【正文】 directly launch impulse sequence, thus ultra wideband (UWB) technology has a wide spectrum and very low average power, which is beneficial to coexist with other systems, so as to improve the frequency spectrum utilization rate, which brings a lot of system capacity. 5) low power Ultra wideband (UWB) technology use intermittent pulses to send data, pulse lasted for a very short time, is in monly ns ~ ns between, have very low accounted for empty factor, the system power consumption can be done very low, in high speed munications system when consume only for hundreds of muon W ~ dozens mW. At the same time because ultra wideband (UWB) technology of spread spectrum signal processing is relatively large, even if the gain USES low gain omnidirectional antenna with emission, also can use less than 1mW launch power realization thousands of meters of munication. 6) good safety UWB safety performance in two aspects: one is to adopt the jump spread spectrum, receiver only known the sender spread spectrum yards to work out emission data?；跓狳c(diǎn)的接入服務(wù)曾經(jīng)一度被看成是對(duì)3G的巨大沖擊， 但WiFi技術(shù)傳輸距離短和信號(hào)穿透能力差的特點(diǎn)同樣也是不可克服的。 4）頻譜利用率高，系統(tǒng)容量大 因?yàn)椴恍枰a(chǎn)生正弦載波信號(hào)，可以直接發(fā)射沖激序列，因而 UWB系統(tǒng)具有很寬的頻譜和很低的平均功率，有利于與其他系統(tǒng)共存，從而提高頻譜利用率，帶來了極大的系統(tǒng)容量。在短距離（13m 以下）有很大優(yōu)勢(shì)，最高傳輸速度可達(dá) 1Gb/S。在超幀開始時(shí)，點(diǎn)協(xié)調(diào)器可以在給定時(shí)間內(nèi)獲得控制權(quán)和發(fā)布輪詢，這由選項(xiàng)決定。有幀要傳輸?shù)恼军c(diǎn)先監(jiān)聽媒體。分布式接入?yún)f(xié)議對(duì)于對(duì)等工作站形式的自組網(wǎng)絡(luò)是有意義的，同時(shí)也可能對(duì)主要是突發(fā)性通信量的其他一些無線局域網(wǎng)頗具吸引力。無線局域網(wǎng)中最小的模塊是基本服務(wù)集（Basic Service Set, BSS）,它由一些執(zhí)行相同MAC協(xié)議并爭(zhēng)用同一共享媒體完成接入的站點(diǎn)組成。并列的網(wǎng)絡(luò)操作：隨著無線局域網(wǎng)變得越來越流行，很可能有兩個(gè)或者更多無線局域網(wǎng)同時(shí)存在于一個(gè)區(qū)域內(nèi)，或在局域網(wǎng)之間可能存在干擾的某些區(qū)域內(nèi)運(yùn)行。漫游接入在某種延伸的環(huán)境下也是十分有用的，如在建筑群之外操作的一臺(tái)電腦或一次商務(wù)行為。其次，隨著數(shù)據(jù)傳輸技術(shù)的發(fā)展，人們?cè)絹碓揭蕾囉陔p絞線連接的局域網(wǎng)。隨著這些問題的逐步解決，無線局域網(wǎng)很快就開始流行起來了。在這種情況下，兩個(gè)樓之間采用點(diǎn)對(duì)點(diǎn)的無線鏈接。電池能量消耗：移動(dòng)工作人員用的是由電池供電的工作站，它需要在使用無線適配器的情況下，電池供電時(shí)間足夠長(zhǎng)。 無線局域網(wǎng)有一個(gè)特性是人們樂意接受的，雖然不是必要的，那就是不需要通過麻煩的授權(quán)過程就能使用。ESS轉(zhuǎn)移：它的定義是指站點(diǎn)從一個(gè)ESS的BSS到另一個(gè)ESS的BSS移動(dòng)。DCF不包括沖突檢測(cè)功能（CSMA/CD），因?yàn)樵跓o線網(wǎng)絡(luò)中進(jìn)行沖突檢測(cè)是不實(shí)際的。因?yàn)镻IFS比DIFS小，所以點(diǎn)協(xié)調(diào)器在發(fā)布輪詢和接收響應(yīng)時(shí)能獲取媒體并封鎖所有的異步通信量。1 超寬帶無線通信 超寬帶技術(shù)簡(jiǎn)介 UWB（Ultra Wideband，超寬帶）技術(shù)是目前正被廣泛研究的一種新興無線通信技術(shù)，現(xiàn)在已經(jīng)成為高速無線個(gè)人網(wǎng) （WPAN）的首選技術(shù)。因此，與 IEEE 、IEEE 和藍(lán)牙相比，在同等碼速條件下，UWB具有更強(qiáng)的抗干擾性?，F(xiàn)在 WiFi 產(chǎn)品利用WED（Wired Equivalent Privacy）技術(shù)作資料加密之用。 and small offices where installation and maintenance of wired LANs is not economical. In all of these cases, a wireless LAN provides an effective and more attractive alternative. In most of these cases, an organization will also have a wired LAN to support servers and some stationary workstations. For example, a manufacturing facility typically has an office area that is separate from the factory floor but which must be linked to it for networking purposes. Therefore, typically, a wireless LAN will be linked into a wired LAN on the same premises. Thus, this application area is referred to as LAN extension.CrossBuilding InterconnectAnother use of wireless LAN technology is to connect LANs in nearby buildings, be they wired or wireless LANs. In this case, a pointtopoint wireless link is used between two buildings. The devices so connected are typically bridges or routers. This single pointtopoint link is not a LAN per se, but it is usual to include this application under the heading of wireless LAN.Nomadic AccessNomadic access provides a wireless link between a LAN hub and a mobile data terminal equipped with an antenna, such as a laptop puter or notepad puter. One example of the utility of such a connection is to enable an employee returning from a trip to transfer data from a personal portable puter to a server in the office. Nomadic access is also useful in an extended environment such as a campus or a business operating out of a cluster of buildings. In both of these cases, users may move around with their portable puters and may wish access to the servers on a wired LAN from various locations.Ad Hoc NetworkingAn ad hoc network is a peertopeer network (no centralized server) set up temporarily to meet some immediate need. For example, a group of employees, each with a laptop or palmtop puter, may convene in a conference room for a business or classroom meeting. The employees link their puters in a temporary network just for the duration of the meeting.Wireless LAN RequirementsA wireless LAN must meet the same sort of requirements typical of any LAN, including high capacity, ability to cover short distances, full connectivity among attached stations, and broadcast capability. In addition, there are a number of requirements specific to the wireless LAN environment. The following are among the most important requirements for wireless LANs:Throughput. The medium access control protocol should make as efficient use as possible of the wireless medium to maximize capacity.Number of nodes. Wireless LANs may need to support hundreds of nodes across multiple cells.Connection to backbone LAN. In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily acplished through the use of control modules that connect to both types of LANs. There may also need to be acmodation for mobile users and ad hoc wireless networks.Service area. A typical coverage area for a wireless LAN may be up to a 300 to 1000 foot diameter.Battery power consumption. Mobile workers use batterypowered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to constantlymonitor access points or to engage in frequent handshakes with a base stationis inappropriate.Transmission robustness and security. Unless properly designed, a wireless LAN may be interferenceprone and easily eavesdropped upon. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping.Collocated network operation. As wireless LANs bee more popular, it is quite likely for two of them to operate in the same area or in some area where interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may