Welcome!

AJAX & REA Authors: Sebastian Kruk, RealWire News Distribution, Harald Zeitlhofer

Blog Feed Post

The Hype & Reality of Small Cells Performance

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.

 

B1 - Figure 1 Heterogeneous Network Architecture.png

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:

 

  1. 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,
  2. 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.

 

B1 - Figure 2 Small Cell Interference Scenarios.png

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

Read the original blog entry...

More Stories By Deborah Strickland

The articles presented here are blog posts from members of our Service Provider Mobility community. Deborah Strickland is a Web and Social Media Program Manager at Cisco. Follow us on Twitter @CiscoSPMobility.

Cloud Expo Latest Stories
The 16th International Cloud Expo announces that its Call for Papers is now open. 16th International Cloud Expo, to be held June 9–11, 2015, at the Javits Center in New York City brings together Cloud Computing, APM, APIs, 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 business opportunity. Submit your speaking proposal today!
14th International Cloud Expo, held on June 10–12, 2014 at the Javits Center in New York City, featured three content-packed days with a rich array of sessions about the business and technical value of cloud computing, Internet of Things, Big Data, and DevOps led by exceptional speakers from every sector of the IT ecosystem. The Cloud Expo series is the fastest-growing Enterprise IT event in the past 10 years, devoted to every aspect of delivering massively scalable enterprise IT as a service.
Hardware will never be more valuable than on the day it hits your loading dock. Each day new servers are not deployed to production the business is losing money. While Moore’s Law is typically cited to explain the exponential density growth of chips, a critical consequence of this is rapid depreciation of servers. The hardware for clustered systems (e.g., Hadoop, OpenStack) tends to be significant capital expenses. In his session at 15th Cloud Expo, Mason Katz, CTO and co-founder of StackIQ, to discuss how infrastructure teams should be aware of the capitalization and depreciation model of these expenses to fully understand when and where automation is critical.
Over the last few years the healthcare ecosystem has revolved around innovations in Electronic Health Record (HER) based systems. This evolution has helped us achieve much desired interoperability. Now the focus is shifting to other equally important aspects – scalability and performance. While applying cloud computing environments to the EHR systems, a special consideration needs to be given to the cloud enablement of Veterans Health Information Systems and Technology Architecture (VistA), i.e., the largest single medical system in the United States.
In his session at 15th Cloud Expo, Mark Hinkle, Senior Director, Open Source Solutions at Citrix Systems Inc., will provide overview of the open source software that can be used to deploy and manage a cloud computing environment. He will include information on storage, networking(e.g., OpenDaylight) and compute virtualization (Xen, KVM, LXC) and the orchestration(Apache CloudStack, OpenStack) of the three to build their own cloud services. Speaker Bio: Mark Hinkle is the Senior Director, Open Source Solutions, at Citrix Systems Inc. He joined Citrix as a result of their July 2011 acquisition of Cloud.com where he was their Vice President of Community. He is currently responsible for Citrix open source efforts around the open source cloud computing platform, Apache CloudStack and the Xen Hypervisor. Previously he was the VP of Community at Zenoss Inc., a producer of the open source application, server, and network management software, where he grew the Zenoss Core project to over 10...
Most of today’s hardware manufacturers are building servers with at least one SATA Port, but not every systems engineer utilizes them. This is considered a loss in the game of maximizing potential storage space in a fixed unit. The SATADOM Series was created by Innodisk as a high-performance, small form factor boot drive with low power consumption to be plugged into the unused SATA port on your server board as an alternative to hard drive or USB boot-up. Built for 1U systems, this powerful device is smaller than a one dollar coin, and frees up otherwise dead space on your motherboard. To meet the requirements of tomorrow’s cloud hardware, Innodisk invested internal R&D resources to develop our SATA III series of products. The SATA III SATADOM boasts 500/180MBs R/W Speeds respectively, or double R/W Speed of SATA II products.
As more applications and services move "to the cloud" (public or on-premise) cloud environments are increasingly adopting and building out traditional enterprise features. This in turn is enabling and encouraging cloud adoption from enterprise users. In many ways the definition is blurring as features like continuous operation, geo-distribution or on-demand capacity become the norm. NuoDB is involved in both building enterprise software and using enterprise cloud capabilities. In his session at 15th Cloud Expo, Seth Proctor, CTO at NuoDB, Inc., will discuss the experiences from building, deploying and using enterprise services and suggest some ways to approach moving enterprise applications into a cloud model.
