JP2008072540A - Wireless base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless base station with less interference and without reducing communication capacity by appropriately specifying location in a sub channel such as an Uplink individual channel. <P>SOLUTION: An interference amount of the same channel in an Uplink control channel assignable area divided into a plurality of areas in the frequency direction is measured and a control channel is first located at a part with the fewest interference amount. After that, the interference amount of the same channel in a plurality of individual channel assignable areas is periodically measured, or its measurement results are stored and the Uplink control channels are sequentially assigned to individual channels from the one with the fewest interference amount based on the measurement results if necessary. Thus, wireless channels are precisely arranged by determining location of the Uplink channels in the frequency direction. In addition, since the Uplink individual channels are dynamically assigned to parts with less interference of the same channel, deterioration of communication quality by interference of the same channel is also suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio base station, and more particularly to a radio base station that measures co-channel interference using Uplink using OFDMA (Orthogonal Frequency Division Multiple Access) or SC-FDMA (Single Carrier Frequency Division Multiple Access). It is.

  Unlike FDMA (Frequency Division Multidimensional Connection) such as TACS (Total Access Communication System) and AMPS (Advanced Mobile Phone Service), OFDMA and SC-FDMA are multiple for each carrier or subcarrier and for each symbol. Can be connected. In other words, it is a multiple access method that combines FDMA and TDMA. Therefore, the multiple access method is more flexible than the conventional FDMA system. Also, frequency multiplexing has higher frequency utilization efficiency than conventional FDMA systems because it uses orthogonality for multiplexing in the frequency direction.

  In OFDMA or the like, interference (co-channel interference) occurs between adjacent cells when channels of the same frequency are used in a plurality of base stations forming each cell (see FIG. 6). Such interference becomes interference with each other and deteriorates the channel capacity in each cell, so it is necessary to avoid it by devising channel allocation. Conventionally, there is known one that performs channel allocation by detecting the amount of interference (see Patent Documents 1 to 3 below). In particular, in the [0013] paragraph of Patent Document 1, “the base station directly collects the uplink SINR (Signal to Interference + Noise Ratio) of each subcarrier from the access channel (by measuring the bit error rate (BER), etc.). It can be done ".

In addition, the conventional method of using HARQ (Hybrid Automatic Repeat Request) is to transmit data once, and when a NACK is returned, the same data is transmitted in the Chase synthesis method, and the new method is used in the IR (Incremental Redundancy) method. Is sending data. In this method, taking into account fluctuations in the radio channel due to transmission time differences, errors in received data are distributed, and data is transmitted and received with an error correction coding gain.
JP-T-2005-502218 JP-T-2004-523934 JP 2006-050545 A

  However, IEEE802.16-2005, which employs OFDMA for the uplink mentioned above, does not stipulate how the uplink control channel or uplink dedicated channel is arranged in the subchannel. Also, in 3GPP Long Term Evolution adopting SC-FDMA for Uplink, it is not defined how to arrange Uplink dedicated channels.

  In addition, in the case of the method described in Patent Document 1 cited secondly, in a multipath environment in which delayed waves exceeding the guard interval and high-speed fading may occur, the SINR deteriorates because the own signal becomes interference, and the same. Despite not being channel interference, channel allocation is not performed. Since such a channel can be used by using a modulation scheme that is resistant to fading or the like, the determination that it is not used unconditionally has a problem of reducing the communication capacity of the entire system.

  Furthermore, the conventional method of using HARQ (Hybrid Automatic Repeat Request) described in the third is that when data is transmitted once and NACK is returned, the same data is transmitted in the Chase combining method, and IR (Incremental Redundancy) was sending new data. In this method, taking into account fluctuations in the radio channel due to transmission time differences, errors in received data are distributed, and data transmission / reception is performed using error correction coding gains. There is a delay.

  The present invention has been made in order to solve the above-described problems. Uplink for a radio base station is OFDMA or SC-FDMA, and how an uplink control channel and an uplink dedicated channel are arranged in subchannels. Providing a radio base station that appropriately defines and prevents the communication capacity from being reduced by accurately determining whether or not the interference is the same channel when interference occurs, and does not cause delay in data transmission / reception The purpose is to do.

