前言：
本篇主要转载
【Optimization Hassle - Q & A Interviews】 What is beamforming in 5G NR
Beamforming 仿真工具数学原理:
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https://en.wikipedia.org/wiki/Phased_array
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目录：
- what is beamforming in 5G
- what is factors that effect beamforming performance
- SRS & UCI
- what is 3D or FD beamforming
- what are types of beamforming?
- what is transmission mode(TM) in beamforming?
一 what is beamforming in 5G
A radar antenna focuses transmitted energy in a narrow（狭窄）, conical-shaped beam（圆锥形的波束） (see Figure 1). The angular width of the radar beam is defined as that region of transmitted energy that is bounded by one-half (-3 dB) the maximum power. Around 80% of the energy is contained within the main beam（主波束）, with the sidelobes(旁瓣） generally being more than 1000 times less intense in a high quality antenna (unlike in the p-theta graph)
二 what is factors that effect beamforming performance
N = number of elements
Ge = element gain
Gt = antenna gain
Pt = total transmitter power
Pe = Power of per element
Tn = noise temperature
三 SRS & UCI
NR上行物理信号包括探测参考信号（Sounding Reference Signal，SRS）
上行控制信息（Uplink Control information，UCI）,用于向基站报告UE的状态，如HARQ接收的状态、信道状态信息等。
四 what is 3D or FD beamforming
Answer:
3D beamforming refers to use of mMIMO for steering beams both in the horizontal
(Azimuth 方位角) dimention and vertical垂直(elevation 高度) dimentions
if we have a contol in beams in both vertical & horizental domain，
so we have 3D or Full-mMiMo beamforming
五 what are types of beamforming?
Answer:
----------------------------------------------------------Beamforming types are 3 and they are:
1 Digital beamforming:
each antenna branch have seperate TRX .
so if for example, we have 32 Antenna-element, so we have to implement 32TRX
--can transmit multiple antenna pattern (beams) simulanously
--used for low frequency band as limited antenna element is required as TRX needed
per antenna branch
- high power comsumption and high cost
2 Analog beamforming:
- all antenna branch have only single TRX so if for ex,we have 32 antenna-element
so we have to implement only one TRX
- can transmit only one antenna patterns(beams) at a time in specific direction
-used for high frequency band as no limitation in number of TRX(only one) as in digital
beamforming.
-low power consumption and low cost
3 Hybrid beamforming:
-combines the digital beamforming and analog beamforming
- the number of TRXs and RF Chains in the beamforming antenna are in
general lower than the number of antennas
- The motivation for hybrid beamforming is to minimize the number of RF chains,
which will reduce energy consumption and design complexity , making it more general
cost-effective
六 what is transmission mode(TM) in beamforming?
Answer:
when enabling beamforming in mMIMO ,we have switch to three types of transmission
mode TM and there are:
TM7:
Use single-stream beamforming(one code-word) Rank as diversity mode without spatial
multiplexing
use antenna port number-S
TM8:
Use dual-stream beamforming(two-code-wod)rankd2 as spatial-multiplexing MIMO.
use antenna port 7&8
TM9:
use 8 streams beamforming as 8T8R MIMO.
use antenna port 7,8,9,10,11,12,13,14
