Patent Issued for System and Method for Inter-Channel Interference Reduction

By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Lee, Gaspar (Bade, TW); Cheng, Hao-Ren (Yuanli Township, TW); Chu, Chih-Yuan (Hsinchu, TW); Ou, Kuang-Chung (Kaohsiung, TW), filed on March 5, 2009, was cleared and issued on December 18, 2012.

The patent's assignee for patent number 8335284 is Qualcomm Atheros, Inc. (San Jose, CA).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to interference reduction in digital communication systems in general and more specifically to inter-channel interference reduction in mobile, wireless OFDM systems.

"Advanced multimedia services continue to drive requirements for increasing data rates and higher performance in wireless systems. High performance communication systems such as those specified by the European terrestrial digital video broadcasting (DVB-T) standard and the Japanese integrated services digital broadcasting terrestrial standard (ISDB-T) may use communication methods based on Orthogonal Frequency Division Multiplexing (OFDM). The performance of an OFDM receiver may be sensitive to inter-channel interference between different sub-carrier frequencies in a time-varying environment, such as for a mobile, wireless device.

"A received OFDM symbol in an OFDM system may consist of both data and pilot synchronization information transmitted on multiple sub-carriers multiplexed together and spanning multiple sample periods. Modulation and demodulation in an OFDM system may use an inverse fast Fourier transform (IFFT) at the transmitter and an FFT at the receiver respectively. At the transmitter, a cyclic prefix of a section of the IFFT output for each OFDM symbol may be appended to the beginning of the OFDM symbol as a guard interval (GI) to provide some protection from inter-symbol interference (ISI). The length of the OFDM symbol before adding the guard interval may be known as the useful symbol period duration. At the receiver, the cyclic prefix (guard interval) may be removed prior to the FFT demodulation by positioning appropriately an FFT window, whose size may be equal to the useful symbol period duration, along a received sample sequence. The FFT demodulation may transform the window of received time domain samples, in the received sample sequence, to a frequency domain (OFDM) symbol. While the addition of the cyclic prefix guards against ISI, it may not compensate for inter-channel interference (ICI) that may occur between sub-carriers in an OFDM symbol when the communication channel varies in time during the OFDM symbol.

"Prior art techniques for ICI mitigation may estimate an amount of ICI in a receive OFDM symbol by estimating the communication channel's frequency domain transfer characteristic, the rate of change of the transfer characteristic and the transmitted OFDM symbol. An ICI estimate may then be subtracted from the receive OFDM symbol, thereby resulting in an ICI-reduced receive OFDM symbol. The performance of the ICI mitigation method may depend on the quality of these estimates, especially in a rapidly time-varying mobile environment. Some prior art methods to provide accurate estimates may be too complex and costly to implement, while others may be too simple to provide excellent performance. Thus, there exists a need for a readily implementable ICI reduction technique that estimates the ICI accurately and exhibits high performance in a mobile environment."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "An apparatus and method in a multiple sub-carrier digital communication receiver for reducing inter-channel interference (ICI) are provided. The apparatus and method can include a channel estimation block for calculating channel estimates, an interpolation block for calculating interpolated channel estimates, and an ICI reduction block for calculating ICI reduced receive symbols. Channel estimates are calculated based on receive symbols or ICI reduced receive symbols using pre-determined transmit symbols. Interpolated channel estimates are calculated by Wiener filter interpolation of a set of channel estimates. ICI estimates are calculated based on a set of interpolated channel estimates and either receive symbols or ICI reduced receive symbols. ICI reduced receive symbols are generated by subtracting ICI estimates from receive symbols."

For additional information on this patent, see: Lee, Gaspar; Cheng, Hao-Ren; Chu, Chih-Yuan; Ou, Kuang-Chung. System and Method for Inter-Channel Interference Reduction. U.S. Patent Number 8335284, filed March 5, 2009, and issued December 18, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=26&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1254&f=G&l=50&co1=AND&d=PTXT&s1=20121218.PD.&OS=ISD/20121218&RS=ISD/20121218

Keywords for this news article include: Qualcomm Atheros Inc.

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