JP5846978B2 - MIMO base station and transmission control method using MIMO base station - Google Patents

Description

  The present invention relates to a MIMO base station and a transmission control method by the MIMO base station for realizing power saving in downlink transmission in a radio base station incorporating MIMO and considering power saving.

  MIMO (Multiple-Input Multiple-Output) is applied to high-speed communication such as IEEE 802.11n and LTE (Long Term Evolution).

  FIG. 9 shows an example of downlink MCS (Modulation and Coding Scheme) for each LTE terminal category. As shown in FIG. 9, downlink transmission of a base station in LTE has 1 to 5 as UE (User Equipment) categories, and in the case of MIMO, it corresponds to MIMO 5 MHz × 2 to MIMO 20 MHz × 4. it can. The above support rates support QPSK, 16-QAM, and 64-QAM, respectively, as modulation schemes.

On the other hand, FIG. 10 is an explanatory diagram of a conventional LTE downlink allocation technique. As shown in FIG. 10, in the downlink in LTE, resources are allocated from the base station 1 to the terminal 2, and the method is as follows.
(Procedure 1) Transmits downlink reference signal from base station 1 to terminal 2 (Procedure 2) Reports CQI (Channel Quality Indicator) from terminal 2 to base station 1 (measures downlink reference signal)
(Procedure 3) Resource blocks are allocated based on CQI, QoS, and buffer content state in the base station 1, and notified from the base station 1 to the terminal 2 as downlink L1 / L2 control information. (Procedure 4) From the base station 1 to the terminal 2 Send data to

  As a resource block allocation generally allocated in 3G-LTE, a technique for performing control so that transmission can be performed with the highest throughput by transmitting with the most efficient MCS satisfying a predetermined block error rate (generally 10%). Yes (see Non-Patent Document 1, for example).

  FIG. 11 shows an example of downlink MCS in the case of IEEE 802.11n (up to MCS = 23). As shown in FIG. 11, also in IEEE802.11n using MIMO in a wireless LAN, MCS is defined as in LTE. In the case of a wireless LAN, the downlink transmission rate is determined in consideration of the previous Received Signal Strength Indication (RSSI), PER (Packet Error Rate), and the like at the time of transmission.

  Further, there is a conventional method and apparatus for reducing the energy consumption of a mobile terminal during data transmission (see, for example, Patent Document 1).

JP 2010-539743 Gazette

IEEE 802.11nTM-2009 IEEE Standard for information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications-Amendment 5: Enhancements for Higher Throughput

However, the prior art has the following problems.
In IEEE802.11n and 3G-LTE, when MIMO is applied to the downlink, in general, high efficiency is the main focus. Therefore, the power consumption of the base station 1 increases due to MIMO multiple antenna transmission. There is.

  Further, in Patent Document 1, power saving of the terminal 2 is achieved by uplink transmission control. However, no consideration is given to power saving on the base station 1 side.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a MIMO base station that realizes power saving in downlink transmission and a transmission control method by the MIMO base station.

The MIMO base station according to the present invention is a MIMO base station considering power saving equipped with MIMO, and consumes per bit at the time of transmission to a terminal located in an area where a plurality of MCSs can be selected. A power-saving transmission control unit that performs downlink resource allocation so that power is minimized , and the power-saving transmission control unit obtains terminal information including battery information from the terminal, when transmitting to the terminal and Downlink resource allocation is performed so that the sum of power consumption per bit during reception at the terminal is minimized .

Further, the transmission control method by the MIMO base station according to the present invention is a power saving transmission method by the MIMO base station considering power saving equipped with MIMO, and is located in an area where a plurality of MCSs can be selected. On the other hand, the step of specifying the MCS that minimizes the power consumption per bit at the time of transmission, and the terminal information including battery information from the terminal, when transmitting to the terminal and when receiving at the terminal Allocating downlink resources so that the sum of the power consumption per bit in is minimized .

