EP1316158A2 - Procede et appareil permettant de fournir un signal de reference de donnees pilote multiplexees par repartition dans le temps - Google Patents

Procede et appareil permettant de fournir un signal de reference de donnees pilote multiplexees par repartition dans le temps

Info

Publication number
EP1316158A2
EP1316158A2 EP01968250A EP01968250A EP1316158A2 EP 1316158 A2 EP1316158 A2 EP 1316158A2 EP 01968250 A EP01968250 A EP 01968250A EP 01968250 A EP01968250 A EP 01968250A EP 1316158 A2 EP1316158 A2 EP 1316158A2
Authority
EP
European Patent Office
Prior art keywords
symbols
pilot
reference signal
pilot symbols
data
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP01968250A
Other languages
German (de)
English (en)
Inventor
Jeremy H. Lin
Avneesh Agrawal
Daisuke Terasawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Qualcomm Inc
Original Assignee
Qualcomm Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Qualcomm Inc filed Critical Qualcomm Inc
Publication of EP1316158A2 publication Critical patent/EP1316158A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • 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
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H04B1/70751—Synchronisation aspects with code phase acquisition using partial detection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/70701—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation featuring pilot assisted reception
    • 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
    • H04B2201/70702—Intercell-related aspects
    • 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
    • H04B2201/70707—Efficiency-related aspects

Definitions

  • the present invention relates to data communication. More particularly, the present invention relates to a novel and improved method and apparatus for providing a reference signal from time division multiplexed (TDM) pilot data.
  • TDM time division multiplexed
  • CDMA code division multiple access
  • a CDMA system is typically designed to conform to one or more standards.
  • One such first generation standard is the "TIA/EIA/IS-95 Terminal- Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System," hereinafter referred to as the IS-95 standard and incorporated herein by reference.
  • IS-95 compliant CDMA systems are able to transmit voice data and (albeit not efficiently) packet data.
  • a newer generation standard that can more efficiently transmit packet data is offered by a consortium named "3 rd Generation Partnership Project" (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214, which are readily available to the public.
  • the 3GPP standard is hereinafter referred to as the W-CDMA standard and incorporated herein by reference.
  • the W-CDMA standard defines a channel structure capable of supporting a number of users and designed for efficient transmission of packet data.
  • a user at a terminal is typically assigned a "dedicated" channel on the downlink and the uplink for the duration of the call.
  • the downlink refers to transmission from the base station to the terminal
  • the uplink refers to transmission from the terminal to the base station.
  • the dedicated channel can be used for voice communication and may also be used for transmission of packet data.
  • the dedicated channel has a time division multiplexed (TDM) structure in which a data transmission is partitioned into radio frames, with each radio frame having a duration of 10 msec and including 15 slots.
  • TDM time division multiplexed
  • Each slot is further partitioned into a number of fields used to carry packet data and other information. For example, one field in each slot is used for pilot data associated with the particular dedicated channel, one or more fields in each slot are used for packet data, and other field(s) may be used for signaling information.
  • the packet, signaling, and pilot data is used to modulate an inphase and quadrature carrier signals.
  • the time-multiplexed pilot data is processed and used to generate a "reference" signal having phase and amplitude that approximate that of the received (quadrature) carrier signals.
  • the reference signal is then used to coherently demodulate the received signal to recover the packet and signaling data.
  • the pilot data is only available for a fraction of each slot, and the reference signal is estimated for the time periods in which pilot data is not present.
  • the reference signal is typically generated at the receiver using pilot data that periodically appears for a short period of time.
  • the accuracy of the generated reference signal directly impacts the performance of the demodulation process, which in turn determines the performance of the communication system.
  • the demodulation can be performed in real-time, thereby reducing or eliminating the need to temporarily store the received data.
  • the present invention provides techniques to generate reference signals representative of future estimates (i.e., predictions) of the phase and amplitude of the carrier signals used to generate a modulated signal in the communication system.
  • Each reference signal is generated based on currently available pilot data (e.g., from prior slots).
  • An aspect of the invention provides a method for generating a reference signal based on time-multiplexed pilot data.
  • a modulated signal is received and processed to provide received samples, which are then further processed to provide pilot symbols.
  • a reference signal is generated based on the available pilot symbols.
  • the reference signal comprises a sequence of "predicted" pilot symbols representative of future estimates of one or more characteristics (e.g., the phase and amplitude) of one or more carrier signals used to generate the modulated signal.
  • the reference signal can be generated using a number of techniques. For example, the reference signal can be generated by (e.g., linearly) extrapolating pilot symbols from prior slots, curve fitting the pilot symbols, (normal or ensemble) averaging the (unweighted or weighted) pilot symbols, or some other technique.
  • the receiver unit includes a receiver and at least one demodulator element.
  • the receiver receives and processes a modulated signal, and provides received samples indicative of the data transmitted on the physical' channel.
  • Each demodulator element includes a data processing unit and a pilot processing unit.
