CN101981842B - Receiver - Google Patents
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- CN101981842B CN101981842B CN200980110750.1A CN200980110750A CN101981842B CN 101981842 B CN101981842 B CN 101981842B CN 200980110750 A CN200980110750 A CN 200980110750A CN 101981842 B CN101981842 B CN 101981842B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/3488—Multiresolution systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0044—Control loops for carrier regulation
- H04L2027/0063—Elements of loops
- H04L2027/0067—Phase error detectors
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Abstract
A receiver (10) is provided with a circuit (16) for discriminating multilevel modulation system, a circuit (17) for selecting phase correction system, a phase correction circuit (14), and a judgment circuit (15). The circuit (16) discriminates a multilevel modulation system used for a modulation signal on the basis of the modulation signal received from a transmitter. The circuit (17) selects a phase correction system to be used for the phase correction of the symbol of the modulation signal from a plurality of prepared phase correction systems on the basis of the multilevel degree of the multilevel modulation system discriminated by the circuit (16). The circuit (14) corrects the phase of the symbol using the phase correction system selected by the circuit (17). The circuit (15) judges the bit string of the symbol phase-corrected by the circuit (14) on the basis of the multilevel modulation system discriminated by the circuit (16).
Description
Technical field
The present invention relates to receiver, especially for the receiver of communication system that has utilized adaptive modulation system.
Background technology
In the past, existed the communication system of having utilized adaptive modulation system.This communication system has the different multiple many-valued modulation system of many-valued degree (bit rate), for example, switch the many-valued modulation system that will use according to self residing environment (circuit quality).In this case, can obtain best efficiency of transmission according to circuit quality.Here, as many-valued modulation system, for example there is BPSK (Binary Phase Shift Keying according to bit rate order from low to high, two-phase PSK), QPSK (Quadrature Phase Shift Keying, Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation, quadrature amplitude modulation) and the mode (for example,, with reference to the publication communique 2007-150906 of Japan, IEEE 802.11a-1999) such as 64QAM.
But the transmitter and the receiver that form communication system possess reference signal source separately.Reference signal source utilizes crystal emitter.The frequency of oscillation (being called " reference frequency " below) of each reference signal source of transmitter and receiver comprises error because of the precision of crystal emitter.Its result, carry out modulation treatment transmitting pusher side reference frequency and carry out having produced between the reference frequency of receiver side of demodulation process the error of a few millionths.The error of this reference frequency becomes the reason of the phase rotating of the data that receive in receiver.The error rate (Bit Error Rate: be below called " BER ") of the generation of this phase rotating after on demodulation brought very large impact.Therefore the phase rotating that, receiver docks at solution timing the data of receiving is proofreaied and correct.Particularly, using OFDM (Orthogonal Frequency Division Multiplexing, OFDM) in the situation of many-valued modulation of multi-carrier modulation of modulation etc., because the impact of separating the phase rotating that the frequency error of timing causes becomes large.This is that the interval of phasing is elongated because the holding time of 1 symbol becomes large.
In the past, the phasing mode of proofreading and correct as the phase rotating that carries out symbol, (for example there is the phasing mode of use pilot sub-carrier, with reference to the publication communique 2008-22339 of Japan) and used the phasing mode (for example,, with reference to the publication communique 2006-352746 of Japan) of frequency pilot sign.
In the phasing mode that has used pilot sub-carrier, in the transmission characteristic that causes signal because of the impact of multipath fading, exist larger frequency selectivity, it is large that correction error becomes.
Therefore,, in the stronger transmission environment of frequency selectivity, the phasing mode that has used frequency pilot sign is effective.
On the other hand, used the phasing mode of frequency pilot sign, the phasing mode of pilot sub-carrier is different from having used, and is not the correction successively by each OFDM symbol.Therefore, the larger interval that frequency pilot sign is embedded to modulation signal of the many-valued degree of many-valued modulation system must be narrower and small.So if carry out meeting the phasing of all many-valued modulation systems in adaptive modulation system, particularly in the lower many-valued modulation system of many-valued degree, efficiency of transmission can decline.
In addition, for the phasing that has used frequency pilot sign, owing to cannot carry out phasing before obtaining frequency pilot sign, so it is long to carry out the interval of phasing.Therefore,, in the case of the many-valued modulation system of the many-valued degree of height, in demodulation process process, the error of phase rotating may exceed allowed band.
Like this, in phasing mode, exist being applicable to and being not suitable for for many-valued modulation system.But receiver in the past uses identical phasing mode to the modulation signal receiving from transmitter.Therefore, receiver in the past cannot carry out best phasing according to the many-valued modulation system using in transmitter.
Summary of the invention
The present invention completes in view of the foregoing.The object of the invention is to, a kind of receiver that can carry out according to the many-valued modulation system using in transmitter best phasing is provided.
The receiver the present invention relates to is used to adaptive modulation communication system together with transmitter, and this transmitter sends the modulation signal that use generates according to the selected many-valued modulation system of circuit quality from multiple many-valued modulation systems.Above-mentioned modulation signal has the symbol string that represents the data that send to above-mentioned receiver.Determined the corresponding relation of above-mentioned symbol and bit string by selected many-valued modulation system in above-mentioned transmitter.The receiver the present invention relates to possesses many-valued modulation system judegment part, phasing mode selection portion, phasing portion and detection unit.Above-mentioned many-valued modulation system judegment part is configured to, and differentiates the above-mentioned many-valued modulation system for above-mentioned modulation signal according to the above-mentioned modulation signal receiving from above-mentioned transmitter.Above-mentioned phasing mode selection portion is configured to, and the many-valued degree of the above-mentioned many-valued modulation system determining according to above-mentioned many-valued modulation system judegment part is selected the phasing mode for the phasing of the symbol of above-mentioned modulation signal from pre-prepd multiple phasing modes.Above-mentioned phasing portion is configured to, the phase place that uses the selected above-mentioned phasing mode of above-mentioned phasing mode selection portion to proofread and correct above-mentioned symbol.Above-mentioned detection unit is configured to, and the above-mentioned many-valued modulation system determining according to above-mentioned modulation system judegment part is judged the above-mentioned symbol corresponding bit string being corrected with phase place in above-mentioned phasing portion.
