高效能被動式超高頻無線射頻辨識系統設計與研究(II)

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行政院國家科學委員會專題研究計畫成果報告

高效能被動式超高頻無線射頻辨識系統設計與研究(II) 研究成果報告(精簡版)

計畫類別：個別型

計畫編號： NSC 97-2221-E-011-002-

執行期間： 97 年 08 月 01 日至 98 年 07 月 31 日執行單位：國立臺灣科技大學電機工程系

計畫主持人：劉馨勤

計畫參與人員：碩士班研究生-兼任助理人員：林旺旗碩士班研究生-兼任助理人員：林銘昱博士班研究生-兼任助理人員：花盟昌

報告附件：出席國際會議研究心得報告及發表論文

處理方式：本計畫涉及專利或其他智慧財產權，2 年後可公開查詢

中華民國 98 年 10 月 28 日

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行政院國家科學委員會補助專題研究計畫 ■ 成果報告

□期中進度報告高效能被動式超高頻無線射頻辨識系統設計與研究（II）

計畫類別：

■

個別型計畫 □ 整合型計畫計畫編號：NSC 97-2221-E-011 -002－

執行期間： 97 年 8 月 1 日至 98 年 7 月 31 日

計畫主持人：劉馨勤共同主持人：

計畫參與人員：花盟昌台灣科技大學電機工程所林旺旗台灣科技大學電機工程所林銘昱台灣科技大學電機工程所

成果報告類型(依經費核定清單規定繳交)：

■

精簡報告 □完整報告

本成果報告包括以下應繳交之附件：

□赴國外出差或研習心得報告一份

□赴大陸地區出差或研習心得報告一份

■

出席國際學術會議心得報告及發表之論文各一份

□國際合作研究計畫國外研究報告書一份

處理方式：除產學合作研究計畫、提升產業技術及人才培育研究計畫、

列管計畫及下列情形者外，得立即公開查詢

■

涉及專利或其他智慧財產權，□一年

■

二年後可公開查詢

執行單位：台灣科技大學

附件一

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一、中文摘要及關鍵詞

最近射頻辨識(RFID)系統由於其廣泛的應用潛力受到了許多注意。由於其標籤成本低、體積小、而且感測距離長，超高頻被動式射頻辨識系統特別受到 EPCglobal 組織的提倡。特別值得注意的是 2005 年 EPCglobal 發佈了「Gen2」超高頻被動式射頻辨識系統規格，其規格也於 2006 年被 ISO 所採納。

由於 Gen2 標籤從 Gen2 射頻辨識讀取器發射的連續波取得它的電源，並以此連續波作為它的調變反向散射信號的載波，因此其可讀取範圍受到高傳播路徑損失的限制。而除自由空間衰減之外，多重路徑衰落也經常導致讀取問題。經鏈接預算分析證明，標籤接收的電力是決定讀取距離的因素。而因為被動式標籤沒有外部電源不能運作，所以標籤電源問題是被動式射頻辨識系統中一個不可避免的問題。此外，標籤衝突問題是另一個影響標籤識別的正確性及效率的因素。再者，在 Gen2 標準之「密集讀取器模式」中存在的讀取器衝突問題，也可能嚴重地降低系統效能。目前已有一些研究使用不同的方法來解決這些問題，然而尚未有研究將這些問題做一個整體的考量。

在本連續性計劃中，我們提出一個高性能被動式射頻辨識系統。此系統能有效地解決標籤電源問題、標籤衝突問題以及讀取器衝突問題。我們計畫使用差異性結合技術改善標籤電源問題、分碼多重擷取技術搭配空間區分多重擷取技術避免標籤衝突問題、及結合適應性波束合成與跨階層技術防止讀取器衝突問題。除理論分析之外，我們使用軟體定義無線電架構，實現一個讀取器，以實際驗證計劃所提出的方法。本報告為前二年計畫累積之成果報告。

關鍵詞：射頻辨識、衝突防止、軟體定義無線電、分碼多重擷取、空間區分多重擷取、差異性結合、跨階層技術

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二、英文摘要及關鍵詞

The radio frequency identification (RFID) systems have recently received extensive attention due to its potential in pervasive applications. Owing to the low cost, small size, long accessible range tags, the UHF passive RFID system is especially promoted by EPCglobal. The

“Gen2” specification for UHF passive RFID system released by EPCglobal in 2005, which has also been adopted by ISO in 2006, is extremely noteworthy.

Because a Gen2 tag derives its power from the continuous waves (CW) emitted by a Gen2 RFID reader and uses the CW as the carrier of its modulated backscatter signals, the readable range is hence limited due to the large propagation loss. Besides the free space attenuation, the multipath fading effect can often result in readability problems. The link budget analysis validates that the readable distance is determined by the power received by a tag. Since a passive tag cannot operate without external power source, the tag power problem is an inevitable problem in a passive RFID system. Moreover, the tag collision problem is another factor that affects the correctness and efficiency of tag identification. In addition, there exists a reader collision problem in the “dense reader mode” specified in Gen2, which can also severely degrade the system performance.

There are a few researches using various approaches to alleviate these problems. However, none of them consider these problems as a whole.

In this continuous project, we propose a high performance passive RFID system, which can effectively mitigate the tag power problem, the tag collision problem, and the reader collision problem. We plan to use diversity combining technique to alleviate the tag power problem, CDMA+SDMA techniques to avoid the tag collisions, and the adaptive beamforming incorporating with cross layer techniques to prevent the reader collision problem. In addition to theoretical analysis, we implement a reader using software defined radio architecture to verify the proposed scheme empirically. This report presents the first two year research outcome of this project.

Keywords: RFID, anti-collision, software defined radio, CDMA, SDMA, diversity combining cross layer.

