LTE-Advanced heterogeneous networks (HetNets), consisting of conventional Macrocells overlaid by Picocells and forming a hierarchical cell structure, constitute an attractive way of improving the Macrocell capacity and coverage. However, the inter-tier interferences in such systems can significantly reduce the capacity and cause unacceptably high levels of control channel outage. Thus time domain Enhanced Inter-cell Interference Coordination (eICIC), such as almost blank subframe (ABS) and cell range expansion (CRE) techniques, has been proposed to mitigate the interference and improve the system capacity in HetNets. In order to acquire the benefit of eICIC technology efficiently, the three parameters, i.e. ABS ratio, ABS power and CRE bias, should be carefully configured jointly. Motivated by the above considerations, we first propose a single parameter optimization algorithm that fixes the other two parameters and then optimizes them separately. Then, a heuristic joint parameter optimization algorithm is proposed to maximize the system throughput. Extensive simulation results illustrate that the proposed algorithms clearly outperform the fixed parameter configuration, and is close to that of the traversal search algorithm even though they have lower computation complexity

A high-rate coding scheme that polar codes are concatenated with low density generator matrix (LDGM) codes is proposed in this paper. The scheme, referred to as polar-LDGM (PLG) codes, can boost the convergence speed of polar codes and eliminate the error floor behavior of LDGM codes significantly, while retaining the low encoding and decoding complexity. With a sensibly designed Gaussian approximation (GA), we can accurately predict the theoretical performance of PLG codes. The numerical results show that PLG codes have the potential to approach the capacity limit and avoid error floors effectively. Moreover, the encoding complexity is lower than the existing LDPC coded system. This motives the application of powerful PLG codes to satellite communications in which message transmission must be extremely reliable. Therefore, an adaptive relaying protocol (ARP) based on PLG codes for the relay satellite system is proposed. In ARP, the relay transmission is selectively switched to match the channel conditions, which are determined by an error detector. If no errors are detected, the relay satellite in cooperation with the source satellite only needs to forward a portion of the decoded message to the destination satellite. It is proved that the proposed scheme can remarkably improve the error probability performance. Simulation results illustrate the advantages of the proposed scheme

The original single-shot multibox detector (SSD) algorithm has good detection accuracy and speed for regular object recognition. However, the SSD is not suitable for detecting small objects for two reasons: 1) the relationships among different feature layers with various scales are not considered, 2) the predicted results are solely determined by several independent feature layers. To enhance its detection capability for small objects, this study proposes an improved SSD-based algorithm called proportional channels' fusion SSD (PCF-SSD). Three enhancements are provided by this novel PCF-SSD algorithm. First, a fusion feature pyramid model is proposed by concatenating channels of certain key feature layers in a given proportion for object detection. Second, the default box sizes are adjusted properly for small object detection. Third, an improved loss function is suggested to train the above-proposed fusion model, which can further improve object detection performance. A series of experiments are conducted on the public database Pascal VOC to validate the PCF-SSD. On comparing with the original SSD algorithm, our algorithm improves the mean average precision and detection accuracy for small objects by 3.3% and 3.9%, respectively, with a detection speed of 40FPS. Furthermore, the proposed PCF-SSD can achieve a better balance of detection accuracy and efficiency than the original SSD algorithm, as demonstrated by a series of experimental results.