Department of Electronics, University of York
Heslington, York, YO10 5DD, UK
Abstract----Due to increasing demand of data traffic, the existing 3G network has nearly reach its capacity limitation. Carriers have paid more attention to the evolution scheme called LTE. According to different duplex mode, LTE has two different standards, which are TD-LTE and LTE-FDD separately. Although LTE-FDD is advanced now compared with TD-LTE, TD-LTE has some inherent advantages. With the shortage of spectrum resources, TD-LTE evolution solution could be considered by more and more carriers. This paper will discuss the key feature of TD-LTE and find out its advantage by comparing with FDD-LTE. Also it will make a overview about the next generation of TD-LTE, which is the evolution direction of TD-LTE in the future.
Keyword----TD-LTE, LTE-FDD, Network evolution, Duplex mode, Spectrum. II. INTRODUCTION
As the development of mobile devices such as smartphones or tablets, the demand of data traffic is increasing rapidly. It also changes the mobile network, which has mainly provided voice service traditionally, to be more data-oriented. The mobile data traffic growth rate will maintain in 50% approximately each year, which is forecasted by Cisco . The capability of existing 3G systems cannot satisfy the requirements of data traffic growth, even they has improved a lot in data service from 2G. In order to achieve the demand of mobile traffic, many carriers have been turning to the enhanced technology called long-term evolution (LTE). LTE is defined by 3rd Generation Partnership Project (3GPP) in release 8 . LTE system has many advantages to adopt the age of mobile Internet. It could provide high speed, low delay, efficient usage of spectrum, low cost and easy maintenance in its new network construction . LTE supports two kinds of duplex mode, which are frequency-division duplex (FDD) and time-division duplex (TDD) separately. So it can upgrade smoothly from all commercial operating 3G system including wide-band code division multiple access/ high-speed packet access (WCDMA/HSPA), code division multiple access 2000 (CDMA2000) and time division-synchronous code division multiple access (TD-SCDMA) . It also can reduce the carriers’ infrastructure cost on evolution from existing network system. Actually, many carriers are willing to accept this scheme. TD-LTE, also called LTE-TDD, is time-division duplex mode LTE standard. Because of base on time-division duplex mode, it “is considered as the evolution of TD-SCDMA” . As one of the two standards of LTE, TD-LTE possesses all features of LTE. Due to different duplex mode, TD-LTE has its significant characteristics and advantages compared with LTE-FDD. All of these TD-LTE special features will be discussed in detail in next part. However, TD-LTE and LTE-FDD are both based on the same fundamental, which leads them share some key specifications like Orthogonal Frequency-Division Multiplexing (OFDM) in downlink data transmission and Single-Carrier Frequency-Division Multiple Access (SC-FDMA) for uplink transfer [3, 5]. That is to say, these two standards can be merged together. Actually, the fusion is the target of some carriers and will lead LTE evolve to next generation mobile network system more smoothly and easily . It will be more concerned about TD-LTE in this paper. In the articles in [2, 3] provide comprehensive LTE knowledge. The 3GPP has started the research and established standard for evolution of LTE, also considered as LTE-Advanced, since 2008 after finished the first release of LTE . LTE-Advanced is the specification that 3GPP using to fulfill the “IMT-Advanced” standard made by International Telecommunication Union (IMT) as the next generation (4G) mobile network system. In 2012, IMT confirmed that LTE-Advanced is one of the standards for 4G...