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Spacing Out…Getting the Most out of MIMO with Proper Antenna Spacing

While “MIMO” has been a buzz word in the mobile communications industry for some time, it is only now gaining real traction and will be a key enabler as networks migrate from 4G to 5G.  Base Station Antennas are a critical component in MIMO architectures, and there is a science to proper spacing in order to achieve the highest Quality of Service (QoS) and Quality of Experience (QoE) while minimizing interference and PIM. 

Let’s take a quick look at what how MIMO works, what it brings to mobile networks, and how proper antenna spacing is a key to maximizing throughput.4x4 MIMO image

A Quick Tour of MIMO

MIMO, or Multiple Input Multiple Output, utilizes multiple antennas at both the transmitter and the receiver (smartphone) to increase link reliability and spectral efficiency. Spatial Multiplexing makes it possible to transmit separate data streams from multiple antennas on the same frequencies. Signal processing hardware splits the data into multiple streams and transmits these streams using multiple antennas. The receiver then reverses this process, recreating the original data stream inside the phone. Obviously, propagation conditions between the transmitter and the receiver must be good for MIMO to work effectively.

What’s the result of all this?  MIMO increases the capacity of a cell without using more bandwidth. With 2×2 MIMO (two transmit and two receive) it is theoretically possible to double the throughput, while 4×4 MIMO can quadruple throughput. In an LTE network, the peak throughput using SISO (single input, single output) is about 100 Mbps. Utilizing 2×2 MIMO and 4×4 MIMO, throughput can ideally reach 173 Mbps and 326 Mbps, respectively. 

Mobile operators have implemented 2×2 MIMO in their LTE 4G networks for a number of years and are now beginning to deploy 4×4 MIMO to meet increased data demands.  Just last fall, Samsung’s Galaxy S7 became the world’s first 4×4 MIMO capable smartphone. The challenge with placing four antennas so close together in a phone (along with Wi-Fi, GPS and Bluetooth antennas) is that it can cause the transmission paths to couple, limiting MIMO performance and increasing signal interference.

While handset manufacturers were busy developing smartphones with 4×4 MIMO capable antennas, antenna manufacturers, like Kathrein, were developing 4×4 MIMO ready antennas for the cell sites.  

Optimum Macro Antenna Spacing for 4×4 MIMO

A lot of research that has been done on the proper placement of 4×4 ready MIMO antennas on cell towers. When determining optimum spacing between horizontal antenna columns for 4×4 MIMO, a balance must be found between improving gain while reducing inter-sector interference (I-SI).

Mounting antennas with proper spacing helps operators achieve maximum MIMO performance by keeping the antenna pattern in the “desired” area of the sector, with minimum energy in the “undesired” area where there is higher inter-sector interference.

Sector Power Ratio Image

Measurement studies performed by Kathrein engineers at the low band shows the optimal spacing between columns to be 0.8λ (wavelengths). For perspective, at 780 MHz, one wavelength is about 15 inches. It was determined that at mid band (1.7-2.7 GHz) gain became more important than I-SI to improve 4×4 MIMO performance. Therefore, the preferred spacing between columns for the low band has been set near 0.8λ to ensure I-SI is minimized; however, the spacing at high-band in a shared aperture is chosen for improved gain, near the 1.3λ or 1.8λ spacing, (based on bands under the radome) in an attempt to minimize I-SI as well.

Kathrein Makes Antenna Spacing Easy

Antenna Bracket for side by side

2 X Panel Mounting Kit

Kathrein recently released new 4, 8 and 12 port macro antennas that are 508 mm in width.  These wider antennas support 4×4 MIMO under one radome (click to view the datasheets: 80010901, 80010964, 80010991).  Operators can mount these antennas and be 4×4 MIMO ready without worrying about spacing two separate antennas.  For 378 mm antennas, Kathrein offers 2x Panel Mounting Kits (85010103/850108) that provide pre-configured optimum spacing for 4×4 MIMO applications.

Moving Forward with MIMO

MIMO is already offering huge dividends by increasing network throughput and capacity.  Moving forward, we will see more 4×4 MIMO implementations, as well as 8×8 MIMO, and eventually 64×64 Massive MIMO as operators move into 5G and beyond.

