# Cellular Network
###### tags: `Wireless Communications`
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A cellular network is a radio network distributed over land through cells where each cell includes a fixed location transceiver known as base station. These cells together provide radio coverage over larger geographical areas. User equipment (UE), such as mobile phones, is therefore able to communicate even if the equipment is moving through cells during transmission.

## Structure of GSM networks

GSM standards divide networks into four distinct parts:
* Mobile Station
* Base Station Subsystem (BSS)
* Network and Switching Subsystem (NSS)
* Operations Support System (OSS)

### Mobile Station
The Mobile Station is essentially the access point someone uses to connect to the network. It’s a device (such as an alarm system) with a Subscriber Identity Module (SIM). The SIM associates the device with an individual subscriber, which allows the device to connect to the nearest Base Station Subsystem.

### Base Station Subsystem (BSS)
The BSS contains Base Transceiver Stations(BTS) and a Base Station Controller(BSC).
* The BTSs include components like receivers and antenna, which allows connected devices to send and receive signals.
* The BSC allows the Base Transceiver Stations to relay signals through the network, via the Network and Switching Subsystem.

### Network and Switching Subsystem (NSS)
The Network and Switching Subsystem is a term for the major components of a 2G core network. The NSS originally helped facilitate connection-oriented voice calls with the Home Location Register (HLR), Authentication Center (AuC), Message Service Center (MSC), and Visitor Location Register (VLR).

**Mobile Switching Centre (MSC)**
* It is a main part of the GSM and CDMA network system which acts as a control center of a Network Switching Subsystem (NSS). It connects calls between subscribers by switching the digital voice packets between network paths

**The home location registers (HLR)**
* Store permanent data about subscriber like profile, location info, status.
* Subscription info of registered user PS stored.

**The Visitor Location Register (VLR)**
* Stores temporary info integrated with MSC & it work in co-ordination with HLR.

**The Authentication Centre (AUC)**
* Protected database.
* Stores a copy of secret key.
* Used for authentication.
* Protects from different type of fraud.

**The Equipment Identity Register (EIR)**
* Db that contain list of all valid mobile on network.
* IMEI used to indentify each MS.
* IMEI is marked as invalid in case of stoles.

**Operation Maintenance Center (OMC)**
* This dept maintain all telecommunications hardware and network operations with a particular market.
* It also Manage all charging and billing procedures.
* It also Manage all mobile equipment in the system.
### Operations Support System (OSS)
The Operations Support System is a conglomeration of processes, data, applications, and tech that allows providers to manage their network. Carriers can use their OSS to:

1. Configure network elements
2. Manage and configure the services they offer
3. Handling system errors and managing the system’s state
4. Monitor performance based on quality of service and quality of experience KPIs

## What is GSM

Every GSM radio channel is 200 kHz wide and is additionally divided into frames of 8-time slots. The global system for mobile communication (GSM) was first known as Groupe Special Mobile, which is the reason for the acronym. The GSM system comprises mobile stations, base stations, and intertwining switching systems.

The GSM program enables 8 to 16 audio users to share every radio channel, and every radio transmission location may have multiple radio channels. Because of its simplicity, affordability, and accessibility, GSM is presently the most commonly used network technology in the Internet of Things (IoT)
Opens a new window applications.

## How Does GSM Work?
The Mobile Station International Subscriber Directory Number is the complete phone number for a particular SIM, including all prefixes. Lastly, MSRN is an abbreviation for Mobile Subscriber Roaming Number, and it is a short-term cellphone number given to a cellular station if it is not on the local network (roaming). Therefore, any calls or communication systems can be tied to it.

Numerous GSM network carriers have roaming agreements with foreign corporations, allowing people to use their phones when traveling internationally. SIM cards with household network access designs can be changed to those with a metered local connection, lowering roaming costs while maintaining service. The global system for mobile communication organizes the geographical area into hexagonal cells, the size of which is controlled by the transmitter’s power and the number of end-users. The middle of the cell has a base station consisting of a transceiver (which combines the transmitter and reception) and an antenna.

Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) are the two critical approaches used by GSM:

* FDMA is the technique of subdividing frequency bands into many bands, each of which is allocated to specific users. In GSM, FDMA separates the 25MHz bandwidth into 124 carrier frequencies by 200 kHz. Every base station has one or more carrier frequencies assigned to it.
* Time Division Multiple Access (TDMA) is the practice of allocating the same frequency to multiple users by separating the bandwidths into various time slots. Every subscriber is assigned a timeslot, allowing different stations to split the same transmission area.

## Applications of GSM
### Sending and receiving short messages
The ability to send and receive text messages to and from mobile phones is known as the Short Message Service (SMS).

SMS delivers short text messages of up to 140 octets over the GSM platform’s control system air interface. The Short Message Service Center (SMSC) stores and transmits short messages from mobile users to their intended recipients. One may use it to send and receive brief messages, saving time due to the rapid transmission of communications. Furthermore, there is no need to go online; the mobile device has a signal, and it can send and receive short messages.

### GSM and data security
This same system can instruct users via SMS from a particular phone number on how to change the condition of the home appliance based on the person’s needs and preferences. The client is configured via SIM, allowing the system to observe Mobile subscribers on the database. GSM also includes features for signal encryption.

The second element of GSM security is security alert, which would be accomplished in such a way that upon identification of an invasion, the system would allow for the automatic creation of SMS, thereby notifying the user of a potential threat.

### GSM for mobile system handover
The procedure of handover in any mobile system is critical. It is a necessary process, so handover could lead to call loss if done improperly. Undelivered calls could be especially aggravating to subscribers, and as the percentage of undelivered calls grows, so does user dissatisfaction, so they’re more likely to switch to another network.

As a result, GSM handover was given special consideration when creating the standard. Whenever a cellular customer switches cells, the radio signal shifts from past to new. Even though the GSM network is complicated, in contrast to other systems, the flexibility of the GSM procedure provides better performance to subscribers. In a GSM network, there are four basic types of handoffs:
* Intra-cell handover: This type of handover is used to improve data traffic in the cell or to strengthen connection performance by modifying the carrier signal.
* Inter-cell handover: Additionally, it is known as intra-BSC handover. In this instance, the mobile changes cells while remaining in the BSC. Here, the BSC is in control of the transfer procedure.
* Inter-BSC handover: It’s also known as an intra-MSC handover. Because BSC can only handle a restricted number of cells, we may have to move a phone from one BSC to the other. Here, the handover is managed by the MSC.
* Inter-MSC handoff: This occurs when a mobile device moves from one MSC area to the next. MSC is spread over a wide area.

### GSM in medical services
If the patient is severely injured or sick, but all they have access to is a phone, trying to connect with the closest hospital would be simple. If the patient is connected to the doctor, they can receive initial care while on the way to the healthcare facility. In the event of a disease, doctors can review patient history and prepare for additional tests while providing proper care.

Whenever a patient, attendant, or hospital member of staff becomes stranded on hospital grounds due to a power outage, GSM-fixed cellular terminals allow the individual to connect very fast with the closest emergency responders. An individual in that circumstance can request help using the GSM SIM in the installed Fixed Cellular Terminal (FCT). Telemedicine services are responsible for the entire situation. One could use the telemedicine system in any of the three ways listed below.

* Utilizing video conferencing, patients seated in one location can directly communicate with physicians, thus continuing the healing process.
* Leveraging health monitoring sensors that continuously update information about the patient’s health and guide hospitals and doctors to continue treatment.
* Conveying the obtained health records and transmitting obtained data for consultation and processing.

## GPRS(General Packet Radio Service)
It is a mobile data service/technology available to GSM mobile phone users. It is often described as "2.5G", which means that this technology is between the second generation (2G) and third generation (3G) mobile communication technology. It utilizes unused TDMA channels in the GSM network to provide medium-speed data transmission services.

### GPRS Mobile Terminal
GPRS mobile terminals (Mobile Station, MS) are divided into three categories.

1. Type A terminal: MS can transmit GSM voice and GPRS data at the same time.
2. Type B terminal: MS can register in the network by means of GSM and GPRS at the same time. MS can automatically switch to use GPRS service or GSM service, but it cannot transmit voice and data at the same time. Therefore, when the MS is transmitting data, if it receives an incoming call, it will suspend the transmission of data, and continue to transmit data after answering the call.
3. Type C terminal: the function is to only transmit GPRS data. Such terminals are for example PCMCIA GPRS network cards for notebook computers.

