蜂窝网结构wikipedia

1、cellular networkfrom wikipedia, the free encyclopediatop of a cellular radio towera cellular network is a radio n etwork distributed over la nd areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. when joined together these cells provide ra

2、dio coverage over a wide geographic area. this enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed tran sceivers and teleph ones an ywhere in the n etwork, via base stati ons, eve n if some of the transceivers are moving t

3、hrough more than one cell during transmission.cellular networks offer a number of advantages over alternative solutions: in creased capacity reduced power use larger coverage area reduced interferenee from other signalsan example of a simple non-telephone cellular system is an old ta)<i driver

4、9;s radio system where the taxi company has several transmitters based around a city that can communicate directly with each taxi.contentshide1 the concept2 cell signal cncoding3 frequency reuse 1 directional anlennas5 broadcast messages and paging6 movement from cell to cel 1 and handover7 example

5、of a cellular network: the mobi1e phone network7. 1 structure of the mobi1e phone cellular network7. 2 cellular handover in mobile phone networks7. 3 cellular frequency choice in mobi1e phone networks7. 4 coverage comparison of different frequencics8 see also9 referenceseditithe conceptexample of fr

6、equency reuse factor or pattern 1/4in a cellular radio system, a land area to be supplied with radio service is divided into regular shaped cells, which can be hexagonal, square, circular or some other irregular shapes, although hexagonal cells are conventional. each of these cells is assigned multi

7、ple frequencies （斥 fq） which have corresp on ding radio base stati ons. the group of freque ncies can be reused in other cells, provided that the same freque ncies are not reused in adjace nt neighbori ng cells as that would cause cochannel interferenee.the in creased capacity in a cellular n etwork

8、, compared with a network with a single tran smitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission. if there is a single plain transmitter, only one transmission can be used on any given frequency. unfortunately, there is

9、 inevitably some level of interference from the signal from the other cells which use the same frequency. this means that, in a standard fdma system, there must be at least a one cell gap between cells which reuse the same frequency.in the simple case of the taxi company, each radio had a manually o

10、perated channel selector knob to tune to different frequencies as the drivers moved around, they would change from channel to channel. the drivers know which freciuency covers approximately what area when they do not receive a signal from the transmitter, they will try other channels until they find

11、 one that works. the taxi drivers only speak one at a time, when invited by the base station operator (in a sense tdma),editicell signal encodingto distinguish signals from several different transmitters, freauencv division multiple access (fdma) and code division multiple access (cdma) were develop

12、ed.with fdma, the transmitting and receiving frequencies used in each cell are different from the freque ncies used in each n eighbouri ng cell .in a simple taxi system, the taxi driver manu ally tuned to a frequency of a chosen cell to obtain a strong signal and to avoid interferenee from signals f

13、rom other cellsthe principle of cdma is more complex, but achieves the same result; the distributed transceivers can select one cell and listen to it.other available methods of multiplexing such as polarization division multiple access (pdma) and time division multiple access (tdma) cannot be used t

14、o separate signals from one cell to the next since the effects of both vary with position and this would make signal separation practically impossible. time divisio n multiple access, however, is used in combi nation with either fdma or cdma in a number of systems to give multiple channels within th

15、e coverage area of a single cell.editifrequency reusethe key characteristic of a cellular n etwork is the ability to re-use freque ncies to in crease both coverage and capacity. as described above, adjace nt cells must utilize different frequencies, however there is no problem with two cells suffici

16、ently far apart operating on the same frequency. the elements that determine frequency reuse are the reuse distanee and the reuse factor.the reuse distanee, d is calculated aswhere r is the cell radius and n is the number of cells per cluster. cells may vary in radius in the ranges (1 km to 30 km).

17、the boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells the frequency reuse factor is the rate at which the same frequency can be used in the n etwork .it is 1/k (or k accordi ng to some books) where k is the nu mber of cells which can no

18、t use the same freque ncies for tran smissi on. com mon values for the freque ncy reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).in case of n sector antennas on the same base station site, each with different direction, the base station site can serve n dif

19、ferent sectors. n is typically 3. a reuse pattern of n/k denotes a further division in frequency among n sector antennas per site. some current and historical reuse patterns are 3/7 (north american amps), 6/4 (motorola namps), and 3/4 (gsm).if the total available bandwidth is b, each cell can only u

20、tilize a number of frequency channels corresponding to a bandwidth of b/k、and each sector can use a bandwidth of b/nk.code division multiple access-based systems use a wider frequency band to achieve the same rate of transmission as fdma, but this is compensated for by the ability to use a freque nc

21、y reuse factor of 1, for example using a reuse pattern of 1/1 in other words, adjace nt base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. while n is shown as 1 in this example, that does not mean the cdma cell has o

