Digital communication receiver using partial knowledge of the channel state information
The present invention proposes a demodulator device, a receiver and a demodulation method for M-ary amplitude shift keying systems (MASK) that requires partial knowledge of the CSI, namely, the channel attenuation coefficient. Therefore, the new demodulator, receiver and demodulation method do not require the knowledge of the channel phase shift. Consequently, no complicated channel estimation techniques are required, and the system will be very robust to the system impairments such as phase noise, I-Q imbalance, etc. In this sense, the new technique is denoted as semi-coherent demodulation (SCD). To reduce the complexity of the new SCD, a suboptimal demodulator is derived which has much lower complexity than the optimal while providing almost the same error probability.
1. A digital communication receiver for detecting signals transmitted by a digital transmitter through a communication channel, the channel having a channel attenuation |h| and a channel phase shift having a multipath fading effect on the transmitted signals, the receiver comprising a demodulator configured to demodulate signals received by the receiver using channel attenuation coefficients α representing the channel attenuation only without any knowledge of the channel phase shift, wherein
the demodulator is robust to phase noise, lame phase variations and time-varying I-Q imbalance;
the demodulator uses a M-ary amplitude shift keying technique, the transmitted signals being modulated by the transmitter using said same technique before transmission using a modulation order M equal or superior to 2;
the detected signals have a symbol Error Rate (SER) intermediate in terms of performance between a coherent detection and a non-coherent detection assuming a same spectral efficiency;
the demodulator is less complex than a coherent demodulator, and wherein the SER performance of the detected signals using the demodulator is substantially similar to a SER performance obtained using a coherent demodulator;
the channel is a multi-path fading channel;
the channel attenuation coefficients α are obtained by:
inserting pilot symbols d PSK {l} within the transmitted signals d ASK {l} with a particular time spacing for forming a transmitted frame with data symbols having the following structure d=[d PSK {1} , s ASK {2} , . . . , d ASK {Q} , d ASK {Q+1} , d ASK {Q+2} , . . . , d ASK {2Q} , d PSK {2Q+1} , . . . ], where the pilot symbols have a constant modulus |d PSK {l} | 2 =C {l} =1 ∀l, where C is a constant, and where Q is a constant set a priori based on configuration criteria;
using least-squared estimation to compute α such that a channel attenuation coefficient obtained from an lth pilot symbol is in accordance with the following equation:
α
^
=
r
PSK
2
d
PSK
2
=
α
+
h
*
d
PSK
*
w
+
hd
PSK
w
*
+
w
2
where r PSK is a received signal that corresponds to a given pilot symbol;
forming the following sparse vector using the computed α:
a=[{circumflex over (α)} {1} ], 0 {2} , . . . , 0 {Q} , {circumflex over (α)} {Q+1} , 0 {Q+2} , . . . , 0 {2Q} , {circumflex over (α)} {2Q+1} , . . . ], 2Q+1=L;
using interpolation to compute {circumflex over (α)} {i} where=l mod Q≠1.
2. The digital communication receiver as claimed in claim 1 , wherein the demodulation of the signals comprises detecting the transmitted signals by computing {circumflex over (d)} ASK {l} =|r ASK {l} | 2 /{circumflex over (α)} {l} , l mod Q≠1.
3. The digital communication receiver as claimed in claim 2 , wherein the demodulation of the signals further comprises, once {circumflex over (d)} ASK {l} is obtained, obtaining channel state information for all data symbols by:
compiling ĥ ASK {l} =r ASK {l} /{circumflex over (d)} ASK {l} , l mod Q≠1;
using interpolation to find ĥ PSK {l} , l mod Q≠1;
constructing a vector ĥ=[ĥ {1} , ĥ {2} , . . . , ĥ {L} ].
4. The digital communication receiver as claimed in claim 3 , wherein the demodulation of the signals further comprises detecting an entire received vector comprising the data symbols coherently by:
{circumflex over (d)}=ĤĤ H r
where r=[r {1} , r {2} , . . . , r {L} ], Ĥ=diag{ĥ {1} , ĥ {2} , . . . ĥ {L} }, and (⋅) denotes the Hermitian transpose operation.
