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System for estimating data using iterative fast fourier transform error correctionRelated Patent Categories: Pulse Or Digital Communications, Spread Spectrum, Direct Sequence, ReceiverSystem for estimating data using iterative fast fourier transform error correction description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060126704, System for estimating data using iterative fast fourier transform error correction. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of U.S. patent application Ser. No. 10/004,370, filed Nov. 1, 2001, which claims priority from U.S. Provisional Patent Application No. 60/282,387, filed on Apr. 6, 2001, which are incorporated herein by reference as if fully set forth. BACKGROUND [0002] The invention generally relates to wireless communication systems. In particular, the invention relates to data detection in a wireless communication system. [0003] FIG. 1 is an illustration of a wireless communication system 10. The communication system 10 has base stations 12.sub.1 to 12.sub.5 (12) which communicate with user equipments (UEs) 14.sub.1 to 14.sub.3 (14). Each base station 12 has an associated operational area, where it communicates with UEs 14 in its operational area. [0004] In some communication systems, such as code division multiple access (CDMA) and time division duplex using code division multiple access (TDD/CDMA), multiple communications are sent over the same frequency spectrum. These communications are differentiated by their channelization codes. To more efficiently use the frequency spectrum, TDD/CDMA communication systems use repeating frames divided into time slots for communication. A communication sent in such a system will have one or multiple associated codes and time slots assigned to it. The use of one code in one time slot is referred to as a resource unit. [0005] Since multiple communications may be sent in the same frequency spectrum and at the same time, a receiver in such a system must distinguish between the multiple communications. One approach to detecting such signals is multiuser detection (MUD). In MUD, signals associated with all the UEs 14, users, are detected simultaneously. Another approach to detecting a multi-code transmission from a single transmitter is single user detection (SUD). In SUD, to recover data from the multi-code transmission at the receiver, the received signal is passed through an equalization stage and despread using the multi-codes. Approaches for implementing MUD and the equalization stage of SUD include using a Cholesky or an approximate Cholesky decomposition. These approaches have a high complexity. The high complexity leads to increased power consumption, which at the UE 14 results in reduced battery life. To reduce the complexity, fast fourier transform (FFT) based approaches have been developed for MUD and SUD. In some FFT approaches, an approximation is made to facilitate the FFT implementation. This approximation results in a small error being introduced in the estimated data. Accordingly, it is desirable to have alternate approaches to detecting received data. SUMMARY [0006] A system for estimating data from a received plurality of data signals in a code division multiple access communication system. The data signals are transmitted in a shared spectrum at substantially the same time. A receiver receives a combined signal of the transmitted data signals and a sampling device samples the combined signal. A channel estimating device estimates a channel response for the transmitted data signals. A data detection device estimates data of the data signals using the samples and the estimated channel response. The data estimation uses a Fourier transform based data estimating approach. An error in the data estimation introduced from a circulant approximation used in the Fourier transform based approach is iteratively reduced. BRIEF DESCRIPTION OF THE DRAWINGS [0007] FIG. 1 is a wireless communication system. [0008] FIG. 2 is a simplified transmitter and a FFT based data detection receiver using iterative error correction. [0009] FIG. 3 is an illustration of a communication burst. [0010] FIG. 4 is a flow chart of iterative error correction. [0011] FIG. 5 is a flow chart of a receiver selectively using iterative error correction. [0012] FIG. 6 is a flow chart of an example of a FFT based SUD using iterative error correction. [0013] FIG. 7 is a flow chart of an example of a FFT based MUD using iterative error correction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0014] FIG. 2 illustrates a simplified transmitter 26 and receiver 28 using a FFT based data detection with iterative error correction in a TDD/CDMA communication system, although iterative error correction is applicable to other systems, such as frequency division duplex (FDD) CDMA. In a typical system, a transmitter 26 is in each UE 14 and multiple transmitting circuits 26 sending multiple communications are in each base station 12. The iterative error correction receiver 28 may be at a base station 12, UEs 14 or both. [0015] The transmitter 26 sends data over a wireless radio channel 30. A data generator 32 in the transmitter 26 generates data to be communicated to the receiver 28. A modulation/spreading/training sequence insertion device 34 spreads the data and makes the spread reference data time-multiplexed with a midamble training sequence in the appropriate assigned time slot and codes for spreading the data, producing a communication burst or bursts. [0016] A typical communication burst 16 has a midamble 20, a guard period 18 and two data fields 22, 24, as shown in FIG. 3. The midamble 20 separates the two data fields 22, 24 and the guard period 18 separates the communication bursts to allow for the difference in arrival times of bursts transmitted from different transmitters 26. The two data fields 22, 24 contain the communication burst's data. [0017] The communication burst(s) are modulated by a modulator 36 to radio frequency (RF). An antenna 38 radiates the RF signal through the wireless radio channel 30 to an antenna 40 of the receiver 28. The type of modulation used for the transmitted communication can be any of those known to those skilled in the art, such as quadrature phase shift keying (QPSK) or M-ary quadrature amplitude modulation (QAM). [0018] The antenna 40 of the receiver 28 receives various radio frequency signals. The received signals are demodulated by a demodulator 42 to produce a baseband signal. The baseband signal is sampled by a sampling device 43, such as one or multiple analog to digital converters, at the chip rate or a multiple of the chip rate of the transmitted bursts. The samples are processed, such as by a channel estimation device 44 and a FFT based data detection device 46, in the time slot and with the appropriate codes assigned to the received bursts. The channel estimation device 44 uses the midamble training sequence component in the baseband samples to provide channel information, such as channel impulse responses. The channel impulse responses can be viewed as a matrix, H. The channel information and spreading codes used by the transmitter are used by the data detection device 46 to estimate the transmitted data of the received communication bursts as soft symbols. An iterative error correction device 48 processes the estimated data to correct errors resulting from the FFT based detection. [0019] Although iterative error correction is explained using the third generation partnership project (3GPP) universal terrestrial radio access (UTRA) TDD system as the underlying communication system, it is applicable to other systems and other FFT linear equation based applications. That system is a direct sequence wideband CDMA (W-CDMA) system, where the uplink and downlink transmissions are confined to mutually exclusive time slots. [0020] Data detection is typically modeled using a linear equation per Equation 1. Zx=y Equation 1 For SUD, data detection is typically modeled per Equations 2 and 3. r=Hs+n Equation 2 s=Cd Equation 3 r is the received samples as produced by the sampling device 43. H is the channel response matrix as produced using the channel responses from the channel estimation device 44. s is the spread data vector. The spread data vector, s, as per Equation 3, is a vector multiplication of the channel codes C and the originally transmitted data d. Continue reading about System for estimating data using iterative fast fourier transform error correction... 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