《通信工程英文论文》由会员分享，可在线阅读，更多相关《通信工程英文论文（9页珍藏版）》请在金锄头文库上搜索。
1、英文原文RESEARCH OF CELLULAR WIRELESSCOMMUNATION SYSTEMAbstractCellular communication systems allow a large number of mobile users to seamlessly and simultaneously communicate to wireless modems at fixed base stations using a limited amount of radio frequency （RF） spectrum 。 The RF transmissions receive
2、d at the base stations from each mobile are translated to baseband, or to a wideband microwave link， and relayed to mobile switching centers （MSC）, which connect the mobile transmissions with the Public Switched Telephone Network （PSTN）。 Similarly， communications from the PSTN are sent to the base s
3、tation, where they are transmitted to the mobile. Cellular systems employ either frequency division multiple access （FDMA）, time division multiple access （TDMA）, code division multiple access （CDMA ）， or spatial division multiple access （SDMA）。1 IntroductionA wide variety of wireless communication s
4、ystems have been developed to provide access to the communications infrastructure for mobile or fixed users in a myriad of operating environments. Most of todays wireless systems are based on the cellular radio concept。 Cellular communication systems allow a large number of mobile users to seamlessl
5、y and simultaneously communicate to wireless modems at fixed base stations using a limited amount of radio frequency （RF） spectrum. The RF transmissions received at the base stations from each mobile are translated to baseband， or to a wideband microwave link， and relayed to mobile switching centers
6、 （MSC）, which connect the mobile transmissions with the Public Switched Telephone Network （PSTN）. Similarly， communications from the PSTN are sent to the base station, where they are transmitted to the mobile。 Cellular systems employ either frequency division multiple access （FDMA）， time division mu
7、ltiple access （TDMA）， code division multiple access （CDMA）, or spatial division multiple access （SDMA） .Wireless communication links experience hostile physical channel characteristics, such as timevarying multipath and shadowing due to large objects in the propagation path。 In addition, the perform
8、ance of wireless cellular systems tends to be limited by interference from other users, and for that reason ， it is important to have accurate techniques for modeling interference. These complex channel conditions are difficult to describe with a simple analytical model ， although several models do
9、provide analytical tractability with reasonable agreement to measured channel data . However, even when the channel is modeled in an analytically elegant manner, in the vast majority of situations it is still difficult or impossible to construct analytical solutions for link performance when error c
10、ontrol coding ， equalization， diversity, and network models are factored into the link model 。 Simulation approaches, therefore, are usually required when analyzing the performance of cellular communication links.Like wireless links, the system performance of a cellular radio system is most effectiv
11、ely modeled using simulation， due to the difficulty in modeling a large number of random events over time and space. These random events, such as the location of users, the number of simultaneous users in the system ， the propagation conditions ， interference and power level settings of each user, a
12、nd the traffic demands of each user ，combine together to impact the overall performance seen by a typical user in the cellular system。 The aforementioned variables are just a small sampling of the many key physical mechanisms that dictate the instantaneous performance of a particular user at any tim
13、e within the system 。 The term cellular radio system,therefore， refers to the entire population of mobile users and base stations throughout the geographic service area， as opposed to a single link that connects a single mobile user to a single base station. To design for a particular systemlevel pe
14、rformance, such as the likelihood of a particular user having acceptable service throughout the system, it is necessary to consider the complexity of multiple users that are simultaneously using the system throughout the coverage area 。 Thus， simulation is needed to consider the multi-user effects u
15、pon any of theindividual links between the mobile and the base station。The link performance is a small-scale phenomenon, which deals with the instantaneous changes in the channel over a small local area, or small time duration ， over which the average received power is assumed constant . Such assump
16、tions are sensible in the design of error control codes, equalizers, and other components that serve to mitigate the transient effects created by the channel。 However， in order to determine the overall system performance of a large number of users spread over a wide geographic area, it is necessary to incorporate large-scale effects such as the statistical behavior of interference and signal levels experienced by individual users over large distances， while ignoring the tr