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三、計畫緣由與目的：

射頻辨識（RFID），隨著技術進步及廣泛的應用，近年來受到很多的矚目，並已進行實際運用。如同許多其他先進通訊技術，射頻辨識技術亦歷經長期研究，而於近年蓬勃發展。射頻辨識系統依其操作頻段，可略區分為以下不同類別並依其特性各有不同應用；低頻射頻辨識系統(LF RFID)（125 KHz 到 134.2 KHz)，高頻射頻辨識系統(HF RFID) (13.56 MHz)，超高頻射頻辨識系統(UHF RFID) (860 MHz 到 960 MHz)，及微波 RFID (2.45 GHz) 等。

射頻辨識系統通常由標籤（tag or transponder）及讀取器（reader or interrogator）

所組成。每個標籤至少具有一顆晶片及天線，其功能為儲存資料、接收讀取器指令（reader command）及發射回應訊號。而依照標籤之電源供應，又可區分為主動式標籤（active tag）、半主動式標籤（semi-active tag）、被動式標籤（passive tag）等類別。其中被動式標籤因不需電池，所以有體積較小、價格便宜、不需維護、及使用壽命較長等優點，

因此特別受到重視。目前高頻被動射頻辨識標籤(HF passive RFID tag)已被廣泛使用於悠遊卡、晶片信用卡等。而超高頻被動射頻辨識標籤(UHF passive RFID tag)，因為讀取距離較高頻被動射頻辨識標籤遠，因此適用於供應鍊（supply chain）管理、車輛管制、

及室內定位等應用，其他可能應用亦隨著該技術發展而日新月異。目前高頻被動射頻辨識標籤發展及應用已臻成熟；然而超高頻被動射頻辨識系統，因全球化標準之訂定[1, 2]

較晚，且其多樣性功能及應用有可能於技術成熟後取代低頻被動射頻辨識系統，而吸引了許多研究者的投入。

因超高頻被動射頻辨識標籤（以下簡稱標籤）不具電池，必須仰賴其天線之感應電流以提供其晶片操作電力，因此超高頻被動射頻辨識系統之讀取器（以下簡稱讀取器），除負責發射讀取器指令及接收標籤之回應外，同時必須發射連續波以提供標籤之操作電力。

標籤除汲取讀取器所發射之連續波作為電源之外，並利用它作為其回應之反向散射信號（backscattered signal）載波。囿於電力限制，目前標籤之調變信號多使用振幅位移鍵(Amplitude Shift Keying, ASK)調變、二位元相位位移鍵(Binary Phase Shift Keying, BPSK)調變等調變訊號[3, 4]。同時因標籤無法進行載波感測多重擷取（Carrier Sense Multiple Access, CSMA），因此目前被動式標籤多使用較簡易之防衝突演算法

（Anti-collision Algorithm），如二元樹演算法（Binary Tree Algorithm）及時槽阿羅哈

（Slotted ALOHA，S-ALOHA）演算法等[5]。為提升標籤之辨識率，於[1]中，FM0 碼及 Miller 碼被使用來降低標籤反向散射信號之接收位元錯誤率（BER）[3, 6]。目前針對標籤方面已有許多天線設計及降低晶片耗電量之相關研究[7, 10-19]。然而，囿於有限、不連續且不穩定之電源限制，被動式標籤無法進行複雜運算，因此對於通訊品質之改進相當有限。反觀讀取器則無此方面問題，因此，許多複雜先進之通訊技術較易由讀取器端實現，並藉此改善射頻辨識系統之通訊品質。本計劃亦希望能藉由研製高性能讀取器，來解決目前超高頻被動式射頻辨識系統所遭遇之問題。

經由系統效能評估之相關文獻[7-10]得知，目前射頻辨識系統所遭遇主要問題可分為以下數項：標籤電源問題（或讀取距離問題）、標籤衝突（tag collision）問題、及讀取器衝突（reader collision）問題等。因為被動式標籤本身並無電池，必須仰賴讀取器提供其電源，使得標籤電源問題成為系統能否運作之主要關鍵[8, 11]。在[10]中指出，讀取器與標籤通訊的限制在於標籤之晶片靈敏度（chip sensitivity），亦即所需最小

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有效電源（minimum effective power），遠低於讀取器之接收靈敏度；因此限制了被動式標籤之讀取距離。要解決標籤電源問題，可分別由標籤端及讀取器方面分別進行。在標籤方面，晶片的改良可提高其靈敏度；此外增加其天線之增益，改變其天線之極化，

及改善晶片與天線之阻抗匹配，皆能有效改善此項問題[4]。在讀取器方面，增加讀取器發射功率及其天線之指向性，是直接有效的辦法。然而，囿於法規之最大有效等向輻射功率(EIRP) 限制，無限制的增加其發射功率的方案，並不可行。

對於發射功率在行進路徑上的衰減，許多文獻皆以自由空間路徑衰減（free space path loss)之 Friis 公式，來計算讀取器發射功率與標籤接收功率之間的關係，因此認為標籤所接受之功率，與讀取器與標籤之間的距離平方成反比或類似關係（由環境及介質決定）。然而在實際應用中，考慮多重路徑（multipath）之影響，實際標籤接收功率，

還要考慮衰落通道（fading channel）的問題。於[9]之量測及模擬顯示，多重路徑衰落通道的確影響了標籤之接收功率。此項結果也與申請人所完成的研究相符[12]。在[9]

中之量測，同時顯示使用兩支不同位置的發射天線（於 953MHz 附近頻率，相隔 11cm），

所產生之空間差異性（space diversity），能有效舒緩衰落問題。目前已有部分新型讀取器[13]採用多支發射天線來解決該項問題。而申請人亦於[14, 15]中，提出一種新型分離式讀取器設計，以解決此項問題。

另一個射頻辨識系統所遭遇的問題為標籤衝突問題；一個讀取器所涵蓋的範圍中常同時存在多個標籤。對同一讀取器指令，同時可能有多個標籤回應，因此造成了標籤衝突問題。當多個標籤同時回應時，其回應訊號可能互相干擾（ tag-to-tag interference），因而導致讀取器無法辨識或辨識錯誤；或辨識其中之一，而忽略了其它的標籤，導致標籤遺失（tag missing/lost）問題。目前解決標籤衝突問題，已有相當多的研究。其中[5]對現行射頻辨識系統標準中的標籤防衝突演算法，及讀取器防衝突演算法作了詳細的整理；一般而言，於射頻辨識系統中，阿羅哈類演算法效率優於樹狀結構類演算法。以目前效能最好的 Gen2 標準[1]為例，規範訂定的正是一種動態訊框時槽阿羅哈（adaptive framed slotted ALOHA）演算法，稱之為Ｑ演算法（Q-algorithm）。

於[16]中，申請人也對此演算法，藉由標籤數目估測結合連續衝突/閒置時槽偵測（burst collision/idle slot detection），提出效能改進辦法。該演算法效能，有賴於正確標籤數目估測。最近，於[17]中，則提出另一種標籤標籤數目估測方法；但其缺點為複雜度甚高，且當標籤數目不多時，該方法未必實用。綜觀現有之標籤防衝突演算法，皆為分時多重擷取（Time Division Multiple Access, TDMA）方式，使得其性能受到侷限。因此，

