JP2004129075A - Lsi with sttd decoding function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an exclusive area of a circuit for performing STTD decoding. <P>SOLUTION: Respective fingers 70a to 70n share a complex operating part 60 for performing interpolation synchronous detection to reduce a hardware amount. Selectors 82 and 84 are provided to share the complex operating part 60. Transfer functions estimated by the respective fingers 70a to 70n are given to an STTD decoder 200 through the selectors 82 and 84. In addition, at least a portion of addition operations necessary for STTD decoding processing is performed by using hardware (holding part 104 and adding part 106) in a rake synthesizer 90 thereby to effectively utilize the existing hardware. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an LSI having an STTD decoding function.
[0002]
[Prior art]
One of the standards of IMT2000, which is a globally unified standard for mobile communication, formulated by the ITU (International Telecommunication Union) is the W-CDMA (Wideband Code Division Multiple Access) system.
[0003]
In the W-CDMA scheme, a transmission diversity technique is employed as one of techniques for improving reception characteristics in a terminal. There are several modes for transmit diversity in W-CDMA. One of them is STTD (Space Time Block Coded Transmit Antenna Diversity).
[0004]
FIG. 8 is a diagram showing an STTD encoding and propagation model.
[0005]
In the figure, T indicates a symbol time, S1 indicates a transmission symbol 1 including I and Q components, and S2 indicates a transmission symbol 2.
[0006]
When STTD is applied to the transmission diversity mode, the transmitting station encodes and transmits information symbols using two temporally consecutive symbols and two transmitting antennas.
[0007]
That is, at time T, -1 is multiplied by the conjugate complex number of transmission symbol S1 and transmission symbol S2, and transmission antenna 1 and transmission antenna 2 transmit the same at the same time.
[0008]
Next, at time 2T, the conjugate complex numbers of transmission symbol S2 and transmission symbol S1 are simultaneously transmitted from transmission antenna 1 and transmission antenna 2, respectively. After time 3T, the same operation is repeated using the next two consecutive symbols.
[0009]
As described above, STTD encoding is achieved by performing temporal encoding by combining two transmission symbols and simultaneously transmitting the signals from two spatially different transmission antennas.
[0010]
Next, the transmitted information symbols undergo amplitude fluctuation and phase fluctuation under the influence of Rayleigh fading in a mobile communication environment, and are received.
[0011]
That is, the symbol transmitted from the transmitting antenna 1 is received after being multiplied by the transfer function (channel estimation value) α1 of the amplitude fluctuation and the phase fluctuation.
[0012]
Similarly, the symbol transmitted from transmitting antenna 2 is received after being multiplied by a transfer function (channel estimation value) α2 of the amplitude fluctuation and the phase fluctuation.
[0013]
At this time, it is reported that the propagation delay between the two antennas at the receiving end is sufficiently shorter than the chip rate. Therefore, received symbol R1 or R2 is received in a state where information symbols transmitted simultaneously from the two antennas are added.
[0014]
Therefore, the reception symbols R1 and R2 are represented by the following equation (1), assuming that white noise is ignored.
R1 = S1 · α1−S2 * · α2 (S2 * indicates a conjugate complex number of S2)
R2 = S2 · α1 + S1 * · α2 (S1 * indicates a conjugate complex number of S1) Expression (1)
The receiver performs synchronous detection and STTD decoding using reception symbols R1 and R2 represented by Expression (1) and transfer function estimated values α1 and α2 in the propagation path of each transmission antenna, and demodulates S1 and S2. I do.
[0015]
That is, when the transmission symbols S1 and S2 are demodulated using Expression (1), they are expressed as Expression (2).
[0016]
2 · S1 = R1 · α1 * + R2 * · α2
2 · S2 = −R1 · α2 + R2 · α1 * Equation (2)
Incidentally, an interpolation and synchronous detection method is known for transfer function estimation and synchronous detection.
