WO1998008319A1 - Recepteur rake pour demodulation de signal a spectre etale - Google Patents

Recepteur rake pour demodulation de signal a spectre etale Download PDF

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Publication number
WO1998008319A1
WO1998008319A1 PCT/US1997/014783 US9714783W WO9808319A1 WO 1998008319 A1 WO1998008319 A1 WO 1998008319A1 US 9714783 W US9714783 W US 9714783W WO 9808319 A1 WO9808319 A1 WO 9808319A1
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Prior art keywords
signal
rake
multipath
segments
projecting means
Prior art date
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PCT/US1997/014783
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English (en)
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WO1998008319A9 (fr
Inventor
Wolfgang Kober
John K. Thomas
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Data Fusion Corporation
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Application filed by Data Fusion Corporation filed Critical Data Fusion Corporation
Priority to GB9904000A priority Critical patent/GB2331436B/en
Priority to AU43280/97A priority patent/AU4328097A/en
Publication of WO1998008319A1 publication Critical patent/WO1998008319A1/fr
Publication of WO1998008319A9 publication Critical patent/WO1998008319A9/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H04B1/7107—Subtractive interference cancellation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/2605—Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/0845—Weighted combining per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/10—Polarisation diversity; Directional diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/1081—Reduction of multipath noise
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/711—Interference-related aspects the interference being multi-path interference
    • H04B1/7115—Constructive combining of multi-path signals, i.e. RAKE receivers

