Smart Antennas which are also known as Adaptive Array Antennas, digital antenna arrays, multiple antennas, or MIMO is antenna arrays with smart signal processing algorithms used to identify spatial signal signatures like the direction of the arrival of the signal. Smart antenna techniques are used in signal processing, track, and scan radar, radio astronomy, telescopes, WCDMA, LTE, and 5G technologies. There are two main types of smart antennas which include switched beam smart antennas and adaptive array smart antennas. Switched beam systems have several available fixed beam patterns. An adaptive array allows the antenna to steer the beam to any direction of interest while simultaneously nulling interfering signals. They are also a defining characteristic of MIMO systems. Multiple antennas can be used at either the transmitter or the receiver. MIMO supports spatial information processing, in the sense that conventional research on Smart antennas has focused on how to provide a digital beamforming advantage by the use of spatial signal processing in wireless channels. It includes spatial information coding such as spatial multiplexing and diversity.
It is the application of multiple radiating elements transmitting the same signal at an identical wavelength and phase. The more radiating elements that make up the antenna, the narrower is the beam. The beamforming concept has side lobes and the main lobe. Side lobes are unwanted radiation of the signal that forms the main lobe in different directions. The more radiating elements that make up the antenna the more focused the main beam is and the weaker the side lobes are.
Beam steering and Beam Switching
Beam steering is achieved by changing the phase of the input signal on all radiating elements. Phase-shifting allows the signal to be targeted at a specific receiver. An antenna can employ radiating elements with a common frequency to steer a single beam in a specific direction. Different frequency beams can be steered in different directions to serve different users. The direction a signal is sent in is calculated dynamically by the base station as the endpoint moves, effectively tracking the user.
MIMO is Multiple Input Multiple Output. MIMO antenna is a feature of commercial public wireless and Wi-Fi systems, but 5G demands the application of Massive MIMO. It is a multi-user MIMO technology that can provide uniformly good service to wireless terminals in high-mobility environments. Massive MIMO can provide uniformly good service to wireless terminals in high-mobility environments. Massive MIMO increases the number of transmitting antennas from tens to hundreds of antennas at the base station. MU-MIMO (Multi-user MIMO) further expands the total capacity per base station by enabling communication with multiple devices using the same resources. MU-MIMO is a multi-user with knowing multiple inputs multiple outputs. In MU-MIMO, the base station sends multiple data streams, one per UE, using the same time-frequency resources. Hence, it increases the total cell throughput i.e the cell capacity. It enables the UEs to operate without the need for knowledge of the channel or additional processing to obtain the data streams. MU-MIMO in the downlink significantly improves the capacity of the gNB antennas. It can scale with the minimum of the gNB antennas which can achieve higher capacity gains.
Methods of implementing Antenna Beamforming
There are three methods of implementing Antenna Beamforming:
- Analogue Beamforming
- Digital Beamforming
- Hybrid Beamforming
It is the simplest method, in which the signal phase is changed in the analog domain. The output from a single RF transceiver is split into a number of paths, corresponding to the number of antenna elements in the array. Each signal path then passes through a phase shifter and is amplified before reaching the antenna element.
In digital beamforming, each antenna element is fed by its own transceiver and data convertors and each signal is precoded in baseband processing before RF transmission. It enables several sets of signals to be generated and superimposed onto the antenna array elements, which enables a single antenna array to serve multiple beams, and hence multiple users. It requires more hardware and signal processing, leading to increased power consumption, particularly at mmWave frequencies, where several antenna elements are possible.
It is considered a cost-effective solution for large-scale, mmWave antenna arrays and various architectures developed for gNB. These architectures are divided broadly into fully connected, where each RF chain is connected to all antennas, sub-connected or partially connected, in which each RF chain is connected to a set of antenna elements.
In all Architectures, communication between the gNB and the UE is coordinated using a technique known as beam sweeping, along with synchronization signals (SS), and Channel State Information (CSI), obtained via a Channel State Information Reference Signal (CSI-RS) a type of pilot signal sent from the gNB to the UE.
In beam sweeping, the gNB transmits bursts at regular intervals in different spatial directions. The UE listens for these burts and uses the CSI to determine a channel quality associated with each one.
Benefits of beamforming
- It effectively uses the science of electromagnetic interference to enhance the precision of 5G connections, working with MIMO to improve the throughput and connection density of 5G network cells.
- Beamforming’s ability to cancel out or “null” interference is also a significant benefit in crowded, urban environments with high densities of UEs, where multiple signal beams can potentially interfere with each other.