JP2001156744A - Ofdm-ds-cdma communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration in an error rate characteristics of an OFDM- DS-CDMA communication system. SOLUTION: Adder sections 102a1, 102am multiplex k/2-sets of spread information signals to generate a multiplexed signal. The adder sections 102a1-102am-1 multiplex k-sets of spread information signals to generate a multiplexed signal. An IFFT section 103 assigns the multiplex signal from the adder section 102a1 to a subcarrier 1 whose characteristics is deteriorated and the multiplex signal from the adder section 102am to a subcarrier m whose characteristics is deteriorated respectively and assigns the multiplex signal from the adder sections 102a1-102am-1 to subcarriers 2-m-1 with excellent characteristics respectively to conduct frequency division multiplexing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device used in a digital mobile communication system, and more particularly, to a CD.
MA (Code Division Multiple)
Access) and OFDM (Orthogona)
l Frequency Division Multi
OFDM-CD combining the multiplexing method
The present invention relates to a communication device that performs MA-type wireless communication.

[0002]

2. Description of the Related Art Recently, communication of the OFDM-CDMA system, which combines the CDMA system and the OFDM system, has attracted attention and has been actively studied. The OFDM-CDMA method mainly includes a method of arranging spread signals in the frequency direction (generally referred to as an “OFDM-CDMA” method) and a method of arranging spread signals in a time axis direction. (Generally called “OFDM-DS-CDMA” system). Hereinafter, OFDM-DS-CDM
A communication device using the A method (hereinafter referred to as “OFDM-DS-CD
MA communication device ". ) Will be described.

FIG. 6 shows a conventional OFDM-DS-CDMA.
FIG. 3 is a block diagram illustrating a configuration of a transmission system in the communication device. Here, as an example, the total number of used subcarriers (carriers) is m.

[0006] Referring to FIG. 6, k spreading units and one adding unit are provided for each subcarrier to be assigned. That is, for subcarrier 1, k spreading sections 601a ₁ and adding section 602a ₁ are provided, and for subcarrier 2, k spreading sections 60a ₁
1a ₂ and adding unit 602a ₂ is provided, Similarly, for sub-carrier m, k-number of diffusions 601a _m and the adding unit 602a _m is provided.

[0005] Of the mk signals (information signals), signal 1
K signals consisting of signals k + 1 to 2k are signals assigned to subcarrier 2, and k signals consisting of signals k + 1 to 2k are signals assigned to subcarrier 2. Similarly, signals (m -1) k signals of k + 1 to signal mk are signals allocated to subcarrier m.

[0006] The k signals assigned to subcarriers n (n = 1 to m) are respectively spread by spreading units provided for the subcarriers. That is, the signal 1 signal k allocated to the subcarriers 1 is spread by the spreading unit 601a ₁ provided for the sub-carrier 1. Similarly, signals allocated to the subcarriers m (m-1) k + 1~ signal mk is spread by the spreading unit 601a _m provided for subcarrier m.
In the k spreading unit 601a _n provided for the sub-carrier n, mutually different spreading code sequences are used.

[0007] k-number of signal spread by the spreading unit 601a _n are multiplexed by the adder unit 602a _n. Adder 6
The total number of signals multiplexed by 02a _n (hereinafter referred to as "signal multiplexing.") Becomes k. Multiplexed signal by the adding unit 602a _n (hereinafter referred to as "multiplex signal".) Is, IF
FT (Inverse Fast Fourier T)
(transform) unit 603.

In IFFT section 603, adders 602a _n
(Inverse Fourier Transform) processing, that is, frequency division multiplexing processing, is performed on the multiplexed signal from. More specifically, the multiplexed signal from the adder 602a _n is assigned a subcarrier n, frequency division multiplexing processing is performed.

The method of allocating subcarriers is as shown in FIG. That is, subcarrier 1 is assigned to the multiplexed signal from adder 602a ₁ and adder 602a
The multiplexed signal from a ₂ sub-carrier 2 is assigned, similarly, the sub-carrier m is assigned to the multiplexed signal from the adder 602a _m.

