Presentation: Smart Antennas and SON

Smart Antennas and SON

View more presentations from Zahid Ghadialy.

Presented by Kevin Linehan, VP, CTO Antennas, Andrew Solutions in the 4G World, Oct. 2010

The Path to 4G: LTE and LTE-Advanced

The Path to 4G: LTE and LTE-Advanced

View more presentations from Zahid Ghadialy.

The Path to 4G: LTE and LTE-Advanced presented by James Seymour, Alcatel Lucent in 4G World, 20th Oct. 2010.

7 transmission modes in LTE Rel-8

In Brief:

In Detail:

The Seven Modes of MIMO in LTE

View more documents from All About 4G.

Recap of MIMO Technologies in 3GPP LTE and LTE-Advanced

MIMO Technologies in 3GPP LTE and LTE-Advanced

View more documents from All About 4G.

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.

Coordinated Multi-Point (CoMP) transmission and reception

The industry’s first live field tests of Coordinated Multipoint Transmission (CoMP), a new technology based on network MIMO, were conducted in Berlin in October 2009. CoMP will increase data transmission rates and help ensure consistent service quality and throughput on LTE wireless broadband networks as well as on 3G networks. By coordinating and combining signals from multiple antennas, CoMP, will make it possible for mobile users to enjoy consistent performance and quality when they access and share videos, photos and other high-bandwidth services whether they are close to the center of an LTE cell or at its outer edges.

The following is from the 3G Americas report on CoMP:

Coordinated Multi-Point transmission/reception (CoMP) is considered by 3GPP as a tool to improve coverage, cell-edge throughput, and/or system efficiency.

The main idea of CoMP is as follows: when a UE is in the cell-edge region, it may be able to receive signals from multiple cell sites and the UE’s transmission may be received at multiple cell sites regardless of the system load. Given that, if the signaling transmitted from the multiple cell sites is coordinated, the DL performance can be increased significantly. This coordination can be simple as in the techniques that focus on interference avoidance or more complex as in the case where the same data is transmitted from multiple cell sites. For the UL, since the signal can be received by multiple cell sites, if the scheduling is coordinated from the different cell sites, the system can take advantage of this multiple reception to significantly improve the link performance. In the following sections, the CoMP architecture and the different CoMP schemes will be discussed.

CoMP communications can occur with intra-site or inter-site CoMP as shown in Figure 7.7.


With intra-site CoMP, the coordination is within a cell site. The characteristics of each type of CoMP architecture are summarized in Table 7.1.



An advantage of intra-site CoMP is that significant amount of exchange of information is possible since this communication is within a site and does not involve the backhaul (connection between base stations). Inter-site CoMP involves the coordination of multiple sites for CoMP transmission. Consequently, the exchange of information will involve backhaul transport. This type of CoMP may put additional burden and requirement upon the backhaul design.



An interesting CoMP architecture is the one associated with a distributed eNB depicted in Figure 7.8. In this particular illustration, the Radio Remote Units (RRU) of an eNB are located at different locations in space. With this architecture, although the CoMP coordination is within a single eNB, the CoMP transmission can behave like inter-site CoMP instead.

DL COMP

In terms of downlink CoMP, two different approaches are under consideration: Coordinated scheduling, or Coordinated Beamforming (CBF), and Joint Processing/Joint Transmission (JP/JT). In the first category, the transmission to a single UE is transmitted from the serving cell, exactly as in the case of non-CoMP transmission. However, the scheduling, including any Beamforming functionality, is dynamically coordinated between the cells in order to control and/or reduce the interference between different transmissions. In principle, the best serving set of users will be selected so that the transmitter beams are constructed to reduce the interference to other neighboring users, while increasing the served user’s signal strength.

For JP/JT, the transmission to a single UE is simultaneously transmitted from multiple transmission points, across cell sites. The multi-point transmissions will be coordinated as a single transmitter with antennas that are geographically separated. This scheme has the potential for higher performance, compared to coordination only in the scheduling, but comes at the expense of more stringent requirement on backhaul communication.

