Radio Frequency Design

The Aruba ESP Radio Frequency Design section describes the technical design principals used in the design and implementation of an Aruba ESP WLAN. Topics covered include RF design, roaming optimization, and Wi-Fi 6.

Table of contents

• Radio Frequency Design
  • RF Design Methodology
    • Approach to a Proper RF Design
    • RF Signal Coverage
    • Access Point Placement
      • AP Capacity
      • AP Selection
      • AP Placement
      • AP Mounting
    • UXI Sensor Placement
    • AirMatch
    • ClientMatch
    • Channel Planning
      • 5 GHz Channel Width
      • 6 GHz Channel Width
      • Wi-Fi 6E Preferred Scanning Channels
      • Mixing Different Access Point Models
    • Transmit Power Settings
      • AirMatch
      • ARM
    • Transmit and Basic Data Rates
    • Wi-Fi 6 Enhancements
      • High Efficiency
      • OFDMA
      • Downlink MU-MIMO
      • Transmit Beamforming
      • Target Wake Time
    • Considerations When Upgrading to Wi-Fi 6E
      • Traditional WLAN Design Considerations
    • Device Classes in 6 GHz
      • Low Power Indoor (LPI) APs
      • Standard Power (SP) APs
      • Device Class Summary
        • LPI APs
        • SP APs
      • Enterprise Wi-Fi 6E LPI RF Layering Considerations

RF Design Methodology

The foundation of a stable, resilient, and efficient WLAN is a proper Radio Frequency (RF) design. It requires thoughtful planning, accurate installation, and appropriate configuration of wireless access points and antennas to achieve optimal coverage and minimize interference.

For more complex environments such as manufacturing floors or unique architectures, a physical site survey provides the most accurate AP design information because it measures both Wi-Fi data and non-Wi-Fi RF interference onsite. An onsite survey involves placing an AP in the environment to be covered and using software to measure the signal propagation.

As reliance on mobility and Wi-Fi continues to grow, an improperly designed WLAN can lead to decreased client performance and increased IT time required to troubleshoot inconsistent performance issues.

Suboptimal RF design can give rise to coverage gaps due to insufficient signal strength or signal quality, co-channel interference resulting from too much signal, and various other issues that affect clients adversely.

Allocating resources to a well-executed RF design is an essential step toward a successful WLAN deployment, ultimately providing users with a high-quality wireless experience.

Approach to a Proper RF Design

Aruba advises conducting a wireless design survey for all Wi-Fi installations, especially when migrating to Wi-Fi 6E due to potential differences in the 6 GHz band’s propagation characteristics. Predictive survey tools can provide reliable AP location estimates for typical environments such as offices, schools, and hotels, while complex environments such as manufacturing floors may require a physical site survey to measure Wi-Fi data and non-Wi-Fi RF interference.

Both methods generate a heat map and recommend AP locations, but onsite surveys offer greater accuracy in RF design, AP mounting details, cabling requirements, and antenna orientation recommendations. Aruba recommends both types of surveys, performed by wireless professionals.

RF Signal Coverage

RF design should account for the varying propagation patterns between higher and lower frequencies. WLAN designs should focus on signal coverage requirements for 5 GHz or 6 GHz bands to ensure optimal performance and capacity. A well-designed 5 GHz network may be upgraded to 6 GHz with 1:1 AP replacement, depending on client density, throughput requirements, and physical environment.

For Wi-Fi 6 and 6E deployments, identify a suitable RSSI target to drive cell size for AP ranges from -55 dBm to -65 dBm, depending on requirements and capacity needs. For instance, if designing for MCS11 at 40 MHz channel bandwidth in a high-density environment, the target should be closer to -55 dBm.

To maximize performance in Wi-Fi 6 and 6E deployments, the minimum Received Signal Strength Indicator (RSSI) should be -55 dBm at cell edge to deliver an MCS11 data rate on a 40 MHz-wide channel with soft roaming support.

