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RTN510 V100 TDMA User Manual 04

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This topic describes TDMA basics.


Time division multiple access (TDMA) is a channel access method for shared-medium networks (usually radio networks). It allows several users to share the same carrier channel by dividing the carrier channel bandwidth into different time segments (timeslots).


In a WLAN system, the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) of the 802.11 standard is used to allow the multiple access to the same carrier channel.

Collision avoidance means that, before sending its own data, each node listens to the shared medium to determine whether another node is sending data. If another node is sending data, the node backs off for a random amount of time calculated by an algorithm before attempting to send data to avoid collision. If a collision occurs, the node waits for another backoff period before attempting to send data.

The coverage of WLAN devices is limited, and WLAN terminals use omni-antenna. Therefore, WLAN terminals can hear each other in most cases. In rare cases, a WLAN terminal may not hear another terminal, which is called a hidden node. In this case, collision may occur. Therefore, high throughput can be ensured in most cases.

However, RTN510 has a large coverage and RT uses directional antenna. An RT can hear only the AP and a smaller number of other RTs, leading to a large number of hidden nodes. If only CSMA/CA is used, collision will be severe, significantly reducing the service throughput.

Therefore, in addition to CSMA/CA, TDMA is also used in RTN510 so that an RT sends data only in the timeslots assigned to the RT by the AP to avoid collision and ensure transmission efficiency.

Hidden Node

If two client nodes on a PtMP network are too far away from each other or are blocked by obstacles between them, the two nodes cannot receive the signals of each other. Such two nodes are hidden nodes.

Figure 1-1 shows hidden nodes.
  • In scenario 1, RT1 can receive the signals from RT2, but RT2 cannot receive the signals from RT1. Therefore, RT1 is a hidden node of RT2.
  • In scenario 2, the coverage of RT1 and that of RT2 do not intersect. Therefore, RT1 and RT2 are hidden nodes of each other.
Figure 1-1 Hidden Node
Updated: 2019-09-09

Document ID: EDOC1100010050

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