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WO2013172808A1 - Égaliseur nlms dirigé par décision par désétalement avec un code parent d'un groupe de codes actifs - Google Patents

Égaliseur nlms dirigé par décision par désétalement avec un code parent d'un groupe de codes actifs Download PDF

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Publication number
WO2013172808A1
WO2013172808A1 PCT/US2007/073401 US2007073401W WO2013172808A1 WO 2013172808 A1 WO2013172808 A1 WO 2013172808A1 US 2007073401 W US2007073401 W US 2007073401W WO 2013172808 A1 WO2013172808 A1 WO 2013172808A1
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WO
WIPO (PCT)
Prior art keywords
pcpich
symbol
equalizer
partial
codes
Prior art date
Application number
PCT/US2007/073401
Other languages
English (en)
Inventor
Ralph Rudolf VESELI
Tamela J. CRAFT-MOLARAHIMA
Original Assignee
Nxp B.V.
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 Nxp B.V. filed Critical Nxp B.V.
Publication of WO2013172808A1 publication Critical patent/WO2013172808A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
    • H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
    • H04L25/03038—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception with a non-recursive 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
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/709—Correlator structure
    • H04B1/7093—Matched filter type
    • H04B2001/70935—Matched filter type using a bank of matched fileters, e.g. Fast Hadamard Transform
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/03592—Adaptation methods
    • H04L2025/03598—Algorithms
    • H04L2025/03611—Iterative algorithms
    • H04L2025/03617—Time recursive algorithms

