WLAN Troubleshooting Guide (V200)

WLAN Network Planning

WLAN Network Planning

What Is the Recommended Output Power on Antenna Interfaces in an Indoor Wireless Distribution System?

The recommended output power on antenna interfaces ranges from 8 dBm to 15 dBm.

  • When the output power on 2.4 GHz antenna interfaces of indoor APs is 8 dBm, an RSSI of over –70 dBm can be provided within 25 m if signals are not blocked by obstacles. When the output power is 15 dBm, an RSSI of over –70 dBm can be provided within 19 m if signals pass through a brick wall.
  • When the output power on 5 GHz antenna interfaces of indoor APs is 8 dBm, an RSSI of over –70 dBm can be provided within 8.6 m if signals are not blocked by obstacles. When the output power is 15 dBm, an RSSI of over –70 dBm can be provided within 6.8 m if signals pass through a brick wall.

An AP's coverage area is calculated based on the output power of its antennas as follows:

  1. Link budget: RSSI = P + Tx + Rx – L – S
  2. Path loss:
    • 2.4 GHz: L = 46 + 10 x n x lg(d)
    • 5 GHz: L = 53 + 10 x n x lg(d)
  • RSSI: indicates the field strength, in dBm.
  • P: indicates the transmit power, in dBm.
  • Tx: indicates the transmit antenna gain, in dB.
  • Rx: indicates the receive antenna gain, in dB.
  • L: indicates the path loss, in dB.
  • S: indicates the penetration loss, in dB.
  • n: indicates attenuation factor, which is 2.5 for 2.4 GHz signals and 3 for 5 GHz signals.
  • d: indicates the antenna coverage distance, in meters.

For example, the coverage distance of a 2.4 GHz antenna is calculated as follows:

  • If RSSI is –70 dBm, P is 8 dBm, Tx is 3 dB, Rx is 0 dB, and S is 0 dB (no obstacle), the coverage distance (d) is 25 m, calculated using the above formulas.
  • If RSSI is –70 dBm, P is 15 dBm, Tx is 3 dB, Rx is 0 dB, and S is 10 dB (caused by a brick wall), the coverage distance (d) is 19 m, calculated using the above formulas.
  • The calculated values are provided for reference only.

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.

Figure 6-8 Signal radiation of an omnidirectional antenna

When an AP is placed horizontally or wall-mounted, the major lobes of antennas should be placed vertically to receive the optimal signal coverage and then it will have the best connection.

How Are APs and Antennas Selected Based on Site Environments?

The following table lists the basic principles for selecting APs and antennas.

Basic principles

No.

Factor for Consideration

Description

1

Usage scenario and purpose

  • Indoor scenarios: Use indoor APs and antennas to provide signal coverage.
  • Outdoor scenarios: Use outdoor APs and antennas with a high Ingress Protection (IP) grade and certain surge protection capability to provide signal coverage and bridge backhaul.
  • Rail transportation scenarios:
    • Train-ground communication: Use outdoor APs and antennas with a high IP grade and certain anti-vibration capability.
    • Compartment coverage: Use indoor APs and antennas with certain anti-vibration capability to provide signal coverage.
    • Station platform coverage: Use the same APs as those in common outdoor and indoor scenarios.

2

Local standards and regulations

The transmit power and maximum gain of antennas must strictly comply with local standards and regulations. For the rail transportation scenarios, the performance, environment adaptability, and anti-vibration capability of the antennas must also confirm to requirements of the related railway authorities.

3

Mapping between APs and antennas

For details, see the section "Antenna Selection Policy" in WLAN Planning Quick Start.

4

Coverage/Backhaul area and distance

  • Coverage: Directional antennas are recommended for long and narrow areas, while omnidirectional antennas are recommended for round and square areas.
  • Backhaul: Directional antennas are usually used. If the backhaul distance is long, high-gain antennas should be used; if the backhaul target is concentrated, small-angle antennas should be used.

5

Transmission frequency for radio signals

  • Coverage: To implement 2.4 and 5G signal coverage, use 2.4G and 5G antennas separately in the same area or use dual-band antennas.
  • Backhaul: 2.4G antennas are not used for backhaul.

