# Transmit beamforming and beamtracking

Transmit beamforming, as shown in Fig. 1, is a widely adopted technique in wireless communications for signal transmission from an array of multiple antennas to one or multiple users simultaneously served in the cellular network. In the fifth generation (5G) wireless networks, a very large number of antennas are employed at the base station, which enables to generate multiple, very narrow beams simultaneously pointing to individual users. As such, the signal power at the intended user is efficiently increased, while the interference to non-intended users is greatly reduced. Hence, both spectral and energy efficiency can be effectively improved for massive MIMO systems.

Let’s consider a massive MIMO downlink scenario, where the base station equipped with $N$ antennas communicates with $K$ single-antennas users. The power minimization-based transmit beamforming problem can be formulated as

$\begin{array}{rcl}&\min\limits_{\boldsymbol{w}_{1}, \cdots, \boldsymbol{w}_{K}}&\sum_{k=1}^{K} \| \boldsymbol{w}_{k} \|^{2} \nonumber \\ &\mbox{subject to}& \mbox{SINR}_{k} \le \gamma_{k}, \nonumber\end{array}$

where $\boldsymbol{w}_{k} \in \mathbb{C}^{N}$ is the linear beamforming weight vector associated with the $k$-th user with the allocated transmission power $\|\boldsymbol{w}_{k} \|^{2}$, $\mbox{SINR}_{k}$ is the signal-to-interference-plus-noise ratio (SINR) at the $k$-th user, and $\gamma_{k}$ is the required SINR of the $k$-th user for achieving certain data rate. By solving the above convex optimization problem, the optimal transmit beamforming scheme can be easily obtained.

Meanwhile, the users’ velocities in the era of 5G have a high dynamic range, which depends on walking, driving, even flying. Benefited from the very large number of antennas employed at the base station, the transmit beam widths in massive MIMO systems are very narrow, which, consequently, can not cover a large range as the beam generated by a single antenna or a small number of arrays. Hence, the choice of optimal pointing direction is crucial to achieve effective beam tracking when the served users are moving especially fast moving. Among various beam tracking methods, well developed Kalman filters, e.g., extended Kalman filter, can be chosen as the tracking filter considering its low complexity. As such, the required transmission data rate via the high SNR is guaranteed.

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VOCAL Technologies offers custom designed, sophisticated transmit beamforming and beam tracking solutions in 5G systems. Our custom implementations of such systems are meant to deliver optimum performance for your specific beamforming and tracking tasks. Contact us today to discuss your solution!