According to this invention, the many-valued degree selected phase correcting mode of the above-mentioned many-valued modulation system based on using in above-mentioned transmitter.Therefore, can correspondingly with the above-mentioned many-valued modulation system that uses in above-mentioned transmitter carry out best phasing.
Preferably, above-mentioned transmitter has primary modulation mode and secondary modulation mode.Above-mentioned primary modulation mode is the many-valued modulation system of selection of reference frame according to the rules from the different multiple many-valued modulation system of many-valued degree, generates the primary modulation symbol that represents above-mentioned symbol.Above-mentioned secondary modulation mode is multi-carrier modulation.Above-mentioned secondary modulation mode generates secondary modulation symbol according to above-mentioned primary modulation symbol by the multiple subcarrier stacks that formed complex amplitude.Above-mentioned secondary modulation mode forms the above-mentioned modulation signal being made up of multiple above-mentioned secondary modulation symbols.Above-mentioned modulation signal has frequency pilot sign every the stipulated time.Above-mentioned frequency pilot sign is known secondary modulation symbol for above-mentioned receiver.Above-mentioned known secondary modulation symbol is made up of the subcarrier with known complex amplitude.Above-mentioned secondary modulation symbol comprises pilot sub-carrier.Above-mentioned pilot sub-carrier is known subcarrier for above-mentioned receiver.Above-mentioned known subcarrier has known complex amplitude.Above-mentioned phasing mode selection portion is configured to, if the above-mentioned many-valued degree of the above-mentioned many-valued modulation system that above-mentioned many-valued modulation system judegment part determines is less than setting, the above-mentioned frequency pilot sign of choice for use is proofreaied and correct the 1st phasing mode of the phase place of above-mentioned symbol, if above-mentioned many-valued degree more than setting; the above-mentioned pilot sub-carrier of choice for use is proofreaied and correct the 2nd phasing mode of the phase place of above-mentioned symbol.
In this case, in the time that the many-valued degree of the above-mentioned many-valued modulation system using in above-mentioned transmitter is less than setting, even carry out in the stronger transmission environment of frequency selectivity phasing effect also larger use the phasing of above-mentioned frequency pilot sign.On the other hand, when the many-valued degree of the above-mentioned many-valued modulation system using in above-mentioned transmitter is in the time that setting is above, easily realize high-transmission efficiency use the phasing of above-mentioned pilot sub-carrier.So, can correspondingly with the above-mentioned many-valued modulation system that uses in above-mentioned transmitter carry out best phasing.
More preferably, above-mentioned phasing mode selection portion is configured to, if the above-mentioned many-valued degree of the above-mentioned many-valued modulation system that above-mentioned many-valued modulation system judegment part determines is less than setting, only select above-mentioned the 1st phasing mode, if above-mentioned many-valued degree more than setting, is selected above-mentioned the 1st phasing mode and above-mentioned the 2nd phasing mode.
In this case, always used above-mentioned the 1st phasing of above-mentioned frequency pilot sign.Therefore, the control of above-mentioned phasing portion becomes simple.And, in above-mentioned the 1st phasing mode, by each above-mentioned subcarrier execution of phase correction.So, even under the stronger communication environments of frequency selectivity, also always can realize the effect of good phasing.
Further preferably, above-mentioned phasing portion is configured to, when selected above-mentioned the 1st phasing mode and above-mentioned the 2nd phasing mode in above-mentioned phasing mode selection portion in the situation that, after according to above-mentioned the 2nd phasing mode, the phase place of above-mentioned symbol being proofreaied and correct, according to above-mentioned the 1st phasing mode, the phase place of above-mentioned symbol is proofreaied and correct again.
In this case, can use pilot sub-carrier to carry out phasing by each symbol.And, can be by having used the phasing of frequency pilot sign to remove the error that the phasing because having used pilot sub-carrier produces.So, can carry out best phasing to the larger many-valued modulation system of many-valued degree.
Efficiency of transmission in the situation of preferably, the phase place of above-mentioned symbol being proofreaied and correct by the selected above-mentioned phasing mode of above-mentioned phasing mode selection portion according to above-mentioned phasing portion is set afore mentioned rules value.
In this case, can correspondingly with the many-valued modulation system that uses in above-mentioned transmitter carry out best phasing, and can improve efficiency of transmission.
Accompanying drawing explanation
Fig. 1 is the skeleton diagram of the receiver of execution mode 1.
Fig. 2 is the skeleton diagram that possesses the communication system of the same receiver.
Fig. 3 is the key diagram of 16QAM planisphere.
Fig. 4 is the key diagram of the configuration of subcarrier and pilot sub-carrier.
Fig. 5 is the key diagram of the structure of ofdm signal.
Fig. 6 is the key diagram of the embedded structure of frequency pilot sign.
Fig. 7 is the skeleton diagram of the receiver of execution mode 2.
Embodiment
(execution mode 1)
The receiver 10 of present embodiment has formed adaptive modulation communication system (being called " communication system " below) as shown in Figure 2 together with transmitter 20.Communication system is carried out based on being modulated by transmitter 20 packet communication of the ofdm signal of (being OFDM modulation in the present embodiment).In addition, for from transmitter 20 to the transmission channel 30 of receiver 10 transmission OFDM modulating waves can be wired can be also wireless.
Transmitter 20 adopts many-valued modulation system as primary modulation, adopts OFDM to modulate as secondary modulation.The data (information bit string) that transmitter 20 subtend receivers 10 send are carried out error correction coding.In addition, transmitter 20 carries out serial parallel transformation to the data after error correction coding.The symbol of transmitter 20 based on being determined by many-valued modulation system and the corresponding relation of bit string, generate the complex symbol (primary modulation symbol) (Symbol matching) for modulated sub-carriers according to the data after serial parallel transformation.Transmitter 20 carries out inverse discrete Fourier transform (secondary modulation) afterwards to complex symbol successively, by the complex baseband ofdm signal (OFDM symbol or secondary modulation symbol) of parallel serial conversion generating digital form.Transmitter 20 carries out digital-to-analog conversion (DA conversion) to complex baseband ofdm signal.Transmitter 20 utilizes the ofdm signal after the filter of the aliasing signal for removing DA conversion generation converts above-mentioned DA to carry out filtering, with carrier multiplication (carrying out frequency translation), the fixed signal of the professional etiquette of going forward side by side amplifies, and generates thus OFDM modulating wave.The above-mentioned OFDM modulating wave generating is thus sent to transmission channel 30 by transmitter 20.