  According to the MIMO base station and the transmission control method by the MIMO base station according to the present invention, at the time of downlink transmission or resource allocation of a base station that realizes high speed in MIMO such as LTE and IEEE802.11n, By considering the power consumption reduction effect of the base station, it is possible to obtain a MIMO base station that realizes power saving in downlink transmission and a transmission control method by the MIMO base station.

It is a block diagram of a MIMO base station (LTE) in Embodiment 1 of the present invention. It is a block diagram of a MIMO base station (IEEE802.11n) in Embodiment 1 of the present invention. In Embodiment 1 of this invention, it is an image figure of the area of the terminal 2 at the time of setting it as concentric form centering on a base station. It is a flowchart regarding a series of processing of power saving control by the power saving transmission control unit of the LTE base station in Embodiment 1 of the present invention. It is a flowchart regarding a series of processing of power saving control by the power saving transmission control unit of the IEEE 802.11n base station in Embodiment 1 of the present invention. It is a flowchart regarding a series of processing of power saving control by the power saving transmission control unit of the LTE base station 1 in Embodiment 2 of the present invention. It is a flowchart regarding a series of processing of the power saving control by the power saving transmission control unit of the IEEE 802.11n base station in Embodiment 2 of the present invention. It is the figure which showed the comparison of the transmission time at the time of the continuous transmission in Embodiment 3 of this invention, and a division | segmentation transmission. An example of conventional downlink MCS for each LTE terminal category is shown. It is explanatory drawing of the conventional downlink allocation method of LTE. An example of downlink MCS in the case of IEEE802.11n is shown.

  Hereinafter, preferred embodiments of a MIMO base station and a transmission control method by the MIMO base station of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram of a MIMO base station (LTE) in Embodiment 1 of the present invention. The base station 1 in the LTE of Embodiment 1 shown in FIG. 1 includes an antenna unit 10, a radio unit 20, and a control / baseband unit 30.

  Here, the radio unit 20 includes a DUP unit 21 that multiplexes radio signals, a PA (Power Amplifier) unit 22 that amplifies radio signals to be transmitted, an LNA (Low Noise Amplifier) unit 23 that amplifies received radio signals, and a terminal. The transmission unit 24 performs downlink transmission, the reception unit 25 performs reception from a terminal, and the orthogonal modulation unit 26 performs OFDM (Orthogonal Frequency Division Multiplexing) modulation.

  The control / baseband unit 30 includes a baseband unit 31, a control unit 35 that controls the radio unit, Ethernet (registered trademark) that receives IP packets by wire, a transmission path interface unit 36 that has an interface such as light, A timing control unit 37 that generates various clocks used in the base station based on a reference clock extracted from the transmission path or GPS, and a power supply unit 38 that returns a power source such as DC-48V to a voltage used internally. Configured.

  Here, the baseband unit 31 performs conversion (modulation / demodulation) between an IP packet exchanged through the transmission path interface and an OFDM signal (baseband signal) to be placed on the radio. Furthermore, the baseband unit 31 includes a power saving transmission control unit 32 that performs power saving transmission control, which is a feature of the present invention. The power saving transmission control unit 32 includes an area location detection unit 33, and resource allocation. The unit 34 is configured to be included.

  Similarly, FIG. 2 is a block diagram of a MIMO base station (IEEE802.11n) in Embodiment 1 of the present invention. The base station 1a in the IEEE802.11n of the first embodiment shown in FIG. 2 includes a radio unit 40, a baseband unit 50 that performs conversion (modulation / demodulation) of an OFDM signal (baseband signal) to be placed on the radio, and a MAC unit 60. A transmission path interface unit 70 that receives IP packets by wire and a power source unit 80 that is supplied with power via an outlet or Ethernet.

