MXPA97003356A - Extend spectrum demodulation unit - Google Patents

Abstract

The present invention relates to an improved demodulation system allocates a receiving time for the demodulation of a multi-path component of a transmission signal in accordance with an estimated rate of change of a correlation level of a multi-path component. An averaging circuit is provided to determine an average correlation level of a multi-path component according to an averaging range, wherein the averaging interval is determined according to an estimated rate of change in the level of correlation of a component multiple trajectories. A motion velocity display unit is provided to determine and display a relative movement speed between the transmitter and the receiver in accordance with an estimated rate of change of the correlation level of a multi-path component. A correlation level prediction circuit is provided to predict the level of correlation of a multi-path component according to past measurements of the correlation level. A phase allocation circuit determines an allocation of the reception time according to the estimated level of correlation to demodulate a multi-path component of a transmission signal by a demodulation circuit.

Description

EXTENDED SPECTRUM DEMODULATION UNIT The present invention relates to a receiver unit and specifically to an extended spectrum receiver to provide improved reception by means of a mobile station during movement.

BACKGROUND OF THE INVENTION In recent years, the demand for land mobile communications including cell phones and mobile phones has increased markedly. As a consequence, the need for improved technology has increased, which more effectively uses limited frequency bands to ensure larger subscriber capacities. One type of system that has been offered for the most effective use of the frequency is the code division multiple access (CDMA) system. The CDMA system depends on the transmission of extended spectrum and provides improved reception on the first transmission methods through the modulation of information signals by extended codes which have an extremely low cross-correlation and al. they also have very broad autocorrelation characteristics. An example of a land mobile communication system using the CDMA system for REF: 24523 transmission is described in U.S. Patent No. 4,901,307. In the United States, existing CDMA transmission systems use a modulation method known as a direct expansion system, which allows a receiver known as a RAKE-type receiver to separately demodulate and combine a plurality of multipath components detected from a signal. An example of a RAKE type receiver of the prior art is described on pages 328 and 353 of IEEE. Processed Voltage. 68, No. 3 (March 1980). As an antecedent to the description of the following invention, an extended spectrum communication system of the prior art, which uses the direct expansion system, will now be described. FIGURE shows the basic construction of an extended spectrum transmitter of the prior art. As shown in FIG. 1, the transmission data 49 is input to information modulation means 50, which are used to modulate the transmission data. The means generating the extended code 51 generates an extended code to be used in the expansion of the modulated transmission data. The spread spectrum modulation means 52 uses the extended code generated to produce a modulated spread spectrum signal. A transmission antenna 53 connected to it is then used to transmit the modulated signal. FIGURE Ib shows the basic construction of an extended spectrum receiver including a receiving antenna 54, extended spectrum demodulation means 56 connected thereto, extended code acquisition means 55, and information demodulation means 57. The means of Extended code acquisition 55 are used to generate the extended code in the same phase as the extended code that was used in the transmitter to modulate the detected signal. The spread spectrum demodulation means 56 is used to demodulate the signal detected in a process which is complementary to that used by the spread spectrum modulation means 52 in the transmitter (FIGURE la). The information demodulation means 57 is used to further demodulate the output of the spread spectrum demodulation means 56 to produce the reception data 58. The information modulation means 50 of the transmitter (FIG. narrow band having sufficient bandwidth only to carry the transmission data 49. After the modulation with the extended code, however, the resulting signal is enlarged many times in bandwidth compared to the narrow band information signal original. In the receiver (FIGURE Ib) the extended spectrum demodulation means 56 converts the wideband signal back into a narrow band information signal by multiplying this by the same extended code generated in the same phase by the extended code acquisition means 55 and then integrating the result. The transmissions detected in the receiving antenna 54 (FIGURE Ib) contain components of disturbing frequency due to spurious frequency signals and environmental thermal noise (shown as transient peaks and high-spectrum interface components raised in FIGURE Ib). The reception of the spread spectrum