畢業(yè)設(shè)計(jì)外文翻譯-基于matlab的td-scdma通信系統(tǒng)的調(diào)制與解調(diào)仿真程序設(shè)計(jì)(編輯修改稿)
2025-01-06 16:51 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 her uplink or downlink,with one or more breakpoints between the two in a frame defined. In this way, it is well suited to packet traffic, since this allows great flexibility in dynamically dimensioning for asymmetry in traffic flow. The TDD system should not really be considered as an independent work, but rather as a supplement for an FDD system to provide hotspot coverage at higher data rates. It is rather unsuitable for large scale deployment due to interference between sites, since a BTS may be trying to detect a weak signal from a UE, which is blocked out by a relatively strong signal at the same frequency from a nearby BTS. TDD is ideal for indoor coverage over small areas. Since FDD is the main access technology being developed currently, the explanations presented here will focus purely on this system. UMTS Bearer Model The procedures of a mobile device connecting to a UMTS work can be split into two areas: the access stratum (AS) and the nonaccess stratum (NAS). The access stratum involves all the layers and subsystems that offer general services to the nonaccess stratum. In UMTS, the access stratum consists of all of the elements in the radio access work, including the underlying ATM 附錄 4 transport work, and the various mechanisms such as those to provide reliable information exchange. All of the nonaccess stratum functions are those between the mobile device and the core work, for example, mobility management. Figure 7 shows the architecture model. The AS interacts with the NAS through the use of service access points (SAPs). UMTS radio access work (UTRAN) provides this separation of NAS and AS functions, and allows for AS functions to be fully controlled and implemented within the UTRAN. The two major UTRAN interfaces are the Uu, which is the interface between the mobile device, or User Equipment (UE) and the UTRAN, and the Iu, which is the interface between the UTRAN and the core work. Both of these interfaces can be divided into control and user planes each with appropriate protocol functions. A Bearer Service is a link between two points, which is defined by a certain set of characteristics. In the case of UMTS, the bearer service is delivered using radio access bearers. A Radio access bearer (RAB) is defined as the service that the access stratum () provides to the nonaccess stratum for transfer of user data between the User Equipment and Core Network. A RAB can consist of a number of subflows, which are data streams to the core work within the RAB that have different QoS characteristics,such as different reliabilities. A mon example of this is different classes of bits with different bit error rates can be realised as different RAB subflows. RAB subflows are established and released at the time the RAB is established and released, and are delivered together over the same transport bearer. A Radio Link is defined as a logical association between a single User Equipment (UE) and a single UTRAN access point, such as an RNC. It is physically prised of one or more radio bearers and should not be confused with radio access bearer. Looking within the UTRAN, the general architecture model is as shown in Figure 8 below. Now shown are the Node B or Base Station (BTS) and Radio 附錄 4 Network Controller (RNC) ponents, and their respective internal interfaces. The UTRAN is subdivided into blocks referred to as Radio Network Subsystems (RNS), where each RNS consists of one controlling RNC (CRNC) and all the BTSs
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