Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0056—Systems characterized by the type of code used
  • H04L1/0071—Use of interleaving
• • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0041—Arrangements at the transmitter end
  • H04L1/0042—Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape
• • 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
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0045—Arrangements at the receiver end

Definitions

• the present invention relates to an arrangement for handling transportation of digital information bearing signals through a non-static channel in a communications system.
• the invention also relates to transmitting means for transmitting a digital data signal through a non-static channel.
• the invention relates to a receiving arrangement for receiving a signal transported through a non-static communication channel.
• the invention also relates to a method of transmitting a digital information bearing signal through a non-static communication channel and of receiving a signal transmitted through a non-static communication channel.
• FDMA Frequency Division Multiple Access
• TDMA Time Division Multiple Access
• TMDA is for example used in GSM.
• a frequency band is then divided into eight time slots and eight mobile stations can then use one and the same frequency band by using different time slots.
• CDMA Code Division Multiple Access
• a CDMA-system differs from a TDMA-system in that the users are separated by different codes. All users can use the whole bandwidth and time simultaneously. In a TDMA-system on the other hand, the users are separated through different time slots and frequencies as referred to above. Since in CDMA all users are using the same frequency, it is of importance that the signals from every user arrive at the base station with approximately the same power.
• Multipath fading occurs e.g. when a signal takes more than one path from a transmitting antenna to a receiving antenna. This means that the signal is not received directly from the transmitting antenna but from a number of other directions, i.e. the signal reaches the receiver via several reflections against for example buildings. The result is that the received signal is a sum of a number of identical signals which differ only in phase (and to some extent also in amplitude) . Since signals are added like vectors the vector sum may be close to zero which means that also the signal strength gets close to zero and a severe fading dip has occurred. Multipath fading produces fast variations when a transmitting arrangement and a receiving arrangement move in relation to one another.
• Each signal comprises a number of information bits (which can be modulated into data symbols containing a number of bits, e.g. two bits) .
• Bit errors often occur in bursts. This is because of the fact that long fading dips affect several consecutive bits.
• Channel coding is a method that can be used to detect and correct signal errors and error bursts which are not too long.
• an interleaving scheme is used for separating consecutive bits of a message so that they are sent in a non-consecutive way. Interleaving is used in TDMA-systems to decrease the effects of fading.
• US-A-5 341 396 discusses a communication system in which interleaving is done on chip level.
• the minimum quantity of information is a bit but the transfer unit is one chip which has some averaged fractional relationship to a bit, i.e. a bit comprises a number of chips.
• the channel only varies in amplitude and there does not arise any multipath fading. Thus the problems of multifading are not relevant .
• chip interleaving as disclosed in US-A-5 341 396, the received data symbols sent through the channel get substantially the same quality, but this would not function in a mobile communication system in which the channels have a varying phase.
• the mere application of chip interleaving in such a system would have as a result a very poor receiving performance because of the variations in phase.
• WO 95/16310 also discusses the use of chip interleaving. Although this document refers to the use in a mobile communication system no solution is given as to how to take the phase variation into account, i.e. the problem has not even been observed, and therefore the receiving performance will not be good. It will also be impossible to deinterleave the chips if the phase is not correct, or varies. Thus, neither intentionally, nor unintentionally does WO 95/16310 solve the problem of a channel varying in phase.
• What is needed is therefore an arrangement which can handle signals transferred on a channel which at least varies in phase.
• Transmitting means are also needed through which a signal can be transmitted through a channel varying in phase or a multipath channel.
• a receiving arrangement is also needed which can handle the reception of a signal transmitted over a channel varying in phase or a multipath channel .
• Still further a method for handling a signal transported through a multipath channel is needed.
• a method for transmitting a digital signal onto a multipath channel is needed as well as a method for receiving a signal transmitted through a multipath channel.
• a mobile communication system is needed having a high capacity and a good performance and in which multipath channels can be handled in an efficient manner without reducing the capacity or the performance of the system.
