This is a complete guide for designing the best deployment for a high density environment. The article is divided in Planning, Design, Deployment and Config.
Table of Contents
What is High-Density Wireless?
By definition, High-Density (HD) wireless scenarios refer to WLANs whose coverage area contains a relatively high concentration of APs and connected client devices. As mobile networking trends toward scenarios where users carry multiple client devices, HD WLANs become increasingly more commonplace. Therefore, WLAN administrators tasked with designing a successful HD network can do so using Ubiquiti’s UniFi platform, provided they carefully consider and account for all of the unique design variables surrounding the enterprise project.
UniFi Demo Simulator - FedEx Forum Site
Throughout the HD WLAN Design Guide, we’ll reference the “FedEx Forum” Site, inside the UniFi Demo Simulator. The “FedEx Forum” Site mimics a real-world HD deployment that supports more than 7,000 simultaneous Wi-Fi users today: https://demo.ubnt.com
Why HD WLANs Generally Fail?
Ubiquiti identifies three major areas that impact the performance of every HD WLAN deployment:
Four Part HD WLAN Design Guide
This four-part guide presents and explains from start-to-finish, the implementation of an HD WLAN using the Ubiquiti UniFi platform:
Part 1.1 - Planning: Application Requirements
The Purpose of the HD WLAN
Regardless of user density, the purpose of every WLAN is to support the wireless users’ application requirements. Therefore, the very first step when planning for the WLAN is to understand the user applications and behavior. Typical projects involving HD WLANs include stadiums, auditoriums, concerts, and other events where a high volume of users gather across the coverage area. The most common applications for these HD scenarios range from social media to live video/VoIP streams to simple web browsing. Consequently, use of these applications may see varied levels of activity due to the nature of the event, such as with spontaneous traffic bursts (e.g., everyone posts to social media during breaks) or as more constant streams of data (e.g., students taking notes in a lecture hall).
Core Applications Define Planning & Design
Recognizing the core applications and types of users on the network, begin to plan and design the HD WLAN with regards for the unique limitations and requirements of the planned project. For example, the performance of latency-sensitive applications like VoIP can degrade as WLAN usage reaches peak levels. Why? Because the wireless channel is shared among all nearby, active stations, an 802.11 station (i.e., the VoIP user) must ‘wait’ to transmit until the channel is free of activity. Fundamentally speaking, the principal applications and services on the network dictate the architecture and design of the WLAN—especially in HD scenarios.
Realistic WLAN Planning/Design
Can a WLAN simultaneously support latency-sensitive applications, as well as high bandwidth users? With total control over all of the variables affecting the WLAN, including client devices and the physical environment for deployment, the realization of both objectives in a single, culminating project becomes more realistic. When faced however with “bring your own device” (BYOD) scenarios, as HD WLANs often are, limited control over environmental variables during planning, forces the network to choose between supporting high throughput or low latency applications.
Part 1.2 - Planning: User Bandwidth
Client Traffic Analysis via UniFi DPI
Following deployment, enterprise network administrators can take advantage of the Deep-Packet Inspection (DPI) engine running on the UniFi Security Gateway (USG) to review the applications in use by client devices on the network. The UniFi Controller summarizes the total bandwidth consumed by the user applications, as well as the individual activity of users, so WLAN administrators can make firewall and other configuration changes to improve the performance of the network.
What is “Service Level Assurance”?
Prior to deployment however, anticipate which applications will be serviced by the HD WLAN to develop a plan for “Service Level Assurance” (SLA) ahead of estimating the “Per-Client Bandwidth”. A clearly-defined SLA identifies the primary applications and services to be supported on the intended network (such as VoIP or YouTube), and therefore, guides the early stages of planning and designing the WLAN architecture. Keep in mind that although low-end VoIP and video calls require minimal bandwidth, their tolerance for latency is also much lower, and therefore are designed uniquely. Although UniFi APs give “Quality of Service” (QoS) priority to such traffic (per WMM standards), initial planning/design for the HD WLAN should cater the specific needs of the applications.
