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

Wednesday, 2 May 2012

LTE 'Antenna Ports' and their Physical mapping

People who work with LTE Physical layer and maybe higher layers would be aware of this term called 'Antenna Ports'. I have always wondered how these antenna ports are mapped to physical antennas.

The following is from R&S whitepaper:

The 3GPP TS 36.211 LTE standard defines antenna ports for the downlink. An antenna port is generally used as a generic term for signal transmission under identical channel conditions. For each LTE operating mode in the downlink direction for which an independent channel is assumed (e.g. SISO vs. MIMO), a separate logical antenna port is defined. LTE symbols that are transmitted via identical antenna ports are subject to the same channel conditions. In order to determine the characteristic channel for an antenna port, a UE must carry out a separate channel estimation for each antenna port. Separate reference signals (pilot signals) that are suitable for estimating the respective channel are defined in the LTE standard for each antenna port. 

Here is my table that I have adapted from the whitepaper and expanded. 




The way in which these logical antenna ports are assigned to the physical transmit antennas of a base station is up to the base station, and can vary between base stations of the same type (because of different operating conditions) and also between base stations from different manufacturers. The base station does not explicitly notify the UE of the mapping that has been carried out, rather the UE must take this into account automatically during demodulation (FIG 2).


If there is another way to show this physical mappings, please feel free to let me know.

The R&S Whitepaper is available here if interested.

Friday, 9 March 2012

'Blue Tick' for better RF performance


Last year I blogged about 'Antennagate'. From what I hear, iPhone 4S has left this problem far behind and have a much better RF performance than other rivals.

The Australian operator Telstra operates a scheme where it gives a 'blue tick' to all mobiles that have superior RF performance than other average mobiles.

The following is an interesting comment from their Crowdsupport site:


Telstra offers three classes of coverage, A B and C.


C Class coverage is Blue Tick coverage. These phones are designed in such a way that they will outperform other phones in coverage. That is ,they will hold onto a signal further than B or A class phones


Most smartphones due to the way they are manufactures are B class, because of their thinness and materials (such as glass and plastic)


The Atrix and Defy are Blue Tick because the plastic chassis that houses the antenna stops your hand from attenuating the signal.


The iPhone 4S is Blue Tick because the dual antenna design intelligently switches antennas if one gets attenuated.


Blue Tick phones do not assist with high traffic areas. They only assist users in low coverage areas. So a phone in the Melbourne CBD would behave much like any other Telstra phone. Whereas a Blue Tick phone out in rural areas would have better signal coverage than a B or A class phone.


Telstra empirically tests all it's phones because we reach more of the population and many rural people rely on mobile phones with each passing year.


It may be a good idea that operators in other countries start supporting a similar scheme so users who get very little reception in their houses or places of work can get a phone with better RF capabilities.

Any similar schemes operating in other countries?

Wednesday, 14 December 2011

AT&T on Distributed Antenna System (DAS)


From the 4th LTE North America Conference, 8 - 9 November 2011, Dallas, Texas, USA

More about DAS on Wikipedia here.

Monday, 5 December 2011

UE Antenna Sizes on different frequencies


The biggest problem with Antennas for mobiles and now the tablets have been how to arrange antennas for MIMO since the wavelength needs to be λ/4. The picture gives an idea how the antenna size changes with different frequencies. Higher frequencies are better for having multiple antennas as their length and the distance between then decreases.

From a presentation by Shirook M. Ali, RIM in the 4th LTE North America Conference, 8 - 9 November
2011, Dallas, Texas, USA.

Thursday, 21 July 2011

Smart Deployment with Smart Antennas and ORI

This is from a presentation by Dr. Peter Meissner, Operating Officer, NGMN Alliance.

Its very interesting the way the Antennas are evolving.


If you are interested in reading more about ORI, see the earlier post here.

Thursday, 7 July 2011

Antenna height and coverage

From a presentation by Ed Candy of '3' in FWIC.
Self explanatory.

