|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 Events announced today that On the Avenue Marketing Group, a sales and marketing firm that utilizes events to market and sell products to consumers, 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. On the Avenue Marketing Group (OTA) is a sales and marketing firm that utilizes events to market and sell products to consumers. On behalf of our clients, we attend thousands of fairs, festivals, exp...
Apr. 26, 2015 07:30 PM EDT Reads: 3,507
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch ...
Apr. 26, 2015 07:00 PM EDT Reads: 2,892
While DevOps most critically and famously fosters collaboration, communication, and integration through cultural change, culture is more of an output than an input. In order to actively drive cultural evolution, organizations must make substantial organizational and process changes, and adopt new technologies, to encourage a DevOps culture. Moderated by Andi Mann, panelists will discuss how to balance these three pillars of DevOps, where to focus attention (and resources), where organizations m...
Apr. 26, 2015 05:15 PM EDT Reads: 2,051
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Apr. 26, 2015 05:00 PM EDT Reads: 4,492
of cloud, colocation, managed services and disaster recovery solutions, 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. TierPoint, LLC, is a leading national provider of information technology and data center services, including cloud, colocation, disaster recovery and managed IT services, with corporate headquarters in St. Louis, MO. TierPoint was formed through the strategic combination of some of t...
Apr. 26, 2015 04:30 PM EDT Reads: 1,667
SYS-CON Events announced today that Column Technologies, a global technology solutions company, will exhibit at SYS-CON's DevOps Summit 2015 New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Established in 1998, Column Technologies is a leader in application performance and infrastructure management for commercial and federal markets. The company is headquartered in the United States, with a diverse and talented team of more than 350 employees around th...
Apr. 26, 2015 04:00 PM EDT Reads: 1,807
Health care systems across the globe are under enormous strain, as facilities reach capacity and costs continue to rise. M2M and the Internet of Things have the potential to transform the industry through connected health solutions that can make care more efficient while reducing costs. In fact, Vodafone's annual M2M Barometer Report forecasts M2M applications rising to 57 percent in health care and life sciences by 2016. Lively is one of Vodafone's health care partners, whose solutions enable o...
Apr. 26, 2015 03:00 PM EDT Reads: 1,535
SYS-CON Events announced today that Ciqada 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. Ciqada™ makes it easy to connect your products to the Internet. By integrating key components - hardware, servers, dashboards, and mobile apps - into an easy-to-use, configurable system, your products can quickly and securely join the internet of things. With remote monitoring, control, and alert messaging capability, you will mee...
Apr. 26, 2015 03:00 PM EDT Reads: 1,934
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
Apr. 26, 2015 03:00 PM EDT Reads: 2,515
SYS-CON Events announced today that GENBAND, a leading developer of real time communications software solutions, has been named “Silver Sponsor” of SYS-CON's WebRTC Summit, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. The GENBAND team will be on hand to demonstrate their newest product, Kandy. Kandy is a communications Platform-as-a-Service (PaaS) that enables companies to seamlessly integrate more human communications into their Web and mobile applicatio...
Apr. 26, 2015 02:00 PM EDT Reads: 2,752
Public Cloud IaaS started it's life in the developer and startup communities and has grown rapidly to a $20B+ industry, but it still pales in comparison to how much is spent worldwide on IT: $3.6 trillion. In fact, there are 8.6 million data centers worldwide, the reality is many small and medium sized business have server closets and colocation footprints filled with servers and storage gear. While on-premise environment virtualization may have peaked at 75%, the Public Cloud has lagged in ado...
Apr. 26, 2015 02:00 PM EDT Reads: 1,322
Dave will share his insights on how Internet of Things for Enterprises are transforming and making more productive and efficient operations and maintenance (O&M) procedures in the cleantech industry and beyond. Speaker Bio: Dave Landa is chief operating officer of Cybozu Corp (kintone US). Based in the San Francisco Bay Area, Dave has been on the forefront of the Cloud revolution driving strategic business development on the executive teams of multiple leading Software as a Services (SaaS) ap...
Apr. 26, 2015 02:00 PM EDT Reads: 1,579
The best mobile applications are augmented by dedicated servers, the Internet and Cloud services. Mobile developers should focus on one thing: writing the next socially disruptive viral app. Thanks to the cloud, they can focus on the overall solution, not the underlying plumbing. From iOS to Android and Windows, developers can leverage cloud services to create a common cross-platform backend to persist user settings, app data, broadcast notifications, run jobs, etc. This session provide...
Apr. 26, 2015 02:00 PM EDT Reads: 1,429
SYS-CON Events announced today that BroadSoft, the leading global provider of Unified Communications and Collaboration (UCC) services to operators worldwide, has been named “Gold Sponsor” of SYS-CON's WebRTC Summit, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. BroadSoft is the leading provider of software and services that enable mobile, fixed-line and cable service providers to offer Unified Communications over their Internet Protocol networks. The Compa...
Apr. 26, 2015 01:30 PM EDT Reads: 2,562
The 5th International DevOps Summit, co-located with 17th International Cloud Expo – being held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the...
Apr. 26, 2015 01:00 PM EDT Reads: 2,240
DevOps tasked with driving success in the cloud need a solution to efficiently leverage multiple clouds while avoiding cloud lock-in. Flexiant today announces the commercial availability of Flexiant Concerto. With Flexiant Concerto, DevOps have cloud freedom to automate the build, deployment and operations of applications consistently across multiple clouds. Concerto is available through four disruptive pricing models aimed to deliver multi-cloud at a price point everyone can afford.
Apr. 26, 2015 12:30 PM EDT Reads: 1,716
ProfitBricks has launched its new DevOps Central and REST API, along with support for three multi-cloud libraries and a Python SDK. This, combined with its already existing SOAP API and its new RESTful API, moves ProfitBricks into a position to better serve the DevOps community and provide the ability to automate cloud infrastructure in a multi-cloud world. Following this momentum, ProfitBricks has also introduced several libraries that enable developers to use their favorite language to code ...
Apr. 26, 2015 12:00 PM EDT Reads: 1,708
What exactly is a cognitive application? In her session at 16th Cloud Expo, Ashley Hathaway, Product Manager at IBM Watson, will look at the services being offered by the IBM Watson Developer Cloud and what that means for developers and Big Data. She'll explore how IBM Watson and its partnerships will continue to grow and help define what it means to be a cognitive service, as well as take a look at the offerings on Bluemix. She will also check out how Watson and the Alchemy API team up to off...
Apr. 26, 2015 12:00 PM EDT Reads: 1,869
The IoT Bootcamp is coming to Cloud Expo | @ThingsExpo on June 9-10 at the Javits Center in New York. Instructor. Registration is now available at http://iotbootcamp.sys-con.com/ Instructor Janakiram MSV previously taught the famously successful Multi-Cloud Bootcamp at Cloud Expo | @ThingsExpo in November in Santa Clara. Now he is expanding the focus to Janakiram is the founder and CTO of Get Cloud Ready Consulting, a niche Cloud Migration and Cloud Operations firm that recently got acquir...
Apr. 26, 2015 12:00 PM EDT Reads: 1,678
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding bu...
Apr. 26, 2015 12:00 PM EDT Reads: 2,329