WO2004109953A1 - Procede et appareil pour systeme d'acces multiple par repartition de code a multiporteuse - Google Patents

Procede et appareil pour systeme d'acces multiple par repartition de code a multiporteuse Download PDF

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Publication number
WO2004109953A1
WO2004109953A1 PCT/SG2003/000138 SG0300138W WO2004109953A1 WO 2004109953 A1 WO2004109953 A1 WO 2004109953A1 SG 0300138 W SG0300138 W SG 0300138W WO 2004109953 A1 WO2004109953 A1 WO 2004109953A1
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WIPO (PCT)
Prior art keywords
sequence
phase
modulator
phase value
sub
Prior art date
Application number
PCT/SG2003/000138
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English (en)
Inventor
Appukuttan Nair Saraswathy Amma Madhukumar
Po Shin François CHIN
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Agency For Science, Technology And Research
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Priority to AU2003239104A priority Critical patent/AU2003239104A1/en
Priority to PCT/SG2003/000138 priority patent/WO2004109953A1/fr
Publication of WO2004109953A1 publication Critical patent/WO2004109953A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2614—Peak power aspects
    • H04L27/2621—Reduction thereof using phase offsets between subcarriers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • 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
    • H04B1/692—Hybrid techniques using combinations of two or more spread spectrum techniques
    • 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
    • H04B2201/70706—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation with means for reducing the peak-to-average power ratio
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0014—Three-dimensional division
    • H04L5/0016—Time-frequency-code
    • H04L5/0021—Time-frequency-code in which codes are applied as a frequency-domain sequences, e.g. MC-CDMA

