See the Picture: How the Set-top Box Tuner Impacts Cable Video Quality
Microtune White Paper: See the Big Picture Page 1 of 6 See the Picture – How the Set-top Box Tuner Impacts Cable Video Quality By Jaime Chunda, Microtune®, Inc. Microtune White Paper: See the Big Picture Page 2 of 6 SEE THE PICTURE – HOW THE STB TUNER IMPACTS CABLE VIDEO QUALITY by Jaime Chunda, Microtune®, Inc. Competing for market share against telecommunications and satellite service providers like never before, cable operators look to improve video reliability in order to satisfy consumer demands and retain cable subscribers. SUMMARY The transition to digital TV and high-definition TV has made consumers much more aware of the quality of their video and any interruptions to its delivery. The current economic downturn has the potential to drive demand higher for in-home entertainment, including increased use of video-on-demand (VOD) services. With consumers spending more time looking at their TV screen, this could be good news for cable multiple service operators (MSOs)—as long as they can deliver the quality of service that consumers expect. The competition for delivering in-home entertainment continues to be fierce, with cable MSOs battling it out with satellite providers as well as telecommunications service providers (telcos). New and growing competition from free online video sites, like YouTube® and Hulu, downloadable TV episodes on broadcast network sites, as well as downloadable and mail order movies from Netflix and Blockbuster puts even more pressure on cable providers. One differentiator is to ensure a higher level of video reliability via the cable network. Today's MSOs have borrowed language from their new competitors, and are striving for ’five 9s’ reliability, or 99.999% uptimei. In their quest for market share, cable MSOs are making no secret of the need for improved video reliability. Cable executives have expressed that improving video reliability is a top priority, pointing out that 98% uptime could still translate into a customer experiencing technical issues 20% of the timeii. A recent cable operator study showed that service quality problems were responsible for 40% or more of all customer churn, second only to costiii Many who are looking to monitor the digital video quality of a cable network are considering an “end-to-end” measurement and analysis philosophy when transporting digital video signals to the consumer. The MPEG video compression at both front-end of the source distribution and the outbound transmission via satellite or terrestrial fiber along with later rate shaping/grooming are the “touch-points” that are the major causes of video impairments in a cable video distribution system. Current efforts focused on these touch- points will definitely improve video quality for the consumer. Eventually, though, the focus for video quality will progress downstream to what one cable operator CEO referred to as “the most valuable asset I own” and that is “the last mile to the houseiv.” One of the major touch-points in the last mile is the digital cable set-top box, which is the entry point to the network for every consumer. Inside the set-top box, the tuner is the most critical component for quality. The good news for MSOs is that high-quality silicon tuners for the cable set-top box are already available. The most important component in rejecting interference in the cable set-top box is the tuner. The good news is: high- quality silicon tuners are already available. Microtune White Paper: See the Big Picture Page 3 of 6 ENSURING QUALITY OF SERVICE In terms of video reliability, MSOs are armed with industry specifications and proprietary standards that were developed and fine tuned as networks evolved and adapted to changing service scenarios and channel allocation plans. However, the demand to deliver more revenue-generating content through increased channel loading has heightened the stress on the network components to deliver to these specifications. In some cases, additional or improved specifications may be required to satisfy higher expectations for quality of service. Currently, the cable industry specifications to ensure video reception quality are outlined in the Open Cable™ Specifications and Society of Cable Telecommunications Engineers (SCTE) specifications. The ANSI/SCTE40 Digital Cable Network Interface Standard, for example, specifies the network conditions in which a set-top box must operate. All of the components used in the signal chain, such as the tuner, must undergo thorough testing to ensure compliance with these industry specifications. Manufacturers can go to CableLabs® to have their products certified to OpenCable specifications. However, many MSOs also have their own proprietary network-specific tests. As a result, their suppliers must have rigorous in-house testing facilities in order to satisfy each MSO's unique requirements. Ensuring quality requires knowledge of the errors and inaccuracies that can be introduced by real-world issues. Often operating in less than ideal circumstances, the set-top box and its tuner must be able to adjust to changing conditions in order to ensure that they will operate properly. As a result, conformance tests should include those for noise, AM hum, micro-reflections, interferences from strong adjacent channels, and other interferences that can occur under full channel loading (see Figure 1). Figure 1 Using a test set up such as this one will determine ANSI/SCTE40 compliance. Microtune White Paper: See the Big Picture Page 4 of 6 There are a number of tuner performance characteristics that are essential in order to meet the requirements for video reliability. These include dynamic range, selectivity and linearity. Dynamic Range A tuner must be able to pick up very large or very small video signals, the size of which can vary depending on the set-top box's location on the cable plant. There is also a 'tilt' in the transmission of the spectrum, which derives from frequency-dependent losses in the cabling and the methods used to compensate for it. The tuner needs to be able to adjust to eliminate these effects. One way to achieve good dynamic range in a tuner is to integrate filtering and gain control. To ensure good quality reception, then, the cable tuner must be able to detect an extremely strong signal, which could be as high as +21dBmV, as well as receive a weak signal, as low as -24dBmV, attenuate or amplify it, and pass it through the system in the presence of many other competing signals that could be much stronger than the desired signal. Selectivity In addition to having wide dynamic range, the tuner must also discriminate a desired signal