1947，Frequency Reuse

Frequency Reuse is a well known concept that has been applied to wireless systems over the past two decades e.g. in GSM systems. As the name suggests Frequency Reuse implies using the same frequencies over different geographical areas. If we have a 25MHz band then we can have 125 GSM channels and 125*8=1000 time multiplexed users in a given geographical area. Now if we want to increase the number of users we would have to reuse the same frequency band in a geographically separated area. The technique usually adopted is to use a fraction of the total frequency band in each cell such that no two neighbor cells use the same frequency. Typically the frequency band is divided into 3 or 7 cells.

The division of the frequency band in to smaller chunks reduces the system capacity e.g. one cell with 25 MHz bandwidth would have much higher capacity then 7 cells having 3.5 MHz each. To overcome this problem a frequency reuse of 1 has been proposed i.e. each cell has the full system bandwidth (nearly). The problem of co-channel interference at the cell boundaries is resolved by dedicating a small chunk of the available spectrum for the cell edges.

In Soft Frequency Reuse (SFR) the cell area is divided into two regions; a central region where all of the frequency band is available and a cell edge area where only a small fraction of the spectrum is available. The spectrum dedicated for the cell edge may also be used in the central region if it is not being used at the cell edge. The lack of spectrum at the cell edge may result in much reduced Shannon Capacity for that region. This is overcome by allocating high power carriers to the users in this region thus improving the SINR and the Shannon Capacity.

频率复用(Frequency Reuse)是BELL LAB于1947年提出的概念，这个概念是蜂窝移动通信的基石。无线通信刚刚出现的时候采用的是大区制，也就是说一个城市只有一个基站，天线架设在很高的塔上，用很大的功率进行发射。后来随着用户数量的增加，大区制出现了信道不够的问题，频率复用技术就是在这种背景下出现的。由于电磁波在空间传播的衰减特性，一个频率在一个区域使用之后，在离这个区域比较远的地方功率已经衰减了很多，干扰降低到可以接受的程度，于是这个频率就可以再用（reuse）一次，这个就是频率复用的概念。“频率复用”是中文的习惯翻译，已经被广泛接受，其实应该翻译为“频率再用”。与大区制相比，频率复用技术成倍地提高了系统容量，后来所有的移动通信都是基于频率复用技术的蜂窝系统。

蜂窝技术的早期，频率复用因子是比较大的。频率复用因子表示一个频率复用簇（Reuse Cluster）当中的频点的数量。复用因子越大，表示复用距离越大。第一代移动通信（AMPS)的复用因子为9~11，第二代移动通信（GSM)的复用因子为4~7。在CDMA技术出现以后，由于CDMA技术的抗干扰的特性，普遍采用了复用因子为1，也称为普遍频率复用（Universal Frequency Reuse）和同频复用。同频复用被认为是CDMA的技术优势，这个观点在三代移动通信（UMTS, CDMA2000）上得到了加强和广泛传播，并以其巨大的认知惯性延续到了后3G, 如Flarion的Flash OFDM系统就采用了快跳频OFDM和同频复用作为基本技术框架

众所周知，OFDM系统将取代CDMA作为后3G系统的多址技术。OFDM的优势在于它克服了CDMA的自干扰特性，可以实现更高的频谱效率。那么，如何设计OFDM的频率复用方案呢? 一个重要的派别认为OFDM应该做到同频复用，比如快跳频技术就是为了实现同频复用而采用的干扰平均化。也有一些学者认为OFDM也是一种频分多址（FDMA），其频率复用因子应该为3或者更大一些以抵抗同频干扰。不过这样一来，频谱效率就会降低，这也是CDMA支持者对OFDM的重点攻击方向。在这种情况下，一部分学者主张采用折中技术：把频谱分成两个部分，一部分频谱用同频复用，一部分频谱采用复用因子为3，这就是reuse partitioning,或者叫部分频率复用技术（Fractional Frequency Reuse).

