How to Easily Conduct Wi-Fi Network Planning
Wireless network planning is always considered high-level work. A wireless network planning engineer can plan a large number of network devices. However, network planning engineers without practical experience in site surveys or onsite project delivery can hardly make accurate and feasible network planning.
As a Huawei network planning engineer, I have accumulated abundant onsite planning experience from many site surveys, which are the keys for accurate network planning and optimization. They have helped me greatly in overcoming network planning difficulties.
Outdoor Wi-Fi Network Deployment: Site Surveys Are Important
Challenges Caused by Unexpected Interference Sources on Building Roofs
BGC is a central business district in Manila of Philippines. When it came time to improve BGC’s security, a Wi-Fi network was used as a foundation for its new video surveillance system. Because of low costs, fast deployment, and little impacts on environments, a Wi-Fi network was the best choice for this venture.
Whether videos can be smoothly transmitted on a Wi-Fi network is determined by the Line Of Sight (LOS) between APs, as well as possible interference between transmitters and receivers. To ensure smooth video transmission, APs are generally installed on roofs of tall buildings to prevent signal blocking by obstacles. In addition, the 5 GHz band is generally used for long-distance backhaul in Wi-Fi bridging scenarios because interference on the 2.4 GHz band is severe.
In the BGC project, what impressed me most was the site survey in the center of an office building. This site transmitted data with the surrounding four branch sites and collected backhaul video signals. Therefore, the quality of its surrounding wireless environment was crucial. Because of the three APs and a microwave site that had been deployed, the wireless interference plus impacts from local radar channels became a huge obstacle to overcome.
Typically speaking, keeping proper distances from other deployed devices can reduce interference. However, understanding the use of channels and possible interference in working environments can fundamentally help avoid signal interference during channel planning and ensure smooth backhaul in wireless bridging scenarios.
Outdoor Network Planning Tips
Spectrum analysis is necessary since there are many unexpected factors in outdoor environments. For outdoor backhaul and coverage scenarios (such as roads, plazas, and pedestrian streets), the following network planning tips are provided:
- Outdoor backhaul scenarios
- When evaluating a wireless environment, you can use a spectrum analyzer to scan channels on the 2.4 GHz and 5 GHz bands, and analyze the use of the channels, especially local radar channels on the 5 GHz band.
- Check that LOS and bandwidth requirements are met between backhaul sites. For example, in safe city projects, the data bandwidth of cameras is generally 2 Mbit/s to 4 Mbit/s, so the backhaul bandwidth must be over 8 Mbit/s if two cameras are installed along each backhaul link.
- Select suitable antennas based on site conditions. In Point-to-Point (P2P) backhaul scenarios, use small-angle antennas with high gains, such as antennas with 15º horizontal and vertical lobe width and 18 dBi gain. In Point-to-MultiPoint (P2MP) scenarios, use large-angle antennas, for example, antennas with 60º horizontal lobe width, 30º vertical lobe width, and 12 dBi gain.
- Outdoor coverage scenarios
- Select directional or omnidirectional antennas according to shapes of target coverage areas and installation locations of APs. Along narrow roads, APs are generally installed on lamp poles, and directional antennas are recommended for providing coverage in the same direction. In open areas such as park centers, APs can be installed on lamp poles for convenient power supply, and omnidirectional antennas are recommended for providing coverage for surrounding areas.
- To provide wireless coverage along roads, APs with built-in antennas of 10 dBi gain are deployed alternatingly on both sides of the roads. It is recommended that the APs be installed at a height of 6 m to 10 m. If they are installed at a higher place, coverage holes may occur at the bottom of lamp poles. If there is no obstacle, the recommended coverage distance of a single AP is about 120 m.
- In open areas such as parks and plazas, APs and external omnidirectional antennas with the gain of 4 dBi to 7 dBi are generally deployed to provide wireless coverage. It is recommended that the APs be installed at a height of 4 m to 6 m, and the coverage distance of a single AP be about 80 m if there is no obstacle.
