Nokia Siemens Networks Active Antenna System White Paper 26-01-12

White paper

Active Antenna SystemsA step-change in base station site performance

2 Active Antenna System

complement the macro layer as a key provider of capacity and coverage. This makes it essential to boost macro layer efficiency to meet the modern network’s ever-growing demand for mobile broadband services.

Now a rising technology is complementing network development. Active antenna system technology integrates several radio frequency (RF) components (power amplifiers and transceivers) with the antenna dipoles. This enables the phase and amplitude of the signals from each dipole inside the antenna to be electronically controlled. Benefits include more flexible deployment, improved capacity and coverage, smaller installation and lower power consumption, while also supporting a multi-technology network

Active antenna systems will boost existing base station site efficiency and performance. The technology can even be used to create micro and macro cells simultaneously by using the same hardware located at the macro base station. Active antenna system technology is set to bring new levels of flexibility to the base station and create a customer experience matched to the needs of every individual.

Nokia Siemens Networks has pioneered work on active antenna systems and has already publicly demonstrated working examples of the technology. Flexi Multiradio Antenna System, based on active antenna system technology, integrates eight RF

Executive summary

Conventionally, expanding the capacity of mobile networks has been achieved mainly by adding more base stations to the existing infrastructure. However, this is a relatively slow and costly way to roll out capacity that has impeded the growth of mobile broadband and in today’s highly competitive markets is becoming challenging. Smaller cells have been enabled to provide a more cost-effective and faster way to add capacity in selected hot spot areas and to fill coverage gaps, especially indoors. However, small cell deployment will not replace but rather

Figure 1. Integrated RF components enable intelligent beam forming, which boosts base station efficiency.

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Contents2. Executive Summary3. The evolution of

radio networks5. The evolution of antenna

technology6. Active antenna systems

deliver more flexibility7. Efficient utilization of

active antenna systems9. Active antenna system is

a fast-developing technology

10. Nokia Siemens Networks Flexi Multiradio Antenna System

11. Conclusion: A step-change in base station development

11. Abbreviations

components directly to the antenna dipoles creating unique beam forming capability. This intelligent integration and beam forming delivers significant performance enhancement and high energy efficiency. Initial deployments of Flexi Multiradio Antenna System have shown improvement of base station capacity by up to 65% and coverage by up to 30%, making it a very valuable option for operators to meet traffic demand growth with existing installed infrastructure.

Additionally, site space and power consumption savings are realized through the intelligent integration of RF components, thus minimizing feeder line losses and the number of hardware items to be implemented. As a result, active antenna system enables operators to not only cut site costs substantially, but to meet the dynamic demands of their mobile customers much more cost effectively.

It is clear that active antenna systems are bringing about a step-change in the radio networks. Nokia Siemens Networks is spearheading the way forward with its Flexi Multiradio Antenna System, a critical pillar of Liquid Radio that is in turn part of the Liquid Net approach. Liquid Net unleashes frozen network capacity into a reservoir of resources that can flow to fulfil unpredictable demand, wherever and whenever people use broadband.

Over the years, networks have been extended principally by adding macro cells for additional capacity and coverage. However, the acquisition and running of base station sites are among the biggest drains on operator finances.

Additionally, a dedicated base station was installed for every new technology, leading to insufficient space at existing sites to add more equipment. Finding new site locations is becoming impossible, resulting in growing site rental fees adding to rising energy costs.

These difficulties have restricted the pace with which operators have been able to roll out new mobile

The evolution of radio networks

3Active Antenna System

technologies, capacity and new features in order to improve network performance. Clearly, new ways of boosting base station efficiency are urgently needed.

The revolution of base stations

The industry has followed a trend in which the size of base station hardware has reduced dramatically through the introduction of modular base stations and Single RAN equipment, helping to reduce site costs. The Single RAN is a flexible platform that supports multiple radio access technologies through software-defined radio running on multipurpose baseband hardware.

Meanwhile, the introduction of modular base stations led to a distributed architecture with remote RF units, which include the power amplifiers, connected to the antenna system with standard RF cables. The RF unit and baseband unit communicate with each other via a fiber optic interface which enables flexible installation and improved radio performance, with better coverage compared to centralized cabinet designs.

