Chip-Interleaved Block-Spread Code Division Multiple Access

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Georgios Giannakis Title: "Chip_interleaved Block-Spread Code Division Multiple Access" CCR-0105612 With the demand for higher data rates and wireless services rising as fast as the Internet permeated our lives, the need to cope with the idiosyncrasies of the shared wireless medium increases along with the challenges : multi-user interference (MUI), fading propagation effects, mobility-induced impairments, and high-performance telecommunication systems that are also bandwidth- and power-efficient. Today's Code-Division Multiple Access (CDMA) relies on long aperiodic pseudo-noise codes and strict power control to suppress MUI. On the other hand, CDMA proposals with symbol-periodic short spreading codes relax the need for power control at the expense of high-complexity MUI cancellation which is less affordable at the mobile unit in the downlink. But also in the uplink, the frequency-selective fading that asynchronous high-rate transmissions experience as they propagate through multipath-rich channels, degrades performance unless bandwidth is sacrificed. The CDMA system of this grant relies on the novel idea of spreading a block of symbols with long, yet structured and deterministic, user codes. Our block-spread transmissions can be viewed as (and are implemented by) chip-interleaving of symbols spread by short codes. The attractive features of the resulting Chip-Interleaved Block-Spread (CIBS) CDMA system: i)flexibility to revert as block-spread TDMA, FDMA, Direct-Sequence-, or, Multicarrier-CDMA; ii)power- and bandwidth-efficiency; iii)MUI avoidance by-design; iv)full-multipath diversity and no loss of optimality with matched-filter reception; and v)low-complexity. Basic research directions include: performance analysis and comparisons with competing alternatives in terms of capacity and bit error rates; mobility studies and development of timing-offset, carrier-frequency offset and channel estimation algorithms for acquisition and tracking; incorporation of multiple antennas to enhance diversity with space-time coding gains; investigation of optimal precoding, power-and-bit loading and adaptive modulation; and study of cellular system-level issues.