Wednesday, 6 April 2011

Mobile Phone Antennas and Networks

We all remember the so called 'Antennagate' where the iPhone 4 loses coverage due to the way its held. As can be seen from the above picture, there are a lot of antennas already in the phones and yes they are on the increase with LTE and other technologies being added all the time.

Apple admitted the fault and claimed to have fixed the problem but its well known in technical circles that the fix is more of a software hack which doesn't really fix the problem just pretends to fix it. That is why the networks dread it and you can find awful lot of information on the web about the problems.

In a recent Cambridge Wireless event, I heard an interesting talk from Trevor Gill of Vodafone and one of the slides that caught my attention was the impact of these poorly designed phones on the network. The slide is embedded below.

It is estimated that the RF performance of iPhone4 is around 6dB worse than most other 3G phones. What this means is that you may be getting 4 bars of reception on your other phone where iPhone4 may be having only 1 or 2 bars or reception. So if the reception is poor with 1 or 2 bars, iPhone4 may have no reception at all.

To fix this problem, either the networks can increase the number of base stations to double the existing amount which is a huge cost to the networks and extra radiation or the phones can fix it themseles by having an extra antenna. In fact as the slide says, extra antenna on each phone would translate to increase in network capacity by 20-40%, cell area by 30% and cell edge throughput by 40-75%.

One final thing that I want to mention is that testing (RF, RRM, Conformance, etc.) are mandated by the networks for most phones but they overlook the testing procedure for phones like iPhone. What this means is that they do get a lot more new customers but they get new sets of problems. If these problems are not handled well, the impression they give is that the particular network is rubbish. Another thing is that the devices use a certain build/prototype for testing but the one that they release may contain other patches that can cause chaos. One such problem was Fast Dormancy problem that I have blogged about here.

Hopefully the networks will be a bit more careful and will put quality before quantity in future.

Friday, 14 May 2010

Whitepaper; MIMO and Smart Antennas for 3G and 4G Wireless Systems

3G Americas has published an educational white paper titled, MIMO and Smart Antennas for 3G and 4G Wireless Systems: Practical Aspects and Deployment Considerations. The report is a complete tutorial reference document that outlines the considerable importance of various smart antenna schemes for improving the capacity and coverage of the emerging generations of wireless networks.

With the rapid growth of wireless data traffic, now greatly exceeding voice traffic in many developed markets, operators are anxious to quickly expand the capacity and coverage of their wireless networks. To address these demands for increased capacity in a cost effective way, 3GPP standards have incorporated powerful techniques for using “smart antennas.”

“The gains in spectral efficiency being advanced by new wireless air interface technologies, such as LTE and LTE-Advanced, will be enabled by the application of MIMO and other smart antenna technologies,” stated Kevin Linehan, Vice President and Chief Technology Officer – Base Station Antenna Systems, Andrew Solutions. Linehan, one of the project leaders for the creation of the 3G Americas report continued, “It is critical that operators and others in the industry appreciate these advanced technologies and their practical application.”

The term smart antennas refers to adaptive array antennas – those with electrical tilt, beam width and azimuth control that can follow relatively slow-varying traffic patterns; intelligent antennas, which can form beams aimed at particular users or steer nulls to reduce interference; and MIMO antenna schemes, predominately featured in LTE and LTE-Advanced.

