Design of Out-of-Band Protocols to Transmit UHDTV Contents in the CATV Network ()
1. Introduction
The advance of television technologies introduces new services, such as High-Definition TV (HDTV), 3DTV, IPTV, and Smart TV. Furthermore, the requirements of audiences that is to use high-quality TV contents lead to the development of an Ultra High-Definition TV (UHDTV) [1-5]. The UHDTV is a digital video format that has 3840 × 2160 (4 K) or 7680 × 4320 (8 K) pixel resolutions, which are 4 or 16 times larger than 1920 × 1080 (2 K) pixel resolution of the standard full HDTV, respectively. The large pixel resolution of the UHDTV content requires a large screen size and a frame rate. The commercial version of the screen is between about 350 and 600 inches (889 to 1524 centimeters) in size. The frame rate is 30 or up to 60 FPS (Frame per second), more than that of the standard HDTV, 24 FPS. As the pixel resolution, the luminance resolution, and the frame rate are larger, the UHDTV requires a very high data transfer rate. The data rates required for 4 K UHDTV and 8 K UHDTV contents are about 5 Gbps and 20 Gbps, respectively. Although a codec that compresses 100 times is used, the required data rates are 50 Mbps and 200 Mbps.
A digital cable TV (CATV) uses Quadrature Amplitude Modulation (QAM) for broadcast video services. After receiving of video contents from video servers, a headend modulates them through QAM transmission devices. Modulated video contents are transmitted to a broadcast receiving device of a subscriber (e.g., a set-top box) through a transmission channel (QAM channel) predetermined for the video broadcast content stream. The standard in the United States provides both 64-QAM and 256-QAM for a signal transmission over digital cable television systems. This method carries 38.47 Mbps using 256-QAM on a 6 MHz channel. Since 2009, 1024- QAM and 4096-QAM have been proposed and developed in order to increase the transmission efficiency and to transmit a large capacity data [6-8]. The data rate of 1024-QAM and 4096-QAM are about 50 Mbps and 80 Mbps, respectively.
A current digital CATV system assigns one QAM channel for an individual video content stream. As the data rate of UHDTV contents is about 200 Mbps as described above, one QAM channel is not sufficient to transfer UHDTV contents. When a 1024-QAM is used, a 4 K single program transmission stream (SPTS) may be transmitted through a single transmission channel, whereas 4 K multiple program transmission stream (MPTS) may not be transmitted. Furthermore, 8 K video broadcast contents may not be provided through a single QAM channel although 1024-QAM or 4096-QAM is used. In order to provide peak data rates in excess of 50 or 80 Mbps to customers, UHDTV contents are dynamically distributed over a set of transmission channels for delivery to a single user. For example, to transfer an 8 K UHDTV video content, four 1024-QAM channels or three 4096-QAM channels are required.
The focus of this paper is on transmitting 8 K UHDTV contents through a set of QAM channels. For the purpose of this paper, we apply a channel bonding mechanism to transporting UHDTV contents in the CATV network. Channel bonding introduced by the Data over Cable Interface Specification (DOCSIS) 3.0 standard [9] is a principle that combines multiple channels to carry one data stream, and refers to the ability to schedule packets for a single service flow across those multiple channels. The aim of channel bonding is to offer significant increases in the peak data rate that can be provided to a single subscriber. However, the channel bonding is suggested for data services in a DOCSIS network, not for video broadcast services in a CATV network. So, the ultimate goal of this paper is to design new protocols to transmit UHDTV contents in the CATV networks by using the channel bonding.
In this paper, we propose two protocols to transmit UHDTV contents in CATV networks: 1) an Out-of-Band (OOB)-based protocol and 2) a DOCSIS Set-Top Gateway (DSG)-based protocol. The current headend system and set-top boxes use the OOB protocol [10-12] or the DSG protocol [13] as a signaling protocol. In order to minimize the overhead of changing protocols used in the current CATV network and provide the simplicity of applying, this paper proposes protocols based on the OOB protocol or the DSG protocol. We design the OOBbased protocol such as a short term solution to be well adoptable to traditional CATV networks because most of traditional CATV networks use the OOB protocol. On the other hand, to use the DSG protocol requires that a headend and a set-top box provide DOCSIS functionalities. We design the DSG-based protocol for a long term solution as current CATV networks are being equipped with DOCSIS functional modules.
We design network architectures and signaling messages to support channel bonding process. A headend and a STB share the signaling information of bonding channels by signaling messages. Also we propose the process of the set-top box. We make a protocol simulator based on the OPNET and analyze the performance of proposed protocols.
The rest of the paper is organized as follows. In Section 2, this paper provides background information on a channel bonding mechanism, the OOB protocol and the DSG protocol. I design network architectures and protocols in Section 3. Section 4 describes to make an OPNET simulator and to analyze the performance of the protocol. In Section 5 this paper makes the conclusion.
2. Related Works
2.1. Channel Bonding Mechanism
The channel bonding mechanism is a logical process that separates one higher-speed data stream into multiple data packets sent though multiple independent channels, and combines data packets received on multiple independent channels into one higher-speed data stream. An example of the deploying of the channel bonding mechanism in order to transfer 200 Mbps UHDTV contents is as shown in Figure 1. By a 1024-QAM device, the data rate of each channel is 50 Mbps. A 200 Mbps stream is transmitted on a set of four 1024-QAM channels.
2.2. OOB Protocol
The OOB protocol is one of the out-of-band signaling protocol which is specified for transmission of a signaling information in the cable networks. The primary function of the OOB protocol is to establish and maintain an OOB channel that carries signaling messages for exchanging of the signaling information. A network using the OOB protocol consists of a control server, a headend, and STBs. The control server (e.g., a video server or a STB control server) generates control information and frames to maintain Conditional Access System (CAS)/Electronic program guide (EPG)/STB systems. A headend makes OOB messages from signaling information received from control servers, modulates them by using QPSK scheme, and sends modulated frames to STBs on OOB channels.
2.3. DSG Protocol
The DSG specification defines an interface and associated protocol that introduces additional requirements on a DOCSIS CMTS and DOCSIS CM to support the configuration and transport of out-of-band messages between a Set-top Controller (or application servers) and STBs. Like the OOB protocol, the DSG uses a dedicated channel for signaling which is separated from the video channels.
A DSG system physically consists of set-top controllers, CMTSs located in distribution hubs or headends, and set-top devices located in the subscriber’s home.
Figure 2 shows the logical diagram of a DSG system. Out-of-band messages are generated by a DSG server, passed through the DSG agent, and terminated at the DSG client. A DSG channel and a DSG tunnel within a DSG channel are established and maintained for transfer of out-of-band messages between a DSG agent and a DSG client.