Tag Archives: Carrier aggregation

Carrier Aggregation and the Road to Cognitive Radio and Superwide Spectrum

16 Jan

Carrier Aggregation

Often, the least hyped technologies are the most effective, get the widest adoption, and have the greatest impact. Carrier aggregation is one such technology that I don’t think it received its fair share of attention. LTE did bring a number of new features that were not available in 3G, such as MIMO. But MIMO was already deployed in other technologies including both Wi-Fi and WiMAX. Carrier aggregation on the other hand developed by the requirement to achieve higher data rates in LTE network. True channel bonding is a feature of Wi-Fi, but it applies to adjacent channels. Carrier aggregation on the other hand combines distinct channels in different bands. From that perspective, I am not aware of any wireless technology that has implemented carrier aggregation.

Carrier Aggregation - LTE-Advanced

Carrier Aggregation – LTE-Advanced: Up to 5 20 MHz Carriers can be combined for 100 MHz bandwidth.

If necessity is the mother of invention, then carrier aggregation has a few mothers! Data rate requirement is one, but another very important aspect is spectrum fragmentation. To date, there are 44 bands defined for LTE operation between 400 and 3800 MHz. Each band supports anywhere from 2 to 6 different channelizations for a total of 159 different profiles! Trunking theory stipulates higher efficiency and greater capacity in wider channels than narrow channels. In fact, a 20 MHz LTE channel carries 103% more capacity on average than 10 MHz channel – that’s a 3% gain in capacity. Carrier aggregation is therefore a mean to achieving greater capacity with fragmented spectrum.

LTE Spectrum Fragmentation

Carrier aggregation is an important development because it is the first step along the long road to realize cognitive radio implementation in wireless networks. Cognitive radio involves the capability of spectrum sensing to identify suitable bands for operations (which is a very challenging task). The radio would in effect ‘stitch’ different bands together to meet the application performance requirements. The importance of this cannot be overstated. Spectrum utilization is highly variable and can include long idle periods. This encouraged the concept of spectrum sharing techniques in which cognitive radio will play a part. Carrier aggregation is therefore a first step on that road.

Implementation of carrier aggregation is the result of integrating and optimizing multiple developments. On the handset side, we now have available on the market wideband RFICs and frontend chipsets with highly integrated power amplifiers that span the entire sub 6 GHz spectrum: example is the Qualcomm RF360 chipset. We also have developments in antenna design and tuning and matching techniques that allow support for multiple bands. Although implementation on the base station side can be easier because some parameters such as space and cost can be more relaxed than the handset side, numerous challenges related to integrating multiple high-power carriers had to be resolved. Finally, the LTE functions to support carrier aggregation had to be put in place such as cross-scheduling.

There have been a number of trials of carrier aggregation to date. Commercially, it is operational on all three carrier networks in Korea. It is the first feature of LTE-Advanced (Release 10) to be deployed. Users can therefore expect better capacity which translates also into lower delay. Operators can use carrier aggregation to support a greater number of users in a single cell. Furthermore, small cells and hetnets can make use of carrier aggregation to coordinate operation and avoid interference. This can be particularly advantageous when coupled with shared spectrum access in bands such as 3.5 GHz (US) and 2.3 GHz (Europe).

LTE Advanced Carrier Aggregation Downlink Throughput

Probability Distribution Function of LTE Advanced Carrier Aggregation Downlink Throughput. (Source: Signals Research Group)

Country Operator Max Downlink Speed (Mbps)
Australia Telstra (2×20 MHz, 1800/2600 MHz, Ericsson) 300
Australia Optus (TD-LTE, 2×20 MHz, 2300 MHz, Huawei)(TD-LTE, 4×20 MHz, 2300 MHz, Huawei) 160520
Austria A1 Telekom Austria (NSN) 580
France SFR (2×10 MHz, 800/2600 MHz, Ericsson) 174
China China Mobile (TD-LTE, 2×20 MHz, ZTE) 233
Japan NTT DOCOMO 300
Philippines Smart Communications (Huawei) 211
Portugal Optimus (Huawei) 300
Russia Yota (Huawei) 300
South Africa Telkom Mobile (TD-LTE, 2×20 MHz, 2300 MHz, Huawei) 200
South Korea SK Telecom (2×10 MHz 800/1800 MHz, Samsung, Ericsson, NSN) 150*
South Korea LG U+ (2×10 MHz, 800/2100 MHz, Samsung, Ericsson, NSN) 150*
South Korea Korea Telecom (2×10 MHz, 900/1800 MHz, Samsung, Ericsson, NSN) 150*
Turkey Turkcell (Huawei) 150900 (Lab)
UK EE (2×20 MHz, 1800/2600 MHz) 300

Table 1. Carrier Aggregation Trials & Deployments (*)

As we evolve from 4G LTE/LTE-Advanced, carrier aggregation is set to play a major role in any future 5G technologies through cognitive radio and in what is called “super wideband spectrum.” That is what makes carrier aggregation such an important development in wireless technologies. The potential for innovation is truly great and we are still at the beginning of this journey.

Source: http://frankrayal.com/2014/01/14/carrier-aggregation-and-the-road-to-cognitive-radio-and-superwide-spectrum/


On LTE-Advanced and Carrier Aggregation

2 Jul

LTE-AdvancedNews of LTE-Advanced is making headlines. SK Telecom aggregated two 10 MHz carriers in 800 and 1800 MHz to achieve 150 Mbps downlink throughput with a version of the Samsung Galaxy S4 handset built upon Qualcomm’s Snapdragon 800 SoC. Verizon announced that its LTE network is nearly complete and suggested carrier aggregation (CA) is the next step. AT&T on the other hand has plans to use carrier aggregation over its 700 MHz unpaired lower D and E blocks.

