Energy-Efficient Random Access for Machine- to-Machine (M2M) Communications

Hano Wang,Choongchae Woo 보안공학연구지원센터 2013 International Journal of Software Engineering and Vol.7 No.1

Interference Reduction through Multi-hop Transmission in Cognitive Radios

Hano Wang,Jemin Lee,Daesik Hong 대한전자공학회 2010 ICEIC:International Conference on Electronics, Inf Vol.1 No.1

We propose a multi-hop transmission scheme which reduces interference to the primary user in systems with dynamic spectrum access. In the proposed multi-hop transmission scheme, the secondary user's link is transformed into a multi-hop link. The overall path loss reduction obtained via this multi-hop transformation makes it possible to reduce the transmission power of the secondary user without an accompanying throughput loss, which in turn reduces the interference to the primary user. Numerical results show that the proposed multi-hop transmission scheme gives the secondary user more chances to access the primary user's spectrum by reducing the primary user's outage probability while enhancing the secondary user's throughput.

Capacity enhancement of secondary links through spatial diversity in spectrum sharing

Hano Wang,Jemin Lee,Sungtae Kim,Daesik Hong IEEE 2010 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.9 No.2

<P>Previous investigations on capacity of secondary users in spectrum-sharing environments have determined the capacity of a secondary link based on the interference power threshold set at the primary receiver. In contrast to these previous works, we show that the capacity of a secondary link is determined based on a geographical relationship expressed as the ratio of the distance between the primary receiver and secondary transmitter to the distance between the secondary transmitter and receiver. Proceeding from that and in an effort, to enhance the capacity of the secondary user, which is limited by this distance-ratio, we adopt a secondary transmitter with M antennas. Furthermore, we analyze the capacity achieved using a simple antenna selection process.</P>

Power Allocation Scheme for Secondary User under Primary Full Duplex Relay System in Cognitive Radio Network

Hano Wang 보안공학연구지원센터 2013 International Journal of Control and Automation Vol.6 No.1

Capacity of Secondary Users Exploiting Multispectrum and Multiuser Diversity in Spectrum-Sharing Environments

Hano Wang,Jemin Lee,Sungtae Kim,Daesik Hong IEEE 2010 IEEE Transactions on Vehicular Technology VT Vol.59 No.2

<P>In spectrum-sharing environments, secondary users are permitted to share the primary user's spectrum only if limited interference to the primary user can be guaranteed. Hence, the capacity of the secondary link is limited by interference constraints given by the primary user. This fact motivated us to investigate selection diversity as a way of enhancing secondary link capacity. Selection diversity in conventional licensed wireless communication systems can be achieved only by selecting the user with the strongest channel gain. On the other hand, spectrum-sharing environments allow the secondary user to select not only the best secondary receiver with the strongest channel gain multiuser diversity (MUD) but the best primary spectrum with the weakest interference link gain multispectrum diversity (MSD) as well, thus doubling the opportunities for the secondary user. In this paper, we analyze the capacity gain of a secondary user exploiting MSD and MUD in spectrum-sharing environments in the form of a closed-form expression in a Rayleigh-fading channel. We then separately extract the MSD and MUD capacity gains, which results in an asymptotic capacity expression. Our results show that MSD and MUD play different roles in capacity enhancement in the spectrum-sharing environment, with capacity enhancement for secondary receivers as a whole and transmit capacity enhancement for the secondary transmitter.</P>

Advanced Sensing Techniques of Energy Detection in Cognitive Radios (Invited Paper)

Hano Wang,Gosan Noh,Dongkyu Kim,김성태,Daesik Hong 한국통신학회 2010 Journal of communications and networks Vol.12 No.1

Recently, spectrum sensing has been intensively studied as a key technology in realizing the cognitive radio. There have been advances in the performance of spectrum sensing through both multi-antenna and cooperative sensing schemes. In this paper,the performances and complicated scenarios of the latest spectrum sensing schemes are analytically compared and arranged into a technical tree while considering practical concerns. This paper will give a macroscopic view of spectrum sensing and will also provide insight into future spectrum sensing works.