When deploying a Wi-Fi 6 network using dual or tri-band APs, 2.4 GHz radios for some of the APs should be turned off to reduce co-channel interference. This helps accommodate the limited number of channels and provides greater propagation of a 2.4 GHz signal. Use VisualRF or onsite tools to ensure that coverage gaps do not occur when disabling the radios.

Note: Although signal availability is critical for WLAN operation, Aruba ESP wireless networks should be designed for user and device capacity, not RF coverage.

Access Point Placement

AP Capacity

Assess the current WLAN’s performance and determine the capacity and coverage requirements for the new WLAN. The 6 GHz band provides greater bandwidth, so consider the number of users, the types of applications they use, and the quality of service (QoS) required.

AP Selection

Choose the appropriate 6 GHz APs to meet capacity and coverage requirements. Consider the different features and capabilities, such as radio types, available Ethernet ports, and PoE requirements, to determine which AP model(s) meet specific requirements.

Refer to Aruba’s Indoor Access Points page to compare AP features and capabilities.

AP Placement

Use the following recommendations as a starting point for designing Aruba indoor omnidirectional access points within a typical open office environment:

• Space APs 30-50 feet (10-15 meters) apart.
  • Consider client performance, architecture, and interior design. Newer drywall construction can be very forgiving for Wi-Fi transmissions, while cinder block walls or other dense material may impede signals.
  • Remember that the 6 GHz band might have different propagation characteristics, so the AP placement may not be the same as that used for the 5 GHz design depending on coverage requirements.
• Design for the following capacity:
  • 30-40 clients per AP
  • 2.5 Wi-Fi devices carried per user (laptop, phone, tablet, smartwatch, etc.) with a 50% connection rate.
• Add APs to areas with frequent or increased user density.
  • Conference rooms, atriums, or special event areas.
  • Identify peak-load periods when the WLANs have the highest usage or visibility.

The figure below shows a sample office layout with APs. The staggered spacing between APs is equal in all directions and ensures suitable coverage with seamless roaming.

Sample Office AP Layout

AP Mounting

AP mounting height, location, and orientation are as crucial for wireless coverage as streetlamp locations are for roadway lighting. Follow the guidelines below when mounting indoor omnidirectional down-tilt antenna APs:

• With the exception of the hospitality-style AP, and certain outdoor AP models, in general, avoid mounting AP-xx5 series APs vertically on a wall.

• AP-xx5 series APs should be mounted horizontally with the radome (white surface) facing down at a height of 12-25 ft (4-8 meters).

• If mounting on a wall, use a 90° AP mount that supports the AP models used, available for purchase from a third-party vendor.

• In general, do not install APs above drop ceilings. This introduces attenuation between APs and clients and can negatively impact the user experience as well as Aruba AirMatch calculations.
• Avoid mounting APs on building columns, pillars, or I-beams unless intentionally using a physical structure to create RF shadows.
• Avoid installing APs in credenzas, bookcases, or other furniture that would introduce unnecessary attenuation.
• Aruba highly recommends consulting with an experienced and certified WLAN engineer to perform a pre-install survey and review planned AP locations.

UXI Sensor Placement

In a base design, UXI sensors should be deployed in approximately a 1:5-8 AP ratio, or one per small building floor. Mount the sensors 4-5 feet high from ground level to simulate where Wi-Fi-connected devices are typically positioned. Business and technical requirements may call for different placement.

As with any other client, the sensor connects to the best available AP. This does not necessarily mean the AP with the best RSSI. AP association is based on several variables, including client load balancing and RF metrics. Ultimately, the sensor associates to the AP available to respond to the probe request. The aim is to simulate client experience rather than test each AP in the area. 

UXI sensors re-associate to the WLAN each test cycle. The best BSSID to connect can change between test cycles due to changes in the network environment.

More design and deploy guidance can be found in the UXI Design and UXI Deploy guides within this VSG.

Note: When a WLAN is deployed with overlapping cell coverage, the failure of an AP typically is not detected from the user’s perspective. The same is true for the UXI sensor. A network management platform, such as Aruba Central, is required to detect device failures.

