Considerations in Wi-Fi 6 AP Design

PublishTime： 2022-11-06 Article Source：Renesas Blogs

Purpose

In this blog, we will cover considerations helpful to those of you who are presently operating or deploying service with Wi-Fi 5, or an older generation of Wi-Fi and are looking to move forward to Wi-Fi 6.

Start by Prioritizing the Goals for the AP Design

One of the key questions you need to address is, “What are the target services that you would like to enable with this new access point?” Are these the same rates or class of data, video, and voice services that you previously provided or are you adding new services? Defining your targeted services will help determine the port load definition for the AP to carry or enable.

Another key point to consider is defining your key constraints. Are they time-to-market - do you want to be among the first riding the Wi-Fi 6 marketing wagon? Or are you more conservative and performance conscious and driven by the reliability and maturity of the technologies as opposed to being an early adopter?

For most service providers, a prime decision-influencing factor is WAN technology. Will it be the same generation and class of service as your existing Wi-Fi 5 infrastructure or is there a need to migrate and design a completely new WAN infrastructure as well?

Let’s assume that with Wi-Fi 5 you have already built a 1Gbps or near 1Gbps capable infrastructure and APs, such as DOCSIS 3.1, xDSL, fiber, etc. In addition, if you have a properly designed 4x4 Wi-Fi 5 AP, you can enable a very rapid design cycle and Wi-Fi 6-enabled next-generation successor AP or modem.

System Dimensioning

Selecting the right Multiple Input Multiple Output (MIMO) configuration for Wi-Fi 6 can be quite misleading. Since Wi-Fi 6 technology supports higher modulation and channel bandwidth, one may be confused that a 2x2 Wi-Fi 6 system can reach, in 5GHz, similar PHY rates to those of a Wi-Fi 5 4x4 system.

This may be true for a high-efficiency wireless (HE)/802.11ax Wi-Fi-6 client at 160MHz; however, it is far from being the case for existing Wi-Fi 5 clients or for Wi-Fi 6 clients in 80MHz channels - the likely channel bandwidth to be available in 5GHz.

So if you are expecting your Wi-Fi 6 AP to perform at least as well as your Wi-Fi 5 AP for its current devices (keeping in mind the huge installed base of Wi-Fi 5 or earlier generation devices), you must match or exceed the MIMO dimensions of your current AP. This assumes you’re planning a 1-to-1 replacement of your legacy AP with the new AP, replacing one box with multiple boxes is a different case. If you fail to do this, you will find your new Wi-Fi 6 with lesser coverage and capacity for the existing client devices than that of your existing infrastructure.

Form Factor

Consumers of today’s electronic devices are demanding sleeker, smaller size/volume and footprint, lower power consumption, and ease of use.

Antenna

The antenna system also influences the form factor; however, we are not covering this aspect here because, under a similar system sizing (namely same MIMO dimension), Wi-Fi 5 and Wi-Fi 6 are similar in this sense.

Power Supply Heat Dissipation and Cooling

As a designer, you will need to consider thermal aspects such as heat dissipation, cooling, external surface temperature, low EMI interference, and no or low audible noise (i.e. internal cooling fan yes/no). Most of the Wi-Fi 6 solutions on the market today need a larger PCB footprint, to consume more power and generate more heat than existing Wi-Fi 5 solutions.

You would want your new Wi-Fi 6 design in a similar or even smaller form factor than your existing gateways because consumers will expect a reduced form factor and greener designs. This customer need may complicate a Wi-Fi 6 design if not carefully addressed. Designers need to address the implications of their design size and cost, especially for the thermal architecture chosen.

Selecting the Right Components

Time to market is a crucial parameter for a new Wi-Fi 6 design. Let’s look at how we can accelerate a Wi-Fi 6 design by using much of your existing Wi-Fi 5 architecture.

WAN Technology

Keeping the same modem WAN technology, you may not have to change the prime SoCs. You may keep the similar Wi-Fi architecture as in your Wi-Fi 5 design (peripheral component interconnect), meaning designers can have a very fast hardware design cycle. This is especially true if the Wi-Fi 6 solution is capable of fitting into similar physical dimensions as the replaced Wi-Fi 5. By keeping a similar solution architecture to that of your Wi-Fi 5, you can also have a relatively fast software integration cycle between your existing solution and its full SoC and Software Development Kit (SDK) application. Keeping the same prime SoC (i.e. same applications, tool-chain, etc as you have matured in the Wi-Fi 5 solution), and keeping a similar host-to-Wi-Fi interconnection can save you significant time, effort, and risks.

Hardware & Software

With all the surrounding applications of the video engines, the voice, and all those aspects that you have already cleared out and de-bugged, you could have a relatively fast refresh that only changes the Wi-Fi hardware portion. From a system standpoint, this does not have the burden of a significant software integration or hardware integration effort. The hardware portion can be easier as well if your Wi-Fi 6 sub-system does not force you to increase your required overall form factor on your PCB. If this design demands a similar space to that of the Wi-Fi 5 system, you will be on a path to a rapid spin of your existing hardware design.