signal reduces those disturbing components by expanding the detected signals with an extension code that has a very low cross-correlation with respect to the disturbing signals. In a mobile communication environment, transmission over a channel frequently occurs along different transmission paths, due to reflection, refraction, diffraction, and scattering of the transmitted signal, as shown in FIGURE 2a. Such effects are commonly referred to as multipath transmission. For example, in FIGURE 2a, a base station 59 and a mobile station 60 are located proximate a reflective object 61 such as a building. The path 62 shows a direct path for a transmission that arrives directly from the base station 59. The path 63 shows an indirect path for the same transmission which is delayed after being reflected by the building 61. FIGURE 2b shows the levels of respective correlation for each multi-path component that are detected at different reception times with respect to the direct transmission path 62 and the delayed transmission path 63, respectively. In order to demodulate correctly an extended-spectrum signal having different reception times according to different multipath components, the extended-spectrum demodulation means 56 of a receiver must be assigned to demodulate the multi-path components at the correct reception time. The signals that are subjected to a multipath transmission due to reflections caused by buildings and other objects are subjected to the location that depends on the destructive interference between the components of multiple different trajectories. RAKE type receivers, which have a plurality of spread spectrum demodulation means 56 can be used to compensate for such multipath transmission by separating the demodulation means 56 to demodulate the different components of multiple paths. The operations of a conventional RAKE type extended spectrum receiver will now be described. In FIGURE 3, a schematic and block diagram of a demodulator of the conventional RAKE type is shown. As illustrated in FIGURE 3, an input signal 1 received from an antenna is applied to the different spread spectrum demodulation means 2, 3, 4, and 5. The spread spectrum demodulation means 2 to 5 are each assigned to different reception times to demodulate separately the multi-path components of a transmission signal that has been received along different transmission paths. The outputs 6 to 9 of the spread spectrum demodulation means 2 to 5 are applied to the means combining the received signal 10, which combine them as a weighted sum to produce a combined signal of maximum ratio. The extended spectrum modulator incorporates correlation level search means 12 to determine a correlation level 13 for each time a signal is received according to its different multipath components. The correlation level 13 for each reception time is input to the phase allocation means 14, which sets the reception times of the extended spectrum demodulation means 2 to 5 for use in the demodulation of the multiple components of multiple trajectories detected. FIGURE 4 illustrates an example of the correlation levels for multi-path components of a transmission signal. Specifically, FIGURE 4 illustrates the correlation levels 16 through 20 of the multi-path components that are detected at the respective reception times tO through tl4. As indicated in FIGURE 4, the correlation levels 16 to 20 are at a maximum for the reception times tO to tl4 for each of the respective multipath components. The allocation of the reception time for demodulation by the spread spectrum demodulation means 56 is performed to select the subset of reception times at which the highest correlation levels are observed. In this way, in this example, the extended spectrum demodulation means will be assigned to demodulate at the reception times tO, ti, tl2 and tl4 in which the correlation levels 16, 17, 18 and 20 are detected, respectively. The reception time tl3 at which the lowest correlation level 19 was observed will now be selected for assignment to the extended spectrum demodulation means because this could result in less demodulation operation. In a mobile communication environment, Rayleigh fading and other phenomena cause large time-dependent variations in the levels of correlation of signals received along particular transmission paths. Rayleigh fading is a periodic phenomenon which varies with time in a particular place in proportion proportional to the speed at which the mobile station moves. The level of correlation for each multipath component subjected to such fading can vary independently by more than 20 dB. As a result, the means seeking the level of correlation 12 must continuously track the level of correlation detected for each component of multiple paths of a signal. Notwithstanding such fading, a system and a method is required which allows the phase allocation means of a spread-spectrum RAKE-type receiver to allocate receive times to demodulate different multipath component signals by the spectrum demodulation means. extended 2 to 5, which will always correspond to the group of multiple components of multiple trajectories detected that have a higher correlation level.

