Last Post: January 31, 2013:
I'm new to the forum after passing my CWTS on Friday. I have a quick question that i'd be grateful for some help on, not sure if this is the correct place so please let me know if i'm barking up the wrong tree!
I just wanted to know, with regards to spatial multiplexing, subcarriers and diversity antenna configuration; the data that is being sent on multiple carriers or paths, is this a replication of the same data or is it different data being sent at the same time?
The way i see it at the moment, is that diversity is the same data being sent twice to avoid mutlipath issues and also provide strongest signal. I believe that with spatial multiplexing or using subcarriers of a channel the data is different bits of data being sent simultaneously which is what provides the higher speeds and throughput.
If someone could help clarify this that would be great, i can't seem to find any definitive answers online.
First, let's define diversity (simple diversity). With antenna diversity the data sent is only sent once, but it can be sent out one of two or more antennas in the diversity array. But remember, only one antenna is used to transmit that specific data stream.Now, with spatial multiplexing or spatial streams, the data is split and transmitted on separate antennas at the same time. This is different portions of the data that has been coded for transmission.As to what provides higher speeds (data rates) and ultimately higher throughput, it is a combination of coding techniques, modulation techniques, bandwidth used and the number of spatial streams. All of this together impacts the speed of the WLAN. Interestingly, simple diversity can improve the throughput of a WLAN because it can reduce retransmissions, which, when in excess, can be destructive to the performance of any network.
Many thanks for your response Tom, i'm learning very quickly that WLAN isnt as easy as it first seems!
You will find that .11n is much more complex than pre.11n.
If I were starting in Wireless I would study the "pre" stuff first. Pay extra attention to the particular details of OFDM though, as that is what .11n and newer techologies are using.
I work in the PHY area mostly, so things like the number of sub-carriers and Pilot's, and their spacing across the 20 -vs- 40 MHz channels are important. For the typical WLAN professional it's probably enough to know they are different.