beamforming basic part-2

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In this section we will learn about how beamforming benefits are obtained in practice with massive MIMO antennas. With the deployment of NR, the target is to make 5G radio design fully optimized for massive MIMO beamforming. Unlike a traditional solution, beamforming sends the data with narrow beams to the users. The same resource can be reused for multiple users within a sector, thus minimizing the interference and increasing the cell capacity.

Massive MIMO is the extinction of traditional MIMO technology to antenna arrays having a large number of controllable transmitters. 3GPP defines massive MIMO as more than 8 transmitters. To deliver either a fixed grid of beams or UE specific beamforming beams can be formed in a number of different ways.

Suppose, if the antenna has 2 TRX (transceiver) branches it can send with two parallel streams to one UE.  Similarly, if the antenna has 4 TRXs it can send 4 streams to one UE having 4 antennas or dual-stream to two UEs simultaneously with multi-user multiple inputs multiple outputs (MU-MIMO). Also if the antenna has 64 TRXs, it can send data to multiple UEs in parallel. The number of TRX s is an important design factor in massive MIMO antennas. The larger the number of TRXs used the more beams can be generated thus giving more capacity.  

But including more number of TRXs also makes the antenna larger and increases the costs. The number of antenna elements is another important antenna design factor, which can be greater than the number of TRXs. The number of antenna elements defines the antenna coverage and its gain. The use of more antenna elements increases the antenna gain and makes the antenna larger. Also, the spacing of the antenna elements depends on the frequency (physical size of the antenna is larger at lower frequencies).

Also the number of antenna elements defines the antenna gain and antenna size. The size is dependent on the frequency. The antenna becomes smaller at high frequency.

The number of TRXs defines the capacity gain and can be equal or lower than the number of antenna elements.

Number of MIMO streams states the peak data rate capability and is mainly dependent on the baseband processing capability. The number of MIMO streams can be lower than or equal to the number of TRXs. The additional elements are typically added as more rows if the number of antenna elements is larger than the number of TRXs.

Why beamforming can yield more gain in 5G than in LTE???       

Some of the reasons are:
·       The user-specific reference signals in 5G support user-specific beamforming. LTE must use CRSs (cell-specific reference signals) that cannot be used for beamforming.
·       5G supports more transmission branches. NR supports initial feedback for 64TX while LTE supports 4TX in release 8,8TX in release 10, 16TX in release 13 and 32TX in release 14.
·       Beamforming is supported for 5G common channels with beam sweeping. Beam sweeping is the operation where the broadcast channel and synchronization signal are transmitted in different beams in the time domain.
·        LTE beamforming is based on uplink sounding RS (reference signal) measurements since legacy devices do not support beamforming feedback. Whereas there are no legacy device limitations in 5G since beamforming is included in NR from the first specifications.

In Upcoming Part, we will learn more about digital and analogue beamforming and its interview question and its answer. And for more learning please go through our 5G and LTE page.

Stay tuned for more Update…………………

Pinal Dobariya…


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