WO2013153946A1

WO2013153946A1 - Communication system and communication method

Info

Publication number: WO2013153946A1
Application number: PCT/JP2013/058661
Authority: WO
Inventors: 良太山田; 貴司吉本; 梢横枕; 加藤　勝也
Original assignee: シャープ株式会社
Priority date: 2012-04-13
Filing date: 2013-03-26
Publication date: 2013-10-17
Also published as: JP2015122546A

Abstract

Provided are a communication system and a communication method with which a reduction in throughput is inhibited while each terminal device is distributed to a corresponding base station device, and with which, in cases when a terminal device connects to a base station device other than the base station device providing maximum reception power, a plurality of base station devices work in coordination with each other in order to attenuate interference with the terminal device. A communication system (1) is provided with a plurality of base station devices (300-A, 300-B), and a terminal device (400-1) for connecting to at least one of the plurality of base station devices (300-A, 300-B), said plurality of base station devices being disposed such that the whole or a part of the connectable ranges of the base station devices overlap each other. The base station device (300-B) having the terminal device (400-1) connected thereto is controlled so as to cooperate with the other of the plurality of base station devices in order to attenuate inter-cell interference received by the terminal device (400-1).

Description

Communication system and communication method

The present invention relates to a communication system and a communication method.

In a wireless communication system such as a mobile phone, a base station device constituting a cell (communication service area) for providing a wireless communication service to a plurality of terminal devices is arranged in a city and its surrounding area. In particular, in a wireless communication system, a cellular configuration in which a plurality of base station devices are arranged is formed, and the communication area is expanded.

Many of the next-generation mobile communication systems employ OFDM (Orthogonal Frequency Division Multiplexing). As a multiple access using OFDM using a plurality of orthogonal carriers, there is OFDMA (Orthogonal Frequency Multiple Access: Orthogonal Frequency Division Multiple Access). In OFDMA, data of a plurality of terminal devices is allocated using an area (for example, referred to as a resource block) configured from a predetermined frequency band or time zone as an allocation unit. In the case of broadband transmission, a transmission signal transmitted from a transmission-side base station apparatus is received by a reception-side terminal apparatus via a plurality of transmission paths. This is called a multipath environment.

When data is received and transmitted in a multipath environment, there are resource blocks with good reception quality and resource blocks with poor reception quality, so that each base station allocates resource blocks with good reception quality to each terminal device. By carrying out a process called “”, transmission with large capacity and high reception quality is realized.

However, in recent years, with the rapid urbanization, high-rise buildings, condominiums, etc. are constructed, and many reception insensitive areas or weak electric field areas are generated. In these areas, the connection between the terminal device and the base station device can often be restricted. Also, as the number of terminal devices connected to the base station apparatus increases, the base station apparatus cannot allocate resource blocks with good reception quality to some terminal apparatuses, and the scheduling effect may be significantly reduced.

Also, with the increase in the speed of mobile communication systems, it is required to further improve the throughput for terminal devices. As a method of improving the throughput, a part or all of the range of the macro cell formed by the main base station apparatus (macro base station), and a low power base station (pico cell base station, femto cell base having a maximum transmission power smaller than that of the macro base station) A technology for constructing a heterogeneous network in which a plurality of base station devices are arranged so as to overlap with the cell range of a station etc. and each terminal device is distributed (load distribution) to each base station device Has been proposed.

Generally, received power is applied as a reference when the main base station apparatus selects a base station apparatus to which each terminal apparatus is connected. When a base station device to which a terminal device is connected is selected based on received power, a high power base station is always selected, so that the terminal devices are concentrated on one base station device, and the dispersion effect is low. In order to prevent the terminal apparatus from concentrating on one base station apparatus, a technique for connecting the terminal apparatus to a low power base station using a distance (path loss) standard, a biased power standard, or the like as a new standard has been proposed. (Non-Patent Document 1).

However, in Non-Patent Document 1, when the transmission / reception apparatus is not connected to the base station apparatus having the maximum reception power, the terminal apparatus can obtain the dispersion effect, but the signal from the base station apparatus having the maximum reception power interferes. Therefore, there is a problem that the throughput deteriorates. Further, in Non-Patent Document 1, an emphasis is placed on increasing the number of terminal devices connected to the low power base station device by biasing the received voltage, and the base station device that does not achieve the maximum received power for the terminal device. When connected, the signal is interfered with from the base station device that provides the maximum received power, and the received SINR (Signal-to-Interference plus noise power ratio) decreases. .

The present invention has been made in view of the above circumstances, and other than a base station apparatus that suppresses a decrease in throughput while distributing each terminal apparatus to a corresponding base station apparatus, and the terminal apparatus provides the maximum received power. It is an object of the present invention to provide a communication system and a communication method for reducing interference with a terminal device in cooperation with a plurality of base station devices when connecting to the base station device.

In order to solve the above-described problems, the configuration of the communication system according to the present invention is as follows.

The communication system of the present invention includes a plurality of base station devices and a terminal device connected to at least one of the plurality of base station devices, and the plurality of base station devices are connectable ranges of the base station devices. A plurality of base station apparatuses cooperate with each other to reduce inter-cell interference by a base station apparatus connected to the terminal apparatus. It is characterized by selecting whether or not to perform.

