256 QAM Modem for Multicarrier 400 Mbit/s Digital Radio |
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Authors: | Nakamura Y Saito Y Aikawa S |
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Affiliation: | Nippon Telegraph and Telephone Corp., Kanagawa, Japan; |
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Abstract: | This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10-4) and 2 dB (at BER of 10-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system. |
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