The demand for superior network coverage to deliver high speed services, both indoors as well as outdoors, is driving small cell deployment in the country. To undertake large-scale small cell deployments, it is important to develop suitable solutions for their backhaul. According to ABI Research, the number of small cell backhaul links is expected to increase from 1.6 million in 2021 to 6.1 million in 2027, at a compound annual growth rate (CAGR) of 25.8 per cent.
However, there is no one-size-fits-all solution for small cell backhaul and a trade-off among capacity, coverage and cost is often inevitable. Typically, operators and vendors employ a combination of backhaul solutions with a mix of wireline and wireless solutions. At present, wireline backhaul technologies such as fibre, satellite, copper, and wireless technologies such as mmWave, E-band and V-band are being adapted to serve as backhaul networks for small cells.
A look at some small cell backhaul
technologies and the challenges faced in their deployment…
Over the years, optical fibre has been a preferred backhaul solution for the deployment of small cells. With fibre backhaul, small cells can support fast speeds and increased bandwidth for smart applications and new technologies such as 5G. According to ABI Research, fibre will be the most popular mode of backhaul for small cells, with almost 3 million links by 2027. Further, the adoption rate of fibre for small cells will record a robust CAGR of 26.3 per cent between 2021 and 2027. According to another industry report, the number of small cells used in the global mobile industry will reach 12 million by 2026, of which 42 per cent will be backhauled through fibre.
That said, the industry expects fibre optic backhaul links to grow incrementally as operators will steadily install optic fibre in business and residential districts. Further, in locations where fibre is already in place, it is likely to be upgraded. The cost of upgrades can be justified by the competitive advantage that comes with fibre deployment. Although fibre connections provide high throughputs, they can be expensive in the absence of an established infrastructure.
While fibre is preferred by operators, not all urban cell sites can be supported by fibre. In this scenario, the most promising solutions for meeting backhaul requirements for small cell deployment are mmWave technologies including E-band (70-80 GHz) and V-band (60 GHz).
mmWave frequencies play a pivotal role in 5G backhaul as they offer a large amount of spectrum and a greater number of capacity links. According to industry reports, the mmWave network may yield cost savings of up to 54 per cent, when a considerable percentage of data traffic from devices is supported by indoor 5G services. These frequency bands in mmWave are at different stages of regulatory approval. mmWave equipment categories include microsites, lamp sites and pole sites and indoor 5G small cell solutions. Most of the microsites, lamp and pole sites serve the 26 GHz or 28 GHz spectrum in a 2T2R 800 MHz or a 4T4R 400 MHz set-up. These small cells help in providing coverage to outdoor hotspots. Further, vendors are releasing indoor 5G small cells using mmWave to provide continuous 5G mmWave coverage. These small cells can ensure higher speed in the mmWave spectrum using compact, lightweight equipment.
E-band is suitable for high density and high capacity wireless backhaul applications. It offers a wide spectrum range and very high capacities similar to fibre. The demand for E-band is growing rapidly with the move to disaggregated network architectures and the growing requirement for ultra-high capacity. According to industry reports, E-band is estimated to be the most popular mmWave frequency range for small cells, growing from around 280,000 small cell backhaul links in 2021 to 668,000 small cell backhaul links in 2027 at a 13.2 per cent CAGR.
Further, E-band solves the spectrum congestion problem in urban and suburban areas. It has large bandwidth (10 GHz) capabilities, which allow the transmission of high-speed data over short distances (2-3 km). Besides, E-band’s frequencies enable peer-to-peer and loss-of-sight (LoS) radio communication. The popularity of E-band is primarily due to its versatility, delivered capacity, throughput, and complementarity with lower frequency bands across different deployment sites.
Over the years, V-band has attracted the interest of operators and backhaul vendors. Spectrum in V-band can be delicensed and used for backhaul to support multi-gigabit throughputs. It is suitable for links in the 300-500 metre range and reduces intersystem interference. The atmospheric and oxygen attenuation that makes the V-band unfit to cover long distance links is actually beneficial in a small-cell environment. This is because small cells require a short range, which means less interference among adjacent links. This also allows a greater reuse of the spectrum available. However, the LoS requirements make V-band difficult to integrate with the backhaul module within the small cell. The relay links can be brought into use to overcome LoS limitations. Some of the advantages of V-band spectrum are:
- The V-band does not require any channelisation or antenna design that increases the flexibility of solutions in this band. It also makes it possible to widen the beam width and reduce the antenna size.
- The V-band high frequency allows for smaller antennas, which are a requirement for small cell installations.
Challenges and the way forward
The implementation of small cell backhaul technologies poses several challenges for mobile operators and backhaul vendors planning and operations. While wireline backhaul solutions provide optimal capacity and throughput capabilities, players face limitations due to the lack of copper and fibre availability. In addition, fibre deployments demand a significant capital expenditure, manpower and time. Wireless backhaul has its relative advantages in terms of cost and accessibility, but requires navigation through varying LoS conditions. Further, while small cells expand the network capacity, their architecture increases capacity requirements from the backhaul network. They may also require additional aggregation sites. According to industry experts, in this situation, network operators can consider planning aggregation links of at least 1 Gbps, with scalability up to 2 Gbps. Besides, the increased cell density with the use of small cells adds complexity to existing backhaul networks as the proximity of cell sites creates possible interference issues. Further, their use of spectrum demands special attention as additional frequency pairs are added to the backhaul system. The traffic levels for small cell backhaul are expected to increase due to the concentration of users close to the site, and the backhaul connection may quickly become a bottleneck.
Challenges notwithstanding, the small cell space is projected to grow by leaps and bounds in the coming years. A key factor driving the surge in small cell roll-outs will be the launch of 5G services. It is important for stakeholders to develop a viable business model for setting up independent small infrastructure companies to deploy small cells, which could be shared among communication service providers in the future. Moreover, a framework needs to be developed in order to identify the best sites for small cells, expedite the approval process for their use, and keep deployment costs in check.