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  1. 1. IEEE EIT 2007 Proceedings 470 . Framework for Delivering IPTV Services over WiMAX Wireless Networks Ioan Vlad Uilecan, Chi Zhou, Member, IEEE, Guillermo E. Atkin, Member, IEEE network has many advantages such as bandwidth efficiency. Abstract—The Internet Protocol Television (IPTV) service is Besides TV contents, the networks can also carry digital audio, becoming more and more popular among telecommunications telephony and data, allowing cable and phone companies to companies because it can deliver TV programs anytime deliver triple play services over the same existing anywhere. Based on IP protocol, IPTV features advantages like bandwidth efficiency and ease of management. IPTV supports infrastructure. both broadcast and unicast services like LiveTV and However, while there are many advantages to using IP, there VideoOnDemand. WiMAX wireless system, capable of ensuring are also considerable challenges. For example, transmitting TV high bandwidths and low latencies, is suitable for delivering services over IP faces significant Quality of Service (QoS) multimedia services. In addition, it also provides wide area challenges for the service provider. Video over IP is unreliable coverage, mobility support, and non-line-of-sight operation. and something as simple as channel surfing can easily become a Therefore, WiMAX is a promising solution for delivering IPTV services anytime anywhere, especially to rural areas or remote problem on an IP network. locations. This paper identifies the challenges in delivering IPTV The premises that made possible the appearance of IPTV over WiMAX wireless system and proposes a framework to services include the development of Gigabit Ethernet, the provide some solutions to those challenges, at MAC and Physical appearance of high speed switches and routers, and the layers. Taking advantage of the WiMAX features, IPTV services availability of QoS provisioning for IP networks. IPTV has a can be delivered at low costs and with high audio/video service typical bandwidth requirement of 2Mbps/channel to quality. 8Mbps/channel (HDTV) and it requires a broadband Index Terms— IPTV, QoS, WiMAX, VideoOnDemand, connection with QoS support. The only certain way, until now, LiveTV to meet the consumer’s needs is to use fiber all the way to the home. This allows bandwidth up to 1Gbps, and can provide I. INTRODUCTION 30-75 Mbps per user [8], [12]. With a typical 20Mbps for a HDTV channel we have to keep T he increase of satellite services and digital cable, and the appearance of HDTV have had a big impact on the television market. Besides the standard TV services, nowadays in mind that when changing the channels, even for a short time, there are two streams simultaneously transmitted. This means people want to be able to watch their favorite TV programs and about 40Mbps for only one TV. If we count multiple TV sets in shows anytime anywhere using their mobile devices, all these a household and add the data traffic and voice, all these can without a loss in video or audio signal quality. They also want reach to about 100Mbps per connection. Fortunately, PON to be able to use the same device for other services such as networks can provide this kind of fast speed. Until now, there voice and data. The telecommunications companies are trying are many companies delivering IPTV over optical fiber to explore the existing technologies to provide all these by the networks [15]. The quality of the signals delivered using optical means of the TripplePlay services. fiber is superior to that of cable TV systems. Fiber systems A new TV delivery method, the Internet Protocol Television make it possible to supply signal to several TV sets, including (IPTV), has appeared as a solution to ubiquitous TV access. reasonable cable loss. Given that many fiber systems have IPTV is a system capable of receiving, decoding and displaying adequate bandwidth to deliver an MPEG-2 signal (even video streams transmitted as Internet Protocol (IP) packets. The HDTV) using IP, this is a very feasible solution. video content is first compressed and encoded into video IPTV is very popular as it delivers the content to users streams, which are then transmitted over the network as IP whenever they want. The next step is to deliver this content datagrams. Sending digital video using compression over an IP wherever the users are. This is where a wireless technology that supports mobility is needed. Worldwide Interoperability for Microwave Access (WiMAX) technology is based on IEEE I. V. Uilecan, Dr. Chi Zhou, and Dr. Guillermo E. Atkin are with the 802.16−2004 and 802.16e−2005 standards for fixed and mobile Department of Electrical and Computer Engineering, Illinois Institute of wireless access in metropolitan area networks (MAN) [3]. It Technology, Chicago, IL 60616, USA (phone: 312-567-3417, Fax: 312-567-8976; e-mail:,, supports data rates of 70Mbps over ranges of 30km with mobility support. Nowadays, WiMAX is the only wireless 1-4244-0941-1/07/$25.00 c 2007 IEEE
