IPTV over WiMAX: Key Success Factors, Challenges and Solutions
                                   James She, Fen Hou, Pin-...
architecture. Section III positions the future trends of IPTV.    request to watch the content back from the beginning onc...
the screen. Alternatively, a web browser can obtain the           multiple flows of live contents across the whole transpo...
• Advanced Video Coding Technologies                            TV quality and experiences similar to that of the
MPEG 4/H...
mobile users to access these unmanaged contents without        however, has been little noticed in the legacy cellular
channel conditions. For ensuring the video quality, the base
[2] B. Larribeau, “2006 IPTV Standards Survey Report —               [8] C. Cicconetti, L. Lenzini, E. Mingozzi, and C. Ek...
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IPTV over WiMAX: Key Success Factors, Challenges and Solutions


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IPTV over WiMAX: Key Success Factors, Challenges and Solutions

  1. 1. IPTV over WiMAX: Key Success Factors, Challenges and Solutions James She, Fen Hou, Pin-Han Ho, and Liang-Liang Xie Electrical & Computer Engineering, University of Waterloo, Canada network infrastructures, which include the middleware Abstract – The advances in Broadband Internet access and released by Microsoft, field trails conducted by Swisscom Voice-over-IP (VoIP) technologies have made it possible for and SingTel, as well as the infrastructure equipment the Internet Protocol television (IPTV), which is expected to launched by Alcatel–Lucent, etc., for enabling IPTV serve as the next killer-application for the modern Internet carriers in the metropolitan areas. With the recent release of services over the wired Internet. With the prevalence of IEEE 802.16e (or WiMAX), Broadband Wireless Access wireless communications, we have witnessed the recent (BWA) has been envisioned to further extend the IPTV advances in miniaturization of mobile devices, affordable services to a new application scenario with wireless and wireless communication equipments, and improved small- mobility. It is a very strategic but challenging leverage for a scale energy supplies. In this premise, a new application wireless network carrier to glimpse the ultimate potentials of scenario on IPTV over wireless networks has been IPTV by focusing on a number of key features in using envisioned, which aims to promote the existing IPTV WiMAX. To identify the benefits and explore the best services toward better convenience, flexibility, and cost- potential in IPTV over WiMAX, this article aims to introduce a framework based on a channel coding technique of 2-level effectiveness by taking advantage of the wireless Superposition Coded Multicasting. Promising results were metropolitan area network (MAN) technologies such as observed through simulation to validate our approach, which IEEE 802.16 (or referred to as WiMAX). The WiMAX demonstrate that the optimal video quality is achievable with technology has gradually been considered as an effective much less system capacity consumption. but challenging leverage to extend the IPTV services in the Index terms: IPTV, WiMAX, Superposition coding, IEEE dimension of wireless and mobility. 802.16 Though IPTV is still at the infancy stage, a few limited but well-organized literatures [3, 6, 7, 13, 14] are reported I Introduction to give a general picture of IPTV in terms of requirements, deployment architecture, services, and quality assurance. IPTV is not the first attempt by the telecommunications Instead of presenting another up-to-date survey or industry to offer compelling real-time entertainment video discussing particular components of nowadays IPTV services. Substantial efforts were made in the mid 1990s systems, the study takes on the faiths of the current IPTV [3], which nonetheless did not fly due to a number of technologies by just understanding the major building factors back then. Beside the fact that the popularity of the blocks but focusing on their possible trends and potential on Internet was low, all of the associated technologies were fusing with WiMAX. Up to our knowledge, this study will certainly early and expensive, from video servers to MPEG be the first attempt to discuss the launching of IPTV over compression and decompression hardware, to the network WiMAX. switching fabric which was predominantly asynchronous This article firstly aims to identify the key success factors transfer mode (ATM)-based at that time, to Digital leading to positive economies of scale in launching a Subscriber Line (DSL) access systems. successful IPTV service. With the belief on the prevalence In the recent years, the unprecedented advancements in and pervasiveness of the future wireless MAN technology, multimedia technologies, such as H.264/MPEG4 Advanced WiMAX is evaluated as the supporting Internet access Video Coding (AVC) [4], have made it possible for real- technology for facilitating these key success factors by time encoded High-Definition Television (HDTV) over the complementing the existing wired solutions. Since IPTV is Internet. On