| 摘要: | 隨著科技的進步，無線通訊網路的技術不斷推陳出新，以滿足現代人對於無線通訊的不同需求。然而，在無線通訊技術不斷演進的同時，因應不同的無線網路環境可能存在著不同的架構與規範，如何在新舊無線通訊網路技術之間取得一個平衡或取捨，將是一大問題。為此，基於不破壞原有技術的前提下進行技術的提升，應是較為人們所期待的方式。 近年來，機器對機器（Machine to Machine；M2M）無線通訊網路已逐漸萌芽，其特性在於毋須人為操作或透過有限的人機互動情況下，使不同裝置之間能相互溝通且進行資料交換。隨著未來市場對於M2M無線通訊網路的渴望，現有的無線通訊網路業者，莫不爭先恐後導入M2M的觀念，以求此創新的服務概念能夠帶來廣大的利益。 在現有無線通訊網路系統的架構下，所制定的通訊規範都是基於人對人（Human to Human；H2H）的行為與需求進行設計；除此之外，在未同步之無線裝置欲上傳資料至基地台之前，彼此之間必須先透過一隨機存取的機制競爭上行傳輸的頻寬，以獲取上行傳輸的機會。然而，基於M2M的潛在數量非常龐大，以及每個設備皆有小量資料傳輸需求的特性，欲將M2M的觀念導入現有無線通訊網路系統的架構中，仍有許多技術性的議題與系統衝擊亟待克服。 在現有的第三代合作夥伴計劃（3rd Generation Partnership Project；3GPP）之長期演進技術（Long Term Evolution；LTE）系統的架構下，一使用者設備（User Equipment；UE）欲上傳資料至一基地台（evolved Node B；eNB）至少必須透過下列步驟：(1)UE自64個前置碼（Preamble）中擇一向eNB提出上行傳輸請求；(2)eNB因應該前置碼回應一相關訊息至UE；(3)UE因應該相關訊息向eNB提出上行頻寬請求；以及(4) eNB進行排程處理，允許UE上傳資料。 在現有LTE系統的架構下，64個前置碼是由各個UE所共享，一旦多個UE選擇到相同的前置碼，將會於競爭過程中發生碰撞，而在碰撞發生後，UE必須自行退讓一段時間，才能重新向eNB提出上行傳輸請求。不幸地，當整合M2M無線裝置至現有的H2H無線通訊網路中，大數量的M2M無線裝置將與現有的H2H無線裝置共享64個前置碼，以致於整合後的無線通訊網路，無論是M2M無線裝置或是H2H無線裝置都極易於上行傳輸資料時發生碰撞。 有鑑於此，如何在不破壞現有無線通訊網路架構的前提下，有效改善M2M無線裝置與H2H無線裝置極易於上行傳輸資料時發生碰撞之問題，確為亟需解決之問題。本論文著眼於此，針對固定週期上行回報資料之M2M設備設計一具自我調整之持續性排程競爭方式，除了解決該類型M2M設備對H2H設備造成的衝擊外，更在不破壞原有系統架構的前提下將M2M設備的競爭行為與所使用的上行頻寬最佳化，以期達到最有效率的下一代通訊系統運作方式。 With the advance of science and technology, various wireless communication network technologies have been developed in succession to satisfy different demands of the modern people. However, making a balance or compromise between new and old wireless communication network technologies becomes a serious problem because different wireless network technologies may correspond to different frameworks and specifications. For this purpose, improving wireless communication network technologies without violating the existing technologies shall be a desirable way. Machine to Machine (M2M) wireless communication networks, which allow different devices to communicate and exchange data with each other without the need of (or with the need of only a limited amount of) human to machine interactions, have been developed in recent years. In order to accomplish the modern M2M wireless communication networks, most of wireless communication network service providers promote the concept of M2M to gain extensive benefits from such innovative services. Wireless communication networks, which are established according to the conventional wireless communication network frameworks, are all designed on the basis of human to human (H2H) behaviors and demands. Besides, when wireless devices have not synchronized with the communication system, they must contend with each other through a random access mechanism to gain an opportunity for uplink transmission. However, the M2M communications are different to contemporary mobile network communication services as it involves a very large number of communication terminals with little traffic requirement, many technical issues and system impacts have to be tackled in order to realize the M2M communications on existing wireless communication networks. Under the framework of the Long Term Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP), a user equipment (UE) and the serving evolved Node B (eNB) must perform at least the following steps when it desires to upload data to the serving eNB: (1) the UE selects one of sixty-four preambles for transmitting an uplink transmission request to the eNB; (2) the eNB replies a relevant message to the UE in response to the preamble; (3) the UE transmits an uplink bandwidth request to the eNB in response to the relevant message; and (4) the eNB makes a schedule to allow the UE to upload data. Under the framework of the LTE system of 3GPP, the sixty-four preambles are shared by individual UEs, and once one of the preambles is chosen by multiple UEs, it would cause a collision. When such a collision occurs, the UEs must wait for a backoff time before they can transmit an uplink transmission request to the eNB again. Unfortunately, when M2M wireless devices are integrated into an existing H2H wireless communication network, all M2M wireless devices will share the sixty-four preambles with the existing H2H wireless devices. Consequently, the integrated wireless communication network would suffer from a serious blocking rate of uplink data transmissions from either the M2M wireless devices or the H2H wireless devices. According to previous discussions, it is an urgent requirement to overcome the collision problem effectively without violating the existing wireless communication network framework. This thesis focuses on the serious collision problem and proposes a self-adaptive persistent contention scheme for scheduling based M2M devices which report data in a periodical manner. In order to make the most effective way to operate the next generation communication system, the proposed scheme not only solves the congestion impact on the legacy devices but also optimizes the uplink bandwidth utilization and contention of M2M devices without violating the existing wireless communication network framework. |
