LTE-Advanced Pro Pushing LTE capabilities towards 5G Page 1 Nokia Networks white paper LTE-Advanced Pro Table of Contents Introduction .................................................................................................................. 3 Multi-Gbps data rates with carrier aggregation evolution .................................... 4 Using the 5 GHz band .................................................................................................. 6 Enhanced spectral efficiency with beamforming (3D MIMO) ................................. 8 Extreme local capacity with Ultra-dense network ................................................ 10 Millisecond latency with flexible frame and Mobile Edge Computing ............... 11 Internet of Things optimization for the Programmable World .......................... 13 Device-to-Device communications ........................................................................ 15 Cloud radio architecture for network scalability .................................................. 16 Evolution to 5G .......................................................................................................... 17 Summary .................................................................................................................... 19 Further reading .......................................................................................................... 20 Abbreviations ............................................................................................................. 21 Page 2 networks.nokia.com Introduction LTE and LTE-Advanced are practical and popular technologies, with more than 700 million subscribers, more than 420 commercial networks and a peak data rate of 450 Mbps. This highly capable technology is set to get even better with the latest enhancements. Improved radio capabilities will make mobile broadband services more efficient, providing higher quality and enabling new sets of services on top of LTE networks. These features, shown in Figure 1, are defined in 3GPP Releases 13/14 and are collectively known as ‘LTE-Advanced Pro’. The developments will enable the Programmable World for billions of connected Internet of Things (IoT) devices, vehicular communication for Intelligent Traffic Systems (ITS) and public safety/critical communications. LTE-Advanced Pro raises user data rates to several Gbps, cuts latency to just a few milliseconds, gives access to unlicensed 5 GHz spectrum and increases network efficiency. It also maintains backwards compatibility with existing LTE networks and devices. LTE-Advanced Pro and 5G can use similar technology components to enhance radio capabilities. 5G is a new non-backwards compatible radio technology that can operate both below and above 6 GHz frequencies and provide even higher data rates and lower latency. LTE-Advanced Pro operates below 6 GHz and evolves in parallel to development work on 5G. The evolutionary paths of LTE-Advanced Pro and 5G are shown in Figure 2. This white paper focuses on the key technical solutions in LTE-Advanced Pro, as well as on the features needed to optimize LTE networks to deliver new 5G services. Figure 1. LTE-Advanced Pro pushes LTE capabilities towards 5G Page 3 networks.nokia.com Figure 2. LTE-Advanced Pro evolves in parallel to 5G towards the programmable world Multi-Gbps data rates with carrier aggregation evolution LTE started with 150 Mbps peak rate and 20 MHz bandwidth. In Release 10, the peak data rates were upgraded by carrier aggregation. Mainstream carrier aggregation in 2015 delivers up to 300 Mbps on 2x20 MHz and the first networks with 3x20 MHz are about to go into commercial operation. Figure 3 shows live network measurements with three-carrier aggregation using 20 + 20 + 10 MHz, with peak data rates exceeding 370 Mbps. 3GPP Release 10 defines a maximum capability up to 5x20 MHz, which gives 1,000 Mbps (1 Gbps) with 2x2 MIMO and 64QAM, and even 3.9 Gbps with 8x8 MIMO. Figure 3. Three carrier aggregation measurements in a live network showing peak rates above 370 Mbps Page 4 networks.nokia.com The data rate can be increased still further with more spectrum and more antennas. A higher number of antenna elements is feasible when using comparatively large base station antennas, however, it is more of a challenge to integrate further antennas into small devices. For these, data rates are more easily increased by using more spectrum. Release 13 makes this possible by enhancing carrier aggregation to enable up to 32 component carriers. In practice, the use of unlicensed spectrum enables LTE to benefit from even further carrier aggregation capabilities. Figure 4 illustrates carrier aggregation evolution and Figure 5 shows the evolution of peak data rates. Figure 4. Aggregation