http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
- 中文 을 입력하시려면 zhongwen을 입력하시고 space를누르시면됩니다.
- 北京 을 입력하시려면 beijing을 입력하시고 space를 누르시면 됩니다.
RISS 인기검색어
- 검색키워드
- 저자 : John Cioffi (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
-
Coordinated Cognitive Tethering in Dense Wireless Areas
Haleh Tabrizi,Golnaz Farhadi,John Cioffi,Ghadah Aldabbagh 한국전자통신연구원 2016 ETRI Journal Vol.38 No.2
This paper examines the resource gain that can be obtained from the creation of clusters of nodes in densely populated areas. A single node within each such cluster is designated as a “hotspot”; all other nodes then communicate with a destination node, such as a base station, through such hotspots. We propose a semi-distributed algorithm, referred to as coordinated cognitive tethering (CCT), which clusters all nodes and coordinates hotspots to tether over locally available white spaces. CCT performs the following these steps: (a) groups nodes based on a modified k-means clustering algorithm; (b) assigns white-space spectrum to each cluster based on a distributed graph-coloring approach to maximize spectrum reuse, and (c) allocates physical-layer resources to individual users based on local channel information. Unlike small cells (for example, femtocells and WiFi), this approach does not require any additions to existing infrastructure. In addition to providing parallel service to more users than conventional direct communication in cellular networks, simulation results show that CCT can increase the average battery life of devices by 30%, on average.
-
Cooperative Distributed Beamforming With Outdated CSI and Channel Estimation Errors
Jung-Bin Kim,Ji-Woong Choi,Cioffi, John M. IEEE 2014 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.62 No.12
<P>This paper investigates the effect of imperfect channel state information (CSI) on the outage performance of cooperative distributed beamforming (DBF). The acquisition of perfect CSI is disturbed by outdated CSI and channel estimation errors. Decode-and-forward relays are considered with individual power constraints at each relay. Considering a training-and-feedback strategy to acquire CSI, a closed-form approximate expression for outage probability and the achievable diversity gain are first provided under Rayleigh fading channels. Numerical observations verify that the approximation is very tight. It is shown that outdated CSI seriously degrades the performance, and therefore, the outage probability is bounded and no diversity is achieved. Conversely, channel estimation errors cause slight performance degradation, and full diversity order is still achievable. However, even when CSI is outdated, it is shown that the asymptotic outage decreases as the number of relays K increases, where the logarithm of the outage probability decreases at the rate of K log K. This paper shows that, when the destination re-estimates the current CSI for decoding, the effect of outdated CSI is greatly mitigated and consequently achieves a diversity gain of one. To re-estimate the current CSI with small overhead, the beamformed training sequence (BFTS) strategy is proposed, in which a new closed-form formula for minimum-mean-square-error estimation is presented using Gaussian approximation. Numerical results verify that the outage performance with the proposed BFTS scheme is close to that of a perfect estimation. A closed-form outage expression of DBF with the proposed BFTS scheme is also presented under an assumption of high-signal-to-noise ratio (SNR), but the expression is very tight even in low-to-moderate SNR regimes.</P>
-
Capacity Scaling and Diversity Order for Secure Cooperative Relaying With Untrustworthy Relays
Jung-Bin Kim,Jaesung Lim,Cioffi, John M. IEEE 2015 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.14 No.7
<P>This paper presents an investigation of the secrecy performance of amplify-and-forward (AF) distributed beamforming (DBF) and opportunistic relaying (OR) through K untrustworthy relays. The capacity scaling and achievable diversity order of a secure communication are derived for K → ∞ and in high signal-to-noise-ratio (SNR) regimes, respectively. The DBF is shown to convey confidential messages with a capacity scaling of 1/2 log K regardless of the trustworthiness of the relays, even without intended jamming (IJ), where 1/2 log K corresponds to the maximal capacity scaling of cooperative relaying in non-eavesdropping environments. However, using multiple untrustworthy relays worsens the secrecy performance of the OR, and as K increases, the secrecy capacity converges to zero. When secrecy outage performance with IJ is considered, the achievable diversity order for both the DBF and OR is limited to one. However, only the DBF exploits the benefits using multiple untrustworthy relays, and its secrecy outage probability decreases exponentially as K increases.</P>
-
Approximate Closed-Form Energy Efficient PA for MIMO Relaying Systems in the High SNR Regime
Chunguo Li,Hyun Jong Yang,Fan Sun,Cioffi, John M.,Luxi Yang IEEE 2014 IEEE communications letters Vol.18 No.8
<P>Energy efficient power coefficients at the relay are derived in a closed-form expression for the green multi-input-multi-output relaying system in the high signal-to-noise ratio (SNR) regime, where the objective is to maximize the energy efficiency (EE), which is defined by the ratio of the spectral efficiency (SE) to total power consumption, with a minimum SE requirement under practical power consumption models. In particular, we derive closed-form solutions using the high SNR approximation, which turn out to be different from the water-filling solution. Simulation results show that the proposed solution nearly achieves the optimal EE in all SNR regimes.</P>
-
ScienceON연관 검색어 추천
이 검색어로 많이 본 자료
활용도 높은 자료
