JP2962299B2 - Multi-carrier signal transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicarrier signal transmission device used in digital radio communication.

[0002]

2. Description of the Related Art In digital wireless communication having a relatively low transmission rate (for example, 1 Mb / s or less), a significant effect of improving a code error rate can be expected by using transmission diversity or reception diversity technology. However, as the transmission speed increases (for example, several tens of Mb / s), the signal spectrum becomes wider, and in single-carrier transmission, the transmission spectrum is wider than the spectrum distortion due to multipath or the like. Can't expect. Therefore, even in the case of high-speed transmission, a multi-carrier transmission is applied, and a band per carrier is narrowed, and a reception band division type diversity combining reception system in which reception diversity is performed for each band has been proposed (see “Reference Document 1”). )).

[0003] Another technique premised on the application of multicarrier transmission is a technique in which all subcarriers are divided into N sets of clusters in a base station and the clusters are transmitted using N different antennas. It has been proposed ("Reference 2"). The present technology focuses on the fact that each divided cluster is affected by fading independently, and expects a diversity effect by combining with an appropriate error correction method.

[0004] Here, since the present invention relates to the diversity technique in the base station, the latter conventional technique in which processing is performed on the base station side will be described with reference to FIG. In the prior art shown in FIG. 3, an OFDM (Orthogonal Frequency) is used in a multicarrier transmission system.
cy Division Multiplexing)
Is used. First, the data encoded by the encoding unit 80 is converted into a parallel signal by the serial-parallel conversion unit 90. The parallelized data is divided into K (K ≧ 2) clusters by the K clustering means 120. The data divided into K clusters is K
Sets of inverse FFT (IFFT) means 120 and parallel
The serial means 130 generates a time-series multicarrier signal for each cluster. When the number of all subcarriers is N, the number of FFT operation points of the IFFT means 120 is N / K. Further, the multi-carrier signal of each cluster sequence is supplied to
The frequency is converted to an antenna transmission frequency by 40 and transmitted by K antennas 150 different for each cluster sequence.

On the terminal side (reception side) 100, the antenna 1
01 and down-conversion means 10
2. Serial-parallel means 103, FFT means 104
, The received signal is converted into a parallel signal separated for each subcarrier. Then, detection is performed by the detection means 105 on a subcarrier basis, and the detected data is converted into serial data by the parallel-serial means 106, and then becomes final reception data by the decoding means 107. The number of operation points of the FFT circuit 84 on the terminal side is N.

[Reference Document 1] Hiroyuki Hamazumi, et al., "Characteristics of Band-Division-Type Diversity Combining Reception System for Wideband Signal Mobile Reception-Example of Performance Improvement in OFDM Mobile Reception", IEICE Transactions, B-ll, Vol . J80-B-1
1, No. 6, pp. 464-474, 1997. [Reference Document 2] J. Cimini, et. al,
“Clustered OFDM with Trans
mitter Diversity and Codin
g ", IEEE GCOM '97, pp. 703-7
07, 1997.

[0007]

SUMMARY OF THE INVENTION TDMA-TDD (t
im division multiple acc
ess-time division duplex)
In low-speed transmission based on the premise, as a technique for improving the bit error rate without burdening the terminal device, the base station side receives the signal with a plurality of antennas, and selectively transmits using the antenna with a better reception state. The transmission diversity technology is effective. However, in single carrier transmission, when the transmission speed is high, the improvement effect of diversity cannot be expected because the band of the transmission spectrum is wider than the spectrum distortion due to multipath or the like.

Accordingly, a reception band division type diversity combining reception system has been proposed in which multicarrier transmission is applied, a wideband signal is narrowed into subchannels, and reception diversity is performed for each subchannel. However, in this case, the burden on the terminal device is large, and it is disadvantageous in terms of miniaturization and low power consumption.

[0009] As another method for multicarrier transmission, in the base station, the total number of subcarriers is set to K
A method has been proposed in which the data is divided into sets of clusters and transmitted using K different antennas for each cluster.
As described in Reference 2, although the peak power reduction effect and the error correction effect when the error correction code is applied can be expected, there is a problem in that the effect of a significant characteristic improvement by the diversity effect cannot be obtained. Also, in order to apply the latter method to transmission from the terminal side, K
It is necessary to transmit using a book antenna, which is also disadvantageous in miniaturization and low power consumption.

The multicarrier signal transmission apparatus according to the present invention makes it possible to apply the transmission diversity technology on the base station side even when the transmission speed is high (in the case of wideband communication) on the premise of TDMA-TDD communication. It is intended to greatly improve the code error rate characteristics without increasing the device load on the terminal side.

