Showing posts with label Antennas. Show all posts
Showing posts with label Antennas. Show all posts

Monday, 23 November 2020

Radio Design Webinar: Optimising Your 700 MHz Deployments

 


Radio Design, the award-winning market leader in the provision of wireless infrastructure sharing solutions and RF filter systems, hosted a webinar last week focused on the deployment of the 700 MHz frequency band. This new 700 MHz spectrum is in great demand across the world, mainly due to its long anticipated use as low band 5G spectrum. The webinar explores the potential of this band, as well as how to prepare for potential challenges when deploying.

For people who are familiar with our trainings, we divide the spectrum into three layers, the coverage layer, the capacity layer and the high-throughput layer. 700 MHz is the most popular coverage layer spectrum worldwide.

The slide above from the webinar talks of the recent Austrian 5G Spectrum auction that we blogged about. See tweet below for details

In the webinar, slides and video embedded below, Radio Design’s founder – Eric Hawthorn – kicks things off by analysing the benefits of deploying the 700 MHz band in the real world, before passing over to Global Engineering Director – Steve Shaw – who explores some of the technical problems which can arise, as well as some of the solutions. Last but not least, COO and co-owner of Keima – Iris Barcia – provides her insight into the benefits of deploying the 700 MHz band.

Related Posts:

Tuesday, 19 November 2019

Cell-free Massive MIMO and Radio Stripes


I wrote about "Distributed Massive MIMO using Ericsson Radio Stripes" after MWC 2019 here. I found it a very interesting concept and it will certainly take a few years before it becomes a reality.

Emil Björnson, Associate Professor at Linköping University have produced couple of videos on this topic. I am embedding both of them below for anyone who may be interested.

"A New Look at Cell-Free Massive MIMO" - based on technical paper from PIMRC 2019 on how to design Cell-free Massive MIMO systems that are both scalable and achieve high performance.



Worth noting the following about this video (based on video comments):
  • There are some minor issues with the sudio
  • Cell-free Massive MIMO is particularly for stadiums, streets, and places with many users or where it is hard to provide sufficient network quality with other methods.
  • This concept is still 4-5 years away from being ready to be practically deployed. It should be ready for later part of 5G, probably 5.5G

"Reinventing the Wireless Network Architecture Towards 6G: Cell-free Massive MIMO and Radio Stripes" looks at the motivation behind Cell-free Massive MIMO and how it can be implemented in 6G using radio stripes.



Worth noting the following on this video (based on video comments):

  • It may be possible that multiple frequency bands can be handled in the same radio stripe. If it is found to be possible then every other antenna  processing unit could manage a different band.
  • In principle, you can make the stripe as long as you need. But you probably need to divide it into segments since the power is supplied from one end of a stripe and it will only reach a limited distance (roughly up to 1 km). There are many implementation ideas and it remains to be seen what works out well in practice.

I am looking forward to see it work as it can solve coverage issues in many tricky scenarios.

Related Posts:

Thursday, 23 May 2019

Presentations on Macro Cells and Millimetre-wave Technology from recent CW (Cambridge Wireless) events


CW (Cambridge Wireless) held a couple of very interesting events from 2 very popular groups.

The first one was on "5G wide area coverage: macro cells – the why and the how". This event looked at the design and optimisation of the macro cell layer and its role within future heterogeneous networks. You can access the presentations for limited time on CW website here.

The presentations available are:
Related posts that may be of interest:


The second one was on "Commercialising millimetre-wave technology". The event reviewed the commercial opportunities at millimetre-wave frequencies, what bands are available and what licensing is needed. You can access the presentations on CW website for limited time here.

The presentations available are:

We recently made a video to educate people outside our industry about non-mmWave 5G. It's embedded below.


Friday, 12 April 2019

Slides from Parallel Wireless Webinar: 5G at #MWC19

I hosted a webinar for Parallel Wireless* yesterday about all the stuff related to 5G at Mobile World Congress 2019. The slides are embedded below and can be downloaded from BrightTalk here. You can also listen to the webinar there.