Carrier Aggregation

Carrier Aggregation (Source: Qualcomm)

While LTE-Advanced has many features aside than carrier aggregation, such news is significant because they indicate how carriers are moving to address the demand for capacity. Implementing carrier aggregation has in my opinion the best cost/benefit of LTE-Advanced features, provided spectrum is available, which is the case with many operators. To put the issue into perspective, consider for instance other highlight features of LTE-Advanced:

* High order MIMO: today’s LTE systems use two transmit antennas at the base station and the handsets are equipped with two receive antennas (2×2). LTE-Advanced supports higher order MIMO such as 4×4, but the gain from this implementation will be limited as capacity cannot increase beyond the minimum number of transmit or receive antennas (so 4×2 results in doubling the capacity, similar to 2×2). Increasing the base station antennas to 4 while the handset remains at 2 antennas will not result in doubling of capacity, but there will be improved service nonetheless as the link between base station and mobile becomes more robust.

* Small cells: much discussed in recent years, small cells remains encumbered by the business case, interference management such as eICIC, SON, site location & expense, backhaul and other challenges. The advantage of small cells is that they can be deployed selectively to increase capacity in certain areas.

* Relays: have not been at the forefront of features as they are considered mainly as a coverage extension tool. Also, there is aversion to using access spectrum for backhaul even on a limited basis. I expect that spectrum sharing techniques can open up low cost spectrum where relays become viable.

* Coordinated Multipoint (CoMP): CoMP requires tight synchronization of transmitters and places a burden on the backhaul network. Many issues remain to be resolved in CoMP but ultimately operating this feature would require fiber connectivity to sites, which is expensive and not all carriers might have that capability.

Considering the cost/benefit equation associated with other major LTE-Advanced features, I expect carrier aggregation to gain traction quickly particularly as many operators now posses TDD spectrum. For example, Sprint’s acquisition of Clearwire can pave the way to use some of the 2.5 GHz spectrum in CA mode to augment downlink capacity. In Europe and other areas of the world, 3GPP Band 38 (2570-2620 MHz) is available for carrier aggregation. This is further supported on the handset site by new SoCs such as the Snapdragon 800. However, we may still have to wait for a short while before CA becomes a mainstream technology as I expect it will.

Source: http://frankrayal.com/2013/07/01/on-lte-advanced-and-carrier-aggregation/

World`s First LTE-Advanced Network launched by SK-Telecom

27 Jun

SK Telecom announced that it today launched the world’s first LTE-Advanced (LTE-A) service through smartphones.  The company achieved such a milestone in only less than two years after commercializing the nation’s first LTE service in July 2011.

To commercialize LTE-A, SK Telecom successfully developed and applied the most-advanced mobile network technologies. The company already applied Carrier Aggregation (CA) and Coordinated Multi Point (CoMP), and plans to apply Enhanced Inter-Cell Interference Coordination (eICIC) in 2014.

CA, commercialized for the first time in the world by SK Telecom, supports up to 150Mpbs speed by combining two 10 MHz components carriers to form an effective bandwidth of 20 MHz spectrum bands.

With the surge of data traffic worldwide, CA will act as the key enabler for network evolution among mobile operators around the world. According to network experts, CA will be further advanced to realize up to 300Mbps speed by aggregating two 20MHz component carriers by 2015, and become capable of combining three component carriers by 2016. In addition, they expect to see the realization of uplink CA by 2016. The current CA standards allow for up to five 20 MHz carriers to be aggregated.

Since launching the nation’s first generation analogue network (1G) in 1984, SK Telecom led the popularization of mobile telecommunications service by commercializing CDMA (2G) for the first time in the world in 1996, and introduced video telephony service through the commercialization of CDMA2000 1X in 2000. In 2006, the company opened the era of mobile data communications service by commercializing the HSDPA technology over its 3G WCDMA network using a mobile phone for the first time in the world. Then, SK Telecom has launched the Korea’s first 4G LTE in 2011 and successfully commercialized the Multi Carrier (MC) technology, for the first time in the world, in July 2012.

SK Telecom announced that its existing LTE price plans will apply to the LTE-A service, meaning that customers will be able to enjoy twice faster network speeds without paying extra. The decision comes as part of its commitment to maximize customer benefits and satisfaction through innovative technologies and services.

With the commercialization of the world’s first LTE-A network, SK Telecom today released Samsung’s ‘Galaxy S4 LTE-A.’ The Samsung device, the world’s first phone optimized to work over LTE-A network, will come in two different colors, red (exclusively available at SK Telecom) and blue.

SK Telecom will embed useful services like ‘Safe Message’ and ‘Safe Data Backup’ as basic features in all its LTE-A phones. Safe Message is designed to protect users from smishing (SMS phishing) attacks by enabling them to check whether the message is sent from a trusted source; and ‘Safe Data Backup’ enables users to upload personal data stored in their smartphones to the cloud server to keep data safe from smartphone loss and accidental deletion. The company also plans to mount these features on all its to-be released LTE phones as well.

Customers can purchase Galaxy S4 LTE-A at SK Telecom’s official online store named T World Shop (www.tworldshop.co.kr), or at one of 2,850 authorized SK Telecom T World retail stores. The company has secured an initial supply of 20,000 units of Galaxy S4 LTE-A.

Furthermore, SK Telecom will vigorously expand its LTE-A phone lineup to boost the popularization of LTE-A service. It plans to provide a total of seven different LTE-A compatible smarphones in the second half of 2013.

Begins offering LTE-A in Seoul and central areas of Gyeongg-do and Chungcheong-do, and plans to expand LTE-A coverage to 84 cities nationwide

SK Telecom plans to expand its LTE-A coverage at an unmatched speed to keep offering the best call quality to customers.

To achieve early commercialization of LTE-A, the company, for the first time in the world, developed the MC technology and applied it to its LTE network in July 2012. During the process, SK Telecom designed and built MC base stations in a way that they can support an optimized evolution towards LTE-A.

