WO1995022208A1 - Recepteur de decorrelation pour canaux amdc asynchrones - Google Patents

Recepteur de decorrelation pour canaux amdc asynchrones Download PDF

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Publication number
WO1995022208A1
WO1995022208A1 PCT/US1995/001482 US9501482W WO9522208A1 WO 1995022208 A1 WO1995022208 A1 WO 1995022208A1 US 9501482 W US9501482 W US 9501482W WO 9522208 A1 WO9522208 A1 WO 9522208A1
Authority
WO
WIPO (PCT)
Prior art keywords
signals
samples
cdma
window
psam
Prior art date
Application number
PCT/US1995/001482
Other languages
English (en)
Inventor
Michael S. Feeney
Original Assignee
Motorola Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc. filed Critical Motorola Inc.
Priority to JP7521276A priority Critical patent/JPH08509343A/ja
Publication of WO1995022208A1 publication Critical patent/WO1995022208A1/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
    • H04B1/7105—Joint detection techniques, e.g. linear detectors
    • H04B1/71052—Joint detection techniques, e.g. linear detectors using decorrelation matrix
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
    • H04B7/2637—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] for logical channel control
    • 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
    • H04B1/709—Correlator structure
    • H04B1/7093—Matched filter type
    • 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
    • H04B1/7105—Joint detection techniques, e.g. linear detectors
    • 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
    • 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