Related posts:



*Full Disclosure: I work for Parallel Wireless as a Senior Director in Strategic Marketing. This blog is maintained in my personal capacity and expresses my own views, not the views of my employer or anyone else. Anyone who knows me well would know this.

Tuesday, 9 April 2019

Distributed Massive MIMO using Ericsson Radio Stripes


One of the interesting things that caught my attention in MWC 2019 was the Ericsson Radio Stripes.

Emil Björnson explains it nicely in his blog as to how this works.

Distributed MIMO deployments combine the best of two worlds: The beamforming gain and spatial interference suppression capability of conventional Massive MIMO with co-located arrays, and the bigger chance of being physically close to a service antenna that small cells offer. Coherent transmission and reception from a distributed MIMO array is not a new concept but has been given many names over the years, including Distributed Antenna System and Network MIMO. Most recently, in the beyond-5G era, it has been called ubiquitous Cell-free Massive MIMO communications and been refined based on insights and methodology developed through the research into conventional Massive MIMO.

One of the showstoppers for distributed MIMO has always been the high cost of deploying a large number of distributed antennas. Since the antennas need to be phase-synchronized and have access to the same data, a lot of high-capacity cables need to be deployed, particularly if a star topology is used. 
...

For those who cannot attend MWC, further conceptual details can be found in a recent overview paper on Cell-free Massive MIMO. An even more detailed description of radio stripes can be found in Ericsson’s patent application from 2017.


The paper explains the Radio stripe system design and also lists the advantages of such a system:

The radio stripe system facilitates a flexible and cheap cell-free Massive MIMO deployment. Cheapness comes from many aspects: (i) deployment does not require highly qualified personnel. Theoretically, a radio stripe needs only one (plug and play) connection either to the front-haul network or directly to the CPU; (ii) a conventional distributed massive MIMO deployment requires a star topology, i.e., a separate cable between each APs and a CPU, which may be economically infeasible. Conversely, radio stripe installation complexity is unaffected by the number of antenna elements, thanks to its compute-and-forward architecture. Hence, cabling becomes much cheaper; (iii) maintenance costs are cut down as a radio stripe system offers increased robustness and resilience: highly distributed functionality offer limited overall impact on the network when few stripes being defected; (iv) low heat-dissipation makes cooling systems simpler and cheaper. While cellular APs are bulky, radio stripes enable invisible installation in existing construction elements as exemplified in Fig. below. Moreover, a radio stripe deployment may integrate for example temperature sensors, microphones/speakers, or vibration sensors, and provide additional features such as fire alarms, burglar alarms, earthquake warning, indoor positioning, and climate monitoring and control.


According to the Ericsson post:

One of the inventors and researchers behind the concept, Jan Hederén, Strategist at Ericsson 4G5G Development, says: 

"Although a large-scale installation of distributed MIMO can provide excellent performance, it can also become an impractical and costly "spaghetti-monster" of cables in case dedicated cables are used to connect the antenna elements.

To be easy to deploy, we need to connect and integrate the antenna elements inside a single cable. We call this solution the "radio stripe" which is an easy way to create a large scale distributed, serial, and integrated antenna system." Says, also inventors and researcher behind the concept."

This visionary concept is an extension of how to build and enhance the capability of current networks. The Radio Stripe systems offers, so to say, new colors and flavors in how we increase the performance of mobile networks.

The Radio Stripe vision is focused on improvements to the reach and quality of radio connectivity in the access part of the mobile network. It shares all other resources (transport, baseband, management, core) with current mobile solutions.

I am looking forward to reading a lot more about this kind of approach in the future and probably some deployment videos too.

Related post:



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I am running a webinar this week looking at 5G @ MWC 2019 on behalf of Parallel Wireless (#PWTechTrain) . Along with antennas, I plan to talk about lot more things. Register here.

Friday, 21 September 2018

Base Station Antenna Considerations for 5G

I first mentioned Quintel in this blog three years back for their innovations in 4T8R/8T8R antennas. Since then they have been going strength to strength.