In March, SK Telecom has launched aggressive plans to expand the coverage of MC base stations to 200 university areas and central areas of 84 cities nationwide. The company has built a total of 20,000 RU (Radio Units) as of June 2013. With MC in place, the company can easily evolve the network to LTE-A s through simple software upgrades.

SK Telecom’s LTE-A, launched today, covers the entire Seoul, central areas of 42 cities in Gyeonggi-do and Chungcheong-do, and 103 university areas. Furthermore, the company will gradually expand its LTE-A coverage to 84 cities across the nation.

On June 27, 2013, the company will launch a group video calling service for up to four users. The service, an upgraded version of the 3G network-based multi-party video conferencing service, will support 12 times better video quality and 2 times clearer audio quality.

SK Telecom’s ‘Btv mobile,’ an IPTV service with 550,000 paid subscribers, will begin providing full HD (1080p resolution) video streaming service, for the first time in the world, from early July. Full HD video streaming requires a speed of 2Mbps or above, which is well supported by the LTE-A network.
※Required speed for each level of image quality – SD: 1Mbps, HD: 2Mbps, Full HD: 4~8Mbps

The company will also launch ‘T Baseball Multiview,’ to enable users to watch two different games on one screen in July 2013. T Baseball is a free, real-time professional baseball game broadcast service optimized to the LTE network. Launched in August 2012, the service is currently enjoyed by 1.1 million users.

Moreover, SK Telecom plans to launch ‘T Freemium 2.0,’ a free multimedia content package that offers three times more contents – e.g. dramas, TV entertainment shows, music videos, sports game highlights, etc.- than its previous version, ‘T Freemium,’ in July 2013.

The company is also planning to launch a new HD video-based shopping service in August 2013 to make shopping more fun and convenient for customers. Users will be able to seamlessly watch 6 different home shopping channels on one screen.

Also, SK Telecom’s online/mobile music portal service MelOn yesterday opened a new service category to allow users to listen to original CD quality music by downloading Free Lossless Audio Codec (FLAC) files.

Meanwhile, SK Telecom will hold a large-scale contest named ‘LTE-A i.con’ to boost the creation and provision of diverse innovative contents and applications optimized for the LTE-A network.

At today’s LTE-A press conference held at SK T-Tower, SK Telecom’s head office, the company demonstrated the speed of its LTE-A network by comparing it with those of LTE and 3G.

It also showcased innovative LTE-A-based mobile value added services including MelOn’s FLAC files, ‘T Baseball Multiview’ and Btv mobile’s full HD video streaming service.

Moreover, Kwon Hyok-sang, Head of Network Division of SK Telecom, made live video calls from SK T-Tower to Gangnam Station and the company’s Daejeon office to show LTE-A’s ultra-fast speed.

Park In-sik, President of Network Business Operations at SK Telecom said, “SK Telecom is proud to announce the world’s first commercialization of LTE-A. By supporting twice faster speeds than LTE, LTE-A will not only enhance customers’ satisfaction in network quality, but also give birth to new mobile value added services that can bring innovative changes to our customers’ lives.”

Source: http://4g-portal.com/worlds-first-lte-advanced-network-launched-by-sk-telecom

Network planning and testing for LTE-Advanced

15 Nov
Streaming video, gaming, advanced applications, and more are putting demands on today’s wireless networks and increasing the need for capacity and tower density.  In response, carriers are looking at options, such as Wi-Fi underlay and backhaul, to limit the load on networks.
Simultaneously, various carriers are conducting trials and looking to introduce LTE-Advanced to the masses in 2013, which promises to make a performance leap by bringing more low-powered nodes closer to the user.  However, issues around standards and how each carrier will make network handovers complicate things when deploying heterogeneous network components such, as smaller cell sites (e.g., picocells, femtocells, etc.).

Why LTE-Advanced?
LTE-Advanced (LTE-A) is a 3rd Generation Partnership Project (3GPP) specification in response to International Telecommunication Union (ITU) requirements for International Mobile Telecommunications-Advanced (IMT-Advanced) systems.  These requirements define what fully compliant 4th generation cell phone mobile communications system needs to satisfy, most importantly:
•    Peak speed requirements at 100 Mb/s for high mobility communication (such as from trains and cars) and;
•    Peak speed requirements at 1 Gb/s for low mobility communication (such as pedestrians and stationary users).

Even though Mobile WiMAX and LTE don’t meet these objectives, they are considered “4G” technologies since they are significantly better performing and capable then initial 3rd generation systems and are early versions of fully IMT-Advance compliant Mobile WiMAX Release 2 and LTE-Advanced.

For the LTE-Advanced system, 3GPP has further required the following:
•    Higher spectral efficiency (from a maximum of 16 bps/Hz in LTE to 30 bps/Hz in LTE-A);
•    Improved performance at cell edges (e.g. for downlink 2×2 MIMO at least 2.40 bps/Hz/cell).

What is new in LTE-A
To meet these requirements, LTE-A systems have some improvements compared to LTE, namely, carrier aggregation (CA), improved multi-antenna techniques and support for relay nodes (RN).  We will look at each one.

Carrier Aggregation
LTE-A systems need considerably more signal bandwidth to meet the requirement of the significant throughput increase compared to 3G and LTE.  Since LTE-A also needs to maintain backward compatibility with the LTE terminals, the LTE-A bandwidth increase is performed by aggregating multiple LTE carriers into a single LTE-A signal.  Each LTE carrier that comprises the LTE-A signal is called component carrier (CC).  A single LTE-A signal can consist of component carriers with different bandwidths as defined in the LTE specification.  This allows for effective utilization of the available spectrum.

Figure 1. The LTE-A component carriers can be of different bandwidth.  The downlink (DL) can have extra carriers compared to the uplink (UL).

Component carriers can be aggregated contiguously, with spectrum gaps between them (non-contiguously) or even across multiple bands (inter-band).  The current standard limits aggregation across no more than any three bands within 0.3 – 6.0 GHz.  In the future, each CC could be located in a separate band.  This again allows for effective utilization of the available spectrum.