Definitions

  • the present invention is generally directed to a system for receiving a spread spectrum signal and specifically to a system for receiving and demodulating a spread spectrum signal.
  • Spread spectrum techniques are finding larger roles in a variety of applications.
  • spread spectrum based systems offer the potential for increased efficiency in the use of bandwidth.
  • the resistance of spread spectrum methods to jamming make them ideally suited for radar and Global Positioning System (GPS) applications.
  • GPS Global Positioning System
  • spread spectrum signals have a lower probability of being intercepted due to the noiselike appearance of spread spectrum waveforms.
  • it may be used to increase the pulse repetition frequency without sacrificing unambiguous range.
  • each transmitted signal or pulse is assigned a time varying pseudo-random code that is used to spread each bit in the digital data stream (i.e., an interference code), such as the long code and PN code in CDMA applications.
  • an interference code such as the long code and PN code in CDMA applications.
  • this spreading causes the signal to occupy the entire spectral band allocated to the Multiple Access System (MAS) .
  • MAS Multiple Access System
  • the different users in such a system are distinguished by unique interference codes assigned to each. Accordingly, all users simultaneously use all of the bandwidth all of the time and thus there is efficient utilization of bandwidth resources.
  • signals are wide-band, the multipath delays can be estimated and compensated for.
  • base-stations can operate with limited interference from adjacent base stations and therefore operate with higher reuse factors (i.e., more of the available channels can be used) .
  • all other spread spectrum signals contribute to background noise, or interference, relative to a selected spread spectrum signal. Because each user (or radar pulse or GPS satellite signal) uses a noise-like interference code to spread the bits in a signal, all the users contribute to the background noise.
  • code filters are used to isolate selected users, filter leakage results in the leakage of signals of other users into the signal of the selected user, thereby producing interference.
  • This leakage problem is particularly significant when the selected user is far away (and thus the user's signal is weak) and the interfering user is nearby (and thus the interfering user's signal is strong) . This problem is known as the near-far problem.
  • the interfering signals are reduced by switching frequency intervals assigned to users. This technique is useless for the intentional jamming scenario in which jammers track the transm- ter frequencies. Frequency switching is not an option for the CDMA standard for cellular telephones. In that technology, all users use all of the frequencies at all times. As a result there are no vacant frequency bands to switch to.
  • the interfering signals are selectively nulled by beam steering. Classical beamsteering, however, does not provide, without additional improvements, the required angular resolution for densely populated communications environments. The above techniques are further hampered due to the fact that signals rarely travel a straight line from the transmitter to the receiver. In fact, signals typically bounce off of buildings, trees, cars, etc. , and arrive at the receiver from multiple directions. This situation is referred to as the multipath effect from the multiple paths that the various reflections that a signal takes to arrive at the receiver.
  • An objective of the present invention is to provide a system architecture for increasing the signal-to-noise ratio (SNR) of a spread spectrum signal. Another objective is to provide a system architecture for removing the interference from a spread spectrum signal, particularly the interference attributable to spread spectrum signals generated by other sources. Yet another objective is to provide a system architecture for removing the interference from a spread spectrum signal that does not employ beam steering. Specific related objectives include providing a demodulating/decoding system for efficiently demodulating/decoding spread spectrum signals generated by far away sources in the presence of spread spectrum signals generated by near sources and/or effectively accounting for the various multipaths of a spread spectrum signal. These and other objectives are addressed by the spread spectrum system architecture of the present invention.
  • the system includes: (i) an antenna adapted to receive a signal, a first signal segment of the signal being attributable to a first source and a second signal segment of the signal being attributable to a source other than the first source; and (ii) an oblique projecting device, in communication with the antenna, for determining the first signal segment.
  • the signal can be any structured signal, such as a spread spectrum signal.
  • a "structured signal” is a signal that has known values or is created as a combination of signals of known values.
  • the oblique projecting device determines the first signal segment by obliquely projecting a signal space spanned by the signal onto a first space spanned by the first signal segment.
  • the "space" spanned by a set "A" of signals is the set of all signals that can be created by linear combinations of the signals in the set "A".
  • the space spanned by the signals in set "A” are defined by the interference codes of the one or more selected signals in the set.
  • the space spanned by interfering signals is defined by all linear combinations of the interfering signals.
  • the signal space can be obliquely projected onto the axis along a second space spanned by the second signal segment.
  • the estimated parameters of the first signal segment are related to the actual parameters of the first signal segment and are substantially free of contributions by the second signal segment. Through the use of oblique projection, there is little, if any, leakage of the second signal segment into computed parameters representative of the first signal segment.
  • oblique projection is preferably performed utilizing the following algorithm:
  • y corresponds to a selected portion of the spread spectrum signal
  • H corresponds to an interference code matrix for the first signal segment (which defines a first space including the first signal)