若要能大幅提升其系統效能，勢必要如同其他先進通訊系統，結合其他不同多重擷取方法。

於[18, 19]研究中分別提出以分碼多重擷取（Code Division Multiple Access, CDMA）技術，結合分時多重擷取技術，以提升標籤之讀取效能。在[20]研究中，則首度提出利用智慧型天線來解決標籤衝突問題。此研究探討以多重輸入多重輸出

（Multiple Input Multiple Output, MIMO），及適應性波束合成（adaptive beamforming）

技術，來提昇系統效能。不過，[20]之研究僅以過於簡化之自由度（degree of freedom, DOF）增加觀念，來探討並模擬標籤防衝突問題，無法確實的估測實際系統效能。

另一方面，在被動式射頻辨識系統實際應用時，勢必有多部讀取器同時在同一環境中使用。因此在[1]中特別將密集讀取器模式（dense reader mode）列入規範。研究顯示，當多部讀取器同時運行時會造成兩種問題，分別為，讀取器與標籤干擾

（reader-to-tag interference）問題，及讀取器間衝突（reader collision）問題。目前讀取器與標籤干擾問題，已於[1]中，因標籤規範改進、及密集讀取器模式制定而受到改善。

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然而於密集讀取器模式中，仍存在不同讀取器於相同覆蓋範圍，同時傳送讀取器指令，

造成標籤無法識別讀取器指令之讀取器干擾問題；或當讀取器跳頻（frequency hopping）

落入同頻道所造成的同通道干擾（Co-Channel Interference, CCI）。

綜合以上所述，可以得知標籤電源問題、標籤衝突問題、及讀取器衝突問題仍為目前射頻辨識系統研究之主要方向。鑒於標籤之低功能性（low functionality），解決這些問題的方式，必須考慮從讀取器端著手。其中[9] 提出以多支發射天線產生之空間差異性，來解決多重路徑干擾所造成的標籤電源問題。在[20]中則提出利用智慧型天線（包括多重輸入多重輸出及適應性波束合成）來解決標籤衝突問題，但是其分析及模擬過於簡化。除此之外，在提升標籤讀取效能方面，於[18, 19]提出結合分碼多重擷取技術的方法，應可大幅提升讀取效率，但於文獻中並未考慮標籤之耗電限制問題。

於讀取器衝突問題方面，大多著重於降低讀取器之間的相互干擾，及減少讀取器之發射功率。雖然目前尚未有文獻使用智慧型天線來解決讀取器衝突問題，但智慧型天線於降低無線通訊干擾，及有效減少發射功率的成效已被証實。因此，智慧型天線之適應性波束合成，及其特有的空間區分多重擷取（space division multiple access, SDMA）

技術，相信亦可有助於解決讀取器衝突問題及標籤衝突問題。因此，本計劃希望研製具智慧型天線之高效能讀取器，搭配低複雜度低耗電性之分碼多重擷取射頻辨識標籤

（CDMA-RFID tag）設計，以提升超高頻被動式射頻辨識系統效能。並且因為超高頻被動式射頻辨識系統為一新興技術，目前國內尚缺乏該項技術人才及其中關鍵技術；本計劃也提出使用軟體無線電技術實現智慧型天線讀取器的目標，以實際了解開發讀取器之關鍵問題，並可用以驗證研究所提出之創新通訊方法與協定。

本計劃原為三年期之研究計畫，計畫的目標為建立一個高效能的超高頻被動式射頻辨識系統。我們已於前二年開發完整系統模擬，並探究使用 CDMA 技術來解決標籤衝突問題之可能性。同時，我們並使用軟體無線電技術實現一個符合實驗需求之讀取器。此外，利用[15]之多載波技術，我們並開發出一種新型之電池輔助標籤。

四、研究方法：

由文獻研究可以得知，目前超高頻被動式射頻辨識系統所遭遇之問題主要為：標籤電源問題、標籤衝突問題、及讀取器衝突問題。由於被動式射頻辨識標籤無法進行複雜運算，

所以我們嘗詴設計高效能讀取器，以解決以上三項問題。然而，要能確切實際的了解這三項問題，除了進行實地實驗之外，建立一個完整的系統模擬，更是一個有效的驗證方法。

此一完整系統模擬，更可對本計劃之後續研究，進行可靠而有效的評估。

在此系統模擬中，如圖 1 所示，我們將以讀取器、通道模擬、及標籤模擬等三部分，

分別進行。

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圖 1 RFID 系統模擬示意圖

由於本系統牽涉射頻傳播（RF propagation）、微波電路、及基頻處理等部份。目前尚未有單一模擬軟體能簡單有效的進行此類模擬。就射頻通道模擬及微波電路模擬而言，

以 Agilent 之 ADS（Advanced Design System）模擬軟體較為擅長；而基頻處理及演算法運算方面，則以 Mathworks 之 Simulink 模擬軟體較佔優勢。於此計劃中，我們結合兩套模擬軟體的優點來完成系統模擬。

鑒於目前標籤衝突問題的解決，大多使用 TDMA 方法，無論使用樹狀搜尋或時槽阿羅哈演算法，其效能提升都相當有限。如欲大幅提升標籤讀取效能，勢必要引入其他多重接取方法。於本計劃中，我們嘗詴使用 CDMA 技術，配合先前研究的改良式時槽阿羅哈演算法[16]，來提升標籤讀取效率。

於被動式射頻辨識系統，除模擬外，實驗驗證才能真正檢視其成果。目前我們已自行開發讀取器，可讀取一般 Gen2 標籤。鑒於許多無線收發機的設計，多採用軟體無線電架構，部分新型讀取器亦採用軟體無線電架構[13]，因此，我們也使用該架構來縮短開發時程。

五、結果與討論

於前兩年計畫執行後，我們已完成：完整系統模擬、使用 CDMA 技術解決標籤衝突問題、使用軟體無線電技術實現符合實驗需求之讀取器、及使用多載波技術開發電池輔助標籤。以下就各項工作分別報告執行進度與成果。

1. 完整系統模擬：目前已利用 Agilent ADS 軟體結合 Matlab 模組，完成 Gen2 RFID 讀取機及被動式標籤之系統模擬（如圖 2 所示），可用以模擬讀取機指令及標籤反射訊號（如圖 3 所示）。

