PatentDe  


Dokumentenidentifikation EP1332554 26.04.2007
EP-Veröffentlichungsnummer 0001332554
Titel SYSTEME ZUR AUTOMATISCHEN FREQUENZREGLUNG UND VERFAHREN ZUR GEMEINSAMEN DEMODULATION
Anmelder Ericsson Inc., Plano, Tex., US
Erfinder HAFEEZ, Abdulrauf, Cary, NC 27513, US;
ARSLAN, Huseyin, Morrisville, NC 27560, US;
MOLNAR, Karl J., Cary, NC 27513, US
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60127288
Vertragsstaaten AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE, TR
Sprache des Dokument EN
EP-Anmeldetag 19.10.2001
EP-Aktenzeichen 012738506
WO-Anmeldetag 19.10.2001
PCT-Aktenzeichen PCT/US01/46721
WO-Veröffentlichungsnummer 2002069493
WO-Veröffentlichungsdatum 06.09.2002
EP-Offenlegungsdatum 06.08.2003
EP date of grant 14.03.2007
Veröffentlichungstag im Patentblatt 26.04.2007
IPC-Hauptklasse H03J 7/04(2006.01)A, F, I, 20051017, B, H, EP

Beschreibung[en]
BACKGROUND OF THE INVENTION

This invention defined in the independent claims relates to digital communication, and more particularly to systems and methods for jointly demodulating a received signal.

Joint demodulation is widely used to detect two or more signals that are received over a common channel. For example, joint demodulation may be used to detect a desired signal from a received signal that includes an interfering signal as well. In joint demodulation, the desired signal and the interfering signal are both demodulated based on information concerning the desired signal and the interfering signal, so as to obtain a better estimate of the desired signal. The document WO-A-0 013 383 discloses a method for reducing co-channel interference.

Two-user joint demodulation for IS-136 TDMA wireless communication terminals has been proposed for cancellation of a dominant interfering signal, also referred to as an "interferer", under the assumptions of a flat, slow fading downlink environment. By subtracting off the interfering signal, the desired signal's bit error-rate can be improved. This occurs since both the channel and symbol data corresponding to the interferer generally are not perfectly correlated to the desired signal, allowing separation of the two signals. Joint demodulation thus may rely upon the ability to estimate the channel and perform symbol detection for each user across the data slot.

For the joint demodulation approach used for the IS-136 system, estimation of the initial channel response generally is performed in the same manner as in conventional single-user demodulation since the synchronization (sync) sequence for the desired signal is known. However, since the interferer sync word generally is unknown, a semi-blind technique may be used to find an estimate of the sample-position offset and the initial channel response of the interferer. Joint detection of the two users' symbol data then may be performed, for example using per-survivor processing using LMS tracking of the channel responses for each user.

A concern in the implementation of joint demodulation is the impact that frequency offset of the users' signals will have on the ability to cancel interference. In single-user demodulation, the carrier frequency of the received signal may be offset from the assumed carrier frequency, for example due to the limited tolerance of the oscillators in the base station and/or wireless terminal. Correcting for this frequency offset is typically a two-step Automatic Frequency Control (AFC) process, that includes initial frequency acquisition and frequency tracking. Frequency tracking can estimate and track the residual frequency offset that remains after initial frequency acquisition, and itself may be a two-step process including long term AFC and local (short term) AFC estimation.

SUMMARY OF THE INVENTION

Embodiments of the present invention can provide systems and methods for jointly demodulating jointly received first and second signals, wherein a joint demodulator is configured to generate an estimated first frequency or first frequency error for the first signal and an estimated second frequency or second frequency error for the second signal. A first long-term automatic frequency control is responsive to the estimated first frequency or first frequency error, wherein the joint demodulator is responsive to the first long-term automatic frequency control. A second long-term automatic frequency control is responsive to the estimated second frequency or second frequency error, wherein the joint demodulator is responsive to the second long-term automatic frequency control. First and second local automatic frequency controls also may be included in the joint demodulator, wherein the first long-term automatic frequency control is responsive to the first local automatic frequency control and the second long-term automatic frequency control is responsive to the second local automatic frequency control.

In some embodiments, the first long-term automatic frequency control and the second long-term automatic frequency control produce respective first and second frequency offset signals that are applied to the joint demodulator. In other embodiments, a difference between the first and second frequency offsets is applied to the joint demodulator and the first frequency offset is applied to a downconverter that downconverts the jointly received first and second signals and provides the downconverted signals to the joint demodulator. Thus, in these embodiments, the frequency offset of the desired signal is used to correct the incoming signal at the local oscillator of the downconverter.

BRIEF DESCRIPTION OF THE DRAWINGS

  • Figure 1 is a block diagram of a conventional long term AFC loop.
  • Figure 2 graphically illustrates relative frequency offset of an interferer according to embodiments of the present invention.
  • Figures 3 and 4 are block diagrams of alternate embodiments of joint demodulation systems and methods according to the present invention.
  • Figure 5 is a block diagram of embodiments of systems and methods for long term AFC for two user joint demodulation according to the present invention.
  • Figure 6 is a block diagram of embodiments of PSP MLSE according to embodiments of the present invention.
  • Figure 7 is a block diagram of multiple survivor MLSE according to embodiments of the present invention.
  • Figure 8 is a block diagram of metric calculation for two user joint demodulation according to embodiments of the present invention.
  • Figure 9 is a block diagram of channel estimation for two user joint demodulation according to the present invention.
  • Figure 10 is a block diagram of local and long term AFC for two user joint demodulation according to embodiments of the present invention.
  • Figure 11 is a block diagram of phase error computation for two user joint demodulation according to embodiments of the present invention.
  • Figure 12 is a block diagram of second order phase lock loops that can be used for joint demodulation according to embodiments of the present invention.
  • Figures 13 and 14 are block diagrams of adaptive demodulation with new frequencies output and with new frequency errors output, respectively, according to embodiments of the present invention.
  • Figure 15 graphically illustrates simulation results of joint AFC according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present.

A block diagram of a long term AFC loop for a single-user detector is shown in Figure 1. As shown in Figure 1, a received signal is received at an antenna 102 and is downconverted by converter 104. The signal then may be filtered by a filter 106, passed through an analog-to-digital converter, sampled and sent to a synchronizer 108. The signal can be sampled once per symbol or multiple times per symbol, as in the IS-136 standard.

The synchronizer 108 synchronizes the signal and can further sample the output signal at a rate to be processed by a detector using one or more samples per symbol. In this embodiment, the detector 110 is a Maximum Likelihood Sequence Estimator (MLSE) which provides a demodulated output signal. In addition, a long term AFC loop 112 is responsive to a frequency error signal fd,err, applied to a smoothing filter 114 to generate a frequency precorrection signal fd,n that is applied to the next data slot at the converter 104.

For joint demodulation at a wireless terminal, the frequency offset for multiple users may arise from the different base stations that transmit the users' signals. For joint demodulation of a desired signal and an interfering signal, the frequency offset may arise due to frequency offsets between the desired signal and the interfering signal. Assume that coarse frequency acquisition has been performed with respect to the desired signal's base station. Further, assume that a residual frequency error of ±200 Hz exists between the base station carrier and the true carrier frequency, and that the mobile terminal can lock to within ±200 Hz with respect to the desired base station carrier frequency after coarse acquisition. Under these assumptions, the maximum frequency errors from the mobile to the desired and interfering base stations are ±200 Hz and ±600 Hz, respectively.

One approach for compensation of frequency offsets together with joint demodulation is described in Murata et al., Joint Frequency Offset and Delay Profile Estimation Technique for Nonlinear Co-Channel Interference Canceller, Proc. PIMRC, November 1998, pp. 486-490. Murata et al. describes a slot-aligned TDMA system where all users' sync sequences are known. The sync sequences are used in training mode to estimate the frequency offsets for each user jointly, and these frequency estimates are then fixed for the subsequent demodulation across the unknown data burst.

The joint AFC approach used in the Murata et al. publication appears to be similar to the single-user AFC approach described above. However, it may not perform adequately for semi-blind joint demodulation. In particular, the desired signal frequency is not used to precorrect the local oscillator frequency prior to synchronization or demodulation. This correction may be desirable if the corrected receive frequency is used as a reference for the transmit frequency, as is true for many IS-136 wireless terminals.

