This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2009-0127729, filed on Dec. 21, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to scattered pilot technology for efficient carrier frequency synchronization in a communication system based on MF-TDMA.
2. Description of the Related Art
DVB-RCS establishes a network through a communication repeater installed in a satellite for data communication in a MPEG2 format. Satellite communication is generally classified into DVB-RCT, DVB-RCS, etc. RCT (Return Channel via Terrestrial) uses a terrestrial network to achieve a reverse link and RCS (Return Channel via Satellite) achieves a reverse link via a satellite. Main Examples of a method of using a terrestrial network includes a method of using PSTN and a method of using Cable and ADSL, and RCS performs direct transmission/reception with a satellite at the position of a subscriber.
Environment of a receiving side in satellite communication has the limitation to power and an antenna size. At the same time, in most of the latest communication standards, it is required that an antenna size be reduced and operation be possible even in a low SNR environment to improve power efficiency. However, a bust structure in DVB-RCS which is a related art has an inserted preamble and remarkably low carrier frequency estimation accuracy in low SNR environment. Therefore, a current DVB-RCS burst structure using a preamble is inadequate to frame structures for the next-generation DVB-RCS standards.
In a burst structure in the DVB-RCS standard based on MF-TDMA according to the related art, there exist four kinds of bursts which includes TRF (Traffic) bursts for information transmission shown in
Here, Lpre represents the length of a preamble, c represents a code rate, n represents the number of ATM cells or MPEG blocks, and the length of a burst is expressed in bytes.
A pilot symbol is used for preamble detection and phase and frequency synchronization. The phase and frequency synchronization is generally divided into coarse frequency synchronization and fine frequency synchronization. The coarse frequency synchronization uses the correlation between a received signal and a preamble. In the coarse frequency synchronization, an estimation limit according to SNR is determined by the Cramer-Rao bound. In a case of using a preamble, a burst has a structure as shown in
When a preamble is used, in the coarse frequency synchronization, an estimation limit according to SNR is determined by the Cramer-Rao bound as expressed in following Equation 1.
In Equation 1, Lpre represents the length of a preamble.
When a preamble is used, the Cramer-Rao bound according to the value of Lpre is shown in
In order to solve the above-mentioned problem, it is an object of the present invention to create a burst structure adequate to the next-generation DVB-RCS standards, to improve the accuracy of carrier frequency estimation in a low SNR environment, to make an operation using a small antenna possible, and to improve power efficiency.
The object of the present invention is not limited to the above-mentioned objects but other objects will be apparent to those skilled in the art from the following description.
According to an aspect of the present invention, it is provided a transmitting method of a DVB-RCS (Digital Video Broadcasting-Return Channel via Satellite) system including: generating a burst by scattering a plurality of pilot symbols; and transmitting the burst.
According to another aspect of the present invention, it is provided a receiving method of a DVB-RCS (Digital Video Broadcasting-Return Channel via Satellite) system including: receiving a burst having a plurality of pilot symbols scattered; and extracting the plurality of pilot symbols from the burst and performing synchronization.
According to a further aspect of the present invention, it is provided a transmitter of a DVB-RCS (Digital Video Broadcasting-Return Channel via Satellite) system including: a burst generating unit configured to generate a burst by scattering a plurality of pilot symbols; and a transmitting unit configured to transmit the burst.
According to a still further aspect of the present invention, it is provided a receiver of a DVB-RCS (Digital Video Broadcasting-Return Channel via Satellite) system including: a receiving unit configured to receive a burst having a plurality of pilot symbols scattered; and a synchronizing unit configured to extract the plurality of pilot symbols from the burst and perform synchronization.
The details of embodiments are included in the specification and drawings.
According to embodiments of the present invention, it is possible to solve the problem in the related art that the accuracy of carrier frequency estimation in a low SNR environment is remarkably low.
Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
A transmitter, a transmitting method, a receiver, and a receiving method for a communication system according to embodiments of the present invention will be described. A transmitter, a transmitting method, a receiver, and a receiving method for a communication system described below may be applied to a satellite communication system, such as VSAT (Very Small Aperture Terminal) and DVB-RCS, as well as a general communication system.
A transmitter, a transmitting method, a receiver, and a receiving method for a communication system according to embodiments of the present invention will be described with reference to
A transmitter 100 according to an embodiment of the present invention generates a burst by scattering a plurality of pilot symbols to 0 to Lp-1, as shown in
Since there is a difference in the phase and frequency synchronization performance between the transmitter 100 and the receiver 200 according to how the transmitter 100 disposes scattered pilots, and adding a pilot may cause overhead of data, it is preferable to improve the phase and frequency synchronization performance and minimize overhead of data. Therefore, it is possible to determine optimal number and optimal positions of scattered pilots through performance evaluation. A transmitter and a transmitting method according to specific embodiments of the present invention will be described below with reference to
As shown in
As shown in
As shown in
As shown in
According to the above-mentioned embodiments, it is possible to improve the accuracy of carrier frequency estimation in the receiver 200 and to improve phase and frequency synchronization performance between the transmitter 100 and the receiver 200.
The results of a performance test on some of the above-mentioned embodiments will be described below with reference to
First, if a number of pilot symbols are divided into two groups (Lp=2) and the groups are positioned in a preamble and a postamble of a burst, respectively, as shown in
Here, Np represents the length of a pilot and N, represents the length of data.
If pilot symbols are uniformly scattered in a burst as shown in
Therefore, when the number of pilot symbols is 32, a format as shown in
(16, 0, 16) of
If comparing
Meanwhile, in the above-mentioned scattered pilot techniques, the length of pilot symbols, the number of scattered pilot groups, the size of data, and the like influence the phase and frequency synchronization performance. Also, since overhead according to pilot insertion reduces a data rate and data throughput, the scattered pilot techniques can be applied considering a trade-off therebetween. Therefore, the transmitter 100 may generate any one burst of the burst structures shown in
The receiver 200 may extract the pilot symbols from the transmitted burst according to the information on the arrangement of scattered pilot symbols in the burst, and estimate the carrier frequency or perform synchronization. For example, the information on the arrangement of scattered pilot symbols may exist in a preamble in the burst. Alternatively, the information on the arrangement of scattered pilot symbols may be transmitted to the receiver 200 as a separate signal. The receiver 200 may obtain information on the arrangement of scattered pilot symbols according to various other conditions.
A transmitter and a receiver of a communication system according to other embodiments of the present invention will be described below in detail with reference to
Referring to
The burst generating unit 110 generates a burst by scattering a number of pilot symbols. For example, the burst generating unit 110 may generate a burst having any one of the burst structures shown in
Here, the burst generating unit 110 may insert information on the arrangement of scattered pilot symbols to the burst. For example, the burst generating unit 110 may insert the information of the arrangement of scattered pilot symbols to a preamble of the burst.
Referring to
The receiving unit 210 receives the burst transmitted from the transmitter 100 of
The synchronizing unit 220 may extract a number of pilot symbols from the received burst and estimate the carrier frequency or perform synchronization. At this time, the synchronizing unit 220 may extract a number of pilot symbols from the burst according to the information on the arrangement of scattered pilot symbols inserted in the burst. The synchronizing unit 220 may obtain the information on the arrangement of scattered pilot symbols from the preamble of the burst. Alternatively, the synchronizing unit 220 may obtain the information on the arrangement of scattered pilot symbols according to a protocol employed for communication between the transmitter 100 and the receiver 200. The synchronizing unit 220 may also obtain the information on the arrangement of scattered pilot symbols according to various other conditions.
Although the embodiments of the present invention have been described above with reference to the accompanying drawings, they are used in a generic and descriptive sense only and not for purposes of limitation. It will be apparent to those skilled in the art that modifications and variations can be made in the present invention without deviating from the spirit or scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
10-2009-0127729 | Dec 2009 | KR | national |