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WO2002039590A2 - Procedes et appareils permettant de coder et de decoder des donnees - Google Patents

Procedes et appareils permettant de coder et de decoder des donnees Download PDF

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Publication number
WO2002039590A2
WO2002039590A2 PCT/GB2001/005011 GB0105011W WO0239590A2 WO 2002039590 A2 WO2002039590 A2 WO 2002039590A2 GB 0105011 W GB0105011 W GB 0105011W WO 0239590 A2 WO0239590 A2 WO 0239590A2
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WO
WIPO (PCT)
Prior art keywords
data signal
data
signal
phase shift
encoded
Prior art date
Application number
PCT/GB2001/005011
Other languages
English (en)
Other versions
WO2002039590A3 (fr
Inventor
Stephen William Wales
Original Assignee
Roke Manor Research Limited
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 Roke Manor Research Limited filed Critical Roke Manor Research Limited
Priority to AU2002215101A priority Critical patent/AU2002215101A1/en
Publication of WO2002039590A2 publication Critical patent/WO2002039590A2/fr
Publication of WO2002039590A3 publication Critical patent/WO2002039590A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0007—Code type
    • H04J13/004—Orthogonal
    • H04J13/0048—Walsh
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/16—Code allocation
    • H04J13/18—Allocation of orthogonal codes
    • 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
    • H04B2201/7097—Direct sequence modulation interference
    • H04B2201/709709—Methods of preventing interference

