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Cellular Distributed Antenna System (DAS): Understanding the Technology and its Patent Landscape

Cellular Distributed Antenna Systems (DAS) play a crucial role in enhancing wireless communication coverage and capacity in various settings. From large commercial buildings, airports, stadiums, and hospitals to smaller-scale indoor and outdoor venues, DAS can help address the limitations of traditional cellular networks and provide seamless connectivity for users.
In the field of cellular distributed antenna systems (DAS), Ericsson has been a major contributor to the development of this technology and has filed numerous patents in this area. Ericsson is a leading provider of telecommunications equipment and solutions, and DAS technology is an important part of its portfolio. Ericsson has recognized the potential of DAS technology to enhance the coverage and capacity of wireless networks, particularly in high-density areas such as stadiums, airports, and shopping centers.

A cellular distributed antenna system (DAS), commonly referred to as an in-building wireless system, is a solution designed to manage poor reception inside a large structure. Introduced in 1987, it was a means of extending the range of wireless networks, overcoming the limitations of traditional cellular towers. A DAS was first designed to provide coverage in places where RF signals could not penetrate but where there was a high user density, such as airports, train stations, stadiums, casinos, hotels, etc. DAS was deployed not just for coverage but also to help with capacity as the use of smartphones and data needs rose. The network was seeing increased traffic that needed to be supported. In the early 2000s, the emergence of 3G and 4G networks increased demand for higher data speeds and improved coverage, leading to the development of more advanced DAS technologies. DAS works in the following manner: a network of antenna nodes connected to a single point, often a base station, to provide wireless coverage in a specific area makes up a cellular distributed antenna system (DAS). In locations where the current wireless network infrastructure is insufficient, a DAS is utilized to increase signal strength and quality. To give improved indoor coverage, it can also be employed in apartment complexes and business buildings.

Why is Cellular DAS important?

Cellular Distributed Antenna Systems (DAS) are important for several reasons. First, traditional cellular networks often have limitations in terms of coverage and capacity, particularly in large buildings, outdoor venues, and other complex settings. DAS can help address these limitations by distributing signals from a central source to multiple antennas throughout the coverage area, providing seamless connectivity for users.


Second, as wireless communication technology continues to advance, users are demanding faster data speeds, lower latency, and more reliable connectivity. DAS can help meet these demands by improving signal strength and quality, reducing interference, and enabling more efficient use of available bandwidth.


Third, DAS can be a cost-effective solution for improving wireless coverage and capacity compared to other options, such as building out traditional cellular infrastructure or relying on Wi-Fi networks. In many cases, DAS can also be more scalable and flexible, allowing for easy expansion and modification as needed.


How Does Cellular DAS Work?

In a typical cellular DAS, a network of remote antenna nodes dispersed across the coverage area is connected to a central base station.


The base station is responsible for interacting with the cellular network and processing signals received from the remote nodes. On the other hand, the distant nodes are in charge of sending and receiving signals between the mobile devices and the cellular network.


A fiber optic or coaxial connection that carries both power and signal connects the remote nodes to the base station. Each node covers a certain zone or area and is distributed strategically throughout the building or covered space.


Mobile devices automatically connect to the remote node with the strongest signal as they move within the coverage region, delivering seamless coverage and constant service quality. Additionally, the system uses strategies like frequency reuse and power regulation to make the best use of the available spectrum and reduce interference.


Components of DAS

A DAS is a system of interconnected hardware and software that enables mobile devices to transmit data with more than one antenna, as opposed to only one. It is used in various sectors, including wireless networks, private company networks, cellular networks, and more.

  • Base Station

A base station is a central hub that links all other DAS components to a fiber optic network while also emitting radio frequency (RF) signals that are distributed throughout your building through coaxial cables. As base stations can be connected via wired or wireless networks, everything can be controlled from a single location.

  • Fiber Optics

Data is transmitted by fiber optics from the base station to the antenna. A fiber optic cable is constructed of glass or plastic, so light impulses rather than electrical signals are sent via it. It can quickly send vast amounts of data across incredibly narrow cables without sacrificing signal quality.

  • Radio Frequency Cables

High-quality cables called RF cables are used to link antennas to the base station. Due to the fact that they resemble the vintage cord used to connect the TV to the antenna, they are also known as RF coaxial cables.

  • Coaxial Cable

An inner conductor is encircled by a tube insulator, which is enclosed by another conductor in a coaxial cable. Many electronics, including computers and televisions, need coaxial connections. The fundamental benefit of coaxial cable over other types of cables is that it has a high bandwidth capacity and low losses while being able to transmit huge amounts of power (wattage). This makes it perfect for sending high-speed data over vast distances, such as between cities.

  • Connectors and Splitters

Fiber optic lines, coaxial cables, and RF cables are connected to the antenna using connectors. Depending on the sort of connection needed by your application, these connectors can be made of plastic or metal and are available in a variety of sizes and forms. Splitters, on the other hand, are utilized to transfer the signal to numerous gadgets. These are passive components that divide a cable into two channels and link them together in series.

  • Antennas

Antennas are devices that broadcast and receive radio waves and communications. Because they may be slanted or rotated to direct their signal in a particular direction, they are sometimes referred to as directional arrays or phased array antennas. This is crucial for wireless communication because it makes it possible to convey messages over great distances without sacrificing their quality.