  • S corresponds to the interference code matrices for signals of all of the other sources (users) in the selected portion of the spread spectrum signal (which defines a second space including the signals of the other sources)
  • ⁇ corresponds to the transpose operation
  • ⁇ z corresponds to the variance of the magnitude of the noise in the selected portion of the spread spectrum signal.
  • the system can have a number of advantages, especially in spread spectrum systems.
  • the system can significantly increase the signal-to-noise ratio (SNR) of the spread spectrum signal relative to conventional spread spectrum demodulating systems, thereby increasing the detection probability. This is realized by the almost complete removal (i.e., nulling) from the spread spectrum signal of interference attributable to spread spectrum signals generated by other sources.
  • Non-orthogonal (oblique) projections are optimum for nulling structured signals such as spread spectrum signals.
  • the system can efficiently demodulate/decode spread spectrum signals generated by far away (weak) sources in the presence of spread spectrum signals generated by near (strong) sources, thereby permitting the base station for a given level of signal quality to service more users and operate more efficiently.
  • An improvement in SNR further translates into an increase in the user capacity of a spectral bandwidth — which is a scarce resource.
  • the system does not require beam steering to remove the interference.
  • the system can include a threshold detecting device, in communication with the oblique projecting device, for generating timing information defining a temporal relationship among the plurality of multipath signal segments (e.g., using mathematical peak location techniques that find the points at which the slope of the surface changes from positive to negative and has a large magnitude) and a timing reconciliation device for determining a reference time based on the timing information (i.e., the multipath delays) .
  • Multipath signal segments correspond to the various multipaths followed by a signal (e.g., the first signal) after transmission by the signal source.
  • the system can include a RAKE processor in communication with the oblique projecting device and the timing reconciliation device for aligning the plurality of multipath signal segments in at least one of time and phase and/or scaling the magnitude (s) of the multipath signal segments.
  • RAKE processing rapidly steers the beam of a multi-antenna system as well as mitigates multipath effects.
  • the RAKE processor preferably aligns and scales using the following algorithm:
  • p is the number of the multipath signal segments (or peaks) ; i is the number of the multipath signal segment; A ⁇ is the amplitude of ith multipath signal segment; j is the amount of the phase shift; ⁇ x is the phase of the ith multipath signal segment; y(k) is the input sequence; and ti is the delay in the received time for the ith multipath signal segment.
  • the RAKE processor effectively focuses the beam on the desired signal source.
  • the oblique projecting device and RAKE processor null out the signals of other sources in the spread spectrum signal and thereby eliminate the need for null steering to be performed by the antenna.
  • the system of the present invention is less complex and more efficient than conventional beam steering systems.
  • the system can include a demodulating device in communication with the RAKE processor to demodulate each of the signal segments.
  • the demodulating device uses the equation noted above with respect to the oblique projecting device.
  • the demodulating device uses the output of the RAKE processor which has aligned and summed all of the multipath signal segments. Both the oblique projecting and demodulating devices use estimates of the transmission time ("trial time") and symbol (“candidate symbol”) and the receive time in determining a correlation function using the above equation.
  • the system includes a plurality of antennas (i.e., an antenna array), with each antenna having a respective oblique projecting device, threshold detecting device, and RAKE processor.
  • a common timing reconciliation device is in communication with each of the respective threshold detecting devices and RAKE processors.
  • a common demodulating component is also in communication with each of the RAKE processors. In this configuration, the demodulating component sums all of the first signals received by each of the antennas to yield a corrected first signal reflecting all of the various multipath signal segments related to the first signal.
  • the system can effectively accommodate the various multipath signal segments related to a source signal.
  • the RAKE processor weights each of the multipath signal segments in direct relation to the magnitude of the peak defined by each multipath signal segment.
  • FIG. 1 is a first embodiment of the present invention
  • Fig. 2 depicts the various components of the correlating device
  • Fig. 3 depicts the unit steps performed by the components of Fig. 2;
  • Fig. 4 depicts graphically the oblique projecting operation
  • Fig. 5 depicts the signal segments contained in a portion of the filtered signal
  • Fig. 6 depicts the three dimensional correlation surface employed by the threshold detecting device
  • Fig. 7 pictorially depicts the operation of the RAKE processor
  • Fig. 8 depicts the various components of the demodulating device
  • Fig. 9 depicts a correlation surface defined by the correlation function output by the demodulating device
  • Fig. 10 is a second embodiment of the present invention for an antenna array
  • Fig. 11 is the first part of a flow schematic of the software for operating the system of Fig. 10;
  • Fig. 12 is the second part of the flow schematic.
  • the present invention provides a software architecture and the underlying mathematical algorithms for demodulating/decoding communications signals containing interference noise. This invention is generally applicable to CDMA systems (and other spread spectrum systems) ,
  • TDMA Time Division Multiple Access systems
  • CDMA Code Division Multiple Access systems
  • interference noise is typically due to a dense population of signals using the same intervals of the frequency spectrum, such as in high user density cellular phone applications, or such as in the intentional interference of radar or communication signals by nearby jammers.
  • the architecture employs a single antenna for receiving CDMA signals.
