There’s a lot of talk about 5G, the benefits it provides and the applications it can enable. For any engineer planning to start playing around with 5G, it’s important to get a bird’s eye view of the challenges that you can expect while designing a mobile device using this technology.
If you take any smartphone, you have an L-shaped PCB at one side and the rest of the space in that phone is carved out for a battery. We need to take that L-shaped PCB (which is already packed to the brim) and figure how to put millimeter wave into. We cannot use the existing antenna setup for LTE here, because the antenna array and other aspects are completely different from what is needed for millimeter wave.
Overall, there are three items that need to be balanced.
Power problems are more of a downlink problem. The gain in your amplifier decides how much power you transmit back to the base station. Power amplified antenna and the choice of the antenna element have an important impact here. Now, certain antenna designs cause the radiation to go forward and narrow instead of wider and shorter. The power amplifier drives each one, so if we have four antennae and power amplifiers, then we can add them together and direct them together to do beamforming.
We can go for an extremely low power amplifier and add four 4dB amps together to get 16 dB of gain. Now, remember that this is going to be a logarithmic addition for dB here, so it’s an order of magnitude higher for each. Once this done, we can use polarization to get an additional 3dB of antenna gain.
The most severe power efficiency impacts will be at the downlink due to multi-gigabit data streams, data processing and related aspects.
The biggest benefit of using 11ad over 11ac is that 11ad gets you much better throughputs at the same power level. The aim here is to balance the power throughput and not just look at the power efficiency.
Even after all this is done, you may still end up grabbing the wrong end of the device and block the module, so we need to design out way out of this – by having more than one module in these milli-metre wave devices.