[0010] The frequency division multiplex processing in the IFFT section 603 as described above, the signal multiplex signal is superimposed on subcarriers from the adder 602a _n is obtained.

A signal obtained by the frequency division multiplexing process is subjected to a predetermined transmission process to generate a transmission signal. The format of the transmission signal is as shown in FIG. Here, T is an OFDM symbol period.
FIG. 9 shows three OFDM symbols. The predetermined transmission process includes a parallel-serial conversion process, a D / A conversion process, a frequency conversion process, a band limitation process, and the like. This transmission signal is transmitted to the communication partner via the antenna 604.

FIG. 7 shows a conventional OFDM-DS-CDMA.
FIG. 3 is a block diagram illustrating a configuration of a receiving system in the communication device. Referring to FIG. 7, k despreading units are provided for each subcarrier. That is, subcarrier n (n =
₁ to _m ), k despreading units 703an are provided.

A signal transmitted by a communication partner is received by the communication device via antenna 701. Note that the communication partner includes the communication device shown in FIG. 6 and transmits a transmission signal obtained by performing the above-described processing.

The reception signal from the antenna 701 undergoes a predetermined reception process. Note that the predetermined receiving process includes:
It includes band limiting processing, frequency conversion processing, amplification processing, A / D conversion processing, serial / parallel conversion processing, and the like. The reception signal on which the predetermined reception processing has been performed is FFT (Fast F
(our transform) section 702.

The FFT section 702 performs an FFT (Fourier transform) process on the received signal subjected to the predetermined reception process, thereby extracting a signal transmitted by each of the subcarriers 1 to m. .

The signal transmitted by subcarrier n is
It is despread by the despreader 703a _n. That is, the signal transmitted by subcarrier 1 is transmitted to despreading section 703.
despread by a _1, Similarly, the signal transmitted by the subcarrier m is despread by the despreader 703a _m. As a result, the extracted k pieces of signals by despreading portion 703a ₁ and a signal 1 signal k, similarly, the signal (m-1) k + 1~ k number of signal composed of signal mk is the despreading unit 703a _m Is extracted.

[0017]

However, in the above-mentioned conventional OFDM-DS-CDMA communication apparatus, as shown in FIG. 8, as the signal transmitted by a subcarrier farther from the center frequency on the center frequency axis, There is a problem that the error rate characteristic deteriorates greatly. Hereinafter, the cause of the deterioration of the error rate characteristic of the signal transmitted by the subcarrier away from the center frequency will be described.

First, there is an influence by an adjacent channel interference wave (hereinafter referred to as "adjacent channel interference wave"). In FIG. 10, a subcarrier group 1001 shows an example of arrangement of subcarriers used for a desired signal (desired channel). Here, a channel adjacent to the desired channel may exist on the frequency axis. In this case, as shown in FIG. 10, the interference waves of adjacent channels, that is, the first adjacent channel interference wave 1002 and the second adjacent channel interference wave 1003,
It may cause interference to the desired channel.

In such a case, in the receiving system,
The analog amplifier used in the amplification process generates an unnecessary frequency component due to the influence of each of the adjacent channel interference waves. As a result, the unnecessary frequency component is superimposed on the desired signal.

Here, as is clear from FIG. 10, the component of the adjacent channel interference wave decreases on the frequency axis as the distance from the center frequency of the adjacent channel increases. In other words, in the desired channel, the influence of the adjacent channel interference wave becomes larger as the subcarriers are away from the center frequency of the desired channel. Therefore, in a desired signal, unnecessary frequency components are more likely to be superimposed on subcarriers farther from the center frequency of the desired channel, so that characteristics are deteriorated. As a result, a signal transmitted by a subcarrier farther from the center frequency on the center frequency axis has a greater deterioration in error rate characteristics.

Second, there is an effect of an analog filter used in the transmission system. Usually, in a transmission system, this transmission signal is passed through an analog filter in order to remove unnecessary frequency components of the transmission signal converted from a digital signal into an analog signal.

