METHOD FOR SYMBOL COMPENSATION AND RECEIVER
20170338993 · 2017-11-23
Inventors
Cpc classification
International classification
Abstract
The present disclosure provides a method for symbol compensation. The method comprises, for a symbol consisting of a first portion and a second portion: estimating a length of the first portion; calculating an average power of the first portion and an average power of the second portion based on the length of the first portion; determining a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion; and compensating for the first portion based on the relative scaling factor.
Claims
1. A method for symbol compensation, comprising, for a symbol consisting of a first portion and a second portion: estimating a length of the first portion; calculating an average power of the first portion and an average power of the second portion based on the length of the first portion; determining a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion; and compensating for the first portion based on the relative scaling factor.
2. The method of claim 1, wherein the symbol is an Orthogonal Frequency Division Multiplexing symbol containing a set of constellation symbols in a modulation constellation.
3. The method of claim 2, wherein said estimating comprises: creating a sequence of amplitude values comprising amplitude values of constellation symbols in the set that are mapped onto constellation points with highest amplitude values in the modulation constellation; deriving a threshold based on the sequence; and estimating the length of the first portion based on the number of amplitude values preceding the first amplitude value in the sequence that is larger than the threshold.
4. The method of claim 3, wherein the amplitude value of each constellation symbol comprises the amplitude of its real part and/or the amplitude of its imaginary part.
5. The method of claim 3, wherein said deriving comprises: deriving, as the threshold, an average of a number of values at the beginning of the sequence and that number of values at the end of the sequence.
6. The method of claim 3, further comprising: obtaining an envelope of the sequence by applying a low pass filter to the sequence, wherein the threshold is an average of a number of values at the beginning of the envelope and that number of values at the end of the envelope and the length of the first portion based on the number of values preceding the first value in the envelope that is larger than the threshold.
7. (canceled)
8. The method of claim 1, wherein said estimating comprises: estimating the length of the first portion based on a difference between a timing advance associated with the symbol and a timing advance associated with another symbol that overlaps the symbol over the first portion.
9. The method of claim 1, further comprising, prior to said compensating: determining that the relative scaling factor is larger than a first threshold.
10. The method of claim 9, further comprising, after said determining the relative scaling factor: setting the first portion to zero when the relative scaling factor is larger than a second threshold, wherein the second threshold is higher than the first threshold.
11. The method of claim 10, further comprising, prior to said setting: determining that a ratio of the length of the first portion to a length of the symbol does not exceed a predetermined upper limit at a given coding rate.
12. The method of claim 2, further comprising: computing soft bits for each constellation symbol in the OFDM symbol having the first portion compensated, while applying to the compensated first portion a Signal to Interference and Noise Ratio (SINR) scaled by the relative scaling factor.
13-24. (canceled)
25. A receiver comprising a transceiver, a processor and a memory, wherein the memory contains instructions executable by the processor whereby the receiver is operative to compensate for a symbol consisting of a first portion and a second portion by: estimating a length of the first portion; calculating an average power of the first portion and an average power of the second portion based on the length of the first portion; determining a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion; and compensating for the first portion based on the relative scaling factor.
26. The receiver according to claim 25, wherein the symbol is an Orthogonal Frequency Division Multiplexing (OFDM) symbol containing a set of constellation symbols in a modulation constellation, wherein the receiver is operative to: create a sequence of amplitude values comprising amplitude values of constellation symbols in the set that are mapped onto constellation points with highest amplitude values in the modulation constellation; derive a threshold based on the sequence; and estimate the length of the first portion based on the number of amplitude values preceding the first amplitude value in the sequence that is larger than the threshold.
27. The receiver according to claim 26, wherein the amplitude value of each constellation symbol comprises the amplitude of its real part and/or the amplitude of its imaginary part.
28. The receiver according to claim 26, operative to: derive, as the threshold, an average of a number of values at the beginning of the sequence and that number of values at the end of the sequence.
29. The receiver according to claim 26, further operative to: obtain an envelope of the sequence by applying a low pass filter to the sequence, wherein the threshold is an average of a number of values at the beginning of the envelope and that number of values at the end of the envelope and the length of the first portion based on the number of values preceding the first value in the envelope that is larger than the threshold.
30. The receiver according to claim 26, further operative to: remove, prior to said deriving, a number of amplitude values from the sequence, the number being dependent on a ratio of a length of a cyclic prefix in the OFDM symbol to a length of the OFDM symbol.