Figure 2. The LTE-A Component Carriers can be discontinuous and even in different bands.

LTE terminals utilize only one of these carriers while the LTE-A terminals can utilize up to five CC.  Per the LTE specification, the maximum bandwidth of a single CC is 20 MHz.  Therefore, the maximum LTE-A bandwidth achievable when aggregating five CCs is 100 MHz.  It is also important to note that the downlink (DL) and uplink (UL) do not need to be symmetrical, and the downlink can have the same number or more CCs than in the uplink transmission direction.  This again allows for effective utilization of the available spectrum, and optimization of the channel based on the throughput required by the user, which is often also asymmetrical.

Figure 3. The LTE-A component carriers (transmitted from the same tower) may form the independent cells with different footprints. 

LTE-A radio resource control (RRC) is handled by one of the CC.  This CC is called LTE-A Primary CC (PCC).  Other CCs are called LTE-A Secondary CCs (SCC).  Some additional RRC messages are introduced in LTE-A to support this division.  Each CC, however, forms an independent cell with potentially different coverage.  This is due to the freedom to adjust transmitting power for each CC but also due to different band and antennas potentially being used for different CCs.  The positive aspect of this is that a heterogeneous network can be formed this way (as we will see later), but the downside is that the LTE-A terminal might not always be able to aggregate all the CCs.

Improved multi-antenna techniques
To meet the requirement of increased spectral efficiency (throughput per bandwidth), LTE-A had to build on LTE multi-antenna techniques.  In high signal-to-noise environments, LTE uses a spatial multiplexing technique called multiple input multiple output (MIMO).  MIMO allows higher throughput communication by using two or more transmit (Tx) streams received (Rx) by two or more antennas at the same time while occupying the same bandwidth.  Each transmit antenna uses a different reference signal which allows separation of the signals by the receiver.  If these antennas are appropriately spaced on the tower and on the terminal, then propagation paths between the transmitting and receiving antennas can be spatially sufficiently different to provide higher throughput with same time/frequency resources.

LTE-A increases the maximum number of the DL antennas from four present in LTE to eight and the maximum number of the UL antennas from the two present in LTE to four.  This results in almost double the spectral efficiency in high signal-to-noise environments.

Support for Relay Nodes
One of the hardest things to achieve in a cellular network is good performance at the edge of a cell just before a new cell begins.  LTE-A addresses this by using a mix of large and small cell sizes.  This mixed layout is called a heterogeneous network (HetNet).  We mentioned above how the carrier aggregation feature allows for adjustments to the footprint of every component carrier in the base station (enhanced Node B or eNB).  An additional LTE-A feature that helps achieve improved cell edge performance is the relay node (RN).  These are small and low power base stations that don’t require backhaul.

RNs are typically deployed at the edge of the cell to increase capacity and throughput there.  Instead of having dedicated backhaul (e.g. fiber, cable, radio link), RNs use a slightly different part of the LTE-A air interface (defined as Un) than that used by normal terminals (known as Uu).  This allows the RN to communicate with the donor/anchor base station (Donor eNB) for the backhaul purposes and provide a local terminal its expected Uu link.  RNs can use the same frequency or a different frequency for communication with the donor base station and the terminals.  In case of a RN operating on the same frequency as its donor base station, steps need to be taken (and will be explained later) to prevent the RN from interfering with itself.  For example, it could be a significant problem if the RN were to be transmitting to the terminals at the same time it’s trying to receive from the donor base station on the same frequency.

Figure 4. The RN uses the Un interface to communicate with the donor base station and the Uu interface to communicate with the terminals.

From the terminal perspective, RNs are fully fledged base stations.  They transmit their own cell identification information (known as a Cell Id) and handle all aspects of the air interface (sync and reference signal, scheduling, control channels, etc.) up to mobility management (handovers).  Donor base stations hide (i.e., abstract) RNs from the rest of the network.

LTE-A also employs advanced interference mitigation techniques between the elements of this heterogeneous network.  These techniques include intelligent node association and the adaptive time/frequency resource allocation (e.g., enhanced time-domain adaptive resource partitioning).  This provides dynamic network load balancing at different locations and times of day.

LTE-A network deployment considerations
Here we review some items to consider when deploying LTE-A networks.

Carrier Placement
LTE allows for a 100 kHz raster (the step between possible signals center frequencies) for carrier RF placement.  In LTE, the OFDM subcarriers are spaced at 15 kHz per the standard.  So in order to maintain the subcarrier orthogonality when aggregating multiple component carriers in the same band, adjacent CCs need to be spaced at 300 kHz raster.

It is also advantageous for component carriers to be placed symmetrically within the band due to the type of receiver (zero IF) used in most terminal and user devices.  If the component carriers are asymmetrical within the band, LTE-A resource elements (frequencies) in the middle of the band will be overlapped within a zero IF receiver’s internal mask and would be lost for communication.

Figure 5. The component carriers need to be symmetric within a band.

If the CCs are available in multiple bands, then the ones with better propagation characteristics (typically lower RF frequencies) should be dedicated for the macro coverage or the cell edge coverage and their antennas properly configured for larger footprint use.  The CCs with physical attributes promoting shorter propagation are better suited for the close-in coverage, and should be dedicated to increasing the terminal’s data throughput.

Figure 6. The Component Carrier with the lower frequency is used for the macro (cell edge) coverage and the higher frequency Component Carrier is used for the throughput increase.

RF implementation of the carrier aggregation can be very challenging depending on the spectrum distance between the component carriers.  If the CCs are in the same band, interference from other signals in the spectrum between CCs creates significant problems.  If the particular band (e.g. PCS) UL frequencies are fairly close to the DL frequencies and the CCs are spread over most of the band, then there can be filtering problems to sufficiently separate DL and UL.  Also, component carrier inter-modulation products could be present that could interfere with the system’s ability to achieve efficient full duplex communication.

