The present application is a divisional application of an invention patent application having an application number of 01140004.8, a filing date of 1995, 6/16 and a title of "phased array spread spectrum method".
Disclosure of Invention
A general object of the present invention is to provide an improved system and method for receiving spread spectrum signals in a multipath environment.
It is another object of the invention to improve the received signal to noise ratio or to reduce the error probability of a spread spectrum signal arriving from two or more paths.
It is another object of the invention to receive a plurality of spread spectrum signals arriving at the antenna from a plurality of different directions, irrespective of the number of antenna elements.
As embodied and broadly described herein, according to the present invention, there is provided a phased array spread spectrum system including receiving means, delay means, combining means, despreading means, generating means, storing means, and comparing means. A receiving device receives a plurality of spread spectrum signals and a plurality of phased versions of the plurality of spread spectrum signals. Typically, the plurality of spread spectrum signals are received by receivers of a first plurality connected to a first antenna and the plurality of phased versions of the plurality of spread spectrum signals are received by receivers of a second plurality connected to a second antenna. The plurality of spread spectrum signals and the plurality of phased versions of the plurality of spread spectrum signals are digitized. The delay means is capable of delaying the plurality of received spread spectrum signals by a plurality of delays relative to a plurality of phased versions of the plurality of spread spectrum signals. The plurality of received spread spectrum signals thereby becomes a plurality of delayed signals.
Combining means combines the plurality of delayed signals and the plurality of phased versions of the spread spectrum signal into a plurality of combined signals. The in-phase component of each delayed signal is combined with the in-phase component of each phased version of each spread spectrum signal, respectively. The quadrature component of each delayed signal is combined with the quadrature component of each phased version of each spread spectrum signal, respectively.
The despreading means despreads the plurality of combined signals into a plurality of despread signals. This may be accomplished by using multiple product detectors with multiple hopping sequences that match the multiple received spread spectrum signals, respectively, or with multiple matched filters having multiple pulse functions that match the multiple hopping sequences of the multiple received spread spectrum signals, respectively.
The generating means generates a plurality of magnitudes from the plurality of despread signals. Each magnitude may be an absolute value or a square of the in-phase and quadrature components of the despread signal.
The storage means stores a plurality of prior magnitude values previously generated by the generation means and a plurality of current magnitude values currently generated by the generation means. The plurality of prior magnitude values and the plurality of current magnitude values are compared by the comparing means, respectively. In response to the comparison, the comparison device outputs a plurality of comparison signals. The delay means may vary any or all of the plurality of delays in accordance with the plurality of comparison signals, respectively.
The present invention also includes a method of maximizing signal strength of a plurality of spread spectrum signals having multipath, comprising the step of receiving the plurality of spread spectrum signals and a plurality of phased versions of the plurality of spread spectrum signals. The plurality of received spread spectrum signals are delayed relative to the plurality of phased versions of the plurality of spread spectrum signals by a plurality of delays to produce a plurality of delayed signals. The plurality of phase-controlled versions of the plurality of delayed signals and the plurality of spread signals are combined into a plurality of combined signals, and the plurality of combined signals are despread into a plurality of despread signals, respectively.
The method includes generating a plurality of magnitudes from the plurality of despread signals, storing a plurality of prior magnitudes and a plurality of current magnitudes. Comparing the plurality of previous magnitude values with the plurality of current magnitude values, and outputting a plurality of comparison signals according to the comparison result. The plurality of delays are varied using the plurality of comparison signals. The step of generating the plurality of magnitudes is a method of determining a maximum value. Other steps for determining the maximum or equivalent methods may also be used.
According to the present invention there is provided a base station for receiving a spread spectrum signal comprising a plurality of channel signals using a set of phased array antennas, each antenna receiving a phased version of the spread spectrum signal, the base station characterised by comprising: means, coupled to one of the phased array antennas, for generating a plurality of delayed signals, each of the plurality of delayed signals corresponding to a channel signal; combining means for combining the plurality of delayed signals with a phased version of each of a plurality of spread spectrum signals into a combined signal; despreading means for despreading the combined signal using a hopping sequence matched to the spread signal to generate a despread channel signal; generating means for generating current and previous magnitudes for each despread channel signal; comparison means for each channel for comparing the current magnitude with a previous magnitude; and delay means for delaying each channel signal in response to the magnitude comparison in the channel such that an antenna beam combined with the delay of the channel is directed to a spreading component of the channel signal having the highest magnitude.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may also be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
Detailed Description
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements.
