无线通信系统PPT学习教案

1、会计学1无线通信系统无线通信系统2022-5-192 Cellular Networks第1页/共46页2022-5-193Cell shapeCircle: Equilateral triangle:Square:Hexagon:22cA3.14rr2hA2.6r2sA2.0r2tA1.3r第2页/共46页2022-5-194Cellular coverage representation第3页/共46页2022-5-195lMacrocell large, covering a wide are range of several hundred kilometres (km) to ten

2、 km mostly deployed in rural and sparsely populated areaslMicrocell medium cell, coverage are a smaller than in macro cells range of several hundred metres to a couple of metres deployed mostly in crowded areas, stadiums, shopping mallslPicocell small, covering a very small area range of several ten

3、s of metres low power antennas, indoorThe size of a cell第4页/共46页2022-5-196第5页/共46页2022-5-197Base station transmitterslIn hexagonal cells, base stations transmitters are either:centre-excited, base station is at the centre of the cell edge-excited, base station at 3 of the 6 cell verticescentre-excit

4、ededge-excited第6页/共46页2022-5-198 Cellular coverage representation SkNCMkNMSC can be used as a measure of capacity 第7页/共46页2022-5-199A mobile communication system uses a frequency reuse factor of 1/7 and 416 channels available. If 21 channels are allocated as control channels, compute its system capa

5、city. Assume a channel supports 8 usersChannels available for allocation = 416 - 21 = 395Channel Number of a cell = 395 / 7 = 57Number of simultaneous users per cell = 8 x 57 = 456Number of simultaneous users in system = 7 x 456 = 3192Example 1第8页/共46页2022-5-1910If a total of 33 MHz of bandwidth is

6、allocated to a particular FDD cellular telephone system which uses two 25 kHz simplex channels to provide full duplex voice and control channels, compute the number of channels available per cell if a system uses four-cell reuse. If 1 MHz of the allocated spectrum is dedicated to control channels, d

7、etermine an equitable distribution of control channels and traffic channels in each cell for each of the system.Example 2第9页/共46页2022-5-1911Method of locating co-channel cells3,2ij第10页/共46页2022-5-1912Channel Assignment StrategiessThree assignment approacheslFixed and static (most common)lDynamicl Hy

8、bridsFixed channel assignmentlall channels in a cell could be in use all the timenew calls are then blocked (no channels left)may be solved by borrowing spare channels from nearby cells第11页/共46页2022-5-1913Dynamic channel assignmentMSC allocates frequencies when a call is madeProvides high channel ut

9、ilisationTo do this it needs real-time information onchannel occupancy traffic distribution and radio signal strength indication (RSSI)high computational load and increased storage第12页/共46页2022-5-1914第13页/共46页2022-5-1915第14页/共46页2022-5-1916BS1BS2BS3MSCPSTNTrunks第15页/共46页2022-5-1917第16页/共46页2022-5-19

10、18第17页/共46页2022-5-1919第18页/共46页2022-5-1920Handoff in different system1G signal strength measurements are made by the base stations and supervised by the MSC GSM MAHO handoff decisions are mobile assisted CDMA pilot channel, soft handoff第19页/共46页2022-5-1921Interference and System Capacity第20页/共46页202

11、2-5-1922Six Effective Interfering Cells of Cell 1 第21页/共46页2022-5-1923Co-channel reuse ratio Q 第22页/共46页2022-5-1924Co-channel reuse ratio vs. frequency reuse pattern 第23页/共46页2022-5-19257-cell reuse pattern第24页/共46页2022-5-192612-cell reuse pattern 第25页/共46页2022-5-192719-cell reuse pattern 第26页/共46页2

12、022-5-1928Co-channel reuse ratio vs. frequency reuse pattern 第27页/共46页2022-5-1929Propagation modelniD第28页/共46页2022-5-1930Co-channel interference ratio 第29页/共46页2022-5-1931Example 3第30页/共46页2022-5-1932More exact geometry layout 第31页/共46页2022-5-1933Closely approximately as 第32页/共46页2022-5-1934Trunking

13、 and Grade of Service (GOS)第33页/共46页2022-5-1935Grade of Service (GOS)第34页/共46页2022-5-1936About Erlang第35页/共46页2022-5-1937Erlang B formulawhere C is the number of trunked channels offered by a trunked radio system and A is the total offered traffic. 第36页/共46页2022-5-1938Trunked mobile network provide

14、cellular service in this area. System has 394 cells with 19 channels each. Find the number of users that can be supported at 2% blocking if each user averages two calls per hour at an average call duration of three minutes. Compute the total number of subscribers that can be supported by this system

15、.Probability of blocking = 2% =0.02Number of channels per cell used in the system, C=19Traffic intensity per user, Au = H= 2 x (3/60) = 0.1 Erlangsfrom the Erlang B chart, the totalcarried traffic, A, is obtained as 12 Erlangs.Therefore, the number of users that can be supported per cell isU=AIAu= 1

16、2/0.1 = 120Since there are 394 cells, the total number of subscribers that can be supported by System A is equal to 120 x 394 = 47280Example 4第37页/共46页2022-5-1939sOften large cells need to be split into smaller ones because the population of users in the big cell has increased beyond what it can sup

17、portlCell splitting increases system capacitylIs used in high density subscriber areas lResults to increased costs (eg. new base stations)Improving Capacity in Cellular System 第38页/共46页2022-5-1940第39页/共46页2022-5-1941第40页/共46页2022-5-1942Cell Splitting 第41页/共46页2022-5-1943Sectoring 第42页/共46页2022-5-194

18、4A cellular system:an average call lasts two minutes, and the probability of blocking is to be no more than 1 %. Every subscriber makes one call per hour, on average. If there are a total of 395 traffic channels for a seven-cell reuse system, there will be about 57 traffic channels per cell. Assume

19、that blocked calls are cleared so the blocking is described by the Erlang B distribution. From the Erlang B distribution, it can be found that the unsectored system may handle 44.2 Erlangs or 1326 calls per hour.If employing 120 sectoring, there are only 19 channels per antenna sector (57/3 antennas

20、). For the same probability of blocking and average call length, it can be found from the Erlang B distribution that each sector can handle 11.2 Erlangs or 336 calls per hour. Since each cell consists of three sectors, this provides a cell capacity of 3 x 336 = 1008 calls per hour. Thus, sectoring d

21、ecreases the trunking efficiency while improving the S/I for each user in the system. Example 5第43页/共46页2022-5-19451.Wireless has rapidly emerged in the communication field. Please use library or internet to find the answers of the following questions.(a)Describe at least one cellular system that being used today, the carrier frequency, the data rate, the RF bandwidth or more.(b)Explain what is WLAN?(IEEE 802.11,wi-fi,etc.) 2.If 20 MHz of total spectrum is allocated for a duplex wireless cellular system and each simplex channe