Wireless Access

Hi,

What is actually  a device   "Tx: Rx:SS  

Is it a ratio? 

How do we calculate or this is from data sheet ? 

How do we interpret this ratio

Thanks

The following description is from the Aruba Outdoor MIMO VRD that explains this pretty well (page 59):

Transmit, Receive, and Spatial Stream Designation

In 802.11a/b/g, only a single antenna and a single stream of data are involved. But 802.11n and 802.11ac adds multiple antennas and multiple streams of data to increase the transmission capabilities of APs and stations. It is important to understand the nomenclature that is used to describe the capabilities of the system to transmit data at certain rates.

Figure 46 shows this nomenclature.

Figure 46 Transmit, receive, and spatial stream nomenclature

* Transmit: The number of antennas that are dedicated to transmitting data.
* Receive: The number of antennas that are dedicated to receiving data.
* Spatial streams: The number of individual data streams that the radio is capable of transmitting. An 802.11 a/b/g AP (1 x 1 : 1) is capable of one stream of data, or one transmission, to a client at a time. 802.11n and 802.11ac APs are capable of transmitting multiple streams of data at the same time to the same client. The number of spatial streams must be less than or equal to the number of transmit or receive antennas, depending on which way traffic is flowing.

<end of cite>

802.11ac wave 2 adds a 4th and 5th digit which is explained here.

Hi,

This is applicable to client also ?

Thanks

Yes, and the maximum that you can reach is the maximum of the combination.

Few examples:

- The number of SS cannot be more than the number of Rx or Tx antennas (both on AP and client)

- If you have a 3x3:3 AP and a 1x1:1 client, you will only get 1 spatial stream in the combination. A two-stream client will get 2 streams, and to get the full potential, you will need a 3x3:3 client as well. A (fictional, I don't think they exist) 4 stream client would only get 3 streams.

- Most smartphones are 1-stream devices, some are 2-stream.

- 3 stream devices are typically larger devices like laptops.

- For 802.11ac wave 2 with MU-MIMO: If you have a 4x4:4:3 AP and a 1x1:1:1 and a 2x2:2:2 client, you will get 1 stream from the AP to the 1x1 client and 2 from the AP to the 2x2 client. Note that MU-MIMO only works from the AP to the client, not from client to the AP in 802.11ac.

For further reading, there should be in depth (going pretty deep technical) in the referred Outdoor MIMO VRD and the 802.11ac Whitepaper that is referred in that document.

Hi,

What if  ap is 2x2:2 and client is 2x2:1 

Could you explain better understanding 

If client has 2 rx and 2 tx antenna and it support only one ss , What will happen . 

Thanks 

In that combination the link can only use one spatial stream and the maximum datarate is limited by that. The additional chain at the AP will help to create a more robust link between the two which may help to sustain a higher MRC (datarate) at a given client location (compared to a 1x1:1 client), but the peak datarate for the link is still half that of one that supports two spatial streams (with a 2x2:2 client).