JP4546145B2 - Multi-carrier transmission system and multi-carrier transmission receiver - Google Patents

Description

  The present invention relates to a multicarrier transmission technique in which a pilot channel and a data channel are code division multiplexed, and more particularly, a multicarrier transmission system and a multicarrier transmission in which a pilot channel despreading method is changed according to a transmission path condition. The present invention relates to a receiving device.

  In wireless communication, reflected waves from various obstacles or the like may overlap to form a multiplex transmission path (multipath). Due to the difference in propagation delay of each transmission path, frequency selective fading in which the frequency characteristics in the transmission band are distorted and intersymbol interference in which adjacent signals (symbols) on the time axis interfere with each other cause deterioration in communication quality. Invite. As a countermeasure against such deterioration, a multi-carrier transmission system has attracted attention.

  In this multi-carrier transmission scheme, information is divided into a plurality of low-rate carriers (subcarriers) and transmitted. That is, in multicarrier transmission, one symbol length can be increased. As a result, since the delay amount is small compared to the symbol length, it is possible to reduce the influence of the interference due to the multipath described above. In particular, the one selected so that the carriers are orthogonal to each other is called an orthogonal multicarrier modulation scheme, and there is orthogonal frequency division multiplexing (OFDM). Further, a radio access scheme such as “MC-CDMA (Multi-Carrier-CDMA)” has been proposed as a radio transmission scheme combining multi-carrier transmission and “CDMA (Code Division Multiple Access)”. This MC-CDMA is a scheme in which data symbols are spread using a spreading code, and the spread data symbols are mapped onto a plurality of subcarriers or OFDM symbols and transmitted in parallel.

Furthermore, when the signal transmitted from the transmitter is affected by the transmission path, it is necessary to restore the information by removing the amplitude and phase fluctuations that occurred in the transmission path in the receiver from the received signal. For this reason, a method is known in which symbols (pilot symbols) with known amplitudes and phases are transmitted between a transmitter and a receiver, and fluctuations occurring in the transmission path are estimated (channel estimation). For example, techniques related to a spreading method and a pilot multiplexing method in MC-CDMA are disclosed (for example, see Non-Patent Documents 1 and 2). Non-Patent Document 1 shows two-dimensional spreading over a frequency (subcarrier) direction and a time (symbol) direction. Two-dimensional spreading is applied to the data channel, and the pilot channel is time-multiplexed and not spread. Non-Patent Document 2 compares the performance of time-multiplexed pilot channels and code-multiplexed pilot channels. The code multiplexed pilot channel is spread using a code orthogonal to the data channel.
Noriyuki Maeda, “VSF-OFCDM using two-dimensional diffusion and its characteristics”, IEICE Technical Report, IEICE, May 2002, RSC 2002-61, p. 59-64 Yoshihisa Kishida, “Examination of pilot channel configuration in VSF-OFCDM”, IEICE Technical Report, IEICE, October 2002, RSC 2002-169, p. 19-24

In the techniques described in Non-Patent Document 1 and Non-Patent Document 2, it is considered that the above-described two-dimensional spreading is used for the code-multiplexed pilot channel. However, control of the despreading method of the pilot channel in consideration of the transmission path condition has not been studied. Therefore, depending on the transmission path conditions, the despreading method of the pilot channel used is not optimal, and the channel estimation accuracy may be degraded.

  The present invention has been made in view of the above-described problems, and provides a multicarrier transmission system and a multicarrier transmission receiver capable of controlling a pilot channel despreading method in consideration of the state of a transmission path in multicarrier transmission. The purpose is to do.

  According to the present invention, the multicarrier transmission system includes despreading method determination table data storage means for recording a despreading method determination table for specifying the despreading rate of the pilot channel with respect to the transmission path condition. The despreading rate of the pilot channel is determined based on the acquired transmission path state. Thereby, the despreading method of the pilot symbols can be changed according to the state of the transmission path, the channel estimation accuracy can be improved, and efficient communication can be performed.

