Recently, we provided closed-form expressions involving two-dimensional (2-D) joint Gaussian Q-function for the symbol error rate (SER) and bit error rate (BER) of an arbitrary 2-D signal with I/Q unbalances over an additive white Gaussian noise (AWGN) channel [1]. In this letter, we extend the expressions to Nakagami-m fading channels. Using Craig representation of the 2-D joint Gaussian Q-function, we derive an exact and general expression for the error probabilities of arbitrary 2-D signaling with I/Q phase and amplitude unbalances over Nakagami-m fading channels.

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In this letter, a novel blind CFO estimation algorithm for the uplink of an OFDMA system is proposed. The proposed method exploits the inherent redundant information in OFDMA symbols and does not require additional pilot or preamble overhead. Since it is a post-FFT estimator, it does not use filter banks to separate the desired user's signal from the others in the time domain. Hence, the subcarriers of a certain user are not restricted to be clustered in the frequency domain. Therefore, the proposed estimator can be applied to OFDMA systems with an arbitrary subcarrier assignment over the entire bandwidth, including IEEE 802.16e, to obtain sufficient frequency diversity in a frequency selective fading channel. The proposed method can be efficiently used for continuous tracking of all active users' CFOs only with two FFT windows within a single OFDM symbol. From simulation results, the performance of the proposed scheme is shown better than that uses preamble symbols.

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A semi-coherent technique for low-complexity frequency offset estimation is presented. The proposed estimation is based on discrete-time Fourier transform (DTFT). Since residual frequency offset can be compensated by channel estimation, frequency offset can be estimated only coarsely. We take advantage of the relationship between frequency resolution and accumulation period in DTFT in deriving the coarse estimator. Based on that, a novel method to balance the coherent and the non-coherent accumulation for frequency offset estimation is proposed. The proposed algorithm has low latency and complexity so that it is particularly suitable for packet traffic. The semi-coherent structure of the proposed algorithm is also scalable so that it can be used for both bursty and continuous traffic.

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This letter deals with blind multiuser detection based on the multi-channel linearly constrained constant modulus algorithm (MLCCMA) for asynchronous code division multiple access (CDMA) systems over frequency-selective Rayleigh fading channels. In conjunction with the decision-feedback generalized sidelobe canceller (DFGSC), we present an efficient approach to combat multiple access interference and intersymbol interference. Computer simulations confirm that the proposed MLCCMA-based DFGSC can significantly speed up convergence and improve the output performance.

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Various space time code (STC) designs have been proposed to obtain full diversity at full rate in multiple-input multiple-output (MIMO) channels for uncoded systems. However, commercial wireless systems typically employ powerful channel codes such as turbo codes and low density parity check (LDPC) codes together with an STC. For these applications, an STC optimized for uncoded systems may not provide the best performance. In this paper, an STC with relatively good performance over a wide range of code rates is proposed. Simulation results show that the performance of the proposed robust STC is very close to the best performance of the SM and the Golden code in various code rates.

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This letter presents a reconfigurable antenna with a microstrip patch that uses PIN-diode connections on slits to achieve frequency diversity. By switching the diodes on or off, a surface current path on the antenna is changed, which effectively results in shifting the operating frequency. Thus the antenna can select both WiBro and DMB bands.

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A full wave voltage multiplier for passive RFID transponders is presented. The current driving capability of the proposed rectifier is remarkably improved at the cost of only a small increase in layout area compared to the widely used conventional half wave voltage multiplier. The communication distance of RFID systems can be extended due to the improved RF carrier to DC power conversion capability of the proposed voltage multiplier.

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A rate control algorithm for logo insertion which does not require full decoding and encoding in compressed video is proposed. A perceptual approach is adopted in order to reduce the distortion introduced by the rate control. The start position of rate control is randomly varied for each frame so that the perceptual distortion is evenly dispersed across the whole picture. The number of rate-controlled slices is changed instead of the quantization scale in order to maintain original bit rate. Simulations show that the original bit rate can be maintained by the rate control without noticeable distortion. The proposed rate control algorithm can be easily extended to other transcoding applications.

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