the other hand, with the successful adoption of such a bandwidth consuming service, it is crucial to enlarge Voice-over-IP (VoIP) technology, telephony services the capacity bottleneck intrinsic in the WiMAX Base offered by the cable companies or other new players have Station (BS) operated in the Point-to-Multi-Point (PMP) generated disruptive impacts to conventional phone mode. The paper addresses the issue of multicasting for companies. All these technological readiness and market IPTV content delivery under the WiMAX PMP mode by competitions have forced many telecoms to migrate from taking advantage of the diversity of fading channels. This is simple data services to triple-play (data, voice and video) or considered as necessary in order to create a multi-customer even quadruple-play services (triple-play services plus and multi-program IPTV system that can support mobile) on a single infrastructure for their survivals and heterogeneous services and sufficient TV channels for new revenues. As a consequence, IPTV is being touted reaching a revenue-generating market scale. A possible again by many companies as the next “killer-application” solution by applying superposition coding on the multicast that will maximize true values of their current customer signals at the physical (PHY) layer is demonstrated. base, and enable future business growth [1, 5]. The rest of the paper is organized as follows. Section II Many industrial activities for meeting the trend of IPTV gives an overview on the IPTV services and the generic have been witnessed over the legacy metropolitan area 1
  2. 2. architecture. Section III positions the future trends of IPTV. request to watch the content back from the beginning once Section IV outlines the key success factors and challenges he/she joins to the channel late. Similar to those satellite of IPTV over WiMAX. In order to solve the bandwidth live broadcast, a live content over IPTV can be the showing thirsty and simultaneously support more TV channels, of a live event or performance encoded in real-time from a Section V introduces a new framework of 2-level remote location, such as a soccer game. superposition coded multicasting by taking advantage of the Managed services: Video content can be offered by the fading channel diversity of different receivers. Section VI phone companies who operate the IPTV business, or concludes this paper. obtained from syndicated content providers, in which the content is usually well-managed in terms of the coding and II Overview of IPTV Services and playout quality as well as the selection of video titles. Architecture Bandwidth for delivery and customer equipment are arranged carefully for serving the best playout performance A Overview on IPTV Services and quality to the customers. Unmanaged services: Technologies of IPTV itself allow In general, IPTV services can be classified by their types of to playout any live or on-demand video content from any content and services. In terms of types of content, video third party over the Internet. Therefore, nothing could stop could be on-demand or live. On the other hand, in terms of the possibility that a customer accesses a video content types of services, the video could be managed or directly from any third party online such as YouTube (or unmanaged. Google Video), individuals or/and an organization. With a On-Demand Video: With pre-encoded and compressed wider range of choices on the content selection is obviously content, a customer is allowed to browse an online movie the advantage of the unmanaged services at the expense of catalogue, to watch trailers, and to select the movie of non-guaranteed playout quality and performance. interest. Different from the case of live video, a customer can request or stop the video content at anytime without B Generic IPTV Architecture bounded by a particular TV schedule. The playout of the selected movies starts nearly instantaneously on the Fig. 1 shows a generic architecture for running IPTV customer's TV or PC. services. Common building blocks are classified in terms of Live Video: In this case, a customer is required to access customer premise, video headend, and transport networks, a particular channel for that content at a specific timing like which are introduced in the following paragraphs. that with a conventional TV channel. A customer cannot Fig. 1. A generic architecture and common building blocks for IPTV services. • Customer Premise with the DSL/cable wiring. STB is usually installed with Set-Top Box (STB): is a device at the customer side that middleware client software to obtain the program guide interfaces the user terminal (i.e., a television or PC/Laptop) data, decode MPEG2, MPEG4 video data, and display on 2
