王海龙——基于MSC-51单片机计算器(6)

哈尔滨远东理工学院学士学位论文 致 谢

通到2个月的努力,毕业设计终于完成了,我感觉这段日子过得非常充实,在这个过程中我学到了很多.首先我要感谢我的导师,张玉伽老师在我完成论文的过程中,给予了我很大的帮助.

在我接到课题的时候,这是一次考验.怎么才能找到课堂所学与实际应用的最佳结合点,怎样让自己的成功地完成它？在我迷茫的时候王老师从我的特长和专业分析,引导我从基础的方向入手学习.

张老师学识渊博,治学严谨.为我规划了合理的设计进度,经常特意抽出时间来辅导我们,多次指出了我设计的失误让我改正.

正是因为张老师的认真教诲,我才能有今天的收获,同时领会到毕业设计的意义,学到了只靠书本掌握不到的知识.

同时我还要感谢许多关心帮助和教育我的老师们,你们的照顾与指导让我难忘,我唯有以努力学习和工作来报答他们无私的关怀.

还有那些与我一起探讨问题的同学,你们陪我走过了这一段充实的日子.谢谢大家！

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哈尔滨远东理工学院学士学位论文 参考文献

[1] 张毅刚．单片机原理及应用［M］．北京:高等教育出版社,2003．

[2] 闫娟．MSC-51单片机汇编语言程序IDE设计与实现[D] ．河南师范大学,2007． [3] 百度百科．单片机[OL]．http://baike.http://www.wodefanwen.com//view/1012.html?wtp=tt． [4] Structure and function of the MCS-51 series[OL] ．

http://wenku.http://www.wodefanwen.com//view/bf7d83114431b90d6c85c762.html． [5] 张迎新等．单片机初级教程:单片机基础[M] ．北京:北京航空航天大学出版社,2006． [6] 单片机从入门到精通[OL] ．

http://wenku.http://www.wodefanwen.com//view/95fabc0ef12d2af90242e600.html． [7] 关德新,冯文全等．单片机外围器件实用手册［M］．北京:北京航空航天大学出版社,1998．

[8] AT89S51 8-bit Microcontroller with 8K Bytes In-System Programmable Flash．ATMEL Corporation,2001． [9]

96系列单片机仿真器研究与设计

[10] Kirk Zurell．C Programming for Embedded systems［D］．CMP Media,Inc．2000． [11] 徐金增．单片机编程仿真实验系统的设计与实现[D].山东师范大学,2009． [12] 刘焕平．MCS-51系列单片机实验板[J].石家庄职业技术学院学报,2002．14(4) :40-41．

[13] Mautice Wilkes．Progress in Computers[D] ．Prestige Lecture delivered to IEE,Cambridge,on 5 February 2004．

[14]张子红．96系列单片机仿真器研究与设计[D] ．哈尔滨:哈尔滨工程大学,2006． [15]赖麟文．8051单片机C语言开发环境事务与设计［M］．北京:科学出版社,2002． [16] LI Yan-qing. LIU Xiang-dong. DONG Ning. et al. The design of vehicle monitoring system based on GPRS/GPS[J] . Control & Automation Publication Group. 2004. 20( 4) : 39-40.

[17] HUANG Cheng-an. ZHANG Yue. YUN Huai zhong. The design of remotemeter control system based on GPRS[J]. Electrical Measurement & Instrumentation. 2003. 8: 42-45.

[18] Comer D E. Internetworking With TCP/IP Volume I: Principles. Protocols. and Architectures [M]. Beijing: Publishing House of Electronics Industry. 2007.

[19] SHENG Li-feng. JIN Xin-yu. ZHANG Yu. et al. Intelligent check and management system for watt-hour meters by using PDA and GPRS technology[J] . East China Electric Power. 2006. 1: 23-25.

[20] HE Zeng-ying. CHEN Jian-rui. Remote shutdown technology of communicating on the basis of Winsock network[J].Information & Communications. 2007. 5: 62-64.