AirMatch

Aruba AirMatch analyzes periodic RF data across the entire network, or a subset of the network, to derive configuration changes algorithmically for every Aruba AP on the network. The APs receive regular updates based on environmental conditions, which benefits both IT staff and users. AirMatch is the enhanced version of Adaptive Radio Management (ARM) technology. It has a new automated channel optimization, transmit power adjustment, and channel width tuning system that uses machine learning intelligence to generate the optimal view of the entire WLAN automatically.

To determine an improvement plan, AirMatch generates an average radio conflict metric. After AirMatch generates a new plan, the plan conflict value is compared with the current operating network, and an improvement percentage is calculated. If the improvement percentage is higher than or equal to the configured quality threshold (8% by default), a new plan will be deployed at the configured “Automatically Deploy Optimization” timer.

An AP can make local channel changes in the case of poor service to a client. These localized channel changes are done without disturbing the entire channel plan. This information is relayed to the AirMatch service so the AirMatch engine can factor in the changes for future channel plans.

Configure the AirMatch wireless coverage tuning value to Balanced. Remember that channel change events are disruptive, so it should be done only when required, outside of production hours.

Note: Aruba’s Adaptive Radio Management (ARM) continues to run locally on APs and can alter the transmit power of an individual AP in response to high interference.

Note: AirMatch is unlikely to overcome poor physical deployment of APs. Good survey and deploy procedures increase the accuracy of AirMatch.

ClientMatch

ClientMatch improves the experience of wireless users by reducing the number of sticky clients, load balancing them between APs and steering them between supported bands. ClientMatch continually monitors the RF neighborhood of each client to determine if it is getting the required level of service from the AP with which it is currently associated. When appropriate, it can steer clients intelligently to an AP radio that can provide better service. Aruba recommends keeping ClientMatch enabled.

ClientMatch is Wi-Fi 6 aware, and there is no special knob for this feature. It is enabled by default, but can be disabled if required. It attempts to match Wi-Fi 6 clients to Wi-Fi 6 radios in a mixed-AP deployment environment.

Note: While ClientMatch is effective at matching clients to the best radio available to them, it should not be used as a replacement for proper RF design.

Channel Planning

Design the channel plan to minimize interference between APs. The 6 GHz band offers more non-overlapping channels than the 5 GHz band, so use these additional channels to reduce co-channel interference. Aruba AirMatch can manage dynamic channel and bandwidth and transmit power assignment for most installations. For RF configurations beyond the recommended AirMatch feature, consult an Aruba or partner system engineer.

5 GHz Channel Width

Channel width is a critical consideration for 5 GHz deployments. Wider channels offer higher throughput for individual clients but fewer non-overlapping channels. Narrower channels yield lower data rates per client but more available channels, reducing co-channel interference risk.

AirMatch does a great job of managing bandwidth dynamically, but WLAN performance requirements may vary within a campus. Because of this, Aruba allows for adjustment of minimum and maximum channel width. Performance requirements may merit adjustment of channel width parameters. For example:

• Example 1: A marketing department may have lower client density and higher throughput requirements for mobile users. Raising the minimum channel width from 20 MHz to 40 MHz ensures that no AP uses channels less than 40 MHz wide.
• Example 2: A distribution center has low throughput requirements for data collection guns, but requires maximum reliability with low interference. Statically assigning the channel width to 20 MHz may be ideal to reduce the risk of co-channel interference that could impact client devices negatively.

Wider channels become increasingly easier to operate as Wi-Fi 6 clients become more prominent within the typical mobile device population. For optimal performance, allow AirMatch to determine channel width whenever possible.

For channel allocation, use AirMatch to detect interference and establish an optimal channel plan to circumvent radar. If specific DFS channels consistently detect radar in the environment, consider removing them from the valid channel plan to avoid coverage issues.

6 GHz Channel Width

While 160 MHz wide channels can be effectively deployed in the 6 GHz space, 80 MHz are used most commonly, especially in the initial years of 6 GHz operation.