Mobile phone
The invention provides a novel phased array spread spectrum system which comprises a receiving device, a delay device, a combining device, a de-spreading device, a generating device, a storage device and a comparison device. The delay means is connected between the receiving means and the combining means. The despreading means is connected between the combining means and the generating means. The storage means are connected between the generating means and the combining means, and the combining means are connected to the delaying means.
The receiving apparatus of fig. 1 receives a spread spectrum signal and a phase-controlled version of the spread spectrum signal. The term "phased-form" as used herein includes the form of a spread spectrum signal having a different phase than the received spread spectrum signal and/or the form of a spread spectrum signal having a time delay relative to the received spread spectrum signal. As shown in fig. 2, such different phases and/or delays are caused by spread spectrum signals 15 bouncing back from different buildings 17, 18 and phased versions 16 of the spread spectrum signals from different paths. The phased array spread spectrum system may be implemented in a base station or Remote Subscriber Unit (RSU) such as handset 19 as shown in fig. 2. The phase change occurs upon each reception because there is one reflection of a first spread spectrum signal 15 and two reflections of a second ray, such as a phased version 16 of the spread spectrum signal. As a result of the time difference between the two signals, the multipath signals may experience phase cancellation and produce fading. The phased array spread spectrum system of figure 1 delays or phase shifts one of the two antennas 11, 12 sufficiently to control the direction of the beam from the two antennas to the building or ray path having the greatest signal strength.
Typically, as shown, the receiving means comprises a first antenna 11 and a second antenna 12. The spread spectrum signal d (t) g (t) cos ω 0t is received by a first receiver connected to the first antenna 11, while the phased form of the spread spectrum signal d (t- τ) g (t- τ) cos ω 0(t- τ) is received by a second receiver connected to the second antenna 12. The first and second receivers include suitable Radio Frequency (RF) and Intermediate Frequency (IF) amplifiers and filters. The received spread spectrum signal and a phased version of the spread spectrum signal may be digitized.
The delay means, shown in fig. 1 as delay means 13, can delay the received spread spectrum signal by one delay with respect to the phase-controlled version of the spread spectrum signal. The received spread spectrum signal thereby becomes a delayed signal with a delay approximately equal to the delay of the phase-controlled version of the spread spectrum signal. A preferred embodiment uses digital signal processing. Thus, the delay means will comprise digital delay means such as a shift register. Alternatively, the analog circuit will use an analog delay device, or a phase shifter.
Although two antennas are shown, the receiving apparatus may include additional antennas for improved performance. The delay means will then have suitable delay circuits for the plurality of antennas.
The combining means, shown as combiner 14, combines the delayed signal and the phase-controlled version of the spread signal into a combined signal. The phase-controlled versions of the delayed signal and the spread spectrum signal have approximately the same phase and time delay. Thus, the in-phase component of the delayed signal is combined with the in-phase component of the phase-controlled version of the spread spectrum signal, and the quadrature component of the delayed signal is combined with the quadrature component of the phase-controlled version of the spread spectrum signal.
Despreading means despreads the combined signal into a despread signal. This can be accomplished by using a product detector with a frequency hopping sequence matched to the received spread spectrum signal or by using a matched filter, such as a Surface Acoustic Wave (SAW) device, with a pulse function matched to the frequency hopping sequence of the received spread spectrum signal. Product detection devices, digital signal processors and SAW devices for despreading spread spectrum signals are well known in the art.
A generating device generates a magnitude value based on the despread signal. The magnitude may be an absolute value, the square of the in-phase and quadrature components of the despread signal, or other magnitudes of the despread signal used to determine relative signal strength values. The magnitude currently being generated by the generating means is referred to herein as the current magnitude. The magnitude previously generated by the generating means is referred to herein as a prior magnitude. Although the prior value may be separated from the current value by time and other values, the prior value generated immediately prior to the current value is used to teach the present invention. Also, more than one prior value may be used. We teach the concept of the present invention using one of the preceding values.
The storage means stores a previous magnitude value previously generated by the generation means and a current magnitude value currently generated by the generation means. In a digital implementation, the storage device may be embodied as a shift register, or equivalently as a gate circuit performing the storage function. In an analog implementation, the storage device may be embodied as two or more capacitors for storing the prior magnitude and the present magnitude.
