Mobile Tv Technologies Information Technology Essay

As the 7th mass media channel, this most common channel of mobile phone gives a potential market on its application of Mobile TV services. The technologies involve could be broadcast with terrestrial transmission; and unicast or multicast with 3G cellular network. The ultimate goals of such technologies are low power consumption, adequate quality of content and stability in reception to combat the constraints introduced by viewing media over handheld devices. In order to effectively implement the service, the underlying technology needs to be analysed.

At present, DVB-H digital terrestrial broadcasting is the most promising standard by having services launched or in trial in various parts of the world. As an extension to DVB-T, the enhancements of time slicing and MPE-FEC in link layer; and 4k mode and in-depth interleavers and DVB-H signaling in physical layer make it feasible to deliver mobile TV services. This is achieved by ability of power saving, smoother handover, virtual interleaving and faster service discovery.

MPEG-4 video and audio coding which has highest compression efficiency is adopted in DVB-H. In video coding, H.264/AVC gives better quality and flexibility in encoding. It improves on MPEG-2 by introducing techniques such as variable block size, multiple reference pictures and ¼-pixel in motion estimation, and entropy coding; but increases the complexity of the encoder. Whereas for audio coding of HE AAC V2, by exploiting the psychoacoustic characteristics in SBR and removing redundancy of stereo signal in PS, excellent quality at lower than 48kbps could be accomplished.

In order to achieve a sustainable mobile TV industry, stakeholders such as content and service providers need to study the users’ requirements, and then identify the viable solution that will meet the requirements. At present, on-demand video is most favorable instead of subscription basis broadcast TV. On top of high capital investment and lack of compatible devices, DVB-H can’t provide interactivity and thus it would not be the promising technology in the future. With the emerging multicast technology of E-MBMS over cellular network, interactivity requirement could be fulfilled but it yields issue on limited capacity.

All in all, the optimum mobile TV network could be a convergence of broadcast and multicast or unicast transmission to serve infocasting or live events and to provide unlimited number of channels selection over limited bandwidth respectively. Besides continuous improvements and efforts on current technologies, awareness on the evolving world of TV such as Web Based TV and IPTV are needed to provide a rich multimedia transmission over handheld devices with the consideration on users’ demand and requirements.

INTRODUCTION TO MOBILE TV

In the 21st century, mobile phone is emerging and acting as the 7th mass media channel which has impact the way people communicating. This channel is ubiquitous as we only need to equip ourselves with the handheld terminal and also usage payment at an affordable price. According to Tomi T Ahonen, unlike legacy mass media channels, mobile phone is the truly personal media and possesses benefits such as continuous availability and always within arm’s reach for most users [1][2].

This predominant media channel urge for creative and innovative applications base on mobility requirement from users and yields Mobile TV which revolutionizes the legacy mass media channel, TV. High demand on such application makes mobile TV a high potential market. With Mobile TV, transmission of mass media such as TV programs, live sporting events or infocasting can be done on various handheld terminals with enabled capability. Therefore, viewing the mass media could be anywhere, anytime by the user instead of being restricted to the location of TV [2][3].

In general, the transmission of unicast via 3G cellular networks or over the internet requires one-to-one connections and the content is downloadable. While for the broadcast via terrestrial medium or satellite networks, the content of the media would be in the form of streaming [3]. For optimum utilization, a combination of unicast and broadcast services are required. For instance, unicast is utilized by offering unlimited number of channels in areas with low demand; whereas broadcast is used to boost up the capacity in areas with multiple users interested in the same content [4]. This will be further discussed in the chapter of future of mobile TV.

In this convergence industry of mobile TV with several stakeholders such as content providers, service providers and technology providers, an optimal network with the capability to deliver multimedia services based on the customer requirements is desired. This can maximize the profits for all the players in the industry. Therefore, analysis need to be carried out to combat the challenges faced in delivering mobile TV services [3].