31. The receiver according to claim 25, operative to: estimate the length of the first portion based on a difference between a timing advance associated with the symbol and a timing advance associated with another symbol that overlaps the symbol over the first portion.
32. The receiver according to claim 25, further operative to: prior to said compensating, determine that the relative scaling factor is larger than a first threshold, and set the first portion to zero when the relative scaling factor is larger than a second threshold, wherein the second threshold is higher than the first threshold.
33. The receiver according to claim 32, further operative to: prior to said setting, determine that a ratio of the length of the first portion to a length of the symbol does not exceed a predetermined upper limit at a given coding rate.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:
[0028]
[0029]
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[0038]
DETAILED DESCRIPTION
[0039] The embodiments of the disclosure will be detailed below with reference to the drawings. It should be noted that the following embodiments are illustrative only, rather than limiting the scope of the disclosure.
[0040]
[0041] The method 600 includes the following steps.
[0042] At step S610, a length of the first portion is estimated.
[0043] In an example, in the step S610, the length of the first portion can be estimated as follows. It is assumed here that the OFDM symbol contains constellation symbols being represented as:
e.sub.0,e.sub.1, . . . e.sub.N-1 (1)
[0044] where N denotes the number of the constellation.
[0045] First, a sequence of amplitude values is created. The sequence includes amplitude values of constellation symbols in the set of constellation symbols that are mapped onto constellation points with highest amplitude values in the modulation constellation. For example, when the modulation constellation is a 16QAM constellation shown in
[0046] Here, the amplitude value of a constellation symbol e.sub.n, n=0,1, . . . N can be |e.sub.n|. When a complex modulation constellation is used, without loss of generality, a constellation symbol e.sub.n, n=0, 1, . . . N can be split into:
d.sub.2n=real(e.sub.n),d.sub.2n+1=imag(e.sub.n) (2).
[0047] In this case, the amplitude value of e.sub.n can be represented as the amplitude of its real part and/or the amplitude of its imaginary part. That is, the amplitude value of e.sub.n can be represented by |d.sub.2n|, |d.sub.2n+1| or both. In the following example, it is assumed that the amplitude value of e.sub.n is represented by both |d.sub.2n| and |d.sub.2n+1|.
[0048] A vector g.sub.i is calculated as:
g.sub.i=max(|d.sub.i|d.sub.(i+1)mod2N|, . . . |d.sub.(i+M−1)mod2N|),i=0,1, . . . 2N−1 (3)
where M=floor(N/x) (e.g., x=100) and mod( ) denotes modulo operation. It is to be noted that the value of x is not limited to 100 but may vary depending on desired accuracy and complexity. The sequence can be represented as:
g.sub.0,g.sub.1, . . . g.sub.2N-1 (4).
[0049] Reference is now made to
[0050] Alternatively, when the modulation constellation has constant amplitude (such as QPSK or BPSK), we have:
g=|d.sub.i|,i=0,1, . . . 2N−1 (5).
[0051] Here, preferably, a number, L, of amplitude values can be removed from the sequence due to FFT window selection in the FFT transform.
[0052] Then, an envelope of the sequence can be derived by applying a Low Pass Filter (LPF) to the sequence. In doing so, a DFT is applied to g.sub.0, g.sub.1, . . . g.sub.2N−L−1 first to transform the sequence to the frequency domain:
[0053] A low pass filter can be applied by setting high frequency elements of h.sub.k to zero:
where w denotes a stop band of the LPF, e.g., w=M.
[0054] Then an IDFT can be applied to h.sub.k to transform it back to the time domain, so as to yield the envelope:
[0055] The waveform of the envelope is also shown in
[0056] It is to be noted here that the LPF is not necessary, e.g., when QPSK or BPSK modulation is used.
[0057] Then, a threshold is derived based on the sequence. In particular, the threshold can be an average of a number of values at the beginning of the sequence and that number of values at the end of the sequence. For example, the threshold can be an average of any one, two, three, four or five of the first five values in the sequence and any one, two, three, four or five of the last five values in the sequence. In the simplest case, the threshold can be an average of the first value and the last value in the sequence, that is:
Th=(g.sub.0+g.sub.2N−L−1)/2 (9).
