CN103369687A - Method for setting carrier sensing threshold of CBTC (Communication Based Train Control) digital communication system (DCS) - Google Patents
Method for setting carrier sensing threshold of CBTC (Communication Based Train Control) digital communication system (DCS) Download PDFInfo
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Abstract
The invention provides a method for setting the carrier sensing threshold of a CBTC (Communications Based Train Control) digital communication system (DCS), relating to the technical field of track traffic and mobile communication. The method provided by the invention comprises the following steps of: firstly, carrying out closed circuit testing to obtain the minimum signal to interference ratio C/Imin, then, dynamically monitoring the signal power Pr, and calculating the maximum interference Imax in real time, wherein the minimum signal to interference ratio C/Imin is required by DCS communication, the signal power Pr is received by a vehicle-mounted terminal of the DCS, and the maximum interference Imax can be borne by the DCS at present; finally, calculating the threshold CCAlevel=Imax-3 according to the maximum interference, wherein the maximum interference can be borne by the DCS; if the calculated CCAlevel is lower than the sensitivity of the DCS, setting the carrier sensing threshold of the DCS as the sensitivity of the system; or otherwise, setting the carrier sensing threshold of the DCS as CCAlevel. By using the method provided by the invention, the interference of a WLAN (Wireless Local Area Network) to the DCS can be effectively relieved, the interference risk of the DCS can be reduced, and the operation safety of a train can be ensured.
Description
Technical field
The present invention relates to track traffic and mobile communication technology field, relate in particular to a kind of CBTC(Communication Based Train Control System, the carrier sense thresholding method to set up of the land mobile communication system train automatic controlling system based on radio communication), this CBTC land mobile communication system adopts 802.11 serial protocols, and Channel Access Mechanism is CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance).
Background technology
The train automatic controlling system (CBTC) based on communication is mostly adopted in urban track traffic, data communication subsystem (DCS wherein, Digtal Communication System) realizes car-ground bi-directional communication function, for train operation control provides basic data and instruction, it is one of key technology of CBTC.802.11 series standard is as the standard of an opening and since its install, safeguard, the advantage of expansion, the aspect such as compatible, by Ka Sike, Siemens and Alcatel etc. both at home and abroad CBTC system research and development merchant as the car-ground communication technology.Because the DCS system uses identical ISM(Industrial Scientific Medical with WLAN) frequency range, inevitably to be subject to the interference of wlan device, affect train operating safety.And the DCS communication requirement is different from general wlan system, and its received signal strength with train operation also in continuous variation.The carrier sense thresholding CCA of present DCS equipment
LevelAll fix, if thresholding CCA
LevelArranged lowly, DCS can keep out of the way the interference that does not originally need to keep out of the way when condition of acceptance is relatively good, thereby causes communication delay to increase; If thresholding CCA
LevelArrange too highly, DCS does not but keep out of the way the interference that needs are kept out of the way when condition of acceptance is poor, thereby causes the error rate to improve, and affects proper communication.Under wlan device is used more and more widely trend, the carrier sense thresholding CCA of the fixing DCS system that arranges
Level, the risk that the DCS system is disturbed can be more and more higher, finally has influence on the security of operation of train.
So, the carrier sense thresholding CCA of DCS equipment
LevelAlso should dynamically arrange according to the communication requirement of DCS system reality and real-time accepting state, when satisfying the communication requirement of DCS, improve as much as possible its interference free performance.
Summary of the invention
The present invention is according to the practical communication demand of CBTC system, the method to set up of carrier sense thresholding of the land mobile communication system of a kind of CBTC is proposed, the method is when satisfying the communication requirement of DCS, can increase the performance that anti-cochannel wlan device disturbs, reduce the DCS system and be disturbed risk, guarantee train operating safety.
The carrier sense thresholding method to set up of the land mobile communication system of CBTC provided by the invention may further comprise the steps:
Step 3, the maximum interference I that can bear according to the DCS system
Max, calculate threshold value CCA
Level=I
Max-3;
If the CCA that calculates
LevelBe lower than the DCS system sensitivity, then the DCS system carrier is intercepted thresholding and is set to system sensitivity; Otherwise the DCS system carrier is intercepted thresholding and is set to CCA
Level
The described DCS employing CSMA/CA of system Channel Access Mechanism uses IEEE802.11 series communication standard protocol, the agreement of perhaps revising based on 802.11 series standards, and the frequency range identical with the wlan device use.
