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Telecommunications

Patent Issued for Wireless Transmission System, Receiver , and Method for Removing Inter-Carrier Interference

2012 JUL 25 (VerticalNews) -- By a News Reporter-Staff News Editor at Telecommunications Weekly -- A patent by the inventors Hsu, Jen-Yuan (Kinmen County, TW); Wang, Lai-Huei (Taoyuan County, TW); Lai, Jiun-Yo (Taichung, TW); Ting, Pang-An (Taichung County, TW), filed on October 1, 2008, was cleared and issued on July 10, 2012, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8218695 is assigned to Industrial Technology Research Institute (Hsinchu, TW).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The invention relates in general to a method for estimating and removing inter-carrier interference (ICI), and more particularly to a lowly complicated method for estimating and removing ICI on a time domain.

"In recent years, orthogonal frequency division multiplexing (OFDM) communication technology has been widely used in communication system. In order to transmit data under wireless channel environment, the symbol time is prolonged, and a cyclic prefix (CP) is added to resolve the multi-path delay spread of wireless channel. However, when the symbol time is longer, the system becomes very sensitive to carrier frequency deviation. In a moving environment, the wireless channel environment is time-variant. When the speed is too high, the wireless channel becomes not fixed within a symbol time. Furthermore, the time-variant channel will damage symbol orthogonality, generate Doppler spread in frequency domain and incur inter-carrier interference (ICI) at the receiving end.

"Many methods for removing ICI have been provided to resolve the above ICI problem. These methods are mainly divided into two categories. The category I methods remove ICI for a symbol in two stages. Stage I is mainly for estimating the time-variant channel, and stage II is for removing the interference. By means of specially designed time domain pilot signals or frequency domain pilot signals, the time-variant channel is estimated, the carrier value is detected, and the interference is removed according to a linear or a non-linear symbol detecting method.

"The other category is called `inter-carrier interference self-cancellation scheme`. According to the inter-carrier interference self-cancellation scheme, the transmitting end modulates the to-be-transmitted original carrier to a plurality of adjacent and alternated carriers with opposite polarities. Each original carrier is mapped to a group of polar and anti-polar carriers. During reception, each polar carrier and anti-polar carrier are respectively multiplied by a positive sign and a negative sign and combined, and then the inter-carrier interference will be self-cancelled. However, as each original carrier corresponds to a group of anti-polar carriers, the utilization efficiency of the frequency spectrum will deteriorate severely."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The invention is directed to a lowly complicated method for estimating and removing ICI on a time domain. As the symbol has repeated data, the method for removing ICI according to the embodiments of the invention effectively estimates and removes ICI for a received symbol by way of simple operation such as addition, subtraction and multiplication.

"According to a first aspect of the present invention, a method for removing inter-carrier interference (ICI) for a received symbol is provided. Firstly, a transmitted symbol is received via a wireless channel within a symbol time so as to obtain the received symbol. The transmitted symbol includes P identical original partial data, wherein P is a positive integer larger than 1. The received symbol includes P received partial data corresponding to the original partial data, respectively. Next, on a time domain at least two of the P received partial data are copied so as to obtain at least two copied partial data. Each copied partial data includes P copies of its corresponding received partial data. After that, an estimated ICI of the time domain is determined according to the product of a predetermined constant array and the difference between the copied partial data. Afterwards, the estimated ICI is subtracted from the received symbol so as to obtain an output symbol

"According to a second aspect of the present invention, a receiver is provided for receiving a transmitted symbol generated by a transmitter via a wireless channel within a symbol time so as to obtain the received symbol and then remove ICI for the received symbol. The transmitted symbol includes P original partial data. Each original partial data includes a plurality of original time domain sampling data. Each original partial data is the same. The received symbol includes a plurality of received partial data corresponding to original partial data, respectively. The receiver includes a data synchronization module, an ICI estimating module, an ICI removing module, a fast Fourier transformer, and a demodulator. The data synchronization module synchronizes the received symbol. The ICI estimating module copies at least two of the P received partial data on a time domain so as to obtain at least two copied partial data. Each copied partial data includes P copies of its corresponding received partial data. P is a positive integer larger than 1. The ICI estimating module determines an estimated ICI according to the difference between the copied partial data and the product of a predetermined constant array. The ICI removing module subtracts the estimated ICI from the received symbol so as to obtain an output symbol. The Fast Fourier transformer converts the output symbol to a frequency domain. The demodulator demodulates the output symbol in the frequency domain.