If on your existing design, you do not need to change your Software Development Kit (SDK) tool and the prime SoC, with which you have been working, you will find that you are on a fast track for your software integration for your Wi-Fi 6 design. Thus, the overall project development cycle will be much faster.

Power Consumption & Heat Dissipation

Fortunately, from a power consumption and heat dissipation standpoint, a new Wi-Fi 6 solution can also have a similar solution to that of the Wi-Fi 5 power design. This will speed up the thermal design and heat dissipation efforts for the Wi-Fi 6 power architecture. This will be true if you keep your present form factor and heat dissipation architectural solutions.

SOC and Wi-Fi Subsystem

Another key component area selection is the interface between the modem/application SoC and the Wi-Fi subsystem. Because Wi-Fi 6 is more competent than Wi-Fi 5, it requires broader capable ports between the SoC and the Wi-Fi subsystem. For example, if you would like to exhaust the maximum capabilities of a Wi-Fi 6 4x4 interface that can attain 4.8Gbps of data link rate, you would not want to limit the SoC and the Wi-Fi interface to 1Gbps (in this case you would not be able to maximize the benefit from the higher-performing Wi-Fi). There would be an internal bottleneck in your system. If you have selected a similar SoC, due to the WAN and software technologies you have presently, you will need to verify that you are not port-limited in your system performance between the SoC and the Wi-Fi subsystem.

PCIe Ports

Some of the Wi-Fi 6 interface solutions require a larger number of PCIe ports from the SoC; this can limit your overall system design. You would not have enough ports for the services and types of interfaces that you need to integrate.

Renesas' solution uses a lesser number of PCIe ports on the host than other solutions, for either dual-band concurrent or tri-band. Figure 1.

With regard to memory, some solutions mandate an additional applications processor which requires memories (Flash and DDR) of their own, causing extra cost burdens in the solution.

Advanced Functionalities

The fact that in the foreseeable future you are serving more legacy devices than newer Wi-Fi 6 devices has consequences. This implies that you will need to behave well with all the advanced techniques of proper airtime management, proper service prioritization, video over Wi-Fi, multi-AP solutions, band-steering, and more.

A misleading conception that many designers make is that Wi-Fi 6 as a scheduled technology, would miraculously save the day and would be a better solution for any current network staggering. For example, if you have ten clients in your home, and those ten clients are legacy clients (Wi-Fi 5 or earlier generations), a Wi-Fi 6 AP can’t employ Wi-Fi 6 techniques on them, thus serving them no differently than a Wi-Fi 5 AP, with the same potential pitfalls that cause customers frustration, to begin with. This is true if it is not applying techniques of advanced Quality of Service (QoS); and will result in deeper frustration following your customers’ raised expectations (and possibly higher pricing…). Check out our OptimizAIR™ functionality as a tool to properly manage services amongst networks, services, and clients.

Conclusion

Wi-Fi 6 has a greater possibility of meeting the shared speed and frequency goals because of its increased ability to support more clients and devices simultaneously with features such as OFDMA, MU-MIMO, and scheduling.

Designers must have a clear understanding of the prime goal and considerations for their Wi-Fi 5 to Wi-Fi 6 refresh cycle. Having the prime service goals, and key considerations priorities clearly defined before hitting the sketch board can significantly reduce costs, project length, and risks involved.

If the goal services allow designers to keep the same prime SoC, the project can actually turn out to be a fast hardware and software spin cycle allowing the introduction of the Wi-Fi 6 variant much faster and at lower risk than designers may expect. As mentioned previously, a well-designed 1Gbps Wi-Fi 5 (11ac) box can be refreshed to a multi-Gbps Wi-Fi 6 box (allowing many of the 1Gbps SoCs to support even 2.5 GE or 5 GE ports), while keeping a similar layout and thermal relief significantly reducing the software effort needed when designing from scratch.

Attention should be paid by designers to ensure that no internal architectural blockers exist (port limited design) preventing them from maximizing the Wi-Fi 6 target speeds they are aiming for.

In Summary...

Benefits based on the CL8080 chip

Two concurrent dual-band Wi-Fi 6 transceivers in a single small PCIe chip
The same chip can be assembled as multiple MIMO options (BOM decision only)
A flexible FEM interface enables the selection of any FEM vendor (for example Skyworks, Qorvo, Richwave)
Not tightly coupled to any host SoC – OEM free to select any platform

Reduced power consumption and heat dissipation compared to comparable alternatives
Real estate advantage compared to alternatives

Single PCIe 11x11mm chip for concurrent dual-band
CL8080 real estate is ~50% compared to other solutions

Easier System Design

Keeping the higher number of PCIe interfaces available on the host SoC for other purposes
Wi-Fi subsystem does not require dedicated memories

Future proof: Major advantage for tri-band architecture (Wi-Fi 6 and Wi-Fi 6E access points) compared to other solutions

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