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Carrier Frequency Offset Estimation in Frequency
Domain for DOCSIS 3.1 Uplink System
Kwanwoong Ryu1, Haechan Kwon1 and Joon-Young Jung1
1 Electronics and Telecommunications Research Institute,
Daejeon, Korea
{kwryu0730, khc1201,jungjy }@etri.re.kr
Abstract. We present an efficient carrier frequency offset (CFO) estimation
algorithm in frequency domain for DOCSIS 3.1 Uplink System. After
performing the CFO algorithm in time domain for DOCSIS 3.1 Uplink receiver,
the residual CFO can be remained. The residual CFO is degraded performance
of the system. To correct residual CFO, we propose CFO algorithm in
frequency domain using pilot and complimentary pilot in DOCSIS 3.1 Uplink
System. The simulation results show that the proposed CFO algorithm is
significantly reduced residual CFO.
Keywords: CFO, DOCSIS 3.1
1 Introduction
Data-Over-Cable Service Interface Specification (DOCSIS) is a global standard for
cable communication systems [1]. The DOCSIS 3.1 specifications introduce a number
of advancements, including: orthogonal frequency division multiplexing (OFDM) to
improve network flexibility and utilization; large channel sizes (up to 192 MHz) to
improve cost effectiveness at higher bandwidths; low density parity check (LDPC)
FEC to improve performance; and adaptive modulation to adjust to different network
conditions.
In upstream channel, DOCSIS 3.1 occupies a bandwidth of 96 MHz. There are two
modes of operation for a DOCSIS 3.1 OFDM system depending on the size of the fast
Fourier transform (FFT) operation: 2048 (2K) and 4096 (4K) modes. Note that in this
example, the system operates in the 4K mode. There are a total of 4096 subcarriers
inside the channel and the spacing between two adjacent carriers is 25 kHz. This
spacing between subcarriers is different but fixed for each mode: it is 25 kHz in the
4K mode and 50 kHz in the 2K mode. DOCSIS 3.1 also supports high-order
modulation schemes of up to 4096 QAM, and therefore theoretically can provide up
to 10 Gbits/s downstream and 1 Gbits/s on the upstream.
In this paper, we consider CFO estimation in frequency domain for residual CFO
correction after CFO estimation in time domain. Although there have been many
studies on the topic of CFO estimation based on OFDM, none of the existing methods
are not directly applicable to DOCSIS 3.1 systems [2]-[3]. Therefore, the main
objective of this research is to develop effective residual CFO estimation algorithms
Advanced Science and Technology Letters Vol.146 (FGCN 2017), pp.60-63