Patent EP-1183839-A1 (EP)
Inventor: OJARD ERIC
IPC: H04L7/04
Filed: 2000-06-02
Abstract: A method and apparatus for obtaining a channel estimate and a baud frequency offset estimate for a communications channel in a communications system. The communications system has a transmitter for transmitting to a receiver over the communications channel signals representing data appended to a preamble signal. The preamble signal is provided as a periodic plurality of preamble sequences, each preamble sequence being generated in accordance with: <maths id="MATH-US-00001" num="00001"> <MATH OVERFLOW="SCROLL"> <MROW> <MROW> <MFRAC> <MN>1</MN> <MN>32</MN> </MFRAC> <MO>⁢</MO> <MROW> <MUNDEROVER> <MO>∑</MO> <MROW> <MI>k</MI> <MO>=</MO> <MN>0</MN> </MROW> <MN>15</MN> </MUNDEROVER> <MO>⁢</MO> <MSTYLE> <MTEXT> </MTEXT> </MSTYLE> <MO>⁢</MO> <MROW> <MSUB> <MI>b</MI> <MI>k</MI> </MSUB> <MO>⁢</MO> <MSUBSUP> <MI>b</MI> <MROW> <MI>mod</MI> <MO>⁡</MO> <MROW> <MO>(</MO> <MROW> <MROW> <MI>k</MI> <MO>+</MO> <MI>n</MI> </MROW> <MO>,</MO> <MN>16</MN> </MROW> <MO>)</MO> </MROW> </MROW> <MO>*</MO> </MSUBSUP> </MROW> </MROW> </MROW> <MO>=</MO> <MROW> <MO>{</MO> <MROW> <MTABLE> <MTR> <MTD> <MROW> <MN>1</MN> <MO>,</MO> <MROW> <MI>n</MI> <MO>=</MO> <MN>0</MN> </MROW> </MROW> </MTD> </MTR> <MTR> <MTD> <MROW> <MN>0</MN> <MO>,</MO> <MROW> <MI>n</MI> <MO><></MO> <MN>0</MN> </MROW> </MROW> </MTD> </MTR> </MTABLE> <MO>.</MO> </MROW> </MROW> </MROW> </MATH> </MATHS> A signal representing the periodic plurality of preamble sequences is sent by a transmitter over the communications channel to a receiver and is received at the receiver as a received signal. The received signal is processed to determine from the received signal both a channel estimate in accordance with: <maths id="MATH-US-00002" num="00002"> <MATH OVERFLOW="SCROLL"> <MROW> <MROW> <MOVER> <MI>h</MI> <MO>^</MO> </MOVER> <MO>=</MO> <MROW> <MFRAC> <MN>1</MN> <MN>64</MN> </MFRAC> <MO>⁢</MO> <MROW> <MSUP> <MI>B</MI> <MI>H</MI> </MSUP> <MO>⁡</MO> <MROW> <MO>(</MO> <MROW> <MSUB> <MI>y</MI> <MN>1</MN> </MSUB> <MO>+</MO> <MSUB> <MI>y</MI> <MN>2</MN> </MSUB> </MROW> <MO>)</MO> </MROW> </MROW> </MROW> </MROW> <MO>,</MO> </MROW> </MATH> </MATHS> wherein B represents a matrix of preamble symbol values, upsampled by four and zero-filled, and y 1 and y 2 are column vectors of received samples, and a baud frequency offset estimate Deltaf<SUB>b </SUB>in accordance with: <maths id="MATH-US-00003" num="00003"> <MATH OVERFLOW="SCROLL"> <MROW> <MI>S</MI> <MO>=</MO> <MROW> <MUNDEROVER> <MO>∑</MO> <MROW> <MI>k</MI> <MO>=</MO> <MN>0</MN> </MROW> <MN>63</MN> </MUNDEROVER> <MO>⁢</MO> <MSTYLE> <MTEXT> </MTEXT> </MSTYLE> <MO>⁢</MO> <MROW> <MSUB> <MI>y</MI> <MI>k</MI> </MSUB> <MO>⁢</MO> <MSUBSUP> <MI>y</MI> <MROW> <MI>k</MI> <MO>+</MO> <MN>64</MN> </MROW> <MO>*</MO> </MSUBSUP> </MROW> </MROW> </MROW> </MATH> </MATHS> <maths id="MATH-US-00004" num="00004"> <MATH OVERFLOW="SCROLL"> <MROW> <MROW> <MROW> <MI>Delta</MI> <MO>⁢</MO> <MSTYLE> <MTEXT> </MTEXT> </MSTYLE> <MO>⁢</MO> <MSUB> <MI>f</MI> <MI>b</MI> </MSUB> </MROW> <MO>≅</MO> <MFRAC> <MROW> <MROW> <MI>real</MI> <MO>(</MO> <MI>S</MI> <MO>)</MO> </MROW> <MO>.</MO> <MSUB> <MI>f</MI> <MI>b</MI> </MSUB> </MROW> <MROW> <MROW> <MROW> <MI>imag</MI> <MO>⁡</MO> <MROW> <MO>(</MO> <MI>S</MI> <MO>)</MO> </MROW> </MROW> <MO>.</MO> <MSUB> <MI>f</MI> <MI>c</MI> </MSUB> <MO>.</MO> <MN>32</MN> </MROW> <MO>⁢</MO> <MI>pi</MI> </MROW> </MFRAC> </MROW> <MO>,</MO> </MROW> </MATH> </MATHS> wherein f<SUB>b </SUB>is a baud frequency and f<SUB>c </SUB>is a center frequency of the transmission signal.