• an arrangement which comprises means for dividing each of a number of data bits of an information bearing signal into a number of chips, interleaving means for interleaving said chips, means for transmitting a pilot signal through the same channel as the information bearing signal or through a substantially identical channel, means for performing a channel estimation using said pilot signal and means for compensating for at least the phase variations of the channel and deinterieaving means for deinterieaving the compensated information bearing signal .
• the channel is a multipath channel such as for example a Rayleigh or a Rice faded channel.
• the amplitude of the channel varies.
• the communication system is a spread spectrum communication system. Still more particularly the system is a CDMA-system, which still more particularly uses direct sequence modulation.
• the interleaved information bearing signal is multiplied by a user code, i.e. a user specifique code, in the transmitting means and particularly the received signal is multiplied by the user code on the receiving side.
• a pilot signal is added to the interleaved information bearing signal in the transmitting means. If the digital information bearing signal is multiplied by a user specifique code, this is advantageously done after the pilot signal has been added to the interleaved information bearing signal.
• the pilot signal is separated from the information bearing signal in separating means in the receiving means and a channel estimation is done on the separated pilot signal, the information bearing signal being multiplied by the complex conjugate of the channel estimate before deinterieaving in the deinterieaving means.
• the compensating means the information bearing signal is thus compensated for the phase variation.
• deinterieaving means is then a deinterieaving operation performed.
• pilot signal is transmitted in parallel to the interleaved information bearing signal through the same channel .
• the two signals can be sent through the channel in different ways, i.e. they can be sent "separately" or without disturbing each other in different ways.
• One advantageous way is to multiply the data signal by one code and to multiply the pilot signal by another code so as to separate the data signal and the pilot signal going through the same channel .
• the pilot channel is transmitted via separate transmitting means through a separate channel having the same phase characteristics as the channel through which the data signal is transported. Separate, closely spaced, transmitting means can then be used for the data signal and the pilot signal respectively.
• the chips incoming to the interleaving arrangement can be arranged in a storing matrix in which the chips are written in rows/columns and read out in columns/rows and vice-versa in the deinterieaving means on the receiving side.
• interleaving can be done in other ways, e.g. through producing a rearrangement of the chips in time or providing a pseudo-random rearrangement of the chips.
• the invention is not limited to any particular way of interleaving.
• the transmitting means are arranged in a mobile station of a mobile communication system and the receiving means are arranged in a base station.
• the transmitting means are arranged in a base station and the receiving means in a mobile station.
• power controlling is provided for.
• Transmitting means are also provided for transmitting a digital information bearing signal. i.e. the data signal, through a multipath channel.
• the transmitting means comprises means for dividing data bits of the data signal into a number of chips, interleaving means for interleaving said chips and means for transmitting said interleaved data signal and a pilot signal, through the same channel or a channel having the same characteristics, at least as far as for the variation in phase is concerned.
• said means for transmitting the data signal and the pilot signal comprises adding means for adding the pilot signal to the interleaved data signal.
• said means for transmitting the data signal and the pilot signal comprises means for sending the data signal and the pilot signal separately through the same multipath channel or alternatively through separate channels as referred to above.
• the transmitting means also comprises multiplying means for at least multiplying the data signal by a user code (which is user specific) .
• the multiplying means comprises means for multiplying the data signal by a user code and means for multiplying the pilot signal by a pilot code so as to separate the signals from each other.
• the invention also provides receiving means for receiving a digital data signal transmitted over a multipath channel.
• the receiving means comprises channel estimation means for performing a channel estimation on a pilot signal sent through the same channel or through a channel having the same phase characteristica, means for compensating for the phase variation of the channel, deinterieaving means for deinterieaving the compensated data signal and combining means for combining the chips of the data signal into data bits.
• the receiving means comprises means for extracting the pilot signal from the data signal and means for combining the complex conjugate of the channel estimate with the interleaved data signal.
• the receiving means comprises multiplying means for multiplying the incoming signal by a user code.
• a method for transmitting a digital data signal comprising a number of data bits through a multipath channel i.e. a channel at least varying in phase.