Aruba Central’s default radio profile is set to 80 MHz min and 160 MHz max, providing up to 14 non-overlapping 80 MHz wide channels or seven 160 MHz wide channels where allowed by regulations. Like the 5 GHz channel width recommendations above, performance requirements should be considered to determine the proper minimum and maximum channel width. The available 6 GHz channels for the US and EU are:

US:

• 59 - 20 MHz channels
• 29 - 40 MHz channels
• 14 - 80 MHz channels
• 7 - 160 MHz channels

EU:

• 24 - 20 MHz channels
• 12 - 40 MHz channels
• 6 - 80 MHz channels
• 3 - 160 MHz channels

Note: Spectrum allocation is a regulated function, and rules differ by nation. This guide covers Wi-Fi 6E regulations in the US and European theaters; most other countries follow one or these models, with minor national variations.

Wi-Fi 6E Preferred Scanning Channels

The traditional way for a client device to discover a suitable AP for connection is to tune its radio to a 20 MHz channel, transmit a number of probe requests, wait on-channel for ~20 msec for probe responses from APs operating on that channel, then tune to the next channel and repeat. Determining APs for 2.4 and 5 GHz takes significant processing time, can result in jitter or data loss as the device is away from its serving AP, and reduces battery life due to extra frame transmissions. Adding Wi-Fi 6E and 59 more 20 MHz wide channels would require a significantly longer time.

To prevent this in 6 GHz, every fourth 20 MHz channel is designated for scanning, and APs should align their transmitting channels with Preferred Scanning Channels (PSCs). For wider channels, 80 MHz or 160 MHz, the primary 20 MHz channel where the beacon is transmitted will align with a PSC when available. This achieves two goals.

• First, client devices searching for a suitable AP only scan 15 channels at most to find a beacon or other advertisement.
• Second, non-PSC channels are not burdened by beacons, probe requests or responses, allowing them to transfer the maximum possible user data. To enforce good behavior, several rules are used to reduce excessive probing and encourage device designers to optimize their probing algorithms.

Mixing Different Access Point Models

Both the AP-5xx and AP-6xx series access points support Wi-Fi 6; however, they should not be combined within the same contiguous RF service area, particularly when activating the 6 GHz radios in AP-6xx series units. Aruba advises using identical AP models within a contiguous RF service area (RF block), which can be perceived as a roaming domain defined by a building or a floor, contingent on the designer’s perspective and user requirements.

Transmit Power Settings

Optimal power settings will vary based on the physical environment. Aruba recommends using AirMatch to decide each AP’s optimal transmit power values.

AirMatch

For AirMatch, use the default Radio Profile as a starting point.

ARM

If the deployment calls for AirMatch not to be used, Adaptive Radio Management (ARM) is available and can be configured within the Aruba Central group. But variables like client density, interference(co-channel or non-Wi-Fi), wall attenuation, and AP elevation must be considered to determine the optimal minimum and maximum Tx power values.

When leveraging ARM, Aruba recommends the following considerations:

• The difference between minimum and maximum Tx power within the same radio should be no more than 6 dBm.
• Tx power of 5 GHz radios should be at least 6 dBm higher than 2.4 GHz radios.
• Tx power of 6 GHz radios should be equal to, or no more than 3 dBm higher than 5 GHz radios.

As an example, for a modern office environment with an open floor plan, use the following ARM configuration as a starting point, then monitor and adjust if required:

• In the 2.4 GHz band, set the minimum power threshold to 6 dBm and the maximum to 9 dBm.
• In the 5 GHz bands, set the minimum power threshold to 15 dBm and the maximum to 18 dBm.
• In the 6 GHz bands, set the minimum power threshold to 18 dBm and the maximum to 21 dBm.

Note: Propagation losses in the 6 GHz band are greater than in 5 GHz, but the difference is slighter than the variation between 2.4 GHz and 5 GHz. Wireless design professionals may not see a difference in open space coverage between 5 and 6 GHz. However, they should consider that the higher frequency is more susceptible to attenuation from walls and other building structures, so environments such as closed office spaces, college dorms, hotels, and other similar buildings may see significant differences in cell size between 5 and 6 GHz.

