WO2016107479A1 - 一种室内das系统与小基站下行干扰避免方法 - Google Patents

一种室内das系统与小基站下行干扰避免方法 Download PDF

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WO2016107479A1
WO2016107479A1 PCT/CN2015/098457 CN2015098457W WO2016107479A1 WO 2016107479 A1 WO2016107479 A1 WO 2016107479A1 CN 2015098457 W CN2015098457 W CN 2015098457W WO 2016107479 A1 WO2016107479 A1 WO 2016107479A1
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das system
small base
base station
signal strength
sinr
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PCT/CN2015/098457
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English (en)
French (fr)
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潘鹏
陈新
严军荣
姚英彪
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三维通信股份有限公司
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Priority to US15/540,858 priority Critical patent/US10075216B2/en
Priority to JP2017552209A priority patent/JP6473521B2/ja
Publication of WO2016107479A1 publication Critical patent/WO2016107479A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/318—Received signal strength
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H04J11/0023—Interference mitigation or co-ordination
    • H04J11/005—Interference mitigation or co-ordination of intercell interference
    • H04J11/0056—Inter-base station aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
    • H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J2211/00—Orthogonal indexing scheme relating to orthogonal multiplex systems
    • H04J2211/001—Orthogonal indexing scheme relating to orthogonal multiplex systems using small cells within macro cells, e.g. femto, pico or microcells

Definitions

  • the invention belongs to the field of mobile communications, and relates to a method for cooperatively suppressing co-channel interference between cells, and particularly relates to a method for avoiding downlink interference of an indoor DAS system and a small base station.
  • Small base stations refer to various low-power, small-coverage, and flexible deployment of wireless access points, which have become a development trend of future sites. They can solve the problems of indoor coverage, hotspot coverage, and deep coverage of mobile communication networks through scale deployment. Make up for the shortage of macro cellular networks, improve spectrum efficiency, improve network capacity, better meet the future development needs of mobile communication services and enhance user experience.
  • 3GPP LTE proposes the concept of full frequency reuse, that is, the mode of using the same frequency network between different cells, which will cause the cell edge users to suffer large co-channel interference and the quality of service ( QoS) is lowered.
  • QoS quality of service
  • the indoor deployment mode of small base stations can easily interfere with existing indoor coverage systems.
  • DAS distributed antenna systems
  • simple delay of traditional macro base stations can meet the problem of signal coverage, but cannot improve the system. Capacity
  • an interference coordination mechanism based on inter-cell cooperation such as ICIC, eICIC and FeICIC.
  • the basic idea is to make the signals of neighboring cells orthogonal to each other in the time domain, the frequency domain or the airspace, so as to avoid mutual interference.
  • the cost of the above interference coordination mechanism is to pay a certain capacity loss.
  • the above-mentioned interference coordination mechanism between the macro stations or between the outdoor macro station and the small base station will be difficult to effectively play its role. Therefore, it is necessary to redesign the corresponding cooperation mode according to the characteristics of indoor deployment and distribution of the DAS system, and introduce signal processing methods to suppress interference.
  • the present invention provides a method for avoiding downlink interference of the indoor DAS system and the small base station, and the specific method is applied to the small DAS system.
  • Downlink co-channel interference synergy suppression method between base station and indoor distributed antenna system (DAS) which can effectively reduce indoor DAS system Mutual interference with the small base station.
  • the present invention solves the technical problems adopted by the technical problems: Before describing the specific steps of the present invention, some abbreviations and symbols are first defined.
  • the main unit of the indoor DAS system is denoted by MU; the remote unit and the antenna connected thereto are denoted by the abbreviation RU, and the RUn (n is a natural number such as 1, 2, 3, . . . ) is defined as the nth RU.
  • the terminal is represented by a UE.
  • UE1 is used to indicate a terminal that accesses the DAS system
  • UE2 is a terminal that accesses the small base station.
  • SINR is the ratio of signal power to interference plus noise power.
  • the threshold values of the two SINRs involved in the implementation steps of the present invention are represented by ⁇ 1 and ⁇ 2, respectively, and ⁇ 1 is smaller than ⁇ 2. Wherein, if the SINR is less than ⁇ 1 indicating that there is a large interference, the signal power needs to be increased; if the SINR is greater than ⁇ 2, indicating that there is a large power margin, the signal power can be appropriately reduced.
  • the indoor DAS system and the small base station downlink interference avoiding method according to the present invention the steps include:
  • Step 1 Determine the initial access RU and establish a signal strength table.
  • the DAS system When UE1 needs to access the DAS system, an access request is sent to the DAS system.
  • the DAS system establishes a signal strength table for UE1 within the MU according to the signal power of the request signal received by each RU.
  • the signal strength table includes the ID of each RU and the corresponding normalized received signal strength.
  • the normalized signal strength is the signal strength of the RU with the actual signal strength of each RU being the strongest as the received signal, and the RU with the strongest received signal is allocated to UE1 as its initial access RU.
  • the DAS system continuously updates the signal strength table during the entire communication with UE1.
  • the MU is a main unit of the indoor DAS system
  • the RU is a remote unit and an antenna connected thereto
  • the UE1 represents a terminal that accesses the DAS system.
  • Step 2 DAS system establishes a downlink selected by trial and RU UE1, UE1 downlink signal detection SINR SINR value, and the preset threshold value comparison ⁇ 1, perform the following procedure:
  • the UE1 performs the following process: establishing a downlink with the RU allocated to the UE1, and starting downlink data transmission;
  • Step 201b UE1 feeds back a SINR value to the DAS system through the control channel.
  • Step 202b The DAS system selects an appropriate number of RUs from the candidate RUs according to the SINR value, and jointly sends data to the UE1.
  • Step 203b The DAS system queries the terminal UE2 that accesses the small base station with the same frequency point by the UE1 through the control channel;
  • the UE2 is a terminal that accesses the small base station.
