Wireless LAN (WLAN) technology is fundamentally different than wired Ethernet. While this difference provides clear advantages to the enterprise, including improved communications, new applications, and increased productivity, it can also be intimidating to enterprises with little in-house RF experience. When implementing a business critical Wireless LAN, it is easy to become overwhelmed by the litany of questions pertaining to network planning and deployment. For example:

• What type of wireless features and services are required?
• Can the WLAN be deployed and managed with existing in-house resources?
• What is the best WLAN deployment approach?
• How should the WLAN equipment be configured?

Fortunately, Airespace has the answers. This practical guide for WLAN design and deployment highlights key planning criteria and discusses multiple options for determining optimum WLAN configuration. Whether leveraging industry best-practices compiled from Airespace's years of real-world RF experience, or using the powerful RF prediction and site survey capabilities integrated within Airespace Control System (ACS) Software, Airespace has the tools that make WLAN planning and deployment easy.

Understanding WLAN Requirements
The first step in WLAN planning and design is to identify user and application requirements and determine how best to satisfy them given existing building characteristics and WLAN capabilities. In a typical WLAN environment, the number and placement of access points and WLAN controllers will be a function of two primary things, required network performance and desired coverage area.

Network Performance
WLAN performance, like Ethernet, is heavily tied to its ability to support applications. As a result, user throughput requirements play a major role in WLAN planning. A corporate environment using wireless connectivity for email and internet access might only require 1 Mbps of throughput per user; an engineering school with bandwidth intensive applications might require 18 Mbps. As the RF is a shared medium, network administrators must determine how best to deliver optimal throughput to each individual user. This is typically a factor of AP signal strength and receiver sensitivity. Poor signal strength, for example, results in heavy packet loss, which ultimately drives down overall throughput.

The performance equation becomes more complicated when time-sensitive applications, such as voice, are introduced into the mix. In these environments, the following requirements must also be considered:

• Real-Time Performance: an average end-to-end latency (AP to switch to AP) of < 10 milliseconds is desired.
• Quality of Service (QoS): the ability to prioritize real-time traffic and to guarantee necessary bandwidth.
• Scalability: the ability to support many simultaneous voice conversations across a single AP without any additional client support.
• Seamless Roaming: the ability to maintain voice sessions while roaming between APs, even across subnets. Inter-subnet latencies below 50 milliseconds are required.

Coverage Area
In addition to performance, IT staff must also determine optimal WLAN coverage area. Is there a specific section of a building that requires wireless access, or should a WLAN extend to all common areas? Is VoIP or other applications driving a need to cover stairways, bathroom facilities, and other "hard to reach areas"? Should RF technology be restricted in specific areas, such as a parking lot, courtyard, or operating room?

AP signal strength plays an important role in determining WLAN coverage. Naturally, the stronger the signal, the larger the area covered by an AP. The key is to intelligently configure the transmit power of each AP so that signal strength is large enough to prevent coverage holes and meet WLAN performance requirements, yet not so large that adjacent APs interfere with one another.

Determining the Best WLAN deployment Strategy
After determining WLAN requirements, the next step is to plan the actual deployment of WLAN equipment. With an understanding of your user requirements and your RF environment, there are several ways that this can be achieved. Airespace provides extensive experience and best-in-class tools to make WLAN deployment easy in all types of building locations, regardless of how much RF experience is in-house. This is achieved via the following methods:

• Best Practices: AP configuration and placement can be determined based on empirical data collected from years of experience building wireless networks in similar types of environments.
• RF Prediction: computer simulation tools can be used to predict optimal AP location and configuration based upon specific building characteristics.

Airespace offers an optional Wireless Site Survey (WSS) tool that IT staff can use to verify the assumptions made via the above mechanisms. By taking live measurements of wireless activity, enterprises can fine-tune WLAN configuration based upon real-world RF parameters.

The type of planning and deployment method used is dependent upon specific performance requirements, building characteristics, and comfort level within the IT department. As there is no single method that is best for all enterprises, Airespace provides a variety of WLAN planning and deployment options.

Industry Best Practices
Every enterprise environment is unique. However, there are common trends in building characteristics and RF behavior that transcend across most locations. Airespace has leveraged years of experience deploying wireless networks to collect empirical data pertaining to these common RF trends, resulting in a collection of industry "best practices" pertaining to WLAN design and deployment.