Transmit and Basic Data Rates

Transmit data rates are important for optimized Wi-Fi roaming because they affect the speed of data transmission between a device and the Wi-Fi access points. When a device roams from one access point to another while maintaining an active Wi-Fi connection, it must maintain a certain level of signal strength and data rate to ensure a smooth transition without disruptions or dropouts.

If the signal strength and data rates drop low too low before a mobile client can establish the next AP, it can lead to dropped voice or video calls, slow downloads, or other performance problems. Because clients, not APs, decide when to roam, it the designer and administrator must monitor and tune the environment every time a new WLAN is deployed or floor space is remodeled to ensure proper performance and optimal client roaming.

Aruba provides highly effective features such as ClientMatch to steer clients to the best AP based on client capabilities and AP load. However, it can take up to 60 seconds or more to make the first steer attempt, so a client can have a bad experience if it does not roam properly on its own. It is important to consider tuning the transmit and basic rate settings in addition to RF transmit power described in the previous section.

An Aruba WLAN can support any environmental requirements, user densities, and applications with proper RF design and correct AP placement. The list below includes settings to consider modifying to promote healthy client-initiated roaming.

Roaming Best Practice

An Aruba WLAN can support any environmental requirement, user density, and application with proper RF design and correct AP placement. The list below provides settings that promote healthy client associations and client-initiated roaming.

Fast Roaming Best Practice

Wi-Fi 6 Enhancements

The following AOS 10 features support specific capabilities for the Wi-Fi 6 standard.

High Efficiency

Each of these Wi-Fi 6 specific features falls within the high efficiency profile. The high efficiency parameter activates all the Wi-Fi 6 features on the radio. High efficiency is enabled by default, and Aruba recommends keeping it enabled.

OFDMA

OFDMA enables a Wi-Fi channel to be divided into smaller subchannels so the AP can send data to multiple clients simultaneously. A 20 MHz–wide channel supports up to nine clients, and the number of subchannels adjusts continually to support fewer higher-speed clients or additional lower-speed clients. Subchannel use is dynamic and adjusts automatically every transmission cycle, depending on client data needs.

This feature is enabled by default for Wi-Fi 6 clients and APs but works only when both sides are Wi-Fi 6 capable. Wider channels support more subchannels. This means an 80 MHz–wide channel can support up to 37 clients at a time. OFDMA currently supports downlink traffic from the AP to the clients and will eventually support uplink traffic from the clients to the AP.

Downlink MU-MIMO

The Wi-Fi 6 standard enhances MU-MIMO to support up to eight clients simultaneously when using an eight spatial stream (SS) AP, such as the Aruba 55X models. Increasing the number of spatial streams has the following benefits:

• Achieving higher data rates when communicating with a single client.
• Achieving higher aggregate performance in an MU-MIMO environment when communicating with multiple clients simultaneously.

Single and Dual Stream Clients

This feature is enabled by default. Keeping it enabled leads to increased capacity and higher speeds per user.

Transmit Beamforming

Wi-Fi 6 employs an explicit beamforming procedure using channel-sounding with a null data packet to compute the antenna weights and focus the RF energy for each user. Keep this feature enabled for optimal performance benefits.

Target Wake Time

An important power-saving feature of Wi-Fi 6 is target wake time (TWT). TWT uses negotiated policies based on expected traffic activity between Wi-Fi 6 clients and a Wi-Fi 6 AP to determine a scheduled wake time for each client. Keep this feature enabled to allow clients to sleep longer and save more power.

Considerations When Upgrading to Wi-Fi 6E

The introduction of new channels and an abundance of spectrum raises questions about optimal deployment strategies across various enterprise settings. When planning an upgrade to Wi-Fi 6E, additional considerations should be evaluated carefully to ensure a successful implementation.

