Crossed dipole antennas have been widely employed for dual-polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional crossed dipole (CD) antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7-2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR35 dB. In addition, stable gain and HPBW are obtained with the variance less than ±0.55 dB and ±3.5° respectively.

There is an urgent demand for massive machine-type terminals to have access into time-division multiple access (TDMA)-based satellite networks by means of random multiple access (RMA). Several RMA protocols have been proposed by exploiting packet repetitions and interference cancellation to achieve high throughput. In this paper, a framework of non-orthogonal slotted aloha (NOSA) protocol is reported to achieve even higher throughput. With a specifically designed tile-based frame structure, it introduces the intra-tile sparse mapping as a special kind of pre-coded packet repetitions and exploits the joint multi-packet detection to blindly detect superimposed packets. By further employing inter-tile packet repetitions and interference cancellation, the NOSA protocol is able to achieve high throughput with affordable complexity while keeping the same transmission efficiency as and comparable power consumptions to available protocols. Simulation results show that the NOSA prototype has the potential in providing RMA for massive machine-type terminals in practical TDMA-based satellite networks.

In this study, new microencapsulated phase change material, with organic composite phase change as the core material and polymethylmethacrylate as the shell, was prepared by in situ interfacial polymerization reaction. The surface morphology of the formed microcapsule was observed by scanning electron microscopy, and its phase change temperature and phase change heat were measured by differential scanning calorimetry. The results of this study indicate that the mean diameter is in the range 2–3 µm, with a uniform size distribution, and the phase change temperature and enthalpy of microencapsulated phase change material are of 26.2°C and 139.68 J/g, respectively. The prepared microcapsule was mixed with ordinary paint in a 1:1 ratio for performing the comparative tests in two rooms with the same dimension and settings. The results indicated that with the introduction of a 2- to 3-mm-thick coating containing microencapsulated phase change material the temperature amplitude decreased by 5°C–6°C. The power monitoring results for the period of the highest temperature in 1 day indicated that the start-up time of air conditioner significantly decreased, thus saving about 26% electric consumption.

By means of random multiple access (RMA), there is a prevailing tendency for massive machine-type terminals to have access into networks without numerous signaling interactions and frequent resource scheduling. Being one of the promising techniques to fulfill this requirement, sparse code multiple access (SCMA) is anticipated to notably broaden connections for the communication system. However, when applying RMA in the SCMA uplink, as massive terminals would randomly transmit their packets in an uncoordinated way, it is quite possible for some terminals to share an identical codebook so as to introduce the codebook collision problem. In this case, an indefinite number of terminals with possible codebook collisions would competitively share a same block of channel resources, resulting in an overloading status and deteriorated performance. To deal with this problem, we illustrate first the potential utilization of codebook collisions for RMA and propose then a partial Gaussian tree approximation (PGTA) detector to relieve heavy computational burden due to overloading conditions. With approximate decomposition of likelihood functions that has rarely been discussed, the proposed PGTA detector with proper message passing rules is able to approach the performance of a traditional message passing detector with considerably lower complexity.

With the dramatic increase in smart machine-type communications (MTC) devices, sparse code multiple access (SCMA) based random access (RA) can be considered as a promising technique for MTC devices to have efficient access into the network. However, the codebook collision problem due to RA may severely decrease the system throughput. In this letter, an optimization problem is formulated to find out optimal strategies in selecting subframes and codebooks for MTC devices, thus maximizing the throughput. To solve this problem, we propose a decoupled distributed Q-learning (DQL) based scheme, in which each device utilizes respectively two Q-learning mechanisms to automatically select its subframe and codebook according to the received feedback signals. By decreasing the dimension of the action set with the decoupled relationship between subframes and codebooks, the proposed scheme could efficiently reduce the convergence time. Numerical results show that the proposed scheme can greatly improve the performance compared with the existing works.

In this paper, a novel random pre-coding (RPC) based random access (RA) scheme is proposed to improve the system performance in the Internet of Things-oriented satellite networks. In this scheme, each device randomly selects a non-orthogonal multi-level complex sequence from a pre-defined pre-coding sequence set to pre-code the transmitted packets in a sub-frame, by which multiple superimposed packets in the sub-frame can be successfully decoded by using the minimum mean squared error (MMSE) based successive interference cancellation (SIC) detection algorithm. Besides, by combining the proposed RPC with the existing contention resolution diversity slotted ALOHA (CRDSA) scheme, which the RPC-CRDSA scheme is generated. The SIC processing should be carried out across sub-frames to remove the received signals that are already recovered, which can further significantly improve the system throughput. The performance of the RPC-RA scheme is evaluated via both theoretical analysis and computer simulation. The collision probabilities of both preamble and pre-coding sequences and an upper bound of throughput are derived, respectively. Simulation results show that the peak normalized throughput of RPC-CRDSA with the pre-coding sequence length L=8 can reach 1.87 bits/symbol, which largely outperforms traditional schemes.