Multicarrier Communication (MC) is a very promising idea for both wireline and wireless communications. MC divides the transmission band into many, narrow bandwidth subchannels, which greatly simplifies the design and implementation of the receiver. In wireline communication where the channel is quasi-static, MC allows near-optimal transmission rates by the means of bit-loading, where each subcarrier can be individually optimized to take full advantage of the channel variations between one subcarrier to the next. This is usually referred to as DMT (Discrete Multi-Tone), and is widely used for broadband access in the xDSL modems.
For wireless communications, MC allows clever error-control coding and interleaving that take advantage of the dynamics of the channel, without bit-loading. This is known as OFDM (Orthogonal Frequency-Division Multiplexing), a strong contender for the present- and next-generation wireless systems. However, multicarrier systems exhibit a large PAR (Peak-to-Average Ratio).
MC allows the application of novel signal processing ideas, and our research focuses on fast bit-loading, PAR reduction, and the use of multiresolution constellation in MC.
Contact: Julius Kusuma, Sandeep S. Pradhan
Based on arithmetic coding, CED allows a tradeoff between error detection speed and redundancy. With traditional error control coding, the decoder needs to wait until the end of the block to detect an error. CED allows detection of error on the fly, without needing to wait until the end of a block.
This feature can be used in conjunction with ARQ....
Contact: Anand Raghavan
Interference suppression in spread-spectrum communication is essential for achieving maximum system performance. Existing interference suppression methods do not perform well for most types of nonstationary interference. We developed a multiple overdetermined tiling (MODT) with an accompanying blind interference excision scheme which appears very promising for mitigating time-frequency-concentrated interference.
Contact: Brian Krongold
The idea of this project is to model the wireless channel as a packet-loss channel by applying RCPC codes to the transmitted data and using CRC codes to determine if the packet is successfully decoded at the receiver, then applying Reed-Solomon codes to allow data to be reconstructed with packet losses. The novel part of this system is the use of an efficient optimizer to choose the protection level for each Reed-Solomon column to reduce the expected error at the receiver. (We actually bias the solution slightly toward reducing the peak error at the expense of the average MSE, so it's not optimal in the strict sense of the word.) The paper "Wireless Image Transmission Using Multiple Description Based Concatenated Codes" describes this system; it is available below.
Contact: Dan Sachs