EP1665693A1 - Correction adaptative du desequilibre iq pour systemes de communication sans fil a porteuses multiples - Google Patents

Correction adaptative du desequilibre iq pour systemes de communication sans fil a porteuses multiples

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Publication number
EP1665693A1
EP1665693A1 EP04784434A EP04784434A EP1665693A1 EP 1665693 A1 EP1665693 A1 EP 1665693A1 EP 04784434 A EP04784434 A EP 04784434A EP 04784434 A EP04784434 A EP 04784434A EP 1665693 A1 EP1665693 A1 EP 1665693A1
Authority
EP
European Patent Office
Prior art keywords
imbalance
error
transformation
adaptive filter
frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04784434A
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German (de)
English (en)
Inventor
Jian Lin
Ernest Tsui
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Intel Corp
Original Assignee
Intel Corp
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Filing date
Publication date
Application filed by Intel Corp filed Critical Intel Corp
Publication of EP1665693A1 publication Critical patent/EP1665693A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0016—Stabilisation of local oscillators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0018—Arrangements at the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end

Definitions

  • Embodiments of the present invention are generally directed to wireless communication systems and, more particularly, to adaptive in-phase (I) and/or quadrature- phase (Q) correction for multicarrier wireless communication systems.
  • I in-phase
  • Q quadrature- phase
  • a multicarrier communication system such as, e.g., Orthogonal Frequency Division Multiplexing (OFDM), Discrete Multi-tone (DMT) and the like, is typically characterized by a frequency band associated with a communication channel being divided into a number of smaller sub-bands (subcarriers herein).
  • Communication of content e.g., data, audio, video, etc.
  • the total number of subcarriers is increased within a given bandwidth, with a corresponding increase in channel throughput.
  • the subcarriers are controlled to be mathematically orthogonal to one another, e.g., wherein the peak of one subcarrier is positioned at a frequency that represents a substantial null to adjacent subcarriers.
  • Wireless communication systems and associated standards are using increasingly use more sophisticated modulation techniques such as 64 QAM and OFDM (orthogonal frequency division multiplex) to increase communication channel throughput.
  • modulation techniques such as 64 QAM and OFDM (orthogonal frequency division multiplex) to increase communication channel throughput.
  • the increased sensitivity of these more sophisticated modulation techniques to small imbalances between the In-phase (I) and Quadrature (Q) paths of a low cost direct- conversion receiver and/or transmitter becomes a significant issue. Phase mismatch occurs when phase difference between local oscillator signal for the In-phase and Quadrature channels is not exactly 90 degrees.
  • Gain mismatch between I and Q channels result from mixer, filters, or analog to digital converter (ADC) as well as non-uniformity between the channels.
  • ADC analog to digital converter
  • the IQ imbalance caused by I and Q arm filter mismatch is likely to also be a function of frequency.
  • IQ imbalance may have frequency independent components, frequency dependent components and may also introduce image interference aliasing into the desired signal band which may interfere with channel estimation.
  • Fig. 1 shows an example data communication system according to an example embodiment:
  • Fig. 2 shows an example equalizer according to one aspect of an example embodiment;
  • Fig. 3 shows points in an IQ plane according to one embodiment;
  • Fig. 4 shows an example adaptive filter suitable for use in accordance with one embodiment;
  • Fig. 5 illustrates a block diagram of an example adaptive filter architecture, according to one embodiment;
  • Fig. 6 illustrates an example equalizer architecture to improve channel estimation, according to one embodiment;
  • Fig. 7 depicts an example approach for frequency dependent IQ imbalance correction, according to one embodiment;
  • Fig. 1 shows an example data communication system according to an example embodiment:
  • Fig. 2 shows an example equalizer according to one aspect of an example embodiment;
  • Fig. 3 shows points in an IQ plane according to one embodiment;
  • Fig. 4 shows an example adaptive filter suitable for use in accordance with one embodiment;
  • Fig. 5 illustrates a block diagram of an example adaptive filter architecture, according to one embodiment;
  • Fig. 6 illustrate
  • Fig. 8 illustrates an example unified approach to frequency dependent and frequency independent IQ imbalance correction that accommodates frequency and timing offsets in channel estimation, according to one embodiment
  • Fig. 9 graphically illustrates example convergence performance according to one embodiment
  • Fig. 10 graphically illustrates example performance characteristics for combined mixer and filter mismatch correction, according to one embodiment
  • Fig. 11 illustrates example performance characteristics for combined imbalance correction in a multipath channel, according to one embodiment
  • Fig. 12 illustrates example performance characteristics for combined imbalance correction in a multipath channel with a significant frequency offset, according to one embodiment
  • Fig. 13 depicts example performance characteristics for combined imbalance correction with a sampling rate offset, according to one embodiment
  • Fig. 14 depicts example performance characteristics for combined imbalance correction with residual frequency and sampling rate offsets in a multipath channel, according to one embodiment.
