Antenna to increase the distance

Discussions related to schematic capture, PCB layout, signal integrity, and RF development

Moderator: robert.ghilduta

Post Reply
Juenda9
Posts: 2
Joined: Sat Sep 23, 2017 11:51 am

Antenna to increase the distance

Post by Juenda9 » Sat Sep 23, 2017 12:00 pm

Dear friends
We are working in a project of building femto-cell to serve our campus with bad connection at low expenses.
the femtocell will be bladeRF based as purchased now.
[ we will try also the USRP]
So we need to increase the distance of the coverage.
[radius of 1 km with some obstacles [buildings in campus .. etc]
If we can purchase the license for legally covering the campus ,
which the best antenna/connectors would be appropriate for such application and compatible with BladeRF [or USRP] ?
Also how to increase the power level of the transmission ?

Thnaks ^_^

User avatar
rtucker
Posts: 17
Joined: Sun Jan 25, 2015 10:38 am

Re: Antenna to increase the distance

Post by rtucker » Mon Sep 25, 2017 8:51 am

Greetings!

So, a lot of this depends on the frequency range(s) you intend to operate at, as well as how much gain you need to satisfy the link budget (both between the base station and the user equipment, and vice versa).

If I were doing it, I'd look at a few things:
  • Antenna, with appropriate pattern, gain, and frequency coverage
  • Power amplifier to boost transmitter output
  • LNA to improve receive sensitivity
  • Antenna combiner
    • If designing a frequency-division, full-duplex system, Bandpass Duplexer to combine simultaneous RX and TX onto one antenna
    • If designing a time-division, half-duplex system, a transmit/receive switch to toggle the antenna between RX and TX mode
  • Environmental protection
    • Weather-proof enclosure
    • Waterproofed RF connectors
    • Lightning protection!!!
    • Grounding, etc
For a proof-of-concept/demo, you could start with a couple omnidirectional antennas temporarily placed at a high location, such as the roof of a building, and some coaxial cable to separate the RX and TX. Add in a power amplifier (take a look at https://www.minicircuits.com/) once you're comfortable with how everything is working at short range. If you eventually want to combine RX and TX into a single sectored antenna like "normal" cell sites, start looking at combiners.

(Quick tip: because omnidirectional antennas generally have a toroidal pattern, vertical separation between omnidirectional antennas is more effective than horizontal. If you do this, put the RX antenna higher than the TX antenna, and your users' batteries will thank you.)

Good luck, and let us know how it goes!
Rey Tucker (she/her)
Systems Engineer, Nuand LLC
Rochester, NY, USA

Juenda9
Posts: 2
Joined: Sat Sep 23, 2017 11:51 am

Re: Antenna to increase the distance

Post by Juenda9 » Fri Sep 29, 2017 9:07 am

Thanks a lot brother.
Your post was so helpful.

We investigated that 1 watt able to cover 1 km in open area[LOS]. [and may be the half of the distance in urban area]
received signal depend on transmitted power , tx antenna gain , rx antenna gain [controllable parts] , lambda , distance [uncontrollable]
there are also fading coefficient.
so roughly we think that 5 watt will be adequate.
In summary :
1-PA with Tx power 5 Watt [37 dbm] at the TX end of bladeRF (NF= 7).

2-PA LNA [With noise figure = 0.4] at the RX end of the bladeRF

Now what is the problem with separate antennas for Tx and Rx [with full duplex] - why we need combiner?
Also If the TX end send with 37 dbm does this will cause harm onto the PA at the adjacent RX end with maximum input power 16dbm ?
:roll:
If we will put the antenna at the campus gate then no need for omnidirectional antenna - we can use Yagi antenna or even little priced quad band SMA antennas ?

Does there any official technical data about the output power from the TX port from bladeRF , the minimum sensible power at the RX port and maximum power could be afforded and don't cause damage to bladeRF at the RX port ?
I searched but reach non-official results. :D

Thanks again brother ^_^

User avatar
rtucker
Posts: 17
Joined: Sun Jan 25, 2015 10:38 am

Re: Antenna to increase the distance

Post by rtucker » Thu Oct 05, 2017 10:21 am

If you can get adequate separation between the antennas, that will work just fine. Sometimes this is possible, sometimes it isn't. On the RX path, if you can filter out the TX frequencies, that will help too. Directional antennas also make this easier. Attenuation is attenuation :)

For TX power, our official spec for maximum is +6 dBm CW typical, which is based on the LMS6002D datasheet. This will vary by frequency. You'll also want to be on the lookout for compression and distortion and other nastiness if you're running near maximum TX power, depending on the modulation you're using. In general, let your PA do as much of the amplification as you can.

On the RX side, this is where the antenna separation and filtering come into play. The LMS6002D datasheet alleges it can handle +23 dBm with no damage. Again, the more of the TX signal you can get rid of, the better... even if it's outside of the filter passband, it may be close enough to affect your dynamic range.

I would measure the power coming in from the RX antenna while the TX antenna + amplifier is pumping out a full-power continuous signal (like a random QPSK signal at a representative symbol rate) before hooking it up to your LNA and bladeRF, and also measure coming out of your LNA before hooking it up to the bladeRF.

Minimum RX power depends on the minimum SNR to meet your system's BER/BLER requirements, along with the noise figure of the bladeRF + LNA (which tend to depend on frequency and RX path on the board; the LMS6002D can vary from 3.5 dB to 10 dB typical), the gain settings on the LMS6002D, and probably the ADC's resolution and ENOB (10 bits).

To more directly answer your question: TX +6 dBm CW typical, RX +23 dBm absolute maximum, and It Depends for minimum RX power.
Rey Tucker (she/her)
Systems Engineer, Nuand LLC
Rochester, NY, USA

Post Reply