Enterprises with fairly straightforward building characteristics and performance requirements can use industry best practices to cost effectively plan for WLAN deployment in their own environment (see insert). By following the basic principles outlined below, an accurate WLAN game plan can be created with minimal time and resources.

AP placement
Each building is composed of different construction material (e.g., glass, drywall, concrete, wood, etc). But, in the typical office environment, these have a minimal impact on determining how many radios are needed in a WLAN deployment. If you look at the typical 2.4 GHz path loss for different building materials (chart 1), for example, you will see that there is not much of a difference in density between those materials most commonly found in office environments - no more than a couple of dBs. This variation is pretty much negligible when it comes to overall network design.

 

2.4 GHz Path Loss Glass Window (non tinted) 2 dB Wooden Door 3 dB Cubicles 3-5 dB Dry Wall 4 dB Marble 5 dB Brick Wall 8 dB Concrete Wall 10-15 dB

Figure 1: Typical path loss in common building material

The fact of the matter is that the typical office building will require approximately one AP every 3,000 to 7,000 square feet for seamless coverage, regardless of the type of material within the building. This is a great rule of thumb that has been proven in many real-world deployments. Whether you lean towards the 3000 or 7000 number is a function of your desired user performance and coverage. Figure 2 provides some "best practices" numbers that help hone this decision.

Industry best practices will result in circular overlapping coverage areas, similar to those depicted in Figure #3. If more granular coverage is required, RF prediction is recommended (as described below).

Things also become a bit more tricky if a building environment has a large number of concrete walls, which can have a RF path loss of 10 to 15 dB (or higher in some environments, such as a sports arena). This can dramatically limit RF propagation, which alters the way that a WLAN should be designed. In these environments, it is also suggested that RF prediction tools be used to get a better understanding of ideal radio placement.

AP Configuration
After the number and location of APs is determined, each AP's signal strength and receiver sensitivity must be properly configured to optimize WLAN performance. Figure 4 gives a good indication as to the effect that different signal strengths can have on network throughput:

Older generation WLAN devices require signal strength to be manually configured on each AP. Fortunately, in an Airespace environment, AP configuration is handled automatically via AireWave Director™ Software. Only Airespace has patent-pending algorithms that are used to monitor the air space and adjust AP configuration for ongoing WLAN optimization. This ensures that there is minimal overlap in AP coverage area or unexpected coverage holes. In addition, if a new AP is added to a WLAN, or if an AP fails, AireWave Director ensures that the entire network is recalibrated in real-time to ensure ongoing network optimization. With AireWave Director Software, the WLAN itself is able to apply industry best practices to real-time RF conditions for best-in-class WLAN performance, reliability, and management.

RF Prediction
As performance requirements become more demanding and building layouts become more complex, it is often useful to supplement industry best practices with Airespace's RF Prediction tools. Rather than rely exclusively an historical data, RF prediction enables IT staff to estimate the manner in which RF technology will behave in specific locations, taking into account exact building topology and make-up.

Airespace's RF Prediction deployment process involves two tools within the Airespace Control System Software: ACS Floorplan Editor (FPE) and the ACS RF Prediction tool. FPE is used to create a map that accurately reflects the RF characteristics of your building. It takes imported building floor plans (.jpg. .bmp, etc) and lets IT staff assign attenuation values to individual walls and structures to reflect specific physical RF characteristics. The picture below illustrates this process:

After the building has been characterized, the map is loaded into the ACS software database where an RF Prediction can be performed. APs are logically placed on the map to mimic expected WLAN configuration. ACS then outputs expected WLAN performance based upon this configuration, including detailed 'heat maps' that illustrate expected RF coverage area (i.e. the Received Signal Strength Intensity, RSSI, is illustrated for numerous parts of the building).

IT staff can move APs and re-generate heat maps to get a clear picture of how their RF environment will react to changes in WLAN configuration. This helps to establish a design that best meets enterprise performance objectives.

Benefits of RF prediction
RF prediction provides a relatively accurate depiction of an RF environment, without requiring a single AP to be physically deployed. In that respect, very specific coverage maps can be determined without spending a lot of time, money, or resources. In some instances, enterprises choose to verify the accuracy of RF predictions after deployment via a minimal site survey. This involves testing the performance metrics of a handful of APs to ensure that they meet expectations, as described below.

