Understanding 5G frequency spectrum bands

Low-band spectrum is currently being used for 2G, 3G and 4G services for voice, MBB services and Internet of Things (IoT). Newly allocated spectrum for mobile networks include the 600 MHz and 700 MHz bands. These bands are ideal for wide-area and outside-in coverage as well as for deep indoor coverage, typically required for eMBB and voice services, but also required for M2M type of communication from outside to inside the building, even in deep basements.

Mid-band spectrum is currently used for 2G, 3G and 4G services. New spectrum has been widely allocated in the 3.5 GHz band, with more spectrum planned to be made available in the 1.5 GHz (L-band) and 5 GHz (unlicensed) bands. Bandwidths of 50 megahertz to 100 megahertz per network will enable high-capacity and low-latency networks ideal for 5G use cases such as enhanced MBB (eMBB) and Ultra Reliable Low Latency Communications (URLLC), for critical IoT applications. With better wide- area and indoor coverage than high-band spectrum, the mid-band spectrum is an optimal compromise between coverage, quality, throughput, capacity and latency. Combining the mid-band spectrum with low-band spectrum leads to exceptional network improvements in terms of capacity and efficiency.

High-band spectrum clearly provides the anticipated leap in data speed, capacity, quality and low latency promised by 5G. New spectrum bands are typically in the range of 24 GHz to 50 GHz, with contiguous bandwidths of more than 100 megahertz per network. The high-band provides a significant opportunity for very high throughput services for xMBB, localized deployments and low latency use cases, e.g. industrial IoT, venues, etc, both for indoor and outdoor deployments. Fixed wireless access (FWA) will also benefit from these higher bands in terms of capacity. As the coverage range is very limited (hundred-meter magnitude), for wider-area coverage, combinations with low-band and mid-band are essential.

Each spectrum band represents unique properties, meaning there are diverse opportunities for a service provider to balance between throughput, coverage, quality and latency, as well as reliability and spectral efficiency. Availability of spectrum will vary globally between countries and regions, both in terms of bands, amounts and timing. The 5G standards also include end-to-end network slicing and mobile edge computing which are vital in supporting the needs of industry vertical sectors. In particular, network slicing will allow operators to create virtual sub-network slices with tailored features for specific types of user or usage requirements. Slicing, among the other characteristics, includes spectrum bands and channels choices. For example, ultra-low latency and high availability slices are a good fit for automated manufacturing, connected cars and remote surgery. Contrastingly, IoT networks with vast numbers of sensors and devices like streaming video cameras can be allocated a slice that is tailored for uplink heavy communications.

Some verticals depend on ultra-low latency capabilities while others need superfast download speeds. Some need highly localized connectivity (e.g. small cells for a factory) while others will need nationwide connectivity (e.g. a vast macro network to support sensors for utility companies). Each of these examples need different spectrum and network resources.

Ultra-low latency services and high-speed broadband services need different spectrum bands, as their radio resource requirements are incompatible. Similarly, high-capacity, localized services better suit capacity bands (i.e. above 1 GHz) whereas nationwide services benefit from coverage bands (i.e. sub-1GHz). Mobile operators are the best placed to provide the wide variety of services envisaged, including private networks with leased spectrum in cases where that is needed due to the specific requirements from verticals. If we consider the bandwidth and penetration requirement, a row subdivision of use cases per frequency spectrum portion can be outlined as follows.

Low-band use cases: small amounts of data need to be exchanged from a large number of distributed devices to the network and vice versa. Low-band is useful in covering large spaces (rural areas) and to penetrate deep indoor (basements). Low latency can be achieved also in this part of the spectrum with ad-hoc slicing strategies.

Mid-band use cases: this band category is the perfect balance between large bandwidth (500Mbps to 1-2Gbps) and coverage of few tenths meters per cell. For the indoor cases, there should be a particular attention to repeat the signal from outdoor to indoor. A trade-off between throughput and latency can be achieved by network slicing.

High-band use cases: this band ensures the support of all those cases requiring a very high data rate especially in media and entertainment market. The user must be close to the access point (few meters). Usually the use cases are those requiring maximum speed, but a trade-off between throughput and latency can be achieved by network slicing, also in this frequency range.