JP2010199942A - Ofdma receiver and ofdma reception method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably control a reception level of a reception signal by OFDMA without depending on transmission power control. <P>SOLUTION: A base station 12 communicates with a mobile station based on an OFDMA system. The base station includes a reception gain decision section 42 for deciding a gain to the reception signal, an AGC amplifier 24 for controlling a reception level of the reception signal according to the gain decided by the reception gain decision section 42, an RSSI detection section 32 for detecting an RSSI indicating the reception level controlled by the AGC amplifier 24 for each sub-channel, and an RSSI determination section 40 for acquiring a demodulable range indicating a range of the reception level required for demodulating the reception signal for each sub-channel and for determining whether each RSSI detected by the RSSI detection section 32 exists within a demodulable range. The reception gain decision section 42 decides the gain based on the maximum RSSI of the RSSIs detected by the RSSI detection section 32 and the demodulable range of the sub-channel from which the maximum RSSI has been detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an OFDMA receiver and an OFDMA reception method, and more particularly to a technique for controlling the reception level of a received signal by OFDMA.

  In the radio receiving apparatus, only a received signal whose reception level is within a dynamic range (hereinafter referred to as “reception dynamic range”) determined by the receiving circuit configuration is correctly demodulated. For this reason, some radio reception apparatuses control the reception level for each channel so that the reception level is maintained within the reception dynamic range.

  In this regard, in OFDMA (Orthogonal Frequency Division Multiple Access) in which communication is performed using a plurality of subchannels within a predetermined frequency band, the number of subcarriers (subcarriers) constituting one subchannel, Since the frequency is variable, it is difficult to apply an analog filter for each subchannel. For this reason, in AGC (Automatic Gain Control), the reception level cannot be controlled for each sub-channel, and it is uniformly changed over the entire reception band. May become impossible to communicate by AGC.

  For example, FIG. 7 is a diagram illustrating reception levels at the base station of radio signals transmitted from three mobile stations (PS # A to C). As shown in FIG. 9A, the reception level of mobile station PS # C exceeds the reception dynamic range of the base station, and conversely, the reception level of mobile station PS # A is within the reception dynamic range. Here, when AGC is applied to the received signal so that the reception level of the mobile station PS # C is within the reception dynamic range, the reception level in the entire reception band is uniformly lowered as shown in FIG. The reception level of the mobile station PS # A that has been within the reception dynamic range until then may fall below the reception dynamic range.

  In order to avoid such problems, conventionally, the reception level of each subchannel has been controlled by transmission power control for controlling the transmission level of the transmission signal for each subchannel or subcarrier (see, for example, Patent Document 1).

JP 2000-332723 A

However, in the conventional transmission power control described above, raising the transmission level of the transmission signal is restricted, and conversely, if the transmission level is lowered, sufficient CNR (Carrier to Noise) is transmitted.
(Ratio: carrier-to-noise power ratio) cannot be ensured.

  The present invention has been made in view of the above-described conventional problems, and provides an OFDMA receiving apparatus and an OFDMA receiving method capable of suitably controlling the reception level of a received signal by OFDMA regardless of transmission power control. With the goal.

  In order to solve the above problems, an OFDMA receiver according to the present invention is an OFDMA receiver that receives signals transmitted from a plurality of communication devices using a plurality of subchannels based on an orthogonal frequency division multiple access scheme. Reception gain determining means for determining a gain for the received signal; reception level control means for controlling the reception level of the received signal in accordance with the gain determined by the reception gain determining means; Of the reception levels controlled by the reception level control means, a first reception level detection means for detecting a first reception level that is a reception level of all subchannels, and a first reception level detected by the first reception level detection means. The first reception level for determining whether or not one reception level is within a first demodulatable range that is the range of the reception level of the OFDMA receiver. Level determination means, wherein the reception gain determination means increases the gain when the first reception level detected by the first reception level detection means is lower than the demodulatable range. And

  According to the present invention, the reception level over all subchannels communicated by OFDMA is detected, and the reception level is compared with the demodulatorable range of the OFDMA receiver, so that the reception level is within the demodulatorable range ( The gain with respect to the received signal is preferably controlled to be close to the upper limit value of the demodulatable range.