6

Construction cost and simplicity

An external directional antenna usually has a large size and needs to be connected to the AP's radio interface through a feeder cable. Compared to a built-in antenna and whip antenna directly installed on an AP, installing an external directional antenna requires higher construction cost and may affect indoor simplicity. To further simplify cable layout (especially in coverage scenarios) without compromising signal quality, you are advised to use built-in or whip antennas directly installed on APs.

Select AP models and antennas based on the onsite environment and customer requirements.

Which Coverage Mode Is Suitable for a Student Dormitory Building?

In scenarios with a high density of users and a high traffic volume, such as student dormitory buildings, central AP + RUs or indoor wall plate AP are recommended. On the condition that co-channel and adjacent-channel interference is prevented, deploy as many APs as possible based on the network planning.

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.

How Many Types of Target Coverage Areas Are There on WLAN Networks? What Are Field Strength Requirements in These Areas?

WLAN networks involve the following target coverage 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.

Depending on WLAN access requirements in the preceding areas, various field strengths must meet the following requirements:

  • 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.

What Jobs Need to Be Done and What Information Needs to Be Collected During Site Survey?

A site survey involves the following tasks:

  • Determine the coverage objects and clarify coverage requirements.
  • Obtain the layout of the areas to be covered from the customer.
  • Learn the network topologies in the areas.
  • Obtain contact information of customer's onsite technical personnel.
  • Identify device installation positions and power supply modes (completed by the property management personnel).
  • Determine the positions to install APs, power cables, and network cables with the property 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.

Collect the following information during a site survey:

  • 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 the signal coverage distance of APs based on the 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 loss caused by walls, doors, windows, and other building materials
  • Interference sources, locations, and signal strengths
  • Requirements of asset owners

Obtain site survey instruction documents: WLAN Network Planning Guide.

How Do I Determine the Number of Required APs, Antenna Installation Positions, and Channels?

The following uses an example to describe the method to determine the number of required APs, antenna installation positions, and channels.

A dormitory building has seven floors, with 20 rooms on each floor. Each room has four users, and each user requires 2 Mbit/s bandwidth. Assuming that maximum number of concurrent users is 30% of the total number of users, plan the indoor distribution system as follows:

  1. Determine the required bandwidth.

    Assuming that maximum number of concurrent users is 30% of the total number of users, plan the indoor distributed system as follows:

    • Bandwidth required on each floor = 20 x 4 x 2 x 30% = 48 Mbit/s
    • Number of required APs on each floor = 48/20 = 2.4
  2. Determine the number of required APs.
    • According to the preceding calculation result, each floor needs 3 APs, so a total of 21 APs are required in the seven-floor dormitory building.
    • A 24-port PoE switch can be used as the aggregation switch and provides PoE power to the APs.
    • Determine the number of required ACs based on the number of APs. The ACs can be connected to a BAS device in bypass mode.
  3. Determine the coverage areas (indoor coverage 50 m x 13 m).
    • Dormitories are major coverage areas.
    • Washrooms, toilets, and corridors are minor coverage areas.
  4. Determine antenna installation positions, coverage radius, and interval between antennas based on signal coverage requirements.
    • Deploy an antenna between every four rooms so that radio signals need to penetrate only one wall. The interval between antennas is 7.5 m.
    • An additional antenna is deployed for the last dormitory room at the end of the corridor to ensure good signal coverage. Washrooms, toilets, and corridors do not need dedicated antennas.

  5. Determine the indoor distributed system layout.
    • If no 2G/3G/4G indoor distributed system is deployed in the dormitory building, establish a WLAN network.
    • Install three APs on each floor. Each AP has two antennas, which are connected to the AP through a two-way splitter.
    • The coverage distance is 50 m, so 1/2-inch cables can be used to connect the APs and antennas.
    • Calculate the length of each cable.
    • APs can be wall-mounted or installed in a cabinet. Choose the installation positions that need the shortest cable length.

  6. Calculate the power of each antenna interface.
    • The expected coverage radius of each antenna is 6.5 m.
    • Use the free-space loss model to calculate signal loss. The loss in a 6.5 m radius is about 56.5 dB.
    • Signals need to penetrate a wall, which brings approximate 25 dB signal loss.
    • The required field strength in the major coverage is -65 dBm.
    • The antenna gain is 2 dBi.
    • Therefore, the transmit power on each antenna interface should be calculated as follows: -65 dBm + 25 dB + 56.5 dB - 2 dBi = 14.5 dBm.