[0017]
Interpolated synchronous detection is performed by estimating a transfer function of a propagation path based on a plurality of received symbols, generating a coefficient for phase compensation based on the estimated transfer function, and multiplying the information symbol by this coefficient. This is a technique for performing phase compensation, and is described in, for example, Patent Document 1 below.
[0018]
STTD encoding and decoding are described in, for example, Patent Document 2 below.
[0019]
[Patent Document 1]
JP 2000-78107 A (FIG. 3 etc.)
[Patent Document 2]
JP-A-2000-138623 (FIG. 5, etc.)
[0020]
[Problems to be solved by the invention]
However, when STTD decoding is performed, the following problem occurs as compared with when STTD is not applied.
[0021]
When transmission diversity by STTD is not applied, the same unencoded symbol is transmitted from two antennas simultaneously. Therefore, when the white noise is ignored, the received symbols R1 and R2 are represented by Expression (3).
[0022]
S1 = R1 · α * (α = α1 + α2)
S2 = R2 · α * Equation (3)
Here, assuming that QPSK (four-phase modulation) is employed as the modulation method of the transmission signal, and expanding Expressions (2) and (3) in consideration of the I component and the Q component, (4), Equation (5) is obtained.
[0023]
Expansion S1i of equation (2) = α1i · R1i + α1q · R1q + α2i · R2i + α2q · R2q
S1q = −α1q · R1i + α1i · R1q + α2q · R2I−α2i · R2q
S2i = α1i · R2i + α1q · R2q−α2i · R1I−α2q · R1q
S2q = −α1q · R2i + α1i · R2q−α2q · R1i + α2i · R1q Equation (4)
Expansion of Equation (3) S1i = α1i · R1i + α1q · R1q
S1q = −α1q · R1i + α1i · R1q
S2i = α1i · R2i + α1q · R2q
S2q = −α1q · R2i + α1i · R2q Equation (5)
7 (a) and 7 (b) show a comparison of the equations (4) and (5).
[0024]
FIG. 7A shows the contents of a transmission symbol demodulation operation (same as Equation 4) when STTD encoding is applied, and FIG. 7B shows a transmission symbol demodulation operation when STTD encoding is not applied. (Same as Expression 5). In FIGS. 7A and 7B, the arithmetic expression is divided into a plurality of terms, and each of them is assigned a number from (1) to (4) so that they can be distinguished.
[0025]
When STTD encoding is not used (case (b) of FIG. 7), only the process (1) is required to perform phase compensation on the information symbol S1.
[0026]
On the other hand, when an attempt is made to realize STTD decoding (in the case of FIG. 7A), to demodulate the information symbol S1, "processing of (1) and (2)" and "(1), ▲" It is necessary to perform the addition process of each operation result in 2).
[0027]
Similarly, to demodulate the information symbol S2, in STTD decoding, it is necessary to perform the processing of (3) and (4) and the addition processing of the calculation results of (3) and (4), and only the processing of (3) Compared to the case where STTD is not applied, demodulation of one symbol requires two complex multiplication processes and one addition process.
[0028]
In order to perform STTD decoding in this way, if the configuration of a complex multiplier required for normal phase compensation is used, it is necessary to add two complex multiplication processes thereafter, which increases the circuit scale. Resulting in.
[0029]
An object of the present invention is to solve such a problem and to reduce the occupied area of an LSI circuit.
[0030]
[Means for Solving the Problems]
An LSI having an STTD decoding function according to the present invention receives an STTD encoded signal with a plurality of fingers, performs despreading with each finger, and performs a complex operation and demodulation of an STTD symbol on an information symbol output from each finger. A complex operation unit commonly used for each finger is provided, the complex operation unit is operated in a time-sharing manner and shared, and at least a part of the addition operation required for demodulation of information symbols is included in the rake combiner. This is performed using an adder.
[0031]
Efficient use of hardware resources is realized by sharing the complex operation unit and utilizing the adder in the rake combiner. Therefore, there is no need to provide a redundant arithmetic circuit, and the area occupied by the LSI chip can be reduced.
[0032]
In one embodiment of the LSI having the STTD decoding function of the present invention, all addition operations necessary for demodulating STTD-encoded information symbols are performed using an adder in a rake combiner.
