Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
• • 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

Definitions

• the present invention relates to the field of communications, and in particular, to a signal detection method for a random access channel. Background technique
• the UE User Equipment, User Terminal
• the UE first performs downlink synchronization through the SCH (Synchronization Channel) to find the receiving start point and the cell number of the radio frame and the subframe ( Cell ID);
• the system information is obtained through the BCH (Broadcast Channel), and the system information includes the configuration information of the RACH (Random Access Channel).
• the uplink synchronization is performed through the RACH to complete the work of the access system. .
• the UE In the process of uplink synchronization, the UE first finds the transmission location of the RACH channel based on the radio frame and the reception start point of the subframe determined in the following row synchronization, and determines the available sequence of the cell for RACH transmission from the obtained system information, and then A random one of the available sequences is selected for transmission as a preamble.
• the base station detects the preamble to determine the amount of uplink timing adjustment and sends it to the UE.
• the UE adjusts the transmission timing of the uplink signal according to the timing adjustment amount, and implements uplink time synchronization.
• the uplink random access preamble of LTE uses a ZC (Zadoff-Chu) sequence, and the w-th ZC sequence is defined as:
• N zc is the length of the ZC sequence and N zc is a prime number, which is specified as 839 in LTE.
• each cell allocates 64 sequences for preambles, which may be different cyclic shift sequences from the same root sequence, or different cyclic shift sequences from different root sequences.
• the ZC sequence is Constant Amplitude Zero Auto-correlation Code (Constant Amplitude Zero Auto-correlation Code, For the sequence of CAZAC, the correlation of ZC sequences has the following characteristics: The correlation between different cyclic shift sequences of the same sequence is 0; the correlation between different root sequences and their cyclic shift sequences is That is, the correlation between different root sequences is very small, approximately 0. Therefore, the base station can perform time domain correlation detection on the random access signal by using the correlation property of the ZC sequence to obtain an uplink timing adjustment amount.
• time domain correlation detection method is intuitively defined as point multiplication of the received signal and the complex conjugate of each cyclic shift of the local sequence and summing to obtain the time domain correlation value of each cyclic shift sample, which can be mathematically Equivalent to the received frequency domain signal and the local frequency domain sequence complex conjugate point multiplication and then converted to the time domain by inverse Fourier transform.
• the mathematical form of time domain correlation detection is expressed as follows:
• the time domain of the received signal is ( ), the frequency domain is ⁇ ⁇ ); the local sequence time domain is x( ), the frequency domain is; ⁇ ) , and the local sequence complex conjugate is in the time domain ( ) , the frequency domain form; the correlation function R(m) of the two, expressed as:
• m is the cyclic shift sample and ⁇ is the number of samples of the ZC sequence. Therefore, for a RACH user using a different cyclic shift of the same root sequence as a preamble, the received signal is converted to the frequency domain and then multiplied by the complex conjugate point of the frequency sequence of the root sequence. The result is converted into the time domain by inverse Fourier transform, and the time domain correlation value corresponding to each cyclic shift sample can be obtained.
• FIG. 1 is a schematic diagram of a RACH time domain correlation detection method.
• the two receiving antennas are taken as an example to describe an implementation method for time domain correlation detection of a received signal, which is briefly described as follows:
• IFFT Inverse Fast Fourier Transform, Fast Fourier transform
• the N time-domain correlation values of the local root sequence are modulo squared for the N time-domain correlation values, and the obtained N-point time-domain correlation value reflects the magnitude of the signal and the noise power; and finally the time of the two receiving antennas
• the domain correlation values are combined to obtain N time-domain correlation values after the antennas are combined, and then peak detection is performed to obtain the position of the preamble and the
• RACH time domain correlation detection ie, detection of preamble, also known as RACH preamble detection
• RACH detection the detection threshold corresponding to the given false alarm rate target is first determined when the signal is not transmitted, and then the detection rate of the random access signal detection when transmitting the signal is tested according to the threshold.
