CN113163506A - Random access method based on cyclic offset real Chirp signal - Google Patents

Random access method based on cyclic offset real Chirp signal Download PDF

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CN113163506A
CN113163506A CN202110254171.7A CN202110254171A CN113163506A CN 113163506 A CN113163506 A CN 113163506A CN 202110254171 A CN202110254171 A CN 202110254171A CN 113163506 A CN113163506 A CN 113163506A
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random access
base station
time
terminal
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CN113163506B (en
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胡东伟
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CETC 54 Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

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Abstract

The invention discloses a random access method based on a cyclic shift real Chirp signal, and belongs to the technical field of wireless communication. In the method, a terminal carries out downlink synchronization according to a received downlink signal of a base station to obtain downlink frame timing; then sending a cyclic offset real Chirp signal; the base station searches the uplink access signal in the random access window; and when the base station detects the uplink access signal, sending the number, the time deviation and the frequency deviation of the uplink access signal. And the terminal sends the uplink access signal again according to the time deviation and the frequency deviation notified by the base station until the qualified information notified by the base station is received, so that the uplink service data is sent on the data channel allocated by the base station. The invention realizes a novel and structured random access signal based on the requirements of the random access signal and the characteristics of a real Chirp signal, can improve the multiple access and detection precision, and accelerates the random access process.

Description

Random access method based on cyclic offset real Chirp signal
Technical Field
The invention relates to the technical field of wireless communication, in particular to a random access method based on a cyclic shift real Chirp signal.
Background
The random access procedure has an important role in wireless communication systems. In the terrestrial mobile communication system, the downlink synchronization and broadcast signals are periodically broadcast. The terminal can synchronize with the base station according to the signal and receive the broadcast information of the base station. Then, the terminal sends information to the base station to request network access. The frame timing at which the terminal transmits the uplink signal is based on the timing at the base station side. The terminal needs to send a signal in advance, so that the uplink signal is exactly aligned with the uplink frame timing of the base station when arriving at the base station. But the terminal does not know the frame timing of the base station and the terminal can only know the frame timing of its own received signal. The frame timing of the terminal receiving signal is the frame timing of the base station downlink signal plus the link delay from the base station to the terminal. Since the time relationship between the downlink and uplink frame timing references of the base station is fixed, the problem is mainly that the link delay from the base station to the terminal (or vice versa) is unknown. In addition, in addition to the unknown transmission time of the terminal, the frequency offset caused by the terminal crystal oscillator is also unknown.
To solve this problem, a random access procedure is commonly set in the terrestrial mobile communication system. A time window is set at the base station side. The terminal estimates the time of the time window and sends a random access signal, and the base station detects in the window. In the window, the terminal does not need to know the accurate time of sending and can have a certain sending time deviation; the base station needs to detect the transmission time offset and frequency offset of the terminal transmission signal in the whole time window. In addition, there may be multiple terminals transmitting random access signals simultaneously, and the base station side needs to distinguish the access signals of different terminals and detect their respective timing errors and frequency offsets. Therefore, the random access signals of different terminals need to have multiple access capability.
The base station side needs to distinguish access signals of different terminals and detect timing errors and frequency offsets of the different terminals, so that higher requirements are provided for the access signal form and the processing algorithm and the processing capability of the base station side. Therefore, the base station side often performs simplification processing, for example, when access signals of two or more terminals collide, the base station ignores the signals, does not perform detection, and the terminal does not receive a response within a certain time, and then re-accesses the terminal by using a random back-off algorithm. Therefore, the terminal may have multiple accesses before success. In addition, after detecting the timing error and frequency offset of a certain terminal, the base station feeds back the timing error and frequency offset to the terminal through a downlink channel, and the terminal performs adjustment, but the terminal cannot be adjusted in place at one time, which often requires multiple rounds of access and feedback until the base station is adjusted to be satisfactory. This multiple round of adjustments further lengthens the time of the random access procedure.