[0033]
As a result, it is not necessary to provide an adder for STTD decoding, and the area occupied by the LSI chip can be further reduced. Reduction of redundant circuits also contributes to reduction of power consumption.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0035]
(Embodiment 1)
FIG. 1 is a diagram showing a configuration example of an LSI (CDMA communication system receiver) having an STTD decoding function according to the present invention.
[0036]
As shown in the figure, this LSI (receiver of the CDMA communication system) includes reception fingers (hereinafter simply referred to as fingers) 70a to 70n, selectors 82 and 84, a control unit 120 for controlling these selectors, and an STTD. Decoder 200 (this section performs phase compensation and rake combining of received symbols when STTD decoding operation is not performed).
[0037]
Each of the fingers 70a to 70n has a transfer path transfer function estimator (40a to 40n) and a symbol storage memory (20a to 20n).
[0038]
The selector 82 selects one of the estimated transfer functions output from each finger and supplies it to the STTD decoder 200.
[0039]
The selector 84 selects one of the information symbols output from each finger and supplies it to the STTD decoder 200.
[0040]
The STTD decoder 200 includes a transfer function selection unit 50, a complex operation unit 60 (having a multiplication unit 100 and an addition unit 102), and a holding unit 104 and an addition unit 106 (which are included in the rake synthesis unit 90). And also functions as a part of an STTD symbol demodulation unit for decoding STTD encoded symbols).
[0041]
The transfer function selecting unit 50 generates a complex multiplication coefficient to be supplied to the complex operation unit 60 based on the transfer path transfer function estimated by the transfer function estimating units 40a to 40n.
[0042]
The transfer function selection unit 50 distinguishes between a case where the STTD encoded signal is demodulated and a case where the normal signal is demodulated, generates a multiplication coefficient required in that case, and supplies the multiplication coefficient to the complex operation unit 60.
[0043]
Next, a characteristic configuration of the LSI in FIG. 1 will be described.
[0044]
As shown in the above equation (4), for example, the I and Q components of the transmission symbol S1 are represented as follows.
S1i = α1i · R1i + α1q · R1q + α2i · R2i + α2q · R2q
S1q = −α1q · R1i + α1i · R1q + α2q · R2I−α2i · R2q
Then, as shown in the upper part of FIG. 7A, the above equation can be divided into two sets of polynomials (1) and (2). Therefore, in order to restore the transmission symbol, it is necessary to perform the calculation of the polynomials (1) and (2) (multiplication and addition of complex multiplication coefficients) and the addition of the results.
[0045]
In the present invention, as shown in FIG. 1, the multiplication and addition of the first half complex multiplication coefficient are performed by the multiplication unit 100 and the addition unit 102 incorporated in the complex operation unit 60 shared by the fingers.
[0046]
Then, the addition in the latter half is performed by the holding unit (flip-flop (FF)) 104 and the adding unit 106 in the rake combiner 90.
[0047]
The selectors 82 and 84 are provided to share the complex operation unit 60 with each of the fingers 70a to 70b.
[0048]
By sharing the complex operation unit 60, the amount of hardware can be reduced, and the power consumption of the circuit can also be reduced.
[0049]
Further, by performing the latter addition processing in the holding unit 104 and the addition unit 106 included in the rake combiner essential for the CDMA receiver, existing hardware can be effectively used. As a result, the amount of hardware and the power consumption of the circuit can be further reduced.
[0050]
FIG. 2 shows main operations in the complex operation unit 60 and the rake combiner 90.
[0051]
First, in the stage (a), the complex operation unit 60 performs the operation of the above polynomial of (1).
[0052]
Subsequently, in the stage (b), the operation result of (1) is held in the holding unit 104 in the rake combiner 90, while the complex operation unit 60 performs the above-described operation of the polynomial of (2).
[0053]
Then, in the stage (c), the addition of the calculation results of (1) and (2) is performed by using the addition unit 106 in the rake combiner 90. As a result, transmission symbols s1i and s1q can be restored.
