Innovative SF-STAR Radios for Tactical Environments

There has been exponential growth in wireless for communicating mission-critical information – voice, video and data – all of which must be conveyed within a finite bandwidth.  Modulation waveforms and signal coding are two techniques that have increased the amount of information that can be conveyed within a given bandwidth. To increase spectral efficiency further, the Army needs new ways to both increase the spectrum efficiency and reduce the degrading effects of interference. The objective of the proposed program is to develop tactical radios with same-frequency simultaneous transmit and receive (SF-STAR) capability. In Year 1 of the program, Photonic Systems, Inc. (PSI) and subcontractor General Dynamics - Applied Physical Sciences (GD-APS) will design and assemble tactical radios based on software-defined radios (SDRs) that simultaneously transmit at the same frequency as they receive, and that suppress the transmit signal at the receiver while also suppressing interference signals. A portion of the required suppression will be performed in the analog domain prior to digitization, and the remainder will occur in the digital domain, with the most advantageous apportionment between these domains to be determined via modeling. Year 1 will end in a demo at an Army site of two such radios communicating in the presence of Electronic Attack (EA) signals. At each receiver this will require suppression of both the “self” interference (that radio’s own transmit signal) and “untethered” interference (the EA signals). In the portion of suppression to be performed in the digital domain, suppression of the self-interference will involve an algorithm that subtracts from the input signal a weighted portion of a reference copy of the known transmit signal so as to maximally suppress the residual transmit signal – i.e., the portion remaining after the suppression that was performed in the analog domain. Suppression of EA signals, however, will require the use of PSI's “self-isolating reference (SIR)” algorithm that suppresses signals without the need for a reference copy of the interferers. In Year 2, the team will adjust the design of the Year 1 tactical radios so that, in addition to its previously demonstrated capabilities, one radio can receive the signal transmitted by a second radio while in the proximity of third and fourth transmitting radios. The team will assemble these 4 radios and demonstrate them at an Army site. At each radio’s receiver the suppression of “untethered” interference will now involve suppressing both the EA signals and the signals transmitted by two other radios. Whereas the SIR algorithm that was used in Year 1 to isolate the EA signals for suppression was what PSI calls the “Y/X” version of the SIR, the Year 2 demonstration will also require the use of what PSI calls the “X/X” version of the SIR to isolate and suppress the third and fourth radios’ transmit signals, which have the same frequency and format as the desired signal.