CN115442196B - Method for enhancing NR PRACH_format_0 coverage capability - Google Patents
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- H04L27/00—Modulated-carrier systems
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- H04L27/2601—Multicarrier modulation systems
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- H04L27/2655—Synchronisation arrangements
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Abstract
The invention provides a method for enhancing the coverage capacity of NR PRACH_format_0, which comprises the steps of expanding the coverage area of a cell by adopting a PRACH double-check mechanism; the PRACH double detection mechanism comprises the following steps: s1, a base station receives a preamble of PRACH format 0; s2, performing preamble detection twice, and recording detection results of the twice; wherein, each preamble detection needs to be configured with different T remove;Tremove to represent the time length of the removed start-end signal before FFT processing; and S3, combining the detection results of the two times. The invention adopts PRACH double detection mechanism to expand the coverage of the cell, and supports the coverage of 30km at maximum.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method for enhancing NR PRACH_format_0 coverage capability.
Background
In the current 5GNR system, the PRACH is used to support the UE to initiate random access to the gNB, which may be used to carry a random preamble sequence (preamble), where the preamble sequence is generated based on a ZC sequence and has good cross-correlation and autocorrelation characteristics, as shown in fig. 1, and CP and GT are further added before and after the ZC sequence when the preamble is sent:
CP is cyclic Prefix (cyclic Prefix) for overcoming inter-symbol interference (ISI) caused by transmission delay, which is actually the last sequence of ZC sequence (the principle is the same as that of CP-OFDM technology);
The GT is a Guard Time (Guard Time) for avoiding interference caused by overlapping of a preamble transmission Time range and other subsequent signals due to excessive transmission delay, and the GT is actually null, so that the UE does not need to transmit any signal in the Time period.
Based on the gNB, the ZC sequence sent by the UE can be detected under the condition of low signal-to-noise ratio (such as SINR is-10 dB or even lower), and the transmission delay is measured, as shown in fig. 2, comprising the following procedures:
(1) The front transmission process, namely OFDM demodulation and down sampling process flow, comprises the process procedures of removing CP, frequency band shifting, down sampling, FFT and the like;
(2) RE demapping: namely, separating a frequency domain sequence corresponding to the PRACH from the frequency domain signal;
(3) And (3) correlation processing: namely, the base sequence and the received PRACH corresponding frequency domain sequence are subjected to correlation processing (conjugate multiplication among sequences);
(4) IFFT: namely, the process of performing IFFT processing on the related sequences obtained by the related processing;
(5) Symbol and antenna combining: combining a plurality of IFFT processing result sequences corresponding to a plurality of antennas;
(6) Pulse peak search: searching pulse peaks in the combined sequence;
(7) preamble detection judgment: judging whether a preamble exists or not and judging the preamble ID according to the size and the position of the searched pulse peak;
(8) TA/RSRP/N0 measurements: TA (UE uplink signal transmission advance), RSRP (preamble signal total power) and N0 (noise power) are calculated according to the size and the position of the pulse front determined to be the preamble.
The mathematical model of the signal after the above-mentioned forward processing is shown as follows:
Wherein:
r p,i (l, k) represents the received signal on the p-th antenna, the l-th OFDM symbol, and the k-th subcarrier;
H p,i (l, k) represents the channel attenuation factor of the ith transmission path on the kth antenna, the kth OFDM symbol, and the kth subcarrier;
W p (l, k) represents interference noise (including inter-carrier interference ICI) corresponding to the p-th antenna, the l-th OFDM symbol, and the k-th subcarrier;
N path represents the number of multipaths that can be considered constant during the preamble transmission time (1 ms);
u represents a root sequence index;
L RA represents the root sequence length;
C v represents a ZC sequence cyclic shift value;
T off (i) represents the equivalent transmission delay of the ith transmission path, T off＝Tdelay(i)+TCP-Tremove,Tdelay represents the transmission delay of the UE and the gNB, T CP represents the CP duration, T remove represents the time length of the signal at the starting end removed before FFT processing, and the value of the signal is required to be T CP according to the OFDM modulation theory, but in order to prevent poor downlink synchronization precision of the UE, the signal is often set to be 0.5 x T CP in the implementation process.