Here, transmitter 20 has many-valued degree different multiple many-valued modulation system, for example 16QAM and 64QAM as primary modulation mode.Transmitter 20 in the time carrying out Symbol matching from the different multiple many-valued modulation system of many-valued degree with regulation the many-valued modulation system of selection of reference frame (that is to say that transmitter 20 carries out Adaptive Modulation).For example, transmitter 20 selects the most much higher value modulation system of many-valued degree so that the transmission speed of data is the fastest.In addition, transmitter 20 also can be according to the many-valued modulation system of Capacity Selection of the state of transmission channel 30 (circuit quality) and data so that transmission speed more than fixed value.
In addition, transmitter 20 possesses the reference signal source (not shown) with crystal emitter.Transmitter 20 uses the reference frequency of reference signal source transmitting to carry out inverse discrete Fourier transform (OFDM modulation) and frequency translation.In addition, in receiving device 10, also possesses reference signal source.
Like this, transmitter 20 sends the OFDM modulating wave that uses from multiple many-valued modulation systems (16QAM, 64QAM) the selected many-valued modulation system of benchmark in accordance with regulations and generate.
Here,, in the many-valued modulation system of the many-valued degree of height of 64QAM etc., the permissible error angle while using the bit string of the complex symbol decision symbol in complex number plane is less.Therefore, need to carry out phasing by each symbol.Below, as an example of 16QAM example, the permissible error angle in QAM is described.
Fig. 3 has represented the symbol configuration (signaling point configuration) in the complex number plane corresponding with bit string [0000]～[1111] of 16QAM.Here Gray code is made as to prerequisite.Blueline L1 in Fig. 3 presses Q (Quadrature-Phase) direction of principal axis by connecting the mid point of the line segment between bit string [1110] and each symbolic point of bit string [1010].Blueline L2 presses I (In-Phase) direction of principal axis by connecting the mid point of the line segment between bit string [1010] and each symbolic point of bit string [1011].The complex symbol receiving at receiver 10 is estimated as this complex symbol and represents that the probability of bit string [1010] is higher being present in the region A12 that is partitioned line L1, L2 encirclement that comprises bit string [1010].But in fact, the complex symbol that the phase rotating (reference arrow Q1) producing because of the error due to reference frequency can cause being present in transmitter 20 in the A12 of region may not be present in the A12 of region in receiver 10.In this case, in the judgement of bit string, produce mistake.
If there is no the error of reference frequency, the corresponding complex symbol of bit string [1010] receiving with receiver 10 is Gaussian Profile centered by the symbolic point that represents bit string [1010].Therefore, do not depart from original region take symbolic point and set the not contradiction of permissible error angle θ 1 of each symbolic point as condition.For example, the in the situation that of 16QAM, permissible error angle θ 1[degree] be 16.88.
In table 1, represent the permissible error angle θ 1 of representative QAM.Permissible error angle θ 1 is along with many-valued degree becomes large and diminishes as can be seen from Table 1.
[table 1]
| Many-valued modulation system | 16QAM | 64QAM | 256QAM | 1024QAM |
| Permissible error angle θ 1 (degree) | 16.88 | 10.55 | 7.69 | 6.06 |
Then, the phase rotating of the each OFDM symbol producing because of the error of reference frequency in OFDM modulation is discussed.As the main cause of the phase error producing due to the phase rotating of OFDM symbol, these two kinds of the errors (the 2nd error) when the error (the 1st error) can consider the needed carrier frequency synchronization of demodulation process (frequency translation) of OFDM time and sample frequency synchronous (fast Fourier transform).If the sample frequency of fast Fourier transform is made as to fs, the size of fast Fourier transform (FFT size) is made as to N point, the time of protecting interval (Guard Interval) is made as to Tgi, the holding time Ta of each OFDM symbol represents by formula (1) below.
[numerical expression 1]
Phase error based on the 1st error and the 2nd error is additivity.Therefore, if carrier frequency is made as to fc, the reference frequency error between two processing of modulation and demodulation is made as to e, the phase error angle θ 2[degree of each OFDM symbol] use formula (2) below to represent.
[numerical expression 2]
For example, according to the specification of IEEE 802.11a-1999 (the specification IEEE 802.11a of the WLAN that IEEE (U.S. electric institute of electronics) formulates), if allowing the reference frequency error of each reference signal source is 20ppm, in two processing of modulation and demodulation, can reach the reference frequency error e of 40ppm.For the error of carrier frequency fc, by utilizing the automatic frequency correction circuit of receiver, generally converge on the frequency error of fs/2.So formula (2) above can be deformed into formula (3) below.
[numerical expression 3]
In addition; according to the specification of IEEE 802.11a-1999; the sample frequency fs of fast Fourier transform is that the holding time Ta of 20MHz, OFDM symbol is that the big or small N of 4 μ sec (wherein, protection interlude Tgi be 0.8 μ sec), fast Fourier transform is 64 points.
If calculate formula (3) above according to the specification of IEEE 802.11a-1999, phase error angle θ 2 is 2.88.So, in 64QAM, just exceeded permissible error angle θ 1 with 4 symbols.In addition, according to the specification of IEEE 802.11a-1999, requiring 1 grouping maximum is 1000 bytes.Therefore,, if the not additional redundant digit based on error correction, the OFDM symbol that can send in 1 grouping is about 27 symbols.So, exceeded permissible error angle θ 1 with 4 symbols in the situation that, correctly 1 grouping of demodulation.
Therefore, IEEE 802.11a-1999 provides as follows: be made as by 4 in whole 52 subcarriers pilot sub-carrier PSC1～PSC4 that it doesn't matter with transfer of data as shown in Figure 4, by 48 remaining subcarrier SC0～SC47 that are made as for transfer of data.Therefore, can use pilot sub-carrier PSC1～PSC4 to carry out by the phasing of each OFDM symbol.
But, in the transmission characteristic that makes signal because of the impact of multipath fading, existing larger frequency selectivity, the S/N ratio that embeds the frequency of pilot sub-carrier likely extremely worsens.In this case, used the correction error of the phasing mode of pilot sub-carrier to become large.Therefore, special in the time being the many-valued modulation system of high many-valued degree, implementing phase is proofreaied and correct BER sometimes and can be worsened on the contrary.For example, near of the pilot sub-carrier PSC1 in Fig. 4, because frequency characteristic 1000 worsens, so used the precision of the phasing of pilot sub-carrier PSC1 to reduce.
