Came across this study, which seems interesting: Data from the Sprint LTE TDD network, comparing performance side-by-side of 64T64R and 8T8R antenna systems.
From the results:
“We observed up to a 3.4x increase in downlink sector throughput and up to an 8.9x increase in the uplink sector throughput versus 8T8R (obviously the gain is substantially higher relative to 2T2R). Results varied based on the test conditions that we identified. Link budget tests revealed close to a triple-digit improvement in uplink data speeds. Preliminary results for the downlink also showed strong gains. Future improvements in 64T64R are forthcoming based on likely vendor product roadmaps.”
Hi Emil, can you kindly elaborate upon the 8.9x UL throughput improvement compared to 8T8R. That sounds huge.
If you can serve 8x more users with the same throughput as before, you will get an 8x improvement. In addition to that, the beamforming gain can ideally increase the SNR by 8x, but that will have a smaller impact on the throughput since it grows logarithmically with the SNR. But it is definitely a combination of serving multiple users and getting a better beamforming.
Thanks for your reply. Though, I am trying to understand the difference in gains between Uplink & Downlink for the same setup. How can the UL throughput gains be 3 times the DL Tput gains, given that – beamforming gains & increase in served users applies to both?
I don’t know the details of the measurement campaign, but I guess the 8T8R base station was using spatial multiplexing in the downlink but not in the uplink. In other words, they compare against a previous system with a better downlink implementation than uplink implementation.
Hi Emil,
Nice to see so good content on Massive MIMO. I have a basic question related with MIMO. What is MIMO Layer? Is it equal to No. of Tx in a radio ? For example, if a Radio is 8T8R what will its MIMO Layer.
No, each layer is a parallel stream of data that is transmitted with a different spatial directivity. It could either be meant for a different user, or transmitted so that a single device can decode multiple layers, since they arrive with different directionality.
The number of layers is upper limited by the number of radios, but a distinguishing factor of Massive MIMO is that the base station has more antennas/radios than the number of layers. The reason is that we can then more easily transmit with a directionality that is easily distinguishable.
Sir, I am still confused between antenna elements, antenna port and antenna. And antenna port is same as channel rank? Please sir, would you clarify one more time?
An antenna element is a physical unit that transmits and receive wireless signals over the air. An antenna port is a transceiver chain that generates signals that will be transmitted by antenna elements and processes the received signals obtained from antenna elements.
The reason that one might want to separate between these things is that one antenna port often is connected to multiple antenna elements in practical implementations. Antenna elements are small and cheap, antenna ports are larger and more expensive. See Figure 4 in the following white paper for a case where 64 antenna elements are connected to different number of antenna ports: https://www.ericsson.com/en/reports-and-papers/white-papers/advanced-antenna-systems-for-5g-networks
The word “antenna” might refer to any of these things. In academia, the words antenna is often synonymous with antenna port and antenna element since it is implicitly assumed that each antenna element is connected to one transceiver chain.
Thank you very much sir.
I am a M.TECH student from india, our professor recommended your book.
Thank you for early reply and great video series on Multiple Antenna Communication.
Dear Sir,
As in the practical implementation of 8T8R, can it be done Azimuth, as well as Elevation Beamforming, considering Digital beamforming,
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a.) column-wise combining with ports (Only Azimuth is possible)
b.) If I make a separate port polarization combination one is vertical combining and another is Horizontal combining (Az and EL possible), what can be challenges that need to face.
Please comment with your views.
Thanks & Regards
Mahesh
I think the desired mapping between antenna elements and ports depend on how the propagation environment looks like, but I think that (in most cases) the users are more easily separable by azimuth beamforming than by elevation beamforming (or a mix of it). This is also the message from the following white paper by Ericsson: https://www.ericsson.com/en/reports-and-papers/white-papers/advanced-antenna-systems-for-5g-networks
Sir, Thanks for your valuable comment.
The number of layers in massive MIMO is 8, which means 8 data streams will be sent for 8 users simultaneously with 8 different beams. Is my understanding correct sir?
Yes, and here is a trial from last year where 16 layers were transmitted (8 users, 2 layers per user): https://ma-mimo.ellintech.se/2020/10/02/reciprocity-based-massive-mimo-in-action/
One more question sir:
If we have 4 sub arrays (3 elements/sub array) vertically positioned in 1 column, which is then arranged horizontally 4 times. In this case how horizontal beam-width calculated.
https://www.ericsson.com/en/reports-and-papers/white-papers/advanced-antenna-systems-for-5g-networks
The beamwidth depends on the antenna radiation pattern of the individual elements as well as the total horizontal width of the array, so it is hard to answer in general. With isotropic antennas that are half-wavelength-spaced, you will get a first-null beamwidth is 2/(number of antennas) radians. It is essentially unaffected by the antenna patterns. However, the 3 dB beamwidth is smaller and also shrinks when using directive antennas.