  • the data processing unit processes the received samples to provide channelized symbols.
  • the pilot processing unit processes the channelized symbols to provide pilot symbols, and also generates a reference signal based on the available pilot symbols.
  • the reference signal comprises a sequence of predicted pilot symbols representative of future estimates of one or more characteristics (e.g., phase and amplitude) of one or more carrier signals used to generate the modulated signal.
  • the reference signal can be generated based on the available pilot symbols and using extrapolating, curve fitting, averaging, weighted averaging, or ensemble averaging, or other techniques.
  • FIG. 1 is a diagram of a spread spectrum communication system that supports a number of users
  • FIG. 2 is a simplified block diagram of an embodiment of the signal processing for a downlink physical channel
  • FIG. 3 is a block diagram of a modulator, a transmitter, and antennas that support transmission of the downlink physical channel over one or two antennas;
  • FIG. 4A is a diagram of a frame format and a slot format for the dedicated physical channel as defined by the W-CDMA standard;
  • FIG. 4B is a diagram of a portion of a particular data transmission on the dedicated physical channel
  • FIGS. 5A through 5E are diagram respectively illustrating the use of interpolation, extrapolation, curve fitting, weighted averaging, and ensemble averaging to generate a reference signal;
  • FIG. 6 is a block diagram of an embodiment of a portion of a receiver unit that can be used to receive and demodulate a physical channel
  • FIG. 7 is a block diagram of an embodiment of a finger element that can be used to implement one finger element of a rake receiver shown in FIG. 6.
  • FIG. 1 is a diagram of a spread spectrum communication system 100 that supports a number of users.
  • System 100 provides communication for a number of cells 102a through 102g, with each cell 102 being serviced by a corresponding base station 104.
  • Various terminals 106 are dispersed throughout the system. In an embodiment, each terminal 106 communicates with one or more base stations 104 on the downlink and uplink at any given moment, depending on whether the terminal is in soft handoff.
  • System 100 may be designed to support one or more CDMA standards, such as the IS-95 standard, the W- CDMA standard, other standards, or a combination thereof.
  • base station 104a transmits data to terminals 106a and 106j on the downlink
  • base station 104b transmits data to terminals 106b and 106j
  • base station 104c transmits data to terminal 106c, and so on.
  • the solid line with the arrow indicates a transmission from the base station to the terminal.
  • a broken line with the arrow indicates that the terminal is receiving the pilot signal, but no user-specific data transmission, from the base station.
  • the uplink communication is not shown in FIG. 1 for simplicity.
  • a terminal can receive multiple transmissions from multiple antennas of a single base station for certain physical channel types such as the downlink dedicated physical channel (DPCH).
  • DPCH downlink dedicated physical channel
  • terminal 106a receives multiple transmissions from base station 104a
  • terminal 106d receives multiple transmissions from base station 104d
  • terminal 106f receives multiple transmissions from base station 104f .
  • FIG. 2 is a simplified block diagram of an embodiment of the signal processing for a downlink physical channel.
  • data is sent, typically in packets, from a data source 212 to an encoder 214.
  • Encoder 214 performs a number of functions, depending on the particular CDMA system or standard being implemented. Such encoding functions typically include formatting each data packet with the necessary control fields, cyclic redundancy check (CRC) bits, and code tail bits.
  • Encoder 214 then encodes one or more formatted packets with a particular coding scheme, performs rate matching of the encoded packet (e.g., by repeating or puncturing the symbols), and interleaves (or reorders) the symbols within the packets.
  • CRC cyclic redundancy check
  • the interleaved data is then segmented into radio frames, further segmented into physical channel, interleaved, and then mapped to one or more physical channels.
  • the processing performed for a downlink physical channel is described in further detail in the W-CDMA standard (e.g., Document No. 3G TS 25-212) and the processing performed for a forward link traffic channel is described in further detail in the IS-95 standard.
  • the channel data designated for each physical channel conforms to a particular frame format defined for that physical channel.
  • the channel data for the dedicated physical channel in the W-CDMA standard includes packet data, signaling data, and pilot data, or a combination thereof, and the frame format for the dedicated physical channel is described in further detail below.
  • the channel data for each physical channel is provided to a modulator (MOD) 216 and may be scrambled with a scrambling sequence (for the IS-95 CDMA system), covered with a channelization code, and spread with spreading codes (e.g., the PN codes).
  • the spreading with the spreading codes is referred to as "scrambing" by the W-CDMA standard.
  • the channelization code can be an orthogonal variable spreading factor (ONSF) code (for the W- CDMA system), a Walsh code (for the IS-95 CDMA system), or some other orthogonal code, again depending on the particular CDMA system or standard being implemented.
  • the spread data is then provided to a transmitter (TMTR) 218 and quadrature modulated, filtered, and amplified to generate one or more downlink signals.
  • the downlink signal(s) are transmitted over the air from one or more antennas 220.
