Until now nothing specific is formally defined for 5G requirement, I think it will be highly probable that the system bandwidth will get extended to at least a couple of hundreds MHz. There will be a lot of issues related to RF (when using millimeter wave) but there will also be tough challenges at base-band level. The first question you would have would be "what would be the sampling rate ?". If the system bandwidth at carrier frequency level is a couple of MHz, the sampling rate at base-band level should be several MHz BW.
It means that you need ADC which can sample and convert at several MHz rate. You may think this would not be a big issue since you may have seen various digital oscilloscope which covers even a couple of Gb sampling rate. This kind of super high frequency ADC is already used in various area especially high end digital oscilloscope. But those high frequency sampling is not done by a single ADC. It is done by multiple ADCs working in parallel and sampling in interleaving pattern. To make this kind of sampling work properly, very complicated hardware design and control algorithm are required. To make this kind of technology usable for a mobile device which should not be as expensive and bulky as a high end digital oscilloscope, great deal of improvement on ADC/DAC technology is required as well.
Why not apply your ideas to WLAN and short-range communication instead of a new ITU-R mobile generation? Channel spacing of several hundreds of MHz, and millimeter waves, are expected in next generation WLAN equipment (Ieee 802.11ad) and are already utilized in short-range communication equipment (UWB). UWB has not been a market success yet, so something needs to be done to make it cheaper and improve its performance. Parallel ADC:s may improve the peak bit rate by increasing the channel bandwidth, but don't you think it may make the equipment even more expensive, and increase the energy consumption? Also, many parallel ADC:s may be an approach to MIMO in today's Wifi and 4G systems, and to antenna arrays and massive-MIMO in future wireless systems.
As you pointed out, when it comes to a 5G radio interface, we can only guess about its future definition. The ITU-R mobile generations have always used radio frequencies rather than micro-wave frequencies, i.e. below 2GHz, suitable for land-mobile communications. There is no free radio frequency band that allows channel spacing of several hundreds of MHz. The Telcos seem to believe that 5G will be about something else than another major increase in peak bit-rate beyond the 4G/LTE-Advanced promises of 1Gbps. Examples may be new applications such as Internet-of-things, meaning that low energy consumption and high system spectral efficiency in bit/s/Hz/site (allowing many devices to communicate simultaneously) are key factors rather than high peak bit rate.
Dear Dr. Aamir Habib,
Dr. Magnus Eriksson explained quite reasonably. I want to add one more point about realizations of ADC and DAC. When we use Successive approximation and Ladder approaches and translate these algorithms in electronic have feasibility limitations.
A typical maximum speed for available ADC is: BW 150 MHz, Sampling: 200 MS/s and Resolution: 8 bits to 21 bits.
- Badges
- Science topic
- Similar topics
- Computer Science
- Computing