Cheol Jeong

Random access in millimeter-wave beamforming cellular networks: issues and approaches

With the formidable growth of various booming wireless communication services that require ever increasing data throughputs, the conventional microwave band below 10 GHz, which is currently used by almost all mobile communication systems, is going to reach its saturation point within just a few years. Therefore, the attention of radio system designers has been pushed toward ever higher segments of the frequency spectrum in a quest for increased capacity. In this article we investigate the feasibility, advantages, and challenges of future wireless communications over the Eband frequencies. We start with a brief review of the history of the E-band spectrum and its light licensing policy as well as benefits/challenges. Then we introduce the propagation characteristics of E-band signals, based on which some potential fixed and mobile applications at the E-band are investigated. In particular, we analyze the achievability of a nontrivial multiplexing gain in fixed point-to-point E-band links, and propose an E-band mobile broadband (EMB) system as a candidate for the next generation mobile communication networks. The channelization and frame structure of the EMB system are discussed in detail.

Maximum Transmission Rate of PSR/TSR Protocols in Wireless Energy Harvesting DF-Based Relay Networks

In this paper, we consider the power splitting relaying (PSR) and time switching relaying (TSR) protocols for decode-and-forward (DF)-based relay networks consisting of a source, a relay, and a destination. For the networks, the relay is assumed to have a rechargeable battery with a certain amount of remaining energy for energy harvesting through the received signal transmitted from the source. Specifically, for the PSR protocol with and without the direct-path, we present the outage probability expression with a given power splitting coefficient, and we obtain the optimum power splitting coefficient to maximize the transmission rate and derive its transmission rate and outage probability, where the optimum coefficient depends on channel conditions and remaining energy. For the TSR protocol with and without the direct-path, we present the outage probability expression with a given time switching coefficient, and we obtain the optimum time switching coefficient to maximize the transmission rate and derive its transmission rate, where the optimum coefficient also depends on channel conditions and remaining energy.

Areal capacity limit on the growth of small cell density in heterogeneous networks

We consider heterogeneous network (HetNet) systems comprising of two different types of base-stations (BSs): macro and small BSs. In the previous studies for HetNet, it is observed that the distribution of signal to interference plus noise ratio (SINR) is independent of the BS density. This implies that network throughput increases linearly with the number of BSs. In this paper, however, we have identified key practical factors which degrade the SINR distribution for dense HetNet. On the contrary to the previous studies, limited network throughput is verified by evaluating the areal capacity with respect to the density of BS under the practical channel model. The observation is made regardless of the deployment scenario whether the two types of BSs share the same frequency band or not. Based on the analysis and the simulation results provided in this paper, we present principal guidelines for cell deployment and system operation to improve the areal capacity of dense HetNet systems.

Large-scale ad hoc networks with rate-limited infrastructure: Information-theoretic operating regimes

The impact and information-theoretic limits of infrastructure support with rate-limited wired links are analyzed in hybrid ad hoc networks, where multi-antenna base stations (BSs) are deployed and the rate of each BS-to-BS link scales at an arbitrary rate relative to the number of randomly located wireless nodes. For the operating regimes with respect to the number of BSs and the number of antennas per BS, we first analyze the minimum rate of each BS-to-BS link, Cbs, required to guarantee the capacity scaling for the network using infinite-capacity backhaul links. We then identify the operating regimes in which the required rate CBs scales much slower than 1. We also show the achievable throughput scaling for the case where the rate of each BS-to-BS link scales lower than CBs.

Capacity Scaling of Hybrid Erasure Networks Based on Polynomial Power-Law

A capacity scaling law is studied for a hybrid erasure network where a number of wireless nodes and infrastructure nodes, or equivalently base stations, exist. A polynomial decay model is used to suitably characterize an erasure probability for transmission between nodes. Based on the model, upper and lower bounds on the total capacity scaling are derived. Our result indicates that the two bounds are of exactly the same order under a certain condition on the decay parameter for the hybrid erasure network.