  • the downlink processing is described in further detail in the IS-95 and W-CDMA standards.
  • the downlink signal(s) are received by an antenna 230 and routed to a receiver (RCNR) 232.
  • Receiver 232 filters, amplifies, (quadrature) demodulates, samples, and quantizes the received signal.
  • the digitized samples are then provided to a demodulator (DEMOD) 234 and despreaded (or descrambled) with despreading codes and, for each physical channel being processed, channelized with a channelization code.
  • the despread samples are descrambled with a descrambling code after the channelization.
  • the dispreading, descrambling, and channelization codes used at the receiver unit correspond to the codes used at the transmitter unit.
  • the demodulated data is, then provided to a decoder 236 that performs the inverse of the functions performed at encoder 214 (e.g., the de-interleaving, decoding, and CRC check functions).
  • the decoded data is provided to a data sink 238.
  • a controller 240 can direct the operation of demodulator 234 and decoder 236.
  • a memory unit 242 couples to demodulator 234 (and possibly also to controller 240, as indicated by the dashed line) and, in certain modes of operation, can be used to store intermediate results, or data, from demodulator 234.
  • the hardware supports transmissions of packet data, messaging, voice, video, and other types of communication on the downlink.
  • a bi-directional communication system also supports uplink transmission from the terminal to the base station.
  • the uplink processing is not shown in FIG. 2 for simplicity.
  • FIG. 3 is a block diagram of a modulator 300, a transmitter 302, and antennas 304 that support transmission of a physical channel over one or two antennas on the downlink.
  • the processing units shown in FIG. 3 can be used to support the "no Transmit Diversity" mode defined by the W-CDMA standard in which data transmission occurs over one antenna and the "Transmit Diversity” mode in which data transmission occurs over two antennas.
  • the Transmit Diversity mode is also referred to as the "space time block coding transmit antenna diversity" (STTD) mode in the W-CDMA standard.
  • STTD space time block coding transmit antenna diversity
  • the data for the physical channel (i.e., the channel data) is provided to a STTD encoder 310 that generates STTD encoded data for each of the antennas used to transmit the channel data.
  • the operation of STTD encoder 310 is described in further detail in U.S. Patent Application Serial No. 09/655,609, entitled “METHOD AND APPARATUS FOR PROCESSING A PHYSICAL CHANNEL WITH PARTIAL TRANSPORT FORMAT INFORMATION,” filed on the same date herewith and assigned to the assignee of the present invention and incorporated herein by reference.
  • the STTD encoded data for each antenna is provided to a respective channelizer 320 that "covers" the data with a channelization code assigned to the physical channel to generate "channelized” data.
  • the same channelization code is used for both antennas in the STTD mode.
  • the STTD encoded data is provided to an I/Q demultiplexer (DEMUX) 322 that demultiplexes the data into inphase (I) and quadrature (Q) data.
  • the I data and Q data are provided to respective multipliers 324a and 324b and covered (i.e., multiplied) with the channelization code, C d , assigned to the physical channel.
  • Multipliers 324a and 324b perform covering using the channelization code in similar manner as the covering performed with Walsh code in the IS-95 CDMA system. Channelization is described in further detail in the IS-95 and W-CDMA standards and in the aforementioned U.S.
  • Patent Application Serial No. 09/655,609 filed on the same date herewith For the IS-95 CDMA system, Walsh codes having a fixed length of 64 chips are used to cover the traffic channels, with each traffic channel having a variable but limited data rate (e.g., ⁇ 32 Kbps). For the W-CDMA system, OVSF codes having a variable length are used to cover the traffic channels. The length of the OVSF code varies from 4 to 512 chips and is dependent on the data rate of the physical channel. OVSF codes are described in further detail in the W-CDMA standard and the aforementioned U.S. Patent Application Serial No. 09/655,609 filed on the same date herewith.
  • the covered Q data from multiplier 324b is provided to a multiplier 326 and multiplied with the complex symbol, j, to generate the imaginary part of the channelized data.
  • the real part from multiplier 324a and the imaginary part from multiplier 326 are combined by an adder 328 to provide the complex channelized data.
  • the channelized data for each antenna is then scrambled (i.e., spread) with a complex scrambling code, PN, by a multiplier 328 and scaled with a weight factor, G, by a multiplier 330.
  • the weight factor, G is used to adjust the transmit power of the physical channel.
  • the scrambled and weighted data from multiplier 332b comprises the processed data for the physical channel.
  • the processed channel data for each antenna is provided to a respective combiner 334 that also receives the processed data for other physical channels to be transmitted from that antenna.
  • Each combiner 334 combines the processed channel data received for the physical channels and generates output data for the associated antenna.
  • the composite data for each antenna is further multiplied with a complex weight factor, W, by a multiplier 336.
  • W complex weight factor
  • the weight factor is used for phase adjustment in closed loop mode 1 and for phase /amplitude adjustment in closed loop mode 2.