from adjacent TV channels or in-band interference that could be caused by the environment. To be successful, the tuner must be able to pull in a channel in a fully loaded spectrum and conform to the ANSI/SCTE40 specification. Sharp filtering to attenuate the adjacent channels that are not desired is the key to achieving good selectivity. This filtering can be performed within the tuner or external to the tuner with a surface acoustic wave (SAW) filter or a combination of both. Distributed automatic gain control to adjust the level of the signal as it passes through stages of filtering is also key to good selectivity and dynamic range as well. Linearity To meet the ANSI/SCTE40 specification, the tuner must avoid generating distortion. This requires high linearity in the tuner signal path. Linearity is characterized by the following performance parameters: composite second order (CSO), composite triple beat (CTB), and cross modulation (XMOD). These parameter requirements are -60/-63/-57dBc according to the OpenCable Host Device 2.1 specification. Therefore, it is important for the set-top box to have a very linear tuner in order to ensure good dynamic range and a distortion-free picture. In a traditional single-tuner set-top box, routing the signal is fairly straightforward. However, today it is more typical for multiple tuners to be deployed in a single set-top box, so it is important to carefully split the signal. The major parameter of concern here is noise figure, which is a measure of how much noise is added to the signal during its path through the set-top box (see Figure 2). Microtune White Paper: See the Big Picture Page 5 of 6 Figure 2 Typical set-top boxes include multiple tuners, so it is critical to carefully split the signal and minimize noise but preserve linearity to ensure video reliability. For instance, if a signal is passively split between two tuners, the noise figure (NF) will be immediately degraded by 3.5dB to 4 dB, which is a significant amount. The way to address this issue is to use a low noise but also highly linear amplifier at the front end before splitting the signal. In this type of design, the splitter loss will be compensated by the amplifier. The amplifier must have the adequate combination of low NF and high linearity as to not degrade the performance of the cascading tuners. Achieving Video Reliability To achieve ‘five 9s’ reliability in cable video, the network, set-top box, and its electronic components must meet the stringent test conditions that validate ASTA/SCTE40 compliance. Robust testing scenarios should confirm flawless video reception in the presence of strong adjacent channels that are transmitted simultaneously with a full spectrum of analog AM modulated channels and digital QAM modulated channels. To ensure real-world reliability, testing should also add positive or negative tilt network conditions. In order to address sloped network interference issues, Microtune developed ClearTune™ technology, which includes a switched filter that works to attenuate out-of-band carriers (see Figure 3). Using ClearTune technology, the tuner receives the desired signal by attenuating stronger signals in the spectrum tilt, which limits the energy entering the mixer. Large analog channels transmitting directly adjacent to a QAM channel are suppressed by external SAW filters. ClearTune technology works with these filters to ensure reliable reception even with perturbations in the cable network. This approach can significantly reduce impairments to audio and video signals, which has a direct impact on perceived quality. Copyright © 2009 Microtune, Inc. All rights reserved. Microtune is a registered trademark and MicroTuner and ClearTune are trademarks of Microtune, Inc. All other company and/or product names may be trade names, trademarks and/or registered trademarks of the respective owners with which they are associated. Microtune White Paper: See the Big Picture Page 6 of 6 Figure 3 To reliably receive digital QAM signals, undesired signals need to be attenuated to ensure video quality. Featuring ClearTune technology, the MicroTuner™ MT2131 was engineered specifically to solve the interference issues commonly identified by consumers as sources of digital TV dissatisfaction: TV picture break-up, freezing, and loss. Designed using Microtune's patented silicon tuner architecture, the MT2131 exceeds the performance requirements specified by the SCTE 40 Digital Cable Network Interface Standard. It is technically challenging to achieve superior sensitivity, selectivity, and linearity along with low noise in RF, analog, and mixed signal ICs. Despite this, the MT2131's linearity performance combined with ClearTune enables it to provide industry-leading cable reception especially in those networks with tilted transmissions. Like all of the Microtune MicroTuner devices, the MT2131 is highly integrated, including RF power detectors, closed-loop automatic gain control (AGC), LNA, and an intermediate frequency variable gain amplifier for direct connection to digital demodulators. With a small number of required components in the silicon tuner bill of materials (BOM), the MT2131 offers reliable and industry tested performance at a low cost. Looking Ahead Video reliability may be the most critical concern for MSOs who are looking to maintain or increase market share in the highly competitive home-entertainment market. The needs of most proprietary networks already exceed industry specifications, so it is wise to select an architecture that can deliver on more demanding specifications. In the end, successful 'five 9s reliability' will require a tuner with field-proven capability that can reduce time to market, improve performance, and ensure video reliability. Other Microtune White Papers To read other Microtune White Papers on the cable industry, please visit www.microtune.com.  Flexible, Scalable and Future-Ready DOCSIS®/EuroDOCSIS™3.0 Gateways;  Enabling Tuner Technology for All-Digital Cable Networks;  Bandwidth: Key Weapon in Cable-Telco Battle for Subscribers; and  Quickly Enable DOCSIS 3.0 Functionality and Counter Telco Market Incursion. i Burke, Steve. COO, Comcast. “CEO Panel.” Interview. Cable-Tec Expo. Pennsylvania Convention Center, Philadelphia, PA. 25 June 2008. ii Burke, Steve. COO, Comcast. “CEO Panel.” Interview. Cable-Tec Expo. Pennsylvania Convention Center, Philadelphia, PA. 25 June 2008. iii March 31, 2008, “Cable Operator Video Quality Study,” Multimedia Research Group, Inc. (MRG, Inc.) iv Esser, Patrick. CEO, Cox Communications. “Agenda for the New Media Era.” Interview. The Cable Show. Washington Convention Center, Washington, DC. 1 April 2009. MT2131 Tuner