In this letter, a lattice-reduction-aided (LRA) minimum mean square error (MMSE) Tomlinson-Harashima precoding (THP) is proposed for multiple input multiple output (MIMO) systems. The extended channel is exploited to develop the LRA MMSE-THP based on the lattice reduction method. Simulation results show that the proposed scheme significantly outperforms the conventional MMSE THP and the LRA zero-forcing (ZF) THP and achieves full diversity order.

In this letter, the k-out-of-n rule for cooperative sensing is considered. For a given n, we derive the optimal value of k that minimizes the total sensing error probability subject to the sensing accuracy, considering both the effective of sensing errors and the primary activities. According to the optimal k, we analyze the performance and compare with other schemes, which illustrate the effectiveness of the proposed scheme.

In this paper, a channel allocation scheme is studied for overlay wireless networks to optimize connection-level QoS. The contributions of our work are threefold. First, a channel allocation strategy using both horizontal channel borrowing and vertical traffic overflowing (HCB-VTO) is presented and analyzed. When all the channels in a given macro-cell are used, high-mobility real-time handoff requests can borrow channels from adjacent homogeneous cells. In case that the borrowing requests fail, handoff requests may also be overflowed to heterogeneous cells, if possible. Second, high-mobility real-time service is prioritized by allowing it to pre-empt channels currently used by other services. And third, to meet the high QoS requirements of some services and increase the utilization of radio resources, certain services can be transformed between real-time services and non-real-time services as necessary. Simulation results demonstrate that the proposed schemes can improve system performance.

This letter proposes a sliding window method with iterative tuning for channel estimation of UWB signals. The iterative tuning scheme, which is based on multiple iterations of least mean square (LMS) algorithm, is utilized for modifying the output of the conventional sliding window channel estimator. By using this, the proposed method is more flexible due to the tradeoff between the processing time and accuracy, which makes it more suitable for practical UWB wireless communications. Simulations are also provided for demonstrating the validation of the proposed method.

In this letter, we investigate the blind channel estimation in MIMO-OFDM systems based on the second-order statistics of the channel outputs only. We exploit the cyclostationarity induced by OFDM with cyclic prefix, establish the sufficient identifiability conditions, and develop a subspace algorithm. Finally, we demonstrate the validity of the algorithm by computer simulations.

To mitigate the inter-cell interference in multicell downlink systems, this letter consider the robust precoder design for multicell cooperation where the knowledge of channel state available at the base station is imperfect. Assuming that imperfect channel state information (CSI) can be exchanged among cells but with no data sharing, we investigate the worst-case performance optimization problem with bounded CSI error. Our objective is to minimize the weighted sum mean-square-error (MSE) subject to per-base-station power constraints. A distributed solution is obtained by reformulating the upper bound of MSE and exploiting the Lagrangian method for the optimal problem. Simulation results demonstrate that the proposed algorithm is robust to guarantee the worst-case sum rate performance and has lower computational complexity than the SINR-based design.

Tamper proofing is a crucial problem in the watermarking application. Aiming at the credibility of multimedia, we present a semi-fragile watermark based on the image permutation. Watermarking detection is performed without resorting to the host image and it is only controlled by secrete keys, thus the whole scheme does not have certain security gaps. The simulation experiments show that it can survive the JPEG compression and effectively specify the region of the image that has been modified maliciously.

A novel geometrically invariant watermarking scheme based on gravity center is presented which treating the geometrically invariant gravity centers of host image and its supplement image as reference points. Thus watermark synchronization is obtained. Simulation results show the effectiveness of our scheme to the geometrical distortion including rotation and/or scaling.

The performances of a PCTH-based communication UWB system with diversiform modulation schemes are compared on the classic AWGN channel propagation and the realistic IEEE-UWB channel model. By employing different versions of modulation at the transmitters, the performances of an optimal receiver and a Rake receiver with various combining schemes are studied in this paper. The numerical results for several compared cases illustrate the tradeoff between transmitter diversity and receiver complexity. It is shown that the actual performance of the PAM-PCTH scheme can be better in both kinds of channel propagation. We also find that the PCTH-based UWB system with the Rake receiver has better performance than the conventional proposal for overcoming the multipath propagation effects in the UWB indoor environment.

In this letter, dynamic decode-and-forward (DDF) protocol and static decode-and-forward (SDF) protocol are considered in a two-way half-duplex fading system, where two sources are equipped with multiple antennas and a relay is equipped with a single antenna. Their closed-form expressions of diversity multiplexing tradeoff (DMT) are derived, respectively. From the results, DDF always outperforms SDF in terms of DMT, achieves DMT gain over nonorthogonal amplify-and-forward (NAF) in low spectral efficiency scenarios, but is inferior to NAF in high spectral efficiency scenarios.