In the stronger transmission environment of frequency selectivity, it is effective using the phasing mode of frequency pilot sign.Frequency pilot sign is made up of known symbol in receiving device 10 and transmitter 20.In addition, frequency pilot sign with regular time interval be embedded in the modulation signal (grouping) being formed by OFDM symbol.Therefore, can use frequency pilot sign to carry out the phasing by each subcarrier.
But the phasing mode that has used frequency pilot sign is not the correction successively by each OFDM symbol.Therefore, the larger interval that embeds frequency pilot sign in modulation signal of the many-valued degree of many-valued modulation system must be narrower and small.For example, in 16QAM, it is enough in modulation signal, embedding frequency pilot sign every 5 symbols.On the other hand, in 64QAM, the interval that embeds frequency pilot sign must be set for every 3 symbols in modulation signal.So in adaptive modulation system, if be configured to the phasing that can carry out meeting whole many-valued modulation systems, particularly in the lower many-valued modulation system of many-valued degree, efficiency of transmission reduces.
In addition, for the phasing that has used frequency pilot sign, owing to cannot carry out phasing before obtaining frequency pilot sign, so it is long to carry out the interval of phasing.Therefore,, in the case of the many-valued modulation system of the many-valued degree of height, in demodulation process process, also likely exceed permissible error angle θ 1.
So, transmitter 20 so that receiver 10 can optionally use the phasing of frequency pilot sign and use the mode of the phasing of pilot sub-carrier to generate modulation signal.
For example, modulation signal (grouping), is made up of short preamble SP, long preamble LP and data portion D as shown in Figure 5.
In order to set up timing synchronization, every basic cycle T1 (=0.8 μ sec) by transmitter 20 and receiver 10 all known synchronization pattern (specific pattern) X repeat 10 times (X1～X10) and form short preamble SP.That is to say, form short preamble SP by the repeating signal of basic cycle T1.
For channel estimating, every basic cycle T2 (=3.2 μ sec) by transmitter 20 and receiver 10 all known synchronization pattern Y repeat 2 times (Y1, Y2) and form long preamble LP.
Data portion D is the region of the data of information for transmitting save data position and modulation system etc.
In modulation signal, according to the short preamble SP of arranged in order of short preamble SP, long preamble LP, data portion D, long preamble LP and data portion D.
In addition, added in the front in each region of long preamble LP and data portion D the protection interval GI1, the GI2 that the later half part in each region are copied and obtain.Can reduce the impact of multipath by protection interval GI1, GI2.
Automatic frequency correction circuit 11, after baseband signal having been carried out to analog/digital conversion (AD conversion), uses short preamble SP and long preamble LP to proofread and correct the phase rotating of each ofdm signal.
Automatic frequency correction circuit 11 is initial uses short preamble SP to detect the larger frequency error between the reference frequency of transmitter 20 and the reference frequency of receiver 10.The modulation signal for example having postponed after conjugate complex number and the basic cycle T1 of modulation signal of basic cycle T1 by use multiplies each other to carry out the detection of frequency error.
Then, automatic frequency correction circuit 11 uses long preamble LP to detect frequency error.Used the detection of the frequency error of long preamble LP according to the order same with the detection of frequency error that has used short preamble SP.If use long preamble LP, can detect this smaller frequency error of 1/{2T2} (=fs/{264}).
Automatic frequency correction circuit 11 multiplies each other the antiphase of the frequency error that uses short preamble SP and long preamble LP to detect and the modulation signal receiving.Thus, automatic frequency correction circuit 11 carries out phasing (frequency correction).
Protection interval is removed circuit 12 and is removed by transmitter 20 additional protection interval GI1 and GI2 in modulation signal.
The sample frequency of fast Fourier transform circuit 13 use based on reference frequency carried out discrete Fourier transform to ofdm signal.Thus, fast Fourier transform circuit 13 carries out becoming for partial wave the multicarrier demodulation of multiple sub-carrier signals.Extract thus the component of the complex symbol of each subcarrier.
Phase-correcting circuit 14 is proofreaied and correct the phase rotating of the primary modulation symbol based on frequency error.Phase-correcting circuit 14 possesses the portion of inferring 141, equalization portion 142 and phase error and removes portion 143.
Inferring portion 141 uses frequency pilot sign to infer the impulse response of the frequency field of the transmission channel 30 of each subcarrier.Impulse response represents the transmission characteristic of each subcarrier.About the modulation signal of following preamble, infer portion 141, the given data of preamble (the synchronization pattern X of short preamble SP or long preamble LP synchronization pattern Y) is considered as to frequency pilot sign, infers phase rotating and the amplitude error (impulse response of each subcarrier) of this given data.About modulation signal below, per stipulated time has frequency pilot sign, infers phase rotating and amplitude error according to this given data.For the phase rotating of inferring out and amplitude error, can be made as use next frequency pilot sign proofread and correct before effectively, the value that also can obtain for the correcting value of the correcting value to next frequency pilot sign and current pilot symbol being carried out suitable weighting process is made as the corrected value based on next frequency pilot sign.In addition, for frequency pilot sign, also can, using the complex amplitude of whole subcarriers as given data, still also can only in the subcarrier of the larger frequency field of frequency selectivity, embed given data.In this case, derive the transmission characteristic of the subcarrier that does not embed given data according to the transmission characteristic of the subcarrier that has embedded given data.
The contrary characteristic of the impulse response of each subcarrier of inferring out in the portion of inferring 141 and the complex symbol of each subcarrier of following preamble are multiplied each other in equalization portion 142.Thus, the distortion of frequency domain is proofreaied and correct by equalization portion 142 by each subcarrier, and proofreaies and correct the phase rotating based on frequency error.In addition, the transmission channel larger to adjusting amplitude of vibration, not only amplitude error is also proofreaied and correct in phase calibration rotation.
Like this, infer portion 141 and equalization portion 142 and use the 1st phasing mode of the phase place of frequency pilot sign correction symbol.Use the phasing of frequency pilot sign, owing to carrying out phasing by each subcarrier, so even if also have good phasing effect in the stronger transmission environment of frequency selectivity.
