當手機想要與基地台做存取資源的時候，必須先經過隨機接入程序(Random Access Procedure)。隨機接入程序可分為兩種型態，分別為競爭型隨機接入程序，與非競爭型隨機接入程序。競爭型隨機接入程序共有 4 個步驟，首先第一步，會由使用者(UE)自行選擇 Preamble (Msg1)以上行RACH 傳送給基地台，Preamble 與上行 RACH 的選擇範圍是由基地台配置，只能在基地台所規定配置的位置上傳。第二步由基地台以下行 DL-SCH 回覆使用者Random Access Response (Msg2)，Response 裡提供使用者上行資源。第三步(Msg3)由使用者以Msg2 提供的上行資源傳送給基地台，告知基地台接入的目的或需求。最後一步則由基地台以 DL-SCH 或 PHY 層的 DCI 發送競爭消除消息(Msg4)告知是否讓使用者進入網路。 而本篇論文以軟體定義無線電的方式，實現LTE上行Preamble訊號之傳送以及下行鏈路發射機與接收機之對傳同步(手機與基地台之對傳)。透過搭載實務軟體定義無線電平台，可以實際即時的在特定頻段、特定時間發射與接收空中的訊號，也可以改變發射及接收增益來觀察訊號在經過空氣後發生的變化，以及探討訊號的品質評斷系統優劣度等等。 ;When the cell phone want to access the resource with the base station, it must use Random Access Procedure. And there are two kinds of Random Access Procedure. One is competitive Random Access Procedure, and the other is non-competitive Random Access Procedure. Competitive Random Access Procedure has four steps, the first step UE(User Equipment) will choose randomly selects an RA preamble sequence from the set of sequences available in the cell(Msg1) transmits the Preamble on RACH. The Preamble and uplink RACH are configured by the BS(base station). The second step, BS will transmits the RA Response(Msg2) on the DL-SCH channel. The message carries the timing and uplink resource allocation for the UE. The third step, (Msg3) UE send “RRC Connection Request” using T-CRNTI it got from “RACH Response”. The last step, BS sends “RRC Connection Setup” message which carries C-RNTI. In this thesis, we used Software-define-radio to achieve LTE uplink and downlink transmitter and receiver (communication of user and base station). By the Software-defined-radio platform, we can immediatly transmit preamble signal at specific subframe and receive signal in the air on some particular band. Also, we can change transmit and receive gain to observe the transformation of the signal in the air, or discuss on the quality of the signal and system, etc.