Transmitter for R->T link Receiver for T->R link

Multipath fading

channel Tag

Tag

Tag Multipath fading

channel

Multipath fading channel

R->T Link

T->R Link R->T->R Link Reader

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讀取機(Reader) 標籤(Tag) 標籤 RF部分

標籤 DSP部分

讀取機 TX部分讀取機 RX部分

讀取機(Reader) 標籤(Tag)

標籤 RF部分

標籤 DSP部分

讀取機 TX部分讀取機 RX部分

圖 2 Gen2 RFID 系統模擬

圖 3 ADS Gen2 RFID 系統模擬結果

2. 使用 CDMA 技術解決標籤衝突問題：鑑於 Gen2 標籤之鏈結時程參數(link timing parameter)T 存在相當的容忍值，因而可能導致標籤至讀取器(T-R)為非同步通訊。₁ 經實驗量測驗證亦證實存在此現象[21]。因此我們必須將 T-R 通訊視為非同步通訊；此外因標籤之回應訊號強弱受距離、天線方向影響而產生甚大差異，故遠近效應(near-far effect)亦是不可忽視之因素。有鑑於此，我們提出應用霍夫曼序列 (Huffman sequence)當作標籤回應之展頻碼，以同時克服非同步通訊及遠近效應之因素。該研究成果已發表於 IOT2008 研討會。該研討會錄取率為 25%，筆者論文有幸列於兩篇錄取之 RFID 技術論文之一。該論文並已收錄於 Springer LNCS 論文集。

3. 使用軟體無線電技術實現符合實驗需求之讀取器：目前我們使用 GNU radio 之 USRP 平台及 Lyrtech 之 SFFSDR 平台進行 Gen2 RFID 讀取器開發，並已獲得相當進展。其中 SFFSDR 平台已可完成完整 Gen2 通訊，如圖 4 所示。

0.5 1.0 1.5 2.0 2.5

0.0 3.0

0.05 0.10 0.15

0.00 0.20

time, msec mag(mv)

Tag backscatter Query

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圖 4 使用 SFFSDR 平台開發之讀取器通訊過程；顯示讀取器已能獲取標籤之 EPC 碼

4. 使用多載波技術開發電池輔助標籤:目前被動式標籤受限讀取距離過短而半被動式標籤或主動式標籤受限於電池使用年限；且不同類標籤需使用不同通訊協定，

故需使用不同讀取器。本研究利用多載波技術開發出電池輔助標籤，當使用電池時其讀取較被動式標籤延伸約一倍；而電池耗盡時，該標籤仍可被正常讀取如同一般被動式標籤。且該標籤通訊協定與一般 Gen2 標籤相同，無需特殊讀取器即可應用。該研究已發表於 IEEE Transaction on Microwave Theory and

Technology[22](全文詳見附件一)。圖 5 為所開發之電池輔助標籤原型。

圖 5 使用多載波技術開發電池輔助標籤原型

六、成果自評：

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本計畫已完成了原訂之目標，並分別於理論突破及具體實現兩方面獲得如預期之成果。參與之學生除了發表論文之外，也藉由實際之讀取器開發對 RFID 系統獲得深刻了解。

本計畫除所提及論文發表之外，並據研究成果進行五項國內外專利申請。相信藉由本計畫之研究可對國內之 RFID 相關研究及產業能有所貢獻，也對後續之延伸研究奠定了良好的基礎。

七、參考文獻：

[1] "Class 1 Generation 2 UHF Air Interface Protocol Standard Version 1.1.0," EPCglobal, 2007.

[2] "18000-6 Part 6 – Parameters for Air Interface Communications at 860 to 930 MHz,"

International Organization for Standardization, 2004.

[3] Y. Han, Q. Li, and H. Min, "System Modeling and Simulation of RFID," 2004.

[4] G. De Vita and G. Iannaccone, "Design criteria for the RF section of UHF and microwave passive RFID transponders," Microwave Theory and Techniques, IEEE Transactions on, vol. 53, pp. 2978-2990, 2005.

[5] D. Shih, P. Sun, D. Yen, and S. Huang, "Taxonomy and survey of RFID anti-collision protocols," Computer communications, vol. 29, pp. 2150-2166, 2006.

[6] M. Simon and D. Divsalar, "Some interesting observations for certain line codes with application to RFID," Communications, IEEE Transactions on, vol. 54, pp. 583-586, 2006.

[7] O. Technologies, "The RFID Gen 2 Tag Benchmark," ODIN Technologies Laboratories 2006.

[8] N. Adair, "Radio Frequency Identification (RFID) Power Budgets for Packaging Applications," Available: www.iopp.org/pages/index.cfm?pageid=1154, 11-30-05.

[9] J. Mitsugi, "UHF Band RFID Readability and Fading Measurements in Practical Propagation Environment," Available:

http://www.autoidlabs.org/uploads/media/AUTOIDLABS-WP-HARDWARE-015.pdf, 2005.

[10] P. V. Nikitin and K. V. S. Rao, "Performance limitations of passive UHF RFID systems,"

in Antennas and Propagation Society International Symposium 2006, IEEE, 2006, pp.

1011-1014.

[11] "Monza: Gen 2 tag chip," Available: http://www.impinj.com, 2006.

[12] "配電設備利用射頻辨識(RFID)技術進行資料傳輸之研究結案報告," 台灣電力股份有限公司 2006 年 11 月.

[13] "Speedway: Gen 2 UHF Reader," Available: http://www.impinj.com, 2006.

[14] H.-C. Liu, Y.-T. Chen, and W.-S. Tzeng, "A Multi-Carrier UHF Passive RFID System " in 2007 International Symposium on Applications and the Internet - Workshop on Networked RFID (SAINT 2007), Hiroshima, Japan, Jan. 2007.

[15] H.-C. Liu, Y.-F. Chen, and Y.-T. Chen, "A Frequency Diverse Gen2 RFID System with Isolated Continuous Wave Emitters," JOURNAL OF NETWORKS, vol. 2, pp. 54-60, Sept.

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2007.

[16] L.-C. Wang and H.-C. Liu, "A Novel Anti-Collision Algorithm for EPC Gen2 RFID Systems," in 3rd International Symposium on Wireless Communications Systems (ISWCS’06), Valencia, Spain, Sept. 5-8, 2006.