MIMO Antennas
On the base station side, each sector could have eight MIMO antennas on the tower.  With this large number of antennas, sectorization on the tower requires close attention.  For example, for a particular tower, would three sectors on the tower with each having eight antennas or maybe six sectors on the tower with each having four antennas produce a better solution?  Further, instead of having eight sets of the expensive and lossy cables going up the tower for each sector, it might start making more sense to use remote radio heads on the tower in the proximity of the antennas.

On the terminal side, having four antennas properly spaced is a challenge for mobile phones.  It is also challenging to meet the LTE-A processing power and throughput needs in this form factor.  It is therefore expected that the initial LTE-A terminals will be laptop and tablet computers.

Relay Node Carrier Assignment
If the RN uses the same component carrier for communication with the donor base station and the terminals, self interference can result.  RN transmission to the donor base station interferes with RN reception from the terminals and vice-versa.  To avoid this, RN antennas intended to communicate with the donor base station should be isolated (separated, distanced) from the RN antennas meant for communication with terminals.

If this is not practical (which often is the case), the RN needs to use a different component carrier than the donor base station for communication with the terminals.  Another solution is to schedule the backhaul and access communication in the RN at different time instances.

Relay Nodes vs Pico Cells
A key decision the network planner must make is how to choose between augmenting the macro cell with RNs rather than deployment of pico cells.  The biggest factor is usually availability of a backhaul needed for a pico cell where it is intended to be deployed.  If increased capacity is required in the macro cell and the backhaul to the small cell location is less expensive than the LTE spectrum, you would typically want to place a pico cell there, leaving the spectrum that would be consumed by the backhaul available to serve other terminals.

If, on the other hand, a small cell’s purpose is to patch a gap in the coverage, there are no significant capacity issues in the macro cell yet.  Or, if another form of backhaul isn’t readily availability, it is probably appropriate to install a RN to serve the area.  As discussed, this will use part of the unused macro cell spectral capacity for its backhaul, which may be of little concern in more rural/less dense areas.  If in the future macro cell utilization begins to approach its capacity, then converting this RN into a pico cell and providing a dedicated backhaul for it might be necessary.

Other Areas for Consideration with LTE-A
Wi-Fi Underlay
If the pico cells are required to augment the macro LTE-A base stations, it is prudent to look at possibility for Wi-Fi to fill in this role.  The majority of the current mobile terminals are equipped with Wi-Fi.  There exists greater availability of spectrum for Wi-Fi as compared to that available for cellular communications.  Wi-Fi has recently also been significantly improved through IEEE standardization work.  The IEEE 802.11ac standard will enable speed of up to 1 Gbit/s in the 5-GHz band, which is on par with LTE-A.  By the end of 2012, this new standard is expected to be finalized and by the end of 2013, be fully approved.  Integration of Wi-Fi into the cellular networks is also being standardized as is roaming between the two technologies.  The primary standard being developed for this roaming is IEEE 802.11u.  Maintaining the cellular quality of service, while roaming on the Wi-Fi networks, is also being addressed.

Wi-Fi backhaul
If, due to the capacity issues, pico cells need to be installed, but there is no backhaul capability for them, then point-to-point Wi-Fi links might be the right solution.  The existing 802.11n devices can probably handle most of the LTE-A Pico cell requirements, but, if not, the above mentioned 802.11ac should be available in time for the first LTE-A deployments.

Receiver/Scanner and Test Tools
Initial fields test before the LTA-A signals start to be transmitted are no different than for any other cellular technology.  If the new part of the spectrum is to be utilized we first need to make sure that no interference is present in it from any other system.  This can be accomplished by performing a drive test in the area where LTE-A deployment is to be made using a scanning receiver that just measures power in the part of the spectrum to be used by the LTE-A system.  If interference is discovered, then a more detailed drive test might need to be performed to localize and try to identify it using the spectrum analyzer feature of the scanning receiver.  Identified interference should be removed in order to properly deploy the LTE-A system in this spectrum.  Alternative tools for this phase of deployment can be a fast and sensitive spectrum analyzer or a specialized interference hunting tool with directional antennas.

If the LTE-A channel aggregation is utilized it is prudent to check for presence of the in and out of band interference due to inter-modulation products that can potentially be created when multiple component carriers are transmitting.  The same tools as above can be used for that.

An LTE-A deployment can be planed by determining the position and the configuration of each LTE-A base station.  If a new base station location or a new spectrum region are to be used, then it might be necessary to test the base station RF propagation characteristics to properly plan the network.  This can be done using an omni-directional test transmitter radiating in the still empty LTE-A spectrum and mounted where the base station antenna is to be located.  A local drive test with the scanning receivers measuring the power of this transmitter can be conducted to determine the amount of path loss for this base station.  Instead of a scanning receiver, a fast and sensitive spectrum analyzer could also be used for this test function.

Once the spectrum is clear of interference and the LTE-A network plan implemented, its actual performance needs to be determined and optimized before it is ready for commercial service.  This is accomplished by measuring the power and the quality of signals coming from particular base stations.  Most of the synchronization, common reference and broadcast signals are carried over from LTE to LTE-A (intentionally, due to backward compatibility reasons).  So, as in LTE, base station reference sequences are used for the power measurement that is still called reference sequence received 0ower (RSRP). Either reference sequence received quality (RSRQ) or carrier to interference and noise ratio (CINR) is used for the base-station quality measurement.  The LTE-A physical cell identities (PCIDs) detected, as in the LTE, identify the base station to which the measurements belong.  A typical LTE scanning receiver would support these LTE-A measurements and base station identities, but various LTE phone-based tools could support them too with a tradeoff between the capability, price and size of the equipment.