Further, in the communication system of the present invention, the inter-cell interference is reduced when the base station apparatus connected to the terminal apparatus is a base station apparatus other than the base station apparatus that provides the maximum received power in the terminal apparatus. It is characterized by this.

Further, in the communication system of the present invention, when the base station apparatus connected to the terminal apparatus connects to a base station other than the maximum transmission power among the plurality of base station apparatuses, the inter-cell interference is reduced. It is characterized by this.

In the communication system of the present invention, the base station device other than the maximum transmission power is a pico base station device.

In the communication system of the present invention, the base station apparatus reduces the inter-cell interference by precoding.
In the communication system according to the present invention, the terminal device reduces the inter-cell interference by using a reception weight.

The communication method of the present invention includes a plurality of base station devices and a terminal device connected to at least one of the plurality of base station devices, wherein the plurality of base station devices connect each base station device. A communication method in a communication system arranged such that all or some of cells in a possible range overlap each other, wherein the plurality of base station devices cooperate with each other by base station devices to which the terminal devices are connected. A step of selecting whether or not to reduce interfering interference.

According to the present invention, a communication system includes a plurality of base station apparatuses and a terminal apparatus connected to at least one of the plurality of base station apparatuses, and the plurality of base station apparatuses are connected to each base station apparatus. The communication system is arranged such that all or some of the connectable cells overlap each other, and the plurality of base station devices cooperate with each other by the base station device to which the terminal device is connected. By selecting whether or not to perform the reduction, select whether or not to suppress inter-cell interference in cooperation with a plurality of base station devices, when connecting to other than the base station device that is the maximum received power, Since the inter-cell interference arriving at the terminal device from the base station apparatus that has the maximum received power can be effectively suppressed, it is possible to achieve an excellent effect that it is possible to suppress a decrease in throughput.

According to the present invention, the communication system reduces the inter-cell interference when the base station apparatus connected to the terminal apparatus is a base station apparatus other than the base station apparatus that provides the maximum received power in the terminal apparatus. By doing so, it is possible to effectively suppress the inter-cell interference that arrives at the terminal device, so that it is possible to achieve an excellent effect that it is possible to suppress a decrease in throughput.

According to the present invention, in the communication system of the present invention, when the base station apparatus to which the terminal apparatus is connected is connected to a base station other than the maximum transmission power among the plurality of base station apparatuses, the inter-cell interference By reducing this, it is possible to effectively suppress inter-cell interference that arrives at the terminal device, so that it is possible to achieve an excellent effect of suppressing a reduction in throughput.

According to the present invention, since the base station apparatus other than the maximum transmission power is a pico base station, even a pico base station apparatus having a transmission power lower than that of the macro base station apparatus can effectively prevent inter-cell interference coming to the terminal apparatus. Therefore, it is possible to achieve an excellent effect of suppressing a decrease in throughput.

According to the present invention, the base station apparatus reduces the inter-cell interference by precoding, and the terminal apparatus reduces the inter-cell interference by reception weight, thereby achieving a scheduling effect. Thus, it is possible to achieve an excellent effect that communication with good reception characteristics is possible.

According to the present invention, a communication method includes a plurality of base station devices and a terminal device connected to at least one of the plurality of base station devices, and the plurality of base station devices A communication method in a communication system arranged so that all or part of cells that can be connected overlap each other, wherein the plurality of base station devices cooperate with each other by base station devices to which the terminal devices are connected. A base station apparatus that has a step of selecting whether or not to reduce inter-cell interference, thereby selecting whether or not a plurality of base station apparatuses cooperate to suppress inter-cell interference and achieving maximum received power. When connecting to other than the above, it is possible to effectively suppress the inter-cell interference that arrives at the terminal device from the base station apparatus that has the maximum received power, and therefore, it is possible to suppress the decrease in throughput. A can achieve.

It is the schematic which shows the structure of the communication system which concerns on 1st Embodiment. It is the schematic which shows a part of structure of the communication system which concerns on 1st Embodiment. It is the schematic which shows the structure of the base station apparatus of the communication system which concerns on 1st Embodiment. It is the schematic which shows the structure of the terminal device of the communication system which concerns on 1st Embodiment. It is a sequence diagram which shows the process between the base station apparatus of the communication system which concerns on 1st Embodiment, and a terminal device. It is a sequence diagram which shows the process between the base station apparatus of the communication system which concerns on 2nd Embodiment, and a terminal device.

<First Embodiment>
In the communication system 1 according to the first embodiment, a plurality of base station apparatuses 300-j (j is an arbitrary positive integer) and a plurality of terminal apparatuses 400-k (k is an arbitrary positive integer) use OFDM. An example of data transmission will be described. Note that the present embodiment is not limited to this, and other transmission methods can be applied.

FIG. 1 is a schematic diagram showing a configuration of a communication system 1 according to the first embodiment of the present invention. The communication system 1 according to the first embodiment includes a plurality of base station apparatuses 300-j (300-1, 300-2) having different cell radii and a plurality of terminal apparatuses 400-k (400-1, 400-2). ).