  • This invention is generally related to communication devices and more particularly to CDMA communication devices.
  • FDMA frequency division multiple access
  • TDMA time division multiple access
  • DS-CDMA direct sequence code division multiple access
  • multiplexing is achieved by assigning a unique signature sequence to each mobile user; knowledge of a particular user's code is required at the base station in order to demodulate that user's date.
  • CDMA Code Division Multiple Access
  • a disadvantage traditionally associated with CDMA is the so called near-far problem, which can arise when the received energies of the mobile signals arrive at the base station with unequal strengths.
  • power control has been suggested to overcome the near-far problem.
  • power control adds a great deal of complexity to the system, and it does not eliminate the near-far effect, it only reduces it.
  • the decorrelating detector requires the inversion of an MK by MK correlation matrix, where M is the common message length of all users. For large M, the computation of the matrix inverse will not be practical. As an alternative implementation, it was shown in this reference that for the limiting case
  • the decorrelating detector becomes a K-input K-output linear time-invariant filter with a transfer function determined by the cross- correlations between the users' signature sequences (spreading codes).
  • This solution is not comprehensive, however, because it will not accommodate the addition and/or deletion of users to the system.
  • Another approach suggests a time windowed decorrelating receiver. This appears in an article by S. S. H. Wijayasuriya, J. P. Mcgeehan and G. H. Norton titled "Sliding window decorrelating algorithm for DS-CDMA receivers", printed in Electronics Letters, Volume 28, Number 17, pp. 1596-1598, August 13, 1992.
  • This approach suggests a rather complex scheme to estimate bit polarities by incorporating a rate 1/2 convolutional code into the transmitter chain of each of the users.
  • This approach greatly restricts the overall application of such a scheme in a receiver.
  • this approach requires interleaving/de interleaving of the incoming signals. These two requirements adds to the complexity of both the transmitters and receivers used in the system.
  • the window suggested by this reference is a sliding one.
  • a sliding window is one that slides the bits from one window to another. In other words, for a window length of 5 bits, the first window would contain bits 1 through 5 and the second window would contain bits 2 through 6 and so on. This scheme of windowing the incoming signals results in a large number of partially overlapping windows.
  • FIG. 1 shows a block diagram of a communication device in accordance with the present invention.
  • FIG. 2 shows a flow chart of the operation of a communication device in accordance with the present invention.
  • FIG. 3 shows a communication system in accordance with the present invention.
  • the present invention provides for a pilot symbol to be periodically added to the signal at the transmitter. At the receiver, these pilot symbols are used as separators in forming windows. Since the polarity of the pilot symbols are known, no estimation is required hence the windows don't have to overlap. Interference within the window are removed using inverse correlation matrix. Interference from outside of the window is minimized using the known polarities of the pilot symbol bits. This approach significantly reduces the delay and the overall complexity of the receiver.
  • the principles of the present invention will be better understood by referring to a number of figures and more particularly to FIG. 3 where a communication system in accordance with the present invention is shown.
  • the system 300 includes a communication device 100 which acts as the base station for the system 300.
  • a plurahty of radios 302, 304, and 306 each having an antenna 303, 305, and 307, respectively are also included.
  • the radios 302, 304, and 306 communicate with each other using Direct Sequence Code Division Multiple Access (DS-CDMA) signals modulated using Pilot Symbol Assisted Modulation (PSAM).
  • DS-CDMA Direct Sequence Code Division Multiple Access
  • PSAM Pilot Symbol Assisted Modulation
  • the CDMA signal includes a signal that has been modulated via a sequence code, often called a "signature code.” All the coded signals are then communicated using the same channel.
  • the demodulation is accomplished via decorrelation which essentially separates the signals based on their individual signature codes.
  • the communication device 100 is aware of the signature codes used by each radio 302, 304, and 306. This is because the device 100 either assigned the code to the radios to begin with or acquired information on the code otherwise.
  • the communication device 100 In order to reduce the effects of near-far problem on signals received by each of the radios 302, 304, and 306, the communication device 100 must first decorrelate the signals and then re-transmit them, synchronously. The synchronous transmission of signals provides for a simple demodulation at the receiving unit independent of the near-far problem.
  • the elements of the communication device 100 provide for a mechanism by which a number of asynchronous DS-CDMA-PSAM signals are decorrelated without needing power control or introducing significant delay.
  • a plurality of DS-CDMA-PSAM are received at an antenna 101. These signals are coupled to a delay device 102 and a time delay analyzer 115.
  • the received signal passing through the antenna is the sum of the individual DS-CDMA-PSAM signals transmitted from each of the K radios 302, 304, and 306, plus additive channel noise.
  • the radio transmitters insert a pilot symbol: (a "+1", for example) into their outgoing data streams after every L ⁇ h data symbol. These pilot symbols are used to remove interference from the decorrelated signals.
  • the time delay analyzer determines the time delays associated with each of the received signals. These delays are sent to a bank of matched filters 103 and to a computing device 105.
  • the delay device 102 delays the received signals until the matched filter bank 103 has obtained the time delays from the time delay analyzer 115.
  • the matched filter bank 103 includes K number of filters each of which is matched to one of the code sequences of the incoming DS-CDMA-PSAM signals.
  • the K outputs of the matched filters are coupled to a sampler 104.
  • the sampler 104 samples each of its K input signals at the end of every symbol interval and discards every (L +1)TM 1 set of inputs (pilot symbols).
  • the set of K outputs is sent to a memory unit 107.
  • the memory unit 107 stores L consecutive sets of K inputs, thus forming a vector containing L x K elements.
