Despite the increase in complexity of wireless standards and devices, cellular technologies maintain a set of common principles that form the basis behind the design of cellular systems.
Radio fundamentals for cellular networks: Cellular networks enable devices such as smartphones and Internet of things (IoT) devices to communicate wirelessly. Cellular technologies have advanced from first generation (1G) analog technologies to advanced high-performance fourth generation (4G) and fifth generation (5G) systems in just about four decades.
Throughout the development of each wireless generation, these cellular networks have shared a number of common core attributes. Many of the protocol-based communications exchanges between the device and the base station follow a similar philosophy of identifying a potential cell, registering and authenticating with the core network and support for mobility through handover signaling. These principles are highly likely to be incorporated into 6G systems, whatever that standard turns out to be in the future. Certainly, the implementation of these underlying principles will vary from one standard to another and sometimes even within revisions of a given standard.
The Basics
Though the exact network architecture differs from one generation to another, a typical cellular network consists of a radio access network (RAN), a core network (CN) and a services network. The RAN contains base stations (BS) that communicate with the wireless devices using radio frequency (RF) signals, and it is this interface between the base station and the devices. The RAN allocates radio resources to the devices to make wireless communications a reality. The CN performs functions such as user authentication, service authorization, security activation, IP address allocation and setup of suitable links to facilitate the transfer of user traffic such as voice and video. The services network includes operator-specific servers and IP multimedia subsystem (IMS) to offer a variety of services to the wireless subscriber, including voice calls, text messages (SMS) and video calls.
Transmitters
The first common principle of cellular networks is the use of many lower power (100 W or less), smaller transmitters with narrower coverage areas instead of a single, powerful transmitter with a wider coverage area. These transmitters are housed on base stations, better known as cellular towers. Base stations also house receivers and additional control units.
Cells
Coverage areas are divided into cells, each served by its own antenna (transmitter). A frequency band is allocated to the transmitter/receiver depending on the network carrier. Cells are arranged so that antennas in a coverage area are in a hexagonal pattern. This is because it requires fewer cells to represent a hexagon compared to triangle or square – meaning network carriers can cover a wider area with less base stations. Another advantage of hexagonal cellular system is that frequency reuse is possible using this shape.
Frequency Reuse
The second common core design principle of cellular networks is frequency reuse. Frequency reuse is the process of using the same radio frequencies on base stations and other radio transmitter sites within a geographic area. These sites are separated by a sufficient distance to cause minimal interference with each other. By using geographically small, low-power cells, frequencies can be reused by non-adjacent cells.
The reason for frequency reuse is the limited number of carrier allocated frequencies set by the regulator bodies.
Cell Splitting
Cell splitting is the process of subdividing a congested cell into smaller cells such that each smaller cell has its own base station. These smaller cells feature antennas with reduced height and transmitter power. The two smaller cells increase the capacity of a cellular network since the number of times channels are reused increases.
In a popular cellular network configuration, one base station controls three geographic regions called sectors (or cells), where each sector covers 120° region. Three sectors together provide 3 × 120° = 360° coverage around the base station.
Cellular Handover
As a mobile device moves around in a given area, it crosses cell boundaries. Handover is a process where the dedicated radio connection between the device and the radio access network is switched from one cell to another. Cellular handover ensures that the device has a dedicated radio connection with the best possible communications link. In addition, handover may be used to balance the load among serving base stations and among carrier frequencies available in a cell or sector.
Handover takes place when the system perceives the current cell signal strength system to be weaker than a cell the user is approaching. Different cellular generation architecture uses different terminology for the device which detects the signal strength and providing the handoff capability. Cell handover is under the central control of a mobile telephone switching office (MTSO), which is also known as mobile switching office (MSO) or the mobile switching center (MSC). When the call is handed off to the second cell, the user should not be aware of the handoff and hear nothing.
Conclusion
Despite the increase in complexity of wireless standards and devices, cellular technologies maintain a set of common principles that form the basis behind the design of cellular systems. Read a more in-depth analysis of these common radio fundamentals for cellular networks.
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