The prior magnitude and the current magnitude are compared by a comparison means. In response to the comparison, the comparison means outputs a comparison signal. For example, if the current magnitude is greater than the prior magnitude, the comparison means outputs a comparison signal to increase the delay τ of the delay means, whereas if the current magnitude is less than the prior magnitude, the comparison means outputs a comparison signal to decrease the delay τ of the delay means. The delay means varies the first delay in dependence on the comparison signal. If a plurality of prior values are used, a scheme with comparing means weighting the plurality of prior values may be used.
The present invention provides an improvement if the delay τ is less than the time of the chip Tc. The present invention operates in closed multipath. For extreme multipath, noise is a product. The invention therefore finds application in buildings or in areas where τ < Tc. For τ > Tc, a RAKE system should be used.
In the exemplary arrangement shown in fig. 3, is embodied as a first antenna 11, a first RF/IF section 21, a first analog-to-digital converter 23, a second antenna 12, a second RF/IF section 22, and a second analog-to-digital converter 24. The first RF/IF section 21 is connected between the first antenna 11 and the first analog/digital converter 23. The second RF/IF section 22 is connected between the second antenna 12 and a second analog/digital converter 24. Typically, the first RF/IF section 21 produces an in-phase component and a quadrature component of the received spread spectrum signal. The second RF/IF section 22 produces an in-phase component and a quadrature component of the phase-controlled version of the received spread spectrum signal.
As illustrated in fig. 3, the outputs of the first and second analog/digital converters 23, 24 may enter other portions for processing different channels of the spread spectrum signals 25, 26.
The delay means is embodied as a first digital delay means 27. The delay means may additionally comprise a second digital delay means 28. The first delay means 27 are connected to the first analog/digital converter 23. If a second digital delay means 28 is included, this second delay means 28 is connected to the second analog/digital converter 24.
The combining means are embodied as a first summer 29 and a second summer 30. The first summer 29 is connected to the first digital delay means 27 and the second digital delay means 28. The second summer 30 is connected to the first digital delay means 27 and the second digital delay means 28. If the second digital delay means 28 is not included, the first summer 29 is connected to the first digital delay means 27 and the second analog/digital converter 24, and the second summer 30 is also connected to the first digital delay means 27 and the second analog/digital converter 24.
The despreading means are embodied as a despreader 31. The despreader 31 may be embodied as a product device coupled to a suitable frequency hopping sequence generator and synchronization circuitry for despreading the received spread spectrum signal. Alternatively, the despreader 31 may be a digital signal processor including suitable multiplication means, or a matched filter having an impulse response matched to the frequency hopping sequence of the received spread spectrum signal. As is well known in the art, Surface Acoustic Wave (SAW) devices having an impulse response that matches the hopping sequence can be used.
The generating means is embodied as a measuring means 32. The measurement means 32 are connected to the despreader 31. Typically, the despreader 31 is connected to additional circuitry that demodulates data contained in the received spread spectrum signal.
The storage means is embodied as a shift register 33. The shift register 33 is connected to the measurement means 32. The storage device may also be embodied as a plurality of gates, registers, or other circuitry for storing a magnitude.
The comparison means may be embodied as a comparator 34 and an up/down counter 35. The comparator 34 typically has two outputs connected to the shift register 33. An up/down counter 35 is connected to the output of the comparator 34 and to the first digital delay means 27 and/or the second digital delay means 28.
The first antenna 11 receives the spread signal amplified by the first RF/IF section 21. The first RF/IF section 21 outputs an in-phase component and a quadrature component to the first analog/digital converter 23. The first analog/digital converter 23 converts the in-phase component and the quadrature component into a digitized in-phase component and a digitized quadrature component. These components can be processed by coupling the output of the first analog/digital converter 23 at the output using components similar to the phase compensation circuit 40.
Similarly, a phase-controlled version of the spread-spectrum signal is received by the second antenna 12 and then amplified and filtered by the second RF/IF section 22. The second RF/IF section 22 has outputs for an in-phase component and a quadrature component which are fed to a second analogue-to-digital converter 24. The output 26 of the second analog/digital converter 24 may enter a component similar to the phase compensation circuit 40 for handling different hopping sequences. For example, a spread spectrum signal may have multiple spread spectrum channels, each defined by a different hopping sequence. Each component is therefore available for a corresponding spread spectrum channel, and is processed with that particular hopping sequence.