  • the system includes the antenna 50 adapted to receive the spread spectrum signal and generate an output signal 54, filters 58 and 60 for filtering the in-phase ("I") and quadrature ("Q") channels to form filtered channel signals 62 and 66, a correlating device 70 for providing a hypothetical correlation function characterizing a filtered signal segment, which may be multipath signal segment (s) of a source signal (hereinafter collectively referred to as a "signal segment”), transmitted by a selected user, a threshold timing device 74 for generating timing information defining the temporal relationship among a plurality of peaks defined by the hypothetical correlation function, a timing reconciliation device 78 for determining a reference time based on the timing information, a RAKE processor 82 for aligning multipath signal segments for each selected user in time and phase and outputting an aligned signal for the selected user, a demodulating device
  • the antenna can be of any suitable configuration for receiving a structured signal and providing the output signal based thereon, such as an antenna having one or a number of antenna elements.
  • the output signal is a mix of a plurality of signal segments transmitted by a number of mobile units (or users) .
  • the output signal is coherently shifted down from radio frequency and split into an in-phase (I) channel and a quadrature (Q) channel.
  • the I and Q channels of the output signal are filtered by the filters, H * (f), designated as 58 and 60, to form the filtered signals 62 and 66.
  • Filtered signal 62 corresponds to the I channel of the output signal while filtered signal 66 corresponds to the Q channel.
  • the filters 58 and 60 are counterparts to the filter H(f) applied at the mobile unit to contain the transmitted signal within the specified bandwidth .
  • the correlating device 70 includes a user code generator 94, a projection builder 98, and a bank of projection filters 102.
  • the user code generator 94 selects 106 a user (i.e., the selected user) transmitting a selected signal segment in a selected portion of the filtered signal to be decoded, selects 110, for the selected user and signal segment, a set of trial transmit times ("trial times") and candidate symbols and, for each trial time and candidate symbol in the set, generates 114 a candidate user code (or interface code) for the selected user and signal segment.
  • the base-station is assumed to have approximate synchronization with each of the mobile units.
  • the base station has a set of trial times at which each selected mobile unit may have transmitted the selected signal segment included in the filtered signals 62 and 66.
  • the user code generator 94 For each trial time, t p , in the set of trial times for the selected user and signal segment, the user code generator 94 generates one or more candidate user codes indexed by trial time and candidate symbol.
  • the set of trial times used by the user code generator for determining the set of candidate user codes for a given signal segment is determined by known techniques.
  • the user code generator will use a time interval centered on the receive time for the signal segment that has a width of about 200 milliseconds or less and more typically of about 50 milliseconds or less.
  • the projection builder 98 selects 118 a portion of the filtered signal to process, collects 122 appropriate candidate user codes for the users transmitting signal segments of the selected filtered signal portion from the output of the user code generator, and, using the receive time offsets, trial times, and candidate symbols, creates 126 a set of hypothetical projection operators.
  • the hypothetical projection operators are generated using the algorithm:
  • H corresponds to an interference code matrix for the selected signal segment
  • S corresponds to the interference code matrices for all of the other signal segments in the selected filtered signal portion
  • ⁇ corresponds to the transpose operation.
  • the variables H and S depend upon the interference codes determined by the user code generator 94. Accordingly, H and S depend, respectively, upon the transmit time for the selected signal segment, and the transmit times of all of the other signal segments in the selected filtered signal portion. Because the data is indexed by the receive time, S is also a function of the receive time.
  • the projection builder 98 estimates the transmit times and symbols of each of the signal segments in the selected filtered signal portion.
  • the trial time is an estimate of the transmit time and the candidate symbol of the symbol.
  • the bank of projection filters 102 with one filter corresponding to each trial time and candidate symbol (i.e., to each hypothetical projection operator), provide a set of filter outputs (i.e., hypothetical correlation functions) to be threshold detected by the threshold detecting device 74.
  • Each of the bank of projection filters correlates 130 a plurality of multipath signal segments for a given trial time and candidate symbol.
  • the projection filters 102 extract an estimated signal segment attributable to a given user from each selected filtered signal portion while simultaneously nulling out the other signal segments from other users.
  • the equation used to generate the various hypothetical correlation functions is:
  • y space 134 spanned by y onto H space 138 spanned by H to yield an estimate of the signal segment 142 is illustrated in Fig. 4.
  • Y space 134 spanned by Y is obliquely projected onto the H space 138 along S space 146 spanned by S.
  • Oblique projections are more effective than orthogonal projections in removing interference attributable to the other users where the Walsh codes are not synchronized and thus not orthogonal, such as in the reverse link of a CDMA system. In such cases, the correlation function is independent of the amplitudes of the signal segments of other users and, therefore, power control of the transmitter is not a significant consideration.
  • Fig. 5 illustrates a four (4) user system in which the various users are transmitting symbols representing bits of data.
  • the source signals are received by the antenna 50 as a number of multipath signal segments.
  • a first multipath signal segment 150 is transmitted by a first user, a second multipath signal segment 154 by a second user, a third multipath signal segment 158 by a third user, a fourth multipath signal segment 162 by the first user, and a fifth multipath signal segment 166 from a fourth user.