  In order to solve the above-described problems, a radio base station according to the present invention uses a radio base station that uses OFDMA or SC-FDMA for uplink, and the radio base station performs co-channel interference on an uplink dedicated channel that has already been allocated. In order to measure the amount, the mobile station is instructed to generate a Null data period, which is a part where no data exists on the Uplink dedicated channel, and at which timing the Null data period is set in the radio base station. , Perform random backoff, determine the insertion timing of the Null data period based on the result, instruct the mobile unit to create a Null data period on the Uplink dedicated channel, and instruct the mobile unit The amount of co-channel interference is measured in the data period.

  Since the present invention is configured as described above, the radio base station sets a null data period on the uplink dedicated channel in order to measure the co-channel interference amount on the uplink dedicated channel that has already been allocated. , It can be managed dynamically so that the communication quality of the uplink dedicated channel already allocated does not deteriorate. In addition, when determining the insertion timing of the Null data period, random backoff is performed, thereby reducing the problem that the Null data period occurs at the same timing as the adjacent cells, preventing data delay and the same. Channel interference can be accurately grasped.

  Further, in the present invention, when it is determined from the measurement result that the same channel interference amount does not satisfy the communication quality of the uplink dedicated channel, the radio base station determines that the uplink dedicated channel is a different uplink dedicated channel. When moving to the assignable area, the bandwidth of the individual channel of the movement destination is changed according to the bandwidth request amount from the mobile device.

  Further, in the present invention, the radio base station determines from the measurement result that the co-channel interference amount does not satisfy the communication quality of the uplink dedicated channel, and tries to allocate the uplink dedicated channel to another uplink dedicated channel. When the communication quality cannot be satisfied with one new individual channel, one more individual channel is added to the current individual channel, and when the uplink transmission data is short, the current uplink individual The same uplink transmission data is transmitted between the channel and the newly added uplink dedicated channel, the HARQ (Hybrid Automatic Repeat Request) of the Chase combining method is performed at the radio base station, and if the uplink transmission data is long, the current uplink dedicated channel And the newly added Uplink dedicated channel, one Uplink transmission data is separated into two Uplink dedicated channels and transmitted, and the wireless base Performing HARQ (Hybrid Automatic Repeat Request) of Incremental Redundancy method at the station.

  As described above in detail, according to the present invention, a radio base station can precisely arrange a radio system by measuring the amount of co-channel interference and determining the arrangement of uplink channels in the frequency direction. . In addition, since an uplink dedicated channel is dynamically allocated to a portion with less co-channel interference, it is possible to suppress deterioration in communication quality due to co-channel interference. In addition, data delay can be prevented by using HARQ together with Uplink at the same time.

Embodiments of the present invention will be described below with reference to the drawings.
1 to 19 are diagrams for individually explaining various functions of the radio base station according to the embodiment of the present invention, and FIG. 20 is a block diagram showing the radio communication system according to the embodiment of the present invention. .

  The wireless communication system in the present embodiment shown in FIG. 20 includes a wireless base station 1 and a plurality of mobile stations 2. The radio base station 1 includes a channel control unit 11 that performs channel control, an instruction unit 12 that performs a predetermined instruction in the present embodiment, a modulation unit 13, a demodulation unit 14, and a channel interference amount in the present embodiment. A quality measuring unit 15 for measuring is provided. The plurality of mobile stations 2 includes a control unit 21, a demodulation unit 22, and a modulation unit 23.

Hereinafter, the operation of the present embodiment will be described with reference to FIGS.
(1) First, an uplink control channel allocation method will be described with reference to FIG. 1 and FIG.
1) The quality measurement unit 15 in the radio base station determines “uplink control within the band as shown in FIG. 1 in order to determine the arrangement position of the uplink control channel in the frequency direction based on the instruction from the instruction unit 12. First, the same channel interference amount is measured for each of the channel allocatable regions 1, 2, to, n-1, n, n + 1 ".
2) Based on the measurement, the channel control unit 11 arranges the uplink control channel in the region where the co-channel interference amount is the smallest, for example, as shown in FIG. 2, based on the measurement result of the quality measurement unit 15. . The uplink control channel corresponds to, for example, Ranging, CQICH, and ACK-CH in IEEE 802.16-2005. Thus, by arranging in the place with the least amount of interference, the co-channel interference of the control channel can be reduced.