In the described step 1, when utilizing the minimum signal interference ratio of closed circuit test macro signal post's need, the parameter setting meets the following conditions:
(1) the fixing carrier sense thresholding CCA of DCS system
Level
(2) guarantee that DCS system received signal power is higher than carrier sense thresholding CCA
Level
(3) added Gauss's white noise power should be lower than ripple and intercepts thresholding CCA
Level
The DCS system of overwhelming majority CBTC is the same with WLAN, adopts 802.11 serial protocols, is operated in identical unauthorized frequency range with wlan device, can't avoid the interference of wlan device fully.The present invention has proposed a kind of dynamic adjustment carrier sense thresholding method to set up according to the actual demand of DCS system, can effectively alleviate WLAN to the interference of DCS system, reduces the DCS system and is disturbed risk, guarantees train operating safety, has stronger practicality.
Description of drawings
Fig. 1 is the whole flow chart of steps of carrier sense thresholding method to set up of the present invention;
Fig. 2 is the closed circuit test block diagram of the DCS of CBTC;
Fig. 3 is DCS data delay and the C/I relation curve of CBTC;
Fig. 4 is the DCS disturbed test spectrogram of CBTC;
Fig. 5 is DCS packet loss and the C/I relation curve under different thresholdings of CBTC.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.Following specific implementation process is used for explanation the present invention, but is not used for limiting the scope of the invention.
The carrier sense thresholding method to set up of CBTC land mobile communication system provided by the invention by dynamically arranging the carrier sense thresholding, can effectively be alleviated the co-channel interference of WLAN wireless device CBTC.As shown in Figure 1, the inventive method may further comprise the steps:
Step S1 according to the data communication needs of DCS system, draws the required minimum signal interference ratio C/I of system communication by closed circuit test
Min, C represents useful carrier frequency power, I represents interfering signal power.The DCS system adopts the CSMA/CA Channel Access Mechanism, uses IEEE802.11 series communication standard protocol, the agreement of perhaps revising based on 802.11 series standards, and the frequency range identical with the wlan device use.
When test macro signal post needed minimum signal interference ratio, the parameter setting should meet the following conditions:
(1) the fixing carrier sense thresholding CCA of DCS system
Level
(2) guarantee that DCS system received signal power is higher than carrier sense thresholding CCA
Level
(3) added Gauss's white noise power should be lower than carrier sense thresholding CCA
Level
Concrete testing procedure is as follows:
1) builds test environment by Fig. 2.Among Fig. 2, the first test instrumentation, DCS-AP, the first variable attenuator, mixer, power splitter, the second variable attenuator, DCS-SA and the test instrumentation of being connected connect successively, and mixer also is connected with signal source, and power splitter also is connected with frequency spectrograph.DCS-AP(Digital Communication System-Accss Point) be the DCS WAP (wireless access point); DCS-SA(Digital Communication System-Station Adapter) be the DCS car-mounted terminal; Two test instrumentations are for equipping the computer of monitoring software, in order to monitor the operating state of DCS system; Two variable attenuators are in order to regulate the received power of DCS-AP and DCS-SA; Signal source is disturbed in order to produce white Gaussian noise; Mixer is incorporated into the DCS communication link with interference signal; Frequency spectrograph is in order to monitor DCS signal of communication and interference signal; Power splitter is with the signal one-to-two of DCS communication link, and one the tunnel connects frequency spectrograph, and one the tunnel meets DCS-SA.The input that power splitter is set is the A point, and output place of mixer is the B point.
2) according to DCS system actual working state, transmitting power and the working channel of DCS-AP is set.
3) regulate two variable attenuators, so that signal in A point signal strength signal intensity is-65dBm.
Usually the received power of DCS-SA-65dBm～-40dBm is interval, at test C/I
MinUsually choose the most not good enough-65dBm.
4) press system under test (SUT) DCS type of service and send packet.
5) frequency spectrograph carries out the channel power test to the 2.4-2.4835GHz frequency range, the record inband signaling; Adopt testing software record DCS Time Delay of Systems and loss of throughput, differentiate the DCS working state of system.If in the communication disruption patient time, DCS-SA does not receive packet, then DCS is abnormal operating state, otherwise DCS belongs to normal operating conditions.Concrete minimum signal interference ratio C/I
MinDo not determine according to receiving this judgment condition of packet in " communication disruption patient time ".
6) start signal source, with DCS be the signal of 0dBm with release strength frequently, and progressively increase the signal strength signal intensity of signal source, until the second test instrumentation monitoring DCS of DCS-SA end is abnormal operating state, namely DCS-SA does not receive packet in regulation " communication disruption patient time ".
7) frequency spectrograph records variation and DCS Time Delay of Systems, throughput and the operating state of C/I in this process.
