• 2 months ago
Welcome to the section on the 5G Radio Access Network (RAN)! In this session, we'll dive into how 5G NR (New Radio) revolutionizes the wireless interface compared to LTE, using technologies like MIMO and Beamforming to handle new use cases and improve performance. We'll break down the basic concepts and how they contribute to 5G's enhanced data rates, coverage, and low-latency services.

Topics Covered:
* 5G NR and its Requirements: Learn how 5G must optimize millimeter-wave spectrum and handle new use cases, leading to the development of NR (New Radio).
* LTE & 5G Coexistence: How 5G NR works in conjunction with LTE to maximize performance.
* Massive MIMO Explained: Understand how MIMO (Multiple Input Multiple Output) technology uses multiple antennas to improve the capacity, throughput, and reliability of the 5G network.
* Beamforming Techniques: Learn how Beamforming focuses signals towards users, improving coverage and efficiency in high-frequency bands like millimetre waves.
* Diversity and Spatial Multiplexing: Discover how MIMO leverages diversity to improve signal-to-noise ratios and uses spatial multiplexing to send multiple data streams for higher throughput.
* Analog, Digital, and Hybrid Beamforming: Get to know the different forms of Beamforming used in 5G and how they improve coverage and performance, particularly in high-frequency millimetre-wave bands.


Key Takeaways:
* Understanding MIMO: Learn the basics of SISO, MISO, and MIMO and how these systems improve signal quality and data capacity.
* Massive MIMO: Discover the benefits of massive MIMO, a key 5G technology that boosts network capacity by using arrays of 16 or more antennas.
* Beamforming: Find out how Beamforming works in both analog and digital forms, and how it's used in 5G NR to maximize signal strength and coverage.
* Millimetre-Wave Challenges: Learn why millimetre-wave bands require special techniques like Beamforming to ensure efficient coverage despite their poor propagation.
If you’re curious about how 5G RAN enhances mobile broadband, low-latency applications, or want a detailed understanding of MIMO and Beamforming, this video is for you!

