- [Presenter] For most of us, -[主持人]对我们大多数人来说，
a mobile phone is a part of our lives. 手机是我们生活的一部分。
But I'm sure you're curious minds 但是我确定你是个好奇的人
have always been struck by such questions 一直被这样的问题打动
as how a mobile phone makes a call, 就像手机拨打电话一样
and why there are different generations 为何会有不同的世代
of mobile communications? 移动通信？
(upbeat music) （欢快的音乐）
Let's explore the technology behind mobile communications. 让我们探索移动通信背后的技术。
When you speak on your phone, 当您在电话上讲话时，
your voice is picked up by your phone's microphone. 手机的麦克风会拾取您的声音。
The microphone turns your voice into a digital signal 麦克风将您的声音变成数字信号
with the help of MEMS sensor and IC. 借助MEMS传感器和IC。
The digital signal contains your voice 数字信号包含您的声音
in the form of zeros and ones. 以零和一的形式。
An antenna inside the phone receives these zeros and ones 手机内部的天线会接收这些零和一
and transmits them in the form of electromagnetic waves. 并以电磁波的形式传输它们。
Electromagnetic waves transmit the zeros and ones 电磁波传输零和一
by altering the wave characteristics, 通过改变波浪特征
such as the amplitude, frequency, phase, 例如幅度，频率，相位，
or combinations of these. 或这些的组合。
For example, in the case of frequency, 例如，对于频率，
zero and one are transmitted 传输零和一
by using low and high frequencies respectively. 分别使用低频和高频。
So, if you could find a way 所以，如果你能找到办法
to transmit these electromagnetic waves 传播这些电磁波
to your friend's phone, 到你朋友的电话，
you would be able to establish a call. 您将可以建立呼叫。
However, electromagnetic waves 但是，电磁波
are incapable of traveling long distances. 不能长途旅行。
They lose their strength due to the presence 他们由于存在而失去力量
of physical objects, electrical equipment, 物理对象，电气设备，
and some environmental factors. 和一些环境因素。
In fact, if there were no such issues, 实际上，如果没有这样的问题，
even then, electromagnetic waves would not carry on forever, 即使那样，电磁波也不会永远持续下去，
due to the Earth's curved structure. 由于地球的弯曲结构。
To overcome these issues, cell towers were introduced, 为了克服这些问题，引入了手机信号塔，
using the concept of cellular technology. 使用蜂窝技术的概念。
In cellular technology, 在蜂窝技术中
a geographic area is divided into hexagonal cells 地理区域分为六边形单元格
with each cell having its own tower and frequency slot. 每个小区都有自己的发射塔和频槽。
Generally, these cell towers are connected through wires, 通常，这些手机信号塔通过电线连接，
or more specifically, optical fiber cables. 或更具体地说，是光缆。
These optical fiber cables are laid under the ground 这些光缆铺设在地下
or the ocean, 或海洋
to provide national or international connectivity. 提供国家或国际连接。
The electromagnetic waves produced by your phone 手机产生的电磁波
are picked up by the tower in your cell 被您的牢房中的塔楼拾起
and convert them into high frequency light pulses. 并将其转换为高频光脉冲。
These light pulses are carried to the base transceiver box, 这些光脉冲被传送到基本收发器盒，
located at the base of the tower 位于塔的底部
for further signal processing, 为了进一步的信号处理，
After processing, your voice signal is routed 处理后，您的语音信号被路由
towards the destination tower. 朝向目的地塔。
Upon receiving the pulses, 收到脉冲后
the destination tower radiates it outwards 目的地塔向外辐射
in the form of electromagnetic waves, 以电磁波的形式
and your friend's phone then receives the signal. 然后您朋友的电话会收到信号。
This signal undergoes a reverse process, 该信号经过反向处理，
and your friend hears your voice. 然后您的朋友听到您的声音。
So, it's true that mobile communications 因此，移动通信的确是
are not entirely wireless, 不完全是无线的
they do use a wired medium too. 他们也确实使用有线媒体。
This is how mobile communications are carried out. 这就是进行移动通信的方式。
However, there was a big issue 但是，有一个大问题
that we intentionally left unanswered. 我们故意没有答案。
Mobile communication is only successful 移动通信只有成功
when your tower transfers the signal to your friends tower. 当您的发射塔将信号传送到您的朋友发射塔时。
But how does your tower know 但是你的塔怎么知道
in which cell tower area your friend is located? 您的朋友位于哪个手机信号塔区域？
Well, for this process, the cell tower gets help 好吧，在此过程中，手机信号塔获得了帮助
from something called a mobile switching center. 来自所谓的移动交换中心。
The MSC is the central point of a group of cell towers. MSC是一组手机信号塔的中心点。
Before moving further, 在继续之前，
let's explain more information about the MSC. 让我们解释一下有关MSC的更多信息。
When you purchase a SIM card, 购买SIM卡时，
all the subscription information 所有订阅信息
is registered in a specified MSC. 已在指定的MSC中注册。
This MSC will be your home MSC. 该MSC将成为您的家庭MSC。
The home MSC stores information such as service plans, 本地MSC存储诸如服务计划，
your current location, and your activity status. 您当前的位置以及您的活动状态。
If you move outside the range of your home MSC, 如果您移出家庭MSC的范围，
the new MSC, which serves you instead, 新的MSC为您服务，
is known as a foreign MSC. 被称为外国MSC。
As you enter a foreign MSC region, 当您进入国外MSC地区时，
it communicates with your home MSC. 它与您的家庭MSC通信。
In short, your home MSC always knows 简而言之，您的家庭MSC始终知道
which MSC area you are in. 您所在的MSC区域。
To understand in which cell location the subscriber is 了解订户在哪个小区位置
