- For Efficient Use of Satellite Transponders and More Secure Communications - Nippon Telegraph and Telephone Corporation (hereinafter NTT) has developed a technique named "Direct Spectrum Division Transmission (DSDT)" that divides the spectrum of satellite communications signals into multiple sub-spectra, then making communications after allocating them to the unused frequency slots of the operating band of a transponder (*1) in space, and finally recombining the divided sub-spectra into a single carrier signal. The practicality of this technique was verified by satellite experiments. Simply by attaching a "DSDT adapter" to the existing satellite modem (*2), the spectrum of the signal can be divided up and recombined, so that unused frequency resources scattered throughout the operating band of the transponder can be used without affecting existing signals of other users that share the same transponder. In addition, this technique enhances communication security by dividing the signal into multiple sub-spectra in the transmitter and combining the multiple sub-spectra back into the original signal in the receiver. NTT conducted satellite experiments on a preproduction prototype showing that the proposed technique is a practical way of exploiting unused frequency resources scattered on the satellite transponder. Hereafter, NTT will study an effective method of allocating unused frequency resources to multiple users that share the same transponder and further improve spectral efficiency of satellite transponders. Glossary (*1) A relay node in space that receives a wireless signal from an earth station and transmits it again to the Earth after amplifying it, converting its frequency, and so forth. (*2) A piece of hardware equipped with a function that modulates information and generates a Tx signal, as well as a function that demodulates the received signal and extracts the information. Original News Release https://www.ntt.co.jp/news2019/1912e/191211a.html Attachments Fig. 1 Concept of spectrum division and combining https://www.ntt.co.jp/news2019/1912e/image/191211aa.gif Fig. 2 Spectrum-editing technique https://www.ntt.co.jp/news2019/1912e/image/191211ab.gif Fig. 3 Spectrum synchronous combining technique https://www.ntt.co.jp/news2019/1912e/image/191211ac.gif Fig. 4 Examples of spectrum division https://www.ntt.co.jp/news2019/1912e/image/191211ad.gif Fig. 5 Experimental parameters https://www.ntt.co.jp/news2019/1912e/image/191211ae.gif Fig. 6 BERs in satellite experiments https://www.ntt.co.jp/news2019/1912e/image/191211af.gif Source: Nippon Telegraph and Telephone Corporation