Last week, the FCC published a Notice of Inquiry (NOI) to investigate the possibility of using frequencies above 24GHz for cellular wireless systems — specifically, for next-gen mobile data standards such as 5G. Given how we’ve essentially run out of spectrum in the cellular sweet spot, and how Europe and Asia have already started on their own 5G inquiries, it’s high time for the FCC to dig into the possibility of super-fast cellular networks in the Super High and Extremely High Frequency bands that are as capable as standard wireline (DSL and cable) broadband. All mobile network systems currently operate on frequencies in the UHF (Ultra High Frequency) band, which comprises of 300MHz to 3GHz. The UHF band is considered the “sweet spot” of cellular today, with a decent mix of frequencies that travel far and wide (low-band spectrum) and frequencies that provide substantial capacity for data performance (high-band spectrum). As we’ve previously discussed, mobile network operators use a mix of low-band and high-band spectrum to provide optimal coverage and capacity to meet the needs of their subscribers. However, the amount of available spectrum that can be allocated for cellular wireless systems in the UHF band has dwindled away in recent years — which is why we’re now considering new blocks of spectrum that are very much outside the sweet spot. The FCC inquiry centers on the usage of frequencies in the upper portion of the SHF (Super High Frequency, 3GHz to 30GHz) band and the lower portion of the EHF (Extremely High Frequency, 30GHz to 300GHz) band for cellular systems. Specifically, the FCC is examining the possibility of licensing 24GHz to 90GHz for use of cellular mobile network services. SHF and EHF bands are very high capacity, but traditionally these high frequencies can only travel a very short range. EHF (also called millimeter wave, or mmWave) band frequencies are currently in use for high-bandwidth wireless systems that do not require much distance, like WiFi on 60GHz. The reason for this is simple: the higher the frequency, the harder it is for it to pass through obstacles. Conventionally speaking, EHF requires unobstructed line-of-sight connections (which is why 60GHz WiFi generally needs it to be useful).
However, as part of the many efforts on 5G going on in the background across multiple countries, using SHF and EHF for 5G networks comes up quite a lot. In fact, Samsung Networks (the networking division of Samsung Electronics) demonstrated a 28GHz cellular system that offered 1.2Gbps (150MB/s) in a mobile environment (moving at 60 mph) last week. In a stationary environment, that same system pushed an eye-watering 7.5Gbps (940MB/s) wirelessly. The mobile environment could download an 8GB DVD in one minute, and the stationary environment could download it in nine seconds! In its eventual peak, LTE-Advanced will barely be able to reach 1Gbps in a stationary environment, with no chance of getting anywhere near that in a mobile one. The Samsung demonstration perfectly exemplifies the key reason for exploring the use of these frequencies for cellular: the immense bandwidth of these frequencies. For example, the 28GHz band is 1000MHz wide (as opposed to the 3GHz band, which is only 100MHz wide). That means that it is entirely possible for mobile network operators to end up with 100-300 MHz channels for a 28GHz cellular wireless network. That kind of channel size (especially with full duplex wireless) would enable wireless networks of being capable of replacing home wireline internet connections like DSL and cable and offer gigabit speeds. Critically, data caps (common on wireless broadband today) would not be necessary to ensure that users get a high quality of service. If it could be done reliably across great distances with cost-effective radios, that would make it perfect for capacity-oriented wireless! Fortunately, it appears that it may be possible to use smart antennas to achieve that goal. Keeping in mind that no advancement in technology can change physics, microcell networks using smart antennas to implement range-enhancing techniques like beamforming (which focuses the radio energy to create strong “beams” of signal) and radio steering (aiming the transmission and reception elements in antennas) to maximize coverage can be used to provide truly dense cellular networks.
But a microcell network requires a high degree of automated coordination to ensure that none of the cells create interference with each other. This is where C-RAN (Cloud/Centralized Radio Access Network) comes in. In traditional networks (known as D-RAN, or Distributed RAN), the baseband (resource management and signal processing system) systems for the radio network are physically located at every radio transmission site. In a C-RAN system, these are moved to a separate location and pooled so that all cells are connected to a unified, elastic baseband pool. This allows an unprecedented degree of coordination of all resources (backhaul, signal processing, etc.) and prevents any waste of network resources. With this coordination and the elasticity of the pool, it is possible to install smaller, lighter, but more powerful radios anywhere (cell towers, lamp posts, buildings, trees) to build the dense network necessary for this to be possible. The pieces are now falling into place for the development of the next generation of cellular wireless systems. As 5G continues to be developed, regulators like the FCC have to keep track and ensure that they are part of the process too. The examination and the release of spectrum to enable this new kind of wireless service will be critical to enabling the future of wireless connectivity that is unquestionably better than what wireline will generally provide in any affordable manner to the public. Let’s just hope that networks like these will become a reality soon enough!Is 28GHz the future of ultra-fast 5G networks?
