時間-空間-都卜勒超寬頻系統(UWB)設計應用於漸褪頻道

Space-Time-Doppler UltrawideBand (UWB) System Design for Fading Channels

鄧陳興(Shing Tenqchen)

指導教授 ： 馮武雄

國立臺灣大學/電機資訊學院/電機工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.01803

摘要

在本論文中我們處理超寬頻(UWB)系統在時間、空間、都卜勒基本的數學及物理問題：多輸入多輸出無線通訊系統利用可適性濾波器及估計理論來提供給系統正確的參數。超寬頻系統無線頻道是一種混合型的科技結合在一起的產品，諸如：網路、雷達、影像、及定位系統。由美國聯邦通訊委員會主導，在2002年提出一套規則建議：釋放出在雜訊層3.6~10.6兆頻(GHz)頻段，UWB可與射頻(RF)系統重複運作共通性的使用低功率超短波的方式運載資訊。此短距離高解析的寬頻擷取網路上的資訊，是一種好的方法來提升無線通訊的價值，以局部區域可行的運作方式，高解析式可穿透地層、牆壁
、衣服及家具等的資訊運作方式，提供各種不同的商業用途：諸如導航及物品追蹤等。至目前為止有三種基本的調變方式：多頻道正交頻段劃頻多工(MB-OFDM)、脈衝超寬頻(I-UWB)或展頻超寬頻(DS-UWB)，本文將比較著重在後兩者並比較其相互之性能。I-UWB或DS-UWB從零至幾個毫微秒內，以極微的能量散發從零至至幾個兆元的微波訊號。因此I-UWB可聚集一大堆使用者於一個小區域，故在如此寬頻限制的輻射功率脈衝的規範考量須符合FCC之ㄧ些規定，無線脈衝大多運作在3.1GHz頻段內。再者，UWB訊號必需不能與窄頻現存細統的訊號，如2G/2.5G/3G無線通訊系統相互干擾。為符合這些條件，通常利用跳頻/展頻技術來避開。一種簡單的方法來實現展頻就是時間跳頻，它是以單位位元攜帶許多數舉的脈衝方式來做數位調變。另外一種展頻的方法叫多頻段正交劃時多工(MB-OFDM UWB)調變，對脈衝超寬頻可更寬一點區分為邊界或調整範圍的偵測器或同步同耦合的偵測器(CCD)及鈀型(RAKE)接收機，多用戶偵測器及混合型接收器可視為是對窄頻干擾的壓制的一種韌性作法，變得越來越普遍。
本論文主要考慮對高數據位元率無線通訊傳輸，定向電波時間空間多輸入多輸出以直角正交頻率劃頻多工為基礎的無線區域網路系統之二維(2-D)展頻通道傳輸的訊號處理，訊框偵測、時間同步、頻率同步、通道估計及同步追蹤使用試驗用次載波及二維多輸入多輸出偵測理論。我們主要貢獻如下：

▇ 與利用最大歸納的機率(MAP)解調變器，利用低複雜度現性的最小均方誤差MMSE法可執行一個有限範圍空間非耦合的通道性能遺失。
▇ 由於展頻與解展頻結合最小均方誤差MMSE法的頻率領域等化器，低雜訊次載頻在平均錯誤位元率(BER)不良影響的性能上有顯著的改善，因此可以有效地回復原來的訊號。
▇ 在測試狀態下，以直角正交頻率劃頻多工為基礎的無線區域網路系統之二維(2-D)展頻通道傳輸系統均符合IEEE802.15.3a的規範。
▇ 從模擬結果在不考慮相位誤差及量化誤差之影響情況，可以用到直接視線(LOS)及非直接視線(NLOS)(如穿過牆壁XPD)的模型的架構，利用WHT的轉換，符合Bezout Identity 的原則下，在低雜訊每一支天線的編碼時，仍然比複雜的PAC軟輸出效果要好。

UWB的漸褪頻道擁有低/高的訊號雜訊比(SNR)，多路徑效應、多使用者干擾等均會導致位置誤差，因此所設計的位置引擎，必須能執行下列工作：
▇ 數據融合技術
不同的數據技術可使用時到達時間(TOA)、到達角度(AOA)或結合兩者之技術
▇ 通道模型
一個簡單的多路徑多使用者環境之產生，可以計算模型路徑遺失、陰影效應、瑞雷(Rayleigh)漸褪、及都卜勒頻率效應。
▇ 參數估計
到達時間(TOA)及到達角度(AOA)估計的方法可當作位置尋找引擎的一部份，此部份有不同的變化產生及性能比較。
超寬頻通訊系統中大部分使用在尋找性能引擎及傳輸架構有PPM-TH、PAM-TH，及PAM-DS等符合IEEE802.15.3a。他們均可以最少的改變使用於室內或室外的環境。本文之位置尋找引擎可使無線超寬頻系統可用：
▇ 建立不同物理層給不同的無線通訊系統
調整物理層的參數使得這各模擬器可用於不同的通訊系統，這些參數包刮：展頻因子、封包大小、封包訓練長度、試驗封包、調變型態、調變技術、載波頻率、傳送信號功率、及傳送與接收之天線的數目。
▇ 建立無線使用者環境
無線通道模型取決於都卜勒頻率在使環境內的頻率，都卜勒頻率取決於無線的數率及載波頻率當作輸入及產生一個瑞雷(Rayleigh)漸褪，產生一個U-型的都卜勒頻譜。
▇ 建立環境參數及網路地理結構
影響無線位置系統的效能的是環境型態(諸如：較差的都會區、一般都會區、次都會區或郊區)。在較差的都會區環境型態可能有許多的障礙物及建築物，非視線範圍(NLOS)效應扮演在估算範圍內系統參數的精確度。此模擬器應調整通道的模型來捕捉這些建築物所引起的效應(陰影漸退及非視線範圍效應)。