  • Embodiments of an apparatus and method for adaptive IQ imbalance correction for multicarrier wireless communication systems are generally presented. More specifically, embodiments of the invention are directed to a unified approach for jointly estimating and minimizing transmitter and receiver IQ imbalance, while correcting for residual frequency and timing offsets. According to one embodiment, the technique is implemented with an adaptive filter that converges rapidly, adapts to temperature and aging effects, and is computationally relatively inexpensive, although the invention is not limited in this respect. [0007] Reference throughout this specification to "one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention.
  • aspects of the present invention may well be used to implement any of a number of wireless communication platforms such as, e.g., wireless local area network (WLAN), wireless personal area network (WPAN), wireless metro-area networks (WMAN), cellular networks, and the like.
  • WLAN wireless local area network
  • WPAN wireless personal area network
  • WMAN wireless metro-area networks
  • cellular networks e.g., cellular networks, and the like.
  • This disclosure models the effects of IQ imbalance due to both mixer and filter mismatches on OFDM systems and discusses how the remote transmitter and local receiver IQ imbalances can be jointly "balanced" adaptively with fast convergence for each individual packet. Jointly eliminating IQ imbalance in the transmitter and receiver is important to wireless high performance for future high order QAM (64 and above) systems. Adaptive corrections account for different transmitters in ad hoc networks and allow for temperature and aging IQ variations with time. Frequency dependent corrections are required for low cost systems where complex analog matching circuits for in-phase and quadrature arm filters can be eliminated. The techniques described herein correct both constant (frequency independent) and frequency dependent IQ imbalance based on different sets of adaptive equalizers in the frequency domain. Jointly balancing of transmitter and receiver imbalance for frequency dependent IQ effects is also a novel aspect of this work, although the scope of the invention is not limited in this respect.
  • IQ imbalance can be relatively constant over frequency (e.g., for mixer mismatch, etc.) or frequency dependent (e.g., for filter mismatch, etc.).
  • in-phase and quadrature mixer mismatches are frequency independent.
  • Mixer mismatch includes gain mismatch and phase mismatch between I and Q RF down/up- conversion channels.
  • the phase deviation from the ideal 90 degrees between I and Q local oscillator signal causes I signal leakage to the Q channel and vice versa.
  • the resultant "channel" may be expressed mathematically as a 2x2 matrix: ,; B,, H f Cosai H;Sin cCi H-mbcer H remember H HqSin asweeping H q Cosa q
  • In-phase and quadrature arm filter mismatches of the cutoff frequency, ripple, and group delay generally will be frequency dependent and causes image frequency interference, however it does not cause I (Q) leakage into Q (I).
  • This filter mismatch can be expressed as:
  • the Hmixe and H ⁇ i ter can express either transmitter or receiver, or a combination of both.
  • the received frequency domain signal i r> k, q r , k can be expressed as ,k H SI + H, H iq ⁇ H qi H ii ⁇ H qq iq + H ql -k ' 2 1r,k - H iq + H qi HJI + H qq 9t,k ' 2 + H q ⁇ + H iq - Hjj + H qq Qt,-k 1 2
  • equation [4] may be read to show that the filter IQ imbalance also has two effects, like the case of constant IQ imbalance.