In recently proposed asymmetric watermarking schemes, the public detection is less robust than the private detection. To resolve this problem, a robust asymmetric watermarking scheme using the multiple detection watermarks for public detection is proposed in this letter. In this scheme, the private watermark used for embedding is constructed by secretly selecting the partial elements of those public watermarks. It provides the same robustness for the public and the private detections, and the robustness is demonstrated in the computer simulations.

We propose a geometric mean decomposition (GMD) based vector precoding (VP) for multiple input multiple output (MIMO) systems. Minimum mean square error (MMSE) criterion is used for the joint VP design. The application of GMD method eliminates the imbalance among subchannel gains and obtains a better perturbation vector than the conventional method. We then exploit the extended channel matrix for further performance improvement. Simulation results show the proposed schemes significantly outperform the existing VP schemes.

A spectrum sensing scheme for cognitive radio that includes coarse and fine sensing stages based on cyclostationarity is proposed in this paper. The cyclostationary feature detection (CFD) based on a single cyclic frequency (SCF) is used in the coarse sensing stage and that based on multiple cyclic frequencies (MCF) is employed in the fine sensing stage. Whether the fine sensing stage is performed or not is decided by comparing the statistic constructed in the coarse sensing stage with two thresholds. Theoretical analyses and simulation results show that the proposed sensing scheme has superior sensing performance and needs shorter sensing time.

A reduced complexity quantization error correction method for lattice reduction aided (LRA) vector precoding is proposed. For LRA vector precoding,Babai's approximation procedure can generate quantization errors leading to performance loss. Instead of making a list to correct all possible errors as is done in the existing scheme, we propose a novel method in which only a subset of all possible errors are corrected. The size of the subset is determined by the probability distribution of the number of actual errors. Thus, the computation complexity of our correction procedure is reduced with little performance loss compared with the existing correction scheme.

A watermarking system is secure as long as it satisfies Kerckhoffs principle according to the cryptography. In this letter, two novel techniques named the encrypted orthogonal transformation and its improved scheme as useful preprocessing methods are presented to apply to the watermarking field, which can enhance the security of the watermarking scheme. Compared to discrete cosine transform watermarking algorithms, this method has similar robustness but higher security.

In this letter, a novel wavelet-based semi-fragile watermarking scheme is presented which exploiting the time-frequency feature of discrete wavelet transform (DWT) and high sensitivity on initial value of chaotic map. We also analyze the robustness to mild modification and fragility to malicious attack of our scheme. Its application includes tamper detection, image verification and copyright protection of multimedia content. Simulation results show the scheme can detect and localize malicious attacks with high peak signal-to-noise ratio (PSNR), while tolerating certain degree of JPEG compression and channel additive white Gaussian noise (AWGN).

This letter investigates price-based power control for cognitive radio networks (CRNs) with interference cancellation. The base station (BS) of the primary users (PUs) will admit secondary users (SUs) to access by pricing their interference power under the interference power constraint (IPC). We give the optimal price for BS to maximize its revenue and the optimal interference cancellation order to minimize the total transmit power of SUs. Simulation results show the effectiveness of the proposed pricing scheme.

In a two-way half-duplex system where source nodes are equipped with multiple antennas and a relay with a single antenna, we study the diversity multiplexing tradeoff (DMT) achieved by orthogonal decode-and-forward (ODF), orthogonal amplify-and-forward (OAF), non-orthogonal decode-and-forward (NDF) and non-orthogonal amplify-and-forward (NAF), respectively. Their closed-form DMT are derived with given transmission time of each terminal, and optimized by allocating the transmission time. From these analyses, NDF achieves the best performance in terms of DMT in low spectral efficiency scenarios, while NAF outperforms other protocols in high spectral efficiency scenarios.

To conserve energy, periodic active/sleep dynamics is adopted in wireless sensor networks. At the same time, the QoS guarantees, such as packet delay, packet loss ratio and network throughput need to be satisfied. We develop a finite queuing model for sensor nodes and derive network performance for contention-based wireless sensor networks with synchronous wakeup patterns. Furthermore, the impact of active/sleep duty cycle, time scale and node buffer size on the tradeoff between energy efficiency and QoS guarantees is studied based on the model. Simulation results well match our analytical results and validate the accuracy of our model and approach.

In this paper, we propose a successive signal-to-leakage-plus-noise ratio (SLNR) based precoding with geometric mean decomposition (GMD) for the downlink multi-user multiple-input multiple-output (MU-MIMO) systems. The known leakages are canceled at the transmit side, and SLNR is calculated with the unknown leakages. GMD is applied to cancel the known leakages, so the subchannels for each receiver have equal gain. We further improve the proposed precoding scheme by ordering users. Simulation results show that the proposed schemes have a considerable bit error rate (BER) improvement over the original SLNR scheme.