行政院國家科學委員會專題研究計畫 期中進度報告
具高展頻效率新世代分碼多工無線通訊系統之研究(2/3)
計畫類別： 個別型計畫 計畫編號： NSC92-2213-E-110-015- 執行期間： 92 年 08 月 01 日至 93 年 07 月 31 日 執行單位： 國立中山大學通訊工程研究所 計畫主持人： 陳曉華 報告類型： 精簡報告 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： 本計畫可公開查詢中 華 民 國 93 年 5 月 10 日
行政院國家科學委員會補助專題研究計畫
□ 成 果 報 告 ■ 期中進度報告具高展頻效率新世代分碼多工無線通訊系統之研究(2/3)
計畫類別：■ 個別型計畫 □ 整合型計畫
計畫編號：NSC 92－2213－E－110－015
執行期間：92 年 8 月 1 日至 93 年 7 月 31 日
計畫主持人：陳曉華
共同主持人：無
計畫參與人員：
葉育清、趙乾堯、林玉信、林哲民、顏健益、蔡政憲
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：國立中山大學 通訊工程研究所
中 華 民 國 93 年 5 月 10 日
行政院國家科學委員會專題研究計畫成果報告
具高展頻效率新世代分碼多工無線通訊系統之研究(2/3)
(精簡報告)
計畫編號：
NSC 92-2213-E-110-015
執行期限：
92 年 8 月 1 日至 93 年 7 月 31 日
主持人：陳曉華 中山大學通訊工程研究所
一、中文摘要 第三代行動通訊系統很快地將在全球投入 布署。第三代行動通訊技術從概念到商用 系統的日漸成熟使我們有必要考慮未來可 能的新世代行動通訊系統的架構。相比於 目前即將使用的第三代行動通訊系統，新 世代行動通訊系統應能提供更快的資料傳 輸速度。顯然，可借由二種不同的方式來 達到這個目的。最簡單的方法是直接將更 寬的頻帶分配給新世代行動通訊系統，以 提供高速資料傳送速度。但是，其條件是 存在足夠多的空閑頻寬以供其使用。另外 一個方法是採用具更高頻帶利用效率的無 線分碼多工擷取技術，以提供新世代行動 通訊系統所應具有的高速資料傳送功能。 很明顯，第一種方法的實施有賴於採用更 高的載波頻率，例如在 10-30 GHz，以便能 利用那里大量的空閑頻段以供 B3G 系統來 使用。但是，可用來作為地面行動通訊系 統載波頻率的最高頻率仍受到行動通道各 種傳播特性之限制：即頻率不能太高以至 於其傳播特性將明顯地受到气候條件之影 響。因此，相比之下，較為現實的方法應 該是靠提昇分碼多工擷取技術之頻帶利用 效率，以便在一定的頻段內能盡可能提高 其資料傳播速度。 傳統的 2G 及 3G 行動通訊系統，像 IS-95、W-CDMA 和 cdma2000 等，其工作 原理都採用類似的展頻方式，即對每一資 料位元均利用一個完整的展頻碼來作直接 序列展頻，以完成擴展頻率及分碼多工之 功效。這種傳統的展頻技術能利用一個簡 單的展頻調變器(即模二加法器)來完成。但 是，缺點是它的『展頻效率』相當的低。 展頻效率被定義為單位 chip 能傳送的資料 位元數目。低展頻效率等價於低頻帶利用 效率，因為通道中發送訊號之頻帶寬度直 接將由 chip 之時間寬度所決定。所以，2G 及 3G 行動通訊系統之展頻效率僅僅為 1/N bit/chip, 其中 N 為所採用之展頻碼的長 度。由此可見，目前的 2G 及 3G 行動通訊 系統仍有相當大的『展頻效率』改善空間。 這也給了我們一個用新的、具更高展頻效 率的 CDMA 架構，來實現 B3G 行動通訊 系統之機會。 本 計 劃 之重 點 是提 出及 研 究新型 的 CDMA 系統架構，並以提昇現有第二、三 代行動通訊系統之『展頻效率』為訴求。 我們將著重於更新現有 2G 及 3G 行動通訊 系統中所採用的展頻技術，以便將其『展 頻效率』提高到接近一之水準，從而帶動 提昇全系統的頻帶利用效率，以支持要比 2G 及 3G 行動通訊系統高得多的資料傳送 速率。為達到這一目的，目前有幾種實現 方案在考慮之中。其中之一是使用完成互 補 碼 來 將 系 統 的 展 頻 效 率 提 高 到 1/M bit/chip 的水準，其中 M 為所採用的一組完 成互補碼中子碼的個數。一般地，M 的值 遠小於 N。配合使用一套新型的展頻技 術，『交錯重疊展頻技術』，採用完成互補 碼的分碼多工系統能為同步的下鏈及非同 步上璉均能提供一個理想的無多用戶干撓 (MAI-free)的工作條件，從而有可能大大提 高整個系統的容量。另一個正在考慮的方 案是採用『理想循環移位碼』(perfect cyclic shifted code)來實現一個分碼多工系統。由 於『理想循環移位碼』具有其獨特優良的 自相關函數及相關函數互相關函數，從而 保証了採用該碼的分碼多工系統能在一個 大致同步的通道中確保無多用戶干撓及多 路徑干撓存在。因為一個原本非同步的上 璉也可借用一套閉環及開環的同步控制系統來實現上璉的精確同步，正如已經在 TD-SCDMA 系統做的那樣，採用『理想循 環移位碼』的分碼多工系統將是一個十分 具有吸引力的方案。另一個可能的方案是 採用在 LAS-CDMA 標準中提出的 LS 展頻 碼。它甚至不需要一套閉環及開環的上璉 同步控制系統也能在同步及非同步的通道 中實現無多用戶干撓及多路徑干撓的環 境。 在本計劃的研究過程中，我們將考慮 到多種行動通訊系統實際工作條件，例如 通道中的衰減現象、雜訊、展頻處理增益 的大小、多用戶干撓、多重路徑效應及非 理想之上璉同步控制等，以保証由本子計 劃得到的研究結果能為今後 B3G CDMA 之實際系統研發作參考。 關鍵詞：CDMA、B3G 行動通訊系統、互 補正交碼、展頻效率、無多用戶干撓運作、 無多路徑干撓運作。 二、緣由與目的
The great success of worldwide 2G mobile communications has a tremendous impact on the today’s life-style of the people around world. In recent years, the voice-oriented services provided by the 2G mobile communication infrastructures in many countries are attracting increasing number of users. In Taiwan, more than 75% population is the subscribers of GSM mobile phone services. More than 200 millions people in China are using mobile phones and each year more than 20 millions people become new subscribers. The increasing trend in the penetration rate is expected to continue, especially in many developing countries.
