Cellular networks
Cellular networks provide wide-area wireless access to billions of phones and devices. Each generation, from 1G voice to 5G, has redesigned the radio and core networks.
Cells and base stations
A cellular network divides an area into cells, each served by a base station: an eNodeB in 4G or a gNodeB in 5G. Neighbouring cells use different frequencies or coordinated resources to limit interference, while distant cells reuse the same frequencies, allowing capacity to grow by using more, smaller cells in busy areas.
The generations
1G (1980s) was analogue voice. 2G (1990s, notably GSM) was digital and added text messaging. 3G (2000s) brought mobile data. 4G LTE (from about 2009) is an all-IP network with tens to hundreds of Mbit/s. 5G, launched commercially in 2019, offers higher speeds, lower latency, and support for vast numbers of devices, with standards developed by the 3GPP.
4G architecture
A 4G LTE network has a radio access network of base stations and an all-IP core called the Evolved Packet Core. Key elements include the Mobility Management Entity (MME), which handles signalling and mobility; the Home Subscriber Server (HSS), which stores subscriber information and keys; and serving and packet data network gateways, which carry user traffic to and from the internet.
SIMs and authentication
Each subscriber has a SIM, now often an embedded eSIM, holding an identity and a secret key shared with the home network. When a phone attaches, the network and the SIM perform mutual authentication using that key and derive encryption keys for the radio link, so the phone knows the network is genuine and the network knows the subscriber is.
Radio access
LTE and 5G use orthogonal frequency-division multiple access (OFDMA), splitting the channel into many narrow subcarriers and allocating blocks of subcarriers and time slots to different users every millisecond. Schedulers in base stations assign resources based on demand and channel quality, and devices use MIMO antennas to send multiple data streams at once.
5G
5G New Radio uses low bands for coverage, mid bands (around 3.5 GHz) for a balance of speed and range, and millimetre-wave bands (24 GHz and above) for very high capacity over short distances. Its service-based core uses software functions in the cloud. 5G targets enhanced mobile broadband, ultra-reliable low-latency communication for industrial control, and massive machine-type communication for IoT sensors.
Network slicing and the edge
5G allows network slicing: running several virtual networks with different guarantees over one physical network, such as a low-latency slice for factory robots alongside ordinary phone traffic. Multi-access edge computing places computing resources near base stations, so latency-sensitive applications like augmented reality or vehicle coordination avoid long trips to distant data centres.
Worked example
A commuter streams music while a train moves through a city. Her phone, attached via a 5G mid-band cell, is authenticated using keys from her eSIM. As signal quality from the current cell drops and a neighbouring cell's improves, the phone reports measurements and the network hands it over to the new cell within tens of milliseconds, while the core keeps the same IP address and data session, so the music never stops.
Key takeaways
Cellular networks divide areas into cells served by base stations, reusing frequencies at a distance and adding small cells for capacity. Generations moved from analogue 1G to digital GSM 2G, data-focused 3G, all-IP 4G LTE (about 2009), and 5G (2019), standardised by 3GPP. The 4G Evolved Packet Core includes the MME, HSS, and gateways. SIMs and eSIMs hold keys for mutual authentication and encryption. OFDMA schedules subcarriers among users; MIMO multiplies streams. 5G uses low, mid, and millimetre-wave bands, a cloud-based core, network slicing, and edge computing.
Flashcard
Area served by one base station
Check your understanding
Why do mobile operators install many small cells in busy city centres?