In addition, in the present embodiment, as shown in Figure 4,4 in whole 52 subcarriers is the pilot sub-carrier PSC1～PSC4 irrelevant with transfer of data, and remaining 48 is subcarrier SC0～SC47 for transfer of data.Symbol on pilot sub-carrier PSC1～PSC4 is given data (known symbol).
Phase error is removed portion 143 and is used 4 pilot sub-carrier PSC1～PSC4 to carry out the phasing of each OFDM symbol.Phase error is removed portion 143 and is detected the frequency error in each pilot sub-carrier according to the known symbol of pilot sub-carrier PSC1～PSC4.Phase error is removed portion 143 and is used the frequency error computing that detects identical OFDM symbol to be carried out to the phase error of each complex symbol that discrete Fourier transform obtains.And phase error is removed portion 143 antiphase of the phase error calculating and each complex symbol is multiplied each other.Thus, phase error is removed portion 143 and proofreaies and correct the phase rotating of the symbol based on frequency error.
Like this, phase error is removed portion 143 and carries out the 2nd phasing mode of the phase place for using pilot sub-carrier correction symbol.
Modulation system judging circuit 16 is differentiated the many-valued modulation system for modulation signal according to the modulation signal receiving from transmitter 20.In the present embodiment, according to the information of the modulation system comprising the data portion D of the modulation signal receiving from transmitter 20, (identical OFDM symbol is carried out obtain after discrete Fourier transform each complex symbol) many-valued modulation system of differentiating each OFDM symbol is 16QAM or 64QAM.
Correcting mode selects circuit 17 according to the many-valued degree of the many-valued modulation system determining in modulation system judging circuit 16, selects the phasing mode of the phase place of the symbol for proofreading and correct modulation signal from pre-prepd multiple phasing modes.In the present embodiment, it is 16QAM, to select the 1st phasing mode in the differentiation result of modulation system judging circuit 16 that correcting mode is selected circuit 17, selects the 2nd phasing mode in the situation that differentiation result is 64QAM.
Phase-correcting circuit 14 uses correcting mode to select selected above-mentioned phasing mode in circuit 17 to proofread and correct the phase place of symbol.
The phase error angle θ 2 of each OFDM symbol is 2.88 ° as described above.Table 2 represents the value of θ 1/ θ 2 in the each many-valued modulation system of QPSK, 16QAM and 64QAM.In addition, table 2 has represented in order to be no more than permissible error angle θ 1 in demodulation process process, frequency pilot sign to be embedded the minimum mark space M (the maximum positive integer of θ 1/ θ below 2) of modulation signal.Table 2 has also represented frequency pilot sign to be embedded to the efficiency of transmission P1=M/ (M+1) in the situation of modulation signal with minimum mark space M.
[table 2]
| Many-valued modulation system | QPSK | 16QAM | 64QAM |
| θ1/θ2 | 15.63 | 5.86 | 3.66 |
| |
15 | 5 | 3 |
| P1＝M/M+1 | 0.94 | 0.83 | 0.75 |
As shown in Figure 6, in each many-valued modulation system, every M symbol, frequency pilot sign PS is embedded in modulation signal.Thus, prevented that phase error exceedes permissible error angle θ 1 in demodulation process process.In addition, efficiency of transmission also becomes the highest.
Using in the 1st phasing mode of frequency pilot sign, proofread and correct interval longer than using the situation of pilot sub-carrier.This is owing to being the opportunity that the equalization parameter of equalization portion 142 is updated every M symbol.So, at the many-valued modulation system of the many-valued degree of height, i.e. (minimum mark space M=3) 64QAM, if the interval of frequency pilot sign 5 just have that in demodulation process process phase error exceedes permissible error angle θ 1 may.
On the other hand, using the 2nd phasing mode of pilot sub-carrier PSC1～PSC4 is the correction successively by each OFDM symbol.Therefore, can carry out best phasing by each OFDM symbol (carrying out each complex symbol that discrete Fourier transform obtains for the OFDM symbol to identical).So, even the many-valued modulation system of high many-valued degree also can prevent that the situation that in demodulation process process phase error exceedes permissible error angle θ 1 from occurring.
In the 1st phasing mode, need many-valued degree larger shorter to the interval of the frequency pilot sign embedding in modulation signal.Therefore, efficiency of transmission easily becomes lower.As shown in table 2, efficiency of transmission P1=0.83 in 16QAM, efficiency of transmission P1=0.75 in 64QAM.On the other hand, in the 2nd phasing mode, by 4 in whole 52 subcarriers for pilot sub-carrier PSC1～PSC4.Therefore, having used the efficiency of transmission P2 in the situation of pilot sub-carrier is 0.92 (=48/52).So the 2nd phasing mode easily realizes high-transmission efficiency than the 1st phasing mode.
As described above, according to the receiver 10 of present embodiment, the many-valued degree selected phase correcting mode of the many-valued modulation system based on using in transmitter 20.Therefore, can correspondingly with the many-valued modulation system of use in transmitter 20 carry out best phasing.
Particularly, the many-valued degree of many-valued modulation system using in transmitter 20 is less than setting (the many-valued degree corresponding with 64QAM), though carry out in the stronger transmission environment of frequency selectivity phasing effect also larger use the phasing of frequency pilot sign.On the other hand, the many-valued degree of many-valued modulation system using in transmitter 20 in the case of more than setting (the many-valued degree corresponding with 64QAM), easily realize high-transmission efficiency use the phasing of pilot sub-carrier.So, can correspondingly with the many-valued modulation system of use in transmitter 20 carry out best phasing.
But phasing mode selects circuit 17 also can form as below.; if the many-valued degree of the many-valued modulation system determining in many-valued modulation system judging circuit 16 is less than setting (the many-valued degree corresponding with 64QAM), phasing mode selects 17, circuit to select the 1st phasing modes, if many-valued degree more than setting (the many-valued degree corresponding with 64QAM); phasing mode select circuit 17 to select the 1st phasing mode and the 2nd phasing mode.
In this case, always used the phasing of frequency pilot sign.Therefore, the control of phase-correcting circuit 14 becomes simple.And, in the 1st phasing mode, press each subcarrier execution of phase correction.So, even under the stronger transmission environment of frequency selectivity, also can make the effect of phasing become large.