However, the extended spectrum demodulator of the conventional RAKE type is not always able to assign receive times for demodulation which corresponds to the highest correlation level because the correlation level of each multi-path component changes constantly as a consequence of the movement of the mobile station. In addition, the phase assignment means 14 of the conventional RAKE-type receiver is subject to control delays caused by the detection operations performed by the search means of the correlation level 12 and the additional delays in the phase allocation means. in changing the settings of the reception time of the spread spectrum demodulation means 2 to 5. As a result, the RAKE type receiver of the prior art often does not operate at the maximum correlation level during the movement of a station. mobile and consequently does not provide optimal reception quality. With reference to Figure 5a, a phase assignment operation by the receiver of the RAKE type of the prior art in which the time change in the level of correlation of a multi-path component is slow compared to the control response speed of the phase allocation means 14. Referring to FIG. 5b, a phase assignment operation by the receiver of the RAKE type of the prior art in which the time change in the level is described will be described. The correlation for a multi-path component is fast compared to the control response speed of the phase assignment means 14. For simplicity we will consider the case in which the number of multipath components is 2 and the receiver contains only a means of modulating the extended spectrum. Figure 5a illustrates an example in which the time change in the correlation level for a multi-path component of a communication is slower than the control speed effected by the phase assignment means 14. The curve 30 shows a change of time at the level of correlation for a multi-path component A of a multi-path signal. Curve 31 shows a time change in the correlation level of a multi-path component B of a multipath signal. The time point 33 indicates that the time at which the correlation levels for the multi-path components A and B intersect, so that path B has the highest correlation level therefore. The time point 34 indicates the time at which the extended-spectrum modulation means switches the demodulation at the time of reception of the multi-path component A to that of the multi-path component B. Thus, the control delay to carry out the change in the allocation of the reception time is shown by the interval 32. The interval 35 indicates when the phase of the extended spectrum modulation means is fixed so that the multi-path component A, and the interval 36 indicate when the phase of the spread spectrum demodulation means are fixed for that multipath component B. In this way, the phase assignment means 14 is capable of switching the assignment of the reception type of the demodulation means to one time. reception for a different multipath component to which the highest correlation level was detected, after a delay of and control 32. Figure 5b illustrates an example in which the time change in the level of correlation for a multi-path component is faster than the speed of control effected by the phase assignment means 14. The curve 37 shows a time change in the level of correlation for a multi-path component C of a multi-path signal. Curve 38 shows a time change in the level of correlation for a multi-path component D of the multipath signal. The intervals 39 indicate when the reception time of the spread spectrum demodulation means is fixed so for that multi-path component C, and the intervals 40 indicate how much time of reception of the extended spectrum demodulation means are fixed for that multi-path component D. In this example, due to the slowness of the control response made by the phase assignment means 14 , compared to the change of time in the correlation levels, the RAKE type receiver of the prior art is unable to effect a session of the reception time which results in the demodulation of the signal of the higher correlation level. According to the operation of the existing system as shown in Figure 5a, although the time change in the correlation levels for the multi-path components is slow compared to the speed of the control response of the media of phase assignment 14, the reception quality deteriorates during the interval of the control delay 32 at which the demodulation is performed at the reception time for the lowest signal correlation level. However, according to the operation of the existing system as shown in Figure 5b, when the time change in the level of correlation of a multi-path component is faster than the control response speed of the allocation means of phase 14, the reception time allocation results in the demodulation of a multi-path component which is lower at the level of correlation at a given point in time than the multi-path component C, which also has the highest average signal correlation level. In such a case, as shown in Figure 5b, it may be desirable to avoid frequent switching in the allocation of the reception time of the spread and allocated spectrum demodulation means and reception time that reflects the highest average signal correlation level. . Although the above examples have illustrated, for simplicity, cases in which the number of components of multiple trajectory is 2, and the receiver includes only one extended spectrum demodulation means, those skilled in the art should understand that this applies to cases wherein a number of spread spectrum demodulation means are , as in the RAKE type receiver of the prior art, to separately demodulate a number of multi-path components to be chopped as a demodulated signal of maximum ratio. The present invention seeks to solve the problems ca by the conventional phase assignment techniques of the prior art receiver systems such as the RAKE type receiver.