Moreover, in the Murata et al. publication, the frequency offsets are estimated directly over the sync sequence and then applied as a phase correction to the hypothesized signal in the metric when demodulating the data burst. Since frequency is the derivative of phase, it may be a noisy estimate, and a phase tracker may need to be used. Finally, in a semi-blind joint demodulation approach, the sync sequence for the interferer is unknown. Thus, both the channel and frequency estimates of the interferer are not very reliable after training. Instead of fixing the frequency estimate for data demodulation, it would be desirable to track it instead. Unfortunately, AFC loops, in general, are designed for tracking small frequency errors. Thus, it may be preferred to track the residual frequency error, i.e., the difference between the estimated frequency offset and the true frequency offset.

Embodiments according to the present invention now will be described. These embodiments can assume that the precorrection of the frequency for the desired signal is performed prior to filtering and synchronization. This impacts the relative frequency offset of the second signal, such as an interfering signal, also referred to as an "interferer", to a converter such as a local oscillator (LO) at the receiver.

For example, as shown in Figure 2, a wireless terminal, also referred to as a mobile station (MS), has a 200 Hz offset from transmitters such as base stations BS1 (desired) and BS2 (interferer). If the mobile station corrects its frequency to align itself with BS1, then it may be 400 Hz offset from BS2. When the frequency correction is applied, then fBS2-fBS1 is the frequency offset from the mobile station to the interferer, when fMS becomes fBS1. In estimating the frequency offsets directly, this may present a problem since the offsets change relative to the mobile carrier fMS.

Instead, according to embodiments of the invention, an estimate of the frequency offsets relative to a reference is obtained, so that the fixed frequency offset need not change after applying the frequency precorrection. Additionally, in the MLSE, it may be desired to track the residual frequency error as this will, hopefully, be small after some settling time. To do this, embodiments of the invention may account for the fixed-frequency terms in the MLSE metric and channel estimator.

Referring now to Figure 3, first embodiments of systems and methods 300 for demodulating jointly received first and second signals according to the present invention, now will be described. As shown in Figure 3, a converter 310, such as a baseband converter or baseband demodulator, is configured to downconvert jointly received first and second signals S1 and S2. A joint demodulator 320 is responsive to the downconverted, jointly received first and second signals, and is configured to separately generate an estimated first frequency f1 or an estimated first frequency error f1,err for the downconverted first signal, and an estimated second frequency f2 or an estimated second frequency error f2,err for the downconverted second signal. As shown in Figure 3, the joint demodulator 320 may include a first local AFC 322a and a second local AFC 322b that may be used to generate the first frequency/first frequency error and the second frequency/second frequency error, respectively.

Still referring to Figure 3, a first long-term automatic frequency control 330a is responsive to the first frequency/first frequency error, to generate a first frequency offset f 1 that is applied to the joint demodulator 320. A second long-term automatic frequency control 330b is responsive to the second frequency/second frequency error, to generate a second frequency offset f 2 that is applied to the joint demodulator. Thus, the joint demodulator is responsive to both the estimated second frequency/second frequency error and the estimated first frequency/first frequency error, to jointly demodulate the downconverted jointly received first and second signals.

Referring now to Figure 4, second embodiments of systems and methods 400 for demodulating jointly received first and second signals are shown. As shown in Figure 4, a converter 310, a joint demodulator 320 including first local AFC 322a and second local AFC 322b and first and second long-term AFC 330a and 330b respectively can operate as was described above in connection with Figure 3. In Figure 4, a subtractor 440 also is provided, wherein the difference between the first frequency offset f 1 and the second frequency offset f 2 is generated and applied to the joint demodulator 320. In these embodiments, the joint demodulator assumes that there is no first frequency error, as illustrated in Figure 4.

Additional discussion of the embodiments of Figures 3 and 4 now will be provided. In embodiments of the invention, the first signal S1 may be a desired signal and the second signal S2 may be an interfering signal. Moreover, the jointly received first and second signals may be received over a series of repeating slots and are sampled more than once during each slot. The local AFC 322a and 322b can operate at a first rate and the long-term AFC 330a and 330b can operate at a second rate that is lower than the first rate. In some embodiments, the first rate is once per sample, and the second rate is once per slot. The outputs from the local AFC 322a and 322b can be either an estimate of the frequency offset or an estimate of the error in the frequency offset. The long-term AFC 330a, 330b can be configured to handle either kind of estimate from the input. A fixed frequency term can be input to the local AFC 322a, 322b, so that the local AFC only estimates the error frequency.

In Figure 4, the desired signal's frequency estimate f 1 can be sent to the local oscillator in the converter 310, to correct the signal prior to demodulation. Alternatively, in embodiments of Figure 3, the desired signal's frequency offset f 1 can be sent directly to the joint demodulator.

Figure 5 is a block diagram of other embodiments of joint demodulation systems and methods according to the invention. Referring to Figure 5, the joint demodulator 320 outputs estimates of the residual frequency errors f1,err and f2,err for each user after demodulating a slot of data. These residual error estimates each are input to long term AFC loops 330a, 330b, each of which includes a smoothing filter 560a, 560b, to calculate the total frequency offset for each user. The desired signal frequency offset f 1 is applied to the local oscillator 530 of the converter 310 while the difference f 2 - f 1 from summer 440 is applied to the joint demodulator 320 as the initial frequency offset for the interferer. Also shown explicitly is that zero frequency offset 550 is input to the joint demodulator 320 as the initial frequency offset for the desired signal. A conventional filter 532 and synchronizer 534 also are used in the converter 310. The smoothers 560a, 560b operate as the long term AFC 330a, 330b, when connected as shown.

A description of metric computation and channel estimation for joint demodulation in the joint demodulator 320 now will be described. For the two-user case with symbol-spaced receive samples, the receive signal is modeled at the /th sample using y l = y ^ 1 , l e j &phgr; 1 , err + y ^ 2 , l e j &phgr; 1 , err ,

where the terms &phgr;1,err and &phgr;2,err represent the phase error for the desired and interfering users, respectively, given that the phase has been estimated and corrected up through time l. The term i,l is the hypothesized receive signal for user i precorrected up to sample l, and is given by y ^ i , 1 = k = 0 K i - 1 c i , k , l s i , l - k e j 2 &pgr; f i lT s e j&phgr; i , l = e j 2 &pgr; f i lT s e j&phgr; i , l c i , l T s i , l ,

where Ki is the number of dispersive taps for user i. The hypothesized signal contains the fixed frequency component fi for each user, which does not vary across the slot. Alternatively, the fixed frequency component fi can be set to zero and incorporated as the initial value of the frequency component of the second order phase-locked loop. The adaptive phase error term &phgr;i,1 is the phase correction applied after demodulating the (l-1)st receive sample. Assume that this phase error is modeled by a second-order digital phase-locked loop, as in the single-user case, so that residual frequency error can be estimated for each user. The objective is then to determine how to calculate the phase error terms &phgr;i,err for users i=1 and i=2, which are then used to form the updated phase corrections &phgr;i,l+1.

Both Per Survivor Processing (PSP) and multiple-survivor MLSE may be used for joint demodulation. In each case, branch metrics are generated for hypothesized paths in the MLSE trellis. For PSP-MLSE, as shown in Figure 6, the path corresponding to the best total accumulated metric 610a-610m at the input of each new state is declared a surviving path at block 620. For multiple-survivor MLSE with QPSK signaling, as shown in Figure 7, the accumulated metrics 710a-710m are ranked at block 720 and the M paths with the best metrics survive to be further propagated. In each case, the channel and AFC estimates are updated for the surviving states or paths at block 630 and 730, respectively.

