Sounding reference signal processing for LTE
A wireless communication receiver including a serial to parallel converter receiving an radio frequency signal, a fast Fourier transform device connected to said serial to parallel converter converting N FFT corresponding serial signals into a frequency domain; an EZC root sequence unit generating a set of root sequence signals; an element-by-element multiply unit forming a set of products including a product of each of said frequency domain signals from said fast Fourier transform device and a corresponding root sequence signal, an N SRS -length IDFT unit performing a group cyclic-shift de-multiplexing of the products and a discrete Fourier transform unit converting connected cyclic shift de-multiplexing signals back to frequency-domain.
1. A wireless communication receiver comprising:
a serial-to-parallel converter receiving a time sample sequence and generating parallel signals;
a fast Fourier transform (FFT) device connected to said serial-to-parallel converter and converting said signals from a time domain into a frequency domain;
an Extended Zadoff-Chu (EZC) root sequence unit generating a set of root sequence signals;
an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit, said element-by-element multiply unit forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X;
an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, wherein said group cyclic shift de-multiplexing performed by said IDFT unit includes:
Y=F N SRS N FFT ( r )
y=F N SRS −1 diag( X * Y T )
where: Y is the frequency domain product of an element-wise multiplication, r is the received time sample sequence, y is the time domain product of an element-wise multiplication, F N SRS N FFT is a N SRS by N FFT matrix corresponding to N FFT -point FFT and N SRS sub-carriers de-mapping, X is the expected root sequence; and F N SRS is a N SRS by N SRS matrix, thereby producing for each Sounding Reference Signal (SRS) comb a concatenated Channel Impulse Response (CIR) sequence y of all received wireless users multiplexed on a same root sequence; and
a discrete Fourier transform unit connected to said IDFT unit to convert said impulse responses back to frequency domain.
2. A wireless communication receiver comprising:
a serial-to-parallel converter receiving a time sample sequence and generating parallel signals;
a fast Fourier transform (FFT) device connected to said serial-to-parallel converter and converting said signals from a time domain into a frequency domain;
an Extended Zadoff-Chu (EZC) root sequence unit generating a set of root sequence signals;
an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit, said element-by-element multiply unit forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X;
an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, wherein said group cyclic shift de-multiplexing performed by said IDFT unit includes:
y u =(0, . . . ,0,y n 1 (u) ,y n 2 (u) , . . . ,y n L (u) ,0, . . . ,0) T
Ĥ u =F N SRS y a
where: y is the time domain product of an element-rise multiplication, F N SRS is a N SRS by N SRS matrix corresponding to N SRS -point DFT; and n 1 (u), . . . ,n L (u) are the samples defining the cyclic shift window of user u, involving zeroing out the remaining samples outside the cyclic shift window of user u and Ĥ u is the channel estimate across frequency chunk c produced by the last stage N SRS -length DST-based frequency interpolation; and
a discrete Fourier transform unit connected to said IDFT unit to convert said impulse responses back to frequency domain.
3. A method of operating a wireless communication receiver comprising:
receiving a time sample sequence and generating parallel signals, by a serial-to-parallel converter;
converting said signals from a time domain into a frequency domain, by a fast Fourier transform (FFT) device connected to said serial-to-parallel converter;
generating a set of root sequence signals, by an Extended Zadoff-Chu (EZC) root sequence unit;
forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X, by an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit;
performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, by an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit, wherein said group cyclic shift de-multiplexing performed by said IDFT unit includes:
Y=F N SRS N FFT ( r )
y=F N SRS −1 diag( X * Y r )
where: Y is the frequency domain product of an element-wise multiplication, r is the received time sample sequence, y is the time domain product of an element-wise multiplication, F N SRS N FFT is a N SRS by N FFT matrix corresponding to N FFT -point FFT and N SRS sub-carriers de-mapping, X is the expected root sequence; and F N SRS is a N SRS matrix, thereby producing for each Sounding Reference Signal (SRS) comb a concatenated Channel Impulse Response (CIR) sequence y of all received wireless users multiplexed on a same root sequence; and
converting said impulse responses back to frequency domain, by a discrete Fourier transform unit connected to said IDFT unit.
4. A method of operating a wireless communication receiver comprising:
receiving a time sample sequence and generating parallel signals, by a serial-to-parallel converter;
converting said signals from a time domain into a frequency domain, by a fast Fourier transform (FFT) device connected to said serial-to-parallel converter;
generating a set of root sequence signals, by an Extended Zadoff-Chu (EZC) root sequence unit;
forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X, by an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit;
performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, by an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit, wherein said group cyclic shift de-multiplexing performed by said IDFT unit includes:
y u =(0, . . . ,0,y n 1 (u) ,y n 2 (u) , . . . ,y n L (u) ,0, . . . ,0) r
Ĥ u =F N SRS y u
where: y is the time domain product of an element-wise multiplication, F N SRS is a N SRS by N SRS matrix corresponding to N SRS -point DFT; and n 1 (u), . . ., n L (u) are the samples defining the cyclic shift window of user u, involving zeroing-out the remaining samples outside the cyclic shift window of user u and Ĥ u is the channel estimate across frequency chunk c produced by the last stage N SRS -length DFT-based frequency interpolation; and
converting said impulse responses back to frequency domain, by a discrete Fourier transform unit connected to said IDFT unit.
