Cellular network(Cellular network), also known asMobile network(Mobile network) is a kind ofmobile communicationThe hardware architecture is divided into analog cellular network and digital cellular network.Due to the various communications constituting the network coverageBase platformThe signal coverage ofhexagonSo that the whole network looks like a cell.
The reason why cellular networks are widely used is from a mathematical conclusion, that is, when the circle center is atRegular hexagonThe center of each regular hexagon of the mesh, that is, when the center of the circle is located in theLattice pointThe minimum number of circles is used.Although it is still an unknown problem to be solved even if nodes are required to be on a grid with translational characteristics like isomorphic lattice, it is usually reasonable to use circles to express practical requirements in communication, so in consideration of saving equipment construction costs,Triangular meshes, also known as simple hexagonal meshes, are the best choice.The network formed in this way is covered together and shaped like a cell, so it is called a cellular network.
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The cellular network consists of the following three parts: mobile stations,Base station subsystem，Network subsystem。Mobile station is the networkterminal equipment, such as mobile phones or some cellular industrial control devices.Base station subsystem includes mobile base station (big iron tower)Wireless transceiver、private network (usually optical fiber), wireless digital equipment, etc.The base station subsystem can be regarded aswireless networkConverter with wired network.
Cell: divide a large area into multiple small cells, and use multiple low-power transmitters instead of one high-power transmittertransmitter。General useRegular hexagonTo describe the honeycomb shape.
Frequency multiplexing: Each cell uses one set of channels.If the two cells are far enough apart, the same set of channels can be used.Cluster: A cell group consisting of N cells, which uses allFrequency resourcesFrequency reuse factor: 1/N For hexagonal cells,N=i^2+i*j+j^2,i>=1,j>=1，When i>1, j ≥ 0 or when j>1, i ≥ 0. Therefore, N=3,4,7,9,12
Geometric representation of honeycomb
Honeycomb is usually represented by a regular hexagon.As for why it is a regular hexagon rather than a circle.Because vertex toGeometric centerEquidistantpolygonThe possiblegeometryyes:square、Equilateral triangleAnd regular hexagon.Among square, equilateral triangle and regular hexagon, regular hexagon has the largest area.
Use (i, j) to represent the coordinates of a cell.For example, the coordinates of cell A are (2,1)
Cellular Channel Allocation
FDMA system: Use the signal attenuation principle.Key: divide the spectrum into several channels (user channel carrier), and multiplex the channel when the distance is far enough.
Static channel allocation: Each cell allocates a set of fixed channels in advance, which is simple to implement.
Dynamic channel allocation: Base station from MSCDynamic allocationFor one channel, the cell can use all the channels, which reduces the blocking probability and is complex to implement. It requires real-time traffic detection and coordinated processing between base stations.
A distributed cellular network (100) providesMobile station(102) Conductedwireless communication 。MultipleBase transceiverNetwork Components(104) is configured in aWireless MediaTo communicate with a plurality of mobile stations (102), each of whichBase transceiver stationBoth include anetwork interface。At least one mobile station controller network component (108) includes a network interface suitable for coupling to the network (100).The system (100) is configured so that for efficiencyBase station controllerCommunication between (106) and mobile switching center (108)Business volumeconductload balancing 。The invention has the advantages of low costTransceiver(104) is combined with flexible deployment to achieve communication coverage in large areas at low cost.
A distributed cellularcommunication system , including: a network;OnecouplingTo this networkPublic Switched Telephone Network(PSTN)；MultipleTransceiverMultiple transceivers are geographically separated from each other, and each transceiver is configured toMobile stationCommunication;At least onedata processing systemThe at least one data processing system is configured to execute the computerprogramThe computer program includes software suitable for enabling multiple transceivers to transfer data between mobile stations and between a mobile station and PSTNFunction blockThese software function blocks include: aMobility Management(MM) function block;One implementationVLRVisitors to the featureLocation registration(VLR) function block;An implementation of CM functionCommunication management(CM) function block;Multiple implementationsRRFunctionalRadio resources(RR) function block, the RR function includes switching the communication between multiple transceivers when the mobile station moves from one cell to another, so as to maintain the communication between the mobile station and the network.
The so-called cellular mobile phone refers toservice areaIt is divided into several adjacent cells, each of which has a base stationnetwork structure。Since each community is positivehexagon, and they are adjacent to each other. On the whole, the shape resembles a honeycomb, so people call it a "honeycomb" network.Use severalHoneycombThe large and medium capacity mobile phone system that covers the whole service area in the community is calledCellular mobile telephone system, referred to as cellular mobile phone.
The biggest advantage of cellular mobile phones is that frequencies can be reused.As you may know, when using mobile phones for communication, everyone needs to occupy a channel, that is, the system needs to provide a channel for you to use.When there are more people talking at the same time, the limited channel may not be enough, and then communication congestion will occur.With the cellular structure, the same set of frequencies can be used repeatedly in several cells separated by a certain distance, thus saving moneyFrequency resourcesThe purpose of.For example, we divide a city into 72 sub districts, and every 12 sub districts form a sub district group.Let them use 300 channels together.Then, we can divide 300 channels into 12 channel groups, with 25 channels in each group. Cell 1 of the first cell group uses the first group of channels, Cell 2 of the first cell group uses the second group of channels, and so on.After proper arrangement, channel groups of cells with the same number in different cell groups can be reused.Although these cell base stations useRadio frequencySame, but because they are far away from each otherScope of actionLimited, they will not interfere with each other.In this way, a group of frequencies can be reused for 6 times. Originally, 300 channels can only allow 300 users to talk at the same time, but 1800 users can talk at the same time.
wirelessCellular networkImprovingwireless networkOfCoverageAspects play a key role.In broadband wireless MANReticular structureTo achieve low-cost and efficient coverage in a large area.Mesh structure has many advantages, such as providing effectiveCircuitous routeTo ensure smooth communication;With special line orDaisy chainCompared with, it is more resilient and reliable, and the network has the ability of self configuration, self-organization and self-healing.