#### Speed
When GPRS uses all 8 time slots (Timeslots) for communication at the same time, the maximum transmission rate can reach 171.2 kbps (theoretical value), which is three times that of today's Fixed Telecommunications Networks (Fixed Telecommunications Networks) and ten times that of GSM circuit switching data services. times.

#### Connect now
The performance of GPRS fast connection, so that consumers do not need to waste time waiting for the Internet. It also does not need to dial up the Internet through a modem, allowing users to enjoy the convenience of "Always Connected". "Instant Connect" is why GPRS (and SMS) are superior compared to circuit-switched data services (dial-in modems).

#### Support Internet application software
GPRS supports Internet application software, allowing users to implement online chatting, browsing the Internet, sending emails and files, remote control, home appliance remote control and other applications through the mobile communication network.

### Features offered to network operators
#### Packet switching
Through GPRS, the information to be transmitted is divided into associated individual packets, and these packets are reassembled at the receiving end to restore the original information. Packet switching is like a jigsaw puzzle. The image (Image) is divided into several pieces by the factory and packed in a bag, and then delivered to the user's home. The user assembles the puzzles in the bag piece by piece, and finally restores the original appearance of the image. All the tiles (packets) are related and fit together, but they are transmitted and assembled differently. Internet itself is the most typical and famous packet data network.

#### Save bandwidth resources
Under the same bandwidth and the same communication unit (Cell), a large number of users can share limited radio resources. The maximum number of users that can be provided is determined by the type of application and the size of the data. Since GPRS saves bandwidth resources, there is no need to establish an additional peak spare capacity (Idle Capacity), so GPRS allows network operators to use their network resources more effectively and flexibly, and also increases customer utilization and income. In order to simultaneously improve the peak capacity of the GSM network, GPRS must:

1. Support "Virtual connectivity" to effectively allocate scarce bandwidth resources.
2. Use GPRS instead of circuit switching data transmission, and use GPRS/SMS interface specification to reduce the load of SMS.

#### Mobile Internet (Mobile INTERNET)
GPRS is the first technology to connect the mobile communication network with the Internet, any application on the Internet, such as: file transfer (File Transfer Protocol; FTP), browsing (Web Browsing), chat (Chat), Email, Telnet, video games, etc.

Internet users increase year by year, and applications go deep into all walks of life, and GPRS network can be regarded as a sub-network of Internet, and the development of GPRS follows the development of Internet. Every GPRS mobile phone has its own website, so every GPRS mobile phone is a "mobile website" (Mobile Host), which cannot be provided by PC at present.

### Limitations of GPRS
#### limited communication capacity
Although GPRS allows several users to share its bandwidth resources at the same time, the communication unit capacity of GPRS is still limited.

When different requirements arise, such as simultaneous transmission of voice and GPRS data, bandwidth resources are even more stretched. Therefore, resources must be reserved for GPRS channels, and the dynamic channel management function of GPRS is designed for reserving GPRS channels, but at peak times, it is transmitted in GPRS channels by sending SMS instead of GPRS packets to reduce total transfer volume. Therefore, the selection of the packet type (Packet Type) is the main task of GPRS dynamic channel management, and GPRS has to rely on SMS, which makes SMS the most important complementary "communication carrier (Bearer)" of GPRS.

Because SMS provides store and forwarding (Store and Forward Service) services, GPRS will first use text messages to inform users that there are letters to receive for emails sent during peak hours, but at this time because users are using GPRS mobile phones to talk on the phone, So the email will be temporarily stored in the SMS center.

After the user finishes speaking, the GPRS network leaves the peak hour, and the user then downloads (forwards from) the letter using the GPRS data packet to the SMS center, thus avoiding the "big traffic jam" on the network.

#### slower than theoretical
To achieve the theoretical maximum transmission rate of GPRS of 172.2 kbps, only one user must be allowed to occupy all eight time slots, and any Error Protection mechanism cannot be used.

