本文將包括四個部分，第一部份是我在德國的生活，第二部分是我所遭遇與觀察到關於台灣與德國之間的一些文化差異，第三部份則是我與德國學術單位合作的研究，最後是心得與建議。
在德國的生活:
會申請這次的暑期實習主要是在偶然的機會看到相關的資訊，由於正巧要申請其他的獎學金，也就一並準備資料，沒想到很幸運能獲得錄取。其實從出發前的單位分發到到達德國的基本認識，DAAD的Knapp女士就已經幫我們坐了充分的準備，基本上我僅僅只需要將生活必需品備妥而已。到德國真正的挑戰是從波昂離開抵達我的實習單位: 杜易斯堡-艾森大學(Duisburg-Essen University)電信工程系才開始。由於實習單位離杜易斯堡火車站(Duisburg Hbf)不遠，我是事先被通知可以直接步行過去，然而到底人生地不熟，出了車站看著地圖真的感覺一陣盲然，這時候一位熱心的德國老太太主動詢問我是否需要幫助，不過因為他不懂英文，比手畫腳一會兒後，就表示要我跟著她走，就這樣我就順利的到達我實習的單位。到實習單位後，因為要安置我的行李，稍微了解隔天要做的準備工作後，我又自己拉著行李去找我的宿舍，也再次在路上迷路了，這時候一位熱心的研究生適時出現，主動地帶我到我宿舍附近的道路上，並且詳細的跟我描述方向。非常感謝那位熱心的老太太還有研究生，讓我在第一天就能順利的安頓下來。當天下午我又去附近的超級市場購買一些日常用品等等，並且在附近走走了解一下週遭環境，打通電話向Knapp女士報平安。那天晚上其實有點兒失眠，對未來將近三個月在陌生環境生活有些不安。但是，之後的日子證明，這項計劃真的是一項很棒的體驗，不僅僅讓我認識很多朋友，包括一起參加這個計劃的八位夥伴，還有德國系上的同學，熱情招待我們的中國大陸同學，一同合作研究的德國同事，還有在火車上、在旅途中無意間相遇的外國朋友們。也讓我對德國這個在世界經濟、政治與科技工業扮演重要角色的大國有更深的認識，確實有滿多地方值得台灣來借鏡。這將近三個月的生活中，除了週一到週五的實習之外，最重要的部分就是旅行。就我自己來說，足跡最東到達德勒斯登(Dresdem)，最南到德國第一高峰楚格峰，最西到荷蘭的鹿特丹，其他還去過鈕倫堡、柏林、波茲坦、阿姆斯特丹、露迪斯海姆、德勒斯登、科隆與波昂，以及魯爾區的波鴻，多特蒙。每次的旅行都充滿讓人驚喜的意外，例如去露迪斯海姆的火車上，就有熱情的德國旅客，拿出他們的法國葡萄酒與我們共飲；在楚格峰山腳下的小鎮參與他們啤酒節的慶祝活動; 在德勒斯登正巧遇到慶祝建城八百週年紀念，煙火、演唱會和市集讓整個城市成為不夜城。柏林的同性戀遊行，在阿姆斯特丹騎自行車，在多特蒙看德語發音的電影，第一次在河邊過夜，第一次在德國人家作客用餐，第一場的德國甲組職業球賽，第一次受邀參加德國朋友的生日派對，以及德國的食物，豬腳，麵包，香腸，雖然不習慣，但是都是道地的德國味。而去楚格峰的那星期，從出發到到達，含轉車一共坐了11個小時的火車，從星期五晚上出發，直到星期六清晨才到達，現在回想起來，那股拼勁還真是很不可思議。在旅行的過程中，最讓我欽佩的是德國交通的四通發達，特別是德國鐵路。這應該是在德國旅行之後，所有旅客都會同意的(但是誤點也滿常見的)。不僅中、大城市之間有鐵路連接，小城或是小鎮也有電車可以到達，一般有點規模的城市之內都會有輕軌電車。就算沒電車，也會有公共汽車可以到達。相較於台灣，除了台北交通網路比較具有規模之外，其他地區的大眾交通真的需要再多多加強了！因為減少汽機車的使用，不僅節約能源、減少污染，也舒緩塞車問題、提昇都市的生活品質。我在杜易斯堡就發現，即便它是德國第十一大城，沒見過上班時間塞車現象，空氣也依然清新。
我對德國的一些觀察:
