|By Deborah Strickland||
|February 12, 2013 10:26 AM EST||
Heterogeneous networks (HetNets) consist of large (macro) cells with high transmit power (typically 5 W – 40 W) and small cells with low transmit power (typically 100 mW – 2 W). The small cells are distributed beneath the large cells and can run on the same frequency as the large cell (co-channel), or on a different frequency. As an evolution of the cellular architecture, HetNets and small cells have gained much attention as a technique to increase mobile network capacity and are today one of the hot topics in the wireless industry. Many of the initial deployments of small cells are of the co-channel type. Standards such as LTE have focused on incorporating techniques to improve the performance of co-channel deployments in earlier releases of the technology standard leaving the handling of multi-frequency deployment type to later releases. In all, operators today have multiple options of small cell deployment scenarios, operational techniques and technology roadmaps to choose from.
Figure 1 Simplified Heterogeneous Network Architecture.
To illustrate some of the deployment issues related to small cells, I will provide in this article a qualitative review of small cell performance and explore their impact on the operator's small cells deployment strategy. The focus is on co-channel deployments which aside from being common in this early stage of HetNet evolution, they provide for a complex radio frequency environment.
Throughput Performance: The overall throughput experienced by users on both downlink (base station to the mobile subscriber) and uplink (mobile to base station) paths will generally increase as small cells are deployed. This applies to both users camped on the macro cell and those on the small cells, but for different reasons:
- The users on the macro cell will benefit as more small cells are added because fewer users will share the common capacity resources. Therefore, the more small cells are added, the better likelihood a user on the macro cell will experience higher throughput; meanwhile,
- Users on the small cell will experience better throughput than those on macro cell because of higher probability of line-of-sight connection to the serving base station.
If the mobile subscribers are uniformly distributed over the coverage area, then the likelihood a user will experience a certain level of throughput is approximately similar as the number of small cells increases. But in reality, the distribution of users is not uniform as they tend to concentrate in certain "traffic hotspots." In this case, a small cell in a traffic hotspot is expected to provide lower throughput than a small cell in a uniform user distribution area. In the meantime, a user on the macrocell will experience a more pronounced increase in throughput because a higher proportion of users are offloaded from the macro cell. As even more small cells are added, interference will increase leading to successively diminishing marginal increase in throughput.
This last note is an important one: small cells are beneficial up to a point. The user experience will be affected by the density of small cells with a diminishing marginal return followed by actual degradation of service as the number of small cells exceeds a certain threshold. When this threshold is reached depends on a number of factors that include the type of technology, morphology, and cell density and distribution. Inter-small cell interference is one factor that limits small cell performance. Another factor is that as we add more small cells, we create more 'cell-edge' regions within the coverage area of macrocells that can also limit performance as I will expand upon below.
The throughput performance will depend on the location of the small cells and their proximity to macrocells. A small cells close to a macrocell is more likely to be affected by interference than one located at the cell-edge resulting in lower throughput performance. Correspondingly, the performance will depend on the size of the macrocell, or rather, the macrocell density. Small cells deployed close to the cell edge of a large macrocell will provide better performance than those deployed in high-density macrocell area where the average radius is relatively small.
Throughput performance will also depend on the output power of the small cell. Simulations show that for a certain macrocell radius, higher power small cells provide better throughput performance than lower power ones given the same small cell base station density.
Nevertheless, the key take away here is this: it pays to find out where the traffic hot spots are as otherwise, the gain achieved from small cells will be small. Small cell deployment would have to be 'surgical' in select areas to achieve the maximum return on investment.
Interference and Coverage Performance: While small cells improve performance in general, there are certain situations where they cause interference or even a coverage hole. One decisive factor is the large power imbalance between the small cell and the macrocell. The power imbalance is larger than simply the rated transmit power because macrocells implement high-gain sectored antennas (13-16 dBi) while small cells typically implement a much lower gain omni-directional antenna (3-6 dBi). The power imbalance results in asymmetric downlink and uplink coverage areas. Because the macrocell has much higher power than the small cell, the downlink coverage area of the small cell would be smaller than the uplink coverage area. This shifts the handover boundary closer to the small cell increasing the possibility of uplink interference to the small cell with which the interfering mobile might have a line-of-sight path. This type of interference is potentially very damaging since it affects all the users in a cell and forces the mobile units served by the small cell to transmit at higher power. The power imbalance also increases the risk of downlink interference although this type of interference is more limited because it affects a single user. The uplink-downlink imbalance is a leading reason why LTE Release 8 small cell gain is limited because cell selection is decided by downlink signal strength and the options for interference mitigation are limited.
Figure 2 Co-channel interference scenarios in small cell deployments.
