Rice, Michael; Hogstrom, Christopher; Nash, Chris; Ravert, Jeff; Saquib, Mohammad; Afran, Md. Shah; Cole-Rhodes, Arlene; Moazzami, Farzad; Perrins, Erik; Temple, Kip (International Foundation for Telemetering, 2017-10)
This paper summarizes the analysis of bit error rate data captured during ﬂight tests designed to compare data-aided equalizers with SOQPSK-TG to unequalized and currently available blind, adaptive equalizers with SOQPSK-TG. The number of bit errors,on a second-by-second basis, are analyzed. The results are different for each test point. Given the uncertain behavior of the preamble detector for the data-aided equalizer and the differing channel conditions between the data-aided equalizer channel and the conventional serial streaming telemetry channel, we are unable to draw any ﬁrm comparative conclusions.
Afran, Md. Shah; Saquib, Mohammad; Rice, Michael (International Foundation for Telemetering, 2017-10)
This paper investigates the performance of sparse minimum mean squared error (MMSE) equalizer for generalized time-reversed space-time block codes (GTR-STBC) in aeronautical telemetry. GTR-STBC equipped with MMSE equalizer performs the best trade-off between the signal-tonoise ratio and inter-symbol interference by allocating unequal power over aeronautical telemetry channels. However, aeronautical telemetry channels are in general consists of larger delay spreads which make the MMSE equalization of aeronautical channels with GTR-STBC computationally complex. Interestingly enough, in spite of larger delays aeronautical channels are made of few sparsely distributed multipaths and therefore their MMSE equalizers are highly compressible. In this paper, compressed sensing based greedy algorithm is used for the design of sparse MMSE equalizer and a convex curve-ﬁtting algorithm is used to ﬁnd the sub-optimum power allocation parameter at the same sparsity level for GTR-STBC. Our simulation results show that 75-90% of the non-zero equalizer taps can be reduced with a slight relaxation of the mean-squared error (or equivalentlyslight degradationof bit-errorrate performance). It isalso observedthat the optimum transmitter power proﬁle for the sparse MMSE equalizer is different than that of the non-sparse equalizer.
Rice, Michael; Hogstrom, Christopher; Nash, Christopher; Ravert, Jeffrey; Cole-Rhodes, Arlene; Moazzami, Farzad; Saquib, Mohammad; Afran, Md. Shah; Perrins, Erik; Temple, Kip (International Foundation for Telemetering, 2016-11)
This paper describes the results of flight tests designed to compare data-aided equalization to blind, adaptive equalization using SOQPSK-TG in aeronautical telemetry. The flight tests were conducted on 3 June 2016 at the Air Force Flight Test Center, Edwards AFB, at upper L band (1801.5 MHz) and at C band (4711.5 MHz). Five data-aided equalizers were implemented and compared to a commercially available blind equalizer. In addition, all equalized bit streams were compared to an unequalized reference. The results show that the blind equalizer tends to be either really good or really bad. In contrast, the data-aided equalizers tend to exhibit more graceful degradation. Which equalization method is “best” is not clear as of this writing. The answer depends on a number factors that will become clear as more data from the experiments is analyzed.
Afran, Md. Shah (International Foundation for Telemetering, 2015-10)
This paper presents a frequency domain equalization (FDE) technique for aeronautical telemetry channels. The FDE has significantly lower computational complexity compared to its time-domain counterpart, however both are found to exhibit almost identical performance. A cyclic prefix is generally needed to implement the FDE. In this paper, we exploit the repetition of iNET preamble and ASM bits in place of cyclic prefix.
Rice, Michael; Afran, Md. Shah; Saquib, Mohammad (International Foundation for Telemetering, 2014-10)
This paper presents performance analysis of the minimum mean squared error (MMSE) equalizers applied to aeronautical telemetry channels. The challenge for equalizing received samples of the modulated signal lies in the fact that the underlying continuous-time SOQPSK-TG waveform is not wide-sense stationary. However it is assumed so in order to meet real-time implementation requirements. Two approximations of the autocorrelation function of the SOQPSK-TG waveform are used for designing MMSE equalizers. Their performance are investigated against the zero forcing equalizer for measured aeronautical telemetry channels.
Rice, Michael; Afran, Md. Shah; Saquib, Mohammad; Cole-Rhodes, Arlene; Moazzami, Farzad (International Foundation for Telemetering, 2014-10)
This paper demonstrates the effectiveness of the zero-forcing, minimum mean-squared error, and constant-modulus equalizers in improving the BER performance of iNET-formatted SOQPSK-TG. The equalization algorithms leverage the existence of known bit sequences in the preamble and ASM fields of the iNET packet to realize data-aided equalizers. The effectiveness of these equalization techniques over ten test channels, derived from channel sounding experiments at Edwards AFB, was evaluated. The BER curves for nine out of the ten test channels display the desirable "waterfall" shape. The BER curve for the remaining test channel displays a "BER floor." Fortunately, the "BER floor" is low enough to allow error correcting codes, such as the iNET LDPC code, to correct the errors and provide virtually error-free performance.
Rice, Michael; Afran, Md. Shah; Saquib, Mohammad (International Foundation for Telemetering, 2015-10)
Modern digital communication techniques leverage the capabilities of advanced digital signal processing to improve the bit error rate performance of modulated carrier in harsh radio frequency (RF) environments. This improvement requires the knowledge of the RF environment (e.g., frequency offset, multipath channel coefficients, noise variance). In this paper we derive the theoretical performance bound of the joint frequency offset, channel and noise variance estimators. Performance of the joint maximum likelihood estimators are compared with this bound for two of the measured aeronautical telemetry channels with iNET-formatted SOQPSK-TG samples.
Rice, Michael; Afran, Md. Shah; Saquib, Mohammed (International Foundation for Telemetering, 2014-10)
Generalized time-reversed space-time block codes (GTR-STBC) are introduced as a conceptual tool to examine the impact of unequal power allocation in aeronautical telemetry channels. Two transmitting antennas are employed to exploit partial channel state information. GTR-STBC are observed to perform the best trade-off between the signal-to-noise ratio and inter symbol interference. It is also observed that the optimum transmitter power profile for the measured channel is significantly different than that in the statistical channel model.
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