[17] K. Murali and N. Thyaga, "Fast and reliable estimation schemes in RFID systems," in Proceedings of the 12th annual international conference on Mobile computing and networking Los Angeles, CA, USA: ACM Press, 2006.

[18] Y. FUKUMIZU, S. OHNO, M. NAGATA, and K. TAKI, "Communication Scheme for a Highly Collision-Resistive RFID System " IEICE-Tran Fund Elec, Comm & Comp Sci, vol. E89-A, pp. 408-415, 2006.

[19] A. Rohatgi and G. D. Durgin, "Implementation and Applications of an Anti-Collision Differential-Offset Spread Spectrum RFID System," Available:

http://www.propagation.gatech.edu/Archive/PG_CP_060710_AR/PG_CP_060710_AR.P DF 2006.

[20] L. Jeongkeun, K. Taekyoung, C. Yanghee, K. D. Sajal, and K. Kyung-ah, "Analysis of RFID anti-collision algorithms using smart antennas," in Proceedings of the 2nd

international conference on Embedded networked sensor systems Baltimore, MD, USA:

ACM Press, 2004.

[21] Hsin-Chin Liu and Xin-Can Guo,"A Passive UHF RFID System with Huffman Sequence Spreading Backscatter Signals," Internet of Things 2008, Zurich, Switzerland, Mar. 26-28, 2008.

[22] Hsin-Chin Liu, Meng-Chang Hua, Chih-Guo Peng, and Jhen-Peng Ciou, “A Novel Battery-Assisted Class-1 Generation-2 Radio Frequency Identification Tag Design,”

IEEE Transactions on Microwave Theory and Techniques, vol. 57, no. 5, pp. 1388-1397, May 2009.

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附件一

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1388 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 57, NO. 5, MAY 2009

A Novel Battery-Assisted Class-1 Generation-2 RF Identification Tag Design

Hsin-Chin Liu, Member, IEEE, Meng-Chang Hua, Chih-Guo Peng, and Jhen-Peng Ciou

Abstract—This paper presents a new design of an enhanced pas- sive tag (EPT) that can extend the read range of an EPCglobal Class-1 Generation-2 tag by attaching a battery-assisted circuit (BAC) to the tag integrated circuit. The BAC generates a low-power unmodulated continuous wave with frequency outside the tag oper- ating band to supply additional power to the tag. Empirical results demonstrate that a prototype EPT has a much longer read range and is more resistant to multipath fading than a regular Class-1 Generation-2 tag. Unlike a semipassive tag that depends on its local battery to work, a powerless EPT can function as a regular Class-1 Generation-2 tag. In other words, an EPT with a charged battery is similar to a semipassive tag; after the EPT runs out of its bat- tery power, it behaves as a regular Class-1 Generation-2 tag. Note that whether the EPT is powered or not, it is fully compatible with EPCglobal Class-1 Generation-2 specification.

Index Terms—Battery assisted, EPCGlobal, multipath fading, passive tag, read range, RF identification (RFID), ultra high fre- quency (UHF).

I. INTRODUCTION

T

HE RF identification (RFID) is a promising technology toward the future of internet of things. A variety of RFID systems have been deployed to various applications based on their distinctive demands. In general, RFID tags (transponders) are usually categorized into three types according to their power source: passive, semipassive, and active. A passive tag harvests its power from an incident radio wave to provide its operating power, and uses the incident radio wave as its modulated backscatter signal (MBS) carrier. Such a passive tag is defined as a Class-1 tag (identity tag) or a Class-2 tag (higher functionality tag) according to the tag class definition of EPCglobal.¹A semipassive tag has a local battery to provide its operating power. However, like a passive tag, it communicates passively and uses an incident radio wave as its MBS carrier.

Such a semipassive tag is also called a Class-3 tag (battery-assisted passive tag) . An active tag uses its local battery to drive its circuitry to transmit its signals, which is very similar to a conventional bidirectional radio communication device. In

Manuscript received January 29, 2008; revised December 08, 2008. First published April 07, 2009; current version published May 06, 2009. This work was supported in part by the National Science Council of Taiwan under Grant NSC 97-2221-E-011-002.

The authors are with the Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (e-mail:

hcliu@mail.ntust.edu.tw; M9607313@mail.ntust.edu.tw; spopo316@yahoo.

com.tw; M9507334@mail.ntust.edu.tw).

Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TMTT.2009.2017319

1EPCglobal tag class structure, 2007.

the EPCglobal tag class structure, an active tag is defined as a Class-4 tag.

Due to the cost concern, passive tags are presently extensively used in diverse applications. In general, a passive UHF tag using radiative coupling has a longer read range (the maximum stable readable distance from tag to reader) than a passive HF tag using an inductive coupling, which is very attractive in many applications requiring larger reader coverage. In particular, EPCglobal announced a standard of Class-1 tags in 2005 as “Class-1 Gen- eration-2 UHF Air Interface Protocol Standard v. 1.0.9” [2], which was later adopted as ISO 18000-6 part C [3]. In 2006, a revision of the standard named “Class-1 Generation-2 UHF Air Interface Protocol Standard v. 1.1.0” [4] was also disclosed.

Up to now, there are millions of Class-1 Generation-2 (C1G2) tags (following standards [2]–[4]) in the market already. Due to the huge market, this emergent technology has drawn intensive research attention.

A C1G2 tag does not require a local battery, and hence, has a longer lifespan than a semipassive or an active tag. How- ever, because of relying on the power of an incident radio wave, the strength of the tag power source varies significantly in different environments. In general, the power consumption of a typical state-of-the-art C1G2 tag integrated circuit (IC) is be- tween 10–30 W. Taking the power harvester efficiency into account, a minimal power requirement of a C1G2 tag is around 10 dBm [1]. Owing to the path loss, the read range of a C1G2 tag for a reader with 1-W effective isotropic radiated power (EIRP) is usually limited to 3 m. Moreover, the received power of a tag can also easily fall below its minimum power requirement due to the multipath fading [5]–[7], which results in an un- stable tag read range problem. The multipath fading in a passive RFID system can affect the read range of a tag in the forward (reader-to-tag) link and the reverse (tag-to-reader) link. How- ever, based on [1] and [8], the link budget in the forward link is the main factor that determines the tag read range. Conse- quently, it is a stringent challenge to extend the forward-link- limited range in a passive ultra-high-frequency (UHF) RFID system.