软频率复用（Soft Frequency Reuse）是传统频率复用（Frequency Reuse）技术的进一步发展。与传统频率复用技术不同的是，在软频率复用技术当中，一个频率在一个小区当中不再定义为用或者不用，而是用发射功率门限的方式定义该频率在多大程度上被使用，系统的等效频率复用因子可以在1到N之间平滑过渡。软频率复用的主要原则是：

1. 可用频带分成N个部分，对于每个小区，一部分作为主载波，其他作为副载波。主载波的功率门限高于副载波；

2. 相邻小区的主载波不重叠；

3. 主载波可用于整个小区，副载波只用于小区内部

4. 通过调整副载波与主载波的功率门限的比值，可以适应负载在小区内部和小区边缘的分布。

可以看到，在软频率复用方案里面，一个频率不再是被定义为用或者不用，而是用功率门限的形势规定了其在多大程度上被使用，复用因子可以在1~3之间平滑过渡，这就是其得名的由来。与FFR相比，软频率复用没有机械地将频谱割裂成两个部分，而是用功率模版规定了其使用程度，因此无论在小区边缘还是在小区内部，都可以获得更大的带宽和频谱效率。软频率复用的另外一个特点是，通过调整副载波与主载波的功率门限的比值，可以适应负载在小区内部和小区边缘的分布，这也是一个崭新的特性，可以进一步提高频谱效率。

软频率复用是Beyond 3G无线通信系统的关键技术，在3GPP LTE, Wimax系统当中得到广泛应用。

软频率复用技术于2005年由华为公司提出[1]，Wimax论坛2006年发表的技术白皮书[2]当中描述的“Fractional Frequency Reuse”与软频率复用类似。

1930's, the first transatlantic fax services

The 20's and 30's saw the continued advancement and use of the fax machine. In 1922 the first transatlantic fax services were provided by RCA. In 1925 AT&T introduced the wirephoto. RCA followed up with the radiophoto in 1926.

The first major users of fax services were newspapers that transmitted and received photographs from around the world. The next major users were weather services that faxed weather charts around the world. Leading up to World War II, fax services were also used by the military to transmit maps, orders and weather charts.

1901, the communicated signals across the Atlantic Ocean

Guglielmo Marchese Marconi, Italian electrical engineer and Nobel laureate, known as the inventor of the first practical radio-signaling system. He was born in Bologna and educated at the University of Bologna. As early as 1890 he became interested in wireless telegraphy, and by 1895 he had developed apparatus with which he succeeded in sending signals to a point a few kilometers away by means of a directional antenna.

After patenting his system in Great Britain, he formed (1897) Marconi's Wireless Telegraph Company, Ltd., in London. In 1899 he established communication across the English Channel between England and France, and in 1901 he communicated signals across the Atlantic Ocean between Poldhu, in Cornwall, England, and St. John's, in Newfoundland, Canada. His system was soon adopted by the British and Italian navies, and by 1907 had been so much improved that transatlantic wireless telegraph service was established for public use.

Marconi was awarded honors by many countries and received, jointly with the German physicist Karl Ferdinand Braun, the 1909 Nobel Prize in physics for his work in wireless telegraphy. During World War I he was in charge of the Italian wireless service and developed short-wave transmission as a means of secret communication. In the remaining years of his life he experimented with shortwaves and microwaves.

1895年夏天，马可尼又完成了一次非常成功的实验。到了秋天，实验又获得很大的进步。他把一只煤油桶展开，变成一块大铁板，作为发射的天线。把接收机的天线高挂在一棵大树上，用以增加接收的灵敏度。他还改进了洛奇的金属粉末检波器，在玻璃管中加入少量的银粉，与镍粉混合，再把玻璃管中的空气排除掉。这样一来，发射方增大了功率，接收方也增加了灵敏度。他把发射机放在一座山岗的一侧，接收机安放在山岗另一侧的家中。当给他当助手的同伴发送信号时，他守候着的接收机接收到了信号，带动电铃发出了清脆的响声。这响声对他来说比动人的交响乐更悦耳动听。这次实验的距离达到2.7公里。 