The corresponding mathematical model of the above-mentioned correlation process is as follows:
Wherein:
R local (k) represents a locally generated ZC sequence;
n represents the FFT point number in the forward processing.
The IFFT processing corresponding mathematical model is as follows:
Wherein: n IFFT represents the number of IFFT points (different from the number of IFFT/FFT points in the process of the forwarding), the value is not less than L RA, and the power of 2 is as great as possible, for example 1024 and 2048, and the larger the value is, the higher the granularity of the finally obtained relevant power spectrum is.
The mathematical model corresponding to the antenna and symbol combination process is as follows:
Wherein: p and L represent the total number of receive antennas and the total number of OFDM symbols carrying preamble, the resulting physical meaning is the relevant power spectrum.
Obviously, based on the determination of the size and the position of the pulse front of the relevant power spectrum, preabmle detection results and measurement results such as transmission delay, RSRP, noise power and the like can be obtained.
Considering the initial access scenario, the UE is not uplink-synchronized with the gNB, and only transmits the preamble based on the downlink synchronization time reference, which leads to a delay of T delay when the preamble is transmitted compared to the gNB time reference, and further leads to a transmission delay of about 2T delay when the preamble reaches the gNB, which is a loopback delay (RTD) between the UE and the gNB, as shown in fig. 3. From this, it can be deduced that in the NR system, the maximum designed transmission distance d max of the preamble is as follows,
Wherein:
c represents the light speed of 3 x 10 8 m/s;
T CP denotes CP duration, and the PRACH format 0 in the NR standard is defined to have a value of 103.125us;
T GT denotes GT duration, and the value 96.875us is defined for PRACH format 0 in the NR standard;
T multi-path represents the maximum multipath delay spread, the value is related to the channel environment, generally not more than 1us, and the value is 0 when the preamble limit coverage capability is calculated.
Obviously, the maximum design transmission distance limit of the preamble defined by PRACH format 0 defined by the NR standard can be calculated by the above equation to be 14531.25m, about 14.5km.
When the 5G network is deployed, the PRACH format 0 which occupies 1ms is used for supporting the outdoor coverage scene, and the PRACH format B4/C2 which occupies 1 slot time is used for supporting the indoor coverage scene. However, as described above, PRACH format 0 theoretically can only support a maximum of 14.5km, and this distance is not suitable for special situations such as wild mountain, desert, lake, offshore sea surface, etc.: which requires a coverage distance of maximally 20-30 km.
According to the protocol, for a coverage distance of 14.5km or more, PRACH format1 and PRACH format 2 may be used, and their maximum designed transmission distances d max are about 102.66km and 22.89km, respectively. They also require longer signal transmission times: respectively 3ms and 4ms, which is difficult to meet in practical network deployments: considering compatibility with an LTE network, the current 5GNR TDD network adopts 30kHz subcarrier spacing, DDDSUDDSUU (7:3), DDDDDDDSUU (8:2) and other slot configurations, rarely adopts slot proportion for continuously supporting continuous 3-4 ms uplink transmission time, and the realization complexity and cost of a base station are obviously increased due to continuous 3-4 ms uplink reception.
Disclosure of Invention
The invention aims to provide a method for enhancing the coverage capability of NR PRACH_Format_0, so as to effectively improve the transmission distance of PRACH format 0 to 30km only through the optimization of a base station side, and further enlarge the coverage range of a cell.
The invention provides a method for enhancing the coverage capacity of NR PRACH_format_0, which comprises the step of expanding the coverage area of a cell by adopting a PRACH double-check mechanism; the PRACH double detection mechanism comprises the following steps:
s1, a base station receives a preamble of PRACH format 0;
S2, performing preamble detection twice, and recording detection results of the twice; wherein, each preamble detection needs to be configured with different T remove;Tremove to represent the time length of the removed start-end signal before FFT processing;
and S3, combining the detection results of the two times.