  Moreover, in one aspect of the present invention, second reception level detection means for detecting a second reception level that is a reception level for each subchannel among the reception levels controlled by the reception level control means; It is determined whether or not the second reception level detected by the second reception level detection means is within a second demodulatable range that is a reception level range corresponding to the modulation method for each subchannel of the OFDMA receiver. A second reception level determination means, and when the second reception level is lower than the second demodulatable range, the modulation scheme of the subchannel is changed to a modulation scheme having a lower required reception level. It is characterized by that.

  As a result, whether or not the received signal can be demodulated is determined for each sub-channel based on the reception level after gain control and the demodulatable range. Thus, in the present invention, the reception level of the received signal by OFDMA can be suitably controlled regardless of the transmission power control.

  Further, when the second reception level is lower than any of the second demodulatable ranges, a handover may be instructed to a mobile station that performs communication on the subchannel.

  The first reception level may be calculated from the reception level for each subcarrier and the number of used subcarriers.

  An OFDMA reception method according to the present invention is an OFDMA reception method for receiving signals transmitted from a plurality of communication apparatuses using a plurality of subchannels based on an orthogonal frequency division multiple access scheme, wherein the reception is performed. A reception gain determination step for determining a gain for the received signal, a reception level control step for controlling a reception level of the received signal according to the gain determined in the reception gain determination step, and a reception level control step. Of the controlled reception levels, a first reception level detection step for detecting a first reception level that is a reception level of all subchannels, and a first reception level detected by the first reception level detection step are A first determination is made as to whether or not the signal is within a first demodulatable range that is a reception level range of the OFDMA receiver. A reception level determination step, wherein the reception gain determination step lowers the gain when the first reception level detected by the first reception level detection step is higher than the demodulatable range. Features.

1 is an overall configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a block diagram which concerns on the reception function of the base station which concerns on embodiment of this invention. It is a figure which shows an example of an RSSI threshold value table. It is a figure which shows the required CNR according to a modulation system. It is a figure which shows the demodulation possible range which concerns on 64QAM and (pi) / 4 shift QPSK. It is a flowchart which shows a part of reception process of a base station. It is a figure which shows the reception level in the base station of the radio signal transmitted from each of three mobile stations (PS # A-C).

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

  FIG. 1 is an overall configuration diagram of a mobile communication system 10 according to an embodiment of the present invention. As shown in the figure, the mobile communication system 10 includes a base station 12 and a plurality of mobile stations 14 (here, three). The mobile station 14 is, for example, a portable mobile phone, a portable information terminal, or a data communication card.

  The base station 12 transmits / receives a radio signal to / from each mobile station 14 by a TDD (Time Division Duplex) method, and also uses an OFDMA (Orthogonal Frequency Division Multiple Access) method and a TDMA (Time Division Time). Division Multiple Access (Time Division Multiple Access) is used to perform multiplex communication.

  Hereinafter, the configuration and functions of the base station 12 regarding the reception of radio signals will be described in more detail.

  FIG. 2 is a block diagram relating to the reception function of the base station 12. As shown in the figure, the base station 12 includes an antenna 20, a receiver 22, an AGC amplifier 24, an ADC (A / D converter) 26, a DAC (D / A converter) 28, a demodulator 30, and a controller 34. It consists of

  The antenna 20 receives a radio signal transmitted from the mobile station 14 and outputs the received radio signal to the receiving unit 22. The receiving unit 22 down-converts the radio signal received by the antenna 20 into a baseband signal, and further outputs the baseband signal subjected to symbol synchronization, guard interval (Guard Interval) removal, and the like to the AGC amplifier 24.

  The AGC amplifier 24 is a variable gain amplifier that controls (amplifies or attenuates) the reception level of the baseband signal input from the receiving unit 22 in accordance with the gain control voltage input from the DAC 28. The gain control voltage input from the DAC 28 is a voltage corresponding to the gain determined by the reception gain determination unit 42 described later.

The ADC 26 converts the baseband signal whose gain is controlled by the AGC amplifier 24 into a digital signal, and outputs the converted digital signal to the demodulation unit 30. However, the baseband signal that is normally digitally converted is limited to a signal whose reception level is within the dynamic range of ADC 26 (range from the noise floor to the allowable input level). This dynamic range is an SNR (Signal to Noise Ratio) determined by the effective number of bits (ENOB) of the ADC 26, and is, for example, 72 dB in an ADC having an effective bit number of 12 bits.

  The demodulator 30 converts the digital signal input from the ADC 26 into a subcarrier component of a complex symbol representing the phase and amplitude of each subcarrier by fast Fourier transform (FFT). Then, according to the modulation scheme of each subcarrier, these complex symbols are converted into corresponding binary data, and the converted binary data is output to the control unit 34.

