CN107018568B - Pre-compensation method for random access Doppler frequency offset for air-to-ground communication - Google Patents
Pre-compensation method for random access Doppler frequency offset for air-to-ground communication Download PDFInfo
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- CN107018568B CN107018568B CN201710315818.6A CN201710315818A CN107018568B CN 107018568 B CN107018568 B CN 107018568B CN 201710315818 A CN201710315818 A CN 201710315818A CN 107018568 B CN107018568 B CN 107018568B
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- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000004891 communication Methods 0.000 title claims abstract description 15
- 125000004122 cyclic group Chemical group 0.000 claims abstract description 5
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 4
- 238000009795 derivation Methods 0.000 description 2
- 230000010354 integration Effects 0.000 description 1
- 238000010295 mobile communication Methods 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18502—Airborne stations
- H04B7/18506—Communications with or from aircraft, i.e. aeronautical mobile service
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/002—Transmission of channel access control information
- H04W74/004—Transmission of channel access control information in the uplink, i.e. towards network
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
- H04J13/0007—Code type
- H04J13/0055—ZCZ [zero correlation zone]
- H04J13/0059—CAZAC [constant-amplitude and zero auto-correlation]
- H04J13/0062—Zadoff-Chu
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Abstract
The invention belongs to the technical field of wireless communication, and particularly relates to a precompensation method of random access Doppler frequency offset for air-to-ground communication. The main method of the invention is as follows: the air user obtains the distance between the air user and the ground base station; the air user calculates Doppler frequency offset according to system parameters; judging whether the Doppler frequency offset obtained in the step S2 is integral multiple frequency offset or decimal frequency offset, and if the Doppler frequency offset is integral multiple frequency offset, performing frequency offset precompensation of random access prefix by cyclic shift of the ZC sequence; if the frequency deviation is decimal times, generating a compensation sequence according to the specific frequency deviation multiple, and multiplying the compensation sequence by the ZC sequence for precompensation. The invention has the beneficial effects that: a method for pre-compensation of random access Doppler frequency offset for air-to-ground communication is presented.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a precompensation method of random access Doppler frequency offset for air-to-ground communication.
Background
In a mobile communication system, a transmitting party and a receiving party move relatively to generate Doppler frequency offset, and particularly in an air-to-ground communication scene, because the moving speed of an airplane user can reach 1000-1200 km/h, the high-speed movement can generate large Doppler frequency offset, and the success rate of random access is greatly reduced.
According to the existing LTE protocol, the maximum supportable mobile speed does not exceed 500km/h, so that the current equipment is difficult to support random access in an air-ground scene.
Disclosure of Invention
The invention aims to solve the problems and provides a method for pre-compensating random access Doppler frequency offset for air-ground communication.
The technical scheme of the invention is as follows: a method for precompensation of random access doppler frequency offset for air-to-ground communications, comprising the steps of:
s1, the aerial user obtains the distance between the aerial user and the ground base station;
s2, calculating Doppler frequency offset by the air user according to the system parameters;
s3, judging whether the Doppler frequency offset obtained in the step S2 is integral multiple frequency offset or decimal multiple frequency offset, and if the Doppler frequency offset is integral multiple frequency offset, entering the step S4; if the frequency offset is a decimal frequency offset, the process goes to step S5;
s4, performing frequency offset precompensation of random access prefix by cyclic shift of the ZC sequence;
and S5, generating a compensation sequence according to the specific frequency offset multiple, and multiplying the compensation sequence by the ZC sequence for pre-compensation.
Further, the specific method of step S2 is as follows:
doppler shift △ f is calculated by the following equation:
where v is the moving speed of the user in the air, f is the carrier frequency,
θ is the angle between the moving speed v of the air user and the direction of the carrier frequency f, c is the speed of light, h is the flying height of the air user, and d is the distance between the air user and the ground base station obtained in step S1.
Further, the specific method for determining whether the doppler frequency offset obtained in step S2 is an integer multiple frequency offset or a decimal frequency offset in step S3 is as follows:
using △ to represent the ratio of doppler frequency offset to subcarrier, △ is △ f/fRA，fRAFor the subcarrier frequency, a final determination △ is made as to whether the integer or fractional number.
Further, the compensation sequence in step S5 is an exp (-j2 pi △ n/Nzc) sequence, where n is 0,1,2, …, Nzc-1.
Corresponding to the above scheme, the present invention further provides a user equipment, comprising:
the first processing module acquires the distance between the first processing module and the base station through a positioning system;
the second processing module calculates Doppler frequency offset according to the system parameters;
the third processing module is used for judging whether the frequency deviation is integral multiple frequency deviation or decimal frequency deviation, wherein the integral multiple frequency deviation refers to that the ratio of the Doppler frequency deviation to the subcarrier is an integer, and the decimal frequency deviation refers to that the ratio of the Doppler frequency deviation to the subcarrier is a decimal;
the fourth processing module is used for processing the precompensation of the random access integer frequency offset;
and the fifth processing module is used for processing the precompensation of the random access decimal frequency offset.
The invention has the beneficial effects that: a method for pre-compensation of random access Doppler frequency offset for air-to-ground communication is presented.
Drawings
FIG. 1 is a schematic diagram of an air-ground communication scenario in an embodiment;
FIG. 2 is a flow chart of pre-compensation of random access prefix frequency offset according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a ue according to the present invention.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and embodiments:
examples
Fig. 1 is a schematic diagram of a typical air-to-ground communication scenario. As shown in fig. 1, the scenario includes an aircraft user and a base station. The frequency offset precompensation method in the embodiment of the invention is executed by the airplane user side.
