Cross-Layer Optimized Architecture of MBS over Mobile WiMAX

Transcription

1 Cross-Layer Optimized Architecture of MBS over Mobile WiMAX Joohan Lee, Juho Lee, Sungkwon Park* Department of Electronics and Computer Engineering Hanyang University Seoul, Republic of Korea ABSTRACT: Mobile WiMAX access network is being developed to support various multimedia services such as mobile Internet Protocol Television (IPTV), mobile Video-on-Demand (VoD), and mobile Internet services. In multimedia systems, one of the major challenges is how to reduce a channel change response time. In order to solve this problem, many methods have been proposed. In this paper, we propose Cross-Layer Optimization and System Architecture of Multicast Broadcast Service (MBS) over mobile WiMAX. Proposed method reduces the channel change response time efficiently as viewers watch mobile IPTV channels without IGMP join process when those are shared. Simulation results show that the channel change response time is significantly decreased compared to the existing MBS architecture. Keywords: Component, Mobile WIMAX, MBS, Mobile IPTV, Channel Change Response Time Received: 24 January 2015, Revised 22 February 2015, Accepted 2 March DLINE. All Rights Reserved 1. Introduction The IEEE std e working group developed the mobile Worldwide Interoperability for Microwave Access (mobile WiMAX) which provides a wireless solution in the metropolitan area access networks. The WiMAX is capable of wide range coverage, high data rates, secured transmission and mobility supported at vehicular speeds. It also supports Multicast and Broadcast Service (MBS). The concept of MBS is defined in IEEE e standard [1] which supports mobility. This is a downlink point-to-multipoint service in which a common set of multimedia data packets are transmitted with coordination from one or more Base Stations (BSs) to multiple terminals in the designated MBS service area. The attributes of MBS refer to efficient mechanisms transmitting same data to multiple users using shared system resources. The mobile IPTV viewers must endure several milliseconds of the channel change response time when they change channels, i.e, time for IGMP join/leave delay and MBS configuration. Channel change response time is considered to be one of the most important parts of IPTV QoE. Particularly, IGMP join/leave delay is the main source of channel changing delay. Journal of Networking Technology Volume 6 Number 2 June

2 In the multicast transmission zone, all Subscriber Stations (SSs) can receive both the multicasting channel they requested and other channels they did not request. In other words, if a viewer is joining a specific multicast group, other viewers in the same multicast zone also can receive the channel at the same time, even though they did not join the same specific multicast group. This paper proposes new MBS method for mobile IPTV using the sharing property of wireless networks. This new method allows viewers to change channels immediately without IGMP join/leave process. This paper is organized as follows. We briefly introduce about some related works in Section 2. Section 3 presents the proposed architecture in detail. Performance analysis and results are presented in Section 4. Finally, a conclusion is given in Section Related Work 2.1 MBS Architecture MBS may be deployed to deliver local, regional, or national multimedia content to users across a large network in which cell sizes, frequency reuse, and user s mobility may widely vary. The MBS content may be delivered as real-time streaming or non real-time and prescheduled transmissions. Figure 1 depicts the content distribution architecture overview for MBS services. The MBS content channels are typically transmitted to a geographic area called the MBS transmission zone, which may consist of one or more MBS zones. Each MBS zone consists of one or more BSs. The MBS transmission zones are configured independently based on target service areas for each content channel or groups of channels, for example, at local, regional, and national levels. The MBS transmission zone, therefore, may be overlapping for different programs/contents. The data transport between the MBS controller/server to the MBS zone is through IP multicasting. The network should be able to deliver MBS data to all subscribed MSs concurrently with their unicast services and even when the MS is in its power saving modes. The MS should also receive incoming call/service notification while receiving MBS programs. Once subscribed and provisioned with target channels, the MS should only need minimal or no interaction with BS/ network for channel switching among those channels while moving within a MBS zone. Even across MBS zones, the network may provide the MB with MBS configuration information of neighboring zones such that the MS does not need to request this information upon entry to the new zone. Figure 1. Network architecture for MBS services 52 Journal of Networking Technology Volume 6 Number 2 June 2015

