Hybrid Ultrawideband Modulations Compatible for Both Coherent and Transmit-Reference Receivers

Abstract

This paper considers signaling schemes for heterogeneous ultrawideband communications networks that contain both coherent (rake) and transmitted-reference (TR) receivers. While coherent receivers are capable of receiving TR signals, they do so with a 3 dB penalty, because they cannot make use of the energy invested into the reference pulse. We propose a new signaling scheme that avoids this drawback, by encoding redundant information on the reference pulse. The resulting scheme does not affect the operation of a TR receiver, while recovering the 3 dB penalty and furthermore providing an additional 1.7 dB coding gain to a coherent uncoded binary scheme. This can be explained by interpreting the scheme as a trellis-coded modulation. We also provide an alternative implementation that can be viewed as a recursive systematic convolutional encoder. Combining this version further with a simple forward error correction encoder results in a concatenated code that can be decoded iteratively, providing a bit-error rate of 10-3 at 2.8 dB signal-to-noise ratio in additive white Gaussian noise. The convergence behavior of this iterative code is analyzed by using extrinsic information transfer charts. IEEE Transactions on Wireless CommunicationsThis work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Abstract-This paper considers signaling schemes for heterogeneous ultrawideband communications networks that contain both coherent (rake) and transmitted-reference (TR) receivers. While coherent receivers are capable of receiving TR signals, they do so with a 3 dB penalty, because they cannot make use of the energy invested into the reference pulse. We propose a new signaling scheme that avoids this drawback, by encoding redundant information on the reference pulse. The resulting scheme does not affect the operation of a TR receiver, while recovering the 3 dB penalty and furthermore providing an additional 1.7 dB coding gain to a coherent uncoded binary scheme. This can be explained by interpreting the scheme as a trellis-coded modulation. We also provide an alternative implementation that can be viewed as a recursive systematic convolutional encoder. Combining this version further with a simple forward error correction encoder results in a concatenated code that can be decoded iteratively, providing a bit-error rate of 10 −3 at 2.8 dB signal-to-noise ratio in additive white Gaussian noise. The convergence beh...

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