In this letter, we address the beamforming in full-duplex self-energy recycling relay system, where an amplify-and-forward relay delivers the source message to the destination in a single time slot while recycling a portion of its RF energy through energy harvesting. The signal received at the realy is divided into two circuits, one for the full-duplex relaying and the other for the energy harvesting. The beamforming vectors and the power division ratio at the relay are optimized to maximize the harvested energy while maintaining a certain reception quality threshold at the destination. Simulation results show various advantages and trade-offs of the proposed system.

A low complexity pilot allocation scheme is proposed for a large OFDM block with null subcarriers. The proposed scheme allocates pilots to the edge part of the active subcarrier region according to the 2nd order polynomial and to the middle part of the active subcarrier region according to the 1st order polynomial or the comb‐type pilot pattern. To find a parameter of the 2nd order polynomial, the proposed scheme applies exhaustive search of a single parameter by using an integer unit resolution. It is shown by simulation that the proposed scheme is a close‐to‐optimal pilot allocation scheme yielding better symbol error rate (SER) performance than the traditional 3rd and 5th order polynomial‐based schemes although the proposed scheme has lower computation and implementation complexity.

Blind selected mapping (BSLM) is a technique to reduce the peak to average power ratio (PAPR) of OFDM by using a set of scrambling sequences. Since the side information (SI) on the scrambling sequence selected by the transmitter is not directly sent to the receiver in BSLM, the SI needs to be estimated by the receiver. In this paper, a BSLM scheme that applies a new SI estimation approach is proposed. The proposed BSLM scheme estimates the SI by selecting the minimum of the candidate metrics that are computed with the received pilot signal, the pilot symbol sequence, and the scrambling sequences. It is shown by simulation that the proposed BSLM scheme yields better SI error rate (SIER) and bit error rate (BER) performance and lower implementation complexity than four traditional BSLM schemes.

We investigate self-energy recycling (S-ER)-based RF powered multi-antenna relay channels (RCs) for the coverage extension in sensor networks or small cells. In the S-ER-based RF powered RC, the power used at the relay station for data transmission depends only on the energy from the access point and the recycled energy from its own transmission. We propose an optimal beamforming scheme with associated protocols and study their behaviors for both cases of downlink only and joint up-down link. Strategies for the power allocation between data transmission and RF powering are provided and a comparison with the conventional RF powered RC is made. For the proposed power allocation strategies, the performance of the conventional RC is achieved by the proposed RF powered RC only when infinite RF power is available. A high value of S-ER helps the proposed systems to reach the performance of conventional relay systems. In the joint up-down link protocol, we show that the up-down rate region can simply be constructed with easy power allocation strategy.

This study investigates the cooperative multicast of scalable video over dedicated relay‐based cellular networks. Different layers in a scalable video tend to have different transmission quality requirements, and legacy cellular network has limitations in providing homogeneous service quality within its coverage area. The authors propose two realistic cooperative transmission schemes with a capacity performance analysis for scalable video over dedicated relay‐based cellular networks. The proposed transmission schemes with multiple antennas at an evolved node B and the dedicated relay utilise the combinations of beamforming and space‐time coding in order to enhance the multicast performance of scalable video. The proposed schemes ensure that the received base layer (BL) of scalable video guarantees the minimum video quality to all user terminals throughout the cell coverage with given outage probability, while the terminals inside the relay coverage can achieve better video quality by receiving both the BL and additional enhancement layer data according to the received channel condition. The antennas configuration and the video type determine which multicast scheme to choose.

The outage probability of two‐way relaying network with orthogonal space–time block coded (STBC) transmission is analysed. Two sources equipped with different numbers of antennas send orthogonal STBC coded signals with different parameters. The channel gain between two antenna elements is assumed to be Rayleigh faded. The amplify‐and‐forward (AaF) relay with a single antenna repeats the received signal after power scaling. Exact expressions for the outage probabilities are provided, where the authors integrate out the outage probability over one of the three different regions on the plane defined by the inverses of channel gains. According to the orthogonal STBC code rates and the source and relay powers, one integration region is selected among the three. The closed‐form expression is verified via a set of comparisons with the simulation results. The authors also show that the maximum diversity is attained when the orthogonal STBC is applied at both sides of the two‐way channel.