  2. 2. IEEE EIT 2007 Proceedings 471 . system capable of offering high QoS at high data rates for IP provider’s network. networks. The video streams are received by a local office, which WiMAX medium access control (MAC) layer supports real delivers them out to the subscribers. Here some local content time polling services (rtPS) ensuring required bandwidth and (TV stations, advertising, and video on demand) can be added. minimum latencies for video services through quality of service Also the user authentication, channel change requests, billing, (QoS). It uses orthogonal frequency division multiplexing Video-on-Demand requests are done at the local office. (OFDM) and orthogonal frequency division multiple access At the receiver side, a residential gateway serves the role of (OFDMA) physical layer (PHY). It also uses adaptive both an end point of the Internet and a starting point of a home modulation and coding schemes and forward error correction network. It transmits incoming traffics from the Internet to the (FEC) to increase service quality [3]. Moreover, it is an all IP home network while maintaining its QoS. If the incoming access network and offers transparency for packet based core traffic has no QoS information, the residential gateway should networks. All these make WiMAX an ideal choice for IPTV add new QoS information to the traffic. The QoS method applications with ubiquitous access. described in IEEE802.1Q has a weakness, i.e., the service Nowadays, some telecom providers have already deployed traffic belonging to the same priority group has no difference in IPTV systems (Verizon offers 300+ channels of television their priority level. In this case, a residential gateway should service) but the service is not delivered over WiMAX, but by dynamically regenerate the QoS priority of the requested IPTV fiber running directly to the home. In the future, WiMAX could channel in order to give higher priority than any other TV deliver IPTV to rural regions, off-shore rigs and other remote streams. locations, with high degree of video and audio quality at At the user’s side, a set top box (STB) or a computer, affordable prices. It may also be well suited for medium quality connecting to the home DSL, fiber or wireless line, reassembles video services delivered to mobile devices such as notebooks the IP packets into a coherent video stream and then decodes and WiMAX capable phones. the contents. In this paper we aim to identify the challenges related to In general, the consumers highly expect that IPTV works the delivery of IPTV services over WiMAX networks Then we same way as standard TV. They expect to be able to turn on the propose a framework that we would like to use next in TV, navigate through channels, and watch all the way through implementing a system capable of delivering IPTV services without the transmission breaking down. They do not expect to over an IP based WiMAX network. We try to give some wait seconds for changing the channels or to watch a TV solutions especially from the Physical and MAC layers. program which stutters. This may pose a major challenge for The paper is organized as follows. The background of the companies that plan to use IP networks to transmit television problem is explained in Section II. The challenges are in more programs. details presented in Section III. The proposed framework and In a video stream, even with high QoS network support, solutions are given in Section IV while our conclusions come in errors may occur. For unicast, the STB can request the server to Section V. resend lost or corrupted packets but for multicast streams, it is very important to ensure that the network is well designed. In II. BACKGROUND this case, owning the network is a great advantage since the provider can improve the quality of their delivered services A. What is IPTV and how does it work? themselves, instead of relying on third parties or internet. Also IPTV is a system where a digital television service is by using QoS they can prioritize the video traffic to prevent delivered using the IP protocol over a network infrastructure. It delay or fragmentation of the signal. Without end-to-end covers both live TV (broadcasting) as well as stored video control, it would be more difficult since QoS requests are not (Video on Demand). The playback of IPTV requires either a often recognized between operators. personal computer or a "set-top box" connected to a TV. Video content is typically compressed using either a MPEG-2 or a B. IPTV Network Elements MPEG-4 codec and then sent in an MPEG transport stream An IPTV network, as illustrated in Fig. 1, consists of four delivered via IP Multicast in case of live TV or via IP Unicast in case of Video on Demand. At the broadcaster’s side, the following steps occur: the broadcaster encodes the TV program into MPEG2 and sends the stream to the satellite uplink (IP QoS is applied by the IP stream platform). The video stream is up linked to the service provider’s satellite in DVB format. At the national head end, the video signals are pulled from satellites and encoded if necessary (e.g., MPEG-2, H.264). The Fig. 1 IPTV Architecture video stream is broken up into IP packets and sent into the major elements.