3 The MBS user should also be able to receive or reject his or her subscribed MBS program while at home or roaming. The network provides the means for program discovery and initial acquisition of service information, including a program/content guide, as well as MBS access and acquisition information. The system should also support MS- or network-initiated activation of additional MBS channels/services while delivering the current MBS and/or unicast data. The key functional elements in the reference network architecture described below; MBS Content Server. The MBS content server is used to store the contents of MBS services and provide the contents to the MS. MBS Controller/Server. The MBS controller/server is a logical network entity that manages the MBS services in the NSP domain. It includes service-guide construction and distribution, and application-layer security management to ensure that the content can be viewed only by the authorized users and to manage the program and IP multicast groups. MBS Client. The MBS client function is located at the MS and it complies with the IEEE e standard to receive the data and control information through the air interface. The MBS client function also supports the IP multicast based on the IPv4 and IPv6 stack, and all other upper-layer functions that ensure the MS can receive and display the MCBCS contents properly. 3. Cross-layer Optimized Architecture of MBS In this Section, we propose a cross-layer optimized MBS structure that effectively achieves reducing channel change response time in multicast multimedia over WiMAX. The proposed cross-layer optimized architecture is shown in Figure 2. Mobile WiMAX access network is a shared radio medium. In other words, all SSs in the same multicast transmission zone receive all shared channels whatever they requested or not. The key idea of our proposed architecture is reducing Channel Change Response Time using the sharing property of WiMAX. In the proposed enhanced architecture, it simplifies the Multicast Connections and CID filtering process at PHY layer. Figure 2. Basic operation of Proposed MBS architecture 3.1 MBS Channel Mapping Table To watch shared contents which are streamed to SSs in the same multicast transmission zone without these procedures and MBS configuration, SSs need those each layers information in advanced. In the proposed MBS architecture, it uses the MBS Channel Mapping Table. BSs make the MBS Channel Mapping Table and broadcast it to all SSs on broadcast CID. SSs receive the first MBS Channel Mapping Table, when they are authenticated by the BS they belong to for IPTV services. The MBS Channel Mapping Table consists of Channel ID, Multicast CID (MCID), OFDM Sub-channel elements. The Channel ID is the name of the contents which are shared in the cell which the SS belongs to. MCID is the assigned CID corresponds to the each multicast content for multicast connection at MAC layer. And OFDM subchannel element is DL sub-frames information of OFDM frames correspond to MCID. Journal of Networking Technology Volume 6 Number 2 June

4 Channel ID MCID OFDM subchannel 037 0x0F x5E xB Table 1. MBS Channel Mapping Table 3.2 Operation of the proposed MBS with Channel Mapping Table Figure 3 is an illustration of the operation flow chart of the proposed MBS. We assume that the MBS Channel Mapping Table is already made by BS and broadcasted to all SSs on broadcast CID. To change channels, the following steps are involved. 1. When a viewer (SS) wants to change the channel (press the button on remote controller), the SS does not do DSA/DSC procedure and IGMP join message procedure. It looks up the Channel ID in the MBS Channel Mapping Table and checks the corresponding content in MBS Channel Mapping Table for checking wanted content is being shared or not. 2. If wanted content is shared (i.e., corresponding Channel ID exists in the MBS Channel Mapping Table), the SS establish a multicast connection with a corresponding content MCID without DSA/DSC procedure at MAC layer and a IGMP Join/Leave procedure. And the SS also gets OFDM sub-channel elements of the corresponding content to skip CID filtering procedure. Using OFDM sub-channel elements, the SS is able to listen to the wanted content s DL sub-frames without CID filtering. Figure 3. Procedure of channel change in the proposed MBS structure 54 Journal of Networking Technology Volume 6 Number 2 June 2015

