A combined PSK/ASK transmission system for commercial telephony via satellite

This study addresses three modulation schemes capable of increasing the voice channel capacity of the INTELSAT TDMA/DSI System operating with INTELSAT V spacecraft. In particular, a combination digital Amplitude-Shift Keying/Phase-Shifting Keying (APK) technique is evaluated with respect to signal design, thermal noise performance, bandwidths limitations, co-channel interference, adjacent channel interference, TWT distortion and modem complexity in an INTELSAT TDMA system environment. In a linear channel some APK signal designs are known to require significantly less average SNR than PSK to achieve the same probability of symbol error. However, when operated through a satellite channel containing at least one TWT, the reduction in average power required to accommodate amplitude variations causes APK performance to fall below that of PSK for the same alphabet size. Signal predistortion and/or TWT linearization can eliminate the effect of TWT distortion and restore the performance advantage, although the overall performance of APK is still inferior to PSK. However, in a heavily interference limited environment, such as INTELSAT V, the lower average power requirements caused an APK system to perform better, in some cases considerably better, than the corresponding PSK case. Modem implementation considerations include how the signal set can be generated, the type and method of predistortion compensation, the detection method and the equipment required for the reconstruction of phase and amplitude references. The evaluation techniques of APK described include mathematical models, computer simulations (including the development of a unified error performance expression) and logical extrapolation from the QPSK case. Finally, a simple 8 level APK hardware modem was constructed and evaluated. It is concluded that an APK system may be of advantage as a retrofit in the INTELSAT TDMA system operating at 6/4 GHz, but be of significant advantage at 14/11 Ghz where the higher signal/noise ratios can yield an increase in capacity of up to 50 percent

A comparison between APSK and QAM in wireless tactical scenarios for land mobile systems

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Equalizers for communications satellites

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 57).This thesis investigates equalization for advanced protected satellite communications systems in development at MIT Lincoln Laboratory. Equalizers facilitate high data rate communication by correcting dispersion in the transmitter and receiver signal chains. An automated calibration procedure for finding optimal equalizers was developed. Repeated testing addressed questions about noise amplification, filter complexity requirements, and narrow band performance degradation. After examining various architectures, it was determined that the FIR filter was the best equalizer structure given the nature of the channel. The basic calibration procedure was also extended for use at high RF frequencies by using a spectrum analyzer as a tuned receiver.by Leon Fay.M.Eng

Virtual SATCOM, Long Range Broadband Digital Communications

The current naval strategy is based on a distributed force, networked together with high-speed communications that enable operations as an intelligent, fast maneuvering force. Satellites, the existing network connector, are weak and vulnerable to attack. HF is an alternative, but it does not have the information throughput to meet the distributed warfighting need. The US Navy does not have a solution to reduce dependency on space-based communication systems while providing the warfighter with the required information speed. Virtual SATCOM is a solution that can match satellite communications (SATCOM) data speed without the vulnerable satellite. It is wireless communication on a High Frequency (HF) channel at SATCOM speed. We have developed an innovative design using high power and gain, ground-based relay systems. We transmit extremely wide-wideband HF channels from ground stations using large directional antennas. Our system starts with a highly directional antenna with a narrow beam that enables increased bandwidth without interfering with other spectrum users. The beam focus and power provide a high SNR across a wideband channel with data rates of 10 Mbps; 1000 times increase in HF data speed. Our modeling of the ionosphere shows that the ionosphere has more than adequate bandwidth to communicate at 3000 km and high speeds while avoiding detection. We designed a flexible structure adjustable to the dynamic ionosphere. Our design provides a high-speed communications path without the geo-location vulnerability of legacy HF methods. Our invention will benefit mobile users using steerable beam forming apertures with wide bandwidth signals. This dissertation will focus on three areas: an examination of the ionosphere’s ability to support the channel, design of a phased array antenna that can produce the narrow beam, and design of signal processing that can accommodate the wideband HF frequency range. Virtual SATCOM is exciting research that can reduce cost and increase access to long-range, high data rate wireless communications

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

Adaptive Bit Allocation With Reduced Feedback for Wireless Multicarrier Transceivers

With the increasing demand in the wireless mobile applications came a growing need to transmit information quickly and accurately, while consuming more and more bandwidth. To address this need, communication engineers started employing multicarrier modulation in their designs, which is suitable for high data rate transmission. Multicarrier modulation reduces the system's susceptibility to the frequency-selective fading channel, by transforming it into a collection of approximately flat subchannels. As a result, this makes it easier to compensate for the distortion introduced by the channel. This thesis concentrates on techniques for saving bandwidth usage when employing adaptive multicarrier modulation, where subcarrier parameters (bit and energy allocations) are modulated based on the channel state information feedback obtained from previous burst. Although bit and energy allocations can substantially increase error robustness and throughput of the system, the feedback information required at both ends of the transceiver can be large. The objective of this work is to compare different feedback compression techniques that could reduce the amount of feedback information required to perform adaptive bit and energy allocation in multicarrier transceivers. This thesis employs an approach for reducing the number of feedback transmissions by exploiting the time-correlation properties of a wireless channel and placing a threshold check on bit error rate (BER) values. Using quantization and source coding techniques, such as Huffman coding, Run length encoding and LZWalgorithms, the amount of feedback information has been compressed. These calculations have been done for different quantization levels to understand the relationship between quantization levels and system performance. These techniques have been applied to both OFDM and MIMO-OFDM systems

Advanced Modulation and Coding Technology Conference

The objectives, approach, and status of all current LeRC-sponsored industry contracts and university grants are presented. The following topics are covered: (1) the LeRC Space Communications Program, and Advanced Modulation and Coding Projects; (2) the status of four contracts for development of proof-of-concept modems; (3) modulation and coding work done under three university grants, two small business innovation research contracts, and two demonstration model hardware development contracts; and (4) technology needs and opportunities for future missions