  3. 3. IEEE EIT 2007 Proceedings 472 . 1) Video Head-End: This is where video is captured and video streams sent from the local office to the subscriber is processed before being sent over the IP network. A head-end about four due to the limited bandwidth. takes each individual channel and encodes it into a digital video When a user changes the channel on their STB, it does not format (e.g., MPEG-2). "tune" a channel like a cable system, but it switches channels by 2) Service Provider Core/Edge IP Network: This is the core using the IP Group Membership Protocol (IGMP) to join a new network of the service provider and includes hardware from multicast group. This way, only signals that are currently being many vendors to construct this network. watched are actually sent from the local office to the user and 3) Access Network: The access network connects the Service so, the WiMAX available bandwidth may be enough for Provider to the Subscriber’s home. Currently it can be a DSL delivering IPTV services. line or PON using optical fiber. 4) Home Network: The home network is the last mile. This III. APPLICATIONS AND CHALLENGES distributes the IPTV services throughout the home. The In this section, we identify the challenges which the system connection gets into the household through the device and is may face when delivering IPTV services over WiMAX then connected to a computer or to the STB which in turn is networks. We are relating all these challenges to the connected to the TV. applications they are addressed for. C. IPTV offered services A. Multicast capability The IPTV services can be classified as multicast services One great advantage of the WiMAX is its multicast (live TV) and stored services, i.e., Video on Demand (VoD). capability. The multicast technology allows a base station (BS) 1) Video on Demand: VoD is a service that allows a to send video packets to a subset number of stations. For subscriber to order certain programs. The user orders from a example, during a Super Bowl game, a large number of viewers menu and a request signal is sent from his terminal to a video may want to watch a single channel. Using the multicast feature file server in order to play the requested program. This kind of of WiMAX, all of these users can be served by consuming a service may accept some delays in transmission and even relatively very small bandwidth. The idea can be extended to retransmissions are possible in order to increase quality of any TV channel as it is expected to be more than a single viewer service. The following additional functions need to be for any TV show. integrated in this service in order to meet the client expectations: easy menu navigation and Fast forward/reverse B. Instant Channel Change function. VoD is a point-to-point service as opposed to a On an IP-based network though, channel surfing can become broadcast service, and IP is an efficient mechanism for an issue because only one stream of video is transmitted to the delivering such services because it can satisfy the QoS TV at any one time. When the TV viewer wants to change the requirements. channel, he punches a remote that sends the signal to the 2) Live TV: LiveTV refers to television broadcasts of events television set which, in turn, sends another signal on to a router or performances in real time, with very small delays. As on the network. The router then has to stop sending the original opposed to VoD, this kind of service may not experience any stream and then send a new stream based on the requested delays in transmission, so the management of the network is channel. This creates a delay between the time the router stops very important in this case. This kind of service has another set sending over the old channel and when it starts sending over the of functions that it needs to fulfill: PiP – picture in picture new requested channel. The situation is worsened when the capability, instant channel change, and easy menu navigation. router is subjected to multiple change requests all at the same For both services, it is also necessary to be able to deliver time. multiple channels simultaneously, in order to support the C. Mobility picture-in-picture mode, simultaneous record and watch functions, and multiple TV’s in different rooms. IPTV is expected to provide ubiquitous access with mobility support. Providing services to mobile users is always a D. WiMAX capacity for IPTV delivery challenge, especially the multimedia services. Another While all the streams are multicast from the national head advantage of WiMAX is the support for data communications end to local offices at the same time