In satellite communication systems, the requirements for random access signals are more demanding. Because the time delay of the satellite communication link is long, the number of times of iteration in the random access process is small, and therefore the type, the arrival time and the frequency offset of the random access signal can be estimated more quickly and accurately when the random access signal is detected. This then puts higher demands on the random access procedure.
The Chirp signal is a broadband signal widely used in a radar system, and the frequency of the Chirp signal increases or decreases linearly within a certain time, so that the frequency and the time delay have a certain conversion relation. The real Chirp signal is formed by superposing two Chirp signals of a forward frequency sweep and a reverse frequency sweep. The real Chirp signal can conveniently estimate the time delay and the frequency offset of the signal at the same time, so the real Chirp signal can become a better choice of a synchronous signal in a communication system.
Disclosure of Invention
In view of this, the present invention provides a random access method based on a cyclic shift real Chirp signal, which implements a novel structured random access signal based on the requirements of the random access signal and the characteristics of the real Chirp signal, and can improve multiple access and detection accuracy and accelerate the random access process.
In order to achieve the purpose, the invention provides the technical scheme that:
a random access method based on a cyclic shift real Chirp signal comprises the following steps:
(1) defining a basic real Chirp signal s0(t) is:
Figure BDA0002967232720000021
wherein A is the signal amplitude, a is the sweep frequency slope of the Chirp signal,
Figure BDA0002967232720000022
for the initial phase of the signal, T is the duration of the signal, f0For initial frequency offset, t is timeThe variables are the variables of the process,
Figure BDA0002967232720000023
is a fixed value in the range of [0,2 π);
defining N time offsets ti，i＝1，2，...，N：
ti＝T/2+(i-1)*T/(2N)
Defining an offset real Chirp signal si(t) is:
Figure BDA0002967232720000024
thus, N random access signals pi(t) is:
pi(t)＝(s0(t)+si(t))/2；
(2) the terminal carries out downlink synchronization according to the received downlink signal of the base station to obtain downlink frame timing; then, the terminal estimates the position of an uplink access window of the base station and sends a cyclic shift real Chirp signal si(t)；
(3) The base station searches the uplink access signal in the random access window; the concrete mode is as follows:
(301) the signal collected by the random access window is r (T), T is more than or equal to 0 and less than Tw，TwIs the access window width; at intervals of time TshiftIntercept the signal of T duration in r (T), and record it as
Figure BDA0002967232720000025
Figure BDA0002967232720000026
Wherein, k is the serial number of the signal in the intercepted r (t), and k is more than 1;
(302) to pair
Figure BDA0002967232720000031
Performing fast Fourier transform:
Figure BDA0002967232720000032
wherein, FFT represents fast Fourier transform, fr (t) is the transform result;
defining two local signals
Figure BDA0002967232720000033
And
Figure BDA0002967232720000034
Figure BDA0002967232720000035
wherein exp is an exponential function of a natural number e, and j is an imaginary unit;
will be provided with
Figure BDA0002967232720000036
And local signal
Figure BDA0002967232720000037
And
Figure BDA0002967232720000038
dot multiplication is carried out, inverse Fourier transform is carried out, and f is obtainedu(t) and fd(t)：
Figure BDA0002967232720000039
Wherein IFFT represents an inverse fourier transform,. indicates a dot product;
(303) to fu(t) and fd(t) taking the modulus to obtain | fu(t) | and | fd(t) |, will | fu(t)|、|fd(t) | is compared with a threshold TH to find | fu(t)|、|fdL times exceeding the threshold TH in (t) | are recorded as
Figure BDA00029672327200000310
And
Figure BDA00029672327200000311
(304) will be provided with
Figure BDA00029672327200000312
Two by two are compared when
Figure BDA00029672327200000313
Then, the random access signal p in the up-scanning signal is determinedi(t) present; wherein m, n is 1,2, …, L, mod is remainder operation;
will be provided with
Figure BDA00029672327200000314
Two by two are compared when
Figure BDA00029672327200000315
Then, the random access signal p in the down-scan signal is determinedi(t) present; wherein u, v ═ 1,2, …, L;
when the random access signal p exists in both the up and down scanning signalsi(t) then confirming detection of the random access signal pi(t); at this time, p in the scanning signal is recordedi(t) a starting time of
Figure BDA00029672327200000316
P in the lower scanning signali(t) a starting time of
Figure BDA00029672327200000317
Thus, the random access signal pi(t) an arrival time of
Figure BDA00029672327200000318
Deviation of frequency of
Figure BDA00029672327200000319
(4) The base station detects the random access signal piAfter (t), whether the time deviation and the frequency deviation are qualified is detected, if so, qualified information is sent to the terminal through a downlink channel, and an uplink data channel is distributed to the terminal; otherwise, sending p through downlink channeli(t) number, time offset and frequency offset;
(5) after receiving the number of the random access signal sent by the terminal on the downlink channel, the terminal sends the random access signal again according to the time deviation and the frequency deviation notified by the base station, so that the random access process is repeated until the time deviation and the frequency deviation qualified information notified by the base station is received, at this time, the uplink service data is sent on the uplink data channel allocated by the base station, and the random access is completed.