    Antenna gains of STAs are not considered in the preceding formula. If the antenna gain of STAs is 2 dBi, a transmit power of 12.5 dBm is enough. Actually, antenna gains of STAs are not taken into account because the antenna gains cannot be determined in practice.

  7. Calculate the loss of the antenna system and set APs' transmit power.

    Each AP has two antennas. The output power of the two antennas may be different due to loss on the cables. The transmit power of each antenna interface is calculated using the power calculator as follows:

    • Set the transmit power of AP1 to 20 dBm.
    • Output power of ant1 is 15.4 dBm.
    • Output power of ant2 is 14.5 dBm.
      • Set the transmit power of AP2 to 22 dBm.
    • Output power of ant3 is 15.5 dBm.
    • Output power of ant4 is 13.7 dBm.
      • Set the transmit power of AP3 to 24 dBm.
    • Output power of ant5 is 14.4 dBm.
    • Output power of ant6 is 13.5 dBm.
  8. Select radio channels.
    • Use the channel distribution with the lowest co-channel interference.
    • If the AP's channels conflict with channels of users' Wi-Fi devices, adjust the channel distribution.
    • If channel conflicts cannot be avoided by adjusting APs' channel distribution, discuss with owners of the Wi-Fi devices to re-distribute the channels.

Obtain site survey instruction documents: WLAN Network Planning Guide.

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.

How Can AP's Channels Be Distributed to Avoid or Reduce Internal and External Interference?

Use a cellular channel distribution to avoid channel overlapping. For example, there are only three non-overlapping channels in the 2.4 GHz frequency band: channel 1, channel 6, and channel 11. A proper channel distribution can greatly reduce co-channel interference on a WLAN network. Follow these principles when distributing radio channels:

  • 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.

How Can Channels Be Allocated to Obtain a Better Performance?

There are only three non-overlapping channels in the 2.4 GHz frequency band: channels 1, 6, and 11. If channels of neighboring APs conflict, channel interference occurs, degrading user access experience.

  • Make an AP channel plan before you perform data configurations. You are advised 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.

Use spatial staggered channels to increase network capacity.

  • 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, 161, and 165.

Can Obstacles Exist Between Two Antennas During Signal Backhaul?

No. If obstacles exist between two antennas, wireless signals are attenuated or even blocked, affecting backhaul effects. Therefore, install antennas at high places with no obstacle.

What Should I Do If the Drawing Is Not Completely Parsed or Fails to Be Parsed?

This problem occurs usually when a drawing is in the Tangent's drawing format. Use the Tangent software to convert the drawing into a standard CAD drawing (with a file name ending with t3), as shown in the following figure.

What Should I Do If the Lines in a CAD Drawing Are Thick and Disordered After Being Parsed?

In most cases, this problem occurs when the scale in a drawing is set too large. Manually adjust the scale by modifying the resolution.

How Can Obstacles in a CAD Drawing Be Automatically Identified?

  • Obstacles can be identified only on parsed CAD drawings. After a drawing is uploaded, obstacles can only be manually drawn.
  • One-click identification can be automatically configured based on some keywords (such as door and window) on each layer, which can be modified as required.
  • On the parsing page, you can set the obstacle type of a layer level in either of the following ways: 1. (Recommended) Right-click on the drawing and set the obstacle type; 2. Set the obstacle type in the layer toolbar on the right.

Do I Need to Set the Scale of a CAD Drawing?

By default, the tool reads the scale in a drawing and allows the scale modification.

How Can I Operate a CAD Drawing When Drawing Obstacles and Areas?

Scroll the mouse scroll wheel to zoom in or out on a drawing. Press and hold the space key so that the drawing moves with your mouse, which facilitates more refined drawing.

Failed to Export CAD Drawings. What Should I Do?

Ensure that a drawing is imported in the CAD format so that you can successfully export the CAD drawing.

Automatic Deployment for a Project. Failed What Should I Do?

Meet the following conditions for automatic AP deployment:

  • Indoor scenario
  • The selected APs are indoor APs equipped with omnidirectional antennas.
  • A coverage area has been drawn.

How Can I Quickly Replace AP Models?

You can use the replacement function to inherit the attributes of existing APs in batches. For the attributes that cannot be inherited, the default values are used.

How Can I Quickly Distinguish APs of Different Models at the Same Layer in the Report?