The white paper was created by a 3G Americas technical work group and concentrates on the practical aspects of antennas and their deployment for 3G and 4G wireless systems, specifically downlink antenna techniques available in 3GPP LTE Release 8. The comprehensive report highlights a substantial and growing body of theoretical and field experience that provides reliable guidance on the tradeoffs of various antenna configurations. Some of the areas addressed in the paper include:
  • Smart antennas provide the next substantial increase in throughput for wireless networks. The peak data rates tend to be proportional to the number of send and receive antennas, so 4X4 MIMO is theoretically capable of twice the peak data rates as 2X2 MIMO systems. For another example, in upgrading from HSPA (1X2) to LTE (2X2) a gain of 1.6x is seen (Rysavy Research, 2009).
  • The practical tradeoffs of performance with the realistic constraints on the types of antennas that can be realistically installed, cognizant of zoning, wind loading, size, weight and cabling challenges and constraints from legacy terminals and other equipment. Constraints are, of course, present in both the base station and the terminal side of the air interface, where MIMO technology promises useful gains if multiple antennas, amplifiers, receivers and baseband processing resources can be made available in terminals.
  • Beyond the single antenna or beamforming array cases, 3GPP Release 8 of the LTE standard supports MIMO antenna configurations. This includes Single-User (SU-MIMO) protocols using either Open Loop or Closed-Loop modes as well as Transmit Diversity and MU-MIMO. Closed-Loop MIMO mode, which supports the highest peak data rates, is likely to be the most commonly used scheme in early deployments. However, this Closed-Loop MIMO scheme provides the best performance only when the channel information is accurate, when there is a rich multipath environment and is appropriate in low mobility environments such as with fixed terminals or those used at pedestrian speeds.

The white paper, MIMO and Smart Antennas for 3G and 4G Wireless Systems: Practical Aspects and Deployment Considerations, was written collaboratively by members of 3G Americas and is available for free download HERE.

While MIMO and Smart Antennas for 3G and 4G Wireless Systems concentrates on the practical aspects of deploying antennas in emerging wireless markets, 3G Americas’ June 2009 white paper, MIMO Transmission Schemes for LTE and HSPA Networks, provides additional background information on the processing gains feasible with smart antennas.

Wednesday, 1 July 2009

3G Americas releases White Paper on MIMO (Smart Antennas)



3G Americas, a wireless industry trade association representing the GSM family of technologies including LTE, announced that it has published an educational report titled, MIMO Transmission Schemes for LTE and HSPA Networks as a tool to increase awareness of smart antenna systems – also known as multiple-input multiple-output (MIMO) technology – and help guide their deployments in HSPA and LTE networks within 3GPP’s specifications and technology standards. The 3GPP evolution continues to be the leader in standardizing the most advanced forms of multiple-input multiple-output (MIMO) antennas.

Smart antenna, or MIMO, technology is commonly defined as, the use of two or more unique radio signals, in the same radio channel, where each signal carries different digital information, or two or more radio signals that use beam forming, receive combining and spatial multiplexing (SM). Relative to a traditional 1x1 antenna system, a 2x2 MIMO system is expected to deliver significant cell throughput gain.

The MIMO Transmission Schemes for LTE and HSPA Networks report provides an overview and detailed information of the current and emerging MIMO techniques that significantly increase the performance of HSPA and LTE networks.

“Smart antenna technology has arrived and will be a vital part of mobile broadband communications,” stated Pantelis Monogioudis, Ph.D, of Alcatel-Lucent LTE-Advanced Technology Strategy. “It is an exciting time for smart antenna technology as 3GPP has provided the leading technical standards for MIMO that the industry will utilize to improve the capabilities of mobile broadband.”

MIMO was first standardized in 3GPP Release 6 (Rel-6), and was further developed in Rel-7 with spatial multiplexing for HSPA+ using Double Transmit Adaptive Array (D-TxAA). As the report highlights, the use of multiple antennas at both transmitter and receiver allows:

  • Substantial increase in peak data rate
  • Significantly higher spectrum efficiency, especially in low-interference environments
  • Increased system capacity (number of users)

Based on simulation results presented in the report, it was shown that the relatively simple MIMO transmission scheme based on 2x2 closed-loop SM, at low user equipment (UE) speeds, can increase by 20 percent the downlink (DL) sector spectral efficiency relative to a single antenna transmission, as well as increase the cell edge efficiency by approximately 35 percent. More advanced antenna configurations can provide benefits that are significant for users that are receiving a strong signal as well as cell edge users.

The 3GPP Rel-8 LTE specifications, completed in March 2009, included the most advanced forms of MIMO of any standard in the industry, and now, 3GPP is studying even more advanced MIMO enhancements for inclusion in 3GPP Rel-9 and Rel-10 for LTE-Advanced.

The white paper, MIMO Transmission Schemes for LTE and HSPA Networks, was written by members of 3G Americas, and is available for free download on the
3G Americas website here.

