All 5G system networks will use MIMO (mass input, mass output) antenna arrays and beamforming. Many 5G systems will work with millimeter-wave (millimeter-wave) spectrum. Designing a MIMO array that operates at millimeter-wave frequencies is challenging for a variety of reasons. System-level design will be the best way to meet these challenges.
Millimeter wave signals have difficult propagation conditions and greater path loss. 5G networks need to maintain maximum system flexibility in multi-user applications.
If each subsystem from the antenna array to RF chain to signal processing is tuned into a system during the design process, it will be easier to meet these and other system-level performance requirements.
Designers have two options for beamforming, one more practical than the other. If cost and power consumption are not limited in a 5G system, dedicated receive and transmit paths can be added for each MIMO array element. This "all-digital" beamforming architecture will provide maximum flexibility from a system level perspective to form beams in large multi-user scenarios.
However, cost and power consumption are limited, and hybrid beamforming - "hybrid" is left behind, because analog phase shifters are integrated with digital circuits. And, whenever digital and analog are integrated, this is another place where system-level design approaches are recommended.
Demand Hybrid Beams for Hybrid Beamforming
The main goal of the forming design is the proper division of the architecture between the RF and digital domains. The design also includes precoding weights and RF phase shift groups that are required to meet the design goals of improving the virtual connection between the base station and the user equipment (UE).
From a system perspective, the balance is to find the best split between RF and digital beamforming. Partitioning is possible, and engineers can build systems efficiently without having to implement a separate mapping between MIMO array elements and transmit/receive (T/R) signal chains. Still enough flexibility can be achieved to satisfy multi-user scenarios.
One of the advantages of moving to the millimeter wave frequency is that the antenna element size changes with the wavelength. This method can implement a large number of elements with reasonable physical dimensions.
Trade-offs are more elements per element and more RF connections add complexity. The array design must allow MIMO operations to support spatial multiplexing to achieve higher channel capacity. These factors add complexity, as more hardware and control are needed. Since there are a large number of antenna elements in the MIMO array, the design must also take into account the actual coupling between the antenna elements.
Hybrid beamforming designs are developed by combining multiple array elements into sub-array modules. The AT / R module is dedicated to subarrays within a larger array, so fewer T / R modules are required in the system. You can choose the number of elements and the position in each subarray to ensure that system-level performance is satisfied over a range of steering angles. This method translates directly into less system hardware.
A MIMO array implemented using hybrid beamforming implements a series of spatial processing capabilities. Signal processing algorithms include direction of arrival estimation, beamforming, and spatial multiplexing all make final applications possible. These algorithms also help characterize the channel between the base station and the UE.
For hybrid beamforming designs, it is also important to include a full suite of system components in the system model to ensure optimized link-level system performance. Knowing how the design choice affects the bit error rate (BER), spectrum efficiency, and channel capacity is critical before the system is manufactured. It is also important to choose the most effective signal processing method. Creating a model for each part of the system makes the system design easier. You can try out ideas at the lowest cost point in the project life cycle.
From the architectural point of view, hybrid beamforming zoning systems can be formed in a variety of ways. Figure 1 shows a typical high-level configuration.
Figure 1 possible partition strategy. Source: The MathWorks
In Figure 2 , we can see that on the sending side, the number of T/R switches, N TRF , the number of antenna elements smaller than N, and small Ť . In order to provide more flexibility, each antenna element can be connected to one or more T/R modules. In addition, an analog phase shifter can be inserted between each T/R module and the antenna to provide some limited steering capability.
Figure 2 Hybrid beamforming example of RF and digital steering. Source: The MathWorks
The configuration of the receiver is similar, as shown in Figure 2 . The maximum number of data streams N S that the system can support is the smaller of N TRF and N RRF . In this configuration, it is not possible to apply digital weights to each antenna element as it is in the all-digital case. In contrast, digital weights can only be applied to each RF chain. At the component level, the signal is adjusted by an analog phase shifter, which only changes the phase of the signal. Therefore, precoding and merging are completed in two stages. Because this method performs beamforming in both digital and analog fields, it is called hybrid beamforming.
The development of 5G MIMO arrays is challenging, but the required hybrid beamforming system design can be modeled before any hardware is built. This modeling effort can save hardware costs and save time during design and development. Design issues can be identified at the earliest stages, where they are the most cost-effective remedies. The resulting system design can achieve complete system-level requirements.
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