With the emergence of new technologies and the transformation of mobile communication concepts, in order to grasp a new wave of technology and maintain its leading position in the field of mobile communications, 3GPP initiated research and standardization on 3G evolution, namely LTE, at the end of 2004. With the freezing of the LTE R8 and R9 standards, LTE is increasingly becoming a hot spot in the industry. The LTE system defines both Frequency Division Duplexing (FDD) and TIME Division Duplexing (TDD). However, due to differences in wireless technologies, different frequency bands, and interests of various manufacturers, The LTE FDD support camp is more powerful, and both standardization and industry development are ahead of LTE TDD. In November 2007, the 3GPP RAN1 conference adopted the proposal of LTE TDD fusion frame structure jointly organized by 27 companies, and unified the two frame structures of LTE TDD. The LTE TDD frame structure after convergence is based on the frame structure of TD-SCDMA, which lays a foundation for the successful evolution of TD-SCDMA to LTE and even 4G standards. Under the leadership of the TD-LTE Working Group of the Ministry of Industry and Information Technology, the norm-setting, MTNet testing and the 6-city trial network are being carried out in an orderly and orderly manner. With the continuous improvement of technical standards, the continuous maturity of the industry chain and the continuous improvement of system capabilities, TD-LTE will soon enter the commercial era. As we all know, interference is one of the key factors affecting network quality, and it has a significant impact on call quality, dropped calls, handover, congestion, and network coverage and capacity. How to reduce or eliminate interference is an important part of TD-LTE network performance, and it is also one of the important tasks of network planning and optimization. TD-LTE network interference is divided into internal interference and external interference. Internal interference includes intra-frequency interference and inter-frequency interference. External interference includes inter-system interference and other random interference. This article will focus on the analysis of co-frequency and inter-frequency interference within the system, as well as interference between systems and TD-SCDMA. The TD-LTE network includes two modes: the same frequency and the different frequency. For the same frequency network, all cells in the coverage of the entire system can use the same frequency band to provide services for users in the cell, so the spectrum efficiency is high. However, there is a strict requirement for orthogonality between sub-channels, otherwise it will cause interference. For the different frequency networking, due to the difference in frequency, a certain degree of isolation is generated, but reasonable frequency planning is still needed to ensure the minimum network interference, and at the same time, due to the limitation of the frequency band resources, there is a problem of balance between interference control and frequency band use. . 1.1.1. Inter-cell interference Since the subchannels of OFDM are orthogonal, this feature determines that intra-cell interference can be overcome by orthogonality. If interference between sub-channels is caused by factors such as carrier frequency and phase offset, this interference can be minimized at the physical layer by using advanced wireless signal processing algorithms. Thus, generally considered to be within the OFDMA system cell interference is small. 1.1.2. Inter-cell interference For co-channel interference between cells, interference suppression techniques may be employed, including interference randomization, interference cancellation, and interference coordination. Interference randomization and interference cancellation are passive interference suppression techniques that have no effect on the carrier-to-interference ratio of the network. Interference randomization averaging the interference of the system in both time and frequency by means of scrambling, interleaving, frequency hopping, spread spectrum, dynamic scheduling, and the like. The interference cancellation uses the colored characteristic of the interference to suppress the interference to a certain extent, that is, the spatial colored interference is suppressed by the multiple antennas of the UE. In the spatial dimension, beamforming is performed by estimating the spatial spectral characteristics of the interference, and multi-antenna anti-interference combining is performed. In the frequency dimension, the equalization parameters are optimized by estimating the spectral characteristics of the interference, and single antenna suppression, such as IRC, is performed. Interference coordination imposes certain restrictions on the time-frequency resources available at the cell edge. Orthogonalization or semi-orthogonalization is an active control interference technique. The ideal coordination is to allocate orthogonal resources, but such resources are usually limited; Non-ideal coordination can reduce interference by controlling the power of the interference. Interference coordination is mainly divided into static ICIC, semi-static ICIC and dynamic ICIC. The core of the static ICIC is that the radio resources of each cell are allocated and used according to certain rules. The cell edge user uses a part of the entire available frequency band, and the neighboring cells are orthogonal to each other, and the user transmits the full power; the cell center user can use the entire available frequency band, but reduces the power transmission; The dynamic ICIC is based on the static ICIC for real-time scheduling through the eNodeB, and coordinates the use of frequency resources between adjacent cells to achieve the purpose of suppressing interference and adapting to the uneven load between cells; The situation of the edge band of the zone to prevent conflicts; According to the above analysis, the TD-LTE system does not have co-channel interference in the cell, and the interference mainly comes from neighbor cells using the same frequency. If the inter-frequency is maintained between the serving cell and the most neighboring cell, the same-frequency cell is isolated by the spatial propagation distance, so that the same-frequency interference can be reduced as much as possible. In the inter-frequency network, neighboring cells use different frequencies to reduce interference, and the spectrum efficiency is worse than the same frequency. However, the RRM algorithm is simple, and the edge rate is higher than that of the same-frequency network. Therefore, if an inter-frequency networking is adopted, reasonable frequency planning is required to ensure minimum network interference. At the same time, due to the limitation of band resources, there is a problem of balance between interference control and band usage. The simulation results also show that compared with the same-frequency networking, the inter-frequency networking has greatly improved the carrier-to-interference ratio C/I capability. This means that under the same coverage area, the user has a higher transmission rate in the case of obtaining the same frequency resource unit. At the same time, the peak rate of the edge users of the coverage area can be increased.
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January 30, 2023