3.1 WLAN Network Planning
3.1.1 How Can I Determine Orientation of Antennas?
A good signal coverage can be obtained if you place antennas with a correct polarization direction. From the following figure, you can see that the gain of an AP's omnidirectional antenna is the highest in the direction vertical to the antenna.
When an AP is placed horizontally or wall-mounted, the major lobes of antennas should be placed vertically to receive the optimal signal coverageand then it will have the best connection.
3.1.2 Which Coverage Mode Is Suitable for a Student Dormitory Building?
A student dormitory building has a high density of users who require high bandwidth. Therefore, indoor DAS APs or indoor APs are recommended.
3.1.3 If Multiple Users Deploy APs in the Same Area, Can These APs Work Properly?
WLAN signals are transmitted on the 2.4 and 5 GHz frequency bands. If multiple APs are deployed in the same area and work on overlapping channels, co-channel interference will cause signal disorder. As a result, users in this area cannot obtain expected wireless network access.
3.1.4 How Many Types of Target Coverage Areas Are There on WLAN Networks? What Are Field Strength Requirements in These Areas?
- Major coverage areas: places where many users need to connect to the Internet, such as dormitories, libraries, classrooms, hotel lobbies and guest rooms, meeting rooms, offices, and exhibition halls.
- Minor coverage areas: places where few users need to connect to the Internet, such as bathrooms, stairways, lifts, corridors, and kitchens.
- Special coverage areas: special areas where users allow or prohibit WLAN access.
- Hotspot field strength: The field strength in major coverage areas ranges from -40 dBm to -65 dBm. A field strength higher than -40 dBm may cause receiver overload, and a field strength lower than -65 dBm may reduce the network connection rate.
- Edge field strength: It is determined based on the receiving sensitivity and edge bandwidth. Generally, the edge field strength should be higher than -75 dBm. The network connection rate in minor areas can be lower than that in major areas.
- Interference field strength: The co-channel interference strength in an area cannot exceed -80 dBm.
- Leakage field strength: The leakage field strength 10 m away from a building cannot exceed -90 dBm.
3.1.5 What Jobs Need to Be Done and What Information Needs to Be Collected During Site Survey?
- Determine the coverage objects and requirements.
- Obtain the layout of the areas to be covered from the customer.
- Learn about the network topologies in the areas.
- Obtain contact information of customer's onsite technical personnel.
- Identify device installation positions and power supply mode (completed by the asset management personnel of the property management).
- Determine the positions to install APs, power cables, and network cables with the asset management personnel. Check whether Internet access resources are available.
- Determine whether a distributed antenna system (DAS) is required according to the coverage objectives. If a DAS is available, obtain the DAS design drawings from the customer. If not, ask the carrier whether a DAS is required. If a new DAS needs to be established, determine the positions of antennas with the asset owners.
- Check the construction materials and calculate signal loss.
- Check for interference sources.
- Layout of the coverage areas
Mark the cabling routes and device installation positions on the layout drawings.
- Building arrangement and structure in the coverage areas
Calculate signal coverage distance of APs based on building arrangement and structure.
- Number of users and required bandwidth
Calculate the network capacity based on the number of users and bandwidth required.
- Device installation positions
- Topology and bandwidth resources of the wired network
- Whether there are sufficient optical fibers and wired network resources to transmit WLAN data
- Signal losses caused by walls, doors, windows, and other construction materials
- Locations and signal strengths of interference sources
- Requirements of users
3.1.6 How Can I Evaluate Influence of Co-Channel Interference on Bandwidth on an AP's Air Interface? How Can I Avoid Interference Between Devices Using the Same Channel?
Co-channel interface is a major factor that reduces an AP's maximum throughput. When APs are placed close to each other, their signals have a large overlapping coverage area, resulting in severe co-channel interference. In this case, APs' maximum throughput decreases greatly.
To avoid co-channel interference, adjust APs' transmit power and increase the intervals between APs. You can also use directional antennas and smart antennas to restrict the signal coverage area.
3.1.7 How Can AP's Channels Be Distributed to Avoid or Reduce Internal and External Interference?
- Use non-overlapping channels in adjacent areas.
- Adjust APs' transmit power to avoid co-channel interference between areas.
- Use a cellular channel distribution so that channels can be multiplexed without causing overlapping coverage areas.