Definitions

  • the invention generally relates to multi-carrier code division multiple access (MC-CDMA) applications, and more particularly, to partial transmit seq uence (PTS) approach for peak to average power ratio (PAPR) reduction in MC-CDMA applications.
  • MC-CDMA multi-carrier code division multiple access
  • PTS partial transmit seq uence
  • PAPR peak to average power ratio
  • OFDM Orthogonal frequency division multiplexing
  • I CI inter-symbol interference
  • CP cyclic prefix
  • FFT fast Fourier transform
  • Uncoded OFDM transmission technique applied in a multipath environment has a bit error rate (BER) comparable to that of a narrow band radio channel because the fading of each subcarrier is frequency non-selective.
  • BER bit error rate
  • CDMA code division multiple access
  • MC-CDMA multicarrier CDMA
  • PAPR peak to average power ratio
  • the signal When passed through a non-linear device, such as transmit power amplifier, the signal may suffer significant spectral spreading and in-band distortion.
  • a non-linear device such as transmit power amplifier
  • the transmit amplifier In order to prevent spectral growth of the multicarrier signal intermodulation among subcarriers and out-of-band radiation the transmit amplifier must operate in its linear region, where the conversion from direct current to radio frequency power is highly inefficient.
  • the required large linear range directly translates into significantly more expensive devices, limiting widespread industrial applications.
  • PAPR problems are solved using either a linear amplifier or back off the operating point of a nonlinear amplifier. But both approaches result in significant power efficient penalty.
  • Some other methods have been suggested to solve PAPR problems. The simplest is to clip the signal before amplification as discussed in R. O'Neill et al. , "Envelope variations and spectral splatter in clipped multicarrier signals", Proceedings of PIMRC95, pp. 71 -75, which gives a good PAPR but at the expense of some performance degradation.
  • Non-linear block coding is another method as discussed in A. E. Jones et al.
  • Phase of each sub-block is modified by a set of rotation factors to achieve PAPR to be as low as possible.
  • the receiver readjusts this phase shifts and recovered the data. To do that both transmitter and receiver share the same information on phase rotations that make the system design very complicated.
  • Amplitude limiting and coding schemes are not very successful for reducing PAPR because of bandwidth expansion and high complexity, respectively.
  • the dynamic allocation of spread codes and/or restricting the number of spread codes for the reduction of PAPR is obviously not an optimal choice.
  • This method will significantly reduce the system capacity in terms of number of spread codes available for transmission.
  • the overall PAPR obtained by this method is not the absolute minimum since the size of user group can be less than total number of users in the system. Also, the complexity of transmitter and receiver units will significantly increase by using this method.
  • Partial-transmit sequence with phase rotation is a better alternative for PAPR reduction.
  • the practical implementation of this approach faces several challenges. It is obvious that the receiver must have knowledge about the generation process of the transmitted symbol in each FFT period. Thus the set consists of all optimum phase rotation factors that have to be transmitted to the receiver so that the subcarriers can be phase adjusted appropriately. When the phase changes continuously, a huge number of bits will be required as side information. Moreover, the detection error in this phase information will severely degrade the BER performance. Therefore, there is a need to solve the problem to translate into the optimisation of phase information into a finite number of predetermined levels, and designing a suitable method to convey the phase information to the receiver of a MC-CDMA system without increasing the complexity of the receiver.
  • Embodiments of the invention provide an apparatus for transmitting an output transmit signal in multicarrier code division multiple access (MC-CDMA) applications, the apparatus comprising a spreader for spreading an input signal in accordance to a predefined spread code for providing spread data corresponding to the input signal, a modulator for the spread data corresponding to the input signal to generate an output sequence having a phase sequence and a transmit sequence together in a single output sequence; and a transmission subsystem for transmitting the transmit sequence.
  • MC-CDMA multicarrier code division multiple access
  • An embodiment may further comprise at least two modulators, each modulator having different phase sequences corresponding to a phase value selected for each modulator, and a selector for comparing each output sequence of each modulator and selecting the output sequence with the lowest peak to power ratio (PAPR) selected as the transmit sequence;
