无线都域(宽频)网路-WiMAX
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无线都域(宽频)网路-WiMAX
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无线都域网路-WiMAX
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WiMAX-Protocol
IEEE 802.16 (WiMAX)
ProtocolRelease DateFrequencyBandwidth
IEEE 802.16December 20056 -66 GHzup to 75 Mbps
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WiMAX 技术(I)
WiMAX 的技术目前可分为两类,一个是固定式WiMAX(以802.16-2004
标准为主).另一种为行动式WiMAX(802.16-e)其标准预计於2005 年
9 月完成.不论哪一种,都以支援高速无线上网而著称
固定式WiMAX 被视为是电信服务通往终端消费者的「最后一哩」解决方
案,简单的说,电信业者可以不用再辛苦的建设ADSL线路到用户家里,
仅需建设WiMAX 基地台,用户於家中即可连网.
而行动式WiMAX 具有支援封包传输的能力,使用者能於跨区移动的情况
下保持连线而不中断,被视为是3G的竞争者.Nokia 与Intel 所宣布的合作
案,就是在行动式WiMAX 的技术上进行.由於WiMAX 的基地台可含盖
30英里的范围,属於大范围的广域网路,因此一个共通的,甚至是全球统
一的无线频段是需要的.
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WiMAX 技术(II)
举凡讨论固定式WiMAX 的文献,大都会提到它有高达75M 的传输速率,
加上建设成本较低,因此认定它是非常具有竞争力的技术.然而却很少有
人提到这样的速率对於消费者的意义是什麼.
家用ADSL在达到2M的速率之后,大部分消费者就觉得够用了.中华电信
的326 万ADSL用户中,使用12M 速率的仅1 万多户,8M 的也仅17 万户
.虽然高速ADSL价格较贵或许也是因素,但用户比例也实在很低.当然
,消费者一定觉得速度越快越好,只要价格便宜.然而事实是,绝大部分
目前网路使用者常用的网路服务,例如网路游戏,收发邮件,即时传讯,
甚至是下载音乐,看影片,打网路电话等,2M很够了.
WCDMA 3G通讯技术连网速率已可达到384K(实测值约100多K),等
到其升级版HSDPA 推出时,速率可达3.6M到14.4M (目前的实测约
1.4M ),这绝对是「足够的频宽」.消费者需要75M频宽的理由是什麼
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WiMAX 技术(III)
频宽不是问题,应用才是重点.在所有的连网应用中,与频宽最没关系的
就是网路电话,因为此种网路应用的频宽消耗较低,新一代连网技术几乎
都可以毫无问题的支持,完全不需要75M 的速率.
WLAN之前的问题就在於其移动性不佳,如果要透过它来打网路电话就必
须在固定的地点进行,使用者若从基站A 移动到基站B 时电话就断了.虽
然有发展出补强技术,但毕竟其先天特性就是不利於移动.
行动式WiMAX 解决了这问题,甚至可能进行跨国漫游.如果Nokia 支持
这样的技术承诺为其生产终端,这才是撼动电信业生态的关键.各式上网
应用不是重点,网路电话才是重点,而这跟频宽大小根本无关.
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WiMAX 市场(I)
WiMAX 的出现,不但填补了WiFi短距离的传输限制,也补足了3G频宽不足
的问题,似乎很多问题,都将随著这项通讯技术的出现而获得改善.
WiMAX在设计之初,就是试图利用无线通讯的方式来解决家用(用户端)与
基地台(局端)这段属於"最后一哩"的需求.
WiMAX 似乎可以取代许多目前现有的通讯技术.但即使在纯粹技术上具有
取代性,但在考量成本,效益等各多方面的因素下,该项技术在应用上仍
有其限制,以下将就WiMAX在产品与市场上的的主要发展方向进行概要的
分析:
未来主要产品市场为笔记电脑而非行动电话:目前主要的移动通讯平台分
别为笔记型电脑以及行动电话,而WiMAX在其成本,体积以及耗电量的设
计乃是以电脑为基础,与行动电话轻,薄,小的发展目标以及需要长时间
待机的的考量不同.通讯技术的普及必须与相关硬体平台的基本设计做相
对应的结合,故WiMAX未来除基础建设设备之外,在近年内与笔记电脑结
合及相关应用应是其主要发展方向.
