https://scholars.lib.ntu.edu.tw/handle/123456789/122284
標題: | 高速多天線分頻正交多工無線區域網路的整合介質存取控制及實
體層設計(1/3) Integrated MAC and Physical Layer Design for a High Speed Multi-Antenna OFDM WLAN (1/3) |
作者: | 蘇炫榮 | 關鍵字: | WLAN;60 GHz;OFDM;MIMO;diversity;smart antenna;MAC;Hybrid ARQ;adaptive modulation and coding (AMC);power control;scheduling;multiple access;dirty paper coding;無線區域網路;正交分頻多工調變;多輸入多輸出通道;多重性;智慧型天線;介質存取控制;混合自動重新傳輸;可適性調變編碼;傳輸功率控制;排時;多重存取;髒 紙編碼 | 公開日期: | 31-七月-2005 | 出版社: | 臺北市:國立臺灣大學電信工程學研究所 | 摘要: | Wireless LAN has enjoyed a growing popularity in recent years due to its unlicensed, low-cost and high-rate nature compared to cellular networks. This success has triggered a change in the end-user demand toward high quality, rate-hungry multimedia applications such as wireless high definition digital videos and games. As a result, the current 2.4 GHz and 5 GHz wireless LAN bands are becoming inadequate to fulfill the demand, partly due to insufficient bandwidth, but also due to the inefficient medium access control (MAC) protocols that are being used in the current wireless LAN. In view of this, it is the purpose of this project to investigate the physical layer (PHY) and MAC issues involved in deploying wireless LANs with wideband transmission in the 60 GHz band where ample unlicensed bandwidth is available. In addition to wide transmission bandwidth, multiple-input multiple-output (MIMO) antenna techniques will be used to further boost the transmission rate. To ease the complexity of equalization in such a wide bandwidth, orthogonal frequency division multiplexing (OFDM) is adopted. A coordinated, cellular-like network structure is considered to enhance the MAC throughput and frequency reuse. In the first year of the project, some PHY and MAC issues have been considered for the proposed MIMO OFDM system. Specifically, we considered two multiplexing schemes for multiple users to share the downlink channel capacity increased by MIMO: grouped transmission, and overlapped transmission. In the former, for simplicity, the available transmission antennas are divided into a few groups, and each user is assigned a group of antennas. For such a scheme, each receiver only receives useful data from its corresponding transmission antennas, therefore it may know only the channel gains from these antennas through training. In order to achieve a good detection performance, the receiver will need an adaptive mechanism to measure the statistics of the interference from the other transmission antennas in order to suppress it. We investigate in this report an adaptive maximum signal-to-noise ratio (SNR) filter bank receiver for such a grouped transmission. The overlapped transmission is the optimal capacity sharing scheme in terms of maximizing the total transmission rate. For such a scheme, all users use all the transmission antennas, thus interfering with one another. We apply the Dirty Paper Coding (DPC) method to suppress mutual interference among users. The optimal design parameters for Vector (i.e., MIMO) DPC are derived for a specific superposition coding realization. To improve the network-wide throughput, a power control and allocation method was adopted for multi-cell OFDM networks to achieve interference avoidance between cells. Such a method relies on a simple power allocation mechanism autonomously run by each co-channel cell to achieve multi-cell water filling. As the mechanism runs, each cell will snatch sub-carriers that are good for it, and gradually release the sub-carriers with bad channel conditions to reduce interference to other cells. Such a method has another inherent benefit of lower peak-to-average power ratio as compared to conventional equal power allocation method. The advantage is also investigated in this report. Finally, as adaptive modulation and coding (AMC) and Hybrid ARQ (HARQ) are becoming popular in new high speed wireless network standards for their ability to maximize the end-to-end throughput, we will also consider them in the proposed MIMO OFDM system. In the first year of the project, we proposed a simple adaptive method to find the optimal parameters for operating AMC and HARQ. This method is very general that it can be easily ported to any PHY structure, including MIMO OFDM. 無線區域網路因其所在頻段無需使用執照,且較行動通訊成本低、傳輸率高的優勢,於近年來 蓬勃發展。然而隨著無線多媒體影音及遊戲等應用的風行,無線區域網路所使用的2.4 GHz 及5 GHz 頻段已逐漸有擁塞、不敷使用的現象。追根究底,其原因除了現有頻段不夠容納高品質的多 媒體需求外,介質存取控制協定效率低也是主要原因之一。本子計畫的目的為研究在具有極大可 用頻寬的60 GHz 頻段設置無線區域網路所可能遭遇的實體層及介質存取控制上的問題。除了使用 寬頻外,多天線技術(MIMO)將被採用來進一步增加傳輸速率。至於因寬頻而引發的高複雜度 等化器問題,我們將採用正交分頻多工調變(OFDM)的架構來解決。此外,我們將採用具協調 性、類似(行動通訊系統的)蜂巢網路的架構來增加介質存取控制層的產率及系統的頻率重複使 用率。 在第一年的計畫裡,我們探討了一些MIMO OFDM 的實體層及介質存取控制設計上的問題。 首先我們考慮了兩種可以讓多用戶分享因MIMO 而增加的下行通道容量的方式:第一種是分群傳 輸、第二種是重疊傳輸。分群傳輸是將發射端天線分為幾群,每個用戶使用一群的簡單辦法。當 使用這種方式時,接收端同常只在乎從本群天線傳來的信號,因此只會估測本群天線的通道參 數。這時候抑制由其他發射天線造成的干擾、以增加資料傳輸的正確率通常必須藉由可適性統計 及信號處理來完成。在這個報告中,我們探討了用於分群傳輸的可適性最大訊噪比濾波方式。重 疊傳輸則可達到最佳的通道容量分享及最大的總和傳輸率。這種分享方式讓所有用戶都使用所有 的發射天線。用戶間的干擾則藉由「髒紙編碼」來降低。在這個報告中,我們針對疊加性MIMO 髒紙編碼推導出最佳的設計參數。 蜂巢狀OFDM 網路的系統產率則是藉由電力分配及控制來提升。我們用了一個簡單、可由各基 地台及所屬用戶獨立執行、而不需額外全網路協調的電力分配機制來避免不同基地台間的相互干 擾。隨著通道狀況改變,這個機制能讓每個基地台逐漸佔用對它來說比較有利的OFDM 子通道, 而釋放出不好的通道以降低對其他佔用這些通道的基地台的干擾。這個電力控制機制還有低峰均 值的優點。這個優點在報告中一併探討。 最後,我們考慮使用最近許多高速無線通信系統都具備的可適性調變編碼及混合自動重新傳輸 技術於MIMO OFDM中。在計畫的第一年,我們提出了一個間單的可適性機制讓系統能自動搜尋 最佳的可適性調變編碼及混合自動重新傳輸設計參數。這個方法具有普遍性,可以被使用在任何 有可適性調變編碼及混合自動重新傳輸的通信系統。 |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/20333 | 其他識別: | 932219E002015 | Rights: | 國立臺灣大學電信工程學研究所 |
顯示於: | 電信工程學研究所 |
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