  • Step 204b After confirming that the UE1 uses the same frequency point, the UE2 reports the DAS system through the control channel.
  • Step 205b The DAS system subsequently allocates a free time slot to the UE2, and requests the UE2 to send a training sequence.
  • Step 206b UE2 sends a training sequence in the allocated time slot, and the DAS system then estimates the channel of the selected RU to UE2;
  • Step 207b DAS transmitted by a plurality of tie RU selected to UE1 precoded data such that the SINR of the received signal is greater than the UE1 ⁇ 1, to ensure the corresponding QoS.
  • the precoding method makes the signal not interfere with the received signal of UE2.
  • Step 3 UE1 DAS system remains allocated to the downlink and one or more of which is RU, and a certain time interval SINR value is continuously detected during communication, 1, perform the following operations according to whether it is above ⁇ :
  • SINR value is less than ⁇ 2 , then continue to maintain communication with multiple RUs allocated to the DAS, and continue to detect the SINR value at certain time intervals during the communication process;
  • the RU is sequentially removed according to the received signal strength from weak to strong, until the predicted SINR value of the DAS system is slightly higher. ⁇ 1 , or only one RU left.
  • the RU is selected as follows: if the current SINR value is ⁇ , according to the signal strength table, according to the normalized signal strength from high to low (excluding the RU with a normalized signal strength of 1), in turn Select RU until the following formula is met:
  • P i represents the normalized signal strength of the RU in which the normalized signal strength is ranked in the i-th bit from the highest to the lowest in the signal strength table; and the parameter N represents the number of RUs required to satisfy the condition of the formula (1).
  • the precoding method is:
  • h 1 [h 1,1 , h 2,1 ,..., h N,1 ] represents a row vector composed of N channel fading coefficients of the RUs participating in the joint transmission to UE1.
  • J is the interference of the downlink signal from the small base station to the UE2 to the UE1
  • W is the noise
  • the DAS system participates in the nth RU of joint data transmission, and its transmission signal is w n x 1 , that is, the data transmitted by the RU is weighted on the data x 1 sent to UE1 by w n .
  • the received signal of UE2 is:
  • scalar h channel state information of the small base station to UE2 x 2 is the data transmitted to the small base station UE2.
  • the precoding matrix w is The eigenvector corresponding to the zero eigenvalue.
  • v be a matrix The eigenvector corresponding to the zero eigenvalue, then the precoding matrix is:
  • the preset threshold value ⁇ 1 takes a value of -3 dB to 3 dB
  • the preset threshold value ⁇ 2 takes a value of 5 dB to 15 dB.
  • the present invention does not require small base stations to participate in operations, and is convenient for home users and SOHO users to independently select small base stations of different brands and different functions.
  • FIG. 1 is a schematic diagram of a downlink interference scenario of a DAS system and a small base station.
  • FIG. 2 is a schematic diagram of a DAS system according to the present invention.
  • FIG. 3 is a flow chart for avoiding downlink interference of an indoor DAS system and a small base station.
  • Figure 4 is a specific embodiment 1 of the present invention.
  • FIG. 5 is a second embodiment of the present invention.
  • Figure 6 is a flow chart of multi-RU joint data transmission in the DAS system.
  • FIG. 1 is a schematic diagram of a specific application scenario of the present invention, where a DAS system and a small base station system are included in the scenario.
  • DAS systems improve indoor signal coverage by means of multiple RUs distributed throughout the building, but do not increase network capacity.
  • Small base stations are used for coverage of hotspots, which can effectively increase capacity, but for large buildings, full coverage like DAS systems cannot be achieved. Therefore, for a long time to come, it will be a hybrid deployment of the DAS system and the small base station system, which can not only meet the comprehensive signal coverage of the building, but also ensure the capacity requirements of the hotspot area.
  • the invention is in this scenario, and proposes a scheme for avoiding downlink interference between the DAS system and the small base station system, so that the same frequency deployment becomes possible.
  • UE1 is a terminal that accesses a DAS system
  • UE2 is a terminal that accesses a small base station.
  • the downlink transmission signal of the small base station may cause interference to UE1; meanwhile, the downlink transmission signal of the DAS system may also interfere with UE2.
  • the transmit power of a small base station is 25 dBm, while the transmit power of a single RU is only 15 dBm.
  • the present invention mainly considers the interference problem of the small base station to the UE1; at the same time, the multi-antenna characteristic of the DAS system is fully utilized in the process, and the precoding technology is used to prevent the interference of the DAS system to the UE2.
  • the indoor DAS system mainly includes a MU and various RU modules. Among them, the functions of the MU related to the present invention are:
  • the functions of the RU associated with the present invention are:
  • Figure 3 is a table of normalized received signal strengths established by the MU.
  • the MU establishes a normalized received signal strength table as shown in FIG. 3 for each UE accessing the DAS system.
  • the table corresponding to the table of each UE is named the ID of the UE.
  • Each table contains two fields, the ID of the RU and the normalized received signal power.
  • the normalized received signal power is the received power of the RU and the received power of the RU with the highest received power among all the RUs. Therefore, for the RU with the highest received power, the normalized received signal power is 1, and the normalized received signal power of the other RUs is less than 1.
  • FIG. 4 is a flow chart for avoiding downlink interference of an indoor DAS system and a small base station. A specific embodiment of the problem solving flowchart disclosed in FIG. 4 is given in conjunction with the scenarios set forth in FIGS. 5 and 6.
  • the distance from RU1 to UE1 is 14 meters; the distance from RU2 to UE1 is 10 meters; the distance from RU3 to UE1 is 40 meters, the distance from RU4 to UE1 is 35 meters, and the distance from small base station to UE1 is 17 meters.