Until recently, many organizations required specialized departments to perform mapping and geospatial analysis, and they used Esri on-premise solutions for that work. In his session at 15th Cloud Expo, Dave Peters, author of the Esri Press book Building a GIS, System Architecture Design Strategies for Managers, will discuss how Esri has successfully included the cloud as a fully integrated SaaS expansion of the ArcGIS mapping platform. Organizations that have incorporated Esri cloud-based applications and content within their business models are reaping huge benefits by directly leveraging cloud-based mapping and analysis capabilities within their existing enterprise investments. The ArcGIS mapping platform includes cloud-based content management and information resources to more widely, efficiently, and affordably deliver real-time actionable information and analysis capabilities to your organization.
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity. In his session at Internet of @ThingsExpo, Mac Devine, Distinguished Engineer at IBM, will discuss bringing these three elements together via Systems of Discover.
Cloud and Big Data present unique dilemmas: embracing the benefits of these new technologies while maintaining the security of your organization’s assets. When an outside party owns, controls and manages your infrastructure and computational resources, how can you be assured that sensitive data remains private and secure? How do you best protect data in mixed use cloud and big data infrastructure sets? Can you still satisfy the full range of reporting, compliance and regulatory requirements? In his session at 15th Cloud Expo, Derek Tumulak, Vice President of Product Management at Vormetric, will discuss how to address data security in cloud and Big Data environments so that your organization isn’t next week’s data breach headline.
The cloud is everywhere and growing, and with it SaaS has become an accepted means for software delivery. SaaS is more than just a technology, it is a thriving business model estimated to be worth around $53 billion dollars by 2015, according to IDC. The question is – how do you build and scale a profitable SaaS business model? In his session at 15th Cloud Expo, Jason Cumberland, Vice President, SaaS Solutions at Dimension Data, will give the audience an understanding of common mistakes businesses make when transitioning to SaaS; how to avoid them; and how to build a profitable and scalable SaaS business.
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridstore delivers vmOptimized™ Storage that self-optimizes to each application or VM across both virtual and physical environments. Leveraging a grid architecture, Gridstore delivers the first end-to-end storage QoS to ensure the most important App or VM performance is never compromised. The storage grid, that uses Gridstore’s performance optimized nodes or capacity optimized nodes, starts with as few a...
SYS-CON Events announced today that Solgenia, the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, 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 social, mobile and cloud user experiences, our solutions help large and medium-sized organizations dramatically improve productivity, reduce collaboration costs, and increase the overall enterprise value by bringing collaboration and infrastructure solutions to the cloud.
Cloud computing started a technology revolution; now DevOps is driving that revolution forward. By enabling new approaches to service delivery, cloud and DevOps together are delivering even greater speed, agility, and efficiency. No wonder leading innovators are adopting DevOps and cloud together! In his session at DevOps Summit, Andi Mann, Vice President of Strategic Solutions at CA Technologies, will explore the synergies in these two approaches, with practical tips, techniques, research data, war stories, case studies, and recommendations.
Enterprises require the performance, agility and on-demand access of the public cloud, and the management, security and compatibility of the private cloud. The solution? In his session at 15th Cloud Expo, Simone Brunozzi, VP and Chief Technologist(global role) for VMware, will explore how to unlock the power of the hybrid cloud and the steps to get there. He'll discuss the challenges that conventional approaches to both public and private cloud computing, and outline the tough decisions that must be made to accelerate the journey to the hybrid cloud. As part of the transition, an Infrastructure-as-a-Service model will enable enterprise IT to build services beyond their data center while owning what gets moved, when to move it, and for how long. IT can then move forward on what matters most to the organization that it supports – availability, agility and efficiency.