The AP attributes are marked with five colors: blue, red, green, yellow, and black. You can use the replacement function to set the same color for APs of the same model in batches for quick identification.

What Should I Do to Design Another Network Planning Solution?

According to your requirements:

  • To re-create the entire project, export the project and then import the project as a new one.
  • To re-set the floor, building, or outdoor level, right-click the corresponding node in the navigation tree on the left and choose Copy from the shortcut menu.

How Large Is the Coverage Radius of an AP?

  • In indoor scenarios, an AP's coverage distance varies depending on the environment. During network planning, the coverage radius of an AP is planned as 20 m.
  • In outdoor scenarios, an AP may cover up to hundreds of meters based on coverage requirements. You are advised to plan the coverage radius of an AP as 200 m for laptop terminals and 100 m for mobile phone terminals.

The onsite test is recommended for testing the coverage effect.

How Many Users Does an AP Support?

During network planning, plan an AP to allow access from 40 users on the two frequency bands when 2 Mbit/s bandwidth is available. For the number of users supported by an AP under different bandwidth, use WLAN Planner for simulation and plan, or contact technical support personnel.

How Do I Measure the Signal Loss Caused by Obstacles?

Measure the signal loss caused by an obstacle as follows:

  1. Place and start a signal source. Place the signal source at a proper position. Ensure that no obstacle exists between the signal source and obstacle to be measured, and keep a certain distance from the signal source to the obstacle. If the signal source is close to the obstacle to be measured, the field strength near the signal source fluctuates greatly, leading to inaccuracy of measured values.
  2. Use a signal scanning tool to measure field strengths on both sides of the obstacle. The difference between the measured values is the signal loss.

As shown in Figure 6-9, configure the 2.4 GHz and 5 GHz radios of a Fat AP. The field strengths of 2.4 GHz and 5 GHz signals measured at test point 1 are both -50 dB, and the field strengths of 2.4 GHz and 5 GHz signals measured at test point 2 are -60 dB and -65 dB, respectively. The loss of 2.4 GHz signals caused by the obstacle is 10 dB, while the loss of 5 GHz signals is 15 dB.

Figure 6-9 Measuring the signal loss caused by an obstacle

How Much Is the Attenuation of Typical Obstacles?

The following table lists the attenuation of typical obstacles.

Obstacle

Width (mm)

2.4 GHz Signal Attenuation (dB)

5 GHz Signal Attenuation (dB)

Synthetic material

20

2

3

Asbestos

8

3

4

Wooden door

40

3

4

Glass window

50

4

7

Heavy colored glass

80

8

10

Brick wall 1

120

10

20

Brick wall 2

240

15

25

Armored glass

120

25

35

Concrete

240

25

30

Metal

80

30

35

You can define the attenuation of other obstacles in WLAN Planner based on the test result.

What Measures Can Be Taken to Lower Interference?

Interference is a common problem in a high-density network plan. To lower interference, you can:

  • Reduce the AP transit power to narrow the coverage radius of a single AP.
  • Avoid adjacent AP channels to prevent overlapping.
  • Use onsite obstacles to lower AP signal strength.

What Are the Differences Between Single-Polarized and Dual-Polarized Antennas?

A dual-polarized antenna can implement MIMO. An AP requires only one dual-polarized antenna but two single-polarized antennas.

What Dimensions Are Required on a Pole for Installing an Antenna?

The dimensions of a pole refer to the length and diameter. The length of a pole must allow the pole to be fixed to a building and reserve the space for installing the AP and antenna.

The space for installing the AP and antenna can be determined based on the dimensions and installation methods of the AP and antenna. The length for fixing the pole to a building can be determined based on site requirements.

The antenna specifications specify the diameter range of a pole. In most cases, a medium value is recommended. For example, the antenna SL12844AASB115G00 supports poles of which the diameter ranges from 35 mm to 114 mm. A pole with a diameter of 60 mm is recommended.

How Do I Select the Feeder Line Length When Installing an Antenna?

Currently, Huawei provides feeder lines of 2 m, 3 m, and 5 m. Feeder lines can be made onsite. In most cases, a feeder line only needs to connect an antenna to an AP. The feeder line reduces signal strength. Therefore, when the requirement is met, a shorter feeder line is recommended.

What Rules Should I Follow When Selecting Antennas for Signal Backhaul?