  • the transmission power of each RU is 15 dBm, and the transmission power of the small base station is 25 dBm.
  • ⁇ 1 takes a value of 1 (ie, 0 dB)
  • ⁇ 2 takes a value of 4 (ie, 6 dB)
  • the path The loss is inversely proportional to the distance from the fourth power, and the received signal SNR is 10 dB.
  • the UE 2 also maintains communication with the small base station during the entire UE1 and DAS system communication period.
  • UE1 sends an access request to the DAS system through the control channel.
  • Each of the RUs of the DAS system receives the request signal, and uploads the received power of the signal to the MU.
  • the MU establishes a normalized received signal strength table based on the obtained signal power:
  • the system selects RU2 as the initial access RU of UE1.
  • Step 2 RU2 UE1 and attempts to establish a downlink, RU2 transmits data to UE1, UE1 calculates the SINR of the received signal is about 0.83 (i.e. -8.63dB), less than the preset ⁇ 1. So execute:
  • Step 201b UE1 feeds back a SINR value to the DAS system through the control channel.
  • Step 202b The DAS system combines the normalized intensity table according to the SINR value, and selects an appropriate number of RUs to perform joint data transmission on the UE1.
  • Step 203b The DAS system interrogates the UE2 that uses the same frequency point to access the small base station by the UE1 through the control channel;
  • Step 204b After confirming that the UE1 uses the same frequency point, the UE2 reports the DAS system through the control channel.
  • Step 205b The DAS system subsequently allocates a free time slot to the UE2, and requests the UE2 to send a training sequence.
  • Step 206b UE2 sends a training sequence in the allocated time slot, and the DAS system then estimates the channel of the selected RU to UE2;
  • Step 207b DAS transmitted by a plurality of tie RU selected to UE1 precoded data such that the SINR of the received signal is greater than the UE1 ⁇ 1, to ensure the corresponding QoS. At the same time, by precoding, the signal will not interfere with the received signal of UE2.
  • Step 3 Since in the present embodiment, in the communication between UE1 and DAS, UE2 always communicates with the small base station. Therefore, the SINR is always 1.046, which is greater than ⁇ 1 and less than ⁇ 2 , so the system only continuously detects the SINR at certain time intervals. This time interval can be set in the system configuration file according to the actual situation.
  • the distance from RU1 to UE1 is 6 meters; the distance from RU2 to UE1 is 5 meters; the distance from RU3 to UE1 is 10 meters, the distance from RU4 to UE1 is 6 meters; the distance from RU5 to UE1 is 15 meters; the distance from RU6 to UE1 It is 14 meters; the distance from the small base station to UE1 is 9 meters.
  • the transmission power of each RU is 15 dBm
  • the transmission power of the small base station is 25 dBm
  • ⁇ 1 is 1 (ie, 0 dB)
  • ⁇ 2 is 4 (ie, 6 dB)
  • the path loss is inversely proportional to the distance from the 2.5th power.
  • the received signal has a signal-to-noise ratio of 10 dB.
  • UE1 sends an access request to the DAS system through the control channel.
  • Each of the RUs of the DAS system receives the request signal, and uploads the received power of the signal to the MU.
  • the MU establishes a normalized received signal strength table based on the obtained signal power:
  • the system selects RU2 as the initial access RU of UE1.
  • step 2 RU2 and UE1 try to establish a downlink, and RU2 sends data to UE1. Since there is no downlink interference of the small base station at this time, the SINR is the signal-to-noise ratio of the system, which is 10 dB, which is larger than ⁇ 1 . Then, step 201a is started.
  • Step 3 UE1 maintains the downlink of the RU2 allocated with the DAS system, and continuously detects the SINR value at certain time intervals during the communication.
  • the SINR if the UE2 is not connected to the small base station, the SINR remains unchanged, the system does not perform an operation, and the UE1 continuously detects the SINR value according to the set time interval.
  • UE1 can detect the change of SINR at the next SINR detection time.
  • the SINR is now reduced to about 0.43 (i.e., -3.7 dB).
  • the system proceeds to execute 201b-207b.
  • Step 202b The DAS system combines the normalized intensity table according to the SINR value, and selects an appropriate number of RUs to perform joint data transmission on the UE1.
  • Step 203b The DAS system interrogates the UE2 that uses the same frequency point to access the small base station by the UE1 through the control channel;
  • Step 204b After confirming that the UE1 uses the same frequency point, the UE2 reports the DAS system through the control channel.
  • Step 205b The DAS system subsequently allocates a free time slot to the UE2, and requests the UE2 to send a training sequence.
  • Step 206b UE2 sends a training sequence in the allocated time slot, and the DAS system then estimates the selected RU to UE2. channel;
  • Step 207b DAS transmitted by a plurality of tie RU selected to UE1 precoded data such that the SINR of the received signal is greater than the UE1 ⁇ 1, to ensure the corresponding QoS. At the same time, by precoding, the signal will not interfere with the received signal of UE2.
  • h 1 [h 1,1 ,h 2,1 ,h 3,1 ,h 4,1 ]
  • h 2 [h 1,2 ,h 2,2 ,h 3,2 ,h 4,2 ].
  • Matrix Is a 4 ⁇ 4 matrix, and there are 1 non-zero eigenvalue and 3 zero eigenvalues. The eigenvector corresponding to one of the zero eigenvalues is randomly selected, and obviously h 2 v H 0.
  • the SINR of the DAS system is reduced due to the multi-RU joint transmission of the DAS system.
  • the SINR of UE2 will drop by 3 dB.
  • step 207b After completing step 207b, it will proceed to step 3.
  • Step 3 UE1 maintains the downlink with RU1, RU2, RU3, and RU4 allocated to it by the DAS system, and continuously detects the SINR value at certain time intervals during the communication. If UE2 does not exit, the SINR remains unchanged, the system does not perform operations, and UE1 continuously detects the SINR value according to the set time interval. If the system enters the third phase as shown in Figure 6, that is, UE2 quits communication before UE1, the SINR will be much higher than the system signal-to-noise ratio (SNR) in this embodiment because the interference disappears.
