How can multiple users operate on the same frequency?Radio is like speaking in a meeting.多个用户如何在同一频率上运行？电台就像在会议上发言。
If everyone speaks at the same time, no one understands anything.如果每个人都在同一时间说话，没有人会理解任何事情。
With radio, it’s the same thing.有了广播，这是一回事。
When several pieces of equipment transmit at the sametime, interference is likely.当多个设备同时传输时，可能会产生干扰。
All radio systems have to find a solution to share the resource between users.
所有无线电系统都必须找到一种在用户之间共享资源的解决方案。
In this video, we will see how L. T. E. does this.在这个视频中，我们将看到L. T. E.如何做到这一点。
And, at the end, we will get a global view of the transmission chain.最后，我们将获得传输链的全局视图。
Radio resources are rare and expensive.无线电资源很少且昂贵。
And users don’t need to communicate continuously.并且用户不需要持续通信。
So, it’s preferable to allocate resources to users onlywhen they need them.因此，最好只在用户需要时为用户分配资源。
L. T. E. operates on a band of the radio spectrum betweena minimum and a maximum frequency.L. T. E.在最小和最大频率之间的无线电频谱上工作。
L. T. E. ’s band-witdth can vary from 1.4 to 20 Megahertz.L. T. E.的带宽可以在1.4到20兆赫之间变化。
It is divided into sub-carriersand each sub-carriers can be allocated to a different user.它被分成子载波，每个子载波可以分配给不同的用户。
These frequencies are periodically re-allocated, based onthe evolution of users needs.根据用户需求的变化，定期重新分配这些频率。
So, L. T. E. shares the resources both in frequency and in time.因此，L。T. E.在频率和时间上共享资源。
In the previous video, we saw that the smallest piece ofinformation produced by a modulation is a symbol.在之前的视频中，我们看到调制产生的最小信息是一个符号。
Each symbol constitutes a “Resource Element”.每个符号构成“资源元素”。
A Resource Element occupies 15 kHzof frequency space and lasts 66 microseconds.资源元素占用15 kHz的频率空间并持续66微秒。
Because it is so small, it is complicated to allocatethese resources one by one.因为它太小，所以逐个分配这些资源是很复杂的。
Therefore, they are grouped in what is called “Resource Blocks”.因此，它们被分组在所谓的“资源块”中。
A Resource Blocklasts half a millisecond.资源块持续半毫秒。
It consists of 84 Resource Elementsspread over 12 sub-carriers.它由分布在12个子载波上的84个资源元素组成。
One resource block occupies 180 kHz.一个资源块占用180 kHz。
The number of available Resource Blocks varies from 6when operating on a 1.4 MHz wide band to one hundred when working with a 20 MHz large band.可用资源块的数量从在1.4 MHz宽带上工作时的6变化到在使用20 MHz大带时工作时变为100。
Every millisecond, L. T. E. re-allocates the Resource Blocks to the users that need to communicate.每毫秒，L。T. E.将资源块重新分配给需要通信的用户。
Since a Resource Block lasts half a millisecond,this means that Resource Blocks are allocated by pairs.由于资源块持续半毫秒，这意味着资源块是按对分配的。
The pattern formed by the Resource Blocks during a 1msperiod of time is called a “sub-frame”.资源块在1ms时间段内形成的模式称为“子帧”。
It’s important to THAT 1 millisecond.重要的是1毫秒。
In a way, it’s the pulse of L. T. E, its heartbeat.在某种程度上，它是L. T. E的脉搏，它的心跳。
And all allocation mechanisms of L. T. E.are based on this 1ms period or on a multiple of it.L. T. E.的所有分配机制都是基于这个1ms周期或它的倍数。
To sum up: the available spectrum is cutinto Resource Blocks that are allocated every millisecond.总结一下：可用频谱被切割成每毫秒分配的资源块。
These Resource Blocks ares allocated to this phone in yellow.这些资源块以黄色分配给此手机。
The pattern formed every millisecond by allthe resource blocks is called a sub-frame.所有资源块每毫秒形成的模式称为子帧。
Each resource block contains 84 Resource Elements.
