Coexisting with WiFi | Cypress Semiconductor
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Coexisting with WiFi
1. How exactly does the CY4632 WirelessUSB LS KBM RDK cope with the situation where it is occupying a ISM channel when someone switches on a 802.11 network which occupies the same channel. Will the keyboard malfunction momentarily? Will it cause keyboard / mouse errors?
How long does it take from initially detecting interference on PERT to high or RSSI to re-locate to a clean channel and rebind? Will this have an effect on the keyboard or mouse operation being used?
Please note that these devices are obsolete. Instead please proceed with WirelessUSB LP which offers enhanced features.
Because of DSSS even if the WiFi channel overlaps the LS channel in many cases depending on range and signal strength the WirelessUSB signal will continue to be received correctly without changing channels. If the WiFi channel overlaps the WirelessUSB channel and the WiFi signal is sufficiently strong to cause a high bit error rate in the WirelessUSB link then after several unsuccessful retries the WirelessUSB 2-Way protocol will automatically cause the device and the dongle to relocate to another channel. After a certain number of retries the dongle and the device realize that the channel has gone bad and go into reconnect mode to establish an alternate good channel. This process typically takes a few hundred milliseconds. During this time keystrokes or mouse movement may not be recongnized, but spurious keystrokes and the adherent mouse movement will not be caused because the error checking in the corrupted packets prevents bad packets from being accepted. If a key was already pressed at the time that the interference appeared the lack of reception of a keep alive signal from the keyboard by the dongle will cause the dongle to send a USB packet showing a key up event thus preventing the appearance of a stuck key condition.
General note: Our tests have indicated almost total immunity to Bluetooth devices. With WiFi, PCMCIA cards and access points are a little difference from each other because the transmit power from the PCMCIA cards is typically somewhat lower. Typically, provided that a WiFi PCMCIA transmitter is at least twice as far from the WirelessUSB dongle as the WirelessUSB transmitter, WirelessUSB continues to work well without needing to change channels. Access points typically need to be a little further away. Our latest co-location and interference validation reveals that even in the presence of two WiFi networks and 20 of our WirelessUSB LS KBM RDK systems, all fully function as expected. We have also tested the following WiFi interfence environment:
- 3 WiFi access points, at the points of an equilateral triangle who's vertices are all 20 meters in length. Each access point performing continuous file transfer to another WiFi device outside the triangle.
- A WirelessUSB keyboard and mouse system with a dongle and a laptop is then operated within the triangle with the range between the keyboard, mouse, and dongle at a 10 meter range. No location for either keyboard, mouse, or dongle was found within the triangle at which the WirelessUSB system failed to operate perfectly. Of course, at various times as the dongle (laptop) was moved around within the triangle there were slight short (few hundred milliseconds) pauses as the WirelessUSB system changed channels. But these were fewer that might be expected.