22、nly one sector, but rather that the entire cell bandwidth is also available to each sector individually.depending on the size of the city, a taxi system may not have any frequency-reuse in its own city, but certai nly in other n earby cities, the same freque ncy can be used .in a big city, on the ot

23、her hand, frequency-reuse could certainly be in userecently also orthogonal frequencvdivision multiple access based systems such as lte are being deployed with a frequency reuse of 1. since such systems do not spread the signal across the frequency band, inter-cell radio resource management is impor

24、tant to coordinates resource allocation between different cell sites and to limit the inter-cell interferenee. there are various means of inter-cell interferenee coordination (icic) already defined in the standard .coordinated scheduling, multi-site mimo or multi-site beam forming are other examples

25、 for inter-cell radio resource management that might be standardized in the future逊directional antennascellular telephone frequency reuse pattern. see us patent 444,4"although the original 2-way-radio cell towers were at the centers of the cells and were omn i-directi onal, a cellular map can b

26、e redraw n with the cellular teleph one towers located at the corners of the hexago ns where three cells con verged each tower has three sets of di recti onal antennas aimed in three different directi ons with 120 degrees for each cell (totaling 360 degrees) and receiving/transmitting into three dif

27、ferent cells at different frequencies this provides a minimum of three channels (from three towers) for each cell the numbers in the illustration are channel numbers, which repeat every 3 cells. large cells can be subdivided into smaller cells for high volume areaseditibroadcast messages and pagingp

28、ractically every cellular system has some kind of broadcast mechanism. this can be used directly for distributing information to multiple mobiles, commonly, for example in mobile telephonv systems, the most important use of broadcast information is to set up channels for one to one communication bet

29、ween the mobile transceiver and the base station. this is calledpaging.the details of the process of paging vary somewhat from network to network, but normally we know a limited number of cells where the phone is located (this group of cells is called a location area in the gsm or umts system, or ro

30、uting area if a data packet session is involved). paging takes place by sending the broadcast message to all of those cells. paging messages can be used for information transfer. this happens in pagers, in cdma systems for sending sms messages, and in the umts system where it allows for low downlink

31、 latency in packet-based conn ections 逊movement from cell to cell and handoverin a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed. if a communication was interrupted due to a l

32、oss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency.in a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a different cell freque

33、ncy is done electronically without interruption and without a base station operator or ma nual switching. this is called the handover or han doff typically, a new cha nnel is automatically selected for the mobile unit on the new base station which will serve it. the mobile unit then automatically sw

34、itches from the current channel to the new channel and communication continues.the exact details of the mobile system's move from one base station to the other varies considerably from system to system (see the example below for how a mobile phone network man ages handover).editiexample of a cel

35、lular network: the mobile phone networkgsm network architecturethe most common example of a cellular network is a mobile phone (cell phone) network. a mobile phone is a portable telephone which receives or makes calls through a cell site (base station), or transmitting tower. radio waves are used to

36、 transfer signals to and from the cell phone.modern mobile phone networks use cells because radio frequencies are a limited, shared resource. cell-sites and handsets change frequency under computer control and use low power transmitters so that a limited number of radio frequencies can be simultaneo

37、usly used by many callers with less interferenee.a cellular network is used by the mobile phone operator to achieve both coverage and capacity for their subscribers. large geographic areas are split into smaller cells to avoid lin e-of-sight sign al loss and to support a large nu mber of active pho

38、nes in that area. all of the cell sites are connected to telephone exchanges (or switches), which in turn connect to the public telephone network.in cities, each cell site may have a range of up to approximately % mile, while in rural areas, the range could be as much as 5 miles it is possible that

39、in clear open areas, a user may receive signals from a cell site 25 miles away.since almost all mobile pho nes use cellular tech no logy, includi ng gsm, cdma, and amps (analog), the term '"cell phoneh is in some regions, notably the us, used interchangeably with "mobile phone”. howeve

40、r, satellite phones are mobile phones that do not communicate directly with a ground-based cellular tower, but may do so indirectly by way of a satellite.there are a number of different digital cellular technologies, including: global system for mobile communications (gsm), general packet radio serv

41、ice(gprs), code division multiple access (cdma), evolutiomdata optimized (ev-do), enhanced data rates for gsm evolution (edge), 3gsm, diqital enhanced cordless telecommunications (dect), digital amps (is-136/tdma), and integrated digital enhanced network (iden).editistructure of the mobile phone cel

42、lular networkmain article: gsmstructure of a 2g cellular networka simple view of the cellular mobile-radio network consists of the following: a network of radio base stations forming the base station subsystem. the core circuit switched network for handling voice calls and text a packet switched net

43、work for handling mobile data the public switched teleph one n etwork to conn ect subscribers to the wider teleph onyn etworkthis network is the foundation of the gsm system network. there are many functions that are performed by this network in order to make sure customers get the desired service i