每个资源块包含84个资源元素。
Each one transport one symbol.每一个都运输一个符号。
Howeve, in the resource blocks, some resourceelements are reserved for L. T. E. internal control.但是，在资源块中，为L. T. E.内部控制保留了一些资源元素。
On this graphic, we’ve colored them in purple or red.在这张图片上，我们将它们用紫色或红色着色。
We’ll come back to that when we talk about physical channels.当我们谈论物理渠道时，我们会回过头来看看。
For the moment, just remember that only resource elementsin white can be used to transmit messages.目前，请记住，只有白色的资源元素可用于传输消息。
When a device needs to transmit data, it is provided withone or several of Resource Blocks for the next 1ms.当设备需要传输数据时，它会在接下来的1ms内提供一个或多个资源块。
Should this resource not be enough, additional resourceswill be allocated on next sub-frames.如果该资源不够，则将在下一个子帧上分配额外的资源。
This allocation is managed by the eNode B.该分配由eNode B管理。
We will see how in the next videos.我们将在接下来的视频中看到。
The amount of data a device can send during agiven sub-frame is called a “Transport Bloc”.设备在给定子帧期间可以发送的数据量称为“传输集团”。
Its size depends on the number of resource blocksavailable for this user.其大小取决于此用户可用的资源块数。
It also depends on the modulation, or more precisely, onthe MCS used with this user.它还取决于调制，或者更确切地说，取决于与该用户一起使用的MCS。
Obviously, the more efficient the modulation, thebigger the transport block.显然，调制效率越高，传输块越大。
This table gives the size of transport blocks in bits,depending on the MCS in use and thenumber of resource blocks allocated.此表以位为单位给出传输块的大小，具体取决于使用的MCS和分配的资源块数。
It's a lot of numbers, but don't panic.这是很多数字，但不要惊慌。
We'll just make a few observations.我们只是做一些观察。
And come back to it during the exercises.并在练习期间回到它。
Firstly, it is easy to transpose the transport block size into throughput.首先，很容易将传输块大小转换为吞吐量。
Indeed, there are one thousand sub-frames per second.实际上，每秒有一千个子帧。
So, all we need to do is multiply the figures of this tableby one thousand to get the throughput.因此，我们需要做的就是将此表的数字乘以一千来获得吞吐量。
Here, we can see that the maximum achievable throughputis 75 Megabits per second.在这里，我们可以看到最大可实现的吞吐量是每秒75兆比特。
Secondly: The size of transport blocks varies widely,ranging from 16 bitswhen using only one Resource Block and an MCS of 0to just over 75 kilobitswhen using all the Resource Blocks with an MCS of 28.其次：当使用MCS为28的所有资源块时，传输块的大小变化很大，从仅使用一个资源块时的16位和使用0的MCS到超过75千位的MCS不等。
Lastly: the same transport block size can be found in several cells.最后：在几个单元格中可以找到相同的传输块大小。
For example, with this value of 256 that we’ve colored green.例如，使用256的值，我们将其设为绿色。
This property is interesting if the modulation changesafter a transport block was generated.如果在生成传输块之后调制发生变化，则此属性很有用。
For example, imagine that we were allocated 2 Resource Blocksto transmit a transport block of 256 bits using an MCS of 8.例如，假设我们被分配了2个资源块来使用8的MCS传输256位的传输块。
If conditions get worse and we now have to use an MCS of 4.如果情况变得更糟，我们现在必须使用4的MCS。
We can keep the same transport blockand we just have ask for 4 Resource Blocks instead of 2.我们可以保持相同的传输块，我们只需要4个资源块而不是2个。
In conclusion: L. T. E. shares resources by both time and frequency.总之：L。T. E.在时间和频率上共享资源。
A Resource Element corresponds to one symbol.资源元素对应于一个符号。
To facilitate allocation, L. T. E. defines Resource Blockswhich are groups of 84 Resource Elements.为了便于分配，L.T.E.定义了资源块，它是84个资源元素的组。
At every millisecond, the eNodeB defines the size of thetransport block for each device on the current sub-frame.在每毫秒，eNodeB定义当前子帧上每个设备的传输块的大小。
As promised, we now have a global view of the transmission chain.正如所承诺的，我们现在对传输链有一个全球视野。
First, we fill a transport block of the size that was allocated to us.首先，我们填写分配给我们的大小的运输区块。
We did not discuss that yet, butwe add a cyclic redundancy check, or CRC, to let thereceiver check whether received data are correct.
我们还没有讨论，但我们添加循环冗余校验或CRC，让接收器检查接收的数据是否正确。
The packet then passes through the coding stage whichadds redundancy to enable error correction.
然后该分组通过编码级，这增加了冗余以实现纠错。
The flow of bits is then modulated by a digitalmodulation to produce symbols.然后通过数字调制来调制比特流以产生符号。
These symbols will be inserted in one the the ResourceBlocks that have been allocated to us on the current sub-frame.这些符号将插入到当前子帧中已分配给我们的资源块中。
This process repeats every millisecond.这个过程每毫秒重复一次。
In the next video, we will see howtheses resources are allocated between different users.在下一个视频中，我们将看到如何在不同用户之间分配这些资源。
转载于:https://www.cnblogs.com/sec875/articles/9957246.html