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哈尔滨远东理工学院学士学位论文 附录 A

Handoff in Cellular Systems

Nishith D. Tripathi, Nortel

Jeffrey H. Reed and Hugh F. VanLandingham MPRG, Virginia Tech

Cellular System

Deployment Scenarios

The radio propagation environment and related handoff challenges are different in different cellular structures. A handoff algorithm with fixed parameters cannot perform well in different system environments. Specific characteristics of the communication systems should be taken into account while designing handoff algorithms. Several basic cellular structures (e.g., macrocells, microcells, and overlay systems) and special architectures (e.g., underlays, multichannel bandwidth systems,and evolutionary architectures) are described next. Integrated cordless and cellular systems, integrated cellular systems, and integrated terrestrial and satellite systems are also described.

Macrocells

Macrocell radii are in several kilometers. Due to the low cellcrossing rate, centralized handoff is possible despite the large number of MSs the MSC has to manage. The signal quality in the uplink and downlink is approximately the same. The transition region between the BSs is large; handoff schemes should allow some delay to avoid flip-flopping. However, the delay should be short enough to preserve the signal quality because the interference increases as the MS penetrates the new cell. This cell penetration is called cell dragging. Macrocells have relatively gentle path loss characteristics . The averaging interval (i.e., the time period used to average the signal strength variations) should be long enough to get rid of fading

fluctuations. First- and second-generation cellular systems provide wide-area coverage even in cities using macrocells .Typically, a BS transceiver in a macrocell transmits high output power with the antenna mounted several meters high on a tower to illuminate a large area.

Microcells

Some capacity improvement techniques (e.g., larger bandwidths, improved methods for speech coding, channel coding,and modulation) will not be sufficient to satisfy the required service demand. The use of microcells is considered the single most effective means of increasing the capacity of cellular systems.Microcells increase capacity, but radio resource management becomes more difficult. Microcells can be classified as one-, two-, or threedimensional,depending on whether they are along a road or a highway, covering an area such as a number of adjacent roads,or located in multilevel buildings, respectively . Microcells can be classified as hot spots (service areas with a higher traffic density or areas that are covered poorly), downtown clustered microcells (contiguous areas serving pedestrians and mobiles), and in-building 3-D cells (serving office buildings and pedestrians).Typically, a BS transceiver in a microcell transmits low output power with the antenna mounted at lamppost level (approximately 5 m above ground).The MS also transmits low power, which leads to longer battery life. Since BS antennas have lower heights compared to the surrounding buildings, RF signals propagate mostly along the streets.The antenna may cover 100–200 m in each street direction, serving a few city blocks. This propagation environment has low time dispersion,

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哈尔滨远东理工学院学士学位论文 which allows high data rates. Microcells are more sensitive to the traffic and interference than macrocells due to short-term variations (e.g., traffic and interference

variations),medium/long-term alterations (e.g., new buildings), and incremental growth of the radio network (e.g., new BSs) . The number of handoffs per cell is increased by an order of magnitude, and the time available to make a handoff is decreased. Using an umbrella cell is one way to reduce the handoff rate. Due to the increase in the microcell boundary crossings and expected high traffic loads, a higher degree of decentralization of the handoff process becomes necessary.

Microcells encounter a propagation phenomenon called the corner effect. The corner effect is characterized by a sudden large drop (e.g., 20–30 dB) in signal strength (e.g., at 10–20 m distance) when a mobile turns around a corner.

The corner effect is due to the loss of the line of sight (LOS) component from the serving BS to the MS. The corner effect demands a faster handoff and can change the signal quality very fast. The corner effect is hard to predict. A long measurement averaging interval is not desirable due to the corner effect. Moving obstacles can temporarily hinder the path between a BS and an MS,which resembles the corner effect. Reference studies the properties of symmetrical cell plans in a Manhattan-type environment. Cell plans affect signal-to-interference ratio (SIR) performance in the uplink and downlink significantly. Symmetrical cell plans have four nearest co-channel BSs located at the same distance. Such cell plans can be classified into half-square (HS), full-square (FS), and rectangular (R) cell plans. These cell plans are described next.

Half-Square Cell Plan — This cell planplaces BSs with omnidirectional antennas at each intersection, and each BS covers half a block in all four directions. This cell plan avoids the street corner effect and provides the highest capacity. This cell plan has only LOS handoffs. Figure 2 shows an example of a half-square cell plan in a microcellular system.

Full-Square Cell Plan — There is a BSwith an omnidirectional antenna located at every other intersection, and each BS coversa block in all four directions. It is possible for an MS to experience the street corner effect for this cell plan. The FS cell plan can have LOS or NLOS handoffs. Figure 3 shows an example of a fullsquare cell plan in a microcellular system.