  • the projection builder 98 selects a first receive time offset ⁇ t ⁇ and thereby selects the first, second and third multipath signal segments 150, 154 and 158.
  • the width of the receive time offset is determined by the control system for the base station using known techniques.
  • the projection builder 98 employs ⁇ t- and a trial time and candidate symbol in the projection operator equation and generates a hypothetical projection operator for the first user indexed by the trial time and candidate symbol.
  • the projection builder employs ⁇ t ⁇ and a trial time and candidate symbol in the projection operator equation and generates a hypothetical projection operator for second user indexed by the trial time and candidate symbol. This operation is also performed for the third multipath signal segment 158 with a hypothetical projection operator for the third user being likewise generated.
  • the projection builder repeats the above steps for each of the fourth and fifth multipath signal segments 162 and 166 to generate additional projection operators for the first and fourth users.
  • first and fourth miltipath signals are multipaths of a common source signal
  • the hypothetical projection operators for the first and fourth multipath signal segments are different due to differing degrees of interference. These steps are repeated for subsequent receive time offsets.
  • the number of receive time offsets generated is determined by the base station control system using known techniques.
  • the bank of projection filters 102 then apply each of the hypothetical projection operators to the filtered signal portion corresponding to the respective receive time offset to develop a plurality of hypothetical correlation functions for the various users.
  • Each of the hypothetical correlation functions defines a correlation surface 170 of the type depicted in Fig. 6, where the horizontal axes represent receive time and trial time and the vertical axis represents the output of the correlation function for a specific pair of receive times and trial times.
  • One correlation function corresponds to a source signal transmitted by the selected user.
  • Each peak 174a-d represents a multipath signal segment of the source signal.
  • the threshold detecting device 74 uses the hypothetical correlation functions for each user that are outputted by the bank of projection filters 102 to determine the temporal locations of the various multipath signal segments in the hypothetical correlation function. Due to multipath delays, each hypothetical correlation function can have multiple peaks as shown in Fig. 6. As set forth above, the various peaks in the correlation surface can be isolated using known mathematical techniques. Using techniques known in the art and the temporal location of the peaks (or timing information) output by the threshold detecting device 74 , the timing reconciliation device 78 determines a reference time for the RAKE processor 82. The reference time is based upon the receive times of the various peaks located by the threshold detecting device 74. The reference time is used by the RAKE processor 82 as the time to which all of the signal segments for a given user are aligned.
  • the RAKE processor 82 based on the timing information, the peak amplitudes of the hypothetical correlation function(s) detected by the threshold detecting device, and the filtered signals 62 and , 66 scales and aligns (in time and phase) the various multipath signal segments transmitted by a given user and then sums the aligned signal segments for that user.
  • the RAKE processor 82 can be a maximal SNR combiner.
  • the operation of the RAKE processor is illustrated in Fig. 7 (for an antenna array) .
  • the output of the bank of projection filters is the hypothetical correlation function, which in multipath environments typically has multiple peaks.
  • the RAKE process determines the amplitudes, time delays, , and phase delays ⁇ ii ⁇ p *.-. ⁇ *- If y(k) is a sequence defining the filtered signal 62 or 66, then the ARAKED@ sequence is y R (K) :
  • the RAKE processor 82 first sums 178 the outputs of the various antenna elements, shifts 182 the various sequences in the outputs by the amounts of the multipath delays between the corresponding multipath signal segments of a selected signal segment, so that all multipath signal segments are perfectly aligned. It then weights each shifted multipath signal segment by the amplitude of the correlation function corresponding to that segment and sums 186 the weighted components to produce the aligned signal y R (k) .
  • the demodulating device 86 correlates the ARAKED@ sequence, y R (k) with the appropriate replicated segment of the coded signal in the filter bank 102 to produce the correct correlation function for detection by a second threshold detecting device 90. Referring to Fig.
  • the demodulating device 86 like the correlating device 70 includes a user code generator 200, a projection builder 204, and a bank of projection filters 208.
  • the projection builder 204 and bank of projection filters 208 use the equations set forth above to provide projection operators and correlation functions.
  • the demodulating device 86 uses the "RAKED" sequence which has only a single aligned signal segment rather than a plurality of independent multipath signal segments. Accordingly, the demodulating device 86 is able to reliably estimate the actual transmit time for the source signal and therefore requires considerably less processing to determine a correlation function than the correlating device 70.
  • the user code generator 200 in the demodulating device 86 selects the user to decode for each aligned signal segment, selects a transmit time and symbol for the aligned signal segment and, for each transmit time and symbol, generates the user or interference code for the selected user .
  • the projection builder 204 selects a portion of the "RAKED" sequence to process, collects the pertinent user codes from the user code generator 200, and, using the receive times, transmit times, and symbols, creates a series of projection operators for each aligned signal segment in the "RAKED" sequence.
  • the bank of projection filters 208 with one filter corresponding to each pair of transmit times and symbols and therefore each projection operator, provides a set of filter outputs (e.g., correlation functions) each defining a second correlation surface to be threshold detected.