  • filter IQ imbalance is a function of frequency, each frequency (or subcarrier) suffers a different distortion.
  • This understanding is important to understanding the solutions described below.
  • Model of the Effects of OFDM Channel Estimation and Correction on the Signal [0016]
  • channel estimation is often based on an OFDM preamble training signal.
  • the calibrator treats all observable distortions as channel including the IQ effects.
  • Channel corrections derived from the training signal are applied to the entire received signals to compensate for the multipath channel frequency characteristics.
  • the "long preamble" is the training signal for channel estimation.
  • IQ imbalance distortion for frequency k will depend on the particular signal value at image frequency -k. Therefore, if constant IQ imbalance exists, channel correction coefficients will fall into two classes even with an ideal channel. When the channel corrections are applied to the entire received signals, the two classes of distortions will appear and will require separate compensation. Conventional approaches to IQ imbalance correction often deal with this effect as a combined effect, and smooths to remove.
  • embodiments of the invention are generally directed to an architecture and associated methods to recover the transmitted signal it, k, qt, k from the received signal i r> , q r , k - Towards this end, architectures and associated methods to identify and correct for frequency independent IQ imbalance, frequency dependent IQ imbalance, and to compensate for the effect of channel corrections in a signal is detailed, below.
  • FIG. 1 an example communication transmission system 10 within which embodiments of the invention may be practiced is introduced, according to but one example embodiment.
  • system 10 is depicted comprising one or more of a remote transmitter 12, a transmission channel 14, and a local receiver 16.
  • transmitter 12 may include one or more of an inverse discrete Fourier transform (IDFT) block 18.
  • IDFT block may implement an inverse fast Fourier transform IFFT) that may generate a time-domain representation of an input signal containing the symbols to be transmitted.
  • the IFFT block 18 may provide this time-domain representation to an up-sampler 20, the output of which may be filtered by a transmitter filter 22.
  • IDFT inverse discrete Fourier transform
  • the output of the transmit filter 22 is then provided to a multiplexer 24 that modulates each subcarrier with one or more of the symbols to be transmitted.
  • multiplexer 24 may represent one source of IQ imbalance error.
  • the subcarriers radiate from a select one or more of transmitting antenna(e) 26 and enter the transmission channel 14.
  • the subcarriers may encounter additional sources of distortion. For example, reflections from obstacles can result in multipath errors.
  • the frequencies of the subcarriers may be shifted causing intersymbol interference (ISI), and the like.
  • ISI intersymbol interference
  • a receiving antenna 28 at receiver 16 captures at least a subset of the subcarriers of channel 14, together with any white noise in the environment and any other interfering signals. This compilation of signals may then be passed to a demultiplexer 30, which may introduce another source of IQ imbalance error. [0022] The output of the demultiplexer 30 may then be passed to an anti-alias filter 32 and then to an inverse demultiplexer 34, whose function is to remove any IQ imbalance introduced by the demultiplexer 30.
  • the resulting signal is then provided to a frequency- offset-correction block 36 to correct IQ imbalance resulting from frequency offset errors that exist because of any mismatches between the resonant frequency of an oscillator at the local receiver and the corresponding resonant frequency of an oscillator at the remote transmitter.
  • the output of the frequency-offset-correction block is then sampled by a down- sampler 38 and provided to a discrete Fourier transform block 40.
  • DFT block 40 implements a fast Fourier transform, although the invention is not limited in this regard.
  • the DFT block 40 provides a frequency-domain representation of the signal to a channel-estimation-and-correction block 42 that removes errors resulting from multipath along the transmission channel 14. This results in a received signal that, except for any residual IQ imbalance errors, is essentially identical to the input signal provided to the remote transmitter 12.
  • the received signal is provided to an equalizer 44, an example of which is shown in more detail in FIG. 2. Within the equalizer 44 the received signal is provided to a symbol-decision block 46.
  • the symbol-decision block 46 determines the constellation point in the IQ plane that lies closest, in a Euclidean sense, to the received point in the IQ plane.
