In this paper, a novel single layer Multiple Input–Multiple Output (MIMO) antenna for Fifth-Generation (5G) 28 GHz frequency band applications is proposed and investigated. The proposed MIMO antenna operates in the Ka-band, which is the most desirable frequency band for 5G mm-wave communication. The dielectric material is a Rogers-5880 with a relative permittivity, thickness and loss tangent of 2.2, 0.787 mm and 0.0009, respectively, in the proposed antenna design. The proposed MIMO configuration antenna element consists of triplet circular shaped rings surrounded by an infinity-shaped shell. The simulated gain achieved by the proposed design is 6.1 dBi, while the measured gain is 5.5 dBi. Furthermore, the measured and simulated antenna efficiency is $90\%$ and $92\%$, respectively. One of the MIMO performance metrics—i.e., the Envelope Correlation Coefficient (ECC)—is also analyzed and found to be less than 0.16 for the entire operating bandwidth. The proposed MIMO design operates efficiently with a low ECC, better efficiency and a satisfactory gain, showing that the proposed design is a potential candidate for mm-wave communication.

To address atmospheric attenuation and path loss issues in the mmwave portion of the spectrum, high gain and narrow beam antenna systems are essential for the next generation communication networks. This paper presents a novel hook-shaped antenna array for 28 GHz 5G mmwave applications. The proposed antenna was fabricated on commercially available Rogers 5880 substrate with thickness of 0.508 mm and dimensions of 10 × 8 mm${}^2$. The proposed shape consists of a circle with an arc-shaped slot on top of it and T-shaped resonating lengths are introduced in order to attain broad band characteristics having gain of 3.59 dBi with radiation and total efficiency of 92% and 86% for single element. The proposed structure is transformed into a four-element array with total size of 26.9 × 18.5 mm${}^2$ in order to increase the gain up to 10.3 dBi at desired frequency of interest. The four-element array is designed such that it exhibits dual-beam response over the entire band of interest and the simulated results agree with fabricated prototype measurements. The proposed antenna array, because of its robustness, high gain, and dual-beam characteristics can be considered as a potential candidate for the next generation 5G communication systems.

The terahertz (THz) communication has been considered as a promising technique for future 6G wireless networks because of its tens of GHz bandwidth. However, the path direction for THz channel under different subcarrier frequencies is different (i.e., beam squint), which leads to the serious beam gain loss for conventional hybrid precoding design schemes. Thus, the effect of beam squint must be considered for the application of the wideband THz systems. In this paper, we consider the precoding design problem in a wideband THz massive multiple-input–multiple-output (mMIMO) orthogonal frequency division multiplexing (OFDM) systems with beam squint. We first design two new sparse radio frequency chain antenna structures, including fully connected and subarray. Based on the designed structure, we formulate an average rate maximization problem by jointly designing the hybrid analog/digital precoding at the transmitter and analog combine vector at the receiver. Since it is a challenge to optimize the precoding simultaneously, we propose an alternatively iterative algorithm to solve it under each antenna structure. Finally, the simulation results are conducted to show the effectiveness of the designed antenna structure and proposed precoding schemes.

In this paper, we investigate the resource allocation problem in two-tier heterogenous networks (HetNets) with massive MIMO, where two frequency bands, cellular frequency band and millimeter wave frequency band, are used for wireless backhaul links. To coordinate the interference among small cells (SCs), SCs are grouped into multiple SC clusters (SCCs), where SC users are jointly served by SC base stations (BSs) (SBSs) belonging to the same SCC. To eliminate the multi-user and inter-tier interference, we propose a block diagonalization based precoding scheme at macro-BS and each SCC, where the transmit precoding matrix for users is projected onto the null space of interference channels. Following this, we formulate a power allocation optimization problem to maximize the downlink sum rate of the system subject to per-SCC power and users' quality of service requirements. Since the formulated problem is nonconvex, we transform it into a convex one by appropriate approximation, and a constrained concave convex procedure based iterative algorithm is proposed to obtain the solution. Furthermore, we prove that the obtained solution converges to the local optimum. Meanwhile, according to the structure of the original formulated problem, we divide it into multiple subproblems and propose an optimal iterative water-filling algorithm. Next, we extend the original problem with per-SBS power constraint, which results in that the precoding of each SCC has to be redesigned. On this basis, we propose an iterative water-filling algorithm to obtain the optimal power allocation and precoding. Numerical results are presented to verify the performance of our proposed algorithms.

This article presents compact and novel shape ring slotted antenna array operating at mmWave band on central frequency of 28 GHz. The proposed structure designed at 0.256 mm thin Roggers 5880 is composed of a ring shape patch with a square slot etched at the top mid-section of partial ground plane. Through optimizing the ring and square slot parameters high bandwidth of 8 GHz is achieved ranging from 26 to 32 GHz with simulated gain of 3.95 dBi and total efficiency of 96% for single element. The proposed structure is further transformed in a 4 element linear array manner. With compact dimensions of 20 mm × 22 mm for array, the proposed antenna delivers high simulated gain of 10.7 dBi and is designed in such a way that it exhibits dual beam response over the entire band of interest and simulated results well agree with fabricated prototype measurements.

Mobile edge computing (MEC) can effectively overcome the shortcomings of high-latency in mobile cloud computing (MCC) by deploying the cloud resources, e.g., storage and computational capability, to the edge. However, the limited computation capability of the MEC restricts the scalability of offloading. Therefore, the basic requirements of the MEC system are to explore effective offloading decisions and resource allocation methods. To address it, we develop a collaborative computing system composed of local computing (mobile device), MEC (edge cloud) and MCC (central cloud). Based on the proposed collaborative computing system, we design a novel Q-learning based computation offloading (QLCOF) policy to achieve the optimal resource allocation and offloading scheme by prescheduling the computation side for each task from a global perspective. Specifically, we first model the offloading decision process as a Markov decision process (MDP) and design a state loss function (STLF) to measure the quality of experience (QoE). After that, we define the cumulation of STLFs as the system loss function (SYLF) and formulate an SYLF minimization problem. Due to the difficulty to directly solve the formulated problem, we decompose it into multiple subproblems and preferentially optimize the transmission power and computation frequency of the edge cloud by the quasi-convex bisection and polynomial analysis method, respectively. Based on the precalculated offline transmission power and edge cloud computation frequency, we develop a Q-learning based offloading (QLOF) scheme to minimize the SYLF by optimizing offloading decisions. Finally, the numeral results show that the proposed QLOF scheme effectively reduces the SYLF under different parameters.