This is electromagnetic radiation.
You can’t see it, but it’s there.
In fact it’s everywhere.
But here’s a more relatable form.
This is the color cyan.
But more accurately, this is waves
of electromagnetic radiation oscillating at about
616,856,909,465,021 times per second.
As they reach your eyes, light receptive cells
translate the radiation into electric signals which travel to your brain,
and are generally perceived as the color that we collectively refer to as cyan.
If we strip away our interpretation though,
the radiation scaled up about 100,000 times, looks like this.
The color cyan is waves of energy roughly 486 nanometers wide,
but what happens if that width tightens?
At 380 nanometers, a perception changes to this dark purple.
Meanwhile, if it expands to a roomy 780 nanometers,
our brains interpret the radiation as the shade of dark red.
Essentially, as the wavelength changes,
so too do the properties.
So what happens if we change the wavelength more dramatically,
like tightening it by 100 times?
Well, now the waves have much higher energy,
they are much more powerful,
so much so that they can actually pass through some less dense materials
like fabric or human tissue.
But they aren’t quite strong enough to pass through denser materials
like metal or bone.
You can see where this is going.
We refer to these wavelength as X-RAYs,
and use their special properties to look inside bags at airport security,
and inside humans at the hospital.
So what happens at the other end of spectrum?
What if, instead the width of human DNA, the waves were the width of humans?
Well, this is what we’d refer to, as an Ultra High Frequency Radio Wave.
Its comparatively enormous wavelength allows it to travel over huge distances,
pass through obstructions and even bend around obstacles,
all useful properties if you wanted to use electromagnetic radiation
to, say, communicate.
Of course, in order to convey information using a radio wave,
we’d need a way to manipulate the radio wave
that corresponds to the desired information.
For this, there are options.
To start with, there’s the strength of the wave.
We know that a blue light, for example, can be weak or strong,
我们知道 比如一个蓝色的灯 可明可暗
but no matter if it’s weak or strong, it’s still blue,
and the fact that it’s blue means that
it’s still fundamentally the same wavelengths of electromagnetic radiation.
The same principle applies up to spectrum with radio waves.
They can be powerful, weak or anywhere in between
and still be the same wavelength.
In this context, we call that strength, the Amplitude.
这种情况下 我们把其强度称为 振幅
Therefore, we can transmit an audio signal for example,
by modifying that amplitude by a proportional amount.
The receiver just needs to know how to interpret those amplitude modulations
and translate them back to an audio signal.
In the case of an AM radio station
the radio receiver only focuses on the radiation
with a wavelength for 1119 feet or 341 meters long for example,
and it tracks the amplitude modulations
to output the audio signal that we end up hearing.
Amplitude modulation radio communication has a number of useful features.
It’s exceptionally simple, and can work over huge distances,
but it does tend to be highly susceptible to outside interference.
That’s a big reason why AM radio tends to be lower quality,
and a big reason why it’s not as useful a technique
for transmitting bigger trunks of data.
Of course, the wavelength can also be manipulated.
That means that we can essentially do the same thing,
but this time by ever so slightly modifying the distance between waves.
In this context we’d refer to this as the frequency,
which is proportional to wavelength,
but rather than being a physical measure, it’s a temporal one.
How many times the wave oscillates within a second?
So by slightly modulating frequency, we can transmit the same audio signal,
but since this method is less susceptible to interference,
we can generally get higher quality.
Now traditional radio works by encoding the audio signal itself
into radio waves using amplitude or frequency modulation,
but computers, phones, essentially everything digital nowadays, encodes its data
但电脑 手机 基本上所有当今社会的数码产品
into binary code, sequences of ones and zeros.
This only makes communication using electromagnetic radiation better.
We can set it up so that
when the amplitude is high that corresponds to a one,
while when it’s low it corresponds to a zero.
Or rather when frequency is high that’s a one,
and when low that’s a zero.
This is simple and already more efficient
than encoding the analog audio signal,
but it could be even more efficient.
That’s because there’s yet another wave property that we can manipulate.
那是因为 还有另一种我们可操控的 波的属性
For these purposes, we can consider one full cycle of a wave,
going up, down and up again, one phase.
上升 下降 再上升 为一个波段
But we can also consider this,
the wave going down, then up, then down again, one phase as well.
波先下降 再上升 又下降 也是一个波段
Therefore, we could assign this upward phase to the binary digit one,
and this one, the downward phase to the binary digit zero.
Then we can transmit data using a sequence of these different phases.
然后我们就能利用 这些不同波段排成的序列 来传输数据了
The transmitter doesn’t need one phase to seamlessly go into the next,
so it’s an even faster, even more efficient way
所以说 这是一个更快 更高效的
of encoding binary sequences into electromagnetic radiation.
But here’s where things get really cool.
There can be more than two phases.
We could divide the cycle into one phase starting at the midpoint going upward,
one starting at the crest, one starting at the midpoint going downward,
and one starting at the trough.
So with four distinct phases,
one can correspond to the binary sequence zero one,
one to one one, one to one zero and one to zero zero.