  Here, the wireless unit 40 includes an RF switch unit 41 that switches between transmission and reception of a wireless signal, a PA (Power Amplifier) unit 42 that amplifies a wireless signal to be transmitted, an LNA (Low Noise Amplifier) unit 43 that amplifies a received wireless signal, A transmission unit 44 that performs downlink transmission to the terminal and a reception unit 45 that performs reception from the terminal are configured.

  The MAC unit 60 includes a power saving transmission control unit 61. Here, the MAC unit 60 converts an IP packet transmitted / received through a transmission path interface with a baseband unit 50 that performs conversion (modulation / demodulation) of an OFDM signal (baseband signal) to be placed on the radio, into a radio frame, and CSMA / Perform CA-based access control. Further, the MAC unit 60 includes a power saving transmission control unit 61 that performs power saving transmission control, which is a feature of the present invention. The power saving transmission control unit 61 includes an area location detection unit 62, and a resource allocation unit. 63 is comprised.

  In addition, each of the power saving transmission control unit 32, the area location detection unit 33, and the resource allocation unit 34 in FIG. 1, and the power saving transmission control unit 61, the area location detection unit 62, and the resource allocation unit 63 in FIG. Each of these has the same function.

  The area presence detection unit 62 (or the area presence detection unit 33) determines whether or not the terminal is in an area where a plurality of MCSs can be selected. Specifically, the area location detection unit 62 determines this multiple area location detection by CQI or RSSI (Received Signal Strength Indication) shown in the conventional method (procedure 2).

  FIG. 3 is an image diagram of the area of the terminal 2 when the terminal 2 is concentric with the base station 1 as the center in the first embodiment of the present invention. As shown in FIG. 3, the area of the terminal 2 is increased concentrically from the base station 1 in the order of 64QAM91 <16QAM92 <QPSK93.

  The plurality of MCS areas indicate that the area is located in the 64QAM91 or 16QAM92 area in FIG. 3. When the area is in the 64QAM91 area, 16QAM92 and QPSK93 can also be selected. QPSK 93 can also be selected.

  In the present invention, if the LTE base station 1 as shown in FIG. 1 is used, the IEEE 802.11n base station as shown in FIG. In the case of the station 1a, a resource allocation algorithm related to determination of a downlink transmission rate (MCS) is executed by the power saving transmission control unit 61 in the MAC unit 60.

  The flow of the resource allocation method in the power saving transmission control unit 32 (61), which is a feature of the present invention, will be described with reference to the drawings. FIG. 4 is a flowchart related to a series of processes of power saving control by the power saving transmission control unit 32 of the LTE base station 1 according to Embodiment 1 of the present invention. FIG. 5 is a flowchart relating to a series of processes of power saving control by the power saving transmission control unit 61 of the IEEE 802.11n base station 1a according to Embodiment 1 of the present invention.

  First, a series of processing of power saving control by the power saving transmission control unit 32 of the LTE base station 1 will be described based on the flowchart of FIG. Before sending a packet or notifying packet transmission assignment, first, in step S401, checking whether the power saving base station is ON / OFF (that is, whether the setting of the base station itself is power saving compatible). To do.

  If the base station is not a power-saving base station in step S401, the process proceeds to step S402, and the LTE base station 1 assigns resources so as to be highly efficient as in the conventional method.

  On the other hand, if it is a power saving base station in step S401, the process proceeds to step S403, and whether or not the terminal is in an area where a plurality of MCSs can be selected (whether or not the terminal is in a power saving applicable area). Confirm).

  Here, (2) CQI or RSSI shown in the conventional method can be adopted as a method for determining whether or not there is a terminal in the power saving applicable area by the LTE base station 1.

In step S403, if there is a terminal in the power saving area, the process proceeds to step S404, where the power consumption per bit is calculated and compared based on the transmission byte length from a plurality of candidate MCSs. Choose fewer.