1901年马可尼认为实现他的宏伟计划的时机已经成熟，他希望能在大西洋彼岸的美国接受到从英国所发出的电报。他在纽芬兰登岸后，先放起一只用丝竹做成的飞机形状的风筝，却被大风撕裂了。他又放起了一个气球，也被大风刮到海里去了。最后，他放起一只做工很结实的风筝，风筝终于飘上天空。他听了好几小时，急切地盼望能从英国拍来的讯号。就在他要开始灰心丧气的时候，他忽然听见了一点微软的嘀嗒声。然后一声接一声，那就是他们事先商量好了的那种信号——代表字母S的三点。马可尼不禁欣喜万分，很想跑到外面向全世界喊出这一激动人心的消息。然而，他并没有这样做，他怕人们不相信他，所以他一直将这个秘密保守了48小时之久，没有告诉任何人。后来，他鼓起勇气将这件事情的经过拍了10个电报传回伦敦，这一事件立即以其轰动，全世界的各大报纸都报道了这一伟大的新闻，科学界的人大为振奋。

1891, automatic telephone exchange

Strowger's undertaking business was losing clients to a competitor whose telephone-operator wife was intercepting and redirecting everyone who called Strowger - he first conceived his invention in 1888, and patented the automatic telephone exchange in 1891. It is reported that he initially constructed a model of his invention from a round collar box and some straight pins.

1882年2月，阿尔蒙·斯特罗格在堪萨斯州买下了一家殡仪馆。他的第一任妻子去世后他迎娶了第二任妻子，不过1886年他又娶了第三任妻子并在1888年生下了一个儿子。^[3]某日，斯特罗格从报纸上得知自己的一个朋友去世，然而他的亲人却没将这位朋友送到斯特罗格这里。原来电话接线员是他竞争对手的女伴，打给斯特罗格的电话被告知电话繁忙或者是直接转接到了斯特罗格的竞争对手。斯特罗格意识到，要解决这个问题需要发明一种免除人工接线员的自动机器。实际上由于电话时常出问题，他经常向电话公司投诉。斯特罗格利用圆形硬纸盒、针和铅笔制作了一个模型，他在硬纸盒上插了10排10列共100根针，通过控制铅笔的水平以及垂直运动，就可以接通100根针中的一个。^[4]1891年3月10日，斯特罗格获得了编号为447,918的专利。

1880. Gower Bell phone and the telephone network

This set was the first type of telephone used in Spain, Japan, England and other countries in Europe. It replaced the Morse Telegraph and preceded the hand-cranked magneto type telephone. This particular set was donated by the Post Office Telecommunications Museum in London, England to the Bell Telephone Museum in Portland, Oregon. After the dissolving of the Portland Museum it was transferred to the basement of a Bell Telephone building in Eugene, Oregon where it was found years later by its present owner. 

The breakthrough of telephony in Sweden occurred in 1880 the America Bell Company, using American equipment, constructed the first telephone network.

1878, First Commercial Telephone Exchange

On January 28, 1878, the Boardman Building in New Haven became the site of the world’s first commercial telephone exchange, the District Telephone Company of New Haven. The exchange was the brainchild of Civil War veteran and telegraph office manager George Coy in partnership with Herrick Frost and Walter Lewis. 

1876: a revolution in communications --- Bell and his legacy

It is such a common occurrence that no one ever wonders from whence it came. But the telephone has a fascinating story behind it, one that could be entitled. "The Conquest of Solitude." It is the story of Alexander Graham Bell

He was born in Edinburgh, Scotland. in 1847, the son of a man who was consumed,passionately consumed, with the workings of the human voice, how it produced and used, and especially, in teaching the deaf how to use it. For in those days, you see, the deaf lived in permanent solitude. Not only could they no hear, they could not speak. After all, how could they pronounce words, they couldn't hear? Perhaps this obsession of the elder Bell was one of the reasons he marred whom he did. For the woman who would give birth to the inventor of the telephone - was deaf.