  Furthermore, according to the present invention, the despreading rate of the pilot channel is determined using the delay spread as an index indicating the transmission path state. Thus, in a transmission path state with a small delay spread, channel estimation accuracy can be improved and communication can be performed efficiently by increasing the despreading rate in the subcarrier direction of the pilot channel. On the other hand, in a transmission path state with a large delay spread, the despreading rate in the subcarrier direction of the pilot channel can be reduced, the deterioration of channel estimation accuracy due to frequency selective fading can be reduced, and efficient communication can be performed.

  Further, according to the present invention, the despreading code of the pilot channel is estimated using the desired signal power to interference signal power ratio. Here, the despreading ratio orthogonal to the other code-multiplexed channel groups is estimated. When non-orthogonal despreading rates are used, it can be determined from the estimated value of the desired signal power to interference power ratio when orthogonal despreading rates (for example, the spreading rate of the pilot channel used in the base station transmitter) are used. A value far from is estimated. This reveals non-orthogonal spreading factors and leads to spreading factors that can be used for pilot despreading.

  According to the present invention, there is provided a multicarrier transmission system and a multicarrier transmission receiver capable of controlling a despreading method of a pilot channel in consideration of a state of a transmission path in multicarrier transmission and improving channel estimation accuracy. Can be provided.

  An embodiment of multicarrier CDMA transmission (MC-CDMA) embodying a multicarrier transmission system and a multicarrier transmission receiver according to the present invention will be described below with reference to FIGS. In the present embodiment, description will be made using OFDM transmission as multicarrier transmission.

  As shown in FIG. 1, in this embodiment, a channel is configured using a pilot channel 11 and a data channel 12. Here, pilot channel 11 is multiplexed within the same time using a code orthogonal to data channel 12.

  As shown in FIG. 2, each channel (11, 12) is spread over the number of subcarriers and the number of OFDM symbols. Here, the spreading factor (SF) is calculated by multiplying the time axis spreading factor (SFtime) and the frequency axis spreading factor (SFfreq).

Hereinafter, two-dimensional diffusion will be described assuming that SFtime = 2 and SFfreq = 2. Here, for the spreading code with spreading factor SF = 4, as shown in the pattern α in FIG. 3, C (4,0)
~ C (4,3) can be used. In order to perform two-dimensional spreading on these spreading codes, C (4,0) to C (4,3) are developed on the time axis and the frequency axis as shown by the pattern β.

  Next, the relationship between the despreading of the pilot channel and the spreading code will be described with reference to FIG. Here, assuming that C (4,0) is used as the pilot channel spreading code, C (4,1) to C (4,3) are used as the data channel spreading code, and the pattern β1 and C (4,1) are used. ) And a pattern β2 using C (4, 3).

  In the case of the pattern β1, since three data channels are used, the despreading code of the pilot channel orthogonal to the data channel is only C (4, 0). On the other hand, in the case of pattern β2, there are two data channels, and the spreading codes are C (4,1) and C (4,3). Therefore, in this case, there are two types of despreading codes for the pilot channel orthogonal to the data channel, C (2,0) and C (4,0). When frequency selective fading is large, use of C (2, 0) for the despreading code of the pilot channel can reduce channel estimation errors due to inner code interference.

  In the present embodiment, only the function of estimating the despreading code orthogonal to the data channel at the receiving apparatus without receiving notification from the transmitting apparatus is added. The transmission apparatus can also change the transmission power of the pilot channel by setting the data channel to two channels and setting the pilot channel spreading code to C (2, 0).

  Next, the multicarrier transmission system in this embodiment will be described with reference to FIG. This multicarrier transmission system includes a transmission device 20 as a transmission device for multicarrier transmission and a reception device 40 as a reception device for multicarrier transmission.

  First, a case where a signal is transmitted using the transmission device 20 will be described. The transmission apparatus 20 generates a data symbol using the channel encoder 21 for the input transmission data. Then, the transmission apparatus 20 performs data modulation processing in the data modulation unit 22 on the generated data symbol. The data modulator 22 performs multi-level quadrature amplitude modulation such as 16QAM (Quadrature Amplitude Modulation) and 64QAM, BPSK (Binary Phase Shift Keying) modulation, QPSK (Quadrature Phase Shift Keying) modulation, and the like.