I heard David Barker, CTO of Quintel at Cambridge Wireless event titled "Radio technology for 5G – making it work" talking about the antennas consideration for 5G. There are quite a few important areas in this presentation for consideration. The presentation is embedded below:



Related Posts:

Wednesday, 24 January 2018

Inside AT&T Towers


A really good video from Mr. Mobile on YouTube on how the cell towers look from inside. Worth your 9:27 mins.



If you found this interesting then you will also like:

Tuesday, 15 August 2017

AT&T Blog: "Providing Connectivity from Inside a Cactus"


A recent AT&T blog post looks at how the fake cactus antennas are manufactured. I also took a closeup of a fake cactus antenna when I went to a Cambridge Wireless Heritage SIG event as can be seen in tweet below.

The blog says:
To make a stealth site look as real as possible, our teams use several layers of putty and paint. Our goal is to get the texture and color just right, but also ensure it can withstand natural elements – from snowy Colorado to blistering Arizona. 
Tower production takes 6-8 weeks and starts with constructing a particular mold. The molds quickly become 30-foot tall saguaro cacti or 80-foot tall redwood trees.But these aren’t just steel giants. 
The materials that cover the stealth antennas, like paint or faux-leaves, must be radio frequency-friendly. Stealth antennas designed to look like church steeples or water towers are mostly made of fiberglass. This lets the signal from the antennas penetrate through the casing. 
These stealth deployments are just one of the many unique ways we provide coverage to our customers. So take a look outside, your connection may be closer than you think—hidden in plain sight!
This videos gives a good idea


If this is a topic of interest, then have a look at this collection of around 100 antennas:



See also:



Thursday, 13 July 2017

Different types of Mobile Masts



Today's post is inspired by two things. One of them being my most popular answer on Quora. As you can see, its gathered over 19K upvotes.


The other being #EEGoldenSIM competition started by Marc Allera, CEO of UK mobile operator, EE,. The users were required to find a mast, take a picture and share it. This led to a lot of people asking how do masts look like but also generated lots of interesting pictures. You can search #EEGoldenSIM on twitter to see them.

Below is a presentation prepared by my 3G4G colleagues on how different types of antennas and mobile masts look like. Hope you like it.



Sunday, 16 October 2016

Inside 3GPP Release-13 - Whitepaper by 5G Americas


The following is from the 5G Americas press release:

The summary offers insight to the future of wireless broadband and how new requirements and technological goals will be achieved. The report updates Release 13 (Rel-13) features that are now completed at 3GPP and were not available at the time of the publication of a detailed 5G Americas report, Mobile Broadband Evolution Towards 5G: 3GPP Release 12 & Release 13 and Beyond in June 2015.
The 3GPP standards have many innovations remaining for LTE to create a foundation for 5G.  Rel-12, which was finalized in December 2014, contains a vast array of features for both LTE and HSPA+ that bring greater efficiency for networks and devices, as well as enable new applications and services. Many of the Rel-12 features were extended into Rel-13.  Rel-13, functionally frozen in December 2015 and completed in March 2016, continues to build on these technical capabilities while adding many robust new features.
Jim Seymour, Principal Engineer, Mobility CTO Group, Cisco and co-leader of the 5G Americas report explained, “3GPP Release 13 is just a peek behind the curtain for the unveiling of future innovations for LTE that will parallel the technical work at 3GPP on 5G. Both LTE and 5G will work together to form our connected future.”
The numerous features in the Rel-13 standards include the following for LTE-Advanced:
  • Active Antenna Systems (AAS), including beamforming, Multi-Input Multi-Output (MIMO) and Self-Organizing Network (SON) aspects
  • Enhanced signaling to support inter-site Coordinated Multi-Point Transmission and Reception (CoMP)
  • Carrier Aggregation (CA) enhancements to support up to 32 component carriers
  • Dual Connectivity (DC) enhancements to better support multi-vendor deployments with improved traffic steering
  • Improvements in Radio Access Network (RAN) sharing
  • Enhancements to Machine Type Communication (MTC)
  • Enhanced Proximity Services (ProSe)
Some of the standards work in Rel-13 related to spectrum efficiency include:                                                                                                                       
  • Licensed Assisted Access for LTE (LAA) in which LTE can be deployed in unlicensed spectrum
  • LTE Wireless Local Area Network (WLAN) Aggregation (LWA) where Wi-Fi can now be supported by a radio bearer and aggregated with an LTE radio bearer
  • Narrowband IoT (NB-IoT) where lower power wider coverage LTE carriers have been designed to support IoT applications
  • Downlink (DL) Multi-User Superposition Transmission (MUST) which is a new concept for transmitting more than one data layer to multiple users without time, frequency or spatial separation
“The vision for 5G is being clarified in each step of the 3GPP standards. To understand those steps, 5G Americas provides reports on the developments in this succinct, understandable format,” said Vicki Livingston, Head of Communications for the association.