For example, when the power consumption of 1 × 1 MIMO is A [W], the power consumption of 2 × 2 MIMO is B [W], and 1500-byte data is transmitted, the calculation is as follows.
A [W] / 1500 × 8 [bits] (1)
B [W] / 1500 × 8 [bits] (2)

  After the above equations (1) and (2) are calculated, the two are compared. These mathematical expressions are merely examples, and may be a table in advance.

  Further, in the examples of the above formulas (1) and (2), the case where both transmission data is 1500 bytes is exemplified, and as a result, the power consumption depends on the magnitude relationship between A [W] and B [W]. However, if the number of transmission data differs between 1 × 1 MIMO and 2 × 2 MIMO, the wattage per bit should be obtained by the calculation shown in the above equations (1) and (2). Thus, it is possible to select an optimal MCS that minimizes power consumption.

  If the selection process in step S404 has identified one MCS candidate with the lowest power consumption per bit, the process proceeds to step S406. On the other hand, if there are a plurality of MCS candidates with the smallest power consumption per bit by the selection process in step S404, the process proceeds to step S405.

  Then, when the process proceeds to step S405, the packet transmission time when a plurality of MCS candidates with the lowest power consumption per bit is transmitted at 1 × 1 MIMO or 2 × 2 MIMO from the transmission byte length is transmitted. To compare. As a result of the comparison, the MCS with the shortest transmission time is selected.

  When the number of MCS candidates is narrowed down to one in this way, in step S406, the LTE base station 1 assigns the determined resource as a resource notification of the terminal. Further, in step S407, the LTE base station 1 transmits the allocated resource notification to the terminal.

  Next, a series of processing of power saving control by the power saving transmission control unit 61 of the IEEE 802.11n base station 1a will be described based on the flowchart of FIG. The process of FIG. 5 differs from the process of FIG. 4 only in that there is no step S406. That is, the IEEE 802.11n base station 1a proceeds to step S407 at the time of MCS determination, and performs transmission to the terminal.

  As described above, according to the first embodiment, the LTE base station or the IEEE 802.11n base station can perform optimal resource allocation based on the comparison result of transmission power, and can save power in downlink transmission. The MIMO base station to be realized and the transmission control method by the MIMO base station can be obtained. Furthermore, when there are a plurality of MCS candidates with the minimum transmission power, optimal resource allocation can be performed based on the comparison result of the transmission times.

Embodiment 2. FIG.
In the second embodiment, a method for reducing the received power in the downlink direction on the base station side in consideration of terminal information such as the remaining battery level of the terminal 2 will be described.

  When the base station is the LTE base station 1, the terminal 2 transmits (1) the power consumption value for each MCS of the terminal itself in advance when connecting to the base station, and (2) the CQI report after the connection At the time of allocation, it is possible to take measures such as notifying battery information of the terminal itself. Accordingly, the LTE base station 1 can know terminal information indicating the state of the terminal in advance.

  On the other hand, when the base station is the IEEE802.11n base station 1a, the terminal 2 transmits (1) the power consumption value for each MCS in advance when connecting to the base station, and (2) after the connection, In addition, it is possible to respond such as transmitting an action frame loaded with a unique information element such as battery information or a management frame such as a probe request. Therefore, the IEEE 802.11n base station 1a can know the terminal information indicating the state of the terminal in advance.

  Therefore, when such terminal information is known, the base station can select the MCS based on the sum of the W / transmission bit and the W / reception bit in consideration of the terminal information.

  Next, the flow of the resource allocation method considering terminal information will be described with reference to the drawings. FIG. 6 is a flowchart related to a series of processes of power saving control by the power saving transmission control unit 32 of the LTE base station 1 according to Embodiment 2 of the present invention. FIG. 7 is a flowchart relating to a series of processes of power saving control by the power saving transmission control unit 61 of the IEEE 802.11n base station 1a according to Embodiment 2 of the present invention.

