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3G BS antenna bandwidth

Discussion in 'GENERAL Wireless Discussion' started by sis651, Jul 15, 2011.

  1. sis651

    sis651 Junior Member
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    Hi. I have a little wonder but couldn't find sources about that.
    I wonder how much is the theorical maximum downlink and uplink bandwidth of a 3G base station panel antenna.
    For example using HSPA we get download speeds of about 20mbps. If 10 user downloads sth. at the same time, base station antenna will need to send 200mbps to downloaders. I mean if a base station had a theorically speed limitless backhoul connection to internet backbone, how much data it could send to all users totally? On 3G & LTE?
    Is there any such data?
     
  2. RadioRaiders

    RadioRaiders RF Black-Belt
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    It's not a simple answer, because of the variables involved. But in the end it comes down to radio bandwidth (RF spectrum) and modulation. UMTS/HSPA is limited to a fixed 5MHz carrier, altho you can use 2 carriers (MIMO) to double the bandwidth and hence throughput. Regarding modulation (that's how many bits you can cram into that spectrum "pipe"), if you go from QPSK (4PSK) to say 16QAM (16PSK) then you can increase your thoughput by 4x theoretically (but you need better radio conditions of course, you won't get high modulation in areas with alot of interference, for example).

    You can see here how throughput increases when modulation (QAM) and bandwidth (MIMO) increases (look at "UE Catagories"):
    High-Speed Downlink Packet Access - Wikipedia, the free encyclopedia

    Altho the above is about HSPA, it can really apply to most radio technologies. LTE will allow flexable bandwidth (between 1.4MHz to 20MHz), so that's one advantage it will have over HSPA to get more speed.
     
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  3. sis651

    sis651 Junior Member
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    I had checked the table before, but I think max. data rate displayed on the table is the data rate consumers downloads from the base station.
    I was wondering max. how much data all the users can download from the same antenna at the same time. For ex., one user is downloading with 20mbps, second 20 mbps too, thus their both downloads 40mbps from the antenna. If the antenna had max data rate limit of 100mbps, when more than 5 users starts to download sth. at the same time the speed will start to drop 16mbps and less... And assuming the base station backhaul has theorically no max data rate limit.
    I think it is hard to calculate such a thing.
     
  4. RadioRaiders

    RadioRaiders RF Black-Belt
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    Yes, it's a little complicated to calculate, because you have to know all the variables. If considering a antenna has only one 5MHz UMTS carrier (15 channel codes), and is using R7 16QAM, allowing max 21Mbps per cell, then if you are downloading at 21Mbps and a second person starts downloading on the same cell, you will lose throughput, as the radio resource is now being shared.

    There's plenty of documents out there on the internet if you want to read some more, here's on from Qualcomm, a little old, but you can see how cell throughput is calculated from HSPA on R5, and also how UMTS calculates the number of voice users per cell (note: UMTS and HSPA share the same carrier bandwidth, but act on different locgical channels, and behave very differently)

    http://www.qualcomm.com/common/documents/white_papers/Air_Interface_Cell_Capacity__RevB_new.pdf
     
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  5. sis651

    sis651 Junior Member
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    Thanks RadioRaiders.
    I'm checking it out.
     

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