of up to 32 component carriers Figure 5. LTE-Advanced Pro data rate and bandwidth Nokia has already demonstrated the very high data rates possible with carrier aggregation. A throughput of 4.1 Gbps was achieved by aggregating ten LTE carriers, each of 20 MHz, including both FDD and TDD carriers. The total bandwidth used was 200 MHz. For more details see the related press release. Page 5 networks.nokia.com Using the 5 GHz band So far, LTE networks have been deployed using licensed spectrum between 450 and 3600 MHz. With ever increasing amounts of traffic, being able to use unlicensed as well as licensed bands will allow improvements in capacity and peak data rates for LTE-Advanced Pro. The unlicensed 5 GHz band has plenty of available spectrum, suitable in particular for small cell deployments. This large pool of spectrum allows mobile broadband operators to benefit from the carrier aggregation evolution provided by LTE-Advanced Pro. The evolution of LTE spectrum usage is shown in Figure 6, while the spectrum resources available in the unlicensed 5 GHz band are illustrated in Figure 7. Figure 6. LTE spectrum utilization Figure 7. Spectrum availability in the 5 GHz band Page 6 networks.nokia.com LTE-Advanced Pro can use unlicensed band spectrum either through Licensed Assisted Access (LAA), or by integrating Wi-Fi more closely to the cellular network via LTE-Wi-Fi aggregation (LWA). The two solutions are shown in Figure 8. LAA combines the use of licensed and unlicensed spectrum for LTE using carrier aggregation technology. It is a highly efficient method of offloading traffic, since the data traffic can be split, with millisecond resolution, between licensed and unlicensed frequencies. Licensed bands can provide reliable connectivity, mobility, signaling and guaranteed data rate services, while the unlicensed band can give a significant boost in data rates. The technical solution for combining licensed and unlicensed spectrum is based on dual connectivity and carrier aggregation – the same solutions that have already been defined in LTE-Advanced and which can be reused for the 5 GHz band. Figure 8. Combined usage of licensed and unlicensed bands Figure 9. License Assisted Access (LAA) combines licensed and unlicensed spectrum Page 7 networks.nokia.com Refer to the Nokia press release about LAA for T-Mobile USA. LTE-Advanced Pro also allows the aggregation of LTE and Wi-Fi transmissions, offering a further way to make use of unlicensed bands. So far, LTE and Wi-Fi interworking has been implemented on the application layer. Under 3GPP Release 13, the data traffic can be split between LTE and Wi-Fi transmissions, allowing the user device to receive data simultaneously via both paths. This allows full use of Wi-Fi capacity while maintaining the LTE connection for reliable mobility and connectivity. Figure 10. LTE – Wi-Fi aggregation (LWA) Enhanced spectral efficiency with beamforming (3D MIMO) LTE has also provided high spectral efficiency since its introduction. The downlink efficiency of LTE has been boosted further using Multiple Input Multiple Output (MIMO) technology, including 4x2 MIMO, 8x2 MIMO and 4x4 MIMO, a technique made more efficient with interference cancellation and the algorithms of the Nokia Smart Scheduler. LTE-Advanced Pro introduces the next step in spectral efficiency with 3-dimensional (3D) beamforming, also known as Full Dimensional MIMO (FD-MIMO). Increasing the number of transceivers at the base station is the key to unlocking higher spectral efficiencies. Page 8 networks.nokia.com Figure 11. Downlink capacity gain from 3D MIMO Release 13 specifies MIMO modes for up to 16 transceivers at the base station, while Release 14 may allow as many 64. These will bring efficiency gains for downlink transmissions as shown in Figure 11: 16x2 provides a 2.5-fold gain in spectral efficiency compared to 2x2, while 64x2 shows a 3-fold gain. The gain available from 64x2 compared to 8x2 is 50 percent. Note that the 8x2, 16x2 and 64x2 transceiver configurations each have four columns of cross-polarized antenna elements of approximately the same physical dimensions, while the 2x2 transceiver configuration has only one column of cross-polarized antenna elements. The total transmission power is the same in all cases. The efficiency of the uplink can be improved by using a number of receiving antennas. This method has been widely deployed in the field by aggregating the signals received from 4, 8 or even more transceivers in the form of Centralized RAN (CRAN). These uplink improvements are mostly transparent to user devices supporting Release 8 and require no support for LTE-Advanced features. The introduction of a large number of transceivers is made possible with active antenna arrays. In addition to passive