"According to a third aspect of the present invention, a wireless transmission system including a transmitter and a receiver is provided. The transmitter generates and transmits a transmitted symbol of a time domain. The transmitted symbol includes P original partial data, wherein P is a positive integer larger than 1. Each original partial data includes a plurality of original time domain sampling data. Each original received partial data is the same. The receiver receives the transmitted symbol via a wireless channel within a symbol time so as to obtain a received symbol. The received symbol includes P received partial data respectively corresponding to P original partial data. The receiver includes a data synchronization module, an ICI estimating module, an ICI removing module, a fast Fourier transformer, and a demodulator. The data synchronization module synchronizes the received symbol. The ICI estimating module copies at least two of the P received partial data on a time domain so as to obtain at least two copied partial data. Each copied partial data includes P copies of its corresponding received partial data. The ICI estimating module determines an estimated ICI according to the product of a predetermined constant array and the difference between the copied partial data. The ICI removing module subtracts the estimated ICI from the received symbol so as to obtain an output symbol. The fast Fourier transformer converts the output symbol into a frequency domain. The demodulator demodulates the output symbol in the frequency domain.

"According to a fourth aspect of the present invention, a method for removing ICI for a received symbol is provided. This method includes the following steps. Firstly, a transmitted symbol generated by a transmitter is received via a wireless channel within a symbol time so as to obtain the received symbol. The transmitted symbol includes an original data symbol and a cyclic prefix (CP) data. The cyclic prefix data is the same with the rear-end data of the original data symbol. The received symbol includes a received data symbol and a received cyclic prefix data corresponding to the original data and the cyclic prefix data, respectively. A received rear-end data of the received data symbol corresponds to the rear-end data. Next, an estimated ICI is determined according to the product of a predetermined constant array and the difference between at least part of the received cyclic prefix data and at least part of the received rear-end data. After that, the estimated ICI is subtracted from the received symbol so as to obtain an output symbol.

"According to a fifth aspect of the present invention, a wireless transmission system including a transmitter and a receiver is provided. The transmitter generates and transmits a transmitted symbol of a time domain. The transmitted symbol is a data which includes an original data symbol and a cyclic prefix data. The cyclic prefix data is the same with an original rear-end data of the original data symbol. The receiver receives the transmitted symbol via a wireless channel within a symbol time so as to obtain a received symbol. The received symbol correspondingly includes a received data symbol and a received cyclic prefix data corresponding to the original data and the cyclic prefix data, respectively. A received rear-end data of the received data symbol corresponds to the rear-end data. The receiver includes a data synchronization module, an ICI estimating module, an ICI removing module, a fast Fourier transformer, and a demodulator. The data synchronization module synchronizes the received symbol. The ICI estimating module determines an estimated ICI according to the product of a predetermined constant array and the difference between at least part of the received cyclic prefix data and at least part of the received rear-end data. The ICI removing module subtracts the estimated ICI from the received symbol so as to obtain an output symbol. The fast Fourier transformer converts the output symbol into a frequency domain. The demodulator demodulates the output symbol in the frequency domain.

"According to a sixth aspect of the present invention, a method for removing ICI is provided. The method includes the following steps. Firstly, a transmitted symbol generated by a transmitter is received via a wireless channel within a symbol time so as to obtain the received symbol. The transmitted symbol includes at least two identical original partial data. The received symbol includes at least two corresponding received partial data corresponding to the two original partial data, respectively. After that, an estimated IC is determined according to the product of a predetermined constant array and the difference between at least two received partial data. Next, the estimated ICI is subtracted from the received symbol so as to obtain an output symbol.

"The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings."

URL and more information on this patent, see: Hsu, Jen-Yuan; Wang, Lai-Huei; Lai, Jiun-Yo; Ting, Pang-An. Wireless Transmission System, Receiver , and Method for Removing Inter-Carrier Interference. U.S. Patent Number 8218695, filed October 1, 2008, and issued July 10, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=36&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1791&f=G&l=50&co1=AND&d=PTXT&s1=20120710.PD.&OS=ISD/20120710&RS=ISD/20120710

Keywords for this news article include: Information Technology, Information and Data Synchronization, Industrial Technology Research Institute.