• the false alarm rate is defined as the probability that the preamble is detected when there is no preamble transmission; the miss detection rate is defined as detecting an erroneous preamble, or not detecting a transmitted preamble, or detecting the correct preamble However, the probability of occurrence of an error timing adjustment amount or the like is estimated.
• the target false alarm rate is generally required to be 10 or slightly less than 10. False alarm rate is reached when no transmission signal 10_ 3 or slightly smaller than the detection limit of the door 10-3 of the peak detection threshold.
• the threshold for peak detection is divided into absolute threshold and relative threshold.
• the absolute threshold is related to the magnitude of the noise.
• the threshold is independent of the noise power, so the ratio of the signal correlation value to the noise power is used.
• the relative threshold for peak detection When detecting the RACH signal, the system generally presets a relative threshold, and then estimates the magnitude of the noise in the detection. The noise level and the relative threshold multiply can obtain an absolute threshold, so the above is given when the signal is not sent. Determining the corresponding detection threshold under the target of the false alarm rate refers to the relative threshold.
• the RACH signal When the ratio of the correlation value of the received signal to the noise power is greater than the relative threshold, the RACH signal is considered to be present. Under normal circumstances, the higher the relative threshold is, the harder it is for users to access. The lower the setting, the more false alarms. In general, this threshold is taken as: The ratio of the signal to the noise at a false alarm rate of 10 (and therefore also the false alarm threshold). In the false alarm threshold, when the UE transmits RACH signal, if no frequency offset (the offset) and other interference, the false alarm rate is generally not higher than 10-3.
• the energy of the RACH signal will be dispersed, because the preamble uses a ZC sequence, which is defined so that the energy of the RACH signal is dispersed to another cyclic shift sequence when there is a frequency offset, and thus appears. Detection error.
• the frequency offset characteristics of the ZC sequence are described in detail below.
• the frequency offset of the uplink RACH is not particularly large. Due to the movement of the UE The speed is generally less than 375 km/h, so it is generally considered that RACH only has a frequency offset of less than or equal to 1 time.
• a 1x offset (which can be a positive 1x offset or a negative 1x offset) is generated.
• the RACH sequence of the received frequency domain be ZW, and its time domain form is recorded as follows. According to the nature of IDFT (Inverse Discrete Fourier Transform), for the IDFT of N points, we have:
• the sequence between the sequence and the sequence of the original sequence after cyclic shift (the sequence obtained after the original sequence is shifted by 1 frequency), and the received signal and the original sequence without frequency offset and 1
• the sequence generated by the octave offset (that is, the sequence after the cyclic shift of the original sequence) will produce a correlation peak, and two copies of the cyclic shift search window will appear at the same time (called a replica search due to frequency offset). Window, or simply a copy window).
• a cyclic shift of 0 is given in Fig. 2, from which the relationship of d:, and the relationship between the cyclic shift window and the replica window can be understood, wherein the dotted line portion is an equivalent negative frequency offset window, and
• the negative frequency offset window used by the time domain correlation method is a cyclic cyclic shift relationship.
• Figure 3 shows an example of a cyclic shift window and a copy window corresponding to a cyclic shift that is not zero.
• the distance between the two replica windows and their cyclic shift windows can be derived using only the values defined in TS 36.211 (i.e., values less than N zc /2). In fact, it is the distance between the start of the cyclic shift search window and the start of the copy window.
• the cyclic shift used for generating the preamble sequence is divided into an unrestricted set unrestricted set (also called a regular set normal set) and a restricted set restricted set (also called a high speed set high speed set).
• Set Two.
• the limit set (high speed set) takes into account the frequency offset effect caused by the high speed, and in order to ensure that the search windows of the respective preamble sequences do not overlap each other, the cyclic shift amount Cv used for generating the preamble sequence is limited.
• the cyclic shift amount generated by the preamble sequence is not limited, and the value of the leading cyclic shift is generated.
• the frequency offset characteristic of the ZC sequence since the RACH signal received by the base station is frequency offset, in addition to the cyclic shift corresponding search window (referred to as a cyclic shift search window) in the RACH preamble detection, There will also be peaks in the copy window.
• the Doppler frequency is relatively large, so the copy window