In FIG. 11, the analog filter has a characteristic curve 1102 for the subcarrier group 801.
And a filter attenuation characteristic as represented by a characteristic curve 1103.

When a transmission signal passes through an analog filter having the above characteristics, subcarriers close to the cutoff frequency of the filter, that is, subcarriers far from the center frequency, are affected by power attenuation, phase rotation, and the like. Characteristics, the characteristics are degraded. Therefore, in the receiving system,
A signal transmitted by a subcarrier farther from the center frequency has a greater deterioration in error rate characteristics.

As described above, the conventional OFDM-DS-C
In a DMA communication device, the error rate characteristics of a signal transmitted by a subcarrier distant from the center frequency of a desired signal deteriorate due to the characteristics of an adjacent channel interference wave and an analog filter.

The present invention has been made in view of the above points, and an OFDM-DS for reducing deterioration of error rate characteristics is provided.
-To provide a CDMA communication device.

[0026]

SUMMARY OF THE INVENTION OFDM-DS of the present invention
The CDMA communication apparatus includes: a multiplexing unit that generates a multiplexed signal by spreading and multiplexing an information signal; and a frequency division multiplexing unit that performs a frequency division multiplexing process by assigning each of the multiplexed signals to a carrier unique to the multiplexed signal. And the multiplexing means sets the number of information signals to be multiplexed according to the characteristics of the carrier to which the generated multiplexed signal is allocated.

According to the present invention, by setting the number of multiplexed signals to be allocated to each carrier according to the characteristics of each carrier, it is possible to suppress the deterioration of the error rate characteristic of the signal transmitted by the carrier. .

In the OFDM-DS-CDMA communication apparatus according to the present invention, the multiplexing means may use, as the characteristic of the carrier, the magnitude of the influence of an adjacent channel interference wave on the carrier or the magnitude of the influence of an analog filter. Features.

According to the present invention, according to the characteristics of each carrier, that is, the magnitude of the influence of the adjacent channel interference wave on each carrier and the magnitude of the influence of the analog filter characteristic, the signal assigned to each carrier is determined. By setting the number of multiplexed signals, it is possible to suppress deterioration of the error rate characteristics of the signal transmitted by the carrier.

[0030] In the OFDM-DS-CDMA communication apparatus according to the present invention, when the characteristic of the carrier is degraded, the multiplexing means sets the number of information signals to be multiplexed to be smaller than that of other multiplexing means. It is characterized by doing.

According to the present invention, when the characteristics of the carrier to which the generated multiplexed signal is assigned are degraded, the number of multiplexed signals of the signal assigned to this carrier is made smaller than that of the other carriers. Thus, it is possible to suppress the deterioration of the error rate characteristic of the signal transmitted by the carrier.

According to the OFDM-DS-CDMA communication apparatus of the present invention, a predetermined number of information signals out of the information signals multiplexed by the multiplexing means whose carrier characteristics are degraded are spread and multiplexed, whereby A second multiplexing means for generating a multiplexed signal in place of the multiplexing means having deteriorated characteristics, wherein the frequency division multiplexing means allocates the multiplexed signal generated by the second multiplexing means to a DC carrier. And

According to the present invention, the number of multiplexed signals is reduced for a signal assigned to a carrier having deteriorated characteristics,
By assigning the signal in which the reduced information signal is multiplexed to the DC carrier, it is possible to prevent a decrease in transmission efficiency,
It is possible to suppress the deterioration of the error rate characteristic of the signal transmitted by each carrier.

A communication terminal device according to the present invention includes any one of the above-mentioned OFDM-DS-CDMA communication devices.

According to the present invention, the provision of the OFDM-DS-CDMA communication device for reducing the deterioration of the error rate characteristic enables the provision of a communication terminal device that performs good communication.

[0036] The base station apparatus of the present invention may be adapted to use any one of the O
An FDM-DS-CDMA communication device is provided.

According to the present invention, the provision of the OFDM-DS-CDMA communication apparatus for reducing the deterioration of the error rate characteristic enables the provision of a base station apparatus which performs good communication.

