Wi-Fi 7 and 5G for FWA need testing

By Xiang Li, Keysight Technologies

Follow these three steps to ensure your fixed-wireless access (FWA) designs will be compatible with the Wi-Fi fronthaul and 5G backhaul.

Many areas lack the wired infrastructure to bring residential broadband access. Making those connections has become costly and inefficient. Fixed Wireless Access (FWA) has emerged as a compelling alternative to deliver broadband internet without running wires to every home or business. With the latest Wi-Fi 7 and 5G advancements, FWA can provide the same user experience as wired connections. In some cases, FWA could even outperform a wired connection, depending on how much a subscriber can afford. Because FWA uses two wireless technologies, you must test designs for both.

The most common FWA use case involves using cellular network components — base stations and customer premises equipment (CPE) — to establish a high-speed internet connection. The equipment may be broken into two parts:

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Home Residential Gateway and CPE, where Residential Gateway provides Wi-Fi to the house,

A connection via Ethernet to the CPE handles the backhaul cellular link. This setup typically uses directional antennas on the base station and the CPE to optimize signal strength and maximize coverage.

Wi-Fi fronthaul and cellular backhaul in one box have gained popularity for their simplicity of in-home setup. Integrating Wi-Fi 7 and 5G into FWA systems significantly enhances this capability, bringing improvements in speed, latency, and network efficiency. Users can effortlessly pick up 5G cellular signals and seamlessly receive Wi-Fi 7 connectivity within one CPE device. This process does not require traditional copper or fiber-optic cables. Figure 1 shows an FWA deployment example of a household using a CPE to cover cellular and Wi-Fi signals.

Figure 1. A typical FWA gateway uses 5G or LTE as a backhaul and Wi-Fi as a fronthaul. (Image: Verizon)

FWA for homes and IoT

FWA’s convenient deployment applies to both mobile operators and end users. Operators do not need to spend money and time to deploy physical wires to establish connections. End users only need a CPE as a plug-and-play device to access the internet without drilling holes in their houses for wired connections. More than 500 operators in 170-plus countries and territories offer FWA services using either LTE/4G or 5G as backhaul access.

Smart devices are becoming more powerful. Consumer and enterprise use cases are expanding dramatically in the Internet of Things (IoT) sector. These developments collectively drive the adoption of FWA using 5G and Wi-Fi 7 technologies. Only 5G and Wi-Fi 7 working together seamlessly can fulfill the increasing demand for speed, latency, capacity, and reliability. Figure 2 illustrates the projected growth in FWA connections from 2020 to 2026.

Figure 2. An example of FWA deployment shows customer-premises equipment (CPE) connected to the cellular network and user devices over Wi-Fi.

Challenges of FWA with 5G and Wi-Fi 7

It is building effective FWA devices due to the combination of cellular and Wi-Fi operation request design and test strategies. First, there is a fundamental mismatch between throughput rates between Wi-Fi and cellular. Wi-Fi in the home could be using 160 MHz channels with multiple 2×2 devices achieving close to 2 Gb/sec, whereas cellular, depending on the configuration and MIMO level, would have speeds in the low 100s Mbps. A demanding house with virtual reality applications, multiple video conferencing streams, and online gaming will have direct throughput demands that could overwhelm the cellular connection.

Secondly, different applications in the home have different quality of service (QoS) requirements matching their quality of experience (QoE) expectations. The correct mapping of these streams from Wi-Fi to and from cellular must work correctly, so background streams are not getting prioritized over real-time streams that have clear latency, throughput, and jitter requirements.

For example, security camera video streaming requires minimal jitter to function smoothly in real time. Conversely, tasks such as software updates or large file downloads, which are less time-sensitive, can be deprioritized to ensure that real-time applications receive the bandwidth they need. By effectively managing these QoS parameters, the Wi-Fi 7 FWA network can ensure a seamless and optimized experience for all users and applications within the home.

The last challenge is ensuring consistent and reliable throughput. 5G network speeds, influenced by numerous factors beyond user control, can vary significantly. A reliable and consistent connection is essential for FWA to offer a consistent user experience and serve as a viable alternative to wired connections. Thus, FWA devices must reliably provide stable connection speeds ranging from 50 Gb/sec to 100 Gb/sec to be considered effective and marketable.

With 5G mobile cellular networks, they started to support millimeter-wave frequency range 2 (FR2). Signals at these high frequencies have limited travel distances and are subject to serious path losses. Integrating FWA devices into mobile networks introduces additional complexity to monitoring 5G reception. Operators must have the capability to adjust resources dynamically according to changing usage.