  • the modulator may further comprise a coder for coding the selected phase value of the modulator into a coded sequence of the phase value of the modulator, a spreader for spreading the coded sequence of the phase value into spread data corresponding to the coded sequence of the phase value, a partitioner for partitioning the spread data into at least two sub-blocks of partial data, an adder for adding each sub-block of partial data together with the spread data corresponding to the coded sequence of the phase value of the partial data providing a sum , and a multiplier for multiplying the sum with the phase value for a sub-block sequence of the sub-block, and an inverse fast fourier transformer (I FFT) for transforming the output sequence of each sub-block to provide the output sequence of the
  • MC-CDMA multicarrier code division multiple access
  • the generating of the output sequence may be generated with at least two modulators, each modulator having different phase sequences corresponding to a phase value selected for each modulator; and comparing with a selector each output sequence of each modulator and selecting the output sequence with the lowest peak to power ratio (PAPR) selected as the transmit sequence.
  • PAPR peak to power ratio
  • the generating of the output sequence may further comprise coding with a coder the selected phase value of the modulator into a coded sequence of the phase value of the modulator, spreading with a spreader the coded sequence of the phase value into spread data corresponding to the coded sequence of the phase value, partitioning with a partitioner the spread data into at least two sub-blocks of partial data, adding with an adder each sub-block of partial data together with the spread data corresponding to the coded sequence of the phase value of the partial data providing a sum; and multiplying with a multiplier for the sum with the phase value for a sub-block sequence of the sub-block, and transforming with an inverse fast fourier transformer (I FFT) the output sequence of each sub-block to provide the output sequence of the modulator having phase sequence and transmit sequence together in a single sequence.
  • I FFT inverse fast fourier transformer
  • a computer program product for transmitting an output transmit signal in multicarrier code division multiple access (MC-CDMA) applications
  • the computer usable medium having computer readable program code means embodied in the medium for causing the calculation of the output transmit signal
  • the computer program product comprising a computer readable program code for spreading an input signal in accordance to a predefined spread code for providing spread data corresponding to the input signal, a computer readable program code for generating an output sequence having a phase sequence and a transmit sequence together in a single output sequence, for the spread data corresponding to the input signal; and a computer readable program code for transmitting with a transmission subsystem the transmit sequence.
  • the computer readable program code for generating of the output sequence may be generated with at least two modulators routines, each modulator routines having different phase seq uences corresponding to a phase value selected for each modulator routine; and comparing with a selector each output sequence of each modulator routine and selecting the output sequence with the lowest peak to power ratio (PAPR) selected as the transmit sequence.
  • PAPR peak to power ratio
  • the computer readable program code for generating of the output sequence may further comprise coding the selected phase value into a coded seq uence of the phase value of the modulator routine, spreading the coded sequence of the phase value into spread data corresponding to the coded sequence of the phase value, partitioning the spread data into at least two sub-blocks of partial data, adding each sub-block of partial data together with the spread data corresponding to the coded sequence of the phase value of the partial data providing a sum; and multiplying for the sum with the phase value for a sub-block sequence of the sub-block, and transforming with an inverse fast fourier transformer (I FFT) the output sequence of each sub-block to provide the output sequence of the modulator having phase sequence and transmit sequence together in a single sequence.
  • I FFT inverse fast fourier transformer
  • FIG . 1 shows a schematic block diagram of a multi-carrier code division multiple access (MC-CDMA) transmitter structure
  • FIG . 2 shows a schematic block of diagram of peak to average power ratio (PAPR) reduction using a partial-transmit sequence (PTS);
  • PAPR peak to average power ratio
  • PTS partial-transmit sequence
  • FIG. 3 shows a schematic block diagram of a peak-to- average power reduction scheme in accordance with an embodiment of the invention
  • FIG . 4 shows a detailed schematic block for a modulator of FIG. 3 in accordance with an embodiment of the invention
  • FI G. 5 shows a graph comparison a peak-to-average power reduction scheme between a conventional MC-CDMA system and MC-CDMA systems of embodiments of the invention