一個有趣的例子，就可以看出東方與西方一些基本看法的不同。在杜易斯堡的街頭，有滿多讓女性照太陽光線的店。收費不便宜，三十分鐘要四歐元(太陽光是免費)。上門光顧的女性就是希望能將自己原本的白色膚色曬成褐色，聽說SKII化妝品在德國還有一種產品可以幫助女生皮膚變深。主要原因是德國男生覺得褐色皮膚的女生給人很健康的感覺，我辦公室的同事也說他是喜歡褐色皮膚的女生。東方國家對於女性美的感覺就很不相同，普遍都是覺得越白越美。此外，透過在學校的實習，我觀察到一些德國與台灣文化上的一些相異之處。首先，該系的研究生可以說是相當忙碌。我自然也不例外。我到達的第二天，我的同事Alex就分配給我很明確的任務。之後每星期我們會一同討論進度。並且構思該嘗試的方法。在實習單位我觀察到的是﹕每一位新手的研究，都是由一位系裡資深的成員來負責，這些資深的成員一般都是系裡的博士生或是擔任專門職務擁有博士學位的研究員。系上只有一位教授，但是我自己沒有機會跟教授直接作研究，而是由Alex來帶領我。系上工作的時間是早上八點到下午六點，工時長達十小時，這讓我滿意外的.一般來說，下午快六點就陸陸續續有人離開，但是還是有人會留到更晚。週末是不可能有人來工作，因為所有出路口都會上鎖。第二個我注意到的是系裡的研究題目多是與產業界合作的計劃，合作的公司不僅僅德國當地的公司，例如英飛凌、西門子，還有韓國與美國的公司，可以體會該系與產業界密切的合作。另外一點就是德國對博士研究生的觀念與台灣有明顯的不同。德國學制傳統上只有碩士與博士，高中畢業之後進入大學讀五年可以獲得碩士學位，如果申請就讀博士班通過，就等於成為系上的約聘員工之一，除了固定時間上下班，有固定的休假天數，當然還有一份薪水。在交出博士論文之後，即可畢業。所以博士班研究生已經不算是”學生”了。由於台灣的教育制度是仿自美國，博士班研究生其實並沒有這樣的差別。第四點我注意到的就是大學校園觀念是很模糊。在台灣，大學的校園是很明確的，甚至都有圍牆包圍起來方便管理。在北美，例如我去過的皇后大學，校園與周圍的社區是融合的，沒有特別的區隔，然而具體的校園範圍還是存在的。但是在杜易斯堡-艾森大學，可以說是完全沒有校園的概念，所有學校的建築物和設施散布在整個城市，我在該校三個月，偶爾漫步在街道，就會看到一些學校的建築物夾雜在周圍其他樓房之間。當地的學生離開學校建築，就是在附近的餐廳，小吃攤聊天或討論，可以說學生的生活完全是與該城市息息相關。在來的一點則是︰喝啤酒確實是交德國朋友的好方法之一。我與住在同宿舍的德國學生見面往往也只是打聲招呼，同個辦公室工作的德國同事在下班後也幾乎沒什麼交集。然而如果相約一起到酒吧喝點啤酒，或是在像生日派對之類的場合一起喝酒慶祝，是很容易將話題聊開的。感覺平常比較惜字如金的德國朋友，邊喝啤酒邊聊天，似乎變得健談多了。最後一點的觀察是德國人對交友態度的不同。在台灣，我們的生活圈決定了我們的朋友，可能工作，旅遊，進修的朋友都是那幾位熟識的人。但是在我的系上，我的觀察是德國人下班後不太會在另外約同事參與活動。上班的同事是上班的同事，下班後，他們有另一群朋友。上面的觀察或許有點以偏蓋全，還是可以大約感受到東西方文化上明顯的差異。
在德國的研究 :
