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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.

Winding Down the Year with Wireless – the Tradeshow Circuit 2015 Comes to a Close

By Capriccio Martin

It’s been a whirlwind event schedule for the past few months – especially for Kathrein, as we continue to amp up our presence at industry events.  As the oldest antenna manufacturer in the world, we feel it’s our job to share much of what has been learned over the past 100 years and translate that into our vision for 5G, massive MIMO, sectorization, concealment, mmWave, and other antenna innovations. 

We had the pleasure to attend LTE North America this week in Big D – it was a good show and we like that it is in our “backyard”.  It’s a notable industry event in that the organizers do a nice job in bringing in top notch speakers from AT&T, T-Mobile, Verizon, Telus, Sasktel and key analysts from 451 Research, iGR, Senza Fili, and Mobile Experts.

Ken Rehbehn, 451 Research, Moderator of Antenna Evolution Day at LTE North America

Ken Rehbehn, 451 Research, Moderator of Antenna Evolution Day at LTE North America

One resounding message from the Antenna Evolution Focus Day was the importance of Antenna quality in LTE and soon 5G networks.  LTE KPI’s are more stringent than 3GPP and we anticipate 5G to take things even a step further.  Be on the lookout for a new whitepaper from Kathrein that will discuss this topic in more detail.

At the show, the 5G tracks seemed to bring in the biggest audiences from what we observed and it was nice to see big interest in Public Safety as well.  Ken Rehbehn, analyst at 451 Research, as well as a fire fighter himself, tweeted eight times during the presentation from Jeff Bratcher, Acting CTO for FirstNet. It was a fantastic overview on the progress FirstNet has made.  Here’s a few key takeaways:

Acting CTO FirstNet, Jeff Bratcher

Acting CTO FirstNet, Jeff Bratcher

  1. FirstNet has $6.5 Billion to offset network costs. Cannot go back to Congress to ask for more money.
  2. There is excess capacity in the 20MHz of Band 14 and will commecialize the leftover spectrum.
  3. There are 5 Early Builder Projects and all have a Spectrum Lease Agreement (SMLA) with FirstNet: Texas, Los Angeles, New Jersey, New Mexico, Colorado.
  4. FirstNet has close ties with other countries’ public safety plans – specifically in the UK and South Korea. South Korea is pushing voice the fastest.
  5. There will be a single “awardee” to build out and manage the core network, but will incorporate teaming agreements for national, regional, and rural providers.

FirstNet Public Private Partnership Value DistributionEarly Builder Band 14 Projects from FirstNet

Recent Board Decisions Chart from FirstNet

Another recent industry event where Kathrein had the pleasure to attend, speak, and exhibit was HetNet Expo in sunny Los Angeles this past October.  As always, Tracy Ford at PCIA does an excellent job of representing the entire HetNet ecosystem via the topics and speakers. Our favorite presenter hands down was the well-spoken Marc Ganzi, CEO of Digital Bridge (which just closed on the acquisition of ExteNet Systems).  He was bullish on the industry as a whole and seemed particularly jazzed about Small Cells over the next few years. Watch here.

Marc Ganzi, CEO of Digital Bridge, shares his views of the Bandwidth Delivery Model

Marc shared his views of the Bandwidth Delivery Model and noted:

  1. We need to be creative in our 5G site offerings – multiple forms of “Site Solutions”.
  2. Need to account for MIMO in the future.
  3. CRAN and SDN are part of the future network.
  4. “Owning” the network elements and delivery is critical.
  5. “Spectral efficiencies will be where the battle will be won or lost” – efficiencies in radios, battery life, and devices.
  6. Need more Sites – Macro, Small Cell, DAS, Wi-Fi Offload.
  7. Densify and fortify the network with Small Cells – underlay networks.
  8. Wi-Fi is not going away, not a disrupter.
  9. Distributed Network Services (DNS as he calls it – not DAS) – 74,000 Active Nodes in 2014.
  10. Indoor DNS Market will grow to 12,000 locations and 133,000 nodes by 2020.

Kathrein booth at HetNet Expo 2015

We had the honor of presenting on the public safety panel at HetNet Expo 2015 that was moderated by Sandra Wendelken. Panelists were Mel Samples of CADSTAR, Ken Baker of the University of Colorado-Boulder, Jim Nevelle of Kathrein and Battalion Chief Kevin Nida of the Los Angeles Fire Department. 

HetNet Expo 2015 Public Safety Panel

Click here to watch the panel (in segments):

https://youtu.be/oBe_84HZlqM

https://youtu.be/Orunmbf7nyM

We will be sharing more in the coming months including more on Antenna evolution strategies, Multi-band Antennas, Small Cells, and the Importance of the Quality of the Network. Until then, we would like to hear from you.  Your thoughts as we wind down the wireless tradeshow circuit of 2015?