Efficient frequency utilization for enhanced co-existence - Literature survey

The Swedish Armed Forces available frequency bands has decreased as a result of high demand from commercial interests in the last decades. In addition, to meet the new information needs, the number of communication systems, sensors and other emitting systems on modern platforms increases. Therefore, it is important that the frequency bands available to the Swedish Armed Forces are used as effectively as possible. A literature survey on specific research areas that are expected to contribute to more efficient frequency utilization and enhanced co-existence has been carried out. The survey shows that a vast amount of research has been conducted on these subjects during the latest decade. Hence, the content of this report is a selection of techniques that are expected to contribute to a more efficient frequency utilization for enhanced coexistence. Some of the research areas were identified already in previous work, such as dynamic resource allocation (e.g. dynamic spectrum access (DSA) and power control) and adaptive transmit and receive techniques for handling of dynamic interference situations. More efficient frequency utilization by use of adaptivity requires even more intelligent systems. The rapid development of AI and machine learning for intelligent radio systems is considered to help meet this requirement. However, future study of this area is necessary in order to determine new capabilities of AI and which uses of AI that can contribute to more efficient frequency utilization. Furthermore, it is also necessary to evaluate in which part of military radio systems it is appropriate, from a robustness, safety and coexistence concern, to implement AI. The survey shows that the interest for simultaneous transmission and reception on the same frequency, so called in-band full duplex (IBFD), has significantly increased in recent years. For future studies, the usage of IBFD for DSA, relaying and simultaneous electronic warfare and communication is of considerable interest. Within military waveform development in the 30 -- 88 MHz frequency range, the trend is to increase the bandwidth from 25 to 50 or 100 kHz in order to support both speech and data. The UHF band (240 -- 380 MHz) is a relatively diverse band with a mix of different types of systems: narrow band, wide band, fixed frequency and frequency hopping. Technical solutions that provide greater flexibility and denser frequency allocation, as well as relaxing the requirements on how spectrum is utilized, is expected to improve efficiency within the UHF band. The frequency need of 5G, to realize the scenarios specified within the 5G development, is enormous. Accordingly, there is an ongoing debate that aims to get other frequency users, such as the military, to free up spectrum so it can be used by cellular networks. New for 5G, in comparison to previous cellular systems, is the possibility to use highly variable bandwidths and the utilization of very high frequencies (in the range of tens of GHz). Even higher frequencies (in the THz range) is by most assessors deemed necessary for 6G. As such, short distance communication is expected to become even more common which entails denser base station placement compared to today.