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So just how does EVDO work

 
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yossisiegel
EVDO Newbie


Joined: 14 Jun 2005
Posts: 5

PostPosted: Wed Jul 20, 2005 11:15 pm    Post subject: So just how does EVDO work Reply with quote

Is it a software upgrade on the towers? or do they physically run a T1 line to each tower? cant imagine thats what they do..
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Zorog
EVDO Heavy User


Joined: 08 Jul 2005
Posts: 135

PostPosted: Thu Jul 21, 2005 4:09 pm    Post subject: Reply with quote

EVDO cell site equipment can be a hardware "overlay" or embedded in the existing CDMA equipment. Different infrastructure manufactures (ie Motorola, Lucent, Nortel) do it differently.

There are usually large EVDO circuit boards that slide into the base station chassis, connected to amplifiers, which are multiplexed into the existing cables that go up the towers to the antennas.

Additional T-1's (usually 2) are run to the site and are used for packet backhaul. A T-1 only runs 1.5M, so you need to combine at least 2 to support the rates 2.4M.

New base station hardware, new circuits, new software, can all add up to about $50,000 per site for the EVDO upgrade.
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bradsjm
EVDO User


Joined: 05 May 2005
Posts: 29

PostPosted: Fri Jul 22, 2005 2:10 pm    Post subject: Reply with quote

Curious, since a T1 is 1.5M in both directions and EVDO has very limited uplink speed that there would be a lot of unused bandwidth there so I'd have expected them to be slicing it off of an existing T3 and doing something more complex to increase efficiency since I'm sure the voice calls could use that uplink bandwidth.
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Zorog
EVDO Heavy User


Joined: 08 Jul 2005
Posts: 135

PostPosted: Mon Jul 25, 2005 2:23 pm    Post subject: Reply with quote

The T-1's for voice and data are usually bundled together to avoid the 1.5M limit, these bundles function as a single pipe. All capacity is balanced with voice and data.

Very few cell sites generate enough revenue to outweigh the monthly cost of T3 lines. Remember, most cell sites are in fairly inaccessible areas, where Telco costs are high.

The good news is that backhaul is rarely a limiting factor in the performance of the site. It is simply too easy to match up the radio capabilities with the backhaul capacity.

It takes 2 bundled T-1's to give you full rate EVDO, but 2 T-1's can support a ton of voice traffic. The average CDMA site with EVDO probably has 4 T-1's.
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netops1
EVDO Newbie


Joined: 26 Jul 2005
Posts: 8
Location: SoCal

PostPosted: Tue Jul 26, 2005 1:33 am    Post subject: Reply with quote

It all depends on the vendor. In my market which probably isn't typical we have a seperate Nortel BTS and antenna's for EVDO. 2 T1's for packet and one for overhead, 3 T1's per cell. Our voice network is already at capacity with up to 12 T1's for Gold sites but 4-6 are typical for each 800Mhz BTS. With over 1500 cells in our market I am guessing that it's a little more capacity than most places?
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cellgod
EVDO Newbie


Joined: 01 Sep 2005
Posts: 10

PostPosted: Thu Sep 01, 2005 3:13 am    Post subject: t1s at Cell Sites Reply with quote

Each EVDO Cell site has several t1's. Voice and EVDO Data can not share the same t1 as they are handles differently at the MTX (Mbile Telephone Switch). Uauly 2 t1s for Data and anywhere from 1 to 5 t1s for voice.


EVDO uses time division muliplexing for the base to mobile. The Cell site will transmit to 1 user at a time at full power. This ensures full bandwidth for the user. The moble unit uses CDMA to transmit back to the cell site since your uplink doesnt send that much data. Unlike CDMA which uses a simulcasting sceme to "soft hand-off" , EVDO only transmits to you one site at a time, like analog or TDMA.

At the MTX, the imcomming t1s are sent to a router, then to a server that controls the cell. Each cell is assigned an IP, the server also assignes the IP address for your phone as well as control the EVDO cell site.

Unlike conventional cellular, your subscription data is handled by a AAA server in a remote location... for example, if you were on Orlado's EVDO, your authorization data is probably in another switch in another state even though the cell site swithc is in Orlando, FL. (I know where but im not at liberty to discuss the location) Also at the location of the AAA server is the gateway to the internet.

In a way, EVDO at the cell site end is a totaly seperate entity, not sharing many componets with voice. So if EVDO goes down for fails, Voice will remain active, or if voice failes, EVDO will remain active.

Im a cell site Technician and Switch Tech in an EVDO market and so far EVDO has been very exciting and is going to open many doors to new tehcnologys in both voice and data. the End of Analog Cellular is near.
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Polaro
EVDO User


Joined: 29 Mar 2005
Posts: 83
Location: Austin, TX

PostPosted: Thu Sep 01, 2005 9:48 am    Post subject: Reply with quote

This jives with my understanding that EVDO is in a totally different bandwidth spectrum from analog or 2G cell phones. I would be at a loss as to how to share any of the RF side of the hardware. Bundling onto T1s would be possible, but for reliability and QOS this makes no sense. I would consider the sharing of T-1s between cell phone and EVDO to be a false economy in the long run.
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cellgod
EVDO Newbie


Joined: 01 Sep 2005
Posts: 10

PostPosted: Thu Sep 01, 2005 12:47 pm    Post subject: Bandwidth and sharing Reply with quote

Sharing of the t1 by EVDO and voice can not be done due to bandwidth of the t1 and the way the call is handled.

Hardware sharing is only done in the rf section of the cell... namely the filters and amplifiers. in some cases the radio can also be shared if the voice carrier is on pcs and the evdo is pcs... or both or 850 and it is a multi-carrier radio.

the radio spectrum for evdo is a 1.5mhz carrier.. same as 3g1x and 2g. only difference between 2g and 3g is codeing. Analog is only a 4.5khz bandwidth... quite small. one 1.5mhz frequency in 2g and 3g can handle around 64 customers at once.
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xenophon
EVDO Addict


Joined: 30 Aug 2005
Posts: 2033

PostPosted: Thu Sep 01, 2005 5:35 pm    Post subject: Reply with quote

I wonder what this means when VoIP phones over EVDO comes about. There'll need to be a lot more bandwidth piped into each site, I'd think.

Will be cool when there is no separate data/voice network and it's all data phones. Will be able talk (VoIP), browse web, download email and even DUN to laptop all at once on same network connection. Sprint decided to do VoIP over EVDO instead of EVDV, intending to release something by 2007. Anyone know what Verizon is planning for VoIP.
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