Depending on the geographical separation of the antennas, the coordinated multi-point processing method (e.g. coherent or non-coherent), and the coordinated zone definition (e.g. cell-centric or user-centric), network MIMO and collaborative MIMO have been proposed for the evolution of LTE. Depending on whether the same data to a UE is shared at different cell sites, collaborative MIMO includes single-cell antenna processing with multi-cell coordination, or multi-cell antenna processing. The first technique can be implemented via precoding with interference nulling by exploiting the additional degrees of spatial freedom at a cell site. The latter technique includes collaborative precoding and CL macro diversity. In collaborative precoding, each cell site performs multi-user precoding towards multiple UEs, and each UE receives multiple streams from multiple cell sites. In CL macro diversity, each cell site performs precoding independently and multiple cell sites jointly serve the same UE.

UL COMP

Uplink coordinated multi-point reception implies reception of the transmitted signal at multiple geographically separated points. Scheduling decisions can be coordinated among cells to control interference. It is important to understand that in different instances, the cooperating units can be separate eNBs’ remote radio units, relays, etc. Moreover, since UL CoMP mainly impacts the scheduler and receiver, it is mainly an implementation issues. The evolution of LTE, consequently, will likely just define the signaling needed to facilitate multi-point reception.

INTER-CELL INTERFERENCE COORDINATION

Another simple CoMP transmission scheme which relies on resource management cooperation among eNBs for controlling inter-cell interference is an efficient way to improve the cell edge spectral efficiency. The Inter-Cell Interference Coordination (ICIC) enhancement currently being studied for LTE-Advanced can be classified into dynamic Interference Coordination (D-ICIC) and Static Interference Coordination (S-ICIC). In D-ICIC, the utilization of frequency resource, spatial resource (beam pattern) or power resource is exchanged dynamically among eNBs. This scheme is flexible and adaptive to implement the resource balancing in unequal load situations. For S-ICIC, both static and semi-static spatial resource coordination among eNBs are being considered.

More information coule be found in:

• Coordinated Multipoint Trials in the Downlink - Fraunhofer Heinrich Hertz Institute
• 3GPP TR 36.814: Further Advancements for E-UTRA Physical Layer Aspects

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.

Agilent in a three-pronged attack over LTE

Agilent have decided to launch an all-out attack with the view of proving themselves leaders of LTE technology.

Firstly, they released an LTE book just yesterday. The book will now be competing with four other very popular books on LTE already in the market. I managed to get an early preview of the book and I wasn't very impressed. There are nevertheless some sections which are very well written, containing unique information.

Secondly, Agilent are running some MIMO workshops and have released some very good presentations on MIMO on the web. You can download the material from the workshop here.

Finally, Agilent Technologies are to present three technical sessions at 2009 Informa LTE World Summit. Here is an extract from the press release:

Agilent Technologies has announced it will present three technical sessions and exhibit its LTE test application solutions at the fifth Informa LTE World Summit, Berlin, Germany, May 18-20. Agilent will exhibit its design-automation tools and flexible instrumentation for early LTE R&D design in components, base-station equipment and mobile devices.

The technical sessions are:
* MIMO Mia! -- What the Standards Didn't Tell You about MIMO;
* Honey, Who Shrunk My Mega Bits -- Practical Tips on Measuring Application Throughput in the Real World; and
* Doing Less with Moore - Challenges and Opportunities for Future Standards.

Agilent will exhibit its design-automation tools and flexible instrumentation for early LTE R&D design in components, base-station equipment and mobile devices.

The landscape is changing rapidly in mobile communications, combined with the challenges in global economies, yet LTE clearly is gaining momentum, said Benoit Neel, vice president and general manager of Agilent's Europe, Middle East and Africa field operations. Agilent remains fully committed to providing test solutions for the entire LTE development lifecycle -- from early RF and protocol development to conformance test and comprehensive, real-time network optimization and diagnostics.

Session highlights of Doing Less with Moore - Challenges and Opportunities for Future Standards, an LTE Summit workshop track on standardization presented by Moray Rumney, include:
* Examining trends in standardization
* Growing fragmentation and complexity, diminishing returns
* The growing gap between conformance testing and real life operation
* Opportunities for standards in an uncertain world
* Integration of macrocell and small cell technology
* Can femtocells do it all or do we need Wi-Fi

I am going to be there and am hoping to give youll detailed information on the event.