  Next, the transmission apparatus 20 performs two-dimensional spreading in the spreading unit 23. Specifically, the spreading unit 23 performs serial / parallel conversion on the data symbols subjected to the data modulation processing, and divides the data symbols into a plurality of data symbols. Then, the spreading unit 23 duplicates a plurality of data symbols that have been serial-parallel converted and divided into a number equal to the spreading code period of the spreading code corresponding to the data channel that transmits the data symbols. The spreading unit 23 generates a spreading code corresponding to each data channel assigned to each data channel. Then, the transmitting apparatus 20 multiplies the duplicated data symbol by a spreading code corresponding to the data channel for transmitting the data symbol to obtain an information signal.

Next, in transmission apparatus 20, subcarrier mapping section 24 performs an information signal allocation process on a plurality of subcarriers.
Further, the transmission device 20 is code-multiplexed to a predetermined number of channels in a data channel multiplexing unit 25 as data multiplexing means. Here, a pilot signal is inserted into the information signal. The data channel multiplexing unit 25 synthesizes the information signal and pilot signal of each data channel and performs code multiplexing.

Then, the transmission device 20 spreads the code-multiplexed information signal to a plurality of subcarriers having different frequencies for transmitting the information signal. Specifically, the transmitter 20 performs frequency-time signal conversion of the information signal in the IFFT unit 26. Here, inverse fast Fourier transform is performed. Then, an information signal is allocated to a plurality of subcarriers having different frequencies to generate a multicarrier CDMA signal.

  Furthermore, the transmitter 20 inserts a guard interval for each OFDM symbol in the GI adding unit 27. This guard interval prevents interference between OFDM symbols, and is inserted between OFDM symbols. By inserting a guard interval, it is possible to reduce the influence of each OFDM symbol reaching the receiving apparatus 40 with a delay due to the effect of multipath propagation and interfering between OFDM symbols. For example, the GI addition unit can insert a signal obtained by duplicating the latter half of the OFDM symbol as the guard interval at the beginning of the OFDM symbol. The length of the guard interval can be determined in consideration of the delay time.

Then, the transmission device 20 transmits the multicarrier CDMA signal with the guard interval inserted to the reception device 40 via the antenna.
Next, the case where a multicarrier CDMA signal is received using the receiving apparatus 40 shown in FIG. 5 will be described. The antenna of the receiving device 40 receives a multicarrier CDMA signal transmitted by a plurality of subcarriers having different frequencies. In the receiving device 40, the timing detection unit 41 establishes synchronization of the OFDM symbol timing. The receiving device 40 removes the guard interval inserted in each OFDM symbol in the GI removing unit 42.

  Next, receiving apparatus 40 performs fast Fourier transform on the multicarrier CDMA signal in FFT section 43, and separates the CDMA signal spread on a plurality of subcarriers having different frequencies for each subcarrier.

  Further, the receiving device 40 generates a spreading code similar to the spreading code multiplied by the CDMA signal in the despreading unit 45 as the data channel despreading means. Then, the receiving device 40 performs despreading by multiplying the CDMA signal received by the antenna by a spreading code corresponding to each data channel. As a result, the data symbol before being multiplied by the spreading code in the transmission device 20 is restored.

  Next, the receiving device 40 performs parallel-to-serial conversion on the data symbols synthesized and restored over the spreading code period. In the data demodulator 46, the receiving device 40 performs data demodulation processing on the data symbols subjected to parallel-serial conversion. Furthermore, the receiving device 40 performs error correction decoding processing on the data symbols subjected to data demodulation processing. Finally, the receiving device 40 restores the data symbol subjected to the error correction decoding process in the channel decoder 47 to a state in which it can be output to an output device such as a display or a speaker, and outputs the data symbol to the output device.

