Back-to-back WiFi deployments at two high-density stadium venues with very tight timelines was quite challenging. As discussed in the previous two blogs of this series (see Part 1 & Part 2), the venues were different in terms of stadium layout, structure and seating capacity. As a result the WiFi network design also turned out to be different in many ways. Nevertheless, the underlying design principles and methodology were the same.
Starting with a capacity-based estimate of AP count as a rough guideline, the actual AP count was determined using a passive site survey to gain a deeper understanding of the venue, in terms of the layout of seating areas, structural variations across the stadium, practical constraints on AP placement, etc. The horizontal and/or vertical tilts for APs were estimated using measurements taken during the site survey. With the AP height, tilt and desired coverage area known, a rough estimate of its transmit power could be made. These parameters were validated with the help of simulations using the iBwave tool. After the deployment of APs, an active survey was undertaken to validate the RF coverage and throughput at different locations. These measurements served as the basis for further fine-tuning of AP Tx power and tilt, primarily to minimize co-channel interference while maintaining optimal RF coverage across the stadium. Finally, during the first couple of games, live testing was carried out across the stadium to sort out any remaining glitches.
Over a period of 10 weeks, a team of Mojo engineers, working in close coordination with Jio, managed to complete two stadium WiFi deployments. Based on this experience, here are some of the key points, or 10 commandments, to consider for stadium WiFi deployments.
- Capacity estimation is crucial because it is the starting point of the design process. In addition to the average user throughput requirement and number of concurrent users, the distribution of clients in 2.4GHz and 5GHz bands is a very important parameter in AP count estimation for such ultra-HD scenarios. The population of 5GHz clients in stadium like venues is much higher than usual because of the match-day demographic.
- Open venues such as stadiums are interference-limited zones. The expected throughput per AP is degraded significantly by co-channel interference. This needs to be factored in while estimating AP count using the capacity-based calculations.
- Multi-level venues pose an additional challenge with RF spillage across floors. Manual Tx power control and antenna tilt need to be leveraged for controlling spillage.
- Human bodies impede the propagation of the RF signal. This can have significant impact on RF coverage in stadium deployments. The attenuation may be as high as 6-7 dB when spectators are present. The problem is severe when APs are mounted at low height (e.g. in case of pole/wall mounting). Coverage optimization must be done accordingly.
- Interference from LTE transmitters in 2.3 GHz band, deployed in the vicinity of WiFi access points, can severely degrade throughput in 2.4 GHz, especially on Channel 1. In such scenarios, it is better to avoid using the affected channel(s).
- Relying on Auto Channel Selection (ACS) in such deployments may not give the desired outcome in terms of channel re-use and interference minimization. As the APs are deployed in a regular pattern, manual channel planning can be done easily for 2.4GHz band while ACS can be used for 5GHz band.
- From the coverage perspective, it is advisable to keep the 2.4GHz radio power lower than the 5GHz. This helps minimize co-channel interference in the 2.4GHz where only 3 non-overlapping channels are available. At the same time, better 5GHz coverage incentivizes dual-radio clients to prefer the 5GHz band.
- Using directional APs is a must to minimize co-channel interference. A good understanding of antenna pattern is useful in figuring out AP coverage at different heights/tilts. As the vertical and horizontal antenna patterns may not always be the same, even the AP orientation has to be considered during mounting. In situations where APs have to mounted very close to each other (e.g. on same pole), physical separation can be achieved by mounting them at different heights. If this is not possible, then angular separation can be provided pointing them in different directions.
- AP mounting needs to be done such that available structures are used as much as possible, while respecting the constraints posed by aesthetics and ensuring that mounting structures like poles and APs do not obstruct the spectators’ line of vision. Mounts must also be secure enough to handle adverse weather conditions at outdoor locations.
- Active survey is a must for RF optimization. It helps find out areas of low RSSI, high interference zones and test roaming across cells. This information is important for configuring the optimal Tx power.
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