  The demodulator 30 also includes an RSSI detector 32 that detects the reception level after gain control by the AGC amplifier 24. The RSSI detection unit 32 detects RSSI (Receive Signal Strength Indication) for each subcarrier component of the complex symbol obtained by the FFT, and uses the number of subcarriers in each subchannel and the subs of the complex symbol. From the RSSI for each carrier component, the RSSI in each subchannel and the RSSI of the entire reception band, that is, the entire subchannel, are calculated.

  The control unit 34 includes a CPU, a memory, and the like, and controls each unit of the base station 12. In addition, it includes an RSSI threshold table 36, a modulation method management unit 38, an RSSI determination unit 40, a reception gain determination unit 42, and a channel control unit 44, and controls the AGC amplifier 24, changes the modulation method, and the like. These functions are realized by the CPU executing various control programs stored in the memory.

  The RSSI threshold table 36 stores a required CNR and a lower limit value (RSSI threshold) of RSSI required for demodulation of a signal modulated by the modulation scheme for each modulation scheme. FIG. 3 is a diagram illustrating an example of the RSSI threshold value table 36. The required CNR in the figure is determined according to the modulation scheme and the desired BER (Bit Error Rate). The RSSI threshold is determined based on the dynamic range of the ADC 26 and the required CNR corresponding to the modulation method. Hereinafter, a method for determining the RSSI threshold will be specifically described.

FIG. 4 is a diagram showing the required CNR for each modulation method. As shown in the figure, the CNR required to maintain a predetermined BER increases as the modulation scheme has a higher symbol rate. In any modulation scheme, the higher the BER, the higher the CNR required. For example, the CNR required for BER = 0.001% in 64QAM is 25.6 dB. This means that RSSI of 25.6 dB or more is required from the noise floor in order to set the BER of the signal modulated by 64QAM to 0.001% or less. On the other hand, the CNR required for setting BER = 0.001% in π / 4 shift QPSK is 12.9 dB.

  As described above, RSSI must be at least within the dynamic range of the ADC 26 in order to correctly demodulate the received signal. In the block diagram shown in FIG. 2, if the reception gain from the antenna 20 to the demodulator 30 is 40 dB and the dynamic range of the ADC 26 is 72 dB (the number of effective bits is 12 bits), the signal is correctly converted into a digital signal by the ADC 26. The RSSI range (ADC usable range) is −112 to −40 dBm in terms of the input converted value of the antenna 20 (assuming the input level at the antenna 20 is 0 dBm).

  As described above, the demodulatable range indicating the RSSI range required for demodulating the received signal ranges from a level higher than the noise floor by a required CNR to an allowable input level of the ADC 26. That is, each RSSI threshold value stored in the RSSI threshold value table 36 is a value obtained by adding a required CNR corresponding to each modulation method to the noise floor level.

  FIG. 5 shows 64 QAM (A) and π / 4 shift QPSK (when the receiving gain from the antenna 20 to the demodulator 30 is 40 dB, the dynamic range of the ADC 26 is 72 dB, and the desired BER is 0.001%. It is a figure which shows the demodulation possible range which concerns on B). As shown in FIG. 6A, the demodulatable range according to 64QAM is 46.4 dB (−86.4 to −40 dBm in terms of antenna 20 input conversion value) obtained by subtracting the required CNR of 25.6 dB from the dynamic range 72 dB of the ADC 26. Yes, the RSSI threshold is -86.4 dBm. Also, as shown in FIG. 5B, the demodulatable range related to π / 4 shift QPSK is 59.1 dB (−99.1 to −40 dBm), and the RSSI threshold is −99.1 dBm. For the other modulation schemes shown in FIG. 3, the RSSI threshold is determined in the same manner.

The modulation scheme management unit 38 manages the modulation scheme applied to each sub-channel, and notifies the RSSI determination unit 40 of the modulation scheme of each sub-channel in response to a request from the RSSI determination unit 40. . In the mobile communication system 10, π / 4 shift QPSK, 16Q
A modulation scheme such as AM, 64QAM, or 256QAM is used.

  The RSSI determination unit 40 notifies the reception gain determination unit 42 of the RSSI of the entire band detected by the RSSI detection unit 32.