Cell 300-1a (macro cell) of main base station apparatus 300-1 (also referred to as macro base station apparatus or high power base station) and base station apparatus 300 which is a low power base station having a maximum transmission power smaller than that of the macro base station apparatus -2 (also referred to as pico base station, fetom base station, and low power base station) cell 300-2a (pico cell) overlap each other.

There are a plurality of terminal devices 400-k (400-1, 400-2) in the cell, and as will be described in detail later, each terminal device is wirelessly connected based on the traffic of the base station device 300-j. A base station device is selected.

The terminal device 400-1 is wirelessly connected to the base station device 300-1, and the transmission signal from the base station device 300-1 is the desired signal (r11) through the propagation path, and is received through the other propagation path. The transmission signal from the base station apparatus 300-2 to be used becomes inter-cell interference (undesired signal) (s11).

In addition, the terminal device 400-2 is wirelessly connected to the base station device 300-2, and the transmission signal from the base station device 300-2 is the desired signal (r22) through the propagation path, and passes through the other propagation paths. The transmission signal from the base station apparatus 300-1 received in this manner becomes inter-cell interference (undesired signal) (s22).

By constructing such a heterogeneous network (heterogeneous network), it is possible to improve the total frequency utilization efficiency seen from the network side in the area covered by the macro cell.

In addition, as shown in FIG. 2, as the arrangement of a plurality of base station apparatuses 300-j (300-3, 300-4), cells that have the same maximum transmission power and are adjacent to each other and are in a communicable range In other words, the base station apparatus 300-3 and the base station apparatus 300-4 are arranged partially overlapping. In this case, it is assumed that both base station apparatus 300-3 and base station apparatus 300-4 are macro base station apparatuses. In this case, the base station device 300-3 and the base station device 300-4, and the terminal devices 400-k (400-3, 400-4, 400-5) constitute the communication system 1a.

The terminal device 400-3 is wirelessly connected to the base station device 300-3, and the transmission signal from the base station device 300-3 is the desired signal (r33) and is received through another propagation path. -4 is the inter-cell interference (undesired signal) (s33). Similarly, terminal device 400-4 wirelessly connects to base station device 300-4, and the transmission signal from base station device 300-4 is a desired signal (r44), and is received via another propagation path. The transmission signal from the station device 300-3 becomes inter-cell interference (undesired signal) (s55). Further, the terminal device 400-5 existing at the cell edge (end area of the communication service area) of the two overlapping cells 300-3a and 300-4a is wirelessly connected to the base station device 300-3, and the base station device 300- The transmission signal from 3 is the desired signal (r55), and the transmission signal from the base station apparatus 300-4 received through another propagation path is inter-cell interference (undesired signal) (s55).

Next, the configuration of the base station apparatus 300-j (300-1, 300-2) of the communication system 1 according to the first embodiment will be described. FIG. 3 is a block diagram showing a schematic configuration of the base station apparatus 300-j of the communication system 1 according to the first embodiment.

As shown in FIG. 3, the base station apparatus 300-j includes an upper layer 301, an encoding unit 302, a modulation unit 303, a resource mapping unit 304, a reference signal generation unit 305, a control signal generation unit 306, and a transmission weight generation unit 307. , Transmission weight multiplier 308, IFFT units 309-1 to 309-T (Inverse 高速 Fast Fourier Transform, T is an arbitrary positive integer hereinafter), GI insertion units 310-1 to 310T (guard interval) : Guard Interval), transmission units 311-1 to 311T, transmission antenna units 312-1 to 312-T, reception antenna unit 313, reception unit 314, control signal detection unit 315, and base station selection unit 316 .

The base station device 300-j (300-1) receives a signal transmitted from the terminal device 400 via the reception antenna unit 313, and the reception unit 314 can perform digital signal processing such as signal detection processing on the signal. Down-convert (radio frequency conversion) to an appropriate frequency band, and further perform filtering processing to remove spurious, and convert the filtered signal from an analog signal to a digital signal (Analog to Digital conversion).

The control signal detection unit 315 performs demodulation processing, decoding processing, and the like on the digital signal output from the reception unit 314, and detects a control signal. The control signal includes a connection request from the terminal device 400 to the base station device 300, CQI (Channel Quality Indicator), received power of a base station device existing in the vicinity (hereinafter referred to as a peripheral base station device), and the like. .

The base station selection unit 316 selects a base station device to which the terminal device 400-k is connected based on the traffic and received power.

The upper layer 101 is a layer of functions higher than the physical layer (Physical Layer) among the layers of communication functions defined by the OSI reference model, for example, MAC (Media Access Control), data link layer, This corresponds to a layer such as a network layer.

Further, the upper layer 101 also obtains feedback information such as MCS information and the number of spatial multiplexing included in the signal transmitted from the terminal device 400-k. The upper layer 301 outputs information data to the encoding unit 302 based on the feedback information. Further, the upper layer 101 outputs control data to the control signal generation unit 306 in order to request notification of received power from the peripheral base station apparatus connected to the terminal apparatus 400-k. The control data includes information such as a synchronization signal SCH, radio resource allocation (scheduling), MSC (Modulation and Coding Scheme), the number of spatial multiplexing (the number of channels by spatial multiplexing), and frequency allocation. The upper layer 101 also notifies other parameters necessary for each part of the base station apparatus 300-1 to function.