  • memory unit 107 will send its contents to a summer 109, thus emptying itself.
  • the computing device 105 computes an inverse correlation matrix (or an inverse cross correlation matrix) from the timing delays sent from the time delay analyzer 115 and the known CDMA code sequences (signature sequences). This inverse correlation matrix is sent to a second 5 memory device 106.
  • the memory device 106 sends part of the inverse correlation matrix (a submatrix) to a multiplier 108 and sends the entire matrix to a second multiplier 110.
  • the multiplier 108 multiplies the submatrix from the memory unit 106 with the energy
  • the 10 estimates sent from an energy estimator 111. The result is sent to the summer 109. It is noted that when pilot symbols with different polarities are used the output from the energy estimator 111 must include information on the particular polarities of the pilot symbols. This may be achieved by incorporating the polarity of the pilot symbol in the energy
  • a PSAM polarity memory unit 113 stores the polarity of each radio's pilot symbols. In general, some radios could choose pilot symbols (-1) and other could choose (+1).
  • the mixer 114 multiplies the energy estimates by their corresponding polarities arrived from the memory 113.
  • the output of the mixer 108 is coupled to the
  • the summer 109 subtracts the output of the mixer 108 from the vector sent by the memory unit 107. This step removes interference from symbols outside the current data window.
  • the mixer 110 multiplies the inverse correlation matrix with the vector free of outside interference.
  • the output of mixer 110 is sent to the energy estimator 111 and to the decoder 112.
  • the energy estimator 111 estimates the received energy
  • the results are sent to the mixer 108 for use with the next data window.
  • the energy estimator 111 produces energies equal to zero.
  • the decoder 112 forms the final symbols polarity decision for all symbols of each radio within the current data window. The output of the decoder 112
  • FIG. 2 a flow chart of the operation of the communication device 100 in accordance with the present invention is shown. From a start block 200 a plurality of DS-CDMA-PSAM signals are received. These signals are delayed, block 206, and then filtered via the 5 bank of matched filters 103, block 208. The filtered signals are then sampled, block 210 before being stored in the memory 107 as a vector consisting of L consecutive sets of samples, block 212. Next, the inverse correlation matrix and its submatrices are computed, block 214. The multiplier 110 multiplies submatrices by the polarized estimates of
  • the summer 109 subtracts resulting interference from the vector of matched filter outputs to produce a modified vector.
  • the modified vector is multiplied with the
  • the device 100 removes interference in a CDMA
  • the received signal (composite waveform of all the radios 302, 304, and 306) through a bank of matched filters, one filter matched to each allowed signature sequence.
  • the outputs of the matched filters are sampled appropriately and several consecutive outputs (forming a window) are stored in the memory 107.
  • the device 100 computes an inverse correlation matrix from the known active signature sequences and the acquired relative time delays between the radios' received signals. The device 100 then multiplies this matrix by the vector of stored matched filter outputs, in effect “canceling out” the interference or “decorrelating” the signals. Before this multiplication can
  • the device 100 must first subtract out an estimate of the received energies including their polarities of all the radios 302, 304, and 306 immediately before and after the current window.
  • the polarities of the radio signals before and after the window are known since pilot symbols are transmitted between every window.
  • the received energy estimates are
  • the receiver forms its final polarity decisions (+1 or -1) based upon the signs of the resulting outputs.
  • the device 100 would decide that the first bit of user 1 was a +1 and the first bit of use 2 was a -1. The receiver would then use 3.561 as the energy estimate of the first user, and 9.348 as the energy estimate of the second user. These estimates would be subtracted off of the next window's values for user 1 and user 2 before multiplying again by the inverse correlation matrix. This process then continues until the signals are decorrelated.
  • a significant benefit of the present invention is that by using only a small portion of the transmitted sequences at a time (a window), the decoding delay is kept small, the storage requirements are kept small, and a much smaller matrix needs inversion. This saves in the complexity of the device 100 and produces decorrelated results faster with much higher efficiency.
  • PSAM pilot-symbol-assisted- modulation
  • the device 100 does not need to form estimates of the polarities of the bits preceding and following each window. Between every window, all the radios 302, 304, and 306 transmit a pilot bit of known polarity. Thus the device 100 knows the polarity of all the bits between the windows and no estimation scheme is needed.
  • the windows suggested here separate the data into non- overlapping (non-sliding) blocks. For instance, if a window length of 5 bits is chosen, then the first window would contain bits 1 through 5, the second window would contain bits 6 through 10, and so on. This is much more efficient than the windowing scheme proposed in the prior art which utilizes sliding windows.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Un dispositif de communication (100) utilise des symboles pilotes pour décorréler un ensemble de signaux AMDC sans utiliser la commande de puissance. Les signaux reçus sont filtrés dans un banc de filtres adaptés (103) et échantillonnés dans un échantillonneur (104). Un vecteur des échantillons est stocké dans une mémoire (107), et un calculateur (105) détermine la matrice d'intercorrélation inverse. La matrice est ensuite multipliée par les estimations d'énergie dans un multiplicateur (108). Le résultat est ensuite soustrait du vecteur dans un additionneur (109). Le résultat de la soustraction est multiplié par la matrice de corrélation inverse dans un autre multiplicateur (110) pour pouvoir décoder les signaux dans un décodeur (112). Les estimations d'énergie de l'ensemble des signaux AMDC sont générées dans un estimateur d'énergie (111) et les polarités sont basées sur la polarité connue des symboles pilotes. Ces estimations sont utilisées dans la multiplication ultérieure des sous-matrices.
PCT/US1995/001482 1994-02-14 1995-02-03 Recepteur de decorrelation pour canaux amdc asynchrones WO1995022208A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP7521276A JPH08509343A (ja) 1994-02-14 1995-02-03 非同期ｃｄｍａチャネル用の相関解除受信機