• the method comprises the steps of: dividing the data bits of the data signal into a number of smaller time segments, i.e. chips; interleaving said chips; transmitting the interleaved data signal and a pilot signal through the channel or channels having the same phase behaviour; performing a channel estimation using the pilot signal on the receiving side, compensating for the phase variations of the channel using the channel estimate; deinterieaving the compensated signal and combining the chips into data bits.
• the method also comprises the steps of multiplying the interleaved signal by a user code on the transmitting side before sending the signal on to the multipath channel and of multiplying the signal incoming to the receiving side by the user code .
• the method comprises the step of adding the pilot signal to the interleaved data signal on the transmitting side and of extracting the pilot signal from the received signal on the receiving side.
• the method comprises the steps of transmitting the data signal and a pilot signal separately from each other through the same multipath signal.
• the method advantageously comprises the steps of: multiplying the data signal by a user code and multiplying the pilot signal by a separate (i.e. different) pilot code, said user code and pilot code being made orthogonal so as to ensure that the data signal and the pilot signal are transported completely distinguished from each other and so that they do not disturb one another at all.
• the invention also provides a method of transmitting a signal through a multipath channel, thus including the steps belonging to the transmitting side as well as a method of receiving a signal incoming over a multipath channel, thus including the steps as discussed above belonging to the receiving side.
• FIG 1 schematically illustrates an arrangement using chip interleaving
• FIG 2 schematically illustrates the structure of transmitting means according to a first embodiment of the invention
• FIG 3 schematically illustrates the receiving means according to a first embodiment of the invention
• FIG 4 schematically illustrates another embodiment of an arrangement according to the invention including transmitting and receiving means
• FIG 5 illustrates in a simplified manner a data signal to which a pilot signal is added
• FIG 6A schematically illustrates transmitting means according to a third embodiment of the invention
• FIG 6B schematically illustrates receiving means according to a third embodiment of the invention
• FIG 6C shows a data signal and the codes for the data signal and the pilot signal respectively
• FIG 7 is a flow diagram describing transmission of a data signal through a multipath channel using an arrangement according to the invention.
• a digital information bearing signal or a data signal here means a signal comprising a number of data bits.
• Data bits can be arranged into symbols (thus comprising a multibit data word) using well-known modulation techniques, but for reasons of simplicity is simply referred to as a data signal comprising a number of bits.
• a bit in turn can be divided into a plurality of chips.
• chiprate is meant the number of chips per second. The chiprate is higher than the datarate, the datarate being the number of bits per second of the data signal.
• a data signal D in is provided to an interleaver.
• the data signal here comprises N symbols.
• Fig 1 it is not explicitly illustrated how the symbols of the data signal are divided into a number of chips but it is supposed that each symbol 1,...,N is divided into a number of chips.
• an interleaved signal D' is obtained in which every symbol is sent in several time positions over a frame. This means that as long as there are no, or substantially no, phase variations in the channel, only a part of each symbol is lost in the case of a fading dip.
• the interleaved signal is then multiplied by a user code. This multiplication as such has nothing to do with chip interleaving, which can be done in any case; this is merely included in the Figure for exemplifying purposes.
• the chip rate of the user code is higher than the data speed of the data signal .
• the frequency of the signal is then spread over the available frequency band, i.e. the transmitted signal is spread over a frequency band which is much wider than the bandwidth of the information being transmitted.
• the signal is then sent through the channel .
• the interleaved signal is again multiplied by the user code and the result is a signal D" , which is input to a deinterleaver in which an operation opposite to that of the operation done in the interleaver is carried out, thus providing an output signal D out .
• This works as long as the channel does not vary in phase but only in amplitude.
• This arrangement was merely shown in order to illustrate the chip interleaving functionality. It should however be noted that the inventive concept is not dependent on the multiplication by a user code; this merely relates to an advantageous embodiment.
• the chip interleaving functionality is particularly efficient if the correlation time of the channel is short. Furthermore, chip interleaving works particularly well with a high Doppler frequency.
• a digital data signal D 10 which comprises a number of bits, is divided, in the time domain, into a number of chips in dividing means 11.