The first digital delay means 27 delays the digitized spread spectrum signal by a first delay. The output of the first digital delay means 27 is a first delayed signal. The second digital delay means 28 delays the phase-controlled version of the digitized spread spectrum signal by a second delay. The output of the second digital delay means 28 is a second delayed signal. The second digital delay means 28 is optional and is not necessary for the application of the present invention. The term "second delayed signal" refers to a phase-controlled version of the digitized spread spectrum signal output from the second analog-to-digital converter 24 if the second digital delay means 28 is not included.
The first summer 29 combines the quadrature component of the first delayed signal from the first digital delay device 27 with the second delayed signal from the second digital delay device 28. The output of the first summer is a first combined signal.
The second summer 30 combines the in-phase component from the first digital delay device 27 with the in-phase component from the second digital delay device 28. Thus, the in-phase component of the first delayed signal and the second delayed signal are combined into a second combined signal.
The despreading means 31 despreads the first combined signal and the second combined signal into a despread in-phase signal and a despread quadrature signal. The despread in-phase signal and the despread quadrature signal may be processed by other processing means (not shown) for demodulating data contained in the received spread spectrum signal.
The metric means 32 generates a magnitude based on the despread in-phase signal and the despread quadrature signal. The magnitude may be an absolute value determined from the despread in-phase signal and the despread quadrature signal, or the square of the despread in-phase signal plus the square of the despread quadrature signal. Other metrics that establish the same function of determining relative signal strength values may be used. The function of the magnitude is to compare the signal strength of a current magnitude with a previous magnitude.
The shift register 33 stores the previous value and the current value so that a comparison can be made by the comparator 34. When comparing the previous magnitude value with the current magnitude value, the comparator 34 outputs a comparison signal. The comparison signal can control the up/down counter 35 to increase or decrease the delay of the first digital delay means 27. Optionally, the up/down counter 35 may increase or decrease the delay of the second digital delay means 28.
The invention also includes a method of maximizing signal strength of a spread spectrum signal having multipath, comprising the steps of receiving the spread spectrum signal and a phased version of the spread spectrum signal. The received spread spectrum signal is delayed relative to the phase-controlled version of the spread spectrum signal by a delay to produce a delayed signal. The in-phase and quadrature components of the delayed signal and the in-phase and quadrature components of the phase-controlled version of the spread signal are combined into the in-phase and quadrature components of a combined signal, and the combined signal is despread into the in-phase and quadrature components of the despread signal.
The method includes generating a magnitude value from an in-phase component and a quadrature component of the despread signal, and storing a prior magnitude value and a current magnitude value. The previous magnitude value and the current magnitude value are compared, and a comparison signal is output based on the comparison result. The delay is changed by the comparison signal.
Base station
The invention extends to a base station and a novel phased array spread spectrum system for processing a plurality of spread spectrum signals. In this embodiment, the receiving apparatus receives a plurality of spread spectrum signals and a plurality of phased versions of the plurality of spread spectrum signals. As shown in fig. 2, such different phases and/or delays are caused by the spread spectrum signal 15 and the phased version 16 of the spread spectrum signal from different paths, such as bouncing back from different buildings 17, 18. Typically, as shown in fig. 3, 4 and 5, the receiving means comprises a first antenna 11 and a second antenna 12. The receiving means may also comprise suitable RF and IF amplifiers and filters. The received spread spectrum signal and a phased version of the spread spectrum signal may be digitized.
As shown in fig. 4 as delay means 121, delay means 122, …, the delay means of delay means 123 is capable of delaying the received spread spectrum signals by a plurality of delays with respect to the phased versions of the received spread spectrum signals. The received plurality of spread spectrum signals thereby become a plurality of delayed signals, each of the plurality of delayed signals having a delay approximately equal to the delay of the phased version of the respective spread spectrum signal. A preferred embodiment uses digital signal processing. Thus, the delay means will comprise digital delay means such as a shift register. Alternatively, the analog circuit will use an analog delay device, or a phase shifter.
The combining means, shown in fig. 4 as combiner 14, combines the phase-controlled versions of the plurality of delayed signals and the plurality of spread signals into a combined signal. The output of the combining means may comprise suitable RF circuitry and/or IF circuitry 124.
Each of the plurality of delayed signals and each of the respective phased versions of the plurality of spread spectrum signals have the same phase or time delay, respectively. Thus, the in-phase component of the delayed signal is combined with the in-phase component of the phased version of the spread spectrum signal and the quadrature component of the delayed signal is combined with the quadrature component of the phased version of the spread spectrum signal.
