Sprint 3g/4g to antenna? Or not to antenna?

Current setup:

Small remote office

3 computers, 1 server, 1 printer

CradlePoint MBR1200 Firmware 1.7.2

(2) Two Sierra Wireless AirCard 250U modems

Office is located at Cobblerock between Gold Camp Drive and Prospect Park Drive facing North, in Rancho Cordova, CA

Modem Info: Manufacturer: Sierra Wireless, Product: 250U - 4G, Modem Firmware Version: 5.2.2061050032, Signal Strength (%): 33, Signal Strength (dBm): -87, Connection Status: offline / Connected across both USB ports, Connection Type: CDMA, Service Display: 1xEV-DO,1X

We are getting 100% signal on 3g but it's speeds vary widely thru the day. Some days a laptop not connected to the CradlePoint but to a separate U600 gets a bar of 4g and is blazing faster but the signal often gets lost and it's back to 3g.

From time to time the user with the U600 is using in the desktop. We changed the metrics so it uses it as a gateway still access to the LAN. He claims the one U600 (3g or 4g) is faster than the CradlePoint and the two 250U's connected via a Ethernet cable to a Linksys 24 port switch with just one user. The switch is not the issue because we used the switch on the back of the CradlePoint as well with no difference.

We did an indoor survey for the best location of the CradlePoint. We used a Sprint phone and a laptop and a U600, to get an average of results. The dbm's were from low -80's to mid -90's.

After the survey inside the office was completed we placed the CradlePoint in the best location with the lowest dBm's. Currently the two 250U's are directly on the back of the router. There are two Belkin USB extension cables built with RF and EMI/RFI shielding which haven't been put to use. The USB's are going to be taped to the window with an elevation of about 5'8" (12" from top of frame and 2'+ away from fluorescent lights). It should be done tomorrow.

There seems no variation in different elevations in dbm or speed. The window is the farthest away from any electronic equipment and the closest to the nearest Sprint tower FN04XC011. No difference with lights off.

On the laptop with the 600U we noticed in the Sprint Smart View the signal (dbm) would raise when actually pulling pages down off the web and during downloads to 101. Don't know if it's a software glitch or something related to hardware. After the page was done loading it'd go back to it's previous value.

I'd like to add an antenna. I'd like to go 4g all the way.

What is the right antenna for me? Is there any configuration changes I can make with the current hardware to improve performance? Is roof best way to go? What about lightning? Should I go for 3g or 4g? Will any antenna do both? Is it a good idea to have an antenna that does 3g and 4g?

I saw a few products that may work namely the Sprint 250U Broadband Modem Antenna by Sierra. I'm not familiar and need help making a decision.

Background: There is only T1 service available and it's still around $378+. There used to be DSL but AT&T changed the rules about the distance from the CO. The only available DSL in the area was grandfathered. New DSL accounts or a new CO aren't going to happen. It was DSL 144/144.

A few years ago when the office had more personnel we had flex T1. The circuit was split 768 data and the rest of the bandwidth for voice. It was an excellent product. We changed to a full T1 when things got really busy and wrapped into our voice services.

During the down turn we negotiated out of the contract and got 3 POTS and one Sprint wireless card. Recently the office went from one to three people and one field tech who frequents the office a few hours a week. We are only there till December but one of the new users requires a bit more bandwidth to more efficient by decreasing delays in dispatching and data entry. The user requires either VPN or a remote connection to access dispatching thru our accounting/CRM. Either way it's too slow some parts of the day. On the other end its 3.0Mb Bonded T1 Flex solution which never sees 50% utilization. The phones aren't very busy now-a-days so it's not on the hosting end.

Thanks,

ShortChop

P.S. Sorry if posted in wrong section

General observations:

CINR of 6dB is quite low, signal strength worse than -80dBm is not good at all. Sadly if boosting your input signal using high gain, narrowband directional antennas don't solve your CINR issue there's not much you can do about this since this would mean the main problem is interference noise power (from multi-user OFMDA interference).

He claims the one U600 (3g or 4g) is faster than the CradlePoint and the two 250U's connected via a Ethernet cable to a Linksys 24 port switch with just one user. The switch is not the issue because we used the switch on the back of the CradlePoint as well with no difference.

Have not seen this. Our opinion is that there's virtually little statistical difference between these modems. You can never rule out individual modems though but on average we don't see an issue and in fact we like the Sierra 250U and this usually what we integrated in most projects.

We did an indoor survey for the best location of the CradlePoint. We used a Sprint phone and a laptop and a U600, to get an average of results. The dbm's were from low -80's to mid -90's.