Create an SLA for the HD WLAN
To help formulate the SLA for the users on our unique HD WLAN, let’s reference the client device “current-e58ba353” as a baseline example. A quick analysis of the DPI section under the UniFi Client Properties tab reveals its top three applications to be:
- Web Browsing
- Social Media, and,
- Video Download.
“Application Requirements” Data Table
The following “Application Requirements” table relates info about the speed and connection required to service some of the most popular applications used in today’s WLANs.
SLA for Multitasking & Multiple Users Types
In some WLAN scenarios, the SLA may seek to support a variety of user types, or even multiple applications per client device (i.e., network multitasking, background services), and should therefore sum together the total Bandwidth required for each application.
“Application A Bandwidth + Application B Bandwidth + Application C Bandwidth + … ”
For purposes of our HD WLAN example, our SLA assumes that the user (guest) is single-tasking, and therefore, seeks to support the most bandwidth intensive application used by client “current-e58ba353”: Video Download (0.3-4.5Mbps, with 1Mbps assumed for mobile resolution playback). This means that the “Per-Client Bandwidth” (that is, the HD WLAN’s SLA) is approximate 1Mbps.
“Maximum Aggregate Throughput Requirement”
To discover the “Maximum Aggregate Throughput Requirement,” that is, the total amount of bandwidth needed for the HD WLAN to support ALL client devices simultaneously, multiply the “Per-Client Bandwidth Requirement” (1Mbps) by the “Total Number of Client Devices” (the “FedEx Forum” has a seating of 18,119). While not all 18,119 in attendance will bring one mobile device to the event, planning for future growth is an important consideration for every WLAN.
“Per-Client Bandwidth Requirement” x “Total Number of Client Devices” = “Aggregate User Throughput Requirement”
(1Mbps) x 18,119 Clients = 18,119Mbps Aggregate
“Expected Peak Aggregate Throughput”
Therefore, the “Maximum Aggregate Throughput” at the “FedEx Forum” is 18,119Mbps. However, since it is impractical to assume that all 18,119 will ever pass traffic simultaneously, let’s multiply the “Expected Peak Usage” (let’s estimate 50% of total attendance) by the “Maximum Aggregate Throughput Requirement” to determine the “Expected Aggregate Throughput”.
“Maximum Aggregate Throughput Requirement” x “Expected Peak Usage” = “Expected Peak Aggregate Throughput”
(18,119Mbps) x (50%) = 9059.5Mbps “Expected Peak Aggregate Throughput”
Later on, the “Expected Peak Aggregate Throughput” value will directly help to estimate the minimum number of Access Points required for the HD WLAN deployment.
Upstream Data Links
The ~9Gbps of data passed on the HD WLAN by the guest users is Internet traffic, and therefore, the upstream pipe to the ISP should support the “Expected Peak Aggregate Throughput” to account for the offered SLA at the event. Throughout the HD WLAN, make sure that upstream network infrastructure (e.g., switches) accommodates the traffic bandwidth downstream (i.e., aggregation switches at core, access switches at edge).
Part 1.3 - Planning: WLAN Capacity
What is Capacity?
In the context of all WLANs, capacity is defined as the data rates supported by an AP and its respective clients. Capacity is therefore, twofold dependent on the characteristics of both client devices and APs (hereafter called “stations”). By anticipating and analyzing the characteristics of stations, we can accurately calculate the capacity of the network in order to estimate the total number of access points required to support the planned HD WLAN.
Choose the Best AP Possible
Although “bring your own device” (BYOD) scenarios mean client devices cannot be consciously chosen, fortunately, WLAN administrators can select access points whose wireless characteristics offer the best performance to match their particular HD WLAN scenarios. This is also important to ensure that the HD WLAN has longevity through down-the-road support for the client devices of today and tomorrow.
