When 1 + 1 ≠ 2: Why adding WLAN access points doesn’t solve the problem

July 17, 2012 12:00 PM

Creating a Radio Frequency plan can help organizations meet their WLAN needs today and in the long-term while controlling costs


The growth in Wireless LANs (WLAN) has accelerated to become an integral part of every office environment. The expanding use of WLAN in recent years has required network administrators to move from installing one or two Access Points (AP), providing guest access in the lobby, to company-wide wireless coverage.  


The demands placed on WLANs has also increased. Their versatility has grown from handling simple data transfer to all forms of multimedia (including voice, video and peer-to-peer) to alternative platforms (such as tablets and smartphones). WLANs are even the preferred replacement for a customers premise wired environment, as they help save cost and improve productivity.


Traditionally, WLANs have been provisioned on an as-needed basis. APs were added to specific areas to support guest and specific user needs. As many network administrators are learning, this works only for a while and then a performance “tipping point” occurs when resolution cannot be addressed by adding another AP. In many cases, “just adding” another AP will make the problem worse.


NCR has provisioned over 200,000 Wi-Fi hotspots globally. As one of the world’s leading providers working on behalf of the world’s leading telecom, OEM and System Integrators NCR has the expertise, experience and sophisticated modelling tools to help organisations successfully deploy company-wide WLAN solutions taking into account their longer-range strategic plans to improve worker connectivity and productivity.


Let’s take a typical office environment and follow its traditional WLAN growth. First, the network administrator installed a few wireless APs to provide conference room coverage. Wanting the maximum coverage from each AP, they were all set to transmit at maximum power. At maximum power, ignoring other factors like attenuation values, a 54MB connection is typically available in a 160’ diameter circle centered on each AP.


Not wanting to restrict connections only to devices that can connect at 54MB, the network administrator allowed connection speeds down to 11MB. This created a coverage area approximately 700’ in diameter for each AP. As the office environment was only 200’x400’, every AP was visible to every user in the office.


As users became accustomed to the convenience of mobile computing, they started using it everywhere in the office. The problem here is that you now have hundreds of users trying to access the network through the same three APs and 100MB uplink connection from the AP to the wired network. While they might get connected, they will not get much in the way of available throughput.


To satisfy the needs of users, the network administrator added more APs to provide more throughput. Soon, they had an environment where every user could see and attempt to connect to all 20+ APs installed. As there are only three non-overlapping channels available in the 2.4GHz radio band, every user saw six to seven APs on each channel.


Having multiple APs on the same channel covering the same area creates a condition called co-channel interference. Image yourself in crowded room where there are 20 people trying to carry on conversations in three different languages. Six or seven of them are all shouting at you at the same time. There may be plenty of volume but the listener can’t make out individual words.


Co-channel interference means transmissions from one cell spread to a nearby cell on the same RF channel, causing dropped transmissions, interference or the client experiencing difficulties decoding the signal.


To address the problem, an overall Radio Frequency (RF) plan needs to be developed meeting the long-term requirements of the facility and user community. The design for the RF plan should dictate not only the AP locations but also the channels and power settings of each device to support both current requirements and future plans while controlling costs. This plan should be implemented in stages, to meet particular needs, without impacting existing coverage and users. 


Creating an RF plan for this type of coverage, while appearing simple, can quickly become very complex. When you consider that each AP supports multiple radios on different frequencies with different propagation characteristics, varying user densities in the coverage areas and a range of response times to roaming and throughput requirements for all applications (including voice and video) accessed through WLAN, traditional trial-and-error methods for WLAN network designs are not effective.


For this reason NCR uses Motorola’s LANPlanner as its preferred WLAN design tool due to its advanced modeling and design capabilities across all RF ranges.  


Motorola’s LANPlanner, when used by a NCR certified WLAN Design Engineer, aids in building RF plans that meet all requirements for a customers WLAN environment. NCR’s WLAN Design Engineer can produce a design that supports data, voice, video and future application needs for both low and high volume users. The RF plan also includes throughput use requirements, response time needs, redundancy standards, security considerations and equipment types as a basis for building the model.