  • SNR system signal-to-noise ratio
  • the RU with the weakest received signal is culled and jointly transmitted. In this embodiment, it is RU3, and then the SINR is calculated. If it is still higher than ⁇ 2 , in this embodiment, it is 4 (6 dB). Continue to reject the RU with the weakest received signal. Accordingly, until the SINR is higher than ⁇ 1 and less than ⁇ 2 , or the SINR is higher than ⁇ 1 and only one RU of the system maintains communication with UE1. In this embodiment, since the signal-to-noise ratio is 10 dB, only RU2 and UE1 maintain downlink communication at the end. Thereafter, the system still proceeds to step 3.
  • Step 3 UE1 maintains downlink communication with RU2, and continues to detect the SINR at a preset time interval, and performs corresponding operations according to the value thereof.

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Abstract

本发明提供一种室内DAS系统与小基站下行干扰避免方法，所述步骤包括：步骤1：确定初始的接入RU，建立信号强度表；步骤2：DAS系统通过所选RU尝试与UE1建立下行链路，检测UE1下行信号的信干噪比SINR值，并与预设门限值γ1进行对比；步骤3：UE1保持与DAS系统分配给其的一个或多个RU的下行链路，并在通信过程中以一定时间间隔持续检测SINR值，根据其是否高于γ1，保证相应的服务质量。本发明有益的效果是：(1)无需在DAS系统与小基站间建立协调机制(共享信息)，降低了对回馈链路的要求。(2)本发明无需小基站参与操作，便于家庭用户、SOHO用户自主选择不同品牌、不同功能的小基站。(3)根据SINR值自适应选择RU个数，降低信道估计以及预编码的复杂性，并使系统性能保持稳定，便于编码、调制等模块的参数固定。(4)适用于没有X2接口的小基站，可以满足小基站"即插即用"的需求。

Description

一种室内DAS系统与小基站下行干扰避免方法 技术领域
本发明属于移动通信领域，涉及一种小区间同频干扰的协同抑制方法，具体涉及一种室内DAS系统与小基站下行干扰避免方法。
背景技术
随着智能终端越来越广泛地普及，对无线数据业务的需求也呈爆发式的增长。据预测，从2010年到2015年，全球移动数据流量的增长将超过24倍，而在2010年到2020年这10年间甚至会超过500倍，这对运营商的服务提供能力提出了巨大的挑战。一般来说，蜂窝网络的移动业务会呈现明显的不均匀特性。据统计，约有60％的语音业务和90％的数据业务是发生在室内。因此，对于运营商而言，能够提供良好的室内覆盖是避免客户流失，提高企业效益的重要手段。但是据调查，约有45％的家庭和30％的企业都不同程度的面临室内覆盖差的问题，其主要原因就在于目前提供室内覆盖的手段，大多是基于户外的宏小区基站。在此背景下，小基站概念作为解决上述问题的一种有效手段被业界所提出。小基站是指各种低功率、小覆盖、灵活部署的无线接入点，成为未来站点的一种发展趋势，可以通过规模部署来解决移动通信网络的室内覆盖、热点覆盖、深度覆盖等问题，弥补宏蜂窝网络的不足，提升频谱效率，提高网络容量，更好地满足未来移动通信业务的发展需求和提升用户体验。
但小基站在实际部署当中，仍然面对着诸多问题。这其中尤以干扰最为突出。3GPP LTE为了进一步提高频谱利用率，提出了全频率复用这一概念，即不同蜂窝间采用同频组网的模式，由此将导致小区边缘用户遭受较大的同频干扰，其服务质量(QoS)被降低。随着小基站的加入，由小基站和传统宏蜂窝基站所组成的异构蜂窝网络，其同频干扰问题将变得更为突出。特别是小基站的室内部署方式，极易与已有的室内覆盖系统产生相互干扰，如分布式天线系统(简称DAS，传统宏基站的简单延时，可以满足信号覆盖的问题，但是无法提高系统容量)，从而限制小基站的实际应用与部署。
在3GPP LTE中，为了降低小区间同频干扰的影响，提出了基于小区间协作的干扰协调机制，如ICIC、eICIC以及FeICIC。其基本思路是使得相邻小区的信号在时域、频域或空域相互正交，从而避免相互干扰。当然，上述干扰协调机制的代价是付出一定的容量损失。然而，当小基站与DAS系统共同部署时，上述基于宏站间，或室外宏站与小基站间的干扰协调机制将难以有效的发挥其作用。因此，需要根据DAS系统的室内部署、分布式等特点，重新设计相应的协作模式，并引入信号处理方法来抑制干扰。
发明内容
为解决室内DAS系统与小基站在下行链路相互间的干扰问题，本发明针对DAS系统具备多天线的特点，提供一种室内DAS系统与小基站下行干扰避免方法，具体是一种应用于小基站与室内分布式天线系统(DAS)的下行同频干扰协同抑制方法，可有效降低室内DAS系 统与小基站的相互干扰。