一个为11 一个为10 还有一个为00
Therefore we can cram twice as much data into the same signal.
因此 我们能将双倍之多的数据 塞进同一个信号中
But it doesn’t stop there.
We can even take this a step further and have eight distinct phases,
so that we can transmit every possible three-digit sequence of ones and zeros,
这样 就能传输每个能得到的 0和1组成的三位数序列
thereby tripling efficiency.
Eight distinct phases is typically the practical limit for wireless data transmission.
It becomes too tough to distinguish between phases with anymore,
so the error rate is too high.
However this is just manipulating one property of the wave,
and there are, of course, two others.
This phase, initially upward from the midpoint,
could be broadcast at a high amplitude or a low amplitude.
So we can say that
the low amplitude version of this correlates to the binary sequence of 0000,
or the high amplitude version 0001.
By adding two amplitude options to each of the eight phases,
we get 16 total transmission options,
meaning we have enough to correlate to
each of the 16 possible four-digit combinations of zeros and ones.
If we have an accurate enough method of transmission,
we can further increase the number of phase
and amplitude combinations to a total of 64,
each corresponding to a six-digit binary sequence.
In fact, the newest WIFI standards have 1024 phase and amplitude combinations,
while extremely accurate copper twisted cables can deal with 32,768 combinations,
each corresponding to a 15-digit sequence.
Constrained by the accuracy of wireless communication,
your cell phone meanwhile,
uses as few as 16 combinations in the case of some 3G networks,
and as many as 1024 in the most advanced 5G networks.
Fundamentally though, this is how your cell phone gets a lot of data
out of a little slice of the radio spectrum.
Of course, transmitting data is only half the battle,
something also needs to receive it.
That something is, of course, a cell site.
Now keep in mind that a cell phone is essentially just a fancy walkie-talkie.
It uses the exact same process, just more advanced.
In fact the earliest portable phones, car phones,
which is one step removed from walkie-talkies.
A telephone company would set up a radio transmitter in a city,
users would install a bulky system in their car,
the system would communicate with the transmitter just as a walkie-talkie would,
and the tower would then plug the signal into the landline network.
Put it another way, it was just a citywide version of cordless landlines.
The only difference from walkie-talkies
was that these car phones would have a dedicated channel for outbound transmission,
and a dedicated channel for inbound transmission,
so that both sides could talk simultaneously,
unlike with a walkie-talkie where one needs to wait and push to talk,
since only one channel is used.
These car phones were fairly similar to today’s cell phones
from a user experience perspective,
but they were horribly inefficient.
In their early days, there were only 32 available channels,
meaning only 32 people in the city could use their car phone simultaneously.
这意味着 全市能同时使用车载电话的 只有32个人
In addition, if one left the service area of that one tower in their home city,
their car phones wouldn’t work.
Of course, the solution was cells.
The idea was this,
a given area would be split up into a pattern of hexagons,
at the center of each of those hexagons was a cell site.
These are generally thought of as cell towers,
but that’s a misnomer since cell sites can be located on buildings,
inside church steeples, at the tops of mountains,
教堂尖塔内 山顶上 或是
or really anywhere that’s elevated relative to the typical user.
Fundamentally, these cell sites just send
and receive radio signals to and from cell phones,
which is a fairly simple process.
Then they need a way to plug into the wire communication network
to convey data over longer distances.
Often this is accomplished through physical fiber optic cables,
but especially in more rural areas, that’s not always practical.
If one put a cell site on the top of a mountain for example,
it would likely have to operate completely offer grid
power by solar or a generator.
And it also couldn’t physically plug into the wire communication network
due to its isolation.
Therefore these more remote cell sites use microwave transmitters.
因此 这些较偏远的基站 会使用微波发射器
Now tiny microwaves, thanks to their extremely rapid frequency,
are incredibly efficient at moving huge amounts of data fast,
the most advanced system have reached over 100 gigabits per second,
but they’re not very resilient.
One needs a direct line of site
between the transmitter and receiver to accurately transmit,
which prevents microwaves used for portable cell phones.
However, for fixed cell sites, this is possible.
So many are set up with microwave transmission systems
that relay signal to the closest site
with a physical link to the wire communication network.
With both a wired and wireless option,
cell sites can be located nearly anywhere,
which is important because their location absolutely matters.
Centering their hexagon,
the signal from each of these sites must reach far enough
that there is some overlap between the cells.
That way, if a cell phone is being used on the move,
the call can be seamlessly passed from one cell site to the next
with no drop off in signal,
and the network can be expanded far beyond the reach of one transmitter.
However, the system starts to seem less ingenious once you do the math.
Originally, only 832 different frequencies were allocated for use by cell phones.
There are a lot of different uses for the radio spectrum,
so regulatory bodies like the American FCC, British Ofcom or German Bundesnetzagentur,
所以像美国联邦通信委员会 英国通信管理局 或德国联邦网络机构这样的管理单位
can only allocate so many frequencies for different industries.
And spectrum allocation is crucial
so that two users don’t try to use the same frequency,
or to render both of their uses useless.