Friday, 13 February 2009

3GPP Humour with MIMO ;)

TSG-RAN WG1 Meeting #56 R1-091041
Athens, Greece, 9 – 13 February, 2009

Source: MIMO Very Late Session
Title:
Text proposal for TR36.814 on M.I.M.O.
Agenda Item:
12
Document for:
Text Proposal


During offline discussion after the parallel session on Agenda Items 12.3 and 12.4, the very late session attendees arrived at the following text proposal for inclusion into TR 36.814.

--- Start text proposal ---
Annex B1: M.I.M.O. (Informative)

B1.1 Scope

The following section describes the M.I.M.O. approach and is best understood in conjunction with the tune of the song “Y.M.C.A.” performed by Village People played in the background.

B1.2 Lyrics

U-E, when your channel looks fine,
I said, U-E, give the network a sign,
Which means, U-E, give a high C-Q-I,
To report what you have measured.

U-E, there is data for you,
And two codewords,
I think they may come through,
So let's put them onto different ports
And use spatial multiplexing.

In other words it is M-I-M-O.
In other words it is M-I-M-O.
You don't need M-L-D,
There are plenty of ways,
Manufacturers have a choice ...

M-I-M-O.
In other words it is M-I-M-O.
Two antennas you need,
Four by four is agreed,
And your throughput can be so high!

U-E, can you see the Node-B?
Come on, U-E, should it do T-x-D?
Alamouti is a simple approach.
But you've got to know this one thing!

Node-B is not serving just you.
I said, Node-B, has a whole cell to do,
And at cell-edge there's no M-I-M-O
'Cause the S-I-N-R is low.

You cannot always do M-I-M-O.
You cannot always do M-I-M-O.
Two R-x ports you have
So you still can combine,
And the coverage should be fine ...

M-I-M-O.
It's good for you to use M-I-M-O.
Two antennas you need,
Four by four is agreed,
And your throughput can be so high!

U-E, if you want to transmit,
I say, U-E, MI-MO isn’t legit,
You will have to wait for L-T-E- A,
Where RAN-1 will make it okay.

That’s where the decisions are made,
And where many MI-MO sessions run late,
So that Dirk says: ‘Juho will you take care
Of this bunch of loopy people?’.

It's fun to standardize M-I-M-O.
It's fun to specify M-I-M-O.
You don't need M-L-D
There are plenty of ways,
Manufacturers have a choice ...

M-I-M-O.
It's fun to specify M-I-M-O.
When your channel looks fine,
Give the network a sign.

M-I-M-O.
Then just go and do M-I-M-O.
Can you see the Node-B?
Should it do T-x-D?

M-I-M-O.

--- End text proposal ---

Friday, 6 February 2009

MIMO schemes in LTE



SU-MIMO (Single User MIMO)

•This is an example of downlink 2x2 single user MIMO with precoding.

•Two data streams are mixed (precoded) to best match the channel conditions.

•The receiver reconstructs the original streams resulting in increased single-user data rates and corresponding increase in cell capacity.

•2x2 SU-MIMO is mandatory for the downlink and optional for the uplink

MU-MIMO (Multiuser MIMO)

•Example of uplink 2x2 MU-MIMO.

•In multiple user MIMO the data streams come from different UE.

•There is no possibility to do precoding since the UE are not connected but the wider TX antenna spacing gives better de-correlation in the channel.

•Cell capacity increases but not the single user data rate.

•The key advantage of MU-MIMO over SU-MIMO is that the cell capacity increase can be had without the increased cost and battery drain of two UE transmitters.

•MU-MIMO is more complicated to schedule than SU-MIMO


Tuesday, 30 December 2008

Improved Antenna to revolutionise mobile battery life

Atif Shamim, revolutionising mobile battery life

­Atif Shamim, an electronics PhD student at Carleton University, has built a prototype that extends the battery life of mobile phones, by getting rid of all the wires used to connect the electronic circuits with the antenna.

The invention involves a packaging technique to connect the antenna with the circuits via a wireless connection between a micro-antenna embedded within the circuits on the chip.

