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Are all Wi-Fi Channels Created Equal?

Mark Poletti
Director, Wireless Network Technologies

Jan 22, 2015

Wi-Fi & RF Performance
Over the years, Wi-Fi networks have evolved into planned, managed networks, delivering faster data rates and reliable service using outdoor Hotspots, Enterprise access points (AP), and Homespot gateways. As Wi-Fi Operators continue to rollout and expand Wi-Fi networks, ensuring reliable service and quality is a critical goal. ‘Carrier Grade Wi-Fi’ is an industry movement that will offer solutions and features to harden Wi-Fi infrastructure and sustain connectivity to achieve this. One main area of focus is RF performance of a Wi-Fi device. Maintaining consistent RF performance across all Wi-Fi devices and across all Wi-Fi channels will provide a more consistent RF link budget and dependable link balance. This will enable Wi-Fi Operators to provide reliable and quality network performance and deliver consistent data rates at expected ranges.

Making Wi-Fi Better

Anechoic ChamberTo facilitate the best customer experience on behalf of its members, CableLabs is collaborating extensively with the Wi-Fi industry to provide studies, standards, methodologies and solutions to establish RF performance criteria for Wi-Fi devices. To provide vendor-neutral unbiased test results to the cable industry, CableLabs tests Wi-Fi devices using industry and customized test plans using an anechoic chamber. The goal of our work is to establish RF performance criteria of a Wi-Fi device by assessing hardware design, device performance, and network performance.

The Unexplored Territory of Wi-Fi: RF Performance

CableLabs has completed an initial set of RF performance tests on Wi-Fi devices using its in-house RF anechoic chamber with a state-of-the-art Over-The-Air (OTA) measurement system. RF test measurements follow an industry-based CTIA/WFA (Cellular Telecommunications Industry Association/Wi-Fi Alliance)[1] methodology and test plan. Of particular interest is the measured RF power of a Wi-Fi device. The Wi-Fi industry has adopted a measurement from the cellular industry called ‘total radiated power’ (TRP). TRP is the measurement of the overall RF power of the Wi-Fi device in an RF free environment (i.e. anechoic chamber) taken at multiple positions (every 15 degrees) as shown in Figure 1.

Figure 1 TRP measurement positions following CTIA test plan
Figure 1. TRP measurement positions following CTIA test plan[2]

TRP is a standard and repeatable method that provides RF characterization of the Wi-Fi device radio and antenna chain as a whole system. TRP is used to characterize the RF performance of transmitter portion of the device.

All Wi-Fi devices must meet ‘not-to-exceed’ regulatory limits that address safety and interference protection to co-existing and adjacent channel inhabitants in unlicensed spectrum. However, historically, there are no minimum RF performance requirements that enforce consistent performance for Wi-Fi devices. Having no minimum RF performance requirements for Wi-Fi devices can introduce inconsistency and variation into Wi-Fi network performance.

Wi-Fi Channel Performance

Results of an initial set of RF characterization measurements on five commercially available Wi-Fi Access Points are shown in Figure 2. The TRP was measured on the low, middle and high channels (1, 6, and 11) in the 2.4 GHz band. The results show a variance in TRP performance within a single access point and across APs on three commonly used channels in the 2.4 GHz band. Such variances make it challenging for a Wi-Fi Operator to provide reliable service and manage a network.

Figure 2 Measured TRP Results of AP vendors illustrating variance within single AP and across multiple AP vendors
Figure 2. Measured TRP Results of AP vendors illustrating variance within single AP and across multiple AP vendors

The significance of these variances to a Wi-Fi user is shown by using an RF indoor prediction tool to generate coverage differences between two channels of an AP in a common residential house floor plan. Figure 3 uses TRP measurements of AP Vendor 1 to illustrate how two different channels can have different downlink coverage at the same data rates. The heat maps shows that Channel 6 covers 20% greater 65 Mbps coverage than Channel 1 of a 2300 square foot residential home.

Figure 3. Downlink coverage prediction of typical residential floor plan using measured TRP Results
Figure 3. Downlink coverage prediction of typical residential floor plan using measured TRP Results

Wi-Fi and You, Today

While the above studies will help cable operators effectively manage the overall Wi-Fi network across a neighborhood, consumers with wireless routers in their homes can also perform some easy steps to assure the strongest signal strength. This blog provides some tips.

Mark Poletti is a Wireless Architect at CableLabs. Neeharika Allanki is an architect at CableLabs. 

[1] http://www.ctia.org/policy-initiatives/certification/certification-test-plans

[2] http://www.ctia.org/policy-initiatives/certification/certification-test-plans