These developments have enabled operators to re-use previous infrastructure investments as part of their evolution strategy and helped operators to improve base station site efficiency.

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Figure 2. The evolution of base stations has brought down equipment size and site costs substantially. Active antennas are the next logical step.

The introduction of multi-layer networks

The conventional way of adding capacity by adding macro cells into the mobile network has become very challenging. This has led to the coverage provided by macro cells being complemented by a multitude of smaller cells, to fill gaps in coverage, to improve indoor coverage and to meet capacity demand in traffic hot-spots.

Yet, the complexity of multi-layer networks with their multiple small cells can be a challenge. They are more complex to manage than today’s networks and the introduction of multiple combinations of cells and layers requires smart optimization and network management solutions, with network configuration and optimization carried out automatically.

Furthermore, as well as additional backhaul and power requirements to support small cells, new site acquisitions are needed, which remains a challenge.


The impact of non-uniform demand

A further difficulty facing operators as they build these uniform networks is that users are not evenly spread out within coverage areas, nor do they exhibit constant demand at all times. This uneven demand means that some cells and areas within cells tend to run under capacity while other areas suffer congestion. Consequently, network investments are not always fully utilized.

At the same time, competition is forcing operators to drive down network costs, while environmental concerns are pushing energy efficiency up the agenda for anyone operating a communications network. Both of these drivers mean that adding capacity by investing in ever greater numbers of base stations, whether macro, micro or smaller, is becoming less attractive.

Thus, one important aspect in today’s networks is how to boost the efficiency of existing base station sites to meet these challenges, without introducing high complexity and large rises in operational expenses.

Figure 3. End user demand is lumpy, varying unpredictably according to location and time.

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As we have seen, base stations have evolved substantially over the past two decades, bringing down the size of the hardware and improving their energy efficiency. There has been less progress in the development of antennas. These have remained passive components, leaving all intelligence on separate RF components and other base station equipment.

The earliest base station antennas were basic omni-directional assemblies radiating equally in all directions and providing relatively low capacity. As demand for mobile communications increased, sectorized antennas became more common. These created a specific radiation pattern, typically three-sector, and with sector-to-sector handoffs as devices moved within the macro-cell. Later still, antennas with integrated two passive cell-sectors inside one antenna radome became available, enabling six sector sites with three antennas for increased coverage and capacity.

These antennas also featured mechanical tilt and, later, electrical tilt to adjust the radiation pattern to optimize handover and reduce interference. Remotely-controlled electrical tilt gives operators greater flexibility to improve network performance.

Multi-band antennas combine low band and high band arrays into a single housing which reduce the antenna size and improve the wind loading, which

helps to lower site costs. But, more recently, multiple-input multiple-output (MIMO) and higher order receiver diversity (4-way RX diversity) technologies have been introduced to provide higher performance, increasing the complexity of antenna selection and configuration. Today antennas do not need to be merely passive elements. With intelligent integration, active antenna technology transforms traditional antenna to contribute to base station efficiency. This enables operators to significantly increase the capacity and coverage targets set for their network. The higher efficiency arising from the use of active antennas will mean higher performance as well as higher energy efficiency; this can all be achieved by integrating RF components directly into the antenna’s radiator elements. Furthermore, feeders to connect separate RF units to traditional antennas are no longer needed.

Additionally, this RF component integration will enable intelligent beam forming, giving increased capacity and coverage as well as improved end-user performance using the existing installed base. Active antennas can effectively double network resources in a given area and boost coverage by making a single cell act as two. Beamforming enables a operator to focus a portion of the cell’s resources on a chosen hotspot, for instance, while still providing blanket coverage throughout the rest of the cell.

Active Antennas are highly flexible and can meet the needs of many scenarios. They also support rising feature complexity including higher-order MIMO and receiver diversity, while retaining a simple and compact form factor.

The evolution of antenna technology


A conventional base station comprises passive antennas connected by RF cables to a separate cabinet that houses the RF modules and baseband processing. A development of this arrangement is the Remote Radio Head (RRH) in which the RF unit is installed next to the passive antenna to reduce cable losses. Currently being promoted is a product called Integrated Antenna System (IAS), in which one or two separate RF units are physically merged to the antenna but without intelligent integration to the antenna radiator elements. This leaves the antenna acting as a passive component in much the same way as the RRH arrangement.