(2) Uplink dedicated channel allocation method:
1) The quality measurement unit 15 of the radio base station periodically measures the same channel interference amount in an area excluding the uplink control channel and the existing dedicated channel in order to determine the arrangement position of the uplink dedicated channel in the frequency direction, The amount of co-channel interference is stored in a memory (not shown). FIG. 3 shows this movement.
2) From the above measurement result or the measurement result in the memory, the channel control unit 11 arranges the uplink dedicated channel where the same channel interference amount is the smallest. FIG. 4 shows an example in which Uplink dedicated channels are arranged. For example, in IEEE802.16-2005, the part called Uplink Burst corresponds to the Uplink dedicated channel, and the minimum unit of the Uplink dedicated channel is determined from the subchannel. Burst is included in each subframe of Uplink and Downlink. Also, Burst can use different frequencies for different OFDMA symbols. In addition, DPCH of 3GPP Long Term Evolution (3GPP TR 25.814) corresponds to the individual channel, Chunk bandwidth represents the size of one individual channel in the frequency direction, and Chunk (cluster of subcarriers) changes the frequency for each slot. it can. That is, as shown in FIG. 5, Uplink dedicated channels can be arranged so that frequency components change in the middle of time.

(3) Uplink dedicated channel reassignment method:
1) The instruction unit 12 of the radio base station generates a portion (Null data period) in which no data exists on the uplink dedicated channel in order to measure the co-channel interference amount on the uplink dedicated channel that has already been allocated. Instruct the mobile device to Based on this instruction, as shown in FIG. 6, the quality measuring unit 15 of the radio base station measures the co-channel interference amount in the null data period set on the uplink dedicated channel that has already been allocated. To determine the timing of the null data period, random backoff is performed based on an instruction from the instruction unit 12 in the radio base station, and the insertion timing of the null data period is determined based on the result. Thus, by performing random back-off, the problem that a null data period occurs at the same timing as the adjacent cell is reduced. This will be described below with reference to FIGS.

  FIG. 7 shows a case where there are terminals (mobile devices) TM1 subordinate to the radio base station RS1 and the radio base station RS1, and there are terminals (mobile devices) TM2 subordinate to the radio base station RS2 and the radio base station RS2. This shows a state where the same frequency (same channel) is used in both cells. In such a state, as shown in FIG. 8, according to random backoff, it is less likely that Null data periods overlap between adjacent cells. After such processing, the mobile station creates a null data period on the uplink dedicated channel according to the instructions of the radio base station. The radio base station measures the co-channel interference amount in the Null data period instructed to the mobile device and stores it in the memory.

2) If the quality measurement unit 15 of the radio base station determines from the above measurement result or the measurement result in the memory that the co-channel interference amount does not satisfy the communication quality, as shown in FIG. The uplink dedicated channel is moved (rearranged) to another Uplink dedicated channel assignable area in the next frame. Further, the bandwidth of the individual channel of the movement destination is changed according to the bandwidth request amount of the mobile device.

  For example, when the mobile device is performing voice communication, if the bandwidth before the movement has sufficient bandwidth for performing voice communication, the bandwidth of the destination may be reduced as shown in FIG. In the case of image communication, the destination band may be changed in accordance with the application of the mobile device and the required bandwidth, such as expanding the destination band as shown in FIG. In this case, it is assumed that the destination of movement is the least amount of co-channel interference in the remaining uplink dedicated channel possible area. The wireless base station notifies the mobile device of this movement instruction.

3) As a simplified method of measuring the co-channel interference amount in the null data period, it is also possible to use the cumulative number of CRC errors of the uplink individual channel or a simple BER. As a simple BER measurement for one transmission, (Equation 1) is used, and the total simplified BER can be calculated by accumulating (Equation 1).

Simple BER for one transmission
= Number of CRC errors in one transmission data amount / One transmission data amount
(Formula 1)

4) The radio base station 1 determines that the uplink dedicated channel does not satisfy the communication quality based on the same channel interference amount measurement by the quality measuring unit 15, and tries to move the uplink dedicated channel to another frequency. As a result of examining other co-channel interference amounts, if it is determined that the communication quality cannot be satisfied with one new uplink dedicated channel, the smallest co-channel interference amount in the examined results Add a new Uplink dedicated channel. That is, as shown in FIG. 12, two channels, the individual channel up to the previous time and the newly added individual channel, are allocated.