but here, the local last mile at vehicular speeds, feature which was impossible until now in line can not support all the channels at once. The question is regular cable TV systems. how to send hundreds of channels to an IPTV subscriber with a D. Jitter WiMAX line? The answer is only sending a few at a time. A Windows Media stream takes up 1.0 to 1.5Mbps for Another problem that arises when IP networks handle video SDTV; ten channels could be sent at once with bandwidth left is due to the way the network handles data. In an IP network, over for voice and data. HDTV uses about 20-25Mbps and for data is broken up into small packets and then sent off H.264 the rates are 7 to 8 Mbps. This means the number of separately. At its final destination, all the data packets are reassembled again. When video is put on an IP network, that
  4. 4. IEEE EIT 2007 Proceedings 473 . video is also broken up into small packets and sent from the intermediate link is needed from the service provider to a source, the broadcaster, through the network, to eventually be WiMAX BS. This may often be SONET, so an reassembled into video that TV viewer gets to watch. Ethernet-SONET mapping is needed at the provider and a While this system is a good way of sending ordinary data SONET-WiMAX demapping needed at the WiMAX base files, when applied to video, it creates problems. Video files are station. The OFDM frames are then transmitted to the WiMAX extremely large and to send a complete file over might take several hours. The solution is to have the video play as the packets are downloaded. However, due to factors such as routing changes, network congestion or timing drift, the packets do not all arrive at the same rate or even in the correct order. This problem is known as jitter. The solution to this problem is a jitter buffer. The jitter buffer stores the packets as they come in. These packets are assembled in the buffer ahead of their use so that late packets can be added. E. Overhead Fig. 2 IPTV over WiMAX Schematic Architecture (fixed subscriber) In a packet based system, each layer is adding significant air link. A subscriber station (CPE) will capture these frames amount of overhead to the initial packet, therefore reducing the and regenerate the traffic streams. These streams are then sent effective payload capacity and the altering the quality of the for display to the IPTV client. In the other way, the client IPTV signal. WiMAX is decapsulating the frames up to the should be able to choose the channels and transmit other MAC layer, therefore it can use payload header suppression signaling options. and compression techniques in order to reduce the amount of IPTV as we said is currently being delivered over fixed overhead at Physical and MAC layers. networks. How about in mobile ones? Such a system may be F. Transceiver Design depicted in Figure 3, where the IPTV is delivered from the WiMAX systems are using very performing radio service provider regardless of the type of network, through a transceivers. The parameters of such a transceiver are high fixed or wireless network. stability, low noise, high linearity and wide dynamic range. The content/rate adapter block is here responsible for Beside these, in order to support IPTV and video applications, a adapting the IPTV service bandwidth to the available WiMAX high bandwidth is also required. bandwidth and is performing the IP decapsulation and G. Power Consumption The power consumption is another important issue in designing a WiMAX system able to support IPTV services. A TV program can last a few hours; therefore the system delivering will use a high amount of power. A good way to reduce the power consumption is to implement different modes of operation that can be changed dynamically according to the needs (e.g. idle mode, sleep mode). Another way to save energy is by using a high sensitivity receiver. H. System Capacity Fig. 3 Delivering IPTV Services to both Fixed and Mobile Subscribers The proposed system has to be able to support multiple users. reincapsulates the video streams. The adaptation, depending on A good way to increase the capacity of the system is to use high the type of network is addressed to, has to be done in two steps: gain sectorized antennas. By using such a method, the IPTV rate adaptation and content adaptation. services can be delivered further away and to a bigger number of customers. B. Proposed System Model A functional block diagram of an IPTV application is IV. WORK PROPOSAL illustrated in Fig. 4, while Fig. 5 shows IPTV protocol stack. A system model was proposed in [2] but in our implementation A. System Architecture we intent to use a traffic classifier at the MAC layer, adaptive A schematic architecture for delivering IPTV over WiMAX modulation and coding at the Physical layer, as well as power (to a fixed subscriber) is presented in Fig. 2. From the service management algorithms at the radio transceiver, in order to provider (if it owns a WiMAX BS) the IPTV transport stream provide an improved multimedia experience to the IPTV users. should be encapsulated into OFDM frames. Otherwise, an
