LTE Picocell

It’s no secret: The proliferation of wireless devices capable of sending and receiving large amounts of data is straining commercial wireless networks. Smart phones, data cards and tablets with such applications as video sharing and conferencing, social networking and gaming consume more wireless network resources than phone calls and texts.

Similarly, the increased use of novel public safety applications, such as video streaming, street cameras, automatic license plate recognition and the coming proliferation of sensors and M2M (machine-to-machine) devices, will increasingly strain public safety’s wireless networks. This strain on capacity has the potential to cause severe bottlenecks, delaying service and, ultimately, increasing the cost of a truly reliable, mission-critical wireless service by increasing the number of base station sites required.

The wireless and public safety communities are working feverishly to improve capacity, secure more spectrum from the government and implement more spectrally efficient air interfaces, such as LTE (long-term evolution). However, with industry data suggesting an increase in wireless data traffic of up to 26 times by 2015, these improvements won’t be enough.

Many agencies are planning to deploy LTE on existing cell sites (macro cells). LTE achieves high-efficiency spectrum use by employing adaptive modulation, a technique that provides higher data speeds to users with strong signal connections, while providing slower speeds to users with weak signals. This generally means that network capacity is higher for users with strong signals closer to the cell’s center and lower away from the cell’s center, which is often where the demand may be greatest. Securing more spectrum is one solution, but generally takes years and costs billions.

Another solution is to shrink the size of the cells that form the wireless network, increasing reuse and spectrum efficiency by placing the supply of wireless data closer to its demand. This wireless network architecture, called heterogeneous networks (HetNets), consists of filling in the existing macro cell coverage with smaller cells called picocells to increase capacity. Picocells are often deployed where the capacity demand is greatest, resulting in a better connection and more bandwidth exactly where it’s needed. Using 3GPP simulation modeling, Powerwave Technologies has predicted that a network with picocells delivers up to 12 times the downlink capacity and 15 times the uplink capacity than a network of macro cells only. The two cell types work together to ensure an optimal mix of network coverage and capacity, providing a seamless end-user experience.

The use of picocells has been limited due to high-equipment costs and the lack of a simple, standards-defined method for adding new cells to an existing macro cell network. This cost is being addressed by chip vendors that are in the process of integrating multiple base station components into a single component: a system-on-a-chip (SoC).

SoCs combine several base station functions into a single chip, including baseband processing, radio resource management, subscriber scheduling, network interfacing and base station management. They also replace components usually found in base stations, such as network processors, digital signal processors, application specific integrated circuits and field-programmable gate arrays. The integration of this functionality into a single chipset enables manufacturers to create low-cost, low-power picocell base stations that can be mounted almost anywhere.

The issue of integrating picocells into an existing macro cell network is being addressed by the 3GPP standards. LTE’s flat network architecture and well-­defined interface between base stations and the operator’s core network make it feasible for operators to add new cells of all sizes from multiple vendors into their network. In addition, the LTE standard defines many interference management techniques that allow the macro cell network to coordinate with and adjust to new picocells nearby. These techniques, known as intercell interference coordination, include fractional frequency reuse, frequency-selective scheduling and adaptive power management. Together, they make it easier than ever to add picocells into an existing macro cell network.

With these issues being aggressively addressed by standards bodies and the manufacturing community, expect to see more and more picocells being deployed in the near future. Deploying picocells requires access to power and backhaul, as well as planning to place them where they are most needed and will provide capacity relief to the existing network. Nevertheless, relative to continuing to add macro cell sites to already crowded communities, picocells offer easier permitting, lower equipment and operating costs, and improved wireless network performance.

About the Author
Juan C. Santiago is vice president of product management for Powerwave Technologies Inc. He has 20 years of experience in various engineering and management positions. Contact him via e-mail at [email protected].

APCO International Commercial Advisory Council contribution originally published in APCO International’s Public Safety Communications, Vol. 77(7):50-51, July 2011.