Testing FWA systems

The industry has been anticipating the introduction of Wi-Fi 7 standards and the opportunities it will bring. For FWA integration, Wi-Fi 7 introduces a set of unique testing challenges. First, Wi-Fi 7 provides higher throughput with 4K QAM and 320 MHz operation. 4K QAM offers a 20% performance increase from 1K QAM and 320 MHz, doubling performance from Wi-Fi 6 160 MHz bandwidths. This means device design engineers need to run extensive stress tests to verify that the FWA system can handle the upper limits of the data throughput with no degradation in service. FWA must also perform well under high network traffic and complex service types.

Step 1: verifying RF performance

As mentioned in the previous section, both 5G and Wi-Fi 7 standards added new bands and channels to carry additional data for higher speed. Therefore, the first step is to revamp the RF design and verify its performance will meet all standards. Once engineers finish their design, they must run an RF verification test against all 5G and Wi-Fi 7 standards.

Ideally, the test setup should be as simple as connecting the design to a testing instrument. The testing instrument acts as an access point, and the DUT works as the client or vice versa. An example is shown in Figure 3. Assume the scenario runs a Wi-Fi 7 RF testing operating at 6 GHz using the 160 MHz bandwidth. The occupied bandwidth shown on the right side of Figure 3 should be around 160 MHz. Based on the measurement summary on the left side, we can see that the measured occupied bandwidth is around 156.62 MHz. That means this design satisfies the bandwidth requirement at 6 GHz using 160 MHz. Engineers can try different bands and bandwidth combinations to verify their designs. Backward compatibility with Wi-Fi 6 and 5 devices must be validated.

Figure 3. FWA connections continue to grow. (Image: Deloitte)

For RF testing, you should also test other values such as spectrum emission mask (SEM), MIMO spectrum flatness, data throughput, power vs time, error vs range, and error vs power. RF must be validated for compliance with the 802.11 RF part of the specification. These values will not only help your designs meet all standards, but they will also provide other insights about the products.

Step 2: perform extensive functional testing

5G and Wi-Fi 7 promised high capacity beyond their predecessors. To test these products, you need to simulate thousands of devices operating simultaneously to see if the FWA system can handle the traffic and the complex real-world scenarios.

Additionally, FWA often uses the cellular network as a backhaul, and the interaction between 4G/5G cellular as backhaul is very complex. Typically, the capacity of a 4G/5G backhaul is lower than that of the Wi-Fi link, potentially creating a bottleneck in the network. You must take this factor into your design process to ensure the network can efficiently manage data traffic without significant delays or losses. During the testing and verification phase, you must also consider this. Figure 4 shows the results of a load test.

Figure 4. Wi-Fi RF performance verification shows a channel’s bandwidth.

Step 3: troubleshoot designs with protocol analysis

Even after conducting tests using steps 1 and 2, you might find that it’s still possible to find performance issues between devices and the network. As a designer, you need visibility into the protocol and physical layer to debug design issues.

Consider the case where the Wi-Fi uplink (UL) throughput exceeds the cellular backhaul capacity. In such cases, it is vital to assess how the system prioritizes and manages traffic, possibly requiring mechanisms to throttle the Wi-Fi throughput to match the backhaul capacity or implement intelligent traffic management strategies to ensure critical data is prioritized.

Figure 5. Load tests let you verify that an FWA device under tests will function appropriately under strenuous use.

Moreover, the inherent characteristics of the 5G link, such as potentially longer latency, can impact the overall quality of service (QoE) for end-users. Conducting detailed QoE analysis for different traffic flows becomes essential. You can run over-the-air communications analysis, real-time protocol decoding, and physical layer analysis. They can help to optimize designs and mitigate negative impacts on user experience. Overall, FWA testing strategies must evolve to address these dynamic interactions between Wi-Fi 7 capabilities and the limitations of 4G/5G backhaul to ensure robust, efficient service delivery.

Conclusion

You can see the potential of revolutionizing broadband access, especially where traditional infrastructure falls short. This integration, however, presents significant challenges, including ensuring sufficient backhaul capacity and managing the variability of 5G networks. These obstacles necessitate continuous innovation, testing, and verification to ensure reliable and efficient service delivery.

Home Residential Gateway and CPE, where Residential Gateway provides Wi-Fi to the house,

A connection via Ethernet to the CPE handles the backhaul cellular link. This setup typically uses directional antennas on the base station and the CPE to optimize signal strength and maximize coverage.