本发明解决其技术问题采用的技术方案：在描述本发明的具体步骤前，先对部分缩写及符号进行定义。室内DAS系统的主单元用MU表示；远端单元及与其相连接的天线用缩写RU表示，并且定义RUn(n为1,2,3···等自然数)为第n个RU。终端用UE表示，特别地，用UE1表示接入DAS系统的终端，UE2为接入小基站的终端。信号干扰加噪声比用SINR表示，为信号功率与干扰加噪声功率之比。本发明实现步骤中涉及两个SINR的门限值，分别用γ1和γ2表示，且γ1小于γ2。其中，若SINR小于γ1表明存在较大干扰，需要增加信号功率；若SINR大于γ2表明存在较大的功率余量，可以适当降低信号功率。
本发明所述的这种室内DAS系统与小基站下行干扰避免方法，所述步骤包括：
步骤1：确定初始的接入RU，建立信号强度表；
当UE1需要接入DAS系统时，向DAS系统发送接入请求。DAS系统根据各个RU接收到该请求信号的信号功率，在MU内建立关于UE1的信号强度表。所述信号强度表包括各个RU的ID以及对应的归一化接收信号强度。所述归一化信号强度为各个RU的实际信号强度比上接收信号最强的RU的信号强度，并将接收信号最强的RU分配给UE1，作为其初始的接入RU。DAS系统在与UE1的整个通信过程中，不断更新该信号强度表。
其中，所述MU为室内DAS系统的主单元，所述RU为远端单元及与其相连接的天线，所述UE1表示接入DAS系统的终端。
步骤2：DAS系统通过所选RU尝试与UE1建立下行链路，检测UE1下行信号的信干噪比SINR值，并与预设门限值γ1进行对比，执行如下过程：
(1)若SINR值大于γ1，则UE1执行以下过程：与分配给UE1的RU建立下行链路，开始下行数据发送；
(2)若SINR值小于γ1，则UE1执行如下过程：
步骤201b：UE1通过控制信道向DAS系统反馈SINR值；
步骤202b：DAS系统根据该SINR值，从候选RU中选取合适数目的RU，用来联合对UE1发送数据；
步骤203b：DAS系统通过控制信道询问与UE1采用同样频点接入小基站的终端UE2；
其中，所述UE2为接入小基站的终端。
步骤204b：UE2在确认与UE1采用同一频点后，通过控制信道上报DAS系统；
步骤205b：DAS系统随后分配空闲时隙给UE2，要求UE2发送训练序列；
步骤206b：UE2在所分配的时隙发送训练序列，DAS系统随后估计所选RU到UE2的信道；
步骤207b：DAS系统通过所选的多个RU联合向UE1发送预编码后的数据，从而使UE1的接收信号的SINR值大于γ1，保证相应的服务质量。同时，通过预编码方法，使得信号不 会对UE2的接收信号产生干扰。
步骤3：UE1保持与DAS系统分配给其的一个或多个RU的下行链路，并在通信过程中以一定时间间隔持续检测SINR值，根据其是否高于γ1，执行如下操作：
(1)若SINR值小于γ1，则转而执行201b-207b的操作；
(2)若SINR值大于γ1，则UE1继续与预设门限值γ2进行对比，执行如下操作：
若SINR值小于γ2，则继续保持与DAS分配给其的多个RU进行通信，并在通信过程中以一定时间间隔继续检测SINR值；
若SINR值大于γ2，UE1上报SINR值，根据SINR值，以及参与数据联合发送的RU的信号强度，按照接收信号强度从弱到强，依次去掉RU，直至DAS系统预测的SINR值略高于γ1，或者只剩下一个RU。
本发明中，所述RU的选取方式如下：若当前SINR值为γ，根据所述信号强度表，按归一化信号强度从高到低(排除归一化信号强度为1的RU)，依次选取RU，直到满足下式：
Figure PCTCN2015098457-appb-000001
其中，Pi表示在信号强度表内归一化信号强度由高到低排在第i位的RU的归一化信号强度；参数N表示满足式(1)条件所需的RU个数。
本发明中，所述预编码方法为：
假设有N个RU参与对UE1的联合数据发送。通过信道估计，可以获得这N个RU到UE2的信道衰落系数，分别表示为hn2(n＝1,…,N)。用h2表示由hn2(n＝1,…,N)所组成的行向量，即h2＝[h1,2,h2,2,…,hN,2]。同样有h1＝[h1,1,h2,1,…,hN,1]，表示由N个参与联合发送的RU到UE1的信道衰落系数组成的行向量。设预编码矩阵为w＝[w1,w2,…,wN]，为一个N长的行向量。则UE1的接收信号为：
y1＝h1wHx1+J+W     (2)
其中，J为小基站到UE2的下行信号对UE1的干扰，W为噪声。
DAS系统参与联合数据发送的第n个RU，其发送信号为wnx1，即该RU发送的数据为发送给UE1的数据x1加权上wn。通过增加RU来提高信号功率，进而提升SINR值，使得UE1能够顺利解调数据。UE2的接收信号为：
y2＝hx2+h2wHx1+W     (3)
其中，标量h为小基站到UE2的信道状态信息，x2为小基站发送给UE2的数据。
从式(3)可看到，当联合发送的RU增多时，会增强对UE2的干扰。因此，需要引入预编码技术，使得h2wH＝0，从而消除对UE2的干扰；同时又能保证h1wH不会降低UE1的接收信号SINR值。实际上，预编码矩阵w即为
Figure PCTCN2015098457-appb-000002
零特征值所对应的特征向量。设v为矩 阵
Figure PCTCN2015098457-appb-000003
的零特征值所对应的特征向量，则预编码矩阵为：
Figure PCTCN2015098457-appb-000004
其中算子|·|表示为
Figure PCTCN2015098457-appb-000005
其中y为行向量。
本发明中，所述预设门限值γ1取值为-3dB到3dB，所述预设门限值γ2取值为5dB到15dB。
本发明有益的效果是：