As can be seen from the above description, the technical scheme of the invention has the beneficial effects that:
1. the invention realizes a novel and structured random access signal based on the requirements of the random access signal and the characteristics of a real Chirp signal, can improve the multiple access and detection precision, and accelerates the random access process.
2. The invention adopts a special random access signal detection method in the random access process, the detection method has small calculation amount, and can detect a plurality of random access signals and the timing and frequency offset thereof by one-time detection, thereby greatly accelerating the random access process and improving the working efficiency of the system.
3. The invention can realize the simultaneous random access of a plurality of users and can correctly estimate the respective timing errors and frequency offsets of the users.
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To more clearly describe this patent, one or more drawings are provided below to assist in explaining the background, technical principles and/or certain embodiments of this patent.
Fig. 1 is a schematic view of a scenario of a random access method in an embodiment of the present invention.
Fig. 2 is a schematic diagram of uplink and downlink frame timing relationship and an uplink access window in the embodiment of the present invention.
FIG. 3 is a basic embodiment of the present inventionChirp signal s0(t) waveform diagrams.
Fig. 4 is a schematic diagram of a time offset when N is 4 in the embodiment of the present invention.
FIG. 5 is a graph of a shifted real Chirp signal s according to an embodiment of the present inventioni(t) and the basic real Chirp signal s0(t) is a graph showing the relationship.
FIG. 6 shows a random access signal p according to an embodiment of the present inventioni(t) and the basic real Chirp signal s0(t), shifting the real Chirp signal si(t) schematic representation of the relationship between.
Fig. 7 is a schematic diagram of an access window received signal and an interception method thereof in an embodiment of the present invention.
Fig. 8 is a schematic diagram of a random access signal detection procedure in an embodiment of the present invention.
Detailed Description
In order to facilitate understanding of the technical solutions of the present patent by those skilled in the art, and to make the technical objects, technical solutions and advantages of the present patent more apparent and fully support the scope of the claims, the technical solutions of the present patent are described in detail in the following embodiments.
