Fig 1. MaxLinear’s MxL101SF is a complete CMOS tuner and demodulator for the DVB-T market that covers the 44- to 885-MHz frequency range. The output transport stream (TS) is common digital audio and video compatible with most processors and displays (a). An evaluation board and reference design also are available (b).
Fig 2. AT&T offers the LG Electronics Vu CU920 cell phone to view its network TV offerings.
In the consumer world, TV isn’t just getting bigger with giant wall-mounted HD screens. It’s also getting smaller, as broadcasters and carriers work together to bring programming to portable gadgets like your laptop, tablet, and smart phone, as well as to your car. Wherever you watch it, though, you need a wireless receiver that’s set up to accept video input from an over the air (OTA) broadcast source or via the cellular phone network, which also is OTA.
With video becoming the app of choice for most smart-phone and tablet users, there’s an increasing interest in providing standard TV programming as well as video on demand (VOD) for these devices—and multiple technologies and services now are available to make it happen. Keep in mind that the industry likes to distinguish between OTA video, which is known as mobile TV, and mobile video, which is available over the cellular network and other sources.
OTA Video
OTA video is available right now and has been for decades. TV stations broadcast free TV to local areas 24/7. All you need is a TV set and antenna. The first portable TV was the Sony Watchman, which debuted in Japan in 1982 and then in the U.S. and Europe in 1984. These devices with their tiny black and white screens were very popular. Millions were sold. You can still find lots of them on eBay.
There have been many models since then, such as the Farenheit DTV-MHU. This black box receiver receives TV broadcasts using the latest U.S. Advanced Television Systems Committee (ATSC) mobile standards and plays them through an existing vehicle navigation or video screen.
Several companies offer TV dongles for laptops that plug into the USB port and accept signals from an external antenna. The internal tuner outputs the recovered video and audio through the USB port. Hauppauge WinTV-Aero-m is such a product with its own small antenna and a remote control.
Recall that in 2009, the Advanced Television Standards Committee (ASTC) digital broadcast method replaced analog TV broadcasts. All contemporary TV sets use the ASTC digital standard to receive local broadcasts. While most consumers get their TV via either cable TV or satellite companies, about 20% still rely on standard OTA broadcasts.
The primary ATSC digital television (DTV) standard was not designed with mobile service in mind. While fixed or nomadic operation is possible, high-speed mobile operation is difficult because of the changing multipath problems that plague all VHF, UHF, and microwave signals.
However, the ATSC has developed a new version of its DTV standard. Called A/153 or ATSC-M/H for mobile/handheld, it adds features that minimize the multipath problem and brings robustness to the DTV downlink.
The regular ATSC DTV standard (A/53) is the only DTV standard that does not use orthogonal frequency division multiplexing (OFDM). OFDM has proven itself to be extremely good in transmitting high-speed digital signals over noisy and multipath links. Virtually all new wireless technologies like Long-Term Evlution (LTE), WiMAX, Wi-Fi, and all the other mobile TV standards use OFDM for these reasons and its maximum spectral efficiency (see “Global Mobile TV Standards”).
The ATSC standard uses a single-carrier system with eight-level vestigial sideband modulation (8VSB). It also uses a 188, 208 Reed-Solomon forward error correction (FEC) process along with trellis error coding and interleaving to ensure a low bit error rate. The resulting 8VSB signal is transmitted in the standard 6-MHz wide channels of the U.S. TV system.
The upper sideband is partially suppressed to minimize signal bandwidth, and a pilot carrier is transmitted to aid signal recovery. The overall symbol rate is 10.76 Msymbols/s. With eight levels, 3 bits are transmitted per symbol. This produces a net data rate of 19.39 Mbits/s factoring in the FEC and other coding.
The video encoding/compression is MPEG-2, and the audio coding is a Dolby digital standard. Multiple video formats can be transmitted including standard-definition TV (480 lines) as well as both 720- and 1080-line progressive or interlaced high-definition video signals.
The ATSC-M/H A/153 standard, approved in October of 2009, adds more FEC coding and training sequences to improve receiver performance. It also uses more efficient H.264 (MPEG-4 AVC) video compression and HE AAC v2 audio coding. The video format is 416 pixels by 240 lines in a 16:9 aspect ratio that’s standard for most mobile devices.