If signals are transmitted from one antenna to multiple antennas, select the antenna with large lobe width to transmit the signals. If signals are transmitted from multiple antennas to one antenna, select antennas with small lobe width to transmit the signals.

What Spatial Streams Do Common Terminals Support?

  • Single spatial stream: supported by common handheld terminals, such as pads and mobile phones.
  • Two spatial streams: supported by most laptops.
  • Three spatial streams: supported only by network adapters of a few high-end laptops.

How Should I Select Outdoor High-Gain Antennas and Relays?

When the transmission distance is within 5 km, high-gain antennas can be used for transmission. For longer transmission distances, relays are recommended. If two ends are blocked by obstacles, the obstacles can be bypassed using the relay.

How to Do Calculate Signal Strength on a WLAN Network?

Wireless signal strength decreases during transmission because of free-space loss, penetration loss, and device and connection loss. You need to consider these link budgets when calculating the signal strength.

  • Free-space loss model

    The 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 4-2 lists transmission losses of various cables.
      Table 6-5 Cable transmission losses

      Name

      Transmission loss in 900 m

      dB/100 m

      Transmission loss in 2100 m

      dB/100 m

      Transmission loss in 2400 m

      dB/100 m

      1/2-inch feed line

      7.04

      9.91

      12.5

      7/8-inch feed line

      4.02

      5.48

      6.8

  • 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.

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.

Table 6-6 Penetration loss of obstacles

Name

Thickness (mm)

2.4 GHz Signal Attenuation Value (dB)

5 GHz Signal Attenuation Value (dB)

Bulletproof glass

120

25

35

Asbestos

8

3

4

Brick wall

120

10

20

Brick wall

240

15

25

Heavy colored glass

80

8

10

Concrete

240

25

30

Glass window

50

4

7

Metal

80

30

35

Synthetic material

20

2

3

Wooden door

40

3

4

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.

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/-45 degree or 0/90 degree) is mainly applied to outdoor directional antennas. Cross-polarized antennas provide wireless signals at 2.4 GHz and 5 GHz frequency bands.

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).

What Measures Can Be Taken Against Multipath Interference?

The following technologies can be used against multipath interference: smart antenna, multiple-input and multiple-output (MIMO) beamforming, MIMO space-time block coding (STBC), and MIMO maximal ratio combing (MRC).

What Is the Standard of Good Radio Signals? What Is the Recommended Signal Overlapping Area of Neighboring APs in Percentage?

Standard of good radio signals: The signal strength is no lower than -65 dBm in indoor areas and no lower than -70 dBm in outdoor areas.

To meet users' normal roaming requirements, the recommended signal overlapping area of neighboring APs is between 10% and 20%.

What Is the Recommended Interval Between APs in Indoor Access Scenarios?

The interval between APs changes according to the field strength and network capacity. In office scenarios, the required per-user bandwidth is 1 Mbit/s to 2 Mbit/s, and the concurrency rate is around 30% to 50%. When the per-user coverage area is 3 square meters, the recommended interval between APs is 15 m to 20 m.

What Is the Radius of the Fresnel Zone?

As shown in the following figure, the Fresnel zone is an ellipsoid. Obstacles in the zone will adversely affect signal transmission. If no obstacle exists in the zone, radio signals can travel in an approximately free space.

Figure 6-10 Fresnel zone

Fresnel zones differ depending on the Fresnel zone radius. In a free space, radio signals are mainly transmitted between antennas in the first Fresnel zone. In normal cases, the Fresnel zone refers to the first Fresnel zone.

The radius of the first Fresnel zone is calculated as follows:

  • r: indicates the radius of the first Fresnel zone, in meters.
  • d: indicates the distance between two antennas, in km.
  • f: indicates the signal frequency, in GHz.

With 5 GHz signals as an example, Table 6-7 lists the radius of the first Fresnel zone in different backhaul distances.

Table 6-7 Radius of the first Fresnel zone

Backhaul Distance (km)

1

2

3

5

10

Radius of the First Fresnel Zone (m)

3.87

5.48

6.71

8.66

12.25

What Is the Relationship Between the Signal Coverage Strength and Distance?

