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Fat AP and Cloud AP V200R008C00 CLI-based Configuration Guide

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Radio Calibration

Radio Calibration


On a WLAN, operating status of RUs is affected by the radio environment. For example, adjacent RUs using the same working channel interfere with each other, and a large-power RU can interfere with adjacent RUs if they work on overlapping channels. The radio calibration function can dynamically adjust channels and power of RUs managed by the same central AP to ensure that the RUs work at the optimal performance.

  • Channel adjustment

    On a WLAN, adjacent RUs must work on non-overlapping channels to avoid radio interference. For example, the 2.4 GHz frequency band is divided into 14 overlapping 20 MHz channels, as shown in Figure 18-1.

    For channels supported in different countries, see the Country Code & Channel Compliance Table. You can obtain this table at Huawei technical support website.
    Figure 18-1  Channels on the 2.4 GHz frequency band

    The 5 GHz frequency band has richer spectrum resources. In addition to 20 MHz channels, RUs working on the 5 GHz frequency band support 40 MHz and 80 MHz channels, as shown in Figure 18-2.
    Figure 18-2  Channels
    • Two neighboring 20 MHz channels are bundled into a 40 MHz channel. One of the two 20 MHz channels is the primary channel, and the other the auxiliary channel. The primary channel is used for transmission of the management and control packets, and the auxiliary channel for other packets, including the data packets.
    • Two neighboring 40 MHz channels are bundled into an 80 MHz channel. In the 80 MHz channel, one 20 MHz channel is selected as the primary channel. The other 20 MHz channel making up the 40 MHz channel with the primary channel is called the auxiliary 20 MHz channel. The 40 MHz channel not containing the primary channel is called the auxiliary 40 MHz channel.

    Figure 18-3 shows the channel distribution before and after channel adjustment. Before channel adjustment, both RU2 and RU4 use channel 6. After channel adjustment, RU4 uses channel 11 so that it does not interfere with RU2.

    After channel adjustment, each RU is allocated an optimal channel to minimize or avoid adjacent-channel or co-channel interference, ensuring reliable data transmission on the network.

    Figure 18-3  Channel adjustment

    In addition to optimizing radio performance, channel adjustment can also be used for dynamic frequency selection (DFS). In some regions, radar systems work in the 5 GHz frequency band, which interferes with radio signals of RUs working in the 5 GHz frequency band. The DFS function enables RUs to automatically switch to other channels when they detect interference on their current working channels.

  • Power adjustment

    A RU's transmit power determines its radio coverage area. RUs with higher power have larger coverage areas. A traditional method to control the radio power is to set the transmit power to the maximum value to maximize the radio coverage area. However, a high transmit power may cause interference to other wireless devices. Therefore, an optimal power is required to balance the coverage area and signal quality.

    The power adjustment function helps dynamically allocate proper power to RUs according to the real-time radio environment.
    • When a RU is added to the network, the transmit power of neighboring RUs decreases. As shown in Figure 18-4, the area of the circle around a RU represents the RU's coverage area after transmit power adjustment. When RU4 is added to the network, transmit power of each RU decreases automatically.
    Figure 18-4  Transmit power of RUs decreases

    • When a RU goes offline or fails, power of neighboring RUs increases, as shown in Figure 18-5.
    Figure 18-5  Transmit power of RUs increases


The radio calibration solution consists of the following components:
  • RU: actively or passively collects radio environment information and sends the information to the central AP. The central AP then delivers the calibration results.
  • Central AP: maintains the RU neighbor topology based on radio environment information received from the RU, use calibration algorithms to allocate RU channels and transmit power, sends calibration results to RUs.

A central AP supports global radio calibration and partial radio calibration:

  • Global radio calibration: takes effect on all RUs managed by a central AP. The central AP controls channels and transmit power of all RUs in the region to achieve best radio performance. Generally, this calibration mode is used on a newly deployed WLAN or a WLAN with a few services.
    The Figure 18-6 shows the global radio calibration process.
    Figure 18-6  Implementation of global radio calibration
    1. After global radio calibration is enabled, the central AP sends a notification to each RU, requesting the RU to start neighbor probing.
    2. The RUs periodically implement neighbor probing and report neighbor information to the central AP.
    3. After the central AP receives probe results of all the RUs, it uses the global radio calibration algorithm to allocate channels and power to the RUs.