“This has not been tried before - that the circuits are connected to the antenna wirelessly. They’ve been connected through wires and a bunch of other components. That’s where the power gets lost,” Mr. Shamim said.

He estimates his module consumes 12 times less power than the traditional, wired-transmitter module. It is also much simpler in design, lowering the overall cost of any hand-held device, he said.

Mr. Shamim has filed patent applications in the U.S. and in Canada.

Earlier this year, the Ottawa Centre for Research and Innovation honoured Mr. Shamim and Mr. Arsalan as student researchers of the year for their work in the field of wireless biomedical sensors.

Shamim says his major goals for the innovation still lie in biomedical applications, including his original radiation sensors as well as remote healthcare sensors to monitor heart-rate, blood pressure and body temperature. He and Arsalan have also started up a company called Vital Signs Monitoring, and the two have already filed patents for the technology they developed. Clearly he has come a long way from when he first came to Canada, but he says his goals are still the same.

"My aim when I came here was to get some real skills in this domain, learn some new things and be an expert of something that would be valuable for me to find employment," said Shamim. "I was looking for a neat application for these small transmitters. ...That's where the trend is: make it cheaper, smaller, more efficient, so I think this is a good step towards that."

Sunday, 27 July 2008

Adaptive Antenna System

Whenever we talk about the evolution of new technology in telecoms world one thing which always occupy the prominent position is the spectral efficiency. The success and efficiency of any wireless system depends on the spectral efficiency.

What is spectral efficiency though?

Spectral efficiency can be defined as bits/seconds/Hz/cell. It measures how well a wireless network utilizes radio spectrum and also determines the total throughput each base station (cell) can support in a network in a given amount of spectrum.

There is no doubt that if a new air interface is to be build it should be built from the ground up to be optimized for spatial processing. Spectral efficiency directly affects an operator’s cost structure. For a given service and grade of service, it determines the following:
  • Required amount of spectrum (CapEx),
  • Required number of base stations (CapEx, OpEx),
  • Required number of sites and associated site maintenance (OpEx), and,
  • Ultimately, consumer pricing and affordability

Spectral efficiency will become even more important as subscriber penetration increases, per-user data rates increase and the as quality of service (esp. data) requirements increase.

There are so many elements for design to achieve high spectral efficiency. Adaptive Antenna System (AAS) is one of the methods to achieve high spectral efficiency.

Adaptive Antenna System (AAS) provides gain and interference mitigation leading to improved signal quality and spectral efficiency.

The use of adaptive antenna systems enables the network operators to increase the wireless network capacity, where such networks are expected to experience an enormous increase in the traffic. This is due to the increased number of users as well as the high data rate service and applications. In addition, adaptive antenna systems offer the potential of increased spectrum efficiency, extended range of coverage and higher rate of frequency reuse.

Adaptive antenna systems consist of multiple antenna elements at the transmitting and/or receiving side of the communication link, whose signals are processed adaptively in order to exploit the spatial dimension of the mobile radio channel. Depending on whether the processing is performed at the transmitter, receiver, or both ends of the communication link, the adaptive antenna technique is defined as multiple-input single-output (MISO), single-input multiple-output (SIMO), or multiple-input multiple-output (MIMO).

Multipath propagation, defined as the creation of multipath signal paths between the transmitter and the receiver due to the reflection of the transmitted signal by physical obstacles, is one of the major problems of mobile communications. It is well known that the delay spread and resulting inter symbol interference (ISI) due to multiple signal paths arriving at the receiver at different times have a critical impact on communication link quality. On the other hand, co-channel interference is the major limiting factor on the capacity of wireless communication systems, resulting from the reuse of the available network resources (e.g., frequency and time) by a number of users.

