A Digitized FH-Group Modem for Adaptive FH and Multi-Carrier Radio Systems

Yoshifumi SUZUKI  Tadashi SHIRATO  

IEICE TRANSACTIONS on Communications   Vol.E79-B    No.3    pp.289-296
Publication Date: 1996/03/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Advanced Adaptive Radio Communication Technologies)
Category: Access, Network
group modem,  adaptive,  frequency hopping,  multi-carrier,  radio communication,  

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This paper proposes a new digitized group modulator and demodulator (a group modem) for adaptive frequency hopping and multi-carrier (AFHMC) radio systems. The group modem can flexibly vary the number of carriers handled simultaneously, especially employing a time division multiplexing technique in the demodulator. We discuss the operational principle of the modem. The required operational clock frequency in the group demodulator is also examined and clarified taking into consideration the frequency characteristics of the baseband filter. The basic performance of the proposed configuration is measured experimentally by constructing a π/4-shift QPSK group modulator and a π/4-shift QPSK group demodulator. First, by measuring the output spectrum of the significant parts in the demodulator, we confirm that the basic operational performance conforms to the design specifications. Secondly, investigating the relationship between the number of multiplexed low-pass filter taps and the required CNR when multiple carriers are simultaneously input confirms that more than 40 taps are enough to obtain the best BER performance in this experiment. Next, examining the relationship between the number of carriers simultaneously input, the required CNR, and the input level of these carriers confirm that the required CNR is roughly constant and there is no significant difference among the cases when D/U is more than 0 dB. Finally, an experiment shows that the required number of quantization bits for A/D input in the demodulator is more than 6, which is enough to obtain the best BER even if simultaneous handled carriers are 4.