  The RSSI determination unit 40 acquires the modulation scheme of each subchannel from the modulation scheme management unit 38 and acquires the RSSI threshold corresponding to each modulation scheme from the RSSI threshold table 36. Then, for each sub-channel, it is determined whether or not the RSSI detected by the RSSI detection unit 32 is within a demodulatable range (more than the RSSI threshold and less than the allowable input level of the ADC 26). Here, for a sub-channel whose RSSI exceeds the RSSI threshold, it is determined whether there is a suitable modulation scheme with a higher required CNR (high symbol rate) such that the RSSI is within the demodulatorable range. The determination is made based on the table 36. Further, for a subchannel whose RSSI is lower than the RSSI threshold, whether there is a suitable modulation scheme with a lower required CNR (a low symbol rate) such that the RSSI is within the demodulation range, the RSSI threshold table. 36 based on the determination. Here, if there is a suitable modulation scheme, the modulation scheme and its subchannel are notified to the channel control unit 44 as a determination result.

  The reception gain determination unit 42 adjusts the RSSI of the baseband signal input from the reception unit 22 based on the RSSI notified from the RSSI determination unit 40 and the allowable input level of the ADC 26 (the upper limit value of the demodulatable range). Determine the gain for. At this time, it is desirable to determine the gain so that RSSI becomes equal to the allowable input level of the ADC 26. By so doing, the RSSI of each sub-channel is amplified within each demodulatable range, so communication with higher throughput can be realized. The gain thus determined is converted into a gain control voltage by the DAC 28 and then input to the AGC amplifier 24.

  Based on the determination result notified from the RSSI determination unit 40, the channel control unit 44 changes the notified subchannel modulation scheme or instructs handover to the mobile station 14 to which the subchannel is assigned. That is, when the modulation scheme and the subchannel are notified from the RSSI determination unit 40 (when a suitable modulation scheme with a higher symbol rate or a suitable modulation scheme with a low symbol rate exists), modulation of the subchannel is performed. When the method is changed to the notified modulation method and only the subchannel is notified, the mobile station 14 to which the subchannel is assigned is instructed to perform handover.

  Next, the reception process of the base station 12 will be described with reference to FIG. FIG. 6 is a flowchart showing a part of the reception process of the base station 12.

  As shown in the figure, when a radio signal is received, the RSSI detection unit 32 detects RSSI for each subcarrier component of the complex symbol obtained by FFT (S100). Then, the RSSI of the entire band is calculated from the RSSI of each subcarrier and the number of subcarriers (S102). Next, the reception gain determination unit 42 acquires the allowable input level of the ADC 26 (S104), and compares the RSSI of the entire band detected in S102 with the allowable input level of the ADC 26 (S106). When the input level is lower than the allowable input level, the gain is determined so that the RSSI of the entire band falls within the allowable input level. The AGC amplifier 24 controls the reception level of the baseband signal input from the receiving unit 22 based on the determined gain (S108).

  Here, the RSSI detector 32 detects the RSSI of each subchannel from the RSSI of each subcarrier and the number of subcarriers (S110). The RSSI determination unit 40 acquires the modulation scheme of each subchannel from the modulation scheme management unit 38 and acquires the RSSI threshold corresponding to the modulation scheme of each subchannel from the RSSI threshold table 36. Then, for each subchannel, it is determined whether the RSSI detected in S110 satisfies the required SNR of a higher modulation scheme with respect to the demodulatable range (S112).

  Here, if the RSSI does not satisfy the required CNR (SNR) of the higher modulation scheme with respect to the demodulatable range, the demodulation process is performed as it is (S128). On the other hand, when the higher required CNR (SNR) is satisfied, the mobile station 14 to which the subchannel is assigned is notified to change the modulation scheme of the notified subchannel to a higher modulation scheme ( S114).

  In S106, when the RSSI of the entire band detected in S102 is higher than the allowable input level of the ADC 26, the reception gain determining unit 42 further determines the gain so that the RSSI of the entire band falls within the allowable input level (the gain Lower). The AGC amplifier 24 controls the reception level of the baseband signal input from the receiving unit 22 based on the determined gain (S116).

  Here, the RSSI detection unit 32 detects the RSSI for each subchannel from the RSSI of each subcarrier and the number of subcarriers (S118). The RSSI determination unit 40 acquires the modulation scheme of each subchannel from the modulation scheme management unit 38 and acquires the RSSI threshold corresponding to the modulation scheme of each subchannel from the RSSI threshold table 36. Then, for each subchannel, it is determined whether the RSSI detected in S118 satisfies the required CNR (SNR) of the demodulatable range (S120). If satisfied, the demodulation process is performed as it is (S128).