A random access method based on a cyclic shift real Chirp signal comprises the following steps:
(1) defining a basic real Chirp signal s0(t) is:
Figure BDA0002967232720000041
wherein A is the signal amplitude, a is the sweep frequency slope of the Chirp signal,
Figure BDA0002967232720000042
for the initial phase of the signal, T is the duration of the signal, f0Is the initial frequency offset, t is a time variable,
Figure BDA0002967232720000043
is a fixed value in the range of [0,2 π);
defining N time offsets ti，i＝1,2,...，N：
ti＝T/2+(i-1)*T/(2N)
Defining an offset real Chirp signal si(t) is:
Figure BDA0002967232720000051
thus, N random access signals pi(t) is:
pi(t)＝(s0(t)+si(t))/2；
(2) the terminal carries out downlink synchronization according to the received downlink signal of the base station to obtain downlink frame timing; then, the terminal estimates the position of an uplink access window of the base station and sends a cyclic shift real Chirp signal si(t)；
(3) The base station searches the uplink access signal in the random access window; the concrete mode is as follows:
(301) the signal collected by the random access window is r (T), T is more than or equal to 0 and less than Tw，TwIs the access window width; at intervals of time TshiftIntercept the signal of T duration in r (T), and record it as
Figure BDA0002967232720000052
Figure BDA0002967232720000053
Wherein, k is the serial number of the signal in the intercepted r (t), and k is more than 1;
(302) to pair
Figure BDA0002967232720000054
Performing fast Fourier transform:
Figure BDA0002967232720000055
wherein, FFT represents fast Fourier transform, fr (t) is the transform result;
defining two local signals
Figure BDA0002967232720000056
And
Figure BDA0002967232720000057
Figure BDA0002967232720000058
wherein exp is an exponential function of a natural number e, and j is an imaginary unit;
will be provided with
Figure BDA0002967232720000059
And local signal
Figure BDA00029672327200000510
And
Figure BDA00029672327200000511
dot multiplication is carried out, inverse Fourier transform is carried out, and f is obtainedu(t) and fd(t)：
Figure BDA00029672327200000512
Wherein IFFT represents an inverse fourier transform,. indicates a dot product;
(303) to fu(t) and fd(t) taking the modulus to obtain | fu(t) | and | fd(t) |, will | fu(t)|、|fd(t) | is compared with a threshold TH to find | fu(t)|、|fdL times exceeding the threshold TH in (t) | are recorded as
Figure BDA00029672327200000513
And
Figure BDA00029672327200000514
(304) will be provided with
Figure BDA00029672327200000515
Two by two are compared when
Figure BDA00029672327200000516
Then, the random access signal p in the up-scanning signal is determinedi(t) present; wherein m, n is 1,2, …, L, mod is remainder operation;
will be provided with
Figure BDA00029672327200000517
Two by two are compared when
Figure BDA00029672327200000518
Then, the random access signal p in the down-scan signal is determinedi(t) present; wherein u, v ═ 1,2, …, L;
when the random access signal p exists in both the up and down scanning signalsi(t) then confirming detection of the random access signal pi(t); at this time, p in the scanning signal is recordedi(t) a starting time of
Figure BDA0002967232720000061
P in the lower scanning signali(t) a starting time of
Figure BDA0002967232720000062
Thus, the random access signal pi(t) an arrival time of
Figure BDA0002967232720000063
Deviation of frequency of
Figure BDA0002967232720000064
(4) The base station detects the random access signal piAfter (t), whether the time deviation and the frequency deviation are qualified is detected, if so, qualified information is sent to the terminal through a downlink channel, and an uplink data channel is distributed to the terminal; otherwise, sending p through downlink channeli(t) knitting ofNumber, time offset and frequency offset;
(5) after receiving the number of the random access signal sent by the terminal on the downlink channel, the terminal sends the random access signal again according to the time deviation and the frequency deviation notified by the base station, so that the random access process is repeated until the time deviation and the frequency deviation qualified information notified by the base station is received, at this time, the uplink service data is sent on the uplink data channel allocated by the base station, and the random access is completed.
Specifically, fig. 1 shows an application scenario of the method. Among them, a plurality of terminals are located under one base station, and a radio link from the base station to the terminal is called a downlink, and a radio link from the terminal to the base station is called an uplink.
Fig. 2 is a schematic diagram showing the timing relationship between uplink and downlink frames and the access window on the base station side. Frame n indicates the nth Frame, and the uplink Frame and the downlink Frame are both aligned in time and Frame count. At the beginning of each uplink frame, there is a block of time-frequency regions, which are dedicated to the random access of the terminal.