We consider beamformer optimization for user equipment (UE) relaying cooperation in heterogeneous cellular networks (HCNs), where the interference from femto cells nearby aggravates the signal-to-interference-plus-noise ratio (SINR) of a macro UE (MUE). A femto UE acts as a relay over device-to-device (D2D) uplink and forward to the MUE, the composite of desired signal and interference to improve the post SINR of the MUE. The beamformers of the UE relay and MUE collaborate to make a balance between the two signals so that the output signal after multistage maximal-ratio combining (MS-MRC) yields a sufficient post SINR for the desired signal. We first consider the case with a single interfering femto access point (FAP) and show that the beamforming for dual-stage MRC can effectively handle the interference. Then, the idea is generalized to the case of two interfering FAPs with a three-stage MRC. A geodesic geometry view allows us to parameterize the BF design with the angles that the involved channel vectors make. This approach makes the optimization of the BF simpler, reduces the feedback overhead, and provides better insight into the problem at hand. Simulations are carried out to validate the performance of the UE relaying cooperation in HCN environments.

Machine-to-machine (M2M) communications, also known as machine-type communications (MTC) in 3GPP LTE systems, provide autonomous connectivity between machines without human intervention to create new service, e.g., the Internet of Things and the smart grid. M2M communications normally involve a large number of MTC devices (MTCDs) to support a variety of sensor applications. Consequently, concurrent and massive access attempts of MTCDs to radio access networks (RANs) may cause intolerable delay, packet loss, and even service unavailability. In this paper, we propose a joint optimal physical random access channel (PRACH) resource allocation and access control mechanism to address the performance degradation caused by concurrent and massive access attempts of MTCDs in LTE systems. We define the notion of random access efficiency and formulate an optimization problem for maximization of the random access efficiency with random access delay constraint. We also propose a dynamic resource allocation and access control algorithm based on estimation of the number of MTCDs for a system with dynamically varying numbers of massive MTCDs. Then, an analytical model is provided using a discrete-time Markov chain for the proposed mechanism. The effectiveness of the proposed algorithm is demonstrated via analysis and simulations. The proposed algorithm was able to maintain the optimal random access efficiency while satisfying the average random access delay requirement of MTCDs to handle massive and dynamic MTCDs per cell.

We propose a set of multiuser two-way relay beam-forming schemes in the cellular network. While the previous schemes are applicable only when there exist a single base station (BS) and a single relay station (RS) with the same number of antennas, multiple BSs or multiple RSs can exist in the proposed scheme without such restriction on the numbers of antennas. The degree of freedoms (DoF) achievable are analyzed and conditions to achieve these DoF values are presented. Both the decode-and-forward (DaF) protocol and amplify-and-forward (AaF) protocol are considered. It turns out that the channel alignment and the interference alignment in the multi-cell environment act the key roles in the development. We also provide an interference alignment scheme in the multi-cell environment that improves the achievable DoF values upon those of the previous schemes. The simulation results corroborate that the proposed beam-forming works as analyzed.

We consider a homogeneous multiple cellular scenario with multiple users per cell, i.e., K ≥ 1 where K denotes the number of users in a cell. In this scenario, a degrees of freedom outer bound as well as an achievable scheme that attains the degrees of freedom outer bound of the multicell multiple access channel (MAC) with constant channel coefficients are investigated. The users have M antennas, and the base stations are equipped with N antennas. The found outer bound is general in that it characterizes a degrees of freedom upper bound for K ≥ 1 and L >; 1 where L denotes the number of cells. The achievability of the degrees of freedom outer bound is studied for two cell case (i.e., L = 2). The achievable schemes that attains the degrees of freedom outer bound for L = 2 are based on two approaches. The first scheme is a simple zero forcing with M = Kβ+β and N = Kβ, and the second approach is null space interference alignment with M = Kβ and N = Kβ + β where β >; 0 is a positive integer.

We consider a system with precoding in the half duplex Decode-Forward (DF) relay networks, where multiple antennas are adopted at the source, the destination and the relay. Based on the channel state information (CSI), a few feedback bits are fed back from the destination to the source and the relay to select the source and the relay precoders. A suboptimal precoder selection criterion for the symbol vector error minimization and an optimal precoder selection criterion for the capacity maximization are proposed for the practical situation where relays are placed between the source and the destination. We analyze the diversity performance of the criteria and show that the full diversity is achieved when the rank one precoder sets span the vector channel space formed by the transmit antennas of the source and the those of the relay.

We consider regularized channel inversion (RI) precoding in the multiuser multiple input multiple output (Mu-MIMO) broadcast channels. To make the RI operate in quantized channel feedback condition, we analyze the quantization error variance and its effect on the signal to interference plus noise power ratio (SINR) of the user signals. The regularization parameter ¿ is optimized to balance the additive noise, the multiuser interference and the interference due to the quantization error and to maximize SINR. Analysis and simulations show that regularization enhances the performance of zero forcing beam forming (ZFBF) over the whole signal to noise power ratio (SNR) range. This is contrasting to the perfect channel status information (CSI) case, where the enhancement is observed in the low SNR region.