Adaptive techniques for tactical communication systems

The current transformation of the Swedish Armed Forces is expected to provide enhanced battlefield awareness, and thereby improved striking power and efficiency of the military forces. The Network Based Defence (NBD) is the concept for transforming the Armed Forces into a defence based on flexible, rapid and controlled engagement capabilities. A high capacity tactical radio network with ad hoc functionality, capable of conveying mixed services and applications, and the ability to support stringent QoS demands, is an essential enabler for the NBD concept. In this report we have examined the use of adaptive techniques for tactical communication systems. General adaptation principles are discussed. Orthogonal Frequency Division Multiplex (OFDM) is an interesting technique for military systems, and the design of an OFDM-system for tactical communications is discussed. Various adaptive techniques for an OFDM-system are presented and simulation results for adaptive modulation in an OFDM-system are presented. A Multiple-Input Multiple-Output (MIMO) system, with antenna arrays at both transmitter and receiver, can yield substantial improvements for an OFDM-system, e.g. increased capacity, quality, range, robustness and stealth. Intersystem interference, e.g. caused by electronic equipment that emits non-Gaussian noise, is a growing problem in wireless communications. An analysis of the effect of pulsed noise on an adaptive modulation system has therefore been performed. Finally, channel knowledge is required in order to perform any kind of adaptation. Hence, the K-factor has been examined as a means to provide insight into the prevailing channel condition.