Blocking artifact is a major limitation of DCT-based codec at low bit rates. This degradation is likely to influence the judgment of a final user. This work presents a powerful post-processing filter in the DCT frequency domain. The proposed algorithm adopts a shift block within four adjacent DCT blocks to reduce computational complexity. The artifacts resulting from quantized and de-quantized process are eliminated by slightly modifying several DCT coefficients in the shift block. Simulation results indicate that the proposed method produces the best image quality in terms of both objective and subjective metrics.

In this paper, we propose a simple, yet effective, multiuser detection scheme for a two-hop cooperative CDMAs. In phase 1, the minimum mean square error (MMSE) detector at the destination is used to identify reliable decisions of direct transmissions from the sources and return them to the relays. Then, in phase 2, based on the reliable decisions, the relays and the destination successively utilize the maximum likelihood (ML) detectors to estimate the residual symbols. Due to the destination estimating the symbols separately from direct transmissions and the relaying signals, as a result the destination does not need the information about the relays' decision performance for the construction of the ML detector. Hence, the proposed scheme is more feasible than existing approaches for practical implementation. In addition, due to the ML detectors in phase 2 only estimating the residual symbols, the number of computations performed by the ML detectors can be reduced significantly. The results of simulations and complexity analysis demonstrate the efficiency and effectiveness of the proposed scheme.