Dual-Cell HSPA in Release 8 and beyond

Some interesting developments are ongoing in the 3GPP standardisation from Release-8 onwards. You must be aware that the current bandwidth in UMTS/HSPA is 5 MHz. Since most of the operators generally won bigger chunk of spectrum of contiguous 5MHz band, they can actually combine these chunks to create a larger spectrum and hence increase data rates.

In Release 8 in downlink, it is possible to increase data rates using either a combination of MIMO and 64QAM or dual-cell HSDPA for operation on two 5MHz carriers with 64QAM, data rates reach up to 42Mbps.

In deployments where multiple downlink carriers are available, the new multicarrier operation offers an attractive way of increasing coverage for high bit rates. Rel-8 introduces dual-carrier operation in the downlink on adjacent carriers. This technique doubles the peak rate from 21Mbps to 42Mbps without the use of MIMO – it doubles the rate for users with typical bursty traffic; therefore, it also doubles the average user throughput, which translates into a substantial increase in cell capacity.

You may remember that I mentioned earlier that the operators are not too keen on going for MIMO for non-LTE technology. This is because they will have to upgrade their hardware and the antennas which could increase their cost significantly for a technology that is not going to be around for long.

Another thing to note before it becomes too confusing is that there are two terms for 'DC' being used right now. One of them is 'Dual Carrier' and other is 'Dual Cell'. In Release 8, the term being used is Dual-Cell for HSDPA which is also known as DC-HSDPA. The Technical specification to follow is 3GPP, TR 25.825 “Dual-Cell HSDPA operation” V1.0.0, May 2008.

The Dual-Cell assumes that both the 5MHz bands are contiguous. If they are not then the better term to refer for DC is Dual-Carrier.

A dual-carrier user can be scheduled in the primary serving cell as well as in a secondary serving cell over two parallel HS-DSCH transport channels. All non-HSDPA-related channels reside in the primary serving cell, and all physical layer procedures are essentially based on the primary serving cell. Either carrier can be configured to function as the primary serving cell for a particular user. As a consequence, the dual-carrier feature also facilitates an efficient load balancing between carriers in one sector. As with MIMO, the two transport channels perform hybrid automatic repeat request (HARQ) retransmissions, coding and modulation independently. A difference compared to MIMO is that the two transport blocks can be transmitted on their respective carriers using a different number of channelization codes. In terms of complexity, adding a dual-carrier receiver to UEs is roughly comparable to adding a MIMO receiver. Because the two 5MHz carriers are adjacent, they can be received using a single 10MHz radio receiver, which is already be available if the UE is LTE-capable.

Following the introduction in Release 8 of dual-carrier operation in the downlink, 3GPP is now discussing operation on multiple 5MHz carriers. Multiband operation of multiple carriers allows a single user to simultaneously aggregate and use the spectrum distributed over different bands. This gives operators greater fl exibility when using available spectrum. Increasing the number of carriers that UEs receive from two to four doubles the peak rate and achievable user throughput. For bursty traffic, this translates into substantially greater capacity, either as a larger number of users at a given data rate, or as a higher data rate for a given number of users. To substantially boost spectral effi ciency, 3GPP is studying the combination of dual-carrier operation and MIMO with 64QAM in the downlink, thereby doubling the peak data rate to 84Mbps. Similarly, they are studying the combination of MIMO, 64QAM and up to four downlink carriers to support peak data rates of more than 100Mbps. The support for UE reception on two frequency bands is an enabler to DC-HSDPA for operators who do not have adjacent 5MHz carriers available in one band, and is therefore of key importance for the further evolution of multi carrier HSPA.

As a consequence of increased data rates in downlink, the uplink data rates need to be improved too. From the aggregation of multiple FDD downlink carriers, the paired FDD uplink carriers can be utilized for improved uplink transmissions. 3GPP studies the usage of two adjacent 5MHz carriers for dual carrier uplink transmissions (DC-HSUPA) supporting data rates of up to 23Mbps. A further benefit of utilizing two uplink carriers is the possibility to support more efficient load balancing in the uplink direction.