The whitepaper as follows:



Related posts:

Monday, 1 August 2016

Antenna evolution: From 4G to 5G


I came across this simple Introduction to Antenna Design videos that many will find useful (including myself) for the basics of Antenna. Its embedded below:


In the recently concluded 5G World 2016, Maximilian Göttl, Senior Director, Research & Development, Mobile Communication Systems, Kathrein gave an interesting presentation on Antenna Evolution, from 4G to 5G. The presentation is embedded below.

Please share your thoughts in this area in the comments section below.



Sunday, 7 February 2016

The Art of Disguising Cellular Antennas

When I did a blog post 'Disguising Small Cells in Rural areas' last year, many people were surprised to see these things. So here is another post showing how the antennas looks like and how they have to be disguised to blend in with the environment.


The above pictures shows fake date trees (with dates) near Koutoubia mosque, Marrakech, designed to blend in with the surroundings. In fact I have been told that these fake date trees are common in the Middle East and North African countries.


The above picture is from Dubai, showing similar palm tree. Source unknown.


The above picture, courtesy of Andy Sutton on Twitter shows a cell site near Blandford Forum. I hope you can spot the fake tree on top right.


Another one, courtesy of Andy Sutton on Twitter shows a cell site between motorway M56, J10 & 11 in Cheshire. Single operator but could be shared, single frequency band, x-pole with 3 cell sectors. Only two of the possible 3 cell sectors connected here. Pointing up and down motorway hence 4 feeders.







Another one courtesy of Andy Sutton on Twitter. Its been disguised to not look out of place unless someone is observing very carefully.
All three are fake trees and each is a separate cellular installation. The location is Lancashire, off the A6 between Slyne and Bolton-le-Sands. They are all different operators, left to right, O2, T-Mobile, Orange - although two will become one as part of EE of course.


Modern Art and Cellular Antenna, courtesy of Andy Sutton on Twitter.

What will happen when we transition to 5G, where we will have a lot more antennas because of MIMO (massive or not). China Mobile is researching into Smart Tiles, which are antennas that can be hidden inside Chinese characters. See the following for example:

With more antennas becoming commonplace in the urban environment, operators and vendors will have to keep up coming with innovative ways to disguise the antennas and hope no one notices.

See Also:


Sunday, 14 June 2015

Using 8T8R Antennas for TD-LTE


People often ask at various conferences if TD-LTE is a fad or is it something that will continue to exist along with the FDD networks. TDD networks were a bit tricky to implement in the past due to the necessity for the whole network to be time synchronised to make sure there is no interference. Also, if there was another TDD network in an adjacent band, it would have to be time synchronised with the first network too. In the areas bordering another country where they might have had their own TDD network in this band, it would have to be time synchronised too. This complexity meant that most networks were happy to live with FDD networks.

In 5G networks, at higher frequencies it would also make much more sense to use TDD to estimate the channel accurately. This is because the same channel would be used in downlink and uplink so the downlink channel can be estimated accurately based on the uplink channel condition. Due to small transmit time intervals (TTI's), these channel condition estimation would be quite good. Another advantage of this is that the beam could be formed and directed exactly at the user and it would appear as a null to other users.

This is where 8T8R or 8 Transmit and 8 Receive antennas in the base station can help. The more the antennas, the better and narrower the beam they can create. This can help send more energy to users at the cell edge and hence provide better and more reliable coverage there.  