Obviously, no telecom company will do this. Moreover, at the beginning of the system modification, only 1 to 3 time slots are supported, and the shared bandwidth is limited, so the number of GPRS users must be limited. Therefore, the actual maximum transmission rate must consider the conditions of the network and terminal stations, and this value must be smaller than the maximum transmission rate of the fixed network. It is impossible for the transmission rate of GPRS to reach 172.2 kbps.

This can only be achieved when EDGE (Enhanced Data Rates For GSM Evolution)" or "Universal Mobile Telephone System (Universal Mobile Telephone System)" (3GSM or ITM2000) comes out.

#### GPRS Telephone Billing Method Still Controversial
The difference between GPRS calls and general GSM calls is distinguished by "Message Type (MT: Message Type)". However, the current mobile phone manufacturers have not yet decided whether to build the GPRS information category into the mobile phone, which will result in the problem that there is no standard to follow in the calculation of GPRS telephone charges.

On the contrary, if the mobile phone has built-in GPRS information, there is still a problem in the calculation of the telephone bill, because no user is willing to pay for spam, and the Internet operator who provides spam may not need to pay. Such uncertainty and contradiction will seriously hinder the promotion of GPRS. In particular, many commercial applications that are going to use GPRS to transmit data will be forced to suspend.

Since it is so difficult to build GPRS information in mobile phones, another alternative has been proposed, which is to use "Gateway GPRS Support Node (GGSN; Gateway GPRS Support Node)", which can solve billing and receive spam However, this still cannot accurately distinguish between GPRS and GSM telephone charges, which also requires that the mobile phone has built-in GPRS information.

However, in order to consider the production cost, major mobile phone manufacturers may not launch mobile phones with built-in GPRS information immediately, and network operators are not willing to install GGSN one-sidedly. In this way, wouldn't users be double exploited.

Therefore, whether the GPRS mobile phone has built-in GPRS information, and whether the GSM network is equipped with a network gateway to support GPRS nodes will be critical to the commercial success of GPRS.

#### transmission delay
Because wireless communication inherently has the problem of communication dead ends, it is difficult to overcome, so GPRS adopts a complex debugging and retransmission (Data Integrity And Retransmission) mechanism, but this will cause transmission delay. Therefore, for applications that require high-quality data transmission, such as: image transmission...etc., the "High Speed Circuit Switched Data" technology (HSCSD; High Speed Circuit Switched Data) must be used again. HSCSD is a simple circuit switching data call (Call), each user can use it to master four different channels at the same time, and because it is a point-to-point connection communication, the transmission delay can be reduced.

#### Store and forward not supporte
Although storage and forwarding are the core functions of SMS, SMS does not provide a storage mechanism for GPRS, so SMS cannot be integrated into GPRS yet, that is, GPRS must be equipped with SMS to provide SMS services.

## UMTS(Universal Mobile Telecommunications System)
UMTS or Universal Mobile Telecommunications Framework, is the 3G successor to the GSM family of measures counting GPRS and EDGE.

3G UMTS employments a completely diverse radio interface based around the utilize of Coordinate Grouping Spread Range as CDMA or Code Division Multiple Access. Although 3G UMTS employments a completely distinctive radio get to standard, the center arrange is the same as that utilized for GPRS and EDGE to carry partitioned circuit exchanged voice and bundle data.

### UMTS Applications
* Streaming / Download (Video, Audio)
* Videoconferences.
* Fast Internet / Intranet.
* Mobile E-Commerce (M-Commerce)
* Remote Login
* Background Class applications
* Multimedia-Messaging, E-Mail
* FTP Access
* Mobile Entertainment (Games)

### Advantages of UMTS
* UMTS could be a successor to 2G based GSM advances counting GPRS and EDGE . Gaining a 3rd title 3GSM since it could be a 3G relocation for GSM
* Support 2Mbit/s information rates.
* Higher Information rates at lower incremental costs.
* Benefits of programmed universal wandering also necessarily security and charging capacities, permitting administrators emigrate from 2G to 3G whereas holding numerous of their existing back-office frameworks
* Gives administrators the adaptability to present unused mixed media administrations to trade clients and buyers
* This not as it were gives client a valuable phone but moreover deciphers higher incomes for the administrator.

### Disadvantages of UMTS
* It is more expensive than GSM.
* Universal Mobile Telecommunication System has poor video experience.
* Universal Mobile Telecommunication System still not broadband.