Working principle behind 0G and 1G communication

 

Mobile generations are the improvement in cellular technology in different periods. In our before topic, we have seen the different types of internet connections among which one is the cellular connection. The cellular connection is the method of transfer of signals from one point to another via electromagnetic radiation (Wireless communication). These radiations are produced by the acceleration of the charged particles, which eliminates the need for a complex wired system. To know more about the types and properties of electromagnetic radiation, please visit the following article.

https://sciencetopic03.blogspot.com/2022/07/electromagnetic-spectrum-and-its-types.html

 Nowadays, every object comes with the feature of wireless technology; from Bluetooth headsets to VR gaming. These wireless technologies have major breakthroughs in mobile technologies via different generations. These breakthroughs in the generations were paved by the invention of the telegraph in 1843 by Samuel Morse in Washington DC. It was the first electrical instrument used for wireless communication. By using this system, radio waves are produced at a specific pattern using dots and dashes. These dots and dashes were then later converted manually into a readable format using Morse code. One of the best examples of this machine can be found in the ship Titanic where the distress message is been sent to another ship Carpathia when it hits an iceberg in North Atlantic in 1912.

Telegraph machine

Upgraded telephone

        But this method enabled only the transfer of messages and not any voice communication. Thus after some years, in 1876, Alexander Graham Bell invented the telephone for voice communication. But this was a wired system. This wired technology had taken over the shape of PSTN (Public Switched Telephone Network) through telephone exchanges (Switching center). These Networks were classified as PCO (Public Call Office), STD (Subscriber Trunk Dialling), and ISD (International Subscriber Dialling). The PCO is the form of local connectivity where it is forwarded only to a local area. Whereas STD happens in between states. The STD usually appears in the form of a regular trunk call, in which the operators would switch the call to the prescribed line. But later on, it is automatically switched via the STD code which is entered by the subscriber itself. The ISD is also the same as STD, but for International calls. There are different costs for each type of call. Thus by these networks, wired communications have taken the role. Later, radio technology was incorporated and the transformation from wired to wireless medium had gotten shape.

In this article, we will see the implementation of different mobile phone communication and the technology implemented in it, with a clear diagrammatic representation. The different generations of wireless technology are,

• Mobile radio telephone (0G)
• First Generation (1G)
• Second Generation (2G)
• Third Generation (3G)
• Fourth Generation (4G)
• Fifth Generation (5G)
• Sixth Generation (6G) (upcoming)

Since there are various technologies implemented in each generation, there will be a huge amount of content to be discussed. So we can see each of the generations in each of the posts. In this post, we can see about the 0G and the 1G communications.

Mobile radio telephone (0G) or pre- cellular (Frequency band: VHF and UHF frequency)

As the name suggests, it is the combination of the PSTN and the radio network. The technologies used in this generation are Push-to-talk, Mobile telephone Service, Improved mobile telephone Service, and Advanced Mobile Telephone System (AMTS). Each of the technologies in the pre-cellular model has improved voice communication. The Push-to-Talk system is the basic type, in which the voice is communicated by pressing a button on the device. The communication is basically done via a single large transmitter which also paves the way for communication with the PSTN network. This is basically a half duplex method in which only one user can talk at a time. At starting these devices are really big and were installed in cars and horses. But later on, its size was reduced and converted into a handheld device. One of the best examples of the handheld device that we still use now with push-to-talk technology is Walkie-Talkie.

Mobile radiotelephone

Half-Duplex vs Full-Duplex

        In MTS, the wireless data is generated directly by an antenna and transferred to an exchange system, which is manually switched to the respective connection. While in Improved Mobile telephone Service, the signal is transferred automatically and the half-duplex mode is transferred to the full-duplex. By using the full-duplex method, the voice transmitted over the channel can be done by both users at the same time. In AMTs, data is transferred at a higher frequency band leading to improved voice communications. The basic architecture of the Pre- cellular model (MTS), looks like a user, a base station a telephone operator, and an end user. By initiating a call, the telephone operator assigns a channel and a mobile number, and the call is transferred to the respective user.

The architecture of Mobile Telephone System

First Generation (1G) (Frequency band: 850MHz)

The first generation is the very first technology introduced after the pre-cellular model. This generation was established with a network of cellular towers instead of a single large transmitter. This network is constructed based on a specific shape. The shape that is chosen for the spread of the signal is a hexagon. The importance of this shape is that it can be able to cover a large area leaving no place without a signal in-between. You can observe the construction of cellular towers in a specific pattern in the below figure.

Cellular Network

The first Generation is only meant for voice communication. There is no data transfer other than voice. But the advantage of 1G is the compatibility and ease of use of the handset. The size of the cell phone is considerably reduced in 1G compared to the big radiotelephone, which you can observe from the figure below. This technology was founded by Japan in 1979. This system follows an analog system. The major technologies used in the 1G are AMPS (Advanced Mobile Phone Systems) and NMT (Nordic Mobile Telephone). These technologies basically consist of a mobile (our handset), a mobile tower (Base Station), a mobile telephone switching office (MTSO), and an end receiver, which either may be a PSTN or a wireless mobile, or both. The MTSO is the control unit for many base stations. Now let’s see the architecture of AMPS as it is one of the widely used technology.