Hotel Scenarios: Solution Selection According to Requirements
Outdoor environments are not typically main Wi-Fi coverage scenarios in hotel scenarios. Wi-Fi networks are instead mainly deployed indoors. In indoor environments, settled AP deployment is the most mature and common deployment solution. However, network coverage may be poor if Wi-Fi networks are improperly planned.
Traditional Indoor Settled AP Solutions Do Not Provide Good Coverage
Hotel A is a three-star hotel. As its Wi-Fi demand increased, the hotel planned to deploy a Wi-Fi network. The hotel building is old, and re-cabling by drilling holes on walls was not allowed during business hours. Under this circumstance, an indoor settled AP solution that uses an AP to cover four rooms was the best choice. However, due to signal attenuation caused by corridor walls and washrooms near doors of guest rooms, as well as sharing of one AP by multiple rooms, problems such as uneven signal coverage and deteriorated performance became inevitable.
Optimal Wi-Fi Deployment Solution for Hotels
The aforementioned problems can be addressed and Wi-Fi coverage can be improved by slightly adjusting network planning. Instead of deploying an AP to cover four rooms on both sides of a corridor, deploy an AP to cover three rooms on one side of the corridor. The AP is installed on the ceiling of the middle room.
After the adjustment, the solution’s investment is only 30% higher than that of the original one, but the signal coverage is improved by at least three times. APs in this solution are installed on ceilings but not on walls. When installed on ceilings, APs can provide the strongest signals on the front to neighboring rooms and weak signals on the back to prevent inter-floor interference. This solution has been verified by success cases and can greatly improve Wi-Fi coverage in hotels.
If higher coverage performance is required, the wall plate AP solution is also a good choice. However, this solution requires large numbers of APs and management licenses, making it more expensive. If room walls are only wooden boards inserted with cotton insulation, the wall plate AP solution using one wall plate AP to cover two rooms is cost-effective.
Is there any solution that can ensure good signal coverage at a low cost? To meet this requirement, mainstream vendors offer distributed Wi-Fi solutions. For example, Huawei Agile Distributed Wi-Fi Solution that consists of central APs and Remote Unites (RUs), is able to fit these requirements successfully. Similar to wall plate AP solutions, an RU is installed in each room to ensure signal coverage. The differences are that an RU costs lower than an AP and does not need to be managed by an AC or load licenses. Compared with indoor settled solutions (one AP for three rooms), Huawei Agile Distributed Wi-Fi Solution provides better wireless coverage and higher performance, and saves 90% of licenses and managed nodes. The cost of Huawei Agile Distributed Wi-Fi Solution is only 65% that of the indoor settled solutions.
Indoor Network Planning Tips
- For scenarios with a high-density of rooms (such as hotels, dormitory buildings, and hospitals), different Wi-Fi solutions have their advantages and disadvantages. Indoor settled Wi-Fi solutions using one AP to cover three rooms can meet network requirements and are applicable to scenarios without high performance requirements. Wall plate Wi-Fi solutions provide good coverage but also have a high cost. Distributed Wi-Fi solutions have comprehensive strength as they can meet network coverage and performance requirements at a low cost.
- Offices are common indoor coverage scenarios. Such scenarios have open spaces, few obstacles, and high requirements on user concurrency rates and bandwidth. During network planning, ensure that deployed APs can meet the requirements of user concurrency rates and bandwidth. You can also reduce AP transmit power to reduce co-channel interference. Generally, AP signals need to penetrate at most one brick wall. If the materials and thickness of obstacles cannot be confirmed, you are advised to measure them onsite. The measuring method is as follows:
- Place and power on a signal source (a Fat AP is recommended).
- Detect and record the signal strength using a signal scanning tool on both sides of an obstacle.
- Subtract one detected signal strength value from another to get the signal attenuation caused by the obstacle.
