Reliability consideration of a mobile communication system with network congestion

Optimal checkpointing interval of a communication system with rollback recovery

As computer communication technology has developed, system control mechanisms have been realized by a number of processors, and, hence, it has become necessary to carry out processing distributively and rapidly. Also, as the system mechanisms have become increasingly complicated, the problems of improving reliability and increasing capabilities have become important. In this paper, we consider a control system which is roughly divided into one mark processor and a group of other processors, and formulate a stochastic model by taking notice of only communications between two processors. We perform scheduled checkpointing and execute rollback recovery to restore the consistency of a whole system when two faults of processor failures and communication errors have occurred. The expected cost is obtained and an optimal checkpoint interval which minimizes it is discussed. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 84(9): 49–55, 2001

Vehicle traffic congestion is reflected as delays while traveling. Traffic congestion has a number of negative effects and is a major problem in today's society. Several techniques have been deployed to deal with this problem. In this paper, we have proposed an innovative approach to deal with the problem of traffic congestion using the characteristics of vehicular ad-hoc networks (VANET). We have used the adaptive proportional integral rate controller, a congestion control algorithm designed for the Internet, to deal with the problem of vehicle traffic congestion in vehicular networks. The adaptive PI rate controller is a rate based controller that employs control theory to manage the problem of data traffic congestion in computer networks. Using simulations we have demonstrated the applicability of the algorithm in the domain of vehicle traffic congestion in a VANET.

The next-generation wireless personal and mobile communication systems are expected to accommodate not only high-quality voice services, but also a broad range of other multirate services. Of the various multiaccess techniques, wide-band code-division multiple access (CDMA) has been regarded as an important part of the third-generation wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multirate services. In this paper, we consider a system with a simplified receiver structure for direct-sequence CDMA (DS/CDMA) wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. We arrive at this system by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. We find that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simple one-finger matched filter is used at the receiver. This system combines the advantages of pre-RAKE diversity and transmit antenna diversity. It is shown that significant system performance and capacity improvements are possible. The numerical results also reveal that this system is not too sensitive to channel estimation errors.

현재 셀룰러 이동통신 시스템이 직면한 가장 큰 문제인 데이터 트래픽 폭증 수용문제를 효율적으로 해결하기 위한 방안으로써 스몰셀 및 단말간 통신 등 다양한 기술 등이 제안되고 있다. 이러한 데이터 트래픽 폭증 문제를 해결하기 위한 방안중 하나로써 기지국의 전송 파워를 서비스 받는 단말로 집중시키는 방향성 전송이 고려되고 있다. 본 연구에서는 셀룰러 이동통신 시스템에서 방향성 전송을 고려한 시스템 레벨 시뮬레이터를 개발하였고 방향성 전송이 사용될 때의 어려움 중 하나인 간섭 예측을 해결하기 위한 새로운 간섭 예측방안을 제안하였다. 본 시뮬레이터를 이용하여 제안된 적응적 간섭 예측 방안의 성능을 확인하였고 방향성 전송이 셀룰러 이동통신 시스템에서 활용될 때의 성능을 살펴보았다. 이를 통해 방향성 전송이 셀룰러 이동통신 시스템의 수율을 130% 이상 향상시킬 수 있음을 보였다. To cope with the explosive growth of traffic which is considered as one of the most biggest threat to current mobile communication systems, various solutions such as small cell and device-to-device communication have been exploited. Directional transmission in which transmission power of base station is focused onto the direction where the mobile station is located, can be used to increase throughput of the system. In this work, we develop a system-level simulator for cellular mobile communication systems using directional transmission and adaptive interference estimation scheme for directional transmission has been proposed. By using the developed simulator, the performance of cellular mobile communication systems with directional transmission is examined. Moreover, it is shown that the overall throughput of cellular system can be improved by utilizing directional transmission.

Simulation studies of the effects of user mobility on the handoff performance of mobile communications

Many analytical approaches have been proposed for handoff analysis because handoff is an important technology in mobile communication systems. In CDMA systems with soft handoff, mobile stations (MS's) within a soft handoff region (SR) use multiple radio channels and receive their signals from multiple base stations (BS's) simultaneously. Therefore, SR size, MS's speed and arrival rate of calls have very great influence on handoff process. In this paper, we study the performance of soft handoff in CDMA systems where is based on the square model. The effects of SR size, MS's speed and call arrival rate on call blocking probability are investigated. The results are compared with hard handoff.

We propose a fuzzy logic-based power command enhancement scheme for the mobile station of a cellular phone system. By defining the necessary linguistic variables of the power commands and corresponding fuzzy inference rules, an embedded fuzzy unit (EFU) is set up. The role of our EFU is to produce appropriate digital power commands instead of one-bit discrete commands directly obtained from the base station. Simulations show that the EFU-based mobile station can generate considerably smoother received power at the base station. The overshoot and channel tracking error are also small. In addition, our method has the advantage of simplicity, and is thus easy to be realized by hardware.

In any mobile communications system, there are poorly covered areas where radio waves are weak or cut-off because of transmission obstacles. These obstacles can be effectively eliminated by using economical relay systems, called “boosters”, between the base and mobile stations. To incorporate a in a W-CDMA system, high sensitivity (low noise) and high selectivity performance are required to expand the coverage and resolve or reduce problems such as interference caused by other systems working at adjacent frequencies or a reduction in user capacity that could be caused by transmission noise. To eliminate areas of weak or even no coverage, we found that an open-area relay booster system using a cryogenic superconductor front-end is indispensable. This paper presents the feasibility of practical application of a cryogenic front-end for an open-area booster. In our experiment, we made a cryogenic front-end with a pinched-off vacuum vessel and 2-W cryocooler. We used a 17-pole high-temperature superconducting filter (HTSF) and, -achieved 20-dB attenuation only 200 kHz from the band edge, for up-link and down-link input filters.