Specifically, the present invention seeks to provide a system and method by which the phase assignment control performed could allow a receiver of the RAKE type to allocate demodulation reception times that most closely correspond to the multipath components that have the highest level of correlation at a given point in time. Through the use of such phase assignment control, the reception quality for multipath transmissions will improve. Accordingly, an object of the present invention is to provide a system and method that allows a receiver of the RAKE type to allocate demodulation reception times that most closely correspond to the multi-path components having higher correlation levels in a given point in time. Another object of the invention is to provide a system and method that allows a mobile communication user to be informed of an estimated movement speed of the mobile communication receiver in relation to a transmitter. Another object of the present invention is to estimate the rate of change of a detected level of correlation and effect the allocation of a reception time based on the estimated speed change.

Still another object of the present invention is to provide an estimated value of a correlation level of a multipath component signal, and to effect the allocation of a reception time based on that estimated value. Still another object of the present invention is to provide averaging means having a selected average range to determine an average correlation level of a multi-path component of a transmission signal in accordance with that average range, and effect the allocation of a time. of reception based on it.

BRIEF DESCRIPTION OF THE INVENTION In the first of several embodiments of the present invention, the means for estimating the variation of speed are coupled to the means that seek the level of correlation of a demodulation system to estimate the rate of change of a level of correlation of a component. Multipath of a transmission signal. The averaging means coupled to the means estimating the velocity variation are provided to select, in accordance with the estimated rate of change, an averaging range over which an average correlation level of a multi-path component is determined. The averaging interval is provided to the phase assignment means 14 which determine, according to the averaging range, an average correlation level for each of the plurality of multi-path components of a transmission signal. The phase allocation means also allocate times of reception to the demodulation means which is based on the average correlation level. The means that estimate the rate of variation are preferably implemented by means of differentiating the correlation level signal of a multi-path component and means for counting the number of crosses at zero of the differentiated correlation level signal per unit of weather. Preferably, the averaging range is selected to be large when the estimated field velocity at the correlation level is rapid. Preferably, the averaging interval is selected short when the estimated rate of change is slow. The means are preferably provided in a demodulation system for determining and detaching, according to the estimated rate of change of the correlation level of a multi-path component of a transmission, a relative movement speed between the mobile communication receiver and a transmitter of that transmission. Preferably, the demodulation system demodulates a transmitted spread spectrum signal. In another modality, the present invention, the correlation level prevention means provide an estimated future correlation level of a multi-path component of a transmission signal which was based on previous measurements of the level of correlation of that multi-path component. The phase assignment means 14 are provided with the estimated level of correlation and effect the allocation of a reception time based on that estimated level of correlation.

BRIEF DESCRIPTION OF THE DRAWINGS The Figure illustrates the structure and operations of an extended spectrum transmission system of the prior art. Figure Ib illustrates the structure and operations of an extended spectrum receiver system of the prior art. Figure 2a illustrates the transmission of multiple paths in a mobile communication environment. Figure 2b is a graph showing the correlation levels of the reception time for the multi-path components of a multipath transmission signal. Figure 3 shows a schematic block diagram of a receiver of the extended spectrum RAKE type of the prior art. Figure 4 is a graph showing the correlation levels of the multi-path components of a transmission signal versus the reception time after the demodulation of the spread spectrum. Figure 5a is a graph according to the prior art reception time allocation control showing the time changes in the correlation levels for the two multi-path components of a transmit signal and a receive time allocation provided to the extended spectrum demodulation means, in which the estimated rate of change of the correlation levels is slow. Figure 5b is a graph according to the prior art reception time allocation control, showing the time changes in the correlation levels for two multi-path components of a transmission signal and a reception time transfer provided to the extended spectrum demodulation means, in which the estimated rate of change of the correlation levels is fast.

Figure 6 is a schematic block diagram of an extended spectrum demodulation receiver constructed in accordance with a first embodiment of the present invention. Figure 7a is a graph according to the first, second and fourth embodiments of the invention, showing the time changes in the correlation levels for two multipath components of the transmission signal and a reception time allocation provided to the extended spectrum demodulation means, in which the estimated rate of change of the correlation levels is slow. Figure 7b is a graph according to the first, second and fourth embodiments of the invention, showing the time changes in the correlation levels for two multipath components of a transmission signal and a reception time allocation provided to the extended spectrum demodulation media, in which the estimation in the levels of correlation is fast. Figure 8 is a schematic block diagram of an extended demodulation receiver according to a second embodiment of the present invention. Figure 9 is a graph showing the time variation of a correlation level for a multi-path component, a differentiation signal thereof, and the zero crossings of the differentiation signal. Figure 10 is a schematic block diagram of an extended spectrum demodulation receiver constructed in accordance with a third embodiment of the present invention. Figure 11 is a graph illustrating the operations of the means that predict the level of correlation according to the third embodiment of the invention. Figure 12a is a graph according to a third embodiment of the invention, showing the time changes and correlation levels for two components of multiple paths of a transmission signal, the estimated correlation levels, and a time allocation of reception provided to the extended spectrum demodulation means, in which the rate of change of the correlation levels is slow. Figure 12b is a graph according to the third embodiment of the invention, showing the time changes of the levels of correlation to two components of multiple paths of a transmission signal, and an allocation of the reception time provided to the levels of extended spectrum demodulation, in which the speed of change of the correlation levels is rapid.

Figure 13 is a schematic block diagram of an extended spectrum demodulation receiver constructed in accordance with a fourth embodiment of the present invention.

