Zero-CP OFDM for DOCSIS-Based CATV Networks

• Published in: IEEE transactions on broadcasting Vol. 65; no. 4; pp. 727 - 741
• Main Authors: Nguyen, Tung T., Nguyen, Ha H., Eric Salt, J., Berscheid, Brian
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-12-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidth; Cable modems; Cable TV; Constellations; cyclic prefix; Digital filters; DOCSIS; DOCSIS 3.1; equalization; OFDM; Orthogonal Frequency Division Multiplexing; Transceivers
• ISSN: 0018-9316; 1557-9611
• DOI: 10.1109/TBC.2019.2904853

The current version of the data over cable service interface specification (DOCSIS), which is DOCSIS 3.1, is markedly different from previous versions in that orthogonal frequency-division multiplexing (OFDM) is used together with high-density QAM constellations (up to 4096-QAM) in both the downstream and upstream directions to facilitate high data rates. This is in a sharp contrast with the single-carrier modulation techniques used in prior versions of DOCSIS. Despite many advantages, a drawback of OFDM is the insertion of a cyclic prefix (CP) at the beginning of each transmitted OFDM symbol to mitigate inter-symbol interference (ISI). The CP, which is configurable, but can be as large as 25% of the symbol time for DOCSIS 3.1 downstream transmission, does not carry useful data and therefore reduces the overall transmission throughput. In general, not only the channel but also the transceivers' digital filters determine the ISI and therefore the length of the CP. In this paper, the aspects that determine the CP length are thoroughly addressed. A novel technique to eliminate the CP is introduced and analyzed. It is demonstrated that the CP can be completely removed with a negligible effect on the transmission performance using this technique. Moreover, the proposed technique requires only a modest amount of hardware, making it a promising candidate to be included in the a future version of DOCSIS.