[0054]
(Embodiment 2)
FIG. 3 is a block diagram illustrating a specific configuration of an LSI having an STTD decoding function according to the second embodiment.
[0055]
In FIG. 3, a received symbol is input to each of the fingers 70a to 70n.
[0056]
3, the selector 80 of FIG. 3 includes a selector 82 that selects one of the estimated transfer functions output from the transfer function estimating units 40a to 40n of the fingers 70a to 70n, and a finger 82 of each of the fingers 70a to 70n. Selectors 84a and 84b for selecting one of the information symbols output from the 70n symbol storage memories 20a to 20n.
[0057]
In the following description, the processing in the finger 70a will be described as an example. Similar processing is performed on other fingers.
[0058]
First, the received data is despread in the despreading unit 10a.
[0059]
The despread information symbols are stored in the symbol storage memory 20a and input to the pilot symbol extracting unit 30a.
[0060]
Pilot symbols used for transfer function estimation are extracted in pilot symbol sampling section 30a and input to transfer function estimation section 40a. The transfer function estimating unit 40a estimates transfer functions α1 and α2 in the propagation paths of the two transmitting antennas, respectively.
[0061]
From the transfer functions α1 and α2 calculated for each finger, the selector 82 selects a transfer function for one finger (here, the transfer function of the finger 70a).
[0062]
One of the information symbols R1 (R1i, R1q) read from the symbol storage memories 20a to 20n is selected by the selectors 84a and 84b.
[0063]
The complex operation unit 60 performs a complex multiplication for demodulation on the STTD encoded signal. Further, the complex multiplying section 60 performs phase compensation by interpolation synchronous detection on a normal received signal.
[0064]
As shown in FIG. 3, the complex operation unit 60 includes four multipliers 62 to 65 and two adders 66a and 66b.
[0065]
The rake combiner 90 has flip-flops (FF) 91a, 91b, 93a, 93b, 94a, 94b and adders 92a, 92b.
[0066]
Demodulated STTD symbols (Si, Sq) output from rake combiner 90 are sent to a channel codec (not shown).
[0067]
Hereinafter, the demodulation operation of the STTD encoded signal will be described in four steps in order.
[0068]
Here, the operations of the blocks (1) to (4) shown in FIG. 7A are sequentially executed for each finger.
[0069]
In the first stage, the information symbols R1 (R1i, R1q) are read from the symbol storage memory 20a and input to the complex operation unit (phase compensation unit) 60.
[0070]
Coefficients α1i, −α1q, α1q, α1i generated by the transfer function selection unit 50 are input to input ports aw, ax, ay, az of the complex operation unit (phase compensation unit) 60, respectively. Then, a predetermined calculation ((1) in FIG. 7A) is performed.
[0071]
The result of the operation is sent to a rake combiner 90 and held in flip-flops (FF) 91a and 91b.
[0072]
In the second stage, an information symbol R2 (R2i, R2q) is newly read from the symbol storage memory 20a and input to the complex operation unit (phase compensation unit) 60.
[0073]
The input ports aw, ax, ay, and az of the complex operation unit 60 receive the coefficients α2i, α2q, + α2q, and −α2i generated by the transfer function selection unit 50. Then, the information symbol is multiplied by the above-described coefficient, and a predetermined addition is performed ((2) in FIG. 7A).
[0074]
The result of the operation is sent to a rake combiner 90 and held in flip-flops (FF) 91a and 91b. On the other hand, the result of the first-stage complex operation held earlier is held in flip-flops 93a and 93b.
[0075]
Next, the adders 92a and 92b add the results of the complex operations in the first and second stages to each other. Then, the addition result (STTD decoded symbol) is temporarily stored in flip-flops (FF) 94a and 94b.
[0076]
Thus, the STTD decoding process for one finger (here, the finger 70a) for the transmission symbol S1 is completed.
[0077]
The processing of the first stage and the second stage described above is sequentially performed for each of the fingers 70b to 70n. Then, the result of each process is subjected to, for example, maximum ratio combining in the rake combiner 90, and finally the transmission symbol S1 (S1i, S1q) is demodulated.