The newly formatted video is transmitted along with the standard ATSC signal without using any more bandwidth. It accomplishes this by choosing some of the MPEG-2 transport packets and using the M/H formatted signals as the payload. This allows both standard ATSC and mobile ATSC enabled devices to receive the broadcasts.
TV broadcast stations can add mobile DTV to their capabilities by including an easily connected ATSC A/153 exciter and some software. The cost is estimated to be around $150,000. According to the Open Mobile Video Coalition (OMVC), an organization dedicated to developing mobile TV in the U.S., 96 U.S. TV stations have done that and are transmitting mobile TV now. The problem is that no one is watching yet. Few if any mobile TV products are available. ATSC-M/H receiver ICs are just now becoming available, so end products are on the way.
Mobile TV Chips
Several semiconductor manufacturers make TV tuner chips and demodulators. Most are for fixed TV sets rather than mobile TV. These tuners are just the RF front end, mainly a low-noise amplifier (LNA), mixer, and frequency synthesizer for channel selection in the VHF and UHF TV bands. The demodulators are typically separate chips.
But a few pioneers are making mobile TV standard receiver ICs with both a tuner and demodulator. Most of these ICs are for the more established Japanese ISDB-T and Europe DVB-T markets. Jim Kappes of MaxLinear indicates that the biggest market for mobile TV is Japan. He estimates that as many as 30% of all Japanese cars have mobile TV, as do a high percentage of cell phones.
Mobile TV using DVB-T is popular in high-end cars in Europe as well, although cell phones aren’t typically equipped with mobile TV. Designed for the DVB-T market, MaxLinear’s MxL101SF is a complete CMOS receiver including the tuner and demodulator (Fig. 1). It covers the 44- to 885-MHz frequency range. The input is a single-ended 75-Ω interface that requires no external transformers. Both serial and parallel digital transport streams (TS) are available.
The chip IF output is also available, making it possible to use it in hybrid devices that can receive DVB-C and DVB-T2 signals using external demodulators. The chip is available in a 7- by 7-mm QFN48 package and draws only 415 mW. No external surface acoustic wave (SAW) filters are needed. MaxLinear also has ISDB-T receivers, and an ATSC-M/H chip is in the works.
LG Electronics, one of the earliest suppliers of ASTC-M/H chips, introduced a cell phone with ASTC-M/H capability a few years ago. It was ahead of the market, which is still developing, though it’s still available.
The SMS1530 ATSC-M/H receiver chip from Siano Mobile Silicon Ltd. is designed for cell phones, tablets, laptops, and automotive applications. It comes in a 7- by 7-mm ball-grid array (BGA) package and includes FM radio coverage with radio data system (RDS). The tuner covers the North American 54- to 240-MHz and 470- to 806-MHz bands. The direct-conversion receiver requires no external components.
The chip has serial peripheral interface (SPI), secure digital input/output (SDIO), and I2C-like serial interfaces as well as both serial and parallel output transport streams (TS). Siano’s Host-API software package includes drivers and libraries for popular host processors and operating systems. Also included is integral support for ATSC-M/H conditional access (CA) that covers content descrambling and control of an external CA surface-mount device (SMD).
Mirics offers an interesting solution for ATSC-M/H video. Its FlexiTV comprises the MSi3101 RF tuner front end and a software demodulator. The tuner chip covers all of the world’s mobile TV bands. The output goes to the Mirics MSi2500 interface chip, which produces a USB 2.0 output.
The USB signal then goes to a laptop or other x86-based computer, where a software modem handles the demodulation and other functions. The Mirics demodulation software can handle virtually any TV standard. Its software addresses the ATSC-M/H, CMMB, DVB-T, DVB-T2, ISDB-T, and T-DMB mobile standards.
Analog Devices, Infineon, Maxim Integrated Products, NXP, and Silicon Labs all are making TV tuners as well, minus the demodulator. There’s no doubt that other receiver chips are on the way.
Design Issues for Mobile TV
The delay in seeing mobile TV devices in cell phones, tablets, and other portable media devices is most likely due to the challenges of designing TV into another device. Even when receiver chips become available, there are other issues to be considered in a successful mobile TV product. In fact, designers face several key problems:
- Power consumption: This is critical to any mobile device. Smart phones already incorporate multiple radios not only for the cellular services but also for Wi-Fi, Bluetooth, GPS, near-field communications (NFC), and even FM radio. Adding a TV receiver kicks up the power consumption measurably and decreases battery charge more rapidly. Chip designers are aware of this and make their devices as power efficient as possible but it’s still a challenge, especially considering how users may want to watch TV for extended periods. Mobile TV is more likely a tablet or laptop feature than a cell-phone feature, but some smart phones certainly will be available to serve this market.
