Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B15/00—Suppression or limitation of noise or interference
• • 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
  • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
  • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
  • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
  • H04B2201/70701—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation featuring pilot assisted reception

Definitions

• the present invention relates to spread spectrum communication
• a conventional spread spectrum signal can be viewed as the result of
• the receiver synchronizes the incoming signal to a locally generated version p 0 [t]
• the spreading signal p[t] is typically a coding sequence of some kind
• CDMA code division multiple access
• forward channel (base to mobile units) employs, as a spreading code, the product
• the spreading signal p[t] for each user is its Walsh code combined with the current 64
• the base station additionally transmits the current PN
• pilot signal z[t] is simply the current PN
• the mobile unit then synchronizes
• the mobile units additionally serve as the mobile units.
• the mobile units include a channel
• One exemplary multipath detector is a rake receiver which optimally
• a multiple-user detection scheme such as is often used in base
• the base station accounts for this distortion during the detection process and, in
• the distortion does not translate into an SNR reduction. Therefore, it is
• this generator bank must further be processed according to some a priori criterion
• MMSE decorrelation / minimum mean squared error
• despreaders are then processed according to the MLSE criterion via the Viterbi
• despreaders is expensive in terms of complexity and power consumption.
• the cancellation involves sequentially
• the system substantially removes the signals of the other
• Stilwell also indicates that, for the mobile receiver, it is enough to remove just the
• pilot signal out of the received signal, especially considering that the pilot signal is
• circuit which includes a bank of units. Each unit contains a conventional
• the present invention does not respread the received signal after the correction
• the present invention additionally removes
• the interference effect is generated from a priori existing channel
• a method for receiving spread-spectrum signals including
• the first user including at least a first user signal and at least one pilot signal, the first user
• the step of detecting can detect multiple user signals from the
• the method removes the interference effect of
• the method also includes the step of decoding the data in the noise
• the step of removing interference includes the steps of determining the
• the spread spectrum signal has been transmitted along a multipath
• the step of determining includes, per selected pilot signal, the steps
• the first step of generating includes the steps of a) determining a
• Fig. 1 is a block diagram illustration of a data detector for a mobile unit
• Fig. 2 is a block diagram illustration of an interference processor useful
• Fig. 3A is a block diagram of a standard prior art rake receiver useful in
• Fig. 3B is a block diagram of an pilot interference removing rake
• Fig. 4 is a block diagram illustration of an alternative data detector for a
• Fig. 5 is a block diagram illustration of a base station multi-user data
• FIG. 1 is a diagrammatic representation of the mobile unit data detector of the present invention.
• FIG. 2 illustrates the elements of an
• Detector 10 forms part of a mobile communication unit which, like prior
• art detectors receives a signal r(n) and comprises a rake receiver 12, a pilot
• pilot processor 11 and an optional decoder 18.
• the pilot processor 11 As in the prior art, the pilot processor
• 11 includes a synchronizer 13 and a channel estimator 14. However, in
• the signal r(n) is the version of the received signal after the latter has
• chip rate is 1.2288x10 6 chips per second, i.e. T ch ⁇ p is about O. ⁇ sec.
• M is set to 1 , i.e. upon receipt, the signal r(n) is sampled once per chip.
• Synchronizer 13 synchronizes the detector to the PN sequence of the
• Channel estimator 14 estimates the channel tap h
• Rake receiver 12 despreads the
• the received signal r(n) consists of the data signals of all
• pilot signal will refer to the pilot signal of the
• interference processor 20 determines the cross-talk interference effect c(n) of the
• every synchronizer 13 can synchronize to it), removing the interference effect c(n)
• interference processor 20 can
• Subtractor 22 removes the interference effect c(n) from the rake receiver
• Interference processor 20 determines the cross-talk through the rake
• the cross-talk is of the form
• p p (k') depends on the baseband filter taps and defines the effect of
• k' is a real number
