Since its introduction for long term evolution (LTE), vehicle-to-everything (V2X) communications have evolved to the recent new radio (NR)-based V2X with enhanced reliability, latency, capacity, and flexibility. One of the key features of NR V2X is the enabling of sidelink (SL) communications between user equipments (UEs) without any assistance from a base station (i.e. support of the out-of-coverage scenario). To this end, NR V2X supports SL resource allocation (RA) mode 2, in which a UE autonomously determines the subset of resources to use for data transmission while avoiding resource collision due to other UEs. This paper summarizes the resource sensing and selection (RSS) mechanisms for SL RA mode 2 specified in releases 16 and 17 of NR V2X. The critical aspect for RSS is the minimization of UE power consumption during resource sensing, which is caused by multiple blind decodings on the physical SL control channel. To address this issue, the effective number of blind decodings for conventional RSS is quantitatively analyzed to determine the potential enhancements required. Furthermore, an enhanced RA mode 2 procedure based on an intelligent partial-sensing (IPS) scheme is proposed to minimize the number of blind decodings. The proposed IPS utilizes a convolutional neural network-based physical channel-type classification model. Simulation and numerical results show that the throughput obtained with the proposed IPS scheme approximates that obtained via full sensing-based RA mode 2, while reducing the number of blind decodings by 90%.

In Internet of Things (IoT) systems, a number of sensor devices monitor the physical system states and exchange information with each other. The main limitation is that the IoT devices are generally energy constrained since those are powered with batteries. To address this energy problem, we consider a cooperative wireless-powered communication network (WPCN), which consists of three phases: 1) downlink (DL) energy transfer from a multi-antenna access point (AP); 2) data sharing among IoT devices; and 3) uplink (UL) information transfer from single-antenna IoT devices. Based on the shared data and the harvested energy, the single-antenna IoT devices in the neighborhood cooperate to form a virtual antenna array in order to transmit their information simultaneously to the multi-antenna AP using a multiple-input multiple-output (MIMO) technique in the UL information transfer phase. In this study, the transmit covariance matrices (i.e., beamforming vectors and the corresponding transmit power allocation) used for both DL energy transfer and UL information transfer are jointly designed to maximize the UL capacity based on the Lagrangian method. Furthermore, the time allocation for each phase is optimized based on a stochastic gradient method. In the numerical results, it is shown that our proposed beamforming scheme and the stochastic time allocation can achieve near-optimal performance.

The conventional studies on virtual multiple-input multiple-output based cooperative time division multiple access (TDMA) have been focused on the cooperative retransmission of failed data. In this paper, we propose an opportunistic cooperative TDMA (OC-TDMA) scheme where a source user transmits its own data and the cooperative users opportunistically transmit low-data-rate users' data. To do this, time slots are divided into non-cooperative and cooperative time slots. The non-cooperative time slots are located at earlier time slots, in which weak users, who cannot satisfy the required signal-to-interference-plus-noise ratio (SINR), are scheduled. The cooperative time slots are located at later time slots, in which strong users, who can satisfy the required SINR, are scheduled. In the cooperative time slots, the source user transmits its own data and the other users (i.e., cooperative users) assist to transmit the weak users' data which was transmitted at the non-cooperative time slots. The optimal and sub-optimal OC-TDMA algorithms are analyzed and evaluated in terms of the required excess capacity, which indicates the capacity additionally required to satisfy the SINR constraints of all the users after all the transmission is finished. Throughout the simulation and numerical results, it is demonstrated that OC-TDMA schemes outperform conventional TDMA schemes.