• the signal divided into chips is here denoted D 10 CH and in this form the signal is input to the interleaver 12.
• the interleaver 12 a chip interleaving operation is carried out.
• the incoming data is arranged in an interleaving matrix written in rows.
• the transmission of the signal is performed columnwise, i.e. the data chips are read out in columns.
• the matrix is filled up in columns and fed out in rows.
• the interleaving operation can be performed in different ways and how it is achieved is not significant for the functioning of the present invention, as long as the interleaving is done at chiprate.
• a pseudo-random rearrangement of the chips is performed or the chips are rearranged in the time domain in a convenient manner. Also other alternatives are possible.
• pilot signal P 10 is added to the interleaved signal D 10 IL in the adding means 13 .
• a pilot signal is a signal wave, normally a single frequency, transmitted over the system, or the channel, to indicate or control its characteristics.
• a pilot signal in the present application contains enough information to enable an estimation of the characteristics of the channel.
• different kinds of pilot signals can be used, the amount of information, the kind of information etc. can be different; it may e.g. be data transferred between a transmitting side and a receiving side etc. e.g. a signal having a known phase.
• the pilot signal is stuffed in at a given rate between the data as illustrated in Fig 5 and the data interleaved signal is sent, together with the pilot signal, via the antenna 15 through a channel varying in phase .
• Fig 3 discloses, according to a first embodiment of the invention, receiving means 20 in which the interleaved data signal D' 10/IL and the pilot signal P' 10 from the transmitting means 10 after passing through the phase varying channel are received.
• the signal is first input to separating means 23 in which the pilot signal P' 10 is separated from the interleaved data signal D' 10 IL , or in other words, the pilot signal is extracted from the combined signal.
• a channel estimation is done on the pilot signal in channel estimating means 24.
• the channel estimation can be done in any appropriate way.
• the channel estimate, or rather the complex conjugate of the channel estimate is used on the interleaved data signal in compensating means 25, in which a compensation is done for the phase variation of the channel.
• the compensated data signal D' 10/Comp is then input to deinterleaver 26 in which a deinterieaving operation is performed.
• the deinterleaved, compensated, data signal D' 10 comp is then input to combining means 27 in which the chips are combined into data bits thus providing an output signal D 10/OUT .
• the combining means 27 do not form part of the inventive concept of the present invention; a combination can be done in any appropriate way, as also the signal can be detected in any appropriate way.
• the invention also relates to an arrangement including the transmitting and receiving means 10, 20 of Figs 2 and 3, the functioning of which however should be clear from the discussion above .
• Fig 4 an arrangement according to a second embodiment of the present invention is illustrated. It comprises transmitting means 310 and receiving means 320.
• a data signal divided into chips D 3O,CH is input to interleaving means 302 and an interleaving operation is performed as discussed under reference to Fig 2.
• a pilot signal P 30 is added to the interleaved signal D 30/IL in adding means 303.
• the signal is multiplied by a user code in multiplying means 304.
• the transmitter 310 is a CDMA-transmitter and a user specific user code is used. The interference from other users will only be suppressed by the spreading factor which is the number of chips a data bit is divided into (before the interleaving operation) .
• the signal is via the antenna means 305 transmitted through the channel 330.
• the receiving means 320 the received signal is again multiplied by the user code in the multiplying means 312.
• the pilot signal is separated from the data signal (the separating means are not illustrated in the figure) and a channel estimation is done in the channel estimating means 314.
• the compensating means 315 the phase variation is compensated for as also discussed above.
• a deinterieaving operation is done in deinterieaving means 316 and the chips of the data signal are combined into bits in the combining means 317.
• the resulting output signal D 30 0UT is then detected in detecting means 318.
• the detection can either be done differentially or coherently; the invention is not restricted to any particular detection method.
• Fig 5 is schematically illustrated how a pilot signal can be sent together with an interleaved data signal, a spreading factor (i.e. the number of chips) of 10 being used on 2 bits in this case .
• a spreading factor i.e. the number of chips
• FIG 6A another embodiment of the invention is illustrated.