  On the other hand, if the required CNR (SNR) of the demodulatable range is not satisfied in S120, the RSSI determination unit 40 further determines whether or not the lower limit value of the required CNR (SNR) of the lower modulation scheme is satisfied. (S122). Here, if the required CNR (SNR) of the lower modulation scheme is satisfied, the lower modulation scheme is assigned (S124), and if the lower limit of the required CNR (SNR) of any modulation scheme is not satisfied, A handover is instructed to the mobile station 14 to which the subchannel is assigned (S126).

According to the mobile communication system 10 described above, at the base station 12, the reception level of the received signal is controlled by the AGC amplifier 24 and acquired based on the dynamic range of the ADC 26 and the modulation scheme of each subchannel. Whether or not the signal can be demodulated is determined for each sub-channel according to the demodulation possible range. In this way, it is possible to suitably control the reception level of the received signal by OFDMA without using the transmission power control of the mobile station 14.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible.

  For example, in the above embodiment, the present invention is applied to a mobile communication system adopting the OFDMA scheme and the TDMA / TDD scheme, but the present invention is applicable to all communication systems employing the OFDMA scheme.

  In the above embodiment, the demodulatorable range is determined based only on the required CNR corresponding to the dynamic range of the ADC 26 and the modulation method. However, the demodulatorable range is determined based on other elements constituting the receiving circuit. Also good. In the above-described embodiment, the upper limit value of the demodulatable range is the same for all subchannels (allowable input level of the ADC 26). Is applicable.

DESCRIPTION OF SYMBOLS 10 Mobile communication system, 12 Base station, 14 Mobile station, 20 Antenna, 22 Receiver, 24 AGC amplifier, 26 ADC (A / D converter), 28 DAC (D / A converter), 30 Demodulator, 32 RSSI detector , 34 control unit, 36 RSSI threshold value table, 38 modulation scheme management unit, 40 RSSI determination unit, 42 reception gain determination unit, 44
Channel control unit.

Claims (5)

An OFDMA receiver that receives signals transmitted from a plurality of communication devices using a plurality of subchannels based on an orthogonal frequency division multiple access scheme,
Receiving gain determining means for determining a gain for the received signal;
Reception level control means for controlling the reception level of the received signal in accordance with the gain determined by the reception gain determination means;
Of the reception levels controlled by the reception level control means, first reception level detection means for detecting a first reception level that is a reception level of all subchannels;
First reception level determination means for determining whether or not the first reception level detected by the first reception level detection means is within a first demodulatable range that is a range of reception levels of the OFDMA receiver;
Including
The reception gain determination means increases the gain when the first reception level detected by the first reception level detection means is higher than the demodulatable range.
An OFDMA receiver characterized by that. The OFDMA receiver according to claim 1, wherein
Of the reception levels controlled by the reception level control means, second reception level detection means for detecting a second reception level that is a reception level for each subchannel;
Whether or not the second reception level detected by the second reception level detection means is within a second demodulatable range that is a reception level range corresponding to a modulation method for each subchannel of the OFDMA receiver. Second receiving level determining means for determining;
Including
When the second reception level is lower than the second demodulatable range, the transmission apparatus is instructed to change the modulation scheme of the subchannel to a modulation scheme having a lower required reception level.
An OFDMA receiver characterized by that. The OFDMA receiver according to claim 2, wherein
When the second reception level is lower than any of the second demodulatable ranges, the mobile station that performs communication in the subchannel is instructed to perform handover.
An OFDMA receiver characterized by that. The OFDMA receiver according to claim 1 or 3,
The first reception level is calculated from the reception level for each subcarrier and the number of used subcarriers.
An OFDMA receiver characterized by that. An OFDMA receiving method for receiving signals transmitted from a plurality of communication devices using a plurality of subchannels based on an orthogonal frequency division multiple access scheme,
A receiving gain determining step for determining a gain for the received signal;
A reception level control step for controlling a reception level of the received signal according to the gain determined by the reception gain determination step;
A first reception level detection step of detecting a first reception level that is a reception level of all subchannels among the reception levels controlled by the reception level control step;
A first reception level determination step for determining whether or not the first reception level detected by the first reception level detection step is within a first demodulatable range that is a range of the reception level of the OFDMA receiver;
Including
The reception gain determination step increases the gain when the first reception level detected by the first reception level detection step is lower than the demodulatable range;
An OFDMA receiving method.