  • Closed loop modes 1 and 2 are two operating modes of the STTD mode.
  • each multiplier 336 is provided to a respective transmitter 302 that converts the data into an RF modulated signal, which is then transmitted from a respective antenna 304.
  • FIG. 4A is a diagram of a frame format and a slot format for the dedicated physical channel as defined by the W-CDMA standard.
  • a different frame format is defined by the W-CDMA standard for each type of physical channel such as the downlink dedicated channel (DPCH), the downlink shared channel (DSCH), and so on.
  • the data to be transmitted on each physical channel is partitioned into radio frames, with each radio frame including 15 slots labeled as slot 0 through slot 14.
  • Each slot is further partitioned into one or more fields used to carry packet, signaling, and pilot data, or a combination thereof.
  • a slot 410 includes a first data (Datal) field 420a, a second data (Data2) field 420b, a transmit power control (TPC) field 422, a transport format combination indicator (TFCI) field 424, and a pilot field 426.
  • Data fields 420a and 420b are used to send packet data for the dedicated physical channel.
  • Transmit power control field 422 is used to send power control information to direct the receiver unit to adjusts its transmit power on the uplink either up or down to achieve the desired performance while minimizing interference.
  • Transport format combination indicator field 424 is used to send information indicative of the format (e.g., the bit rate, channelization code, and so on) of a shared physical channel associated with the dedicated physical channel.
  • Pilot field 426 is used to send pilot data for the dedicated physical channel.
  • each dedicated physical channel is associated with its own pilot information.
  • the dedicated pilot supports beam forming to provide improved directivity for data transmissions, which improves performance and reduces interference.
  • the phase of a modulated signal can (and typically does) vary from one beam-formed signal to another.
  • each dedicated physical channel is provided with its own pilot.
  • the pilot data for each slot comprises a particular symbol pattern (i.e., a defined sequence of complex symbols).
  • the pilot data is used to modulate the inphase and quadrature carrier signals. Because the pilot data is of a known pattern, the receiver unit can process the received signal, recover the pilot data, and estimate the phase and amplitude of the received carrier signals.
  • the pilot data can thus be used to generate a "reference" signal at the receiver unit, which is then used to coherently demodulate the packet and signaling data transmitted on the dedicated physical channel.
  • the reference signal can also be used to coherently demodulate other physical channels such as the shared physical channel.
  • Table 2 lists the pilot symbol patterns defined by the W-CDMA standard for the no diversity antenna.
  • the pilot field can have one of four different lengths ranging from 2 bits to 16 bits.
  • a different pilot symbol pattern is used for each of the 15 slots of a particular radio frame.
  • four sets of 15 pilot symbols patterns are defined and are shown in Table 2.
  • Each pilot symbol pattern includes 1, 2, 4, or 8 complex symbols used to modulate the inphase and quadrature carrier signals at the transmitter.
  • the W-CDMA standard defines two STTD operating modes.
  • the closed loop mode 1 orthogonal pilot symbol patterns are used for the two transmit antennas.
  • the pilot symbol patterns shown in Table 2 are used for the first (non-diversity) antenna and the pilot symbol patterns shown in Table 3 are used for the second (diversity) antenna.
  • the pilot symbol patterns shown in Table 2 are used for both antennas.
  • pairs of data bits in the Datal, TPC, TFCI, Data2, and Pilot fields are grouped into complex symbols that are then used to modulate the inphase and quadrature carrier signals.
  • the receiver unit can process the pilot data and determine the phase and amplitude of the received carrier signals during the time interval in which pilot data is valid.
  • the pilot data is time multiplexed and not available during the transmission of the packet and signaling data. However, the phase and amplitude of the carrier signals are needed at these times to coherently demodulate the data in the Datal, Data2, TPC, and TFCI fields.
  • FIG. 4B is a diagram of a portion of a particular data transmission on the dedicated physical channel. A number of slots are shown, with each slot including a combination of data fields 420a and 420b, TPC field 422, TFCI field 424, and pilot field 426. Pilot data is transmitted at the end of each slot, as designed by pilot fields 426a through 426e in FIG. 4B. The pilot data in pilot fields 426 are used to generate a reference signal that is then used to demodulate the packet and signaling data transmitted between the pilot fields.
  • a number of methods can be used to coherently demodulate packet and signaling data that is time multiplexed with pilot data.
  • the packet and signaling data for the current slot (z) is temporarily stored until the pilot data P(i) for the current slot (which is transmitted at the end of the slot in the W-CDMA system) is received and processed (with old pilot data) to generate the reference signal.
  • the packet and signaling data for the current slot is then retrieved and demodulated using the generated reference signal.
  • the pilot data P( ⁇ ) at the end of the current slot (i) is used to generate "past" estimates of the phase and amplitude of the carrier signals, and the data needs to be temporarily stored until the pilot data is received and processed.