Embodiments of metric generation, for example blocks 610 and 710 of Figures 6 and 7, respectively, now will be described in Figure 8. For each new branch from an existing state (path), the error value e1 is computed. First, the symbol data and channel data are used at block 810 to calculate the signals y i , l = c i , l T s i , l for each user i ∈{1,2}, corresponding to the receive signal in the absence of frequency error. Next, the fixed frequency error term fi is combined at blocks 830a and 830b with the most recent phase correction term &phgr;i,l from block 820, and this is used to rotate yi,l in the complex plane, forming i,l using blocks 840a and 840b. The error term is then formed using blocks 850 and 860 which is used to compute the branch metric. The term pi,l represents the complex rotation performed on yi,l and is given as p i , l = e j 2 &pgr; f i l T s e j &phgr; i , j . Certain variables may be temporarily saved at this point for each best path so that they may be used in the subsequent channel or AFC update. The terms el, pi,l si,l may be saved for performing the channel update, while i,l may be saved for performing the AFC update. Note, that in U.S. Patent Application Serial No. 09/143,821 to Hafeez et al. entitled Methods And Systems for Reducing Co-Channel Interference Using Multiple Timings For A Received Signal, si,l may correspond to the symbol information filtered by a known pulse-shape and may not be the symbol data itself (which is why it should be saved). Also preferably saved as part of the traditional PSP-MLSE or MS-MLSE is the symbol history, channel and phase error states that get propagated for each surviving path.

The channel update can then be performed for two-user joint demodulation as shown in Figure 9, using the temporarily saved path variables described above. The phase correction term is applied to the error signal at blocks 910a and 910b, which is common to each channel update block 920, for a single user. Additionally, for the metric calculation, the phase correction is applied to yi,1, rather than the symbol data. Performing the phase correction in this manner may use fewer operations than the approach used in the Murata et al. publication, where symbol values may need to be rotated for each possible branch metric in the trellis.

Local AFC for joint demodulation according to embodiments of the invention now will be described. The update may be determined for calculating the phase error terms to be used in the AFC loop. Equation (4) describes the received sample after frequency correction, where the residual phase errors &phgr;1,err and &phgr;2,err are to be found. In order to find these phase errors, the following metric may be used: &ggr; = - 1 N y l - y ^ l T w l * 2 , assuming zero-mean AWGN noise and no further interference. The terms y ^ l T = y ^ 1 , l y ^ 2 , l and w l * = e j &phgr; 1 , err e j &phgr; 2 , err T . Then, expanding &ggr; gives &ggr; = - y l 2 + 2 Re y l * y ^ l T w l + y ^ l T 2 An equivalent metric for &ggr; is = - 2 Re y l * y ^ 1 , l e j &phgr; 1 , err + y l * y ^ 2 , l e j &phgr; 2 , err - y ^ 1 , l y 2 , l * e j &phgr; 1 , err - &phgr; 2 , err If an estimate is made of &phgr;1,err, with &phgr;2,err fixed, &ggr; can be maximized using only those terms containing &phgr;1,err. Thus, &phgr; ^ 1 , err = arg max &phgr; 1 , err &ggr; = arg max &phgr; 1 , err Re e j &phgr; 1 , err y ^ 1 , l y l * - y 2 , l * e - j &phgr; 2 , err To maximize this quantity, &phgr;1,err may be chosen such that &phgr; ^ 1 , err = arg y ^ 1 , l * y l - y ^ 2 , l e j &phgr; 2 , err . A similar approach may be used to find an estimate for &phgr;2,err, and results in &phgr; ^ 2 , err = arg y ^ 2 , l * y l - y ^ 1 , l e j &phgr; 1 , err .

Figure 10 is a block diagram of embodiments of local AFC 1010 combined with embodiments of long-term AFC 1020 for a two-user case, where user one is the desired user and user two is the interferer. The output of the local AFC 1010 may be used in the equalizer, but is also output to the long-term AFC 1020. The local AFC output can optionally be sampled at a lower rate, which is then input to the long term AFC block.

More specifically, as shown in Figure 10, embodiments of local AFC 1010 include a phase error computation block 1030 that is configured to compute a first phase error in the first received signal and a second phase error in the second received signal based, for example, on the outputs of an MLSE. One or more second order phase locked loops 1040a and 1040b also may be provided. The first phase locked loop 1040a is responsive to the first phase error, to compute a first frequency error. The second phase locked loop 1040b is responsive to the second phase error, to compute a second frequency error therefrom. These frequency errors then are provided to the long term AFC block 1020, wherein smoothing blocks 1050a, 1050b operate as was already described.

Figure 11 is a block diagram of phase error computation, for example block 1030 of Figure 10, according to embodiments of the present invention. The phase error computation of Figure 11 generates the phase errors that are described above by Equations (7) and (8). As can be seen, each phase error estimate is used to update the other phase error estimate using a feedback process, as shown in Figure 10. Other embodiments for performing or replacing this feedback will be described below.

Figure 12 is a block diagram of second order phase locked loops, such as second order phase locked loops 1040a and 1040b of Figure 10, according to embodiments of the invention. Second order phase locked loops are well known to those having skill in the art and need not be described further herein.

Embodiments of the above-described local two-user AFC techniques, for example as shown in Figures 10-12 use the estimate for &phgr;̂1,err to compute &phgr;2,err. To avoid this interdependence on the estimates, the term &phgr;2,err may be dropped from the estimate, resulting in a form similar to that used in the Murata et al. publication.

Other embodiments can drop the feedback phase error terms from the second user when generating the phase error for the first user. Then, the phase error term for the first user can be fed back to generate the phase error for the second user, and so on for additional users.

After the phase error terms are computed for all users, the process may be repeated. Now, the phase error estimates are available from the first iteration (of phase error computation). For example, in other embodiments, the local AFC described in Figures 10-12 may be iterated one or more times, using the newly computed phase error terms as the feedback phase errors in Figure 11.

Embodiments that can eliminate this dependence (and can eliminate the feedback phase error terms), jointly estimate both phase errors simultaneously. To do this, the metric from Equation (4) is negated: &ggr; = 1 N y l - y ^ l T w l * 2 , and the weight vector w l * that minimizes this metric is found. To perform this operation, the gradient is computed to get w l &ggr; = 1 N - y ^ l * y l - y ^ l T w l * . Setting this to zero results in the set of linear equations R l w l * = p l where R l = y ^ l * y ^ l T and p l = y l * y l . However, for the two-user symbol-spaced case, this system generally is underdetermined. In general, the pseudo-inverse R+ may be used to solve an overdetermined or underdetermined system of equations, and for the underdetermined case R+=RH(RRH)-1. Once w l * is found then &phgr; 1 , err &phgr; 2 , err = arg w l * .

Other alternative embodiments can avoid creating an underdetermined system of equations. To do this, a fractionally-spaced set of receive samples may be used, where the fractional spacing is greater than or equal to the number of users to be jointly demodulated. For example, for a fractional sampling rate of two samples per symbol, yl becomes the vector of receive samples yl=[y(1Ts-Ts/2)y(lTs)], and i is now a 2x2 matrix. For the two-user case, a unique solution for the weight vector may be found. Another alternative embodiment to avoid creating an underdetermined system of equations is to consider two symbol-spaced samples at a time, thus performing the AFC update once every two symbols.

Other embodiments may calculate a joint phase error update in a less accurate manner. For example, in an IS-136 equalizer, the value used for the phase error update is the sign of the phase error. Thus, the update to the local AFC has a fixed magnitude, but varies in sign. A similar approach may be used for joint demodulation embodiments. For example, in the two-user case, the pair of phase update values (&phgr;1,err, &phgr;2,err) could take one of the values belonging to the set {(µ1, µ1), (-µ1, µ1), (µ1, - µ1), (-µ1, -µ1)}. The exact value could be chosen by evaluating Equation (12) for each possible value of (&phgr;1,err, &phgr;2,err) and choosing that pair which minimizes &ggr;. In another embodiment, the arg() function can be replaced by the approximation arg(a.b)=sign(real(a)imag(b)-real(b)imag(a)). To compute &phgr;̂2,err, let a = ŷ1,l and b = y l - ŷ2,l , and to compute &phgr;̂2,err, let a = ŷ2,l and b = y l - ŷ1,l .

Finally, neither per-survivor processing nor multiple-survivor MLSE may be required. Rather, one channel model and/or one AFC model may be sufficient for all hypothesized states (paths) in the demodulator. Thus, an alternate embodiment can use one AFC model to compute a single phase error estimate and a single frequency error estimate for all hypothesized states (paths) at each sample time. The same local AFC update approach described previously may be used, but the data used to perform the update may be taken from the best hypothesized state (path). To allow reliable estimates to be computed, a lag between the current receive sample and the sample used for updating the estimates may be present and information saved along the best path may be used in this case.