SONWav Operator Solution

How do these antennas look like? 8T8R needs 8x Antennas at the Base Station Cell, and this is typically delivered using four X-Polar columns about half wavelength apart. I found the above picture on antenna specialist Quintel's page here, where the four column example is shown right. At spectrum bands such as 2.3GHz, 2.6GHz and 3.5GHz where TD-LTE networks are currently deployed, the antenna width is still practical. Quintel’s webpage also indicates how their technology allows 8T8R to be effectively emulated using only two X-Polar columns thus promising Slimline antenna solutions at lower frequency bands. China Mobile and Huawei have claimed to be the first ones to deploy these four X-Pol column 8T8R antennas. Sprint, USA is another network that has been actively deploying these 8T8R antennas.

There are couple of interesting tweets that show their kit below:

In fact Sprint has very ambitious plans. The following is from a report in Fierce Wireless:

Sprint's deployment of 8T8R (eight-branch transmit and eight-branch receive) radios in its 2.5 GHz TDD LTE spectrum is resulting in increased data throughput as well as coverage according to a new report from Signals Research. "Thanks to TM8 [transmission mode 8] and 8T8R, we observed meaningful increases in coverage and spectral efficiency, not to mention overall device throughput," Signals said in its executive summary of the report.

The firm said it extensively tested Sprint's network in the Chicago market using Band 41 (2.5 GHz) and Band 25 (1.9 GHz) in April using Accuver's drive test tools and two Galaxy Note Edge smartphones. Signals tested TM8 vs. non-TM8 performance, Band 41 and Band 25 coverage and performance as well as 8T8R receive vs. 2T2R coverage/performance and stand-alone carrier aggregation.

Sprint has been deploying 8T8R radios in its 2.5 GHz footprint, which the company has said will allow its cell sites to send multiple data streams, achieve better signal strength and increase data throughput and coverage without requiring more bandwidth.

The company also has said it will use carrier aggregation technology to combine TD-LTE and FDD-LTE transmission across all of its spectrum bands. In its fourth quarter 2014 earnings call with investors in February, Sprint CEO Marcelo Claure said implementing carrier aggregation across all Sprint spectrum bands means Sprint eventually will be able to deploy 1900 MHz FDD-LTE for uplink and 2.5 GHz TD-LTE for downlink, and ultimately improve the coverage of 2.5 GHz LTE to levels that its 1900 MHz spectrum currently achieves. Carrier aggregation, which is the most well-known and widely used technique of the LTE Advanced standard, bonds together disparate bands of spectrum to create wider channels and produce more capacity and faster speeds.

Alcatel-Lucent has a good article in their TECHzine, an extract from that below:

Field tests on base stations equipped with beamforming and 8T8R technologies confirm the sustainability of the solution. Operators can make the most of transmission (Tx) and receiving (Rx) diversity by adding in Tx and Rx paths at the eNodeB level, and beamforming delivers a direct impact on uplink and downlink performance at the cell edge.

By using 8 receiver paths instead of 2, cell range is increased by a factor of 1.5 – and this difference is emphasized by the fact that the number of sites needed is reduced by nearly 50 per cent. Furthermore, using the beamforming approach in transmission mode generates a specific beam per user which improves the quality of the signal received by the end-user’s device, or user equipment (UE). In fact, steering the radiated energy in a specific direction can reduce interference and improves the radio link, helping enable a better throughput. The orientation of the beam is decided by shifting the phases of the Tx paths based on signal feedback from the UE. This approach can deliver double the cell edge downlink throughput and can increase global average throughput by 65 per cent.

These types of deployments are made possible by using innovative radio heads and antenna solutions.  In traditional deployments, it would require the installation of multiple remote radio heads (RRH) and multiple antennas at the site to reach the same level of performance. The use of an 8T8R RRH and a smart antenna array, comprising 4 cross-polar antennas in a radome, means an 8T8R sector deployment can be done within the same footprint as traditional systems.



Anyone interested in seeing pictures of different 8T8R antennas like the one above, see here. While this page shows Samsung's antennas, you can navigate to equipment from other vendors.

Finally, if you can provide any additional info or feel there is something incorrect, please feel free to let me know via comments below.