To address the uplink-downlink coverage imbalance, the coverage area of the small cell base station is extended to allow the small cell to capture more traffic. This is accomplished by adding a bias to the small cell received signal during the cell selection process. But extending the small cell coverage also increases the chances of downlink interference to a mobile subscriber operating at the edge of the small cell.
Aside from co-channel interference, there's also a risk of adjacent channel interference in multicarrier networks where macrocells implement two or more frequency carriers. Consider for example a mobile attached to a macrocell on frequency A while it is very close to a small cell operating on adjacent frequency B. The mobile is susceptible to adjacent channel interference from the small cell which would likely have a line-of-sight path to the mobile in contrast to a non-line-of-sight connection with the macrocell. Another example is that for the uplink: a mobile attached to a macrocell and operating from the edge of a small cell on an adjacent frequency could cause interference to the small cell.
There are other potential interference scenarios in addition to those described here. But the basic fact is that the actual performance and benefit of small cells will vary, and will do so more widely in the absence of interference mitigation/performance enhancing techniques. This is one reason why some requirements for small cell deployments have been hotly debated, without a firm resolution. For example, a basic requirement is that of small cell backhaul capacity: what should it be? Should the backhaul link be designed to handle the peak throughput rate, which is a function technology, or the average throughput rate which is much harder to ascertain and put a value on because it depends on many factors related to the deployment scenario?
Based on the above description, we know that throughput of small cells will depend largely on the load. The more clustered the subscribers, the lower the overall small cell throughput. On the other hand, if there's a light load (few users), then the capacity will be high. If you are an operator, you sure would need to think carefully about the required backhaul capacity! And while we're on the backhaul topic, let's not forget that we also need to make sure that backhaul on the macrocell is dimensioned properly to support higher traffic load which will certainly come as more small cells are deployed.
In this post, I went through some aspects of small cell performance. These problems are well recognized and certain techniques are being developed and integrated into the standards to address them. This raises other important questions to the operator's strategic network planning process, such as: what interference management and performance enhancement features should be considered? And, what is the technology roadmap for these features? I will expand more on some of these techniques in a future blog post.
Follow Frank Rayal on Twitter @FrankRayal
Over the past year, Datical has had amazing success with our flagship product, Datical DB. We’ve seen multiple visionary, sector-leading companies select Datical DB to drive their Application Schema changes. Now that the number has grown rapidly over the past year, we can begin to see patterns in why customers choose Datical DB. One of them turns out to be pretty emblematic of our other customers. So, let's examine the reasons why they chose to adopt Datical DB.
Jan. 30, 2015 06:00 PM EST Reads: 799
At 15th Cloud Expo, Shrikant Pattathil, Executive Vice President at Harbinger Systems, demos a video delivery platform that helps you do interactive videos. He discusses how Harbinger is accomplishing it in the cloud world, the problems they faced and the choices they made to get around these problems.
Jan. 30, 2015 05:45 PM EST Reads: 2,654
Want to enable self-service provisioning of application environments in minutes that mirror production? Can you automatically provide rich data with code-level detail back to the developers when issues occur in production? In his session at DevOps Summit, David Tesar, Microsoft Technical Evangelist on Microsoft Azure and DevOps, will discuss how to accomplish this and more utilizing technologies such as Microsoft Azure, Visual Studio online, and Application Insights in this demo-heavy session.
Jan. 30, 2015 05:15 PM EST Reads: 4,045
Log data provides the most granular view into what is happening across your systems, applications, and end users. Logs can show you where the issues are in real-time, and provide a historical trending view over time. Logs give you the whole picture. Logentries, a log management and analytics service built for the cloud, has announced a new integration with Slack, the team communication platform, to enable real-time system and application monitoring. Users of both services can now receive real-...
Jan. 30, 2015 05:00 PM EST Reads: 1,321
Entuity®, a provider of enterprise-class network management solutions, today announced that it solidifies its position as a market leader through global enterprise customer acquisitions and a refined channel strategy. In 2014, Entuity increased new license revenues in EMEA by over 75 percent, and LATAM by over 125 percent as customers embraced Entuity for its highly automated solution and unified architecture. Entuity’s refined channel strategy focuses on even deeper strategic alignment with ke...
Jan. 30, 2015 05:00 PM EST Reads: 1,013
CloudBees, Inc., has announced a $23.5 million financing round, led by longtime CloudBees investor Lightspeed Venture Partners. Existing investors Matrix Partners, Verizon Ventures and Blue Cloud Ventures also participated in the round. The latest funding announcement follows earlier rounds of $4 million, $10.5 million and $10.8 million, bringing the total investment in CloudBees to just under $50 million since the company’s inception in 2010. Previous venture investment rounds were led by Ma...