Referring now to Figures 13 and 14, embodiments that can perform adaptive demodulation according to the present invention now will be described. As shown in Figure 13, demodulation systems and methods 1300 include a joint demodulator 1310 as was described above, and also add a single-user demodulator 1320, also referred to as a single-user detector. A selector 1330 selects either the joint demodulator 1310 or the single-user demodulator 1320 for the present slot. Accordingly, adaptive selection between joint demodulation and single user demodulation may be provided.

When joint demodulation is used, the long-term AFC can operate as was already described. When single-user demodulation is selected, there may not be a corresponding frequency update for the interferer, since the single-user demodulator need not demodulate the interferer. In this case, the interferer frequency preferably is maintained constant. In Figure 13, a multiplexer 1340 is employed to allow the interferer frequency f2 to be maintained constant without being updated. In contrast, in Figure 14, demodulation systems and methods 1400 also use a single-user demodulator 1420 and joint demodulator 1410, as described above, but output error frequencies. When the selector 1430 selects the single-user demodulation 1420, then the multiplexer 1440 can select a zero input when interference frequency errors are output by the single-user demodulator 1420 and by the joint demodulator 1410.

Simulation results now will be presented for two-user joint demodulation systems and methods according to embodiments of the invention. Figure 15 shows the performance comparing cases for no AFC, independent AFC and joint AFC when no frequency error exists. These AFC modes are designated as AFC 0, AFC 1 and AFC 11, respectively. Also shown in this plot is a conventional demodulator with and without AFC as well as the performance with known true channel information. The number of taps assigned to the desired and interfering signals is denoted as Dn/Im, so that the conventional demodulator is represented as D1/I0. The joint demodulator uses one desired signal and three interferer taps, and is thus designated as D1/I3. Also designated are whether the channel is assumed known (TC) or estimation is used (EC), sync is known (TS) or estimated (ES), and whether the interferer misalignment is known (TM) or estimated (EM). The actual frequency offset for the desired signal and interferer is labeled as Dfd/Ifi in Hz.

Figure 15 shows that in the case of conventional demodulation, AFC does not degrade performance significantly when there is no frequency offset in the desired signal. However, when joint demodulation is used with independent AFC, severe degradation of AFC performance occurs, although there is still an advantage (≈ 1 dB at 1% BER) compared to conventional demodulation. Use of joint AFC restores performance to the original results when AFC is not used (and there are no frequency offsets).

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.


