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Posted on 2006-11-13
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Question about WiFi being half duplex or full.  I said it's half.  Could you guys vouch for me?  Thanks - I'll "owe" you one.  :)

http://www.experts-exchange.com/Networking/Q_22056841.html
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Question by:pseudocyber
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Francis_Beland earned 100 total points
ID: 17933644
WIFI is Half Duplex.
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by:darrenakin
ID: 17933841
WIFI is half Duplex, but what about the new N with dual radios, I believe that these are full duplex. Send and Recieve at the same time.
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by:pseudocyber
ID: 17933885
Hmm.  Darren - you could be right about that - although, I thought N primarily relies on Multiple In, Multiple Out (MIMO) to make better decisions on dealing with Multipath.

But, I needed you guys to back me up on the link I provided so the questioner would believe me, not in this thread. ;)
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by:darrenakin
ID: 17933898
I will look into the N more.
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by:darrenakin
darrenakin earned 100 total points
ID: 17934039
Here is a very interesting article; http://www.deviceforge.com/articles/AT5096801417.html in specific the paragraph is listed below from that article.

Another valuable opportunity MIMO technology may provide is Spatial Division Multiplexing (SDM). SDM spatially multiplexes multiple independent data streams, transferred simultaneously within one spectral channel of bandwidth. MIMO SDM can significantly increase data throughput as the number of resolved spatial data streams is increased. Each spatial stream requires its own TX/RX antenna pair at each end of the transmission (Figure 1). It is important to understand that MIMO technology requires a separate radio frequency (RF) chain and analog-to-digital converter (ADC) for each MIMO antenna. This increasing complexity ultimately translates to higher implementation costs as higher-performance systems are required.
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by:darrenakin
ID: 17934195
So heres my question, I guess Multiplexing is the same as Duplexing???
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by:lrmoore
lrmoore earned 50 total points
ID: 17934729
WiFi is half-duplex
WiFi is shared media just like an old hub - which is half duplex
You would have to have dual radios in both NIC cards and in Access points with one send and one receive to be considered full-duplex.
The copper NIC interface between the Access point and the network switch can be full-duplex
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by:asrdias
asrdias earned 150 total points
ID: 17934882
Hello !!!

Standard Wi-Fi wireless hardware uses one antenna to receive and one to transmit data. This is half duplex plain and simple.


But the standards are changing and the future brought MIMO that uses two or more antennas at each end of a connection to send and receive data, enabling transmitter and receiver to accept signals more efficiently than with a single antenna. Ant this is full duplex.

Quoting:
MIMO is one of the major features of the next standard for wireless networking, 802.11n. The ability of MIMO to handle multiple signal paths enables MIMO-based wireless networks to provide greater throughput than standard wireless networks. Although the final features of 802.11n have not yet been determined, MIMO will be a vital component in the drive to push speeds past 100Mbps.

True MIMO uses three antennas to transmit and receive multiple data streams. A digital signal processor (DSP) is used to divide transmitted data into multiple data streams, while the receiver uses another DSP to reconstruct the multiple data streams -which can be received either directly from the sender or reflected off objects such as walls, floors, doors, and ceilings- into data packets. Airgo refers to this method of transmitting and receiving data as spatial multiplexing. Airgo's True MIMO is the only one of the three MIMO implementations to divide and reassemble multiple data streams.

So the answer is:

WIFI is half duplex if the radios used are 802.11a/b/g and full duplex if 802.11n (Not yet released but MIMO is the so called 802.11 preN

Adias
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by:drawlin
drawlin earned 50 total points
ID: 17935386
asrdias>  In a radio circuit using one antenna to transmit and one to receive (assuming you have a transmitter on one and a receiver on the other/ not a transceiver) is the Definition of a Full Duplex circuit.  Wireless NIC's and built-in wireless adapters only have one antenna.  Current WiFi if half duplex: it can only transmit or receive at one time.  The two antennas you see on may Access points is an attempt to employ an age-old signal enhacement technique called space diversity.  MIMO is a next generation frequency diversity technique (since every transmitted signal has upper and lower harmonics) one signal may make it to the destination better at 50 feet and another harmonic may be better at 150 feet.
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by:MarkWYnne
ID: 17938295
Indeed, Transiever. Does what it says on the tin One device that transmits and recieves. Like a cheap two way radio, you cant hear the other guy while you are talking. But it is the actual device config itself rather than the amount of antennas attached.
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by:saw830
saw830 earned 50 total points
ID: 17949636
Whew!  I was getting really worried that I might be the only one to understand this, until I got to MarkWYnne's comment.

I concur!  WiFi is half-duplex, but not because it is the standard, or because of the number of antennas, etc.  It is half-duplex because the radios in the devices do not transmit and receive simultaniously.  In addition, it's only one device at a time, since all devices in a given Ad Hoc network or associated to a specfic Access Point are using the same channel.  It's just like when you talk on a two-way radio.  Only one person gets to talk at a time on any given channel in any given area, regardless of the number of people listening or wanting to talk.  If more than one person talks, then nobody hears anything useful.
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by:asrdias
asrdias earned 150 total points
ID: 17949976
Hi,

Half-Duplex  - The transmission of data in both directions, but only one direction at a time. For example, two-way radio (push-to-talk phones) use half-duplex communications. When one party speaks, the other party listens.

This is true regarding WIFI 802.11a/b/g

Full-Duplex - Capable of transmitting and receiving over the same media simultaneously. In pure digital networks, this is achieved with two pairs of wires. In analog networks or in digital networks using different carriers, it is achieved by dividing the bandwidth of the line into two frequencies, one for sending, the other for receiving.

If an access point is using a transceiver capable of sending data using a channel and receive using another non overlaped channel with the one used to send then this access point is performing full-duplex because it sends and receives simultaneously.

Some new generation WIFI equipments are starting to use this methods to achieve higher levels of performance. There are equipments using 802.11a and 802.11g standards simultaneously.

More information please check the link:

http://www.netstumbler.com/2004/04/02/improved_wi_fi_repeaters_due_in_2005/

Adias

Adias


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Author Comment

by:pseudocyber
ID: 17950821
Ok.  I'm going to close this ticket.  It was in reference to me telling another questioner that wifi was half duplex and he wanted some other opinions - and you guys were supposed to click on the link at the top of this qestion and go to the other question.  Since you guys were so detailed, and informative, I'll up the points here and split.  Thanks guys.
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