Method Simplifies Validating In-building Public Safety Network Performance

August 7, 2020

Validating public safety wireless network coverage in-building presents obstacles for contractors and network engineers. It is more than the technical challenges created by concrete walls, environmentally treated windows, and other common building materials. There are stringent government regulations to ensure performance in mission critical situations, as well.

Easy-to-use, time-efficient, and economical test solutions to satisfy in-building network verification are necessities, as much of this verification is now the responsibility of building contractors. They must ensure coverage meets local requirements, as well as the national NFPA 72 (National Fire Alarm and Signaling Code) standard published by the National Fire Protection Association. For in-building DAS and Wi-Fi systems, the standard requires 99% floor area radio coverage.

Alternative to GPS Signal

While the general scope may be clear and concise, the same can’t be said for the actual coverage validation process. The biggest hurdle is the in-building unreliability of a GPS signal – the most common way to coordinate position data with any kind of test data results. This lack of GPS signal is especially evident in NFPA72 “critical areas,” such as the fire command center(s), fire pump room(s), exit passageways, elevator lobbies, exit stairs, standpipe cabinets, and sprinkler sectional valve locations. In particular, the latter three areas are especially isolated, making GPS signal availability even more sparse.

While in-building networks are not the legal responsibility of the contractor, there may be occupancy permit requirements from the building owners requiring a certain coverage guarantee. Without the certificate of occupancy (CO), the building owner will not send the final payment to the contractor, creating a financial incentive for the contractor to verify network coverage.

Current building standards are constantly evolving, both at the public safety level and the commercial network level. The emergence of 5G at both Frequency Range 1 (FR1) and Frequency Range 2 (FR2) for in-building networks, and the requirements of high reliability low latency applications have increased the number of bands and air protocols that need to be supported. For example, the plans to introduce the CBRS band into buildings as private LTE will create additional requirements as they are implemented in different industries.

If building contractors must conduct RF scans for every band, the testing exercise will multiply linearly by the number of bands in the entire building. Each band has an associated cost factor for validation, meaning the expense can be dramatic for a contractor. To solve this dilemma, a solution (figure 1) that can validate all bands simultaneously while a technician walks through the building has been developed.

Figure 1: In-building network solution compact enough to fit in a backpack.

Integrated In-building Test Solution

The solution uses a local “tracker” rather than GPS to coordinate its position with the RF readings. A true 3D map is created by the tracker to enable technicians to easily pinpoint weak or no-coverage areas and address them appropriately. It also aids in preparing the necessary documents to satisfy legal requirements.

The solution can scan as many as six different frequencies simultaneously, including LTE bands, Wi-Fi, P25, and TETRA, in a single walkthrough. This saves significant time and cost.

Practicality is also addressed. Weighing less than 10 pounds, it can be carried without strenuous effort through a building, including stairwells. It also has a 4-hour battery, which is enough life to complete a walkthrough of a large multi-story commercial structure.

Integrated Approach Key to Success

To meet all the testing, cost, and efficiency goals associated with streamlining in-building testing, an integrated approach has to be taken. The best tool for this environment combines hardware and software:

Remote Spectrum Monitor: A hardware unit for this application must deliver outstanding sweep speeds, even for smaller resolution (RBW) or video bandwidths (VBW). The latter specifications are important for narrowband public safety communications standards, such as analog FM, P25, TETRA, DMR, and dPMR.

Tracker: Technicians must be able to wear a device that delivers in-building position to the tracking software as they conduct the walkthrough. It can store the technician’s position in 3D, allowing previously hard-to-analyze areas, such as stairwells and elevators, to be accurately tested.

Software: Two software packages are necessary. The first is a signal mapper that controls the remote spectrum monitor by collecting the RF data from the user-defined frequency bands and coordinating it with the position data. The second is command software that analyzes the data gathered by the signal mapper, as well as offers users the capability to prepare any necessary reports and 2D/3D coverage mapping images (figure 2). It also automatically gathers the building outlines from satellite data and accepts photos of building floor plans.

Figure 2: Coverage mapping images created by dedicated software.

Simple Measurement Process

The time necessary to conduct tests is further reduced by a simple measurement process, which also minimizes training. Because the solution has a high level of intelligence, accuracy is not sacrificed for speed. The process consists of:

1. Opening a web browser on any Android device and typing in the IP address of the remote spectrum monitor unit. Once communication with the test unit has been verified, the browser can be closed.
2. Setting up the Signal Mapper and Channel Scanner. This process includes entering all bands of interest by defining frequency, SPAN, RBW, and Ref Level.
3. Accessing Building Outline/Floor Plan. The building outline is automatically input by the command software using current location coordinates and accessing the building outline from a database of satellite images. Next, the user simply snaps a picture of the floor plan normally found at a main entrance/exit to the floor, or the elevator doors and fire exits. The photo of the floor plan is overlaid onto the building floor plan and adjusted by the user until there is a fit (Figure 3). There is also a manual editing mode if a picture of a floor plan is not available.
   
   

   Figure 3: Integration of building floor plan with image taken while in-building.
4. Calibration. Technicians must calibrate the tracking unit with his/her stride by walking at a normal pace for at least 30 feet in a straight line. Once finished, the user needs to mark the end position on the floor plan. While this two-point calibration is sufficient, it is recommended that an additional calibration step be done. The technician should return to the original start position and mark it as the third calibration point for greater accuracy.

Analysis results can be stored locally in the required Android device for security purposes. It can also be uploaded to the cloud for reporting convenience. The results can be displayed in 2D or 3D so engineers can visually inspect for weak coverage areas.

To learn more about how to conduct these in-building measurements on public safety networks, download the Validating In-Building Wireless Coverage of Public Safety, LTE, and Wi-Fi^® Networks app note.