Table 1. Signal Attenuation Caused by Common Obstacles
High-Density Scenarios: Network Planning Based on Site Conditions
Wi-Fi network planning and deployment in high-density scenarios is always difficult. Large stadiums, train stations, airports, and large lecture halls have special building structures, large numbers of users, and high user density, all of which discourage many Wi-Fi vendors from deploying Wi-Fi networks in these scenarios. During the IAAF World Championships Beijing 2015, the Wi-Fi network deployed by Huawei in Beijing National Stadium was highly recognized by the IAAF. However, during planning and deployment of the Wi-Fi network, Huawei encountered many difficulties.
User Bandwidth and User Concurrency Rate Design Based on Comprehensive Analysis
The primary difficulty was the design of a user concurrency rate (which is a common issue in high-density scenarios and must be confirmed before network design). The Beijing National Stadium has about 80,000 fixed seats and 11,000 temporary seats. Even the IAAF Organizing Committee could not confirm how many spectators would go to the stadium during the event, how many spectators would use the Wi-Fi network, and how much bandwidth should be provided to each user. According to experience accumulated from successfully constructed Wi-Fi networks for Europe’s large stadiums, Huawei recommended a user concurrency rate of 30% and per-user bandwidth of 300 kbit/s after analyzing bandwidth requirements of typical applications and terminal types.
Overcoming AP Deployment Difficulties Based on Site Conditions
The building structure of Beijing National Stadium poses another challenge. In high-density scenarios, APs are generally deployed in side, overhead, and floor coverage modes. Site surveys showed that thick cement panels of the stands caused severe signal attenuation. Therefore, APs could not be deployed in floor coverage mode. If APs were deployed at the rear of the stands, signals could only cover the last several rows of seats since the stands are deep from the first row of seats to the last row. In addition, spectators may block signals and cause signal attenuation. In overhead coverage mode, APs need to be deployed on ceilings. However, the ceilings are dozens of meters high, so AP installation would be difficult, signal coverage areas would be hard to control, and interference would be severe.
Huawei’s site survey engineers recommended that APs be installed on catwalks to properly provide wireless coverage to front areas of the stands. They made poles that can have both APs and antennas installed. This installation mode had no impacts on catwalks and improved installation efficiency.
Innovative Channel Planning
Channel planning is difficult in high-density scenarios, which is also a challenge during network planning for Beijing National Stadium. In common scenarios, to ensure compatibility of legacy 802.11b terminals, channel bandwidth must be at least 22 MHz. Therefore, there are only three independent channels available for use on the 2.4 GHz band (channels 1, 6, and 11). However, in high-density scenarios, APs are densely deployed, the three 2.4 GHz channels are insufficient, and co-channel interference is severe. 802.11n and 802.11ac require only 20 MHz channel bandwidth. Therefore, Huawei deployed four independent 20 MHz channels on the 2.4 GHz band. This channel plan improved overall wireless coverage in high-density scenarios.
Channel planning on the 5 GHz band is easier because there are 13 channels (channels 36-64 and 149-165). Interference can be prevented by installing APs working on the same channel far away from each other.
Network Planning Tips in High-Density Scenarios
Stadiums are only one type of high-density scenarios. Wi-Fi networks are more often deployed in airports, lecture halls, and auditoriums, which all have their own specific characteristics. The following provides network planning tips in these scenarios:
- Airports: In most circumstances, the ground-to-ceiling height in airports is over 10 m. When APs are installed on ceilings, small-angle directional antennas are recommended. Figure 1 shows the recommended directional antennas for airports.
Figure 1. Directional Antennas Recommended for Airports
- Lecture halls and auditoriums: The floor-to-ceiling height is different in the front and back of lecture halls and auditoriums. When APs with external antennas are deployed, use antennas with different lobe width. For example, you can use small-angle directional antennas in the front and large-angle directional antennas in the back. When APs with built-in antennas are used, adjust AP directions properly based on the floor-to-ceiling height.