Tuesday, 3 February 2015

5G: A 2020 Vision


I had the pleasure of speaking at the CW (Cambridge Wireless) event ‘5G: A Practical Approach’. It was a very interesting event with great speakers. Over the next few weeks, I will hopefully add the presentations from some of the other speakers too.

In fact before the presentation (below), I had a few discussions over the twitter to validate if people agree with my assumptions. For those who use twitter, maybe you may want to have a look at some of these below:







Anyway, here is the presentation.

 

Saturday, 11 October 2014

A quick update on Antennas

There were couple of very interesting and useful presentations from the LTE World Summit 2014 that I have been thinking for a while to embed in the blog. The first is a market overview from Signals Research Group. The research is focussed more on the US market but it has some very interesting insights. The slideset is embedded below:



The other presentation is from Commscope on Base Station Antennas (BSA) for capacity improvement. I really liked the simplicity of the diagrams. Anyone interested in studying more indepth on the antennas are encouraged to check out my old post here. The complete slideset is below:



Saturday, 27 September 2014

Elevation Beamforming / Full-Dimension MIMO


Four major Release-13 projects have been approved now that Release-12 is coming to a conclusion. One of them is Full dimension MIMO. From the 3GPP website:

Leveraging the work on 3D channel modeling completed in Release 12, 3GPP RAN will now study the necessary changes to enable elevation beamforming and high-order MIMO systems. Beamforming and MIMO have been identified as key technologies to address the future capacity demand. But so far 3GPP specified support for these features mostly considers one-dimensional antenna arrays that exploit the azimuth dimension. So, to further improve LTE spectral efficiency it is quite natural to now study two-dimensional antenna arrays that can also exploit the vertical dimension.
Also, while the standard currently supports MIMO systems with up to 8 antenna ports, the new study will look into high-order MIMO systems with up to 64 antenna ports at the eNB, to become more relevant with the use of higher frequencies in the future.
Details of the Study Item can be found in RP-141644.
There was also an interesting post by Eiko Seidel in the 5G standards group:

The idea is to introduce carrier and UE specific tilt/beam forming with variable beam widths. Improved link budget and reduced intra- and inter-cell interference might translate into higher data rates or increased coverage at cell edge. This might go hand in hand with an extensive use of spatial multiplexing that might require enhancements to today’s MU-MIMO schemes. Furthermore in active antenna array systems (AAS) the power amplifiers become part of the antenna further improving the link budget due to the missing feeder loss. Besides a potentially simplified installation the use of many low power elements might also reduce the overall power consumption. 

At higher frequencies the antenna elements can miniaturized and their number can be increased. In LTE this might be limited to 16, 32 or 64 elements while for 5G with higher frequency bands this might allow for “massive MIMO”. 

WG: Primary RAN1 (RP-141644) 
started 06/2014 (RAN#64), completion date 06/2015 (RAN#68)
work item might follow the study with target 12/2015 (RAN#70) 

Supporting companies
Samsung/NSN, all major vendors and operators 

Based on RAN1 Rel.12 Study Item on 3D channel model (TR36.873) 

Objectives 
Phase 1: antenna configurations and evaluation scenarios Rel.12 performance evaluation with 3D channel model 

Phase 2: study and simulate FD-MIMO enhancement identify and evaluate techniques, analyze specification impact performance evaluation for 16, 32, 64 antenna elements enhancements for SU-/MU-MIMO (incl. higher dimension MU-MIMO) (keep the maximum number of layer per UE unchanged to 8)


An old presentation from Samsung is embedded below that will provide more insight into this technology:



Related post:

Sunday, 13 October 2013

Handset Antenna Design


Came across this presentation on Handset Antenna design from a recent Cambridge Wireless event here. Its interesting to see how the antenna technology has evolved and is still evolving. Another recent whitepaper from 4G Americas on meeting the 1000x challenge (here) showed how the different wavelengths are affecting the antenna design.


