Overview of dry 5G
We all live in the era of 4G network, I am sure you remember the time when the operators to launch 4G technology, every day, we hurried to the scene changing the card. Now you need to tell as "ordinary people" you, 5G have quietly come out. . . .
For the "mobile communications ignorant" of you, so I introduce you to what 5G technology is:
"5G", good high-end ah. It was just us ordinary people called, professional name 5G technology called IMT-2020. This thing developed by the International Telecommunication Union (ITU), China Industry and Information Technology, the National Development and Reform Commission, Ministry of Science and Technology set up a joint quietly behind the scenes to promote the group to follow up with. Why write a 2020 do? Yes, you guessed it, 5G technology that is now also in that trial, expected to come up, bright 24K Titanium X blind eye when I and other civilians in 2020 "well-off society." . . .
That this thing can grow so what ah? I feel good now 4G traffic on the ah! And very quickly and very convenient! 5G is estimated that nothing much changes.
Then you are wrong. Who can not casually called the 5G. Why is still in the experimental stage? 5G is because to achieve the key indicators must be qualified. Some of the most important indicators are:
1. User Experience rate: 0.1-1Gbps. What concept? Now that you download videos with traffic, typically 3-4Mbps. And with the 5G later, download the video at least 100Mbps, you almost finished counting numbers 1 to get away.
2. millisecond delay: end delay down to the millisecond.
3. Connect the number density: the density of 1 million / Km2. Do not think 5G or used in people who are now shouting the slogan "all things Internet" Oh!
Other key indicators will not describe, do Photo give you an intuitive feel:
5G is not a lot of big flowers than 4G? At least 10 times the rhythm ah!
Well! To here, we believe that non-specialists already have a rough idea. Next-oriented professionals, talk about some of the dry goods, and welcome onlookers Ha!
Earlier Ho图:
See can enlarge Oh!
4G and 5G in the end what changes it technically? Please allow the author to explain one by one on the chart you listen to the audience:
We all know that 4G network architecture can be divided into three parts: the wireless access network, core network and bearer network. Then it will introduce changes to these three aspects of 5G.
1. 无线接入网：首先，刚入行的专业人员可能一脸懵逼。RRH？我只听说过RRU啊？这里先做一个简单澄清，RRH和RRU实际上是同一个东西，只不过不同厂商叫法不同而已。好啦！接下来给大家具体介绍一下无线接入网。这部分的重头戏当然是基站了。基站由三部分组成：天线，RRU（射频拉远单元），BBU（基带处理单元）。
在1G和2G时代，BBU，RRU和供电单元等设备是放在一个柜子里的，十分臃肿（我也是醉了）。。。
到了3G时代，提出了分布式基站。也就是将BBU和RRU分离，RRU甚至可以挂在天线下边，不必与BBU放在同一个机柜里。这就是图中左上角看到的D-RAN（分布式无线接入网）。随着技术的发展（很大的原因是运营商维护成本太高了。。。），C-RAN应运而生。
啥叫C-RAN？就是Centralized RAN，中文意思是集中化无线接入。还是采取BBU和RRU分离的方案，但是RRU无限接近于天线，这样大大减少了通过馈线（天线与RRU的连接）的衰减；同时BBU迁移并集中于CO（中心机房），形成BBU基带池；而CO与RRU通过前传网络连接。这样非常有利于小区间协作（比如COMP）和跨基站的载波聚合部署。
这都不算啥。更重大的变革是：无线接入网中的大Boss（BBU）最终被干废了。。。。
为了进一步减小成本，现在将NFV（网络功能虚拟化）技术和SDN（软件定义网络）技术引入到了接入网中，就是说我运营商只需要买一台通用服务器，在上面安装相应的软件就能实现BBU的功能。不再需要专门购买BBU设备了。（华为中兴等设备商要哭死了。。。）同时再结合云计算等技术，最终实现运维人员随便动动手就完成了接入侧的配置、调度等工作。
最后再说一下这个MEC（移动边缘计算）。说白了就是将原来数据中心的服务器和存储器下放到中心机房里，实现维持本地内容缓存，实现缩短网络时延等功能。它与NFV一样，也强调功能软件化和平台开放化。但MEC可以根据无线接入网环境对NFV进行了优化，将移动接入网与互联网业务深度融合。
那么为什么说这个MEC技术呢？这又关乎到5G关键指标了。5G要求时延达到毫秒级，光纤传播速率为200KM/ms，数据要在相距几百公里以上的终端和核心网上之间传输，显然要大于毫秒级。这个问题是硬伤啊！目前没法应用其他技术来缩短物理传输时延。所以只能想到了把内容缓存到接入网侧。也正是有了这个MEC，才为核心网的变革奠定了基础（为什么会在下文中讲到。。。）。
2. 核心网：伴随着高清视频，VR\AR等应用的兴起，超大数据流量给核心网的处理能力带来了巨大的挑战。在5G时代，网络架构采用“全分离”方式。就是说原来4G中的S-GW、P-GW网元被分成了控制面和用户面（SGW分离为SGW－C和SGW－U，PGW分离为PGW－C和PGW－U）。啥意思？用户面的功能直接在接入网侧处理，何必绕一大圈传到核心网侧呢？是不是有点乱？大家目前只需要明白：原来4G中一个核心网集中了用户面和控制面的功能，现在能把用户面下放到接入侧（就是上文说的MEC服务器中），减少了很大开销。
还有一个变化就是“网络切片”机制。所谓“网络切片”就是把网络按照不同的业务需求划分为不同的虚拟子网络。要记得5G是面向万物互联的，不单单像原来2\3\4G一样只面向数据和语音业务。所以大家可以看到上文架构图中，不同的网络切片对应不同的业务。这样做使得网络能够更好的适应、处理业务。