, pp.38-42 http://dx.doi.org/10.14257/astl.2017.146.08 Differential Detection Method of Upstream Burst Signal in Optic based Cable TV Network Jin Hyuk Song, Dong-Joon Choi and Joon-Young Jung Electronics and Telecommunications Research Institute (ETRI) Daejeon, Korea {song020, djchoi, jungjy}@etri.re.kr Abstract. This paper provides the method in order to detecting upstream burst signal in optic based cable TV network. This method is to use only sign of received signal after ADC (Analog-to-Digital Converter) and performs the differential coding. The experiment results show that the upstream burst signal is correctly detected when the differential detection method is applied. Keywords: Differential detection method, RoIP, RFoG, Upstream, Cable TV 1 Introduction RFoG (Radio Frequency over Glass) architecture [1] is emerged to increase capacity on existing HFC (Hybrid Fiber-Coax) network. It is a technology that can enable FTTH (Fiber-To-The-Home) using DOCSIS (Data Over Cable Service Interface Specification) standard [2, 3] and provides downstream bandwidth upto 1 GHz with distance coverage of about 50 Km. With RFoG architecture, the optical AM (Amplitude Modulation) module converting electrical RF signal into optical signal is required in order to use existing fiber optic network. However, due to the high cost of an optical AM module, it is burden for cable TV SOs to install optical AM module to all subscriber terminal. In recent years, RoIP (Radio over Internet Protocol) system proposed in [4] is not required optical AM module because of transmitting digitized upstream RF signal in contrast with RFoG. An example of RoIP system configuration is described in Fig. 1 of [4] and it is consists of RoIP headend and RoIP terminal. For digitizing, the RoIP terminal has to detect the upstream burst signal and get the acquisition time. In this paper, we propose the differential detection method based on preamble and evaluate performance after applying to hardware. ISSN: 2287-1233 ASTL Copyright 2017 SERSC
2 Proposed Differential Detection Method In this section, the differential detection method based on preamble is proposed. As shown in Fig. 1, this method is to use only sign of received signal and performs the differential coding. Fig. 1. The proposed differential detection method. r[ First, the sign of the received signal after ADC (Analog-to-Digital Converter) is determined according to whether positive or negative and it can be represented as following equation. 0, r[ 0, r '[ (1) 1, r[ 0, where r '[ is the binary signal after making a decision. By doing this, the upstream burst signal can be detected regardless of the amplitude and the hardware complexity is reduced since it is possible to bitwise operation. After decision, the differential coding is performed as follows ' r [, n 0, d [ (2) ' ' r [ r [ n 1], n,1 where d [n ] is differential coded signal and denotes modulo-2 sum. The initial value of d [n ] is r '[0 ]. Results of differential coding, the proposed method is robust to frequency offset. The differential coded signal is correlated with pre-coded preamble which is associated with IUCs (Interval Usage Codes). If the values of preamble are different in accordance with IUCs, correlation are processed in parallel. Finally, each result of correlation compares threshold value and, if it is exceeded, the upstream burst signal is detected. Copyright 2017 SERSC 39
3 Real-time Experiment Environments and Results Real-time experiment is performed to verify the detection of the upstream burst signal and environments are summarized in Table 1. Four types (the number of IUCs is 1, 3, 4, 9) of preamble patterns are used and each length are 64, 640, 384, 104. Figure 2 shows that real-time experiments are performed by distributing upstream burst signal between commercial devices using a splitter. Table 1. Experiment environments parameters. DOCSIS parameters Bandwidth Symbol rate Master clock Preamble pattern Modulation order Experiment parameters CMTS CM Value 6.4 MHz 5.12 Msps 10.24 MHz 4 types QPSK - preamble QPSK, 64QAM - data Value Cadant C3 made by ARRIS BRG-35503 made by SSANGYONG Fig. 2. The real-time experiment using HW platform and commercial devices. Figure 3 illustrates the result of correlation with preamble according to IUC type when upstream burst signal is received. As applying the proposed method, the correlation value of IUC type 4 exceeds the threshold at approximately 1600 sample points. That is, the upstream burst signal of IUC type 4 is detected. Finally, the actual captured signal is plotted in Fig. 4. As expected, it can be confirmed that the burst signal exists and starts at approximately 1600 sample points. 40 Copyright 2017 SERSC
4 Conclusion In this paper, we propose the differential detection method based on preamble, and then evaluate performance after applying to hardware with commercial devices. The proposed method can use regardless of the received signal amplitude while reducing hardware complexity. Also, it is robust to frequency offset. The real-time experiment results showed that the upstream burst signal is correctly detected when the differential detection method is applied. Fig. 3. The result of correlation with preamble according to IUC type. Fig. 4. The actual captured signal of IUC type 4. Acknowledgments. This work was supported by Institute for Information & communications Technology Promotion(IITP) grant funded by the Korea government(msip) (No. 2017-0-00299, Development of Inband Full Duplex Transceiving Technology in Cable TV networks for Multi-giga Service). Copyright 2017 SERSC 41
References 1. J.O. Farmer: RFoG - Foggy, or real?. In: Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, pp. 1--3. (2011) 2. Data-Over-Cable Service Interface Specification, MAC and Upper Layer Protocols Interface Specification DOCSIS 3.0. CM-SP-MULPIv3.0-I27-150528 (2015) 3. Data-Over-Cable Service Interface Specification, Physical Layer Specification DOCSIS 3.0. CM-SP-PHYv3.0-I12-150305 (2015) 4. J.Y. Jung, D.J. Choi, and H.M. Kim: Radio over Internet Protocol Transmission in Optic based Cable TV Networks. In: 7th International Conference on Consumer Electronics-Berlin (ICCE-Berlin), pp. 296--297. (2017) 42 Copyright 2017 SERSC