(1)无需在DAS系统与小基站间建立协调机制(共享信息)，降低了对回馈链路的要求。
(2)本发明无需小基站参与操作，便于家庭用户、SOHO用户自主选择不同品牌、不同功能的小基站。
(3)根据SINR值自适应选择RU个数，降低信道估计以及预编码的复杂性，并使系统性能保持稳定，便于编码、调制等模块的参数固定。
(4)适用于没有X2接口的小基站，可以满足小基站“即插即用”的需求。
附图说明
图1为DAS系统与小基站下行干扰场景示意图。
图2为本发明所述的DAS系统示意图。
图3为室内DAS系统与小基站下行干扰避免流程图。
图4为本发明的具体实施案例一。
图5为本发明的具体实施案例二。
图6为DAS系统多RU联合数据发送流程图。
具体实施方式
下面结合附图对本发明的具体实施方式进行详细说明。
图1为本发明所具体应用的场景示意图，场景内包含DAS系统以及小基站系统。一般来说，DAS系统借助于分布于建筑物的多个RU来改善室内信号覆盖，但无法提升网络容量。小基站则用于热点区域的覆盖，可有效提高容量，但对于大型建筑，无法做到像DAS系统那样的全面覆盖。因此在今后的很长一段时间，都将是DAS系统与小基站系统的混合部署，既能满足建筑物的全面信号覆盖，同时又能保证热点区域的容量要求。本发明正是在该场景下，提出DAS系统与小基站系统下行干扰的避免方案，使得同频部署成为可能。如图1所示，UE1为接入DAS系统的终端，UE2为接入小基站的终端。当下行传输时，小基站的下行发射信号会对UE1产生干扰；同时DAS系统的下行发射信号也会对UE2产生干扰。但是，一般来说，小基站的发射功率为25dBm，而单个RU的发射功率仅为15dBm。因此，本发明主要考虑小基站对UE1的干扰问题；同时在过程中也充分利用DAS系统的多天线特性，采用预编码技术防止DAS系统对UE2的干扰。
图2为本发明所述的室内DAS系统示意图。该室内DAS系统主要包括MU和各个RU模块。其中，与本发明有关的MU的功能为：
1)根据各个RU反馈的对于UE1的接收信号功率，建立并维护关于UE1的归一化接收信号强度表；
2)根据各RU接收到的训练序列信号，执行信道估计；
3)根据所估计的信道，计算预编码矩阵，并为各个RU分配加权系数。
与本发明有关的RU的功能为：
1)向MU反馈接收信号的功率；
2)根据MU分配的加权系数，对发送数据进行加权。
图3为MU建立的归一化接收信号强度表。MU为接入DAS系统的每一个UE建立如图3所示的归一化接收信号强度表。对应于每一个UE的表的表名为该UE的ID。每一个表包含两个字段，分别为RU的ID与归一化接收信号功率。其中，归一化接收信号功率为该RU的接收功率比上所有RU中接收功率最大的RU的接收功率。因此，对于接收功率最大的RU，其归一化接收信号功率为1，其它RU的归一化接收信号功率均小于1。
图4为室内DAS系统与小基站下行干扰避免流程图。结合图5和图6所设定的场景，对图4所公开的问题解决流程图给出具体实施方式。
如图5所示的实施例中，DAS系统的总共有4个RU，且在该DAS系统内存在一个小基站。RU1到UE1的距离为14米；RU2到UE1的距离为10米；RU3到UE1的距离为40米，RU4到UE1的距离为35米；小基站到UE1的距离为17米。在本实施例中假设每个RU的发射功率为15dBm，小基站的发射功率为25dBm，本实施例中，γ1取值1(即0dB)，γ2取值为4(即6dB)，路径损耗与距离4次方成反比，接收信号信噪比SINR为10dB。在整个UE1与DAS系统通信时段内，UE2也与小基站保持通信。
根据步骤1，UE1通过控制信道向DAS系统发出接入请求。DAS系统的各个RU接收到该请求信号，除将该接入请求信息上传MU外，还将该信号接收功率值上传MU。MU根据获得的信号功率，建立归一化接收信号强度表：
RU的ID 归一化接收信号强度
RU1 0.2603
RU2 1
RU3 0.004
RU4 0.007
因此，系统选择RU2作为UE1的初始接入RU。
步骤2，RU2与UE1尝试建立下行链路，RU2发送数据给UE1，UE1计算该接收信号的 SINR大约为0.83(即-8.63dB)，小于预设的γ1。因此执行：
步骤201b：UE1通过控制信道向DAS系统反馈SINR值；
步骤202b：DAS系统根据该SINR值，结合归一化强度表，选取合适数目的RU来对UE1进行联合数据发送。
在本实施例中，从归一化接收信号强度表从次高到低依次选取RU，可见首先选取RU1，然后计算式(1)，看是否满足该式。在本实施例中，可见选取RU1即可满足，即0.83×(1+0.2603)＝1.046>1。
步骤203b：DAS系统通过控制信道询问与UE1采用同样频点接入小基站的UE2；
步骤204b：UE2在确认与UE1采用同一频点后，通过控制信道上报DAS系统；
步骤205b：DAS系统随后分配空闲时隙给UE2，要求UE2发送训练序列；
步骤206b：UE2在所分配的时隙发送训练序列，DAS系统随后估计所选RU到UE2的信道；
步骤207b：DAS系统通过所选的多个RU联合向UE1发送预编码后的数据，从而使UE1的接收信号的SINR大于γ1，保证相应的服务质量。同时，通过预编码，该信号将不会对UE2的接收信号产生干扰。
其中，在本实施例中，由于只有RU1和RU2参与联合发送。因此有h1＝[h1,1,h2,1]，h2＝[h1,2,h2,2]。则矩阵
Figure PCTCN2015098457-appb-000006
为一个2×2矩阵，且存在一个非零特征值和一个零特征值。设v为该零特征值所对应的特征向量，显然有h2vH＝0。为了保证预编码后功率不变，因此将预编码矩阵设为w＝|h1|v/|h1v|为一个1×2的矢量。所以，UE1的接收信号为y1＝h1wHx1+J+W，由于增加了一个RU进行联合发送，使得SINR由单独发送时的0.83增加到联合发送时的1.046。同时，UE2的接收信号为y2＝hx2+h2wHx1+W＝hx2+W，DAS系统不会到小基站产生额外干扰。