There are two possible approaches to overcome the range limit in the forward link; one is to decrease the minimal power requirement of a passive tag, and the other is to increase the received power of a passive tag. For the former approach, there have been some progresses in reducing the tag IC power consumption [9]. However, the range limit problem has not yet been completely solved. For the latter approach, increasing the reader transmission power seems like a simple solution. In reality, however, it is impracticable due to health considerations and regu- lation constraints.

Authorized licensed use limited to: National Taiwan Univ of Science and Technology. Downloaded on October 25, 2009 at 21:59 from IEEE Xplore. Restrictions apply.

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LIU et al.: NOVEL BATTERY-ASSISTED CLASS-1 GENERATION-2 RFID TAG DESIGN 1389

Fig. 1. Architecture of a typical C1G2 tag.

In this study, we propose an enhanced passive tag (EPT) by using a battery-assisted circuit (BAC), which provides the tag IC a portion of operating power to extend the forward-link-limited range of a C1G2 tag. Since an EPT requires less power from an incident radio wave, the read range of the EPT is much longer than that of a regular C1G2 tag with the same reader transmission power. An EPT uses a commercial C1G2 IC and is fully compatible with the Class-1 Generation-2 standard [2]–[4]. In addition, an EPT can function as a regular C1G2 tag without a battery as well. Consequently, the life span of an EPT can be as long as a regular passive RFID tag.

This paper is organized as follows. Section II introduces the design principles of an EPT. Section III presents experimental results of a prototype EPT. Section IV provides the conclusions of this study.

II. DESIGNPRINCIPLES OF ANEPT

As depicted in Fig. 1, a typical C1G2 RFID IC comprises five basic elements: a power harvester, a demodulator, a modulator, a logical controller, and an EEPROM. The power harvester extracts the power from an incident radio wave and con- verts the RF power into dc power to supply the power demand of the tag IC; the demodulator is usually an envelope detector, which is responsible to demodulate received reader commands from a reader; oppositely, the modulator is responsible to return the tag response to the reader by backscattering its MBS.

The logical controller is the core of the tag IC, which decodes a reader command and decides the corresponding response according to the Generation-2 air interface protocol [2]–[4]. The tag then backscatters its MBS using the unmodulated continuous wave (CW) from the reader as its carrier. The EEPROM is the memory where the tag ID and other information are stored in.

In order to function normally, a C1G2 tag relies on a sufficient and stable power supply from the power harvester circuitry. Al- though the power harvester circuitry is designed to endure a temporary loss of RF signals, it is unable to resist a slow deep multipath fading. To alleviate this problem, we have proposed a system that utilizes multiple unmodulated CWs with different frequencies to illuminate a passive tag simultaneously, as shown in Fig. 2 [10], [11]. In [11], besides a reader, isolated continuous wave emitters (CWEs) are deployed close to tags so that the tags can obtain the power of the unmodulated CW emitted from their

Fig. 2. Passive UHF RFID system comprises a reader and CWEs. The passive tags (shown as small squares) obtain their power from the reader and CWE simultaneously.

Fig. 3. Architecture of an EPT.

proximate CWEs. Hence, the tags can reduce their dependence of the power from the reader; it is noteworthy that the frequency of the unmodulated CW from a CWE needs to be apart from the frequency of reader signals to prevent reader command distor- tion [11]. Although the system is fully compatible with C1G2 tags, it could be spectrum inefficient because a CWE uses an additional frequency besides the reader signal.

The EPT design is based on the idea of simultaneously pro- viding multiple unmodulated CWs to a tag from different frequencies. Unlike the RFID system with isolated CWEs in [11], an EPT integrates with a CWE. In an EPT, the CWE is replaced with a BAC that generates a fixed frequency unmodulated CW.

The diagram of the EPT is illustrated in Fig. 3. The BAC comprises three parts: an oscillator that generates a single tone unmodulated CW, a battery as the power source of the oscillator, and a transition connecting outputs of the BAC to the RF inputs of the tag IC. The transition produces a phase reverse signal at outputs (depicted as C1 and C2 in Fig. 3) of the BAC. Compared with a regular C1G2 tag, the EPT requires less reader power because of the power from the BAC. Therefore, the read range of the EPT can be longer than a regular C1G2 tag. On the other hand, unlike a commercial semipassive tag that requires a local battery to work, an EPT does not totally depend on the power from its BAC. Consequently, an EPT can function as a regular C1G2 tag without a battery if it can extract sufficient power from the reader signal.

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Unlike in [11], where CWEs occupy some spectra in the RFID operating band, a BAC is directly attached to an or- dinary C1G2 tag in this paper. Therefore the occupancy of additional spectra in the RFID operation band is avoided.

The optimal output power of the battery-assisted circuit that leads to a maximum read range is also derived in this paper.

Since the operating frequency of the BAC is not within the operating band of the tag antenna, a low tag antenna gain in this frequency can be designed, which implies the radiation in the operating frequency of the BAC could be low enough to satisfy a required local regulatory. Moreover, the proposed design can be applied to a low-cost C1G2 commercial tag IC without any modification, i.e., the EPT is fully compatible with the standardized communication protocol of present C1G2 tag. In future applications, the proposed design provides a tag manufacturer an alternative choice to produce a regular C1G2 tag or an EPT tag using the same tag IC.

Although the concept of an EPT is simple, the frequency and the power of its BAC must be selected carefully.

A. BAC Operating Frequency

The frequency of the oscillator in the BAC must be chosen based on three considerations.

First, since the purpose of the BAC is to supply tag required power through the RF inputs of tag IC, the frequency of the oscillator must fall in the frequency range where the power harvester can successfully extract the signal power.

Second, because the outputs of the BAC are connected to the tag antenna, the radiation from the antenna in the corresponding frequency must be considered. The radiation power is desired to be as small as possible to prevent the electromagnetic interference (EMI) problem and the battery power waste.

Third, as discussed in [11], the frequency of the unmodulated CW from the BAC must not be too close to the carrier frequency of the reader signal to prevent envelope detection errors in a reader command.

In our prototype EPTs, the frequency of the oscillator is selected around 800 MHz, which satisfies the three considerations above. Based on our charge pump simulations, an 800-MHz unmodulated CW can successfully provide a sufficient voltage to activate the tag IC as a 900-MHz unmodulated CW does.

