Analysis and Compensation of DC Offset in OFDM Systems Over Frequency-Selective Rayleigh Fading Channels

99學年度易志孝教師升等代表著作[[abstract]]Direct-conversion receivers have become popular in radio-frequency (RF) circuit design for their advantages of low cost, low power consumption, and fewer chip components over other architectures such as heterodyne receivers. However, the direct-conversion receiver architecture often suffers from direct current (dc) offset, which is a consequence of the imperfect direct-conversion process. In this paper, we study the effects of dc offset on the symbol error rate (SER) performance of orthogonal frequency-division multiplexing (OFDM) systems in multipath Rayleigh fading channels. Since OFDM system performance is sensitive to carrier frequency offset (CFO), the CFO must be estimated and compensated at the receiver. Due to CFO compensation, the dc offset caused by direct-conversion receivers and/or mixed-signal circuits no longer only affects the dc subcarrier and is spread over all subcarriers. By deriving the analytical SER formulas for OFDM systems with various modulation formats, the dependency of SER on dc offset and CFO is clearly quantified. These SER formulas can help system designers determine suitable specifications of RF components and understand whether digital DC offset compensation is necessary or not. Finally, we propose and analyze a simple DC offset estimation and cancellation scheme under the assumption that DC offset holds constant in one OFDM symbol duration. Numerical results demonstrate the effectiveness of the proposed DC offset-cancellation scheme.[[notice]]補正完畢[[booktype]]紙

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Rayleigh Fading Channels

[[abstract]]In this paper, we study the effect of finite-power, phase-locked-loop (PLL) based phase noise on the bit-error-rate (BER) of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective Rayleigh fading channels. Based on the conditional Gaussian approximation technique, we derive the BER formulas for BPSK and 16-QAM modulated OFDM signals impaired by phase noise in frequency-selective Rayleigh fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.[[conferencetype]]國際[[conferencedate]]20081130~20081204[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]New Orleans, U.S.A

Performance of Fixed Gain Amplify-and-Forward Relay Systems with Partial Channel State Information

[[abstract]]For amplify-and-forward (AF) relay systems employing coherent modulation, the receiver at the destination requires the full channel state information (CSI) of the sourcerelay-destination (SRD) links and the amplified relay-destination (RD) links to perform maximal ratio combining (MRC). To reduce the burden of channel estimation and CSI forwarding in AF relay systems, we propose an MRC receiver with partial CSI which needs the CSI of the SRD links and the variance of the source-relay (SR) links. We analyze the bit-error-ate (BER) of the proposed scheme based on the moment generating function approach. Compared with the full CSI case, the BER performance degradation due to partial CSI depends on the channel variances of the SR and RD links. When the channel variances of the SR links are much larger than those of the RD links, the performance loss due to partial CSI is negligible.[[sponsorship]]台南大學[[conferencetype]]國內[[conferencedate]]2013111115~20131116[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]臺南, 臺

Effects of Channel Estimation Error in the Presence of CFO on OFDM BER in Frequency-Selective Rayleigh Fading Channels

99學年度易志孝教師升等參考著作[[abstract]]In this paper, we study the effects of channel estimation error on the bit-error-rate (BER) of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective slowly Rayleigh fading channels. Due to the additive white Gaussian noise (AWGN) and the intercarrier interference (ICI) caused by the residual carrier frequency offset (CFO), the channel estimation based on the training symbols is not perfect. We characterize the performance degradation resulting from imperfect channel state information (CSI) by deriving the BER formulas for BPSK, QPSK, 16-QAM, and 64-QAM modulation schemes. The derived BER formulas contain no numerical integrals and can be evaluated easily and accurately. Simulation results validate the correctness of our theoretical analysis.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]EI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]FI

MMSE Multiuser Receiver for Uniformly Quantized Synchronous CDMA Signals in AWGN Channels

99學年度易志孝教師升等參考著作[[abstract]]We analyze and design the minimum mean-square error (MMSE) multiuser receiver for uniformly quantized synchronous code division multiple access (CDMA) signals in additive white Gaussian noise (AWGN) channels. The input-output relationship of the quantizer is represented by the gain-plusadditive-noise model. Based on this model, we derive the weight vector and the output signal-to-interference ratio (SIR) of the MMSE receiver. The effects of quantization on the MMSE receiver performance is characterized in a single parameter named ”equivalent noise variance” which is a function of the sum of each active user’s signal-to-noise ratio (SNR), processing gain, and the number of quantization levels. The optimal quantizer stepsize which maximizes the MMSE receiver output SNR is also determined. Simulation results validate the accuracy of our analysis.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