For the WLAN deployments that take place in uneven network coverage areas due to low RSSI, weak spots where individual AP range does not overlap, and/or the devices are at a farther distance outside the network perimeter or in transitions between two separate areas or buildings, the following aspects need to be fulfilled:
The devices need to hear APs beacons at a larger distance to maintain the connectivity.
The devices need to hear the AP downlink of time-sensitive packets at that same distance.
The AP needs to hear the device uplink of time-sensitive packets at that same distance.
There are several mechanisms that give a 2x2 device more advantages than a 1x1 device to accomplish the three aspects above.
When a 2x2 device hears the AP beacons or AP-downlink from a far distance that have weak signals, the ability to use the maximum ratio combined (MRC) from the two spatial streams improves the chances to decode the signal as valid and distinguish it from the local noise. A 1x1 device is unlikely to be able to decode weak signals.
The 2-antenna design and placement in the 2x2 device help MRC receive signals and reduce the chances that the dynamic positioning of the device (such as the device orientation and the way that the users hold the device) in the 3-dimensional space might impact the ability to hear weak signals.
A 2x2 uses the cyclic delay diversity (CDD) mechanism to achieve full diversity by turning spatial diversity into frequency diversity when transmitting data to an AP as in any 2x2 MU-MIMO transmission. Using CDD increases the chances for the AP to hear the 2 spatial streams of the device that is from a far distance.
When the coverage expectations are known, the potential challenges may be surveyed and corrected by using WLAN coverage survey tools.
It is important to consider that time-sensitive applications in 1x1 devices require a close to ideal WLAN coverage to operate, where the deployed AP power or channels are overlapped and no error in other network criteria. In such deployments, it is recommended to re-survey and re-check the coverage more frequently, especially when the infrastructure-related configuration parameters have changes.