      The global radio calibration algorithm includes the Dynamic Channel Allocation (DCA) algorithm and Transmit Power Control (TPC) algorithm.

    4. The central AP delivers calibration results to the RUs. After the central AP implements the global radio calibration for the first time, the central AP starts the next global radio calibration until it receives neighboring information of all RUs. The central AP implements global radio calibration for consecutive times to obtain the optimal and accurate calibration results.

    Neighbor probe

    Two neighbor probe modes are available.
    • Active probe: The RU actively sends Probe Request frames to notify surrounding RUs of its existence. Active probe is used to establish neighbor relationships and obtain the maximum interference signal strength.

      The active probe process is as follows: A RU periodically sends Probe Request frames destined for a specified multicast address on different channels. After receiving the frames, surrounding RUs learn that the RU is a neighbor and collects information about the RU, in which the RSSI is the key factor.

    • Passive probe: The RU receives neighbor information to detect neighboring RUs. The passive probe is used to collect interference information from neighboring RUs and rogue RUs.

    Global calibration algorithm

    The global calibration algorithm achieves global optimization through partial optimizations. Global calibration is implemented through RU channel and power adjustment. Instead of being coupled to each other, the algorithms for channel adjustment and power adjustment are independent of each other.

    • DCA algorithm: The global calibration divides all RUs into several calibration groups based on relationships between the RUs and allocates channels to each group. In this way, channel allocation for all RUs is implemented. In each radio calibration group, simple exhaustion and iteration algorithms are used to list all possible RU-Channel combinations and choose the optimal combination.
    • TPC algorithm: The TCP algorithm aims to choose the proper transmit power which can meet coverage requirements, without causing large interference to neighboring RUs. The algorithm takes effect in the following ways:
      1. Estimate the deployment density of RUs based on the number of RU neighbors, and determine the initial transmit power, lower and upper interference thresholds.

        Interference specified by the lower interference threshold is low, and within the allowed range. Two neighboring RUs cannot detect interference from each other and can send packets simultaneously. Interference specified by the upper interference threshold is large. Two neighboring RUs can easily detect the interference and can only compete to send packets through CSMA.

      2. Re-detect RSSIs of neighbors. If the interference caused by the neighbor is smaller than the lower interference threshold, the algorithm determines whether to raise transmit power according to their difference. If the interference caused by the neighbor is greater than the upper interference threshold, the algorithm determines whether to reduce transmit power according to their difference.
  • Partial radio calibration aims to adjust working channels and power of some RUs to optimize the radio environment which deteriorates in some areas. Similar to the global radio calibration, the partial radio calibration uses DCA and TPC algorithms. Partial radio calibration is triggered in the following scenarios:
    • A RU goes online: When detecting that a RU goes online, the central AP allocates the working channel and power to the online RU. To achieve the optimal performance, the central AP may re-allocate working channels and transmit power of neighboring RUs. For example, to prevent interference between the new RU and its neighbors, the central AP will reduce the transmit power of the RU neighbors.
    • A RU goes offline: When detecting that a RU goes offline, the central AP executes the calibration algorithm to increase the transmit power of neighboring RUs to eliminate coverage holes. A RU may be restarted unexpectedly or manually restarted for temporary maintenance. In this situation, the central AP does not start the calibration immediately. Instead, the central AP starts radio calibration after the neighbor information is updated.
    • Interference from a rogue RU is detected: A rogue RU is identified through neighbor probe. Interference information is collected and used for radio calibration. The device triggers partial radio calibration according to the interference information. If the interference value exceeds the threshold (-65 dBm by default), the interference is considered serious, and partial radio calibration is triggered. The device adjusts working channels of neighboring RUs to avoid interference from the rogue RU.
    • The radio environment deteriorates: Radio environment deteriorates due to an increase in lost packets and error codes caused by interference or weak signals.
    • Partial radio calibration is manually triggered: You can trigger partial radio calibration based on the AP or AP group.
Updated: 2019-01-11

Document ID: EDOC1000176006

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