[0078]
In the third stage, information symbols R2 (R2i, R2q) are read from the symbol storage memory 20a.
[0079]
Further, coefficients -α2i, -α2q, -α2q, α2i are input to input ports aw, ax, ay, az of the complex operation unit 60.
[0080]
Then, a predetermined complex operation is performed ((4) in FIG. 7A), and the result is held in flip-flops 91a and 91b of the rake combiner 90.
[0081]
In the fourth stage, an information symbol R2 (R2i, R2q) is newly read from the symbol storage memory 20a.
[0082]
Coefficients α1i, −α1q, α1q, α1i are input to input ports aw, ax, ay, az of the complex operation unit 60.
[0083]
Then, a predetermined complex operation is performed ((3) in FIG. 7A). The calculation result is sent to the rake combiner 90 and combined with the previous calculation result (the calculation result of (3) in FIG. 7A), and the combined result is temporarily stored in flip-flops (FF) 94a and 94b. Is accumulated.
[0084]
Thus, the STTD decoding process on the finger 70a for the transmission symbol S2 is completed. By repeatedly performing such three-stage and four-stage processing for each finger, the transmission symbol S2 (S2i, S2q) is finally demodulated.
[0085]
As described above, a complex operation is performed for each finger in a time-division manner, and a part of the addition processing required for STTD demodulation is performed by using hardware in the rake combiner, thereby providing a redundant operation. By omitting the description, an LSI (CDMA receiver) having an STTD decoding function with a very compact configuration is realized.
[0086]
FIG. 9 shows a configuration of an LSI in which the configuration of the present invention is not adopted (LSI of a comparative example). In FIG. 9, a plurality of fingers 7a to 7n include a despreading unit 1a to 1n, a symbol storage memory 2a to 2n, a pilot symbol extracting unit 3a to 3n, a transfer function estimating unit 4a to 4n, and a transfer function, respectively. It has estimation units 5a to 5n and symbol demodulation units 10a to 10n. Reference numeral 9 indicates a rake combiner.
[0087]
In the configuration of FIG. 9, each finger is provided with a complex operation unit (6a to 6n) and a symbol demodulation unit (10a to 10n), so that the number of elements constituting the circuit is dramatically increased.
[0088]
According to the present invention, the number of elements in a circuit can be significantly reduced. The present invention is particularly effective because a mobile phone terminal is strictly required to have a small size and low power consumption.
[0089]
(Embodiment 3)
FIG. 4 is a block diagram illustrating a configuration of an LSI having an STTD decoding function according to the third embodiment.
[0090]
The LSI having the STTD decoding function of FIG. 4 has the same basic configuration and operation as the LSI of FIG.
[0091]
However, the complex operation unit 61 in FIG. 4 has only the multiplication unit 100 (does not have an addition unit as in the case of FIG. 1), and all the addition processing is performed by hardware (holding) of the rake combiner 90. This is different from the mobile phone of the embodiment described above in that it is performed in a time-division manner using the unit 104 and the adding unit 106).
[0092]
A selector 150 is provided in front of the rake combiner 90 in order to perform addition processing in a time-division manner using hardware of the rake combiner 90. The selector 150 is controlled by the control unit 122.
[0093]
Since the adder is removed from the complex operation unit 61, the area occupied by the circuit can be further reduced.
[0094]
FIG. 5 shows a more specific configuration.
[0095]
The configuration of the LSI in FIG. 5 is basically the same as the configuration of the LSI in FIG. However, the difference is that the adder is removed in the complex operation unit 60 and that the selectors 87a and 87b are provided before the rake combiner 90.
[0096]
(Embodiment 4)
The LSI of the present invention can be applied to a CDMA receiver as shown in FIG. In FIG. 6, the LSI of the present invention is shown surrounded by a dotted line. However, the present invention is not limited to this, and all the elements shown in FIG. 6 may be integrated into one chip.