  A case where HARQ (Hybrid Automatic Repeat Request) is performed using the above-described two uplink dedicated channels will be described. In conventional HARQ, when data is transmitted once and NACK is returned, the same data is transmitted by the Chase combining method, and new data is transmitted by the IR (Incremental Redundancy) method. This takes into account fluctuations (non-correlation) of the radio channel due to transmission time differences, disperses errors in received data, and uses gain of error correction correction capability to give gain to data transmission / reception. However, since a time difference is used, data delay occurs. Therefore, this delay becomes a problem when data severe in delay such as voice and image is transmitted.

  However, OFDMA and SC-FDMA systems generally use a wide band (5 to 20 MHz band). In the case of broadband communication, frequency selective fading is performed as shown in FIG. For this reason, when two uplink dedicated channels that are separated in frequency are used, the result is as shown in FIG. In this way, an uncorrelated Uplink dedicated channel can be secured within one frame. Therefore, as shown in FIG. 15, HARQ is used on these two uplink dedicated channels.

  In this case, the Chase synthesis method HARQ is applied to short data such as speech. In this case, as shown in FIG. 16, the same data is transmitted using two uplink dedicated channels. Then, in the radio base station, as shown in FIG. 17, weighting is performed based on the SINR of each individual channel, and synthesis is performed. By doing so, data delay does not occur.

  The IR synthesis method HARQ is applied to long data such as images. In this case, as shown in FIG. 18, the data is divided and different data is transmitted using the two uplink dedicated channels. Then, the radio base station assembles received data as shown in FIG. In this case, since the two uplink dedicated channels are uncorrelated, the error is dispersed, and the probability that received data is correctly decoded by the coding gain of error correction is high. Therefore, data delay is less likely to occur.

  Next, an operation example of a radio base station having the various functions described above will be described. As an example of this case, a case of a radio base station configured according to IEEE 802.16e (hereinafter referred to as WiMAX) will be described. With WiMAX having a bandwidth of 5 MHz, the FFT size is 512, and 272 subcarriers can be used for Uplink. These subcarriers constitute 17 subchannels (also simply referred to as channels). The co-channel interference of the subchannel is obtained as a value obtained by adding the power of each subcarrier constituting the subchannel from the FFT result of the UpLink signal received at the base station.

  When the radio base station is activated, in the state where no subchannel is assigned to UpLink, the same channel interference of all subchannels is measured (FIG. 1) and held as a table (step S1). This table shows the sub-channel number, the co-channel interference amount, the usage status of the channel (which channel or Burst is allocated), and the co-channel interference amount that can limit the quality required for the sub-channel. Is associated. The limit amount of interference is determined by the modulation scheme and error correction code used in the subchannel.

The radio base station determines to allocate control channels such as UL-CQICH, UL-Ranging, UL-AchCH in order from the subchannel with the least co-channel interference (step S2; FIG. 2). Then, the allocation information is recorded in the UL-MAP included in DownLink and transmitted, and the usage status of the table is updated.
The radio base station measures co-channel interference at a constant time period (for example, a frame period) and updates the table (step S3).

When there is a channel whose interference amount exceeds the limit interference amount (assuming that channel is channel A), the radio base station searches for an unused channel with the smallest interference amount (referred to as channel A) ( Step S4).
If the interference amount of the unused channel found is equal to or less than the limit interference amount of channel A, the radio base station rewrites the table and exchanges the channel assignment (FIG. 9). That is, the searched unused channel is assigned instead of channel A (step S5).

  When the limit interference amount is exceeded, the radio base station rewrites the table and assigns both the unused channel and channel A that are searched (step S6; FIGS. 15 and 16).

  When there is a new channel assignment request, the radio base station refers to the table, assigns the remaining unused channels with the smallest amount of interference (FIG. 4), and updates the table (step S7). ).

The radio base station creates a UL-MAP by referring to the current table, and transmits it by including it in DownLink (step S8). Thereafter, steps S3 to S8 are repeated.
As a result, the terminal (mobile device) receives the UL-MAP and transmits UpLink using the dedicated channel indicated by it. Therefore, the co-channel interference measured by UpLink may be immediately reflected in UpLink of the next frame.

