Techniques Involved in 5G NR – mmWave Vision

In this blog, we are going to enlighten about the mmWave implementation needs, design considerations techniques that made this vision realizable. It is time to get into the content, yes let’s begin with a question.

Beamforming — What is beamforming? why do we need it for 5G?
Beamforming has been known since the 1940s, but in recent years beamforming technology has paved way for incredible improvement in wireless networking. As discussed in previous blogs it is known that the 5G NR system uses mmWaves. To avoid high propagation loss in mmWaves and to support the high bandwidth demands of users, beamforming and massive Multiple Input and Multiple Output (MIMO) techniques are needed.

These techniques are used,
• To improve the spectral efficiencies and
• To provide reliable coverage to justify the needs of 5G.

The beamforming technique transmits similar signals at an identical phase and wavelength by using several radiating elements in its system. A single antenna with more emphasized waves in a specific direction helps in targeting the users more precisely.

The terms beamforming and mMIMO are every so often used interchangeably. One way to define is that beamforming is used in mMIMO it means beamforming is a subset of the mMIMO technique.

Massive MIMO is an enhancement of MIMO which breakthroughs the legacy system by adding a larger number of antennas on the base station. In a massive MIMO system, the massive number of antenna elements forms both the horizontal and vertical beams towards the user which increases the data rates.

LTE uses the model of Single User MIMO (SU-MIMO) which means the base station and UE contains multiple antenna ports and multiple data streams are transmitted simultaneously to the UE using the same time or frequency resources, which results in doubling or quadrupling the peak throughput of a single user.

MIMO technology even allows Multi-User MIMO (MU-MIMO), in which the base station sends data streams one per UE using the same time\frequency resources.

It means the messages for different users to travel securely through the same data pipelines then organized to specific users once data reach their mobile devices. The base station has multiple antenna ports, as many as there is a mobile terminal receiving data instantaneously.

Principle of operation—Beamforming
Beamforming uses multiple antennas to regulate the direction of wave-front by appropriately calculating the magnitude and phase of individual antenna signals from an array of multiple antennas. The same signal is sent from multiple antennas which have sufficient space of at least half a wavelength among them. The beamforming technique is classified as follow,

Analog beamforming is the traditional method that creates a single beam by applying phase delay or time delay to each antenna element. In digital beamforming, each antenna acquires a dedicated analog baseband channel which in turn needs a digital transceiver for each antenna. So, it increases the design cost and power consumption in digital beamforming.

Which one is chosen for the 5G system???
By considering these criteria 5G system uses a combination of analog and digital beamforming which is commonly known as the hybrid beamforming technique for data transmission.
In previous cellular systems, conventional wide beam-based cell sector coverage is used and provides 120º wide beam sector coverage. The 5G system uses beam-based cell sector coverage which increases the link budget and overcomes the disadvantages of mmWave.
Finally, we are now familiar that the 5G system is using beam-based cell coverage… we need a beam management technique to deal with the consequences of using beams to transmit and receive data.

Beam management refers to procedure or technique used to acquire and maintain a set of Transmission Reception Point and/or User Equipment beams which are used for DL and UL transmission or reception.
• Beam Sweeping
• Beam measurements
• Beam determination
• Beam reporting
• Beam failure recovery

These are the steps involved in beam management.
 Beam sweeping is a procedure to transmit the beam in all predefined directions in a bust within a regular interval. This should be measured because a narrow beam can only reach a part of the coverage area at a given time. It isolates the optimal beam pair for the gNB and the UE when it successfully receives the broadcast data.
 The evaluation of the quality of the received signal at the gNB or the UE is referred to as beam measurement.
 The selection of suitable beam or beams either at the gNB or at the UE is known as beam determination. This selection is accomplished according to the measurements obtained through-beam measurement
 The UE sends beam quality and beam decision information to the Radio Access Network (RAN), this process is known as the Beam Reporting process.
 Beam failure recovery is done when the mobile terminal is suffering from poor channel condition.

Initial Beam Acquisition is the process by which UE acquires broadcast and synchronization information just after the power-up of the device. This is based on the Beam Sweeping technique.

The information acquired by UE is the details of synchronization signals and the Master Information Block (MIB). The synchronization signals are consisting of Primary Synchronization Signals (PSS) and Secondary Synchronization Signals (SSB) which helps UE to acquire frame, subframe, symbol timing as well as physical cell identity. MIB contains System frame Number and other useful information.

SS/PBCH block is the pre-specified blocks of data which contains synchronization and MIB information for UE. During beam sweeping one SS/PBCH block is transmitted using one beam in one direction and then the next block in a different direction using a different beam and so on. The direction of the signal is sent in is calculated dynamically by the base station as the UE moves, if a beam cannot track the user the UE switches to a different beam. These procedures of beam management repeat periodically to gain optimal beam pair over time.

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