The RSRP and CINR should be measured in particular between the cells or at the cell edges as well as insides the buildings.  Measurements in these areas will indicate if the additional optimization of the base station parameters is necessary or installation of the relay nodes / pico cells there would increase the network performance.

Once the LTE-A network is operational with real end user traffic, it should be evaluated for the uplink and the downlink throughput as well as bit error rate.  The phone-based test tools are usually best for this.  Based on these measurements further network optimization can be undertaken.  Same scanner and phone based test tools can be used for ongoing network maintenance and re-optimization during its lifecycle.

This is all good news for the carriers, because much of their existing LTE deployment tools, ,such as Rhode and Schwarz’s ROMES and PCTEL’s SeeGull, can be directly used with some changes to how they are configured.  Any of the more advanced tools that also include decoding of the layer 3 messages, such as QRC’s ICS-Qp and ICS, as well as ROMES, should be updated to support the additional information present for the LTE-A.  That many of these tools can be utilized with fairly minor upgrade is a significant cost savings in rolling out LTE-A.

Positioning of Relay Nodes/Pico Cells
To determine if a LTE-A macro cell needs, an underlay of the RNs or the pico cells, we need to check if there are coverage gaps, low quality of service areas or capacity bottlenecks in this macro cell.  If we have problems like these, we should try to determine where in the macro cell’s coverage area they occur.  The field measurements (e.g. drive test) with scanning receivers are one way to determine this.  The area with the low DL signal strength would indicate the coverage gaps; the areas with low DL signal quality (high interference) would indicate the areas with low quality of service; and the areas with high DL signal quality but lots of UL spectral activity would indicate the area of high traffic that could cause a capacity crunch in the macro cell.  Once these areas are identified, it can be evaluated if covering them with a RN or pico cell would be cost effective.

Heterogeneous Network Interference Management
Additional improvements in terminal performance in the heterogeneous network can be achieved by employing terminals with advanced receivers that can cancel the interference from the overhead LTE-A channels (e.g. sync, broadcast, common reference signal) transmitted by the macro (donor) cell.  It is not clear at this time when these advanced receivers will be commercially available.

After reviewing major new aspects of LTE-A technology, we can conclude that preparation for carrier aggregation is probably the first and most important challenge.  Appropriate spectrum needs to be obtained/cleared and then allocated to cells in an optimal way.  The next biggest priority from the planning perspective will be how to improve the network with use of the RNs.  By the time service providers are ready to begin implementation of LTE-A, many LTE networks will probably already have an underlay of small cells (LTE pico or Wi-Fi), and RNs should be planed for locations where such cells are needed but there is not an appropriate backhaul for them.  Finally, LTE scanners/receivers will be appropriate for initial LTE-A field tests.

Source: http://www.edn.com/design/test-and-measurement/4401353/Network-planning-and-testing-for-LTE-Advanced

Full Portfolio of LTE Device Test Solutions Supports Public Safety Community

25 Aug

Anritsu Company announces that its full portfolio of LTE device test solutions includes Band 14 capability to support the public safety community. This portfolio includes three LTE-capable test platforms, as well as two LTE-focused test systems. Applications for these solutions cover the complete LTE device development chain from functional test to PTCRB certification and aftermarket repair, and options for advanced functionality, such as Voice over LTE (VoLTE) and LTE Advanced/Carrier Aggregation, are available.

Each of Anritsu’s three LTE-capable platforms – the MD8430A and MD8475A Signaling Testers, and MT8820C One-Box Tester – are capable of establishing LTE calls and performing specific classes of measurements on LTE devices. While the MD8430A is focused on protocol testing, with availability of the most advanced LTE features, including Carrier Aggregation and 4×2 MIMO, the MD8475A is focused on LTE functional and application testing, with added capability for multiple formats, such as W-CDMA/HSPA, GSM/(E)-GPRS, CDMA2K, and others. The MT8820C is capable of a similar mix of LTE and other formats but is focused on lower-layer RF parametric test.

Both Anritsu LTE-focused test systems are built on the MD8430A as the core “engine,” and include the ME7873L RF Conformance Test System and ME7834L Mobile Device Test Platform. The ME7873L allows for quick public safety device certification based on Anritsu having the highest number of available PTCRB-validated Band 14 RF/RRM conformance test cases in the industry. The ME7834L provides similar benefits to the public safety market, with a leading number of PTCRB-validated Band 14 protocol conformance test cases available on the system.

“Anritsu is pleased to support the evolution of public safety communications to LTE,” said Wade Hulon, Vice President and General Manager, Anritsu Americas. “Anritsu has offered the commercial LTE industry the widest range of LTE device test solutions since the initial rollout of LTE networks, and looks forward to assisting the with the rollout of LTE for public safety across the USA.”

The MD8475A is a compact, Windows 7-based tester capable of emulating two base stations or an LTE 2×2 MIMO downlink, with formats including LTE, W-CDMA/HSPA+, GSM/(E)-GPRS, and CDMA2000. For voice call testing, both VoLTE and circuit-switched calls are supported, with circuit-switched fallback (CSFB) support for LTE to 2G and 3G. End-to-end application testing is supported by the tester, with the capability to install user-supplied servers inside the MD8475A or to connect external servers. Anritsu’s SmartStudio GUI provides easy graphical control of the MD8475A, and the internal state machine emulates real network operation without the need for scripts.

Source: http://www.wirelessdesignmag.com/ShowPR.aspx?PUBCODE=055&ACCT=0000100&ISSUE=1208&RELTYPE=LNP&PRODCODE=000000&PRODLETT=EY&CommonCount=0  August 24, 2012

11 Ways Around Using More Spectrum for Mobile Data

19 Aug

Despite widespread calls for more spectrum to carry mobile data, there is a wide range of technologies already being used or explored that could help to speed up networks or put off the day when more frequencies need to be cleared.

Spectrum is the lifeblood of mobile services. The planned purchase by Verizon Wireless of 20MHz of spectrum from a group of cable operators, which the U.S. Department of Justice approved on Thursday, is the latest sign of how important this invisible resource is to mobile operators.