  • FIG. 6 shows a graph comparison of change in peak to average power ratio for different number of uses using an embodiment of the invention
  • FIG. 7 shows a graph of receiver performance of a single user system for a transmitter using an embodiment of the invention
  • FIG. 8 shows a graph of receiver performance of a multiuser system for a transmitter using an embodiment of the invention
  • FIG . 9 shows a flowchart of a method of a PAPR scheme in accordance with an embodiment of the invention.
  • the transmitter structure 20 of MC-CDMA system for downlink transmission is given in FIG. 1 .
  • the spread sequence of all active users (K) are
  • I FFT inverse fast Fourier transform
  • P/S parallel/serial
  • p cyclic prefix of length p
  • inserter 44 between symbols to avoid the intersymbol interference caused by multipath fading .
  • the signal is finally transmitted after radio frequency up-conversion.
  • the baseband transmitted signal for one OFDM block of symbol length T ⁇ can be represented as follows:
  • the PAPR is defined as
  • the input data vector A is partitioned into disjoint sub-blocks, as
  • /? 1, 2, •••p ⁇ and are combined to minimise PAPR.
  • FIG. 2 shows the block diagram for a conventional partial- transmit sequence (PTS) approach for PAPR reduction system 50.
  • PTS partial- transmit sequence
  • the data sequence A [A l ,A 2 ,- ⁇ A N ⁇ (with reference to FI G. 1 ) to be partitioned into P sub-blocks by partitioner 52.
  • the I FFT output of each sub-block is phase rotated by the phase rotation factor.
  • the phase shifted sub-blocks are then added together by adder 62 to produce alternate transmit signals containing the same transmit information, and the optimum phase-rotation vector peak-value is determined by optimization device 60. This process is repeated for all different possible phase rotation factors, and the multicarrier symbol with lowest PAPR is transmitted.
  • the information on transmit signal phase rotation 64 has to be sent as a side information for the correct decoding of data at the receiver.
  • W can be any discrete number.
  • the corresponding values are + 1 and -1 .
  • an embodiment of the invention of a system considers the side information as a user data. The information will be spread using a predefined spread code and added with all other user channels. The sub-blocks corresponding to partial transmitted sequences are then multiplied with respective phase values. By this arrangement extra overhead required for transmission of phase vectors is almost negligible. But to decide OBPS, an exhaustive search with all possible combinations of ⁇ 1 for all sub-blocks is required. The total number of possible choices is 2 P where P is the number of sub-blocks.
  • the number of choices are reduced to 2 ( _1 ⁇ .
  • the number of parallel transmitters required for deciding the transmitted symbol with lowest PAPR is equal to this value.
  • transmitter requires more and/or faster hardware, while the receiver is nearly unaffected, when compared to the original MC-CDMA. Since this scheme is designed for downlink transmission , the more complexity at the transmitter is not a serious issue and keeping the same simplicity for the receiver is an added advantage.
  • FIG. 3 shows the block diagram for an apparatus 70 generating optimised transmit sequence in accordance with an embodiment of the invention
  • FIG . 9 shows a flowchart of a method of PAPR scheme 140.
  • an exhaustive search with all possible combinations of binary phase sequences is required.
  • FIG. 4 Since the number of partitions employed in a practical system is not very large, this search process can be paralleled in the transmitter.
  • the parallel arrangement is shown in FI G. 3.
  • Each modulator 72,74,76, 78 represents a possible combination of binary phase sequence, where the modulator with the lowest PAPR is selected by selector 80.
  • FI G. 4 shows the details of the modulator 72, 74,76,78 corresponding to the binary phase sequence bzip .
  • binary phase information is assigned 146 to each sub-block
  • each partial data is added 146 with the spread data 142 corresponding to binary phase value of the partition (for example ⁇ for p th partition).
  • the phase value is coded by coder 94 to a coded sequence 97 of the phase value, and then spread by spreader 96 to a spread data 98 corresponding to the coded sequence of the phase value.
  • the resultant sum is multiplied 152 with the respective binary phase value to provide an output sequence 93 of the sub-block before IFFT conversion 154 at I FFT converter 92. This process is repeated 1 56 as shown in FI G . 9, or conducted simultaneously in parallel as shown in FIG. 4, for all binary phase sequences.
  • Optimised transmit seq uence 85 is generated after comparing the outputs of all possible modulators, and selecting 1 58 the sequence with the lowest PAPR for transmission 1 59 in a transmission subsystem such as discussed above with reference to FI G . 1 and 2. It will be appreciated that other arrangements may be envisaged, for example there may be multiple or a plurality of I FFTs where each I FFT outputs partial transmit sequences that are added up by adder instead of a single I FFT 92, 1 54 for possible transmission 1 59.
