CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Indian Provisional Patent Application Number 201841034881, filed on September 16, 2018, the entirety of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] Embodiments of the present disclosure are related, in general to communication, but exclusively related to a method and system for detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs).

BACKGROUND

[0003] Physical random access channel (PRACH) is one of the crucial Uplink channel in 5G new radio (NR), between the user equipment (UE) and the base station (BS), primarily meant for initial access. Multiple initial access UEs transmit their corresponding preamble identities (Ids) on PRACH resources as configured in system information block 2. The primary role of PRACH receiver or the base station is to resolve each of these preambles distinctly and compute the propagation delay of each UE and respond back to each UE with Rach access response (RAR) containing with Timing Advancement command (the time each UE need to advance) to ensure uplink synchronization. RAR also contains temporary ID for each UE and also the uplink resource grant for subsequent transmissions.

[0004] There are challenging tasks at receiver for PRACH detection such as correctly detecting the presence of transmit preamble in any given Zero Correlation Zone in presence of AWGN noise and other cell interference, and accurately computing the propagation delay of each UE, once a preamble is detected in a ZCZ.

[0005] With the presence of noise and other cell interference may result in false alarms and sometimes missed detections, a threshold comparator is employed to ensure no faulty detections or missed detections. SUMMARY

[0006] The shortcomings of the prior art are overcome and additional advantages are provided through the provision of method of the present disclosure.

[0007] Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

[0008] In an aspect of the present disclosure, a method of detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs) is provided. The method comprises receiving, by a receiver, an input signal from the plurality of UEs. Also, method comprises de-mapping a plurality of PRACH resources associated with the input signal to obtain a plurality of de-mapped frequency domain PRACH resources. Further, the method comprises obtaining a power delay profile (PDP) estimate for the plurality of de-mapped frequency domain PRACH resources by performing frequency domain correlation, and determining a threshold value by estimating noise variance for each of the plurality of PRACH resources. Furthermore, the method comprises identifying a plurality of preamble identities associated with the PRACH transmission from a plurality of UEs by comparing the PDP estimate with the threshold.

[0009] Another aspect of the present disclosure is a receiver to detect a physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs). The receiver comprises an input unit, a de-mapping unit, a power delay profile (PDP) estimator, a threshold value estimator, and an identifying unit. The input unit receives an input signal from the plurality of UEs. The de-mapping unit de-maps a plurality of PRACH resources associated with the input signal to obtain a plurality of de-mapped frequency domain PRACH resources. The PDP estimator estimate PDP for the plurality of de-mapped frequency domain PRACH resources by performing frequency domain correlation. The threshold value estimator determines a threshold value by estimating noise variance for each of the plurality of PRACH resources. The identifying unit identifies a plurality of preamble associated with the PRACH transmission from a plurality of UEs by comparing the PDP estimate with the threshold. [0010] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of device or system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:

[0012] Figure 1 shows a block diagram of a receiver for detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs), in accordance with some embodiments of the present disclosure;

[0013] Figure 2 shows a block diagram illustration for generating a preamble by a user equipment (UE);

[0014] Figures 3 A and 3B shows a plot illustrating empirical and theoretical distribution of real and imaginary parts of z _u (l) under HO, in accordance with an embodiment of the present disclosure;

[0015] Figure 4A shows a plot illustrating empirical and theoretical distribution of z _r (ί) under H ₀ , in accordance with an embodiment of the present disclosure; and

[0016] Figure 4B shows a plot illustrating empirical and theoretical CDF of T _max for W=l44 are approximately same specially for values of CDF which are close to 1 , in accordance with an embodiment of the present disclosure.

[0017] Figure 5 shows a flowchart illustrating a method of detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs), in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0019] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

[0020] The terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a device or system or apparatus proceeded by“comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the device or system or apparatus.

[0021] The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise.

[0022] The terms "including", "comprising",“having” and variations thereof mean "including but not limited to", unless expressly specified otherwise.

[0023] The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise. [0024] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.

[0025] In a communication network, Physical Random Access Channel (PRACH) is one of the crucial uplink channels employed by any non-synchronized user equipment’s (UEs) for initial access.