Although antennas exist in a variety of sizes and designs, they all include two common elements:

  • A circuit that sends electricity into another device over wires known as transmission lines

  • A network of antenna nodes transforms that signal into an electromagnetic wave, enabling it to move quickly over space and arrive at its destination (or even faster).

Types of Signal Sources for DAS

One of the single most crucial elements in defining the coverage area and capacity of a DAS system is the signal source. A DAS is always constrained by the performance of the signal supplying the network, regardless of how effectively the distribution system functions. What kind of signal the DAS distributes also depends on the signal source. DAS has three types of signal sources: off-air antennas, on-site base transceiver stations (BTS), and small cells.

  • Off-Air Antennas

A donor antenna on the roof is used by a DAS that employs an off-air signal (also known as a repeater) to receive and send signals from a mobile carrier. The most frequent signal source for a DAS is off-air signals. Using an off-air signal is often not possible if the signal at the donor antenna is very poor or the closest tower is too crowded. Yet, an off-air signal is sometimes the simplest and most affordable signal source if the donor signal is strong and clear.

  • Base Transceiver Stations (BTS)

The technology used inside mobile phone towers to produce a cellular signal is called Base Transceiver Station (BTS), NodeB, eNodeB, and gNodeB. These technologies are often called "BTS signal sources" for simplicity.


A dedicated fiber link, which is normally installed by the cell carrier themselves, is typically needed to connect the BTS of a cell carrier to the core network. To handle the strain of tens of thousands of concurrent users calling, texting, and utilizing data, a distributed antenna system in a major stadium or airport may even connect to numerous BTSes—one for each carrier.

  • Small Cells

Macro cells are scaled down into small cells. Distributed antenna systems can be replaced by small cells, although small cells can also be employed as signal sources in DAS. As signal sources, small cells construct secure tunnels back to carrier networks via an internet connection to generate high-quality wireless signal - also designed and built separately from the company IT network and backbone infrastructure. They are utilized to transmit the signal of the public mobile network throughout complex indoor spaces.


Understanding Signal Distribution Methods in DAS

Any signal source that a system uses must be amplified, distributed, and rebroadcast across the building by a DAS. Active, passive, hybrid, and digital signal distribution technologies are the four core categories.

  • Active DAS

The radio frequency transmissions from the source signal are converted by an Active DAS so they may be distributed across an Ethernet or optical cable. This conversion is carried out by a "master unit," which mixes the signals from different carriers. Moreover, some Active DAS systems "digitize" this signal, which raises the price but enhances performance (see below). After being transformed, an Active DAS delivers the digital signal through Ethernet or fiber optic cables to remote radio units (RRUs), which then transform it back into an RF signal. Depending on the vendor and the system design, these RRUs are also referred to as "nodes" or even "active antennas".

  • Passive DAS

To distribute signal inside a structure, a passive DAS employs passive RF elements such coaxial cable, splitters, taps, and couplers. The power transmitted from an antenna will attenuate (lose power) more the further it is from the signal source and any amplifiers. Calculating precise link budgets is necessary for the proper design of a passive DAS in order to ensure that the output power at each antenna is identical.

  • Hybrid DAS

The traits of passive and active systems are combined in a hybrid DAS. The system can use both fiber optic cable and coaxial cable to deliver signals across a building because the RRUs are separate from the antennas. The cost of a hybrid DAS is typically lower than that of an active DAS because this arrangement requires fewer RRUs.


An RRU that transforms the digital signal to analog RF is typically included in a hybrid DAS system on each level. Then, a coaxial cable is used to link the analog RF signal to various antennas on that floor.

  • Digital Distributed Antenna System

Under the Common Public Radio Interface (CPRI) specification, digital distributed antenna systems are a recent development. Without using analog-to-digital conversions, they employ a Base Band Unit (BBU) to connect directly to a master unit. Digital DAS systems are significantly more expensive than analog DAS systems because of the computationally demanding conversion and combination process.


Patent Analysis - Cellular DAS

In the field of cellular distributed antenna systems (DAS), Ericsson has been a major contributor to the development of this technology and has filed numerous patents in this area. Ericsson is a leading provider of telecommunications equipment and solutions, and DAS technology is an important part of its portfolio. Ericsson has recognized the potential of DAS technology to enhance the coverage and capacity of wireless networks, particularly in high-density areas such as stadiums, airports, and shopping centers.


Overall, the leading position of Ericsson, AT&T, and Qualcomm in the DAS technology patent landscape is a reflection of their long-term investment in research and development, their ability to collaborate with others, and their market dominance.


Conclusion

In conclusion, cellular distributed antenna systems (DAS) play a crucial role in enhancing wireless communication coverage and capacity in various settings. From large commercial buildings, airports, stadiums, and hospitals to smaller-scale indoor and outdoor venues, DAS can help address the limitations of traditional cellular networks and provide seamless connectivity for users.


Moreover, as cellular technology continues to evolve, DAS will become increasingly important in delivering the high-speed, low-latency, and reliable connectivity that users expect. With advancements in small cell technology, cloud-based network management, and other related technologies, DAS systems are becoming more efficient, cost-effective, and scalable.

Overall, cellular DAS is a critical solution for improving wireless coverage and capacity in a variety of settings, enabling users to stay connected and productive in an increasingly mobile world.

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