I have been working with Wi-Fi networks for about 10 years now, so an ideal time to collate the top tips that I have learnt. Wi-Fi networks have their own particular set of challenges. Here are my tips to conquering those challenges:
1. Get the coverage right
Getting the coverage right starts with understanding the requirements. The requirements should consider the type of client devices, the expected usage, the coverage areas and the roaming pathways. The requirements should be defined in terms of at least Signal, Signal-to-Noise, Roaming Overlap and Interference overlap. Getting these right will allow for performance requirements such as data rate, roaming, and throughput to be achieved.
2. Design for capacity
Always consider network capacity, ensure that your coverage requirements also hit your capacity requirements. In larger low-density areas such as warehouses capacity does not usually affect the design. However, in high-density office or stadium environments the capacity will likely be of primary concern.
3. Avoid over coverage
As each requirement is considered it can be tempting to just add more and more access points (APs). This can be especially an issue when using a network planner tool. Many assumptions are made when using a planner tool. These assumptions invariable have to be the worst-case scenario and so more and more access points are added to cover for the unknown. Adding more APs quickly hits the point of diminishing returns. There is a finite capacity of the available spectrum that once hit additional APs only add interference. An on-site survey will make the design process far more accurate and will allow you to get the perfect balance of coverage and capacity.
4. AP placement and orientation
Correctly mounting APs will ensure that the coverage is as expected. The coverage pattern of an AP’s radio is a 3-dimensional shape and so vertical and horizontal orientation will affect the coverage. This is especially the case for external antennas that may have their RF energy focussed in a certain direction. APs should be mounted away from RF reflectors or absorbers.
5. Survey for the worst client
When conducting RF design for Wi-Fi it is important to understand the capabilities of the clients. There is no point having APs transmitting at a high power if the clients cannot match the power and talk back. The design should consider the least capable client device. When surveying, the survey AP should have it’s transmit power set lower than the maximum transmit power of the weakest client. Be sure to include the antenna gain in your calculations.
6. Survey for 5GHz
RF at 2.4GHz will propagate significantly further that at 5GHz; particularly through walls and other absorbers. It is important to design using the worst-case scenario so use 5GHz primarily when considering AP placement
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7. Make the most of 2.4GHz
The 2.4GHz spectrum has many disadvantages, mostly due to the low number of available channels and the number of non-WI-Fi devices using the spectrum. However there are advantages such as greater propagation and lower cost, these advantages will suit some applications far better than 5GHz. It is important to consider these in your design. Further details of the advantages of 2.4GHz can be found in my recent blog post here.
8. Always validate
After the deployment it is important to survey again and test to validate the design. Even if an accurate pre-installation survey was completed it is still important to check that the coverage is still the best design for the application and environment. If the Wi-Fi installation was applied to a greenfield site or as part of a refurbishment the environment is likely to have changed significantly. It is also important to note that the presence of people will significantly affect the RF propagation. People are mostly made of water and water is great at absorbing RF energy at microwave frequencies, hence the effectiveness of microwave ovens.
The validation survey should check the coverage and capacity of the network as well as testing the performance of the client devices. The network should be tested under load so should be tested and surveyed at the busiest times. Verification of the design and channel plan should also take place at this time.
9. Consider implementing Quality of Service
As with any network, some traffic will be more important than others. QoS is particularly important in wireless networks as it will control which devices have access to the medium. Wireless is a shared medium where only a single device can transmit at any one time. Under normal circumstances the device granted the ability to transmit is done at random. QoS allows you to favour certain types of traffic allowing them a better chance of winning the ability to transmit.
10. Considerations for Voice traffic
One application where QoS is particularly important is voice traffic. Traditionally Voice and Data networks have been completely separate, having been designed for two very different applications. Data networks have high bandwidth but are bursty. Voice networks have low bandwidth but allow a smooth uninterrupted flow. Getting data networks to handle voice traffic is always going to be tricky. The main challenge is to create the smooth uninterrupted flow of data. This is done by minimising the interruptions. Interruptions are caused in wireless networks by devices having to wait to transmit or the data getting lost in transit or corrupted and failing to be received properly. Efficient transmitting of data is ensured by use of QoS. Efficient receiving of data is done by ensuring a good RF design.
Wireless Networking by Ash Mead 