Also, the upper layer 101 outputs reference signal (referred to as a pilot signal) data for performing channel estimation and reception quality measurement in the terminal device 400-k to the reference signal generation unit 305. Further, the upper layer 101 outputs the connected base station information received from the neighboring base station apparatus to the transmission weight generation unit 307.

The encoding unit 302 performs error correction encoding on the information data input from the upper layer 301. The information data is, for example, an audio signal accompanying a call, a still image or moving image signal representing a captured image, a character message, or the like. The encoding method used when the encoding unit 302 performs error correction encoding is, for example, turbo encoding, convolutional encoding, low density parity check encoding (low density parity check encoding); LDPC).

Note that the encoding unit 302 performs rate matching processing on the encoded bit sequence in order to match the coding rate of the error correction-encoded data sequence with the encoding rate corresponding to the data transmission rate. May be. Further, the encoding unit 302 may have a function of rearranging and interleaving the error correction encoded data series.

Modulation section 303 modulates the signal input from encoding section 302 and generates a modulation symbol. The modulation processing performed by the modulation unit 303 includes, for example, BPSK (binary phase shift keying; two-phase phase modulation), QPSK (quadture phase shift keying; four-phase phase modulation), M-QAM (M-quad quadrature quadrature value; Amplitude modulation, eg M = 16, 64, 256, 1024, 4096). Modulating section 303 may have a function of rearranging generated modulation symbols and interleaving them.

The reference signal generation unit 305 generates a reference signal (pilot signal) composed of a known sequence used for reception power measurement and propagation path estimation, and outputs the generated reference signal to the resource mapping unit 304. For example, the reference signal is a signal used to estimate the propagation characteristics from the transmitting antenna units 312-1 to 312-T of the base station device to the receiving antenna units 401-1 to 401-R of each terminal device 400-k. is there. The estimated propagation characteristics are used for propagation path information for calculating a transmission weight coefficient or propagation path compensation in a terminal device.

The control signal generation unit 306 generates a control signal including control data output from the upper layer 301. The control signal may be subjected to error correction coding and modulation processing.

The resource mapping unit 304 maps modulation symbols, reference signals, and control signals to resource elements based on scheduling information notified from the upper layer 301 (hereinafter referred to as resource mapping). The resource element is a minimum unit for arranging a signal composed of one subcarrier and one OFDM symbol.

The transmission weight generation unit 307 determines (or calculates) the amount of inter-cell interference based on the connected base station information received from the neighboring base station device, which is input from the higher layer 301, and cooperates between a plurality of base station devices. It is determined whether or not to suppress inter-cell interference. Further, when it is determined that the amount of inter-cell interference is greater than a predetermined reference, the transmission weight generation unit 307 generates a transmission weight and outputs the transmission weight to the multiplication unit 308. The connection base station information is information related to the inter-cell interference amount of the base station apparatus to which the terminal apparatus is connected.

When the transmission weight generation unit 307 determines that the amount of inter-cell interference is smaller than a predetermined reference, the transmission weight generation unit 307 notifies the transmission weight multiplication unit 308 of information indicating that inter-cell interference suppression is not performed in cooperation between a plurality of base station apparatuses. To do. Alternatively, when it is determined that the amount of inter-cell interference is less than a predetermined reference, the unit matrix may be output to the transmission weight multiplier 308 as a weight. When a unit matrix is used as a weight, the signal does not change before weight multiplication and after weight multiplication.

The transmission weight multiplier 308 multiplies the reception signal by the transmission weight coefficient V _j that suppresses interference with the terminal device 400-k connected to the cell of the surrounding base station device and the terminal device connected to each base station device. The reception weight coefficient U _k to be calculated is calculated. Further, the transmission weight multiplication unit 107 multiplies the signal output from the resource mapping unit 304 by the transmission weight coefficient V _j . Note that the reference signal generated by the reference signal generation unit 305 may be multiplied by the transmission weight coefficient V _j and / or the reception weight coefficient U _k .

The IFFT units 309-1 to 309-T perform inverse fast Fourier transform (IFFT) on the signal input from the transmission weight multiplication unit 308 to convert it into a time domain signal.

The GI insertion units 310-1 to 310-T insert guard intervals (GI) into the time domain signals converted by the IFFT units 309-1 to 309-T. For example, a part of the latter half of the time domain signal (effective symbol) output from the IFFT units 309-1 to 309-T is copied and added to the head of the effective symbol.

The transmitters 311-1 to 311-T convert the OFDM symbol including the guard interval (GI) inserted from the GI inserters 310-1 to 310-T into digital / analog (D / A). Convert to generate an analog signal. Transmitters 109 to 109-T perform band limitation on the generated analog signal by filtering processing to generate a band limited signal. Transmitters 311-1 to 311-T upconvert the generated band-limited signal to a radio frequency band, output it to transmission antenna units 312-1 to 312-T, and transmit antenna units 312-1 to 312-T. Sent.

Next, the terminal device 400-k (k is an arbitrary integer) in the first embodiment will be described. FIG. 4 is a schematic diagram illustrating a configuration of the terminal device 400-k according to the first embodiment.