  3. 3. the screen. Alternatively, a web browser can obtain the multiple flows of live contents across the whole transport program guide data from a central server. A STB can be network (Fig. 2(a)), the idea of multicasting is to conserve integrated with DSL/cable modem or even an IEEE 802.11 the bandwidth and minimize unnecessary packets switch for home Internet access networking. duplication. A single transmission of each unique video • Video Headend data is shared among a group of customers who demand for Video encoders and Video On-demand servers are basically the same live content (Fig. 2(b)). Data will only be the major sources of video contents for IPTV services. The replicated at appropriate branching locations such as a video headend is composed of the following components. regional edge router when it is necessary to fork another Video encoder: which can encode real-time video analog substream to reach another group of customers or an signals from a content provider or a live event location to a individual customer. digital format based on a given video compression technology such as MPEG2/4. It also deals with on-demand contents stored or redistributed at different video on- demand servers after encoding and other processing such as digital rights and encryption. Live Video Broadcast server: which is in charge of reformatting and encapsulating video streams in case the video streams with different formats from a video encoder or pre-encoded video file are received. Also, it interfaces the core network and transmits the video signal over the (a) (b) core network towards the access network. Fig. 2. (a) Unicasting, and (b) Multicasting Video On-demand (VoD) server: On-demand contents are housed in these servers with streaming engines and III Future Trends of IPTV huge storages. The future IPTV is expected to provision high quality video Content and Subscriber management: These systems contents like HDTV, mobility such as mobileTV, and are not the focus in the article, whereas they are essential to access to the unmanaged contents, where the following facilitate the operation of IPTV services in terms of future trends and possible application scenarios are subscription accounts setup or tear-down for client control, envisioned: billing and authentication for back-office control, as well as • Portable Media Devices at Customer Premise digital right and security issues for content and delivery Beside those big flat panel TVs which are getting more control. capable of a full support of HDTV signals, many portable • Transport Networks multimedia devices like iPod, BlackBerry, as well as There are two major parts of the transport network in powerful cell phones and PDAs, have already been on the general – core, and access networks. shelf to support complete IP-based triple or quadruple Core networks: Depending on the scale of deployment, services in a single device. Watching a live seminar the core transport network, which connects the access presentation on a cell phone while in the train, or retrieving networks to customer premises, can be simply a single a popular video clip from Youtube over the Internet is no national distribution network running Gigabit Ethernet or longer in a science fiction only, but possible in the reality IP/MPLS plus various regional distribution networks today. running carrier-grade Ethernet [6]. Managed contents are • HDTV in Video Headend usually centralized and processed within the national Due to the growing demands from the consumers on better distribution network before delivering to different access video experiences and proactive differentiations among networks. However, a wider range of choices for the competitive media providers, the future IPTV services unmanaged contents by other content providers can be should provide two different types of TV quality: standard made, and the unmanaged contents are fed into the national definition TV (SDTV) and HDTV. The SDTV bandwidth distribution network to the customers through the Internet ranges from 1 to 4 Mbps, while the HDTV bandwidth outside. ranges from 4 to 13 Mbps. The typical number of TV Access networks: which serve as a critical part of the channels available from a provider is between 250 and 300 transport network used to reach each individual customer at SDTV channels, along with additional 10 to 20 more his/her home through the STB. The technologies available HDTV channels [7]. If each home has approximately four today are mainly xDSL [8] and coaxial/ hybrid fiber cable TVs, two to three SDTVs and one to two HDTVs (HFC), or probably fiber techniques such as Fiber-to-the- simultaneously consume up to 20 Mbps. At this point, Node (FTTN), to extend the reach to customer communities bandwidth management among different traffic classes to before xDSL or cable wiring. Since the bandwidth of the homes becomes a critical issue. In case a wireless access access networks is usually very limited to cater all the technology such as WiMAX is adopted, it will be of an customers for simultaneous access of the TV channels, ultimate importance for adopting an efficient multicasting multicasting has been widely adopted to enable a scalable scheme at the BS by fully exploring the fading channel delivery of video data for IPTV. Instead of unicasting diversity of all the receiving Subscriber Stations (SSs). 3