So of those 832 frequencies,
42 were used by the cell network for its own back-end internal communication.
That left 790, but a call required both an outbound
and an inbound frequency,
effectively meaning that there are only 395 call channels.
However, in order to prevent interference,
no two bordering cells could use the same frequency.
As each hexagon has six neighbors,
that meant each cell could only use one seventh of the available channels.
So each cell had 56 channels,
meaning 56 users within each cell could make a call at a given time.
This initially works fine,
but then cell phones got popular.
To keep up with demend,
cell carriers needed to find a way to do more with a single frequency.
When the second generation of mobile network came along,
calls were no longer transmitted as analog audio waves,
rather, they started to use those digital signals encoded using phase and amplitude.
The thing was, this method was more efficient,
meaning using a whole channel to transmit a single voice conversation was overkill,
when only needed part of it.
Of course, the difficulty was that voice conversations happen in a real time,
it’s not like you could compress an entire two-minute call and send it at the end.
它不像可以压缩 然后再发送的 一整段两分钟的语音
Therefore, cell companies divided a given channel into eight time slots.
These time slots would rotate one after another in a rapid succession,
and a given phone would be told to use, say, the third time slot.
So, each time that time slot came up,
it would fire off its ones and zeros quickly
and wait for it to come around again.
But because the data was compressed into an efficient digital signal,
the amount received during a time slot
would be enough to decode into enough of the conversation,
to play until the next time slot came up.
This system meant that one channel
could now be used by eight phones simultaneously.
What was 56 channels, now became 448.
But eventually, as phones became ever more commonplace,
the system of Time Division Multiple Access became
once again, not good enough.
The next evolution was where things got complicated,
but also fascinating.
It’s called Code Division Multiple Access.
It’s an ingenious way
where multiple phones can send and receive data
on the same channel, truly simultaneously.
To explain the incredibly simple version,
let’s say a first user wants to transmit the binary sequence 11,
a second user 01, and a third 10.
Now each of these users would be allocated what’s called a spreading code,
0101, 0011, and 0000 respectively.
0101 0011 和0000
For the first user their first binary digit, 1,
would be compared to each of the four digits of their spreading code.
If the spread code digit and the binary digit is the same,
it would output a zero.
If it’s different, it would output a one.
So for user one, the output sequence would be 1010, 1010.
因此 第一位用户输出的序列 将会是1010 1010
The process would repeat for user two, which output 0011, 1100.
第二位用户也会重复这个流程 输出0011 1100
And user three, which output 1111, 0000.
Next, the sequences are translated
so that zeros become positive ones, and ones become negative ones.
Then each digit of the three sequences of numbers are added together.
That outputs the composite sequence -1, 1, -3, -1, -1 ,1 ,1, 3.
会输出复合序列 -1 1 -3 -1 -1 1 1 3
This composite sequence is what is then transmitted using a single channel.
Now the exact details of this process are not tremendously important,
but what is, is what happens next.
What happens next, is that this process is reversed.
So, the receiver of that composite sequence
would know each user’s unique spreading code.
The spreading code is also translated
so that zeros become positive ones and ones become negative ones.
And then the receiver multiply the composite sequence with this translated spreading code.
For user one,
that outputs -1, -1, -3, 1, -1, -1, 1, -3
输出的是-1 -1 -3 1 -1 -1 1 -3
Now the first four digits of the sequence
which we know correlate with the first digit of the data,
are added together to get negative four,
which is then divided by four to get negative one.
The process repeat for the second set of four to get negative one.
Now if we translate this back so that negative ones become ones,
现在 如果把它们翻译回去 负1变成1
and positive ones become zeros,
then we get the data sequence, 11.
With just the composite sequence and unique spreading code,
this process figured out what user one’s unique data sequence was.
If we repeat this entire decoding process with user two spreading code,
We’ll get 01, it’s data sequence.
And unsurprisingly, it also works for user three.
So, with one composite signal and three unique spreading codes,
we’re able to triple up the use of one channel.
In practice, this process works in a much larger, much more complex scale,
实际应用中 这个流程会在更大 更复杂的规模下运作
but it uses the same mathematical principles.
This fundamentally, is how Cell Service works.
Making a two-wave radio work for one person is simple,
making a two-wave radio work for everyone in the same area,
at the same time, is difficult.
It’s all about packing as much data as possible into a single transmission,
and then packing as many transmissions as possible into a single radio wave.
The aforementioned techniques to accomplish these two goals
are only the tip of the iceberg.
Many of the most advanced networks has moved on to a system
called Orthogonal Frequency Division Multiple Access,
to pack even more transmissions into a single wavelength for example.
以求 在比如说单段波长内 塞入更多次传输
But they are indicative of the process that got us to today.
When we move from 3G to 4G, and 4G to 5,
what’s happening in the background is
incredibly smart people finding more and more ingenious methods of transmitting more data,
using the same resources, also that we, the end users
巧妙绝伦的方法 此时的我们 这些终端用户
can browse Twitter, and watch Youtube, just ever, so slightly, faster.
This is electromagnetic radiation.