Any service on the airwaves needs frequencies it can use without being overwhelmed by interference, whether the frequency it uses comes from an exclusive license or from a sharing arrangement. The more packets of data are being exchanged over a network, the more spectrum will be needed to carry them — unless something else is done.

Mobile operators, technology vendors and governments have been sounding alarms about mobile networks nearing capacity for years, and those alarms are getting louder. A study released last year by investment bank Credit Suisse said mobile networks worldwide were filled to 65 percent of capacity on average, while North American networks were running at 80 percent. The U.S. Federal Communications Commission said in 2009 that it expected mobile data traffic to grow by 35 times in the next five years. Equipment vendor Ericsson predicts 10x growth by 2016. Moreover, the growth in demand is unpredictable, because new applications arrive all the time. And an overloaded spectrum band can slow down users’ mobile experience.

To meet that demand, regulators and carriers are trying to make more spectrum available for mobile data services. In the U.S., the FCC pledged in 2009 to make 500MHz of additional spectrum available for mobile broadband in the coming years. CTIA, the U.S. mobile industry group, had called for 800MHz.

However, if the predictions about traffic growth come true, there won’t be enough “new” spectrum available to keep up with it. Supply and demand are on different orders of magnitude. For example, if the FCC auctioned off 300MHz tomorrow and the two biggest U.S. carriers split it, that will increase their spectrum in the average market by not much more than double, according to independent industry analyst Andrew Seybold. (Then, it would take three or four years to get that spectrum online, he said.)

To fill the gap between those growth rates, governments and industry agree that what’s needed is at least a two-pronged approach, with more spectrum as well as strategies to make better use of the spectrum that’s already available. Carriers also are taking steps that should help to dampen the growth in demand.

Here is an overview of some of the techniques that may help to stave off a mobile crunch. They fall into three main categories: getting more out of service providers’ current mobile data spectrum, making better use of all possible mobile frequencies, and reducing the demand on spectrum assigned to mobile services.

Making better use of existing spectrum

1. Small cells

Mobile operators can serve more subscribers and give them better performance using the very same spectrum they already have. One way to do this is by installing smaller cells to supplement the traditional “macro” cells that cover an entire neighborhood. As long as the two types of cells don’t interfere with each other, subscribers’ mobile devices can connect to a small cell serving a street corner or an office and share it only with the other subscribers nearby. If there are enough small cells in the area, users can be handed off from one to the other without ever taxing the macro cell, which remains available for subscribers who aren’t near to an area of small cells.

The Small Cell Forum industry group says setting up just four small cells within the area of a macro cell can offload 56 percent of the data traffic from the nearest tower. All this requires exactly the same amount of spectrum as the carrier used to operate the original cell tower, and it lets more subscribers use the network simultaneously.

2. LTE-Advanced

The next generation of LTE is actually a variety of new features coming in version 10 of the standard, which is now complete and is expected to be deployed starting next year. Though it draws attention for its theoretical maximum throughput of 100Mbps (bits per second), the enhancements in LTE-Advanced are mainly for efficient use of spectrum, according to Arne Schaelicke, a global LTE product marketing executive at Nokia Siemens Networks. The advances include the ability to use more antennas per cell and a mechanism to manage interference between macro and small cells.

LTE cells have been limited to just two antennas, but with the new standard they can be configured with as many as eight, to create eight separate streams of data for higher throughput. To allow macro and small cells to work in the same area, LTE-Advanced provides a way for the two types of cells to back off from each other once every millisecond so they can use the same frequency and not interfere with each other, Schaelicke said.

3. Carrier aggregation

However, the biggest benefit of LTE-Advanced is expected to be carrier aggregation. This part of the standard lets service providers combine multiple small blocks of spectrum into one block that’s large enough to deliver a strong LTE service. They’ll even be able to tie together frequencies that are in widely different bands, taking advantage of already licensed spectrum that otherwise might have gone unused or underutilized.

Clearwire, the WiMax wholesale operator that plans to launch an LTE-Advanced network next year, plans to use carrier aggregation to combine two 20MHz spectrum blocks into a single block with 40MHz, said John Saw, Clearwire’s chief technology officer. That will outstrip the 20MHz that both Verizon and ATT are using for LTE in most markets. However, any carrier aggregation move has to use spectrum combinations that are certified by the 3GPP so device makers will have a specification to work with, Saw said.


Another technology that can help service providers use their spectrum more efficiently is TDD-LTE (time-division duplexing LTE). Most operators are building their networks with FDD (frequency-division duplexing) systems, which use two paired bands of spectrum, one for upstream and one for downstream traffic. Some are required to do so by regulators. TDD-LTE, on the other hand, uses one block of spectrum for traffic in both directions and segregates them by the amount of time they can take on the network. That better suits real traffic patterns and gives the operator more flexibility in how to use its spectrum, according to Clearwire, which uses TDD-LTE.

“TDD allows me to tailor my spectrum resources to where my customers’ behavior is,” Clearwire’s Saw said. This system can also make it easier to combine multiple chunks of spectrum, because each chunk doesn’t have to be paired with another, he said.

Making better use of all spectrum

5. Spectrum-sharing

Some experts say it’s time to throw out the whole notion of allocating certain frequencies exclusively to commercial mobile services, or to any exclusive use. Instead, they advocate mobile operators sharing spectrum with current users, such as government agencies.

In a report issued earlier this year, the U.S. President’s Council of Advisors on Science and Technology recommended that the secretary of commerce identify 1,000MHz of frequencies where commercial and federal users could coexist. “This study finds that today’s apparent shortage of spectrum is in fact an illusion brought about because of the way spectrum is managed,” the report said.