  • the pilot data P(i - 1) at the end of the prior slot ( ⁇ -1) is processed (typically along with prior pilot data, e.g., P(i — 2) ) to generate the reference signal that is then used to demodulate the packet and signaling data transmitted in the current slot (i).
  • the pilot data in prior slots is used to generate "future" estimates of the phase and amplitude of the carrier signal.
  • FIG. 5A is a diagram illustrating the use of interpolation to generate the reference signal. Interpolation is used to generate "past" estimates of the phase and amplitude of the received carrier signals. Pilot data 510a and 510b is received at slots (i) and (z ' -l), respectively, and processed to generate the phase and amplitude of the reference signal for the time period between the received pilot data 510a and 510b (as represented by a dashed line 520). Packet and signaling data received between pilot data 510a and 510b is temporarily stored until pilot data 510a is received and processed. The stored data is then retrieved and demodulated with the generated reference signal. This method requires storage of one or more slots of packet and signaling data until pilot data 510a at the end of slot (i) is received and processed.
  • FIG. 5B is a diagram illustrating the use of extrapolation to generate the reference signal.
  • Extrapolation can be used to generate "future" estimates of the phase and amplitude of the received carrier signals.
  • Pilot data 510b and 510c is received at slots (z ' -l) and (z ' -2), respectively, and processed to generate the phase and amplitude of the reference signal (as represented by a dashed line 522) for the time period after pilot data 510b, e.g., between pilot data 510b at slot (z ' -l) and the pilot data at slot (i).
  • Packet and signaling data received after pilot data 510b can be demodulated approximately in real-time with the generated reference signal. This method can reduce or eliminate the storage requirement for packet and signaling data.
  • FIG. 5C is a diagram illustrating the use of curve fitting to generate the reference signal.
  • Curve fitting can be used to generate past and/ or future estimates of the phase and amplitude of the received carrier signals.
  • pilot data 510b, 510c, and 510d is received at slots (z ' -l), (z-2), and (z- 3), respectively, and processed using a curve fitting technique to generate the phase and amplitude of the reference signal (as represented by a dashed line 524) for the time period after pilot data 510b.
  • Such curve fitting technique may be a linear regression algorithm, a non-linear regression algorithm, or any curve fitting algorithm known in the art.
  • the linear regression algorithm minimizes the sum of the squares of the vertical distances between the received pilot data and a curve. Fewer or greater number of pilot data (i.e., ⁇ > three) can be used for the curve fitting. Packet and signaling data after pilot data 510b can be demodulated approximately at real-time with the generated reference signal.
  • FIG. 5D is a diagram illustrating the use of weighted averaging to generate the reference signal. Weighted averaging can be used by itself or in combination with one or more other techniques to generate past and/or future estimates of the phase and amplitude of the received carrier signals.
  • Pilot data 510b, 510c, and 510d is received at slots (z ' -l), (z ' -2), and (z ' -3), respectively, and weighted with a set of weighting factors D., D 2 , and D 3 , respectively, to generate the phase and amplitude of the reference signal (as represented by a dashed line 526) for the time period after pilot data 510b.
  • the weighting factors may be selected to weigh recent pilot data more heavily and to give less weight to older pilot data.
  • the pilot data may be exponentially weighted such that pilot data 510b, 510c, and 510d at slots (z ' -l), (z ' -2), and (z-3) are weighted by weighting factors of 0.5, 0.25, and 0.125, respectively.
  • Extrapolation, curve fitting, or other averaging technique can then be used to generate the reference signal based on the weighted pilot data.
  • Packet and signaling data after pilot data 510b can be demodulated approximately in real-time with the generated reference signal.
  • FIG. 5E is a diagram illustrating the use of ensemble averaging to generate the reference signal.
  • Ensemble averaging can also be used by itself or in combination with one or more other techniques to generate past and /or future estimates of the phase and amplitude of the received carrier signals.
  • pilot data 510b, 510c, 510d, and 510e are received at slots (z- 1), (z ' -2), (z ' -3), and (z ' -4), respectively, and used to generate a line (or curve) 530 that best fit the received pilot data (e.g., a line or curve that minimizes the sum of the squares of the vertical distances between the pilot data and the line or curve).
  • the reference signal can then be generated based on line (or curve) 530.
  • the reference signal can be represented with a line 532 having the same slope as line 530 and starting from pilot data 510b (as shown in FIG. 5E), or continuing from the end of line 530, or connected to some other point. Similar to FIG. 5D, the pilot data can be weighted to give greater weight to recent pilot data and less weight to older pilot data.
  • FIGS. 5B through 5E show some techniques that can be used to generate the reference signal comprising future estimates (i.e., "predictions") of the phase and amplitude of the received carrier signals. Other techniques can also be used to generate future estimates of the phase and amplitude and are within the scope of the present invention.
  • the phase and amplitude of the reference signal can be defined with a (complex) polynomial.
  • a first order polynomial can be used for linear interpolation and linear extrapolation.