In this paper, we propose a joint beamforming algorithm for a multiuser wireless information and power transfer (MU-WIPT) system that is compatible with the conventional multiuser multiple input multiple output (MU-MIMO) system. The proposed joint beamforming vectors are initialized using the well established MU-MIMO zero-forcing beamforming (ZFBF) and are further updated to maximize the total harvested energy of energy harvesting (EH) users and guarantee the signal to interference plus noise ratio (SINR) constraints of the co-scheduled information decoding (ID) users. When ID and EH users are simultaneously served by joint beamforming vectors, the harvested energy can be increased at the cost of an SINR loss for ID users. To characterize the SINR loss, the target SINR ratio μ is introduced as the target SINR (i.e., SINR constraint) normalized by the received SINR achievable with ZFBF. Based on that ratio, the sum rate and harvested energy obtained from the proposed algorithm are analyzed under perfect/imperfect channel state information at the transmitter (CSIT). Through simulations and numerical results, we validate the derived analyses and demonstrate the EH and ID performance compared to both state of the art and conventional schemes.

In a quantization based multiuser multiple-input/multiple-output (MU-MIMO) broadcast channel, the effective channel gain (i.e., the norm of a channel vector obtained from the receive combiner) needs to be considered in addition to a reduction of quantization errors for maximizing the signal-to-interference plus noise ratio (SINR). In this work, we prove that the effective channel gains in the space limited by an N_R x M_T MIMO channel form a min(M_T,N_R)-dimensional ellipsoid in the channel space. Utilizing the geometric proof, the achievable effective channel gain is derived as a function of its direction for a given MIMO channel. Based on the derivation, we finally propose a quantization vector selection criterion and an optimal receive combiner to maximize the SINR. The proposed maximum SINR based combining (MSC) is proven to be a better solution for maximizing the SINR compared to quantization based combining (QBC) and maximum gain based combining (MGC), each of which attempts to minimize quantization errors and maximize the effective channel gain.

In multi-cell downlink system, quality of service (QoS) of multiuser MIMO is an important issue, in particular, for cell-edge users. For QoS of cell-edge users in the system, the utilization of multiple-input multiple-output (MIMO) relay stations (RSs) is a promising solution that improves the signal-to-interference plus noise ratio (SINR) from neighboring base stations (BSs) to each RS. Since the capacity between the BS and the RS relies heavily on the receive performance, it is necessary to reflect interference channels in the design of the receive weight vector. In this paper, we use a geometric approach to derive the effective channel gain of the RS according to the receive weight vector. The geometric relationship between the desired and interference channels is also described. Using the description, we propose a receiver, called the maximum lower bound of expected SINR receiver (MLESR). Through a performance analysis of the MLESR over the interference-limited regime, we derive closed terms for the performance bounds in terms of the number of RS antennas, the interference channel rank, and the BS transmit power according to the rate gap of the MLESR with respect to an ideal case, i.e., a no interference case.

This paper models and analyzes an asymptotic visual capacity based on distortions by encoding and wireless transmission. In a limited 2-dimensional area, there are N source and destination node pairs. They are transmitting, receiving and relaying others' traffic. The analysis covers encoding distortion, wireless transmission error and end-to-end delay distribution. Our simulation results show that the visual capacity of the network decreases over the rate of 1/(n log n).

In conventional cellular systems with a frequency reuse factor (FRF) of one, quality of service (QoS) may not be guaranteed for users located at the cell boundary due to inter cell interference (ICI). Even if relay nodes are adopted for cooperative communications, ICI and inter-relay interference (IRI) remain significant obstacles to reliable data transmission at the border region of each cell. This paper presents an efficient fixed relay station (FRS)-cooperative strategy termed interference cancelation based FRS-cooperation (ICFC) to improve the QoS. The proposed scheme enables to improve the performances of two users at cell-edge in each cell through cooperation and interference cancelation, simultaneously. In particular, the ICFC scheme is well applicable to practical systems because no CSIT is required.

Due to multi-user diversity, the performance of a random unitary beamforming (RUB) can be improved upon in proportion to the number of users at the expense of an increase in feedback. It is essential to identify a mechanism to determine a set of orthonormal beams for improving the channel capacity. This paper proposes a unique scheme, named iterative best beam selection-based RUB (I-RUB), in which the base station selects the best beamforming vectors from unitary matrices generated by the proposed iterative algorithm. Using the selected beamforming vector at each stage, the beam set can ultimately be constructed for high sum-rate capacity of downlink, which leads to a reduction in feedback compared to those of other RUB schemes based on the beam set selection.