  • FIG. 3 an example IQ plane having constellation points 48 distributed throughout four quadrants is depicted, according to one example embodiment. These constellation points 48 represent the possible symbols that are understood by the data transmission system 10. Also shown in Fig. 3 is a received point 50 corresponding to the received signal. As a result of IQ imbalance error, the received point 50 does not coincide with any of the constellation points 48. Nevertheless, there does exist a constellation point 52 that lies nearest to the received point 50 in the IQ plane.
  • This nearest constellation-point 52 is defined by a two-dimensional constellation vector c having components c and C Q representative of in-phase and quadrature components of the nearest constellation-point 52.
  • This nearest constellation-point 52 which is assumed to correspond to the symbol that the received point 50 attempts to communicate, forms the output of the symbol-decision block 46.
  • Fig. 2 provides a block diagram of an example equalizer 44 architecture, according to one embodiment of the invention.
  • the equalizer 44 may include one or more adaptive filter system(s) 56, to be discussed more fully below, responsive to weight update element(s) 60 and symbol decision element 46 through summing and/or multiplication nodes, as depicted.
  • equalizer 44 corrects for IQ imbalance introduced as a result of transmit and receive processing, as well as offsets introduced in frequency and time through the communication channel 14.
  • the received signal is also provided to a multiplier, which combines it with the output of an adaptive-filter system (56).
  • the reason the equalizing matrix is a "composite" equalizing-matrix will be apparent from the discussion of FIG. 3, above.
  • a differencing element 58 receives the equalized signal and the nearest constellation-point 52 from the symbol-decision block 46.
  • the output of the differencing element 58 is an error signal indicative of the difference between these two quantities. This difference is characterized in FIG. 3 by a two-dimensional error vector M, having
  • This error signal is then provided to a weight-update block 60.
  • the weight-update block 60 determines a new composite equalizing-matrix that, when used to generate another equalized signal, further reduces the magnitude of the error signal.
  • the output of the weight-update block 60 is then provided back to the adaptive-filter system 56, which then replaces its composite equalizing-matrix with a new composite equalizing-matrix as provided by the weight-update block 60.
  • This new composite equalizing-matrix is then used to generate a new equalized signal.
  • the process continues until the magnitude of the error signal reaches a minimum or a pre-defined threshold.
  • the error signal thus functions as a feedback signal for adjusting the composite equalizing-matrix on the basis of the extent to which the equalized signal differs from the nearest constellation-point 52.
  • Fig. 4 shows an example adaptive-filter system 56, according to one embodiment.
  • Fig. 4 illustrates how the adaptive filter system uses both the positive and negative frequency components of the received signal to generate the composite equalizing-matrix.
  • the adaptive-filter system 56 includes a first adaptive filter 62 for generating a positive-frequency equalizing-matrix from the positive frequency components of the received signal and a second adaptive filter 64 for generating a negative-frequency equalizing-matrix from the negative-frequency components of the received signal.
  • the positive-frequency equalizing-matrix and the negative-frequency equalizing-matrix are then provided to a summer 66, the output of which is the composite equalizing-matrix.
  • the four weighting coefficients that make up the composite equalizing-matrix are updated by incrementing the previous weighting coefficients by an amount proportional to the corresponding error signal and to the received signal.
  • the constant of proportionality is selected to control the speed of convergence.
  • a constant chosen to ensure rapid convergence is apt to result in an unstable system.
  • a constant chosen to ensure a stable system is apt to converge slowly.
  • the IQ imbalance error is so great that the received signal does not correspond to the closest constellation point in the IQ plane. Multipath in the transmission channel can, in many cases, cause IQ imbalance errors of this magnitude.
  • the local receiver includes a channel-estimation-and-correction block 42 to correct these errors.
  • the method carried out by a conventional channel-estimation-and-correction block 42 interferes with the operation of the equalizer 44.
  • the 802.1 la standard provides a training signal that includes a pair of training bits for each subcarrier.
  • One of the pair of training bits is associated with the positive frequency component of that subcarrier; the other is associated with the negative frequency component of that subcarrier.
