To reach a higher bandwidth we will need more sophisticated modulation schemes and more complex encoding algorithms. Let’s closely evaluate the qualities of the transmission methods viable for these higher bandwidths. Read the White Paper Here!
Quadrature Phase Shift Keying
If you have a phase and an amplitude, you have an I and Q grid and a vector, a certain amount of I and Q, this is a phase vector and an amplitude vector. This particular quadrant on the left, 1, 1, 1, 1 gives you negative 2 units of I and negative two units of Q with a certain phase, that gives you a particular symbol.
This symbol on the right is 4 bits wide, so we’ve gone from a 1 Bit bus to a 4 bit bus, if we implement 16 QAM instead of 4 QAM (Quadrature Amplitude Modulation). You can see how we’ve quadrupled the throughput of an AM modulated system. It’s possible to achieve up to 256 QAM.
This particular technology is not anything new, we’ve been doing this for years. We’re just applying it to our 60, 80, 90 or 100 GHz radios.
64 to 128 QAM is achievable for a 10 Gigabits per Second link in a carrier bandwidth of 5 Gigs wide, so within the FCC standards we can achieve this at 60, 70, and 80 Gigs. We’re looking at the feasibility of doing 512 QAM. Again, with higher order modulation, you have more noise, trouble with distance, loss of fidelity, and then there’s your link budget. There’s always a trade-off. We have to be careful not to over encode our signal.
Channelize & Multiplex
Another approach is to take several 1 Gig Ethernet radios and modems, combine them together take, say, 10 of them to make a 10 Gig E. This requires some load balancing in the IP realm, it’s non ideal for video communications, you prefer
the packets to all travel together through one pipe. These systems have such low, low latency that if video packets were split apart and put over 10 different pipes that are virtually and identically in phase, and no delay, I don’t see a big problem with that, but typically you don’t want to do that with video communications. That’s one approach, that we can use lower cost components to combine, putting 10 pips together to get 1 fatter 10 Gig pipe. That’s an approach you can take.
If you Cross Polarize you can cancel out any interference. This is called XPIC or Cross Polarization Interference Cancellation. This adds to the complexity of the antennae system, it’s more expensive. We’re able to do 5 Gigabits per second using this technique.
Here is another approach of taking multiple channels, N times Gigabit Ethernet or N times HD-SDI links to push through more bandwidth. A lot of the 4K cameras will be 4 3G HD-SDI coaxial feeds or fiber optics feeds, so 3Gbps times 4 will give us 10 to 12 Gigabits per Second. We can use this similar technique when it comes to radios, just put radios at different polarizations, radios at different frequencies.
By polarization, what we mean is, the radio waves will come out of 0 polarization or at 90, the receiving antennae has isolation. One element will only see the 0 polarization waves as the waves come out at this way, the other polarization element will see only the wave that way. We can co-locate two radio waves on the same frequency, or we combine slightly different frequencies with polarization, we can get better channel isolation to co-locate or cooperate multiple pass through a given link.
4K through an IP-Based Link
You can run very low latency encoders at very high bit rate for 4K, still maintain good fidelity, and just have the flexibility of a more diverse IP link as opposed to a dedicated SDI link, or 4K SDI link. We also see the merger of data and RF systems, RF over fiber. Still a lot of content is delivered to the home via the cable operator, via RF and we see that going away.
Video is being put more commonly on a traditional IP network. You look at companies like AT&T U-verse, they’re delivering a true IPTV triple play service to the home with video, internet, and television… all IP based. There’s no RF over coax, or RF over fiber. This all leads to the demand for fatter pipes, higher bit rates, and in rural areas where you don’t have access to a fiber or telecom connection, higher wireless bit rate really lends itself.
The bottleneck in any network is the first mile and the last mile, how you get on and off the network. If you don’t have a high bit rate telco, a POP, or connection in your building, you might have to put one of these radios up on your roof and beam to an adjacent building in the metro area to get to that POP. We see demand for this technology growing.