Despreading means despreads the combined signal into a plurality of despread signals. This can be done by using a plurality of despreading means 131, 132, …, 133, as shown in fig. 4. Each despreading means may be implemented using a product detector or mixer with a hopping sequence matched to the received spread spectrum signal for a particular channel. Alternatively, the despreader may be implemented using a matched filter, such as a Surface Acoustic Wave (SAW) device, having a pulse function matched to the frequency hopping sequence of the received spread spectrum signal for the particular channel. Product detection devices, mixers, digital signal processors and SAW devices for despreading spread spectrum signals are well known in the art.
The control means may comprise generating means, storing means, and comparing means. The generating means is capable of generating a plurality of magnitudes from the plurality of despread signals. The storage means stores a plurality of prior magnitude values and a plurality of current magnitude values generated by the generation means. The comparison means compares the plurality of previous magnitude values with the plurality of current magnitude values, and outputs a plurality of comparison signals. One embodiment of the generating means, the storing means and the comparing means is shown in fig. 3.
The delay means changes the plurality of delays in response to the plurality of comparison signals, respectively. Fig. 4 schematically shows how the control circuits 141, 142, …, 143 are connected to the delay means 121, 122, …, 123, respectively. As will be clear to those skilled in the art, the control circuit shown in fig. 4 may be implemented using the circuit of fig. 3 for each spread spectrum channel.
Fig. 5 shows an alternative embodiment with a signal delay device 13 connected to the antenna 11. Also shown is an RF/IF amplifier 21 connected to antenna 11 via delay means 13, and an RF/IF amplifier 22 connected to antenna 12. In fig. 5, each spread channel defined by the frequency hopping sequences g1(t), g2(t), …, gk (t) is despread by a plurality of despreaders 151, 152, …, 153 for a plurality of spread signals. Similarly, the plurality of phase-controlled versions of the plurality of spread signals are despread by the plurality of despreaders 161, 162, …, 163 using the frequency hopping sequences g1(t), g2(t), …, gk (t).
The delay means 13 delays the plurality of spread signals with respect to the plurality of phase-controlled versions of the received plurality of spread signals by one delay, thereby to generate a plurality of delayed signals.
The combining means 153 combines the plurality of delayed signals and the plurality of phase-controlled versions of the plurality of spread spectrum signals into a combined signal. In response to the combined signal, the control circuit 166 changes the delay of the delay means 13.
In use, the phased array spread spectrum system and method may be used in a base station or a remote unit. The spread spectrum signal received by the phased array spread spectrum system and method is received by the first antenna 11 and the second antenna 12, processed by the first and second RF/IF sections 21, 22, and converted into digital form by the first analog/digital converter 23 and the second analog/digital converter 24. Preferably, digital signal processing is used and included in an Application Specific Integrated Circuit (ASIC). The digitized spread spectrum signal from the first analog/digital converter 23 is preferably delayed relative to the phase-controlled version of the digitized spread spectrum signal from the second analog/digital converter 24. The first digital delay means 27 is adjusted by means of an up/down counter 35 until the phase and/or time delay between the digitized spread spectrum signal and the phase controlled version of the digitized spread spectrum signal is close to unity. The change in the up/down counter 35 causes an adjustment to occur in response to the comparison by comparator 34 of the current and previous magnitudes stored in register 33.
Thus, the spread spectrum signal and a phase-controlled version of the spread spectrum signal are received, processed at an intermediate or base frequency, and digitized. The respective in-phase and quadrature components are used and delayed and added. The composite in-phase and quadrature components are then despread. Then extracting the magnitude of the despread spread spectrum signal; which represents the power or signal strength of the desired signal. The current magnitude and the previous magnitude are input to the shift register 33 and compared by the comparator 34. The comparator 34 notifies the up/down counter 35 to count up or down (i.e., up or down), thereby controlling the delay. Thus, an increase in the count may increase the delay, and conversely, a decrease in the count may decrease the delay. To be more efficient, the up/down counter 35 may use various control algorithms.
The phased array spread spectrum system controls the direction of the antenna beam formed by the first antenna 11 and the second antenna 12 in the direction of the strongest multipath. This function can be performed continuously to continuously search for the best multipath. Such antenna beam control can be performed at the base station and at the handset (i.e., remote subscriber unit).
It will be apparent to those skilled in the art that various modifications can be made to the base station phased array spread spectrum system and method of the present invention without departing from the scope and spirit of the invention. The present invention is intended to cover various modifications and variations of the base station phased array spread spectrum system and method, and their equivalents, which fall within the scope of the appended claims.