within the MSE area, 在MSE区域内，
the MSC uses a few techniques. MSC使用了一些技术。
One way is to update the subscriber location 一种方法是更新订户位置
after a certain period. 一定时间后。
When the phone crosses a predefined number of towers, 当电话穿过预定数量的塔楼时，
the location update is again done. 位置更新再次完成。
The last one of these is when the phone is turned on. 最后一个是打开手机的电源。
Let's try to understand all of these procedures 让我们尝试了解所有这些过程
with an example. 举个例子。
Suppose, Emma wants to call John. 假设艾玛想给约翰打电话。
When Emma dials John's number, 当艾玛拨打约翰的电话时，
the call request arrives at Emma's home MSC. 呼叫请求到达Emma的归属MSC。
Upon receiving John's number, 收到约翰的电话号码后，
the request will be forwarded to John's home MSC. 该请求将转发给John的家庭MSC。
Now, John's MSC checks for his current MSC. 现在，约翰的MSC检查他当前的MSC。
If John is in his home MSC, 如果约翰在他的家中MSC，
the call requests will be immediately sent 呼叫请求将立即发送
to his current cell location, 到他目前的牢房位置
and it checks whether John is engaged on another call, 然后检查约翰是否接听另一个电话，
or if his mobile is switched off. 或手机已关闭。
If everything is positive, John's phone rings, 如果一切正常，约翰的电话响了，
and the call will be connected. 通话将接通。
However, if John is not in his home MSC, 但是，如果约翰不在自己的家中，
John's home MSC simply forwards the call request 约翰的家庭MSC只需转发呼叫请求
to the foreign MSC. 到外国MSC。
The foreign MSC 国外MSC
will follow the previously explained procedure 将遵循前面解释的过程
to locate John's phone, 找到约翰的电话，
and will then establish the call. 然后建立通话。
Now, let's discuss why the frequency spectrum 现在，让我们讨论为什么频谱
is quite important in mobile phone communications. 在手机通讯中非常重要。
To transfer zeros and ones in digital communication, 要在数字通信中传输零和一，
each subscriber is allocated a frequency range. 每个用户分配一个频率范围。
However, the frequency spectrum available 但是，可用频谱
for cellular communications is quite limited, 蜂窝通信是非常有限的，
and there are billions of subscribers. 并有数十亿用户。
This issue is solved with the help of two technologies, 借助两种技术可以解决此问题，
one frequency slot distribution, 一种频率分配
and two, multiple access technique. 第二，多路访问技术。
In the first technique, 在第一种技术中
different frequency slots are carefully allocated 精心分配了不同的时隙
to different cell towers. 到不同的手机信号塔。
In the multiple access technique, 在多路访问技术中，
this frequency slot is efficiently distributed 该时隙被有效分配
amongst all the active users in the cell area. 在小区区域的所有活动用户中。
Now, the big question. 现在，一个大问题。
Why are there different generations 为什么会有不同的世代
of mobile phone technologies? 手机技术？
1G originally allowed users, for the first time, 1G最初是允许用户使用的，
to carry a phone without a cable attached to it. 携带没有连接电缆的电话。
But 1G suffered from two major problems. 但是1G遭受两个主要问题。
The first problem was that the wireless transmission 第一个问题是无线传输
was in an analog format. 是模拟格式。
Analog signals that are easily altered by external sources. 模拟信号容易被外部信号源改变。
So, it provided poor voice quality and poor security. 因此，它提供了较差的语音质量和较差的安全性。
The second problem was that it used 第二个问题是它使用了
the frequency division multiple access technique, 频分多址技术
which used the available spectrum in an inefficient way. 这以低效的方式使用了可用频谱。
These factors paved the way for the second generation 这些因素为第二代铺平了道路
of mobile communications, 移动通信
2G used digital multiple access technologies, namely TDMA, 2G使用了数字多址技术，即TDMA，
or CDMA technology. 或CDMA技术。
The second generation 第二代
also introduced a revolutionary data service, SMS, 还推出了革命性的数据服务SMS
and internet browsing. 和互联网浏览。
3G technology was focused 重点关注3G技术
on giving a higher data transfer speed. 提供更高的数据传输速度。
It used a WCD multiple access technique, 它使用了WCD多址技术，
along with an increase in bandwidth. 随着带宽的增加。
To achieve this, the 3G speed of two Mbps 为此，3G速度为2 Mbps
allowed the transfer of data for uses 允许传输数据以供使用
such as GPS, videos, voice calls, et cetera. 例如GPS，视频，语音通话等。
3G was a huge step in the transformation 3G是转型的重要一步
of the basic phone to a smartphone. 基本手机到智能手机的连接。
Next came 4G, which achieved speeds of 20 to 100 Mbps. 接下来是4G，其速度达到20到100 Mbps。
This was suitable for high resolution movies and television. 这适用于高分辨率电影和电视。
This higher speed was made possible 更高的速度成为可能
due to the OFD multiple access technology, 由于OFD多址技术，
and MIMO technology. 和MIMO技术。
MIMO uses multiple transmitter receiver antennas MIMO使用多个发射器接收器天线
inside both the mobile phone and the towers. 在手机和塔中。
The next generation of mobile communication, 5G, 下一代移动通信5G
to be rolled out soon, 即将推出
will use enhanced MIMO technology and millimeter waves. 将使用增强的MIMO技术和毫米波。
It will provide seamless connectivity 它将提供无缝连接
to support the internet of things, 支持物联网，
such as driverless cars and smart homes. 例如无人驾驶汽车和智能家居。
Would you like to learn how a touchscreen works? 您想了解触摸屏如何工作吗？
Please check out this video. 请观看此视频。
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