Definitions

  • the present invention relates to methods and apparatus for encoding and decoding data. More particularly, it relates to the encoding and decoding of data using spreading codes such as Walsh-Hadamard codes or the like to enable multiple channels of data to be encoded into a single expanded bandwidth, and to be selectively decoded upon reception.
  • spreading codes such as Walsh-Hadamard codes or the like
  • Code division multiplexing allows multiple signals to be transmitted in a common bandwidth over a common transmission path, and to be selectively extracted and decoded, to enable a particular user to receive data intended for that user without receiving data intended for another user.
  • spreading codes such as Walsh-Hadamard codes may be employed, as illustrated in Fig. 1.
  • d n ⁇ 10 represents the time variance of a data signal to be transmitted on a particular code, i.
  • One or more from a set of Walsh-Hadamard codes, C n 1*1 12 is allocated to the user i.
  • the corresponding time-variance of the code is illustrated at c m w 12 in Fig. 1.
  • the code c m is composed of a number of chips 14, as is known in the art.
  • the number of chips in a code is also known as the spreading factor (SF) of that code.
  • the data signal d n (l 10 is then multiplied by the Walsh-Hadamard code c m (l) 12, to produce a spread spectrum data signal 16, illustrated in Fig. 1.
  • This signal 16 is then modulated onto a carrier signal exp(j ⁇ t) by multiplication, to produce a modulated spread-spectrum data signal ⁇ d n (l) .c m (l) .g(t-mT c ).exp(j ⁇ t) 20, as illustrated in Fig. 1.
  • g() represents a pulse shaping function
  • t represents time
  • T c represents the chip period.
  • the effect of the modulation is to reverse the phase of the carrier signal at every level transition 22 of the spread spectrum data signal.
  • Walsh-Hadamard codes have the property of being orthogonal, that is, if the coded (spread spectrum) data signal d n (l) .c m w 16 is further multiplied by the Walsh- Hadamard code c m (l) , de-spreading takes place and the original data signal d n (l 10 is obtained. However, another coded (spread spectrum) data signal d n 0) .c m ®, intended for a different user j, and using a different code c ⁇ * will return a zero value when multiplied by the Walsh-Hadamard code c m (l) .
  • Fig. 2 shows an example of a multi-user code-division multiplex system, in which numerous users will receive their own specific data.
  • Data d n (l) , d n ® 10 for each user i, j is encoded in a corresponding spreading modulator 24, and the resultant signals d n (l) .c m (l , d n ()) .c m 0) 16 may be summed together at a summer 26 before modulation by a modulator 28 before transmission as transmit signal tx.
  • a user i will then receive the sum of the data signals rx, demodulate the summed data signals in demodulator 30 and then multiply the summed data signals by the corresponding Walsh-Hadamard code c m (l) in a de-spreader 32 corresponding to the spreading modulator 24, then to a summer which sums the returned values for all chips in the code, thereby to reconstruct the original data signal dn (l) 10 at the output for that user, but will return a zero value for all other data signals d n .
  • each channel has its own data source, and the spreading process is performed for different channels using a different Walsh-Hadamard code.
  • the data for each channel may not be independent so that the data symbols from each source are similar for long periods. This may occur for example in a multi-cast scenario, where each channel is essentially sending the same data. It may also occur when for example data sources produce long sequences of the same data symbol. With multiple sources of this type the same data symbols will occur at the same time on different channels.
  • spreading performed using Walsh-Hadamard codes the result causes a high peak transmit power. At any such peak value of such transmission, a very large power demand is placed on the transmitter, possibly causing compression of the signal to be transmitted, leading to errors in reproduction. Alternatively, or in addition, degradation of the received signal may occur in the receiver due to the very high magnitude of the received signal.
  • the table shown in Figure 3 gives the sum of different numbers of Walsh-
  • the rows represent sequential time periods, indicated by the arrow t, each row corresponding to one chip length within the spreading code which is preferably a Walsh Hadamard code, see for example c m (l) in Fig. 1.
  • the first row shows the sum of the values of all 8, 12 or 16 corresponding Walsh-Hadamard codes during the first chip.
  • the second row shows the sum of their values during the second chip, and so on for the other rows.
  • the illustrated example is a worst- case scenario illustrating the signal strength (voltage) transmitted if a same data signal is transmitted to each of the 8, 12 or 16 users.
  • the present invention aims to reduce such peaks of power and the attendant drawbacks, while remaining within the Walsh-Hadamard coding scheme or other selected orthogonal spreading factors.
  • a phase shift is applied to the spread spectrum (coded) data signal ti n (l) .c m (l .
  • a method for encoding data comprising the steps of: (i) generating a respective data signal for each of a plurality of users; (ii) coding (24) each of the data signals with a respective orthogonal spreading code to produce respective encoded data signals; and (iii) summing the encoded data signals to produce a total encoded data signal, the method further comprising the step of applying a phase shift to one of the data signal, the encoded data signal and the total encoded data signal.
  • the step of applying a phase shift may comprise multiplication of the corresponding term by a term of the form exp(j ⁇ ), between steps (i) and (ii) or between steps (ii) and (iii).
  • Such methods according to the present invention may comprise the steps of:
  • the method may further comprise the step of applying a phase shift to one of the data signal and the encoded signal.
  • the step of applying a phase shift may comprise multiplication of the corresponding term by a term of the form exp(-j ⁇ ), before or after step (ii).
