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  • 1. ENSC 427: COMMUNICATION NETWORKS Spring 2009 Video streaming over WiMAX technology Farshad Taghizadeh (fta1@sfu.ca) Dona Patikiriarachchi (dap1@sfu.ca) Parmeet Kaur (pka17@sfu.ca) 1 Abstract The aim of this project is to simulate bandwidth intensive, delay sensitive video traffic representation of video streaming by using WiMAX which is also known as WirelessMAN and more formally as IEEE 802.16. WiMAX is a set of wireless standards designed to provide high- speed Internet access to a wide range of devices such as laptops, cell phones, cameras, music players, etc. which are being used by clients over the ‘last mile’. It has become a lone frontrunner in broadband access compared to other technologies such as Asymmetric Digital Subscriber Lines and T1 lines in terms of cost and complexity. For effective multimedia streaming across the network, we hope to use compression standards such as MPEG-2 or MPEG-4. Furthermore, we hope to examine specific results such as throughput, packet loss and packet delay of a subscriber station over a WiMAX access network. As Opnet is an industry adopted commercial-based network modeling tool with support for WiMAX, we will use Opnet in this project for simulation purposes. 2 Introduction 2.1 WiMAX overview Worldwide Inter-operability for Microwave Access, largely known as WiMAX is a telecommunication technology designed to provide effective transmission of data using transmission modes "from point-multipoint links to portable and fully mobile Internet access" [4]. The technology is so advanced that it can provide up to 72 Mbps symmetric broadband speed without cables [4]. The traditional cable-based access networks can deliver content only to subscribers at fixed points. This technology appears to be outdated for the modern world where an alarming rate of people use cell phones and other portable electronic devices such as laptops to do their daily work at mobile locations. Therefore, there is an increasing demand for a new technology that can deliver information to mobile users [6]. WiMAX is intended to surpass the current, expensive network transmission technologies such as Asynchronous Digital Subscriber Line (ADSL) and T1 line and provide fast and cheap broadband access especially to rural areas lacking the necessary infrastructure such as optical fiber and copper wires. WiMAX operates in the frequency range of 10GHz - 66GHz as it has less interference and more bandwidth. A lower range of frequency band was later introduced which operates between 2GHz and 11GHz [1].
  • 2. There are two main types of WiMAX services: mobile and fixed. Mobile WiMAX enables users access Internet while traveling whereas fixed WiMAX stations provide wireless Internet access to clients within a fixed radius. Moreover, WiMAX is capable of delivering high speed wireless services up to a range of approximately 50km which is far longer than that of DSL, cable modem, etc. which has a span of approximately 5.5km [2]. WiMAX is an evolving set of the commercialization of IEEE 802.16 standard which was initiated at the National Institute of Standards and Technologies in 1998. In June 2004, it was transferred to the IEEE for the purpose of forming a working group 802.16. The WiMAX forum, which was established in 2001comprises of a group of industry leaders such as Intel, AT&T, Samsung, Motorola, Cisco etc who are entitled to support as well as promote the technology by certifying products that conform to the WiMAX standards [1]. In order to provide effective transmission of data with minimum delay, it is necessary for the WiMAX base station and the subscribers to obtain a clear line-of-sight. Large objects such as buildings and trees can interfere with the signals which would result in packet loss and delay. In order to avoid this unfortunate scenario WiMAX uses mesh mode topology that allows subscriber stations to communicate directly with each other while communicating with the base station. This way, if the line-of-sight between one client and the base station is interfered, the base station can route the information to that client via another client that has a clear line-of- sight. Furthermore, WiMAX uses a scheduling algorithm for exchange of data meaning the subscriber stations transmit data in their scheduled slots which helps minimize interference within networks [1]. 2.1.1 WiMAX physical layer The IEEE 802.16 standard defines one air interface for the bands in the 10GHz - 66GHz range with a single carrier modulation called WirelessMAN-SC (Wireless Metropolitan Area Network - Single Carrier). The bands in the 2GHz - 11GHz range experience higher interference and are therefore more complex to implement. Hence, three air interfaces are defined for the lower frequency bands: -WirelessMAN-SCa (uses Single Carrier modulation) -WirelessMAN-OFDM (uses Orthogonal Frequency Division Multiplexing) -WirelessMAN-OFDMA (uses Orthogonal Frequency Division Multiple Access) [1]. Additionally, the physical layer supports varying frame sizes and scalable bandwidth for multimedia traffic which is ideal for applications such as Internet Protocol TV (IPTV), Voice over IP (VoIP), etc [6]. 