Editing Hidden node problem (section)

== Solutions ==

=== Increasing transmitting power ===
Increasing the transmission power of the nodes can solve the hidden node problem by allowing the cell around each node to increase in size, encompassing all of the other nodes. This configuration enables the non-hidden nodes to detect, or hear, the hidden node. If the non-hidden nodes can hear the hidden node, the hidden node is no longer hidden. As wireless LANs use the [[CSMA/CA]] protocol, nodes will wait their turn before communicating with the [[wireless access point|access point]].

This solution only works if one increases the transmission power on nodes that are hidden.  In the typical case of a [[WiFi]] network, increasing transmission power on the [[wireless access point|access point]] only will '''not''' solve the problem because typically the hidden nodes are the clients (e.g. laptops, mobile devices), not the access point itself, and the clients will still not be able to hear each other.  Increasing transmission power on the access point is actually likely to make the problem worse, because it will put new clients in range of the access point and thus add new nodes to the network that are hidden from other clients.

=== Omnidirectional antennas ===
Since nodes using [[directional antenna]]s are nearly invisible to nodes that are not positioned in the direction the antenna is aimed at, directional antennas should be used only for very small networks (e.g., dedicated [[Point-to-point (telecommunications)|point-to-point]] connections). Use [[omnidirectional antenna]]s for widespread networks consisting of more than two nodes.

=== Removing obstacles ===
Increasing the power on mobile nodes may not work if, for example, the reason one node is hidden is that there is a concrete or steel wall preventing communication with other nodes. It is doubtful that one would be able to remove such an obstacle, but removal of the obstacle is another method of remedy for the hidden node problem.

=== Moving the node ===
Another method of solving the hidden node problem is moving the nodes so that they can all hear each other. If it is found that the hidden node problem is the result of a user moving his computer to an area that is hidden from the other wireless nodes, it may be necessary to have that user move again. The alternative to forcing users to move is extending the wireless [[LAN]] to add proper coverage to the hidden area, perhaps using additional access points.

=== Protocol enhancement ===
There are several software implementations of additional protocols that essentially implement a [[Polling (computer science)|polling]] or [[token passing]] strategy. Then, a master (typically the access point) dynamically polls clients for data. Clients are not allowed to send data without the master's invitation. This eliminates the hidden node problem at the cost of increased latency and less maximum throughput.

The Wi-Fi [[IEEE 802.11 RTS/CTS]] is one handshake protocol that is used. Clients that wish to send data send an RTS frame, the access point then sends a CTS frame when it is ready for that particular node. For short packets the overhead is quite large, so short packets do not usually use it, the minimum size is generally configurable.

=== Cell network ===
With [[cellular network]]s the hidden node problem has practical solutions by time domain multiplexing for each given client for a mast, and using spatially diverse transmitters, so that each node is potentially served by any of three masts to greatly minimise issues with obstacles interfering with radio propagation.