Cellular networks or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called “cells”, each served by at least one fixed-location transceiver, but more normally, three cell sites or base transceiver stations.
It is named because of the hexagonal shape of the signal coverage of each communication base station that constitutes the network coverage, thus making the whole network resemble a honeycomb.
Composition of cellular networks
The cellular network consists of three main parts, mobile station, base station subsystem, and network subsystem.
The mobile station is our network terminal equipment, such as cell phones or some cellular industrial control equipment. The base station subsystem includes the mobile base stations (large towers), wireless transceiver equipment, private networks (usually fiber optic), numerous digital devices, etc. that we see every day. We can consider the base station subsystem as a converter between the wireless network and the wired network.
Reasons for cellular networks
The reason for the widespread adoption of cellular networks stems from the mathematical conclusion that the number of circles used to cover a plane with circles of the same radius is minimal when the center of the circle is at the center of each hexagon of a square hexagonal grid, i.e., when the center of the circle is at the grid point of a square triangular grid.
Although the maximum area of the graph can be covered with a minimum number of nodes is still an open problem to be solved even if the nodes are required to be on a lattice with translation properties like a lattice, it is often reasonable to use circles to express the practical requirements in communication, so for the sake of saving equipment construction cost, the ortho-triangular grid or also called simple hexagonal grid is the best choice.
The network thus formed is covered together and shaped very much like a honeycomb, hence the name cellular network.
Cellular Network Components
Cellular networks are composed of three main components: mobile stations, base station subsystems, and network subsystems.
Mobile stations are network terminal devices, such as cell phones or some cellular industrial control devices.
The base station subsystem includes mobile base stations (large towers), wireless transceiver equipment, private networks (usually fiber optic), wireless digital equipment, and so on.
The base station subsystem can be seen as a converter between wireless and wired networks.
Cellular and Frequency Multiplexing
Cellular:
A large area divided into multiple small cells, using multiple low-power transmitters instead of one high-power transmitter. A square hexagon is generally used to describe the cellular shape.
Frequency multiplexing:
Each cell uses one set of channels. If two cells are far enough apart, the same set of channels can be used. Cluster (cluster):
A group of N cells that uses the entire frequency resource frequency reuse factor (reuse factor):1/N For a hexagonal cellular shape, N=i^2+i*j+j^2, I >=1,j>=1, j≥0 when i>1 or I≥0 when j>1.Thus,N=3,4,7,9,12…
Geometric representation of honeycomb
The honeycomb is usually represented using a regular hexagon. Why is it a square hexagon instead of a circle? Among the polygons equidistant from the vertex to the geometric center, the three possible geometric shapes that can cover a region completely (without overlap) are square, equilateral triangle and regular hexagon. Of the square, equilateral triangle, and square hexagon, the square hexagon has the largest area.
Honeycomb coordinate system
Use (i,j) to represent the coordinates of a certain honeycomb. For example, the coordinates of cellular A are (2,1)
Cellular channel assignment
FDMA system:
Uses the signal fading principle. The key point is to divide the spectrum into several channels (user channel carriers), which can be multiplexed when the distance is far enough.
Static channel allocation:
Each cellular pre-assigned a fixed set of channels, simple to implement.
Dynamic channel assignment:
The base station dynamically assigns a channel from the MSC, and the cellular can use all the channels, which reduces the blocking probability and is complex to implement, requiring real-time traffic detection and coordination among base stations.
Network Types
The common types of cellular networks are GSM networks (called pcs-1900 in some countries), CDMA networks, 3G networks, FDMA, TDMA, PDC, TACS, AMPS, etc.
Distributed cellular network
A distributed cellular network (100) provides wireless communication with multiple mobile stations (102). A plurality of base station transceiver network components (104) is configured to communicate with a plurality of mobile stations (102) over a wireless medium, where each base station transceiver includes a network interface suitable for coupling to the network (110).
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 to load-balance the volume of communication services between the base station transceiver (104), the base station controller (106), and the mobile switching center (108) for efficiency.