The terminal device 400-k includes a plurality of receiving antenna units 401-1 to 401-R (hereinafter, R is an arbitrary positive integer), a plurality of receiving units 402-1 to 402-R, and a GI removing unit 403-1 to 403. -R, a plurality of FFT units 404-1 to 404 -R, reception weight multiplication unit 405, MIMO separation unit 406, channel estimation unit 407, reception power calculation unit 408, demodulation unit 409, decoding unit 410, upper layer 411, control A signal generation unit 412, a transmission unit 413, and a transmission antenna unit 414 are included.

The terminal device 400-k receives the transmission signal of the base station device 300-j via the receiving antenna units 401-1 to 401-R.

Receiving sections 402-1 to 402-R down-convert radio frequency signals input from receiving antenna sections 401-1 to 401-R into a frequency band where digital signal processing is possible, and further filter the down-converted signals To remove unnecessary components (Spurious). Further, the receiving units 202-1 to 202-R convert the filtered signal from an analog signal to a digital signal (A / D; Analog-to-Digital), and the converted digital signal is a GI removing unit 403-. Output to 1 to 403-R.

The GI removal units 403-1 to 403-R remove the guard interval (GI) and output signals from which the GI has been removed to the FFT units 404-1 to 404-R.

The FFT units 404-1 to 404 -R perform fast Fourier transform (FFT: Fast Fourier Transform) to convert the signals input from the GI removal units 403-1 to 403 -R from time domain signals to frequency domain signals. The data is output to channel estimation section 407, reception weight multiplication section 405 and reception power calculation section 408.

The channel estimation unit 407 performs propagation path estimation using a reference signal included in the input signal. Channel estimation section 407 notifies propagation path estimation value to MIMO separation section 406. The propagation path estimated value is, for example, a transfer function, an impulse response, or the like.

The received power calculation unit 408 calculates the received power from each base station apparatus based on the reference signal input via the FFT units 404-1 to 404 -R, and outputs it to the upper layer 411.

Reception weight multiplier 405 multiplies reception weight coefficient U _k corresponding to transmission weight coefficient V _j multiplied by base station apparatus 300-j. The reception weight coefficient U _k is generated and transmitted by the base station apparatus 300-j, but when only the transmission weight coefficient V _j is received from the base station apparatus 300-j, the transmission weight coefficient V _j and the channel It is also possible to calculate the reception weight coefficient U _k using the propagation path estimation value estimated by the estimation unit 407. Further, when the reference signal is multiplied by the transmission weight coefficient V _{j, the} reception weight coefficient that suppresses interference on the terminal device side may be obtained.

The MIMO separation unit 406 performs MIMO separation based on the output of the reception weight multiplication unit 405 and the channel estimation value from the channel estimation unit 407. In MIMO transmission, MIMO separation is performed in order to suppress inter-stream interference caused by receiving a signal transmitted from each transmission antenna after being spatially multiplexed. MIMO separation includes linear detection such as ZF (Zero Forcing) and MMSE (Maximum Mean Square Error), nonlinear detection such as MLD (Maximum Likelihood Detection) and interference canceller. . Further, the interference canceller includes a parallel interference canceller PIC (Parallel Interference Canceller) and a sequential interference canceller SIC (Successive Interference Canceller).

The demodulation unit 409 performs demodulation processing on the output signal from the MIMO separation unit 406. The demodulation process may be either a hard decision (calculation of a coded bit sequence) or a soft decision (calculation of a coded bit LLR).

The decoding unit 410 performs error correction decoding processing on the encoded bit sequence (or encoded bit LLR) after demodulation output from the demodulation unit 409, calculates information data transmitted to itself, 411. This error correction decoding processing method is a method corresponding to error correction coding such as turbo coding and convolution coding performed by the connected base station apparatus 300-j. Either a hard decision or a soft decision can be applied to the error correction decoding process.

The control signal generation unit 412 includes propagation path information between the own station and the base station apparatus 300-j, information including CQI and a channel estimation value, a signal for requesting connection to the base station apparatus 300-j, and a neighboring base station A control signal is generated from information indicating the received power of the apparatus. Specifically, the control signal generation unit 412 generates a control signal for transmitting feedback information (including CQI and the like) to the base station apparatus. The feedback information is determined by the upper layer 411 based on the channel estimation value calculated by the channel estimation unit 407.

The signal including the control signal output from the control signal generation unit 412 is up-converted by the transmission unit 413 before the frequency band that can be transmitted in the downlink, and is connected via the transmission antenna unit 414 to the base station apparatus 300- sent to j.

Next, a calculation method of transmission weight coefficient V _j and reception weight coefficient U _k in transmission weight multiplication section 308 of base station apparatus 300-j will be described.

Hereinafter, description will be made assuming that the number of transmission antenna units (antennas) 312-1 to 312-T of each base station apparatus is T, and the number of reception antenna units 401-1 to 401-R of the terminal apparatus 400-j is R. As described above, T and R are arbitrary integers.

The transmission weight coefficient value of T row and T column in the q-th base station apparatus (q is an arbitrary integer) is V _q , and the reception weight coefficient value of T row and R column in the p-th terminal apparatus (p is an arbitrary integer). U _p , the R-row T-column channel matrix between the q-th base station apparatus and the p-th terminal apparatus is represented as H _qp .