3.1.8 How Can Channels Be Allocated to Obtain a Better Performance?
- Make an AP channel plan before you perform data configurations. You are advertised to manually configure AP channels. The automatic channel adjustment is not recommended.
- If channels of non-Huawei neighboring APs conflict with that of Huawei APs, negotiate with the non-Huawei vendors and change conflicting channels.
- Channels of neighboring APs are staggered. For example, neighboring APs uses channels in the 2.4 GHz frequency band in a fixed sequence of 1, 6, 11, 1, 6, and 11.
- The 5 GHz frequency band is preferred when it is deployed. In the 5 GHz frequency band, non-overlapping channels are channels 149, 153, 157, 164, and 165.
3.2 WLAN Network Optimization
3.2.1 Why Is the Signal Strength That a STA Receives from an AP Weak?
- The transmit power of the AP is low. In this case, increase the transmit power.
- The antenna system of the AP (indoor DAS AP) is not properly deployed.
- The output power on antenna interfaces is low because the AP connects to excess antennas. Or the feeder lines are too long.
- The passive devices (combiner, splitter, and coupler) do not comply with design principles or specifications or are not properly connected.
- The passive devices have unloaded interfaces.
- The STA is far away from the AP's antennas, so the signal loss is large.
- Signals are blocked by a beam, post, concrete wall, metal door, or other obstacles between the STA and antennas. In this case, change the antenna installation positions.
3.2.2 What Measures Can Be Taken If the Network Access Rate Is Low Due to Weak WLAN Signal Strength?
| Symptom | Cause | Measure |
|---|---|---|
| There are too many users that connect to the Internet in some time. | Many users are surfing on the Internet at the same time at night, and traffic volume has exceeded the APs' capacities. Therefore, the network is congested or the network performance deteriorates. | 802.11n APs can be deployed in the dormitory building to provide higher capacities. |
| The signal strength in some corners is weak. | Users are sitting at upper berths far away from the door. | It is recommended that users sit at desk or other positions close to the door. |
| Gaming users are disconnected from the Internet. | Gaming is a delay-sensitive service. If many users play online games in peak hours, the network is congested. | Upgrade the APs or play online games in off-peak hours. |
| The signal strength on STAs is weak (only one or two signal strength bars). | The signal coverage in this room is insufficient. | Check the signal strength of all antennas on the AP covering this room. If all antennas have a weak signal strength, check the AP and combiner. If one antenna has a weak signal strength, check the splitter and this antenna. |
3.2.3 How Can a WLAN Network Be Optimized?
- Adjusting APs' transmit power
- Adjusting the antenna system
- Adjusting APs' channels
- Reducing interference
- Adjusting network-side topology and bandwidth
3.2.4 What Are Common Problems on a WLAN Network?
- Problems at the network side
- Insufficient bandwidth
- Link failures
- Incorrect configuration
- Problems at the AP side
- Incorrect AP working mode
- Power supply failures
- Faults of network cables connected to APs
- Radio coverage problems
- Co-channel interference
- Improper channel distribution
- Insufficient antenna coverage
- Faults of passive devices in the antenna system
3.3 Universal
3.3.1 How to Do Calculate Signal Strength on a WLAN Network?
- Free-space loss modelThe free-space loss model is used to calculate the link budget of indoor DAS APs and indoor APs. The following formulas are used:
- 20logf + 20logd - 28 (f: MHz; d: m)
- 20logf + 20logd + 32.4 (f: MHz; d: km)
- 20logf + 20logd + 92.4 (f: GHz; d: km)
- COST231-Hata model
The COST231-Hata model is used to calculate the link budget of outdoor APs and applies to 2000 MHz or lower frequency bands. To calculate the link budget on the 2.4 GHz frequency band, a correction parameter Cm is used: PL = 46.3 + 33.9lg(f) - 13.82lg(hb)-a(hm) + (44.9-6.55lg(hb))lg(d) + Cm
The Cm value depends on the environment:- Dense Urban: -3
- Urban: -6
- Suburban: -12
- Rural: -20
- In the formula, hb indicates the height of base station antenna (in meters), and hm indicates the height of mobile station antenna (in meters).
- f indicates the antenna working frequency (in MHz), and d indicates the transmission distance (in km).