When factors such as interference and circuit loss are not considered, the formula for calculating the received signal strength indicator (RSSI) is as follows:

RSSI = Transmit power + Antenna gain at the transmit end – Path loss – Obstacle attenuation + Antenna gain at the receive end

The relationship between the path loss and distance is as follows: (L: Path loss, in dB; f: Working frequency, in MHz; d: Distance, in m)
  • Indoor semi-open scenario

    2.4 GHz: L = 46 + 25lg(d)

    5 GHz: L = 53 + 30lg(d)

    The following table lists the typical path loss values at different distances.

    Table 6-8 Relationship between the pass loss and distance in indoor semi-open scenarios

    Distance (m)

    2.4 GHz Path Loss (dB)

    5 GHz Path Loss (dB)

    1

    46

    53

    2

    53.5

    62

    5

    63.5

    74

    10

    71

    83

    15

    75.4

    88.3

    20

    78.5

    92

    40

    86

    101

  • Outdoor coverage scenario

    2.4 GHz and 5 GHz: L = 42.6 + 26lg(d) + 20lg(f)

    The following table lists the typical path loss values at different distances.

    Table 6-9 Relationship between the pass loss and distance in outdoor coverage scenarios

    Distance (m)

    2.4 GHz Path Loss (dB)

    5 GHz Path Loss (dB)

    50

    76.4

    84

    100

    84.2

    91.9

    200

    92

    99.7

    300

    96.6

    104.2

    500

    102.4

    110

    800

    107.7

    115.4

    1000

    110.2

    117.9

  • Backhaul scenario

    5 GHz: L = 32.4 + 26lg(d) + 20lg(f)

    The following table lists the typical path loss values at different distances.

    Table 6-10 Backhaul scenario

    Distance (km)

    5 GHz Path Loss (dB)

    0.5

    100

    1

    108

    2

    115.8

    3

    120.4

    5

    126.1

    8

    131.4

    10

    134

Assume that the transmit power of an indoor AP is 20 dBm and the 5 GHz antenna gain is 6 dBi. In an indoor half-open scenario, the 5 GHz path loss at a point 20 m away from the AP is 92 dB. If the receive terminal is a mobile phone (usually with the antenna gain of 0) and there is no obstacle between the mobile phone and AP, the 5 GHz RSSI of the mobile phone is –66 dBm (20 + 6 – 92 – 0 + 0).

What Is the WLAN Coverage Range?

Generally, the WLAN coverage range various according to the environment. When no external antenna is used, the WLAN coverage range is about 250 meters. In the semi-open space or the space with a compartment, the WLAN coverage range is about 35 to 50 meters. When external antennas are used, the WLAN coverage range increases with the antenna gain and is determined according to customer requirements. If an outdoor antenna and amplifier are used, the WLAN coverage range can reach up to several tens of kilometers.

How Can I Understand the Number of STAs?

As listed in the following table, the number of STAs is described in different ways. The difference between them is the basis for formulating a Wi-Fi solution.

Name

Description

Whether Wi-Fi Is Enabled on STAs

Whether STAs Are Connected to a Wi-Fi Network

Whether STAs Are Generating Traffic

Example

Number of STAs

Number of STAs in a specific space, regardless of whether they are connected to a Wi-Fi network

Yes

No

No

Mobile phones in a dormitory, which have Wi-Fi enabled but do not connect to a Wi-Fi network

Number of STAs connected to a Wi-Fi network

Number of STAs that access a Wi-Fi network in a specific space, regardless of whether wireless traffic is transmitted between the AP and STAs (This is the commonly known "number of access STAs.")

Yes

Yes

No

Mobile phones in a dormitory, which connect to a Wi-Fi network but do not perform operations such as file download or web page browsing

Number of concurrent STAs accessing a Wi-Fi network

Number of STAs that access a Wi-Fi network in a specific space and are simultaneously transmitting data (This is the commonly known "number of concurrent users.")

Yes

Yes

Yes

Mobile phones in a dormitory, which access a Wi-Fi network and are performing operations such as file download or web page browsing.

  • In most cases, the STA concurrency rate is about 20% to 50%. This allows two to four students in a dormitory with eight students to access the Wi-Fi network and compete for Wi-Fi resources.
  • Assume that a student refreshes the web page at t1, which is completed within 1 second, and another student uploads a picture at t1 + 1s. The STAs of the two students, in this case, are not concurrent STAs.
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Update Date:2023-12-01
Document ID:EDOC1000060368
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