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Design And Implementation Of RLC Layer Protocol Software In LTE

Posted on:2011-08-20Degree:MasterType:Thesis
Country:ChinaCandidate:L HongFull Text:PDF
GTID:2178360305455062Subject:Computer software and theory
Abstract/Summary:PDF Full Text Request
With the 3G mobile communication networks put into use around the world, wireless broadband data services grow rapidly, 3G has opened the door of broadband mobile communication for us. To meet the constant demand for increasing bandwidth, 3GPP started the largest project in recent years, LTE, whose goal is to achieve the evolution from 3G network to 4G network, LTE is recognized as the only way to comprehensive broadband mobile communications.Compared with 3G, LTE has a higher data transmission rates and spectrum efficiency, reduce the network delay, achieved wide-area coverage under the premise of the stability of various indicators. and has a good compatibility with the 2G, 3G and 4G network. Therefore, LTE has wide application prospect and great commercial value, which has gained the support of most carriers and manufacturers.In the LTE radio access network, the radio link control function is very important, which is implemented by the RLC layer. RLC layer can offer different data transmission reliability according to different applications, dynamically adjust the data packet size to accommodate the changes of network resources. When using AM, RLC guarantee correct and in-sequence data delivery in radio access network.The purpose of this paper is to design and implement the RLC layer protocol software in LTE system.The design aims to achieve the main functions of RLC layer, including signaling processes of control plane, as well as TM, UM and AM data transfer. RLC protocol software is required to integrated with other user plane software, and achieve long-time stable operation on MSC8144 DSP chip, besides that, the uplink and downlink data transmission rates must meet the system requirement. The whole work is focused on three modes of data transmission, the difficulty is ARQ mechanism, which is specific to AM.RLC protocol software design is divided into three stages: the module design stage, data structure design stage and process design stage.Module design aims to design the structure of the RLC protocol software, different functions will be divided into different modules to achieve. Given in reference to the three RLC entities, we divided RLC protocol software into TM RLC transmitting module and receiving module, UM transmitting module and receiving module, and AM transmitting module and receiving module, additionally, we design RLC Common module, responsible for the control plane function.Functions of AM transmitting module include: segmentation and concatenation, construction of AMD PDU, retransmission, construction of STATUS PDU, STATUS PDU decoding and processing. Functions of AM receiving module include: PDU decoding, AM duplicate detection, AM reordering, RLC SDU reassamble and deliver. Many functions are designed from the implementation point of view. Particularly, we also design a shared storage for the AM transmitting module and receiving module to share STATUS PDU and the receiving-queue information. When use AM, the interactive control information among modules include: RRC layer configs AM transmitting module and receiving module with the help of RLC Common module, AM transmitting module indicates successful delivery of RLC SDU, and messages required by the mechanism of wait-for-send data feedback.TM module, as its simple features, has been integrated into RLC Common module. The UM transmitting module and receiving module can be seen as a simplification of AM.Data structure design aims to classify and organizing various data, makes it easy to use and maintain. We use TX_CONTEXT for transmititng module and RX_CONTEXT for receiving module, to keep the configuration information, transmitting and receiving address, and data needed by various functions. Similarly, we use TX_PDU_CONTEXT and RX_PDU_CONTEXT to keep the PDU header and data field information, which are used when constructing and decoding RLC data PDU. In addition, we design data structure of share storage and messages between layers.The purpose of process design is to describe data transmission processs among functional modules.In the AM uplink data transmission process, if the AM receiving module receive a STATUS PDU, it will write the PDU to the shared storage, and set a status report flag to a readable state. If an RLC AMD PDU or an RLC AMD PDU segment has been received, the AM reveiving module will do duplicate detection first, to discard the data received before, and then insert newly received data to the receiving queue, where the reordering happens, when certain condition is satisfied, AMD PDU will be reassemble into RLC SDUs, then delivered to PDCP.In the AM downlink data transmission process, the query of data to be transmitted will be accomplished first in the query sub-frame of scheduling cycle, the feedback may be the size of RLC SDUs, AMD PDU, or STATUS PDU. When the transmission sub-frame arrives, MAC will indicate the RLC PDU size, RLC AM module will construct and transmit an RLC PDU in the following priority: a STATUS PDU, a retransmitted AMD PDU or AMD PDU segment, or a new AMD PDU.In the implementation part of the RLC protocol software, this article gives details of AM data transmission function. Segmentation and concatenation function together with RLC SDU reassemble function offer RLC protocol software the ability to dynamically adjust the RLC PDU size. The retransmitting function, which the core of ARQ and difficulty of implementation, ensures that the receiving side collected all RLC data PDUs, which is the fundamental of AM reliability. The duplicate detection function allows the receiving side to discard duplicated data, avoid repeatedly submit to PDCP.The testing of RLC protocol software consist of three phases: off-target testing, on-target testing and field-site testing, test environment and purposes are different. In the unit testing and user plane software integration testing of the first phase, we use printing test and stub test. In the testing process, we also work on algorithm and code optimization, improve the efficiency and robustness of software .Test results show that the the RLC protocol software implemented in this thesis meets the design requirements both in function and efficiency.
Keywords/Search Tags:LTE, RLC, Data Transmission, Reliability
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