  • filter outputs e.g., correlation functions
  • the second correlation surface is then detected by a second threshold detecting device 90 to determine the actual transmit time and symbol for each aligned signal.
  • Fig. 9 depicts a representative correlation surface 212 corresponding to a correlation function determined by one projection filter. Compared to the correlation surface 170 of Fig. 6, the correlation surface 212 has only a single peak 214 (due to the alignment of the multipath signal segments in the "RAKED" sequence) as opposed to multiple peaks.
  • the aligned signal segment can be despread to provide the digital data for the aligned signal segment transmitted by each user.
  • the RAKE processor 82 and demodulating device 86 require reconfiguration in applications where the interference in each of the multipath signal segments is substantially different and the interference is significant.
  • the user code generator 200, projection builder 204, and bank of projection filters 208 process each multipath signal segment, corresponding to a peak in the correlation surface, before the RAKE processor has aligned, scaled, and summed each of the multipath signal segments.
  • each multipath signal segment After the interference portion of each multipath signal segment is removed by oblique projection techniques from that signal segment, the various multipath signal segments can be aligned, scaled, and summed by the RAKE processor as set forth above. Alignment and scaling can be performed after oblique projection is completed as to a given multipath signal segment or after all oblique projection is completed for all multipath signal segments.
  • Fig. 10 depicts a multiple antenna system according to another embodiment of the present invention.
  • Each antenna 50a-n is connected to filters 250a-n and 254a-n, correlating device 258a-n, threshold detecting device 262a- n, and a RAKE processor 266a-n.
  • the threshold detecting devices 262a-n for all of the antennas 50a-n are connected to a common timing reconciliation device 270, which in turn is connected to all of the RAKE processors 266a-n. In this manner, all of the RAKE processing for all of the filtered signals is performed relative to a common reference time.
  • the output of the RAKE processors 266a-n is provided to a common demodulating device 274 for determination of the correlation functions and summing of the signal portions received by all of the antennas that are attributable to a selected user.
  • the system in effect Aphases ⁇ the output of each antenna in order to maximize the SNR.
  • the output of each antenna in a conventional antenna array contains a desired signal but at a delay relative to the outputs of the other antennas.
  • the amount of relative delay is a function of the arrangement of the antennas as well as the angular location of the source.
  • Conventional beam-steering methods attempt to compensate for this time delay so that the desired signals add constructively thereby increasing the power of the desired signal.
  • an N antenna system can improve the SNR by a factor of N.
  • the compensation for the relative delays is performed in the RAKE processors 266a-n.
  • the system sums the antenna outputs without compensating for the relative delays.
  • the correlation process may result in Np peaks as opposed to just p multipath induced peaks. These Np peaks are then used to align and scale the various signal segments prior to summation.
  • the RAKE processor in effect, performs the phase-delay compensation usually done in beam-steering.
  • the system architecture of the present invention thus does not require knowledge of array geometries and steering vectors. It does not require iterative searches for directions as is the case for systems that steer the beam using techniques like LMS and its variants. Finally, it is computationally very efficient.
  • the software detects spread spectrum signals in the presence of interference from other users. Initially, a channel is opened 278 to the respective antenna 50a-n, and a user is selected 282 to demodulate the signal segments transmitted by the selected user. The outputted spread spectrum signal of the respective antenna 50a-n is converted 286 into the I and Q channels. The channels are filtered by the filters 250a-n and 254a-n to form the filtered signals 290a-n and 294a-n. As will be appreciated, the filtering operation is generally not performed in radar and GPS applications. Filtered signal portions are selected 298 for processing.
  • P z 3 is set 306 based on candidate interference codes. If not, pz s is set 310 to I.
  • trial times are generated 314 for the selected user.
  • candidate user codes are generated 318 for each of the trial times.
  • hypothetical projection operators are created 322 for each trial time and filtered signal portion to be processed.
  • the filtered signal portion is correlated 326 by user with the trial time, receive time, and candidate symbol to create the hypothetical correlation function.
  • the hypothetical correlation function characterizes the multipath signal segments from the user of interest while nulling out the interference from other known users.
  • a correlation surface is generated and thresholded 330 to identify peaks in the hypothetical correlation functions.
  • timing reconciliation 334 is performed. The minimum receive time of all of the corresponding multipath signal segments is selected as the reference time.
  • RAKE processing 338 is performed on all of the data segments.
  • the outputs from all of the RAKE processors 266a-n are combined 342 to formed a combined output.
  • projection operators are created 346 for each data segment.
  • the aligned multipath signals segments for all of the antennas are correlated 350 and a second correlation surface generated.
  • Threshold detection 354 is performed to provide the digital data. The above-noted steps are repeated for other users and/or other multipath signal segments.
  • the multiple antenna system of Fig. 10 can be utilized to locate the source of a selected signal by triangulation.
  • the multiple antennas on a base-station are evenly spaced, with spacing d, then the time difference between when the first signal from the source impinges on any two antennas can be used to estimate direction of arrival of the signal.
  • This approach assumes that the first signal is a direct signal from the source. If

