MIMO wiretap channel consists of a multiple antenna transmitter, a legitimate multiple antenna receiver and a multiple antenna eavesdropper. Signaling strategy optimization for MIMO wiretap channel, including secrecy capacity maximization problem and power minimization problem with a secrecy rate constraint, are studied. We identify when the two problems are globally solvable. Further, iterative algorithms based on concave-convex procedure are proposed for the two problems, which can monotonically converge to a Karush-Kuhn-Tucker (KKT) point of the two problems. Numerical examples validate the effectiveness of the proposed algorithms.

The paper presents the average bit error rate (BER) of a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver in correlated frequency selective Nakagami fading environments in the presence of multiple co-channel interferences. A closed-form expression of the simple approximated probability density function for the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and multiple RAKE branches in arbitrary fading environments. The effects of spatial and temporal diversity order, angular spread, antenna spacing, average multi-path strength and fading severity on the performance of the MRC 2D-RAKE receivers are all illustrated.

The closed-form expressions of signal-to-interference-plus-noise ratio (SINR) and the outage probability are derived for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver with imperfect power control in a frequency-selective Nakagami fading channel. The impact of power control error (PCE) on the performance of the receiver is analyzed for various fading environments. Numerical results show that the performance of 2D-RAKE receivers degrades due to imperfect power control. But when PCE is not serious, increasing the number of antennae and temporal diversity order can compensate for the performance loss. The exact performance improvement due to space-time processing varies with PCE and the fading environment.

The smart antenna and spatial diversity-combining receiver are two of the most important spatial signal processing technologies. This paper studies the radio propagation characteristics of the transmission path, spatio-temporal channel model and channel characteristics in different environments. On the basis of those analyses, the authors analyzed the operating principle of the smart antenna and spatial diversity-combining technology, and especially showed the differences between these two technologies in several aspects.

Adaptive channel estimation (ACE) and dedicated pilot power adjustment based on the fading-rate measurement is investigated for the pilot-aided direct-sequence (DS) code division multiple access (CDMA) system. A novel adaptive channel estimator is presented, which makes use of an optimum integral duration or selects the optimum finite-impulse response (FIR) filter coefficients based on the fading-rate measurement. Dynamic adjustment of the dedicated pilot power is further proposed for the purpose of increasing the system capacity, based on the fact that the power of the dedicated pilot channel (DPCH) can be reduced when the mobile station moves slowly. Theoretical analysis and computer simulation results show that significant performance improvement can be achieved by using the proposed adaptive channel estimator and the dynamic pilot power adjustment method.