2.1.2 WiMAX Medium Access Control (MAC) layer The WiMAX base station in advance schedules transmission through a flexible frame structure. As a result, the client stations only need to content to when they access the base station for the first time unlike Wi-Fi which has to content every time before transmitting which in turn reduces efficiency. The MAC layer of 802.16 standards support different transport technologies such as Internet Protocol (IP version 4 and 6), Ethernet, and Asynchronous Transfer Mode (ATM). This allows service providers use WiMAX regardless of the transport technology they use. The MAC layer 2
  • 3. also supports Quality of Service (QoS) for base and subscriber stations "through adaptive allocation of uplink and downlink traffic" [1]. The main aim of WiMAX is to replace the wired access networks at the 'last mile' and provide its customers with an easy and efficient broadband experience. In addition, WiMAX is often used in disaster recovery scenes or as a backup where existing network carrier cables have broken down [1]. For example, WiMAX was used to communicate with the victims and support missions in New Orleans during hurricane Katrina and in Indonesia after the recent tsunami. Another intriguing function of WiMAX is providing secure delivery of content to mobile users at vehicular speeds; i.e., a client can access Internet while traveling [6]. This feature only comes with mobile WiMAX. In this project, we would focus our attention on a single fixed WiMAX station proving broadband access to several fixed clients at different distances. 2.2 Video streaming overview Video content are the information provided by various video applications such as newscasts, sports programs and movies that can be stored and viewed later on or live. Since transmitting video content takes a lot of bits, they are broken into a sequence of frames or images, compressed and sent to subscribers which are viewed at a constant frame rate. Due to compression and decompression methods, frame loss up to a certain extent can go unnoticed to the human eye. However, delays or variations in the playback can greatly decrease the quality of the video which leaves the client unhappy. Therefore, video streaming can be considered as a loss-tolerant, delay-sensitive mechanism which has to be carefully balanced to produce quality video at high Signal-to-Noise Ratio levels (SNR). Moreover, video content are characterized by the following parameters: - Video format (the horizontal by vertical pixel resolution) - Pixel color depth (the number of bits/pixel that describes the color of each pixel) - Video coding scheme (the mechanism that compresses/decompresses the video) - Frame inter-arrival rate (the rate at which the frames are received and played back) [3]. Different media uses different video formats and pixel resolutions. A table containing the resolutions and the associated media is shown below [8]: Resolution Video format 350×240 Video CD 330×480 Umatic, Betamax, VHS, Video8 440×480 Analog broadcast D-VHS, DVD, miniDV, Digital8, Digital 720×480 Betacam (pro) 1280×720 D-VHS, HD DVD, Blu-ray, HDV (miniDV) 10,000×7000 IMAX, IMAX HD, OMNIMAX Table 1: Resolution vs. video format 3
  • 4. From the above table, one can see that the number of pixels increases with output quality. Since videos are displayed as a sequence of images, many of these image frames contain spatial (within frame) and temporal (between frames) redundancy. It would cost a lot of memory in order to store all of these frames and thus it appears to be inefficient. As a result, many video coding schemes have been developed to reduce the size video streams by exploiting the redundancies while balancing quality. The most common video codecs are the H.26x standards and the MPEG-x (Motion Picture Exports Group) standards. In this project, we hope to use an MPEG video codec to compress a video stream. The compression and raw data rates of several MPEG codecs are shown in Table 2 below [3]: Codec Raw data rate Compressed rate MPEG-1 30Mbps 1.5Mbps MPEG-2 128Mbps 3-10Mbps MPEG-4 <1.024Mbps Table 2: MPEG-x codec information Video streaming experiences many types of delays while being transmitted from the sender to the receiver. End-to-end delays, propagation delays, processing and queuing delays are the most common types of delays present in video streaming. Later on in this project, we hope to gather statistics of video streaming delays using the Opnet modeler. 3 Opnet Simulation As an initial step, we have designed a simple radio network with a mobile jammer node and two stationary communications nodes as a wireless network. Although, for interim report we have used a preliminary model to create and simulate these scenarios, we hope to create our project using the WiMAX technology and then incorporate it into our project by simulating it using Opnet. The implementation would be very similar to Opnet's wireless tutorial used here as a reference. Figure 1 shows a radio network model created using a transmitter, a receiver, and a jammer node. Figure 1: Node model of the initial network 4