5. A method of operating a wireless communication receiver comprising:
receiving a time sample sequence and generating parallel signals, by a serial-to-parallel converter;
converting said signals from a time domain into a frequency domain, by a fast Fourier transform (FFT) device connected to said serial-to-parallel converter;
generating a set of root sequence signals, by an Extended Zadoff-Chu (EZC) root sequence unit;
forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X, by an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit;
performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, by an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit,
performing a non-biased per-antenna per-sub-carrier channel gain estimator
Ĝ 0 ( a )=| Ĥ ( a )| 2 −{circumflex over (σ)} N 2
where: Ĝ 0 (a) is the channel gain estimate per sub-carrier per antenna, Ĥ(a) is the channel estimate, {circumflex over (σ)} N 2 is an estimate of the noise variance σ N 2 =a 2 σ H 2 , involving estimating and removing the noise variance; and
converting said impulse responses back to frequency domain by a discrete Fourier transform unit connected to said IDFT unit.
6. A method of operating a wireless communication receiver comprising:
receiving a time sample sequence and generating parallel signals, by a serial-to-parallel converter;
converting said signals from a time domain into a frequency domain, by a fast Fourier transform (FFT) device connected to said serial-to-parallel converter;
generating a set of root sequence signals, by an Extended Zadoff-Chu (EZC) root sequence unit;
forming a set of products Y including a product of each of said frequency domain signals from said FFT device and a complex conjugate of one of said corresponding root sequence signals X, by an element-by-element multiply unit connected to said FFT device and said EZC root sequence unit;
performing a group cyclic-shift de-multiplexing of said products to compute an impulse response for each multiplexed channel, by an Inverse Discrete Fourier Transform (IDFT) unit connected to said element-by-element multiply unit,
performing a non-biased per-antenna per-sub-carrier channel gain estimator
Ĝ 0 ( a )=|Ĥ( a )| 2 −{circumflex over (σ)} N 2
where: Ĝ 0 (a) is the channel gain estimate per sub-carrier per antenna, Ĥ(a) is the channel estimate, {circumflex over (σ)} N 2 is an estimate of the noise variance σ N 2 =a 2 σ H 2 , involving estimating and removing the noise variance,
wherein said gain estimator includes a negative gain avoidance by applying a simple clipping threshold of 0.01 according to
Ĝ Clip ( a )=max{|Ĥ( a )| 2 −{circumflex over (σ)} N 2 ; G floor }
where: Ĝ Clip (a) is the channel gain estimate per sub-carrier per antenna, Ĥ(a) is the channel estimate, {circumflex over (σ)} N 2 is an estimate of the noise variance σ N 2 =a 2 σ H 2 and G floor is the clipping threshold; and
converting said impulse responses back to frequency domain by a discrete Fourier transform unit connected to said IDFT unit.
7. A method of operating a wireless communication Sounding Reference Signal (SRS) receiver comprising:
converting a received radio frequency signal and generating N FFT corresponding parallel signals by a serial to parallel converter;
receiving said N FFT corresponding parallel signals and converting said N FFT corresponding serial signals from a time domain into a frequency domain by a fast Fourier transform device connected to said serial to parallel converter;
generating a set of root sequence signals by a EZC root sequence unit;
forming a set of products including a product of each of said frequency domain signals from said fast Fourier transform device and a corresponding root sequence signal by an element-by-element multiply unit connected to said fast Fourier transform device and said EZC root sequence unit;
computing an impulse response for each multiplexed channel through a frequency-domain computed periodic correlation by an N SRS -length IDFT unit connected to said element-by-element multiply unit performing a group cyclic-shift de-multiplexing of said products employing a sounding reference symbol Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiple Access symbol structure and a Constant Amplitude Zero Auto-Correlation sequence to; and
receiving cyclic shift de-multiplexing signals to convert them back to frequency-domain by a discrete Fourier transform unit connected to said IDFT unit and
combining the amplitude delay profiles across antennas from the concatenated delay profiles sequence y and searching for the highest peak in the user's timing offset window, by a timing offset estimator, according to:
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where: A is the number of antenna; C u is the cyclic shift of user u; T S is the sampling period of sequence y; and I τ,u is the timing offset window of user u, defined as:
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where: I τ,u (N early +1)=0 coincides with the first sample of the cyclic shift window of user u; ±τ max is the maximum expected timing error; W M is the main energy region within the user delay spread; and τ is the delay spread of the user; and
converting said products back to frequency-domain by a discrete Fourier transform unit connected to said IDFT unit.