In summary, uplink multicarrier operation increases availability as well as coverage of high data rates in the uplink.

In Conclusion, Rel-8 defines improvements in HSPA to achieve higher rates through dual carrier or combined 64QAM+MIMO operation. With the Rel-8 specification nearing completion (targeted for March 2009), planning is already under way in 3GPP for Rel-9 and Rel-10. Further multi-carrier and MIMO options are being explored for HSPA in Rel-9 and Rel-10

If you want to explore this topic further see:

• Nomor research White Paper – Dual Cell HSDPA and its Future Evolution.
• WirelessMoves - Dual Carrier HSDPA - The Push Beyond 5 MHz
• Ericsson - Continued HSPA Evolution of mobile broadband

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 ---

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

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.

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.

300 Mbps with 'Super-FOMA'

NTT DoCoMo, Inc. announced that this month it began testing an experimental Super 3G system for mobile communications. With this experiment, DoCoMo will seek to achieve a downlink transmission rate of 300Mbps over a high-speed wireless network.

For people who are unaware, LTE is being branded as Super-3G as this term is more appealing as compared to LTE which would mean nothing to ordinary people.

DoCoMo will begin with an indoor experiment to test transmission speed using one transmitting and one receiving antenna. The company will then expand the experiment to examine downlink transmission by employing up to four Multiple-Input Multiple-Output (MIMO) antennas for both the base station (transmission side) and mobile station (receiving side); the goal is to achieve a downlink transmission speed of 300Mbps. MIMO is an antenna technology for wireless communications in which different data streams are spatially multiplexed using multiple antennas for both transmission and reception on the same frequency. Also to be examined is the "handover function" — switching of the connection between two base stations.

NTT DoCoMo's Super-3G timetable is available here

The reason i am calling this setup as Super-FOMA is because going back to when 3G was being introduced, DoCoMo wanted to be the first with 3G. As a result, they adopted a 3GPP Release version that wasnt stable and released it as FOMA. Now they are doing the same with LTE. LTE wont be stable in that timeframe so they might end up with Super-FOMA instead of Super-3G.

The company has also been aggressively pursuing 4G system development. In late December, the carrier came close to hitting a 5Gbit/sec. data transmission speed from an experimental 4G system to a receiver moving at 10 kilometers per hour.

Possibly it may be the first one with a 4G system and it might end up as Hyper-FOMA :)

Long Term Evolution gaining momentum

There is lot of activity going on regarding the 3GPP Long Term Evolution popularly known as LTE (and i also refer to this term as Long Term Employment).

There have already been couple of high profile announcements this month on LTE. A press release from Nokia announced, "A group of world leading telecom technology manufacturers and network operators comprised of Alcatel-Lucent, Ericsson, France Telecom/Orange, Nokia, Nokia Siemens Networks, Nortel, T-Mobile, and Vodafone have announced a joint initiative aimed at driving forward the realisation of the next-generation of high performance mobile broadband networks based on 3GPP Release 8 "Long Term Evolution / System Architecture Evolution" (LTE/SAE) specifications."

I suppose this initiative is more of a reaction to the advancement of WiMax. There have been some high profile announcements about operators adopting WiMax as the technology of their choice rather than 3G and its evolution. The press release also said: "The companies participating in this initiative will collaborate on demonstrating the potential of 3GPP LTE/SAE mobile broadband technologies through a series of joint tests including radio transmission performance tests, early interoperability tests, field tests and full customer trials. Joint activities will commence in May 2007, and are expected to run for a period of 18-24 months."

Another press release, from Nokia-Siemens networks told us that using virtual MIMO the UL data rate has been increased in LTE from 54Mbps to 108Mbps. At present i cannot think of why we would need these high speeds but i am sure its always good to have the facility.

An Interview in a Indian newspaper with Nokia-Siemens networks head for the region gives an indication that Nokia is trying to play down WiMax card and promote LTE (which i think is sensible anyway).

At present it looks like only Nokia but i am sure other major players like Nortel, Ericsson and Qualcomm are not far behind.