BRIEF DESCRIPTION OF THE PREFERRED MODALITIES A schematic block diagram of a first embodiment of the present invention is shown in Figure 6. The elements of circuit 1 to 15 of Figure 6 are the same as shown in Figure 3 and described above. The variation rate estimation means 21 operates after the detected correlation level 13 for each multipath component to provide an estimated rate of change 22 for each level of correlation. The averaging means 23 is coupled to the phase assignment means 14 and determines an average correlation level 24 for each multipath component according to an averaging interval which is based on the estimated rate of change of the correlation level. . In cases where the estimated rate of change 22 is slow, the averaging interval of averaging means 23 is set short or short. In other cases in which the estimated rate of change 22 is rapid, the averaging interval becomes long or long. Using the estimated rate of change 22 and the average signal correlation level 24, the phase allocation means 14 allocate different reception times to be used for demodulation by each of the extended spectrum demodulation means 2, 3, 4, and 5. The operations of the extended spectrum modulation system according to the first embodiment of the present invention will now be described. The rate of variation estimation means 21 provides an estimated rate of change 22 of the correlation level 13 of a multi-path component that is detected by the means illustrating the level of correlation 12. The averaging means 23 selects a range average which is based on the estimated rate of change for the multi-trajectory component and determines an average correlation level of the multi-trajectory component according to the averaging interval. The average correlation level 24 is provided to the allocation means 14. Based on the average multipath signal correlation levels, which are determined in accordance with the averaging interval, the phase assignment means 14 determines which Correlation levels at a given point are the highest correlation levels detected. The phase assignment means 14 then allocate the reception times to the spread spectrum demodulation means accordingly. An example of a specific operation will now be described with reference to Figure 7a, in which the rate of change of the correlation level of a multi-trajectory component is slow; and a specific operation example will be described with reference to Figure 7b in which the speed of change is rapid. For simplicity, the case in which the number of multi-path components is 2 will be considered and only one extended spectrum demodulation means is provided in the receiver. Curves 31 and 31, crossing points 33 and phase assignments 35 and 36 shown in Figure 7a refer to the same characteristics that are shown and described with reference to Figure 5a above. The reference numbers 41 and 43 indicate control delays which are due to the search time in the search means of the correlation level 12 plus the delay caused by the averaging means 23. The reference number 42 denotes a point of time when the the reception time of the extended-spectrum demodulation means 2 was assigned to the reception time of the multi-path component A of that multi-path component B. The reference number 44 (FIG. 7b) indicates a range in which the reception time of the extended spectrum demodulation means was assigned to demodulate the multi-path component C. FIGURE 7a shows a case in which the estimated rate of change of a level of correlation of a multi-path component is slow. Since the averaging interval in averaging means 23 was set short, this results in the phase allocation means the rapid reallocation of the reception time of the extended spectrum demodulation means 2 of that multi-path component A to the time of reception of the multiple path component B which has a level of Largest correlation FIGURE 7b shows a case in which the estimated rate of change of the correlation level of a multi-path component is rapid. By setting the cycle of the averaging means 23 with respect to the estimated rate of change, this results in the phase allocation means maintaining the allocation of the reception time in the signal with the largest average correlation level, of so that there is no rapid change in the allocation of reception time. In this way, the demodulation takes place in the reception time for which the level of total correlation with time is greater. In the operation example described above, the case in which the number of components of multiple trajectories is two was considered and only the allocation of an extended spectrum modulation means was considered. One skilled in the art will understand the operation of the present invention in a case in which a plurality of spread spectrum demodulation means are used to demodulate a plurality of multi-path components. Through the improvements provided by the present invention as described above, the receive type assignments used for demodulation by a receiver of the RAKE type can be maintained to demodulate the multi-path components that are most closely associated with the level of maximum correlation instead of that made by the receiver of the RAKE type of the prior art. FIGURE 8 is a block diagram and schematic which shows a receiver of the RAKE type improved according to a second embodiment of the present invention. In FIGURE 8, references 1 to 15, and 22 to 24 denote the elements that are similar to those shown in FIGURE 6 and are described in the accompanying text. As shown with the specific interconnections illustrated in FIGURE 8, the means of estimating the rate of variation were constructed in accordance with this embodiment of the present invention through differentiation means 25 and a zero crossing counter 27. Differentiation means 25 were used to differentiate the level of correlation 13 from a multi-path component of a detected transmission signal. The reference numeral 26 indicates a differentiation signal thereof, and the reference numeral 27 indicates a zero crossing counter used to provide a count of the number of crossing points at zero of the differentiation signal per unit of time. FIGURE 9 shows an example of operation specific to the operation according to this embodiment of the present invention. In FIGURE 9, the reference numeral 66 denotes a change of time in the correlation level for a given multipath component, the reference number 67 indicates a differentiated level of the time change 66, and the reference number 68 shows the junctions in zero of the differentiated level 67. As can be seen from FIGURE 9, the fundamental cycle of the correlation level can be estimated by counting the number of crosses at zero per unit of time in the differentiated signal 66. In operation, according to the estimated fundamental cycle of the correlation level that is provided by the zero crossing counter 27 the phase allocation means allocate a time of reception for demodulation by the demodulation means 2, which corresponds to the largest correlation level.

