臺灣博碩士論文加值系統

合適的傳輸技術可以改善傳輸效率整合在在有線或無線通訊. 這些技術通常在time-varying的頻道上更改傳輸功率, 傳輸封包的長度, 碼率以及調變技術. 例如 V.34 數據機利用調變技術在低品質的電話線中保障可接受的位元錯誤率. 同樣地, ADSL使用 DMT 調變技術來分配資料位元在子頻道上來改善訊號雜訊比(SNR).這裡提出一個提高傳輸量的觀念, 允許mobile termial 在靠近cell 中心的地方使用高傳輸率的調變方式, 在較遠離cell 中心的地方使用低傳輸率的調變方式以獲得較低的SNR. 同樣的觀念應用在IEEE 802.11 無線區域網路, Harris及Lucent兩家公司參考Complementary Code”而提出的高速調變架構“Complementary Code Keying” (CCK). 而IEEE 802.11 工作小組最後採用了CCK 將無線區域網路的速度提升到5.5Mbps 及11Mbps. 為了相容於舊有的1/2Mbps無線區域網路, Harris提出了一個基頻的處理器來相容四種不同的調變方式 (DBPSK/DQPSK/CCK/MBOK) 和傳輸速度 (1/2/5.5/11Mbps). 直覺地來看, 所有的移動站 (MS) 應該都要使用高速率的傳輸調變方式來取得網路中最大的總傳輸量. 然而, 要得到最大的資料傳輸速率會使得傳輸的距離縮短. 在一般的觀念上, 高速的傳輸調變方式比低速的調變方式需要更高的SNR值來維持相同的位元錯誤率. 假如我們只考慮距離帶來的fading效應, 我們可以發現SNR會隨著距離而變低. 在兩個收發端如果在調變方式的傳輸距離界限以內的話, 就可以得到這種調變方式的最高資料傳輸率. 而且, 在這個界限範圍內, 資料可以利用這個特定的調變方式傳送成功.IEEE 802.11 定義了兩種無線區域網路. 一種是IBSS (Independent Basic Service Set) 或稱為 Ad Hoc無線區域網路. 另一種是ESS (Extended Service Set) 或稱為 Infrastructure 無線區域網路(IWLAN). 在Ad Hoc無線區域網路, 一群 MSs 可以不需要透過已經建立的公共機構或主控者的仲裁來快速地傳送資料. 一個IWLAN 需要透過擷取點將 MSs 連接到有線網路. 基本上, 擷取點是一個固定的基地台用來提供 MSs 存取整個分散式系統, 也就是說IWLAN 延伸了MS’s 的通訊範圍且應用到實際的無線網路上. 然而, 兩台MSs 不管彼此之間有多接近, 要互相通訊還是必須要透過擷取點來傳遞封包. 並且, 不同的調變方式只能用於調變方式的距離限制, 當一個 MS 在擷取點附近移動時, MS的調變方式必須要對應於對擷取點的距離而有所不同. 此外, 由於距離擷取點較遠的MS 只能分享較少的頻寬, 會造成網路頻寛分配的不公平. 不幸地, 這些問題並沒有在IEEE 802.11 標準中被解決. 所以, 這裡將設計一個不同的通訊協定來規範 MS的傳輸規則使每個MS能獲得相同的頻寬.回憶之前的調變方式, 傳送距離較短者（長者）將提供較高（低）的資料速率.一個傳送站(MS)在IWLAN網路中將會根據其和擷取點(AP)之間的距離遠近而改變其調變方式.如果我們考量一個圓盤的大小和高度當作調變方式的覆蓋範圍與資料速率, 則此類的網路有點像是‘Tower of Hanoi’.在這‘Tower of Hanoi’中, 一個圓盤的高度（資料速率）和大小（覆蓋範圍）由內到外將分別逐漸的降低與增加.為了簡化識別IWLAN的特性, 在整篇論文中我們將稱此種多速率的IWLAN為‘Tower of Hanoi’網路(THN).我們注意到, 在THN中內部的資料速率將會高於外部的資料速率.