But, infer that portion 141 is used the known symbol of preamble and the frequency pilot sign that embeds with fixed intervals is inferred the impulse response of transmission channel 30 in modulation signal.For frequency pilot sign, all subcarriers are embedded to given data.Therefore,, if use frequency pilot sign, can carry out high-precision phasing to all subcarriers.But, before obtaining frequency pilot sign, cannot carry out the inferring of impulse response of transmission channel 30.That is to say, in the phasing of use frequency pilot sign, correction interval is elongated.Therefore,, in the case of the many-valued modulation system of the many-valued degree of height, in demodulation process process, may exceed the complex amplitude of subcarrier, i.e. the permissible error angle θ 1 of primary modulation symbol.
On the other hand, phase error is removed portion 143 and is used pilot sub-carrier to infer the impulse response of transmission channel 30.Therefore, can upgrade by each OFDM symbol the impulse response of transmission channel 30.But, be to utilize extrapolation and interpolation to calculate according to the impulse response of pilot sub-carrier about the presumed value of the impulse response of the subcarrier (that is to say the subcarrier for transfer of data) beyond pilot sub-carrier.Therefore, contain error for the presumed value of the impulse response of the subcarrier of transfer of data.
So, upgrade impulse response if only use phase error to remove portion 143, owing to using the contrary characteristic calculating according to the impulse response after upgrading to carry out equalization, so all can accumulate at each renewal time error of impulse response in equalization portion 142.Therefore, if through certain time the accumulation of error can exceed allowance (permissible error angle θ 1), the effect of phasing disappears.Particularly because its permissible error angle of many-valued modulation system θ 1 that many-valued degree is larger is less, so the possibility that the effect of phasing disappears is higher.
So, the many-valued degree of the many-valued modulation system determining in many-valued modulation system judging circuit 16 (selects to have selected in circuit 17 situation of the 1st phasing mode and the 2nd phasing mode in phasing mode) in the case of more than setting (the many-valued degree corresponding with 64QAM), preferably, phase-correcting circuit 14 forms as below., phase-correcting circuit 14 is proofreaied and correct the phase place of symbol according to the 1st phasing mode after the phase place of symbol being proofreaied and correct according to the 2nd phasing mode again.
By doing like this, can use pilot sub-carrier to carry out phasing by each OFDM symbol.And, can be by because the error of having carried out using the phasing of pilot sub-carrier to produce is removed by the phasing that has used frequency pilot sign, so, can carry out best phasing to the larger many-valued modulation system of many-valued degree.
But, in above-mentioned example, select the setting of circuit 17 to be made as the many-valued degree corresponding with 64QAM phasing mode.But, also can select the efficiency of transmission in situation that the selected phasing mode of circuit 17 proofreaies and correct the phase place of symbol to set setting according to phase-correcting circuit 14 use phasing modes.
For example, consider that transmitter 20 has QPSK, 16QAM and the 64QAM situation as many-valued modulation system.
It is any of QPSK, 16QAM and 64QAM that the information of the modulation system comprising the data portion D of the modulation signal that in this case, many-valued modulation system judging circuit 16 bases receive from transmitter 20 is differentiated for the many-valued modulation system of modulation signal.
Here,, the in the situation that of the 1st phasing mode, each efficiency of transmission P1 of QPSK, 16QAM and 64QAM was 0.97,0.83 and 0.75 (with reference to table 2).
On the other hand, the in the situation that of the 2nd phasing mode, efficiency of transmission P2 is 0.92.
In this case, phasing mode select circuit 17 for efficiency of transmission P1 than the much higher value modulation system of efficiency of transmission P2 (=0.92), the phasing of choice for use frequency pilot sign.The QPSK that, phasing mode selects circuit 17 to be 0.97 at efficiency of transmission P1, select the 1st phasing mode.On the other hand, for the efficiency of transmission P1 many-valued modulation system lower than efficiency of transmission P2, the phasing of choice for use pilot sub-carrier.The 16QAM that, phasing mode selects circuit 17 to be 0.83 at efficiency of transmission P1, select the 2nd phasing mode.Equally, the 64QAM that phasing mode selects circuit 17 to be 0.75 at efficiency of transmission P1, select the 2nd phasing mode.
That is to say, phasing mode selects the many-valued degree of the many-valued modulation system (QPSK or 16QAM or 64QAM) that circuit 17 uses in transmitter 20 lower than the phasing that uses pilot sub-carrier the setting based on efficiency of transmission P2.On the other hand, phasing mode selects the many-valued degree of the many-valued modulation system that circuit 17 uses in transmitter 20 in the case of more than the setting based on efficiency of transmission P2, to use the phasing of frequency pilot sign.
For this situation, can correspondingly with the many-valued modulation system of use in transmitter 20 carry out best phasing, and can improve efficiency of transmission.
(execution mode 2)
The receiver 40 of present embodiment is for carrier wave communication system.
Transmitter 20 for carrier wave communication system carries out error correction coding to the data that mail to receiver 40.In addition, transmitter 20 generates complex symbol (Symbol matching) according to the corresponding relation of the symbol being determined by many-valued modulation system and bit string according to the data after error correction coding.Transmitter 20 is after the DA conversion of complex symbol being carried out to suitable waveform formation processing, by baseband signal and carrier multiplication are carried out to frequency translation, in necessary frequency band, carry out after displacement, the signal stipulating amplifies to generate modulating wave, and this baseband signal is to use the symbol string obtaining by removing the filter filtering of the aliasing signal producing in DA conversion to generate.Transmitter 20 sends to transmission channel 20 modulating wave generating.
Here, transmitter 20 has many-valued degree different multiple many-valued modulation system, for example QPSK and 16QAM.Transmitter 20, in the time carrying out Symbol matching, is selected the fastest many-valued modulation system of transmission speed (that is to say, transmitter 20 carries out Adaptive Modulation) from the different multiple many-valued modulation system of many-valued degree according to the state of transmission channel 30.
In addition, and transmitter 20 possesses the reference signal source (not shown) with crystal emitter.Transmitter 20 uses the reference frequency of reference signal source transmitting to carry out said frequencies conversion etc.In addition, in receiver 40, also possesses reference signal source.
Transmitter 20 sends the modulating wave that uses the many-valued modulation system of selecting according to circuit quality from multiple many-valued modulation systems (QPSK, 64QAM) to generate.Modulating wave has the symbol string of the data that send to receiver 40 of indicating.Determined the corresponding relation of this symbol and bit string by the many-valued modulation system of selecting in transmitter 20.
