Showing papers by "Kyoung-Jae Lee published in 2017"

Simultaneous Wireless Information and Power Transfer for Cooperative Relay Networks With Battery

Abstract: In this paper, we investigate simultaneous wireless information and power transfer in a cooperative communication network consisting of one source, one battery-enabled relay, and one destination node. An amplify-and-forward relaying method is considered, where the relay node harvests energy from the received signal power to charge its battery, which is used to forward the received signal to the destination. We also consider a direct link between the source and the destination. The direct link signal can be combined with the relaying signal at the destination node using maximum ratio combining. Under the delay-limited transmission mode, closed form expressions for outage probability are derived for a battery-enabled relay. Our analytical results reveal the advantage of cooperative relay networks with a direct link. Also, we extend our design to a multiple-relay scenario, where the best relay is selected from the available number of relays, based on the information of relay locations. Finally, we demonstrate from simulation results based on outage probability that our proposed methods are efficient in comparison with Monte Carlo simulations.

Inter-Cluster Design of Wireless Fronthaul and Access Links for the Downlink of C-RAN

Abstract: This letter studies the joint design of wireless fronthaul and radio access links for the downlink of a cloud radio access network (C-RAN). In a C-RAN, high spectral efficiency can be achieved by migrating the baseband processing functionalities to a baseband processing unit (BBU). However, due to the increased system cost, the size of cluster should be kept relatively small, and hence the spectral efficiency performance tends to be limited by the impact of inter-cluster interference signals. This letter tackles the problem of jointly optimizing the fronthaul and access links across multiple clusters with the goal of maximizing the sum-rate of all the user equipments belonging to the clusters while satisfying the power constraints at the BBUs and remote radio heads. Via numerical results, the effectiveness of the proposed algorithm is confirmed.

Designs of MIMO Amplify-and-Forward Wireless Relaying Networks: Practical Challenges and Solutions Based on MSE Decomposition

Abstract: Amplify-and-forward (AF) relaying is an efficient way to extend radio range and improve link reliability with a low implementation cost While the research on the AF relaying in a single-antenna scenario has matured, its application to broadband radio transmission utilizing multiple-input multiple-output techniques still needs more effort to overcome several practical challenges, such as large overheads for channel estimation and vulnerability to the channel estimation errors This paper reviews some recently proposed linear transceiver designs based on the minimum mean squared error (MSE) criterion and shows that the proposed MSE decomposition and relaxation method can lead to an efficient solution for those challenges Insightful observations and comprehensive discussions are also made on both analytical and numerical results from practical implementation perspectives

Compressed cooperative reception for the uplink of C-RAN with wireless fronthaul

Abstract: This work deals with a joint design of radio access and fronthaul links for the uplink of cloud radio access network (C-RAN) equipped with wireless fronthaul link. A conventional uplink system based on per-cell decode-and-forward (DF) relaying, in which the message sent by each user equipment (UE) is decoded by the closest remote radio head (RRH) and forwarded to a baseband processing unit (BBU) via wireless fronthaul link, is first reviewed. Since decoding at each RRH might be affected by the interference signals of the other UEs, we present a compress-and-forward (CF) based cooperative reception scheme whereby each RRH quantizes and compresses its received signal and transmits the quantization output to the BBU through the fronthaul link. For the both approaches based on the DF and CF relaying, we tackle the problem of maximizing the sum-rate of the UEs subject to the per-UE and per-RRH power constraints. Link-level simulation results are reported that validate the advantages of the CF-based cooperative scheme compared to the DF-based per-cell reception scheme.

Uplink/downlink achievable rate analysis of heterogeneous networks with massive MIMO full-duplex backhaul link

Abstract: Heterogeneous networks (HetNets) which involves densifying a high powered macro cell (MC) with a number of low powered small cells (SCs), has been identified as key technology for 5G communication. This technology requires that MC is connected to SCs with high speed fiber optic cable for control and coordination. However connecting fiber links to all cells is expensive, labor intensive and less flexible. This paper proposes HetNet topology where massive MIMO with full-duplex (FD) provides wireless backhaul link for SCs. Communication is achieved in two phases. In the first phase, we assume cells in the HetNet are equipped with massive receive antennas and single transmit antennas whereas in the second phase a circulator switches massive antenna receivers into transmitters and single antenna transmitters into receivers. We derive accurate approximations for uplink/downlink (UL/DL) rate under the assumption of imperfect channel state information. Our results indicate that the strength of loop interference (LI) and SC-to-SC interference which occur due to FD operation depends largely on the number of SCs. By increasing the number of SCs, achievable rates also increase but requires more antennas to overcome the deleterious effects of LI and SC-to-SC interference.

Sustainable Wireless Information and Power Exchange for Energy-Constrained Communication Systems

Abstract: This paper considers point-to-point wireless communications where an energy-constrained node, which has insufficient energy for data transmission, wants to exchange messages with a node with enough energy. In this system, we study power splitting (PS) based energy cooperation methods by exploiting wireless energy transfer techniques and propose a new concept called sustainable wireless information and power exchange (SWIPE). In this SWIPE protocol, the node which has sufficient energy first transmits the information signal to the energy-constrained node. Then, the received signal at the energy-constrained node is utilized for both information decoding and energy harvesting via a PS circuit. At the consecutive time slot, by using the harvested energy, the energy- constrained node is now able to send a signal to the other node which employs a similar PS technique. This procedure continues by switching the operations of two nodes at each time slot. For the proposed SWIPE protocol, we present the optimal PS ratio computation algorithm in order to maximize the weighted sum throughput performance. Simulation results confirm the efficacy of the proposed SWIPE protocol over conventional schemes.