Further, in step S2:
Configuring T remove＝0.5TCP in the first preamble detection;
and configuring T remove＝TCP+TGT in the second preamble detection.
Further, the two detection results in step S2 are respectively:
If the preamble result of the N1 item is detected, the preamble detection result of the first time is recorded as SET1= { preambleID i1,Tdelay_i1,RSRPi1,N0i1 } i, and i is more than or equal to 0 and less than N1; wherein preambleID i1 represents a preamble ID of an i-th preamble result detected by the first preamble, T delay_i1 represents a transmission delay between UE and gNB of the i-th preamble result detected by the first preamble, and RSRP i1 represents a total power of a preamble signal of the i-th preamble result detected by the first preamble; n0 i1 represents the noise power of the ith preamble result detected by the first preamble;
If the preamble result of the N2 item is detected, the second preamble detection result is recorded as SET 2= { preambleID i2,Tdelay_i2,RSRPi2,N0i2}i,0≤i<N2; wherein preambleID i2 represents a preamble ID of an i-th preamble result detected by the second preamble, T delay_i2 represents a transmission delay between UE and gNB of the i-th preamble result detected by the second preamble, and RSRP i2 represents a total power of a preamble signal of the i-th preamble result detected by the second preamble; n0 i2 represents the noise power of the ith preamble result detected by the second preamble.
Further, in step S3, the combined result after combining the two detection results is denoted as SET 3= { preambleID i3,Tdelay_i3,RSRPi3,N0i3}i3; wherein preambleID i3 represents a preamble ID of an ith preamble result in the combined result, T delay_i3 represents transmission delay between UE and gNB of the ith preamble result in the combined result, and RSRP i3 represents total power of preamble signals of the ith preamble result in the combined result; n0 i3 represents the noise power of the ith preamble result in the combined result; the method for combining the two detection results comprises the following steps:
s31: initializing SET3 = SET1, i = 0;
S32: check if preambleID i2 in SET2 is also present in SET 3:
If not, merging the preamble result corresponding to preambleID i2 into SET3, namely SET 3= { x|x ε SET3 or x= { preambleID i2,Tdelay_i2,RSRPi2,N0i2 };
If so, the existing entry of SET3 is noted as the j-th entry, preambleID i2＝preambleIDj3, and the preamble result corresponding to preambleID i2 is combined with the existing entry of SET 3: if RSRP j3<RSRPi2, then call the ith preamble result of SET2 to update the jth item in SET 3: t delay_i3＝Tdelay_i2,RSRPi3＝RSRPi2,N0i3＝N0i2; otherwise, do nothing;
S33：i＝i+1；
s34: if i=n2, the process of combining the two detection results is ended, otherwise, the process goes to step S32.
Further, the method further comprises employing a RACH resource spectrum avoidance mechanism to perform preamble spectrum avoidance; the RACH resource spectrum avoidance mechanism includes:
The preamble occupies an RB set { RB preamble_i}i };
If the M OFDM symbols at the beginning of the next slot of the preamble distribution slot have uplink OFDM symbols, when the base station performs uplink scheduling, { RB preamble_i}i resources on the M OFDM symbols can not be allocated to be used for transmission of any uplink channel and signal;
If there are downlink OFDM symbols in M OFDM symbols at the beginning of the last slot of the preamble distribution slot, when the base station performs downlink scheduling, { RB preamble_i}i resources on the M OFDM symbols may not be allocated to be used for transmission of any downlink channel and signal.
Further, the value of M is set according to the subcarrier spacing of the preamble distribution slots.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
1. The invention adopts PRACH double detection mechanism to expand the coverage of the cell, and supports the coverage of 30km at maximum.
2. The invention adopts the RACH resource spectrum avoidance mechanism to carry out preamble spectrum avoidance, and inhibits the scheduling of spectrum resources possibly occupied by the preamble on 1-2 slots after preabmle as required so as to avoid the overlapping of the preamble transmission time range and other subsequent signals caused by overlarge transmission delay, thereby causing interference.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly describe the drawings in the embodiments, it being understood that the following drawings only illustrate some embodiments of the present invention and should not be considered as limiting the scope, and that other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of the preamble sequence structure defined in 5 GNR.
