The Experts below are selected from a list of 63642 Experts worldwide ranked by ideXlab platform
K.j.r. Liu - One of the best experts on this subject based on the ideXlab platform.
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non cooperative resource competition game by virtual referee in multi cell ofdma networks
IEEE Journal on Selected Areas in Communications, 2007Co-Authors: Zhu Han, K.j.r. LiuAbstract:In this paper, a distributive non-cooperative game is proposed to perform sub-channel assignment, adaptive modulation, and Power control for multi-cell multi-user orthogonal frequency division multiplexing access (OFDMA) networks. Each individual user's goal is to minimize his/her own Transmitted Power in a distributed manner under the constraints that the desirable rate is achieved and the Transmitted Power is bounded. The pure non-cooperative game may result in non-convergence or some undesirable Nash Equilibriums with low system and individual performances. To enhance the performances, a virtual referee is introduced to the networks and is in charge of monitoring and improving the outcome of non-cooperative competition for resources among the distributed users. If the game outcome is not desirable, either the required transmission rates should be reduced or some users should be prevented from using some radio resources such as sub-channels, so that the rest of users can share the limited resources more efficiently. Moreover, it can be shown that the introduction of the virtual referee does not increase the complexity of the networks. From the simulation results in a two-cell case, the proposed scheme reduces the Transmitted Power by 80% and 25% compared with the fixed channel assignment algorithm and the iterative water-filling algorithm in the literature, respectively. The achievable rate can be improved by 10%. In a multi-cell case, the proposed scheme can have up to 40% Power reduction compared with the iterative water-filling algorithm when the co-channel interferences are severe.
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GLOBECOM - Power minimization for multi-cell OFDM networks using distributed non-cooperative game approach
IEEE Global Telecommunications Conference 2004. GLOBECOM '04., 2004Co-Authors: Zhu Han, K.j.r. LiuAbstract:In this paper, we use a noncooperative game approach to have distributed subchannel assignment, adaptive modulation, and Power control for multi-cell OFDM networks. The goal is to minimize the overall Transmitted Power under each user's maximal Power and minimal rate constraints. Our contribution is to model and solve this complicated problem by a distributed noncooperative game approach: Each user water-fills its Power to different subchannels regarding other users' Powers as interference. A noncooperative game is constructed for each user to compete with others. A method is constructed as a mediator (judge) for the game. From the simulation results, the proposed scheme reduces the overall Transmitted Power greatly compared with the fixed channel assignment algorithm and pure water-filling algorithm.
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WCNC - Dynamic real time distortion management over multimedia downlink CDMA
2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733), 2004Co-Authors: Andres Kwasinski, Zhu Han, K.j.r. LiuAbstract:In CDMA networks it is possible to increase the maximum number of users of real time applications by smoothly increasing each end-to-end distortion. We study a protocol for downlink CDMA that allocates source coding rate, channel coding rate and Transmitted Power based on each user's channel state. The allocation of resources is performed with the constraints of users' maximum distortion and base station's maximum Transmitted Power in such a way that users operate under carefully controlled distortions. The optimization goal is to minimize the overall distortion in downlink single-cell systems. When the system is highly loaded, the idea for the proposed solution is to initialize the resource allocation with that corresponding to maximum distortion for all users, and then incrementally allocate the remaining Transmitted Power quota to the user that, at each step, can reduce the distortion with the least use of Power. We show that this user must have a high distortion, experience a good channel condition, or generate small interference. We also extend our study to include speech's talk spurt-silence nature and to consider a dynamic model with different offered loads. From simulation results, the proposed algorithm fundamentally reduces the distortions and the necessary maximum Transmitted Power when the number of users is large, compared with a traditional CDMA scheme (with no distortion control).
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transmit beamforming and Power control for cellular wireless systems
IEEE Journal on Selected Areas in Communications, 1998Co-Authors: F Rashidfarrokhi, K.j.r. Liu, Leandros TassiulasAbstract:Joint Power control and beamforming schemes are proposed for cellular systems where adaptive arrays are used only at base stations. In the uplink, mobile Power and receiver diversity combining vectors at the base stations are calculated jointly. The mobile Transmitted Power is minimized, while the signal-to-interference-and-noise ratio (SINR) at each link is maintained above a threshold. A transmit diversity scheme for the downlink is also proposed where the transmit weight vectors and downlink Power allocations are jointly calculated such that the SINR at each mobile is above a target value. The proposed algorithm achieves a feasible solution for the downlink if there is one and minimizes the total Transmitted Power in the network. In a reciprocal network it can be implemented in a decentralized system, and it does not require global channel response measurements. In a nonreciprocal network, where the uplink and downlink channel responses are different, the proposed transmit beamforming algorithm needs to be implemented in a centralized system, and it requires a knowledge of the downlink channel responses. The performances of these algorithms are compared with previously proposed algorithms through numerical studies.
Geza Benke - One of the best experts on this subject based on the ideXlab platform.