The OFDM-DS-CDMA communication method according to the present invention comprises a multiplexing step of generating a multiplexed signal by spreading and multiplexing an information signal, and a frequency division by assigning each multiplexed signal to a carrier unique to the multiplexed signal. A frequency division multiplexing step of performing multiplexing processing, wherein the multiplexing step sets the number of information signals to be multiplexed according to the characteristics of a carrier to which the generated multiplexed signal is allocated.

According to the present invention, according to the present invention, by setting the number of multiplexed signals to be assigned to each carrier according to the characteristics of each carrier, the error rate characteristic of the signal transmitted by the carrier is set. Deterioration can be suppressed.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention is that the number of multiplexed signals assigned to each carrier is set according to the characteristics of the carrier (subcarrier).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a transmission system of an OFDM-DS-CDMA communication apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram illustrating a configuration of a reception system of the OFDM-DS-CDMA communication device according to the first embodiment of the present invention. here,
As an example, OFDM-DS-C according to the present embodiment
The subcarriers (carriers) used by the DMA communication device are subcarriers 1 to m.

The OFDM-D according to the present embodiment
In the S-CDMA communication apparatus, the center frequency of the adjacent channel interference wave is known, and the characteristics of the analog filter used are also known. Specifically, for example, this adjacent channel interference wave is composed of subcarrier 1 and subcarrier m farthest from the center frequency on the frequency axis.
(In other words, the characteristics of the subcarrier 1 and the subcarrier are degraded by the influence of the adjacent channel interference wave), and the analog filter Affects the sub-carrier 1 and the sub-carrier m such as power attenuation and phase rotation exceeding a predetermined threshold (in other words, the characteristics of the sub-carrier 1 and the sub-carrier m are deteriorated by the influence of the analog filter. ).

First, the OFDM-D according to the present embodiment
The transmission system of the S-CDMA communication device will be described with reference to FIG. Referring to FIG. 1, k spreading units and one adding unit are provided for each subcarrier to be assigned (excluding subcarrier 1 and subcarrier m). However, subcarrier 1 to be assigned
For subcarrier m, k / 2 spreading sections and one adding section are provided.

That is, for subcarrier 2, k
Is provided with one spreading section 101a ₂ and one adding section 102a _2. Similarly, for the subcarrier m-1, k spreading sections 101a _m-1 and one adding section 102a _{m-1 are provided.} Is provided. Also, for subcarrier 1, k
/ 2 diffusion units 101a ₁ and one addition unit 102a ₁
Is similarly provided, and for subcarrier m, k /
Two diffusions 101a _m and one of the adder 102a _m is provided.

Of all signals (all information signals), k / 2 signals consisting of signal 1 to signal k / 2 are signals allocated to subcarrier 1, and k / 2 signals consisting of signal k / 2 + 1 to signal k. / 2 signals are signals allocated to subcarrier m. Of all signals (all information signals), k signals including signals k + 1 to 2k are signals allocated to subcarrier 2, and similarly, signals (m-2) k + 1 to signals (m- 1) k signals of k are
This is a signal assigned to subcarrier m-1.

Each of k / 2 signals assigned to subcarrier j (j = 1, m) is spread by a spreading unit provided for this subcarrier. That is, signals 1 to k / assigned to subcarrier 1
2 is a spreading unit 101 provided for subcarrier 1
It is spread by a _1. Similarly, signals k / 2 + 1 to k assigned to subcarrier m are subcarrier m
It is spread by the spreading unit 101a _m provided for. In k / 2 spreading sections 101a _j provided for subcarrier j, different spreading code sequences are used.

Each of the k signals assigned to subcarrier n (n = 2 to m-1) is spread by a spreading unit provided for the subcarrier. That is, signals k + 1 to 2k assigned to subcarrier 2 are provided by spreading section 10 provided for subcarrier 2.
It is diffused by 1a _2. Similarly, subcarrier m-1
(M-2) k + 1 to signal (m-
1) k is spread by a spreading unit 101am _-1 provided for the subcarrier m-1. In the k spreading unit 101a _n provided for the sub-carrier m, mutually different spreading code sequences are used.