Fig. 2 is a flow chart of a typical PRACH reception procedure.
Fig. 3 is a schematic diagram of a transmission timing relationship of a preamble between a UE and a gNB. Wherein T delay denotes a signal transmission delay between a base station (gNB) and a terminal (UE), GP denotes a switching period from downlink transmission to uplink transmission, and the duration of the switching period may not be greater than a guard time interval in an S slot defined by the 5GNR protocol. It is obvious that, since the UE does not complete uplink synchronization when initially transmitting the preamble, the preamble transmitted by the UE arrives at the gNB and is delayed by 2T delay; after the random access completes the uplink synchronization, the UE may send the uplink signal in advance, so as to ensure that the uplink signal reaches the alignment of the time instant and the uplink receiving time expected by the gNB.
Fig. 4 is a flowchart of a PRACH double check mechanism in an embodiment of the present invention. The gNB needs to perform two detections after receiving the PRACH, wherein the difference is that the T remove is configured differently, and the results are combined after the completion.
Fig. 5 is a schematic view of gNB scheduling of RACH resource spectrum avoidance mechanism in an embodiment of the present invention. Wherein, the gNB needs to avoid allocating or scheduling specific RB resources of the first M OFDM symbols of the specific slot start, where a specific slot refers to a RACH resource using PRACH format 0 distributed on the previous slot of the slot, and a specific RB resource refers to an RB resource used by the RACH resource.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Examples
As shown in fig. 1, this embodiment proposes a method for enhancing the coverage capability of NR prach_format_0, which includes:
a PRACH double-detection mechanism is adopted to expand the coverage area of a cell;
And adopting a RACH resource spectrum avoidance mechanism to carry out preamble spectrum avoidance.
Specifically:
(1) PRACH double detection mechanism
For the PHY layer, the receiving processing process of the PRACH is mainly optimized, a PRACH double-checking mechanism shown in figure 4 is realized, and when the RACH resource distribution of PRACH format 1 exists on the received slot, the PRACH double-checking mechanism is triggered; the PRACH double detection mechanism comprises the following steps:
s1, a base station receives a preamble of PRACH format 0;
S2, performing preamble detection twice according to the preamble detection process shown in FIG. 2, and recording the detection results of the two times; in this embodiment, T remove＝0.5TCP is configured during the first preamble detection; configuration T remove＝TCP+TGT;Tremove during the second preamble detection represents the time length of the removed starting end signal before FFT processing;
Thus, the two detection results are respectively:
If the preamble result of the N1 item is detected, the first preamble detection result is recorded as SET 1= { preambleID i1,Tdelay_i1,RSRPi1,N0i1}i,0≤i<N1; wherein preambleID i1 represents a preamble ID of an i-th preamble result detected by the first preamble, T delay_i1 represents a transmission delay between UE and gNB of the i-th preamble result detected by the first preamble, and RSRP i1 represents a total power of a preamble signal of the i-th preamble result detected by the first preamble; n0 i1 represents the noise power of the ith preamble result detected by the first preamble;
If the preamble result of the N2 item is detected, the second preamble detection result is recorded as SET 2= { preambleID i2,Tdelay_i2,RSRPi2,N0i2}i,0≤i<N2; wherein preambleID i2 represents a preamble ID of an i-th preamble result detected by the second preamble, T delay_i2 represents a transmission delay between UE and gNB of the i-th preamble result detected by the second preamble, and RSRP i2 represents a total power of a preamble signal of the i-th preamble result detected by the second preamble; n0 i2 represents the noise power of the ith preamble result detected by the second preamble.