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Radiofrequency electromagnetic field exposure assessment: a pilot study on mobile phone signal strength and Transmitted Power levels
Journal of Exposure Science & Environmental Epidemiology, 2019Co-Authors: Christopher Brzozek, Berihun M. Zeleke, Michael J. Abramson, Kurt K. Benke, Geza BenkeAbstract:In many epidemiological studies mobile phone use has been used as an exposure proxy for radiofrequency electromagnetic field (RF-EMF) exposure. However, RF-EMF exposure assessment from mobile phone use is prone to measurement errors limiting epidemiological research. An often-overlooked aspect is received signal strength levels from base stations and its correlation with mobile phone transmit (Tx) Power. The Qualipoc android phone is a tool that provides information on both signal strength and Tx Power. The phone produces simultaneous measurements of Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), Received Signal Code Power (RSCP), and Tx Power on the 3G and 4G networks. Measurements taken in the greater Melbourne area found a wide range of signal strength levels. The correlations between multiple signal strength indicators and Tx Power were assessed with strong negative correlations found for 3G and 4G data technologies (3G RSSI −0.93, RSCP −0.93; 4G RSSI −0.85, RSRP −0.87). Variations in Tx Power over categorical levels of signal strength were quantified and showed large increases in Tx Power as signal level decreased. Future epidemiological studies should control for signal strength or factors influencing signal strength to reduce RF-EMF exposure measurement error.
Kenneth R Foster - One of the best experts on this subject based on the ideXlab platform.
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area averaged Transmitted Power density at skin surface as metric to estimate surface temperature elevation
IEEE Access, 2018Co-Authors: Daisuke Funahashi, Akimasa Hirata, Sachiko Kodera, Kenneth R FosterAbstract:In the international guidelines/standards for human protection, the specific absorption rate (SAR) is used as a metric to prevent excessive surface temperature elevation at frequencies up to 3 or 10 GHz. Above that transition frequency, including the frequency region assigned to 5th generation wireless communication systems, an area-averaged incident Power density on human body surface is used as the physical quantity to specify the restrictions on human exposure to electromagnetic fields. However, the incident Power density is an external physical quantity, resulting in frequency-dependent temperature elevation, which is attributable to frequency-dependent variations in the reflection coefficient at the skin surface and energy penetration depth into tissue. In this paper, we discuss analytically and computationally the effectiveness of the Transmitted Power density (TPD) at the skin as a new metric to estimate the steady-state skin temperature elevation above the transition frequency. We also consider simplified models for uniform and Gaussian beam patterns and the analytical solutions to the bioheat equation for an one-dimensional model, which are in good agreement with numerical solutions. These show that the TPD provides an excellent estimate of skin temperature elevation through the millimetre-wave band (30–300 GHz) and a reasonable and conservative estimate down to 10 GHz, whereas the SAR is a good metric below 3 GHz. Computational results for the dipole and patch antenna arrays demonstrated that the one-dimensional analysis is conservative metric as compared with the TPD averaged over the area of 4 cm2 (2-cm square). Considering extreme cases, averaging area smaller than 4 cm2 is needed above 30 GHz for beam exposure with small diameters. Finally, we consider the choice of averaging area as related to peak temperature increases for small beams. For extremely small exposure areas, limits on peak Power density may be needed.
Bruce A. Wooley - One of the best experts on this subject based on the ideXlab platform.
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A 5-GHz CMOS transceiver for IEEE 802.11a wireless LAN systems
IEEE Journal of Solid-State Circuits, 2002Co-Authors: Masoud Zargari, Chik Patrick Yue, Shahriar Rabii, D. Weber, Brian J. Kaczynski, Srenik Mehta, K. Singh, S. Mendis, Bruce A. WooleyAbstract:A 5-GHz transceiver comprising the RF and analog circuits of an IEEE 802.11a-compliant WLAN has been integrated in a 0.25-/spl mu/m CMOS technology. The IC has 22-dBm maximum Transmitted Power, 8-dB overall receive-chain noise figure and -112-dBc/Hz synthesizer phase noise at 1-MHz frequency offset.
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A 5 GHz CMOS transceiver for IEEE 802.11a wireless LAN
2002 IEEE International Solid-State Circuits Conference. Digest of Technical Papers (Cat. No.02CH37315), 1Co-Authors: Masoud Zargari, Shahriar Rabii, D. Weber, Brian J. Kaczynski, Srenik Mehta, K. Singh, S. Mendis, P. Yue, Bruce A. WooleyAbstract:A 5 GHz transceiver comprising the RF and analog circuits of an IEEE 802.11a-complaint WLAN using a 0.25 /spl mu/m CMOS technology occupies 22 mm/sup 2/. The IC has 22 dBm maximum Transmitted Power, 8 dB overall receive-chain noise figure, and -112 dBc/Hz synthesizer phase noise at 1 MHz offset.
Mohamed-slim Alouini - One of the best experts on this subject based on the ideXlab platform.
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Variable-rate variable-Power non-coherent M-FSK scheme for Power limited systems
IEEE Transactions on Wireless Communications, 2006Co-Authors: F.f. Digham, Mohamed-slim AlouiniAbstract:In response to the ongoing demand for low Power applications, the two first authors have recently proposed in F.F. Digham and M.-S. Alouini (2004) a discrete-modulation and fixed-Power non-coherent M-ary frequency shift keying scheme. In this paper, we propose an extension of that work by studying a discrete-modulation and continuous-Power (DMCP) scheme for further Power saving over Nakagami fading channels. The modulation level and Power assignment are selected in order to minimize the average Transmitted Power while meeting average spectral efficiency and bit error rate constraints. We further investigate the problem with an additional peak Power constraint. In this case, the modulation switching thresholds are shifted to higher values yielding reduction in both the achievable average spectral efficiency and the average Transmitted Power. However, the Power loading function can be re-shaped to maintain the same average Power of transmission for the cases on no-peak and with-peak Power constraints. This reshaping is designed so as to involve constant Power portions which can be of interest from a practical stand point