Abstract

L'architecture (54, 58, 60, 62, 66, 70, 74, 78, 82, 86, 90) de la présente invention est fondée sur un algorithme comportant l'intégration de corrélateurs obliques (70) et d'un filtrage de type RAKE (62, 66, 82) pour annuler l'interférence d'autre signaux à spectre étalé. Les corrélateurs obliques (70) sont basés sur des projections non-orthogonales, optimales pour réduire à zéro les signaux structurés tels que les signaux à spectre étalé. Le filtrage RAKE (62, 66, 82) est utilisé pour orienter rapidement le faisceau du système multi-antennes pour limiter les effets par trajets multiples.
PCT/US1997/014783 1996-08-23 1997-08-22 Recepteur rake pour demodulation de signal a spectre etale WO1998008319A1 (fr)

Priority Applications (2)

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GB9904000A GB2331436B (en) 1996-08-23 1997-08-22 Rake receiver for spread spectrum signal demodulation
AU43280/97A AU4328097A (en) 1996-08-23 1997-08-22 Rake receiver for spread spectrum signal demodulation

Applications Claiming Priority (2)

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US2452596P 1996-08-23 1996-08-23
US60/024,525 1996-08-23

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WO1998008319A1 true WO1998008319A1 (fr) 1998-02-26
WO1998008319A9 WO1998008319A9 (fr) 1998-05-22

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EP0969603A2 (fr) * 1998-06-29 2000-01-05 Nec Corporation Procédé et dispositif de réception de signaux à spectre étalé
WO2001095534A2 (fr) * 2000-06-02 2001-12-13 Essex Corporation Architecture de recepteur avancee avec processeur optique (opera)
US6771214B2 (en) 2001-09-12 2004-08-03 Data Fusion Corporation GPS near-far resistant receiver
EP1442551A1 (fr) * 2001-10-02 2004-08-04 Tensorcomm Incorporated Annulation de brouillage dans un signal
DE19882633B4 (de) * 1997-06-26 2005-05-19 Electro-Radiation Inc. Digitales Störungs-Unterdrückungssystem für hochfrequente Störsignal-Beseitigung
EP1775598A2 (fr) * 1999-02-01 2007-04-18 Snaptrack, Inc. Procédé et dispositif de traitement relatif aux mésures des signaux d'un positionnement de satellite
EP2106081A2 (fr) * 2008-03-28 2009-09-30 France Telecom Procédé de traitement des interférences dans un système xdsl
US7626542B2 (en) 2005-02-25 2009-12-01 Data Fusion Corporation Mitigating interference in a signal
US7787518B2 (en) 2002-09-23 2010-08-31 Rambus Inc. Method and apparatus for selectively applying interference cancellation in spread spectrum systems
US9319152B2 (en) 2002-09-23 2016-04-19 Iii Holdings 1, Llc Method and apparatus for selectively applying interference cancellation in spread spectrum systems

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CN110752861B (zh) * 2019-09-25 2021-11-09 浙江海洋大学 采用rake接收技术的水声混沌扩频通信系统及方法