  • phase information is transmitted as spread data.
  • the receiver despreads the phase vector using the assigned spread code, and decides the phase values based on the presence of transition.
  • the system represents +1 with identical bits and -1 with a transition of bits. Since this approach does not require any additional computation , the receiver complexity remains the same with the added feature of OBPS.
  • the multiplication with phase values in the transmitter can be simplified as a simple sign change in case of -1 and remain same for + 1 .
  • the complexity mainly lies in OBPS selection at transmitter, which can be paralleled. Of course, it will be appreciated that greater than two-bit representation schemes may be implemented , for example three, four, etc. , multi-bit representation schemes.
  • FIG. 5 and FIG . 6 The simulation results of the methods of FIG. 3 and 4 in MC- CDMA systems are shown FIG. 5 and FIG . 6, where in this embodiment a MC-CDMA system with 256 subcarriers is assumed. Each multicarrier symbol consists of 16 data symbols and the processing gain is 16. The spread codes are selected from orthogonal Walsh-Hadamard transform. Additional details of simulation parameters are shown in the Table 2:
  • FI G . 5 shows the improvement in PAPR at transmitter with the increase in the number of PTS in a MC-CDMA system.
  • the probability of PAPR crossing a threshold value (PAPRo) is plotted.
  • the number of active users for the system under test is selected as 16, which includes the spread data corresponding to PTS.
  • the MC-CDMA system with 2, 4 and 8 partial transmit sequences 1 02, 104, 1 08 respectively, are compared against a system without PTS optimisation 100.
  • the PAPR reduces considerably when the number of PTS increases.
  • the computational complexity at the transmitter also increases with the number of PTS. For example, if a system uses 8 PTS, then it requires 2 8 parallel modulators to decide the optimal binary phase sequence (OBPS).
  • OBPS binary phase sequence
  • FIG. 6 shows PAPR where the probability of exceeding certain peak power, prob(PAPR>PAPRo), is 10 "3 , with respect to the number of users. As the number of users increases, the PAPR improves considerably.
  • the MC-CDMA system with 2, 4 and 8 partial transmit sequences 1 12, 1 14, 1 1 8 respectively, are compared against a system without PTS optimisation 1 10. It is because, for large number of users, the superimposed sequences tend to cancel out the elements of several subcarriers, resulting in the reduction of effective number of subcarriers, and if the actual number of subcarriers is reduced without changing the average power, eventual PAPR becomes lower. This feature is true for all MC-CDMA systems, but the absolute value of PAPR will change according to the number of partial transmit seq uences used.
  • FIG . 7 and 8 show graphs of receiver performance of the MC-CDMA system after the incorporation of partial transmit sequence of the simulation parameters of Table 1 .
  • the graph of FIG. 7 represents a single user system, while the graph of FIG. 8 represents a multi-user system of 8 users.
  • the single user MC- CDMA system of FIG. 7 has 2, 4 and 8 partial transmit sequences 122, 124, 128 respectively, are compared against a system without PTS optimisation 120.
  • the m ulti-user MC-CDMA system of FIG. 8 has 2, 4 and 8 partial transmit sequences 132, 134, 138 respectively, are compared against a system without PTS optimisation 1 30.
  • any decision error on the sequence affects the overall performance of the system . It is reflected in the slight degradation of performance in low signal to noise (SNR) regions.
  • SNR signal to noise
  • the embodiments depicted herein may generally be implemented in and/or on computer architecture that is well known in the art.
  • the functionality of the embodiments of the invention may generally be implemented in hardware or software, or a combination of both.
  • An embodiment may be implemented in hardware, where a component is a functional hardware unit designed for use with other components, such that a component may be implemented with discrete electrical components, or may form a portion of an entire electronic circuit such as an application specific integrated circuit (ASIC).
  • ASIC application specific integrated circuit
  • An embodiment may be implemented in software, where the system may be a program, process or portion thereof that usually performs a particular function or related functions.
  • Computer architectures to run such programs or processes are well known in the field. There are numerous other possibilities that exist, those skilled in the art would appreciate that such a program or process may also be implemented as a combination of hardware and software components.
  • MC-CDMA multicarrier code division multiple access