  • the first order polynomial for the reference signal, P(i, j) can be expressed as:
  • P(i, j) ( (0 • j + a ⁇ (0 / E q (!)
  • a (i) and a 0 ( ⁇ ) are the coefficients for the polynomial and are applicable for slot z, the index ;
  • ' is the time unit (e.g., in symbol periods, as described below) within slot z
  • P(i, j) is a complex sequence that represents the phase and amplitude of the reference signal at time unit / of slot i.
  • the coefficients a.( ⁇ ) and a 0 (i) are typically recomputed as new pilot data is received, but may be reused (e.g., extrapolated to the new slot) if the received pilot data is degraded (or not available).
  • the reference signal comprises a sequence of complex "reference symbols", one reference symbol for each symbol time.
  • Each reference symbol identifies the instantaneous phase and amplitude of the reference signal at the particular symbol time.
  • each slot includes a particular number of bits, with the number being dependent on the bit rate of the slot. A pair of bits is grouped to form a complex symbol, and the number of symbols in each slot is thus half the number of bits.
  • a reference symbol indicative of the instantaneous phase and amplitude of the reference signal at symbol time ; ' is used to demodulate one or more symbols received for one or more physical channels at symbol time ; ' .
  • the number of reference symbols generated for each slot is dependent on the particular slot format, and ranges from five symbols (for 15 Kbps) up to 640 symbols (for 1920 Kbps).
  • the index thus ranges from (0, 1, ... 4) for the lowest bit rate of 15 Kbps, up to (0, 1, ... 639) for the highest bit rate of 1920 Kbps.
  • equation (1) For linear extrapolation, the coefficients for equation (1) can be expressed as:
  • FIG. 6 is a block diagram of an embodiment of a portion of a receiver unit 600 that can be used to receive and demodulate a physical channel, including one transmitted from multiple transmit antennas in the STTD mode defined by the W-CDMA standard.
  • One or more RF modulated signals from one or more transmit antennas are received by an antenna 610 and provided to a receiver (RCVR) 612 that conditions (e.g., amplifies, filters, and so on) the received signal and quadrature downconverts the conditioned signal to an intermediate frequency (IF) or baseband.
  • Receiver 612 also samples and quantizes the downconverted inphase and quadrature signals to generate received samples that are provided to a rake receiver 620.
  • a rake receiver is shown in FIG. 6 for processing the physical channel, other receiver structures and implementations can also be used and are within the scope of the present invention.
  • the received signal is sampled at a sample rate, f s , that is higher than the chip rate, f c , of the received signal.
  • the higher sample rate allows for fine adjustment of the timing to "zoom in" on a path position.
  • rake receiver 620 includes a searcher element 622 and a number of finger elements 630a through 630n. Each of these elements receives the samples from receiver 612 and performs the tasks associated with the element or as directed by a controller 640.
  • searcher element 622 may be instructed by controller 640 (or assigned) to search for strong instances of the received signal.
  • the strong signals may be present at different time offsets, and can be identified by searcher element 622 by processing the samples with different parameters (e.g., different PN codes, different time offsets, and so on).
  • Searcher 622 may be designed to provide data corresponding to the searched signal or an indication of the search result to controller 640.
  • Controller 640 assigns finger elements 630 to demodulate the strongest instances of the received signal, as determined with the assistance of searcher element 622.
  • Each assigned finger element 630 performs demodulation of one physical channel for one instance of the received signal (i.e., a signal at a particular assigned time offset), as directed by controller 640.
  • Each assigned finger element 630 provides recovered symbols (e.g., S A ) corresponding to the assigned instance of the received signal. The demodulation to generate the recovered symbols is described in further detail below.
  • the recovered symbols from all assigned finger elements 630 e.g., S A , S B , ... S N
  • the combined symbols represent the recovered channel data, and are provided to the subsequent processing block (e.g., the decoder).
  • each finger element can also include a lock detector that computes a quality indicator (e.g., an average energy) of the recovered symbols at the finger element and masks the recovered symbols from the finger element if the quality indicator does not exceed a particular threshold.
  • a quality indicator e.g., an average energy
  • FIG. 7 is a block diagram of an embodiment of a finger element 700 that can be used to implement one finger element 630 in FIG. 6.
  • the finger element is also referred to as a demodulation element.
  • the received samples from receiver 612 are provided to a multiplier 710 and descrambled with a complex descrambling code, PN, corresponding to the scrambling code used at the transmitter unit and having a time offset assigned to the finger element.
  • the descrambled samples include data for all physical channels in the received signal.
  • each physical channel is channelized with a respective channelization code (e.g., a particular Walsh code in the IS-95 CDMA system, or a particular OVSF code in the W-CDMA system) to generate data that is orthogonal to those of other physical channels.
  • a respective channelization code e.g., a particular Walsh code in the IS-95 CDMA system, or a particular OVSF code in the W-CDMA system
  • the descrambled samples are provided to a multiplier 712 and decovered (i.e., multiplied) with the channelization code, C d , assigned to the physical channel being processed.
