<p> In this thesis, we consider a multiuser downlink OFDM system for which the channel state information ( CSI) is known to both the transmitter and the receiver. </p> <p> For such a system, we design an optimal precoder that minimizes the total mean square error (MSE) subject to a total power constraint for which a minimum MSE (MMSE) equalizer is employed. We show that, the MMSE precoder can be obtained by optimally allocating the subcarriers and optimally allocating the power. This problem can be solved by a two-stage process, in which we minimize the lower bound of the MSE to obtain the optimal power for each subcarrier, followed by seeking an optimal precoder to achieve this minimized lower bound. Specifically, our subcarrier allocation strategy states that, each subcarrier should be allocated to only one user that has the largest subchannel gain in that subcarrier. </p> <P> Moreover, based on this subcarrier allocation strategy, we perform an optimal power loading and design the corresponding optimal precoder that minimizes the average bit error rate (BER). Here, the MMSE equalizer is also employed. This optimization problem is solved by two stages. In the first stage, we derive the lower bound of the average BER and minimize this lower bound. After we employ the MMSE subcarrier allocation strategy, the optimal power loading problem can be efficiently solved by interior point methods. In order to reduce computation complexity, an alternative, efficient power loading method is proposed here, which is much more efficient when the number of subcarriers is large. In the second stage, to achieve the minimized lower bound, we seek a design of an optimal precoder. Simulation results show that for moderate to high signal-to-noise ratio (SNR), the performance of the minimum BER {MBER) precoder employed with the MMSE equalizer design is superior to several other design methods, including the MMSE precoder design. </p> / Thesis / Master of Applied Science (MASc)

Yes / Wavelets are alternative building kernels of the multicarrier systems, such as the orthogonal frequency division multiplexing (OFDM). The wavelets can be designed by changing the parent basis functions or constructing new filters. Some two new wavelets are considered for multicarrier design; one is designed using raised-cosine functions while the other was constructed using ideal filters. The spectrums of raised cosine wavelet filters are controlled by a roll-off factor which leads to many distorting sidelobes. The second family of wavelet, which the raised-cosine wavelet is compared to, have no distorting sidelobes. It will be shown that raised-cosine wavelets are less suitable for multicarrier design in multicarrier environment, in terms of BER when compared to the wavelet constructed from the ideal filter.

Link adaptation is important to guarantee robust and reliable wireless communications with- out wasting valuable radio resources. This technique has become more feasible with the recent appearance of Software Defined Radios (SDRs), which allow easy reconfiguration of their parameters via software. As the environment changes over time, the transmitter needs to be able to effectively estimate its performance under different radio input parameters to be able to find a close to optimal solution. In most wireless communications, an equalizer is implemented at the receiver to estimate the channel impulse response. This estimate can be fed back to the transmitter via a feedback channel, which can in turn help generate a sub-optimal transmission solution for the current situation. In this thesis, a link adaptation method is proposed that uses Orthogonal Frequency-Division Multiplexing (OFDM) in conjunction with blind channel estimation. With the use of OFDM, it can be assumed that the frequency fading at each subcarrier is approximately flat. In addition, under the assumption that the channel is quasi-stationary, the Bit Error Rate (BER) at each subcarrier can be estimated by using the well-known BER formulas for an Additive White Gaussian Noise (AWGN) channel. However, the effect of imperfect channel estimation must also be taken into account. A novel OFDM blind channel estimator is developed. Finally, both simulations and real over-the-air results are presented. / Master of Science

Spectral coexistence and cooperative spectrum sharing techniques are vital to the continued development and proliferation of wireless communications systems. Government directives indicate that certain frequency bands which once were reserved for radar-only applications must now support wireless broadband systems. The effect of co-site interference upon detection techniques for wireless broadband systems is evaluated. Cyclostationary feature based detection methods are evaluated against gaussian noise and interfering radar signals. Alternative decision algorithms utilizing support vector machines are proposed and evaluated and compared against traditional general likelihood ratio test algorithms. Recommendations for certain algorithms and observation window lengths to maximize e ectiveness and minimize computational complexity are developed. / Office of Naval Research grant N00014-12-1-0062 and contract N00014-12-C-0702 / Master of Science