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Transcript
00:00Hi, in the last session, we talked about different 5G deployment options.
00:05And I hope you have some background and overview on 5G now.
00:09Now let's focus on the 5G Radio Access Network or 5G RAN.
00:14Compared to the LTE AIR interface, the 5G AIR interface should meet main two requirements.
00:21First, it must efficiently utilize the new spectrum which also lies in the millimeter
00:27wave band.
00:28Second, it needs to support the various new use cases introduced in 5G.
00:34This leads to the development of a new wireless access called NR or New Radio.
00:40In the 5G ecosystem, NR will not be the only wireless technology.
00:44Instead, it will work together with other wireless technologies such as LTE.
00:49In the new 5G designs, there are many enhancements that cater to the different goals of 5G.
00:56For enhanced mobile broadband, 5G also introduced some new concepts such as massive MIMO, beamforming,
01:03wideband carriers, and carrier aggregations, etc.
01:07Also to support the ultra-reliable low-latency use cases, 5G included new features like flexible
01:14numerology, preemptive scheduling, and grant-free uplink access.
01:18To improve the cost efficiency and flexibility, there are new concepts like virtualizations.
01:25So starting from this session and in next few sessions, we will explore these defining
01:30features of the 5G radio access network and we will know how they function.
01:36Let's start with MIMO.
01:38So the question is, how can we use the advancements in the antenna technologies to improve the
01:44capacity and the data rates in 5G?
01:47Let's begin that by exploring the evolutions of MIMO technology first.
01:52So at very beginning, omnidirectional antennas were used.
01:56They offer broad coverage, but that is uniform coverage.
02:00You can see in the top left picture, we have antenna which is providing uniform coverage
02:05in that radius.
02:07Then it was realized that the capacity of the network can be improved by using sectors
02:12which brought the coverage like this, like at the bottom right section here.
02:17So you can see that this approach creates three different cells from a single base station.
02:24Now we can further enhance this by directional beams, more precisely to a specific user equipment
02:30or UAE or some directive points.
02:33This is where beamforming comes in picture.
02:36But before learning about massive MIMO, we have to understand the basics of MIMO.
02:41In a single input and single output system, which is generally called a SISO system, we
02:47have one transmit antenna.
02:49The signal passes through a fading channel and reaches to the single receiving antennas.
02:55Now in this step and according to the Shannon equation, the capacity of this system can
03:01be enhanced by either increasing the channel bandwidth or by improving the signal to noise
03:06ratio or SNR at the receiver side.
03:10Now if you have multiple transmit antennas and a single receive antenna, then this configuration
03:16is known as multiple input, single output or MISO system.
03:21And in this setup, if the antennas are placed at least at the half of the wavelength, then
03:27each transmit antenna creates an independent fading channel to the receive antenna.
03:33This phenomena is known as transmit diversity.
03:37Now when the same data sent through these multiple channels, then they are affected
03:41by their independent channels.
03:44And by combining these received signals at the receiver, the signal to noise ratio or
03:48SNR gets improved and that enhances the channel capacity.
03:54This approach is especially beneficial for downlink because the multiple antenna setup
03:59requires more space.
04:01So they can easily locate it at the base stations.
04:04In a similar fashion, if there is a single transmit antenna and multiple receive antennas,
04:10then we also achieve independent fading channels.
04:13This is called receive diversity.
04:16And it also enhances the received signal to noise ratio or SNR by combining the effects
04:22of different fading channels.
04:25In this setup, the signal processing occurs at the receiving end.
04:29Now when the multiple antennas are used at the both end, means at the transmitting end
04:34and at the receiving end, then this is referred as MIMO or multiple input, multiple output
04:41setup.
04:42And when there are at least 16 transmit antennas and 16 receiving antennas, then it is often
04:48called as massive MIMO.
04:50However, some says that the minimum number of antennas for massive MIMO should be 32
04:56antennas or more for each side.
04:59Now MIMO offers three main methods to enhance the data transfer rate.
05:04First when signal to noise ratio is low, then the diversity techniques can be applied to
05:09improve the signal to noise ratio, just like before.
05:13However, if signal to noise ratio is high, then special multiplexing can be used to increase
05:19the data rates and system throughput.
05:22In special multiplexing technique, throughput is improved by transmitting multiple data
05:27streams simultaneously over the channel.
05:31Now there are two variants of special multiplexing.
05:35First is open-loop special multiplexing and second is closed-loop special multiplexing.
05:41In open-loop special multiplexing, the transmitter does not require channel state information.
05:47However, it is less efficient than the closed-loop special multiplexing.
05:51In the closed-loop special multiplexing, the transmitter receives the channel state information
05:56through the feedback from the receiver.
05:59And with the knowledge of the transmitter, appropriate pre-coding is done in the transmitter
06:05and processing is done in the receiver side.
06:08This allows the data streams to be separated effectively.
06:12The maximum number of streams in such MIMO systems is limited by the minimum number of
06:17either transmit antennas or receiving antennas.
06:22Now if all the received antennas belong to the same UE, it's known as single-user MIMO.
06:29Like you see in the top section of this picture, where all the receiving antennas belong to
06:34the same UE.
06:35So it is called single-user MIMO.
06:38Same way if multiple streams belong to the multiple UE at receiving end and these simultaneous
06:44streams received by different UEs at the same time, then this setup is called multi-user
06:50MIMO.
06:51Like you see in the bottom section of this picture.
06:55Now this is the third MIMO technique, where the same signal is transmitted from each transmitting
07:01antenna.
07:02But these signals are phase shifted.
07:05And the phase adjustment is done in such a way that the signal power is maximized to
07:10some specific point, where the UE is receiving the data.
07:15So this process is known as beamforming, which can be implemented in three different ways.
07:22The first method is analog beamforming.
07:25In analog beamforming, the phase of individual antenna signals are adjusted in the radio
07:30frequency domain.
07:32This adjustment influences the radiation pattern and the gain of the antenna array to provide
07:38the enhanced coverage.
07:40In digital beamforming, which is also called as baseband beamforming or precoding, this
07:46signal is precoded during the baseband processing, before the RF transmissions, means the processing
07:53occurs in the frequency domain.
07:55As a result, different signals are transmitted from each antenna.
08:00These are represented by different colors in this picture here.
08:04And the third is hybrid beamforming, when both analog beamforming and digital beamformings
08:10are combined.
08:12This technique is referred as hybrid beamforming.
08:16Hybrid beam enables the concentration of power towards a specific spatial region or
08:21a specific UE.
08:23So you see in this picture here.
08:25As a result, now the scheduler has an additional responsibility, because now it has to plan
08:31not only the time domain and frequency domain, but also the spatial domain.
08:36So this is how the beamforming works in 5G.
08:39LTE and its evolutions support different forms of MIMO, like transmit diversity, spatial
08:46multiplexing, multi-user MIMO, etc.
08:50But in 5G NR, since there are spectrums in the millimeter wavebands, and as a result,
08:56the antenna size reduces significantly with such increasing frequencies.
09:02So it is easy to place many numbers of antennas in some form of array and paste them together
09:08in one small package.
09:10So this huge array of antennas transmits narrow beams, and when the power from the different
09:15antennas combine in one direction, it acts like a strong beam.
09:21So this is the concept of beamforming.
09:24So in beamforming, the phase of the transmitting signals is adjusted in such a way that it
09:30adds a power in some specific direction to form a beam and eliminates each other power
09:36in the other directions.
09:38So that was one thing.
09:40But we also consider that millimeter waves have poor propagation characteristics.
09:45So for millimeter frequency bands, beamforming is important to serve 5G users.
09:51So here is a quick summary on what are the key benefits of using massive MIMO in 5G NR.
09:58Number one, massive MIMO systems have a larger number of active antennas elements.
10:04Number two, massive MIMO allows for more focused energy to improve signal strength.
10:10Number three, high intensity beam signals are less impacted by interference.
10:15So it has better signal quality.
10:18Number four, in good SNR conditions, more special multiplexing layers are possible.
10:24So you can enhance the data transmissions.
10:27Number five, massive MIMO improves the cellular network throughput and coverage.
10:33Number six, massive MIMO can serve more users simultaneously.
10:38Number seven, massive MIMO supports two-dimensional beamforming.
10:42So it offers better signal precisions in both horizontal and vertical planes.
10:48Okay, so that's it for today.
10:50In the next session, we will be talking about 5G spectrum.
10:54So stay tuned for the updates.
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