Introducing the UAP-AC-HD
The UAP-AC-HD is Ubiquiti’s premiere 4x4 MU-MIMO Access Point for HD WLAN deployments. The UAP-AC-HD features the latest, cutting-edge 802.11 technology for breakthrough speeds (2.5Gbps aggregate PHY rates) at a revolutionary price that undercuts all competitors. The unbeatable price/performance advantage entices WLAN administrators tasked with deploying HD-ready APs on a tight budget, since more APs (beneficial in HD WLAN) can be deployed for a fraction of the price. And as Wave-2 802.11ac client devices begin to flood the consumer market, the UAP-AC-HD’s MU-MIMO technology especially targets HD WLANs, inasmuch as its synchronous, multi-client data streams push airtime efficiency to new levels in extremely dense coverage areas.
Introducing the UAP-AC-M
Alternatively, the UAP-AC-M unit supports versatile coverage options through external connectors for pairing with directional antennas. For example, by pairing the UAP-AC-M with a 45° airMAX sector antenna, WLAN administrators can produce small, controlled 5GHz cells—ideal in certain HD WLAN scenarios. By comparison, the omnidirectional antennas and mounting capabilities make the UAP-AC-HD well-suited for low-ceiling and wall deployments, while the UAP-AC-M (a Wave 1 “Single User” (SU) MIMO AP) is ideal for high-vaulted ceilings seen in auditoriums, stadiums, and concert halls.
WLAN Capacity Variables
To review, there are five variables that determine the supported data rates of a WLAN, including:
- 802.11 Protocol - the hardware standard characterizing the 802.11 stations on the WLAN (a, b, g, n, ac Wave 1, ac Wave 2). As a backward-compatible AP, the UAP-AC-HD immediately serves in HD deployments today, while anticipating growth as WLANs scale to support more client devices for years to come.
- Spatial Streams - the total number of data streams simultaneously transmitted and received by the AP and clients. “Multiple In, Multiple Out” (MIMO) operation traditionally has been limited by the supported data streams of the single client with whom the AP communicates. As a Wave 2 802.11ac access point, the UAP-AC-HD boosts the available airtime through true “Multi-User” MIMO mode, concurrently pushing up to 8 streams of data to clusters of 2G & 5G clients. And since most client devices opt for less antennas (i.e., fewer spatial streams) to conserve battery life, the UAP-AC-HD’s MU-MIMO technology is critically important to ensuring maximum WLAN performance.
- Channel Width - the bandwidth over which an AP and its clients transmit data signals (20/40/80 MHz). While 40/80 MHz channels are tempting, HD WLANs dictate use of 20 MHz channel widths to conserve the number of channels available for reuse during deployment (especially true in extreme HD scenarios). In contrast, larger channel widths in HD scenarios generally creates a fundamentally flawed WLAN design where closely-placed AP cells operating on same or nearby channels see degraded SNR performance and increased contention for use of the wireless channel.
- Signal-to-Noise Ratio (SNR) - the difference in receive signal (the desired data signal) and noise (the combined level of in-band interference). From the point-of-view of HD networks, SNR poses the greatest threat to performance since by nature, densely-packed WLANs face greater interference. In order to ensure strong SNR levels for clients, HD WLANs necessitate careful cell planning, including methodical channel assignments, very low, controlled transmit power levels, and precisely deployed AP locations.
- Guard Intervals (GI) - 802.11n/ac WLANs support “long” and “short” waiting periods between transmitted symbols (data). Although a short GI is desirable, UniFi APs automatically toggle between “long” and “short” GI depending on the WLAN performance.
PHY Rates vs. Throughput
Now that we have identified the factors that determine capacity, it's important to distinguish that these are physical-layer (PHY) data rates. What does this mean? Due to overhead in the 802.11 protocol, the actual amount of real TCP data payload sent over wireless signals is approximately half of the advertised PHY rates. When estimating the capacity of the HD WLAN, we’ll factor a 50% reduction of the calculated PHY rates to align with speed results experienced in the real-world.
Estimate Client Throughput
Returning to “current-e58ba353” as our baseline example, the reported 72.2Mbps PHY rate assumes that a ‘typical’ client device is characterized as:
- An 802.11n client device,
- With a single (1x1) data stream,
- Operating on a 20MHz channel,
- With the best SNR,
- And short GI.
By halving the PHY rate (72.2Mbps), we estimate that for the planned HD WLAN, the “Achievable Real-World Client Throughput” of 36.1Mbps.