步骤3：由于在本实施例中，在UE1与DAS的通信中，UE2始终与小基站进行通信。因此SINR始终为1.046，满足大于γ1，且小于γ2，因此系统只是以一定时间间隔持续检测SINR。这一时间间隔可在系统配置文件中根据实际情况进行设定。
在图6所示的实施例中，考虑RU密集部署的情况，DAS系统的总共有6个RU，且在该DAS系统内存在一个小基站。RU1到UE1的距离为6米；RU2到UE1的距离为5米；RU3到UE1的距离为10米，RU4到UE1的距离为6米；RU5到UE1的距离为15米；RU6到UE1的距离为14米；小基站到UE1的距离为9米。在本实施例中假设每个RU的发射功率为15dBm，小基站的发射功率为25dBm，γ1为1(即0dB)，γ2为4(即6dB)，路径损耗与距离2.5次方成反比，接收信号信噪比为10dB。在整个UE1与DAS系统通信时段内，UE2与 小基站的通信分为3个阶段。在第一阶段，小基站与UE2不进行通信；在第二阶段，小基站与UE2进行通信；在第三阶段，小基站与UE2通信完毕。
根据步骤1，UE1通过控制信道向DAS系统发出接入请求。DAS系统的各个RU接收到该请求信号，除将该接入请求信息上传MU外，还将该信号接收功率值上传MU。MU根据获得的信号功率，建立归一化接收信号强度表：
RU的ID 归一化接收信号强度
RU1 0.6339
RU2 1
RU3 0.1768
RU4 0.6339
RU5 0.0642
RU6 0.0762
因此，系统选择RU2作为UE1的初始接入RU。
步骤2，RU2与UE1尝试建立下行链路，RU2发送数据给UE1。由于此时无小基站的下行干扰，因此SINR即为系统的信噪比，为10dB，大于γ1。则开始执行步骤201a。
步骤3：UE1保持与DAS系统所分配的RU2的下行链路，并在通信过程中以一定时间间隔持续检测SINR值。
在本实施例中，若UE2未接入小基站，则SINR保持不变，系统不执行操作，UE1只是按照设定的时间间隔持续检测SINR值。一旦UE2接入小基站，如图6阶段二所示，则UE1在下一个SINR检测时间可以检测到SINR的变化。根据本实施例中的参数假设，此时SINR降低到约0.43(即-3.7dB)。此时，SINR小于γ1，则系统转而执行201b-207b。
步骤201b：UE1通过控制信道将SINR＝0.43反馈给DAS系统。
步骤202b：DAS系统根据该SINR值，结合归一化强度表，选取合适数目的RU来对UE1进行联合数据发送。
在本实施例中，从归一化接收信号强度表从次高到低依次选取RU，可见首先选取RU1(或RU4，随机选择)，然后计算式(1)，看是否满足该式。若不满足，继续选取RU。在本实施例中，可见需要选取RU1、RU4以及RU3方可满足，即0.43×(1+0.6339+0.6339+0.1768)＝1.051>1。
步骤203b：DAS系统通过控制信道询问与UE1采用同样频点接入小基站的UE2；
步骤204b：UE2在确认与UE1采用同一频点后，通过控制信道上报DAS系统；
步骤205b：DAS系统随后分配空闲时隙给UE2，要求UE2发送训练序列；
步骤206b：UE2在所分配的时隙发送训练序列，DAS系统随后估计所选RU到UE2的 信道；
步骤207b：DAS系统通过所选的多个RU联合向UE1发送预编码后的数据，从而使UE1的接收信号的SINR大于γ1，保证相应的服务质量。同时，通过预编码，该信号将不会对UE2的接收信号产生干扰。
其中，在本实施例中，由于只有RU1和RU2参与联合发送。因此有h1＝[h1,1,h2,1,h3,1,h4,1]，h2＝[h1,2,h2,2,h3,2,h4,2]。则矩阵
Figure PCTCN2015098457-appb-000007
为一个4×4矩阵，且存在1个非零特征值和3个零特征值。随机选取其中一个零特征值所对应的特征向量，显然有h2vH＝0。为了保证预编码后功率不变，因此将预编码矩阵设为w＝|h1|v/|h1v|为一个1×4的矢量。所以，UE1的接收信号为y1＝h1wHx1+J+W，由于增加了3个RU进行联合发送，使得SINR由单独发送时的0.43增加到联合发送时的1.051。同时，UE2的接收信号为y2＝hx2+h2wHx1+W＝hx2+W，DAS系统不会到小基站产生额外干扰。
若未采取预编码技术，且UE2处于小基站覆盖范围的边缘，则由于DAS系统的多RU联合发送，导致其SINR降低。在本实施例中，考虑到UE2与RU2、RU4以及小基站的位置关系(假定UE2到RU2、RU4以及小基站的距离都为6米)，则UE2的SINR将下降3dB。
完成步骤207b后，将继续进入步骤3。
步骤3：UE1保持与DAS系统分配给其的RU1、RU2、RU3、RU4的下行链路，并在通信过程中以一定时间间隔持续检测SINR值。若UE2未退出，则SINR保持不变，系统不执行操作，UE1只是按照设定的时间间隔持续检测SINR值。若系统进入如图6所示第三阶段，即UE2先于UE1退出通信，则由于干扰消失，SINR将远高于系统信噪比，在本实施例中为10dB，则执行如下操作：
首先根据归一化信号强度表，将接收信号最弱的RU剔除联合发送，在本实施例子为RU3，然后计算SINR，若仍高于γ2，在本实施例中为4(6dB)，则继续剔除接收信号最弱的RU。依此直至SINR高于γ1且小于γ2，或SINR高于γ1且系统只有一个RU与UE1保持通信。在本实施例中，由于信噪比为10dB，因此最后只有RU2与UE1保持下行通信。此后，系统仍进入步骤3。