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US5237586A (en) * 1992-03-25 1993-08-17 Ericsson-Ge Mobile Communications Holding, Inc. Rake receiver with selective ray combining
US5602833A (en) * 1994-12-19 1997-02-11 Qualcomm Incorporated Method and apparatus for using Walsh shift keying in a spread spectrum communication system

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US5151919A (en) * 1990-12-17 1992-09-29 Ericsson-Ge Mobile Communications Holding Inc. Cdma subtractive demodulation
US5237586A (en) * 1992-03-25 1993-08-17 Ericsson-Ge Mobile Communications Holding, Inc. Rake receiver with selective ray combining
US5602833A (en) * 1994-12-19 1997-02-11 Qualcomm Incorporated Method and apparatus for using Walsh shift keying in a spread spectrum communication system

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19882633B4 (de) * 1997-06-26 2005-05-19 Electro-Radiation Inc. Digitales Störungs-Unterdrückungssystem für hochfrequente Störsignal-Beseitigung
EP0969603A3 (fr) * 1998-06-29 2003-08-20 Nec Corporation Procédé et dispositif de réception de signaux à spectre étalé
EP0969603A2 (fr) * 1998-06-29 2000-01-05 Nec Corporation Procédé et dispositif de réception de signaux à spectre étalé
EP2037290A1 (fr) * 1999-02-01 2009-03-18 Snaptrack, Inc. Procédé et appareil pour le traitement de mesures de signaux de système de positionnement par satellite (SPS)
JP2009168804A (ja) * 1999-02-01 2009-07-30 Snaptrack Inc 衛星測位システム（ｓｐｓ）信号の測定処理用の方法および装置
EP1775598A2 (fr) * 1999-02-01 2007-04-18 Snaptrack, Inc. Procédé et dispositif de traitement relatif aux mésures des signaux d'un positionnement de satellite
EP1788405A1 (fr) * 1999-02-01 2007-05-23 Snaptrack, Inc. Procédé et dispositif de traitement relatif aux mésures des signaux d'un système de positionnement de satellite
EP1775598A3 (fr) * 1999-02-01 2007-07-04 Snaptrack, Inc. procede et dispositif de traitement relatif aux mesures des signaux d'un systeme de positionnement de satellite
WO2001095534A2 (fr) * 2000-06-02 2001-12-13 Essex Corporation Architecture de recepteur avancee avec processeur optique (opera)
WO2001095534A3 (fr) * 2000-06-02 2003-08-21 Essex Corp Architecture de recepteur avancee avec processeur optique (opera)
US7130292B2 (en) 2000-06-02 2006-10-31 Essex Corporation Optical processor enhanced receiver architecture (opera)
US6771214B2 (en) 2001-09-12 2004-08-03 Data Fusion Corporation GPS near-far resistant receiver
EP1442551A1 (fr) * 2001-10-02 2004-08-04 Tensorcomm Incorporated Annulation de brouillage dans un signal
EP1442551A4 (fr) * 2001-10-02 2006-04-05 Tensorcomm Inc Annulation de brouillage dans un signal
US7787518B2 (en) 2002-09-23 2010-08-31 Rambus Inc. Method and apparatus for selectively applying interference cancellation in spread spectrum systems
US9319152B2 (en) 2002-09-23 2016-04-19 Iii Holdings 1, Llc Method and apparatus for selectively applying interference cancellation in spread spectrum systems
US9954575B2 (en) 2002-09-23 2018-04-24 Iii Holdings 1, L.L.C. Method and apparatus for selectively applying interference cancellation in spread spectrum systems
US7626542B2 (en) 2005-02-25 2009-12-01 Data Fusion Corporation Mitigating interference in a signal
EP2106081A2 (fr) * 2008-03-28 2009-09-30 France Telecom Procédé de traitement des interférences dans un système xdsl
FR2929472A1 (fr) * 2008-03-28 2009-10-02 France Telecom Procede de traitement des interferences dans un systeme xdsl
EP2106081A3 (fr) * 2008-03-28 2011-03-09 France Telecom Procédé de traitement des interférences dans un système xdsl

Also Published As

Publication number Publication date
GB2331436A (en) 1999-05-19
GB9904000D0 (en) 1999-04-14
GB2331436B (en) 2001-01-10
AU4328097A (en) 1998-03-06

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