  • these training bits For half of the subcarriers, these training bits have the same sign. For the remaining half of the subcarriers, these training bits have different signs.
  • the equalizer segregates the subcarriers into two classes and processes them separately.
  • the first class includes those subcarriers for which the corresponding training bits in the training signal have the same sign.
  • the second class includes those subcarriers for which the corresponding training bits in the training signal have different signs.
  • IQ imbalance errors for symbols carried by subcarriers in both the first and second classes are corrected in the manner described above. Segregating subcarriers into two classes in this manner prevents the multipath correction performed on the first class from interfering with convergence of an equalizing matrix for subcarriers in the second class, and vice versa.
  • FIG. 5 is a block diagram depicting an example adaptive filter architecture, according to one example embodiment.
  • a filter element 62 is responsive to input from a weight update 504 and symbol decision 506 through one or more summation elements.
  • two equalizers 62 e.g., represented in Fig. 2 as 62 and 64
  • the I equalizer will update its weight Wa, k for each updated input signal and copy updated weight W q i, k from Q equalizer and the Q equalizer will update its weight W q ⁇ , k for each new input signal and
  • the weight adapts according to the least mean square (LMS) error criterion by the LMS algorithm.
  • LMS least mean square
  • W ⁇ ,k(2) W ⁇ ,k(2) + ⁇ i, k ⁇ ir,-k
  • W ⁇ ,k and W q i, k are both constant for all frequencies k. Therefore, only one set of adaptive equalizers is needed. Equalizer weights are updated for each new signal.
  • channel estimation treats IQ imbalance as effective "channel”. IQ imbalance also has impact on channel estimation, which can also degrade channel correction. The impacts of channel correction are equivalent to modify the weights in equation [5]. In the case of 802.1 la, channel correction coefficients will fall into two classes as discussed in above.
  • the two-set adaptive equalizer approach may be used to address this problem.
  • the signal after channel correction is organized into two classes and each class is processed separately.
  • the first class includes signal carried by those frequencies for which the corresponding bits in the long preamble have same signs as their image frequencies.
  • the second class includes signal carried by those frequencies for which the corresponding bits in the long preamble have different signs as their image frequencies.
  • Two classes signal are processed by two sets of equalizers, as shown by Fig. 6.
  • R s (k) and R d (k) denote two
  • the architecture of Fig. 6 solves the problem by, first, the channel estimation technique (e.g., using the long preamble signal as is done normally) and, second, use of the 802.1 la SIGNAL symbol to concurrently estimate the IQ parameters and equalize the IQ imbalance.
  • the result is a more direct and timely estimation and compensation algorithm (e.g., without square roots, etc.) for IQ imbalance.
  • no specific training sequence tone modulation sequences between image and direct frequencies are required to remove the effects of the imbalance.
  • An adaptive method that adjusts for IQ distortion per packet necessarily requires some time to obtain convergence.
  • OFDM signal formats have a pre-amble or a control signal that conveys information about the modulation and coding format to the receiver.
  • the IEEE 802.1 la standard specifies a 4 micro-second OFDM symbol, denoted as the "SIGNAL" symbol, which is transmitted immediately after the long preamble via BPSK modulation. Due to the BPSK modulation, a decision-directed approach to update the IQ correction weights can be employed since errors will be minimized by the BPSK modulation. Therefore, the weights can be applied to all higher modulated OFDM data symbols without being updated during the packet. This will not only minimize the effect of decision errors via data symbols but also conserve on the operations to update the equalizer.
  • the convergence behavior for two of the weights is shown in Fig. 9.
  • the equalizers used to correct frequency independent IQ imbalance are adapted only during SIGNAL symbol (a symbol for which management and control information is transmitted on BPSK only in the 1 la standard).
  • SIGNAL symbol a symbol for which management and control information is transmitted on BPSK only in the 1 la standard.
  • Each equalizer has only 24 samples or 4 useconds (at 20 Msps) to update its weights. This requires the equalizers to converge or almost converge at the end of SIGNAL symbol.
  • the ⁇ value for MMSE equalizer is set to 0.1 for the first 5 samples, then step down to 0.05, and then down to 0.01 after 12 samples.