  • the output from multiplier 712 is provided to an accumulator 714 and accumulated over the length of the channelization code, C d , to generate channelized symbols.
  • accumulator 714 accumulates the decovered samples from multiplier 712 over a 4-chip period to provide the channelized symbols.
  • accumulator 714 accumulates the decovered samples over a 512-chip period to provide the channelized symbols.
  • a "hypothesized" channelization code can be used to process the received samples to generate intermediate results (i.e., "channelized samples") that can be stored and, upon determination of the actual channelization code used for the physical channel, further processed provide the channelized symbols.
  • This partial processing of the physical channel is described in detail in the aforementioned U.S. Patent Application Serial No. 09/655,609filed on the same date herewith.
  • the channelized data from accumulator 714 include time-multiplexed packet, signaling, and pilot data.
  • orthogonal pilots are used for the two transmit antennas.
  • the orthogonal pilots for the two antennas are generated by using different pilot symbol patterns, W P1 and W P2 , defined in Table 2 and Table 3, respectively.
  • the pilot symbol patterns are removed by multiplying the channelized symbols with the same pilot symbol patterns, W P1 and W ⁇ , by multipliers 720a and 720b, respectively.
  • Each complex pilot symbol from each of multipliers 720a and 720b is indicative of the instantaneous phase and amplitude of the respective pilot at the particular symbol time.
  • the pilot symbols from multipliers 720a and 720b are then provided to respective pilot processors 722a and 722b.
  • Each pilot processor 722 receives the pilot symbols, P , for each slot and generates the reference signal, P , based on pilot symbols from previous slots.
  • the pilot field for a particular slot can vary from 2 bits (i.e., one symbol) to 16 bits (i.e., eight symbols).
  • each pilot processor 722 receives one to eight pilot symbols for each slot and can filter the pilot symbols for each slot to generate one or more filtered pilot symbols.
  • each pilot processor 722 can filter (e.g., average) the pilot symbols received in each slot to generate one filtered pilot symbol representative of the phase and amplitude of the pilot for that slot.
  • each pilot processor 722 may not performed any filtering of the pilot symbols.
  • Each pilot processor 722 further processes the filtered pilot to generate the reference signal, P .
  • pilot processor 722 can generate the reference signal, P(i, j), for the current slot (z) based on the pilot data, P(i - 1) and P(i - 2) , for the two immediately previous slots (z ' -l) and (z-2).
  • Each pilot processor 722 can also generate the reference signal using curve fitting, weighted averaging, ensemble averaging, or other techniques.
  • pilot data is transmitted in time-multiplexed time intervals separated by packet and signaling data.
  • the received pilot data is filtered and processed in the manner described above to generate one or more reference signals, P ⁇ and P 2 (depending on the operating mode), which are used to demodulate the packet and signaling data.
  • the pilot data may also be provided to a pilot detector (DET) 738 that provides an indication of the quality of the received pilot(s).
  • pilot detector 738 measures the power of the received pilot(s) and provides a pilot quality estimate, P Q .
  • the reference signals, P 1 and P 2 , from pilot processors 722a and 722b and the channelized symbols, X , from accumulator 714 are provided to a data recovery element 740 that performs the necessary computations to generate the recovered symbols for the finger element.
  • the data recovery processing is described below.
  • multipliers 720a and 720b and pilot processors 722a and 722b comprise a portion of the pilot processing unit of the finger element.
  • multipliers 720a and 720b and pilot processors 722a and 722b comprise a portion of the pilot processing unit of the finger element.
  • Multiplier 712 and accumulator 714 comprise a portion of the data processing unit of the finger element.
  • the reference signals are estimates of the carrier signals that are modulated by the data at the transmitter unit. Due to propagation delays and path loss, the amplitude and phase of the received modulated signal vary over time. These variations are also reflected in the pilot, and are detected and estimated by the reference signals. Thus, the reference signals are used to coherently demodulate the received signal.
  • the reference signal, P and the channelized symbols, X , (which are estimates of the "actual" received symbols, X ), can be expressed as:
  • the dot and cross products scale the channelized symbols, X , from a particular finger element by the relative strength of the pilot received by that finger, which is estimated by the reference signal, P .
  • the scaling is used to weigh the contributions from the assigned finger elements for efficient combining.
  • the dot product performs the dual role of both phase projection and finger weighting that are characteristics of a coherent rake receiver. Dot product computation is further described in the aforementioned U.S. Patent Nos. 5,764,687 and 5,490,165.
  • the physical channel being processed may be transmitted from one antenna or two antennas (e.g., for the STTD mode in the W-CDMA system).
  • the physical channel may be modulated using either BPSK modulation (e.g., for the IS-95 CDMA system) or QPSK modulation (e.g., for the W-CDMA system).