• a data signal D 40 CH which already has been divided into a number of chips in dividing means (not shown) is input to an interleaver 42 in which an interleaving operation is performed.
• multiplying means 44 the interleaved signal is multiplied by a user code which is user specific.
• a pilot signal P 40 is provided from a pilot signal generator (not shown) .
• pilot multiplying means 44A the pilot signal P 40 is multiplied by a pilot code which is different from the user code used on the data signal.
• adding means 43 the spread data signal and the spread pilot signal are added.
• the resulting signal is then via antenna means 45 output on a channel, the phase of which is varying.
• the user code intended for the data signal and the pilot code intended for the pilot signal are completely orthogonal. In that case there will be no interference at all between the information bearing data signal and the pilot signal .
• a receiving arrangement 50 for receiving a signal e.g. transmitted by transmitting arrangement 40, over a channel varying in phase is illustrated.
• the signal is received by an antenna 51.
• the data signal and the pilot signal are separated from each other in separating means (not shown) .
• multiplying means 52 the data signal is multiplied by the user code (advantageously the same as was used on the transmitting side) .
• pilot multiplying means 52A the pilot signal in a similar manner is multiplied by the (a) pilot code.
• adding means the sum is taken over a pilot bit.
• compensating means 55 the data signal is compensated for the phase variation of the channel using the channel estimate obtained in the channel estimating means 54.
• the compensated data signal is then deinterleaved in deinterieaving means 56.
• the combining means 57 the chips are arranged into data bits.
• the receiving means are synchronized in any convenient manner. This is not further discussed herein since it is supposed to be wellknown to the man skilled in the art.
• the detection can also be done in different ways, e.g. through coherent detection which is advantageous, but also other alternatives are possible.
• Fig 6C the data signal is illustrated as compared to the user code for the data signal, code D , and the code for a pilot signal, code p .
• pilot signal is transmitted through a separate channel, which at least has the same phase variation characteristics as the channel through which the data signal is transmitted.
• Separate transmitting means may be arranged adjacent to the transmitting means for the data signal, as well as separate closely arranged receiving means may be provided.
• a frame comprising a number of data bits, for example K, is created, 100.
• the data bits are then repeated N times which means that the data bits are divided into N chips each, 101.
• a pilot sequence i.e. a pilot signal, is then added to the interleaved data signal, 103.
• a multiplication is done using the user specific code, for example a CDMA-code (in the case a CDMA-system is used) , 104.
• the resulting signal is then transmitted over the radio channel, 105.
• the received signal is multiplied by the user specific code, 106.
• the pilot signal i.e. the pilot sequence
• the pilot sequence is then separated from the data signal, 107.
• Using the pilot sequence a channel estimation is done, 108, and using the channel estimate the data signal is compensated, 104.
• the compensated data signal is then deinterleaved, 110, and chips from the same data bits are combined, 111. Finally the data bits are detected, 112.
• pilot signal in combination with interleaving on chip level has shown to be particularly efficient in reducing the variation in the channel, particularly if the correlation time of the channel is short.
• power control is applied.
• Power control means are e.g. arranged on the transmitting side and power control commands are sent as a result of a feedback signal from the receiving side.
• the variance in the power control will be reduced approximately with the number of power control commands sent during the frame.
• the invention is applied to a so called RAKE-receiver which is a receiver structure for a CDMA- system.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Error Detection And Correction (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
• Mobile Radio Communication Systems (AREA)

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Citations (3)

• 1997
  • 1997-05-02 SE SE9701655A patent/SE511561C2/sv not_active IP Right Cessation
• 1998
  • 1998-04-23 EP EP98921934A patent/EP0974204A1/en not_active Withdrawn
  • 1998-04-23 AU AU74585/98A patent/AU7458598A/en not_active Abandoned
  • 1998-04-23 WO PCT/SE1998/000739 patent/WO1998051017A1/en not_active Application Discontinuation
  • 1998-04-23 JP JP54796198A patent/JP2001524288A/ja active Pending

Patent Citations (3)

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