Adaptive antenna systems can improve link quality by combining the effects of multipath propagation or constructively exploiting the different data streams from different antennas. More specifically, the benefits of adaptive antennas can be summarized as follows:

  • Increased range/coverage: the array or beam forming gain is the average increase in signal power at the receiver due to a coherent combination of the signal received at all antenna elements. The adaptive antenna gain compared to a single element antenna can be increased by an amount equal to the number of array elements, e.g., an eight element array can provide a gain of eight (9 dB).
  • Increased Capacity: One of the main reasons of the growing interest of adaptive antennas is the capacity increase. In densely populated areas, mobile systems are normally interference-limited; meaning that interference from other users is the main source of noise in the system. This means that the signal to interference ratio (SIR) is much larger than the signal to thermal noise ratio (SNR). Adaptive antennas will on average, increase the SIR. Experimental results report up to 10 dB increase in average SIR in urban areas. For UMTS networks, a fivefold capacity gain has been reported for CDMA.
  • Lower power requirements and/or cost reduction: Optimizing transmission toward the wanted user achieves lower power consumption and amplifier costs.
  • Improved link quality/reliability: Diversity gain is obtained by receiving independent replicas of the signal through independently fading signal components. Based on the fact that one or more of these signal components will not be in a deep fade, the availability of multiple independent dimensions reduces the effective fluctuations of the signal.
  • Increased spectral efficiency: Spectral efficiency is a measure of the amount of information –billable services- that carried by the wireless system per unit of spectrum. It is measured in bits/second/Hertz/cell, thus it includes the effect of multiple access methods, modulation methods, channel organization and resource reuse (e.g., code, timeslot, carrier). Spectral efficiency plays an important role since it directly affects the operator cost structure. Moreover, for a given service and QoS, it determines the required amount of spectrum, the required number of base stations, the required number of sites –and associated site maintenance-, and ultimately, consumer pricing and affordability. Equation (1) shows a simplified formula to estimate the required number of cells per square kilometer. (the offered load is in bits/seconds/km2).
  • Security: It is more difficult to tap a connation, since the intruder has to be position himself in the same direction of arrival as the user.
  • Reduction of handoff: there is no need for splitting the cells for the sake of capacity increase, and in consequence less amount of handoff.
  • Spatial information: the spatial information about the user would be available at any given time, which enables the introduction of Location Based Services.

In addition to the above-mentioned benefits and liken any other systems AAS has got it’s own drawbacks as well. One must point out the following drawbacks (or costs) of the adaptive antennas:

  • Transceiver Complexity: It is obvious that the adaptive antenna transceiver is much more complex than the conventional one. This comes from the fact that the adaptive antenna transceiver will need separate transceiver chains for each of the array elements and accurate real-time calibration of each of them.
  • Resource Management: Adaptive antennas are mainly a radio technology, but they will also put new demands on network functions such as resource and mobility management. When a new connection is to be set up or the existing connection is to be handed over to a new base station, no angular information is available to the new base station and some means to “find” the mobile station is necessary.
  • Physical Size: For the adaptive antenna to obtain a reasonable gain, an array antenna with several elements is necessary. Typically arrays are consisting of six to ten horizontally separated elements have been suggested for outdoor mobile environments. The necessary element spacing is 0.4-0.5 wavelengths. This means that an eight-element antenna would be approximately 1.2 meters wide at 900 MHz and 60 cm at 2 GHz. With a growing public demand for less visible base stations, this size, although not excessive, could provide a problem.

An Adaptive Antenna System (AAS) can focus its transmit energy to the direction of a receiver. While receiving, it can focus to the direction of the transmitting device. The technique used in AAS is known as beamforming or beamsteering or beamshaping. It works by adjusting the width and the angle of the antenna radiation pattern (a.k.a. the beam). Combined with multiple antennas in the Base Station (BS), AAS can be used to serve multiple Subscriber Stations (SSs) with higher throughput. A technique known as SDMA (Space Division Multiple Access) is employed here where multiple SSs that are separated (in space) can transmit and receive at the same time over the same sub-channel.

AAS also eliminates interference to and from other SSs and other sources by steering the nulls to the direction of interferers.AAS is feature suits very well for LTE and it is an optional feature in WiMAX as it yet to be included in WiMAX certification. But due to its effectiveness in improving performance and coverage especially in Mobile WiMAX case, many vendors integrate AAS capability into their products.