First, the transmission weight coefficient value V _q is set to an arbitrary value. _However, setting the ^V _q V _q H = _I transmission weight coefficient value _{V q} that preserves the relationship of _T (H is a complex conjugate transposed matrix, _{I N} is the identity matrix of N rows and N columns).

Next, the covariance matrix Q _p of interference in the p-th terminal device is calculated based on the following (Equation 1). N _TX represents the number of base station apparatuses.

Subsequently, eigenvectors corresponding to T eigenvalues from the smaller one of the covariance matrix Q _p are calculated as reception weight coefficient values (U _p ). By reversing the uplink and downlink (transmission direction from a base station apparatus to a terminal) (transmission direction from the terminal apparatus to the base station apparatus), regarded as a reception weight coefficient value U _p and the calculated transmission weight factor values.

At this time, the covariance matrix Q _q ^r of interference in the base station apparatus is calculated based on the following (Formula 2).

Nu represents the number of users.

Eigenvalues corresponding to T eigenvalues from the smaller of the covariance matrix Q _q ^r are calculated as new reception weight coefficient values. The uplink and downlink are reversed, and a new reception weight coefficient value is further calculated as a new transmission weight coefficient value (V _q ).

A counter (not shown) that counts the number of times of processing is incremented by one, and the above processing is repeated until a predetermined number of times I is reached. When reaching the predetermined number of times, the process ends, V _q obtained at the _time, respectively transmit weights U _p, and receive weights. In this way, the above processing is repeated to suppress interference.

The transmission / reception weight obtained above is a weight that maximizes SIR (Signal-to-Interference Power Ratio), but SINR (Signal-to-interference and noise power ratio: Signal-) is as follows. A weight that maximizes to-Interference (and Noise (Power) Ratio) can also be used.

The weights that maximize SINR are as follows, for example.

The weights u _{p, t} obtained by (Equation 3) are the reception weights of the t-th stream spatially multiplexed, and v _{q, t} obtained by (Equation 5) are the transmission weights of the t-th stream. In (Expression 4) and (Expression 6), d represents the number of streams. Thus transmission and reception weights each _{_{_{u p = [u p, 1}}} , ···, u p, d], v q = [v q, 1, ···, v q, d] is. Here, σ _n ² is noise power, and I _N is a unit matrix of N rows and N columns.

In this way, a new transmission weight coefficient value and reception weight coefficient value are repeatedly calculated to suppress interference. However, the present invention is not limited to this, and even if interference is suppressed using only the transmission weight coefficient value. good. Further, as represented by the following (Expression 7) and (Expression 8), interference may be suppressed by using the weight of zero forcing on the terminal device side.

Also, as in (Equation 9), a weight that minimizes the desired signal interference and noise power of the base station apparatus may be used.

Next, a connection procedure in the base station device 300-j (base station devices 300-A and 300-B) and the terminal device 400-k (terminal device 400-1) in the communication system 1 will be described. FIG. 5 is a sequence diagram illustrating an example of a processing operation in which the base station devices (300-A and 300-B) to which the terminal device 400-1 is connected are selected in the communication system 1.

First, the base station devices (base station devices 300-A and 300-B) periodically transmit synchronization signals and reference signals to the terminal device 400-1 at predetermined time intervals (steps 501 and 502). ). The terminal device 400-1 is in a communicable and waiting state (idle state).

There are multiple types of synchronization signals. For example, in LTE (Long Term Evolution), the primary synchronization channel (Primary SCH: Primary Synchronization Channel) and the secondary synchronization channel (Secondary SCH: Secondary Synchronization Channel type). is there. In order for terminal apparatus 400-1 to receive a signal from the base station apparatus, a synchronization channel is transmitted from each base station apparatus in order to shorten the cell search. The terminal device 400-1 detects the sector ID on the primary SCH, detects the cell ID on the secondary SCH, and determines each cell.

After the power is turned on, the terminal device 400-1 uses a synchronization signal to start a process (cell search) for detecting a cell (cell ID) that can be used for communication (step 503). The cell search is a procedure for identifying a cell (communication service area) that can be connected after the terminal device is turned on.

The terminal device 400-1 makes a connection request to the base station device (in this case, the base station device 300-A) having the cell ID with the maximum received power (step 504).

The base station device 300-A measures its own current traffic (total traffic with other terminal devices connected to its own cell). When it is determined that the current communication volume is greater than the predetermined amount, the base station apparatus is connected to another base station apparatus with a small communication volume, so that other base station apparatuses (base station apparatus 300-B in FIG. 5) exist in the vicinity. ) Is sent an instruction (communication amount request) to notify its current communication amount (step 505).

The base station device 300-B that has received the communication amount notification instruction sends its current communication amount to the base station device 300-A (communication amount notification) (step 506).

Receiving the connection request in step 504, the base station apparatus 300-A determines the base station apparatus to which the terminal apparatus 400-1 is connected in consideration of the traffic, received power, biased received power, or the like (step 507). .