5. The digital communication receiver as claimed in claim 4 , wherein the configuration criteria based on which Q is set comprises at least one of a channel coherence time, a spectral efficiency, and an interpolation error tolerance.
6. The digital communication receiver as claimed in claim 5 , wherein the pilot symbols are modulated by the transmitter using phase shift keying (PSK).
7. A computer-implemented demodulation method comprising:
receiving from a digital communication receiver signals transmitted by a digital transmitter through a communication channel, the channel having a channel attenuation |h| and a channel phase shift having a multipath fading effect on the transmitted signals; and
demodulating the signals received by the receiver using only channel attenuation coefficients α representing the channel attenuation without any knowledge of the channel phase shift for detecting the transmitted signals, wherein
the demodulation method is robust to phase noise, large phase variations and time-varying I-Q imbalance;
the demodulation method uses a M-ary amplitude shift keying technique, the transmitted signals being modulated by the transmitter using said same technique before transmission using a modulation order M equal or superior to 2;
the detected signals have a symbol Error Rate (BER) intermediate in terms of performance between a coherent detection and a differentially coherent detection assuming a same spectral efficiency;
the demodulation method is less complex than a coherent demodulation, and wherein the SER performance of the detected signals using the demodulation method is substantially similar to a SER performance obtained using a coherent demodulation;
the channel is a multi-path fading channel;
the channel attenuation coefficients α are obtained by:
inserting pilot symbols d PSK {l} within the transmitted signals d ASK {l} with a particular time spacing for forming a transmitted frame with data symbols having the following structure d=[d PSK {1} , s ASK {2} , . . . , d ASK {Q} , d ASK {Q+1} , d ASK {Q+2} , . . . , d ASK {2Q} , d PSK {2Q+1} , . . . ], where the pilot symbols have a constant modulus |d PSK {l} | 2 =C {l} =1 ∀l, where C is a constant, and where Q is a constant set a priori based on configuration criteria;
using least-squared estimation to compute α such that a channel attenuation coefficient obtained from an lth pilot symbol is in accordance with the following equation:
α
^
=
r
PSK
2
d
PSK
2
=
α
+
h
*
d
PSK
*
w
+
hd
PSK
w
*
+
w
2
where r PSK is a received signal that corresponds to a given pilot symbol;
forming the following sparse vector using the computed α:
a=[{circumflex over (α)} {1} ], 0 {2} , . . . , 0 {Q} , {circumflex over (α)} {Q+1} , 0 {Q+2} , . . . , 0 {2Q} , {circumflex over (α)} {2Q+1} , . . . ], 2Q+1=L;
using interpolation to compute {circumflex over (α)} {i} where=l mod Q≠1.
8. The demodulation method as claimed in claim 7 , wherein the demodulation of the signals comprises detecting the transmitted signals by computing {circumflex over (d)} ASK {l} =|r ASK {l} | 2 /{circumflex over (α)} {l} , l mod Q≠1.
9. The demodulation method as claimed in claim 8 , wherein the demodulation of the signals further comprises, once {circumflex over (d)} ASK {l} is obtained, obtaining channel state information for all data symbols by:
compiling ĥ ASK {l} =r ASK {l} /{circumflex over (d)} ASK {l} , l mod Q≠1;
using interpolation to find ĥ PSK {l} , l mod Q=1;
constructing a vector ĥ=[ĥ {1} , ĥ {2} , . . . , ĥ {L} ].
10. The demodulation method as claimed in claim 9 , wherein the demodulation of the signals further comprises detecting an entire received vector comprising the data symbols coherently by:
{circumflex over (d)}=ĤĤ H r
where r=[r {1} , r {2} , . . . , r {L} ], Ĥ=diag{ĥ {1} , ĥ {2} , . . . ĥ {L} }, and (⋅) denotes the Hermitian transpose operation.