The method of allocating the spreading code sequence to the spreading unit is based on the condition that the spreading code sequence assigned to each spreading unit is different from the other spreading units in the spreading unit provided for each subcarrier. Can be determined as follows. That is, a spreading code sequence common to all subcarriers may be assigned to a spreading unit provided for each subcarrier, or a unique spreading code may be assigned to each spreading unit provided for each subcarrier. A code sequence may be assigned. Further, in a spreading section provided for each subcarrier, a common spreading code sequence can be assigned to a spreading section corresponding to a specific subcarrier.

K / 2 diffused by the diffusion unit 101a _j
Number of signals are multiplexed by addition section 102a _j, k-number of signal spread by the spreading unit 101a _n is adder 60
2a _{n are} multiplexed. Signal multiplexing number in the addition section 102a _j is k / 2, and the signal multiplexing in addition section 102a _n becomes k. That is, signal multiplexing is performed for subcarriers (subcarrier 1 and subcarrier m) that are affected by interference due to adjacent channel interference waves exceeding a predetermined threshold or power attenuation or phase rotation that exceeds the predetermined threshold. The number is set to k / 2, which is smaller than the number k of multiplexed signals of other subcarriers.

The multiplexed signal from the adder 102a _j and adding unit 102a _n is sent to IFFT section 103. IFF
In the T section 103, the adding section 102a _j and the adding section 102
IFFT (Inverse Fourier Transform) processing for multiple signals from a _n, i.e., frequency division multiplexing processing is performed.
Specifically, subcarriers 1 to m are allocated to the multiplexed signals from the adding sections 102a _j and 102an _n , and frequency division multiplexing is performed.

The method of assigning subcarriers is as shown in FIG. That is, subcarrier 1 is assigned to the multiplexed signal from adder 102a ₁ and adder 602
The multiplexed signal from a ₂ sub-carrier 2 is assigned, similarly, the sub-carrier m is assigned to the multiplexed signal from the adder 602a _m.

[0053] The frequency division multiplex processing in the IFFT section 103 as described above, the signal multiplex signal is superimposed on subcarriers from the adder 102a _j and adding unit 102a _n is obtained.

A signal obtained by the frequency division multiplexing process is subjected to a predetermined transmission process to generate a transmission signal. The format of the transmission signal is as shown in FIG. Here, T is an OFDM symbol period.
FIG. 3 shows a state of three OFDM symbols. The predetermined transmission process includes a parallel-serial conversion process, a D / A conversion process, a frequency conversion process, a band limitation process, and the like. This transmission signal is transmitted to the communication partner via the antenna 104.

Next, the OFDM-D according to the present embodiment
The receiving system of the S-CDMA communication device will be described with reference to FIG. Referring to FIG. 2, k / k
Two or k despreading units are provided. That is, k / 2 despreading units 203a _j are provided for subcarrier j (j = 1, m), and subcarrier n (n
= 2 to m-1 with respect to), k despread section a _n are provided.

The signal transmitted by the communication partner is received by the communication device via the antenna 201. The communication partner includes the communication device shown in FIG. 1 and transmits a transmission signal obtained by performing the above-described processing.

The reception signal from the antenna 201 undergoes a predetermined reception process. Note that the predetermined receiving process includes:
It includes band limiting processing, frequency conversion processing, amplification processing, A / D conversion processing, serial / parallel conversion processing, and the like. The reception signal subjected to the predetermined reception processing is sent to FFT section 202.

The FFT section 202 performs an FFT (Fourier transform) process on the received signal on which the above-described predetermined receiving process has been performed, thereby extracting a signal transmitted by each of the subcarriers 1 to m. .