The base station device 300-A that has received the communication amount notification determines the communication amount of the base station device 300-B based on a predetermined amount that is set in advance, and determines that the communication amount is small (depending on the preset communication amount) If there are fewer, a cooperative communication request is transmitted to the base station apparatus 300-B (step 508a). When it is determined that the communication volume is large, the base station apparatus 300-A instructs the other base station apparatus (not shown) that can be connected to notify its current communication volume (communication volume request). )

When the base station apparatus 300-A transmits a cooperative communication request to the base station apparatus 300-B so as to connect to the terminal apparatus 400-1, the base station apparatus 300-A sends the terminal apparatus 400-1 to the terminal apparatus 400-1 almost simultaneously. 1 notifies the base station ID of the base station apparatus to be connected (ID unique to the base station apparatus) (connection base station notification) (step 509).

Upon receiving the connection base station notification, the terminal device 400-1 makes a connection request to the base station device 300-B (step 510).

The base station device 300-B that has received the connection request notifies (ACKs) the connection permission to the terminal device 400-1 (step 511).

The terminal device 400-1 notifies the base station device 300-B of a channel quality display (CQI: Channel Quality Indicator) indicating the channel state (transmission path state) (step 512). The channel state includes a modulation and coding scheme (MCS: Modulation and Coding Scheme), information for determining the number of MIMO ranks, between the peripheral base station apparatus including the base station apparatus 300-B and the terminal apparatus 400-1. Of channel estimates.

The base station apparatus 300-B performs scheduling, MCS setting, rank setting setting, and the like based on the CQI transmitted from the terminal apparatus 400-1 (step 513).

Further, base station apparatus 300-B suppresses interference given to base station apparatus 300-A and base station apparatus 300-B to terminal apparatus 400-1 and other terminal apparatuses connected to the peripheral base station apparatus. The transmission weight coefficient to be transmitted is calculated, and the transmission weight coefficient of the base station apparatus 300-A is transmitted to the base station apparatus 300-A (transmission weight notification) (step 514).

The base station apparatus 300-A performs control so as to suppress the interference given to the terminal apparatus 400-1 using the transmitted transmission weight coefficient (step 515).

The base station apparatus 300-B performs precoding (weighting) based on the obtained transmission weighting coefficient (step 516). Further, the base station apparatus 300-B calculates a reception weight coefficient used in the terminal apparatus 400-1, and transmits the reception weight coefficient to the terminal apparatus 400-1 (step 517).

Subsequently, the base station device 300-B transmits a data signal to the terminal device 400-1 (step 518).

As described above, in the first embodiment, when a terminal apparatus is connected to a base station apparatus that does not have the maximum received power, the base station apparatus does not receive interference from the base station apparatus that has the maximum received power. By cooperating, it is possible to effectively suppress inter-cell interference arriving at the terminal device, so that it is possible to suppress a decrease in throughput, and it is possible to effectively suppress inter-cell interference. In addition, since it is possible to connect to a base station apparatus with a small communication amount, it is possible to obtain a scheduling effect and to perform communication with good reception characteristics.
<Second Embodiment>
In the first embodiment, interference suppression is performed when the terminal device is connected to a base station other than the base station having the maximum received power. In the second embodiment, a base other than the base station having the maximum transmission power is used. An example of performing processing for suppressing interference when connecting to a station will be described.

The communication system 1b according to the second embodiment includes a plurality of different base station devices (macro base stations and picocell base stations), and constructs a heterogeneous network. Part or all of the macro cell range formed by the macro base station (FIG. 6, base station apparatus 300-D) and the pico cell base station (FIG. 6, base station apparatus 300-C) having a maximum transmission power smaller than that of the macro base station It is arranged so that it overlaps the cell range.

The configurations of the base station devices 300-C and 300-D and the terminal device 400-2 included in the communication system 1b according to the second embodiment are the same as those of the base station device included in the communication system 1 according to the first embodiment. Since the configuration is the same as that of the terminal 300-j (300-A, 300-B) and the terminal device 400-k (400-1), description thereof is omitted.

FIG. 6 is a sequence diagram showing an example of processing of the base station devices 300-C and 300-D and the terminal device 400-2 in the present embodiment in the communication system 1b.

First, the base station devices (base station devices 300-C and 300-D) periodically transmit a synchronization signal and a reference signal to the terminal device 400-2 at predetermined time intervals, respectively (steps 601 and 602). ). The terminal device 400-2 is in a communicable and waiting state (idle state).

After the power is turned on, the terminal device 400-2 starts a process (cell search) for detecting a cell (cell ID) that can be used for communication using a synchronization signal (step 603), and receives power (or bias) The cell ID of the base station apparatus (base station apparatus 300-C in FIG. 6) having the largest received power is acquired, and a connection request is made to the base station apparatus 300-C (step 604).

The base station device 300-C permits (ACKs) the connection to the terminal device 400-2 and the connection is established (step 605).

The base station device 300-C transmits a cooperative communication request to the base station device 300-D (step 610).

The terminal apparatus 400-2 notifies the base station apparatus 300-C of a channel quality display (CQI) indicating the channel state (transmission path state) (step 611). The channel state includes a modulation and coding scheme (MCS), information for determining the number of MIMO ranks, and a channel estimation value between the peripheral base station apparatus including the base station apparatus 300-D and the terminal apparatus 400-2. Including.

The base station apparatus 300-C performs scheduling, MCS setting, rank setting setting, and the like based on the CQI transmitted from the terminal apparatus 400-2 (step 612).

The base station apparatus 300-C transmits a channel information notification to the base station apparatus 300-D in order to share the channel quality indication (CQI) received in step 611 with the base station apparatus 300-D (step 613).

