LTE-TDD, also known as TD-LTE in China, evolves in real time and in long term, and is jointly formulated by major global enterprises and operators covered by 3GPP. The two modes of FDD and TDD in LTE standard are essentially the same, with only a small difference, and the similarity is 90%. [1] TDD time division duplex is one of the duplex technologies used in mobile communication technology, corresponding to FDD frequency division duplex. TD-LTE is the TDD version of LTE technology, and FDD-LTE technology is the FDD version of LTE technology. TD-SCDMA is CDMA (Code Division Multiple Access) technology, while TD-LTE is OFDM (Orthogonal Frequency Division Multiplexing) technology. They are different in coding and decoding, frame format, air interface, signaling and network architecture.
3. The rapid development of the industry has basically achieved the synchronous development with other international mobile broadband technologies, representing the most advanced level of the mobile communication industry in the world today.
As early as June 5438+065438+ 10, 2004, at the meeting held by 3GPP in Quebec, 3GPP decided to start the research project of long-term evolution of 3G system. Major operators and equipment manufacturers around the world began to form the initial demand for LTE system through meetings and email discussions.
As an advanced technology, LTE needs the system to further improve the peak data rate, cell edge rate and spectrum utilization rate, and reduce the operation and network construction costs. At the same time, in order to make users get the "always-on" experience, it is necessary to reduce the delay of control and user plane. The system must be compatible with the existing system (2G/2.5G/3G).
On the radio access network (RAN) side, CDMA technology will be changed to OFDM (Orthogonal Frequency Division Modulation) technology, which can effectively combat multipath interference in broadband systems and has higher spectrum utilization efficiency. OFDM technology originated in 1960s, and has been continuously improved and developed since then. Since 1990s, with the development of signal processing technology, signal processing technology has been widely used in digital broadcasting, DSL and wireless local area network. OFDM technology has many advantages, such as anti-multipath interference, simple implementation, flexible support for different bandwidths, high spectrum utilization, efficient adaptive scheduling and so on, and is recognized as the future 4G reserve technology.
In order to further improve the spectrum efficiency, MIMO (Multiple Input Multiple Output) technology has also become a necessary technology for LTE. MIMO technology can transmit multiple data streams at the same time by using the spatial channel characteristics of multi-antenna system, thus effectively improving the data rate and spectrum efficiency.
In order to reduce the delay of the control plane and the user plane and meet the requirements of low delay (the delay of the control plane is less than 100ms and the delay of the user plane is less than 5ms), the current structure of NodeB-RNC-CN must be simplified, the RNC will no longer exist as a physical entity, and the NodeB will have some functions of the RNC and become an eNodeB, which is interconnected in the mesh through X2 interface and connected to CN. The change of this system will inevitably affect the change of network architecture, SAE (System Architecture Evolution) is also in progress, and 3GPP is also planning the smooth evolution of RAN/CN.
Due to the requirements of LTE, the evolution of TDD system and FDD system is synchronous.
At the 3GPP conference held in France in June 2005, Datang Mobile, as the leading manufacturer in the United Nations, proposed a TDD evolution mode scheme based on OFDM. In the same year, the 3GPP working group meeting held in Seoul adopted the LTE TDD technical proposal for the subsequent evolution of TD-SCDMA led by Datang Mobile.
By June, 2006, the feasibility study stage of LTE was basically over, and the specification formulation stage began.
In September 2007, at the 37th meeting of 3GPP RAN, several international operators jointly proposed a TDD frame structure supporting TYPE2. In June165438+1October of the same year, Jeju Working Group adopted the proposal of LTE TDD convergence technology, and the frame structure based on TD unified two TDD(TD-SCDMA LCR/HCR) modes that continued the existing standards. At the 38th plenary meeting of RAN, the scheme of merging frame structure was adopted and formally written into the 3GPP standard.