하향링크 직교주파수분할다중접속 셀룰러 시스템을 위한 부반송파 기반 핸드오버 기법

왕한호(Hano Wang),이성은(Sungeun Lee),홍대식(Daesik Hong) 대한전자공학회 2008 電子工學會論文誌-TC (Telecommunications) Vol.45 No.-

본 논문에서는 직교주파수분할다중접속(Orthogonal Frequency Division Multiple Access) 하향링크 시스템에서 부반송파 별 채널 이득(channel gain)이 다름을 이용하여 시스템의 용량을 향상시킬 수 있는 핸드오버 기법을 제안한다. 제안하는 기법에서 핸드오버 중인 사용자는 소스 기지국(source base station)과 타겟 기지국(target base station)에서 할당 받은 부반송파 중 강한 채널이득을 가진 부반송파를 선택해 줌으로써 이득을 얻는다. 부반송파 선택 과정에서 탈락한 부반송파에 대한 정보는 기지국으로 피드백(feedback)되어 사용하지 않도록 하여 시스템 전체의 간섭(interference)량을 줄인다. 제안하는 기법은 핸드오버하고 있는 사용자의 오수신 확률을 22% 줄였으며, 이에 따라 시스템 전체의 전송률이 향상된다. In this paper, a new subcarrier-based handover scheme which exploits different channel gains of subcarriers in downlink OFDMA cellular systems. In this handover scheme, mobile users can obtain diversity gain by subcarrier selection. Feedback for unselected subcarriers reduces interference. The capacity enhancement by the handover scheme is originated from the following two characteristics of OFDMA systems. One is that interference per subcarrier is proportional to the traffic load. The other is that every subcarrier has different channel gain 엳 새 the Rayleigh fading channel. Therefore, selecting subcarriers with stronger channel gains results in diversity gain. Simulation results confirm that the proposed handover scheme improves the capacity of the OFDMA systems by reducing 24 percentage of the outage probability.

Mean Value-Based Power Allocation without Instantaneous CSI Feedback in Spectrum Sharing Systems

Sungmook Lim,Hano Wang,Hyungjong Kim,Daesik Hong IEEE 2012 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.11 No.3

<P>In this paper, we investigate a power allocation method without feedback of the instantaneous channel gain between a secondary transmitter (ST) and a primary receiver (PR) in spectrum sharing systems where channel information between the ST and the PR is outdated. We propose a mean value-based power allocation scheme (MVPA), which uses only the mean value of the channel gain of the ST-PR link. The proposed MVPA satisfies the interference outage constraint at the PR without feedback of the instantaneous channel information, which enables MVPA to reduce feedback burden. We also derive the ergodic capacity based on MVPA in closed-form and compare the ergodic capacity based on MVPA with that of a power allocation method using the outdated channel information instantaneously. Through the comparison, we convincingly demonstrate that MVPA without feedback of instantaneous channel information provides more reliable and superior capacity performance by reducing capacity loss from which the power allocation method using the outdated channel information severely suffers.</P>

Reporting Order Control for Fast Primary Detection in Cooperative Spectrum Sensing

Gosan Noh,Hano Wang,Junho Jo,Byoung-Hoon Kim,Daesik Hong IEEE 2011 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.60 No.8

<P>Although cooperative spectrum sensing improves sensing accuracy in cognitive radio systems, additional reporting time is required to report the local test statistics until the existence of the primary user is verified, resulting in detection delay. To reduce the reporting time, we propose controlling the reporting order of the local test statistics, so that the local test statistics are reported to the fusion center in descending order of magnitude. As a result, the global test statistic at the fusion center accumulates faster than the case without reporting order control, reducing the reporting time needed to determine when the threshold for detecting the primary user has been exceeded. To do this, we propose, based on distributed access control, a combination of order identification, which finds the order of the local test statistic, and transmission probability calculation according to the identified order. Simulation results show that the proposed reporting order control significantly reduces the reporting time for detecting the primary user.</P>

Sensing threshold control for fair coexistence of heterogeneous systems in open spectrum

Jemin Lee,Hano Wang,Sungtae Kim,Daesik Hong IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.12

<P>A critical problem in open-spectrum communications is fairness with respect to the coexistence of heterogeneous systems with different resource units and traffic models. In addition, the sensing performances of different systems can also lead to unfair resource utilization between systems. To address this problem, we derive a continuous-time Markov chain model to show the effect of sensing performance on system coexistence. The analysis derived from this model is then used as the basis for a sensing threshold control (STC) scheme to achieve fairness. The proposed STC determines the sensing threshold for each system as a way of balancing resource utilization among systems, while guaranteeing target detection probability. Numerical results on the amount of resource utilization by each system demonstrate that the proposed STC achieves a full degree of fairness.</P>