• the correlation value of the RACH signal will be relatively large. It is considered that the cyclic shift window and the two duplicate windows may have signals at the time of detection. It is necessary to comprehensively detect the cyclic shift window and the two replica windows, because the high-speed cell uses the limit set, each The cyclic shift window corresponding to each preamble and its copy window do not coincide with the cyclic shift window of other preambles and its copy window, so that there is no phenomenon that two different preambles are in one search window. For medium and low-speed cells, the Doppler frequency offset is relatively small, and the signal correlation value in the cyclic shift window is often much higher than the signal correlation value in the replica window. Therefore, only the signal in the cyclic shift window is considered during the detection, that is, only Preamble detection is performed in the cyclic shift window, and the replica window is not detected.
• the medium-low speed cell uses an unrestricted set, that is, there is no cyclic shift.
• Bit limit although the cyclic shift window corresponding to each preamble does not coincide with the cyclic shift window of other preambles, the cyclic shift window corresponding to each preamble may coincide with the copy window of other preambles.
• the signal correlation value in the cyclic shift window is much larger than the signal correlation value due to the frequency offset in the replica window, but when the signal-to-noise ratio is high, the correlation value brought by the frequency offset in the replica window It will be big.
• the preamble C1 is transmitted, and the preamble C2 is not transmitted.
• the frequency offset copy signal of C1 may fall to the cyclic shift search window of C2.
• the technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a signal detection method for a random access channel, which suppresses false alarms caused by frequency offsets of cells using non-limiting sets (middle and low speed cells).
• the present invention provides a signal detection method for a random access channel, including:
• step B If there are remaining detection points, and the largest time domain correlation value in the remaining detection points is greater than the peak detection threshold, then jump to step B; otherwise, the detection of the current root sequence is ended;
• N zc is the length of the root sequence
• d u is the distance between the start of the cyclic shift search window and the start of the replica window.
• step B after finding the m-max, the following operations can also be performed:
• a point greater than or equal to m3 and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to m4 is regarded as a non-detection point; otherwise, a point greater than or equal to m3 and less than or equal to m4 is regarded as non-detection Point; and/or
• a point greater than or equal to m5 and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to m6 is regarded as a non-detection point; otherwise, a point greater than or equal to m5 and less than or equal to m6 is regarded as non-detection Point
• step B after the m_max is found, other detection points exceeding the peak detection threshold that belong to the same cyclic shift search window as the m-max may be found in the current detection point: m[l] m [K]; identifies m[k] - d u and/or m[k] + d u in the current detection point as non-detection points;
• step B after the detection point is found: m[l] m[K], the following operations can also be performed: If m7[k] > m8[k] , a point greater than or equal to m7[k] and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to m8[k] is used as a non-detection point; otherwise, a point greater than or equal to m7[k] and less than or equal to m8[k] as a non-detection point; and/or
• a point greater than or equal to m9[k] and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to ml0[k] is used as the non-detection point; otherwise, a point greater than or equal to m9[k] and less than or equal to ml0[k] as a non-detection point;
• m7[k] (N+m[k] - d u - X) mod N
• m8[k] (N+m[k] - d u + X) mod N
• m7[k] and m8 [k] is a positive integer
• m9[k] (N+m[k] + d u — X) mod N
• ml0[k] (m[k] + d u + X) mod N
• m9 [ k] and mlO [k] are positive integers
• X int(N/(N zc x 2)) , int means rounded up or down.
• step B after the m_max is found, all the detection points in the current detection point that belong to the same cyclic shift search window as the m-max may also be identified as non-detection points.
• O - JmodA ⁇ ⁇ 1 , greater than or equal to 2 and less than N /2 ; where int() means round up or round down.
• the peak detection threshold can be determined by the following steps:
• noise estimation on the received signal to obtain a noise mean value; using the product of the above noise mean value and a preset relative threshold value as a peak detection threshold;
• the relative threshold is a ratio of a false alarm signal to a noise that reaches a target false alarm rate when no signal is transmitted.
• noise mean can be determined by the following steps:
• root sequence is a ZC sequence.
• FIG. 1 is a schematic diagram of a method for detecting RACH time domain correlation
• FIG. 2 is a schematic diagram showing the relationship between the positive and negative frequency offset window and the cyclic shift window when the cyclic shift is 0 in the RACH time domain correlation detection;