  • Figure 9 shows equalizer convergence speed.
  • the theoretic (noise-free) values show a mixer mismatch with the I branch phase deviation at 10° and gain factor deviation at 10%.
  • the weights of equalizers shown in Fig. 9 at the end of SIGNAL symbol (at the 24 th sample) show a correction for a mixer mismatch, whose I branch phase deviation is 8.6° and gain factor is 7.7%. The correction does not fully correct IQ imbalance but is good enough.
  • the remaining IQ imbalance distortion is then corrected by 48 sets of equalizers, which is used to correct frequency dependent IQ imbalance which will be discussed in the below. Note the decrease of the rms error by 10 dB due to the correction of the frequency-dependent I/Q imbalance by the 48 equalizers.
  • a Sixth-order Chebyshev type-I low-pass filter was used with In-phase filter cutoff frequency of 0.905 of the sampling frequency and ripple was 1.05 dB (+ 0.5025 dB).
  • Q branch filter had a cutoff frequency of 0.900 of the sampling rate and 1.00 dB ripple.
  • Fig. 10 show simulation results for un-coded 64QAM for AWGN channel. The performance with IQ correction is always better with such correction than without. More particularly, Fig. 10 shows the performance for combined filter and mixer mismatch correction. Note that the uncoded curve eventually shows deviations from ideal. However at the low error rates at which this happens, the decoding will essentially yield sufficiently low error decoded error rates.
  • Fig. 11 shows simulation results for un-coded 64QAM with the addition of multipath.
  • An example multipath was assumed consisting of 5 paths with a 0 dB path at 0 ns, -17.5 dB at 50 ns delay,-28.6 dB at 100 ns, -37.6 dB at 150 ns, and -50.3 dB at 200 ns.
  • Fig. 12 shows the effects considered above with the addition of a significant frequency offset of- 40 ppm (208 kHz). Most of the offset is corrected by automatic frequency control (AFC) loops but a residual error remains of ⁇ 4.2 kHz at the start of the I/Q correction.
  • the solid diamond curve shows the effects of just residual frequency offset which degrade the OFDM demodulation severely via the phase shifting of the QAM constellation points but the use of the IQ correction results in the bottom curve (open diamond curve) for an excellent performance improvement due to the good phase tracking abilities of the adaptive filters.
  • the addition of IQ mismatch to the impairment list results in severe performance degradation (top curve of open boxes) and this is again corrected to the open oval curve by the adaptive filters.
  • Fig. 13 shows the effects of having A/D sampling frequency offsets with no other impairments except for AWGN. Again, the adaptive IQ equalizer performance is robust enough to correct for as much as an 80 Hz sampling rate offset (2 ppm for 40 Msps A/D sampling rate).
  • IQ imbalance can cause large degradations in an OFDM receiver. It scales and rotates transmitted signal and results in image interference aliasing into the desired signal band. Channel estimation can also increase deleterious IQ imbalance effects.
  • a novel IQ imbalance correction approach is introduced which implements frequency domain adaptive equalization. The approach can correct both constant and frequency dependent IQ imbalance.
  • the present invention includes various operations.
  • the operations of the present invention may be performed by hardware components, such as those shown in Figs. 1 and/or 2, or may be embodied in machine-executable content (e.g., instructions) 702, which may be used to cause a general-purpose or special-purpose processor or logic circuits programmed with the instructions to perform the operations. Alternatively, the operations may be performed by a combination of hardware and software.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

L'invention porte d'une manière générale sur une correction adaptative du déséquilibre entre le signal en phase (I) et le signal en quadrature de phase (Q) dans des systèmes de communication sans fil à porteuses multiples.
EP04784434A 2003-09-15 2004-09-15 Correction adaptative du desequilibre iq pour systemes de communication sans fil a porteuses multiples Withdrawn EP1665693A1 (fr)

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PCT/US2004/030572 WO2005029798A1 (fr) 2003-09-15 2004-09-15 Correction adaptative du desequilibre iq pour systemes de communication sans fil a porteuses multiples

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