  5. 5. IEEE EIT 2007 Proceedings 474 . At the video head end, the video streams are encoded and classifier. The BS receives the downlink IP traffic which may compressed (e.g., MPEG2) from live and stored programs. The contain data for different kind of services (internet data, voice, video, etc.). According to the type of service it is addressed to, this traffic is QoS classified as UGS, rtPS, nrtPS or BS. The video streaming uses rtPS. A traffic classifier has the role to sort the incoming traffic according to the priority and QoS demands. First it extracts the Fig. 4 System Model for IPTV Applications MPEG channels are encapsulated as real time transport protocol (RTP) and transported as a UDP or TCP streams to the Fig. 6 MAC Layer QoS Support IP layer. The IP packets are encapsulated into Ethernet frames header information from the IP packets and sends it to the and then sent over the network through the physical layer. The connection management unit. Based on the header info, the WiMAX BS receives this data and decapsulates them up the IP connection management assigns a unique FlowID to each layer and re-encapsulates them into specific MAC and PHY packet. The FlowID will contain information about the type of PDUs. The physical layer performs FEC, symbol mapping and service and type of connection for each packet and will be modulation while the radio transceiver transmits the resulted assigned according to the QoS policy protocol stored in the signals to the mobile nodes. Here, the video streams are sent to QoS Database. For IPTV services, this protocol has to be the STB or PC decoder and regenerated into video content. designed by taking into account specific parameters as: The MAC and Physical Layer together with the radio Minimum/Maximum Delay, Minimum/Maximum Data Rate, transceivers are the components where we will focus our Retransmission and Requests Policy, etc. The traffic classifier attaches the generated FlowID to the IP packets and the Scheduling/Queuing block will sort the IP traffic accordingly. In this case, the video IPTV stream has to have the maximum priority. In the end, the specific WiMAX MAC PDU will be generated and sent to the Physical layer. The same process has to be implemented in the reverse way. 2) Physical Layer (PHY) Fig. 7 shows the block diagram of our Physical Layer implementation. According to the WiMAX standard [4], at the Physical layer, the packets arriving from the MAC layer are first subject to Channel Coding and Modulation. The Channel Coding consists of randomization, forward error correction, Fig. 5 The IP Protocol Stack for IPTV transmission coding (such as Reed Solomon and convolutional line coding) attention at, with the remark that the MAC implementation is a and interleaving. The Physical layer supports different modulation types (QAM, BPSK, and QPSK). In our design we key component because here is where the queuing and scheduling of service is done. The MAC layer implementation propose an adapting modulation technique at optimal coding is also the one that will facilitate the QoS provisioning rates, in order to maximize the bandwidth efficiency with necessary for our system. respect to quality. 1) Medium Access Control (MAC) Layer Following the modulation, the Inverse Fast Fourier WiMAX is a point-to-multipoint system, Transform (IFFT) transforms the signal from the frequency connection-oriented. The WiMAX MAC layer protocol is a domain to the time domain, followed by time-domain Dynamic service “editing” protocol [4], with processing (such as spectral shaping, interpolation). Finally, Add/Change/Delete functions, which allows a management of there is a frame construction block which adds preamble and the message payload format. One of the biggest advantages is cyclic prefix, followed by the Radio Interface (IF and RF that it offers flexible QoS provisions and this major advantage interfaces). is exploited in our proposal. The reverse path is similar. It includes time/frequency Fig. 6 shows the proposed implementation of the MAC layer synchronization, channel estimation, equalization,