• FIG. 3 is a schematic diagram of a cyclic shift search window and a frequency offset copy window corresponding to a cyclic shift that is not 0 in RACH time domain correlation detection;
• FIG. 4 is a flowchart of a RACH time domain correlation detecting method according to an embodiment of the present invention.
• Figure 5 is a schematic diagram of the false alarm caused by the frequency offset in the RACH correlation detection.
• the basic idea of the present invention is that, since the frequency offset causes a large number of false alarms, the position of the false alarms can be found according to the frequency offset characteristic of the ZC sequence when performing peak detection in the RACH time domain correlation detection process, and these possibilities are removed. It is the location of false alarms to achieve the purpose of false alarm suppression.
• FIG. 4 is a flow chart of a RACH time domain correlation detection method according to an embodiment of the present invention.
• FIG. 4 partially merges and simplifies FIG. 1, and only describes a single receiving antenna as an example.
• the method includes the following steps:
• N zc is the length of the ZC sequence, which is specified as 839 in LTE.
• This step is an optional step.
• the time domain correlation value after the modulo square processing actually reflects the signal power value.
• the peak detection is performed on the N time-domain correlation values of each sequence. The following takes the u-th root sequence as an example, which specifically includes the following steps:
• Threshold B can be calculated as follows:
• Threshold A can be equal to: Maximum time domain correlation value X noise estimation ratio; where noise estimation ratio is greater than 0 and less than 1, for example, noise estimation ratio The value can be taken as 0.6.
• the noise mean Calculate the mean of all time-domain correlation values less than threshold A (called the noise mean); the noise mean actually reflects the amount of noise power.
• the threshold A and the noise mean can also be calculated using other methods of the prior art.
• the relative threshold can be the ratio of the false alarm signal to the noise at the target false alarm rate (for example, 0.1%) when no signal is sent.
• threshold B the role of the peak detection threshold is to distinguish between noise and signal. In the present invention, only the function of stopping detection is performed (that is, the time domain correlation value less than the threshold is not detected), in the prior art. There are many other settings and calculation methods.
• ml (N+m - max - d u ) mod N
• m2 (m— max + d u ) mod N
• ml and m2 are both positive integers.
• m- max - d u and m- max + d u to Xi Bu can capture interval ⁇ [m- max- d u - X, m- max - d u + X] and [m- max + d u - Other values in X, m - max + d u + X] are removed from the set of points to be detected.
• [ ] denotes a closed interval
• X int(N/(N zc x2)), and int denotes rounding up or down.
• M5 (N+m - max + d u - X) mod N
• m6 (m - max + d u + X) mod N
• m5 and m6 are positive integers.
• d u is the distance between the start point of the cyclic shift search window and the start of the replica window.
• du l
• the loop shift window and the copy window almost coincide, and it is not necessary to delete the point of the copy window. Therefore, it is possible to limit the operation of step 406 only when d u is greater than or equal to 2.
• N ZC N ZC
• the preamble corresponding to the cyclic shift window in which the maximum correlation value in the current set of points to be detected is located is used as the detected preamble, and the position of the maximum correlation value, m_max, and the maximum correlation value are cyclically shifted.
• to-be-detected point set further includes a to-be-detected point, skip to step 405, otherwise Peak detection of the uth root sequence of the beam.
• Fig. 5 is a schematic diagram of a false alarm caused by frequency offset in RACH correlation detection; an application example of the present invention will be described below with reference to Fig. 5.
• the time domain correlation values smaller than the threshold A are averaged, and the mean values of the data reflect the noise power mean of the root sequence. Means and noise false alarm rate relative to the target gate 10-3 when the threshold limit value as the product of B.
• the length of the search window configured by the system is Ncs
• the user uses a cyclic shift Cvl of a certain root sequence
• the user's cyclic shift search window from Cvl to Cvl+Ncs, one
• the copy window is Cvl - d u to Cvl - d u + Ncs
• the other copy window is Cvl + d u to Cvl + d u + Ncs.
• the replica window of the cyclic shift Cvl may be a cyclic shift search window of other RACH users.
• point x2 will be judged as another RACH user whose cyclic shift is Cv2, and point x2 will become a false alarm. If the signal-to-noise ratio is high, a false alarm will appear in the copy window corresponding to the cyclic shift window of the RACH signal, which will bring a lot of signal overhead.
• the distance between point x2 and point xl is exactly d u , which means that point x2 may be caused by the frequency offset of point xl.