Tropos, Mesh Network and BelAir Network were the first companies to enter this market. In addition, Nortel Networks did not want to lag behind.Internet andFTTH（FTTH）It's all cellularapplication area 。
For a long time,wireless networkBelieving in the central control mode also brings potential risks, such as transmission bottlenecks, legacy old systems orSingle point of failureEtc.However, as another technology of wireless switching, wireless cellular network is rising.Grid organized bytopological structure , from switch toAccess point, cellular networks can allocate intelligence.
Cellular network allows nodes or access points to communicate with other nodes without routing to the central switching point, thus eliminating centralized failures and providing self recovery andSelf organizationFunction of.Although traffic decisions are made locally, the system can be managed globally.
Wireless expansion
The wireless local cellular network is based on802.11a/B/g standards, but they can be extended to any RF technology, such as UltraWideband or 802.15.4 Zigbee.Because network intelligence is retained at each access point, there is no need for centralized switches - only intelligent access points andNetwork processor, exchange capability and system software.
Cellular network
Network onHoneycomb structureWhen connecting to each other in, first of all, the node's self discovery function must determine whether they serve as the access point of the wireless device or as theinformation contentOfbackbone networkOr both.
Secondly, a single node uses the discovery query/response protocol to locate their neighbors.these ones hereNetwork ProtocolIt must be concise, so it cannot increase the burden of information traffic, that is, they cannot exceed 1% to 2% of the available bandwidth.
Once a node recognizes another node, they calculate the path information, such as the strength of the received signalthroughput, error rate and legacy old systems.This information must be exchanged between nodes, but it cannot occupy too much bandwidth.Based on this information, each node can choose the best path to its neighbor, so thatService qualityAchieve the best.
Network Discoveryandpath choice The process ofRecalculateBest path.Because if a node is disconnected from the network during maintenance, rescheduling, or failure, neighboring nodes can quickly reconfigure their information lists and recalculate paths to maintain information flow when the network changes.This self-healing feature or error correction capability is the combination of cellular structure andHubThe difference between radiation networks.
Node Discovery
Each node isSelf managementAs part of an organized network, it can serve as a single entity fromCenter pointManaged and configured.useSNMP protocol，system administratorYou can set up and monitor individual elements, nodes, domains, or the entire network.The discovery protocol simplifies the task of finding and locating nodes and displaying them on the management screen.
Because of honeycombNetwork dependencyIn order to manage, control and discover information, they must ensure the security of their own traffic and user traffic.In band information is transmitted through encrypted tunnels to prevent eavesdropping or similar attacks.Standards basedSecurity technology, such as802.1xandAdvanced Encryption Standardetc.Encryption technology, ensure that only authorizedwireless networkDevices and nodes can be connected and correctly encrypted.
In the enterprise market, cellular architecture enables IT departments toWireless coverageIt extends to areas without cabling infrastructure.In this case, the cellular access pointwireless networkAccess point consolidation to extendWi-Fi, covering areas that cannot be accessed by cable.It should be noted that honeycombNetwork access pointThe increase of will increase the potential of the network.stayeight hundred and two point one oneEnvironment, whendata packetstayUser equipmentandWired networkEach wireless hop will increase the delay of 1ms~2ms during transmission between.
Therefore, when designing a cellular network, it is necessary to carefully consider the size of the cellular network and the type of application software used.Another concern is that cellular networks are privately owned.However, we are beginning to see that the standardization efforts are constantly being implemented, because some companies are based on the existingeight hundred and two point one oneDevelop the system technically.In fact, the IEEEeight hundred and two point one oneAt the working group meeting, a research group was established to establish an industry recognized standard for cellular network development.This is a significant step forward, as the use of cellular networks will evolve with the formation of standards.By expandingwireless networkBeyond the existing physical boundaries, the cellular technology will beeight hundred and two point one onewirelessNetwork systemProvide a good supplement.
The cellular concept includes several important parts, which is the basis of the development of mobile communication.
1. Frequency reuse.Limited frequency resources can be reused within a certain range.
twoCell division。When the capacity is insufficient, the range of cells can be reduced, more cells can be divided, and the efficiency of frequency utilization can be further improved.[1]
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The concept of honeycomb has solvedmobile communicationThe problem of limited medium frequency resources has directly led to the great development of mobile communications since the 1980s.However, the concept of honeycomb has its limitations.The main problem is that cells cannot be split without limitation, which leads to the inability to further improve the system capacity, which hindersmobile communicationFurther development.[1]
4G/5G cellularMobile networkIncreasingly popular,Analysis and predictionCellular mobilitynetwork user More and more attention has been paid to the data usage of.Cellular mobility at presentnetwork data In terms of consumption forecast, statistics and depth are mainly usedlearning methodTo make predictions, a lot of statistics are neededCommunication behaviorThe data usage of cellular mobile network varies greatly, and the statistics can only getaverage valueAnd trend. If the cellular mobile network data usage varies greatly in the same tariff scheme, the statistical and deep learning methods will probably get a larger cellular mobile network data usageEstimation error。[2]