S3, combining the detection results of the two times; the combined result after combining the two detection results is recorded as SET3= { preambleID i3,Tdelay_i3,RSRPi3,N0i3}i3; wherein preambleID i3 represents a preamble ID of an ith preamble result in the combined result, T delay_i3 represents transmission delay between UE and gNB of the ith preamble result in the combined result, and RSRP i3 represents total power of preamble signals of the ith preamble result in the combined result; n0 i3 represents the noise power of the ith preamble result in the combined result; the method for combining the two detection results comprises the following steps:
s31: initializing SET3 = SET1, i = 0;
S32: check if preambleID i2 in SET2 is also present in SET 3:
If not, merging the preamble result corresponding to preambleID i2 into SET3, namely SET 3= { x|x e SET3orx = { preambleID i2,Tdelay_i2,RSRPi2,N0i2 };
If so, the existing entry of SET3 is noted as the j-th entry, preambleID i2＝preambleIDj3, and the preamble result corresponding to preambleID i2 is combined with the existing entry of SET 3: if RSRP j3<RSRPi2, then call the ith preamble result of SET2 to update the jth item in SET 3: t delay_i3＝Tdelay_i2,RSRPi3＝RSRPi2,N0i3＝N0i2; otherwise, do nothing;
S33：i＝i+1；
s34: if i=n2, the process of combining the two detection results is ended, otherwise, the process goes to step S32.
(2) RACH resource spectrum avoidance mechanism
For the related processing of the MAC layer, the preamble spectrum avoidance is mainly needed in the uplink and downlink scheduling and uplink and downlink control channel resource allocation process; the RACH resource spectrum avoidance mechanism includes:
The preamble occupies an RB set { RB preamble_i}i };
If the uplink OFDM symbol exists in M (the value of M is set according to the subcarrier interval of the preamble distribution slot) at the beginning of the next slot of the preamble distribution slot, when the base station performs uplink scheduling, { RB preamble_i}i resource on the M OFDM symbols cannot be allocated to be used for transmission of any uplink channel and signal (PUSCH/PUCCH/SRS/PRACH), so as to avoid that the preamble transmission time range overlaps with the subsequent uplink signal due to the overlarge transmission time;
If there are downlink OFDM symbols in M (the value of M is set according to the subcarrier interval of the preamble distribution slot) at the beginning of the next slot of the preamble distribution slot, when the base station performs downlink scheduling, { RB preamble_i}i resources on the M OFDM symbols may not be allocated to be used for transmission of any downlink channel and signal (PDSCH/PDCCH/SSB/CSI-RS), so as to avoid overlapping of the preamble transmission time range with the subsequent downlink signal due to excessive transmission time.
Examples: as shown in fig. 5, the processing procedure of the RACH resource spectrum avoidance mechanism is as follows, where slot that needs to schedule or allocate a resource is recorded as slot_n:
Step 1: if the subcarrier spacing of slot_n is smaller than 240kHz, the following processing is carried out, otherwise, the Step 2 is skipped:
If the RACH resource of PRACH format 1 exists on slot_ (n-1), recording a preamble occupation RB set as { RB preamble_i}i, marking { RB preamble_i}i on the first M OFDM symbols of the slot as unusable and not being able to be scheduled and allocated;
otherwise, no processing is done.
Step 2: at this time, the subcarrier spacing of slot_n is not less than 240kHz, and the following processing is performed:
If the RACH resource of PRACH format 1 exists on slot_ (n-1), recording a preamble occupation RB set as { RB preamble_i}i, marking { RB preamble_i}i on all OFDM symbols of the slot as unusable and not being able to be scheduled and allocated;
If the RACH resource of PRACH format 1 exists on slot_ (n-2), recording a preamble occupation RB set as { RB preamble_i}i, marking { RB preamble_i}i on the first (M-14) OFDM symbols of the slot as unusable and not being capable of being scheduled and allocated;
If the two conditions are not satisfied, no treatment is carried out.