- a is a function, which also depends on the environment:
- Dense urban and urban: a(Hr) = 3.2log2(11.75 Hr) - 4.97
- Suburban and rural: a(Hr) = (1.1log(f) - 0.7) Hr – (1.56log(f) – 0.8)
- Penetration loss
APs' coverage area is restricted by the multipath effect. Penetration and diffraction capabilities of wireless signals are weak; therefore, wireless signals attenuate greatly when blocked by obstacles. The following are penetration loss values of 2.4 GHz radios when penetrating various materials:
- 8 mm board: 1-1.8 dB
- 38 mm board: 1.5-3 dB
- 40 mm wooden door: 2-3 dB
- 12 mm glass: 2-3 dB
- 250 mm concrete wall: 20-30 dB
- Brick wall: 15 dB
- Inter-floor penetration: 30 dB
- Elevator: 20-40 dB
- Device and connection losses
Radio frequency (RF) devices, such as cable connectors, splitters, couplers, combiners, and AC filters, have insertion losses.
- The insertion loss of a cable connector ranges from 0.1 dB to 0.2 dB.
- The insertion loss of a combiner is 0.5 dB.
- For the insertion losses of passive devices, see corresponding product manuals. Table 3-1 lists transmission losses of various cables.
- Link budget calculation method
- Power budget
Transmit power + Tx gain - path loss + Rx gain = Signal strength
- AP transmit power
An AP's transmit power depends on its specifications.
- AP Tx antenna gain and STA Rx antenna gain
The antenna gain is determined by antenna specifications. Generally, the value is 2 dBi.
- Path loss
Path losses include free-space loss, penetration loss, and loss on cables.
The penetration loss cannot be calculated accurately because it depends on wall materials and signal transmission angle. Generally, the penetration loss count as 25 dB.
- Power budget
3.3.2 What Are Penetration Losses Caused by Various Obstacles?
Obstacles in the coverage area of an indoor or outdoor AP can cause an obvious loss of signals. The following table lists the path losses in 2.4 GHz and 5 GHz frequency bands caused by various obstacles.
| 2.4 GHz Path Loss | |
|---|---|
| Glass window (non tinted) | 2 dB |
| Wooden door | 3 dB |
| Cubicles | 3 to 5 dB |
| Dry wall | 4 dB |
| Marble | 5 dB |
| Brick wall | 8 dB |
| Concrete wall | 10 to 15 dB |
| 5 GHz Path Loss | |
|---|---|
| Typical interior wall | |
| PVC plate | 0.6 dB |
| Gypsum plate | 0.7 dB |
| Plywood | 0.9 dB |
| Gypsum wall | 3.0 dB |
| Rough chipboard | 2.0 dB |
| Veneer board | 2.0 dB |
| Glass plate | 2.5 dB |
| 6.2 cm Sound proof door | 3.6 dB |
| Typical exterior wall | |
| Double-glazed window | 11.7 dB |
| Concrete block wall | 11.7 dB |
If there are metal objects, load-bearing columns, or beams in the target coverage area, ensure that wireless signals are not blocked by them because they cause a large penetration loss.
The penetration loss is minimum when signals penetrate a wall vertically, and the penetration loss is much larger when wireless signals penetrate a wall obliquely. Therefore, when you install APs, try to reduce the incidence angle of signals.
3.3.3 Can Circular Polarization and Cross Polarization Be Used on WLAN Networks? What Are Their Usage Scenarios?
Circular polarization has not been applied to WLAN networks. Cross polarization (+45 and - 45 degrees) is used on outdoor post antennas. Cross-polarized antennas provide wireless signals at 2.4 GHz and 5 GHz frequency bands.
3.3.4 Can APs Automatically Select Channels with Higher Quality? Can They Change Channels When Current Channels Encounter Interference from an Electromagnetic Wave Source such as a Microwave Oven?
Huawei APs support automatic channel selection. However, in large-scale AP deployment, channels are selected before deployment. Changing one AP's channel will cause channel switching on other APs, affecting wireless services on the entire network. Therefore, automatic channel selection is not recommended.
3.3.5 How Do Signal Measurement Tools Calculate the SNR? Does a Higher SNR Value Indicate a Better Signal Quality?
The SNR value obtained using a signal measurement tool is not the actual SNR on a network adapter. The tool obtains the SNR value by comparing the detected signal strength with a predefined noise value (-96 dBm for example). A high SNR value does not indicate a good signal quality because the high SNR may be caused by interference signals. The signal quality should be evaluated by the SNR and signal to interference ratio (SIR).