The receiver 40 of present embodiment as shown in Figure 7, possesses A/D converter 41, FIR filter 42, down sample circuit 43, phase-correcting circuit 44, decision circuit 45, many-valued modulation system judging circuit (many-valued modulation system judegment part) 46 and phasing mode and selects circuit (phasing mode selection portion) 47.The analog signal processing circuit that has omitted in the drawings that signal in simulation part amplifies, disturbing wave is removed filter etc.
A/D translation circuit 41 uses the reference frequency of reference signal source (not shown) transmitting of transmitter 40 to generate carrier wave.A/D translation circuit 41 carries out down-conversion by above-mentioned carrier wave and the modulation signal receiving via transmission channel 30 are multiplied each other to modulation signal and generates baseband signal.A/D translation circuit 41 carries out analog/digital conversion to baseband signal and exports to FIR filter 42.
Down sample circuit 43 carries out down sample to the baseband signal of accepting via FIR filter 42.Down sample circuit 43 is exported the baseband signal after down sample to phase-correcting circuit 44.
Phase-correcting circuit 44 possesses phase error and removes portion 441, modulator 442 and phase estimating portion 443.Phase-correcting circuit 44 optionally uses and has utilized the phasing mode of modulating again and used these two kinds of phasing modes of phasing mode of frequency pilot sign to proofread and correct the phase rotating based on frequency error.
Remove portion 441, modulator 442 and phase estimating portion 443 by phase error and used the phasing mode of modulation again.In the case of having used the phasing mode of modulation again, phase error is removed portion 441 by the keep intact constant decision circuit 45 that is sent to of the output of down sample circuit 43.The IQ signal that the bit string that modulator 442 is judged decision circuit 45 is transformed on complex plane utilizes plural number to carry out modulating again of symbolism.The modulation signal again that phase estimating portion 443 exports modulator 442 and the output of down sample circuit 43 long-pending carries out computing.Thus, phase estimating portion 443 calculates phase error.The antiphase (phase coefficient) that phase error is removed the phase error that portion 441 calculates phase estimating portion 443 multiplies each other with each complex symbol.Thus, phase error is removed portion 441 and is proofreaied and correct the phase rotating based on frequency error.That is to say, phase-correcting circuit 44 has used the phasing of modulation again.Use again the phasing of modulation to be performed on a regular basis.
Remove portion 441 and used the phasing mode of frequency pilot sign by phase error.Here, although the frequency pilot sign in present embodiment is the known symbol with known phase, be not the frequency pilot sign after the such multi-carrier modulation of execution mode 1.But, use the phasing mode of this known symbol identical with execution mode 1, therefore the description thereof will be omitted.
The many-valued modulation system that many-valued modulation system judging circuit 46 is differentiated each grouping according to the information of the modulation system comprising the modulation signal receiving from transmitter 20 is QPSK or 16QAM.
Phasing mode selects circuit 47 to be chosen in the phasing mode that will carry out in phase-correcting circuit 44 according to the many-valued degree of the many-valued modulation system determining in many-valued modulation system judging circuit 46.
Here, the in the situation that of 16QAM, because the intersymbol distance on complex plane is shorter, so the permissible error angle θ 1 of each symbolic point compares little with QPSK.Therefore, be in the situation of 16QAM for many-valued modulation system, if use the phasing mode same with above-mentioned QPSK, in the bit string after demodulation, may comprise more mistake, then complex symbol after modulating may not be correct.
So it is QPSK in the differentiation result of many-valued modulation system judging circuit 46 that phasing mode is selected circuit 47, choice for use again modulation phasing mode.It is 16QAM in the differentiation result of many-valued modulation system judging circuit 46 that phasing mode is selected circuit 47, choice for use the phasing mode of frequency pilot sign.
As described above, the receiver 40 of present embodiment, when the many-valued degree of the many-valued modulation system (QPSK or 16QAM) using is less than setting (the many-valued degree corresponding with 16QAM), used the phasing of modulation again in transmitter 20.In addition, receiver 40, when the many-valued degree of many-valued modulation system using in transmitter 20 is in the case of more than setting (the many-valued degree corresponding with 16QAM), has used the phasing of frequency pilot sign.
Like this, according to receiver 40, the many-valued degree selected phase correcting mode of the many-valued modulation system based on using in transmitter 20.Therefore, can correspondingly with the many-valued modulation system of use in transmitter 20 carry out best phasing.
Claims (5)
1. a receiver, is characterized in that,
Be used from adaptive modulation communication system with transmitter one, and this transmitter sends the modulation signal that uses from multiple many-valued modulation systems the selected many-valued modulation system of benchmark according to the rules and generate,
Above-mentioned modulation signal has the symbol string of the data that send to above-mentioned receiver of indicating;
Determined the corresponding relation of above-mentioned symbol and bit string by selected many-valued modulation system in above-mentioned transmitter;
Above-mentioned receiver possesses many-valued modulation system judegment part, phasing mode selection portion, phasing portion and detection unit;
Above-mentioned many-valued modulation system judegment part is configured to, and differentiates the above-mentioned many-valued modulation system for above-mentioned modulation signal according to the above-mentioned modulation signal receiving from above-mentioned transmitter;
Above-mentioned phasing mode selection portion is configured to, the many-valued degree of the above-mentioned many-valued modulation system determining according to above-mentioned many-valued modulation system judegment part, from pre-prepd multiple phasing modes, selection is for the phasing mode of the phasing of the symbol of above-mentioned modulation signal;
Above-mentioned phasing portion is configured to, the phase place that uses the selected above-mentioned phasing mode of above-mentioned phasing mode selection portion to proofread and correct above-mentioned symbol;
Above-mentioned detection unit is configured to, and the above-mentioned many-valued modulation system determining according to above-mentioned modulation system judegment part is judged the above-mentioned symbol corresponding bit string being corrected with phase place in above-mentioned phasing portion.