A distributed cellular communication system comprising a network; a public switched telephone network (PSTN) coupled to the network; a plurality of transceivers coupled to the network, the plurality of transceivers being geographically separated from each other and each configured to communicate with a mobile station in an associated cell over a wireless medium;
At least one data processing system coupled to the network, the at least one data processing system is configured to execute a computer program comprising software function blocks adapted to enable a plurality of transceivers to pass data between mobile stations and between a mobile station and a PSTN, the software function blocks comprising:
Mobility management (MM) function block implementing MM functions;
A visitor location registration (VLR) function block implementing VLR functions;
A CM function for communication management (CM) function block;
A plurality of radio resource (RR) function blocks implementing RR function, said RR function comprising switching communication between a plurality of transceivers while the mobile station is moving from one cell to another, thereby maintaining communication between the mobile station and the network.
Cellular mobile telephony
Cellular mobile telephony refers to a network structure in which the service area is divided into a number of cells adjacent to each other, and a base station is established in each cell. Because each cell is hexagonal, and adjacent to each other, from the overall view, the shape is similar to a honeycomb, so people call it a cellular network. A number of cellular cells covering the entire service area of large and medium-capacity cell phone systems is called a cellular cell phone system, referred to as a cellular cell phone.
The biggest advantage of a cellular cell phone is that the frequency can be reused. As you may know, when we use cell phone handsets for communication, each person has to occupy a channel, which means that the system has to come up with a channel for you to use. When more people talk at the same time, the limited channel may not be enough, so there will be a communication blockage phenomenon.
With cellular architecture, the same set of frequencies can be reused in a number of cells separated by a certain distance, thus saving frequency resources. For example, we divide a city into 72 cells, and every 12 cells form a cell cluster. Let them use 300 channels together.
Then, we can divide 300 channels into 12 channel groups, each group of 25 channels, the first cell group of cell 1 uses the first group of channels, the first cell group of cell 2 uses the second group of channels, and so on. With proper arrangement, the channel groups of the same numbered cells in different cell groups are reusable.
Although the radio frequencies used by these cell base stations are the same, they do not cause interference with each other because they are far away from each other and the radio wave action range is limited. In this way, a group of frequencies can be reused 6 times, the original 300 channels can only be used for 300 users to talk at the same time, but can be used for 1800 users to talk at the same time.
Cellular cell phone system mainly consists of mobile stations (car phones, cell phones, etc.), wireless base stations, and cell phone exchange centers. Each cell base station is connected to the cell phone exchange to form a cellular cell phone network.
The cell phone network is also connected to the city public telephone network as well as the domestic and international long-distance telephone network, so that cell phone users can make calls not only to cell phone users within the network but also to mobile users and fixed users in a wider area.
Reliability
Wireless cellular networks play a key role in improving the coverage of wireless networks. In broadband wireless metropolitan networks, mesh structure can be used to achieve large area coverage with low cost and high efficiency.
Mesh structure has many advantages, such as providing effective detour routes when the network fails to ensure uninterrupted communication; more resilient and reliable compared with private lines or daisy chains, and the network is self-configuring, self-organizing, and self-healing.
The first to enter this market were Tropos, Mesh-Network, and BelAir Networks, in addition to NortelNetworks, which is not far behind. The Internet and FTTH (Fiber to the Home) are both application areas for cellular networks.
Wireless networks have long believed in a centralized control model, which also brings potential risks such as transmission bottlenecks, legacy old systems, or single points of failure. However, wireless cellular networks are emerging day by day as another technology for wireless switching. By organizing into a grid topology, cellular networks are able to distribute intelligence from the switch to the access point.
The development of this topology is in line with the evolution of the architecture of the computer industry.
First, the computing environment was a stand-alone host system, followed by client/server, and then peer-to-peer networks. The architecture of the network will undoubtedly evolve into a distributed, dynamic wireless architecture.
Cellular networks allow nodes or access points to communicate with other nodes without routing to a central switching point, thus eliminating centralized failures and providing self-restoration and self-organization. While traffic decisions are implemented locally, the system can be managed globally.
Wireless Scaling
Today’s wireless local area cellular networks use standards based on 802.11a/b/g, but they can scale to any RF technology, such as UltraWideband or 802.15.4 Zigbee. because network intelligence is retained at each access point, no centralized switch is required – only intelligent access points and network processors, switching capabilities, and system software are required.