我在德國研究的主題是:低密度同位檢查碼。這是在通道編碼領域很新的題目。低密度同位檢查碼早在五十年前就被提出，但是因為當時電腦運算能力的不足，一直無法驗證它真正的效能，導致相關的研究者早已遺忘了它。直到1999年一位英國學者重新驗證它的效能，發現它比現知所有的通道編碼方法都更接近薛農極限，引起該領域的震撼。目前，低密度同位檢查碼已經被相當多的通訊標準所使用，我所參考的標準是IEEE 802.16e，也就是簡稱WiMAX的新一代通信標準。在德國的三個月中，我完成了WlMAX使用的低密度同位檢查碼的編碼器與解碼器程式，並且為了實現在數位信號處理器(DSP)上，改以化簡過後的解碼量度來實現解碼演算法，並且解碼過程全部採用定點(fix-point)運算。模擬的結果確實達到Alex對我要求的效能衰減不能大於0.1dB的限制。其中最大的困難時間應該是剛開始的階段，原因是對我與對Alex來說，低密度同位檢查碼都是新的題目，我們之前都未有深入了解過。Alex幫我從圖書館借一些相關的書籍，我也利用網際網路和電子資料庫找尋能幫助我入門的論文，並且開始寫模擬程式。先從解碼器、編碼器開始，再修改資料結構使得解碼器、編碼器都可以以更快速度運算。之後加入interleaver與de-interleaver。再之後是加入更多調變方式，進而是新的通道模型。緩慢但是謹慎的打造各個模組，也在實習結束前完成所有預期的工作。我也將這段期間完成的工作，寫成一份科技報告。對我來說，我沒有預期我可以完成，但是在第一個解碼器完成之後，一切就步入軌道，甚至超出我預期。Alex每週固定的討論對我很有幫助，雖然他不是實質的直接幫我解決問題，但是往往可以給我一些我沒想到的方向去嘗試。此外，以往在台灣的研究我會太依賴老師，可是在德國我被逼著必須自己獨立解決，對我是很好的啟發和鼓舞，因為我發現我是有能力這麼做的，也確實做到了。在WiMAX的低密度同位檢查碼有個特性(或問題)就是碼長不很長，最長是2304位元，這跟學理討論的碼動輒兩三萬位元的碼長非常的不同，導致它的一些優異特點沒有被明顯的表現出來。也就有比較Turbo Codes跟低密度同位檢查碼的必要。原本我也要進一步比較使用Turbo Code和使用低密度同位檢查碼在效能上，實作複雜度，解碼運算複雜度的種種不同，供之後研究生在做Software define radio相關研究的參考。但是因為時間的不足，最後只好決定將這部分帶回台灣繼續進行，作為我與Alex合作的題目。
心得與建議 :
對於這次的實習，我獲益良多。一方便是有機會能與德國一樣從事相關題目的研究生交流，交換彼此在這項研究上的心得﹔另一方面，也實際體驗德國大學如何訓練研究生。德國大學對研究生的態度和訓練方法，確實是跟台灣很不一樣﹔此外，也親身體驗了德國的文化，很多對德國一些固有的想法也被打破，例如﹕台灣人會說德國火車從不誤點的，事實上火車誤點在德國不會不常見﹔以前也一直以為豬腳是全德國都有的在地食物，但是其實豬腳只是德國巴伐利亞地區的特產。但是也有些對德國人固有印象真實的呈現，很多德國人做事的認真和一絲不苟，真的讓人佩服。唯一對這項計劃的建議，可能是加強宣傳。這真是很棒的暑期交流計劃，但是聽說德國方面申請很熱烈，台灣方面申請人數卻是不多。或許是因為台灣博士班研究生對這項計劃不了解所以裹足不前所致，如果能有更多的文宣或是說明，也許能讓更多人認識這個計劃也申請這個計劃。
There are four parts in this report. In the first part, I begin by the life during my internship. The second part is on the differences of cultures between Chinese people and Germany people. The third part is about my research cooperating with German university. The final part is summary and my suggestion for this exchange program.