關鍵字

時間 ； 空間 ； 都卜勒 ； 超寬頻系統 ； 多路徑漸褪頻道

並列摘要

In this thesis, we cope with the fundamental mathematical and physical problems of the space-time-Doppler UWB system design for fading channels: multi-input multi-output (MIMO) wireless communication with adaptive filtering. The estimation algorithm from equalizer providing an accurate parameters estimate is investigated. UWB radio is a fast emerging technology with uniquely attractively features inviting major advances in wireless communications, networking, radar, imaging, and positioning systems. By its rule-making proposal in 2002, the Federal Communications Commission (FCC) in the United States essentially unleashed huge new bandwidth (3.6-10.6 GHz) at the noise floor, where UWB radios overlaying coexistence RF systems cerate using low-power ultra-short information bearing pulses. Right now, there are three basic types of UWB: multiband OFDM UWB (MB-OFDM UWB), impulse-UWB (I-UWB), and direct sequence UWB (DS-UWB). We focus on I-UWB and MB-OFDM-UWB, and compare their performance.
A simple means for spreading the spectrum of low duty cycle pulse trains is time hopping (TH), with pulse position modulation (PPM) for data modulation at the rate of many pulses per data bit. The main contribution of this thesis for I-UWB is the design of leading edge detectors, coherent correlation detector (CCD), and pilot performance enhancement compared with different Rayleigh and Ricean fading conditions. For MB-OFDM UWB, we have considered the performance analysis and design criteria of MIMO OFDM UWB systems for high data-rate wireless transmission. The signal processing of frame detection, time synchronization, frequency synchronization, channel estimation, synchronization tracking using pilot subcarriers and 2-D MIMO detection algorithms is discussed. The main contributions of this thesis are
1) Compared with receiver employing the Maximum Likelihood (ML) detector, the receiver employing a low-complexity linear Minimum Mean Square Error (MMSE) demodulator can perform a limited performance loss in spatially uncorrelated channels.
2) Due to the operations of spreading and dispreading combined with MMSE-based frequency domain equalization, the adverse effects of the low-SNR subcarriers on the average BER performance are potentially improved. This is a direct consequence of spreading, because even if the signal corresponding to a specific chip is obliterated by a deep frequency domain channel fade, after dispreading these effects are spread over the Walsh-Hadamard Transform (WHT) length. Hence there is a high chance of still recovering all the partially affected subcarrier symbols without errors.
3) As a test case, the OFDM-based 200 Mb/s MB-UWB network (IEEE 802.15.3a) are considered, but the simulation results are shown above section.
4) The simulation channel can be easily applied to NOS and NLOS situation with WHT transformation from Simulink model.
The fading channels of UWB with low/high signal to noise ratio (SNR), multipath effects, and multiuser interference may introduce large errors in location. The location engine performs the following tasks:
█ Data fusion techniques:
Different data fusion techniques are implemented using Time Of Arrival (TOA), Angle Of Arrival (AOA), or a combination of both.
█ Channel modeling:
A multipath, multiuser channel environment is created that models path loss, shadowing, Rayleigh fading, and Doppler frequency effects.
█ Parameter estimation:
TOA and AOA estimation algorithms are implemented as part of the location finding engine. Different variations of algorithms are implemented for performance and comparison purposes.
█ Configuring the physical layer for different wireless networks.
Among the programmable parameters are spreading factor, packet size, training length, constellation type, modulation technique, carrier frequency, level of transmitted signal power, and the number of antennas at the transmitter for both sides.
█ Configuring the mobile user conditions.
The wireless channel models depend on the Doppler frequencies present in the environment. The Doppler frequency depends on the mobile speed and carrier frequencies as input and generates a Rayleigh fading channel with the U-shape Doppler spectrum.
█ Configuring the environmental parameters and network geographical structure.
One of the factors affecting the performance of the wireless location system is the environment type (e.g., bad urban, urban, suburban, or rural area). For example, in a bad urban area with many blocking objects and buildings, non-line of sight (NLOS) effects plays an important role in the estimation accuracy.

並列關鍵字

Time ； Space ； Doppler ； Ultrawideband System ； Multipath Fading Channel

參考文獻

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