It is a figure which shows the method of measuring the co-channel interference amount in a frequency direction, in order to determine the arrangement | positioning of a frequency direction about the control channel assignable area | region of Uplink. It is a figure which shows the example which has arrange | positioned the Uplink control channel in the place where there was the least interference amount based on the result of having measured the amount of co-channel interference as shown in FIG. It is a figure which shows the method of measuring the co-channel interference amount in order to determine the arrangement position of the frequency direction of an uplink dedicated channel. It is a figure which shows the example which allocated the uplink separate channel to the place with the least interference amount based on the result of having measured the amount of co-channel interference by the method shown by FIG. It is a figure which shows the case where the frequency component of the area | region allocated to the separate channel is changed in the middle of time. It is a figure which shows the method of measuring the co-channel interference amount on the uplink dedicated channel already arrange | positioned. It is a figure which shows the state which is using the same frequency (same channel) between two adjacent radio base stations. In the environment of FIG. 7, it is a figure which shows that the time of a Null data area | region differs by random backoff, and can measure the interference amount of an adjacent same channel. If the radio base station determines that the co-channel interference amount does not satisfy the communication quality based on the measurement result shown in FIG. 6 or FIG. 8 or the measurement result stored in the memory, the uplink dedicated channel It is a figure which shows the method of moving to another uplink dedicated channel allocatable area | region. As shown in FIG. 9, when moving the Uplink dedicated channel to another Uplink dedicated channel allocatable area, it is a diagram illustrating a method of moving by increasing the new bandwidth allocation amount of the destination. As shown in FIG. 9, when moving the uplink dedicated channel to another uplink dedicated channel allocatable area, it is a diagram illustrating a method of moving by reducing the new bandwidth allocation amount of the destination. It is a figure which shows the example which added the uplink separate channel by the uplink separate channel already arrange | positioned by the same channel interference amount. It is a figure which shows that it becomes frequency selective fading in wideband communication. FIG. 13 is a diagram illustrating an example in which a newly added dedicated channel is arranged when frequency selective fading exists as shown in FIG. It is a figure which shows the operation example in the case of performing HARQ with the uplink separate channel already arrange | positioned and the newly added Uplink separate channel. It is a figure which shows the Uplink transmission data allocation method in the case of performing Chase synthetic | combination method HARQ with the uplink separate channel already arrange | positioned and a newly added Uplink separate channel. It is a figure which shows decoding of Chase combining method HARQ in a radio base station. It is a figure which shows the uplink transmission data allocation method in the case of performing IR (Incremental Redundancy) method HARQ with the uplink dedicated channel already arrange | positioned and the newly added Uplink dedicated channel. It is a figure which shows decoding of IR method HARQ in a wireless base station. It is a block diagram which shows the radio | wireless communications system in embodiment of this invention.

Explanation of symbols

1, RS1, RS2 radio base station, 2, TM1, TM2 terminal (mobile device), 11 channel control unit, 12 instruction unit, 13 modulation unit, 14 demodulation unit, 15 quality measurement unit, 21 control unit, 22 demodulation unit, 23 Modulator.

Claims (3)

A radio base station that measures co-channel interference in a radio base station that uses OFDMA or SC-FDMA for uplink,
Instructs the mobile station to generate a null data period, which is a part where no data exists on the uplink dedicated channel that has already been allocated, and performs a random back-off as to when the null data period should be Based on the result, the insertion timing of the Null data period is determined, the mobile unit is instructed to create a Null data period on the Uplink dedicated channel, and the same channel interference amount is determined in the Null data period instructed to the mobile unit. Radio base station to measure. In the radio base station according to claim 1,
When it is determined from the measurement result that the same channel interference amount does not satisfy the communication quality of the uplink dedicated channel, when moving the uplink dedicated channel to another uplink dedicated channel assignable area, A radio base station that changes the bandwidth of a dedicated channel of a moving destination in accordance with a bandwidth request amount. In the radio base station according to claim 1,
From the result of the measurement, when it is determined that the co-channel interference amount does not satisfy the communication quality of the uplink dedicated channel and it is attempted to assign the uplink dedicated channel to another uplink dedicated channel, the communication quality of the new single dedicated channel If it is not possible to satisfy this condition, add another dedicated channel to the current dedicated channel. If the Uplink transmission data is short, the same Uplink transmission data is used for the current Uplink dedicated channel and the newly added Uplink dedicated channel. If the uplink transmission data is long, two uplink transmission data are transferred to the current uplink dedicated channel and the newly added uplink dedicated channel, if HARQ (Hybrid Automatic Repeat Request) of Chase combining method is performed. It is separated and transmitted to uplink dedicated channels, and HARQ (Hybrid Automatic Repeat Request) of Incremental Redundancy method is performed. Base station.

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