An active antenna goes a step further and is created by integrating several RF components (power amplifiers and transceivers) - conventionally part of the base station - with the antenna’s radiating elements. This enables the phase and amplitude of the signals from each radiating element inside the antenna to be electronically controlled, using signal processing to shape and steer the direction of the radiated beam vertically and horizontally.

Precise control of the radiated pattern can only be achieved by the active antenna system in which one or a few radiating elements are individually controlled by an RF component. This provides much more control over coverage and capacity than the RRH and IAS in which all the radiating elements are fed by a single, common RF component.

An active antenna system is typically of a similar size to a conventional passive antenna, yet offers much greater performance and brings major benefits to operators. These include more flexible deployment, improved capacity and coverage and lower power consumption, while also supporting a multi-technology network.

Beamforming increases capacity

A principal advantage of active antennas is their ability to create and steer beams within the cell. Beamforming works by changing the phase and relative amplitude of the signal emitted from each radiating element, to create constructive or destructive interference. Constructive

interference is used to amplify the beam in a given direction, while destructive interference is used to focus the beam, enabling it to be steered precisely. Beamforming can be applied to radiating and receiving antenna elements independently.

Beamforming is a powerful technique, well-established for decades in military radar and other applications, that brings new flexibility to mobile networks. Vertical beamforming can be used to create two cells per conventional cell sector. By creating two dedicated cells, sector area resources are doubled. This will significantly improve performance in the whole sector area and also uniquely bring dedicated resources at the edge of sector. Capacity gains of more than 65% have been shown to be achievable, accompanied by significant coverage improvement.

Operators can automatically adjust the sizes and positions of the two cells to better serve the non-uniform demand from users across the macro-sector area. Highly flexible deployment is possible with beamforming, enabling an operator to cater for almost any demand profile within the macro-sector.

Active antenna systems deliver more flexibility

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Figure 4. Active antennas open up a wide range of deployment options for operators to cater for varying demand across macro-sectors.


Carrier-specific tilting

Unlike conventional non-active antennas that can only tilt all carriers, carrier-specific tilting can enable different carriers to be used to meet different demand scenarios.

Operators using three, or even four, carriers can benefit from improved utilization of all carriers by tuning each carrier independently, for example to meet high peak data rates using HSDPA and MIMO. The upper frequencies can deliver a smaller cell range than other frequencies in order to reduce interference from other base stations, which is vital for achieving peak throughputs.

System-specific tilting

Similar to carrier-specific tilting, active antennas can independently control the tilt of different technologies using the same frequency, for example GSM and WCDMA at 900 MHz or GSM and LTE at 1800 MHz. Again, unlike a conventional single-column antenna

which tilts all technologies by the same amount, an active antenna can be used to provide different coverage and capacity profiles for each technology, all this in a single-column antenna form factor.

For example, WCDMA at 900 MHz could be tuned to deliver more focused coverage than GSM at 900 MHz. This would be achieved by tilting the WCDMA beam more than the GSM beam using the same antenna. System-specific tilting can be used to achieve better control of interference and other performance requirements of individual technologies.

Multi-operator network sharing

Network sharing is a growing trend that substantially reduces costs for operators by enabling them to share network infrastructure. In a similar way to system-specific tilting, an active antenna system can be used to share transmission power between operators using the same antenna.

Signals for different operators can be tilted and resources allocated independently to meet the needs of each operator according to subscriber density or other parameter. For example, one operator could be allocated only 20W of active antenna power while another would need 40W.

Boosting performance with SON

The high performance of active antennas can be further improved through the use of Self-Organizing Networks (SON) solutions. With the support of SON, dynamic steering of the beam becomes possible to distribute capacity precisely to where users need it when they need it.

SON will enable the optimization of active antenna parameters according to actual traffic mix, traffic location and user demands. This will enable fully-automated user-tracking beamforming in which the beam follows the user and allocates resources to provide the best customer experience for each user at all times.

Efficient utilization of active antenna systems

Figure 5. Carrier-specific tilting is used to limit interference between cells to increase peak throughput.