Thursday, 27 December 2007

Multiuser Cooperative Diversity and Virtual MIMO



MIMO (Multiple Input Multiple Output) by definition requires multiple antenna but it is also possible to use one antenna with Co-operative Diversity to create Cooperative MIMO or Virtual MIMO.

Earlier this year, Nokia Siemens Network reported the following on Virtual MIMO:

Researchers at Nokia Siemens Networks have demonstrated in lab conditions how a virtual Multiple Input Multiple Output (MIMO) technique can be used for the uplink in LTE (Long Term Evolution) networks.

Tests at its labs in Munich, Germany, have shown how, using such an SDMA (Space Division Multiple Access) based technique, two standard mobile devices, each with only one physical transmission antenna, can communicate with a base station simultaneously and on the same radio channel.

On the uplink transmission, data rates of 108Mbit/s were achieved, double the usual speed, while the downlink managed 160Mbit/s.

The researchers say that while MIMO on the downlink primarily generates higher peak data rates for the end user, virtual MIMO on the uplink makes it possible for an operator to increase network capacity and better utilize the available spectrum.

Nokia Siemens also said the technique contributes to one of the crucial prerequisites for the success of LTE by reducing power consumption of LTE based devices to "acceptable levels" even when used for very high data-intensive applications and that this should be achieved at "moderate prices."

The researchers say that with virtual MIMO only one power amplifier and transmission antenna is necessary for each device, contributing to reduced production costs and power needs.

In the LTE test bed, developed and built in collaboration with the Fraunhofer Institute for Telecommunications (Heinrich Hertz Institute), two co-operating end-user devices form a virtual MIMO system in which the antenna elements are distributed over the two devices. The two devices can be supplied simultaneously with data over the same frequency band using space division multiplexing.


The following is an extract from EURASIP Journal onWireless Communications and Networking:

Multihop relaying technology is a promising solution for future cellular and ad hoc wireless communications systems in order to achieve broader coverage and to mitigate wireless channels impairment without the need to use high power at the transmitter.

Recently, a new concept that is being actively studied in multihop-augmented networks is multiuser cooperativediversity, where several terminals forma kind of coalition to assist each other with the transmission of their messages.

In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version to the intended destination node. The destination node combines the signal received from the relays, possibly also taking into account the source’s original signal.

Cooperative diversity exploits two fundamentals features of wireless medium: its broadcast nature and its ability to achieve diversity through independent channels.

There are three advantages from this:

(1) Diversity. This occurs because different paths are likely to fade independently. The impact of this is expected to be seen in the physical layer, in the design of a receiver that can exploit this diversity.

(2) Beamforming gain. The use of directed beams should improve the capacity on the individual wireless links.The gains may be particularly significant if space-time coding schemes are used.

(3) Interference mitigation. A protocol that takes advantage of the wireless channel and the antennas and receivers available could achieve a substantial gain in system throughput by optimizing the processing done inthe cooperative relays and in the scheduling of retransmissions by the relays so as to minimize mutual interference and facilitate information transmission by cooperation.


Source: Multiuser Cooperative Diversity forWireless Networks by George K. Karagiannidis, Chintha Tellambura, Sayandev Mukherjee and Abraham O. Fapojuwo, Volume 2006, Article ID 17202


There are 3 main types of co-operative diversity which are self-explanatory in the diagram above:

Decode and Forward
  • Simple and adaptable to channel condition (power allocation)
  • If detection in relay node unsuccessful => detrimental for detection in receiver (adaptive algorithm can fix the problem)
  • Receiver need CSI between source and relay for optimum decoding

  • Amplify and Forward
  • Achieve full diversity
  • Performance better than direct transmission and decode-and-forward
  • achieve the capacity when number of relays tend to infinity

  • Coded Cooperation
  • transmit incremental redundancy for partner
  • Automatic manage through code design
  • no feedback required between the source and relay
  • Rely on full decoding at the relay => cannot achieve full diversity!
  • Not scalable to large cooperating groups.
  •