IJ Multiple antenna systems have been shown to provide significant performance improvements for network nodes; however, the vast majority of nodes in military networks will be limited to single channel devices due to mobility (size and power) and ease of use considerations. In this paper we apply a new joint synchronization-pilot sequence (JSPS) optimization design technique to multiple transmitter OFDM systems. We consider the cases where the transmitters could be co-located or distributed (i. e. multiple single-channel transmitters) in space. Independent JSPSs are designed for each transmitter in a multiple antenna system and can be utilized to estimate the carrier frequency offset (CFO) and sampling frequency offset (SFO) of each antenna independently. We study the mean square error (MSE) for the estimation of CFO and SFO and compare the performance of our estimators to a closed form solution for A WGN channels. We show that the performance of our proposed iterative estimators for distributed CFO and SFO estimation is approximately equivalent to the estimation performance in the co-located CFO and SFO estimation case. The iterative estimator for the distributed case is also found to be of low complexity, with only a linear complexity increase over the co-located estimator. We have also measured, via simulation, the performance of the CFO estimator for distributed Rayleigh fading multipath channels.

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P OFDM offers high bandwidth efficiency and low receiver equalization complexity; consequently OFDM is growing in popularity for adoption into robust high data rate services in wireless multipath channels. While these advantages have been proven for many wireless applications (including numerous IEEE wireless standards), one potential disadvantage ofOFDM is that it exhibits high peak-toaverage power ratios (PAPR). The high PAPR characteristic of OFDM can induce in-band and out-of-band distortions when the peaks of the OFDM waveform enter the compression region of the transmitter power amplifier (PA). Several techniques exist to reduce the PAPR and, in addition, signal pre-distortion can be applied prior to the PA to linearize the signal; however, significant distortion can still reach the receiver. We introduce a PA subcarrier interference cancellation (SCIC) method that improves upon previous receive-side non-linear interference cancellation (NLIC) techniques and show the resulting improvement using actual PA devices. Initially we derive theoretical performance analysis that enables us to predict the performance analytically and confirm the improvements via simulation of our SCIC technique. We demonstrate at least a 5 dB SNR improvement, at 0 dB input backoffofthe PA, using our OFDM design with SCIC. We conclude that robust channel estimation, using optimized pilot designfor OFDM with null edge subcarriers, and SCIC are jointly critical for improving OFDM's robustness when transmitted through nonlinear PA devices.

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Arbitrary sample rate conversion (ASRC) is a critical digital signal processing function for any signal that is received and down converted from analog RF to either digital-IF or -baseband. There are numerous ASRC applications, including, but not limited to commercial and military communications, radar-and audio-signal processing, and multi-function systems (such as coexistence of EW and communication systems). Furthermore, variable fractional delay (VFD) processing is critical when synchronizing to any transmit signal, for precise timing in geolocation processing or for any receiver process where accurate timing is required. There are many designs for VFD-ASRC which may operate across a wide range of parameters in a functional sense, but which do not perform equally across their operational range. Few methods exist in the literature for evaluating the performance of these designs in a generalized fashion for applicability to project specifications. This work proposes a method for evaluating the performance of any VFD-ASRC system. The generalized technique uses a high performance filter bank followed by frequency-domain magnitude-and group delay-error metrics to provide a measure of the quality of a VFD-ASRC design. The method can be applied to any single-and multiple-carrier modulation signal.