4G LTE-Advanced technology characteristics and development analysis

LTE-Advanced refers to the technical version of LTE in Release 10 and later. At the end of 2004, the standardization of LTE was started in 3GPP. Unlike 3G, which is based on CDMA technology. According to the trend of wireless communication towards broadbandization, LTE uses OFDM technology as the basis, combined with multi-antenna and fast packet scheduling design. The concept has formed a new air interface technology for the next-generation mobile communication system, also known as the 3G evolution system (LTE, Long Term Evolation).

1 Introduction

LTE-Advanced refers to the technical version of LTE in Release 10 and later. At the end of 2004, the standardization of LTE was started in 3GPP. Unlike 3G, which is based on CDMA technology. According to the trend of wireless communication towards broadbandization, LTE uses OFDM technology as the basis, combined with multi-antenna and fast packet scheduling design. The concept has formed a new air interface technology for the next-generation mobile communication system, also known as the 3G evolution system (LTE, Long Term Evolation). At the beginning of 2008, the first version of the LTE system technical specifications, namely Release 8, was completed. After this, 3GPP continued to improve and enhance the technology, and just completed the second technical version (Release 9), and is currently in the process of researching the Release 10 version.

While conducting LTE technology research in 3GPP, the International Telecommunication Union (ITU) has been conducting research on the market demand and frequency planning of next-generation mobile communication systems in preparation for formulating international standards and recommendations for 4G technology. In March 2008, ITU started the solicitation and standardization process of candidate technologies, called IMT-Advanced. In response to the ITU’s call for 4G IMT-Advanced technology, the 3GPP referred to the LTE Release 10 and later technology versions under study as LTE-Advanced, and submitted candidate technologies to the ITU.

LTE supports both FDD and TDD duplex modes. In the LTE Release 8 version, with a 20MHz communication bandwidth, the downlink peak rate of the air interface exceeds 300Mbit/s, and the peak rate in the uplink direction exceeds 80Mbit/s. The LTE Release 10 version (LTE-Advanced) will support a communication bandwidth of 100MHz, and the peak rate of the air interface will exceed 1Gbit/s. It is worth mentioning that, as the follow-up evolution of TD-SCDMA technology, the TDD mode of LTE is also called TD-LTE/TD-LTE-Advanced. Out of concern for the TD-SCDMA technology evolution route, Chinese member units have deeply participated in the relevant system design process in 3GPP. In October 2009, the Chinese government formally submitted the TD-LTE-Advanced proposal to the ITU as a 4G international standard. Candidate technology.

2 Technical characteristics

2.1 Multiple access methods and resource allocation

LTE adopts OFDM technology as the basis, and according to the respective characteristics of the uplink and the downlink, single-carrier DFT-SOFDM and OFDMA are respectively adopted as the specific realization of multiple access methods in the two directions. The OFDM technology allocates frequency resources in units of subcarriers. The LTE system uses a subcarrier bandwidth of 15kHz. According to the number of subcarriers, it can support various system bandwidths of 1.4, 3, 5, 10, 15 and 20MHz. The carrier aggregation technology that will be introduced in the Release 10 version can achieve a full system bandwidth of 100MHz by aggregating five 20MHz component carriers (see Figure 1).

4G LTE-Advanced technology characteristics and development analysis
Figure 1 Carrier aggregation

2.2 Fast packet scheduling

The wireless fading channel changes in time and frequency. In LTE, a TTI (transmission time interval) with a time length of 1 ms is combined with a frequency width of 12 sub-carriers (180KHz) to form a PRB (Physical Resource Block). According to the change of the channel, the system performs fast scheduling and allocates the best physical resources to users. On the selected physical resources, AMC (Adaptive Coding and Modulation) technology is further used to form the best use of resources. Such adaptive scheduling realizes the optimal allocation and utilization of resources from the perspective of the entire system, and improves the performance of the entire system. At the same time, flexible scheduling can also provide a reasonable QoS guarantee for a single user based on business characteristics, and related mechanisms have become a basic technology in the design of all new generation mobile communication systems.

2.3 Multi-antenna technology

Multi-antenna (MIMO) technology is a key technology for LTE systems to improve throughput. According to antenna deployment patterns and actual application conditions, three different MIMO implementation schemes can be used: transmit diversity, spatial multiplexing, and beamforming. For example, for a large-spacing non-correlated antenna array, a spatial multiplexing scheme can be used to transmit multiple data streams at the same time to achieve a high data rate; for a small-spacing related antenna array, beamforming technology can be used to direct the antenna beam to the user to reduce Inter-user interference. For scenarios that require better assurance of reception accuracy, such as control channels, transmit diversity is a reasonable choice.