Further, receiving apparatus 40 performs despreading of pilot symbols in pilot channel despreading section 44. A plurality of despread rates can be used.
Then, using the despreading result generated here, parameter control unit 48 determines an optimal pilot channel despreading rate. That is, the parameter control unit 48 functions as control means and despread code estimation means in the claims. The parameter control unit 48 includes a despreading method determination table data storage unit 50. In this despreading method determination table data storage means 50, a despreading method determination table 51 for specifying the despreading rate of the pilot channel with respect to the transmission path condition is recorded. Specifically, a table for determining the despreading rate of the pilot channel in association with the delay spread is recorded in the despreading method determination table 51.

  Therefore, processing in the parameter control unit 48 will be described with reference to FIG. Note that the processing related to the selection of the pilot channel despreading ratio described below is executed at the start of communication.

  The parameter control unit 48 takes over the despreading result from the despreading of the pilot channel and calculates the signal power (step S1). Here, for example, the calculation is performed by calculating the average value of the signals. Thereby, the desired wave power is calculated.

  Further, the parameter control unit 48 calculates interference power (step S2). Here, for example, the calculation is performed by calculating a variance value of the signal. Thereby, the interference wave power is calculated.

  Then, the parameter control unit 48 calculates a desired signal power to interference signal power ratio (CIR) (step S3). Specifically, the ratio between the signal power calculated in step S1 and the interference power calculated in step S2 is calculated. Here, when despreading is performed using a despreading code that is not orthogonal to other code-multiplexed channel groups, an orthogonal despreading code (for example, a spreading factor of a pilot channel used in a base station transmitter) ) Is used, a value extremely deviated from the estimated value of the desired signal power to interference signal power ratio is estimated. Thereby, a non-orthogonal spreading factor can be specified, and a spreading code that can be used for pilot despreading is derived.

  On the other hand, the delay spread is calculated using the parameters of the pilot channel (for example, the spreading factor of the pilot channel used in the base station transmitter). Here, since the transmitted signal reaches the receiving antenna through a plurality of propagation paths having different distances, a time shift corresponding to the path difference occurs, and the received signal spreads in the time direction. The shape of the spread of the power distribution with respect to the delay time is called a delay profile, and its dispersion value is called a delay spread. Both of these become transmission path conditions. Here, the parameter control unit 48 calculates a transmission line response (step S4). Then, the parameter control unit 48 calculates a delay spread from this response (step S5).

  Then, an appropriate pilot channel despreading rate is determined using the despreading rate and delay spread orthogonal to the other multiplexed channel groups derived (step S6). Here, the despreading method determination table 51 recorded in the despreading method determination table data storage unit 50 is referred to.

  As described above, the simulation result while changing the despreading rate of the pilot channel according to the state of the transmission path is shown in FIG. Here, the carrier-to-noise ratio (CNR) dependence of throughput is shown under two conditions (A, B). Here, the condition A is 15 data channels and 1 pilot channel. SF = 16 was used as the despreading rate of the pilot channel. On the other hand, under condition B, the data channel is 12 channels and the pilot channel is 1 channel. SF = 4 was used as the despreading rate of the pilot channel. The number of subcarriers was calculated as 768, the subcarrier frequency interval was 131.83 kHz, the number of inverse Fourier transform points was 1024, and the guard interval was 226. Here, it is assumed that the graph 510 is “0.43 μs” as the delay spread, and the graph 520 is “0.043 μs” as the delay spread. Thus, in both transmission path conditions, the throughput is reversed between condition A and condition B.

According to the multicarrier transmission of the above embodiment, the following effects can be obtained.
In the above embodiment, the reception device 40 performs reception processing using the pilot channel despreading ratio derived by the parameter control unit 48. For this reason, in transmission line conditions with a small delay spread, the spreading factor of the pilot channel is increased, while in transmission line conditions with a large delay spread, the spreading factor of the pilot channel is reduced and the channel estimation accuracy is improved. As a result, better throughput can be obtained. In this way, high-quality communication with higher throughput can be provided by using an appropriate pilot channel despreading rate according to the state of the transmission path and multiple channels.

