1. Purpose and Functionality:

   - DAS: A network of spatially separated antennas connected to a common source, designed to distribute wireless signals evenly across large or complex areas (e.g., stadiums, airports, campuses). It ensures consistent coverage by splitting and routing signals through multiple nodes.

   - BDA: A standalone device that amplifies weak existing signals bidirectionally (uplink and downlink) to enhance coverage in localized areas (e.g., small buildings, tunnels). It acts as a "signal booster" for specific spots.

2. Scale and Complexity:

   - DAS: Scalable and complex, involving a central hub, fiber/coaxial cabling, and multiple remote antenna units. Suitable for large-scale deployments and multi-carrier/multi-frequency support.

   - BDA: Simple, single-unit solution for small-scale coverage. Limited to amplifying signals within its operational frequency range.

3. Coverage Area:

   - DAS: Provides blanket coverage across extensive indoor/outdoor areas, overcoming structural obstacles and ensuring uniform signal strength.

   - BDA: Targets isolated weak spots where a signal exists but needs amplification, such as dead zones within a building.

4. Infrastructure and Components:

   - DAS: Includes a head-end (signal source), distribution network (fiber/coaxial), and remote antennas. May integrate with carriers' base stations.

   - BDA: Comprises a receiver, amplifier, and transmitter in one device, often installed with minimal infrastructure.

5. Flexibility and Use Cases:

   - DAS: Supports multiple operators, technologies (e.g., 4G, 5G, Wi-Fi), and high user density. Ideal for future-proofing and large venues.

   - BDA: Cost-effective for quick fixes in small areas but limited to specific frequencies and carrier signals.

6. Regulatory Considerations:

   - DAS: Requires coordination with carriers and compliance with complex regulations due to its distributed nature.

   - BDA: Must be certified to avoid interference, as improper use can disrupt existing networks.

Summary: 

DAS is a comprehensive solution for large, high-capacity environments, offering scalable and uniform coverage through a distributed network. BDA is a simpler, localized tool for amplifying signals in specific weak spots. While BDAs address immediate coverage gaps, DAS provides robust, future-ready infrastructure for complex needs.

A Distributed Antenna System, known as a DAS System, is dedicated antenna infrastructure distributed throughout a building to improve cellular In-Building Coverage (IBC), i.e. mobile phone reception. A Distributed Antenna System is typically only evident to the occupants of the building as the antennas mounted below the ceiling, which vary in appearance but usually resemble a circular smoke detector in shape and size and radiate the mobile phone signal to the targeted areas indoors.

Distributed Antenna Systems are deployed in all sorts of high-traffic buildings and are largely taken for granted. Distributed Antenna System sites aim to provide a seamless end to end mobile reception and connectivity across a variety of sites types including road tunnels and bridges, rail tunnels, hotels, hospitals, universities, stadiums, carparks, shopping centres, airports, commercial office space and everything in between.

Distributed Antenna System systems can vary in size and strictly speaking even the smallest system comprising of a few antennas upwards to systems with 500+ antennas are all a type of Distributed Antenna System. The size of the system typically dictates the topology and type of Distributed Antenna System deployed, and the appropriate RF source to provide connectivity into the various carrier cellular networks.

Distributed Antenna Systems are typically multi-operator. There are some exceptions when systems are small and designed for use with Signal Boosters (Repeaters) for one carrier only. But even these smaller DAS systems can be shared by all operators when designed properly from the outset.

Initial 5G NR launches will depend on existing 4G LTE infrastructure in non-standalone (NSA) mode, before maturation of the standalone (SA) mode with the 5G core network. Additionally, the spectrum can be dynamically shared between 4G LTE and 5G NR.

Non-standalone mode

The non-standalone (NSA) mode of 5G NR refers to an option of 5G NR deployment that depends on the control plane of an existing 4G LTE network for control functions, while 5G NR is exclusively focused on the user plane. This is reported to speed up 5G adoption, however some operators and vendors have criticized prioritizing the introduction of 5G NR NSA on the grounds that it could hinder the implementation of the standalone mode of the network.

Dynamic spectrum sharing

To make better use of existing assets, carriers may opt to dynamically share it between 4G LTE and 5G NR. The spectrum is multiplexed over time between both generations of mobile networks, while still using the 4G LTE network for control functions, depending on user demand. Dynamic spectrum sharing (DSS) may be deployed on existing 4G LTE equipment as long as it is compatible with 5G NR. Only the 5G NR terminal needs to be compatible with DSS.

Standalone mode

The standalone (SA) mode of 5G NR refers to using 5G cells for both signalling and information transfer.It includes the new 5G Packet Core architecture instead of relying on the 4G Evolved Packet Core, to allow the deployment of 5G without the LTE network. It is expected to have lower cost, better efficiency, and to assist development of new use cases.

5G NR (New Radio) is a new radio access technology (RAT) developed by 3GPP for the 5G (fifth generation) mobile network.It was designed to be the global standard for the air interface of 5G networks.

The 3GPP specification 38 series provides the technical details behind 5G NR, the RAT beyond LTE.

The study of NR within 3GPP started in 2015, and the first specification was made available by the end of 2017. While the 3GPP standardization process was ongoing, the industry had already begun efforts to implement infrastructure compliant with the draft standard, with the first large-scale commercial launch of 5G NR having occurred in the end of 2018. Since 2019, many operators have deployed 5G NR networks and handset manufacturers have developed 5G NR enabled handsets.

5G NR uses frequency bands in two frequency ranges:

1. Frequency Range 1 (FR1), for bands within 410 MHz – 7125 MHz

2. Frequency Range 2 (FR2), for bands within 24250 MHz – 52600 MHz