Estimate Minimum Required APs
By dividing the total “Aggregate User Throughput Requirement” (9059.5Mbps) by the “Achievable Real-World Client Throughput” (36.1Mbps), we calculate 251 radios (rounded up from 250.955679) as the minimum number of radios required to service the HD WLAN.
“Aggregate User Throughput Requirement” ÷ Achievable Real-World Client Throughput” = “Minimum Required Radios”
(9059.5Mbps) ÷ (36.1Mbps) = 250.955679 Radios
In some scenarios, 2G and 5G bands can and should be used. Note however, that in many HD WLANs, such as stadiums and arenas, only 5G channels are deployed since propagation characteristics make 2G difficult to control.
Therefore, a “Minimum AP Estimate” of 251 APs could satisfy the capacity requirements for the “FedEx Forum” site, based on the following assumptions:
- Full person attendance at event is 18,119.
- “User-to-Client Device” ratio is 1:1.
- “Total Client Devices” at the event is 18,119.
- “Expected Peak Usage” is 50%.
- “Expected Peak Aggregate Throughput” is 9059.5Mbps.
- ‘Typical’ client device is 802.11n, 1x1, with strong SNR.
- WLAN operates on 20 MHz channels with short Guard Intervals.
- “Achievable Real-World Client Throughput” is 36.1Mbps.
The “Minimum AP Estimate” is a function of two capacity variables: “Aggregate User Throughput Requirement” and “Achievable Real-World Client Throughput”. In simpler words, a client’s speed and bandwidth requirements directly affect the capacity offered by an AP. Increased client speeds (e.g., more spatial streams, improved SNR) means fewer APs are required since each AP reaches greater capacity. Conversely, decreased client speeds means more APs are required. And bandwidth consumption on the network increases, more capacity is needed to support the user applications, thereby requiring more APs.
Theoretical vs. Actual APs Deployed
As a theoretical number, the “Minimum AP Estimate” gives network administrators starting point as they undertake the important task of designing the HD WLAN. The actual number of APs deployed will depend on a broad range of physical factors noted during site visits, floor plan analysis, as well as site surveys conducted at the intended HD WLAN site.
Part 2.1 - Design: Cell Sizing & Channel Patterns
Capacity, Coverage & “Cells”
Recall that WLAN capacity is directly dependent on the SNR of stations across the wireless coverage area. The primary design objective of each HD WLAN is to limit the coverage area provided by each AP (hereafter called “cells”), then apply an effective channel reuse pattern to ensure a high SNR for every station. HD WLANs perform poorly when AP cells are overextended or if channel reuse patterns are not respected.
Although the 2.4GHz band contains eleven 20MHz channels on which a WLAN can operate, only 3 may be used in a non-overlapping channel pattern: 1, 6, and 11. By contrast, the 5G band supports over 20 non-overlapping 20MHz channels, depending on the region. The availability of more channels gives the 5G band a distinct advantage in limiting the interference of neighbor cells through more flexible channel reuse patterns. And due to propagation characteristics, certain HD WLANs may only deploy on 5G channels, especially in open settings like stadium and arena, where controlling the effective size of a 2G cell can be physically challenging.
There are seven fundamental points to consider that can affect a cell’s coverage area:
In the 5G band, Dynamic Frequency Selection (DFS) operation requires APs stop broadcasting if radar signatures are detected. As part of the site survey, WLAN administrators must scan these channels prior to deployment and for planning. Whenever possible, include DFS channels in the HD WLAN design for a more robust channel reuse pattern.
Floor Plan Example
The following floor plan shows 118 UAP-AC-M deployed using a strict channel reuse pattern across the entire HD WLAN coverage area. The floor plan illustrates three fundamental characteristics of a properly designed HD WLAN:
Adjacent channels refer to WLAN channels whose bandwidth (channel width) edges touch. By contrast, non-adjacent channels are WLAN channels whose bandwidth edges are spaced with 20 MHz or more. For example, 5G channels 36 and 40 are adjacent channels; 36 and 44, non-adjacent channels. When deployed on neighbor and overlapping cells, non-adjacent channels see better performance, a principle that holds especially true in HD WLANs, where the combined total of competing, in-band signals is much higher. The adjacency of 2G channels 1, 6, and 11 causes SNR to degrade quickly, giving 5G the advantage in HD WLAN scenarios.