  First, a series of processes of power saving control by the power saving transmission control unit 32 of the LTE base station 1 will be described based on the flowchart of FIG. The processing in FIG. 6 is different from the processing in FIG. 4 that does not consider terminal information in that the processing in steps S401 to S407 is the same, and the processing in steps S601 to S603 is added. Yes. Therefore, this added step will be mainly described.

  If there is a terminal in the power saving area in step S403, the process proceeds to step S601, and the LTE base station 1 determines whether or not terminal information has been acquired. If the terminal information has not been acquired, the process proceeds to step S404, and steps S404 to S407 are performed as in the first embodiment.

On the other hand, if the terminal information has been acquired, the process proceeds to step S602 to calculate and compare the total power consumption per bit based on both the transmission byte length and the reception byte length from a plurality of candidate MCSs. Select a device that consumes less power.

  When the selection process in step S602 identifies one MCS candidate with the smallest total power consumption per transmission / reception bit, the process proceeds to step S406. On the other hand, if it is determined in step S602 that there are a plurality of MCS candidates with the smallest total power consumption per transmission / reception bit, the process proceeds to step S603.

  When the processing proceeds to step S603, the transmission byte length / reception byte length is changed from the transmission byte length / reception byte length to 1 × 1 MIMO or 2 × 2 for a plurality of MCS candidates with the smallest total power consumption per bit of transmission / reception. The packet transmission / reception time for transmission / reception in MIMO is obtained and compared. As a result of the comparison, the MCS having the shortest transmission / reception time is selected.

  When the number of MCS candidates is narrowed down to one in this way, a series of processing from step S406 onward is performed as in the first embodiment.

  Next, a series of power saving control processes by the power saving transmission control unit 61 of the IEEE 802.11n base station 1a will be described with reference to the flowchart of FIG. The process of FIG. 7 differs from the process of FIG. 6 only in that there is no step S406. That is, the IEEE 802.11n base station 1a proceeds to step S407 at the time of MCS determination, and performs transmission to the terminal.

  The processing in steps S601 to S603 added from FIG. 5 in the first embodiment is the same as that in FIG. That is, after determining whether or not the terminal is in an area where a plurality of MCSs can be selected (after step S401 and step S403), the presence / absence of terminal information is confirmed (step S601). In some cases, a comparison is made after calculating the sum of both W / bits for transmission and reception (step S602).

  If terminal information is considered and there are a plurality of MCS candidates, the transmission / reception times are compared (step S603). Then, after selecting the one with the smallest sum of the transmission time from the base station and the reception time on the terminal side, the process proceeds to step S407.

  As described above, according to the second embodiment, the LTE base station or the IEEE 802.11n base station can perform optimal resource allocation based on the comparison result of transmission and reception power, and can save power in downlink transmission. The MIMO base station to be realized and the transmission control method by the MIMO base station can be obtained. Furthermore, when there are a plurality of MCS candidates with the minimum transmission / reception power, optimal resource allocation can be performed based on the comparison result of the transmission / reception times.

Embodiment 3 FIG.
In the first and second embodiments, the case where the transmission time is obtained in consideration of the byte length of the transmission packet has been described (corresponding to the processing in step S405 in FIGS. 4 to 7). On the other hand, in the third embodiment, when the transmission packet byte length is divided by the determined byte length, the transmission time at the time of division is obtained, and the packet length is divided and transmitted rather than continuously transmitted. If the length is shorter, consider dividing the packet to reduce power consumption.

  FIG. 8 is a diagram showing a comparison of transmission times during continuous transmission and divided transmission according to Embodiment 3 of the present invention. For example, in a state where a plurality of MCSs remain, as shown in FIG. 8, the divided transmission time 95 divided into six and transmitted by a plurality of MIMOs is earlier than the continuous transmission time 94 determined by the transmission byte length. In this case, split transmission is performed to reduce power consumption.

  As described above, according to Embodiment 3, it is possible to perform optimal resource allocation based on the comparison result between the continuous transmission time and the divided transmission time, and to realize power saving in downlink transmission. And a transmission control method by a MIMO base station can be obtained.