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Abstract

La présente invention se rapporte à un procédé (140) et à un appareil (70, 72) permettant de mettre en oeuvre une technique de séquence de transmission partielle (PTS) pour une réduction du rapport valeur de crête sur valeur moyenne (PAPR), dans des applications d'accès multiple par répartition de code à multiporteuse (MC-CDMA), de façon à transmettre une séquence de transmission optimisée (85), les informations de phase étant transmises sous forme de données étalées. L'invention concerne également un appareil possédant un modulateur (72) destiné aux données étalées et fournissant une séquence de transmission possédant une séquence de phase et une séquence de transmission réunies en une séquence unique (85) destinée à être transmise.
PCT/SG2003/000138 2003-06-04 2003-06-04 Procede et appareil pour systeme d'acces multiple par repartition de code a multiporteuse WO2004109953A1 (fr)

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Application Number Priority Date Filing Date Title
AU2003239104A AU2003239104A1 (en) 2003-06-04 2003-06-04 A method and apparatus for a multicarrier code division multiple access system
PCT/SG2003/000138 WO2004109953A1 (fr) 2003-06-04 2003-06-04 Procede et appareil pour systeme d'acces multiple par repartition de code a multiporteuse

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007066871A2 (fr) * 2005-12-10 2007-06-14 Electronics And Telecommunications Research Institute Procédé d'affectation d'un code d'étalement en domaine fréquence dans une station de base d'un système de communication mc-cdma
EP1798923A1 (fr) * 2005-12-16 2007-06-20 Siemens Aktiengesellschaft Procédé pour transmission de signaux
US8611837B2 (en) 2011-08-30 2013-12-17 Motorola Mobility Llc Method and apparatus for power cutback in a simultaneous dual frequency band call
CN104079523A (zh) * 2014-07-17 2014-10-01 电子科技大学 一种有效抑制papr的部分传输序列方法
US11695609B2 (en) 2019-04-30 2023-07-04 Huawei Technologies Co., Ltd. Side information transmission method based on partial transmit sequence technology, and apparatus

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Publication number Priority date Publication date Assignee Title
EP0929161A2 (fr) * 1998-01-13 1999-07-14 Lucent Technologies Inc. Système à transmission multiporteuse AMDC avec diversité en fréquence et en espace
WO1999059265A1 (fr) * 1998-05-12 1999-11-18 Samsung Electronics Co., Ltd. Dispositif et procede destines a reduire le rapport puissance de crete/puissance moyenne de la puissance d'emission d'une station mobile
EP1128592A2 (fr) * 2000-02-23 2001-08-29 NTT DoCoMo, Inc. AMRC multiporteuse et estimation de canal

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0929161A2 (fr) * 1998-01-13 1999-07-14 Lucent Technologies Inc. Système à transmission multiporteuse AMDC avec diversité en fréquence et en espace
WO1999059265A1 (fr) * 1998-05-12 1999-11-18 Samsung Electronics Co., Ltd. Dispositif et procede destines a reduire le rapport puissance de crete/puissance moyenne de la puissance d'emission d'une station mobile
EP1128592A2 (fr) * 2000-02-23 2001-08-29 NTT DoCoMo, Inc. AMRC multiporteuse et estimation de canal

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007066871A2 (fr) * 2005-12-10 2007-06-14 Electronics And Telecommunications Research Institute Procédé d'affectation d'un code d'étalement en domaine fréquence dans une station de base d'un système de communication mc-cdma
WO2007066871A3 (fr) * 2005-12-10 2010-11-11 Electronics And Telecommunications Research Institute Procédé d'affectation d'un code d'étalement en domaine fréquence dans une station de base d'un système de communication mc-cdma
US8305875B2 (en) 2005-12-10 2012-11-06 Electronics And Telecommunications Research Institute Method for allocating frequency domain spread code in base station of MC-CDMA communication system
EP1798923A1 (fr) * 2005-12-16 2007-06-20 Siemens Aktiengesellschaft Procédé pour transmission de signaux
US8611837B2 (en) 2011-08-30 2013-12-17 Motorola Mobility Llc Method and apparatus for power cutback in a simultaneous dual frequency band call
US8995939B2 (en) 2011-08-30 2015-03-31 Google Technology Holdings LLC Method and apparatus for power cutback in a simultaneous dual frequency band call
CN104079523A (zh) * 2014-07-17 2014-10-01 电子科技大学 一种有效抑制papr的部分传输序列方法
US11695609B2 (en) 2019-04-30 2023-07-04 Huawei Technologies Co., Ltd. Side information transmission method based on partial transmit sequence technology, and apparatus

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