- Memory: TV requires more memory for buffering the video. Current memories are already impressively large but even more is needed, further affecting power consumption.
- Processing power: At one time this may have been a problem, but today most smart phones and tablets use the hot new dual-core 1-GHz processors that can for the most part handle the extra load of video. Still, extra processor power is needed.
- Antenna size: Since mobile TV occurs at frequencies well below the cellular bands, longer antennas are needed for the best results. No one wants a whip antenna on their cell phone or rabbit ears on their tablet, but for the best reception, a good antenna is imperative. Where do you put it? Tablets and laptops offer the best solution as they are larger. Smaller antennas are being developed, and they will eventually solve the problem. In early mobile TV devices, small telescoping whip antennas will not be unusual.
The Developing Market
While a recent survey declared that 88% of adults had some interest in watching news, weather, and other information on mobile TV, that interest has not translated into a thriving market, at least in the U.S. The negative experience of Qualcomm’s MediaFLO from its FLO TV subsidiary services has brought serious doubt to any company evaluating the mobile TV market.
MediaFLO was an OTA service deployed with Qualcomm’s own OFDM TV standard and a nationwide network of broadcasting stations using the 716- to 722-MHz UHF channel. The service offered about 20 news, information, and entertainment channels. The receiver was a neat handheld device that could be easily transported and installed in vehicles. The service closed last year because of an insufficient number of subscribers. While it was a pay TV service, U.S. OTA transmissions are free and that may be the difference between success and failure in the mobile TV market.
With nearly 100 U.S. stations broadcasting ATSC-M/H mobile TV signals, the market is ready to emerge. We can look for end products in the near future. While cell-phone receivers won’t be common, tablets will feature mobile TV—something Apple doesn’t have yet. Portable handheld and vehicle receivers as well as dongles for laptops should be appearing near the end of 2012 according to one estimate. A good place to watch for progress in this field is the annual International CES in Las Vegas each January.
While mobile TV is very popular in Japan and South Korea, it was tried in Europe but was basically a failure. Different implementations in the different countries are partially to blame, though other factors were involved. Who can say that it won’t eventually succeed?
There is a significant positive movement in China, which could one day be the biggest market for mobile TV. The market is still developing in the U.S. We have the technology to do it, but something is holding it back or giving it serious competition. One likely reason is the lack of suitable receivers. Another is the onrush of video from the cellular networks and the cable TV companies. That is the other story of mobile TV.
Non-Broadcast Mobile TV
There are several other ways to get video to a cell phone, tablet, laptop, or special receiver over the existing cellular network, via Wi-Fi networks and cable TV offerings.
AT&T’s Live TV service lets you download some of the company’s U-Verse Internet Protocol television (IPTV) offerings on selected Android and BlackBerry phones. It costs $9.99 per month (Fig. 2). Verizon’s V CAST service also lets you download selected TV shows to your cell phone. The service includes regular TV series, sports, and news. It costs $10 per month.
Time Warner Cable streams selected channels from its cable TV offerings via Wi-Fi to your iPad. The service is free, but you need to download the app first. Comcast Cable offers shows on demand on the iPad with a special app. Called Xfinity, the service lets you watch TV via any available Wi-Fi connection.
T-Mobile offers 15 live and on-demand channels of news, sports, and kids programming for a range of smart phones. A prime service offers 65 premium channels for $9.99 or $12.99 for HD. A similar program for the Dell streak and G-Slate tablets with five free channels and eight premium channels of on-demand programming costs $4.99 per month plus classic movies for $5.95 more.
Cable companies like Cox are also offering cellular service. Cox uses the Sprint network, while Comcast and Time Warner use Clearwire 4G WiMAX networks. Some limited mobile TV services are offered.
There are other efforts around the country. No one way has become the standard mainly because each method has its disadvantages. Primarily, the cellular network still does not have the capacity to accommodate TV on a grand scale. Despite the widespread availability of 3G networks and the growing number of LTE and 4G offerings as well as backhaul upgrades, capacity is still limited.
It takes at least 500 kbits/s of bandwidth to stream quality but compressed video and audio to meet a minimum of QVGA resolution (320 pixels per 240 lines) and a frame rate of 30 frames per second (fps). No system can sustain such data rates for many customers. It is still overload for most cellular networks, LTE 4G or not.
