Since fabrication and miniaturization is easy, will it be beneficial to realize large number of array of spiral antennas ?
Today, nearly all of the base station antennas are linearly polarized. Therefore a circularly polarized antenna (in theory) will compromise the diversity and MIMO schemes currently implemented. That said, the mobile environment is highly variable and polarization from a subscriber unit is all over the place when it finally arrives at a base station antenna. The key to future 4G/5G air interfaces is the use of multiple antenna apertures. I am not aware of research done using multiple spiral antennas (circularly polarized) on a subscriber unit. It would be interesting to see how a subscriber unit performed with 2,3, or even 4 circularly polarized antenna apertures compared to a similar number of linearly polarized antenna apertures. In theory, one might expect approximately 3dB lower average signal strength, but with fewer deep fades.
Wireless base stations already use MIMO (multiple-input multiple-output) on the downlink, and some subscriber units are capable of supporting uplink MIMO as well. (The Wi-Fi modem in your laptop has used at least two antennas on the uplink for years.)
The use of MIMO on the downlink and uplink will get much more intense as the industry moves towards 5G. In practical terms you can use MIMO to achieve one of two objectives on the air interface:
-Virtual beam forming to increase gain towards a particular base station or to null one or more interfering signals, limited by the number of antenna apertures you have available. Each antenna represents an independent equation.
-Increasing data rates by setting up orthogonal data streams on the same frequency.
One could argue that optimizing for either of those two objectives is sort of the same thing, and I'd agree with that from a purely mathematical standpoint. From the user's or the network operator's perspective though; you have to pick one or the other. Optimize for interference rejection (beam steering / beam forming), or higher bandwidth on the air interface.
Look to www.3gpp.org as a great technical resource for all thing related to the existing and future versions of LTE.
-Mike
The 3GPP website has graphics, technical documentation, and maybe even a video that can explain it much better than I'll be able to do here.
Multiple uplink data streams on LTE is similar to CDMA in so much that if your two signals are orthogonal, they are essentially independent. In order to do this, you've got to have at least two antennas on the subscriber unit and the base station. Most subscriber units can't do this today, there are no smartphones that I know of which can support uplink MIMO. The first applications for multiple data streams to utilize uplink MIMO will likely come from fixed LTE installations, wireless broadband modems in the home for example. In that type of application, the subscriber unit can get the antenna spacing or polarization diversity necessary.
The base station is easy, there are already at least two antenna apertures running on any downlink frequency. I don't have the data in front of me to confirm, but I wouldn't be surprised if some networks have 4-branch MIMO already deployed. It's surely headed in that direction, and future iterations of the LTE standard suggest 8-branch MIMO is not too far off.
Ahmed, depends on which part of the world you're working in. 4G to 5G could be no more than a software upgrade on an exiting base station if the operator chooses to make the transition to 5G in the same frequency band.
If a country has the luxury of rolling out 5G on a newly allocated frequency band, then new antennas will be needed on the base station along with new/additional radios and filters. There is no general rule, it depends on the existing frequency allocations in the country and how 5G services are rolled out.
"5G" is mostly for marketing purposes; it's really just another evolution of the LTE standards. Main differences include: lower latency on the core network, higher order modulation schemes, channel aggregation, and MIMO support on the uplink and downlink.
What will need to change are the subscriber units. As I mentioned in an earlier response, almost none of the existing subscriber units have multiple antenna apertures on the same frequency and they definitely don't have the antenna spacing to make MIMO work properly. For that reason, I don't think you'll see uplink MIMO in a handset. Laptops yes, larger tablets maybe. At 2.5 GHz and higher you can get enough antenna spacing to make 2x2 MIMO work.
Also, MIMO can be used two ways. The system can set up multiple data streams to a single subscriber unit to theoretically double transmission speed. The system can also be set up to reject an interfering signal. You may have also heard this called "virtual beam forming". In this case, the network operator is increasing the number of customers the network can support. Instead of giving you both orthogonal data streams, you get one, and another customer in a different part of the same cell gets the other. The radio channel still carries double the data, but it's split across two subscriber units. Unfortunately, has to pick one or the other; they can't do both at the same time.
As for Planar antennas, they should work fine. Most handheld subscriber units already use some form of patch antenna. On some phones, like the Galaxy S3, if you take the back cover off you can see the antenna patches for each frequency embedded in the black case material.
MIMO, or virtual beam forming; different names for basically the same thing, requires at least two antenna apertures. They must be of different polarity and/or spatially separated by at least one wavelength. For example, one wavelength at 2.4GHz is 12.5 cm, so placing one antenna in each corner of a laptop computer display or opposite corners of a tablet computer is practical. A handset is just too small.
On the base station, it is easy to achieve separation of multiple wavelengths between each antenna. The base station receiver adjusts the phase on each of the receive branches to null an interfering signal and reinforce a desired signal. Thus, the base station can resolve two uplink signals even though they are using the same frequency.
You've experienced this if you've ever listened to an FM radio in a moving vehicle. The signal "flutter" you hear is the selective fading as the single receive antenna moves through the variable RF environment. If the receiver had a second antenna and the capability to switch or phase each antenna for constructive reinforcement, it would reduce the fading, and coincidentally reduce the probability of interference. This is what the base station does on the uplink receive, but it can also do the same on the downlink.
It's possible to do the same on the downlink (to the subscriber unit), but again it requires the antenna separation on the device and does add some receiver complexity and cost.
I recommend looking at some of the tutorials on the 3GPP website. Its much easier to understand with some visuals.
-Mike
No need Antenna for massive connections & support all 5G carriers with 128 TRx
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