Seung Min Yu

Feasibility of cognitive machine-to-machine communication using cellular bands

We evaluate the feasibility of cognitive machine-to-machine communication on cellular bands from engineering and business perspectives. We propose a hierarchical network structure for cognitive M2M communication, where cluster headers gather M2M traffic using cognitive radio and forward it to the cellular networks. This structure can resolve the congestion problem that arises in conventional M2M systems. We obtain the optimal network parameters that minimize congestion at the radio access network. In addition, we investigate the business value of cognitive M2M on cellular bands. Taking into account the network usage fee, service fee, and hardware production costs, we model the profit structure of M2M services and derive the condition under which the CR type of M2M communication is superior to conventional M2M communication. We find that the optimal network design parameters (i.e., the number of cluster headers and cluster size) for business value would be different from the parameters expected from an engineering point of view. We believe that cognitive M2M communication can be a good solution for dealing with excessive M2M traffic in cellular networks, in terms of technical feasibility and business opportunity.

The Capacity of Energy-Constrained Mobile Networks with Wireless Power Transfer

We derive the throughput of an energy-constrained mobile network, where wireless charging vehicles recharge the battery of each mobile node. We find that the throughput is closely related to the ratio between the number of nodes n and the number of wireless charging vehicles m. Through analytic and numerical results, we show that the scaling law of the throughput is Θ(min(1, m/n) cmin(1, m/n)), where c is constant (0<;c<;1).

End-to-end delay in wireless random networks

The focus of this letter is to derive a scaling law for the ene-to-end delay of wireless random networks under node mobility, where n nodes randomly move with the speed of v. To that end, we apply the cover time analysis and relate it to the delay scaling law. As a result, we derive that the mean delay per S-D pair as ¿(n) or ¿(¿(n)/v), and the worst case delay is ¿(n log n) or ¿(¿(n) log n/v), corresponding to one slot time length that is either constant or 1/v¿(n).

Guaranteeing user welfare in network service: comparison of two subsidy schemes

Due to the emergence of smart devices, mobile data traffic grows exponentially. A Cisco report predicts that global mobile data traffic will increase 26-fold between 2010 and 2015. Therefore, the spectrum shortage continues and the spectrum price increases, which will eventually lead to decrease of user welfare. Another side effect of the data traffic growth is the polarization of data traffic among users. To resolve these problems, we introduce two subsidy schemes (i.e., price and quality of service (QoS) subsidy schemes) and mathematically analyze the effect of each scheme. We identify that if the regulator has sufficient spectrum amount for the network service, then the QoS subsidy scheme will be a good choice for all players in the network service market. Otherwise, the price subsidy scheme can be better from user welfare perspective. Even though our analytic results are derived under some assumptions for mathematical tractability, it will provide good intuitions for spectrum regulation.

Optimization of Spectrum Allocation and Subsidization in Mobile Communication Services

The mobile traffic explosion has caused spectrum shortage and polarization of data usage among users, which will eventually decrease user welfare (UW) in mobile communication services. Governments around the world are planning to make more spectrum available for mobile broadband use, and the key policy issue is to find an efficient spectrum allocation method that will improve UW. In this paper, we propose a data subsidy scheme where the regulator offers a spectrum price discount to mobile network operators (MNOs) in return for imposing the responsibility of providing a predefined data amount to users free of charge. To analyze the subsidy effect, we adopt the two-stage approach of Cournot and Bertrand competition and find a Nash equilibrium (NE) of the competition. An interesting observation is that the increase in UW does not involve MNO profit (MP) loss and that the increasing amount is higher than the regulators expenses for implementing the data subsidy scheme. Most of the paper concerns the duopoly competition, which is finally extended to the general case.

Optimal Detection of Spatial Opportunity in Wireless Networks

The scarceness of the radio spectrum leads to opportunistic spectrum access or cognitive radio. In this letter, we analyze the spectrum sensing threshold to improve reliability of opportunity detection in the spatial domain. We minimize the weighted sum of exposed- and hidden node probabilities, and derive the optimal spectrum sensing threshold as a closed form formula. We take the estimation error into account, which is parameterized into the sensing threshold. Our analytic results will provide a fundamental framework for opportunistic spectrum access networks or wireless LANs.

Utility-Optimal Partial Spectrum Leasing for Future Wireless Services

One of the challenges facing the next-generation wireless networks is to cope with the expected demand for data. This calls for an efficient spectrum regulation that can enable mobile subscribers to support high quality of service (QoS) and mobile network operators (MNOs) to leverage their profit streams. In this paper, we present a new spectrum allocation policy in a monopoly situation. The problem is formulated as a Stackelberg game. We show that the conventional spectrum leasing contract may lead to the unprecedented scenario in which costs outweigh their revenues. On the other hand, our proposed spectrum leasing contract can not only maximize user welfare but also leverage MNOs profit streams. We show that our spectrum leasing contract can increase user welfare and MNOs profit up to 75% and 20%, respectively, relative to the conventional spectrum leasing contract. Thus, regulators must rewrite their spectrum allocation policy in order to maximize user welfare and leverage MNOs profit streams.

On the Frequency Allocation for Coordinated Multi-Point Joint Transmission

Main purpose of this paper is to investigate the frequency allocation schemes combined with a downlink Coordinated Multi-Point (CoMP) joint transmission system. We suggest 6-sector directional antenna and according sector based frequency reuse scheme for CoMP system, and compare the edge user performance of conventional Fractional Frequency Reuse (FFR) systems and suggested CoMP system. The numerical results show that the suggested scheme is better than the conventional FFR systems in the performance and the energy efficiency perspectives.

Radio resource efficient cellular broadcast networks

Rapid and relentless video traffic growth has brought about network congestion. To alleviate the problem, this paper considers a video content broadcast cellular network via the same frequency channels, enabling to save radio resource compared to the conventional unicast networks. We investigates its efficient resource usage for different user demand by means of stochastic geometric analysis. Consequently, we analytically verify increasing popularity of broadcast contents makes radio resource usage more efficient while decreasing the amount of waste radio resources.