Evolving Wi-Fi® network topologies to meet growing Wi-Fi performance expectations

Qualcomm Technologies study addressing spectrum needs

In a recent study conducted by Qualcomm Technologies, researchers addressed the question how a throughput performance expectation of 1 Gbps of sustained Wi-Fi® coverage can be achieved in dense residential and enterprise deployment scenarios. A whitepaper describing the approach and results of the study can be found here.

The research focuses on IEEE 802.11ax – the forthcoming generation of Wi-Fi that will enable higher performance in congested environments – Wi-Fi performance assuming downlink full buffer traffic while simulating the throughput performance achieved throughout a particular coverage area. One way to look at the approach is modeling the results of applying a downlink ‘speed test’ application through a large number of spots in the coverage area under analysis and calculating the overall amount of spectrum needed to achieve 1 Gbps throughput in 99% of the coverage area.

In Part 1, I highlighted some key conclusions resulting from the study regarding future spectrum requirements for unlicensed spectrum.

In addition to spectrum requirements, the study provided quantifiable insights into the impacts on performance achieved and spectrum required of various network topologies. In particular, the study assessed impacts of the deployment of multiple APs per home, the use of wireless mesh technology, the use of 60 GHz for the last hop, the use of multiple antenna technology, and the user of wider channel bandwidths. 

A Wi-Fi AP in every room

One sobering finding was that the 1 Gbps sustained throughput target was not achievable in the dense residential scenario with only one AP per apartment coupled with two antenna clients. With one AP per apartment and four antenna clients, the target can be achieved using 1280 MHz of spectrum.

When we look at topologies with an AP in each of the four rooms in the apartment, with Wi-Fi connections between APs (see figure 1), the 1 Gbps target can be met. This scenario will require 960 MHz of spectrum with two antenna clients, and 800 MHz of spectrum with four antenna clients.

Figure 1. Wi-Fi connection between client and AP, four APs per apartment, and Wi-Fi backhaul connection between APs

At the current time, there are a number of new entrants in the Wi-Fi network infrastructure market, including eero and Plume, that have developed innovative approaches for achieving these mesh (‘all wireless’) topologies.   

A topology that would further lead to reduced spectrum requirements is the case where we assume Ethernet connections exist between the APs in an apartment. To achieve the 1 Gbps target, the overall amount of spectrum required is 480 MHz with two antenna clients, and 320 MHz with four antenna clients.

60 GHz to the rescue

With the impending launch of the Wi-Fi CERTIFIED WiGig™ interoperability program for devices operating in 60 GHz, the technology is on the cusp of entering the mainstream market and accelerating broad industry adoption. 1 Gbps coverage can be relatively easily achieved with one WiGig® (60 GHz) AP per room and 60 GHz WiGig client radios.

Assuming 5 GHz is used for Wi-Fi backhaul between the APs in an apartment, 480 MHz of spectrum will be required to enable the 1 Gbps performance target. A 2.5 Gbps coverage target can even be met using 1920 MHz of spectrum, with 802.11ax technology used for backhaul between eight antenna 5 GHz backhaul radios in the dual radio WiGig AP.

Multiple antenna technology

One of the more forward leaning assumptions in the study is that we assume a minimum of two antennas per client in 802.11ax technology. The vast majority of clients deployed in the market today are 1 antenna devices. With single antenna devices, the amount of spectrum required would typically need to be doubled to achieve the 1 Gbps target, putting the target out of reach in many of the scenarios analyzed. As indicated earlier, the 1 Gbps target can only be met with one AP per apartment in case we assume 4 antennas per client. A key conclusion is that multiple antenna technology at AP (e.g. eight or more antennas at the AP radio) and at the client (two, four antennas or more) will have to be part of the industry roadmap in order to meet expanding customer expectations, and to remain competitive with alternative technologies.

Some data points from the enterprise scenario that illustrate the value of multiple antenna technology:

• With two antennas at the client, 1280 MHz of spectrum is required to achieve the 1 Gbps target, whereas only 640 MHz is required assuming four antenna clients
• The 2.5 Gbps sustained throughput target can be met with clients using four or more antennas

Wider Channels

The 160 MHz wide channel feature has first been introduced as a new feature of Wi-Fi CERTIFIED™ ac. The use and availability of 160 MHz wide channels has been relatively slow to take off in the marketplace. The analysis indicates that in a number of the dense networking scenarios, the 1 Gbps target can only be met with the use of 160 MHz wide channels.

Below are some examples of scenarios where the 160 MHz feature is a necessity to achieve the 1 Gbps target:

• Enterprise setting, with two antenna clients
• Residential scenario, single AP per apartment (four antenna clients)
• Residential scenario, one AP for every room, backhaul over Ethernet, with two antenna clients.

One of the recommendations included in the whitepaper is that multiple (three or more) 160 MHz wide channels should be made available for unlicensed use.

Innovation drivers for wireless performance

As it turns out, the analysis highlighted and quantified some of the most important innovative drivers for wireless performance in future generations of the Wi-Fi technology:

• Densification of network deployments and the use of wireless mesh topologies in homes
• Use of millimeter wave technologies (e.g. WiGig)
• Multiple antenna technology (e.g. Multi-user MIMO)
• Use of wider channel bandwidths

To continue the tremendous success of Wi-Fi as the predominant bearer of wireless data traffic, innovation along these four dimensions coupled with sufficient expansion of relatively unencumbered unlicensed spectrum availability throughout the world, is of utmost importance at this critical juncture.

Scenarios:
To recap: the dense residential scenario assumes a three-story apartment building with 30 apartments overall. Each apartment is dimensioned 10m x 10m, with four rooms per apartment. The enterprise scenario assumes one floor in an office building, which has eight rooms, with four access points (APs) each (in total 32 APs). This forward looking analysis assumes that the best available, 802.11ax Wi-Fi technology is deployed in the 5 GHz frequency band. Further details on deployment scenarios and modeling assumptions are included in the Qualcomm Technologies whitepaper.