Definitions

  • This invention relates to radio communications systems, and more particularly to overcoming multi-path effects in direct-sequence code-division multiple access receivers.
  • the received coding chip waveform, distorted by the multi-path channel, is equalized prior to de-spreading, so the orthogonality of the signal from the basestation can be restored at the code chip-level.
  • Radio communications systems can use many types of modulation.
  • AM amplitude modulation
  • FM frequency modulation
  • Modern cellular telephones and wireless local area networks now use direct- sequence code-division multiple access (CDMA) modulation techniques that allow many users to share the same frequency channels.
  • CDMA direct- sequence code-division multiple access
  • More sophisticated schemes use several of the radio channels in a band, e.g., eight frequency channels, in various orthogonal techniques to frequency hop among individual channels to avoid sources of interference. Some of these schemes can survive one or more of the channels becoming useless, and still lose none of the data.
  • Ideal non-adaptive zero-forcing (ZF) and MMSE chip equalizer receivers can restore the orthogonality and suppress the MUI in DS-CDMA systems employing aperiodic scrambling codes, but these receivers cannot deal with rapidly fading multipath channels.
  • No continuous training chip sequence is available to allow receiver chip equalizers to track fast enough.
  • pilot-aided adaptive fractionally-spaced chip equalizer receivers These use the continuous pilot signal in third generation cellular and LEO satellite communication systems to continuously update at the symbol rate. E.g., using a simple normalized least mean square (NLMS) or a more advanced recursive least squares (RLS) adaptive scheme.
  • NLMS normalized least mean square
  • RLS more advanced recursive least squares
  • Such a receiver supposedly out-performs RAKE receivers with perfect channel knowledge over a wide range of normalized Doppler spreads, and its complexity is independent of the number of users.
  • Adaptive interference suppression has been successfully used for base-to-mobile downlinks in direct sequence (DS) based cellular communication systems.
  • Each base station transmits all the signals destined for the different mobiles.
  • Orthogonal spreading sequences are used for different mobiles to avoid intra-cell interference.
  • the orthogonality is, in practice, disturbed by having to use channels plagued by multi-path effects.
  • channel-equalizing terminal receivers are being used for wideband code-division multiple-access (WCDMA) downlinks.
  • the channel equalizers provide the multiple access interference (MAI) suppression needed to maintain adequate receiver performance with large numbers of active users.
  • Equalizers are now being universally employed in CDMA mobile receivers to compensate for multipath- effects.
  • Minimum mean square error (MMSE) focused equalizers focus on both suppressing noise and interference at the same time, and so they perform better than signal-to-noise ratio (SNR) maximization- oriented RAKE receivers.
  • SNR signal-to-noise ratio
  • the RAKE receiver uses a filter matched to the spreading operations, pulse shape filtering and channel filtering.
  • SINR signal-to-interference-plus-noise ratio
  • Pilot-aided equalizer designs for CDMA systems are more complex than for global system for mobile communications (GSM) and other time-division multiple access (TDMA) systems.
  • TDMA systems have a common pilot signal which is time-multiplexed with the payload data. User data cannot interfere with the pilot signals. Only additive white Gaussian noise (AWGN) interferes.
  • AWGN additive white Gaussian noise
  • the primary common pilot channel (PCPICH) data is code-multiplexed with all the other existing user and control channels. So they are also subject to the same interferences, it cannot be used for equalizer weight training at the chip rate. Some considered despreading the received signal with the pilot tone's channelization code, to suppress most of the interference over the PCPICH signal. Others extended this to fractionally spaced implementations. A basic schematic of this "conventional" scheme is shown in Fig. 3, and is quite effective. The long despreading operation adapts only once every 256-chips, e.g., one PCPICH period. This technique is slow to converge and track the ever-changing channels.
  • OVSF code generator blocks generate OVSF code from a set of orthogonal codes. Such are primarily used to preserve the orthogonality between different channels in a communication system.
  • CN is only defined for N a power of 2. It follows by induction that the rows of CN are orthogonal.
  • the OVSF codes can also be defined recursively by a tree structure, as shown in Figs. 1 and 2.
  • [C] is a code length 2r at depth r in the tree, where the root has depth 0, the two branches leading out of C are labeled by the sequences [C, C] and [C, -C], which have length 2r+l .
  • Two OVSF codes are orthogonal if and only if neither code lies on the path from the other code to the root. Since codes assigned to different users in the same cell must be orthogonal, this restricts the number of available codes for a given cell. If a code C4, 1 in a tree is assigned to a user, the codes C1,0, C2,0, C8,2, C8,3, and so on, cannot be assigned to any other user in the same cell.
  • Fig. 3 is typical of a conventional pilot-aided symbol level LMS module 300 for equalization. Such includes a tap delay line 302, a descrambler and despreader 304 with the PCPICH channelization code
  • Adaptive filter is the conventional NLMS algorithm that trains via xn, yn and "d".
  • Fig. 3 shows a T-spaced implementation, wherein a fractionally spaced scheme is well- known to artisans.
  • a method for equalization in a code-division multiple access radio receiver adapts a pilot-aided equalizer more than once every primary common pilot channel (PCPICH) symbol period for tracking fast time-varying channels. It then uses partial-despreading over a PCPICH period with a parent code to obtain a plurality of consecutive y-filter outputs during each PCPICH period, wherein an interference subspace region may also include active codes.
  • PCPICH primary common pilot channel
  • An advantage of the present invention is a receiver is provided which avoids most of the interference generated due to the existence of PCCPCH, and other child codes, and enables training the equalizer weights at higher rates.
  • OVSF orthogonal variable spreading factor
  • a still further advantage of the present invention is a receiver is provided for WCDMA systems, and more particularly to improving high speed downline packet access (HSDPA) service quality with decision directed NLMS equalizers in receivers with OVSF multi-access codes and FDD downlinks.
  • HSDPA high speed downline packet access
  • FIG. 1 is a diagram representing an OVSF code hierarch tree
  • FIG. 2 is a diagram representing a OVSF subtree rooted from Cch,16,0 branch;
  • LMS symbol level least mean squares
  • WCDMA wideband code-division multiple access
  • FIG. 4 is a diagram representing a decision directed pseudo-symbol level LMS data filtering and symbol estimation module embodiment of the present invention
  • FIG. 5 is a diagram representing a decision directed pseudo-symbol level LMS filter adaptation module embodiment of the present invention
  • Fig. 4 represents a decision directed pseudo-symbol level LMS data filtering and symbol estimation module embodiment of the present invention, and is referred to herein by the general reference numeral 400. Such is useful in WCDMA receivers.
  • Module 400 does a partial-despreading instead of the full despreading over the PCPICH.
  • the parent code of Cch, 16,0 is used to obtain sixteen consecutive y- filter outputs during each 256-chip long PCPICH period.
  • de-spreading will not be restricted to only the PCPICH.
  • the PCCPCH, and all the other active child codes of the parent code Cch, 16,0 will also de-spread, as represented in Fig. 2.
  • the code subspace shown by interference subspace region 202 might contain the possible active codes. Mathematically, the de-spread signal will be:
  • PCPICH _ partial
  • PCCPCH _ partial
  • n . sum of interference plus noise due to multipath, intercell interference and thermal noise.
  • Embodiments of the present invention re-characterize - and 1 . Instead of being interfering signals "n”, these become desired signals "d". This transformation is done by finding the
  • An algorithmic process is run on consecutive packets of data each relevant to one CPICH transmitted symbol.
  • a processing window of 256-chips is moved like a sliding window for the next packet processing.
  • Adapted filter weights from the previous packet are used for data filtering.
  • the filter weights from the conventional RAKE receiver are used for the initial packet filter weight assignments.
  • a received chip rate signal (rn) is passed through a FIR filter 402 whose weights are obtained in the previous PCPICH symbol period.
  • a mixer 404 and correlator 406 are used to descramble and despread with the sixteen child codes of Cch, 16,0 at level 256, e.g., ⁇ Cch,256,0,
  • a first correlator output corresponds to a PCPICH linear symbol estimate
  • a second correlator output is a PCCPCH symbol estimate 2 (appears at the 9th place in the FWHT output which is just an output order difference)
  • the remaining are the pseudo-symbol estimates represented from any active code in the interference subspace 202.
  • a serial to parallel converter (S/P) 408 follows.
  • a hard decision block 414 uses a linear PCCPCH symbol estimate 2 to obtain a refined estimate
  • Each of the remaining codes estimate the received powers as ⁇ ⁇ and a linear minimum mean square error (LMMSE) weighting module 418 outputs + ⁇ )
  • a filter adaptation module 500 includes a FWHT 502, a parallel-to-serial converter
  • the final estimates e.g., ⁇ Sl , * 2 , S ⁇ , (Fig. 4) are connected to the corresponding FWHT 502 input ports, where they are re-spread to level sixteen. Such produces sixteen consecutive desired-signal estimates d in each PCPICH symbol period. These sixteen values are used to adapt the NLMS equalizer weights sixteen times in the same packet interval.
  • Final equalizer weights are
  • Equalizer method embodiments of the present invention can be implemented in both software and hardware. In both cases, an input buffering of at least 256-chips is necessary, and the total processing of the two stages 400 and 500 must be completed in one PCPICH symbol period. Therefore, chip- level processing should progress at least twice the chip rate.
  • Higher spreading factors such as 32, 64, or 128, e.g., despreading with Cch,32,0, Cch,64,0 or Cch, 128,0, would be more suitable for low SNR and low speed conditions.
  • lower spreading factors such as 2,4,8 would be more suitable for high SNR and high speed conditions.
  • Window sizes smaller than 256-chips can be used in high speed packet data access (HSDPA) service.
  • HSDPA packet data access
  • Knowing the codes can help improve making reliable symbol estimates via hard decisions. It may be appropriate not to exploit the code space under parent code Cch, 16,0. For example, if there are eight existing HSDPA codes occupying codes ⁇ Cch,16,8, Cch,16,9, Cch,16, 10, Cch, 16,l 1, Cch,16,12,
  • the window size can be set to sixteen
  • the window size in such a scheme will be much less than 256, in this case two, it will be much more robust than the original scheme for highly varying channel conditions because the filter weight latency is only 2-chips for the next window.
  • the window size is set to sixteen
  • the hard decision values are fed to a FWHT-4 input.
  • the desired signal "d" is output every four chips.
  • the corresponding SF for the adaptive filtering part in Fig. 3 will be four, and the despreading code will be Cch,4, l .
  • a third example uses three existing HSDPA codes, ⁇ Cch, 16,4, Cch, 16,5, Cch,16,6 ⁇ .
  • the fourth code in the previous example, Cch,16,7, is not used to carry HSDPA service. With this single difference, LMMSE weighting over the soft estimate of Cch, 16,7 can be employed.
  • An alternative embodiment of the present invention for HSDPA service uses the PCPICH and PCCPCH aided scheme described by Figs. 4 and 5, and switches to the HSDPA codes aided schemes once a certain equalization quality level is achieved.
  • DD-NLMS and other schemes can be jumped between, depending on the knowledge of codes, the energy over the code domain, Ior/Ioc values, mobile speed, etc.
  • a method for equalization in a code-division multiple access radio receiver comprising:
  • PCPICH primary common pilot channel
  • PCCPCH primary common control physical channel