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US19634294A 1994-02-14 1994-02-14
US08/196,342 1994-02-14

Publications (1)

Publication Number Publication Date
WO1995022208A1 true WO1995022208A1 (fr) 1995-08-17

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PCT/US1995/001482 WO1995022208A1 (fr) 1994-02-14 1995-02-03 Recepteur de decorrelation pour canaux amdc asynchrones

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JP (1) JPH08509343A (fr)
CA (1) CA2160382A1 (fr)
WO (1) WO1995022208A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996006487A1 (fr) * 1994-08-25 1996-02-29 Nokia Telecommunications Oy Methode de reception cdma et recepteur
WO1998008312A1 (fr) * 1996-08-16 1998-02-26 Telefonaktiebolaget Lm Ericsson (Publ) Dispositif et procede pour systeme de transmission
WO1998038805A2 (fr) * 1997-02-28 1998-09-03 Nokia Mobile Phones Limited Procede de reception et recepteur
WO2001095653A1 (fr) * 2000-06-05 2001-12-13 Linkair Communications, Inc. Procede de selection de site de cellule dans un systeme cellulaire avec fenetre sans interference
CN110428510A (zh) * 2019-08-23 2019-11-08 深圳市金溢科技股份有限公司 Psam卡集中管理方法、装置以及安全云盒系统

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2974004B1 (ja) 1998-05-12 1999-11-08 日本電気株式会社 Ｃｄｍａ受信装置およびｃｄｍａ通信システム
US6678313B1 (en) 1998-12-25 2004-01-13 Kokusai Electric Co., Ltd. Correlation circuit for spread spectrum communication

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US5136612A (en) * 1990-12-31 1992-08-04 At&T Bell Laboratories Method and apparatus for reducing effects of multiple access interference in a radio receiver in a code division multiple access communication system
US5341395A (en) * 1992-11-24 1994-08-23 At&T Bell Laboratories Data recovery technique for asynchronous CDMA systems
US5343496A (en) * 1993-09-24 1994-08-30 Bell Communications Research, Inc. Interference suppression in CDMA systems
US5363403A (en) * 1993-04-22 1994-11-08 Interdigital Technology Corporation Spread spectrum CDMA subtractive interference canceler and method

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5136612A (en) * 1990-12-31 1992-08-04 At&T Bell Laboratories Method and apparatus for reducing effects of multiple access interference in a radio receiver in a code division multiple access communication system
US5341395A (en) * 1992-11-24 1994-08-23 At&T Bell Laboratories Data recovery technique for asynchronous CDMA systems
US5363403A (en) * 1993-04-22 1994-11-08 Interdigital Technology Corporation Spread spectrum CDMA subtractive interference canceler and method
US5343496A (en) * 1993-09-24 1994-08-30 Bell Communications Research, Inc. Interference suppression in CDMA systems

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU686866B2 (en) * 1994-08-25 1998-02-12 Nokia Telecommunications Oy CDMA receiving method and receiver
WO1996006487A1 (fr) * 1994-08-25 1996-02-29 Nokia Telecommunications Oy Methode de reception cdma et recepteur
CN1077747C (zh) * 1994-08-25 2002-01-09 诺基亚电信公司 码分多址(cdma)接收方法和接收机
US6011812A (en) * 1994-08-25 2000-01-04 Nokia Telecommunications Oy Receiving method and receiver
GB2331682B (en) * 1996-08-16 2001-01-17 Ericsson Telefon Ab L M A receiver apparatus and method for a band-spread telecommunication system
WO1998008312A1 (fr) * 1996-08-16 1998-02-26 Telefonaktiebolaget Lm Ericsson (Publ) Dispositif et procede pour systeme de transmission
GB2331682A (en) * 1996-08-16 1999-05-26 Ericsson Telefon Ab L M An apparatus and a method for a telecommunication system
US5946345A (en) * 1996-08-16 1999-08-31 Telefonktiebolaget Lm Ericsson Apparatus and a method for telecommunication system
WO1998038805A2 (fr) * 1997-02-28 1998-09-03 Nokia Mobile Phones Limited Procede de reception et recepteur
WO1998038805A3 (fr) * 1997-02-28 1998-12-17 Nokia Mobile Phones Ltd Procede de reception et recepteur
US6665334B1 (en) 1997-02-28 2003-12-16 Nokia Mobile Phones Ltd. Reception method and a receiver
WO2001095653A1 (fr) * 2000-06-05 2001-12-13 Linkair Communications, Inc. Procede de selection de site de cellule dans un systeme cellulaire avec fenetre sans interference
CN110428510A (zh) * 2019-08-23 2019-11-08 深圳市金溢科技股份有限公司 Psam卡集中管理方法、装置以及安全云盒系统

Also Published As

Publication number Publication date
CA2160382A1 (fr) 1995-08-17
JPH08509343A (ja) 1996-10-01

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