Credit: By Redrum0486 - http://en.wikipedia.org/wiki/File:DynaTAC8000X.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6421950

Architecture of AMPS

When a user makes a call by dialing the number, it is forwarded to the nearest mobile tower using a separate control channel. This message is then forwarded to the Mobile Telephone Switching Office (MTSO) using a wired line. Now the MTSO looks for the receiver via the location update. Upon the location update, if the base station is within its covered area, it will transfer the signal to its base station. If not, then it will direct it to another MTSO, which has the corresponding Base station. Upon reception, the mobile tower locates the receiver and transmits the signal through the available voice channel (frequency channel) in the hexagonal area. In case the end receiver is a PSTN, the call request from the MTSO flows through the telephone exchange and reaches the telephone.

The architecture of Advanced Mobile Phone System (AMPS)

Bandwidth in 1G

 Bandwidth is the specified width of the frequency band that should be used for transferring a medium. Consider transferring a medium in the frequency range allotted from 3MHz-30 MHz. So the bandwidth of the frequency range will be 30MHz-3MHz=27MHz. The bandwidth is mainly considered for the amount of data that can be transferred in a time. If the bandwidth is high (more space), the quantity of the data transfer will be high, and if the bandwidth is low (less space), the quantity of data transfer will be low.

Bandwidth in a spectrum

The AMPS technology operates on the 850MHz band, which has a frequency range from (824MHz- 849MHz) and (869MHz-894MHz). These frequency ranges accompany a total of 832 (416+416) frequency channels. The reason for these two different frequency ranges is, to communicate the transmission in a full duplex system, which enables the simultaneous transmission and reception between the user and the tower. 1G communication uses the technique of a Full-duplex system called FDD (Frequency Division Duplex). By using this method, the available spectrum is divided for transmission and reception. The transmission of the signal (from the user to the tower) is called the Uplink and the reception of the signal (from the tower to the user) is called the Downlink. The remaining channels in between the two frequencies are used for spacing to avoid interlink between the uplink and the downlink frequency.

Frequency Division Duplex (FDD)

        In AMPS communication, the bandwidth of the transmission and the reception signal is 60 kHz, thereby each carrying 30 KHz. As there are 832 voice channels, 395 of 416 channels are used for transmission (uplink) and 395 of 416 channels are used for reception (reception). The remaining 21 channels in both uplink and downlink are used as control channels. The control channels are used for connecting and establishing a connection between the user and the station. Also, to avoid overlapping between the adjacent base stations in the network, these 395 voice channels are divided by the number of cells surrounding a particular cell. If there is a maximum of 7 cells adjacent to each other, then the voice channels will be divided as 395/7=56 channels per cell, which means only 56 users can talk at a time in that cell at maximum adjacent.  

Voice Channels in AMPS network

Multiple Access and Multiplexing techniques in 1G

Another main thing in wireless communication is the usage and transmission of the spectrum. As wireless communication can be passed only at a specific frequency, careful allotment of the frequency spectrum should be done, to maintain privacy and make it available for future use.

The usage of the spectrum is done via a few techniques called Frequency Slot Distribution and Multiple Access Techniques. In frequency slot distribution each mobile tower is allotted a specific set of frequencies and in the multiple access techniques, that set of frequencies is divided among several users without overlapping. As different frequency range is allotted to different mobile station, frequency reuse can also be done, which reserves the frequency slot for future use. The next one is the multiple access technique. The multiple access technique implemented in the 1G technology is Frequency Division Multiple Access (FDMA). In this method, each user is allotted a separate frequency band for the whole time; the user is transmitting the signal. When the user stops signaling, the frequency band is allotted to another user who wants to transmit the signal. As old phones use wired mediums, people's conversations were private. But as we move to wireless phones, we end up on the spectrum in which each frequency band is allotted to different users. In this technology, the frequency bands may mix which may make the users' conversation public. Thus to make the conversation private, guard bands are introduced in the spectrum to separate each frequency band. The disadvantage in the frequency division multiple access is, that a user cannot perform the action if he/she requires a higher bandwidth to transmit the signal. Also as the frequency slot is assigned to the user for the whole period, the spectrum becomes demandable, as the need for cell phone will get increases.

Frequency Division Multiple Access (FDMA)

Frequency Modulation (FM)

        The next part is the transmission of the spectrum, where technologies like multiplexing and demultiplexing are used. This method is mainly used to utilize the bandwidth of the channel efficiently. One of the important processes in this technology is the modulation technique. As humans can hear the frequency of sound waves from only 20Hz to 20kHZ, the wavelength of the sound waves will be very large. Thus to transfer this higher wavelength in wireless communication, the antenna size must be very larger. Thus to avoid it, modulation techniques are used. By using this technique, the antenna size is considerably reduced by converting the longer wavelength (original signal-baseband signal) into a shorter one, by combining the low-frequency signal into a high-frequency signal. The modulation technique used in the 1G system is Frequency Modulation (FM). We can find more about the modulation technique in another article. Once modulated, many such signals are combined and made into a composite signal and passed on to a single channel. This process in 1G is called Frequency Division Multiplexing (FDM). Guard bands are introduced in between each signal to avoid overlapping. One such example of this technique can be found in broadband systems (such as RF waves, Optical fiber cables) as many signals are meant to be transmitted in a single channel. Once the composite signal is transmitted and received at the receiver end, the process is carried out in a reverse way, with some extra filters, to extract the original baseband signal. This is the concept of 1G. We can continue our post on the 2G spectrum from the next article.

Frequency Division Multiplexer (FDM)