Advances in technology, including small cells and radio performance improvements, help make it possible for mobile networks to use the same frequencies as other services, as long as potentially interfering signals don’t rise above a certain level, the report said. It cited the success of Wi-Fi in unlicensed spectrum as an example. Sharing could multiply the effective capacity of spectrum by a factor of 1,000, the group said.

In a response to the PCAST report, CTIA, the main industry group for U.S. mobile operators, cast doubt on its conclusions. CTIA said cleared, exclusive spectrum is the “gold standard” for mobile service, and some technologies that PCAST cited aren’t available yet.

6. Spectrum refarming

As carriers adopt LTE, which uses spectrum much more efficiently than earlier technologies, they plan to gradually migrate users off of their oldest networks and reuse those frequencies. Those moves ultimately will make a significant amount of additional spectrum available for high-speed data services, but it’s not an overnight solution.

Earlier this month, ATT announced it would phase out its 2G GSM and EDGE networks by the beginning of 2017, shifting customers to 3G and 4G services market by market. It estimated 12 percent of its subscribers use 2G phones. In May, Sprint Nextel won FCC approval to use spectrum in the 800MHz band, which is now used for its aging iDEN network and has been limited to narrowband technology, for LTE services that use wider bands.

7. Wi-Fi

When mobile users shift over from a cellular network to Wi-Fi, their traffic stops using the carrier’s spectrum altogether. Wi-Fi is a big part of carriers’ so-called offload strategies because it offers two fat bands of unlicensed spectrum and is built into nearly all smartphones and tablets. Many carriers have already built or bought extensive networks of Wi-Fi hotspots, and all encourage users to move their devices from the cellular network to their own Wi-Fi at home.

Continual advances in Wi-Fi technology, including the IEEE 802.11ac gear expected to be widely available next year, make wireless LANs even better for handling large numbers of users. Going from cellular to Wi-Fi may also become easier with new systems such as the Wi-Fi Alliance’s Passpoint standard. Efforts are now under way to let users roam automatically, among hotspots operated by different carriers and by aggregators such as Boingo.

The experience would be like roaming between cell networks and it could send a lot more mobile traffic off the scarce cellular frequencies, helping mobile operators to get by longer with the spectrum they already own. But carriers are expected to adopt the new roaming technology slowly. Consumers should note that unlike the access offered now on carrier-owned hotspots, Wi-Fi roaming may not always be free for subscribers.

Reducing the amount of data on the network

8. Compression

No matter what frequencies are used to carry mobile data, less traffic means less spectrum is needed. Data compression is a time-honored way of cutting files down, but it has its limits as a solution to the wireless crunch, according to Rajat Roy, a senior product line manager at Broadcom. To start with, the biggest files, such as video, audio and images, are already compressed using standard protocols such as JPEG and MPEG. For other types of files, the industry is still trying to settle on a common standard so mobile devices will have the software to decompress what’s been compressed in the network.

However, Broadcom has targeted one type of traffic that doesn’t make for huge files but is often inefficient. The company builds technology into its wireless base-station chips that can compress the header fields of VOIP (voice over Internet Protocol) packets. Though voice doesn’t take up much bandwidth, the packet headers containing routing and other information are sometimes twice the size of the payload itself, Roy said. Compressing the headers reduces the load on the network.

9. Caching

There are at least two ways in which caching could help reduce the need for spectrum. One is time-shifting traffic to reduce peak demand. The growing amount of storage capacity on devices and in removable flash cards could allow users to download large files such as video automatically during off hours, said Tolaga Research analyst Phil Marshall. Users who signed up to have that content sent could then watch it later on the device. Security and digital rights management are possible barriers to adopting this technique, Marshall said.

Broadcom has another caching idea: The company equips its cellular base station processors to identify and cache multimedia content while sending it out to client devices. The idea is to keep filling the “time slots” on a wireless pipe that the network allocates for the file transfer. Letting those slots go unfilled wastes network capacity. Broadcom’s chips can store enough packets of a file or a multimedia stream in memory so that the base station can pack as much data as possible into every time slot devoted to that application, Roy said.

10. Reducing signaling traffic

In some cases, it isn’t mobile video or big email attachments that are consuming an operator’s spectrum, but small signals sent between devices and networks. With busy applications such as push email, social networking and even Web browsers, these small signals can add up.

“We’ve seen cases where carriers had lots of data capacity … available in their network and congestion being defined by signaling capacity limits,” said Peter Carson, a senior director of marketing at Qualcomm. He expects the problem to get worse.

In its mobile modem chips, Qualcomm is implementing several technologies that reduce signaling. One is a more efficient way for applications to request network resources and switch between communication modes. Another helps the modem to combine network requests and data traffic from a device’s application processor in batches. These techniques also tend to slash power consumption, extending battery life. They should be available soon in devices equipped with Qualcomm modems, Carson said.

11. Pricing and data caps

Finally, technical and regulatory solutions are only part of the picture. The most powerful tool to prevent spectrum becoming overloaded may be regulating mobile traffic through service plans.

Most carriers are well along in phasing out unlimited data plans, if they ever had them. Now that monthly usage caps are in place, the service providers can modify them as needed to discourage subscribers from using too much network capacity. They can also fine-tune subscriber behavior by encouraging time-shifting or charging more for plans where the subscriber’s packets get priority over other traffic.

“If I have a flat-rate plan on my iPad, and I can jump onto LTE whenever I like, that’s what I’ll do. But if it’s a plan that doesn’t allow me to do that, and I’ll pay a premium to use that LTE network, chances are, I’m going to jump on to Wi-Fi,” Marshall of Tolaga Research said.

If one carrier can make its spectrum support a plan that satisfies consumers, others will use whatever tools they need to try to match it, Marshall said. “It’s market competition that will define how many cell sites, how much spectrum, and what techniques are used to deliver the service, as opposed to pure demand,” Marshall said.

Source: http://mobilemarketing.name/11-ways-around-using-more-spectrum-for-mobile-data/ August 18, 2012

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