  4. 4. • Advanced Video Coding Technologies TV quality and experiences similar to that of the MPEG 4/H.264 was recently standardized by ITU-T, and conventional cable, satellite or digital TV services by a was designed to packetize the video data into Real-time IPTV channel. Offering managed and scheduled SDTV Transport Protocol (RTP) [4], such that a substantial programs with a quality guarantee is necessary for securing improvement over MPEG-2 performance, especially for the head-start success of the IPTV service. both HDTV and VoD contents, can be obtained. Whereas, B Why Is It WiMAX? the latest video coding schemes allow the same contents being encoded once while supporting heterogeneous To facilitate the abovementioned success factors for the conditions of transport and end-users devices, which makes IPTV services, particularly in the mobility support and cost it possible that the same content can be subscribed by home effectiveness, WiMAX should never be excluded from the and mobile users with different types of plan of access network infrastructure deployment. The device/communication media at the same time. goals of realizing IPTV over WiMAX are listed as follows. • Evolution of Access Networks Maximize the number of subscribers: Obviously, the Currently, some mobile service providers are already success of launching the IPTV services is determined by the offering on-demand unicast streaming of mobileTV via time and volume of profitable operations. Getting the 2.5G GPRS and 3G. New compression technologies allow maximum number of subscribers as soon as possible for a on-demand streaming of TV channels but with limited newly launched IPTV service program is a clear goal for capacities supported by existing cellular networks On the any service provider. It has been reported from time to time other hand, Triple or Quadruple Play services (broadband, that xDSL and cable broadband access may not be available voice, TV and mobile) over a single IP-infrastructure are in some areas due to the geographical distance and users- highly demanded by many service providers, where IPTV density. Meanwhile, the deployment of xDSL and cable over wireless networks is obviously a must. Enabling wiring overheads are not as easy and scalable as that with wireless capability for delivering IPTV through the latest wireless MAN technologies. wireless technologies such as WiMAX, Cellular IP, IP over As an alternative to the conventional wired access CDMA, etc. is highly expected. network technologies, WiMAX offers the ease of deployment like the other wireless technologies, while with larger service coverage and more bandwidth. The cost for IV Key Success Factors of IPTV over infrastructure deployment and service provisioning can be WiMAX dramatically reduced. Delivering IPTV services over It is important to foresee what are going to happen in the WiMAX to complement the current IPTV deployment can future IPTV services in order to pick the right technologies capture the maximum number of subscribers under the for corresponding extensions, but it is even more critical to same infrastructure and provide even better accessibility of see what are actually essential to launch a successful IPTV the same pool of video contents to the mobile users in the services based on nowadays technologies. In this section, future. we will first identify the key success factors for running a Converged wireless broadband access network: successful IPTV today, including the aspects of economies Telecoms are actively seeking ways to offer Triple or of scale, scheduled live content and quality assurance, Quadruple Play services, WiMAX is taken as a very good followed by the justifications on how WiMAX can fit in. candidate to be invested for providing new services like wireless broadband access and mobile VoIP telephony. A The Key Success Factors Launching IPTV over WiMAX can further achieve the Economy of Scale: Economy of scale characterizes a economy of scales in terms of more services and better production process or service operation, in which an service availability under common infrastructure. increase in the number of producing units may cause a Supporting the future trends: We have enumerated the decrease in the average fixed cost of each unit. By emerging trends of IPTV in the aspects of mobility, optimizing the economy of scales for operating IPTV accessing unmanaged contents, and supporting high-quality services, it can minimize the risks and secure the early video like HDTV. WiMAX is found to gain merits in such advent of an ultimate success. That translates to the need of trends of promotion with its reservation-based bandwidth an access network technology which can support more allocation, cost-effective and infrastructure-free subscribers and mobileTV for the future needs. deployment, and a stringent QoS support for the four types Scheduled Live Content and Quality Assurance: of service: Unsolicited Granted Service (UGS), real-time Quality of Service and Quality of Experience to the end Polling Service (rtPS), non real-time Polling Service users have been identified as critical requirements of IPTV (nrtPS), and Best Effort (BE) traffic [8]. services [2]. In the long run, watching IPTV contents will Enabling rtPS in the wireless broadband access can be really just like surfing different websites over the perfectly support the bandwidth requirements of managed Internet. Watching unmanaged live or on-demand contents content of the IPTV service providers, especially for the offered by different service and media providers over the paid HDTV and SDTV. With more and more portals world would gain the true values of IPTV services to the available in the Internet core which offers tons of rich and customers. However, it is still critical to ensure comparable free on-demand video content, it is a very attractive approach to allow not only home IPTV users but also 4