HierHybNET: Capacity scaling of ad hoc networks with cost-effective infrastructure

Abstract In this paper, we introduce a large-scale hierarchical hybrid network (HierHybNET) consisting of both n wireless ad hoc nodes and m base stations (BSs) equipped with l multiple antennas per BS, where the communication takes place from wireless nodes to a remote central processor (RCP) through BSs in a hierarchical way. To understand a relationship between capacity and cost, we deal with a general scenario where m, l, and the backhaul link rate can scale at arbitrary rates relative to n (i.e., we introduce three scaling parameters). In order to provide a cost-effective solution for the deployment of backhaul links connecting BSs and the RCP, we first derive the minimum backhaul link rate required to achieve the same capacity scaling law as in the infinite-capacity backhaul link case. Assuming an arbitrary rate scaling of each backhaul link, a generalized achievable throughput scaling law is then analyzed. Moreover, three-dimensional information-theoretic operating regimes are explicitly identified according to the three scaling parameters. We also characterize an infrastructure-limited regime where the throughput is limited by the backhaul link rate.

GreenInfra: Capacity of Large-Scale Hybrid Networks With Cost-Effective Infrastructure

The cost-effective impact and fundamental limits of infrastructure support with rate-limited wired backhaul links (i.e., GreenInfra support), directly connecting base stations (BSs), are analyzed in a large-scale hybrid network of unit node density, where multiantenna BSs are deployed. We consider a general scenario such that the rate of each BS-to-BS link scales at an arbitrary rate relative to the number of randomly located wireless nodes n. For the operating regimes with respect to the number of BSs and the number of antennas at each BS, we first analyze the minimum rate of each backhaul link CBS, required to guarantee the same throughput scaling as in the infinite-capacity backhaul link case. We then identify the operating regimes in which the required rate CBS scales slower than nϵ for an arbitrarily small ϵ>0 (i.e., the regimes where CBS does not need to be infinitely large). We also show the case where our network with GreenInfra is fundamentally in the infrastructure-limited regime, in which the performance is limited by the rate of backhaul links. In addition, we derive a generalized throughput scaling law including the case where the rate of each backhaul link scales slower than CBS. To validate the throughput scaling law for finite values of system parameters, numerical evaluation is also shown via computer simulations.

A New Codebook Structure for Enhanced Multi-User MIMO Transmission in mmWave Hybrid-Beamforming System

A multi-user hybrid-beamforming (H-BF) system consisting of both analog beamforming and digital beamforming is considered for millimeter-wave (mmWave) channels. In the hybrid-beamforming system, analog beams are first allocated to scheduled users and then each user reports channel state information of the effective channel, i.e. channel between transmit and receive digital paths. Since amplitudes of the effective channel elements can largely be different from each other due to the analog beamforming which has a certain directivity, the conventional feedback scheme, e.g. precoder matrix indicator (PMI) in long-term evolution (LTE), that does not reflect this channel characteristic may not work well. In this paper, we propose a new feedback scheme for multi-user H-BF systems in mmWave channels. The proposed feedback scheme jointly utilizes two types of codebooks: 1) a direction of the H-BF channel; and 2) amplitudes of the channel elements. In numerical results, it is shown that the proposed feedback scheme largely improves the average throughput performance, especially when the analog beamwidth is narrow.

Ad hoc networking with rate-limited infrastructure: Generalized capacity scaling

Capacity scaling of a large hybrid network with unit node density, consisting of wireless ad hoc nodes, base stations (BSs) equipped with multiple antennas, and one remote central processor (RCP), is analyzed when wired backhaul links between the BSs and the RCP are rate-limited. We first derive the minimum backhaul link rate required to achieve the same capacity scaling law as in the infinite-capacity backhaul link case. Assuming an arbitrary rate scaling of each backhaul link, a generalized achievable throughput scaling law is then analyzed in the network based on using one of pure multihop, hierarchical cooperation, and two infrastructure-supported routing protocols, and moreover, information-theoretic operating regimes are identified. In addition, to verify the order optimality of our achievability result, a generalized cut-set upper bound under the network model is derived by cutting not only the wireless connections but also the wired connections.

Capacity of large hybrid erasure networks with random node distribution

The Gupta–Kumar’s nearest-neighbor multihop routing with/without infrastructure support achieves the optimal capacity scaling in a large erasure network in which n wireless nodes and m relay stations are regularly placed. In this paper, a capacity scaling law is completely characterized for an infrastructure-supported erasure network where n wireless nodes are randomly distributed, which is a more feasible scenario. We use two fundamental path-loss attenuation models (i.e., exponential and polynomial power-laws) to suitably model an erasure probability. To show our achievability result, the multihop routing via percolation highway is used and the corresponding lower bounds on the total capacity scaling are derived. Cut-set upper bounds on the capacity scaling are also derived. Our result indicates that, under the random erasure network model with infrastructure support, the achievable scheme based on the percolation highway routing is order-optimal within a polylogarithmic factor of n for all values of m.