Jan. 30, 2015 04:45 PM EST Reads: 1,057
We are all here because we are sold on the transformative promise of The Cloud. But what good is all of this ephemeral, on-demand infrastructure if your usage doesn't actually improve the agility and speed of your business? How must Operations adapt in order to avoid stifling your Cloud initiative? In his session at DevOps Summit, Damon Edwards, co-founder and managing partner of the DTO Solutions, will highlight the successful organizational, process, and tooling patterns of high-performing c...
Jan. 30, 2015 04:15 PM EST Reads: 4,094
“The year of the cloud – we have no idea when it's really happening but we think it's happening now. For those technology providers like Zentera that are helping enterprises move to the cloud - it's been fun to watch," noted Mike Loftus, VP Product Management and Marketing at Zentera Systems, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 04:00 PM EST Reads: 3,713
Technology is enabling a new approach to collecting and using data. This approach, commonly referred to as the "Internet of Things" (IoT), enables businesses to use real-time data from all sorts of things including machines, devices and sensors to make better decisions, improve customer service, and lower the risk in the creation of new revenue opportunities. In his General Session at Internet of @ThingsExpo, Dave Wagstaff, Vice President and Chief Architect at BSQUARE Corporation, discuss the ...
Jan. 30, 2015 03:45 PM EST Reads: 4,333
"ElasticBox is an enterprise company that makes it very easy for developers and IT ops to collaborate to develop, build and deploy applications on any cloud - private, public or hybrid," stated Monish Sharma, VP of Customer Success at ElasticBox, in this SYS-CON.tv interview at DevOps Summit, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 03:30 PM EST Reads: 4,202
Agility is top of mind for Cloud/Service providers and Enterprises alike. Policy Driven Data Center provides a policy model for application deployment by decoupling application needs from the underlying infrastructure primitives. In his session at 15th Cloud Expo, David Klebanov, a Technical Solutions Architect with Cisco Systems, discussed how it differentiates from the software-defined top-down control by offering a declarative approach to allow faster and simpler application deployment. Davi...
Jan. 30, 2015 03:30 PM EST Reads: 5,176
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.
Jan. 30, 2015 03:15 PM EST Reads: 5,101
Cloud Technology Partners on Wednesday announced it has been recognized by the Modern Infrastructure Impact Awards as one of the Best Amazon Web Services (AWS) Consulting Partners. Selected by the editors of TechTarget's SearchDataCenter.com, and by votes from customers and strategic channel partners, the companies acknowledged by the Modern Infrastructure Impact Awards represent the top providers of cloud consulting services for AWS including application migration, application development, inf...
Jan. 30, 2015 03:00 PM EST Reads: 2,544
“Will Jaya is a direct source for server integration and storage solutions. If you are looking for any specific configurations for a project we can help you configure based on your needs and requirements," explained Netty Goya, CEO of Will Jaya, in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 03:00 PM EST Reads: 2,575
“We help people build clusters, in the classical sense of the cluster. We help people put a full stack on top of every single one of those machines. We do the full bare metal install," explained Greg Bruno, Vice President of Engineering and co-founder of StackIQ, in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 02:45 PM EST Reads: 4,180
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 02:30 PM EST Reads: 4,510
In this demo at 15th Cloud Expo, John Meza, Product Engineer at Esri, showed how Esri products hook into Hadoop cluster to allow you to do spatial analysis on the spatial data within your cluster, and he demonstrated rendering from a data center with ArcGIS Pro, a new product that has a brand new rendering engine.
Jan. 30, 2015 02:30 PM EST Reads: 2,895
"Blue Box has been around for 10-11 years, and last year we launched Blue Box Cloud. We like the term 'Private Cloud as a Service' because we think that embodies what we are launching as a product - it's a managed hosted private cloud," explained Giles Frith, Vice President of Customer Operations at Blue Box, in this SYS-CON.tv interview at DevOps Summit, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jan. 30, 2015 02:30 PM EST Reads: 4,193
Performance is the intersection of power, agility, control, and choice. If you value performance, and more specifically consistent performance, you need to look beyond simple virtualized compute. Many factors need to be considered to create a truly performant environment. In his General Session at 15th Cloud Expo, Harold Hannon, Sr. Software Architect at SoftLayer, discussed how to take advantage of a multitude of compute options and platform features to make cloud the cornerstone of your onlin...
Jan. 30, 2015 02:15 PM EST Reads: 5,257
The Software Defined Data Center (SDDC), which enables organizations to seamlessly run in a hybrid cloud model (public + private cloud), is here to stay. IDC estimates that the software-defined networking market will be valued at $3.7 billion by 2016. Security is a key component and benefit of the SDDC, and offers an opportunity to build security 'from the ground up' and weave it into the environment from day one. In his session at 16th Cloud Expo, Reuven Harrison, CTO and Co-Founder of Tufin,...
Jan. 30, 2015 02:15 PM EST Reads: 2,645