电子通信类专业英语论文
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Simulation of a cellular radio system
Your name
Image Processing Lab Wuhan University of Technology, WHUT Wuhan430070,China Heruoln@whut.edu.cn
Abstract -A wide variety of wireless communication systems have been developed to provide access to the communications infrastructure for mobile or fixed users in a myriad of operating environments. Most of today’s wireless systems are based on the cellular radio concept. Cellular 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 received 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 station, where they are transmitted to the mobile. Keywords: Cellular communication, RF,MSC, PSTN
System-Level Description： Cellular systems provide wireless coverage over a geographic service area by dividingthe geographic area into segments called cells as shown in Figure 2-1. Theavailable frequency spectrum is also divided into a number of channels with a groupof channels assigned to each cell. Base stations located in each cell are equippedwith wireless modems that can communicate with mobile users. Radio frequencychannels used in the transmission direction from the base station to the mobile arereferred to as forward channels, while channels used in the direction from the mobileto the base station are referred to as reverse channels. The forward and reversechannels together identify a duplex cellular channel.When frequency divisionduplex(FDD) is used, the forward and reverse channels are split in frequency. Alternatively,when time division duplex (TDD) is used, the forward and reverse channelsare on the same frequency, but use different time slots for transmission.
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 time 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 tБайду номын сангаас a single link that connects a single mobile user to a single base station. 2. CELLULAR RADIO SYSTEM
clusters of N cells, as shownin Figure 2-2, where N is known as the cluster size.
there are six co-channel cells. The secondtier consists of 12 co-channelcells, the third, 18, and so on. The total co-channelinterference is, therefore, the sumof the co-channel interference signals transmittedfrom all co-channel cells of all tiers. However, co-channel cells belonging to the firsttier have a stronger influence on the total interference, since they are closer to thecell where the interference is measured. 3.
Figure1:Basic architecture of a cellular communications system High-capacity cellular systems employ frequency reuse among cells. This requiresthat co-channel cells (cells sharing the same frequency) are sufficiently farapart from each other to mitigate co-channel interference. Channel reuse is implementedby covering the geographic service area with
1.
INTRODUCTION
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). Wireless communication links experience hostile physical channel characteristics, such as time-varying multipath and shadowing due to large objects in the propagation path. In addition, the performance 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 provide analytical tractability with reasonable agreement to measured channel data [1]. 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 control 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 effectively 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, and the traffic demands of each user ,combine together to impact the overall performance seen by a typical user in the cellular system.
Your name
Image Processing Lab Wuhan University of Technology, WHUT Wuhan430070,China Heruoln@whut.edu.cn
Abstract -A wide variety of wireless communication systems have been developed to provide access to the communications infrastructure for mobile or fixed users in a myriad of operating environments. Most of today’s wireless systems are based on the cellular radio concept. Cellular 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 received 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 station, where they are transmitted to the mobile. Keywords: Cellular communication, RF,MSC, PSTN
System-Level Description： Cellular systems provide wireless coverage over a geographic service area by dividingthe geographic area into segments called cells as shown in Figure 2-1. Theavailable frequency spectrum is also divided into a number of channels with a groupof channels assigned to each cell. Base stations located in each cell are equippedwith wireless modems that can communicate with mobile users. Radio frequencychannels used in the transmission direction from the base station to the mobile arereferred to as forward channels, while channels used in the direction from the mobileto the base station are referred to as reverse channels. The forward and reversechannels together identify a duplex cellular channel.When frequency divisionduplex(FDD) is used, the forward and reverse channels are split in frequency. Alternatively,when time division duplex (TDD) is used, the forward and reverse channelsare on the same frequency, but use different time slots for transmission.
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 time 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 tБайду номын сангаас a single link that connects a single mobile user to a single base station. 2. CELLULAR RADIO SYSTEM
clusters of N cells, as shownin Figure 2-2, where N is known as the cluster size.
there are six co-channel cells. The secondtier consists of 12 co-channelcells, the third, 18, and so on. The total co-channelinterference is, therefore, the sumof the co-channel interference signals transmittedfrom all co-channel cells of all tiers. However, co-channel cells belonging to the firsttier have a stronger influence on the total interference, since they are closer to thecell where the interference is measured. 3.
Figure1:Basic architecture of a cellular communications system High-capacity cellular systems employ frequency reuse among cells. This requiresthat co-channel cells (cells sharing the same frequency) are sufficiently farapart from each other to mitigate co-channel interference. Channel reuse is implementedby covering the geographic service area with
1.
INTRODUCTION
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). Wireless communication links experience hostile physical channel characteristics, such as time-varying multipath and shadowing due to large objects in the propagation path. In addition, the performance 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 provide analytical tractability with reasonable agreement to measured channel data [1]. 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 control 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 effectively 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, and the traffic demands of each user ,combine together to impact the overall performance seen by a typical user in the cellular system.