To answer your questions and hopefully provide some clarity to the information out there regarding 802.11n technology.
>1. Does the uplink and downlink are co-existing and co-operating? similar to ethernet switch full duplex?
All wireless has an uplink and downlink in the same manner as a hub does 802.11n is no different (exception to this will be clarified below), but why are they shown seperately in many specs sheets and marketing stuff well it's because it was discovered that some manufacturers access points had a slower uplink speed than the downlink speed. This issue is well documented on many different brands, it is for that reason that some now market the connections seperately.
>2. The max. through put of 802.11n is 540M, why some document mentions to be 200M?
This discrepancy is easy to explain, First lets remember that 802.11 can run in two different modes - 20Mhz Channels or 40Mhz Channels.
bascially a wireless access point is a hub it has a shared bandwidth that is no different with 802.11n when it's a 20Mhz channel, but if you enable the 40Mhz channel with Channel bonding you get a higher data rate since it spreads the transmission and reception across the 40Mhz span. it is not full duplex like a switch supports. The other factor in the throughput can be the M-Drive or Client Link piece which means that the access point can dynamically adjust transmit time, power level, and antenna to optimize a signal to a particular client. The number of clients that any given access point will support varies by model and manufacturer. Right now Cisco is the only one that truly has M-Drive although others have something similar.
For the Q1, the behavior of uplink and downlink of AP should be the same hub. So, the uplink and down link can co-exist but cannot operate in the same time. When the uplink transfer the data, the downlink cannot work because it is occupied by uplink. Is it correct?
For Q2, cisco can support 540M, other manufacturers may support 540M or less. Is it correct?