The traffic congestion often occurs in urban road network. When one of the sections becomes congested, it will lead to a series of congestions in other sections. The traffic congestion spreads rapidly until part of road network becomes congestion ultimately. In this case, the paper investigates the mechanism of the traffic congestion in urban road network and points out that subsystems of the traffic congestion always perform completive and cooperative functions in the process of traffic congestion. The process behaves in a manner of self-organized criticality, which can be forecasted. The paper also establishes synergetic predictive models based on self-organized criticality of the synergetic theory. Finally, the paper takes Beijing road network as an example to forecast the widespread traffic congestion. The result shows that the established models are accuracy, and the traffic congestion is featured of self-organized criticality.

This paper investigates the effect of multiplexing-based least squares (LS) channel estimation on uplink large-scale MU-MIMO-OFDM in the presence of terminal mobility. In uplink large-scale MU-MIMO, the same number of pilot symbols as that of mobile stations (MSs) is generally required, which results in the consumption of a substantial amount of resources for channel estimation. This overhead can be reduced by using the LS channel estimation in user multiplexing because this method has only to use a limited number of subcarriers, with a multipath length at most. In addition, the achieved overhead reductions can be effectively utilized for improving the tracking capability of channel estimation under varying channels. Since our performance evaluation focuses on mobile communications systems such as 6G, uplink large-scale MU-MIMO is assumed, and Gaussian belief propagation (GaBP) is applied to detect multiple uplink signals. The effectiveness of this method relative to that of the traditional LS method with the same number of pilot symbols is demonstrated under time selective fading through computer simulations.

For several years, effort have been devoted in standardization fora to develop network architecture(s) for third generation mobile communication systems. Based on the three-stage methodology defined in ITU-T Recommendation 1.130 [1], mobile and Intelligent Network experts within ITU and ETSI are currently working on the functional modelling of respectively FPLMTS (Future Public Land Mobile Telecommunication Systems) and UMTS (Universal Mobile Telecommunication System). One of the major issues in deriving functional model(s) for future mobile communication systems concerns the harmonization of mobility features with the Intelligent Network (IN) principles. The support of mobility service features requires the analysis of how radio related control functions could impact on the development of future IN capability sets (CS-2 and CS-3). This paper addresses some of the issues related to the modelling of the radio access subnetwork and its interactions with IN functionalities.KeywordsMobile TerminalRadio ResourceUniversal Mobile Telecommunication SystemRadio InterfaceUniversal Mobile Telecommunication SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Satellite communication is one of the key focuses of the sixth generation (6G) mobile communication systems, and aerial hybrid reconfigurable intelligent surface (AHRIS) -assisted satellite communication has recently emerged as a promising candidate for practical deployment in the 6G wireless networks. System design and gain rely heavily on accurately modeling of the underlying channel characteristics, which is challenging due to the high mobility of AHRIS and the unique properties of satellite communication. In this paper, we propose a novel three-dimensional (3D) non-stationary wideband geometry-based stochastic model (GBSM) for AHRIS-assisted satellite communication systems, where AHRIS movements and satellite trajectories are specifically considered. Moreover, two AHRIS phase correction schemes are proposed based on the characteristics of AHRIS in satellite communication systems. Following this, channel correlation function, Doppler power spectral density (PSD) and channel capacity are derived according to the proposed model. Simulation results show that the proposed model can accurately capture the characteristics of the AHRIS-assisted satellite communication systems, and the proposed phase correction schemes can effectively improve the channel statistical characteristics and increase the system capacity.

Perform ability modelling and evaluation of wireless and mobile systems have been of interest for recent research work. Especially, because of the complexity of the next generation wireless and mobile systems, modelling and performance evaluation is essential to improve the architecture according to the quality of service. (QoS ) requirements and performance characteristics. A considerable amount of the existing work in literature focuses on handover phenomena using analytical modelling and/or simulation of mobile communication systems. This paper presents a perform ability evaluation framework of mobile communication systems with different handover strategies using analytical modelling approaches. The availability and mobility issues are also considered in the proposed models. Well-known approximate Markov reward model solution and the exact Spectral expansion solution approaches are considered. Perform ability measures of proposed models, such as blocking probability and mean queue length are presented.

As for radio channel control of a cellular mobile communication system, location measurement is an important technique for determining the base station to be Connected with the mobile station. This paper describes the radio zone selection characteristic when a part of the control channel is time‐shared by base stations and the reception level of each base station is measured at mobile stations. MSSC (Multitransmitter Simul/Sequential Casting) of control channels is proposed, which improves the location measurement and is suitable for a high‐capacity system. The MSSC channel consists of simul‐cast parts and sequential‐cast parts. Its speech connection control sequence when applied to the cellular mobile communication system is shown. Next, the relation between the reception level variation characteristic in land mobile communication and the average reception level measurement accuracy when burst signals are received several times is studied. Both analytical results and laboratory experimental simulation results are shown. Finally, the zone selecting rate of a mobile station is calculated and the effect of the proposed control channel configuration is clarified.