11. The demodulation method as claimed in claim 10 , wherein the configuration criteria based on which Q is set comprises at least one of a channel coherence time, a spectral efficiency, and an interpolation error tolerance.
12. The demodulation method as claimed in claim 11 , wherein the pilot symbols are modulated by the transmitter using phase shift keying (PSK).
13. A demodulator device for detecting signals transmitted by a digital transmitter to a digital receiver through a communication channel, the channel having a channel attenuation |h| and a channel phase shift having a multipath fading effect on the transmitted signals, the demodulator device being configured to communicate with the digital receiver for demodulating signals received by the receiver using channel attenuation coefficients α representing the channel attenuation only without any knowledge of the channel phase shift, wherein
the demodulation is robust to phase noise, large phase variations and time-varying I-Q imbalance;
the demodulator device uses a M-ary amplitude shift keying technique, the transmitted signals being modulated by the transmitter using said same technique before transmission using a modulation order M superior to 2;
the detected signals have a Bit Error Rate (BER) intermediate in terms of performance between a coherent detection and a differentially coherent detection assuming a same spectral efficiency;
the demodulator device is less complex than a coherent demodulator, and wherein the BER performance of the detected signals using the demodulator is substantially similar to a BER performance obtained using a coherent demodulator;
the channel is a multi-path fading channel;
the channel attenuation coefficients α are obtained by:
inserting pilot symbols d PSK {l} within the transmitted signals d ASK {l} with a particular time spacing for forming a transmitted frame with data symbols having the following structure d=[d PSK {1} , s ASK {2} , . . . , d ASK {Q} , d ASK {Q+1} , d ASK {Q+2} , . . . , d ASK {2Q} , d PSK {2Q+1} , . . . ], where the pilot symbols have a constant modulus |d PSK {l} | 2 =C {l} =1 ∀l, where C is a constant, and where Q is a constant set a priori based on configuration criteria;
using least-squared estimation to compute α such that a channel attenuation coefficient obtained from an lth pilot symbol is in accordance with the following equation:
α
^
=
r
PSK
2
d
PSK
2
=
α
+
h
*
d
PSK
*
w
+
hd
PSK
w
*
+
w
2
where r PSK is a received signal that corresponds to a given pilot symbol;
forming the following sparse vector using the computed α:
a=[{circumflex over (α)} {1} ], 0 {2} , . . . , 0 {Q} , {circumflex over (α)} {Q+1} , 0 {Q+2} , . . . , 0 {2Q} , {circumflex over (α)} {2Q+1} , . . . ], 2Q+1=L;
using interpolation to compute {circumflex over (α)} {i} where=l mod Q≠1.
14. The demodulator device as claimed in claim 13 , wherein the demodulation of the signals comprises detecting the transmitted signals by computing {circumflex over (d)} ASK {l} =|r ASK {l} | 2 /{circumflex over (α)} {l} , l mod Q≠1.
15. The demodulator device as claimed in claim 14 , wherein the demodulation of the signals further comprises, once {circumflex over (d)} ASK {l} is obtained, obtaining channel state information for all data symbols by:
compiling ĥ ASK {l} =r ASK {l} /{circumflex over (d)} ASK {l} , l mod Q≠1;
using interpolation to find ĥ PSK {l} , l mod Q≠1;
constructing a vector ĥ=[ĥ {1} , ĥ {2} , . . . , ĥ {L} ].
16. The demodulator device as claimed in claim 15 , wherein the demodulation of the signals further comprises detecting an entire received vector comprising the data symbols coherently by:
{circumflex over (d)}=ĤĤ H r
where r=[r {1} , r {2} , . . . , r {L} ], Ĥ=diag{ĥ {1} , ĥ {2} , . . . ĥ {L} }, and (⋅) denotes the Hermitian transpose operation.
17. The demodulator device as claimed in claim 16 , wherein the configuration criteria based on which Q is set comprises at least one of a channel coherence time, a spectral efficiency, and an interpolation error tolerance.
18. The demodulator device as claimed in claim 17 , wherein the pilot symbols are modulated by the transmitter using phase shift keying (PSK).