In many military and law-enforcement covert missions, wireless communication links need to remain undetected. In this paper, a novel spectrum spread technique based on noise modulated (NM) transmission is proposed and a feasibility study was conducted. In NM transmissions a reference pseudo-noise signal is generated and is superposed with the information signal, with a time delay. The pseudo-random noise sequence is transmitted separately and used to recover the signal from the noise modulated information signal. The transmitted information signal is noise like making it difficult to detect or decode by an adversary. If an adversary does discover the transmission, decoding is difficult without the pseudo-random noise sequence and time delay between noise and signal. Conventional NM uses polarized antennas to orthogonally transmit the noise modulated information signal and pseudo-noise signal. However, the two polarized antennas are rarely, if ever, completely isolated in practice making signal recovery difficult if not impossible. In this paper a feasibility study was performed on a novel multi-frequency NM scheme for NM communications with a single polarized antenna. A universal software radio peripheral (USRP) software defined radio (SDR) testbed was used to demonstrate that multi-frequency NM transmission masks a QPSK signal from an adversary and the signal can be successfully recovered by a friendly receiver.
Proc. SPIE. 10196, Sensors and Systems for Space Applications X
KEYWORDS: Signal to noise ratio, Human-machine interfaces, Transmitters, Modulation, Visualization, Calibration, Databases, Receivers, Field programmable gate arrays, Control systems, Telecommunications, Signal processing, Embedded systems, Satellite communications, RF communications, Research facilities, Standards development
Software defined radio (SDR) has become a popular tool for the implementation and testing for communications performance. The advantage of the SDR approach includes: a re-configurable design, adaptive response to changing conditions, efficient development, and highly versatile implementation. In order to understand the benefits of SDR, the space telecommunication radio system (STRS) was proposed by NASA Glenn research center (GRC) along with the standard application program interface (API) structure. Each component of the system uses a well-defined API to communicate with other components. The benefit of standard API is to relax the platform limitation of each component for addition options. For example, the waveform generating process can support a field programmable gate array (FPGA), personal computer (PC), or an embedded system. As long as the API defines the requirements, the generated waveform selection will work with the complete system. In this paper, we demonstrate the design and development of adaptive SDR following the STRS and standard API protocol. We introduce step by step the SDR testbed system including the controlling graphic user interface (GUI), database, GNU radio hardware control, and universal software radio peripheral (USRP) tranceiving front end. In addition, a performance evaluation in shown on the effectiveness of the SDR approach for space telecommunication.
In this work, we propose a novel beam-forming power allocation method for a satellite communication (SATCOM) multiple-input multiple-output (MIMO) system to mitigate the co-channel interference (CCI) as well as limiting the signal leakage to the adversary users. In SATCOM systems, the beam-forming technique is a conventional way of avoiding interference, controlling the antenna beams, and mitigating undesired signals. We propose to use an advanced beam-forming technique which considers the number of independent channels used and transmitting power deployed to reduce and mitigate the unintentional interference effect. With certain quality of service (QoS) for the SATCOM system, independent channels components will be selected. It is desired to use less and stronger channel components when possible. On the other hand, considering that SATCOM systems often face the problem that adversary receiver detects the signal, a proposed power allocation method can efficiently reduce the received power at the adversary receiver. To reduce the computational burden on the transponder in order to minimize the size, mass, power consumption and delay for the satellite, we apply a hybrid onboard and ground based beam-forming design to distribute the calculation between the transponder and ground terminals. Also the digital channelizer beam-forming (DCB) technique is employed to achieve dynamic spatial control.