[0011]

Means for Solving the Problems OFDM (Orthog)
onal Frequency DivisionMu
In a multi-carrier signal transmission apparatus using a multi-carrier modulation scheme such as
Down conversion means for converting the received signals received by the plurality of antennas into low frequency signals suitable for subsequent signal processing for each antenna series and outputting the converted signals, A subcarrier signal separating unit that separates and outputs a multicarrier signal output from the unit into subcarrier signals for each antenna sequence, and a subcarrier signal separating unit that outputs the subcarrier signal for each antenna sequence. A best reception state antenna designating means for each subcarrier frequency, which measures a signal quality (signal strength or the like) and designates an antenna in a best reception state for each subcarrier frequency using the measurement result; Best reception state antenna information for each subcarrier frequency obtained by each best reception state antenna designating means Based on the above, information bit to be transmitted is allocated to a corresponding subcarrier of each antenna sequence, and each antenna sequence transmission bit allocating means, and in each antenna sequence, each antenna sequence transmission bit allocation means is used by each antenna sequence. A sub-carrier selection type multi-carrier signal generating means, which receives as input a bit sequence allocated to a power sub-carrier and selectively outputs only a corresponding sub-carrier as a multi-carrier signal, and Up-conversion means for converting the output signal of the selective multi-carrier signal generation means to an antenna transmission frequency ;
Carrier frequency common to the up-conversion means
With a single carrier frequency oscillator
A multicarrier signal transmission device is provided according to the present invention.
You .

[0012]

FIG. 1 shows a configuration of a multicarrier signal transmission apparatus according to one embodiment of the present invention. FIG. 2 shows a more specific configuration example when OFDM is used for the multicarrier transmission scheme. The embodiment will be described below with reference to FIG.

First, the operation of the base station apparatus at the transmission frame timing on the base station side in TDMA-TDD communication will be described. The data encoded by the encoding unit 80 is converted into parallel data by the serial-parallel conversion unit 90. Transmission bit allocation means 1 for each antenna sequence
0 assigns the parallel data in association with the subcarriers used in the IFFT means 21 of each antenna series based on information of the best reception antenna designating means 70 (the operation will be described later) for each subcarrier frequency. For each subcarrier not used for transmission, the corresponding subcarrier output can be set to zero (that is, unused) by allocating a signal of zero amplitude in each antenna sequence transmission bit allocating unit 10. . The parallel signal output from the IFFT means 21 is converted into a serial signal by the parallel-serial conversion means 22, converted into an antenna transmission frequency by the up-conversion means 30, and the individual antenna 40 is used for each antenna series. Sent.

Next, the operation of the base station apparatus at the base station side reception frame timing in TDMA-TDD communication will be described. First, the multicarrier signal transmitted from the terminal side received by the M different antennas passes through the down-conversion means 50, is converted into a parallel signal by the serial / parallel conversion means 60, and is input to the FFT means 61. You. The FFT means 61 separates an input signal into respective subcarrier signals by an FFT operation and outputs the separated subcarrier signals. Then, the best reception antenna designating means 70 for each subcarrier frequency measures the signal quality (signal strength, etc.) of the signal separated for each subcarrier, output from the FFT means for each antenna series, and the measurement result Using,
The antenna in the best reception state is specified for each subcarrier frequency. Then, the sub-carrier best reception antenna selecting means 70 transmits the antenna information having the best reception state for each sub-carrier frequency to the antenna sequence transmission bit allocating means 10. This information is used at the next base station side transmission frame timing.

Here, a series of the above processes will be formulated. It is assumed that the number of IFFT / FTT operation points is N and the number of base station-side antennas is M. i-th (i = 1,
A set of subcarriers used in (2,..., M) antennas is represented by {m _i } = {subcarrier number chosen for Antenna #i}. Incidentally, {1,2, ..., N} = {m 1} ∪ {m
₂ ｝ ∪… {m _M }. Assuming that the synchronization of the OFDM symbol is in an ideal state, the baseband transmission signal represented by the complex number is given by c _n = a _n + jb _n (1) (subscript n: subcarrier number). At this time, the output of the parallel-serial conversion circuit 22 in the i-th antenna series is

[0016]

(Equation 1)

## EQU1 ## Even when a plurality of carrier frequency oscillators are used in the up-conversion means 30 of each antenna series, if the frequency difference between them is negligibly small (or a common carrier frequency is supplied by a common carrier frequency oscillator). If [corresponding to claim 2), the output signals from each antenna, as omega _RF to RF frequencies,

[0018]

(Equation 2)

[0019] Note that Δt _i ≡T _i −
T ₁ indicates a transmission signal time difference (based on the position of the first antenna) caused by the position difference of the i-th antenna. Therefore, the signal after spatial synthesis is