Further, base station apparatus 300-D suppresses the transmission weight coefficient that suppresses the interference that base station apparatus 300-D gives to terminal apparatus 400-2, and the interference that base station apparatus 300-C gives to the terminal apparatus of another cell. The transmission weight coefficient and the terminal device 400-2 are calculated, and the transmission weight coefficient for the base station device 300-C is transmitted to the base station device 300-C (transmission weight notification) (step 614).

Also, the base station apparatus 300-D calculates a reception weight coefficient used in the terminal apparatus 400-2 and transmits the reception weight coefficient to the terminal apparatus 400-2 (step 615).

Meanwhile, the base station apparatus 300-C performs precoding (weighting) based on the transmission weight coefficient transmitted from the base station apparatus 300-D (step 616).

Subsequently, the base station device 300-C transmits a data signal to the terminal device 400-1 (step 617).

The terminal device 400-2 is notified of the base station ID (ID unique to the base station device) of the base station device to which the terminal device 400-2 should connect (connection base station notification) (step 613).

The base station apparatus 300-C performs control so as to suppress the interference given to the terminal apparatus 400-2 using the transmitted transmission weight coefficient (step 618).

As described above, in the second embodiment, when a terminal device is connected to a base station device other than the maximum transmission power, the plurality of base station devices cooperate with each other by cooperation between the plurality of base station devices. The influence of inter-cell interference can be suppressed, and the inter-cell interference arriving at the terminal device can be effectively suppressed, so that a reduction in throughput can be suppressed.

Note that the program that operates on the terminal device according to the present invention is a program that controls the CPU or the like (a program that causes a computer to function) so as to realize the functions of the above-described embodiments according to the present invention. Information handled by these devices is temporarily stored in the RAM at the time of processing, then stored in various ROMs and HDDs, read out by the CPU, and corrected and written as necessary. As a recording medium for storing the program, a semiconductor medium (for example, ROM, nonvolatile memory card, etc.), an optical recording medium (for example, DVD, MO, MD, CD, BD, etc.), a magnetic recording medium (for example, magnetic tape, Any of a flexible disk etc. may be sufficient. In addition, by executing the loaded program, not only the functions of the above-described embodiment are realized, but also based on the instructions of the program, the processing is performed in cooperation with the operating system or other application programs. The function of the invention may be realized.

Also, when distributing to the market, the program can be stored in a portable recording medium for distribution, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is also included in the present invention. Moreover, you may implement | achieve part or all of the terminal device and base station apparatus in embodiment mentioned above as LSI which is typically an integrated circuit. Each functional block of the receiving apparatus may be individually formed as a chip, or a part or all of them may be integrated into a chip. When each functional block is integrated, an integrated circuit controller for controlling them is added.

Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, when an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology can also be used.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and the design and the like within the scope not departing from the gist of the present invention are also claimed. Included in the range.

1, 1a Communication system 300-1, 300-2, 300-3, 300-4

Base station apparatus

301, 411 Upper layer 302 Encoding section 303 Modulation section 304 Resource mapping section 305 Reference signal generation section 306 Control signal generation section 307 Transmission weight generation unit 308 Transmission weight multiplication unit 303-1, 309-T IFFT unit 310-1, 310-T, 413 Transmission unit 312-1, 312-T, 414 Transmission antenna unit 313, 401-1, 401-R Reception antenna unit 314, 402-1, 402-R Reception unit 315 Control signal detection unit 316 Base station selection unit 400-1, 400-2, 400-3, 400-4 Terminal device 403-1, 203-R GI removal Unit 404-1, 404-R FFT unit 405 reception weight multiplication unit 406 MIMO separation unit 407 channel estimation 408 reception power calculation unit 409 demodulation unit 410 decoding unit 412 control signal generating unit

Claims

A plurality of base station devices, and a terminal device connected to at least one of the plurality of base station devices, wherein the plurality of base station devices are connected to each base station device in the entire range or one cell. The communication system is arranged so that the parts overlap each other,
A communication system, wherein a plurality of base station devices select whether to reduce inter-cell interference in cooperation with a base station device to which the terminal device is connected.
The inter-cell interference is reduced when the base station apparatus connected to the terminal apparatus is a base station apparatus other than the base station apparatus that provides the maximum received power in the terminal apparatus. The communication system described.
The base station apparatus connected to the terminal apparatus reduces the inter-cell interference when connecting to a base station other than the maximum transmission power among the plurality of base station apparatuses. 2. The communication system according to 2.
The communication system according to claim 3, wherein the base station device other than the maximum transmission power is a pico base station device.
The communication system according to any one of claims 1 to 4, wherein the base station apparatus reduces the inter-cell interference by precoding.
The communication system according to any one of claims 1 to 5, wherein the terminal device reduces the inter-cell interference by a reception weight.
A plurality of base station devices, and a terminal device connected to at least one of the plurality of base station devices, wherein the plurality of base station devices are connected to each base station device in the entire range or one cell. A communication method in a communication system arranged so that parts overlap each other,
A communication method comprising the step of selecting whether or not the plurality of base station apparatuses cooperate to reduce inter-cell interference by a base station apparatus connected to the terminal apparatus.