The triumph of the 2G systems has also paved the way for the deployment of new generation mobile communications currently on the way in many developed countries. In October of 2001, Japan has initiated the world first commercial service of 3G mobile communications based on the W-CDMA technology [1-2], which can deliver various multi-media services on top of existing voice-oriented and slow-rate data services available in the current 2G systems. In Taiwan, the government has closed the bidding process of five 3G licenses recently
and it is expected that the island-wide 3G services will be made ready in 2003, which is in phase with other countries in the world.
The maturing of the 3G mobile communication technologies [1-3][5-13]from their concepts to commercially deliverable systems motivates us to start to work on the
possible architectures for the future
generations of mobile communications
beyond 3G (B3G). Although at the time when this proposal is being written nobody is
very sure what the B3G mobile
communications will look like, what can be sure at this moment is that the systems beyond 3G ought to deliver a much higher data rate than what achievable in currently almost-ready 3G systems. Some people expect that the possible data rate for the 4G systems should be roughly at a range of 10 to 100 Mbps. Bearing this objective in mind, our question is how to guarantee such a high data rate in a highly unpredictable and hostile mobile channels, and what types of air-link architecture are qualified to deliver such a high date rate services.
Considering the constraints on the
available radio spectrum suitable for
terrestrial mobile communications (from a few hundreds MHz to less than 100 GHz), we would like to argue that probably the most relevant and feasible way to achieve such a goal promised by the B3G systems is to work out some enabling technologies capable to improve as much as possible the air-link bandwidth efficiency of the systems. In this proposed research project, we will
tackle this issue comprehensively by
proposing some new CDMA architectures that should be potential for future mobile communications.
It is well known that all current CDMA-based 2G and 3G standards (i.e. IS-95, cdma2000 [3] and W-CDMA [1-2])
use traditional direct-sequence CDMA
techniques based on an identical principle that each bit is spread by one single spreading code comprising N contiguous chips to attain certain processing gain or spreading factor. The bandwidth of all those systems is determined by the chip width of the spreading codes used. Thus, it is natural to define a merit parameter called "spreading
efficiency" (SE) in unit of bit(s) per chip to measure the bandwidth-efficiency of a CDMA system. Therefore, it is clear that the SE's of all conventional CDMA-based mobile communication systems, such as IS-95, cdma2000 and W-CDMA, are equal to 1/N, which is far less than one. This in turn explains why those systems cannot offer a better bandwidth-efficiency.
