Private:mobileTV

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Mobile TV Networks

Mobile TV allows users to watch their favorite TV shows and games on small hand-held devices while traveling. It, therefore, extends the Prime Time viewing of users and provides more business opportunities for content providers. The market for mobile TV is huge: it is expected to grow to up to 20 billion Euros with 500 million customers by 2011[1]. In fact, mobile TV has already been deployed in parts of Europe and Asia and in pilot-testing in several locations in North and South Americas (official DVB-H site). This rapid adoption is fueled by the desire of users for multimedia content and by the technological advances in wireless mobile devices, such as personal digital assistants (PDAs), smart cellular phones, and mobile media players. Many of these devices have evolved to almost full-fledged mobile computers with high resolution displays, fast network links, large memory and storage space, and fast processors. Therefore, multimedia content can be rendered on most of these mobile devices, which further stimulates the user demands for more content and better quality.

We consider various quality-of-service metrics and propose efficient algorithms to maximize them in mobile TV networks. The considered metrics include: energy saving, channel switching delay, and network utilization. For mobile TV users, energy saving and channel switching delay are the two most important metrics. This is because higher energy saving results in longer watch time, and longer channel switching delay degrades view experience as many users quickly flip through numerous TV channels before they decide to watch the specific ones. For mobile TV network operators, network utilization is the most important issue, because wireless spectrum is very expensive: often costs multi-million dollars. We have proposed several algorithms to: (i) maximize energy saving on mobile devices, (ii) guarantee the switching delay from a TV channel to any other channel is short, and (iii) maximize the number of channels concurrently broadcast within a given wireless spectrum. We analytically analyze the proposed algorithms and conduct extensive simulations to evaluate their performance. Most importantly, we have also implemented a real mobile TV testbed in our Lab, which provides us a realistic platform for analyzing the performance of the proposed broadcast schemes. The mobile TV testbed has two parts: a commodity Linux box as the base station and several smart phones as receivers. Our simulation and experimental results indicate that the proposed broadcast schemes are: (i) optimal/near-optimal, (ii) efficient and scalable, and (iii) practical for real mobile TV networks.

People

  • [Farid Molazem (MSc student)]

Publications

Press Coverage

  • July 1, 2009: Our mobile TV research is also featured in the July issue of the ACM Tech News: see article or local PDF
  • June 15, 2009: Omni-TV featured Cheng and our mobile TV project (in Mandarin): local mpeg file


Mobile TV (DVB-H) Testbed

We have implemented a complete end-to-end testbed for DVB-H (Digital Video Broadcast--Handheld) networks. The testbed provides a realistic platform for analyzing various aspects of these networks, including the energy saving achieved by the time slicing mechanism, average channel switching delay, network capacity in terms of number of TV channels that can be broadcast, visual quality of TV channels transmitting different types of video streams, information exchange and interactivity between base station and receivers, among many others. The details of testbeds and pilot networks created by companies are usually not published, and the source code is not available. Thus academic researchers designing algorithms and protocols for mobile TV networks, including ourselves, had to resort to simulation and/or theoretical analysis. To address this problem, we make the details and source code of our testbed available to the research community.

The main components of our mobile TV testbed are shown in the following figure.

Mobile TV Testbed

Base Station. The base station is a Linux box (Intel Quad-Core Xeon E5420 (2.5 GHz) PC running Ubuntu Linux) in which we installed the RF signal modulator: Dektec DTA-110T DVB-T/H Modulator and UHF Upconverter for PCI Bus. This modulator implements the physical layer of the protocol stack and transmits DVB-H standard compliant signals via an indoor antenna. The RF output level of the modulator, however, is quite low (-29 dBm) and can only reach up to 1-meter broadcast range with a 6 dB receiver antenna. Using a low-power amplifier, the RF signal can be boosted to about 0 dBm, which gives us approximately 20-meter range in our lab environment.

IP packets of the video streams are encapsulated in MPEs and FEC-coded using an IP Encapsulator. In the initial setup, we adopt an open-source IP Encapsulator, which implements simple time slicing techniques. We extended that IP encapsulator to support more sophisticated and optimal time slicing schemes. Recently, we have re-designed the base station software to be well-structured with defined interfaces in order to facilitate implementing and comparing different current/future algorithms, including multimedia streaming and time slicing algorithms. This new base station design follows multi-threaded paradigm, and can fully utilize multi-processor systems, which is common nowadays. We continue improving the base station implementation.