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

Abstract

Un procédé d'égalisation dans un récepteur radio d'accès multiple par répartition en code adapte un égaliseur assisté par pilote plus d'une fois lors de chaque période de canal pilote commun primaire (PCPICH) pour suivre des canaux à variation temporelle rapide. Il utilise ensuite le désétalement partiel sur une période PCPICH avec un code parent afin d'obtenir une pluralité de sorties de filtre y consécutifves pendant chaque période PCPICH, une région de sous-espace de brouillage pouvant également comprendre des codes actifs.
PCT/US2007/073401 2006-07-12 2007-07-12 Égaliseur nlms dirigé par décision par désétalement avec un code parent d'un groupe de codes actifs WO2013172808A1 (fr)

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US60/830,626 2006-07-12

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015126055A3 (fr) * 2014-12-31 2015-11-26 상명대학교 천안산학협력단 Procédé d'analyse récursive pour une transformée de walsh-hadamard
CN110213184A (zh) * 2019-06-03 2019-09-06 北京理工大学 一种基于修正代价函数的自适应信道盲均衡方法

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US20040127164A1 (en) * 2002-12-20 2004-07-01 Texas Instruments Incorporated Reconfigurable chip level equalizer architecture
WO2005039068A1 (fr) * 2003-10-17 2005-04-28 Qualcomm Incorporated Demodulation de donnees destinee a un systeme de communication cdma
FR2868639A1 (fr) * 2004-04-06 2005-10-07 Wavecom Sa Procede de determination de codes d'etalement utilises dans un signal cdma et dispositif de communication correspondant
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US6680902B1 (en) * 2000-01-20 2004-01-20 Nortel Networks Limited Spreading code selection process for equalization in CDMA communications systems
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US20040127164A1 (en) * 2002-12-20 2004-07-01 Texas Instruments Incorporated Reconfigurable chip level equalizer architecture
WO2005039068A1 (fr) * 2003-10-17 2005-04-28 Qualcomm Incorporated Demodulation de donnees destinee a un systeme de communication cdma
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015126055A3 (fr) * 2014-12-31 2015-11-26 상명대학교 천안산학협력단 Procédé d'analyse récursive pour une transformée de walsh-hadamard
CN110213184A (zh) * 2019-06-03 2019-09-06 北京理工大学 一种基于修正代价函数的自适应信道盲均衡方法

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