Moreover, with a 11.94-dBm 800-MHz unmodulated CW (at the output of the oscillator), the strongest radiation power measured by a standard half-wavelength dipole antenna at 1 m away from an EPT is lower than 50 dBm, which is a relatively weak signal. In addition, the prototype EPTs can successfully respond to a standard Query command from a commercial reader and various modified Query commands generated by an Agilent E4438C vector signal generator, which demonstrates that the 800-MHz unmodulated CW does not interfere the envelope detector of the tag IC.

B. BAC Output Power

The BAC output power is also an important factor that determines the performance of an EPT. As mentioned before, the purpose of the BAC is to provide an additional power source to a C1G2 tag so that the tag has a longer read range and is less af- fected by multipath fading effects. One may think that an EPT

Fig. 4. T period and T period in a Query command and the corresponding tag reply.

Fig. 5. From [2], modulation depth calculation of an ASK modulated reader command.

tag can act as a semipassive tag if its BAC output power satisfies the power requirement of its tag IC. Unfortunately, it is not true due to the difficulty of reader command demodulation, as explained below.

In order to activate an EPT, the tag minimum power requirement must be satisfied. In an EPT, the tag IC can harvest a reader signal power and its BAC output power simultaneously.

The actual power transferred into the tag IC from the BAC can be defined as .

In order to analyze the performance of an EPT, we divide one reader command transmission into two stages: the actual reader command stage with s, and the unmodulated CW stage with s. The two stages are illustrated in Fig. 4 using a Query command as the example.

According to [2], the reader average transmitted powers in the period and in the period are different. During the period, the reader sends a reader command to a tag using a pulse-interval encoding (PIE) format [2]. Assuming that the reader sends a reader command using an amplitude-shift keying (ASK) modulation with 100% modulation depth (an on–off keying (OOK) modulated signal), the tag only receives reader power during the on period of a reader command. Note that the modulation depth is defined as , where and are the maximum and minimum amplitudes of the RF envelope indicated in Fig. 5, respectively.

On the other hand, during the period, the reader keeps sending an unmodulated CW as the carrier of tag MBS. Con- sequently, the tag can almost always obtain the reader signal power, except when it backscatters its MBS.

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Let the average power that the tag IC actual harvests from the reader in the period and the period be and , respectively. The average harvested power from the reader can be expressed as

(1)

Let , (1) can be rewritten as

(2) In order to avoid an EPT from a power outage, (3) must be satisfied as follows:

(3) where denotes the minimum power requirement of the tag IC.

In [2], an activated passive tag listens to a received reader command, and then returns its response accordingly. Therefore, it is very important that the tag can demodulate and decode a reader command correctly. In general, a passive tag uses a simple envelope detector circuit to demodulate an ASK modulated reader command [11].

Assuming that the intermodulation due to the unmodulated CW from its BAC is negligible, the amplitude of the RF envelope received by the EPT IC is proportional to the square root of the received RF power. Thus, for an OOK modulated reader command, the minimum amplitude of the RF envelope received by an EPT IC is proportional to the square root of (since only the unmodulated CW from its BAC presents in the off period of a reader command). Without a loss of generality, we can express as

(4) where the constant may vary with different tag designs. Sim- ilarly, the maximum amplitude of the RF envelope received by an EPT IC is approximately equal to

(5) where is the total time of the on periods in . The ratio is introduced because the reader only sends signal during on periods. Note that we assume the constant in (5) is nearly frequency independent for the frequencies of an unmodulated CW from the BAC and the reader signal.

From (4) and (5), the modulation depth of the reader command received by the tag IC can, hence, be written as

(6) where . From (6), the value of can be further derived as

(7) Note that, when increases, decreases accordingly. Let , the minimum value of in (6), denote the minimum

modulation depth of a reader command that can be correctly demodulate by the tag IC. The range of can be obtained as

(8) It is also noteworthy that the ratio may vary with different reader commands. In order to satisfy the modulation depth requirement of each reader command, without changing the value of , the minimum value of ratio in each reader command must be used.

From (3) and (8), we can further specify the range of as (9) As in the proof shown in the Appendix, the optimum that results in the longest read range of the EPT is

(10)

where and

. It is noteworthy that is a ratio that indicates the distribution of reader transmission power. Given a fixed reader transmission power, to lower the value of is to lower the reader transmission power during the period , where only an unmodulated CW is sent by the reader. In other words, by reducing the value of , more power is transmitted in a reader command, which can alleviate the constraint of modulation depth of a received reader command that limits the tag read range, as stated in the Appendix.

By using optimum , the maximum read range of the EPT can be obtained as

(11) Equation (11) represents that increases as decreases.

Considering the path loss only, the maximum read range of a C1G2 tag in the forward link can be written as

. Comparing the two maximum read ranges, we can express the ratio of read range extension as

(12) Based on our measurement results of Texas Instrument (TI) Incorporated C1G2 tags, we have an approximation of

. Considering a regular Query command and 40-kHz FM0 encoding, we have ; Using and indicated in Fig. 4, an approximate ratio is obtained. By substi- tuting these parameters into (12), the maximum ratio of read range extension is about 2.65 for . However, is unrealistic because a reader needs to send an unmodulated CW as the carrier of the tag MBS. Similarly, is also imprac- tical since a reader has to send reader commands as well. Fig. 6 shows the optimum BAC power derived from (12) with various values of and . Likewise, the comparison of maximum EPT read-range extension with various and is illustrated in Fig. 7.

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Fig. 6. Optimum BAC power with various values of modulation depth limit M (which is denotes as M) and reader command power distribution ratio.

Fig. 7. Optimum EPT read range extension with various values of modulation depth limitM (which is denotes as M) and reader command power distribution ratio.

III. EXPERIMENTALRESULTS

A prototype EPT is implemented by connecting a BAC to a regular TI C1G2 tag, as shown in Fig. 8.

Due to the size of the transition, the BAC is about two times larger than a TI C1G2 tag. We use a subminiature A (SMA) connector at the transition input so that the EPT source can be conveniently changed. An EPT source comprising a JTOS-850VW voltage-controlled oscillator (VCO),²peripheral circuit, and two batteries is also shown in Fig. 8.