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WiMAX 市场(II)
2.主要地区市场为偏远地带与新兴国家:在目前已开发国家中,固网
(ADSL,Cable)早已天罗地网似的密布在主要的城镇之中,电信业者若再
付出WiMAX的架设成本-而弃已完成之固网,则不合其成本效益.但对於偏
远地区,WiMAX则可免除布线之工程,直接采用无线的方式供使用者与网
路连结,新兴国家亦同,在没有固网成本的包袱下,WiMAX可说是替代固
网的绝佳选项.
本报告认为,就搭配之硬体平台而言,WiMAX目前应属笔记电脑相关的无
线通讯技术,与行动电话的3G在目前并不相互冲突.而纯就取代固网而言
,WiMAX在偏远地区与新兴国家的确具有相当优势,但值得注意的是,在
地狭人稠且固网密集度高的台湾地区,若强力推动WiMAX建设是否符合整
体发展成本及相关效应,仍需进一步的考量.
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WLAN:WiMAX (I)
WiMAXis defined as Worldwide Interoperability for Microwave Access by
the WiMAX Forum, formed in April 2001 to promote conformance and
interoperability of the standard IEEE 802.16, also known as WirelessMAN.
The Forum describes WiMAX as "a standards-based technology enabling the
delivery of last milewireless broadband access as an alternative to cable and
DSL."
The last mileis usually referred to by the telecommunications and cable
television industries, it is typically seen as an expensive challenge because
"fanning out" wires and cables is a considerable physical undertaking. Outside
of the USA, the phrase "last kilometre" is sometimes used.
In business, the Last Milecan be used to describe the process of getting any
deliverable to the final customer or consumer
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WLAN:WiMAX (II)
The IEEE 802.16 media access controller (MAC) is significantly different from
that of IEEE 802.11 Wi-Fi MAC. In Wi-Fi, the MAC uses contention access —
all subscriber stations wishing to pass data through an access point are
competing for the AP's attention on a random basis. This can cause distant
nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes,
greatly reducing their throughput. And this makes services, suchas VoIP or
IPTV which depend on a determined level of quality of service (QoS) difficult
to maintain for large numbers of users.
In contrast, the 802.16 MAC is a scheduling MAC where the subscriber station
only has to compete once (for initial entry into the network). After that it is
allocated a time slot by the base station. The time slot can enlarge and constrict,
but it remains assigned to the subscriber station meaning that other subscribers
are not supposed to use it but take their turn.
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WLAN:WiMAX (III)
The WiMAX specification improves upon many of the limitations ofthe Wi-Fi
standard by providing increased bandwidth and stronger encryption. WiMAX is
a wireless alternative to cable and DSL for last mile (last km) broadband access.
However, the field of uses is broader and overlaps those for mobile WAN (wide
area networks) and WLANs. IEEE 802.16 provides up to 50 km (31 miles) of
linear service area range and allows connectivity between users without a direct
line of sight. However, practical limits from real world tests seem to be around
3-5 miles (5-8 km). The technology has been claimed to provide shared data
rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough
bandwidth to simultaneously support more than 60 businesses withT1-type
connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity.
Real world tests, however, show practical maximum data rates between
500kbit/s and 2 Mbit/s, depending on conditions at a given site
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WLAN:WiMAX (IV)
Most cable and traditional telephone companies are closely examining or
actively trial-testing the potential of WiMAXfor "last mile" connectivity. This
should result in better price-points for both home and business customers as
competition results from the elimination of the "captive" customer bases both
telephone and cable networks traditionally enjoyed. Even in areas without
preexisting physical cable or telephone networks, WiMAXcould allow access
between anyone within range of each other.
Given developing countries' (such as in Africa) limited wired infrastructure, the
costs to install a WiMAXstation in conjunction with an existing cellular tower
or even as a solitary hub will be diminutive in comparison to developing a
wired solution. The wide, flat expanses and low population density of such an
area lends itself well to WiMAXand its current diametrical range of 30 miles.
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