Embodiment 4 FIG.
In the first and second embodiments, the power consumption per 1 bit when continuously transmitting is compared (corresponding to the process in step S404 in FIGS. 4 to 7). On the other hand, in the fourth embodiment, power consumption per bit is compared when divided transmission is performed using divided packets. That is, power consumption is calculated by dividing by the byte length determined from the byte length of the transmission packet, calculating the power consumption by the number of packets assumed to be divided, and reducing the power consumption.

  As described above, according to Embodiment 4, optimal resource allocation can be performed based on the comparison result of power consumption with the number of packets assumed to be divided, and power saving in downlink transmission is realized. A MIMO base station and a transmission control method by the MIMO base station can be obtained.

  In the first to fourth embodiments described above, the MCS selection is performed based on the power consumption in the base station or the terminal station, but the number of selected MCS streams does not match the number of antennas to be used. But it can work. For example, when an MCS with two streams is selected, three antennas may be used. When the number of antennas to be used is increased, improvement in characteristics can be expected due to a diversity effect or the like. On the other hand, an increase in power consumption can be considered by increasing the number of antennas to be used. In order to optimize power consumption, the MCS and the number of antennas to be used may be set in an explicit manner. For example, the number of antennas to be used is determined in advance for each MSC shown in FIGS. 9 and 11, and the number of antennas to be explicitly used is set to 2 for an MCS with 2 streams. Thus, by limiting the number of antennas to be used based on the number of MCS streams, the power saving effect can be further enhanced.

  1, 1a Base station, 2 terminal, 10 antenna unit, 20 radio unit, 21 DUP unit, 22 PA unit, 23 LNA unit, 24 transmitting unit, 25 receiving unit, 26 orthogonal modulation unit, 30 control / baseband unit, 31 Baseband unit, 32 power saving transmission control unit, 33 area presence detection unit, 34 resource allocation unit, 35 control unit, 36 transmission path interface unit, 37 timing control unit, 38 power supply unit, 40 radio unit, 41 RF switch unit , 42 PA unit, 43 LNA unit, 44 transmission unit, 45 reception unit, 50 baseband unit, 60 MAC unit, 61 power saving transmission control unit, 62 area presence detection unit, 63 resource allocation unit, 70 transmission path interface unit 80 Power supply unit.

Claims (5)

It is a MIMO base station considering power saving equipped with MIMO,
A power-saving transmission control unit that allocates downlink resources so that power consumption per bit at the time of transmission is minimized for terminals located in an area where a plurality of MCSs can be selected ,
When the terminal information including battery information is acquired from the terminal, the power saving transmission control unit minimizes the sum of power consumption per bit at the time of transmission to the terminal and reception at the terminal. A MIMO base station that performs downlink resource allocation as described above . In the MIMO base station according to claim 1 ,
The power saving transmission control unit performs downlink resource allocation by specifying an MCS having the shortest transmission time from a plurality of MCSs when there are a plurality of MCSs having the minimum power consumption. base station. In the MIMO base station according to claim 2 ,
The MIMO power base station, wherein the power-saving transmission control unit selects an MCS having the shortest transmission time in consideration of a transmission time when divided transmission is performed with a fixed length. In the MIMO base station according to any one of claims 1 to 3 ,
The MIMO power base station, wherein the power saving transmission control unit selects an MCS that consumes the shortest power in consideration of power consumption when divided transmission is performed with a fixed length. A transmission control method by a MIMO base station in consideration of power saving equipped with MIMO,
The terminal which is located in a plurality MCS Selectable area, identifying the MCS which power consumption per bit in transmission is minimized,
When acquiring terminal information including battery information from the terminal, performing downlink resource allocation so that the sum of power consumption per bit at the time of transmission to the terminal and reception at the terminal is minimized When
A transmission control method by a MIMO base station.

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