44、ncluding mobility management, registration, call set up, andhandoverany phone connects to the network via an rbs in the corresponding cell which in turn connects to the msc. the msc allows the onward connection to the pstn the link from a phone to the rbs is called an uplink while the other way is t

45、ermed downlink.radio channels effectively use the transmission medium through the use of the following multiplexing schemes: frequency division multiplex (fdm), time divisionmultiplex (tdm), code division multiplex (cdm), and space division multiplex (sdm).corresponding to these multiplexing schemes

46、 are the following access techniques: frequency division multiple access (fdma), time division multiple access (tdma), code division multiple access (cdma), andspace division multiple access (sdma)色editicellular handover in mobile phone networksmain article: handoffas the phone user moves from one c

47、ell area to another cell whilst a call is in progress, the mobile station will search for a new channel to attach to in order not to drop the call. once a new cha nnel is found, the n etwork will comma nd the mobile un it to switch to the new cha nnel and at the same time switch the call onto the ne

48、w channel.with cdma, multiple cdma handsets share a specific radio channel. the signals are separated by using a pseudo noise code (pn code) specific to each phone. as the user moves from one cell to another, the handset sets up radio links with multiple cell sites (or sectors of the same site) simu

49、lta neousl y. this is known as ” soft han doff' because, un like with traditi onal cellular tech no logy, there is no one defined point where the pho ne switches to the new cell.in is95 inter-frequency handovers and older analog systems such as nmt it will typically be impossible to test the tar

50、get channel directly while communicating. in this case other techniques have to be used such as pilot beacons in is-95. this means that there is almost always a brief break in the comm un ication while searchi ng for the new cha nnel followed by the risk of an unexpected return to the old channel.if

51、 there is no ongoing communication or the communication can be interrupted, it is possible for the mobile unit to spontaneously move from one cell to another and then notify the base station with the strongest signal.editicellular frequency choice in mobile phone networksmain article: gsm frequency

52、bandsthe effect of frequency on cell coverage means that different frequencies serve better for different uses. low frequencies, such as 450 mhz nmt, serve very well for countryside coverage. gsm 900 (900 mhz) is a suitable solution for light urban coverage. gsm 1800 (1.8 ghz) starts to be limited b

53、y structural walls. umts, at 2.1 ghz is quite similar in coverage to gsm 1800.higher frequencies are a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. pico cells, covering e.g. one floor of a building, become possible, and the same frequency can be us

54、ed for cells which are practically neighbourscell service area may also vary due to interfere nee from transmitting systems, both within and around that cell. this is true especially in cdma based systems the receiver requires a certain signaltonoise ratio. as the receiver moves away from the transm

55、itter, the power transmitted is reduced. as the interferenee (noise) rises above the received power from the transmitter, and the power of the transmitter cannot be increased any more, the signal becomes corrupted and eve ntually unu sable .in cdma-based systems, the effect of interferenee from othe

56、r mobile transmitters in the same cell on coverage area is very marked and has a special name, cell breathinq.one can see examples of cell coverage by studying some of the coverage maps provided by real operators on their web sites. in certain cases they may mark the site of the transmitter, in othe

57、rs it can be calculated by working out the point of strongest coverage editicoverage comparison of different frequenciesfollowing table shows the dependency of frequency on coverage area of one cell of a cdma2000 network:frequency (mhz)cell radius (km)cell area (km2)relative cell count4504& 9752

58、1195026.922693.3180014.061812.2210012.044916.2蜂窝网络从wikipedia, h由的百科全书返回蜂窝无线电塔一个移动电话网络是一种无线网络领域分布在土地称为单元，每个位置由最少一个固定收发 器,一个被称为蜂肉肚站或墓站0当这些细胞连在一起的地理区域提供了一个广泛的无线覆 盖。这使得如，大型收发器（数字便携式移动电话，寻呼机等）相互z间以及与网定电话的 任何地方收发器和相应的网络，通过电台进行通信，即使收发-些比移动通过更一个单元在传输 过程中。蜂肉网络提供了超过替代解决方案优势：提髙能力减少川电更大的覆盖范围减少莫它信号的干扰例如一个系统的一个简单的非移动电话是一个老出租乍司机的无线电系统，其中拥有各类出租 车出租车公司与多家发射机根据各地的城市，可以直接沟通。内容隐藏1概念2细胞信号编码3频率复用4定向天线5广播消息和寻呼6运动从细胞到细胞和移交7范例蜂窝网络：移动电话网络o7.1结构的移动电话蜂竟网络o7.2蜂竟移动电话网络中切换o7.3蜂竟电话网络在移动频率的选择o7.4不同频率范围的比较8参见9参考文献编紺概念例如频率复用因子或模式1/4在蜂窝无线电系统，土地供应面积与传统的广播服务分为定期形细胞，它可以六角，方形，圆 形或不规则形状等，虽然六角形细胞。其中的每个细胞被分配多个频率