Yong Alexander Graham Bell grew up with his father's passions. In 1870, because of poor health, he migrated to Canada. It was not long before his success in teaching the deal to speak brought him to the attention of a wealthy merchant in Boston who had a deaf daughter, Mabel. Would Mr. Bell please teach Mabel how to speak? Yes, he would. And did. And they fell in love. I year later, in 1877, he and Mabel were married. He later became an American citizen.



Alexander Graham Bell died in 1922: Mabel five months later. She loved him that much. His name is likely to live as long as man recalls history. After all, there is this constant reminder of how he brought the human family into closer touch.

The first voice to travel over a wire was even a surprise for its inventor. Alexander Graham Bell. He was experimenting in his laboratory late one night, and quit by accident he succeded in transmitting a message to his assistant in the next room. What Mr. Bell could not know at the time was that nigh in 1876 would mark the stat of a revolution in communications.

1835: The Birth of the Telegraph

回忆起电为人类服务的历程，最早的要算是电报了。有趣的是，发明电报的人不是物理学家，也不是工程师，而是一位画家，他的名字叫塞缪尔•莫尔斯。一个搞美术的，竟成为有线电通信的开创者，这好像有些不可想象，让我们了解一下其中的故事吧！

　　1832年十月一日，一艘名叫“萨丽”号的邮船，满载旅客和邮件，在法国北部的勒阿弗尔港启碇，驶向纽约。   

　 　邮船在浩翰的大西洋上破浪前进，船尾上空飞着海鸥。这种例行的远航大多是枯燥无味的。旅客们或是聊天、下棋，或是在甲板上眺望无边的大海，消磨时光。一 天傍晚，旅客们正在餐厅里准备进餐，被一个年轻旅客的演说吸引住了。这位青年名叫查尔斯•杰克逊，他是美国马萨诸塞州波士顿的医生，但是对电学研究却有浓 厚的兴趣。当时，电磁感应刚发现不久，人们对一切有关电磁的现象都觉得新奇。杰克逊向大家展示了一个名叫电磁铁的新装置。这是一个上面绕着绝缘铜线的马蹄 形铁块，当铜线通电的时候，马蹄形铁块就产生了磁性。杰克逊用孩子般的热情滔滔地解说着。  

　　“先生们！”他说，“请记住，我们快要利用一种无限的力量了。最近有实验表明，绕在铁芯周围的导线越多，磁铁的吸力就越强。而且有人已经证明，电能够神速地通过一段导线，不管有多长。科学就要创造出改变我们生活的电的奇迹啦！”  

(Then came the turning point in the life of Samuel Morse. In the autumn of 1832, while travelling home by ship, Samuel Morse joined a conversation with a few scientists scientific men who were on board. One of the passengers asked this question: "Is the velocity of electricity reduced by the length of its conducting wire?" One of the men replied that electricity passes instantly over any known length of wire and referred to Franklin's experiments with several miles of wire, in which no appreciable time elapsed between a touch at one end and a spark at the other.
This was the seed of knowledge that led the mind of Samuel Morse to invent the telegraph.)




　 　青年医生的话不时被打断，餐厅里响起一阵欢呼和热烈的议论。最后，演说家被大家抬了起来。人们都被一种神奇的幻想陶醉了。谁也没有注意到，听众中有一个 皮肤黝黑的中年男子，一言不发地望着讲台，两眼闪烁着异样的光芒。夕阳映照在他的脸上，象火在燃烧。他的心也在燃烧。他就是四十一岁的美国画家塞缪尔•莫 尔斯。   

莫尔斯和他发明的电报机

　　一连几天，莫尔斯坐卧不安，晚上也兴奋得不能入睡。他的情绪完全被神奇的电所左右。几天以后，邮船到达目的地。旅客们挥手告别，有关电磁铁的议论，不过成为记忆中的一朵浪花罢了。 