Maybe its better to move to higher frequencies from the handset design point of view. Anyway, the Cambridge Wireless presentation is embedded below:


Wednesday, 17 July 2013

Decision Tree of Transmission Modes (TM) for LTE


4G Americas have recently published whitepaper titled "MIMO and Smart Antennas for Mobile Broadband Systems" (available here). The above picture and the following is from that whitepaper:

Figure 3 above shows the taxonomy of antenna configurations supported in Release-10 of the LTE standard (as described in 3GPP Technical Specification TS 36.211, 36.300). The LTE standard supports 1, 2, 4 or 8 base station transmit antennas and 2, 4 or 8 receive antennas in the User Equipment (UE), designated as: 1x2, 1x4, 1x8, 2x2, 2x4, 2x8, 4x2, 4x4, 4x8, and 8x2, 8x4, and 8x8 MIMO, where the first digit is the number of antennas per sector in the transmitter and the second number is the number of antennas in the receiver. The cases where the base station transmits from a single antenna or a single dedicated beam are shown in the left of the figure. The most commonly used MIMO Transmission Mode (TM4) is in the lower right corner, Closed Loop Spatial Multiplexing (CLSM), when multiple streams can be transmitted in a channel with rank 2 or more.

Beyond the single antenna or beamforming array cases diagrammed above, the LTE standard supports Multiple Input Multiple Output (MIMO) antenna configurations as shown on the right of Figure 3. This includes Single User (SU-MIMO) protocols using either open loop or closed loop modes as well as transmit diversity and Multi-User MIMO (MU-MIMO). In the closed loop MIMO mode, the terminals provide channel feedback to the eNodeB with Channel Quality Information (CQI), Rank Indications (RI) and Precoder Matrix Indications (PMI). These mechanisms enable channel state information at the transmitter which improves the peak data rates, and is the most commonly used scheme in current deployments. However, this scheme provides the best performance only when the channel information is accurate and when there is a rich multi-path environment. Thus, closed loop MIMO is most appropriate in low mobility environments such as with fixed terminals or at pedestrian speeds.

In the case of high vehicular speeds, Open Loop MIMO may be used, but because the channel state information is not timely, the PMI is not considered reliable and is typically not used. In TDD networks, the channel is reciprocal and thus the DL channel can be more accurately known based on the uplink transmissions from the terminal (the forward link’s multipath channel signature is the same as the reverse link’s – both paths use the same frequency block). Thus, MIMO improves TDD networks under wider channel conditions than in FDD networks.

One may visualize spatial multiplexing MIMO operation as subtracting the strongest received stream from the total received signal so that the next strongest signal can be decoded and then the next strongest, somewhat like a multi-user detection scheme. However, to solve these simultaneous equations for multiple unknowns, the MIMO algorithms must have relatively large Signal to Interference plus Noise ratios (SINR), say 15 dB or better. With many users active in a base station’s coverage area, and multiple base stations contributing interference to adjacent cells, the SINR is often in the realm of a few dB. This is particularly true for frequency reuse 1 systems, where only users very close to the cell site experience SINRs high enough to benefit from spatial multiplexing SU-MIMO. Consequently, SU-MIMO works to serve the single user (or few users) very well, and is primarily used to increase the peak data rates rather than the median data rate in a network operating at full capacity.

Angle of Arrival (AoA) beamforming schemes form beams which work well when the base station is clearly above the clutter and when the angular spread of the arrival is small, corresponding to users that are well localized in the field of view of the sector; in rural areas, for example. To form a beam, one uses co-polarized antenna elements spaced rather closely together, typically lamda/2, while the spatial diversity required of MIMO requires either cross-polarized antenna columns or columns that are relatively far apart. Path diversity will couple more when the antennas columns are farther apart, often about 10 wavelengths (1.5m or 5’ at 2 GHz). That is why most 2G and 3G tower sites have two receive antennas located at far ends of the sector’s platform, as seen in the photo to the right. The signals to be transmitted are multiplied by complex-valued precoding weights from standardized codebooks to form the antenna patterns with their beam-like main lobes and their nulls that can be directed toward sources of interference. The beamforming can be created, for example, by the UE PMI feedback pointing out the preferred precoder (fixed beam) to use when operating in the closed loop MIMO mode TM4.

For more details, see the whitepaper available here.

Related posts: