International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / The future of range operations in the area of expendable launch vehicle (ELV) support is unquestionably headed in the direction of space-based rather than land- or air-based assets for such functions as metric tracking or telemetry data collection. To this end, an effort was recently completed by the Air Force’s Eastern Range (ER) to certify NASA’s Tracking and Data Relay Satellite System (TDRSS) as a viable and operational asset to be used for telemetry coverage during future Titan IV/Centaur launches. The test plan developed to demonstrate this capability consisted of three parts: 1) a bit error rate test; 2) a bit-by-bit compare of data recorded via conventional means vice the TDRSS network while the vehicle was radiating in a fixed position from the pad; and 3) an in-flight demonstration to ensure positive radio frequency (RF) link and usable data during critical periods of telemetry collection. The subsequent approval by the Air Force of this approach allows future launch vehicle contractors a relatively inexpensive and reliable means of telemetry data collection even when launch trajectories are out of sight of land-based assets or when land- or aircraft-based assets are not available for support.

There have been proposals of many parity inducing techniques like Forward ErrorCorrection (FEC) which try to cope the problem of channel induced errors to alarge extent if not completely eradicate. The convolutional codes have been widelyidentified to be very efficient among the known channel coding techniques. Theprocess of decoding the convolutionally encoded data stream at the receiving nodecan be quite complex, time consuming and memory inefficient.This thesis outlines the implementation of multistandard soft decision viterbidecoder and word length effects on it. Classic Viterbi algorithm and its variantsoft decision viterbi algorithm, Zero-tail termination and Tail-Biting terminationfor the trellis are discussed. For the final implementation in C language, the "Zero-Tail Termination" approach with soft decision Viterbi decoding is adopted. Thismemory efficient implementation approach is flexible for any code rate and anyconstraint length.The results obtained are compared with MATLAB reference decoder. Simulationresults have been provided which show the performance of the decoderand reveal the interesting trade-off of finite word length with system performance.Such investigation can be very beneficial for the hardware design of communicationsystems. This is of high interest for Viterbi algorithm as convolutional codes havebeen selected in several famous standards like WiMAX, EDGE, IEEE 802.11a,GPRS, WCDMA, GSM, CDMA 2000 and 3GPP-LTE.

No description available.

Multiuser and cooperative orthogonal frequency division multiplexing(OFDM) systems are being actively researched and adopted in wireless standards, owing to their advantages of robustness to multipath fading, modularity, and ability to achieve high data rates. In OFDM based systems, perfect frequency and timing synchronization is essential to maintain orthogonality among the subcarriers at the receiver. In multiuser OFDM on the uplink, timing offsets (TOs) and/or carrier frequency offsets (CFOs) of different users, caused due to path delay differences between different users, Doppler and/or poor oscillator alignment, can destroy orthogonality among subcarriers at the receiver. This results in multiuser interference (MUI)and consequent performance degradation. In this thesis, we are concerned with the analysis and mitigation of the effect of large CFOs and TOs in multiuser OFDM systems, including uplink orthogonal frequency division multiple access (OFDMA),uplink single-carrier frequency division multiple access(SC-FDMA), and cooperative OFDM. Uplink OFDMA: In the first part of this thesis, we analytically quantify the effect of large CFOs and TOs on the signal-to-interference plus noise ratio(SINR) and uncoded bit error rate(BER) performance of uplink OFDMA on Rayleigh and Rician fading channels, and show analytical results to closely match with simulation results. Such an SINR/BER analysis for uplink OFDMA in the presence of both large CFOs as well as TOs has not been reported before. We also propose interference cancelling(IC) receivers to mitigate the performance degradation caused due to large CFOs and TOs of different users. SC-FDMA versus OFDMA: An issue with uplink OFDMA is its high peak-to-average power ratio(PAPR).Uplink SC-FDMA is proposed in the standards as a good low-PAPR alternative to uplink OFDMA; e.g., SC-FDMA has been adopted in the uplink of 3GPP LTE. A comparative investigation of uplink SC-FDMA and OFDMA from a sensitivity to large CFOs and TOs view point has not been reported in the literature. Consequently, in the second part of the thesis, we carry out a comparative study of the sensitivity of SC-FDMA and OFDMA schemes to large CFOs and TOs of different users on the uplink. Our results show that while SC-FDMA achieves better performance due to its inherent frequency diversity advantage compared to OFDMA in the case of perfect synchronization, its performance can get worse than that of OFDMA in the presence of large CFOs and TOs. We further show that use of low-complexity multistage IC techniques, with the knowledge of CFOs and TOs of different users at the receiver, can restore the performance advantage of SC-FDMA over OFDMA. Cooperative OFDM: Cooperative OFDM is becoming popular because of its ability to provide spatial diversity in systems where each node has only one antenna. In most studies on cooperative communications, perfect time synchronization among cooperating nodes is assumed. This implies that the transmissions from different cooperating nodes reach the destination receiver in orthogonal time slots. In practice, however, due to imperfect time synchronization, orthogonality among different nodes’ signals at the destination receiver can be lost, causing inter-symbol interference(ISI).In the third part of the thesis, we investigate cooperative OFDM communications using amplify-and-forward(AF) protocol at the relay, in the presence of imperfect timing synchronization. We derive analytical expressions for the ISI as function of timing offset for cooperative OFDM with AF protocol, and propose an IC receiver to mitigate the effects of timing offset induced ISI.