Anspruch[de]
Gemeinsames Demodulationssystem zum gemeinsamen Demodulieren erster und zweiter Signale (S1, S2), mit: einem Umwandler (310), der konfiguriert ist, die gemeinsam empfangenen ersten und zweiten Signale (S1, S2) herabzuwandeln; und einem gemeinsamen Demodulator (320; 1310), der auf die herabgewandelten, gemeinsam empfangenen ersten und zweiten Signale antwortet und der konfiguriert ist, eine geschätzte erste Frequenz/einen ersten Frequenzfehler (f1) für das herabgewandelte Signal und eine geschätzte zweite Frequenz/einen zweiten Frequenzfehler (f2) für das herabgewandelte zweite Signal zu erzeugen; wobei der gemeinsame Demodulator (320; 1310) auf einen Unterschied zwischen der geschätzten zweiten Frequenz/dem zweiten Frequenzfehler f 2 und der geschätzten ersten Frequenz/dem ersten Frequenzfehler f 1 antwortet, um gemeinsam die herabkonvertierten, gemeinsam empfangenen ersten und zweiten Signale (S1, S2) zu demodulieren. System nach Anspruch 1, wobei der Umwandler (310) auf die geschätzte erste Frequenz/den ersten Frequenzfehler (f1) antwortet, um die gemeinsam empfangene ersten und zweiten Signale (S1, S2) herabzuwandeln. System nach Anspruch 1 oder 2, wobei der gemeinsame Demodulator (320; 1310) angeordnet ist, anzunehmen, dass kein erster Frequenzfehler da ist. System nach Anspruch 2, wobei das erste Signal (S1) ein gewünschtes Signal ist und wobei das zweite Signal (S2) ein Störsignal ist. System nach Anspruch 2, weiter mit: einer ersten Rückkopplungsschleife, die zwischen der geschätzten ersten Frequenz/dem ersten Frequenzfehler und dem Umwandler (310) gekoppelt ist, so dass der Umwandler (310) die gemeinsam empfangenen ersten und zweiten Signale auf Grundlage der geschätzten ersten Frequenz/des ersten Frequenzfehlers herabwandelt; und eine zweite Rückkopplungsschleife, die zwischen der geschätzten zweiten Frequenz/dem Frequenzfehler und dem gemeinsamen Demodulator (320; 1310) gekoppelt ist, so dass der gemeinsame Demodulator (320; 1310) getrennt auf Grundlage der geschätzten zweiten Frequenz/des zweiten Frequenzfehlers die geschätzte erste Frequenz und den zweiten Frequenzfehler erzeugt. Gemeinsames Demodulationssystem nach Anspruch 1, weiter mit: einer ersten Rückkopplungsschleife, die zwischen der Schätzung einer ersten Frequenz/einem ersten Frequenzfehler und dem gemeinsamen Demodulator (320; 1310) gekoppelt ist, so dass der gemeinsame Demodulator (320; 1310) die gemeinsam empfangenen ersten und zweiten Signale auf Grundlage der Schätzung einer ersten Frequenz/eines ersten Frequenzfehlers demoduliert; und eine zweite Rückkopplungsschleife, die zwischen der Schätzung des zweiten Frequenzfehlers und dem gemeinsamen Demodulator (320; 1310) gekoppelt ist, so dass der gemeinsame Demodulator (320; 1310) ebenso die gemeinsam empfangenen ersten und zweiten Signale auf Grundlage der Schätzung der zweiten Frequenz/des zweiten Frequenzfehlers demoduliert. System nach Anspruch 5, wobei der gemeinsame Demodulator (320; 1310) ein erstes lokales automatisches Frequenzsteuersystem (322a) umfasst, das einen Frequenzversatz in dem erstem Signal bei einer ersten Rate korrigiert und wobei die erste Rückkopplungsschleife umfasst: ein erstes automatisches Langzeitfrquenzsteuersystem (330a), das mit dem ersten lokalen automatischen Frequenzsteuersystem (322a) gekoppelt ist, um einen Frequenzversatz in dem ersten Signal bei einer zweiten Rate zu korrigieren, die niedriger als die erste Rate ist, wobei das erste automatische Langzeitfrequenzsteuersystem (330a) mit dem Umwandler gekoppelt ist. System nach Anspruch 1, wobei der gemeinsame Demodulator (320; 1310) umfasst: ein erstes lokales automatisches Frequenzsteuersystem (322a), das einen Frequenzversatz in dem ersten Signal (S1) bei einer ersten Rate korrigiert und wobei die erste Rückkopplungsschleife umfasst: ein erstes automatisches Langzeitfrequenzsteuersystem (330a), das mit dem ersten lokalen automatischen Frequenzsteuersystem (322a) gekoppelt ist, um einen Frequenzversatz in dem ersten Signal (S1) bei einer zweiten Rate zu korrigieren, die niedriger als die erste Rate ist, wobei das erste automatische Langzeitfrequenzsteuersystem mit dem gemeinsamen Demodulator (320; 1310) gekoppelt ist. System nach Anspruch 1 oder 5, wobei der gemeinsame Demodulator (320; 1310) ein zweites lokales automatisches Frequenzsteuersystem (322b) umfasst, das einen Frequenzversatz in dem zweiten Signal (S2) bei einer ersten Rate korrigiert und wobei die zweite Rückkopplungsschleife umfasst: ein zweites automatisches Langzeitfrequenzsteuersystem (330b), das mit dem zweiten lokalen automatischen Frequenzsteuersystem (322b) gekoppelt ist, um einen Frequenzversatz in dem zweiten Signal (S2) bei einer zweiten Rate zu korrigieren, die niedriger als die erste Rate ist, wobei das zweite automatische Langzeitfrequenzsteuersystem (330b) mit dem gemeinsamen Demodulator (320; 1310) gekoppelt ist. System nach Anspruch 7 oder 8, wobei die gemeinsam empfangenen ersten und zweiten Signale (S1, S2) über einer Serie von sich wiederholenden Schlitzen empfangen werden und mehr als einmal während jedem Schlitz abgetastet werden, wobei die erste Rate einmal pro Probe ist und wobei die zweite Rate einmal pro Schlitz ist. System nach Anspruch 7 oder 8, wobei die erste lokale automatische Frequenzsteuerung (322a) umfasst: einen Phasenfehlercomputer, der konfiguriert ist, einen Phasenfehler in dem ersten empfangenen Signal (S1) bei einer ersten Rate zu berechnen; und eine Phasenverriegelungsschleife, die auf den Phasenfehler reagiert und die konfiguriert ist, einen ersten Frequenzfehler aus diesem bei einer ersten Rate zu berechnen. System nach Anspruch 9, wobei die zweite lokale automatische Frequenzsteuerung (322b) umfasst: einen Phasenfehlercomputer, der konfiguriert ist, einen Phasenfehler in dem zweiten empfangenen Signal (S2) bei einer ersten Rate zu berechnen; und eine Phasenverriegelungsschleife, die auf den Phasenfehler reagiert und die konfiguriert ist, einen ersten Frequenzfehler aus diesem bei einer ersten Rate zu berechnen. System nach Anspruch 11, wobei die erste automatische Langzeitfrequenzsteuerung (330a) umfasst: eine Rückkopplungsschleife, die auf den ersten Frequenzfehler reagiert und die konfiguriert ist, einen zweiten Frequenzfehler aus diesem bei einer zweiten Rate zu bestimmen. System nach Anspruch 12, wobei die zweite automatische Langzeitfrequenzsteuerung (330b) umfasst: eine Rückkopplungsschleife, die auf den ersten Frequenzfehler reagiert und die konfiguriert ist, einen zweiten Frequenzfehler aus diesem bei einer zweiten Rate zu bestimmen. System nach Anspruch 1 oder 2, weiter mit: einem Einzelbenutzerdemodulator (1320), der auf die herabgewandelten, gemeinsam empfangenen ersten und zweiten Signale reagiert, und der konfiguriert ist, den ersten Frequenzfehler abzuschätzen; und einem Auswähler (1330), der den gemeinsamen Demodulator (320; 1310) oder den Einzelbenutzerdemodulator (1320) auswählt. System nach Anspruch 15, wobei der geschätzte zweite Frequenzfehler konstant beibehalten wird, wenn der Auswähler (1330) den Einzelbenutzerdemodulator (1320) auswählt. Demodulationssystem für gemeinsam empfangene erste und zweite Signale (S1, S2), mit: einem gemeinsamen Demodulator (320; 1310), der konfiguriert ist, eine geschätzte erste Frequenz/einen ersten Frequenzfehler (f1) für das erste Signal (S1) und eine geschätzte zweite Frequenz/einen zweiten Frequenzfehler (f2) für das zweite Signal (S2) zu schätzen; einer ersten automatischen Langzeitfrequenzsteuerung (330a), die auf die geschätzte erste Frequenz/den ersten Frequenzfehler reagiert, wobei der gemeinsame Demodulator (320; 1310) auf die erste automatische Langzeitfrequenzsteuerung (330a) reagiert; und einer zweiten automatischen Langzeitfrequenzsteuerung 330b), die auf die geschätzte zweite Frequenz/den zweiten Frequenzfehler reagiert, wobei der gemeinsame Demodulator (320; 1310) auf die zweite automatische Langzeitfrequenzsteuerung (330b) reagiert. System nach Anspruch 17, weiter mit: einem Subtrahierer (440), der auf das erste und zweite und die zweite automatische Frequenzsteuerung reagiert, wobei der gemeinsame Demodulator (320; 1310) auf den Subtrahierer (440) reagiert. System nach Anspruch 17, weiter mit: einem Umwandler (310), der konfiguriert ist, die gemeinsam empfangenen ersten und zweiten Signale (S1, S2) herabzuwandeln; wobei der gemeinsame Demodulator (320; 1310), der auf die herabkonvertierten gemeinsam empfangenen ersten und zweiten Signale reagiert; und wobei der Umwandler (320) ebenso auf die erste automatische Langzeitfrequenzsteuerung (330a) reagiert. System nach Anspruch 17, wobei das erste Signal (S1) ein gewünschtes Signal ist und wobei das zweite Signal (S2) ein Störsignal ist. System nach Anspruch 17, wobei der gemeinsame Demodulator (320; 1310) eine erste lokale automatische Frequenzsteuerung (322a) umfasst, die einen Frequenzversatz in dem ersten Signal (S1) bei einer ersten Rate korrigiert, und wobei die erste automatische Langzeitfrequenzsteuerung (330a) mit der ersten lokalen automatischen Frequenzsteuerung (322a) gekoppelt ist, um einen Frequenzversatz in dem ersten Signal (S1) bei einer zweiten Rate zu korrigieren, die niedriger als die erste Rate ist. System nach Anspruch 17, wobei der gemeinsame Demodulator (320; 1310) eine zweite lokale automatische Frequenzsteuerung (322b) umfasst, die einen Frequenzversatz in dem zweiten Signal (S2) bei einer ersten Rate korrigiert, und wobei die zweite automatische Langzeitfrequenzsteuerung (330b) mit der ersten lokalen automatischen Frequenzsteuerung (322a) gekoppelt ist, um einen Frequenzversatz in dem ersten Signal (S1) bei einer zweiten Rate zu korrigieren, die niedriger als die erste Rate ist. System nach Anspruch 21, wobei die gemeinsam empfangenen ersten und zweiten Signale (S1, S2) über eine Serie von sich wiederholenden Schlitzen empfangen werden und mehr als einmal während jedem Schlitz abgetastet werden, wobei die erste Rate einmal pro Probe und wobei die zweite Rate einmal pro Schlitz ist. Gemeinsames Demodulationsverfahren zum Demodulieren gemeinsam empfangener erster und zweiter Signale (S1, S2), mit: Herabwandeln der gemeinsam empfangenen ersten und zweiten Signale (S1, S2); und getrenntem Erzeugen einer geschätzten ersten Frequenz/eines ersten Frequenzfehlers für das herabgewandelte erste Signal und einer geschätzten zweiten Frequenz/eines zweiten Frequenzfehlers für das herabgewandelte zweite Signal; wobei das getrennte Erzeugen einer geschätzten ersten Frequenz/eines ersten Frequenzfehlers für das herabgewandelte erste Signal und einer geschätzten zweiten Frequenz/eines zweiten Frequenzfehlers für das herabgewandelte zweite Signal auf einen Unterschied zwischen der geschätzten zweiten Frequenz/dem zweiten Frequenzfehler und der geschätzten ersten Frequenz/dem ersten Frequenzfehler reagiert. Verfahren nach Anspruch 24, wobei das Herabwandeln der gemeinsam empfangenen ersten und zweiten Signale (S1, S2) auf die geschätzte erste Frequenz/den ersten Frequenzfehler reagiert. Verfahren nach Anspruch 24 oder 25, wobei das erste Signal (S1) ein gewünschtes Signal ist und wobei das zweite Signal (S2) ein Störsignal ist. Verfahren nach Anspruch 25, wobei das getrennte Erzeugen einer geschätzten ersten Frequenz/eines ersten Frequenzfehlers (f1) für das herabgewandelte erste Signal und einer geschätzten zweiten Frequenz/eines zweiten Frequenzfehlers (f2) für das herabgewandelte zweite Signal umfasst: Korrigieren des Frequenzversatzes in dem ersten Signal (S2) bei einer ersten Rate; und Korrigieren des Frequenzversatzes in dem frequenzversatzskorrigierten ersten Signal bei einer zweiten Rate, die niedriger als die erste Rate ist, um dadurch die erste Frequenz/den ersten Frequenzfehler zu schätzen. Verfahren nach Anspruch 25, wobei das getrennte Erzeugen einer geschätzten ersten Frequenz/eines zweiten Frequenzfehlers für das herabgewandelte erste Signal und einer geschätzten zweiten Frequenz/eines zweiten Frequenzfehlers für das herabgewandelte zweite Signal umfasst: Korrigieren des Frequenzversatzes in dem zweiten Signal (S2) bei einer ersten Rate; und Korrigieren des Frequenzversatzes in dem frequenzversatzskorrigierten zweiten Signal bei einer zweiten Rate, die niedriger als die erste Rate ist, um dadurch die zweite Frequenz/den zweiten Frequenzfehler zu schätzten. Verfahren nach Anspruch 28, wobei die gemeinsam empfangenen ersten und zweiten Signale (S1, S2) über eine Serie von sich wiederholenden Schlitzen empfangen werden und mehr als einmal während jedem Schlitz abgetastet werden, wobei die erste Rate einmal pro Probe ist und wobei die zweite Rate einmal pro Schlitz ist. Verfahren nach Anspruch 27, wobei das Korrigieren des Frequenzversatzes in dem ersten Signal bei einer ersten Rate umfasst: Berechnen eines Phasenfehlers in dem ersten empfangenen Signal (S1) bei der ersten Rate; und Berechnen eines ersten Frequenzfehlers aus diesem bei der ersten Rate. Verfahren nach Anspruch 25, weiter mit: Schätzen des ersten Frequenzfehlers in dem herabgewandelten ersten Signal; und selektivem Durchführen des getrennten Erzeugens einer geschätzten ersten Frequenz/eines ersten Frequenzfehlers für das herabgewandelte erste Signal und einer geschätzten zweiten Frequenz/einem zweiten Frequenzfehler für das herabgewandelte zweite Signal oder des Schätzens des ersten Frequenzfehlers in dem herabgewandelten ersten Signal. Verfahren nach Anspruch 31, weiter mit konstantem Beibehalten der geschätzten zweiten Frequenz/des zweiten Frequenzfehlers in Reaktion auf das selektive Durchführen des Schätzens des ersten Frequenzfehlers in dem herabgewandelten ersten Signal.
Anspruch[en]
A joint demodulation system for demodulating jointly received first and second signals (S1, S2), the joint demodulation system comprising: a converter (310) that is configured to downconvert the jointly received first and second signals (S1, S2); and a joint demodulator (320; 1310) that is responsive to the downconverted jointly received first and second signals, and that is configured to separately generate an estimated first frequency/first frequency error (f1) for the downconverted first signal and an estimated second frequency/second frequency error (f2) for the downconverted second signal; wherein the joint demodulator (320; 1310) is responsive to a difference between the estimated second frequency/second frequency error (f2) and the estimated first frequency/first frequency error (f1) to jointly demodulate the downconverted jointly received first and second signals (S1, S2). The system according to Claim 1, wherein the converter (310) is responsive to the estimated first frequency/first frequency error (f1) to downconvert the jointly received first and second signals (S1, S2). The system according to Claim 1 or 2, wherein the joint demodulator (320; 1310) is arranged to assume that there is no first frequency error. The system according to Claim 2, wherein the first signal (S 1) is a desired signal and wherein the second signal (S2) is an interfering signal. The system according to Claim 2 further comprising: a first feedback loop that is coupled between the estimated first frequency/first frequency error and the converter (310), such that the converter (310) downconverts the jointly received first and second signals based on the estimated first frequency/first frequency error; and and a second feedback loop that is coupled between the estimated second frequency/frequency error and the joint demodulator (320; 1310), such that the joint demodulator (320; 1310) separately generates the estimated first and second frequency errors based on the estimated second frequency/second frequency error. A joint demodulation system according to Claim 1 further comprising: a first feedback loop that is coupled between the estimate of a first frequency/first frequency error and the joint demodulator (320; 1310), such that the joint demodulator (320; 1310) demodulates the jointly received first and second signals based on the estimate of a first frequency/first frequency error; and a second feedback loop that is coupled between the estimate of the second frequency error and the joint demodulator (320; 1310), such that the joint demodulator (320; 1310) also demodulates the jointly received first and second signals based on the estimate of the second frequency/second frequency error. The system according to Claim 5 wherein the joint demodulator (320; 1310) includes a first local automatic frequency control system (322a) that corrects for frequency offsets in the first signal at a first rate, and wherein the first feedback loop comprises: a first long term automatic frequency control system (330a) that is coupled to the first local automatic frequency control system (322a) to correct for frequency offsets in the first signal at a second rate that is lower than the first rate, the first long term automatic frequency control system (330a) being coupled to the converter. The system according to Claim 1 wherein the joint demodulator (320; 1310) includes

