Venkatesh Vadde

Partial response signaling for enhanced spectral efficiency and RF performance in OFDM systems

An OFDM system traditionally modulates each orthogonal subcarrier with a single data sample. We introduce a new method of partial response (PR) signaling where each data sample is spread over multiple subcarriers. The deliberately introduced dispersion in frequency can help compress the signal in time leading to significant time and/or bandwidth gains. We evaluate the performance of a PR signaled OFDM system in Rayleigh fading channels. We show that PR-OFDM can give spectral efficiency gains of up to 40% and mitigate peak-to-average power ratio by up to 5 dB.

Optical information storage in cellular mobile terminals

The trend towards so-called digital convergence (multiple functionality within a single terminal) is opening up a need for high-capacity storage within the cellular mobile terminals (CMT). Solid-state memories and magnetic microdrives are the most commercially mature options. Optical disk technology in this size range is immature, but has a unique potential: no other medium at present has the capability to be simultaneously low-cost, high-capacity, and exchangeable. In this paper, we explore the requirements for the implementation of optical disk storage in a CMT environment. From the technical point of view, these requirements include small form factor, high-enough data density and throughput, low power consumption, robustness, low cost, mass productability, and modularity. Although current technologies may satisfy some of these requirements individually, there is a need for combined optimization of all of these parameters. From the commercial point of view, the most crucial requirement is global standardization. Such standardization is crucial if wide interoperability is wanted (between CMT manufacturers, and even more crucially between CMTs and other appliances). Current optical storage standards are industry-driven and tend to be proprietary and/or incompatible. Even if the technical challenges can be met, optical data storage is not likely to be accepted in CMT applications unless global standardization proceeds more quickly than it is doing at present.