The capacity of downlink multiple-input multiple-output (MIMO) cellular networks is significantly limited by inter-cell interference (ICI), particularly at cell boundaries. Recently, two types of coordinated multiple point transmission (CoMP) technologies, joint processing and transmission (JPT) and coordinated scheduling and beamforming (CSB), were proposed. These technologies are intended for the latest cellular communication standard in order to improve the performance of cell-edge users who suffer from significant ICI. In this paper, we propose an ICI cancellation technique based on a user selection algorithm for CoMP-CSB. Under partial channel state information (CSI) and no data sharing condition, each base station (BS) concentrates more on the direction of interference to the adjacent cell's users, during the user selection process. Unlike prior concepts for a single-cell environment, in which each BS generates a precoding matrix for selected users to be served, the proposed technique considers the effects of interference to users located in adjacent cells. Although there are obvious trade-offs between ICI mitigation and the number of simultaneous scheduled users in terms of system capacity, the simulation results demonstrate that our proposed algorithm achieves higher sector throughput and is more robust against ICI if the system is limited by interference. Furthermore, through simulation we are able to obtain the preferred option for the coordination distance (R) and the number of degrees of freedom for ICI nulling (ξ).

Throughput and quality-of-service (QoS) over multicell environments are two of the most challenging issues that must be addressed when developing next generation wireless network standards. Currently, multiple-input/multiple-output (MIMO), inter-cell coordination and multi-hop relay technologies are viable options for improving channel capacity or coverage extension. Nevertheless, severe QoS degradation occurs in the outer region of multi-cells due to significant interference from neighboring cells or relay stations, thereby limiting overall performance. This paper describes an effective technique, fixed relay station cooperated beam-forming (FCBF), which combines MIMO, multi-hop relay and multi-cell coordination. Simulated testing of FCBF demonstrates an increase of 10% in the average sum-rate and a decrease of 25% in the outage probability compared with conventional techniques. In particular, throughput at the cell boundary is remarkably increased with FCBF compared with traditional beam-forming technologies.

This paper investigates the problem of MAI (multiple access interference) occurrence when timing misalignment occurs in the downlink channel of OFDM-based networks. The adaptive guard band allocation scheme is mainly designed to achieve timing synchronization while reducing guard carrier redundancy and maintaining high channel throughput in asynchronous OFDM-based networks. Thus, the proposed scheme reduces the effect of MAI for users receiving multiple transmission signals from surrounding BSs (Base Stations). In a simulation, it is noteworthy that this adaptive carrier allocation is very effective in reducing MAI for asynchronous multi-cell network.

Various approaches for analyzing handover have been developed to guarantee the QoS (Quality of Service) of multimedia services over mobile communication networks. However, no framework for multicarrier-based broadband systems, such as MC-CDMA (Multi-Carrier Code Division Multiple Access) or OFDMA (Orthogonal Frequency Division Multiple Access) is available, from the perspective of link capacity. This paper presents a handover technique, referred to as semi-soft handover utilizing macro diversity, which permits both hard and soft handover advantages for services over multicarrier-based broadband networks to be retained. A theoretical analysis is then performed to measure the handover gain over the forward link in terms of an outage probability. The simulation data verifies that the semi-soft handover outperforms other traditional handover techniques, in particular, for high data rate services.

FRPA(frequency reuse power allocation) technique by employing the frequency reuse notion as a strategy for overcoming the ICI(intercell interference) and maintaining a QoS(quality of service) at the cell boundary is described for broadband cellular networks. In the scheme, the total bandwidth is divided into sub-bands and two different power levels are then allocated to sub-bands based on the frequency reuse for forward-link cell planning. In order to prove the effectiveness of the proposed algorithm, a Monte Carlo simulation was performed. The simulation shows that this technique can achieve high channel throughput while maintaining the required QoS at the cell boundary.