5 3. If wanted content is not being shared (i.e., corresponding Channel ID does not exist in the MBS Channel Mapping Table), the SS joins a multicast group by sending an IGMP Join message to ASN-GW. When the BS receives new multicast stream which has not received yet, updates the MBS Content Table by adding new Channel ID, MCID, OFDM sub-channel element of the multicast stream. And the BS broadcasts the updated MBS Channel Mapping Table to all SSs with a broadcast CID. After the SS establishes a multicast connection which corresponds to MCID, it receives all OFDM DL frames and filtering DL sub-frames which correspond to MCID. 3.3 Multicast Connection The key idea is to perform an assigning multicast CID from the MBS Channel Mapping Table. Instead of sending DSA/DSC messages, SSs can establish Multicast Connection which corresponds to MCID by using the MBS Channel Mapping Table. The procedure for Multicast Connection is shown in Figure 9, and it can be summarized as follows: 1. The SS joins a multicast group by sending the IGMP Join message to the ASN-GW. 2. The ASN-GW stores the multicast IP address, MAC address of the BS which covers the SS which requests the multicast. 3. The multicast stream is sent by the multicast Router. 4. If the multicast stream address exists, the ASN-GW delivers the multicast stream of which the destination address is the multicast IP address. 5. When the BS receives the multicast stream from the ASN-GW, updates Content Table by adding new multicast stream with new Channel ID, MCID, OFDM sub-channel element. And the BS broadcast the updated MBS Channel Mapping Table to all SSs with a broadcast CID. 6. The SS receiving the updated MBS Channel Mapping Table, establishes a multicast connection with a corresponding MCID, receives all OFDM DL frames and filtering DL sub-frames which correspond MCID. 4. Performance Analysis The proper modeling of the distribution of user s interest in various contents and media in the system is a key building block for system design and performance analysis. We now present a model for channel popularity. We use Zipf-like model to capture the long term channel popularity distribution among different channels and mean reversion model to capture the stochastic process of popularity fluctuation for individual channels. We naturally model it using Zipf-like distribution. Where f i = 1/i θ, and θ is a parameter that specifies the skew factor. In the Zipf-like distribution, an object of the rank f i has the access probability of C f i, where C =1/Σ Ν i = 1 f is a normalization i constant, N is the total number of channels. In this simulation, we assume that the number of channels is 150 and i is sorted by channel popularity. The most popular channel has index 1 and the less popular channel has index N. The cumulative distribution function of equation (1) is P I (i) = f i Σ Ν f i, for i = 1, 2,..., N, (1) i = 1 P{0 < I < N} = Ν P I (i) d i = 1 (2) 0 When the skew factor is 1 and the number of channels is 150, the event P{0 < I < 10}, is about 79%. P{0 < I < 15} is about 83% and P{0 < I < 20} is about 86%. Let us assume that C shared is a set of channels are being shared in a service node and c select is the next channel a viewer wants to watch. The channel duplication probability is defined as the probability that viewer s next channel c select is already included in Journal of Networking Technology Volume 6 Number 2 June

6 Figure 4. Channel popularity of on subscriber Figure 5. CDF of channel popularity C shared set. We shall repeat the experiment M times and determine the probability that c select C shared is observed exactly r times out of the independent M trails. The probability of immediate channel changing is equation (3). P{c select C shared } = C r M p r (1 p) M r (3) 56 Journal of Networking Technology Volume 6 Number 2 June 2015

7 5. Conclusion The issue of providing multimedia service through IP multicast method using radio access resources such as WiMAX is concerned about to reduce the viewer s waiting time when they change channels. Mobile WiMAX access network is a shared radio medium. In other words, all SSs in the same multicast transmission zone receive all shared channels whatever they requested or not. Therefore, we have proposed the Cross-Layer Architecture MBS method for IPTV services which allows immediate channel switching. In the newly proposed MBS method, we use the MBS Channel Mapping Table. The MBS Channel Mapping Table consists of Content ID, Multicast CID (MCID), OFDM Sub-channel elements. When the wanted content is being shared, the enhanced MBS system allows immediate channel changing without obtaining MCID in MAC layer, IGMP Join/Leave process in Network layer and CID filtering process in PHY layer. Simulation result shows that the multicast group Join/Leave message delay of the channel change response time is decreased significantly compared to the existing MBS in case of the channel is already shared in the same MBS multicast zone. Acknowledgment This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the C-ITRC(Convergence Information Technology Research Center) (IITP-2015-H ) supervised by the IITP(Institute for Information & communications Technology Promotion) References [1] IEEE IEEE Std e-2005: IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2 : Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, Feb [2] Lee, J., Park, H., Choi, S., Choi, J. (2009). Adaptive Hybrid Transmission Mechanism for On-Demand Mobile IPTV over WiMAX, IEEE Transactions on Broadcasting, 55 (2), June. [3] Liao, N., Shi, Y., Chen, J., Li, J. (2009). Optimized Multicast Service Management in a Mobile WiMAX TV System, IEEE. [4] Cho, C., Han, I., Jun, Y., Lee, H. (2004). Improvement of Channel Zapping Time in IPTV Services Using the Adjacent Group Join-Leave Method, The 6 th International Conference on Advanced Communication Technology. [5] Eunjo Lee., Sungwkon Park. (2010). Internet Group Management Protocol for IPTV Services in Passive Optical Network, IEICE Transactions on Communications Journal of Networking Technology Volume 6 Number 2 June