  • BPSK modulation e.g., used in the IS-95 CDMA system
  • the recovered symbols, S can thus be expressed as:
  • S A1 represents the symbol sequence ⁇ S 0 , S., S 2 , S 3 , ... ⁇ transmitted from the first transmit antenna and S ⁇ represents the symbol sequence ⁇ -S. * , S,, * , -S 3 * , S 2 * , ... ⁇ transmitted from the second transmit antenna.
  • the actual received signal, X is a weighted sum of the two RF modulated signals, and can be expressed as:
  • a and ⁇ are the path losses from the first and second transmit antennas, respectively, to the receive antenna
  • X is the received symbol sequence ⁇ X 0 , X j , X 2 , X 3 , ... ⁇ .
  • the received symbols can be expressed as:
  • X is a scaling factor
  • K 1/(
  • the scaling factor, K is used to scale the recovered symbols from various assigned fingers prior to combining the symbols such that more reliable symbols are weighted more heavily.
  • the processing units described herein can be implemented in various manners such as an application specific integrated circuit (ASIC), a digital signal processor, a microcontroller, a microprocessor, or other electronic circuits designed to perform the functions described herein.
  • ASIC application specific integrated circuit
  • the processing units can be implemented with a general-purpose or specially designed processor operated to execute instruction codes that achieve the functions described herein.
  • the processing units described herein can be implemented using hardware, software, or a combination thereof.
  • the memory unit can be implemented memory technologies including, for example, random access memory (RAM), Flash memory, and others.
  • RAM random access memory
  • Flash memory Flash memory
  • the memory unit can also be implemented with storage element such as, for example, a hard disk, a CD-ROM drive, and others.
  • storage element such as, for example, a hard disk, a CD-ROM drive, and others.
  • Various other implementation of the memory unit are possible and within the scope of the present invention.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

La présente invention concerne des techniques permettant de générer un signal de référence fondé sur des données pilote multiplexées par répartition dans le temps. Un signal modulé est reçu (fig. 7) et traité de façon à fournir des échantillons reçus, qui sont ensuite à nouveau traités de façon à fournir des symboles pilote. Un signal de référence est généré à partir des symboles (722a, 722b) pilotes disponibles. Ce signal de référence comprend une séquence de symboles pilote «prédits» représentatifs d'estimations futures d'une ou de plusieurs caractéristiques (par exemple la phase et l'amplitude) d'un ou de plusieurs signaux de porteuse utilisés pour générer le signal modulé (fig.5A, 5E). On peut générer ce signal de référence en utilisant un certain nombre de techniques. On peut, par exemple, générer ce signal de référence en extrapolant (linéairement par exemple) des symboles pilote à partir des intervalles de temps précédents (fig 5B), de courbe s'adaptant aux symboles pilote (fig. 5C) ou en établissant une moyenne (d'ensemble ou normale) (pondérée ou non) des symboles pilote (fig. 5D, 5E). Dans le cadre de la norme W-AMRC (W-CDMA), le traitement permettant de générer les symboles pilotes consiste habituellement à récupérer les échantillons reçus avec un code de bande indicatrice de direction de façon à fournir des symboles à canal réparti (720a, 720b), et à multiplier ces symboles à canal réparti avec un diagramme de symboles pilote particulier. Les symboles pilotes en provenance de chaque fenêtre peuvent aussi être filtrés de façon à générer un ou plusieurs symboles pilote.
EP01968250A 2000-09-06 2001-08-28 Procede et appareil permettant de fournir un signal de reference de donnees pilote multiplexees par repartition dans le temps Withdrawn EP1316158A2 (fr)

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US65561000A 2000-09-06 2000-09-06
US655610 2000-09-06
PCT/US2001/026947 WO2002021716A2 (fr) 2000-09-06 2001-08-28 Procede et appareil permettant de fournir un signal de reference de donnees pilote multiplexees par repartition dans le temps

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US8259852B2 (en) * 2006-07-19 2012-09-04 Broadcom Corporation Method and system for satellite communication
US8391253B2 (en) * 2008-11-20 2013-03-05 Telefonaktiebolaget L M Ericsson (Publ) Time-division multiplexed pilot signal for integrated mobile broadcasts
US7639726B1 (en) * 2009-03-20 2009-12-29 On-Ramp Wireless, Inc. Downlink communication
WO2010123301A2 (fr) * 2009-04-22 2010-10-28 엘지전자 주식회사 Procédé et appareil pour transmettre un signal de référence
CA2776454C (fr) * 2009-09-30 2016-07-05 Interdigital Patent Holdings, Inc. Procede et appareil d'emission multi-antenne de liaison montante

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US6556634B1 (en) * 1999-02-10 2003-04-29 Ericsson, Inc. Maximum likelihood rake receiver for use in a code division, multiple access wireless communication system

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CN1473399A (zh) 2004-02-04
CN1229921C (zh) 2005-11-30
WO2002021716A3 (fr) 2002-06-06

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