  6. 6. IEEE EIT 2007 Proceedings 475 . demodulation and decoding and it moves the signals from time adaptive modulation and coding scheme, power management mechanism, and resource allocation algorithm to facilitate IPTV over WiMAX. REFERENCES [1] Maneesh Bakshi, “VoIP / Multimedia over WiMAX (802.16)”, [2] Francis E. Retnasothie, M. Kemal ¨Ozdemir, Tevfik Y¨ucek, Hasari Celebi, Joseph Zhang, and Ranesh Muththaiah, “Wireless IPTV over WiMAX: Challenges and Applications”, IEEE Wamicon (invited paper), Clearwater, FL, December 2006 [3] Junqiang Hu, Dayou Qian, Haijun Yang, Ting Wang, Steve Weinstein, “Triple Play Services over a Converged Optical/Wireless Network”, Fig. 7 PHY Layer Architecture OFC/NFOEC Digest, 2006 domain to frequency domain. [4] IEEE Standard 802.16 Working Group, "IEEE Standard for Local and Metropolitan Area Networks part 16: Air Interface for Fixed Broadband The block diagram for the WiMAX BS transceiver is given Wireless Access Systems" IEEE, 2004. in Fig. 8. It consists of digital and analog part. Here we intend to [5] ”Application Usage Scenarios Using WiMAX Technology”, December implement a power management algorithm that will tune the 2005, Prepared by Application Working Group WiMAX Forum [6] Wan-Ki Park, Chang-Sic Choi, Youn-Kwae Jeong, Intark Han – “An transceiver parameters (e.g., amplifier gain, power level, carrier Implementation of the Broadband Home Gateway supporting frequency) in order to achieve the optimum quality of the Multi-Channel IPTV Service ”, Consumer Electronics, 2006. ISCE '06. signal. 2006 IEEE Tenth International Symposium [7] Yongsun Ryu, Eunjin Ko, Hyuncul Kang, Gilheang Lee, YoungSun Kim From the Physical layer, the digital signal with the I and Q – “The Web based SLA System for Customer Quality Assurance in components is first Digital Up-Converted. This signal is then Providing IPTV Services”, Broadband Convergence Networks, 2006. BcN 2006, p. 1-10 [8] Lev B. Sofman, Bill Krogfoss, Anshul Agrawal – “Dimensioning of Active Broadcast Channels in Access IPTV Network”, Optical Fiber Communication Conference, 2006 and the 2006 National Fiber Optic Engineers Conference, OFC/NFOEC Digest, 2006 [9] Denis Gallant – “Optical Network Foundation for Triple Play Services Roll-out”, OFC/NFOEC Digest, 2006 [10] Mark Abrams and Ariel Maislos – “Insights on Delivering an IP Triple Play over GE- PON and GPON ”, OFC/NFOEC Digest, 2006 [11] Mohamed El-Sayed, Ying Hu, Samrat Kulkarni, Newman Wilson – “Access Transport Network for IPTV Video Distribution”, OFC/NFOEC Fig. 8 Radio Transceiver Diagram Digest, 2006 [12] Junqiang Hu, Zhong Pan, Zuqing Zhu, Haijun Yang, Venkatesh Akella, converted to the analog domain by the DAC while a two stage S. J. B. Yoo – “First experimental demonstration of combined up converter (IF and RF) uploads the signal to the desired radio multicast and unicast video streaming over an optical-label switching network”, OFC/NFOEC Digest, 2006 frequency. The resultant transmit signal is amplified by a [13] Wan-Ki Park, Sung-Il Nam, Chang-Sic Choi, Youn-Kwae Jeong and Power Amplifier. The amplified signal is passed to the antenna Kwang-Roh Park,– “An Implementation of FTTH based Home through the switch or duplexing device, depending on the Gateway Supporting Various Services ”, IEEE Transactions on Consumer Electronics, Volume: 52, Issue: 1, page: 110- 115 duplexing method (TDD or FDD). [14] Sangjae Lee, Chunglae Cho, Intark Han Digital Home Division – “FTTH In the other way, the received signal is amplified using a low Residential Gateway and IP Tuner for IPTV Service”, Consumer noise amplifier (LNA) down converted to the IF stage using the Communications and Networking Conference, 2006. CCNC 2006. 2006 3rd IEEE, Volume: 1, page 497- 501 two-stage down converter (RF and IF). This signal is digitized [15] Benjamin Alfonsi – “I Want My IPTV: Internet Protocol Television and I/Q samples are downconverted and sent to the Radio Predicted a Winner”, Distributed Systems Online, IEEE, 2005, Volume: interface. 6, Issue: 2 [16] James 0. Farmer Wave7 Optics, Inc. – “Delivering Video, Voice and Data to Consumers via an All-Fiber Network”, Optics Express, Vol. 13, V. CONCLUSION Issue 8, pp. 2887-2891 IPTV enables users to have VoD services as well as to subscribe whichever broadcast channel of their choice anytime anywhere. With WiMAX offering high data rates to both mobile and fixed users with low cost and high quality, the implementation of IPTV over WiMAX become promising. In this paper, we have introduced IPTV, identified the challenges in implementing IPTV, and setup a framework for delivering IPTV over WiMAX. As a future work, we intend to design and develop specific