The LTE Release 8 version supports the transmission of up to 4 antennas in the downlink, and the parallel transmission of up to 4 data streams can be spatially multiplexed. In the case of a 20MHz bandwidth, a peak rate of more than 300Mbit/s can be achieved. In Release 10, the number of antennas supported in the downlink will be expanded to 8. Correspondingly, the parallel transmission of 8 data streams can be spatially multiplexed at most, and the peak spectrum efficiency is doubled to 30bit/s/Hz. At the same time, the MIMO function will also be introduced in the uplink to support up to 4 antenna transmissions, and up to 4 data streams can be spatially multiplexed to achieve an uplink peak spectral efficiency of 16bit/s/Hz (see Figure 2).

4G LTE-Advanced technology characteristics and development analysis
Figure 2 MIMO technology enhancement

2.4 Relay technology

Relay (Relay) technology is another important feature that LTE will begin to introduce in Release 10 (see Figure 3). Traditional base stations need to provide wired link connections on the site for “backhaul transmission”, while relay stations perform network backhaul transmission through wireless links, so deployment can be more convenient. According to different usage scenarios, relay stations in LTE can be used to relay base station signals to expand the coverage of the network; or to reduce signal propagation distance, improve signal quality, and thereby increase data throughput in hotspots.

4G LTE-Advanced technology characteristics and development analysis
Figure 3 Relay technology

2.5 Performance evaluation

In the preparation process as a 4G candidate proposal, the LTE/LTE-Advanced system performance was comprehensively evaluated in accordance with the evaluation scenarios specified by the ITU, including spectrum efficiency, VoIP capacity, service/handover delay and other key indicators. Or exceed the ITU IMT-Advanced technical requirements. Figure 4 shows the evaluation of the average spectrum efficiency of the LTE system in four scenarios.

4G LTE-Advanced technology characteristics and development analysis
Figure 4 LTE/LTE-Advanced performance evaluation

3 Standard development

LTE (Long Term Evolution) is a new system design after 3G. 3GPP began technical research and system standardization at the end of 2004. By the beginning of 2008, the system technical specifications of the first version of Release 8 were completed, and a brand-new technical architecture based on OFDM/MIMO technology for the next generation of mobile communication systems was formed. The LTE Release 8 version has achieved the design goal of 100Mbit/s throughput. On this basis, 3GPP will continue to improve the system and enhance the technology in subsequent versions.

As of March 2010, various standardization projects for LTE Release 9 have been completed. The new functions of the system include user positioning, multicast/broadcast functions, dual-stream beamforming, femtocells, and self-organizing networks. Although the peak throughput of the system has not been increased, these functions have further improved the system. On the basis of the new system framework formed in the previous version, the LTE Release 9 version has enriched the business capabilities of the system.

Currently, research work is underway in the LTE Release 10 version, and the research content that has been determined includes the previously introduced carrier aggregation, MIMO technology enhancement, relay technology, and heterogeneous networks. The further enhancement of carrier aggregation technology and MIMO technology will significantly improve the throughput capacity of the system and achieve the performance goal of exceeding 1Gbit/s of the next-generation mobile communication system. The completion time of the LTE Release 10 plan is early 2011, when the system performance of LTE will be significantly enhanced and improved. Figure 5 shows the technological development of LTE.

4G LTE-Advanced technology characteristics and development analysis
Figure 5 LTE technology development

LTE is one of the most important development directions of next-generation mobile communication systems after 3G. Various domestic units have made great investments in related technical research and international standardization. According to statistics, so far Chinese companies have submitted about 5000 LTE contributions in 3GPP, accounting for about 14% of the total number of related contributions. With the continuous development of the LTE standard, the participation of domestic companies is constantly increasing, and the proportion of manuscripts in the total is also increasing year by year, reaching more than 20% in the second half of 2009. For the TD-LTE system design that we are focusing on, the number of manuscripts submitted by Chinese companies is closer to 50% of the total.

4 Conclusion

3GPP LTE takes OFDM/MIMO as the basic technology and adopts a large number of the most advanced technologies and design concepts in the current mobile communication field. Starting from Release 8, LTE has completed Release 9 and is currently in the process of research on Release 10. In response to the work of the ITU on the IMT-Advanced international recommendations, LTE Release 10 and subsequent versions are also called LTE-Advanced, which is one of the most important development directions for mobile communication systems in the 4G phase. The TDD mode of LTE-Advanced is also called TD-LTE-Advanced, which is a technological evolution of 3G TD-SCDMA in the next generation mobile communication system 4G. The performance simulation evaluation results conducted in accordance with the evaluation scenarios specified by the ITU show that the various system performance indicators of LTE-Advanced/TD-LTE-Advanced all meet or exceed the ITU IMT-Advanced technical requirements.

Chinese companies have invested a lot in the international standardization of LTE, and continue to increase their participation with the development of the LTE standard. In the recent standardization work in the LTE Release 10 phase, the number of manuscripts submitted by Chinese companies has reached more than 20% of the total number of manuscripts in the conference (see Figure 6). While fully participating in the international standardization of LTE technology, it has effectively guided TD-LTE technology. The direction of development.

4G LTE-Advanced technology characteristics and development analysis
Figure 6 Proportion of contributions from Chinese companies to the total number of 3GPP LTE contributions

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