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Lower overall site costs

Combining the RF components and antenna creates major operational cost savings. Active antenna systems are faster and easier to install and have fewer components by eliminating the need for Mast Head Amplifier (MHA) and Remote Electrical Tilt (RET) equipment. They are also lighter and more streamlined which reduces wind loading compared to traditional passive antenna systems with separate radio units, all of which helps to lower site capital and operational costs.

Improved network availability

With many integrated RF components, active antennas feature much greater inherent redundancy than conventional antennas because the failure of one or more transceivers will not disrupt services. Even multiple transceiver failures can be tolerated, maintaining network availability.

The intelligence within the antenna recognizes any failure and automatically adjusts the beamforming pattern to achieve the best performance possible. This ‘soft-recovery’ capability helps to reduce operational costs substantially by eliminating many emergency service call-outs by engineers and by enabling a more flexible maintenance program. Furthermore, a faulty module can be replaced without taking the entire antenna out of duty.

Higher energy efficiency and RF performance

Integrating the RF function within the antenna means that less coaxial cabling is needed, with fewer components such as feeders and connectors. This reduces power losses significantly compared to conventional antennas, making gains in coverage of up to 30% possible. Reducing power losses within the system also raises overall energy efficiency to shrink power costs and carbon emissions for a much greener site.

Reduced network evolution costs

By increasing the capacity of the existing macro-cellular layer, the active antenna system reduces the need for costly new sites, while its beamforming capabilities can be used to cover hot-spots, reducing the need to deploy many additional small cells.

Furthermore, the active antenna system enables more cost-effective network modernization, while also being a future-proof solution even with the advent of LTE-Advanced. By providing multi-radio capability to support GSM/EDGE, WCDMA/HSPA, LTE and LTE-Advanced, the active antenna system can minimize an operator’s future investments in radio technologies and protect its existing site investments by enabling new technologies to be deployed without the need for new radio units. 2100 MHz

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Figure 6. Much less hardware and easier installation reduce overall site costs compared to conventional integrated antenna systems.

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Figure 7. The evolution from integrated antenna systems to advanced active antenna systems with SON control promises to meet the liquid demand of a diverse use base.


The standardization of active antennas is at an early stage. In the summer of 2011, the RAN4 group of the 3GPP standards body approved a new study item on Active Antenna Systems, responding to intensified interest from several major operators, as well as vendors interested in implementing the technology. This was driven by the realization of the potential of this technology and following demonstrations of a working platform such as the Nokia Siemens Networks Flexi Multiradio Antenna System.

Clearly, active antenna system has potential to develop and enjoys solid backing by the industry. As described earlier in this paper, the use of SON technology to automate dynamic user-tracking of beams is a promising development. A single column antenna deployed as part of a heterogeneous network would have the adaptive vertical beamforming capability to meet the natural ebb and flow of demand from users in real time.

Active antenna system is a fast-developing technology

The development of multi-column antennas will introduce horizontal beamforming capabilities. Ultimately, many cells can be created from a single antenna.


Nokia Siemens Networks has pioneered work on Active Antenna Systems and has publically demonstrated working examples of the technology since it was introduced in 2008.

Similar in size to conventional passive antennas, the Nokia Siemens Networks Flexi Multiradio Antenna System is a true active antenna system that integrates the base station’s radio frequency elements into the antenna. This is achieved by using 8 x 10 W power amplifiers to feed the passive antenna elements. Not only does this bring huge cost and performance benefits, but it also paves the way for features such as fully adjustable electrical tilt per carrier or RAT and beamforming.

Flexi Multiradio Antenna System increases site capacity and coverage with advanced features like vertical beamforming, 2 x 2 Multiple-Input Multiple-Output (MIMO) and independent Tx and Rx electrical tilting per frequency or RAT. Vertical beamforming provides up to 65% capacity gain and up to 30% coverage gain compared to a standard 3-sector feederless site. Furthermore, when used with industry-leading Nokia Siemens Networks SON functions, the customer experience and service quality will be raised to completely new levels. Future active antenna developments are expected to support multiple columns and horizontal beamforming, to further enhance the capacity.