Adaptive transmission techniques have been extensively investigated for the improvement of transmission performance in wired and wireless communications. These techniques vary the transmission power , transmission packet length , coding rate/scheme, and modulation technology under the time-varying channel. The adaptive modulation technology had been implemented in part of products such as V.34 modem standard to maintain an acceptable bit error rate (BER) over poor quality telephone lines. Similarly, the Asymmetric Digital Subscriber Line (ADSL) uses the DMT (Discrete Modulation Technique) modulation/coding to adaptively allocate more data bits in sub-channel which has a better signal-to-noise ratio (SNR). Besides, the adaptive modulation scheme used in two-way data transmission over cable and the variable-rate QAM has also been proposed in third-generation wireless systems. In summary, all of them are trying to improve the effective data rate under a specified bit error rate (BER).
Authors proposed the concept that throughput would be increased by permitting mobile terminal, which nears the central of the cell, to use the high-level modulation scheme. In contract, mobile terminal nears the fringes of cell must use a low level (binary) modulation to cope with the lower SNR. The same concept has also been applied on IEEE 802.11 wireless LAN (WLAN). Companies Harris and Lucent have proposed high data rate modulation scheme “Complementary Code Keying” (CCK)], which was referred from the “Complementary Code”. The IEEE 802.11 working group finally adopted CCK to support data rate up to 5.5Mbps and 11Mbps. To provide the interoperability for existing 1/2Mbps networks, Harris had proposed a baseband processor, which has the ability to provide four different modulation schemes (DBPSK/DQPSK/CCK/MBOK) and four data rates (1/2/5.5/11Mbps) for IEEE 802.11b WLAN. Intuitively, all mobile stations (MS) should use the highest level modulation scheme with the highest data rate all the time to achieve the maximum network throughput. However, the maximum data rate may not always be obtained since the data rate is inversely proportional with the transmission distance. The general concept is that a higher-level modulation scheme requires a higher SNR to obtain the same specified BER in respect to a lower level modulation scheme. That is, if we only consider the fading caused by the distance, we could find that the SNR degraded with the distance (from the signal power’s degradation). The maximal data rate of a modulation scheme will be obtained only when the distance between two transceivers is not over the transmission distance boundary of the modulation scheme. Furthermore, within this bounded area, data can be transmitted successfully by using the specified modulation scheme. The relationships between data rate and transmission distance in IEEE 802.11 WLAN is shown in Figure 1 .
The IEEE 802.11 defines two types of wireless network. One is called as IBSS (Independent Basic Service Set) or Ad Hoc WLAN. The other is the ESS (Extended Service Set) or Infrastructure WLAN (IWLAN). In Ad Hoc WLAN, a collection of MSs can quickly form a network without the aid of any pre-established infrastructure or centralized administration. An IWLAN connects MSs to a wired network via access point (AP). Basically, the AP is a fixed station that provides MSs the access to the Distribution System (DS). That is, an IWLAN extends MS’s communication range and is often used in realistic wireless networks. However, in the case of two MSs desire to communicate with each other, their data packets must be relayed via AP no matter how close they are. Moreover, since different kinds of modulation schemes (with different data rates) can only be used in their transmission ranges, when an active MS moves around the AP’s coverage area, the modulation scheme must be adjusted according to the distance. Besides, it will also incur unfairness since the MS locates within outer area will share a lower bandwidth quota than the others within inner area. Unfortunately, these problems are not considered or solved by the IEEE 802.11 standard. Thus, it is desired to design an efficient protocol to inform MSs about its location and to equally allocate bandwidth for every MS.
Recall that a modulation scheme with shorter (longer) transmission distance will provide a higher (lower) data rate. An MS in IWLAN network may change its modulation scheme according to the
distance between AP and itself. Such kind of network is somewhat like the ‘Tower of Hanoi’ if we consider the ‘size’ and ‘height’ of plates as the ‘coverage range’ and ‘data rate’ of modulation schemes. In the ‘Tower of Hanoi’, the height (coverage range) and the size (data rate) of plates are gradually reduced and increased respectively from inner to the outer. For simplicity to identify the characteristics of IWLAN, we call such multi-rate IWLAN as ‘Tower of Hanoi’ Network (THN) throughout this paper. We note that, in THN, the inner side always provides a higher data rate than the outer side.

第一章 緒論
1.1 無線區域網路簡介 1
1.2 無線區域網路之多種傳輸速率 10
第二章 系統模型
2.1 IEEE 802.11無線區域網路的傳輸方式 13
2-2 THN系統模型 18
2-3 THN的問題 22
第三章 原理及方法介紹
3-1 THN的Frame格式 27
3-2 AP與MS的流程 29
3-3 Sub-Frame時間區間分配規則 36
第四章 模擬模型及結果
4-1模擬環境 38
4-2移動性的影響 41
第五章結論與未來展望
5-1結論 45
5-2未來展望 47
參考文獻 　 48
附錄：
附錄一　論文發表　　　　 　　　　　　 　51
附錄二 Wireless LAN Side Survey Tool 68
附錄三　BlueTooth Protocol 驗證 81
附錄四 2.4GHz 天線實作 93
附錄五 Layer 3 Switch 硬體製作 101

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