Part 2.2 - Design: Minimize Interference
Interference & HD WLANs
Interference represents the total amount of competing, in-band signals that prevent a station from ‘hearing’ the intended receive signal with clarity. The extreme proximity of so many client devices on adjacent and non-adjacent channels increases interference levels, and therefore, reduces SNR and performance across the HD WLAN service area. When properly designed, an HD WLAN ensures each connected client device has a strong SNR, while mitigating the potential for collisions and limiting the impact of in-band interference.
What is Co-Channel Interference?
Whenever WLAN administrators deploy two neighbor AP cells on the same channel, the overlapping coverage areas encounter Co-Channel Interference (CCI). With the resulting transmit collisions that occur as a result of CCI, stations must retransmit data, which results in decreased speeds, increased latency, and problems for client device connectivity. This is due to the Clear Channel Assessment (CCA) mechanism, which requires an 802.11 station to listen prior to transmission, and yield the channel in case a station is already transmitting on the wireless channel. An HD WLAN with poor channel design and uncontrolled coverage areas will suffer as CCI plagues the wireless network. Conversely, HD WLANs that deploy AP cells with strict channel reuse patterns and controlled coverage areas can avoid CCI in the wireless network.
What is Adjacent Channel Interference?
Although CCI is largely avoidable in a properly designed, well-controlled wireless network, Adjacent Channel Interference (ACI) presents a significantly greater challenge for HD WLANs, and is not easily countered. ACI describes the overall increase in interfering, in-band wireless signals faced by stations as multiple AP cells are placed in relatively close proximity. By overextending the coverage area in a dense wireless setting, ACI increases aggressively throughout the HD WLAN, thereby reducing SNR levels for client devices, and dropping speeds dramatically. More generally, ACI speaks to the type of interference generated along the ‘tail-ends’ of an 802.11 transmission, which raise noise levels for other nearby in-band stations. Because adjacent channels (i.e., 36 & 40) suffer greater interference levels than non-adjacent channels (i.e., 36 & 165), the channel design for HD WLANs should position AP cells on adjacent channels as distantly as possible.
Best Practices for HD WLAN
To review, an HD WLAN should follow a series of best design practices:
Part 3.1 - Deployment: AP Placement
In general, most client devices as well as all UniFi Access Points feature antennas that are omnidirectional. Similar to a light-bulb, an omnidirectional antennas radiates wireless signals in all directions. More specifically however, the coverage area produced by an omnidirectional antenna looks similar to a donut pattern, with peak signal strength nearest to the center of the donut, and weaker signals at the edges of the ‘cell’. Recognizing that not only UAPs but client devices radiate signals in all directions is crucially important to understanding interference from all station types contributes to the SNR across the HD WLAN coverage area.
Ceiling & Wall Mounted APs
Indoor UniFi Access Points like UAP-AC-HD and UAP-AC-PRO feature easy mount fixtures for quick installation into walls and ceiling tiles. The UAP-AC-HD provides excellent wireless coverage in extremely dense indoor with ceilings under 25 feet height. Although the antenna coverage pattern of each indoor UAP is similar, understand that reflective surfaces and multipath effects in crowded, more dense settings can result in unexpected signal readings from distant and/or nearby APs, therefore necessitating careful cell adjustments based on site survey analysis.
Alternatively, directional antennas can be paired with select UniFi Access Points like UAP-AC-M to produce distinct, controlled coverage areas, making them very popular in outdoor or open indoor settings. When mounting UAPs in open rooms with high ceilings (25 feet and higher), omnidirectional antennas are incapable of producing distinct coverage areas vital in the design of the HD WLANs. Instead, pair the UAP-AC-M with directional antennas pointed at specific areas of the HD WLAN event to produce controlled areas of coverage with robust SNR. Note that when using 5GHz directional antennas with the UAP-AC-M that the 2G radio should be disabled.