2 MOBILE TV TECHNOLOGIES

In technical perspective, unlike normal TV, transmission of mobile TV requires low power consumption, different video format and stability in reception. Such challenges are due constraints introduced by handheld devices. Hence, various technologies have been defined and developed to ensure the delivery of mobile TV [5]. As a consumer, different technologies may seem transparent and even creating a competitive market which yields in advantage of lower cost of usage. Indeed, an exclusive technology might leads to monopoly in the market and service providers will face higher cost of operating.

In this project, the mobile TV technologies on broadcast using terrestrial transmission will be discussed. Such technologies used today are of four main types: DVB-H (Digital Video Broadcast Handheld) which has been deployed mainly in Europe, MediaFLO (Media Forward Link Only) which has been adopted mainly in US, T-DBM (Terrestrial-Digital Multimedia Broadcasting) deployed by certain countries in Asia and Europe, and the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) which is deployed solely in Japan [5][6]. For academic purposes, this report will focus on the open standard of DVB-H [7].

2.1 DVB-H

DVB-H is developed by DVB-H Project for using digital terrestrial broadcasting network and effectively deliver multimedia services to handheld devices [8]. In November 2004, it was formally adopted as an ETSI (European Telecommunications Standards Institute) standard in ETSI EN 302 304 V1.1.1 [9]. DVB-H is an extension of DVB-T and hence compatible with the frequency spectrum of DVB-T networks. With this, DVB frequency bands can be shared for both technologies without any degradation of performance [2]. Since DVB-H follows IP datacast model and having a complete end-to-end IP network, such open standard with full compatibility with DVB-T makes the technology to be dominant in European countries [5].

The key features of DVB-H include the ability to power off during the reception chain. This helps in increasing the battery usage duration. In terms of nomadic, it allows the end user to experience continuity in reception when they travel at various speeds from one transmission cell to another. While for the receiving capabilities, DVB-H is able to alleviate the impact of man-made noise. Also, it could be used in various transmission bands and channel bandwidths in delivering multimedia service to handheld devices around the world [8]. With the above mentioned features, it shows that such technology is capable to combat the challenges discussed and effectively deliver multimedia services to handheld devices.

2.1.1 Overview of DVB-H Interface

Figure (1): DVB-H System for Transmission of IP Services [9]

From the above figure, the system is multiplexing the legacy TV media channel of MPEG-2 services with the IP based DVB-H services. As mentioned earlier, DVB-H is an extension of DVB-T and by focusing on the link layer and physical layer, there are four major enhancements added on top of DVB-T and will be discussed in the following sections.

2.1.1.1 Time Slicing

By implementing time slicing in the link layer, the average power consumption of the receiver or handheld devices could be reduced and able to achieve 90% of power saving. Also, it gives smooth handover where discontinuity of service when the user travel from one transmission cell to another will not be experienced. Besides that, it is possible for the receiver to monitor neighboring cells during the off-times [2][8].

This is achieved by having the receiver only active for a period of time. In other words, the receiver is turned on to take a burst of data at higher instantaneous bit rate, and then off until the next burst of data arrives. By utilizing the off-times for switching of the reception from one transport stream to another, a quasi-optimum handover decision as well as seamless service handover could be accomplished [8].

2.1.1.2 MPE-FEC

MPE-FEC (Multiprotocol Encapsulated-Forward Error Correction) in link layer is optional and it provides additional level of error correction at the MPE layer. Also, time slicing buffer is used to provide virtual interleaving. After adding the Reed-Solomon coding in IP datagram, error-free datagrams can still be obtained after decoding; even in poor reception condition. Such overhead requires a flexible amount of the transmission capacity. However, it could be easily compensated by having a weaker transmission code rate. With the MPE-FEC, C/N (Carrier-to-Noise), Doppler performance as well as tolerance to impulse interference would be improved [2][9].

2.1.1.3 4K Mode and In-depth Interleavers

With 4K mode of modulation in physical layer, network planning flexibility can be improved by trading off mobile reception performance and SFN (Single Frequency Network). As compared to 2K and 8K mode in DVB-T, it has the improvement on the mobile reception over 8K mode. Whereas for 2K mode, it doubled the maximum SFN size [2][8].

