A New 90 MBPS 68 APSK Modem with Honeycomb Constellation for Digital Radio Relay Systems

Hiroshi NAKAMURA
Noboru IIZUKA
Eisuke FUKUDA
Morihiko MINOWA
Yoshimasa DAIDO
Sadao TAKENAKA

Publication
IEICE TRANSACTIONS (1976-1990)   Vol.E71    No.6    pp.591-599
Publication Date: 1988/06/25
Online ISSN: 
DOI: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Radio Communication
Keyword: 


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Summary: 
This paper describes the first realization of the APSK system with a honeycomb constellation (HC) for high capacity digital radio links. Partial Gray coding method to improve receiver sensitivity is also described. It is shown that the 68 APSK modulation can increase receiver sensitivity by 0.7 dB compared with a 64 QAM. Possibility of the system with the HC using the present state of the art is confirmed by theoretical estimation of tolerances for modem impairments. Techniques necessary to realize a system with the HC are also described. Using the techniques, the 68 APSK modem with the HC was experimentally fabricated. The modem we fabricated has a transmission capacity of 90 Mbps within the FCC-authorized bandwidth of 20 MHz in the 4 GHz band. The BER performance and signature for multipath fading have been measured. It is confirmed that the signature of the 68 APSK is almost the same as that of the conventional 64 QAM. The signature improved using 5 tap transversal equalizer correspons to an outage of 2 seconds per year per hop.