Because there are many terminals under a base station and there is also a possibility that many terminals send random access signals in the same uplink frame access window, the base station can allocate the access windows of the uplink frame through a downlink channel, thereby controlling the number of terminals accessed simultaneously in each access window. For example, assuming that there are 64 possible terminals simultaneously having access requirements under one base station, 16 uplink frame access windows (denoted as w) may be allocated0,w1,…,w15) Is one period, so that the control is that in one period, at most 4 terminals can be accessed simultaneously in each uplink frame access window. The control method is that each terminal has its own identification code, and when the lowest 4 bits of the identification code are 0, the terminal is only allowed to access the window w0Internal access; when the lowest 4 bits of the identification code are 1, the terminal is only allowed to be in the access window w1Internal access; and so on.
Fig. 3 shows the basic real Chirp signal s0(t) waveform. Here, the first and second liquid crystal display panels are,
Figure BDA0002967232720000065
a＝14MHz/s，f0＝-22.4KHz。
FIG. 4 shows the time offset t when N is 4iSchematic representation of (a). As can be seen from the figure, all the time offsets are greater than or equal to T/2, and N offsets are uniformly distributed in the range of [ T/2, T). For example, the shift amounts are T/2, 5 × T/8, 6 × T/8, and 7 × T/8, respectively, when N is 4.
Fig. 5 shows a shifted real Chirp signal si(t) schematic representation. As can be seen from FIG. 5, si(t) is s0(t) cyclically right-shifting tiAnd (4) obtaining the product.
Fig. 6 shows a random access signal pi(t) and the basic real Chirp signal s0(t), shifting the real Chirp signal si(t) relationship between them. As can be seen from the figure, the random access signal pi(t) real Chirp signal s based on0(t) and offset real Chirp signal si(t) are added together to obtain. While shifting the real Chirp signal si(t) real Chirp signal s based on0(t) cyclically right-shifting tiObtaining, so that a random access signal pi(t) real Chirp signal s based on0(t) a structured design.
Fig. 7 shows an access window received signal and an interception method thereof. In fig. 7, first, the base station samples all signals in the access window according to the uplink frame timing to obtain r (t). Then, intercepting a signal with a time length of T from r (T) to perform trial detection; next, offset by TshiftAnd then, intercepting the signal with the time length T in the r (T), and performing trial detection, and repeating the trial and error until the whole r (T) is detected.
Fig. 8 shows a detection procedure of a random access signal. First, the received signal is intercepted as shown in FIG. 7, the intercepted signal is FFT, and the FFT and the up-scan local signal are respectively processed
Figure BDA0002967232720000071
Down-scanning local signals
Figure BDA0002967232720000072
And performing dot multiplication, performing IFFT and modulus extraction, and then performing threshold comparison and peak search on the upper branch and the lower branch respectively to search for the time difference of the peak value.
In the upper branch, the time difference provided that there are two peaks is tiIf the random access signal p exists in the upper branch, the judgment is madei(t) and p in the upper branch can be obtainedi(t) starting time
Figure BDA0002967232720000073
In the lower branch, the time difference provided that there are two peaks is tiIf so, it is determined that the random access signal p exists in the lower branchi(t) and obtaining p in the lower branchi(t) a starting time of
Figure BDA0002967232720000074
Provided that the upper and lower branches are simultaneously present with a random access signal pi(t), finally, it is determined that there is a terminal signal pi(t) random access is initiated and a random access signal pi(t) an arrival time of
Figure BDA0002967232720000075
Frequency deviation of
Figure BDA0002967232720000076
It is worth emphasizing that during the peak search of the upper and lower branches, a plurality of time differences t may be detectedi,tj…, a plurality of random access signals p can be determinedi(t),pj(t), …, and their respective time of arrival and frequency offset, thereby enabling simultaneous random access by multiple users.
It should be understood that the above description of the embodiments of the present patent is only an exemplary description for facilitating the understanding of the patent scheme by the person skilled in the art, and does not imply that the scope of protection of the patent is only limited to these examples, and that the person skilled in the art can obtain more embodiments by combining technical features, replacing some technical features, adding more technical features, and the like to the various embodiments listed in the patent without any inventive effort on the premise of fully understanding the patent scheme, and therefore, the new embodiments are also within the scope of protection of the patent.

