In a virtualized environment, such as a cloud computing environment, guest and host operating systems (OS) run simultaneously. Both of the operating systems have page caches for disk accesses. In such an environment, the second level cache does not work effectively because of negative temporal locality of access and duplicated storing in both the caches. In this paper, we propose a method for increasing the hit ratio of the host operating system page cache. The method monitors pages dropped from the guest operating system page cache and stores the pages into the host operating system cache. After the proposal, we introduce the design and implementation of our system. Our implementation aims to be applicable without modification to the hypervisor, and thus it can be applied for an environment with a proprietary hypervisor. Lastly, we present the evaluation of the hit ratio of the host operating system cache, and then demonstrate that our method can improve the cache hit ratio.

This paper reports experimental results regarding radio propagation, transfer, reflection, and scattering characteristics through tempered glass, plasterboard, plywood, plastic tile, and aluminum plate in an anechoic chamber environment at 2.45, 3.5 GHz, 5 GHz, and 10 GHz frequency bands. The time domain measurement method is used for accurate measurement, while the measurement accuracy of the electric wave is 7.5 cm obtained by sweeping 2 GHz bandwidth at the center of the measurement frequency. Simulation results show that fundamental experimental data were obtained for the analysis of actual radio environments, and that the measured data are reliable. The data will be useful for propagation analyses such as ray tracing.

IEEE 802.11b standard provides 1, 2, 5.5, 11 Mbps data rates. These data rates can be made possible by using different modulation techniques: DBPSK, DQPSK, CCK5.5 and CCK11 respectively. Rate adaptation is the process of dynamically selecting a proper modulation scheme depending on channel conditions in order to improve total throughput. Current rate adaptation protocols deal with unicast links rather than multicast. Channel conditions can be estimated by measuring the received signal strength (RSS) of a feedback message (CTS, ACK). However, IEEE 802.11 standard does not provide feedback messages for MAC layer recovery on multicast frames. This is due to collisions which may occur to simultaneous feedback messages from multicast group members. Therefore, in order to rate adapt multicast, a reliable multicast MAC protocol has to be introduced. In this paper, we propose a protocol which provides multicast reliability to WLANs and enhances its throughput by using rate adaptation. Further, we evaluate our protocol by throughput analysis and computer simulation. Simulation results suggest that our protocol performs better than a related/existing protocol in both throughput as well as reliability performances

Wideband CDMA systems are competitive candidates for 3rd generation wireless communication systems. In this paper, the link capacity of a wideband CDMA system with a bandwidth of 4.096 MHz is evaluated for both forward and reverse links in a Rayleigh-fading multipath environment. First, in a single cell, two kinds of user distributions-boundary and uniform-are considered. An analytical method is adopted to evaluate the uniform-distribution (UD) system based on simulation results of the boundary-distribution (BD) system. In the multi-cell environment, since the simulation of multiple users in a cellular system would be prohibitively complex, an analytical method is adopted to obtain the system capacity based on the results in the single cell case. The results show that the forward link always has better performance when both links adopt power control and cell diversity.

We introduce a multiuser receiver based on the Kalman filter, which can be used for joint symbol detection and channel estimation. The proposed algorithm has the advantage of working even when the spreading codes used have a period larger than one symbol interval ("long codes"), unlike adaptive equalizer-type detectors. Simulation results which demonstrate the performance advantage of the proposed receiver over the conventional detector, the minimum mean squared error (MMSE) detector and a recursive least squares (RLS) multiuser detector are presented. A thorough comparison of the MMSE detector and the proposed detector is attempted because the Kalman filter also solves the MMSE parameter estimation problem, and it is concluded that, because the state space model assumed by the Kalman filter fits the code division multiple access (CDMA) system exactly, a multiuser detector based on the Kalman filter must necessarily perform better than a nonrecursive, finite-length MMSE detector. The computational complexity of the detector and its use in channel estimation are also studied.