June 28, 2016
Every mobile communications report published has a recurring theme – mobile date usage is skyrocketing to new heights. People rely on their mobile devices (smartphones, tablets, etc.) more than desktop and laptop computers in everything they do and wherever they are. In fact, approximately 80% of mobile usage happens indoors and not just from the comfort of a living room couch via Wi-Fi. Consumers use their smartphones while shopping in brick and mortar stores (84% of them according to Google) and another study found that three quarters of workers would consider leaving their current mobile operator to get better coverage in their office.
All of this makes it imperative for providers (and landlords) to ensure coverage in malls, office buildings and other venues. Not only will it ensure mobile data usage for potentially increased revenue, it will help reduce churn because consumers have high service quality expectations when using their mobile devices indoors.
There is just one problem – indoor coverage is not simple. “Outside-in” signal loss can be up to 7 dB due to windows, and reach 10 dB for brick or 12 dB for concrete walls. Metal wall framing may cause a loss of up to 10 dB, while concrete floors can result in losses approaching 30 dB, according to one analyst group. That is why there has been tremendous growth in the deployment of In-building Wireless (IBW) systems, specifically Distributed Antenna Systems (DAS).
Despite the challenges associated with DAS, the aforementioned market conditions provide compelling business reasons for operators to deploy indoor networks to accommodate their customers. Providers in North America and Asia-Pacific have particularly taken an interest, evident by the statistics in figure 1.
Figure 1
Understanding DAS
Hybrid and/or passive DAS has become a popular architecture for multi-operator, multi-NEM, multi-technology applications because it is able to accept RF inputs from a variety of signal sources, making the DAS network equipment manufacturer as well as technology (2G, 3G, 4G) neutral. When possible, DAS antennas should be placed in locations with a clear view of the environment they are serving rather than near metal objects such as light fixtures, ceiling tile frames and metal HVAC ductwork. Placement close to these objects can generate high levels of passive intermodulation (PIM), even with transmit power levels as low as 20 dBm (100 mW).
Studies conducted by Anritsu indicate that external PIM sources close to IBW antennas are more likely to impact performance at low frequencies, such as 700 MHz, 850 MHz, and 900 MHz. Best practice when deploying low-frequency band systems is to perform a low power PIM test at each candidate antenna location prior to final installation. Internally generated PIM is worst at the higher frequencies, so in this case a PIM test at one of the higher bands, such as 2100 MHz or 2600 MHz, is best practice. Eliminating PIM in DAS is discussed on our PIM Source blog.
A DAS may require 1,000 to 15,000 traces, photos, and other deliverables to show that the installation meets performance standards. This can be as much as 100x more than what is required when installing a typical tower-based antenna system. When you consider each of these deliverables needs to be inspected, renamed, and perhaps have the markers and limit lines set and judged, the task can become quite lengthy and costly if the traditional manual inspection process is used.
Given the complexity and myriad technologies used in DAS, as well as the technical aptitude of some technicians, there is a definite need for simplified testing processes to the DAS installation workflow. Fortunately, there are now cloud-based tools to ensure time savings for operators and allow contractors to more quickly close out jobs, get paid and move on to the next project. One such solution is SkyBridge Tools™ from Anritsu, which enables reliable and quick creation of test plans, fast and accurate testing, and assists in report creation.
Test Plan
A sound test plan is the best first step in simplifying the test process. Data can be imported from iBwave designer, Excel, and operator-supplied test criteria with the assistance of a wizard to create detailed Test Plans such as the one shown in figure 2. This documentation enables test sequencing, job progress tracking, trace judgement, and report generation.
Figure 2
Test Sequencing
After the test plan is created, pressing one button will create instrument control scripts for that specific plan. Necessary tests, proper instrument setups, limit lines, and accurate file names for traces are included. These scripts can then be run on certain Anritsu field instruments, including Site Master™, BTS Master™, and PIM Master™ handheld analyzers, greatly reducing technician workload. Failures are often visible while the cable is still connected to the instrument. Missing or duplicated tests, misconfigured setups, and misnamed traces are eliminated through this tool.
Reporting
A key element to the DAS testing process is the reporting mechanism to verify the tests were conducted properly and the results sound. Traditional PDF or zipped reports are standard formats but having a CSV file with one row per test is also sometimes necessary and advantageous. Automated reports in a variety of formats forever eliminates the tedious and inconsistent processes used in the past.
There is much more to learn about IBW systems and the various system architectures, such as DAS, Distributed Radio Systems (DRS) and Distributed Small Cells (DSC), as well as how to test each. You can download an Understanding IBW white paper to gain more information.