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / The 46th Test Wing, 846th Test Support Squadron (846 TSS/TSI) at Eglin AFB is currently evaluating their airspace for the use of SOQPSK transmitters and receivers for telemetry. The Squadron will incorporate an IP-compatible OFDM transceiver from Teletronics Technology Corporation (TTC) that will provide a two-way communication channel for controlling configuration settings of the airborne SOQPSK transmitter and receiver. This provides an opportunity to evaluate the effectiveness of an airborne network instrumentation system and measure some critical parameters, with an opportunity to assess the performance and reliability of streaming telemetry and OFDM-based IP communication systems. This paper describes the experimental test setup created for this evaluation and summarizes the measurement and evaluation process.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / OFDM is a preferred physical layer for an increasing number of telemetry and LAN applications. However, joint estimation of the multipath channel and frequency offset in OFDM remains a challenging problem. The Unscented Kalman Filter (UKF) is presented to solve the offset/channel tracking problem. The advantages of the UKF are that it is less susceptible to divergence than the EKF, and does not require computation of a Jacobian matrix. A hybrid analysis/simulation approach is developed to rapidly evaluate UKF performance in terms of symbol-error rate and channel/offset error for the 802.11a OFDM format.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / Synchronization of the iNET communication link is essential for implementing the TDMA channel access control functions within the transceiver MAC transport layer, and providing coherent signal demodulation timing at the transceiver PHY layer. In the following implementation, the 1588 timing reference source is the GPS receiver. Because it is being used in the Ground Station Segment and Test Article Segment, it becomes feasible to utilize the 1588 timing reference for cross-layer (MAC+PHY) iNET transceiver synchronization. In this paper, we propose an unified iNET transceiver synchronization architecture to improve iNET transceiver performance. The results of the synchronization performance analysis are given.

Hyper-wideband communications represent the next frontier in spread spectrum RF systems with an excess of 10 GHz instantaneous bandwidth. In this thesis, an end-to-end physical layer link is implemented featuring 16k-OFDM with a 4 GHz-wide channel centered at 9 GHz. No a priori channel state information is assumed; channel information is derived from the preamble and comb pilot structure. Due to the unique expansive spectral properties, the channel estimator is primarily composed of least squares channel estimates combined with a robust support vector statistical learning approach using autonomously selected parameters. The system’s performance is demonstrated through indoor wireless experiments, including line-of-sight and near-line-of-sight links. Moreover, it is shown that the support vector approach performs superior to linear and cubic spline inter/extrapolation of the least squares channel estimates.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Traditional communication hardware has focused on modular architectures. Now, with the incoming high speed DSP and FPGAs a shift from traditional modular architecture to reconfigurable architecture has taken place. The nature of this architecture allows to optimize various telemetry applications in a single platform. This paper describes a reconfigurable multi channel communication system.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / The main objectives of iNET (Integrated Network Enhanced Telemetry) are increased data rate and improved spectral efficiency [1]. In this paper we propose that transmission scheme for the physical layer is coded 16-QAM OFDM (Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing) which enables high data rate and spectrum efficiency. However in high mobility scenarios, where the channel is time-varying the receiver design is more challenging. Therefore in this paper pilot-assisted channel estimation is used at the receiver, with convolutional coding and error correction to enhance the performance; while the effect of inter symbol interference (ISI) is mitigated by cyclic prefix. The focus of this paper is to evaluate the performance of OFDM with 16-QAM over an aeronautical channel. The 16-QAM with OFDM enables 4 bits/symbol and provides a higher data rate than QPSK hence it is chosen in this paper. The implementation of OFDM is done using Inverse Fast Fourier Transform (IFFT) and the Fast Fourier Transform (FFT). In this paper we simulate how the performance of Coded 16-QAM OFDM is enhanced using equalization to compensate for inter symbol interference, convolutional coding is used for error correction, puncturing for improving data rate and the insertion of cyclic prefix (CP) to avoid inter carrier interference.