Charles C. Wang

An algorithm to design finite field multipliers using a self-dual normal basis

The concept of using a self-dual normal basis to design the Massey-Omura finite-field multiplier is presented. An algorithm is given to locate a self-dual normal basis for GF(2/sup m/) for odd m. A method to construct the product function for designing the Massey-Omura multiplier is developed. It is shown that the construction of the product function based on a self-dual basis is simpler than that based on an arbitrary normal basis. >

On the performance of turbo codes

The performance of the turbo code is sensitive to its code structure, which is made up of code rate, constraint length, tap connection, block size, interleaving pattern and number of decoding iterations. In this paper, mitigation techniques that can lower the error floor are adopted in both encoder and decoder. Optimum tap connections are listed for codes with constraint lengths 3, 4, and 5. Performance variations achieved by changing different parameters are investigated. Simulation results show that (1) using 10 decoding iterations is adequate; (2) the S-random interleaving provides the best performance among the interleavers investigated; (3) using codes with constraint lengths greater than 3 does not buy any additional coding gain for short block size (in the vicinity of 100); (4) for block size greater than 500, no significant improvement is noticed by increasing the constraint length from 4 to 5 in the range of bit error rate (BER) <10/sup -6/; and (5) the punctured rate 1/2 code structure degrades the performance by only 0.5 to 0.7 dB in comparison with the classic rate 1/3 turbo code for constraint lengths 3, 4, and 5.

Satellite payload architectures for wideband communications systems

Future communications satellites will employ broadband communications techniques. In order to provide for a planning of their development and conceptual design, various satellite payload architectures need to be investigated. Of particular interest, the architectures discussed in this paper include no-processing, partial-processing, and full-processing satellite payloads. Functional characteristics and features associated with each of these architectures are described in detail. Typical link budget calculations are presented for comparison. In addition, this paper presents a brief discussion on the issue of implementing the onboard channelization and switching circuitry, comparing the use of analog and digital components.

Asymptotic performances of nonrepetitive and repetitive turbo codes

The analytically calculated asymptotic BER performance of turbo codes using a transfer function bound technique is presented. Good code structures for constraints lengths 3, 4, and 5 are listed. The repetitive turbo code is introduced with two types of decoding algorithms. Its asymptotic BER performance is presented. Good repetitive turbo codes are also listed. It is shown that the BER performance can be improved using the repetitive turbo code.

Improving faded turbo code performance using biased channel side information

Turbo decoding is based on the concept of maximum likelihood decision on blocks of data. The decision on a bit affects the decoding of subsequent bits. Fading is a type of corruption whose effect can be extended over a period of multiple bits, resulting in significant performance degradation for turbo codes. In this paper, a Markov process is utilized to model a fading channel, and bit error rate (BER) performance using BPSK with turbo code is examined. A channel interleaver is used to improve performance. In addition, a technique of using biased channel side information for turbo decoding is introduced. It is demonstrated that this technique can further improve performance.

Onboard Radar Processor Development for Rapid Response to Natural Hazards

The unique capabilities of imaging radar to penetrate cloud cover and collect data in darkness over large areas at high resolution makes it a key information provider for the management and mitigation of natural and human-induced hazards. Researchers have demonstrated the use of UAVSAR data to determine flood extent, forest fire extent, lava flow, and landslide. Data latency of at most 2-3 h is required for the radar data to be of use to the disaster responders. We have developed a UAVSAR on-board processor for real time and autonomous operations that has high fidelity and accuracy to enable timely generation of polarimetric and interferometric data products for rapid response applications. This on-board processor design provides a space-qualification path for technology infusion into future space missions in a high-radiation environment with modest power and weight allocations. The processor employs a hybrid architecture where computations are divided between field-programmable gate arrays, which are better suited to rapid, repetitious computations, and a microprocessor with a floating-point coprocessor that is better suited to the less frequent and irregular computations. Prior to implementing phase preserving processor algorithms in FPGA code, we developed a bit-true processor model in MATLAB that is modularized and parameterized for ease of testing and the ability to tradeoff processor design with performance. The on-board processor has been demonstrated on UAVSAR flights.

Limiter/Discriminator Detection of Narrowband FM in Jamming and Multipath Environments

This paper presents a performance analysis of frequency-hopped (FH) spread spectrum systems for narrowband digital FM with limiter-discriminator (L/D) detection and integrate-and-dump post-detection filtering. The performance improvement provided by using coding and subsymbol diversity is illustrated. It is also demonstrated that a more robust, less complex system can perform better than the conventional system in partial band noise jamming and multipath environments.

X-Band Choke Ring Horn Telecom Antenna for Interference Mitigation on NASA’s SWOT Mission

A low-gain antenna (LGA) is designed for high cross-polarization discrimination (XPD) and low backward radiation within the 8.025-8.4-GHz frequency band to mitigate cross-polarization and multipath interference given the spacecraft layout constraints. The X-band choke ring horn was optimized, fabricated, and measured. The antenna gain remains higher than 2.5 dBi for angles between 0° and 60° off-boresight. The XPD is higher than 15 dB from 0° to 40° and higher than 20 dB from 40° to 60° off-boresight. The calculated and measured data are in excellent agreement.

Novel network test-bed simulators

The novel network testbed simulators are described: the request protocol simulator and the link protocol simulator. These testbeds are useful for evaluating delay-throughput performances of demand-assisted multiple-access (DAMA) protocols in mobile fading environments. The request protocol testbed simulates the multiple-access scheme for making connection requests in the DAMA protocol. The link protocol testbed simulates the link-layer protocol for data transmissions. In both testbeds a physical layer simulator is utilized to perform channel encoding and decoding, interleaving and deinterleaving, modulation and demodulation, and fading channel propagation. The authors present the architecture and some simulation results of both testbed simulators.<<ETX>>