The life during my internship:
After I got the information of this program, I decided to apply for it in this year. Before leaving Taiwan, I didn’t prepare anything because Ms. Knapp helped us to arrange almost everything to go to Germany. I only have to prepare some necessaries. The real challenge was from the time we left Bonn to the university we had our internship there. Due to the school building I would work in is very closed to Duisburg Hbf, the member of the university told me that I can go to there by foot about 10 minutes. However, it was the first time I visit this city, so it was very difficult to find the correct way. I was luck that I met an old lady in street who can’t speak English want to lead me to the building and I arrived the building finally. After having some introduction to the department, I went to my dormitory with help of a strange graduate student who also studied in Duisburg-Essen University. I acknowledge the old lady and the graduate student who helped me in the first day in Duisburg. Actually, in the first day I stayed in Duisburg, I worried about how I can to be used to the life there. However, the following days shows that this program is so great and I shouldn’t worried. The greatest thing in this program is that I made so many friends in Germany. During the three months, I worked on the Monday to Friday and traveled on the weekends. I had been some cities of Germany, for example: Dresdem, Zugspitze, Nürnberg, Berlin, Potsdam, Bochum, Dortmund, Rudesheim, Köln and Bonn. And I also went to the cities of Netherland, including Amsterdam Delft, Utrecht and Rotterdam. Every travel gave me much surprise. For example: in the train which went to Rudesheim, we met some German traveler shared their wine with us; we took part in the beer festival of a small town beside Zugspitze.; we took part in the 800th anniversary of Dresdem. Firework, pop music concert and night market made the whole people in Dresdem didn’t sleep at that night. We took part in the march of gays and lesbians in Berlin; we took the bike in Amsterdam; we watched our first movie, “Superman” which speak German, in Germany. Besides, it is first time I sleep beside the riverside, the first time I have a dinner with a Germany family, the first time I go to the German soccer game. Of course we also taste Germany foods, including German breads, sausages and pettitoes. After so many travels in Germany, the most impressive thing to me is German railway. German cites connect by railway. Although small cities don’t have Deutschen Bahn, they have S-Bahn. In some big cities, they also have U-Bahn inside them. In Taiwan, only Taipei zone has enough transportation system and other cities and town don’t have good public transportation. I think Taiwan’s government should push the public transportation systems right now because of so many advantages. Public transportation systems can reduce the requests of petroleum, reduce the air pollution, and keep off traffic jam.
Some observation of mine in Germany:
First, let me give an interesting example. In Germany, cities have many “Sonne Studios”, ladies go to the shops to make their skin brown. I think it is not cheap because it need 4 euros per 30 minutes, and sunny is free. I also heard that a make-up company, SK-II, has a product in Germany that can make ladies’ skin brown easier. The reason why females in Germany wish their skin brown is because people there thinks that female is more beautiful if her skin is not too white. My coworkers in Germany also think so. I think the viewpoint about the beauty is very different to Chinese culture. Most Chinese people think that female is more beautiful if her skin more white. By this example, I think it can easy to see that there are some very big differences between Chinese culture and Germany culture.Besides, during the internship in university, I can easier to observe Germany life. I note that the graduate students in the department are very busy. And so did I there. In the second day I went to the department, the professor told me that it is better I can arrive at the office at 8:00am and leave the office at 6:00pm. The work hour is about 10 hours. Actually, many graduate students took more than 10 hours a day. Second, the viewpoint of Ph.D. student in Germany is very different to Taiwan. To German, Ph.D. student hold a position in their department. So, a Ph.D. student is actually not a “student” but a “employee”. Ph.D. students in Germany have salary every month and need do some work for the department. Besides, they also have regular vacations. However, Taiwan’s Ph.D. students surely are “student”, it is no problem.In Germany, many universities don’t have their campus. For example, the buildings of Duisburg-Essen University distributes over the whole city. But in Taiwan, campus of a university has a definite area, even most of university campuses are surrounded by walls. Because of the indefinite property of the campus, the life of students who studying in Duisburg-Essen University has very closed relationship with the cities, Duisburg and Essen. After leaving class, students go to the coffee shop or bar to chat or discuss with their classmates.I think to drink beer is a very good way to make friends with German people. Maybe the daily life is busy, I don’t have many chance to talk to my dormmates and coworkers. Usually, when I met them, we just said hello to each other, then we did our job respective. But, drinking beer with Germans in bar and restaurant can makes almost all Germans chat lively.The last point I note is that the German way of making friends. In Taiwan, the circle of our life decides which friends we make. Taiwanese usually work, travel and study with the same group of people. However, Germany people make friends in different ways. For example, based on my observation, my coworkers in the department don’t have activities after leaving office. They have activities with other friends. A German may go fishing with one group of his friends, but travel with another group of his friends.