Nevertheless, TV over the cellular network is underway on a limited scale. These TV offerings are specific to the carriers and are pay services only, and they will surely continue.
The primary reason for the limited ability of the cellular network to stream TV is that the system is inherently unicast—that is, each subscriber is served individually. Even if multiple subscribers are using the same content, each is connected separately. There is no provision for point-to-multipoint (P2M) broadcast.
While some systems such as Multimedia Broadcast Multicast Service (MBMS), evolved MBMS, and Integrated Mobile Broadcast (IMB) have been developed to serve this purpose, none have been adopted. These systems either aren’t a good fit technically with current systems or business models for using them have not been developed.
TV over Wi-Fi is an interesting prospect. There are massive deployments of Wi-Fi access points that could serve as a way to deliver TV. But even though Wi-Fi networks have the bandwidth to handle video, other factors like inconsistent coverage and quality of service (QoS) provisions make it less desirable.
According to Bart Giordano of Marvell, Wi-Fi is always the final link to a laptop, tablet, or cell phone in most of the non-OTA TV methods. If not that, Wi-Fi is a critical link in TV distribution by way of a home broadband router. TV gets downloaded to a laptop or tablet or cell phone via Wi-Fi for later viewing. A forthcoming wireless display addition to the Wi-Fi standard will let you stream TV on a mobile device directly to your large-screen TV using a version of the popular peer-to-peer direct connect capability now available.
As for cable TV services, some systems already have an auxiliary TV distribution system that plays off the regular cable service. This is usually Wi-Fi delivered in the home and does not extend beyond that.
Over the Top TV
Over the top (OTT) TV refers to any television content that is delivered independently of any more traditional broadcast or cable delivery methods. It is IPTV delivered over the Internet, either streamed or downloaded.
A good example is the service provided by Roku. Its accessory box connects to your Internet line either directly or more likely through your Wi-Fi home network router. Its output is usually HDMI to your TV set, enabling you to select a variety of video sources including Netflix, Hulu, and numerous others.
Some of these services are for pay, while others are open. These services include Apple TV, Amazon TV, YouTube, Vudu, and Zediva. Even Google had Google TV, which was withdrawn recently. These boxes and services are inexpensive and let you watch many movies and older TV programs when you want.
Another example, Slingbox, is a piece of equipment and a service that lets you watch your broadcast TV, cable TV, and DVD output on any device remotely. For example, you can take the input from your cable service and connect it to your Slingbox, which in turn goes to your Internet connection.
With the appropriate software, you can access your cable TV from anywhere there is an Internet connection. For example, you can watch from your laptop, your tablet, or your smart phone from anywhere. The Slingbox units and software are very affordable and a real nice resource when you are on the road.
The Future for Mobile TV
That brings us back to OTA broadcast TV. It’s hard to beat as one high-power station can serve hundreds of thousands of users at no additional cost. It’s the most efficient method for TV distribution.
Pay OTA TV models like MediaFLO did not work as special receivers were required and the program offerings were limited. A free system delivering standard TV broadcast programming could work well, though. The business model is based on traditional TV advertising. Special content also could be delivered for a fee. And that brings up a critical issue involving mobile broadcast TV, the conditional access system (CAS).
Most CASs use scrambling and encryption to ensure only valid users can access the content. Such an approach is based on payment services, and both the transmitting facility and the receivers must have the software and hardware to provide that access. This complicates not only the delivery system but makes it necessary for individual receiving devices like cell phones, tablets, laptops, and other terminals to have the special facilities. This is typically impractical for terminal manufacturers, which would prefer to make a single model rather than provision multiple different versions.
According to a white paper by Itzik Klein for Siano Mobile Silicon, the complex and variable CAS was at the root of Europe’s failed mobile TV effort (DVB-H). Different countries had different delivery systems, spectrum, and access methods, and multiple terminal versions were required. The best approach is a simple, open CAS and a business model to make it a success.
The free open U.S. system is a good example. It has a good chance of success. With nearly 100 stations now broadcasting free TV via ATSC-M/H and more on the way, we may be seeing the beginning of another mobile TV success story like Japan, Brazil, South Korea, and China. Now all we need are the chips and the end products like smart phones, tablets, and other devices with embedded receivers. We should be seeing such end products in the coming year.