LTE: The road ahead
Significant progress has been made in deploying LTE, but there are still enhancements and innovations needed to help network carriers give their customers a ubiquitous, high quality experience on their LTE-enabled devices no matter where they use them. These enhancements and innovations will not only be beneficial to today’s LTE networks, they are also necessary for LTE to reach the next step in its evolution, such as LTE Advanced.
There are a variety of issues that need to be addressed so network operators and handset OEMs can take full advantage of the performance benefits of LTE both now and in the future. Three issues of particular concern are multi-mode/multi-frequency support, implementing voice over LTE and how networks will handle interference.
First, let’s consider the different ways LTE is being implemented globally and how this will effect device OEMs looking to support the LTE standard. The radio frequencies used on LTE networks vary from region to region; there are currently over 20 different frequencies ranging from 700 MHz to 2.6 GHz that can be used by LTE networks around the world.
In order to ensure that LTE supports global roaming and realizes the scale of a global technology, LTE smart phone and data card OEMs will need access to chipsets with multi-band, multi-mode radios. These same chipsets must also be backward compatible with existing 3G technologies to provide a comparable experience in areas without LTE coverage or ubiquitous 3G. Supporting multiple technologies and frequency bands in a single chipset is hard enough, but making the chipset small enough and making sure the chipset has the right power management capabilities to provide all day operation is a challenge that few mobile chipset providers are prepared to meet.
Another issue to be addressed is LTE support for voice. Today’s LTE networks support data traffic only; smartphones can use LTE for data traffic, but must fall back on 3G technologies to provide simultaneous voice-and-data or voice-only connections. LTE Release 9 contains enhancements that will minimize the transition time from an LTE data session to a 3G voice call. Native voice support in future LTE networks will be provided using VoIP. To handle the stringent quality and coverage expectations of voice, LTE VoIP networks can seamlessly handover to 3G using the single radio voice call continuity feature (SRVCC). One key advantage of the 3G fallback and voice continuity features of LTE is that they enable the support of tight voice interworking between LTE and 3G in a fully integrated “single radio” chipset. These single radio approaches to voice interworking will maximize the LTE user experience, reduce smart phone cost and extend battery life.
As data usage on mobile networks continues to become increasingly popular, LTE networks will also require the use of more cells with smaller coverage area per cell in order to handle the expected traffic load. But increasing the number of cells in a coverage area presents another problem: interference. Future releases of the LTE standard, specifically Release 10 (also called LTE Advanced) have been specifically designed to address the interference issue through the use of advanced network topologies and by leveraging a wider bandwidth frequency spectrum.
Existing WAN cell coverage can be augmented to handle LTE data traffic growth. Picocells (small base stations with a range of up to 1 km that integrate with the existing macro network) and femtocells (indoor cellular access points with a 10 meter range similar in size, price and range to WiFi access points that are connected to the carrier’s network via the user’s IP network) help augment the existing cell network by using spatial diversity to enhance network capacity and coverage. From a network topology standpoint, future versions of LTE (Release 9) and LTE Advanced have been designed to integrate support for these carrier-deployed picocells and/or user-deployed femtocells. LTE will also support signal relays and repeaters to further improve LTE network coverage and capacity. This mix of existing macrocells with lower power nodes, like picocells and femtocells, create heterogeneous networks (HetNets) that bring the network closer to the user.
However, the addition of more cells to the network creates new cell edges, and users at those edges may experience reduced performance due to radio interference between cells. This situation has been accounted for in the LTE Advanced standard which incorporates several advanced interference management features to maintain network performance on the cell edge. For example, LTE Advanced’s support for intelligent node and adaptive resource allocation will extend network range and improve network capacity by ensuring fairness of service to users by providing data rates that are proportional to their respective signal qualities and mitigating signal interference between cells.
LTE Advanced can utilize a wider frequency spectrum (20 MHz to 100 MHz) through the use of carrier aggregation. Also known as multicarrier, carrier aggregation allows carriers to send and receive data over an aggregated date pipeline to increase data rates and to lower latency. This means that carriers will be able to support high-speed data traffic even in times of peak network usage.
When used in conjunction with the advanced network topology technologies mentioned above, carrier aggregation will efficiently handle any interference and capacity issues presented by the use of HetNets.
All of this would seem to make the evolution from LTE to LTE Advanced networks a daunting task; one that requires the tightly-knit cooperation of network carriers, device OEMs and mobile chipset vendors around the world. But much work has already been done on the development of LTE Advanced, and the standard is set to be ratified in the first quarter of this year. LTE Advanced will require some infrastructure development in order to build HetNets, but the picocells and femtocells used to do this are low-cost solutions that will help minimize capital expenditures. In fact, outside of deploying picocells and femtocells, much of the work needed to upgrade LTE networks to LTE Advanced will happen at the software level.
Technology trials of LTE Advanced have already delivered compelling results. LTE Advanced, like LTE, will enable mobility with 3G network technologies to ensure a seamless user experience for consumers as they move between 3G and 4G networks. LTE Advanced is well on its way to becoming a fully commercial standard, and the high-speed data rates it provides will play an instrumental role in the ongoing evolution of mobile communications and computing.
Cristiano Amon is Senior Vice President of Product Management at Qualcomm CDMA Technologies, Inc.