Fig. 2 is a flow chart of pre-compensation of frequency offset of random access prefix according to an embodiment of the present invention. Referring to fig. 1, the moving speed of the airplane is v, the flying height h and the carrier frequency is f, and the technical solution of the present invention is described in detail with respect to this embodiment.
Step 201: by using a positioning system on the aircraft, the position of the base station can be obtained, so that the distance d between the aircraft and the base station can be measured, and the cosine value of the included angle theta between the speed v and the carrier frequency f can be calculated:
step 202: calculating the doppler frequency offset according to the numerical value and the system parameter calculated in step 201:
step 203, judging whether the Doppler frequency offset obtained by step 202 is integral multiple frequency offset or decimal multiple frequency offset, wherein △ is △ f/fRAIs the ratio of the doppler shift to the subcarrier, i.e., whether △ is an integer or a decimal.
And then, carrying out frequency offset pre-compensation on the random access prefix. The LTE random access prefix baseband signal is generated by a ZC sequence through FFT and IFFT changes, and the ZC sequence is generated as follows:
wherein u is a physical root sequence number of a random access ZC sequence, and Nzc is a ZC sequence length.
The influence of the doppler frequency offset on the random access is directly expressed as the phase rotation of the ZC sequence, which is specifically shown in the following formula:
the frequency offset pre-compensation is performed as follows:
step 204, when △ is an integer, i.e. integer frequency offset, let K be △, according to the derivation:
where du is a parameter related to cyclic shift of ZC sequence, and is determined by u, c ═ exp (j pi u · (Kdu + K)2du2) /Nzc) is a constant. According to the derivation, when the Doppler frequency offset is integral multiple frequency offset, the frequency offset precompensation of the random access prefix can be realized by circularly shifting the ZC sequence.
Step 205, when △ is decimal frequency offset, that is, decimal multiple frequency offset, it is obvious that it can not be pre-compensated by cyclic shift, at this time, it needs to go to module five to directly generate an exp (-j2 pi △ n/Nzc) sequence, and multiply with ZC sequence to perform pre-compensation.
Fig. 3 is a schematic structural diagram of a ue according to the present invention. The apparatus is explained below.
A first processing module 31, which obtains the distance between itself and the base station by using the positioning system; the second processing module 32 calculates the doppler frequency offset according to the system parameters; a third processing module 33, configured to determine whether the frequency offset is an integer multiple frequency offset or a fractional frequency offset; the fourth processing module 34 and the fifth processing module 35 respectively pre-compensate the integer multiple frequency offset and the decimal multiple frequency offset.
The problem of serious Doppler frequency offset of the random access prefix in the air-ground communication scene can be solved through the frequency offset precompensation.
For the invention it is to be noted that: the invention is only applicable in scenarios where the user has a positioning system.
Those of ordinary skill in the art will understand that: all or a portion of the steps of implementing the above-described method embodiments may be performed by hardware associated with program instructions. The modules in the above embodiments may be implemented in the form of hardware, or may also be implemented in the form of software functional modules. The present invention is not limited to any specific form of hardware or software integration.
Claims (2)
1. A method for precompensation of random access doppler frequency offset for air-to-ground communications, comprising the steps of:
s1, the aerial user obtains the distance between the aerial user and the ground base station;
s2, calculating Doppler frequency offset by the air user according to the system parameters; the specific method comprises the following steps:
doppler shift △ f is calculated by the following equation:
where v is the moving speed of the air user and f is the carrier frequencyAnd c is the speed of light,
h is the flying height of the air user, d is the distance between the air user and the ground base station obtained in step S1;
s3, judging whether the Doppler frequency offset obtained in the step S2 is integral multiple frequency offset or decimal frequency offset, wherein the specific method is as follows:
when △ is used to represent the multiple, △ is △ f/fRA，fRAFor the subcarrier frequency, it is finally determined △ whether the integer or the decimal number;
if the integer frequency offset is the integer frequency offset, the step S4 is entered; if the frequency offset is a decimal frequency offset, the process goes to step S5;
s4, performing frequency offset precompensation of random access prefix by cyclic shift of the ZC sequence;
and S5, generating a compensation sequence according to the specific frequency offset multiple, and multiplying the compensation sequence by the ZC sequence for pre-compensation.
2. The method of claim 1, wherein the compensation sequence in step S5 is an exp (-j2 pi △ n/Nzc) sequence, where n is 0,1,2, …, Nzc-1, Nzc is ZC sequence length.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102347924A (en) * | 2010-07-30 | 2012-02-08 | 北京海兰德维通信技术有限公司 | Frequency offset estimation and timing method and device |
| CN102457870A (en) * | 2010-10-21 | 2012-05-16 | 电信科学技术研究院 | Method and device for detecting primary synchronization signal and method and system for searching neighborhoods |
| CN102724149A (en) * | 2012-05-16 | 2012-10-10 | 华为技术有限公司 | Frequency offset precompensation method, random access method, equipment and system |
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| EP2458805B1 (en) * | 2007-01-05 | 2018-06-27 | LG Electronics Inc. | Method for setting cyclic shift considering frequency offset |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102347924A (en) * | 2010-07-30 | 2012-02-08 | 北京海兰德维通信技术有限公司 | Frequency offset estimation and timing method and device |
| CN102457870A (en) * | 2010-10-21 | 2012-05-16 | 电信科学技术研究院 | Method and device for detecting primary synchronization signal and method and system for searching neighborhoods |
| CN102724149A (en) * | 2012-05-16 | 2012-10-10 | 华为技术有限公司 | Frequency offset precompensation method, random access method, equipment and system |
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