When networks are interconnected in cellular architecture, first, the self-discovery functions of the nodes must determine whether they are to serve as access points for wireless devices, as a backbone for the amount of information coming from another node, or both.
Second, single nodes use discovery query/response protocols to locate their neighbors. These network protocols must be concise, so they cannot burden the information traffic, i.e., they cannot exceed 1% to 2% of the available bandwidth.
Once a node identifies another node, they compute path information, such as the strength of the received signal, throughput, error rate, and legacy old systems. This information must be exchanged between nodes, but without taking up too much bandwidth.
Based on this information, each node is able to select the best path to its neighbors so that the quality of service is optimal at each moment.
The network discovery and path selection process runs in the background so that each node keeps a list of existing neighbors and continuously recalculates the best path. Because in case of maintenance, rescheduling, or failure, if a node is disconnected from the network, nodes close to it can quickly reconfigure their information lists and recalculate paths to maintain information traffic when the network changes. This self-restoring feature or error correction capability is what distinguishes cellular structures from hub-and-spoke radial networks.
Node Discovery
Each node is self-managed and, as part of an organized network, it can be managed and configured as a single entity from a central point. Using the SNMP protocol, system administrators 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 display.
Because cellular networks rely on management, control, and discovery information, they must secure their own traffic and user traffic. In-band information is transmitted through encrypted tunnels, which protect against eavesdropping or similar attacks. Standards-based security technologies, such as encryption techniques like 802.1x and advanced encryption standards, ensure that only authorized wireless network devices and nodes can connect and be properly encrypted.
Cellular networks are an excellent wireless technology when cabling is difficult or expensive. The most common cellular network architecture in the commercial market consists of routed packets from a wireless link to a central wired network.
This architecture is optimal for Wireless Internet Providers (WISPs) who wish to create wireless broadband cellular networks, such as 802.11 hotspots to cover a wide geographic area. By utilizing 802.11, a band that does not require government licensing, cellular technologies can provide high bandwidth at a much lower cost than existing cellular technologies.
This result will lead to a future where the cost of cellular access to the Internet remains at a generally acceptable price level, leading to a whole new market for wireless devices and services, such as video delivery on handheld media players.
In the enterprise market, the cellular architecture allows IT departments to extend wireless coverage to areas without wiring infrastructure. In this situation, cellular access points are integrated with existing wireless network access points to extend Wi-Fi to cover areas that are not accessible via wired access. It is important to note that the addition of cellular network access points increases the potential of the network. In an 802.11 environment, each wireless hop will add 1 ms to 2 ms of latency as packets are passed between user devices and the wired network.
Therefore, when designing a cellular network, the size of the cellular network and the type of application software used need to be carefully considered. Another concern is that cellular networks are privately owned.
However, we are starting to see efforts on standardization being put into practice as some companies are developing systems based on existing 802.11 technology. In fact, at the IEEE 802.11 Working Group meeting held January 11-16, a study group was formed to establish an industry-accepted standard for cellular network development.
This is a major step forward, as the use of cellular networks will evolve as standards are formed. By expanding the coverage area of wireless networks beyond existing physical boundaries, cellular technology will provide an excellent complement to existing 802.11 wireless network systems.
Cellular Network Advantages
Since the invention of the cellular concept at Bell Labs in the 1970s, the cellular technology has been the foundation of mobile communications. Sometimes, people just refer to mobile communications as cellular communications.
The cellular concept includes several important components that are the basis for the development of mobile communications.
Frequency multiplexing
A limited frequency resource can be reused within a certain range.
Cell splitting
When there is not enough capacity, the cellular range can be reduced and more cells can be divided to further improve the efficiency of frequency utilization.
Limitations
The cellular concept solved the problem of limited frequency resources in mobile communications, which directly led to the great development of mobile communications after the 1980s. But the cellular concept also has limitations.
The main problem faced is that the cells cannot be split indefinitely, resulting in a system capacity that cannot be further increased, which hinders the further development of mobile communications.
You may also be interested in the below articles.