[0020]

(Equation 3)

Is given by

The operation on the receiving side is the same as that described in the section of [Prior Art], and the signal after spatial synthesis given by the above equation (4) is received using a single antenna. . In this case, the output signal of the FFT means 104 in the terminal side baseband is

[0023]

(Equation 4)

[0024] As shown in the above equation, an arbitrary carrier phase different for each antenna sequence occurs depending on the distance between the antennas installed on the base station side, and this is removed by the detection unit 105 at the subsequent stage in units of subcarriers. It is possible (for example, an arbitrary phase component can be easily removed by using differential detection). According to the above operation principle, the transmission diversity technology can be applied even in broadband communication.

Finally, regarding the relationship between the subcarriers and the transmission / reception signal power at the base station side, the reception power at the terminal side antenna, and the case where the base station side antenna number is 2 and the subcarrier number is 6 (N = 6) FIG. This figure shows that by selecting the antenna having the best reception state for each subcarrier frequency on the base station side, the state of each subcarrier reception power at the terminal side antenna is also improved.

[0026]

The technology of the present invention makes it possible to apply transmission diversity technology to broadband communication, in which a plurality of antennas are installed only in a base station, on the premise of TDMA-TDD multicarrier communication, and to a terminal device. Significantly improve the bit error rate characteristics without increasing the burden.

[0027]

[Table 1]

As an example showing a specific effect, a simulation result (code error rate) in a frequency selective fading channel using the evaluation parameters shown in Table 1 is shown below.
As shown in FIG. As is clear from the figure, the application of the technique of the present invention significantly improves the bit error rate characteristics. Also,
The technology of the present invention is effective in reducing the peak power of a multicarrier signal because the number of subcarriers used in each antenna sequence on the base station side is evenly dispersed. That is, the technology of the present invention has an effect of relaxing the required back condition required in the signal amplifier.

[Brief description of the drawings]

FIG. 1 is a configuration [general example] of a multicarrier signal transmission device according to an embodiment of the present invention.

FIG. 2 is a configuration [specific example using OFDM] of a multicarrier signal transmission device according to an embodiment of the present invention.

FIG. 3 shows a configuration of a multicarrier signal transmission device according to the related art.

FIG. 4 is an example of reception / transmission power at each antenna of a base station and reception power at a terminal (when the number of base station side antennas is 2 and the number of subcarriers is 6).

FIG. 5 is an example of a code error rate in a frequency selective fading channel (in the case of base station transmission and terminal reception).

[Description of Signs] 10 Each antenna sequence transmission bit allocation means 20 Subcarrier selection type multicarrier signal generation means 21 IFFT means 22 Parallel / serial conversion means 30 Up conversion means 31 Common carrier frequency oscillator 40 Antenna 50 Down conversion means 60 Subcarrier Signal separation / extraction means 61 Serial / parallel conversion means 62 FFT means 70 Best reception state antenna designation means for each subcarrier frequency 80 Encoding means 90 Serial / parallel conversion means 100 Terminal side receiver 101 Antenna 102 Down conversion means 103 Serial / Parallel Conversion means 104 FFT means 105 Detection means 106 Parallel / serial conversion means 107 Decoding means

Claims (1)

(57) [Claims] 1. A multi-carrier signal transmission apparatus using a multi-carrier modulation scheme based on an OFDM scheme , comprising: a plurality of antennas; Down-conversion means for converting into a low-frequency signal suitable for output, and a multi-carrier signal output from the down-conversion means, a sub-carrier signal separation means for separating and outputting a sub-carrier signal for each antenna sequence, For each antenna sequence, measure the signal quality of each subcarrier signal output by the subcarrier signal separation means, and use the measurement result to specify the antenna in the best reception state for each subcarrier frequency. Best reception state antenna designation means for each carrier frequency; best reception state for each subcarrier frequency An antenna sequence transmission bit allocating unit for allocating information bits to be transmitted to a corresponding subcarrier of each antenna sequence based on the best reception state antenna information for each subcarrier frequency obtained by the antenna designating unit; In the sequence, by each antenna sequence transmission bit allocating means, as an input, a bit sequence allocated to a subcarrier to be used for each antenna sequence, and output as a multicarrier signal by selectively using only the corresponding subcarrier. Sub-carrier selection type multi-carrier signal generation means, in each antenna sequence, up-conversion means for converting an output signal of the sub-carrier selection type multi-carrier signal generation means to an antenna transmission frequency , common to all the up-conversion means Career
A multicarrier signal transmission device, comprising: a single carrier frequency oscillator for supplying a frequency .