The signal transmitted by subcarrier j is
The signal is despread by the despreading unit 203a _j and the subcarrier n
Signal transmitted by the despread by despreading section 203a _n. As a result, the despreading unit 203a ₁ and the despreading section 203a _m, respectively, the signal 1 signal k / 2
K / 2 signals and signals k / 2 + 1 to k
K / 2 signals are extracted. Also, k-number of signals by despreading section 203a ₂ and a signal k +. 1 to signal 2k is extracted, similarly, by the despreader 203a _m-1 from the signal (m-2) k + 1~ signal (m-1) k K signals are extracted.

As is apparent from the above description, the subcarriers whose interference due to the adjacent channel interference wave exceeds a predetermined threshold value, and the effects of power attenuation, phase rotation and the like by the analog filter exceed the predetermined threshold value. Regarding subcarriers (that is, subcarriers generally separated from the center frequency of a desired signal on the frequency axis), the number of multiplexed signals assigned to the subcarriers is reduced. For example, k / 2 is used as the signal multiplexing number of the signal allocated to the subcarrier 1 and the subcarrier m instead of the signal multiplexing number k of the signal allocated to the other subcarriers.

Generally, in the OFDM-DS-CDMA system, by reducing the number of multiplexed signals, it is possible to suppress the deterioration of the error rate characteristics in the receiving system. Therefore, a demodulated signal obtained by despreading the signal transmitted by subcarrier 1 and subcarrier m is a signal having good error rate characteristics.

Here, although the transmission efficiency of these subcarriers is reduced by reducing the number of multiplexed signals to be allocated to subcarrier 1 and subcarrier m, when the total number of subcarriers is large, the overall A significant decrease in transmission efficiency is slight. For example, if the total number of subcarriers is 32, and if the number of multiplexed signals of signals allocated to two subcarriers farthest from the center frequency on the frequency axis is １ ／, the overall transmission efficiency is reduced by only about 3%. It is.

The case where the center frequency of the adjacent channel interference wave is known has been described so far.
The present invention is also applicable to a case where the center frequency and the signal level of the adjacent channel interference wave are not known, and a case where the signal level and the phase of the adjacent channel interference wave change due to fading or the like. In this case, of all subcarriers,
What is necessary is to detect subcarriers in which the influence of the interference of the adjacent channel interference wave or the like exceeds a predetermined threshold value and reduce the number of multiplexed signals to be allocated to the detected subcarriers.

As described above, according to the present embodiment, of all the subcarriers, the subcarriers that are easily affected by the interference of the adjacent channel interference wave and the analog filter characteristics (particularly, the subcarriers far from the center frequency of the desired signal) By making the number of multiplexed signals of the signal allocated to the carrier) smaller than the number of multiplexed signals of the signals allocated to the other subcarriers, it is possible to suppress the deterioration of the error rate characteristics of the signal transmitted by the subcarrier. In other words, the characteristics of each subcarrier, that is, for example, the number of multiplexed signals to be allocated to each subcarrier according to the magnitude of the influence of the adjacent channel interference wave and the magnitude of the analog filter characteristic in each subcarrier, By setting, it is possible to suppress the deterioration of the error rate characteristic of the signal transmitted by the subcarrier.

In the present embodiment, the number of multiplexed signals for signals allocated to subcarriers that are susceptible to the influence of adjacent channel interference waves and analog filter characteristics is reduced by the number of multiplexed signals for signals allocated to other subcarriers. Although the case of 1/2 has been described, the present invention
The present invention is not limited to this, and can be applied to a case where the number of multiplexed signals is set for each of the subcarriers according to the magnitude of the influence of the adjacent channel interference wave or the analog filter. As a result, even when the influence of the interference of the adjacent channel interference wave and the influence of the analog filter characteristic are different for each subcarrier, the deterioration of the error rate characteristic can be suppressed.

In the present embodiment, the following effects can be further obtained by reducing the number of multiplexed signals to be allocated to subcarriers separated from the center frequency on the frequency axis. That is, OFDM method, OF
In the DM-CDMA system and the OFDM-DS-CDMA system, unnecessary frequency components are generated by sidelobe components of each subcarrier in a certain desired signal. Of these unnecessary frequency components due to the subcarriers, the unnecessary frequency components due to the side lobe components of the subcarriers apart from the center frequency are interference components for other channels due to the desired signal.

