Plan for High Capacity

By Brian Chan

One of the questions I frequently get from new network operators is how many subscribers can I connect to a fixed wireless Access Point (AP)? The answer is that it depends. It depends on several factors that can be answered by the following questions: What is your oversubscription rate? What channel size will you use? What is the interference level in the channel? What Subscriber Modules (SM) will you be deploying? How far away are the SM’s? Are the links line of sight, near line of sight, or non-line of sight (n/N/LOS)?

We have planning tools that can help answer the question of interest as long as the input provided is accurate. The options are to use a capacity planner or LINKPlanner. A capacity planner provides information on how many SM’s an AP can connect based on the packages that are being sold as well as other inputs like distance, SM type, channel size, oversubscription, etc. LINKPlanner is another planning tool that can be used. It performs path analysis based on coordinates and takes in climate factors and rain rates specific to those coordinates into account as it calculates throughput and reliability as well as predicted sector throughput. 

A good how-to video for the PMP 450 capacity planner along with a link to download the tool can be found here.

A link to the equivalent capacity planner for ePMP can be found here. Although we don’t have a how-to video for it like we do for the PMP 450 capacity planner the ePMP capacity planner is user friendly and straight forward.

LINKPlanner can be downloaded here.

Below are some examples of the calculations from the PMP 450 capacity planner for the PMP 450m 3.6GHz in CBRS.

For a WISP that can operate at full power in CBRS in a clean 40Mhz channel with a -90dBm noise floor, they can sell (204) 25/3 Mbps packages to customers with PMP 450b HG SM’s at 5 miles based on 8:1 oversubscription and 4x multiplexing gain from MU-MIMO. With 10:1 oversubscription this increases to (255), which exceeds the (238) SM/AP limit of the PMP 450 platform, so for all intents and purposes this number would be (238). If we were to consider higher speed packages like 100/20 Mbps these numbers become (51) packages for 8:1 oversubscription and (64) for 10:1 oversubscription. That’s a lot of 100Mbps plans!

For a more conservative calculation with numbers common of real-world deployments let’s look at a 20Mhz channel instead of a 40MHz channel and 2.8x multiplexing gain instead of 4x from MU-MIMO. In this case, the WISP can sell (39) 25/3 Mbps packages to customers with PMP 450b HG SM’s at 5 miles based on 5:1 oversubscription. This increases to (62) for 8:1 oversubscription. This is still a lot of high-speed plans for a 20MHz channel!

The technology offers operators a lot of flexibility and choices. The key is knowing which tools to use to make it easy to optimize performance. So how many subscribers do you have on your AP, and how did you plan it? Share your experiences here on the Cambium Community.

Published August 7, 2020