|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
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
Mar. 28, 2015 08:00 PM EDT Reads: 1,736
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborat...
Mar. 28, 2015 07:00 PM EDT Reads: 5,164
WSM International is launching a DevOps services division that offers assessment, consulting and implementation to large enterprises and organizations with complex infrastructures. This is the first independent services company to create a dedicated practice to help organizations looking to transition to the DevOps model. The concept of DevOps is to blend information technology (IT) software development with operations to optimize the computing infrastructure according to the specific needs of ...
Mar. 28, 2015 07:00 PM EDT Reads: 1,478
SYS-CON Events announced today that the DevOps Institute has been named “Association Sponsor” of SYS-CON's DevOps Summit, which will take place on June 9–11, 2015, at the Javits Center in New York City, NY. The DevOps Institute provides enterprise level training and certification. Working with thought leaders from the DevOps community, the IT Service Management field and the IT training market, the DevOps Institute is setting the standard in quality for DevOps education and training.
Mar. 28, 2015 06:30 PM EDT Reads: 963
SYS-CON Events announced today that robomq.io will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. robomq.io is an interoperable and composable platform that connects any device to any application. It helps systems integrators and the solution providers build new and innovative products and service for industries requiring monitoring or intelligence from devices and sensors.
Mar. 28, 2015 06:00 PM EDT Reads: 1,418
Temasys has announced senior management additions to its team. Joining are David Holloway as Vice President of Commercial and Nadine Yap as Vice President of Product. Over the past 12 months Temasys has doubled in size as it adds new customers and expands the development of its Skylink platform. Skylink leads the charge to move WebRTC, traditionally seen as a desktop, browser based technology, to become a ubiquitous web communications technology on web and mobile, as well as Internet of Things...
Mar. 28, 2015 06:00 PM EDT Reads: 1,784
Hosted PaaS providers have given independent developers and startups huge advantages in efficiency and reduced time-to-market over their more process-bound counterparts in enterprises. Software frameworks are now available that allow enterprise IT departments to provide these same advantages for developers in their own organization. In his workshop session at DevOps Summit, Troy Topnik, ActiveState’s Technical Product Manager, will show how on-prem or cloud-hosted Private PaaS can enable organ...
Mar. 28, 2015 05:45 PM EDT Reads: 1,059
Today, IT is not just a cost center. IT is an enabler and driver of business. With the emergence of the hybrid cloud paradigm, IT now has increasingly more capabilities to create new strategic opportunities for a business. Hybrid cloud allows an organization to utilize multi-tenant public clouds, dedicated private clouds, bare metal hosting, and the associated support and services for the right use cases through an on-demand, XaaS model. This model of IT creates tremendous opportunities for busi...
Mar. 28, 2015 05:00 PM EDT Reads: 3,043
Business as usual for IT is evolving into a “Make or Buy” decision on a service-by-service conversation with input from the LOBs. How does your organization move forward with cloud? In his general session at 16th Cloud Expo, Paul Maravei, Regional Sales Manager, Hybrid Cloud and Managed Services at Cisco, discusses how Cisco and its partners offer a market-leading portfolio and ecosystem of cloud infrastructure and application services that allow you to uniquely and securely combine cloud busi...
Mar. 28, 2015 04:15 PM EDT Reads: 1,273
SYS-CON Events announced today that Akana, formerly SOA Software, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Akana’s comprehensive suite of API Management, API Security, Integrated SOA Governance, and Cloud Integration solutions helps businesses accelerate digital transformation by securely extending their reach across multiple channels – mobile, cloud and Internet of Thi...
Mar. 28, 2015 04:15 PM EDT Reads: 1,482
Docker is an excellent platform for organizations interested in running microservices. It offers portability and consistency between development and production environments, quick provisioning times, and a simple way to isolate services. In his session at DevOps Summit at 16th Cloud Expo, Shannon Williams, co-founder of Rancher Labs, will walk through these and other benefits of using Docker to run microservices, and provide an overview of RancherOS, a minimalist distribution of Linux designed...
Mar. 28, 2015 04:15 PM EDT Reads: 2,404
Businesses are looking to empower employees and departments to do more, go faster, and streamline their processes. For all workers – but mobile workers especially – utilizing the cloud to reconnect documents and improve processes without destructing existing workflows can have a dramatic impact on productivity. In his session at 16th Cloud Expo, Mark Grilli, vice president of Acrobat Solutions marketing at Adobe Systems Incorporated, will outline new ways that the cloud is changing the way peo...
Mar. 28, 2015 04:00 PM EDT Reads: 1,259
SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes ...
Mar. 28, 2015 03:30 PM EDT Reads: 2,142
Are your applications getting in the way of your business strategy? It’s time to rethink your IT approach. In his session at 16th Cloud Expo, Madhukar Kumar, Vice President, Product Management at Liaison Technologies, will discuss a new data-centric approach to IT that allows your data, not applications, to inform business strategy. By moving away from an application-centric IT model where data integration and analysis are subservient to the constraints of applications, your organization will b...
Mar. 28, 2015 03:15 PM EDT Reads: 2,509
WSM International has launched a DevOps services division that offers assessment, consulting and implementation to large enterprises and organizations with complex infrastructures. The concept of DevOps is to blend information technology (IT) software development with operations to optimize the computing infrastructure according to the specific needs of the organization. According to a recent press release from Gartner, "By 2016, DevOps will evolve from a niche strategy employed by large cloud ...
Mar. 28, 2015 03:00 PM EDT Reads: 1,193
SYS-CON Events announced today that QTS Realty Trust, one of the nation’s largest and fastest-growing providers of data center facilities and cloud services and a leader in security and compliance, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. QTS Realty Trust, Inc. (NYSE: QTS) is a leading national provider of data center solutions and fully managed services, and a leader in security and compliance...
Mar. 28, 2015 03:00 PM EDT Reads: 1,202
SYS-CON Events announced today that Solgenia will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional S...
Mar. 28, 2015 03:00 PM EDT Reads: 2,743
SYS-CON Events announced today that WSM International (WSM), the world’s leading cloud and server migration services provider, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. WSM is a solutions integrator with a core focus on cloud and server migration, transformation and DevOps services.
Mar. 28, 2015 03:00 PM EDT Reads: 1,200
What’s inside the cloud? Hard work. Cloud operators know the world inside the datacenter is gritty. Vendor marketing speak and cloudwashing quickly melt in the heat of SLAs, uptime guarantees, and users who want it now. In his session at DevOps Summit, Hernan Alvarez, Chief Product Officer at Blue Box Group, will deliver an unvarnished look inside the world of cloud operators, from the perspective of someone who lives it. Attendees get a front-row look into the toolkits and processes that enabl...
Mar. 28, 2015 03:00 PM EDT Reads: 1,518
SYS-CON Events announced today that Liaison Technologies, a leading provider of data management and integration cloud services and solutions, has been named "Silver Sponsor" of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York, NY. Liaison Technologies is a recognized market leader in providing cloud-enabled data integration and data management solutions to break down complex information barriers, enabling enterprises to make sm...
Mar. 28, 2015 03:00 PM EDT Reads: 3,408