The M value is related to the subcarrier spacing of slot_n, and is 2,3,6,11,22 at 15kHz, 30kHz, 60kHz, 120kHz, and 240kHz, respectively.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A method for enhancing the coverage capability of NR PRACH_format_0, which is characterized in that the method comprises the step of expanding the coverage of a cell by adopting a PRACH double check mechanism; the PRACH double detection mechanism comprises the following steps:
s1, a base station receives a preamble of PRACH format 0;
S2, performing preamble detection twice, and recording detection results of the twice; wherein, each preamble detection needs to be configured with different T remove;Tremove to represent the time length of the removed start-end signal before FFT processing;
s3, combining the detection results of the two times;
in step S2:
Configuring T remove＝0.5TCP in the first preamble detection;
Configuring T remove＝TCP+TGT in the second preamble detection;
the two detection results in the step S2 are respectively:
If the preamble result of the N1 item is detected, the first preamble detection result is recorded as SET 1= { preambleID i1,Tdelay_i1,RSRPi1,N0i1}i,0≤i<N1; wherein preambleID i1 represents a preamble ID of an i-th preamble result detected by the first preamble, T delay_i1 represents a transmission delay between UE and gNB of the i-th preamble result detected by the first preamble, and RSRP i1 represents a total power of a preamble signal of the i-th preamble result detected by the first preamble; n0 i1 represents the noise power of the ith preamble result detected by the first preamble;
If the preamble result of the N2 item is detected, the second preamble detection result is recorded as SET 2= { preambleID i2,Tdelay_i2,RSRPi2,N0i2}i,0≤i<N2; wherein preambleID i2 represents a preamble ID of an i-th preamble result detected by the second preamble, T delay_i2 represents a transmission delay between UE and gNB of the i-th preamble result detected by the second preamble, and RSRP i2 represents a total power of a preamble signal of the i-th preamble result detected by the second preamble; n0 i2 represents the noise power of the ith preamble result detected by the second preamble.
2. The method for enhancing the coverage of nrprach_format_0 according to claim 1, wherein in step S3, the combined result obtained by combining the two detection results is denoted as SET 3= { preambleID i3,Tdelay_i3,RSRPi3,N0i3}i3; wherein preambleID i3 represents a preamble ID of an ith preamble result in the combined result, T delay_i3 represents transmission delay between UE and gNB of the ith preamble result in the combined result, and RSRP i3 represents total power of preamble signals of the ith preamble result in the combined result; n0 i3 represents the noise power of the ith preamble result in the combined result; the method for combining the two detection results comprises the following steps:
s31: initializing SET3 = SET1, i = 0;
S32: check if preambleID i2 in SET2 is also present in SET 3:
If not, merging the preamble result corresponding to preambleID i2 into SET3, namely SET 3= { x|x e SET3orx = { preambleID i2,Tdelay_i2,RSRPi2,N0i2 };
If so, the existing entry of SET3 is noted as the j-th entry, preambleID i2＝preambleIDj3, and the preamble result corresponding to preambleID i2 is combined with the existing entry of SET 3: if RSRP j3<RSRPi2, then call the ith preamble result of SET2 to update the jth item in SET 3: t delay_i3＝Tdelay_i2,RSRPi3＝RSRPi2,N0i3＝N0i2; otherwise, do nothing;
S33：i＝i+1；
s34: if i=n2, the process of combining the two detection results is ended, otherwise, the process goes to step S32.
3. The method of enhancing the coverage of nrprach_format_0 of claim 1, further comprising employing a RACH resource spectrum avoidance mechanism for preamble spectrum avoidance; the RACH resource spectrum avoidance mechanism includes:
The preamble occupies an RB set { RB preamble_i}i };
If the M OFDM symbols at the beginning of the next slot of the preamble distribution slot have uplink OFDM symbols, when the base station performs uplink scheduling, { RB preamble_i}i resources on the M OFDM symbols can not be allocated to be used for transmission of any uplink channel and signal;
If there are downlink OFDM symbols in M OFDM symbols at the beginning of the last slot of the preamble distribution slot, when the base station performs downlink scheduling, { RB preamble_i}i resources on the M OFDM symbols may not be allocated to be used for transmission of any downlink channel and signal.
4. The method for enhancing the coverage of nrprach_format_0 as claimed in claim 3, wherein the value of M is set according to a subcarrier interval of preamble distribution slots.
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