　 　可是，莫尔斯却好象换了一个人。在船靠近码头的时候，他忽然对船长说：“先生，不久你就可以见到神奇的‘电报’啦，请记住，它是在你的‘萨丽’号上发明 的呀！”他提着画箱走下邮船，步履坚定，神情庄严。杰克逊那天傍晚的一席话改变了莫尔斯的一生。从此以后，写生画、肖像画不再是莫尔斯的主要兴趣。他告别 艺术，投身到科学领域里去。画家在写生簿上端端正正地写下了“电报”两个字，立志要完成用电传递信息的伟大使命。

　　可是，只要翻开电子科学技术史的最初几页，就可以看到，莫尔斯要完成的使命是非常艰巨的。一个从来没有研究过电磁学的画家，而且已经过了四十岁，居然改行要攀登这座人们都没有征服的高峰，这需要多么大的勇气和决心！    

　 　莫尔斯遇到的最大困难，是他对电和磁的知识几乎一窍不通。但是他一点也不动摇，决心从头学起。经过半年的刻苦学习，莫尔斯初步掌握了电磁原理。特别是美 国物理学家亨利一年以前提出的电报原理，对莫尔斯有很大启发。亨利用电磁铁做成电铃，可以把信号传到1.6公里远的地方。这实际是“电磁音响式电报机”的 最早模型。莫尔斯决定采用亨利的原理，进行深入的实验。      

　　画家买来各种电工器材和工具，在家里夜以继日地干起来。从前的小 画室变成了地道的实验室，到处都是线圈、磁石和导线。他的写生簿也涂满了各式各样的方案和草图。莫尔斯的全部生活和希望都凝聚在这个小小的实验室里了。夜 幕笼罩着城市，只有他实验室里的灯火常常彻夜不熄。冬尽春来，秋去冬至。他画了一张又一张草图，进行了一个又一个试验，但是每次都以失败而告 终。   

　　三年过去了，莫尔斯的积蓄几乎全部花完，电报机还是没有造出来。

　　失败没有使莫尔斯气馁，他变得冷静了。用导线传递信息难道不可能吗？不，经过三年的实践，他更加坚信杰克逊的话是能够实现的。那么失败的原因在哪里呢？莫尔斯苦苦思索着。他反省了自己的设计思路，认真地检查了所有的实验。

　 　多少个不眠之夜过去了，莫尔斯终于找到了问题的症结：踩着别人的脚印是不能走在前面的，必须寻找新路！经过反复思考，一个崭新的思想酝酿成熟了。莫尔斯 的这个构思，是电报发明史上一项重大的突破。莫尔斯设想用点、划和空白的组合来表示字母，只要发出两种电符号，就能够传送消息。这就大大简化了设计和装 置。莫尔斯规定了特定的点、划、空白组合，表示各个字母和数字，这就是著名的莫尔斯电码，也是电信史上最早的编码。

　　1844年五月二 十四日，人类通信史上的庄严时刻到来了。这一天，华盛顿沉浸在节日般的气氛中。在国会大厦联邦最高法院会议厅里，莫尔斯向应邀前来的几位科学家、政府人士 介绍了实验原理，而盖尔等候在六十四公里外的巴尔的摩。大厅外面观众云集，人们怀着极大的兴趣来观看“用导线传递消息”的奇迹。几年以前嘲讽过莫尔斯的那 两个人也赶来了，他们万万没有想到“丑小鸭”飞上了蓝天，变成人人赞美的“白天鹅”。

　　在预定的时间，莫尔斯接通电报机，用一连串的点、划——也就是到今天还在使用的莫尔斯 电码，开始发出电文，盖尔成功的接收到历史上第一份电报：“上帝创造了何等的奇迹！”   

　　试验成功了，人类通信史揭开了新的一页。莫尔斯的发明迅速风行全球。


URL:
http://www.ntt-east.co.jp/business/magazine/network_history/01/
http://inventors.about.com/od/indrevolution/a/telegraph.htm
http://story.kedo.gov.cn/fmqw/321674.shtml