ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper provides an introduction to the Orthogonal Frequency Division Multiplexing (OFDM) scheme which has been proposed for future aeronautical telemetry applications. OFDM offers the potential for high data rates on radio channels with multipath such as aeronautical telemetry channels. This paper provides in introduction to OFDM and demonstrates how orthogonality is maintained over multipath channels by the introduction of a guard band and by the inclusion of a cyclic prefix. The simulation of OFDM in multipath is simulated and performance results are presented that show the degradation of this scheme on a multipath channel with and without the guard band and the cyclic prefix.

Timing offsets result from the use of real clocks that are non-ideal in sampling intervals. These offsets also known as timing jitter were shown to degrade the performance of the two forms of UWB systems impulse radio and orthogonal frequency division multiplexing (OFDM)-based UWB. It was shown that for impulse radio, timing jitter distorts the correlation property of the transmitted signal and the resulting performance loss is proportional to the root-mean-square (RMS) value of the timing jitter. For the OFDM-based UWB, timing jitter introduced inter-channel interference (ICI) and the performance loss was dependent on the product of the bandwidth and the RMS of the timing jitter. A number of techniques were proposed for mitigating the performance degradation in each form of UWB. Specifically, for impulse radio, the methods of pulse shaping and sample averaging were provided, whereas for OFDM-based UWB, oversampling and adaptive modulation were given. Through analysis and simulation, it was shown that substantial gain in signal power-to-noise ratio can be achieved using these jitter-reduction methods.

Wireless relay can be utilized to extend signal coverage, achieve spatial diversity by user cooperation, or shield mobile terminals from adverse channel conditions over the direct link. In a two-hop multi-input-multi-output (MIMO) amplify-and-forward (AF) relay system, the overall noise at the destination station (DS) consists of the colored noise forwarded from the relay station (RS) and the local white noise. We propose blind noise correlation estimation at the DS by utilizing statistics of the broadband relay channel over the RS-DS hop, which effectively improves signal detection at the DS. For further performance improvement, we also propose to estimate the two cascaded MIMO relay channels over the source-RS and the RS-DS links at the DS based on the overall channel between the source and the DS and the amplifying matrix applied at the RS. To cancel cross-talk interference at a channel-reuse-relay-station (CRRS), we utilize the random forwarded signals of the CRRS as equivalent pilots for local coupling channel estimation and achieve a much higher post signal-to-interference ratio (SIR) than the conventional dedicated pilots assisted cancellers without causing any in-band interference at the DS. When an OFDM-based RS is deployed on a high-speed train to shield mobile terminals from the high Doppler frequency over the direct link, inter-subchannel interference (ICI) mitigation is required at the RS. By utilizing statistics of the channel between the base station and the train, we develop both full-rate and reduced-rate OFDM transmission with inherent ICI self-cancellation via transmit and/or receive preprocessing, which achieve significant performance improvement over the existing ICI self-cancellation schemes.