In order to produce a suitable prototype EPT, further analysis is required. An equivalent circuit of the proposed EPT can be represented as Fig. 9, where , , and denote the com- plex impedance of the tag IC, tag antenna, and added BAC.

is the votage induced in the antenna from received reader power, and is the source provided by a signal generator or an oscillator. Since is dependent to frequency and received power,

2K. Harvey, JTOS-850VW. [Online]. Available: http://www.minicir- cuits.com/

Fig. 8. Photograph of a prototype EPT.

Fig. 9. Equivalent circuit of the proposed EPT.

it is very difficult to determine an optimal impedance of . In order not to interfere with the function of a regular tag, the impedance of is desired to be as large as possible. However, if is too large, the power transfer from to the tag IC will be reduced. Thus, to choose a good impedance is not easy, especially with a variant tag IC impedance .

The reflected signal generation power can be measured by the return loss from the SMA input of a prototype EPT, as shown in Fig. 10. Due to the nonlinearity of the tag IC impedance [12], the measured return loss also varies with different input power.

In addition, the -parameters of the transition using a back-to-back measurement are provided in Fig. 11.

Since the attached BAC may draw some received reader power, the reader signal leakage is measured as shown in Fig. 12. The measurement is done by sending 915-MHz unmodulated CWs with various power levels toward an EPT and a spectrum analyzer is used to measure the output power from the SMA connector of the EPT. The loss of each transition calculated using the measured -parameters has been considered and compensated in the measurement. It is noteworthy that without an IC, the ratio of the power flowing into the BAC to the incident power is almost fixed as 26.6%. However, the power leakage in a prototype EPT with an IC behaves nonlinearly when the tag IC is activated (incident power greater than 8 dBm). Note that the tag IC can be activated at 9 dBm according to [12]. Apparently, when the tag IC is activated,

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Fig. 10. Return loss of EPT.

Fig. 11. S-parameters of the transition used in a prototype EPT.

Fig. 12. Reader power leakage into the transition.

only a small portion of the reader signal flows into the BAC.

Thus, the transition works as a power-dependent filter that can reduce the power leakage when the tag is activated.

Considering the intentional interference cause by the BAC, the radiation power at various directions of the EPT main beam are measured with an 800-MHz–11.94-dBm input power (the

Fig. 13. Radiation power at various directions of the EPT main beam are measured with an 800-MHz–11.94-dBm input power. The radiation powers in three IC statuses are slightly different.

Fig. 14. Antenna power pattern comparison of a prototype EPT and a regular tag.

largest power we used in this study) is shown in Fig. 13, which indicates the actual radiation powers are in the order of W. If an antenna with a lower gain in the BAC operating frequency and high gain in the RFID operating band is used, the intentional radiation power can be further reduced without the tag performance degradation.

Due to the attached BAC, the EPT antenna power pattern slightly changes, as shown in Fig. 14. Although the variation of antenna gains could affect the read range comparison of a zero-powered EPT and a regular C1G2 tag, it does not affect the read range comparison of a powerless EPT and a powered EPT because the same EPT is used.

Since the link budget in the forward link determines the read range of a present C1G2 tag, we measure the maximum distance where the tag can correctly respond to a reader command in our experiments. The reverse link signal strength measurement is, hence, not in the scope of this study. A schematic of our experiment setup is illustrated in Fig. 15. The transmitter in

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Fig. 15. Schematic of the experiment setup; SG denotes a signal generator, which can also be used as the EPT power source. A dipole antenna is used in the measurement in the hallway and the distanceR = 33 cm. Inside a chamber, in order to obtain a more accurate result, a horn antenna as the receiver antenna is used behind the transmitter antenna, i.e.,R > R .

Fig. 15 is emulated by an Agilent E4438C vector signal generator with a horn antenna, which sends a Query command toward the test tag. The receiver antenna in Fig. 15 is connected to an Agilent 89611A vector signal analyzer, which can monitor and record signals from the transmitter and the tag. By using Agi- lent RFID modulation analysis software, the tag response can also be decoded. To measure the maximum read range of an EPT without multipath fading, we perform the test in the Na- tional Taiwan University of Science and Technology (NTUST) microwave anechoic chamber. In order to obtain a more accurate result, a horn antenna as the receiver antenna is used behind the transmitter antenna, i.e., . On the other hand, to verify the performance of an EPT with multipath fading, the EPT is tested at a 230-cm-wide and 270-cm-high concrete hallway in the International Building of NTUST. In the measurement at the hallway, a standard dipole antenna is used as the receiver antenna, which is located 33 cm cm away from the tested tag.

A. Experiment Results in the Chamber

Inside the chamber, we let the transmitter iteratively send Query commands to the test tag with 0.5-W EIRP, and use the receiver close to the tag to record the signals. A photograph of the experiment setup is shown in Fig. 16. The measurements within 100 cm are skipped because there is no access problem.

Snapshots of captured various reader commands and the corresponding tag responses are shown in Figs. 17–19, respectively.

Note that, the “x” in the above figures indicates an FM0 vi- olation (i.e., a phase inversion should have occurred, but did not) [4].

In Fig. 17, an 800-MHz–11.17-dBm unmodulated CW is generated from the BAC, and regular Generation-2 Query commands are sent from the transmitter. The snapshot clearly shows that an EPT replies each reader command with the preambles and the RN16 (16 random bits) using a 40-kHz FM0

Fig. 16. Photograph of the experiment inside the NTUST microwave anechoic chamber.

Fig. 17. Top window shows regular Query commands( = 0:54) and the corresponding EPT responses. The middle window illustrates the MBS clearly.

The decoded MBS (shadowed) comprising the preamble and the RN16 are depicted in the bottom window.

Fig. 18. Top window shows modified Query commands( = 0:43) and the corresponding EPT responses. The middle window illustrates the MBS clearly.

The decoded MBS (shadowed) comprising the preamble and the RN16 are depicted in the bottom window.

encoding MBS. The MBS is decoded by the Agilent RFID modulation analysis software, as illustrated in the bottom window.

Note that the 11.17 dBm is the power of the unmodulated CW

高效能被動式超高頻無線射頻辨識系統設計與研究(II)

行政院國家科學委員會專題研究計畫 成果報告

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□期中進度報告 高效能被動式超高頻無線射頻辨識系統設計與研究（II）

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A Novel Battery-Assisted Class-1 Generation-2 RF Identification Tag Design

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行政院國家科學委員會專題研究計畫成果報告

行政院國家科學委員會補助專題研究計畫 ■ 成果報告

□期中進度報告高效能被動式超高頻無線射頻辨識系統設計與研究（II）