2. receiver according to claim 1, is characterized in that,
Above-mentioned transmitter has primary modulation mode and secondary modulation mode;
Above-mentioned primary modulation mode is the many-valued modulation system of selection of reference frame according to the rules from the different multiple many-valued modulation system of many-valued degree, generates the primary modulation symbol that represents above-mentioned symbol;
Above-mentioned secondary modulation mode is multi-carrier modulation, according to above-mentioned primary modulation symbol, the multiple subcarrier stacks that formed complex amplitude is generated to secondary modulation symbol, forms the above-mentioned modulation signal being made up of multiple above-mentioned secondary modulation symbols;
Above-mentioned modulation signal has frequency pilot sign every the stipulated time;
Above-mentioned frequency pilot sign is known secondary modulation symbol for above-mentioned receiver;
Above-mentioned known secondary modulation symbol is made up of the subcarrier with known complex amplitude;
Above-mentioned secondary modulation symbol comprises pilot sub-carrier;
Above-mentioned pilot sub-carrier is known subcarrier for above-mentioned receiver;
Above-mentioned known subcarrier has known complex amplitude;
Above-mentioned phasing mode selection portion is configured to, if the above-mentioned many-valued degree of the above-mentioned many-valued modulation system that above-mentioned many-valued modulation system judegment part determines is less than setting, the above-mentioned frequency pilot sign of choice for use is proofreaied and correct the 1st phasing mode of the phase place of above-mentioned symbol, if above-mentioned many-valued degree more than setting; the above-mentioned pilot sub-carrier of choice for use is proofreaied and correct the 2nd phasing mode of the phase place of above-mentioned symbol.
3. receiver according to claim 2, is characterized in that,
Above-mentioned phasing mode selection portion is configured to, if the above-mentioned many-valued degree of the above-mentioned many-valued modulation system that above-mentioned many-valued modulation system judegment part determines is less than setting, only select above-mentioned the 1st phasing mode, if above-mentioned many-valued degree more than setting, is selected above-mentioned the 1st phasing mode and above-mentioned the 2nd phasing mode.
4. receiver according to claim 3, is characterized in that,
Above-mentioned phasing portion is configured to, when selected above-mentioned the 1st phasing mode and above-mentioned the 2nd phasing mode in above-mentioned phasing mode selection portion in the situation that, after according to above-mentioned the 2nd phasing mode, the phase place of above-mentioned symbol being proofreaied and correct, according to above-mentioned the 1st phasing mode, the phase place of above-mentioned symbol is proofreaied and correct again.
5. receiver according to claim 2, is characterized in that,
Efficiency of transmission in the situation of by the selected above-mentioned phasing mode of above-mentioned phasing mode selection portion, the phase place of above-mentioned symbol being proofreaied and correct according to above-mentioned phasing portion is set afore mentioned rules value.
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| JP2008-082122 | 2008-03-26 | ||
| JP2008082122A JP5215704B2 (en) | 2008-03-26 | 2008-03-26 | Adaptive demodulation method |
| PCT/JP2009/056110 WO2009119736A1 (en) | 2008-03-26 | 2009-03-26 | Receiver |
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| JP (1) | JP5215704B2 (en) |
| KR (1) | KR101209501B1 (en) |
| CN (1) | CN101981842B (en) |
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| WO2010070884A1 (en) * | 2008-12-15 | 2010-06-24 | パナソニック株式会社 | Receiver apparatus and receiving method |
| JP5669668B2 (en) * | 2011-05-18 | 2015-02-12 | 三菱電機株式会社 | Demodulator and communication device |
| IN2014DN08872A (en) | 2012-04-24 | 2015-05-22 | Nec Corp | |
| SG11202000079UA (en) * | 2017-07-06 | 2020-02-27 | Sony Corp | Communication device and communication method |
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| CN1674574A (en) * | 2004-03-23 | 2005-09-28 | 三洋电机株式会社 | Receiving method and apparatus |
| WO2007029406A1 (en) * | 2005-09-07 | 2007-03-15 | Nec Corporation | Adaptive radio/modulation apparatus, receiver apparatus, wireless communication system and wireless communication method |
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| JP2000269919A (en) * | 1999-03-16 | 2000-09-29 | Matsushita Electric Ind Co Ltd | Ofdm communication unit |
| JP3844951B2 (en) * | 2000-09-21 | 2006-11-15 | 三菱電機株式会社 | Receiver and adaptive equalization processing method |
| US6587697B2 (en) * | 2001-05-14 | 2003-07-01 | Interdigital Technology Corporation | Common control channel uplink power control for adaptive modulation and coding techniques |
| JP2004364321A (en) * | 2001-06-01 | 2004-12-24 | Sony Corp | Inverse spread apparatus, propagation line estimate apparatus, receiver and interference suppressing apparatus, inverse spread, propagation line estimate, reception and interference suppressing method, program for them, and recording medium with the program recorded thereon |
| DE60206356T2 (en) * | 2002-04-16 | 2006-05-11 | Sony International (Europe) Gmbh | Orthogonal frequency division multiplexing (OFDM) with channel prediction |
| TWI229981B (en) * | 2003-10-06 | 2005-03-21 | Chunghwa Telecom Co Ltd | Receiver of multi-carrier communication system |
| JP4359162B2 (en) * | 2004-02-24 | 2009-11-04 | 三洋電機株式会社 | Receiver |
| TWI268068B (en) * | 2004-11-10 | 2006-12-01 | Ind Tech Res Inst | Method and device for modulation recognition of digitally modulated signals with multi-level magnitudes |
| KR20080071484A (en) * | 2005-12-06 | 2008-08-04 | 로무 가부시키가이샤 | Frequency modulator and fm transmission circuit using the same |
| WO2008129811A1 (en) * | 2007-03-23 | 2008-10-30 | Panasonic Corporation | Radio transmission device and radio reception device |
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| CN1674574A (en) * | 2004-03-23 | 2005-09-28 | 三洋电机株式会社 | Receiving method and apparatus |
| WO2007029406A1 (en) * | 2005-09-07 | 2007-03-15 | Nec Corporation | Adaptive radio/modulation apparatus, receiver apparatus, wireless communication system and wireless communication method |
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| KR101209501B1 (en) | 2012-12-07 |
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| TWI385990B (en) | 2013-02-11 |
| WO2009119736A1 (en) | 2009-10-01 |
| CN101981842A (en) | 2011-02-23 |
| TW201014291A (en) | 2010-04-01 |
| HK1154131A1 (en) | 2012-04-13 |
| JP5215704B2 (en) | 2013-06-19 |
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