This is not good. The received signal to utilize the highest modulation modes such as 64QAM which yields the best datarates (lower bit-error-rates) is in the -60's range.

On the laptop with the 600U we noticed in the Sprint Smart View the signal (dbm) would raise when actually pulling pages down off the web and during downloads to 101

You mean -101dBm. This means it's getting worse (the more negative the number the weaker the signal). There should be no intentional direct correlation between activity level (amt of download/upload) and RSSI indicator. Notice i said intentional. What does exist however is a correlation between speed and activity level. As the number of bit errors caused by channel impairments increase (and this is more apparent as activity level increases), different feedback mechanisms in the modem start to kick in to try to lower bit error rate. For example ARQ schemes (automatic repeat request) which effectively lowers your throughput or the modulation mode changes to a lower mode that is more immune to low SNR (but which is not as efficient e.g QPSK). Non-intentional stuff would be as you said software of hardware glitches.

I'd like to add an antenna. I'd like to go 4g all the way. What is the right antenna for me? Is there any configuration changes I can make with the current hardware to improve performance? Is roof best way to go?

What is the performance of your modem when you use it outdoors at approximately the same location where you could mount an outdoor antenna? Yes an outdoor roof-mounted antenna will always yield the best performance. One of the biggest problems with Clear wimax is indoor coverage and a large majority of the people we serve have quite good outdoor signal but terrible indoor signal which is the very situation these antennas are supposed to alleviate.

The most popular antenna is the 18dBi panel antenna which you could get as part of this kit: http://www.rfwel.com/shop/4G-USB-Modem-Outdoor-Antenna-Kit.html.

As for configuration changes this would be more of a question for Clear tech support (we only handle RF wireless issues). However, there's little you could do on the CPE side short of relocating or repositioning the CPE/modem to pick up a better signal (or of course adding external antennas).

What about lightning?

Absolutely! In the kit above we say that this is optional since it will work without it but we STRONGLY recommend it. Think about it -- you are hooking up a very good electrical conductor (the antenna and coaxial cable), high up on the roof above any other potential lightning arrestors, then running a conductor into your house to the modem. In the least a direct lightning strike could fry the modem but this is the least of your worries.

Should I go for 3g or 4g? Will any antenna do both? Is it a good idea to have an antenna that does 3g and 4g?

Here is a list of some popular wimax band (2.5-2.7GHz) antennas: http://www.rfwel.com/4g-data/wimax-antennas.php

As you can see there are some antennas such as the 8dBi LPDA antenna that supports both the 3G PCS band at 1.9GHz and the 4G WiMax band (2.5-2.7GHz). The problem with these dual-band/wide-band antenna is that they have lower gain than just the 4G antennas. So to answer this question you need to figure out if after adding for example the 18dBi antenna will your RSSi be strong enough to give you good speed and reliability and reside just on the 4G band. For most people this is the case and for a stationary application like yours you dont ever need to go to 3G if 4G is good enough.

Other people want to have that option to go to 3G if they need to so if your budget allows you could also get two antennas one single band 3G antenna such as the 13dBi PCS 3G yagi and the 4G 18dBi panel. You may then either use a diplexer to hook them up to the same antenna port as in the case of the Sierra 250U or just plug the 3G manually if you ever need to use 3G. Here is an example of the former: http://www.rfwel.com/support/tech-drawings/cellular_wimax_amplifier_sys.pdf

You can find more 3G antennas here: http://www.rfwel.com/signal_improvement/cellular_antennas.php

Again most people just get the 4G since if your outdoor signal is good this should be all you would need.

I saw a few products that may work namely the Sprint 250U Broadband Modem Antenna by Sierra. I'm not familiar and need help making a decision.

Is this what you are referring to: http://www.rfwel.com/shop/Sierra-250U-3G-4G-Booster-Antenna.html ? If so notice that this is a unity gain (2.5dBi antenna). This is no better than the integrated antennas in your modem with the only advantage being you can relocate them away to a better location and away from each other. Recall that dB is a logarithmic scale so the difference between a 2.5dBi antenna and an 18dBi antenna is HUGE!

You are absolutely right! WiMax makes a lot of sense for many people and we know several companies that are cutting their DSL/Cable/T1 and going all WiMax (or some even all 3G HSPA+). The key though is to get that indoor signal just good enough for the fastest speed and so stable enough that it's not trying to search for towers or roam between towers since fading and other channel impairments are knocking signals off.

Last edited by thuor; 08-12-2011, 04:03 PM.

KF7RCQ

Thanks,

It's a lot to digest and I appreciate the feedback. I'll read over what you have provided and follow up. Of course, I'll problably have more questions.