【導(dǎo)讀】病的正確分析、診斷、治療和監(jiān)護(hù)提供客觀指標(biāo)。ECG是一種重要的心電信號(hào)檢測(cè)技術(shù)，它反。映心臟興奮的產(chǎn)生、傳導(dǎo)和恢復(fù)過(guò)程中的生物電變化。確的檢測(cè)方法，其廣泛應(yīng)用于臨床監(jiān)測(cè)中。為方便人們實(shí)時(shí)了解心律的變化，根據(jù)心電信號(hào)。本系統(tǒng)采用高精度通用運(yùn)算放大器AD620對(duì)輸入的心電信號(hào)進(jìn)。和機(jī)器信號(hào)的影響，最后在數(shù)字示波器上得到清晰的心電波形。該心電圖儀設(shè)計(jì)簡(jiǎn)潔，攜帶。方便，經(jīng)過(guò)調(diào)試運(yùn)行流暢，能夠達(dá)到觀察心電信號(hào)的目的。另外本文綜述了ECG基礎(chǔ)理論、心。電檢測(cè)技術(shù)，并對(duì)心電信號(hào)檢測(cè)技術(shù)的發(fā)展趨勢(shì)作了展望。

　　

【正文】 r bit, IP based is all about an integrated, global work that’s based on an open system approach. The goal of 4G is to “replace the current proliferation of core cellular works with a single worldwide cellular core work standard based on IP for control, video, packet data and VoIP. But while 3G haven’t quite arrived, researchers want to contribute their ideas to the development of an asyet undefined wireless world that could bee operational by around 2020. This paper deals with the fundamentals and issues of works, technologies, spectrum, standards,terminals, services of 4G and about the visions that the work operators and service providers see for the evolution of 4G mobile systems and where is future research from their perspective necessary? Keywords： Wireless, 4G, WOFDM, MCCDMA, LASCDMA,UWB. I. INTRODUCTION While carriers and handset manufacturers obviously have their hands full with 3G, some panies are already looking beyond this next generation of wireless technology and works. 4G is simply an initiative by academic Ramp。D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed and meeting its promised performance and throughput .While this 3G has not pletely reached researchers and vendors are expressing growing interest in 4G why? Two main areas are addressed in these initiatives: An increase of capacity in the radio link and seamless mobility across heterogeneous access works. Section 2 discusses about the issues of 3G that has created interest towards 4G developments. Section 3 about evolution and parison,Section 4 describes about the goals and the vision, section 5 explains about some of the technologies for 4G, and in other following sections the applications, the research and other issues for 4G developments are discussed. II. WHY THE LEAP TOWARDS 4G? 3G works are in a very painful phase of their development, with early trials yielding 重慶郵電大學(xué)本科畢業(yè)設(shè)計(jì)（論文） 29 disappointing results, costs ballooning, technical glitches, and work operators being forced to deflate expectations based on unrealistic hype. Despite the hype surrounding the higherspeed 3G mobile works now under construction, the reasons for the leap towards 4G are: A. Performance Industry skeptics say that users will not be able to take advantage of rich multimedia content across wireless works with 3G. 4G munications will feature extremely highquality video equal to that of highdefinition television. In addition, it will enable wireless downloads at speeds exceeding 100 Mbps, about 260 times than 3G wireless work. B. Interoperability There are multiple standards for 3G making it difficult to roam and interoperate across works. We need a global standard that provides global mobility and service portability so that service provider would no longer be bound by singlesystem vendors of proprietary equipment. C. Networking 3G are based on primarily a widearea concept. We need hybrid works that utilize both wireless LAN (hot spot) concept and cell or basestation WAN design. With 4G,the world would have base stations everywhere, ensuring phone users connection to a highspeed work anywhere, anytime. D. Bandwidth We need wider bandwidth and higher bit rates. The 4G technology, with its transmission speeds of more than 20 mbps, would offer highbandwidth services within the reach of LAN hotspots, installed in offices, homes, coffee shops ,and airport lounges. Away from these hotspots, customers could connect to soupedup 2G works for voice and rudimentary data coverage. E. Technology Unlike 3G, 4G will more resemble a conglomeration of existing technologies rather than an entirely new standard. Analysts define 4G as a seamless bination of existing 2G wireless works with localarea works (LANs) or Bluetooth. F. Convergence Convergence involves more than mere technology。 it is a ing together of services and need all work that utilizes IP in its fullest form with converged voice and data capability,which the 4G will achieve. G. Cost 4G systems will prove far cheaper than 3G, since they can be built atop existing works and won39。t require operators to pletely retool and won39。t require carriers to purchase costly extra an open system IP wireless environment would probably further reduces costs for service providers by ushering in an era of real equipment interoperability. H. Scalability Scalability, or the ability to handle increasing numbers of users and diversity of services, is more challenging with mobile works.Design for Scalability, includes information that can help you meet changing usage demands .Because an all IP core layer of 4G is easily scalable, it is ideally 重慶郵電大學(xué)本科畢業(yè)設(shè)計(jì)（論文） 30 suited to meet this challenge. AND COMPARISON OF BROADBAND WIRELESS 1) First Generation (1G): 1G wireless mobile munication systems, was introduced in the early wireless was analog and supported the first generation of analog cell phones. They include a signaling protocol known as SS7 (Signaling System 7). 2) Second Generation (2G): 2G systems, fielded in the late 1980s, were intended primarily for voice transmission and was all about digital PCS. 3) Third Generation (3G): 3G in wireless will be a deliberate migration to faster, datacentric wireless works. The immediate goal is to raise transmission speeds from 125kbps to 2M bit/sec. 4) Fourth Generation (4G): In reality, as of first half of 2020, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless work that will interface with wire line backbone work seamlessly. IV. THE 4G NETWORK THAT THE CELLHEADS DREAM ABOUT 4G can be imagined of as an integrated wireless system that enables seamless roaming between user can be operating in cellular technology work and get handed over to a satellitebased work and bac