Learn More by visiting us at MWC Americas in San Francisco, CA, September 12-14: Booth S.1042.

Advanced Beamforming Transceivers and Antenna Arrays: Keys to 5G Communications?

At the June 29th IEEE luncheon in Plano, TX, Jeyanandh Paramesh, Associate Professor of Electrical and Computer Engineering at Carnegie Mellon University gave a technical presentation titled, “Advanced Multi-Antenna Transceivers for 5G Communications and Beyond.”

Professor Jeyanandh  Paramesh addressing Plano chapter of IEEE

Professor Jeyanandh Paramesh addressing Plano chapter of IEEE

Professor Paramesh and his team of researchers believe that directional communications using antenna arrays will be a centerpiece of next-generation communication systems in the sub-6 GHz bands and in the millimeter-wave bands. While today there are highly integrated phased-array transceivers that support steering the main beam of the antenna array pattern, the university is testing adaptive null-steering, spatial equalization, interference mitigation and various forms of multiple-input-multiple-output (MIMO) communication to see if they can achieve increased data rates, network capacity, and better interference management. Their recent work includes testing advanced beamforming transceivers that can support multi-antenna signal processing; specifically, the design of phased arrays that can address very wide swaths of mm-wave spectrum, and the design of hybrid beamformers that can support millimeter-wave MIMO communication.

As an innovation and technology leader in the connected world, Kathrein is already bringing “future proof” macro and small antennas to market that allow for many configurations of MIMO as 5G standards are still being worked out. It’s latest wide band sub-6 GHz canister antenna supports 2, 3.5, and 5.8 GHz as operators look to shared spectrum to provide increased bandwidth to subscribers. Kathrein believes that mobile communication networks will also have to meet new demands in such areas as Industry 4.0, Internet of Things (IoT) or Connected Car.

Kathrein puts Testbed for LTE and 5G into Operation

Kathrein has opened a test environment for pioneering mobile network technologies at its headquarters in Rosenheim. It will be launched in collaboration with the Swedish communications corporation Ericsson. Kathrein will use the testbed to simulate novel applications in a trial network in order to gain valuable insights in the years to come. This will provide the basis for advancement of the current wireless communication standard LTE and the new standard 5G.

“The test environment will allow us to try out various technologies and their interaction in a single overall system – a capability that is very important for our development work,” explains Maximilian Göttl, Head of Portfolio & Innovation in Kathrein’s Communication Products division. We’re creating our own network, as it were, so as to be able to draw conclusions from live operation.” The insights gained in this way will allow systems to be improved on a step-by-step basis, which is essential in connection with the new wireless communication standard 5G in particular.

KEY INSIGHTS FOR FUTURE PRACTICAL APPLICATION

“In this way we can derive recommendations for industry and network operators in terms of optimum system design,” says Göttl. He adds that this is also relevant to the technology area Massive MIMO (Multiple Input, Multiple Output). MIMO already forms part of current LTE technology, where several reception and transmission antennas are used at the same time. In the case of Massive MIMO, dozens or even hundreds of antenna modules are deployed in an array. This allows very high data throughput rates in a frequency band.

One of the focus areas of the testbed trials will be the automotive sector. Cars will be equipped with the appropriate antenna systems so as to optimise data transmission from and to cars. In this way, test runs conducted in Rosenheim will yield valuable insights in terms of future system design. Kathrein is also collaborating with Altair Engineering GmbH. The global CAE software provider whose German headquarters are in Böblingen, provides WinProp, a programm that simulates mobile network coverage based on maps. Real testbed measurements can then be checked against the computer simulation. The ultimate aim is to be able to use computers alone to conduct test runs for future system architectures.

PROJECT LAUNCH WITH ERICSSON

In the new test environment, Kathrein’s innovation department is collaborating with Ericsson’s research department. The Stockholm-based network supplier has been one of Kathrein’s partners for many years, now providing the base stations and other components for the measurements. “The testbed underpins our aspiration to be a pioneer when it comes to new technologies. In Rosenheim we will shape the future,” says Anton Kathrein, CEO of the Kathrein Group.