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In this paper we study the suitability of constant envelope multi-carrier modulation technique for the implementation of 1Gbps wireless link at 60 GHz. This technique combines orthogonal frequency division multiplexing (OFDM) and phase modulation (PM) where: (1) PM creates a constant envelope signal which allows high power amplifier to operate near saturation levels thus maximizing power efficiency, (2) OFDM increases robustness to multipath fading. Since OFDM-PM symbols satisfy symmetry property, maximumratio combiner (MRC) can be used at the receiver. Our simulations show that in an AWGN channel at bit error level 10 -3 , the OFDM-PM with MRC has about 0.8 dB performance loss compared to OFDM or single carrier minimum shift keying (MSK). For Rician fading channels, we find that OFDM-PM performs comparably to MSK and outperforms uncoded OFDM. Furthermore, we show that both OFDM and OFDM-PM have similar bit error distribution characteristics, and thus the performance of OFDM-PM can be improved by the use of water-filling or coding techniques.

During the New Space era small countries are becoming important players in the space business. While space activities are rapidly increasing globally, it is important to make operations in a sustainable and safe way in order to preserve satellite services for future generations. Unfortunately, the sustainability aspect has been largely overlooked in the existing surveys on space technologies. As a result, in this survey paper, we discuss the multi-layer networking approaches in the 6G era specifically from the sustainability perspective. Moreover, our comprehensive survey includes aspects of some interesting industrial, proprietary, and standardization views. We review the most important regulations and international guidelines and revisit a three-dimensional architecture vision to support the sustainability target for a variety of application areas. We then classify and discuss space safety paradigms that are important sustainability enablers of future satellite communications. These include space traffic management, debris detection, environmental impacts, spectrum sharing, and cyber security aspects. The paper also discusses advances towards a planned European connectivity constellation that could become a third flagship infrastructure along with the Galileo and Copernicus systems. Finally, we define potential research directions into the 2030s.INDEX TERMS Aerospace engineering, Low earth orbit satellites, Radio spectrum management, Spaceborne radar

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