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Fourier-transform based linear equalization for MIMO CDMA downlink

a linear equalization and mimo technology, applied in the field of mimo reception methods, to avoid computationally intense matrix inversion

Inactive Publication Date: 2008-11-13
NOKIA CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

"The present invention provides a method for equalizing downlink MIMO CDMA signals without the need for a computationally intense matrix inversion. The method uses a linear filter process with only FFTs and IFFTs as steps in the filter coefficient generation process. Additionally, the correlation matrix is approximated with a block circulant matrix that is diagonalized by a DFT operation. This simplifies the process and reduces the computational load."

Problems solved by technology

Applying a MIMO configuration to the CDMA downlink presents a significant challenge to the receiver designer because the receiver has to combat both inter-chip interference (ICI) and co-channel interference (CCI) in order to achieve reliable communication.

Method used

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  • Fourier-transform based linear equalization for MIMO CDMA downlink
  • Fourier-transform based linear equalization for MIMO CDMA downlink
  • Fourier-transform based linear equalization for MIMO CDMA downlink

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Embodiment Construction

[0023]In a preliminary discussion covering both single input / single output (SISO) and multiple input / multiple output (MIMO), consider the case of a CDMA downlink with at least one (M) antenna and J active users each of which is assigned a number of codes Kj; for j=1 - - - J. Let K be the total number of active spreading codes (summed over Kj). Note that in our discussion, we use spreading code index, rather than user index, to simplify the notation. At the transmitter, the chip-level signal representation is given by Eq (1) in FIG. 2, where i, m and k are chip, symbol and spreading code indices. The base station scrambling code is denoted by c(i). Meanwhile, ak stands for the power assigned to spreading code k, bk is the information symbol sequence for spreading code k and sk(i) is the spreading code k.

[0024]Let h=[hO; :::hL] be the composite chip-level channel impulse vector of spreading code k. Note h includes the contributions from transmit pulse shaper, the wireless propagation ...

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Abstract

In the reception of a downlink MIMO CDMA signal, the receiving unit performs a simplified process of linear equalization that eliminates the need for inverting the correlation matrix. The correlation matrix is approximated to a good degree by a circulation matrix that is diagonalized by FFT operations, thus substituting two FFTs and one IFFT having a complexity ofO(LF(NΔ)3+(NΔ)2+2(NΔ)2LFlog2LF)for the direct matrix inversion having a complexity of O(LF3).

Description

RELATED APPLICATIONS[0001]This application is a Continuation in Part of U.S. application Sequence Ser. No. 10 / 436,618, filed on May 13, 2003, assigned to the assignee hereof and incorporated herein by reference.FIELD OF THE INVENTION[0002]The invention relates to a MIMO reception method in mobile CDMA telephone systems wherein a desired signal is separated from other interfering signals by means of a linear equalization algorithm that avoids matrix inversion.BACKGROUND OF THE INVENTION[0003]A central problem in designing and implementing a data transmission system is simultaneous transmission and reception of signals from several simultaneous users such that the signals interfere with one another as little as possible. Because of this and the transmission capacity used, various transmission protocols and multiple access methods have been used, the most common especially in mobile phone traffic being FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access), ...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H04J11/00H04B7/216H04L25/03H04B1/00H04B1/707H04B7/08H04L25/02H04L27/01
CPCH04B7/0845H04L25/0204H04L25/0206H04L25/021H04L25/0242H04L25/0244H04L25/0256H04L25/03038H04L25/03159H04L2025/0342H04L2025/03426H04L2025/03522H04L2025/03605
Inventor ZHANG, JIANZHONGMANDYAM, GIRIDHARGUO, YUANBIN
Owner NOKIA CORP