Also, in-depth interleavers of 2K and 4K modes give flexibility of symbols interleaving. This again improves the system by bringing immunity to impulse noise [8].

2.1.1.4 DVB-H Signalling

In the physical layer, signalling using two TPS-bits (Transmitter Parameter Signalling) gives easy access to the receivers and hence speeds up the service discovery. Also, the cell identifier is carried on TPS-bits and it allows quicker signal scan and frequency handover on receivers [8].

2.2 Source Coding of DVB-H

As we are dealing with sources of digital associated sound and video, the issue of available bandwidth and suitable bit rate need to be considered. Furthermore, source coding allows the content providers to decide on various data rates which corresponding to various quality of the source. In source coding, the ultimate goal is to deliver the quality of analogue transmission at a much reduced bandwidth. Various standards have been established and developed for both video and audio coding by ISO/IEC MPEG (Moving Pictures Experts Group) and ITU-T VCEG (Video Coding Experts Group). Standardization on the coding methods is essential as it increases the interoperability between encoders, decoders and storage media [10][11]. The following sections will discuss on the source coding in DVB-H. Since the standards from MPEG-4’s family have been widely used in today’s media products and services and are known of having highest quality and compression efficiency, therefore MPEG-4’s source coding will be discussed [12].

2.2.1 Advanced Video Coding: H.264/AVC

As specified in ETSI TS 102 005 V1.3.1, H.264/AVC developed by both ITU-T and ISO/IEC could be used in DVB-H. Based on the concepts of MPEG-2 and MPEG-4 Visual standards, it defines the format for the video compression and also the method of decoding. The improvements include better quality of compressed video and greater flexibility in encoding, transmitting and storing the video [11].

Figure (2): Encoding and Decoding in H.264/AVC [11]

The encoder as shown in above shall perform the operations of prediction, transform and quantization, in-loop filtering and entropy coding to produce the compressed bit streams. In H.264/AVC, it allows both intra and inter-prediction (motion estimation) for the pictures. As compared to the previous standards, the H.264/AVC allows variable block size, multiple reference pictures and ¼-pixel in motion estimation [14]. Hence, there exist the intra and inter motion compensation which are the subtraction of prediction from the current macroblock, and yields motion vectors in the latter technique [11]. DCT (Discrete Cosine Transform) gives different domain such as frequency domain of data representation; and the lossy and irreversible quantization which exploits the characteristic of human eye-brain system can then be applied [14]. Entropy coding involves converting the information such as transform coefficients and motion vectors to bit streams using VLC (Variable Length Coding) or Arithmetic Coding. By having the above enhancements on the encoding techniques, H.264/AVC requires much higher complexity in the encoder as compared to the previous standard of MPEG-2 [11][14].

2.2.2 Advanced Audio Coding: MPEG-4 HE AAC V2

Again, as specified in ETSI TS 102 005 V1.3.1, HE AAC V2 could be used in DVB-H. This high performance audio codec maintains its compatibility with previous standards while achieving excellent quality at lower bitrates of less than 48kbps. In other words, HE AAC v2 is able to perform almost 50% more efficient than HE AAC [12][15].

Figure (3): MPEG-4 HE AAC V2 Audio Coding [16]

From the above figure, it shows that HE AAV V2 is a combination of three technologies: AAC, SBR (Spectral Band Replication) and PS (Parametric Stereo). AAC is the core for MPEG audio coding and it gives transparent quality at the bitrate of 128kbps. Therefore, further enhancements such as SBR and PS are needed to reduce the bitrate. In AAC, frequency masking which exploits the psychoacoustic model ensures that only audible data are encoded [17].

Figure (4): SBR: High Frequency Signal Reconstructed Base on Low Frequency Signal [17]

Whereas for SBR, having consider just the low frequency signal, the required bits to encode are reduced and lower sampling frequency can be used. From the above figure, the spectral envelope of the input source is used and the high frequency signals can be reconstructed and hence allowing the full bandwidth of the signal to be encoded at a lower bitrate [17][18].

