5G traffic is ramping up dramatically as 4K video and data throughput per user reaches up to 400 Megabits per Second (Mbit/s). Fiber-optic backhaul is invaluable, but E-band Millimeter Wave (mmWave) could prove more versatile and cost-effective for Communication Service Providers (CSPs).
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Backhaul Capacity Needs to Match 5G Traffic Growth
5G is picking up acceleration. The total installed 5G global cell sites are expected to expand from 986,000 cell sites in 2021 to 6.6 million cell sites in 2027 at a Compound Annual Growth Rate (CAGR) of 44.9%. It is not just infrastructure. 5G mobile subscriptions are forecast to grow from 664 million subscribers in 2021 to 4.39 billion in 2027. Similarly, the anticipated traffic generated from 5G in 2027 is estimated to increase to 6,268 exabytes and will account for 83% of all cellular traffic.
Fiber has made inroads into supporting the cellular Radio Access Network (RAN) infrastructure of the mobile telcos, but has a Total Cost of Ownership (TCO) profile that can only be justified in certain deployment scenarios depending on the market. Therefore, microwave/Millimeter Wave (mmWave) backhaul will still account for the majority of global backhaul links from 2021 to 2027, with around 65%. Wireless backhaul has justified its presence in the market through a number of innovations in spectrum use and communications technologies. In particular, the use of mmWave spectrum in the E-band (71 Gigahertz (GHz) to 86 GHz), which can support wider channels, has been a game changer for Communications Service Providers (CSPs) supporting 5G services. A greater reliance on the E-band for short and medium distance backhaul is only expected to increase.
Leveraging the E-Band
Spectrum channels are substantially larger in the E-band—typically 500 Megahertz (MHz) to 2,000 MHz. In comparison, channel sizes in the traditional microwave bands (6 GHz to 56 GHz) typically range from 28 MHz to 56 MHz in width. Data throughput for the E-band is substantially greater than the traditional microwave bands. The narrower spectrum channels of traditional microwave means that throughput is typically in the order of 0.25 Gigabits per Second (Gbps) to 0.5 Gbps per channel, whereas the E-band is capable of achieving at least 3.2 Gbps to 6.4 Gbps for a 500 MHz and 1 GHz channel, respectively. Additional technology enhancements can push these scenarios even higher. In the past, traditional microwave solutions (e.g., in the 15 GHz to 23 GHz bands) were advocated, as they had longer transmission distances. However, using the latest mmWave antennas, bonded channels, Cross Polarization Interference Cancellation (XPIC), improved modulation schemes, radio signal stabilization technologies, etc. is pushing the E-band signal propagation distance beyond its previously humble ~3.5 Kilometers (km) and 3.2 Gbps to 6.4 Gbps data throughputs:
- XPIC: XPIC is a technique that can double the spectral efficiency by propagating two signals in a horizontal and vertical plane over the same channel.
- Channel Bonding: By bonding a microwave band (e.g., the 18 GHz band) with the E-band, mobile operators can boost the propagation range from 3.5 km to 7 km. The link in the lower band is used to assure carrier-grade availability (i.e., 99.995%).
- Antenna Stabilization: Another novel mmWave technology that has boosted signal strength and distance is antenna stabilization. mmWave transmissions effectively travel in a very narrow beam. This is useful for frequency reuse, but high winds and inclement weather can misalign the transmissions.
By combining these technologies, Huawei has reported that its long-reach E-band solution can reach 10 km by implementing an integrated, high-power solution that boosts the transit power to 24 Decibels per Milliwatt (dBm) and offers data throughput of 20 Gbps.
As infrastructure vendors have continued to innovate and miniaturize their electronics, the backhaul Outdoor Units (ODUs) have come down in size and weight. This has made backhaul equipment highly integrated, and more viable on cell sites. As 5G traffic throughput grows exponentially, mobile operators will have to resort to multiple channels needed per cell site. The latest solutions now offer up to 4-in-1 transceivers in a single ODU. Using a 2T2R E-band transceiver with optimized dual polarization, a backhaul link can transmit up to 25 Gbps with single hardware ODU and up to 50 Gbps with an advanced Multiple Input, Multiple Output (MIMO) setup.
E-Band Backhaul Links Could Become the Main Work Horse for 5G
5G subscriber adoption is ramping up as 5G-capable handsets have gone mainstream. 5G cell site rollouts are also starting to build up, not just in very developed markets, but across geographies and demographics. Fiber-optic will remain an invaluable backhaul platform for mobile telcos, but increasingly, mmWave backhaul systems are proving to be a vital platform for a range of small cell and macro cell deployments in urban centers, as well as rural communities. Historically, mobile operators have opted for microwave links in situations where they could not deploy fiber-optic, but the rapid pace of innovation and equipment miniaturization has now opened up the mmWave bands. A raft of technologies developed by backhaul vendors, such as Ericsson, Huawei, Nokia, and ZTE, include highly-integrated multi-transmit, multi-receive ODUs, and multi-band antennas for traditional bands that have improved the propagation characteristics substantially, while delivering on the much-needed 5G-capable capacity.