Here, in the present embodiment, it is possible to reduce the signal level of the subcarrier whose signal multiplexing number is reduced. That is, the signal level of the subcarrier far from the center frequency can be reduced. As a result, the interference of the desired signal on other channels can be reduced.

(Embodiment 2) In this embodiment, a case will be described in Embodiment 1 where the transmission efficiency is not reduced when the total number of subcarriers is small.

In Embodiment 1 described above, when the total number of subcarriers is large, the number of multiplexed signals to be allocated to subcarriers that are susceptible to the influence of adjacent channel interference and analog filter characteristics is reduced. Also,
The overall transmission efficiency does not decrease. However, when the total number of subcarriers is small, reducing the number of multiplexed signals to be allocated to the subcarriers as described above lowers the overall transmission efficiency. For example, when the total number of subcarriers is 4, and the number of multiplexed signals of signals allocated to two subcarriers apart from the center frequency is の of the number of multiplexed signals corresponding to other subcarriers, the overall Transmission efficiency drops to 1/4.

Therefore, in the present embodiment, a signal that is not multiplexed by reducing the number of multiplexed signals to be allocated to a certain subcarrier is transmitted by the subcarrier arranged in DC.

Hereinafter, the OFDM-D according to this embodiment will be described.
The S-CDMA communication device will be described with reference to FIG. 4 and FIG. Only the differences between the present embodiment and the first embodiment will be described. FIG. 4 shows OFDM-D
FIG. 3 is a schematic diagram illustrating a state of arrangement of subcarriers in an S-CDMA communication device. FIG. 5 shows Embodiment 2 of the present invention.
FIG. 2 is a schematic diagram showing an arrangement of subcarriers in the OFDM-DS-CDMA communication device according to FIG.

Referring to FIG. 4, when subcarriers are arranged in DC, the error rate characteristics deteriorate due to DC offset. Furthermore, since the total number of subcarriers is usually an even number, even if subcarriers are arranged in DC, the desired signal band does not change. For this reason, in general, subcarriers are not often arranged in DC in order to prevent deterioration of the error rate characteristics.

Hereinafter, subcarriers allocated to DC will be described. Consider a case where a DC offset exists in the CDMA system. The DC offset after despreading is
It is expressed by the following equation.

(Equation 1) Here, DC is a DC offset, and REF (nT)
Is a spreading code at time nT, N is a spreading ratio, and T is a sample period.

Here, generally, the period (NT) of the spreading code
In, since the DC offset can be considered to be constant, the above equation is expressed by the following equation.

(Equation 2)

In the above equation, (+1 code number) − (−
When (code number of 1) = 1, the DC offset is attenuated to 1 / spreading ratio by despreading. When (the number of codes of +1) and (the number of codes of -1) are the same, the DC offset is completely removed by despreading. As described above, in the CDMA system, the deterioration of the error rate due to the DC offset is reduced.

Therefore, OFD according to the present embodiment
In the M-DS-CDMA communication apparatus, as shown in FIG. 5, subcarriers (subcarrier # 0) are arranged in DC. Hereinafter, the subcarrier arranged in DC is referred to as “DC subcarrier (DC carrier)”.

Further, a signal which is not multiplexed by reducing the number of multiplexed signals to be allocated to a certain subcarrier is allocated to the DC subcarrier. That is, for example, in the example described in the first embodiment, the number of multiplexed signals to be allocated to subcarrier 1 and subcarrier m is changed from k to k / 2. Assign to DC subcarrier.

As described above, according to the present embodiment, a signal that is not multiplexed by reducing the number of multiplexed signals to be allocated to a certain subcarrier is transmitted by the subcarriers arranged in DC, so that Even when the number of carriers is small, it is possible to suppress the deterioration of the error rate characteristics without lowering the transmission efficiency.

OFDM-DS-CDMA according to the present invention
The communication device can be mounted on a mobile station device and a base station device in a digital mobile communication system, and a communication terminal device in a wireless LAN system.