FIGURE 10 is a block diagram and schematic illustrating the construction of a third embodiment according to the present invention. Numerals 1 through 15 and 24 of FIGURE 10 show the same elements shown in FIGURE 6 and described in the accompanying text. In FIGURE 10, the reference numeral 28 denotes the path level prediction means to be used in the estimation of the correlation level for a multi-path component of a multipath signal. The path level prediction means 28 receives the level of correlation 13 for a multi-path component from the search means of the correlation level 12 and provides an estimated level of correlation 24 to the phase assignment means 14 for use in the allocation of a reception time to the extended-spectrum demodulation means 2. The estimated level of correlation can be obtained through the waveform prediction method generally used, for example, in which an estimated value can be obtained through of the weighted average of the correlation level values observed in the past. The operations of the extended spectrum demodulation system according to the third embodiment will now be described. The path level prediction means 28 estimates a level of correlation for a multi-path component from the level of correlation 13 which is detected by each reception time by the search means of the correlation level 12. The means of allocation of phase 14 then use the estimated correlation level 24 to assign a reception time to the extended spectrum demodulation means 2, 3, 4, or 5 according to the value of the estimated correlation level to achieve a more time change of time precise allocation of reception time. An operation example of this embodiment of the present invention will now be described, with reference to FIGURE 11. As shown in FIGURE 11, the numerical references 69 and 72 indicate the time changes in the correlation level observed for a component multipath in which the rate of change of the level of correlation is relatively slow in one case, and in another case the speed of change is rapid. The reference numbers 70 and 73 show the trends of the estimated correlation levels obtained for each of the respective time changes in the correlation levels 69 and 72. The time points 71 indicate when the estimated correlation levels were determined. A sampling interval is indicated by reference number 74.

The prediction value of the correlation level was determined according to the following formula: Xln + l) ~ • S? ak'x (Bk) Jr »0 where ak is the weighting coefficient, x (n) is a sample value at time nT, where T is the sampling interval, n is an integer and N is a period of observation. In this way, an estimated value is obtained by applying a respective weight to a sample value up to the present time. This weight value is selected in advance to minimize the prediction error. In FIGURE 11, trends 70 and 73 are straight lines obtained by the weighted average of past measurements of signal correlation levels, where the correlation level estimated at time point 71 will be determined. where the rate of change of a level of correlation is slow, it is possible to make the prediction with relatively high accuracy. However, in cases where the speed change of a correlation level is rapid, the estimated correlation level remains an inaccurate measure of the actual correlation level and represents an average correlation level for the signal.

As an example of specific operation of a receiver of the RAKE type according to this embodiment of the present invention, a case will be described in which the rate of change of the multi-path component is slow; and another case in which the rate of change of a level of correlation is rapid, with reference to Figures 12a and 12b, respectively. For simplicity, the case in which the number of components of multiple trajectories is two and only one means of demodulation of extended spectrum in the receiver will be considered. In FIGS. 12a and 12b the numerical references 30, 31, 33 and 35 to 38 refer to the same curves and characteristics shown in FIGS. 5a and 5b and described in the accompanying text. The reference numeral 45a indicates the value of the estimated correlation level of the multipath component A after the interval 32a estimated at the time point 33. The reference number 45b indicates the value of the estimated correlation level of the multipath component B after the estimated interval 32a of the time point 33. The estimated value 46 of the correlation level of the multi-path component C is shown in FIGURE 12b as the estimated value 47 of the correlation level of the multi-path component D. The interval 48 indicates when the reception time of the spread spectrum demodulation means is fixed for that multi-path component C. As shown in FIGURE 12a, it can be understood from the estimated correlation levels 45a and 45b of the multi-path components A and B which were made at time point 33 so that the level of correlation of the estimated multipath component B exceeds that of the multipath component A after the time point 33. Based on such prediction, the phase assignment means allocates the reception time of the extended spectrum demodulation means to demodulate the component multipath B, without incurring a control delay after the time point 33 as the receiver of the RAKE type of the prior art. However, in the case illustrated in FIGURE 12b, the estimated correlation levels 46 and 47 are the averages of the correlation levels detected for each of the respective multipath components C and D. In such a case, the phase allocation means 14 allocates the time of reception of the demodulation means 2 to the highest average correlation level that has been determined according to the estimated correlation levels 46 and 47. As a result, the allocation the reception time of the demodulation means 2 is maintained at the reception time for the multi-path component C during the interval 48, so that the allocation of the time of reception of the demodulation means 2 is not frequently switched, with the operation of the resulting decreased demodulation, as occurs in the RAKE type receiver of the prior art. Referring again to FIGURE 10, in the present invention, by allocating the times of reception of the extended spectrum demodulation means 2 to 5 according to the estimated correlation levels 24, the receiver of the RAKE type can be operated in phases that correspond more closely to the maximum correlation level, which therefore improves the quality of reception. A schematic block diagram showing the construction of a fourth embodiment of the present invention is shown in FIGURE 13. Numerals 1 through 15, and 21 through 24 of FIGURE 13 indicate the elements that are the same as those shown. in FIGURE 6 and are described in the accompanying text. In FIGURE 13 the reference numeral 29 indicates a mobile speed visual display unit used to convert a speed change 22 of the correlation level for a particular multipath component to a mobile speed and display the mobile speed. In all other aspects, the construction and operations of the fourth embodiment of the present invention are the same as those of the first embodiment of the present invention. Thus, the construction and operation need not be described in detail again. In this embodiment of the present invention, the mobile speed visual display unit 29 calculates and displays a relative movement speed between a transmitter and a receiver according to an estimated rate of change 22 at the level of signal correlation that was determined by means of estimating speed of variation 21. Since the rate of change 22 of a multi-path component and a relative speed of a transmitter and a receiver are in proportional relation, the relative velocity can be easily obtained with the following formula: v = fD •? where fD is the rate of change 22 of a multi-path component (or maximum Doppler frequency) and? is the carrier frequency. This embodiment provides an advantage in addition to the effects provided by the first embodiment of the present invention, by providing the user with the indication of the relative speed between the transmitter of a transmission and the receiver of that transmission. Although the invention has been described in detail in accordance with certain preferred embodiments thereof, many modifications and changes may be made thereto by those skilled in the art. Accordingly, it is intended that the appended claims cover all such modifications and changes that fall within the true spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (28)