“Under Seat” APs
An increasing more popular AP placement trend in today’s HD WLANs, such as seated sporting events, is mounting APs below users in attendance. By securely installing an AP in a locked boxes under seats or within the building foundations itself, this coverage technique seeks to improve the SNR of client devices by placing APs in closer to the users themselves. The “under seat” technique however presents new challenges for the HD WLAN, including coverage overextension during low attendance events, since less users means fewer bodies attenuating (controlling) the size of each wireless cell.
Part 3.2 - Deployment: Wireless Site Surveys
While important during the planning phase, visiting the HD WLAN site before and after deployment is totally necessary in order to critically assess the area for design and installation guidelines, as well as to conduct crucial site surveys to gather RF information needed for channel assignment. Although the UniFi Controller supports RF scanning with second-generation UniFi Access Points, be sure to also bring sample client devices with spectrum analysis and WLAN scanning software, as well as cameras to document the key areas involved in deployment, such as installation areas, potentially problematic regions, and cable drops.
Map, Topology & Deployment
After visiting the intended deployment site and making adjustments to the final channel plan, WLAN administrators can begin to install UAPs. In addition to the high capacity requirements at HD wireless events, the same-channel requirement for two neighbor UAPs to perform a Wireless Uplink make this topology inappropriate for HD WLANs. Instead, connect each UAP via wired Ethernet cables back to UniFi Switches to support the bandwidth requirements at both the access and core layers of the network.
After supplying POE to the UAPs and updating with the intended channel pattern, consider defining simple SSIDs to uniquely identify each UAP as you walk around the HD WLAN coverage area. With any site walkthrough, you should carry a sample client device (anticipated at time of HD WLAN Planning) to measure and track the most important metrics throughout and across the coverage area including signal strength, noise floor, and SNR. Since the purpose of the initial site walkthrough is to establish, define, and adjust the intended wireless coverage area, be sure to also bring a laptop make immediate configuration changes to the deployed UAPs as well.
Controller Tips for Site Surveys
As part of the Site Walkthroughs, consider using the WLAN Override function to temporarily rename the primary SSID broadcast by each AP to uniquely identify each individual cell to the client device performing the Site Survey. To tweak the HD WLAN coverage area between events, create a backup of the Site that contains the “one-SSID-per-AP-radio” naming convention.
The UniFi Mobile App allows WLAN administrators to collect the most important metrics conducted during the Site Survey, including signal strength and noise levels. Following deployment, use the UniFi Speed Test as well as intended applications during live events to ensure that client devices support the SLA requirements for the HD WLAN.
UniFi RF Scanning
In order to make educated decisions regarding channel operation throughout the wireless network, WLAN administrators must study and analyze the RF environment within the HD WLAN. Before and after deployment, use the RF Scan tool to conduct a spectral analysis from the perspective of each UAP. During the RF Scan, the UAP radio will stop broadcasting WLANs for up to 5 minutes in order to ‘listen’ the RF environment. Following the RF Scan, the UAP radio reports two important characteristics needed to level of interference as well as utilization percentage. Based on the results of each scan, record, replan, and reassign channels before reevaluating the RF environment of the HD WLAN. Be sure to run the RF Scan tool on all APs individually, but not simultaneously, otherwise the data presented by the spectral analysis will not accurately represent the RF environment in which the HD WLAN operates (furthermore, all clients will experience connectivity issues).
UniFi Statistics & Insights
The UniFi Controller gathers and reports the most important Client and WLAN information in real-time needed to make ‘on-the-fly’ changes to the wireless network under management. Here are a few of the most important in-Controller Statistics and Insights to review from the perspective of HD WLANs.
Part 4 - Config: UniFi Controller
When left unchecked, broadcast and multicast network traffic can severely reduce the available airtime on the HD WLAN, leading to decrease in speed, increase in latency, and potential connectivity problems for clients. Consider segmenting the wired and wireless portions of the network through VLAN assignment at time of WLAN creation. Alternatively Port Isolation at the switch layer to limit unnecessary traffic and conserve precious airtime available to stations in the HD WLAN.