[0058] Alternatively, when the envelope has been derived, the threshold can be an average of a number of values at the beginning of the envelope and that number of values at the end of the envelope. In the simplest case, the threshold can be an average of the first value and the last value in the envelop:
Th′=(z.sub.0+z.sub.2N−L−1)/2 (10)
[0059] Next, the length of the first portion can be estimated based on the number of amplitude values preceding the first amplitude value in the sequence that is larger than the threshold. Let g.sub.id be the first amplitude value in the sequence that satisfies g.sub.id>Th.sub.1 the length of the first portion can be estimated as:
L.sub.1=floor(g.sub.id/2)+1 (11).
[0060] Alternatively, when the envelope has been derived, the length of the first portion based on the number of values preceding the first value in the envelope that is larger than the threshold. Let z.sub.id be the first value in the envelope that satisfies z.sub.id>Th′, the length of the first portion can be estimated as:
L.sub.1=floor(z.sub.id/2)+1 (12).
[0061] Alternatively, in the step S610, the length of the first portion can be estimated based on a difference between a timing advance associated with the symbol and a timing advance associated with another symbol that overlaps the symbol over the first portion. Referring to
L.sub.1=|TA.sub.1−TA.sub.2|*16 (13).
[0062] At step S620, an average power of the first portion and an average power of the second portion are calculated based on the length of the first portion.
[0063] Here, the average power of the first portion can be calculated as:
P.sub.1=mean(|d.sub.i|.sup.2),0≦i<id (14).
[0064] The average power of the second portion can be calculated as:
P.sub.2=mean(|d.sub.i|.sup.2),id≦i≦2N−L−1 (15).
[0065] At step S630, a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion is determined.
[0066] Here, the relative scaling factor can be calculated as:
γ=β*P.sub.1/P.sub.2 (16)
where β is an optional adjustment coefficient and can be set to e.g., 1˜1.1.
[0067] At step S640, the first portion is compensated for based on the relative scaling factor. Here, the compensation in the step S640 can be done by applying the following equation:
[0068] In an example, prior to the compensation in the step S640, it is determined that the relative scaling factor is larger than a first threshold. In this case, the step S640 is performed when the relative scaling factor is larger than the first threshold (e.g., 3 dB), so as to avoid unnecessary compensation when the relative scaling factor is too small.
[0069] After the first portion is compensated for in the step S640, soft bits can be computed for each constellation symbol in the OFDM symbol having the first portion compensated, while a Signal to Interference and Noise Ratio (SINR) scaled by the relative scaling factor is applied to the compensated first portion. As an example, when the modulation constellation is 16QAM, the soft bits can be calculated as:
where t is a constant parameter used for 16QAM demodulation, μ is the SINR estimated based on DMRSs.
[0070] Then, the OFDM symbol can be decoded (e.g., turbo decoded) jointly with other OFDM symbols in the same subframe based on the soft bits.
[0071] It is to be noted here that there may be a case where the overlap between two transmissions exceeds one symbol. For example, if in
[0072] In an example, when the relative scaling factor is larger than a second threshold higher than the first threshold, the first portion is set to zero based on the length of the first portion, i.e., the first portion is punctured. As an example, the second threshold can be 15 dB.
[0073] In an example, prior to setting the first portion to zero, it is determined that a ratio of the length of the first portion to a length of the symbol does not exceed a predetermined upper limit at a given coding rate. That is,
L.sub.1/N≦(1−CR/α)*n.sub.OFDM (19)
where CR denotes the coding rate for the OFDM symbol, α denotes a maximum allowable ratio of information bits to coded bits, and n.sub.OFDM denotes the number of OFDM symbols in a subframe.
[0074] Again, there may be a case where the overlap between two transmissions exceeds one symbol. For example, if in
L.sub.1/N≦(1−CR/α)*n.sub.OFDM−1 (20).
[0075]
TABLE-US-00001 TABLE 1 Simulation Parameters Parameter Value Carrier frequency 2.6 GHz Subcarrier spacing 15 KHz System bandwidth 20 MHz ulMCS 18 Modulation 16QAM Number of antennas 1 × 1 Allocated number of RB 90 Doppler frequency 70 Hz Channel model EVA Time length of the overlapped portion 30 μs Tx power reduction 10 dB
[0076] It can be seen that both the compensating and puncturing schemes outperform the conventional scheme where no compensation or puncturing is done. The BLER performance of the compensating scheme is comparable to that of the ideal compensation at high SINRs. The puncturing scheme also achieves a performance gain of around 3 dB when the Tx power reduction is rather high, as shown in the above table.