  In the above embodiment, the parameter control unit 48 includes the despreading method determination table data storage unit 50. In this despreading method determination table data storage means 50, a despreading method determination table 51 in which the despreading rate of the pilot channel is associated with the delay spread is recorded. Thereby, the despreading rate of the pilot channel can be determined using the delay spread. Then, the despread code actually used can be specified from the despread code estimated in step S3.

In addition, you may change the said embodiment as follows.
In the above embodiment, the process related to selection of the pilot channel despreading ratio is executed at the start of communication. Instead of this, pilot symbols may be measured periodically, and processing related to selection of the pilot channel despreading ratio may be performed as necessary.

  In the above embodiment, the receiving device 40 determines the pilot channel despreading rate. Alternatively, a monitoring system other than the reception device 40 may monitor the pilot symbols and notify the transmission device 20 and the reception device 40 of the pilot symbols. Thereby, it is possible to perform communication in consideration of the transmission path environment while reducing the burden on the receiving device 40.

The conceptual diagram of multicarrier transmission. The conceptual diagram of two-dimensional diffusion. Explanatory drawing of the spreading | diffusion code in two-dimensional spreading | diffusion. Explanatory drawing of the despreading rate of a pilot channel. Explanatory drawing of the multicarrier transmission system of this invention. Explanatory drawing of the process sequence of the parameter control part of this invention. Explanatory drawing of the simulation result of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Pilot channel, 12 ... Data channel, 20 ... Transmission apparatus, 25 ... Data channel multiplexing part as data multiplexing means, 40 ... Reception apparatus, 44 ... Pilot channel despreading part as transmission path condition acquisition means, 45 ... Spreading section as data channel despreading means 48... Control means, parameter control section as despreading code estimation means 50. Despreading method determination table data storage means 51. Despreading method determination table

Claims (5)

A multicarrier transmission system in which a pilot channel and a data channel are code division multiplexed,
The multi-carrier transmission system is
Despreading method determination table data storing means for recording the despreading method determination table for determining an inverse spreading factor of the pilot channel for a given transmission channel conditions,
Transmission path condition acquisition means for acquiring a transmission path condition of a transmission path state using parameters of the pilot channel including a spreading factor of the pilot channel used in a base station transmitter ;
Wherein the multi-carrier transmission at the start of communication in the system, the reverse spreading factor of the pilot channel determined on the basis said given transmission channel conditions of the despreading process determination table, to the transmission path conditions of the transmission path state, the characterized in that it comprises a despreading code estimating means for specifying a despreading code by using the inverse spreading factor of the pilot channel, multi-carrier transmission system. The despreading code estimating means, and determining the inverse spreading factor of the pilot channel using the delay spread as the transmission path condition, the multi-carrier transmission system according to claim 1. The despreading code estimating means, characterized in that said estimating despreading code of said pilot channel by using the desired signal power to interference signal power ratio as a transmission path condition, the multi-carrier according to claim 1 or 2 Transmission system. The multicarrier transmission system includes a multicarrier transmission transmitter and a multicarrier transmission receiver,
The multicarrier transmission receiver, characterized by comprising the transmission path condition acquisition means and the despreading code estimating means, a multi-carrier transmission system as claimed in any one of claims 1-3. A receiver for multicarrier transmission that performs communication with a transmitter for multicarrier transmission using a pilot channel and a data channel that are code division multiplexed,
And the data channel despreading means for despreading data symbols in said de Tachaneru,
A transmission path condition acquiring means for acquiring a transmission channel condition of the transmission path state using the parameters of the path for the pilot channel including the spreading factor of the pilot channel used by the base station transmitter,
Control means for controlling these,
And a despreading process determination table data storing means for recording the despreading method determination table for determining an inverse spreading factor of the pilot channel for a given transmission channel conditions,
The control means at the start of communication in the multicarrier transmission system ,
And the given transmission channel conditions of the despreading process determination table, the determined reverse spreading factor of the pilot channel based on the transmission path conditions of the transmission path state, reverse using the inverse spreading factor of the pilot channel A receiving apparatus for multicarrier transmission , characterized by specifying a spreading code.

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