The continuously increasing data volumes in wireless networks and ever higher connection requirements in terms of latency and stability mean that new technical solutions are needed. New antenna technologies such as MIMO or beamforming are an important building block of such solutions.
The problem is a familiar one to every Internet user: the more devices are connected to the Wi-Fi, the slower the data transfer becomes. This is due to the fact that routers are only able to communicate with one device at a time.
If several devices are connected to the WLAN simultaneously, each participant must first wait their turn for data to be transferred. If the volume of transferred data increases on top of this, for instance due to multimedia content like 3D videos or augmented-reality applications, wireless systems can only satisfy the needs of demanding users with the help of smart antennas.
Such smart antennas comprise multiple transmitting and receiving antennas, in addition to the associated signal-processing capability. They make it possible to transfer data at ever higher rates and thus represent one of the key technologies for current and future wireless communication systems alike.
What is MIMO?
As soon as obstacles obstruct this connection, the signals are scattered and dissipated. This causes the connection to become disrupted or even break down entirely. However, visual contact is extremely hard to establish for most wireless applications. MIMO, on the other hand, utilises the scattering of the signals and achieves a better system capacity and better data throughput rates with the various routes that the signals take, in addition to their staggered arrival at the end device. MIMO has been well known for some time already due to its use in WLAN networks and is explicitly defined in high-speed WLAN standard IEEE802.11ac.
The multi-user (MU)-MIMO introduced with IEEE802.11ac Wave 2 makes it possible for a Wi-Fi router to communicate with multiple devices simultaneously. With MU-MIMO, entire departments in a company can simultaneously hold video conferences, download large e-mail attachments and media content, align large files on local file servers or cloud storage services, or stream presentations – all without lagging or buffering.
MIMO technology is also used in mobile-communication networks, where it was introduced with LTE. While LTE usually combines a maximum of eight antenna elements, the future 5G standard will require considerably more power: in the case of the millimetre waves used here, several hundred antennas are frequently used in one transmitting or receiving station.
This optimised multi-antenna technology – called “Massive MIMO” – increases the capacity of the mobile-phone network several times over. Nonetheless, Massive MIMO requires one additional technology in order to exploit the benefits of millimetre waves’ large bandwidth:
Less interference thanks to wireless signals
Signals are emitted evenly in all directions from conventional antennas. If the signals clash with those from other transmitters, interference can occur, and the signal transmission can be seriously disrupted. In combination with beam-forming, the multi-antenna technology of Massive MIMO solves this problem.
By staggering the transmission of the same signal with multiple antennas, the transmitter triangulates the client’s approximate location and directs its transmission accordingly to shape a signal beam – a process referred to as “beamforming”. As a result, a beamforming transmitter can send dedicated signals in different directions to individual receivers. This increases the range, guarantees a more stable connection and higher transmission rates, and also reduces unwanted radio interference.
Reducing power consumption
The MIMO antenna elements require D/A circuits, which convert digital signals into analogue ones so that they can be transmitted by the antenna. However, if digital beamforming is used in the millimetre-wave range, whereby every antenna element features a D/A circuit, multiple high-speed D/A circuits are required. This will result in higher power consumption.
One solution to this problem is so-called “hybrid beamforming”, for which a portion of the signal processing is conducted in the analogue antenna element. Multiple antenna elements can consequently be connected to one single D/A circuit. Power consumption is reduced by doing so because fewer D/A circuits are needed. Using a hybrid beamforming system of this kind results in an economisation in terms of hardware, an improvement in the energy footprint and a reduction of calculation effort.
400 gigabits per second will be transmitted in the future
By implementing these technologies, the future 5G mobile telephony standard promises an enormous power increase in wireless communication, with rates of up to ten gigabits per second. Yet even now, it is already apparent that existing frequency ranges will not be sufficient to cater to the growing demand for stable wireless communication in the future. This is exactly why researchers are already working on the mobile communication standard which will succeed 5G.
The goal is to facilitate a network connection that breaks into a terahertz frequency range; one so stable that it can transport data wirelessly at speeds as high as 400 gigabits per second.