Rectangular Cell Plan — Each BS covers a fraction of either a horizontal or vertical street with the BS located in the middle of the cell. This cell plan can easily be adapted to market penetration. Fewer BSs with high transmit power can be used initially. As user density increases, new BSs can be added with reduced transmit power from appropriate BSs.The street corner effect is possible for this cell plan. The R cell plan can have LOS or NLOS handoffs. Figure 4 shows an example of a rectangular cell plan in a microcellular system. Macrocell/Microcell Overlays Congestion of certain microcells, the lack of service of microcells in some areas, and high speed of some users are some reasons for higher handoff rates and signaling load for microcells. To alleviate some of these problems, a mixed-cell architecture (called an overlay/underlay system) consisting of largesize macrocells (called umbrella cells or overlay cells) and small-size microcells(called underlay cells) can be used. Figure 5 illustrates an overlay system.

The macrocell/microcell overlay architecture provides a balance between maximizing the number of users per unit area and minimizing the network control load associated with handoff. Macrocells provide wide-area coverage beyond microcell service areas and ensure better intercell handoff.Microcells provide capacity due to greater frequency reuse and cover areas with high traffic density (called hot spots). Examples of hot spots include an airport,a railway station,

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哈尔滨远东理工学院学士学位论文 or a parking lot. In less congested areas (e.g., areas beyond a city center or outside the main streets of a city) traffic demand is not very high, and macrocells can provide adequate coverage in such areas. Macrocells also serve highspeed MSs and the areas not covered by microcells (e.g., due

to lack of channels or the MS being out of the microcell range). Also, after the microcellular system is used to its fullest extent, the overflow traffic can be routed to macrocells.One of the important issues for the overlay/underlay system is the determination of optimum distribution of channels in the macrocells and microcells.

Reference evaluates four approaches to sharing the available spectrum between the two tiers. Approach 1 uses TDMA for microcell and CDMA for macrocell. Approach 2 uses CDMA for microcell and TDMA for macrocell. Approach 3 uses TDMA in both tiers, while approach 4 uses orthogonal frequency channels in both tiers.The overlay/underlay system has several advantages over a pure microcell system:

? The BSs are required only in high traffic load areas. Since it is not necessary to cover the whole service area with microcells,infrastructure costs are saved.

? The number of handoffs in an overlay system is much less than in a microcell system because fast-moving vehicles can be connected to the overlay macrocell.

? Both calling from an MS and location registration can easily be done through the microcell system.There are several classes of umbrella cells. In one class, orthogonal channels are distributed between microcells and macrocells.In another class, microcells use channels that are temporarily unused by macrocells. In yet another class,microcells reuse the channels already assigned to macrocells and use slightly higher transmit power levels to counteract the interference from the macrocells.

Within the overlay/underlay system environment, four types of handovers need to be managed [19]: microcell to microcell, microcell to macrocell, macrocell to macrocell, and macrocell to microcell.Reference describes combined cell splitting and overlaying. Reuse of channels in the two cells is done by establishing an overlaid small cell served by the same cell site as the large cell. Small cells reuse the split cell’s channels because of the large distance between the split cell and the small inner cell, while the large cell cannot reuse these channels. Overlaid cells are approximately 50 percent more spectrally efficient than segmenting (the process of distributing the channels among the small- and largesize cells to avoid interference).A practical approach for implementation of a microcell system overlaid with an existing macrocell system is proposed in . This reference introduces channel segregation (a self-organized dynamic channel assignment)and automatic transmit power control to obviate the need to design channel assignment and transmit power control for the microcell system. The available channels are reused automatically between microcells and macrocells. A slight increase of transmit power for the microcell system compensates for the macrocell-to-microcell interference.

Simulation results indicate that the local traffic is accommodated by the microcells laid under macrocells without any significant channel management effort. The methodology of the Global System for Mobile Communications (GSM)-based system is extended to the macrocell/microcell overlay system in. The use of random frequency hopping and adaptive frequency planning is recommended,and different issues related to handoff and frequency planning for an overlay system are discussed. Four strategies are designed to determine a suitable cell for a user for an overlay system. Two strategies are based on the dwell time (the time for which a call can be maintained in a cell without handoff), and the other two strategies are based on user speed estimation. A speed estimation technique based on dwell times is also proposed.A

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