High reliability and smart redundancy is achieved with hot-swap capable radio units and with SON functionalities such as self-healing.

The first products in the Flexi Multiradio Antenna System range are based on a single-column, cross-polarized antenna. With intelligent vertical beam forming, an antenna can be used to create two cells in the same sector, allowing 4-way receiver diversity in uplink to improve end-user performance. Traditionally this requires a two-column, cross-polarized antenna and four receivers.

Flexi Multiradio Antenna System is designed to help operators to reduce the cost of evolving their networks by creating an active antenna system that can be integrated with an existing site solution. Seamless integration drives down costs and speeds up rollout.

Nokia Siemens Networks Flexi Multiradio Antenna System

Nokia Siemens Networks Flexi Multiradio Antenna System comprises the following components:

• Power Amplifier for each radiator element inside the antenna

• Optimized design with 8 transmitters/8 receivers with 8 x 10W power amplifiers

• High output power, up to 2 x 40W for macro deployments.

• Flexible power configuration per carrier (1 carrier at 80W, 2 carriers at 40W, etc)

• High cell and carrier capacity, for example up to 4+4 WCDMA cells in one sector

• Integrated 2 x 2 MIMO

• 4-way RX diversity

Figure 8. The Nokia Siemens Networks Flexi Multiradio Antenna System.

Figure 9. The key elements of Nokia Siemens Networks Multiradio Base Station using Flexi Multiradio Antenna System.


ConclusionA step-change in base station development

Abbreviations3GPP Third Generation Partnership ProjectGSM Global System for Mobile communicationsEDGE Enhanced Data rates for GSM EvolutionHSPA High Speed Packet AccessIAS Integrated Antenna SystemLTE Long Term EvolutionMHA Mast Head AmplifierMIMO Multiple-Input Multiple-OutputRAN Radio Access NetworkRAT Radio Access TechnologyRET Remote Electrical TiltRF Radio FrequencyRRH Remote Radio HeadSON Self Organizing NetworkTRX TransceiverWCDMA Wideband Code Division Multiple Access

Base station site technology has seen dramatic advances over the last two decades, reducing the size of equipment and bringing huge benefits by reducing the radio network’s capital and running costs while also providing ever greater capacity and coverage. Today we are on the verge of similar advances being applied to antenna technology with the deployment of active antenna systems.

The active antenna system enhances mobile network performance significantly by integrating the base station’s radio frequency (RF) elements into the antenna. This is achieved by using several transceivers (TRX) to feed the passive antenna elements. Not only

does this bring huge cost and performance benefits, but it also paves the way for advanced features such as fully adjustable electrical tilt per carrier or Radio Access Technology (RAT) and beamforming.

Similar in size to conventional passive antennas, the Nokia Siemens Networks Flexi Multiradio Antenna System is a true active antenna system that integrates the base station’s radio frequency elements into the antenna.

The benefits to be gained include boosted capacity and coverage, higher energy efficiency, lower site rental fees, lower wind loading and reduced investments as new radio technologies come on line and additional spectrum bands become available. As a result,

active antenna systems enable operators to not only cut site costs substantially, but to also more cost effectively meet the dynamic demands of their mobile customers.

It is clear that active antenna systems will bring about a step-change in the evolution of radio networks. Leading the field is the Nokia Siemens Networks Flexi Multiradio Antenna System, which is a vital part of Liquid Net. This radical new architecture helps operators to cost-effectively address unpredictable demand by creating networks that adapt instantly to changing customer needs, using existing capital investments more efficiently and generating entirely new revenue opportunities. It does this by unleashing frozen network capacity into a reservoir of resources that can flow to fulfill demand, wherever and whenever broadband is used.

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The content of this document is provided “AS IS”, without warranties of any kind with regards its accuracy or reliability, and specifically excluding all implied warranties, for example of merchantability, fitness for purpose, title and non-infringement. In no event shall Nokia Siemens Networks be liable for any special, indirect or consequential damages, or any damages whatsoever resulting form loss of use, data or profits, arising out of or in connection with the use of the document. Nokia Siemens Networks reserves the right to revise the document or withdraw it at any time without prior notice.

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Nokia Siemens Networks Active Antenna System White Paper 26-01-12