In recent a few years, we have been working on a possible solution to improve the SE of a CDMA system with the help of a new spreading technique based on complete complementary (CC) codes, taking into account various implementation constraints of a practical CDMA system as follows. Firstly, the new CDMA architecture ought to be technically feasible by currently available digital technology. Secondly, the new system should not introduce too much multiple access interference (MAI) to ensure a higher
capacity potential than that of the
conventional CDMA systems. Thirdly, the proposed system should preferably have an
inherent ability to mitigate multipath
problems in mobile channels. The
multi-carrier CDMA architecture based on orthogonal CC codes is one such proposal [4], which can satisfy all above-mentioned requirements. We have demonstrated in our recently published paper [4] its capability to achieve a high bandwidth-efficiency and low bit error rate owing to its innovative signaling design in both down-link and up-link channels. We have also discussed several peculiarities pertaining to the new architecture in its receiver design. We have shown that a traditional RAKE receiver is no longer useful in the proposed CDMA architecture and a new adaptive recursive filter is particularly introduced to detect signal in multipath environment. In that article, the technical limitations associated with the new system have also been addressed. The MAI-free operation of the CC CDMA architecture in both down-link and up-ink is illustrated in Figures 1 and 2.
三、計畫成果自評
This project is a 3-year project and is still in progress. What we can say about the project
very well. All proposed research items will be covered in the project. We can also expect that the major objectives of this project will be obtained at the end of the execution of this
project. Five SCI papers and three
international conference papers [14-21] have been published and some more are under preparation. One Taiwanese patent [22] has been granted and two patents [23-24]have been submitted for final approval.
As a final remark before ending this report, in the next year or the final year project, we will expect a huge amount of code searching computation task, which requires a great amount of computing power. For this purpose, we will make a grid-computing system by ourselves, using 20 personal computers to work in a parallel way in order to fit our great needs for the code search and optimization program.
Therefore, we sincerely hope that NSC could help us to offer some more equipment funds to allow us to purchase more PCs to formulate such a parallel computing system. NSC has already given us 250,000 NTD for the IT equipment, but it is not enough for making such a grid computing system. We will appreciate it if NSC could offer 150,000 NTD more on top of the 250,000 NTD, such that we can use in total 400,000 NTD to buy 20 PCs for this purpose.
四、參考文獻
[1] ARIB/Japan, "Japan's Proposal for
Candidate Radio Transmission
Technology on IMT-2000: W-CDMA," June 1998.
[2] ETSI/SMG2, "The ETSI UMTS
Terrestrial Radio Access (UTRA)
ITU-R RTT Candidate Submission," June 1998.
[3] TIA/US, "The cdma2000 ITU-R RTT Candidate Submission," June 1998.
[4] HH Chen, Jun-Feng Yeh & Naoki
Seuhiro, A Multi-Carrier CDMA
Architecture Based on Orthogonal
Complementary Codes for New
Generations of Wideband Wireless
10, pp. 126-135, October 2001.
[5] CATT/China, "TD-SCDMA Radio
Transmission Technology for
IMT-2000," June 1998.
[6] CWTS-SWG2, LAS-CDMA, "Physical layer aspects of TD-LAS high speed packet technology," LAS-TR 25.951, V1.0.0, July 2001. [7] http://www.catt.org [8] http://www.3gpp.org [9] http://www.3gpp2.org [10] http://www.etsi.org [11] http://www.arib.org [12] http://www.cwts.org [13] http://www.itu.org
[14] HH Chen, Yu-Ching Yeh, Cheng-Hsiun Tsai and Wen-Hsiang Chang, Uplink Synchronization Control Technique and
Its Environment-Dependent
Performance Analysis, accepted for publication in IEE Electronics Letters. （SCI, 2003-telecommunications）
[15] HH Chen, Yuh-Tyng Wu and
Chien-Yao Chao, Unified approach for BER analysis of a generic multi-code
CDMA with optimized decision
thresholds, vol. 39, No. 22, IEE Electronics Letters, October 30, 2003. （SCI, 2003-telecommunications） [16] HH Chen, Daoben Li and Qi Bi,
Editorial of the Special Issue:
Ultra-Broadband Wireless
Communications for the Future,
Wireless Communications & Mobile Computing (WCMC) Journal, Wiley InterScience, John Wiley & Sons Ltd., vol. 3, Issue. 6, pp. 659-662, September 2003.