My research in Germany:
My research topic in Germany is low-density parity-check (LDPC) block codes. It is a very new topic of coding theory. The publication of Claude Shannon's 1948 paper, “A mathematical theory of communication”, marked the beginning of coding theory. In his paper, Shannon established that every communication channel has associated with it a number called the channel capacity. While Shannon's noisy channel coding theorem establishes the existence of capacity approaching codes, it provides no explicit guidance as to how the codes should be chosen, nor how messages can be recovered from the noise-corrupted channel output. The challenges to modern communications are to design sets of suitably distinct codewords close to the Shannon limit, and to devise methods for extracting estimates of transmitted messages from the output of a noise-contaminated channel, and to do so without excessive decoder complexity. Low-density parity-check codes are capable of performance very close to the Shannon limit when appropriately decoded with soft iterative decoding algorithm. Soft iterative decoders for LDPC codes make essential use of graphs to represent codes, passing probabilistic messages along the edges of the graph. The use of graphs for iterative decoding can be traced to Gallager, although for over 30 years barely a handful of researchers pursued the consequences of Gallager's work. This situation changed dramatically with the independent rediscovery of LDPC codes by several researchers in the mid-1990s, and graph-based representations of codes are now an integral feature in the development of both the theoretical understanding and implementation of iterative decoders. During the three months internship, I finish the soft iteration decoder and implementation of fast encoding algorithm of LDPC codes in IEEE 802.16e standards. Besides, we want to execute our codec in digital signal processor, so we need to modify the original floating decoding to fix-point decoding. Indeed, our simulations show that the gap between the original version and modified version is under 0.1 dB.The most difficult time during my internship is the beginning time because both Alex, a German Ph.D. student who worked with me, and I don’t have any experience about LDPC codes implementation. Alex helped me to find some useful books from library and I searched some tutorial paper from Internet. After reading those reference data carefully and work hard on the program of sum-product algorithm, I finished the first version of the decoder. Based on this decoder, I can start to writer and verify the other part of simulation program I constructed. Although Alex didn’t help me to solve my problems directly, he discusses with me about me difficulty one time per week. The discussion is useful to me because Alex can give me some idea I never thought.
Summary and Suggestion:
During the three months internship, I study the knowledge of LDPC codes and related papers. Besides, I finish the encoder, interleaver, deinterleaver, SUI channel model and some different decoding methods of LDPC codes in IEEE 802.16e. I also compare the performances of those decoding algorithm by simulations. There are several works we can do in the future. 1. To integrate LDPC codes simulation with OFMD modulation under SUI fading channel models.2. To compare the complexity-reduction decoder to the sum-product decoding under SUI fading channels.3. To derivate the decoding metric of LDPC codes with imperfect channel state information (CSI) or without CSI. This summer program is so good to me. If there is anything I should suggestion for this program, I think it should be let everyone who fit the quality to apply for this program to know it. I know that there are many Germany students apply for it, but there are not many Taiwan Ph.D. student are interesting in it. The reason maybe is Taiwan’s students don’t understand this program enough and have too many questions on it. If NSC can provide more documents to describe the program, Taiwan’s students can know it more and maybe want to apply for this program.
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