步骤3：UE1与RU2保持下行通信，并继续以预设的时间间隔检测SINR，并根据其值执行相应操作。
以上所述，仅为本发明较好的实施方式而已，并不构成对本发明保护范围的限定。任何在本发明精神之内所作的修改、等同替换和改进等，均应包含在本发明的权利要求保护范围之内。

Claims (4)

  1. 一种室内DAS系统与小基站下行干扰避免方法，其特征在于，该方法包括步骤如下：
    步骤1：确定初始的接入RU，建立信号强度表；
    当UE1需要接入DAS系统时，向DAS系统发送接入请求；DAS系统根据各个RU接收到该请求信号的信号功率，在MU内建立关于UE1的信号强度表；所述信号强度表包括各个RU的ID以及对应的归一化接收信号强度；所述归一化信号强度为各个RU的实际信号强度比上接收信号最强的RU的信号强度，并将接收信号最强的RU分配给UE1，作为其初始的接入RU，DAS系统在与UE1的整个通信过程中，不断更新该信号强度表；
    其中，所述MU为室内DAS系统的主单元，所述RU为远端单元及与其相连接的天线，所述UE1表示接入DAS系统的终端；
    步骤2：DAS系统通过所选RU尝试与UE1建立下行链路，检测UE1下行信号的信干噪比SINR值，并与预设门限值γ1进行对比，执行如下过程：
    (1)若SINR值大于γ1，则UE1执行以下过程：与分配给UE1的RU建立下行链路，开始下行数据发送；
    (2)若SINR值小于γ1，则UE1执行如下过程：
    步骤201b：UE1通过控制信道向DAS系统反馈SINR值；
    步骤202b：DAS系统根据该SINR值，从候选RU中选取合适数目的RU，用来联合对UE1发送数据；
    步骤203b：DAS系统通过控制信道询问与UE1采用同样频点接入小基站的终端UE2，其中，所述UE2为接入小基站的终端；
    步骤204b：UE2在确认与UE1采用同一频点后，通过控制信道上报DAS系统；
    步骤205b：DAS系统随后分配空闲时隙给UE2，要求UE2发送训练序列；
    步骤206b：UE2在所分配的时隙发送训练序列，DAS系统随后估计所选RU到UE2的信道；
    步骤207b：DAS系统通过所选的多个RU联合向UE1发送预编码后的数据，从而使UE1的接收信号的SINR值大于γ1，同时，通过预编码方法，使得信号不会对UE2的接收信号产生干扰；
    步骤3：UE1保持与DAS系统分配给其的一个或多个RU的下行链路，并在通信过程中以一定时间间隔持续检测SINR值，根据其是否高于γ1，执行如下操作：
    (1)若SINR值小于γ1，则转而执行201b-207b的操作；
    (2)若SINR值大于γ1，则UE1继续与预设门限值γ2进行对比，执行如下操作：
    若SINR值小于γ2，则继续保持与DAS系统分配给其的多个RU进行通信，并在通信过程中以一定时间间隔继续检测SINR值；
    若SINR值大于γ2，UE1上报SINR值，根据SINR值，以及参与数据联合发送的RU的 信号强度，按照接收信号强度从弱到强，依次去掉RU，直至DAS系统预测的SINR值略高于γ1，或者只剩下一个RU。
  2. 根据权利要求1所述的室内DAS系统与小基站下行干扰避免方法，其特征在于，所述RU的选取方式如下：若当前SINR值为γ，根据所述信号强度表，按归一化信号强度从高到低，排除归一化信号强度为1的RU，依次选取RU，直到满足下式：
    Figure PCTCN2015098457-appb-100001
    其中，Pi表示在信号强度表内归一化信号强度由高到低排在第i位的RU的归一化信号强度；参数N表示满足式(1)条件所需的RU个数。
  3. 根据权利要求1所述的室内DAS系统与小基站下行干扰避免方法，其特征在于，所述预编码方法为：
    假设有N个RU参与对UE1的联合数据发送，通过信道估计，获得这N个RU到UE2的信道衰落系数，分别表示为hn2(n＝1,…,N)；用h2表示由hn2(n＝1,…,N)所组成的行向量，即h2＝[h1,2,h2,2,…,hN,2]；同样有h1＝[h1,1,h2,1,…,hN,1]，表示由N个参与联合发送的RU到UE1的信道衰落系数组成的行向量；设预编码矩阵为w＝[w1,w2,…,wN]，为一个N长的行向量；则UE1的接收信号为：
    y1＝h1wHx1+J+W      (2)
    其中，J为小基站到UE2的下行信号对UE1的干扰，W为噪声；
    DAS系统参与联合数据发送的第n个RU，其发送信号为wnx1，即该RU发送的数据为发送给UE1的数据x1加权上wn；通过增加RU来提高信号功率，进而提升SINR值，使得UE1能够顺利解调数据，UE2的接收信号为：
    y2＝hx2+h2wHx1+W      (3)
    其中，标量h为小基站到UE2的信道状态信息，x2为小基站发送给UE2的数据；
    预编码矩阵w即为
    Figure PCTCN2015098457-appb-100002
    零特征值所对应的特征向量，设v为矩阵
    Figure PCTCN2015098457-appb-100003
    的零特征值所对应的特征向量，则预编码矩阵为：
    Figure PCTCN2015098457-appb-100004
    其中算子|·|表示为
    Figure PCTCN2015098457-appb-100005
    其中y为行向量。
  4. 根据权利要求1所述的室内DAS系统与小基站下行干扰避免方法，其特征在于，所述预设门限值γ1取值为-3dB到3dB，所述预设门限值γ2取值为5dB到15dB。
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