Traditional WLAN Design Considerations

When adding 6 GHz capabilities to a WLAN with existing 5 GHz and 2.4 GHz bands, deciding whether to broadcast all WLANs on all three bands depends on several factors, such as client device support, capacity requirements, and interference. Consider the following when making this decision:

• Client device support: Not all client devices support the 6 GHz band. Before enabling all radios, evaluate the compatibility of the users’ devices to determine if they will benefit from the 6 GHz band. Enabling the 6 GHz band is most beneficial if a significant portion of the devices support it.
• Capacity requirements: The 6 GHz band offers more non-overlapping channels and higher data rates, allowing for increased capacity and reduced congestion compared to the 2.4 GHz and 5 GHz bands. If the network has high capacity demands, enabling all three bands can help distribute the load more effectively.
• Interference: The 2.4 GHz band is prone to interference from various non-Wi-Fi devices, such as microwaves and Bluetooth devices, which can negatively impact performance. The 5 GHz band has less interference but still faces challenges. The 6 GHz band is less congested and offers a cleaner spectrum, providing better performance. Therefore, enabling all three bands can help mitigate interference issues by allowing compatible devices to use the less congested 6 GHz band.
• Coverage: The 6 GHz band has different propagation characteristics compared to the 2.4 GHz and 5 GHz bands. It has a slightly shorter range and, in turn, is slightly more susceptible to signal attenuation by obstacles. As a result, you may need to adjust your AP placement and 6 GHz transmit power settings to ensure optimal coverage when enabling all three bands.

To determine if broadcasting all WLANs on all three bands is preferable, consider the following:

• SSID management: Broadcasting all WLANs on all bands may lead to increased management overhead and unnecessary SSID clutter for users. It is generally recommended to limit the number of SSIDs per band to minimize overhead and simplify management.
• Band steering: Consider implementing band steering to encourage capable client devices to connect to the more efficient 5 GHz or 6 GHz bands instead of the 2.4 GHz band. This can help balance the load across bands and improve overall network performance.
• Application-specific WLANs: If the network has specific WLANs designed for particular applications (e.g., voice, video, or guest access), consider consolidating them and using Aruba’s policy enforcement capabilities to assign different user roles and/or VLANs to different clients within the same WLAN. If consolidation of WLANs is not possible at the time of upgrade, choose to broadcast these WLANs only on specific bands that provide the best performance for those applications.

Incorporating 6 GHz capabilities into a traditional WLAN with 5 GHz and 2.4 GHz bands can yield benefits such as enhanced capacity, reduced interference, and improved performance by enabling all radios and broadcasting all WLANs across the three bands. However, the decision should consider factors such as client device support, capacity requirements, interference, and coverage. Use Aruba AirMatch for band steering and Policy Enforcement Firewall (PEF) to consolidate application-specific WLANs, optimizing the utilization of each band.

Device Classes in 6 GHz

Device classes are designed to regulate and restrict devices in order to safeguard incumbents sharing the 6 GHz band with licensed frequencies from potential interference. The two relevant classes are Low Power Indoor (LPI) and Standard Power (SP). These are briefly discussed below.

Low Power Indoor (LPI) APs

Low Power Indoor (LPI) APs are intended for indoor deployment with fixed installation. To prevent outdoor use and risk to incumbents in the 6 GHz space, regulators prohibit LPI APs from having connectors, weatherproofing, or operation by battery; they also must use wired power.

Standard Power (SP) APs

Standard Power APs require fixed installation and permanent mounting to a structure. They require an Automated Frequency Coordination (AFC) system, similar to the CBRS spectrum access system (SAS). Standard Power devices must automatically detect their location, usually through GPS.

Device Class Summary

The following lists summarize the device class considerations mentioned above:

LPI APs

• Fixed indoor only
• No antenna connectors
• No weatherproofing
• Cannot be powered by battery
• Must have wired power

SP APs

• Fixed indoor/outdoor
• Controlled by AFC database
• Automated geolocation
• Pointing angle restriction

Enterprise Wi-Fi 6E LPI RF Layering Considerations

Customers may explore adding an extra layer of APs, segregating new channels into sub-bands for various device types. In this case, determining optimal channel widths for each layer is essential, as is evaluating the roles of 5 GHz and 2.4 GHz in future managed networks. For RF layering considerations, consult an Aruba or partner systems engineer and refer to the technical paper, “With Wi-Fi 6E, Is It Time to Consider a Layered Network Approach?”

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