[0077] Correspondingly to the method 600 as described above, a receiver is provided.
[0078] As shown in
[0079] In an embodiment, the symbol is an Orthogonal Frequency Division Multiplexing (OFDM) symbol containing a set of constellation symbols in a modulation constellation.
[0080] In an embodiment, the estimating unit 1010 is configured to create a sequence of amplitude values comprising amplitude values of constellation symbols in the set that are mapped onto constellation points with highest amplitude values in the modulation constellation; derive a threshold based on the sequence; and estimate the length of the first portion based on the number of amplitude values preceding the first amplitude value in the sequence that is larger than the threshold.
[0081] In an embodiment, the amplitude value of each constellation symbol comprises the amplitude of its real part and/or the amplitude of its imaginary part.
[0082] In an embodiment, an average of a number of values at the beginning of the sequence and that number of values at the end of the sequence is derived as the threshold.
[0083] In an embodiment, the estimating unit 1010 is further configured to obtain an envelope of the sequence by applying a low pass filter to the sequence. An average of a number of values at the beginning of the envelope and that number of values at the end of the envelope is derived as the threshold and the length of the first portion based on the number of values preceding the first value in the envelope that is larger than the threshold.
[0084] In an embodiment, the estimating unit 1010 is further configured to remove, prior to deriving the threshold, a number of amplitude values from the sequence, the number being dependent on a ratio of a length of a cyclic prefix in the OFDM symbol to a length of the OFDM symbol.
[0085] In an embodiment, the estimating unit 1010 is configured to estimate the length of the first portion based on a difference between a timing advance associated with the symbol and a timing advance associated with another symbol that overlaps the symbol over the first portion.
[0086] In an embodiment, the compensating unit 1040 is configured to determine, prior to compensating for the first portion, that the relative scaling factor is larger than a predetermined threshold.
[0087] In an embodiment, the compensating unit 1040 is further configured to set the first portion to zero when the relative scaling factor is larger than a second threshold. The second threshold is higher than the first threshold.
[0088] In an embodiment, the compensating unit 1040 is further configured to, prior to setting the first portion to zero, determine that a ratio of the length of the first portion to a length of the symbol does not exceed a predetermined upper limit at a given coding rate.
[0089] In an embodiment, the receiver 1000 further comprises (not shown): a computing unit configured to compute soft bits for each constellation symbol in the OFDM symbol having the first portion compensated, while applying to the compensated first portion a Signal to Interference and Noise Ratio (SINR) scaled by the relative scaling factor.
[0090] Each of the units 1010-1040 can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component(s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in
[0091]
[0092] The receiver 1100 includes a transceiver 1110, a processor 1120 and a memory 1130. The memory 1130 contains instructions executable by the processor 1120 whereby the receiver 1100 is operative to compensate for a symbol consisting of a first portion and a second portion by: estimating a length of the first portion; calculating an average power of the first portion and an average power of the second portion based on the length of the first portion; determining a relative scaling factor by which the average power of the first portion is scaled relative to that of the second portion; and compensating for the first portion based on the relative scaling factor.
[0093] The present disclosure also provides at least one computer program product in the form of a non-volatile or volatile memory, e.g., an Electrically Erasable Programmable Read-Only Memory (EEPROM), a flash memory and a hard drive. The computer program product includes a computer program. The computer program includes: code/computer readable instructions, which when executed by the processor 1120 causes the receiver 1100 to perform the actions, e.g., of the procedure described earlier in conjunction with
[0094] The computer program product may be configured as a computer program code structured in computer program modules. The computer program modules could essentially perform the actions of the flow illustrated in
[0095] The processor may be a single CPU (Central processing unit), but could also comprise two or more processing units. For example, the processor may include general purpose microprocessors; instruction set processors and/or related chips sets and/or special purpose microprocessors such as Application Specific Integrated Circuit (ASICs). The processor may also comprise board memory for caching purposes. The computer program may be carried by a computer program product connected to the processor. The computer program product may comprise a computer readable medium on which the computer program is stored. For example, the computer program product may be a flash memory, a Random-access memory (RAM), a Read-Only Memory (ROM), or an EEPROM, and the computer program modules described above could in alternative embodiments be distributed on different computer program products in the form of memories.
[0096] The disclosure has been described above with reference to embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the disclosure. Therefore, the scope of the disclosure is not limited to the above particular embodiments but only defined by the claims as attached.