  • the orthogonal spreading code may comprise a plurality of chips, and the method may further comprise summing the resultant respective data signal, to produce an output data signal.
  • the present invention also provides data encoding apparatus comprising: (i) a data encoder for encoding a respective data signal with a respective orthogonal spreading code to produce respective encoded data signal ; and (ii) a complex summer for summing the encoded data signals to produce a total encoded data signal, characterised in that the apparatus further comprises a phase shift element for applying a phase shift to one of the data signal, the encoded data signal and the total encoded data signal.
  • the phase shift element may comprise a multiplier arranged to multiply the corresponding term by a term of the form exp(j ⁇ ), any such multiplier preferably being located in the signal path before or after the data encoder.
  • the present invention also provides data decoding apparatus comprising a data decoder for decoding a respective data signal from a combined data signal by application of a respective orthogonal spreading code to produce a respective decoded data signal.
  • the apparatus further comprises a phase shift element arranged to apply a phase shift to one of the data signal and the respective decoded signal.
  • the phase shift element may be arranged in the signal path before or after the data decoder, to multiply the corresponding term by a term of the form exp(-j ⁇ ).
  • the orthogonal spreading code may comprise a plurality of chips, and the apparatus may further comprise a summer arranged to sum the resultant respective data signal, to produce an output data signal.
  • Each orthogonal spreading code may consist of one of a set of Walsh-
  • Fig. 1 shows examples of signals used in an encoding method of the prior art
  • Fig. 2 shows an example of data encoding and decoding apparatus according to the prior art
  • Fig. 3 shows transmit signal strength, voltage, values for multicast spreading code encoded signals according to the prior art
  • Fig. 4 shows an embodiment of data encoding and decoding apparatus according to the present invention.
  • Fig. 5 shows transmit signal strength, voltage, values for multicast spreading code encoded signals according to ' the present invention.
  • a phase shift ⁇ i is applied to the spread spectrum (coded) data signal d n (l) .c rn (l) 16. This may conveniently be regarded as a phase shift in the associated Walsh-Hadamard or other code.
  • tx' Re[ ⁇ m d n ( ) .c m ⁇ .g(t-mT c ).exp(j ⁇ .exp(j ⁇ t)]., or by the complete expression:
  • the effect may conveniently be regarded as a phase shift in the associated Walsh-Hadamard code.
  • the phase shifted Walsh-Hadamard codes retain their orthogonal characteristics, that is, that in the receiver, by multiplying the received signal by the corresponding phase-shifted Walsh-Hadamard code, the original data signal may be retrieved.
  • the phase shift of the Walsh-Hadamard code is reversed, that is, to retrieve a data signal encoded with a Walsh-Hadamard code of c m (l) .exp(j ⁇ i), the received signal is multiplied by c m (1*1 .exp(-j ⁇ * ).
  • Fig. 4 illustrates one possible embodiment of the present invention.
  • data signal d n (l 10 to be transmitted is multiplied by the corresponding Walsh-Hadamard code c ⁇ at spreading modulator 24, as in the prior art, but is then further multiplied at complex multiplier 40 by a phase shift term, exp(j ⁇ i).
  • This operation may be correspondingly replicated for the other data signals d n ()) to be transmitted.
  • phase shift ⁇ is applied, every chip in a certain code is multiplied by a same value exp(j ⁇ i). However, each code uses a value of ⁇ which is preferably different from that used by all other codes in use. It is essential, however, that the phase shift ⁇ , applied must be known by the receiver to allow the appropriate decoding at the receiver.
  • the transmitted signal tx' then propagates along a suitable propagation path, e.g. over the air, until it arrives as a received signal rx' at a receiver of user i.
  • the received signal rx' is first demodulated at demodulator 30 by multiplication by exp(-j ⁇ t), then is decoded at de-spreader 32 by further multiplication by the Walsh- Hadamard code c m (l) .
  • the resultant signal is then subjected to a phase shift opposite to that applied to the transmission signal, by multiplication by exp(-j ⁇ j) by complex multiplication at complex multiplier 44.
  • the resultant signal is fed to a complex summer 34, where the resultant signals of each chip of the spreading (Walsh-Hadamard) code are
  • Fig. 3 illustrates the time-variant sum of different numbers of Walsh-Hadamard codes of length 16. Each row represents the time occupied by a particular chip. For example, if all 16 codes are used, a very high magnitude occurs at the first code. This may translate into a very high signal voltage at the receiver, which may cause distortion in the received signal, or may mean that a more costly receiver is necessary, to cope with the high voltage signals. Transmission of such high voltage signals may also lead to distortion of the transmitted signals in the transmitter. As shown in Fig. 3, selection of a subset of, say 8 or 12 of the 16 codes leads to a more dispersed power output but there is still a high voltage signal peak at the beginning.
  • Fig. 5 shows an example of signal strength values for sums of Walsh- Hadamard codes corresponding to those shown in Fig. 3, but having a phase offset applied, according to the present invention.
  • the various rows represent the sum of the values of 8, 12 or all 16 corresponding Walsh-Hadamard codes during the respective chip.
  • the signal strength (voltage) to be transmitted is much more evenly distributed over the length of the spreading code (Walsh-Hadamard code). This significantly reduces the impact of any signal strength peaks caused by same data being transmitted to multiple or all users.
  • the phase shift applied to the spreading code may be selected as follows.
  • the phase shift ⁇ * may be selected to be pj.2 ⁇ /SF, where SF is the spreading factor, that is, the number of chips included within the spreading code, and pi is a member of a selected permutation of the integer set [ 1 ,SF] .
  • the integer set [1,4] consists of the integers 1, 2, 3 and 4.
  • [2 ,3 , 1 ,4] is a permutation of the integer set [ 1 ,4] .