RF prediction also plays an important role in ongoing WLAN operations. By providing ACS with accurate RF topology information, IT staff can accurately track wireless clients. Airespace is the only WLAN infrastructure to use RF fingerprinting for granular location tracking. By comparing information detected in real time APs with the detailed RF topology map created by Airespace's RF prediction tools, ACS can incorporate RF attenuation, propagation, and other RF behavior into its location tracking analysis for accurate results. The result is a much higher degree of accuracy than what is achieved by alternative solutions that rely solely on "closest AP" or "RF triangulation" methods.

 

Best Practices RF Predictions How it Works Leverage empirical data from similar deployments Estimate RF topology based upon building characteristics Selection Criteria "Typical" building and performance requirements Varied building characteristics; Specific performance requirements Sample Environment - 1 Mbps avg throughput - Open cubicles w/ dry wall - Acceptable coverage holes of less than 10% - Guaranteed 5 Mbps throughput - Mix of wall types - Acceptable coverage holes of less than 1% Advantages - No extra s/w or h/w - Quick and easy - No h/w required - High degree of accuracy - Customized for specific building characteristics

A Good Sanity Check - Wireless Site Survey
While industry best practices and RF prediction tools can provide accurate depictions of an RF environment, discerning enterprises will want to verify the accuracy of these planning tools by measuring actual RF characteristics. The best way to do this is via a minimal site survey, whereby a limited number of APs are deployed and tested to ensure that they meet expected WLAN performance and coverage requirements. Airespace offers an integrated Wireless Site Survey (WSS) tool within Airespace Control System Software to make this easy and cost effective.

A minimal site survey works by providing power to a limited number of APs (deployed in accordance with one of the planning methods discussed above). These APs transmit a signal in beacon mode which can be detected by a WSS client located on a laptop. IT staff can walk around with this client and collect detailed RF information that is specific to their building. With WSS, the following RF characteristics can be examined:

• Signal Strength displays the strongest AP 802.11 RSSI per location for the selected group of APs. This tool is ideal to verify wireless network coverage by setting it to visualize the measured coverage above a minimum RSSI value.

• Interference identifies the worst-case scenario of 802.11 interference on the strongest signal AP by location, when all APs send data at the same time.
• Signal to Noise Ratio (SNR) illustrates the worst-case scenario relationship between the strongest AP's RSSI and the 802.11 interference from other APs. To establish good coverage with minimal interference, the SNR value should be close to the RSSI value.
• Data Rate provides a pictorial estimation of throughput by location based on the calculated SNR values and the selected receiver sensitivity value of your desired client network card. This tool can be used to validate that network throughput rates meet your requirements by location for the specific network cards most often used to access your network.
• Strongest Access Point displays the strongest AP by map location. This feature helps to estimate the number of clients who will be associated with each AP.
• Access Point Count illustrates the number of APs at each location transmitting greater than the minimum RSSI. This helps to ensure AP redundancy in case of isolated AP failure.
• Signals by Channel exhibits the strongest signal by map location for each channel. This tool enables IT staff to visualize the effect that dynamic channel coverage has on RF topology.

In an Airespace environment, a minimum site survey is used to provide peace of mind. Airespace's best practices and RF prediction tools are extremely accurate when it comes to WLAN planning information. In addition, the Airespace system comes equipped with AireWave Director™ Software, which self-optimizes network configuration in real-time based upon changing RF conditions. For example, channel assignments and transmit power levels are dynamically adjusted to account for changing RF conditions. Therefore, a site survey is not required when deploying an Airespace network. However, it is a useful tool for those enterprises that want to increase their comfort level with RF networking and verify that Airespace's capabilities work "as advertised."

Ready for Business
With a firm understanding of how to deploy a WLAN, enterprises can get beyond the planning phase and focus on the key deployment and operational aspects of delivering a business critical wireless network. A complete WLAN system, such as the Airespace Wireless Enterprise Platform, helps make this transition easy.

After helping to determine optimal AP placement and WLAN configuration, Airespace provides a robust set of tools for ongoing WLAN management. AireWave Director Software ensures that WLAN configuration remains continuously optimized throughout the life of a wireless network. In addition, ACS provides ongoing visibility into the air space to monitor network performance, enforce enterprise-wide policies, track user locations, and rapidly correct WLAN problems.

Airespace provides a complete WLAN system, designed to support real business requirements. By simplifying all aspects of WLAN operations - from planning and deployment to day-to-day service delivery - Airespace distinguishes itself from other point solutions and WLAN infrastructures. With a long history working with RF technology, Airespace has set the standard for enterprise-grade wireless networking.