  • 5. The transmitter node model consists of a packet generator module, a radio transmitter module, and an antenna module. The packet generator generates 1024-bit packets that arrive at the mean rate of 1.0 packets/second with a constant interarrival time. After they are generated, packets move through a packet stream to the radio transmitter module, which transmits the packets on a channel at 1024 bits/second using 100 percent of the channel bandwidth. The packets then pass from the transmitter through another packet stream to the antenna module. The antenna module uses an isotropic antenna pattern to apply a transmission gain which is uniform in all spatial directions. The network jammer node introduces radio noise into the network. Like the stationary transmitter node, it consists of a packet generator module, a radio transmitter module, and an antenna module. Its behavior is similar to that of the stationary transmitter node, but channel power and signal modulations are different. These differences will make packets transmitted by the jammer node sound like noise to the receiver. The jammer node model is created from a copy of the transmitter node model. The receiver node consists of an antenna module, a radio receiver module, a sink processor module, and the pointing processor module, which helps to point the directional antenna towards the transmitter [7]. The network needs a trajectory to specify node movement. The node model uses an attribute called trajectory. The value of this attribute is the name of an ASCII text file that is created in the Project Editor. The file contains data specifying times and locations that the mobile node will pass through as the simulation progresses. Figure 2 below shows the created network with its trajectory [7]. Figure 2: Trajectory prediction We have yet to collect statistics and simulate the results of the wireless network and use WiMAX technology in the project editor. Therefore, the final report would contain a modified version of the network module with several clients communicating with a WiMAX base station which is streaming video data. 5
  • 6. 4 Discussion and Conclusion In a nutshell, the goal of this project is to simulate the video traffic representation of video streaming using WiMAX technology. The bandwidth and range of WiMAX make it suitable for many potential applications such as Connecting Wi-Fi hotspots to the Internet, providing data and telecommunications services, providing a source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless Internet connection, especially from unrelated providers, they are unlikely to be affected by the same service outage, providing portable connectivity. This technology has a very broad future and in our project we are also expecting to analyze some factors like throughput, packet loss and packet delay of a subscriber station over a WiMAX access network. Companies are closely examining Wi-MAX for ‘last mile’ connectivity. The resulting competition may bring lower pricing for both home and business customers or bring broadband access to places where it has been economically unavailable. 5 References [1] Z. Abichar, P. Yanlin, and J.M. Chang, "WiMax: The Emergence of Wireless Broadband", IT professional, vol. 8, issue 4, pp. 44-48, July-Aug. 2006. [2] M. Chatterje, S. Sengupta, and S. Ganguly, "Feedback-based real-time streaming over WiMax", IEEE Wireless Communications, pp. 64 - 71, Feb. 2007. [3] W. Hrudey, "Streaming Video Content Over IEEE 802.16 / WiMAX Broadband Access", pp. 7-8, April 2008. [4] "WiMAX”, retrieved 12th February 2009 from http://en.wikipedia.org/wiki/WiMAX [5] S. Ahson, and M. Ilyas (editors), “WiMAX Handbook”, published by Boca Raton, Fla. London: CRC Press, 2008. [6] F. Retnasothie, M. Ozdemir, T. Yucek, H. Celebi, J. Zhang, and R. Muththaiah, “Wireless IPTV over WiMAX: Challenges and Applications”, Wireless and Microwave Technology Conference, WAMICON, pp. 1-5, Dec. 2006. [7] Opnet Technologies 14.0, "Creating a Wireless Network", retrieved 7th March 2009 from Opnet Tutorials. [8] "Image resolution", retrieved 6th March 2009 from http://en.wikipedia.org/wiki/Image_resolution [9] Y. Wang, J. Ostermann, Y. Zhang, "Video processing and communications", Prentice-Hall, pp 446-454, 2002. 6