• k' is measured in units of T ch ⁇ p /M.
• p p (k') can be determined a priori for all possible values of k' and
• T ch ⁇ p /M ⁇ (t) is the impulse response of the overall transmit shaping filter and ⁇ (t) is
• L is chosen to indicate that point where p p (k') is very small.
• L is chosen such that « p p (0) ⁇
• the transmit filter impulse response ⁇ (t) is defined in the IS-95 and IS-98 CDMA standards. For IS-95 it is
• the receive filter impulse response ⁇ (t) is a design option and is typically
• generator 32 is stored in lookup table 30, per value of k'.
• priori for all possible values of k and n and stored in a lookup table 34.
• spreading code cross-correlator 36 determines p a ⁇ k,n) as follows.
• q(m,n) are sequences of ⁇ chips and P ⁇ (n) is a periodic extension of a
• Interference processor 20 additionally comprises a finger cross-talk
• determiner 38 which receives the estimated channel taps h t and the estimated finger delays r, from the channel estimator 14 and utilizes them and the
• interference processor 20 begins by determining the value
• cross-talk effect determiner 38 to determine the cross-talk effect a ⁇ n) as follows:
• Equation 3 ⁇ ,» ⁇ R ⁇ h,h; Pa (k,n)p p (k') ⁇ k
• J is a design parameter
• values of 5.25, 6.25, 7.25, 8.25 and 9.25 and k might have values 5, 6, 7, 8 and 9.
• the quantity a tj (n) can be shown to be an estimate of the interference of
• interference processor 20 retrieves the value of
• the value of k 0 ' is first determined as are the ranges of k and k'.
• Interference processor 20 additionally comprises a finger interference
• interference effect determiner 40 determines the interference effect B n) per
• Equation 4 B, (n) ⁇ a l l (n)
• Total interference effect determiner 42 determines the total interference
• interference processor 20 As shown in Fig. 3B described in detail
• the rake receiver 12 can subtract the individual finger interferences
• interference processor 20 computational burden of interference processor 20 is relatively small, in particular
• p a ⁇ k,n can be determined "on-the-fly", from equation 2, since its computation only involves
• Fig. 3B which illustrates an
• Rake receiver 12 has three fingers, each performing approximately the
• Each finger includes a despreader 50, a
• windowing summer 52 a sampler 54, a finger gain multiplier 56 and a
• the second and third fingers include
• the first finger serves as the reference finger.
• the second and third fingers (referred to as the 1 st and 2 nd fingers), respectively,
• Windowing summer 52 sums the output of despreaders 50 over a
• Finger gain multipliers 56 multiply the sampled
• Converters 58 take the real portion of the resultant signal.
• a summer 62 sums the output of
• the rake receiver 12' of Fig. 3B is similar to that of Fig. 3A (and
• Subtractors 64 subtract the finger interference effect B;(n) of the relevant finger
• receiver 12' is the corrected data signal x'(n).
• FIG. 4 illustrates a data detector
• the detector of Fig. 4 is
• the mobile units receive the
• the data detector 10' is similar to data detector 10 of Fig. 1 in that it
• 10' also includes a plurality NB of interference processors 20, one per base
• each pilot processor 11 includes a synchronizer, a channel
• processor 11 synchronizes to the pilot of a different base station and, accordingly,
• each interference processor 20 generates the interference effect of the pilots of the different base stations.
• Subtractor 22 removes the multiple interference effect
• the base station receives.
• the base station receives.
• the base station includes at least one of:
• the base station also serves to control the neighboring pilot signal on the data signal of each user.
• the base station also serves to control the neighboring pilot signal on the data signal of each user.
• NU subtractors 22 one per user, for removing the interference effect

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Noise Elimination (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (2)

Family

ID=11069967

Family Applications (1)

Country Status (8)

Cited By (17)

Families Citing this family (41)

Family Cites Families (10)

• 1997
  • 1997-03-26 IL IL12053897A patent/IL120538A/xx not_active IP Right Cessation
  • 1997-06-11 US US08/873,880 patent/US6034986A/en not_active Expired - Lifetime
• 1998
  • 1998-03-23 JP JP54537298A patent/JP4177901B2/ja not_active Expired - Fee Related
  • 1998-03-23 AU AU64174/98A patent/AU6417498A/en not_active Abandoned
  • 1998-03-23 WO PCT/IL1998/000129 patent/WO1998043362A2/en not_active Ceased
  • 1998-03-23 EP EP98909717A patent/EP0970573A4/en not_active Withdrawn
  • 1998-03-23 CA CA 2283848 patent/CA2283848A1/en not_active Abandoned
  • 1998-03-23 KR KR1019997008755A patent/KR100781415B1/ko not_active Expired - Fee Related

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