the discipline of the preceding paragraph were implemented, the point coordinator would lock out all asynchronous traffic by repeatedly issuing polls. To prevent this situation, an interval known as the superframe is defined. During the first part of this interval, the point coordinator issues polls in a round-robin fashion to all stations configured for polling. The point coordinator then idles for the remainder of the superframe, allowing a contention period for asynchronous access.
At the beginning of a superframe, the point coordinator may optionally seize control and issue polls fora give period of time. This interval varies because of the variable frame size issued by responding stations. The remainder of the superframe is available for contention-based access. At the end of the superframe interval, the point coordinator contends for access to the medium using PIFS. If the medium is idle, the point coordinator gains immediate access, and a full superframe period follows. However, the medium may be busy at the end of a superframe. In this case, the point coordinator must wait until the medium is idle to gain access; this results in a foreshortened superframe period for the next cycle.
UWB technology and other short-range wireless communications technology is compared
As personal communication consumer electronics industry in the rapid development, short-range wireless communication field of all kinds of new skills ,art, new methods to emerge in endlessly, toward faster and more convenient and more safe and effective etc. The new technology in the development of the Intel access, information home appliances, mobile office, industrialization and other fields has been widely used. Among them, ultra-wideband (UWB) Wide Band, the mk-ultra technology is in after 1990's developed a kind of with high potential new wireless communication technology, it was listed as one of the ten future communication technology.
1 uwb wireless communication
1.1 ultra-wideband technology introduction
UWB (the mk-ultra Wideband, ultra-wideband) technology is currently has been widely studied a new wireless communication technology, it has become a high-speed
wireless personal nets (WPAN first choice of the technology. UWB refers to the signal bandwidth than 500MHz or is the signal bandwidth and center frequency ratio is more than 25% of communications technologies. With the common use of continuous carrier communication mode is different, use of UWB wireless signals center frequency 4.1 GHz, bandwidth of 1.4 GHz, spectral range is very wide, but transmission power is very low. Communications speed in 250Kbit ~ between 10Mbit/SEC. In 250Kbit/SEC transmission speeds can ensure as communication distance. In short (13m below) a has great advantage, highest transmission speed can reach 1Gb/S. While the traditional narrowband technology in long distance, low speed transmission dominant.
Ultra-wideband (UWB) technology is initially applied to develop the radar oriented, it is generally thought that it belongs to a kind of carrierless communications technologies. February 2002, the United States the FCC formally its suspension. Currently ultra-wideband (UWB) technology is being integrated into the family cinema and portable products, mainly used for video and audio signal of wireless transmission. Ultra-wideband (UWB) since when published has been regarded as bluetooth technology substitute, and other wireless technologies such as WLAN, bluetooth etc compared ultra-wideband (UWB), with low power waste, high bandwidth and low complexity, the advantages of low cost, can completely satisfy short family entertainment application requirements. 1.2 ultra-wideband performance characteristics.
Uwb wireless communication is a very different to the traditional technology of wireless communication technology. It can realize the wireless LAN LAN and personal regional network PAN wireless Internet and access interface. UWB has the following features:
1) strong anti-jamming performance
UWB signal, the launch will be weak radio pulse signal scattered on the broad band, output power and even lower than ordinary equipment of the noise. Received will signal energy reduction out, in the solution enlarge produced during spread spectrum gain. Therefore, and IEEE 802.11 a, IEEE 802.11 b and bluetooth,compared to the same code speed conditions, the UWB has a strong anti-jamming. 2) transmission rate is high
UWB with very wide frequency bandwidth for high-speed data transmission, and not
alone occupy now already crowded frequency resource, but sharing other wireless technology using frequency band. The data rate can reach dozens megabit per second to hundreds of megabit per second, is expected to 100 times higher than bluetooth, also can prep above IEEE 802.11a and IEEE 802.11b . 3) with very wide bandwidth
UWB use of bandwidth in 1GHz above, up to a few ji hz and can and current narrowband communication system working at the same time and not interfere with each other. This in frequency resource of increasingly scarce today opened up a new time-domain radio resources.
4) spectrum is high efficiency, the system of large capacity
Because it does not need to produce sine carrier signal that can be 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 commonly 0.20 ns ~ 1.5 ns between, have very low accounted for empty factor, the system power consumption can be done very low, in high speed communications 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 omni-directional antenna with emission, also can use less than 1mW launch power realization thousands of meters of communication. 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; On the other hand is the transmission power spectral density is extremely low. Useful information completely submerged in noise, be intercept probability is small, be detection probability is low, with traditional receiver cannot receive. 2 Wi - Fi
2.1 Wi - Fi technology introduction
Wi - Wireless Fidelity, Wireless Fi (high-fidelity) is a kind of Wireless communication protocol, official name is IEEE802.11 b.
Wi - Fi is Ethernet a wireless expand, Wi - Fi network can use to interconnect computer links on the Internet. Wi - Fi network in no license 2.4 and 5 gigabit bandwidth management, Hz radio data rate can reach 11Mbps (802.11 b) ~ 54Mbps (802.11 a), or include the above two bands of products. If the user is located in an access point theoretically around certain region, can with highest about 11Mb/s faster access Web. But in fact, if there are multiple users at the same time through a point access, bandwidth by multiple users to share.
Because Wi - Fi use waves as transmission medium, material package to be intercepted tall, this be the possibility of users are worried about problems. Now Wi - Fi product use Wired Equivalent without (WED) technology data encryption purposes. However, its performance is highly confidential scepticism, support the new generation encryption method Wi - Fi products also arise. Although Wi - Fi in data security than bluetooth technology will send some, but in waves coverage was slightly better, can amount to 100 m or so.
Wi - Fi may provide hot coverage, low mobility and high speed of data transmission, wireless access and transmission with high speed is Wi - Fi technical main characteristics. Domestic telecommunication, CNC, mobile are very concerned Wi - Fi technology development and application. Based on the hotspot access service once considered the huge impact on 3G, but Wi - Fi technology transmission distance is short and signals penetrate the characteristics of poor ability also insurmountable. 2.2 Wi - Fi technical superiority
In recent years, the number of WAP at a rapid pace, wireless network convenience and efficient make its rapid popularization. Whether wireless urban construction, or business unit of LAN opening, or mobile phones Wi - Fi function, all with Wi - Fi technical advantages of itself is not divided: 1) wider LAN coverage
Based on bluetooth radio coverage is very small, radius, and only about 15m Wi - Fi radius criterion of up to 100 m, can cover whole building office building, 2) transmission speed
Wi - Fi technology transmission is very fast, can achieve 11Mbps (802.11 b) or 54Mbps (802.11 a), suitable for high speed data transmission business; 3) without wiring
Wi - the main advantage lies in the Fi don't need wiring, need not suffer wiring condition limit, so very suitable for mobile office users needs. At the airport, station, coffee shop, library such personnel more dense place Settings \high-speed lines will Internet access these places. Users will only support wireless LAN laptop or PDA get within the area, can high-speed access the Internet;
4) health and safety
The launch of IEEE802.11 provisions shall not exceed 100 power HaoWa, actual transmission power, about 60 ~ 70 HaoWa, and mobile transmission power about 200 HaoWa ~ 1 tile between handheld interphone, $5 watts. Compared with the latter, Wi - Fi products of radiation smaller. 3 conclusions
Each kind of wireless communication has its distinctive place, ultra-wideband technology transfer rate is high, Wi - Fi technology bestrow scope. As wireless communications technology development, people on high-speed short-range wireless communication request more and more high, ultra-wideband technology, Wi - Fi technology has broad prospects for development.