According to above-mentioned test result, draw the relation curve of C/I and system's packet loss, and mark working state of system, as shown in Figure 3.Search the required minimum signal interference ratio C/I that works of the system of obtaining by relation curve
Min
Step S2, the signal power P that dynamic monitoring DCS system onboard terminal (MR) receives
r, according to the required minimum signal interference ratio of system, calculate in real time the current maximum interference I that bears of DCS system
Max
The signal power P that the real-time monitoring DCS MR of system receives
r, the maximum interference I that can bear according to the following formula computing system
Max:
I
max=P
r-C/I
min
I
MaxUnit be dBm.
Step S3 can bear maximum interference I according to system
Max, calculate and dynamically arrange the DCS system carrier and intercept thresholding CCA
Level
Calculate and the DCS system carrier be set according to following formula and intercept thresholding:
CCA
Level=I
Max-3, CCA
LevelUnit be dBm.
If the CCA that calculates
LevelBe lower than the DCS system sensitivity, then the DCS system carrier is intercepted thresholding and is set to system sensitivity.
By step S2 and S3, dynamically adjust in real time the carrier sense thresholding that carries DCS, thereby alleviate WLAN to the interference of DCS.
Embodiment
Below in conjunction with accompanying drawing, take the DCS system of the actual CBTC system of certain producer as example, describe a specific implementation process of the present invention in detail.Below concrete case be used for explanation the present invention, but be not used for limiting the scope of the invention.
The closed circuit test of DCS system of step S1:CBTC.
According to the data communication needs of DCS system, draw the required minimum signal interference ratio C/Imin of system communication by closed circuit test, concrete testing procedure is as follows:
1) builds test environment by Fig. 2.
2) according to DCS system actual working state, the transmitting power that DCS-AP is set is 18dBm, and working channel is set to channel 3(2412-2432MHz).
3) regulate variable attenuator so that signal in A point signal strength signal intensity is-65dBm.
4) by fping software the DCS type of service is set, take 500ms as the interval, sends the packet of 125byte.
5) frequency spectrograph carries out the channel power test to the 2.4-2.4835GHz frequency range, the record inband signaling, and the test spectrogram is as shown in Figure 3; Adopt the record DCS of testing software Time Delay of Systems, loss of throughput, differentiate the DCS working state of system, do not receive that with continuous 24s bag is as the judgment condition of system's non-normal working.
6) start signal source, with DCS be the signal of 0dBm with release strength frequently, and progressively increase the signal source signal strength signal intensity, until DCS-SA end test instrumentation is not received packet in regulation " communication disruption patient time (24s) ".
7) frequency spectrograph records variation and DCS Time Delay of Systems, throughput and the operating state of C/I in this process.
According to above-mentioned test result, draw the relation curve of C/I and Time Delay of Systems, and mark working state of system, as shown in Figure 3.Search the required minimum signal interference ratio C/I that works of the system of obtaining by relation curve
Min=16dB.
Step S2: calculate the DCS system and can bear maximum interference I in real time
Max
The signal power P that the real-time monitoring DCS MR of system receives
r, under above-mentioned test condition, P
r=-65dBm, the maximum interference I that can bear according to the following formula computing system
Max:
I
max=P
r-C/I
min=-65-16=-81（dBm）
Step S3 calculates and dynamically arranges the DCS system carrier and intercepts thresholding CCA
Level
Calculate and the DCS system carrier be set according to following formula and intercept thresholding:
CCA
level=I
max-3=-81-3=-84（dBm）
Because the sensitivity of system is-81dBm, so with CCA
LevelBe set to-81dBm.
As the signal power P that more relocates the receiving
rDuring for-50dBm, maximum interference I
MaxBe respectively with the carrier sense thresholding:
I
max=P
r-C/I
min=-50-16=-66（dBm）
CCA
level=I
max-3=-66-3=-69（dBm）
Fig. 4 is the DCS disturbed test spectrogram of CBTC, is the interference power size that loads in the experiment.
Fig. 5 is the DCS system in received power during for-50dBm, CCA
LevelBe respectively-81dBm and-packet loss and C/I relation curve during 69dBm.Work as CCA
LevelWhen not changing with received power, C/I is that 22 o'clock DCS could work, and works as CCA
LevelWhen changing according to received power, C/I is that 20 o'clock DCS just can work.Measured result shows, carrier sense thresholding dynamic setting method of the present invention can improve the interference free performance of the 2dB of DCS system.