  5. 5. mobile users to access these unmanaged contents without however, has been little noticed in the legacy cellular affecting the quality and performance of the other paid live networks. contents. The incorporation of rtPS and BE services can be It is clear that a single-user communication scheme for manipulated to support these demands such that the best optimizing data throughput along a time-varying channel is flexibility and economy can be achieved without losing by way of incorporating adaptive coding, modulation, and much quality of content delivery. The extendibility for power control schemes, etc., in response to the variation of supporting the future trends of IPTV services over common the channel condition [9]. In WiMAX, an optimal video WiMAX access infrastructure creates long-term and transmission bit rate and a strategy for achieving the best growing economies of scales to the state-of-the-art IPTV video quality can be determined at the BS according to the operation. instantaneous system parameters. However, when a single multicast transmission of a video packet is sent from a BS V The Challenge: When Diversity of to multiple SSs, the video packet can be received at all the Fading Channels Meets Multicasting associated SSs but would be subject to different bit error rates due to heterogeneous channel conditions among the In spite of the benefits of including WiMAX as part of SSs. This phenomenon leaves the existing cross-layer access networks for delivering IPTV services, one of the resource allocation and scheduling approaches for most distinguished problems is on the capacity bottleneck throughput optimization under fading channels totally inherent in the BS that may impose a stringent limitation on useless. Fig. 3 illustrated such a scenario in a snapshot, the number of simultaneously multicast channels and active where a multicast signal based on 16QAM is sent from the customers. In order to assure a successful operation of BS, while only those SSs with a “Good” channel state to IPTV over WiMAX, the WiMAX system has to take support 16QAM can decode the received multicast signals. advantage of the fading channel diversity in the process of However, if a lower transmission rate is used (for example, video multicasting. This is a unique problem existing in the BPSK in this case), resource underutilization of those SSs application scenario of IPTV over WiMAX, which, with “Good” channel state is immediately encountered, which leaves much space to improve. Fig. 3. A single multicast transmission of video data under the diversity of fading channels. Minimizing the bandwidth consumption in the content coding is illustrated in Fig. 4 cited from [12]. The nodes are delivery of IPTV is critical. Thus, we are highly motivated indexed in an increasing order according to their distance to investigate possible solutions in order to fully take from the BS. As shown in the figure, when the BS transmits advantage of the fading channel diversity and capitalize the signals to M3 with the targeted SNR level, the SNR seen by true potential of IPTV over WiMAX. both M1 and M2 is much greater than their targeted SNR levels (by the amount of A + B and C, respectively). A Proposed Solution – 2-Level Superposition Similarly, when the BS transmits signal to M2, M1 receives Coded Multicasting additional A dB of power above its targeted SNR level. This In this section, we introduce a possible solution to the implies that M1 has sufficient SNR to decode the messages abovementioned problem by 2-level Superposition Coded intended for both M2 and M3, and M2 has sufficient SNR to Multicast (2-level SCM), which is a framework of applying decode the messages intended for M3. The power disparities the superposition coding at the physical (PHY) layer in at nodes M1, M2 and M3 suggest that the information for M2 WiMAX to form a multicast signal. and M3 can be included in the transmission to M1 through Superposition coding has been introduced for long to the adoption of superposition coding. Similarly, the increase the overall user capacity of a wireless information for M3 can be included while transmitting communication system by exploiting the spatial or temporal information to M2. The dotted line in Fig. 4 indicates that power disparities perceived by multiple users for common the BS transmits information to M2 while transmitting to M3 broadcast signals [10, 11, 12]. An example of superposition at the targeted SNR level by employing superposition coding. 5