• Point x2 and its left and right points may be false alarm points.
• point x2 and The left and right points are removed from the set of points to be detected, so that the signals at these positions are not detected, and no false alarms are generated. Since the preamble signal has been detected by the cyclic shift search window corresponding to the point x1, the non-detection position further includes all points in the cyclic shift search window corresponding to the point x1. In order to avoid repeated detection, it is also necessary to move from Cvl to Cvl.
• Ncs The location of Ncs is marked as a non-detected location.
• all the detectable positions are detected again, and it is found that the time domain correlation value of the threshold B is not exceeded, and then the peak detection process of the root sequence is determined to be ended.
• the final result of the correlation detection of the root sequence is that only the cyclic shift of the point xl is detected.
• the leading position corresponding to the bit search window, corresponding to the cyclic shift search window where the point x2 is located The lead is not reported as a result of the test.
• the peak point of a cyclic shift cvl frequency offset copy coincides with the same sequence and another cyclic shift cv2 peak point.
• the above false alarm suppression method may cause The missed detection of the signal corresponding to cv2 is cyclically shifted, but this situation rarely occurs because the position of each user in the actual system is random from the base station, and the delay is also different. And when the length of the search window is large, the available cyclic shift of the same sequence will be small, and the probability of such coincidence is even smaller.
• d u is less than 2 (that is, in the peak detection, the position determined as the preamble in a certain cyclic shift search window is regarded as the non-corresponding position of the copy window thereof.
• the detection position ensures that there is no missed detection when there is a peak overlap between a cyclic shift window and its own copy.
• the above embodiment has various transformations, such as:
• step 405 after determining m_max, the following processing may also be performed: First, all the points in the set of points to be detected are located in the same cyclic shift search window as m-max, and then located at m-max. The points of the same cyclic shift search window and/or the corresponding points in the copy window corresponding to the cyclic shift search window are deleted from the set of points to be detected.
• m_maxl may be deleted from the set of points to be detected.
• m maxl, m maxl - d u and / or m maxl + d u be the set of detection points may be m maxl - d u and / or m- maxl + d u to be removed from the collection point detection.
• the interval may also be won ⁇ [m- maxl- d u - X, m maxl - d u + X] , and - other values [m- maxl + d u X, m maxl + d u + X] to be in the The detection point is removed from the collection.
• m[l] m[K] the following operations can also be performed: If m7[ k] > m8[k] , then a point greater than or equal to m7[k] and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to m8[k] as a non-detection point; otherwise, greater than or equal to m7 [k] and small a point equal to m8[k] as a non-detection point; and/or
• a point greater than or equal to m9[k] and less than or equal to N, and/or a point greater than or equal to 1 and less than or equal to ml0[k] is used as the non-detection point; otherwise, a point greater than or equal to m9[k] and less than or equal to ml0[k] as a non-detection point;
• m7 [k] (N+m[k] - d u - X) mod N
• m8 [k] (N+m[k] - d u + X) mod N
• m7[k] and m8 [k] is a positive integer
• M9[k] (N+m[k] + d u - X) mod N
• ml0[k] (m[k] + d u + X) mod N
• m9 [k] and mlO [k] are A positive integer.
• the above embodiment describes the present invention by taking a single receiving antenna as an example.
• the present invention is also applicable to the case of multiple receiving antennas, and only needs to add N time-domain correlation values corresponding to the receiving antennas separately. Peak detection is sufficient.
• the set of points to be detected is used, and each point in the set of detection points is subjected to peak detection, and each non-detected point or the detected point is deleted from the set of points to be detected;
• Other methods can be used, for example, to identify detected or non-detected points to avoid repeated detection or detection of false alarm points.
• the method of the present invention can effectively suppress false alarms caused by frequency offset in cells using non-limiting sets (middle and low-speed cells), reduce signaling overhead caused by false alarms, and avoid The missed detection of the random access signal ensures the successful access of more users.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=40308002

Family Applications (1)

Country Status (2)

Cited By (2)

Families Citing this family (24)

Citations (3)

Family Cites Families (2)

• 2008
  • 2008-09-10 CN CN2008102115131A patent/CN101355383B/zh active Active
• 2009
  • 2009-08-07 WO PCT/CN2009/000902 patent/WO2010028537A1/zh active Application Filing

Patent Citations (3)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events