Receivers. We use the Nokia N92 and N96 device as receivers. These devices are equipped with the receiver-side of the DVB-H protocol and video player. The operating system on this device (Symbian) provides several APIs, including APIs for measuring energy consumption. While the N92 device helps in assessing the visual quality of videos, it does not provide detailed logging functions of the low-level signals, which are needed to evaluate the performance of different protocols. To address this shortcoming, we added the Divi Catch RF-T/H transport stream analyzer to the testbed. This analyzer can be attached to a PC via a USB port. The analyzer records traffic streams as well as provides a very detailed information on the RF signal, the MPEs, jitter, time slicing, and so on. It also comes with a visualization software that can run on the PC for analysis.

Running Testbed

Running the test bed: For running the testbed, we have two ways: 

    1-Using Graphic user interface
    2-Using Linux commands

In following sections, those two ways have been explained:

Using Graphic user interface

Step 1: open internet browser (Firefox or IE)

Step 2: in the address bar, type

Step 3: select video file for some channels.

Step 4: click on Start Broadcast for broadcasting

 Each green circle, shows the service whose name is written beside the circle is working

 By this way, you can only see signals in Divicatch software, you should be able to watch the video by VLC player as well, but this service doesn’t work now. It means you can’t watch video with neither N96 nor N92.

Using Linux commands

Step1: Login to 142.58.185.186 with user name: nsladmin and password: nsladmin

Step2: load the modulator card driver by: 

/DVB-H$ sudo Dta1xxInit start

[sudo] password for nsladmin:

This can be skipped if the driver has already been loaded after the last reboot. If you want to demo the video stream on Nokia N96 cell phone. Please do the following:

Step3: cd /home/nsladmin/demo/N96

Step4: ./runN96.sh

Now you are able to watch the TV program on N96 cell phone. In the mean time, you can track and trace the DVB-H stream on our DiviCatch USB analyzer with the frequency set to 690MHz

If you want to demo the video stream on Nokia N92 cell phone. Please do the following:

Step3: cd /home/nsladmin/demo/N92

Step4: ./runN92.sh

Now you are able to watch the TV program on N92 cell phone. In the mean time, you can track and trace the DVB-H stream on our DiviCatch USB analyzer with the frequency set to 562MHz

Running analyzer

Step 1: Run DiviCatch 5.0 from the strart menu.

Step 2: in RF-T/H tab, set RF Frequency to proper value, for example if you used the instruction for N96 demo, you should set frequency to 690.000.

Step 3: Press Tune button.

Step 4: Now you are able to see broadcasted data in other tabs.


Software

We have two testbed implementations: (i) FATCAPS base station, and (ii) integrated base station. The former one is based on FATCAPS implementation, while the later one is implemented by us from scratch.

FATCAPS Based Implementation

We initially implemented our testbed on top of FATCAPS, which is an open source time slicer implementation. Several documents are listed in the following.

MTV Implementation

We have implemented the software of DVB-H base stations called mtv. We continue improving the base station implementation, and we list ongoing/future works in this document.


Mobile TV Testbed for ATSC - M/H Standard


Discussion and Ideas

References and Links

  • Q. Gao, M. Chari, A. Chen, F. Ling, and K. Walker, "MediaFLO Technology: FLO Air Interface Overview": This book chapter explains why mediaFLO achieves short channel switching delay. MediaFLO employs 1-sec superframe and each MLC is transmitted as four bursts in every superframe. Therefore, when user switches the channel in superframe x, the receiver will get all the four bursts in superframe x+1, which takes 1 to 2 secs, where 1 is the best case and 2 is the worst case. This article also indicates that the time-frequency assignment need not be rectangle, which allows finer grained resource allocation and thus better statistical multiplexing gain. However, this paper does not address the relationship between energy saving and time-freq allocation. There is only one sentence saying that the receiving circuit should avoid modulating the symbols irrelevant to the current channel to save energy.
  • M. Chari, F. Ling, A. Mantravadi, R. Krishnamoorthi, R. Vijayan, G. Walker, and R. Chandhok, “FLO physical layer: An overview,” IEEE Transactions on Broadcasting, vol. 53, no. 1, pp. 145–160, March 2007.
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