1. In a demodulation system including demodulation means for demodulating a selected one of one or more of a plurality of multi-path components of a transmission signal in accordance with the receive time assignments, the demodulation system further includes search means of the level of correlation to determine a level of correlation corresponding to a time of reception for each of the components of multiple trajectories, the improvement characterized in that it comprises: means of estimation to estimate the rates of change of the levels of correlation; and phase allocation means for providing the receive time assignments to the demodulation means according to the correlation levels and the estimated rates of change.

2. The demodulation system according to claim 1, characterized in that it further comprises: a movement speed visual representation unit for determining and displaying an estimated relative speed between a transmitter of the transmission signal and the demodulation means based on the estimated rates of change of the correlation levels of the multi-trajectory components.

3. The demodulation system according to claim 1, characterized in that it further comprises: averaging means coupled to the phase assignment means for determining, for each of the multi-trajectory components, an average correlation level over an averaging interval , the averaging interval is selected according to the estimated rates of change of the correlation levels for such a multi-trajectory component; and wherein the phase allocation means selects the allocation of the reception time according to the average correlation level.

4. The demodulation system according to claim 3, characterized in that the selected averaging interval is short when the estimated change rates of the correlation level are slow.

5. The demodulation system according to claim 3, characterized in that the selected averaging range is large when the estimated change rates of the correlation level are rapid.

6. The demodulation system according to claim 3, characterized in that the demodulation means demodulates a transmission signal which has been modulated according to an extended code signal.

7. The demodulation system according to claim 1, characterized in that the means of estimation include means for differentiating the levels of correlation of the components of multiple trajectories and a counter for determining the number of crossings at zero of the differentiated correlation levels.

8. The demodulation system according to claim 7, characterized in that it further comprises: averaging means coupled to the phase assignment means for determining, for each of the multipath components, an average correlation level over an averaging range , the averaging interval is selected according to the estimated rates of change of the correlation levels for such a multi-trajectory component; and wherein the phase allocation means selects the allocation of the reception time according to the average correlation level.

9. The demodulation system according to claim 8, characterized in that the selected averaging interval is short when the estimated change rates of the correlation levels are slow.

10. The demodulation system according to claim 8, characterized in that the selected averaging range is large when the estimated change rates of the correlation levels are rapid.

11. The demodulation system according to claim 9, characterized in that the demodulation means demodulates a transmission signal which has been modulated according to an extended code signal.

12. In a demodulation system including demodulation means for demodulating a selected one of one or more of a plurality of multi-path components of a transmission signal in accordance with the receive time assignments, the demodulation system further includes search means of the level of correlation to determine a level of correlation corresponding to a reception time for each of the components of multiple trajectories, the improvement characterized in that it comprises: means of predicting the level of correlation to predict, for each of the levels of correlation, a future correlation level based on determinations of the past correlation level; and phase allocation means for providing assignments of the reception time to the demodulation means according to the estimated future correlation levels.

