How to Design a DAS for Seamless In-Building Mobile Service
Have you ever walked into a building and immediately noticed your mobile signal plummet to a single bar, causing your important call to drop or your video stream to buffer endlessly? In today’s hyper-connected world, a robust in-building mobile service isn’t just a luxury—it’s an expectation. This is where a Distributed Antenna System (DAS) comes into play, serving as the silent conductor of wireless signals, ensuring that connectivity follows you as seamlessly as your own shadow.
This blog post is your definitive guide to designing a DAS that guarantees seamless in-building mobile service, keeping you connected in a world that never stops moving.
A successful in-building DAS design follows three basic stages:
- Stage 1: Conceptual design
- Stage 2: Feasibility study
- Stage 3: Applied design
How to Design a Distributed Antenna System (DAS) |
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Let’s examine exactly what is involved in each of these steps.
Define the Concept
The primary goal of a conceptual DAS design is to outline a bill of materials (BOM) that can be used to evaluate the approximate cost of a distributed antenna system. At the basic level, a phase one design should include floorplans, compliance criteria, and some idea of the expected venue occupancy. This information allows you to accurately determine the frequency bands and coverage sectors to include in the design.
Each of these categories can be broken down into more granular elements, as follows.
Floorplans
Including the following items in your floorplan design can help achieve a successful DAS design as quickly as possible.
- The use of .DWG files allows for a more accurate and detailed representation of the building
- Identify the location of the main distribution frame (MDF), intermediate distribution frame (IDF) closets, and cable pathways
- Be sure to include any limitations of the physical installation, such as hard ceiling areas, open atriums, or public spaces where aesthetics prevent antenna placement.
Compliance Criteria
Two critical key performance indicators (KPIs) determine the success of any wireless technology installation. The first metric is signal strength, and the second is signal quality.
- Signal strength is typically designated as a coverage criteria of x coverage over n% of an area. A widely accepted minimum is -95dBm Reference Signal Received Power (RSRP) over 95% of the area, which represents a coverage value for both LTE and 5G new radio (NR) technologies.
- Signal quality is a key second measurement when evaluating the compliance of high-capacity venues with many coverage sectors. The signal-to-noise ratio is one of the critical quality metrics studied for both LTE and NR technologies. Minimum values on this metric vary across the different mobile network operators (MNOs); however, a typical value is a SNIR of 8 dB over 95% of the area.
Occupancy
Understanding the expected occupancy of a building or venue can guide an engineer to design a solution that supports the correct number of sectors and bands. A typical sector can support up to 800 simultaneous users. Given that the average user now carries at least two connected devices, this means that most environments require more than one cell sector to support the capacity of any given venue.
In most cases, the maximum occupancy, as dictated by fire codes, can be a good guideline for occupancy figures. However, additional information about where the bulk of the users are expected to be in space and time can provide useful context.
The resulting conceptual design should include the following:
- A three-dimensional model
- Active and passive bill of materials
- Initial electromagnetic energy (EME) compliance report.
Evaluate Feasibility
During the second stage, DAS engineers conduct a feasibility study to confirm assumptions in the conceptual design. This typically involves a site walk, wireless benchmarks, and more detailed conversations with the MNO. For those installations in unusual environments, this is the point where wireless calibration can occur. These calculations can improve accuracy and ensure the design represents an accurate representation of signal propagation.
A site walk is conducted in order to identify all the cable paths, along with the MDF and IDF rooms, space availability, environmental settings, and security needs. In addition, the site walk allows engineers to catalog any existing and reusable infrastructure, such as electrical outlets, available cable trays, and dark fiber. Pro Tip: engineers can perform stage two activities in parallel with the conceptual design phase for greater efficiency.
Detailed data collection can provide useful details to establish a wireless benchmark. This will enable a clear picture of which wireless service providers have signal levels penetrating the venue, and at what signal strength. Overcoming influences from the outside macro network can be a major contributor to increased costs when deploying DAS solutions.
Ideally, engineers will conduct a scanner walk to gain the most accurate information, ensuring the scanner antenna is clear of any bodily obstruction. Be sure to collect all channels across all commercially licensed spectrum to produce a .CSV file for easy integration into wireless design software. Supplementing this data with MNO conversations helps to clarify frequency bands, spatial streams, sector count, and any needed macro mitigation activities.
Current design software can represent many different environments with reasonable accuracy, but unique environments specific to your venue may require additional onsite engineering studies to achieve wireless calibration. These spaces might include tunnels, indoor/outdoor areas, and unique architectural elements. To accomplish this, continuous wave (CW) testing provides a method that determines how well a signal travels in a specific space and provides accurate information about signal losses through materials.
Confirm Design as Built
The last stage of a robust DAS design process is an ‘as-built’ design that takes place after the construction of the solution. This is where the hardware in the design is reconciled with the applied build, enabling confirmation that the active and passive equipment is accurate to the signal path. The infrastructure testing results also can augment the design plan to create a master reference document for benchmarking and replication.
During the applied design stage, DAS engineers can collect data through a post-deployment site walk and import it into the design. This allows the calibration of signal propagation predictions to better represent the DAS system’s performance.
Designing a DAS that is perfectly suited to your building, event venue, or campus helps ensure the availability of reliable, high-quality mobile service. Yet the actual design process requires time and attention to detail. An experienced design engineer familiar with the proper evaluation software who understands RF behavior can optimize design planning time to speed deployment without sacrificing results.
The SOLiD Engineering and Design service provides the resources needed to ensure accuracy in design for fast deployment in any venue. Equipped with the latest tools, software, and technology, experienced SOLiD experts can help reduce design cycles for a more efficient process leading to reduced implementation costs.
To get started with a robust system design that will deliver outstanding performance well into the future, submit your design requirements to our experienced SOLiD Engineering and Design services team today. To learn more, visit: www.solid.com/us/services/engineering-and-design.
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