  6. 6. channel conditions. For ensuring the video quality, the base quality data of each video frame will be modulated by BPSK and the enhanced quality data will be modulated by 16QAM. With such superposition coded multicast signals, each SS can at least decode and obtain the base video quality data of an IPTV channel modulated with BPSK when it is in the “Bad” channel state, or achieve the full video quality with all the data modulated by both BPSK and 16QAM when it is in “Good” channel state. Even in presence of the fluctuation of channel conditions of all the SSs between “Good” and “Bad” time from time, an Fig. 4. Power disparities in a wireless network cited from acceptable video quality of an IPTV channel to every SS [12]. can be achieved. An optimal transmission strategy at the BS By leveraging the superposition coding, we propose a 2- for an IPTV channel can be unhooked from such deadlock level superposition coded multicast scheme as presented situation due to the multicasting over heterogeneous below. The multicast signal is created to contain some data channel conditions. modulated by BPSK and some data modulated by 16QAM, assuming all the SSs can support BPSK in their worst Fig. 5. Proposed 2-level superposition coded multicasting scheme. B Simulation (BPSK and 16QAM), although the proposed framework can Simulation was designed to evaluate the proposed scheme. be applied to the case of any number of modulation types. Assume that the video frames are generated from the video With the legacy scheme (denoted as “Normal” in the source by a constant frame rate (i.e., 30 frames per second). figures), the type of modulation is taken as either BPSK or The size of each frame depends on the type of frame and 16QAM, depending on whether all the SSs can support that content of video sources, which is obtained from the trace modulation type according to their channel feedbacks to the file in webpage http://trace.eas.asu.edu/hd/mars/. The data BS. The results show that the proposed scheme has higher of each frame are categorized into base quality data and PSNR (better video quality) for both SS1 and SS10 than enhancement quality data with a certain percentage, and that with the legacy scheme. In addition, SS1 and SS10 packetized into RTP/IP packets and then to MAC-layer obtain different average PSNR with the proposed scheme Protocol Data Unit (MPDUs) for wireless transmission. The due to their different channel conditions. By comparing Fig. simulation parameters are shown in Table I. Rayleigh 6(a) and Fig. 6(b), it is interesting to observe that the fading channels are assumed and may vary at one frame performance gain in terms of PSNR is larger when the after the other, where the average signal noise ratio (SNR) percentage of base quality data is smaller within a frame. of each SS is given in Table II. The channel state of each SS is unchanged over the duration of each WiMAX Table I. Simulation Parameters transmission frame. Number Frame Downlink Uplink sub- Fig. 6(a) and 6(b) show the simulation results. The sub-frame frame of SSs duration duration duration proposed scheme is compared with the legacy scheme in 10 2 ms 1ms 1 ms terms of the frame-by-frame video quality (i.e. PSNR) OFDM FFT Data Sub- Timeslot perceived by SS10 and SS1, which correspond to the two symbol Size carriers duration SSs with the best and worst averaged SNRs, respectively. duration The percentage of base quality video data is 40% and 80% 4 physical 256 192 11.46 ns symbols of each frame in Fig. 6(a) and Fig. 6(b), respectively. For simplicity, there are only two types of modulations here 6
  7. 7. 70 Normal Proposed scheme (SS1) 60 Proposed scheme (SS10) 50 PSNR(dB) 40 30 20 10 0 50 100 150 200 250 Index of frames (a) 70 Normal 65 Proposed scheme (SS1) Proposed scheme (SS10) 60 55 PSNR(dB) 50 45 40 35 30 25 0 50 100 150 200 250 Index of frames (b) Fig. 6. The comparison of PSNR perceived by SS1 and SS10 under the legacy (denoted as “Normal”) and proposed scheme with different based quality percentage. Table II. The average SNR of each SS. Index of SS1 SS2 SS3 SS4 SS5 SS6 SS7 SS8 SS9 SS10 SS Average 10 12 14 16 18 20 22 24 26 28 SNR(dB) was proposed by exploring the intrinsic natures of scalable VI Conclusions video coding in latest MPEG 4/H.264, where the diversity of fading channels of multiple users can be fully leveraged. This study has evaluated the applicability of IPTV over The simulation results showed that a significant WiMAX. The key success factors and challenges were improvement in the system performance in terms of PSNR highlighted through insight discussions and analysis on the and capacity efficiency can be obtained through the feasibility and benefits in launching such an application proposed framework of 2-level SCM. scenario, where we have clearly justified the necessity of including WiMAX in the access networks serving as a complement to the existing wired technologies. In order to References achieve better system capacity and customer experiences, a [1] S. Ortiz, Jr., “Phone Companies Get into the TV Business,” 2-level Superposition Coded Multicasting (SCM) scheme Computer, Volume 39, Issue 10, Oct. 2006 Page(s):12 – 15 7
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