

Internet and Wireless (Packet-Based) Networks: Current relevant projects include multiple description source codes.

Data Storage Devices: Current relevant projects include multiple description source codes, multi-resolution source coding, universal multi-resolution source coding.