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January 14, 2011

记录一下这个问题

December 14, 2009

上次说到,手机在通过基站覆盖区域的时候,基站之间要进行手机的交接,如果基站之间交接不好,就不能保证手机的通讯畅通,会发生掉线现象。

可是,现在的基站处理速度,应该是可以应付高速公路上面汽车的速度的。高速列车的速度,也不比汽车的速度快很多。那么,为什么会发生高速列车上面,手机经常掉线的事情呢?

一个原因,是基站的密度。新建的高速铁路,会有部分通过人烟稀少地区,那篇报道里面也提到,会经过隧道。隧道造价不菲,通常都是在高山峻岭里才不得不造,这种地方,基站的密度自然就比较小了。另外高山和隧道对信号的阻隔,也是一个因素。高速公路,特别是已经建好的高速公路周围,往往已经有很多基站,信号的覆盖就不再是问题。

还有一个原因,我相信也是不可忽略的,就是手机的密度。按照一般的安全驾驶规范,前后车距应该是4秒,也就是说,一个单向4车道的高速,每秒会有一辆车通过一个检查点。假设这个检查点,正好就是基站A和基站B交接手机的边界,并且每辆车里面有一个手机,那么每秒要交接一个手机,双向就是两个手机。

当然实际操作要远比这个复杂,因为交接不是瞬间完成的,所以交接不是在一个点完成,而是在一段路完成。不过我们这里就是估算一下比例。

假定火车速度和汽车一样快,都是200公里每小时,那么一秒通过检查点的火车长度,就是55.6米。和谐号的总长213.9米,共8节车厢,那么一秒就有两节车厢通过检查点。每个车厢座位大概是72人,如果满员的时候,在每个人都有至少一个手机的中国,一秒种通过检查点的,就是144个手机。

December 4, 2009

昨天为译言伤感了一下,今天早上就看到7个留言。我这个偏僻的blog,还带着厚厚的篱笆,如果有人肯来说话,不是被人扔到了twitter上,就是被keso收录了。

被keso收录,除了会带来读者,去keso那里看别人的贴,也是很好玩的一件事情。比如这个“再谈“Wolfram|Alpha””,除了Wolfram|Alpha是我一直喜欢的可计算的范畴之外,这位blogger的其他内容也很有意思。比如她的那些照片,熟悉的加州高速路牌,还有华源的活动。

所以看keso的收录也挺有意思的,基本上等于开了一个网上沙龙。

不过直到我翻到这一篇“译言的十字路口”,我才想起,原来我早就看过她的文章。

November 9, 2009

要说其实美国和中国之间的用户行为,还是差别很大的。主要原因我看一个是历史习惯,一个是生活方式。当然你说生活方式也算历史习惯,也说得通。

比如美国的手机用语音控制,还是靠谱的。主要是美国人开车多,经常是在路上一两个小时的开,而且多半是自己开。你问我怎么知道的?因为美国很多高速上面有拼车的道(car pool lane),只有超过一个人在车里的时候才可以走。经常早上高速堵的一塌糊涂,但是那个拼车的道上面没几辆车。所以老美每天有几个小时是独自在车里度过的,这个时候打电话就是很正常的事情了。我在湾区的时候,一个大学同学就没事给我打电话,这种时候我就知道,这小子又在路上狂奔了。加上美国很多州对开车打手机罚的很厉害,但是如果手机不是手里拿着,警察就不管了。所以在车里用语音控制手机,或者GPS带语音输出,都是很自然的事情。

这个在中国就不大行得通,首先很多人是依靠公共交通的,没事不小心控制了别人的手机可不是玩的。当然祖国人们现在开车的也越来越多了,不过路上滴人的也不少,手机要是语音控制,先要学会忽略滴人才行。

另外美国这边用手机的比中国少,一个是因为大家早就有固话了,另外一个,就是大家生活都比较单一,就是公司到家,所以手机不容易推广。还有一个就是美国人住的稀疏,基站利用效率不高,记得2004年的时候,还经常发现我的手机在郊外没有信号。同样的居住稀疏的问题,导致美国的宽带覆盖也不足,就是因为要拉很长的线,才能连到一户人家。中国就方便多了,一栋楼就连了几十户人家。

美国人喜欢用语音信箱,连手机上面也是,打过去如果占线,就直接到信箱里面了。这个也是历史习惯的问题。早年电话没有来电显示,美国的电话推销又特别发达,所以很多时候主人不能,或者不愿接电话的时候,能存个消息就是很好的功能了。用习惯以后,大家找不到人就都留言。中国人就没有这个历史包袱,找不到人不要紧,反正手机上面有来电显示,等机主回复就是了,或者干脆一个短信过去。

说到短信,这个也是特色了。有人说这个是因为花费过高导致的。这个也不完全对,毕竟在周围都是人的时候,大声打电话的结果,就是大家都别说了。这个时候,一个短信就简单了,也不用担心听不清。美国人不大用短信,因为周围人少,容易说清楚。不过美国年轻人喜欢用短信,主要是觉得好玩,酷。还有一个就是觉得自己的隐私不让别人知道。

还有一个就是智能手机。现在iphone要到中国上市了,会有什么人喜欢呢?我看主要是有钱的商人。时尚女生会喜欢么?可能,但是未必会很流行。因为iphone实在比女生的纤纤细手大太多了,而且太重,不大能挂在脖子上面当项链。最重要的,是如果一个长发女生把青丝一甩,然后往耳朵边贴一个砖头一样的iphone,实在有点煞风景。所以iphone会因为苹果的时尚符号流行一下,不过估计不太会火。

October 9, 2009

Twinkle, twinkle, E F G,
How I wonder L M N O P,
Up above the T U V,
Like a diamond Y and Z,

Twinkle, twinkle, A B C,
How I wonder Sing with me

September 23, 2009

In today’s RWW there’s a post about RFID smart card. It mentioned 3 other RFID smart card use cases: London, Japan and Hongkong. I have to say, RWW, you’re kinda late on this, cause you missed China.

I do not have many chances to go back to China these days, but I do managed to go back in 2006, and twice last year. In 2006 I stayed in Shanghai for 2 weeks, and found that it was not easy to go out without a RFID public transportation card. The buses and subways do have coin slots and you can buy a one-time use magnetic card, but it was just too much hassle to buy them.

Later on I found that some of my friends back in Shanghai took charged RFID cards as part of their salary. No, not because some evil company or .gov staff forced them to do so. It was because they use RDIF cards everyday, and it was just easier for them to get the card and go - no need to buy and charge.

Last winter I visited Guangzhou and Shenzhen, two major cities next to Hongkong. I had to travel between the two cities. I took the inter-city high speed train, which cruises at 180km/h. The train ticket itself, which costs about 11 USD, is a piece of paper with smart RFID card embedded in it. Placing it against the sun I can see the antenna and the chip inside. The train company recycles those tickets, but I managed to sneak out one. I do not have photo of it right now, but I’ll post one if people are interested.