[17] HH Chen, Jin-Xiao Lin, Shin-Wei Chu, Chi-Feng Wu & Guo-Sheng Chen, Isotropic Air-Interface Technologies for
Fourth Generation Wireless
Communications, Wireless
Communications & Mobile Computing (WCMC) Journal, Wiley InterScience, John Wiley & Sons Ltd., vol. 3, Issue. 6, pp. 687-704, September 2003.
[18] HH Chen & Jun-Feng Yeh, A
complementary codes based CDMA
architecture for wideband mobile
Internet with high spectral efficiency and exact rate-matching, International
Journal of Communication Systems, John Wiley & Sons Inc., vol. 16, pp.
497-512, 2003. （ SCI,
2001-telecommunications, 38/49）
[19] HH Chen and Hsin-Wei Chiu,
Generation of Perfect Orthogonal
Complementary Codes for their
Applications in Interference-Free
CDMA Systems, accepted for
publication in the Record of PIMRC 04, 15th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications,
05.09.2004-08.09.2004, Barcelona-Spain.
[20] HH Chen, Yu-Ching Yeh, Chien-Yao
Chao and Kuo-Sheng Chen,
Interference-Free CDMA Air-Link
Technology Promising Noise-Limited Performance, Proceedings of IEEE VTC 2003-Fall, Orlando, USA, Oct. 4-9, 2003.
[21] HH Chen, Yu-Ching Yeh, Chien-Yao
Chao, Cheng-Hsiun Tsai and
Wen-Hsiang Chang, Isotropic
air-interface in TD-SCDMA: uplink
synchronization control & its
environment-dependent performance
analysis, Proceedings of IEEE VTC 2003-Fall, Orlando, USA, Oct. 4-9, 2003.
[22] HH Chen, Taiwanese Patent, A
Wideband Multi-carrier Orthogonal
Complementary Coded CDMA
Communication System, filing time: March 2002.
[23] HH Chen, Taiwanese Patent, An
Isotropic Interference-Free CDMA
Communication System, filing time: December 2002.
[24] HH Chen, Taiwanese Patent, An Interference-Free
Super-Complementary Code CDMA Communication System, filing time: April 2003.
+ ++ + + + + + + − − + − + + − + +− +− + + + − + + + + + + − + + + + + − + −+ +−− +− + − −− −−− + + + − Local flock + −+ + correlators → → → → → →0 0 0 0 0 (Autocorrelation peak) →0 →0 →0 →0 →0 →0 →0 →0 8 − + − + + − + + + + + + + + + + + − + + − + − + − + + + + − + −+ + + −+ + + − + + + − −− −− − + − −− + −− + − + 1 f f2
+
+
0 A A1}
MAI free{
{
Spreading modulated signal for user 1 Spreading modulated signal for user 2The interference to the desired bit In-phase autocorrelation peak (desired bit)
The chips not involved
×A0 ×B0 ×B1 ×A1 Local correlator + + +− + +− + 0 A
{
Signature code for user 1
+ +−+
+−−−
{
Signature code for user 2 1 A 0 B 1 B 21 b 21 b 11 b 11 b
Figure 1: Down-link signal reception in a 2-user CDMA system in a MAI-AWGM channel using CC codes of length L=4, where the user 1 is the intended one
+ + + + + + + + + − − +− + + − + + − +− + + + − + + + + + + − 0 11 A b × b11×A1 0 21 B b × b21×B1 + + + − Local flock + −+ + correlators − + − + + − + + + + + + + + + + + − + + − + − + →0 →0 →0 →0 →0 + − −− −−− − −− −− +− + + + + − + −+ + + − +− + + + −− + − + − − − − − + − + + + −+ + + + − + − + + + 1 f f2
+
+
0 A A1 (Autocorrelation peak) 8 → → → → → →0 0 0 0 0 →0}
MAI free + +−+ + −−−{
Signature code for user 2 + + +− + + − + 0 A{
Signature code for user 1 1 A B1 0 BThe interference to the desired bit In-phase autocorrelation peak (desired bit)
The chips not involved
c T 2 c T 2 Local correlator
{
{
Spreading modulated signal for user 1 Spreading modulated signal for user 2Figure 2: Up-link signal reception in a 2-user CDMA system in a MAI-AWGM channel using CC codes of length L=4, where the user 1 is the intended one
