A data over cable service interface specification (DOCSIS) standard defines a protocol, and the protocol manages transmission of data in a hybrid fiber coaxial (HFC) network. FIG. 1 describes a higher layer architecture of a coaxial network. The coaxial network mainly includes two types of devices: a cable modem termination system (CMTS) and a cable modem (CM). The CM is a cheap device deployed on a user side on a large scale and used by a user for accessing a network, and the CMTS is an expensive and large device with a complex structure and deployed in a cable operator equipment room. A data link from the CMTS to the CM is referred to as a downlink, and a data link from the CM to the CMTS is referred to as an uplink. The following uses an uplink as an example for description.
Generally, data may be interfered by various noise signals after passing through a channel, and these interference signals may be mixed with received signals. To improve quality of the received signals, a receive end needs to perform a series of synchronization operations to compensate for the interference signals. Therefore, when the CM just accesses the HFC network, the CMTS needs to estimate and compensate for some physical-layer parameters, such as a symbol timing error, a carrier frequency error, and channel attenuation. FIG. 2 describes a structure of an uplink burst packet in a DOCSIS single carrier modulation system. The burst packet includes two parts: a known preamble sequence and load. The CMTS uses the preamble sequence to perform synchronization to complete estimation of the symbol timing error, estimation of the carrier frequency error, and the like. The load after the preamble sequence is useful data sent by the CM.
FIG. 3 describes a design manner of a preamble sequence used for frequency offset estimation in the prior art. The preamble sequence includes multiple repeated cycle subsequences, each with a length of M.
Generally, micro-reflection also exists on uplink and downlink channels, and may result in a multipath effect for an uplink transmission signal and a downlink transmission signal. However, a preamble sequence in the prior art has no anti-multipath interference performance. This causes great difficulties for a receive end to estimate a carrier frequency error, and an obtained frequency offset estimation value has a relatively large error.
USPTO Backgrounds
USPTO Backgrounds