Aamod Khandekar

On the complexity of reliable communication on the erasure channel

We discuss the complexity of achieving channel capacity on the binary erasure channel (BEC) in view of recent advances. We also extrapolate to conjecture complexity bounds on more general channels.

BSC Thresholds for Code Ensembles Based on “Typical Pairs” Decoding

In this paper, we develop a method for closely estimating noise threshold values for ensembles of binary linear codes on the binary symmetric channel. Our method, based on the “typical pairs” decoding algorithm pioneered by Shannon, completely decouples the channel from the code ensemble. In this, it resembles the classical union bound, but unlike the union bound, our method is powerful enough to prove Shannon’s theorem for the ensemble of random linear codes. We apply our method to find numerical thresholds for the ensembles of low-density parity-check codes, and “repeat-accumulate” codes.

Preamble design, system acquisition, and determination in modern OFDMA cellular communications: an overview

The wide choices of deployment parameters in next generation wireless communication systems, such as flexible bandwidth allocation, synchronous/ asynchronous modes, FDD/TDD, full/half duplex, and configurable cyclic prefix duration, etc., present significant challenges in preamble and system acquisition design. This article addresses these challenges, as well as the solutions provided by the next generation wireless standards, such as the IEEE 802.20 Mobile Broadband Wireless Access (MBWA) standard and the 3GPP LTE standard. The design facilitates the maximal flexibility of the system configuration and yet has low overhead, low acquisition latency, and low complexity. System acquisition and determination techniques are also discussed in detail.

Irregular repeat accumulate codes for non-binary modulation schemes

In this paper, we review the performance of irregular repeat accumulate (IRA) codes. We present simulation results on the performance of IRA codes in two non-binary modulation schemes viz., turbo-coded modulation and multilevel coding. These results show that IRA codes are good for high data rate applications and that multilevel coding with IRA codes provides a low complexity alternative to TCM.

Preamble Design and System Acquisition in Ultra Mobile Broadband Communication Systems

The wide choices of deployment parameters in next generation wireless communication systems, such as flexible bandwidth allocation, synchronous/asynchronous modes, FDD/TDD, full/half duplex, and configurable cyclic prefix duration, etc., present significant challenges in preamble and system acquisition design. This paper addresses these challenges, as well as the solutions provided by the 3GPP2 Ultra Mobile Broadband (UMB) standard. The proposed preamble design facilitates the maximal flexibility of the system configuration and yet has low overhead, low acquisition latency, and low complexity. Although the design is discussed under the UMB context, it also serves as a preamble design paradigm for an OFDMA communication system in general.