a first local automatic frequency control system (322a) that corrects for frequency offsets in the first signal (S1) at a first rate, and wherein the first feedback loop comprises: a first long term automatic frequency control system (330a) that is coupled to the first local automatic frequency control system (322a) to correct for frequency offsets in the first signal (S1) at a second rate that is lower than the first rate, the first long term automatic frequency control system being coupled to the joint demodulator (320; 1310).
The system according to Claim 1 or 5, wherein the joint demodulator (320; 1310) includes a second local automatic frequency control system (322b) that corrects for frequency offsets in the second signal (S2) at a first rate, and wherein the second feedback loop comprises: a second long term automatic frequency control system (330b) that is coupled to the second local automatic frequency control system (322b) to correct for frequency offsets in the second signal (S2) at a second rate that is lower than the first rate, the second long term automatic frequency control system (330b) being coupled to the joint demodulator (320; 1310). The system according to Claim 7 or 8, wherein the jointly received first and second signals (S1, S2) are received over a series of repeating slots and are sampled more than once during each slot, wherein the first rate is once per sample and wherein the second rate is once per slot. The system according to Claim 7 or 8, wherein the first local automatic frequency control (322a) comprises: a phase error computer that is configured to compute a phase error in the first received signal (S1) at the first rate; and a phase lock loop that is responsive to the phase error and is configured to compute a first frequency error therefrom at the first rate. The system according to Claim 9, wherein the second local automatic frequency control (322b) comprises: a phase error computer that is configured to compute a phase error in the second received signal (S2) at the first rate; and a phase lock loop that is responsive to the phase error and is configured to compute a first frequency error therefrom at the first rate. The system according to Claim 11, wherein the first long term automatic frequency control (330a) comprises: a feedback loop that is responsive to the first frequency error and is configured to determine a second.frequency error therefrom at the second rate. The system according to Claim 12, wherein the second long term automatic frequency control (330b) comprises: a feedback loop that is responsive to the first frequency error and is configured to determine a second frequency error therefrom at the second rate. The system according to Claim 1 or 2, further comprising: a single-user demodulator (1320) that is responsive to the downconverted jointly received first and second signals, and that is configured to estimate the first frequency error; and a selector (1330) that selects the joint demodulator (320; 1310) or the single-user demodulator (1320). The system according to Claim 15, wherein the estimated second frequency error is maintained constant when the selector (1330) selects the single-user demodulator (1320). A demodulation system for jointly received first and second signals (S1, S2), comprising: a joint demodulator (320; 1310) that is configured to generate an estimated first frequency/first frequency error (f1) for the first signal (S1) and an estimated second frequency/second frequency error (f2) for the second signal (S2); a first long term automatic frequency control (330a) that is responsive to the estimated first frequency/first frequency error, wherein the joint demodulator (320; 1310) is responsive to the first long term automatic frequency control (330a); and a second long term automatic frequency control (330b) that is responsive to the estimated second frequency/second frequency error, wherein the joint demodulator (320; 1310) is responsive to the second long term automatic frequency control (330b). The system according to Claim 17, further comprising: a subtractor (440) that is responsive to the first and second and second automatic frequency controls, wherein the joint demodulator (320; 1310) is responsive to the subtractor (440). The system according to Claim 17, further comprising: a converter (310) that is configured to downconvert the jointly received first and second signals (S1, S2); wherein the joint demodulator (320; 1310) that is responsive to the downconverted jointly received first and second signals; and wherein the converter (320) also is responsive to the first long term automatic.frequency control (330a). The system according to Claim 17, wherein the first signal (S1) is a desired signal and wherein the second signal (S2) is an interfering signal. The system according to Claim 17, wherein the joint demodulator (320; 1310) includes a first local automatic frequency control (322a) that corrects for frequency offsets in the first signal (S1) at a first rate, and wherein the first long term automatic frequency control (330a) is coupled to the first local automatic frequency control (322a) to correct for frequency offsets in the first signal (S1) at a second rate that is lower than the first rate. The system according to Claim 17, wherein the joint demodulator (320; 1310) includes a second local automatic frequency control (322b) that corrects for frequency offsets in the second signal (S2) at a first rate; and wherein the second long term automatic frequency control (330b) is coupled to the first local automatic frequency control (322a) to correct for frequency offsets in the first signal (S1) at a second rate that is lower than the first rate. The system according to Claim 21, wherein the jointly received first and second signals (S1, S2) are received over a series of repeating slots and are sampled more than once during each slot, wherein the first rate is once per sample and wherein the second rate is once per slot. A joint demodulation method for demodulating jointly received first and second signals (S1, S2), the joint demodulation method comprising: downconverting the jointly received first and second signals (S1, S2); and separately generating an estimated first frequency/first frequency error for the downconverted first signal and an estimated second frequency/second frequency error for the downconverted second signal; wherein the separately generating an estimated first frequency/first frequency error for the downconverted first signal and an estimated second frequency/second frequency error for the downconverted second signal is responsive to a difference between the estimated second frequency/second frequency error and the estimated first frequency/first frequency error. The method according to Claim 24, wherein the downconverting the jointly received first and second signals (S1, S2) is responsive to the estimated first frequency/first frequency error The method according to Claim 24 or 25, wherein the first signal (S1) is a desired signal and wherein the second signal (S2) is an interfering signal. The method according to Claim 25, wherein the separately generating an estimated first frequency/first frequency error (f1) for the downconverted first signal and an estimated second frequency/second frequency error (f2) for the downconverted second signal comprises: correcting for frequency offsets in the first signal (S1) at a first rate; and correcting for frequency offsets in the frequency offset corrected first signal at a second rate that is lower than the first rate, to thereby estimate the first frequency/first frequency error. The method according to Claim 25 wherein the separately generating an estimated first frequency/first frequency error for the downconverted first signal and an estimated second frequency/second frequency error for the downconverted second signal comprises: correcting for frequency offsets in the second signal (S2) at a first rate; and correcting for frequency offsets in the frequency offset corrected second signal at a second rate that is lower than the first rate, to thereby estimate the second frequency/second frequency error. The method according to Claim 28 wherein the jointly received first and second signals (S1, S2) are received over a series of repeating slots and are sampled more than once during each slot, wherein the first rate is once per sample and wherein the second rate is once per slot. The method according to Claim 27 wherein the correcting for frequency offsets in the first signal at a first rate comprises: computing a phase error in the first received signal (S1) at the first rate; and computing a first frequency error therefrom at the first rate. The method according to Claim 25 further comprising: estimating the first frequency error in the downconverted first signal; and selectively performing the separately generating an estimated first frequency/first frequency error for the downconverted first signal and an estimated second frequency/second frequency error for the downconverted second signal or the estimating the first frequency error in the downconverted first signal. The method according to Claim 31 further comprising maintaining the estimated second frequency/second frequency error constant in response to the selectively performing the estimating the first frequency error in the downconverted first signal.
Anspruch[fr]
Système de démodulation conjointe, destiné à démoduler conjointement un premier et un second signal reçu (S1, S2), le système de démodulation conjointe comprenant : un convertisseur (310) qui est configuré pour abaisser la fréquence des premier et second signaux reçus conjointement (S1, S2) ; et un démodulateur conjoint (320 ; 1310) qui répond aux premier et second signaux reçus conjointement et abaissés en fréquence et qui est configuré pour produire séparément une estimation de la première fréquence/de la première erreur de fréquence (f1) pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence (f2) pour le second signal abaissé en fréquence ; dans lequel le démodulateur conjoint (320 ; 1310) répond à une différence entre l'estimation de la seconde fréquence/de la seconde erreur de fréquence f 2 et l'estimation de la première fréquence/de la première erreur de fréquence f 1 afin de démoduler conjointement les premier et second signaux reçus conjointement et abaissés en fréquence (S1, S2). Système selon la revendication 1, dans lequel le convertisseur (310) répond l'estimation de la première fréquence/de la première erreur de fréquence (f1) afin d'abaisser en fréquence les premier et second signaux reçus conjointement (S1, S2). Système selon la revendication 1 ou 2, dans lequel le démodulateur conjoint (320 ; 1310) est agencé pour considérer qu'il n'existe pas de première erreur de fréquence. Système selon la revendication 2, dans lequel le premier signal (S1) est un signal souhaité et dans lequel le second signal (S2) est un signal interférant. Système selon la revendication 2, comprenant en outre : une première boucle de contre-réaction qui est couplée entre l'estimation de la première fréquence/de la première erreur de fréquence et le convertisseur (310), si bien que le convertisseur (310) abaisse la fréquence des premier et second signaux reçus conjointement sur la base de l'estimation de la première fréquence/de la première erreur de fréquence ; et une seconde boucle de contre-réaction qui est couplée entre l'estimation de la seconde fréquence/de la seconde erreur de fréquence et le démodulateur conjoint (320 ; 1310), si bien que le démodulateur conjoint (320 ; 1310) produit séparément les estimations de la première et de la seconde erreur de fréquence, sur la base de l'estimation de la seconde fréquence/de la seconde erreur de fréquence. Système de démodulation conjointe selon la revendication 1, comprenant en outre : une première boucle de contre-réaction qui est couplée entre l'estimation de la première fréquence/de la première erreur de fréquence et le démodulateur conjoint (320 ; 1310), si bien que le démodulateur conjoint (320 ; 1310) démodule les premier et second signaux reçus conjointement sur la base de l'estimation de la première fréquence/de la première erreur de fréquence ; et une seconde boucle de contre-réaction qui est couplée entre l'estimation de la seconde erreur de fréquence et le démodulateur conjoint (320 ; 1310), si bien que le démodulateur conjoint (320 ; 1310) démodule également les premier et second signaux reçus conjointement