[0080]

As described above, according to the present invention,
Since the number of multiplexed signals assigned to each carrier is set according to the characteristics of the carrier (subcarrier), the OFDM-DS-C that reduces the deterioration of the error rate characteristic is set.
A DMA communication device can be provided.

[Brief description of the drawings]

FIG. 1 is an OFDM-DS according to a first embodiment of the present invention.
-Block diagram showing the configuration of the transmission system of the CDMA communication device

FIG. 2 is an OFDM-DS according to the first embodiment of the present invention.
-Block diagram showing the configuration of the receiving system of the CDMA communication device

FIG. 3 is an OFDM-DS according to the first embodiment of the present invention.
Schematic diagram showing a format of a transmission signal in a CDMA communication device

FIG. 4 is a schematic diagram showing an arrangement of subcarriers in an OFDM-DS-CDMA communication device.

FIG. 5 is an OFDM-DS according to a second embodiment of the present invention.
-Schematic diagram showing arrangement of subcarriers in CDMA communication apparatus

FIG. 6 is a block diagram showing a configuration of a transmission system in a conventional OFDM-DS-CDMA communication device.

FIG. 7 is a block diagram showing a configuration of a receiving system in a conventional OFDM-DS-CDMA communication device.

FIG. 8 is a schematic diagram showing an example of how subcarriers are arranged in an OFDM-DS-CDMA communication device.

FIG. 9 is a schematic diagram showing a format of a transmission signal in a conventional OFDM-DS-CDMA communication device.

FIG. 10 is a schematic diagram showing the effect of adjacent channel interference waves in a conventional OFDM-DS-CDMA communication device.

FIG. 11 is a schematic diagram showing the influence of an analog filter in a conventional OFDM-DS-CDMA communication device.

[Explanation of symbols]

101a ₁ ~101a _m spreading unit 102a ₁ ~102a _m addition section 103 IFFT section 104 antenna

Claims (7)

[Claims] 1. A multiplexing means for generating a multiplexed signal by spreading and multiplexing an information signal, and a frequency division multiplexing means for performing a frequency division multiplexing process by allocating each of the multiplexed signals to a carrier unique to the multiplexed signal. An OFDM-DS-CDMA communication apparatus, wherein the multiplexing means sets the number of information signals to be multiplexed according to the characteristics of a carrier to which the generated multiplexed signal is allocated. 2. The OFDM according to claim 1, wherein the multiplexing unit uses, as the characteristic of the carrier, a magnitude of an influence of an adjacent channel interference wave on the carrier or a magnitude of an influence of an analog filter. -D
S-CDMA communication device. 3. The apparatus according to claim 1, wherein the multiplexing unit sets the number of the information signals to be multiplexed to be smaller than that of another multiplexing unit when the characteristic of the carrier wave is degraded. The OFDM-DS-CDMA according to claim 2,
Communication device. 4. A multiplexing means in which the characteristic of the carrier is degraded by spreading and multiplexing a predetermined number of information signals among the information signals multiplexed by the multiplexing means in which the characteristic of the carrier is degraded. 4. The method according to claim 1, further comprising a second multiplexing unit for generating a multiplexed signal, wherein the frequency division multiplexing unit assigns the multiplexed signal generated by the second multiplexing unit to a DC carrier. The OFDM-DS-CDMA communication device according to any one of the above. 5. A communication terminal device comprising the OFDM-DS-CDMA communication device according to any one of claims 1 to 4. 6. A base station apparatus comprising the OFDM-DS-CDMA communication apparatus according to any one of claims 1 to 4. 7. A multiplexing step of generating a multiplexed signal by spreading and multiplexing an information signal, and a frequency division multiplexing step of performing a frequency division multiplexing process by assigning each of the multiplexed signals to a carrier unique to the multiplexed signal. The OFDM-DS-CDMA communication method, comprising: setting the number of information signals to be multiplexed according to the characteristics of a carrier to which the generated multiplexed signal is allocated.