[0097]
As shown in the figure, the CDMA receiving apparatus includes a receiving antenna 10, a high-frequency signal processing unit 11 that filters at a predetermined frequency and demodulates to a baseband signal, and an A / D conversion unit 12 that converts an analog signal into a digital signal. A finger unit 13 for despreading the received signal at a predetermined timing and demodulating the data; a synchronous detection unit (also serving as STTD decoding unit) 14 for performing synchronous detection and STTD decoding of the despread data; A rake combining unit 15 for rake combining the multipaths subjected to detection and STTD decoding, and a channel codec unit 16 for performing channel decoding.
[0098]
The received signal is demodulated into a baseband signal in the high-frequency signal processing unit 11, A / D converted and converted into digital data, and then input to the finger unit 13.
[0099]
In the finger unit 13, the data is demodulated by despreading by the despreader for the desired number of multipaths and the number of multiplexed codes.
[0100]
The synchronous detection and STTD decoding unit 14 and the rake combining unit 15 compensate for the phases of the plurality of data and perform rake combining.
[0101]
Use of the LSI of the present invention contributes to downsizing the CDMA receiver itself.
[0102]
【The invention's effect】
As described above, the present invention eliminates a redundant circuit configuration by efficiently using hardware and contributes to the realization of a small and low power consumption LSI (CDMA receiver).
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an LSI having an STTD decoding function according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating a characteristic operation of the LSI in FIG. FIG. 4 is a block diagram showing a specific configuration of an LSI having an STTD decoding function according to a second embodiment of the present invention; FIG. 4 is a block diagram showing a configuration of an LSI having an STTD decoding function according to the third embodiment of the present invention; FIG. 5 is a block diagram showing a specific configuration of an LSI having an STTD decoding function according to a third embodiment of the present invention. FIG. 6 is a block diagram showing an overall configuration of a CDMA receiver using the LSI of the present invention. (A) Diagram showing an arithmetic expression for demodulating transmission symbols when performing STTD decoding processing. (B) Performance for demodulating transmission symbols when not performing STTD decoding processing. Block diagram of a configuration of an LSI comparative example in which no applicable FIGS 8 of STTD encoding content representing expressions, and Figure 9 is a present invention showing a propagation model of STTD encoded signals EXPLANATION OF REFERENCE NUMERALS
10a to 10n Despreading units 20a to 20n Symbol storage memories 40a to 40n Transfer function estimating unit 50 Transfer function selecting unit 60 Complex operation units 70a to 70n Fingers 82, 84 Selector 90 Rake combiner (also used for STTD symbol demodulation)
Reference Signs List 100 Multiplication unit 102 Addition unit 104 Holding unit 106 Addition unit 120 Selector control unit 200 STTD decoder (particularly related to STTD decoding function)

Claims (3)

An LSI having an STTD decoding function of receiving an STTD encoded signal with a plurality of fingers, performing despreading on each finger, performing a complex operation on information symbols output from each finger and demodulating STTD symbols to obtain a decoded signal. And
For the received symbols output from each of the plurality of fingers, a common complex operation unit that performs the complex operation in a time division manner,
An addition operation unit included in a rake combiner built in the LSI, which performs at least a part of addition processing of data necessary for demodulation of the STTD symbol;
An LSI having an STTD decoding function, comprising: In claim 1,
An LSI having an STTD decoding function, wherein the complex operation unit performs only a multiplication operation, and all necessary addition operations are performed in an addition operation unit included in the rake combiner. In claim 1,
The finger is
A symbol storage memory for temporarily storing the information symbols after despreading,
Included in the signal after despreading, a pilot symbol extraction unit that extracts pilot symbols used for transfer function estimation,
A transfer function estimating unit for performing transfer function estimation in the propagation path,
A selector for selecting an estimated transfer function estimated value and an information symbol for each finger, and providing the same to the complex operation unit in a time division manner;
In the complex operation unit, at least, a process of multiplying the information symbol by a coefficient generated based on the transfer function estimated value is performed.
An LSI having an STTD decoding function.

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