Claims (1)

1. A random access method based on a cyclic shift real Chirp signal is characterized by comprising the following steps:
(1) defining a basic real Chirp signal s0(t) is:
Figure FDA0002967232710000011
wherein A is the signal amplitude, a is the sweep frequency slope of the Chirp signal,
Figure FDA0002967232710000012
for the initial phase of the signal, T is the duration of the signal, f0Is the initial frequency offset, t is a time variable,
Figure FDA0002967232710000013
is a fixed value in the range of [0,2 π);
defining N time offsets ti，i＝1,2,...,N：
ti＝T/2+(i-1)*T/(2N)
Defining an offset real Chirp signal si(t) is:
Figure FDA0002967232710000014
thus, N random access signals pi(t) is:
pi(t)＝(s0(t)+si(t))/2；
(2) the terminal is based on the received downlink of the base stationCarrying out downlink synchronization on the signals to obtain downlink frame timing; then, the terminal estimates the position of an uplink access window of the base station and sends a cyclic shift real Chirp signal si(t)；
(3) The base station searches the uplink access signal in the random access window; the concrete mode is as follows:
(301) the signal collected by the random access window is r (T), T is more than or equal to 0 and less than Tw，TwIs the access window width; at intervals of time TshiftIntercept the signal of T duration in r (T), and record it as
Figure FDA0002967232710000015
Figure FDA0002967232710000016
Wherein, k is the serial number of the signal in the intercepted r (t), and k is more than 1;
(302) to pair
Figure FDA0002967232710000017
Performing fast Fourier transform:
Figure FDA0002967232710000018
wherein, FFT represents fast Fourier transform, fr (t) is the transform result;
defining two local signals
Figure FDA0002967232710000019
And
Figure FDA00029672327100000110
Figure FDA00029672327100000111
wherein exp is an exponential function of a natural number e, and j is an imaginary unit;
will be provided with
Figure FDA00029672327100000112
And local signal
Figure FDA00029672327100000113
And
Figure FDA00029672327100000114
dot multiplication is carried out, and inverse Fourier transform is carried out to obtain f (t) and fd(t)：
Figure FDA00029672327100000115
Wherein IFFT represents an inverse fourier transform,. indicates a dot product;
(303) to fu(t) and fd(t) taking the modulus to obtain | fu(t) | and | fd(t) |, will | fu(t)|、|fd(t) | is compared with a threshold TH to find | fu(t)|、|fdL times exceeding the threshold TH in (t) | are recorded as
Figure FDA00029672327100000116
And
Figure FDA00029672327100000117
(304) will be provided with
Figure FDA0002967232710000021
Two by two are compared when
Figure FDA0002967232710000022
Then, the random access signal p in the up-scanning signal is determinedi(t) present; wherein m, n is 1,2, …, L, mod is remainder operation;
will be provided with
Figure FDA0002967232710000023
Two by two are compared when
Figure FDA0002967232710000024
Determining random access signal p in a downlink scanning signali(t) present; wherein u, v ═ 1,2, …, L;
when the random access signal p exists in both the up and down scanning signalsi(t) then confirming detection of the random access signal pi(t); at this time, p in the scanning signal is recordedi(t) a starting time of
Figure FDA0002967232710000025
P in the lower scanning signali(t) a starting time of
Figure FDA0002967232710000026
Thus, the random access signal pi(t) an arrival time of
Figure FDA0002967232710000027
Deviation of frequency of
Figure FDA0002967232710000028
(4) The base station detects the random access signal piAfter (t), whether the time deviation and the frequency deviation are qualified is detected, if so, qualified information is sent to the terminal through a downlink channel, and an uplink data channel is distributed to the terminal; otherwise, sending p through downlink channeli(t) number, time offset and frequency offset;
(5) after receiving the number of the random access signal sent by the terminal on the downlink channel, the terminal sends the random access signal again according to the time deviation and the frequency deviation notified by the base station, so that the random access process is repeated until the time deviation and the frequency deviation qualified information notified by the base station is received, at this time, the uplink service data is sent on the uplink data channel allocated by the base station, and the random access is completed.
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