sur la base de l'estimation de la seconde fréquence/de la seconde erreur de fréquence. Système selon la revendication 5, dans lequel le démodulateur conjoint (320 ; 1310) comprend un premier système local de commande automatique de fréquence (322a) qui corrige les décalages de fréquence dans le premier signal à une première vitesse, et dans lequel la première boucle de contre-réaction comprend un premier système de commande automatique de la fréquence à long terme (330a) qui est couplé au premier système local de commande automatique de fréquence (322a) afin de corriger les décalages de fréquence dans le premier signal, à une seconde vitesse qui est inférieure à la première vitesse, le premier système de commande automatique de la fréquence à long terme (330a) étant couplé au convertisseur. Système selon la revendication 1, dans lequel le démodulateur conjoint (320 ; 1310) comprend : un premier système local de commande automatique de fréquence (322a) qui corrige les décalages de fréquence dans le premier signal (S1) à une première vitesse, et dans lequel la première boucle de contre-réaction comprend : un premier système de commande automatique de la fréquence à long terme (330a) qui est couplé au premier système local de commande automatique de fréquence (322a) afin de corriger les décalages de fréquence dans le premier signal (S1), à une seconde vitesse qui est inférieure à la première vitesse, le premier système de commande automatique de la fréquence à long terme étant couplé au démodulateur conjoint (320 ; 1310). Système selon la revendication 1 ou 5, dans lequel le démodulateur conjoint (320 ; 1310) comprend un second système local de commande automatique de fréquence (322b) qui corrige les décalages de fréquence dans le second signal (S2) à une première vitesse, et dans lequel la seconde boucle de contre-réaction comprend : un second système de commande automatique de la fréquence à long terme (330b) qui est couplé au second système local de commande automatique de fréquence (322b) afin de corriger les décalages de fréquence dans le second signal (S2), à une seconde vitesse qui est inférieure à la première vitesse, le second système de commande automatique de la fréquence à long terme (330b) étant couplé au démodulateur conjoint (320 ; 1310). Système selon la revendication 7 ou 8, dans lequel les premier et second signaux reçus conjointement (S1, S2) sont reçus sur une série d'intervalles de temps qui se répètent et sont échantillonnés plus d'une fois sur chaque intervalle de temps, la première vitesse étant à raison d'un par échantillon et la seconde vitesse étant à raison d'un par intervalle de temps. Système selon la revendication 7 ou 8, dans lequel le premier système local de commande automatique de fréquence (322a) comprend : un calculateur d'erreur de phase qui est configuré pour calculer une erreur de phase dans le premier signal reçu (S1) à la première vitesse ; et une boucle de verrouillage de phase qui répond à l'erreur de phase et est configurée pour calculer une première erreur de fréquence sur cette base, à la première vitesse. Système selon la revendication 9, dans lequel le second système local de commande automatique de fréquence (322b) comprend : un calculateur d'erreur de phase qui est configuré pour calculer une erreur de phase dans le second signal reçu (S2) à la première vitesse ; et une boucle de verrouillage de phase qui répond à l'erreur de phase et est configurée pour calculer une seconde erreur de fréquence sur cette base, à la première vitesse. Système selon la revendication 11, dans lequel le premier système de commande automatique de la fréquence à long terme (330a) comprend : une boucle de contre-réaction qui répond à la première erreur de fréquence et est configurée pour déterminer une seconde erreur de fréquence sur cette base à la seconde vitesse. Système selon la revendication 12, dans lequel le second système de commande automatique de la fréquence à long terme (330b) comprend : une boucle de contre-réaction qui répond à la première erreur de fréquence et est configurée pour déterminer une seconde erreur de fréquence sur cette base à la seconde vitesse. Système selon la revendication 1 ou 2, comprenant en outre : un démodulateur pour utilisateur unique (1320) qui répond aux premier et second signaux reçus conjointement et abaissés en fréquence et qui est configuré pour estimer la première erreur de fréquence ; et un sélecteur (1330) qui sélectionne le démodulateur conjoint (320 ; 1310) ou le démodulateur pour utilisateur unique (1320). système selon la revendication 15, dans lequel l'estimation de la seconde erreur de fréquence est maintenue constante lorsque le sélecteur (1330) sélectionne le démodulateur pour utilisateur unique (1320). Système de démodulation pour des premier et second signaux reçus conjointement (S1, S2), comprenant : un démodulateur conjoint (320 ; 1310) qui est configuré pour produire une estimation de la première fréquence/de la première erreur de fréquence (f1) pour le premier signal (S1) et une estimation de la seconde fréquence/de la seconde erreur de fréquence (f2) pour le second signal (S2); un premier système de commande automatique de la fréquence à long terme (330a) qui répond à l'estimation de la première fréquence/de la première erreur de fréquence, le démodulateur conjoint (320 ; 1310) répondant au premier système de commande automatique de la fréquence à long terme (330a) ; et un second système de commande automatique de la fréquence à long terme (330b) qui répond à l'estimation de la seconde fréquence/de la seconde erreur de fréquence, le démodulateur conjoint (320 ; 1310) répondant au second système de commande automatique de la fréquence à long terme (330b). Système selon la revendication 17, comprenant en outre : un soustracteur (440) qui répond au premier et au second système de commande automatique de fréquence, le démodulateur conjoint (320 ; 1310) répondant au soustracteur (440). Système selon la revendication 17, comprenant en outre : un convertisseur (310) qui est configuré pour abaisser en fréquence les premier et second signaux reçus conjointement (S1, S2), dans lequel le démodulateur conjoint (320 ; 1310) répond aux premier et second signaux reçus conjointement et abaissés en fréquence et dans lequel le convertisseur (320) répond également au premier système de commande automatique de la fréquence à long terme (330a). Système selon la revendication 17, dans lequel le premier signal (S1) est un signal souhaité et dans lequel le second signal (S2) est un signal interférant. Système selon la revendication 17, dans lequel le démodulateur conjoint (320 ; 1310) comprend un premier système local de commande automatique de fréquence (322a) qui corrige les décalages de fréquence dans le premier signal (S1) à une première vitesse et dans lequel le premier système de commande automatique de la fréquence à long terme (330a) est couplé au premier système local de commande automatique de fréquence (322a) afin de corriger les décalages de fréquence dans le premier signal (S1), à une seconde vitesse qui est inférieure à la première vitesse. Système selon la revendication 17, dans lequel le démodulateur conjoint (320 ; 1310) comprend un second système local de commande automatique de fréquence (322b) qui corrige les décalages de fréquence dans le second signal (S2) à une première vitesse et dans lequel le second système de commande automatique de la fréquence à long terme (330b) est couplé au premier système local de commande automatique de fréquence (322a) afin de corriger les décalages de fréquence dans le premier signal (S1), à une seconde vitesse qui est inférieure à la première vitesse. Système selon la revendication 21, dans lequel les premier et second signaux reçus conjointement (S1, S2) sont reçus sur une série d'intervalles de temps qui se répètent et sont échantillonnés plus d'une fois sur chaque intervalle de temps, la première vitesse étant à raison d'un par échantillon et la seconde vitesse étant à raison d'un par intervalle de temps. Procédé de démodulation conjointe, destiné à démoduler des premier et second signaux reçus conjointement (S1, S2), le procédé de démodulation conjointe comprenant les étapes consistant à : abaisser la fréquence des premier et second signaux reçus conjointement (S1, S2) ; et produire séparément une estimation de la première fréquence/de la première erreur de fréquence (f1) pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence (f2) pour le second signal abaissé en fréquence ; dans lequel l'étape consistant à produire séparément une estimation de la première fréquence/de la première erreur de fréquence pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence pour le second signal abaissé en fréquence répond à une différence entre l'estimation de la seconde fréquence/de la seconde erreur de fréquence et l'estimation de la première fréquence/de la première erreur de fréquence. Procédé selon la revendication 24, dans lequel l'abaissement en fréquence des premier et second signaux reçus conjointement (S1, S2) répond à l'estimation de la première fréquence/de la première erreur de fréquence. Procédé selon la revendication 24 ou 25, dans lequel le premier signal (S1) est un signal souhaité et dans lequel le second signal (S2) est un signal interférant. Procédé selon la revendication 25, dans lequel l'étape consistant à produire séparément une estimation de la première fréquence/de la première erreur de fréquence (f1) pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence (f2) pour le second signal abaissé en fréquence comprend les étapes consistant à : corriger des décalages de fréquence dans le premier signal (S1) à une première vitesse ; et corriger des décalages de fréquence dans le premier signal corrigé des décalages en fréquence à une seconde vitesse, qui est inférieure à la première vitesse, afin d'estimer ainsi la première fréquence/la première erreur de fréquence. Procédé selon la revendication 25, dans lequel l'étape consistant à produire séparément une estimation de la première fréquence/de la première erreur de fréquence pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence pour le second signal abaissé en fréquence comprend les étapes consistant à : corriger des décalages de fréquence dans le second signal (S2) à une première vitesse ; et corriger des décalages de fréquence dans le second signal corrigé des décalages en fréquence à une seconde vitesse, qui est inférieure à la première vitesse, afin d'estimer ainsi la seconde fréquence/la seconde erreur de fréquence. Procédé selon la revendication 28, dans lequel les premier et second signaux reçus conjointement (S1, S2) sont reçus sur une série d'intervalles de temps qui se répètent et sont échantillonnés plus d'une fois sur chaque intervalle de temps, la première vitesse étant à raison d'un par échantillon et la seconde vitesse étant à raison d'un par intervalle de temps. Procédé selon la revendication 27, dans lequel l'étape consistant à corriger des décalages de fréquence dans le premier signal à une première vitesse comprend les étapes consistant à : calculer une erreur de phase dans le premier signal reçu (S1), à la première vitesse ; et calculer une première erreur de fréquence, sur cette base, à la première vitesse. Procédé selon la revendication 25, comprenant en outre les étapes consistant à : estimer la première erreur de fréquence dans le premier signal abaissé en fréquence ; et exécuter sélectivement l'étape consistant à produire séparément une estimation de la première fréquence/de la première erreur de fréquence pour le premier signal abaissé en fréquence et une estimation de la seconde fréquence/de la seconde erreur de fréquence pour le second signal abaissé en fréquence ou l'étape consistant à estimer la première erreur de fréquence dans le premier signal abaissé en fréquence. Procédé selon la revendication 31, comprenant en outre le maintien à une valeur constante de l'estimation de la seconde fréquence/de la seconde erreur de fréquence, en réponse à l'exécution sélective de l'estimation de la première erreur de fréquence dans le premier signal abaissé en fréquence.






IPC
A Täglicher Lebensbedarf
B Arbeitsverfahren; Transportieren
C Chemie; Hüttenwesen
D Textilien; Papier
E Bauwesen; Erdbohren; Bergbau
F Maschinenbau; Beleuchtung; Heizung; Waffen; Sprengen
G Physik
H Elektrotechnik

Anmelder
Datum

Patentrecherche

Patent Zeichnungen (PDF)

Copyright © 2008 Patent-De Alle Rechte vorbehalten. eMail: info@patent-de.com