Coherent opportunistic beamforming in multi-user wireless systems

In this paper, we propose a beamforming scheme that exploits the advantages of opportunistic beamforming and coherent beamforming in multi-user environment. It is analytically shown that the proposed scheme achieves multiuser diversity gain and beamforming gain simultaneously, providing much better performance over the conventional ones. The performance of the proposed scheme is analyzed using an upper bound method. Although the proposed scheme involves an additional feedback delay, the analytical result implies that the use of the proposed scheme is quite effective unless the user mobility is too high. Finally, the analytic results are verified by computer simulation.Ministry of Information & Communications, Kore

Pilot signaling for multi-cell OFDMA uplink systems

OFDMA is considered as one of the major candidates for broadband wireless access. The OFDMA signal is usually coherently demodulated, requiring the channel estimation which can be estimated using a known pilot signal. In multicell environment, the performance of channel estimation is mainly limited by intercell interference. It is desirable to use a pilot signal that can estimate the channel information robust to the intercell interference in the OFDMA uplink system. In this paper, we consider two types of pilot signal applicable to multi-cell OFDMA uplink systems: One is time-multiplexed pilot signal and the other is codemultiplexed pilot signal. Simulation results show that the code-multiplexed pilot is suitable for low mobility environment and time-multiplexed pilot is suitable for high mobility environment

Adaptive Transmission with Partial Channel Information in Spatially Correlated MIMO Channels

We propose a new adaptive multiple-input multipleoutput (MIMO) transmission scheme that can work with partial channel information. Utilizing the information on dominant eigendimensions of the channel correlation matrix, the proposed scheme reduces the amount of channel information required for adaptive transmission without noticeable performance degradation. It is analytically shown that the proposed scheme can minimize the performance loss by properly choosing the number of eigen-dimensions of the channel correlation matrix. Simulation results show that the proposed scheme is quite applicable to practical systems where quantized channel information is utilized

A Modified Parallel Interference Canceller in MC-CDMA uplink systems

In the MC-CDMA uplink system, the user signal experiences different fading, suffering from a large amount of interference from other users. For reliable data detection, the use of multi user detector (MUD) with high complexity has been considered in the MC-CDMA uplink system. In this paper, we propose a modified parallel interference cancellation scheme (MPIC) that can provide the performance better than conventional MUD, while requiring affordable complexity

패킷기반 다중사용자 무선통신 시스템에서의 기회적 정합 빔포밍 기법

In this paper, we propose a beamforming scheme that exploits the advantages of opportunistic beamforming and coherent beamforming in multi-user environments. It is analytically shown that the proposed scheme can provide multi-user diversity and beamforming gain simultaneously, achieving significant performance improvement over the conventional ones particularly when the channel is poor. The performance of the proposed scheme is analyzed using an upper bound method. Finally, the analytic results are verified by computer simulation.the Ministry of Information & Communications, Korea, under the Information Technology Research Center (ITRC) Support Program

Comparison of volume-controlled and pressure-controlled ventilation using a laryngeal mask airway during gynecological laparoscopy

Background: Several publications have reported the successful, safe use of Laryngeal Mask Airway (LMA)-Classic devices in patients undergoing laparoscopic surgery. However, there have been no studies that have examined the application of volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV) using a LMA during gynecological laparoscopy. The aim of this study is to compare how the VCV and PCV modes and using a LMA affect the pulmonary mechanics, the gas exchange and the cardiovascular responses in patients who are undergoing gynecological laparoscopy. Methods: Sixty female patients were randomly allocated to one of two groups, (the VCV or PCV groups). In the VCV group, baseline ventilation of the lung was performed with volume-controlled ventilation and a tidal volume of 10 ml/kg ideal body weight (IBW). In the PCV group, baseline ventilation of the lung using pressure-controlled ventilation was initiated with a peak airway pressure that provided a tidal volume of 10 ml/kg IBW and an upper limit of 35 cmH2O. The end-tidal CO2, the peak airway pressures (Ppeak), the compliance, the airway resistance and the arterial oxygen saturation were recorded at T1: 5 minutes after insertion of the laryngeal airway, and at T2 and T3: 5 and 15 minutes, respectively, after CO2 insufflation. Results: The Ppeak at 5 minutes and 15 minutes after CO2 insufflation were significantly increased compared to the baseline values in both groups. Also, at 5 minutes and 15 minutes after CO2 insufflation, there were significant differences of the Ppeak between the two groups. The compliance decreased in both groups after creating the pneumopertoneim (P < 0.05). Conclusions: Our results demonstrate that PCV may be an effective method of ventilation during gynecological laparoscopy, and it ensures oxygenation while minimizing the increases of the peak airway pressure after CO2 insufflation. ��� the Korean Society of Anesthesiologists, 2011

A Framework Design for the Next-Generation Radio Access System

Extensive use of the Internet and huge demands for multimedia services via portable devices require the development of packet-based radio access systems with high transmission efficiency. Advanced radio transmission technologies have recently been proposed to achieve this challenging task. However, few researches have been reported on the design of an integrated system that can efficiently exploit the advantages of these transmission technologies. This paper considers the design of a packet-based cellular system for next-generation radio access. We propose a novel system framework that can incorporate various advanced transmission technologies such as link adaptation, opportunistic packet scheduling, channel coding, and multiantenna techniques. For efficient use of these technologies together, we first investigate the interoperability between these technologies by proposing a so-called cause and effect analysis. Based on this investigation, we design a differentiated-segments-based orthogonal frequency-division multiplexing system, called DiffSeg, to accommodate heterogeneous operating conditions in a seamless manner. Simulation results show that the proposed DiffSeg system can provide a nearly optimum performance with flexible configuration in a wide range of wireless channel conditions

Multi-user diversity and multiplexing with multiple coherent beams in wireless systems

In this paper, we propose a multi-beam multiplexing scheme that can simultaneously achieve spatial multiplexing gain and multi-user diversity (MUD) gain by generating coherent multiple beams in the multi-user domain. Multiple beams are generated to provide multiple channels in parallel, making it possible to achieve the MUD gain through each channel. Since the transmission power is spilt into multiple channels, the signal-to-noise power ratio (SNR) of each channel is reduced inversely proportional to the number of beams. However, multiple beams are utilized to make the multiplexing gain much larger than the decrease of SNR, increasing the overall system capacity. The proposed scheme is applicable to both multi-input multi-output (MIMO) and multi-input singleoutput (MISO) schemes, enabling the use of flexible antenna structures in the receiver.Korea Research Foundation Grant funded by the Korean Government(MOEHRD

Fast cell site selection with interference avoidance in cellular packet based OFDM systems.

In this paper, we consider fast cell site selection (FCS) in packet based OFDM cellular systems. Mobile station (MS) in multi-coverage regions or soft handover region can have opportunities to select a link better than from the current cell. Conventional FCS schemes track the channel fading variation, achieving a selection diversity gain [1]. However, MSs near the cell boundary suffer from other cell interference (OCI) which is highly time-varying and unpredictable. Therefore, it may be desirable for FCS to reduce the OCI effect near the cell boundary. In this paper, we propose an FCS scheme with interference avoidance for a packet based OFDM system and analyze its performance. Finally, the analytic performance of the proposed scheme is verified by computer simulatio