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention porte sur un procédé permettant de coder des données et consistant : à générer un signal de données respectif pour chacun des différents utilisateurs ; à coder chacun des signaux de données avec un code d'étalement orthogonal respectif afin de produire des signaux de données respectifs ; et à calculer la somme des signaux de données codées afin de produire un signal de données codés total. Le procédé selon l'invention consiste également : à appliquer un déphasage à l'un des signaux de données, aux signaux de donnés codées et au signal de données codés total.
PCT/GB2001/005011 2000-11-09 2001-11-09 Procedes et appareils permettant de coder et de decoder des donnees WO2002039590A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002215101A AU2002215101A1 (en) 2000-11-09 2001-11-09 Methods and apparatus for encoding and decoding data

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0027392A GB0027392D0 (en) 2000-11-09 2000-11-09 Code specific phase shifts applied to spread spectrum systems using walsh-handarmed codes
GB0027392.0 2000-11-09

Publications (2)

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WO2002039590A2 true WO2002039590A2 (fr) 2002-05-16
WO2002039590A3 WO2002039590A3 (fr) 2003-05-22

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GB (2) GB0027392D0 (fr)
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8135085B2 (en) 2006-09-19 2012-03-13 Lg Electroncis Inc. Method of transmitting using phase shift-based precoding and an apparatus for implementing the same in a wireless communication system
US8208576B2 (en) 2007-09-19 2012-06-26 Lg Electronics Inc. Data transmitting and receiving method using phase shift based precoding and transceiver supporting the same
US8284865B2 (en) 2007-02-14 2012-10-09 Lg Electronics Inc. Data transmitting and receiving method using phase shift based precoding and transceiver supporting the same
US8284849B2 (en) 2006-05-26 2012-10-09 Lg Electronics Inc. Phase shift based precoding method and transceiver for supporting the same
CN105577703A (zh) * 2016-03-18 2016-05-11 山东省计算中心（国家超级计算济南中心） 大数据警务云系统的用户权限管理方法

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2734955B2 (ja) * 1993-12-24 1998-04-02 日本電気株式会社 無線データ通信装置
JP2780688B2 (ja) * 1995-11-15 1998-07-30 日本電気株式会社 位相変調多重化送信装置
JP3311951B2 (ja) * 1996-12-20 2002-08-05 富士通株式会社 符号多重送信装置
US20010055282A1 (en) * 1997-12-15 2001-12-27 Douglas Knisely Reducing peak to average ratio of transmit signal by intentional phase rotating among composed signals
JP3904754B2 (ja) * 1999-02-25 2007-04-11 富士通株式会社 符号分割多重通信における送信装置、受信装置及びその方法

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8284849B2 (en) 2006-05-26 2012-10-09 Lg Electronics Inc. Phase shift based precoding method and transceiver for supporting the same
US8331464B2 (en) 2006-05-26 2012-12-11 Lg Electronics Inc. Phase shift based precoding method and transceiver for supporting the same
US8135085B2 (en) 2006-09-19 2012-03-13 Lg Electroncis Inc. Method of transmitting using phase shift-based precoding and an apparatus for implementing the same in a wireless communication system
US8213530B2 (en) 2006-09-19 2012-07-03 Lg Electronics Inc. Method of transmitting using phase shift-based precoding and an apparatus for implementing the same in a wireless communication system
US8284865B2 (en) 2007-02-14 2012-10-09 Lg Electronics Inc. Data transmitting and receiving method using phase shift based precoding and transceiver supporting the same
US8208576B2 (en) 2007-09-19 2012-06-26 Lg Electronics Inc. Data transmitting and receiving method using phase shift based precoding and transceiver supporting the same
CN105577703A (zh) * 2016-03-18 2016-05-11 山东省计算中心（国家超级计算济南中心） 大数据警务云系统的用户权限管理方法
CN105577703B (zh) * 2016-03-18 2019-01-25 山东省计算中心（国家超级计算济南中心） 大数据警务云系统的用户权限管理方法

Also Published As

Publication number Publication date
AU2002215101A1 (en) 2002-05-21
WO2002039590A3 (fr) 2003-05-22
GB0127290D0 (en) 2002-01-02
GB0027392D0 (en) 2001-03-07
GB2373691A (en) 2002-09-25

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