13. The demodulation system according to claim 12, characterized in that the future correlation level is estimated based on an average of the past correlation level determinations.

14. The demodulation system according to claim 13, characterized in that the average is a weighted average.

15. The demodulation system according to claim 12, characterized in that the level of future correlation is an average of the determinations of the correlation level passed when the level of correlation varies rapidly.

16. An extended spectrum demodulation system for demodulating and combining a selected plurality of multi-path components of a digital transmission signal that has been modulated according to an extended code signal, characterized in that it comprises: a plurality of code demodulation means extended, each demodulation means demodulates a selected one of one or more of a plurality of multi-path components of the digital transmission signal according to the extended code phase and the receive time assignments; means for searching the level of correlation to determine a level of correlation corresponding to an extended code phase and a receiving time for each of the multi-path components; estimation means to estimate the rates of change of the correlation levels; and phase allocation means for providing an extended code phase and an allocation of the reception time to each of the demodulation means according to the correlation levels and the estimated change rates.

17. A method for providing receive time assignments for use in the demodulation of one or more of a plurality of multi-path components selected from a transmission signal according to the receive time assignments, characterized in that it comprises the steps of: determining a level of correlation corresponding to a reception time for each of the components of multiple trajectories; estimate the rates of change of the correlation levels; and providing the allocations of the reception time to the demodulation means in accordance with the correlation levels and the estimated rates of change.

18. The method according to claim 17, characterized in that it includes the step of: determining and displaying an estimated relative speed between a transmitter of the transmission signal and the demodulation means based on the estimated change rates of the correlation levels of the components of multiple trajectories.

19. The method according to claim 17, characterized in that it further comprises the steps of: determining, for each of the multi-trajectory components, an average correlation level over an averaging interval, the averaging interval is selected according to the estimated rates of change of the correlation levels for the multi-trajectory components; and selecting the allocation of the reception time according to the average correlation level.

20. The method according to claim 19, characterized in that the selected averaging interval is short when the estimated rate of change of a correlation level is slow.

21. The method according to claim 19, characterized in that the selected averaging interval is large when the estimated rate of change of a level of correlation is rapid.

22. The method according to claim 19, characterized in that the transmission signal has been modulated according to an extended code signal.

23. The method according to claim 19, characterized in that the estimated change rates of the correlation levels were determined by differentiating the correlation levels of the multipath components and counting the number of crosses at zero of the differentiated correlation levels.

24. A method for providing receive time assignments for use in the demodulation of one or more of a plurality of multi-path components selected from a transmit signal according to the receive time assignments, characterized in that it comprises the steps of: determining a level of correlation corresponding to a reception time for each of the components of multiple trajectories; predict, for each level of correlation, a future correlation level based on past correlation level determinations; and providing the allocations of the reception time to the demodulation means according to the estimated future correlation levels.

25. The method according to claim 24, characterized in that the level of future correlation is estimated based on an average of the determinations of the past correlation level.

26. The method according to claim 24, characterized in that the average is a weighted average.

27. The method according to claim 24, characterized in that the level of future correlation is an average of the determinations of the correlation level passed when the level of correlation varies rapidly.

28. A method for providing an extended code phase and allocating the receive time to each of a plurality of spread spectrum demodulation means for use in the demodulation of one or more of a plurality of multi-path components selected from a signal digital transmission which has been modulated according to an extended code signal, characterized in that it comprises the steps of: determining a level of correlation corresponding to an extended code phase and a reception time for each of the multiple components trajectories; estimate the rates of change of the correlation levels; and providing an extended code phase and an allocation of the reception time to each of the demodulation means according to the correlation levels and the estimated rates of change. SUMMARY OF THE INVENTION An improved demodulation system allocates a reception time for the demodulation of a multi-path component of a transmission signal according to an estimated rate of change of a correlation level of a multi-path component. An averaging circuit is provided to determine an average correlation level of a multi-path component according to an averaging range, wherein the averaging interval is determined according to an estimated rate of change in the level of correlation of a component of multiple trajectories. A motion velocity display unit is provided to determine and display a relative movement speed between the transmitter and the receiver according to an estimated rate of change of the correlation level. of a multi-trajectory component. A correlation level prediction circuit is provided to predict the level of correlation of a multi-path component according to past measurements of the correlation level. A phase allocation circuit determines an allocation of the reception time according to the estimated correlation level for demodulating a multi-path component of a transmission signal by a demodulation circuit.