Figure (5): Basic Principle of Parametric Stereo [17]

In PS as shown above, instead of encoding left and right input signals, it exploits the redundancy in stereo signals and encodes to a mono signal together with the stereo parameters and hence reducing the required bits. Such parameters are in the form of interchannel intensity difference, cross-correlation and phase difference [17][18].

3 THE FUTURE OF MOBILE TV

From the previous chapter on overview of DVB-H, it is much convinced that such technology is capable to effectively deliver mobile TV services. Also, trials and launched services for DVB-H take place in various parts of the world including Europe, Asia and even US [9]. However, in commercial perspectives, DVB-H as the sole technology to support mobile TV services may not be viable in the future. With DVB-H, the issues aroused are huge capital investment on the transmitter network and content licensing of operators [19][20]. Besides that, lack of compatible receivers or handheld devices also serves as the obstacles [21].

Another main consideration would be the users’ requirements on mobile TV services. Nowadays, end users are keen towards content which matches their interests; or in other words, on-demand. They require interactivity for options or selections to be made instead of having the traditional broadcasting of TV programs onto handheld devices [22]. Furthermore, the subscription basis is not favorable by end users and they rather opt for free-to-air mobile TV [20].

Unlike DVB-H broadcast technology, unicast or multicast using cellular networks such as UMTS provides interactivity and streaming form of mobile TV services. The examples are MBMS (Multicast Broadcast Multimedia Services) by 3GPP (3rd Generation Partnership Project) and BCMCS (Broadcast and Multicast Service) by 3GPP2 [23][24]. Also, it possesses the advantages of compatibility of handheld devices, high scalability and simple implementation as it reuses the existing 3G spectrum. However, inadequate transmission capacity where increasing bitrates results in decreasing cell capacities is the main drawback in this technology [23]. Having said that, E-MBMS is being developed and the specifications are still in the early stage. This standard is expected to be the competitor for DVB-H. It allows single and multi-cell transmissions. For the later transmission, the MBSFN (MBMS SFN) area represents the multiple cells which are covered synchronously such that the signals are perceived as one signal by the handheld devices [25][26].

With this, having observed that the trend of end user demand on interactivity can’t be realized by DVB-H, convergence and continuous improvement need to be done in order to have a sustainable market for mobile TV. Hence, the convergence of broadcast, multicast or unicast transmissions is the optimum solution to combat the challenges of delivering multimedia to handheld devices and yield low power consumption, adequate quality and stability in reception of mobile TV services [23].

4 CONCLUSION

In summary, DVB-H digital terrestrial broadcasting is capable in effectively deliver mobile TV services, and meeting the requirements of low power consumption, good quality in tiny screen and stable reception with mobility. This extended standard from DVB-T was defined in ETSI TS 102 005 V1.3.1 on both link and physical layer specifications.

The major enhancements of DVB-H over DVB-T are time slicing and MPE-FEC on link layer; and 4k mode and in-depth interleavers and signalling in physical layer. Time slicing gives power saving and smoother handover while optional MPE-FEC gives virtual interleaving with the additional error correction. Whereas in physical layer, such enhancements yield flexibility in symbols interleaving and speed up the service discovery respectively.

MPEG-4’s family of source coding ensures that sources are compressed and represented in an adequate quality after decoding. H.264/AVC is an extension to MPEG-2 and its major improvements include variable block size, multiple reference pictures and ¼-pixel in motion estimation, and entropy coding which contribute to greater complexity of the encoder. Whereas for audio coding of HE AAC V2, the three techniques of AAC, SBR and PS reduce the required bits to encode by exploiting the psychoacoustic characteristics and removing redundancy in stereo signal.

In addition to weaknesses of DVB-H in high capital investment and lack of compatible devices, users’ requirements which tend towards on-demand video but not subscription basis broadcast TV lead to infeasibility of DVB-H. The emerging multicast technology of E-MBMS could fulfill the interactivity requirement but leaving the challenge on capacity issue. In a nutshell, the future of mobile TV relies on convergence of broadcast and multicast or unicast transmission as a result of continuous improvement on current leading technologies. Furthermore, the impacts and possibilities on the evolving world of TV which brings Web Based TV and IPTV need to be considered.