Claims (5)
1. the method to set up of the carrier sense thresholding of the land mobile communication system (DCS) of the train automatic controlling system based on radio communication (CBTC) is characterized in that, the method may further comprise the steps:
Step 1 according to the data communication needs of DCS, draws DCS signal post by closed circuit test and needs minimum signal interference ratio C/I
MinC represents useful carrier frequency power, and I represents interfering signal power;
Step 2, the signal power P that the car-mounted terminal of dynamic monitoring DCS receives
r, according to the required minimum signal interference ratio C/I of system
Min, calculate in real time the current maximum interference I that can bear of DCS
Max: I
Max=P
r-C/I
Min
Step 3, the maximum interference I that can bear according to DCS
Max, calculate threshold value CCA
Level=I
Max-3, if the CCA that calculates
LevelBe lower than the DCS system sensitivity, then the carrier sense thresholding of DCS is set to system sensitivity, otherwise the carrier sense thresholding of DCS is set to CCA
Level
2. the method to set up of carrier sense thresholding as claimed in claim 1, it is characterized in that, described DCS adopts the CSMA/CA Channel Access Mechanism, uses IEEE802.11 series communication standard protocol, the agreement of perhaps revising based on 802.11 series standards, and the frequency range identical with the wlan device use.
3. the method to set up of carrier sense thresholding as claimed in claim 1 is characterized in that, in the described step 1, during closed circuit test, the parameter setting meets the following conditions:
(1) the fixing carrier sense thresholding of land mobile communication system;
(2) guarantee that the land mobile communication system received signal power is higher than the carrier sense thresholding;
(3) added Gauss's white noise power is lower than the carrier sense thresholding.
4. such as the method to set up of claim 1 or 3 described carrier sense thresholdings, it is characterized in that, the closed circuit test of passing through described in the step 1 draws the minimum signal interference ratio of DCS signal post need, specifically:
1) build test environment: the first test instrumentation, DCS WAP (wireless access point) (being called for short DCS-AP), the first variable attenuator, mixer, power splitter, the second variable attenuator, DCS car-mounted terminal (being called for short DCS-SA) and the test instrumentation of being connected connect successively, mixer also is connected with signal source, and power splitter also is connected with frequency spectrograph; Two test instrumentations are used for monitoring DCS operating state; Two variable attenuators are respectively in order to regulate the received power of DCS-AP and DCS-SA; Signal source is disturbed in order to produce white Gaussian noise; Mixer is incorporated into the DCS communication link with interference signal; Power splitter is with the signal one-to-two of DCS communication link, and one the tunnel connects frequency spectrograph, and one the tunnel meets DCS-SA; Frequency spectrograph is in order to monitor DCS signal of communication and interference signal;
2) according to the DCS actual working state, transmitting power and the working channel of DCS-AP is set;
The input of 3) establishing power splitter is the A point, regulates two variable attenuators, so that signal is the worst-case value of DCS-SA received power in A point signal strength signal intensity;
4) press system under test (SUT) DCS type of service and send packet;
5) frequency spectrograph carries out the channel power test to the 2.4-2.4835GHz frequency range, Time Delay of Systems and the loss of throughput of record DCS, and the operating state of differentiation DCS, if DCS-SA does not receive bag in the communication disruption patient time, then DCS is abnormal operating state;
6) start signal source, with DCS be the signal of 0dBm with release strength frequently, and progressively increase the signal strength signal intensity of signal source, be normal operating conditions until the second test instrumentation detects DCS;
7) frequency spectrograph records variation and DCS Time Delay of Systems, throughput and the operating state of C/I in this process;
Concrete minimum signal interference ratio is according to not receiving in the communication disruption patient time that this judgment condition of packet determines.
5. the method to set up of carrier sense thresholding according to claim 4 is characterized in that, described 3) and two variable attenuators of middle adjusting, so that A point signal strength signal intensity is-65dBm.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101009679A (en) * | 2007-01-29 | 2007-08-01 | 北京交通大学 | Communication-based interconnected and intercommunicated I-CBIT train operation control system |
| US20100131129A1 (en) * | 2008-11-26 | 2010-05-27 | Wolfgang Daum | System and method to provide communication-based train control system capabilities |
| CN102514597A (en) * | 2011-12-12 | 2012-06-27 | 北京交控科技有限公司 | Method for monitoring track state based on zone control system in CBTC (communication based train control) system |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101009679A (en) * | 2007-01-29 | 2007-08-01 | 北京交通大学 | Communication-based interconnected and intercommunicated I-CBIT train operation control system |
| US20100131129A1 (en) * | 2008-11-26 | 2010-05-27 | Wolfgang Daum | System and method to provide communication-based train control system capabilities |
| CN102514597A (en) * | 2011-12-12 | 2012-06-27 | 北京交控科技有限公司 | Method for monitoring track state based on zone control system in CBTC (communication based train control) system |
Non-Patent Citations (1)
| Title |
|---|
| 张岩等: "CBTC数据通信系统性能分析模型及应用研究", 《铁道学报》 * |
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