A distributed antenna system (DAS) is a network of interconnected antennas that provide RF coverage within a specific area. They improve coverage in areas that are hard to cover by traditional means. Also, they increase network capacity in some area.
Traditionally, network operators install Remote Radio Units (RRUs) on towers to provide coverage. However, indoor users get weak signals because building materials reduce the power of radiofrequency (RF) signals. The loss of power by an RF signal is called attenuation.
Indoor DAS is required in some buildings because of poor RF signals. In some instances, such as in a basement, an indoor DAS is the only means of providing coverage.
Technical Site Survey
A technical site survey (TSS) is the first action to assess the viability of an indoor DAS in a building. You collect existing RF coverage, and building information during the survey.
The existing RF coverage information describes the RF environment. During the TSS, you measure the existing network of all networks within the building. You also sample coverage outside the building for all networks. Infovista TEMS and Keysight NEMO, special tools designed for this purpose. They are a suite of software and engineering phones tuned for collecting network information. Multiple phones and a laptop speed up data collection. A walk test is the process of collecting RF data using the special equipment. The results of the RF test are analyzed using a set of key performance indicators (KPIs). A DAS is recommended, if the data falls below the threshold . Alternatively, if it is above the threshold then a DAS is not recommended.
The building information describes the installation environment. During the TSS, you collect information about possible cable routes and antenna locations. Also, you collect other information such as antenna placement and access restrictions. Again, there is identification of the main equipment room as well as transmission options for the equipment.
Designing the DAS is the next step. One can design an indoor DAS using iBwave. Armed with the floor plans, a designer plans the new coverage solution. The designer factors the cable routes and antenna placement restrictions into the design.
He prepares a link budget showing attenuation as the signal travels from source to destination. The antennas output at a similar level (5dB between maximum and minimum signal) in a good design.
A second TSS is conducted on premises with the design. The landlord also makes comments, if any, on the design. The designer implements the suggestions. The landlord and other stakeholders (such as network operators) approve the final design.
An installation team uses the finished drawings for implementation. They lay and terminate all the cables and connectors. Cable termination must be carried out by trained personnel to ensure it is done properly. The terminated cables connect other devices in the DAS such as antennas, splitters, and couplers.
A site master is used to verify proper cable termination and component connection. This process is called a sweep test. Project managers and owners use the sweep test report to assess the quality of work done by the installation team. The owner declares the site ready for integration (RFI).
Integration of mobile network operator (MNO) equipment is the last step in the process. The MNO bring their base transceiver station (BTS) to the site and connects it to the DAS. A post-installation walk test is conducted to verify that KPIs have been met. Issues may be spotted if the design and survey process was not thoroughly handled. Once, the BTS is integrated without issues, users joy superior network access through the DAS.