To ensure maximum Access Points make efficient use of airtime, limiting the number of SSIDs announced throughout the HD WLAN is a vital detail. Although UAPs support up to 4 SSIDs per radio band, most scenarios (including HD WLANs) only require two SSIDs to support two types of security: Open for ‘Guests’ and WPA2-PSK or -EAP for trusted, ‘Corporate’ users). For client roaming reasons, use the same SSIDs throughout the entire HD WLAN coverage area (e.g., SSID-event) rather than complicated naming schemes (e.g., SSID-11th-floor, SSID-lobby). Any SSID that serves a nominal purpose separate from the capacity objectives of the HD WLAN (e.g., SSID-admins) does not warrant existence.
To limit the impact of data hungry users and applications that jeopardize the availability of bandwidth and airtime on the HD WLAN, define widespread rate limits (in Mbps) via the User Groups feature. Speed limits that are too strict can detrimentally affect the performance of the wireless network, while too high of speed limits the effectiveness of traffic shaping.
Following association and/or when roaming in the HD WLAN coverage area, client devices negotiating at low speeds (due to long distance from the AP) have a negative impact on the aggregate performance of the wireless cell through poor airtime efficiency. Therefore, proper design and architecture of HD WLANs paired with signal threshold levels helps ensure that clients remain connected to the intended AP cell offering them the best performance. When defining the Minimum RSSI setting, WLAN administrators must be careful, since too strict threshold levels can result in severe, widespread connectivity problems that cripple user activity on the network. For HD WLANs, Ubiquiti recommends setting the Minimum RSSI to no greater than -75 dBm, where lower thresholds levels (e.g., -80 dBm) mean clients will remain connected to the AP at greater distances from the center of the cell coverage area. Because UniFi Minimum RSSI uses a ‘soft’ kick implementation, whether or not the station disassociate from the AP is ultimately determined by the client device itself.
Although an increasing number of client devices today support and even prefer 5G operation, balancing the client activity between wireless bands often fails in large part due to the strong signals and propagation characteristics of the 2G band. In dual-band HD WLAN scenarios therefore, steering capable wireless clients to the 5G band is a particularly vital configuration setting to avoid 2G band congestion. Because UniFi Band Steering uses a ‘soft’ steering implementation, whether or not the station associates and remain connected to the 5G band is ultimately the decision of the client device itself.
The unpredictability introduced by variables like user attendance and roaming can often result in scattered wireless activity through the HD WLAN. While emphasis on proper design, architecture, and AP placement precedes and carries more importance than post-deployment configuration ‘tricks’, the UniFi load-balancing technique defines a soft user-ceiling whereby APs attempt to kick the clients with the weakest signals until the total number of associated clients returns to the defined threshold. Because UniFi load-balancing uses a ‘soft’ kick implementation, whether or not the station disassociate from the AP is ultimately determined by the client device itself.
802.11 Rate Configuration
In High-Density WLANs, where airtime efficiency is critically important to the overall performance of the wireless network, carefully consider adjusting the 802.11 RATE AND BEACON CONTROLS—albeit with extreme caution. Improper configuration of this advanced feature, can lead to disruptive performance or widespread connectivity problems for clients throughout the WLAN.
Disabling lower rates benefits HD-WLANs in a few important ways:
- Forces “sticky” roaming clients to re-associate to another AP. If the WLAN is well-designed/implemented, the new AP to which the client roams will offer a better signal and have a twofold impact on improving that client’s speeds as well as the aggregate performance of the previous BSS, since low-rate clients no longer drag down the airtime.
- Lessens the probability of channel contention (i.e., the likelihood that a transmitted signal collides with another signal being received by receiver in the WLAN) since there is less overhead from associated clients within the BSS. With low data rates disabled, clients transfer data as quickly as possible—then remain quiet. This frees up the WLAN for other clients that need to use the channel.
- Reduces the chance of hidden nodes on the network since associated clients are within a closer proximity of each other, and therefore, able to 'hear' whenever a transmitter is actively using the wireless channel.