[0026] Embodiments of the present disclosure provide a method of obtaining a power delay profile for each possible base sequence across all the possible PRACH time frequency resources. Also, embodiments of the present disclosure provide plurality of methods to compute noise plus interference variance which in turn is used to set a threshold in threshold comparator. Two noise variance calculation methods are used for determining of threshold. Also, the methods provide at least one of probability of false alarm which may be as minimum as 0.05, obtaining probability of correct detection that may be as achieved high as 0.95 even at low SNRs and plurality of UEs being multiplexed in same resources.

[0027] Figure 1 shows a block diagram of a receiver for detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs), in accordance with some embodiments of the present disclosure.

[0028] The receiver 100 is used to determine and resolve issue of identifying preamble IDs of each of the multiplexed UEs independently and determine transmission delays of each UE. In an embodiment, the receiver 100 is a format 0 PRACH receiver as shown in Figure 1.

[0029] As shown in Figure 1, the receiver 100, also referred as a base station (BS) or PRACH receiver or a communication system, comprising a processor 102, a memory 104. Also, the BS 100 comprises a plurality of antennas (not shown in the Figure), for transmitting and receiving data or information. The memory 104 may be communicatively coupled to the processor 102. The processor 102 may be configured to perform one or more functions of the BS 100 such as, but not limited to transmitting and receiving signals, and detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs). The UEs are also referred as users. In one implementation, the BS 100 may comprise blocks 106, also referred as units or modules, for performing various operations in accordance with the embodiments of the present disclosure.

[0030] The blocks 106 include an input unit 108, a de-mapping unit 110, a power delay profile (PDP) unit 112, a threshold estimator 114, an identifying unit 116, a plurality of antennas and other blocks (not shown in the Figure).

[0031] The input unit 108, configured in the BS 100, receives an input signal or a plurality of input signals 118, or referred as input. The one or more antennas (not shown in Figures) configured in the receiver of BS 100 receives the input signal 118. The input signal 118 is received from a plurality of user equipment’s, which is a multiplexed signal or a composite signal. In an embodiment, the input signal comprises a Zadoff-Chu sequence that is sent on a plurality of PRACH resources, data and control information sent on a plurality of data resources and a plurality of vacant resources. The Zadoff-Chu sequence that is sent on PRACH resources is dependent on at least one of preamble Id, PRACH resource information, and any other information associated with PRACH.

[0032] In an embodiment, the input signal 118 is random-access preambles from Zadoff-Chu sequences with a zero-correlation zone generated by one or more UE’s. Figure 2 shows a block diagram illustration for generating a preamble by a user equipment (UE). Each of the UE is configured with a cyclic module that can generate different cyclic shifts, that may be generated from each root Zadoff-Chu sequence i.e. PRACH sequences are generated from one or several root Zadoff-Chu sequences via cyclic shifts. The BS or the communication network configures a set of preamble sequences which the UE is allowed to use. The UE transmits a randomly selected preamble sequence from a group of configured sequences. An additional preamble sequences that cannot be generated from a single root Zadoff-Chu sequence, are obtained from the root sequences with the consecutive logical indices The logical root sequence order is cyclic, i.e., the logical index 0 is consecutive to 138. [0033] For every root Zadoff-Chu sequence, random-access preambles with zero correlation zones (ZCZs) each with length N _cs — 1 are defined by cyclic shifts as given in equation 1, in which the value of the cyclic shift depends of the type of the sequence set.

[0034] The sub-carrier spacing Df _RA of PRACH transmission for mm frequencies may be one of 60 kHz and 120 kHz. The number of sub-carriers occupied is equal to the length of preamble which is 139 irrespective of format being used.

[0035] In one embodiment, for low Doppler cases the cyclic shift value is given using the below equation:

Ncs· Base cyclic shift value provided by higher layers

[0036] The one or more antennas of the BS 100 receive a composite signal form all multiplexed UEs, which is the input signal 118, may be represented as:

[0037] In an embodiment, the PRACH frame is identified using a PRACH frame identifier, also referred as PRACH identifier or identifier (not shown in Figure), from the plurality of PRACH resources. The system frame where PRACH is expected is located depending upon configuration index, the PRACH transmissions may occur on all system frames or every alternate frame or every 4 ^th 8 ^th 16 ^th frame respectively. The PRACH frame is identified using the equation:

SFNmodx = y

where SFN is system frame number

[0038] Next, the PRACH identifier performs locating of PRACH slots. The PRACH resources within the radio frame are identified by a PRACH resource index. For FR 2 (mm frequencies) there may be multiple PRACH slots possible, in a given frame. Total number of PRACH slots possible and corresponding exact location is specific to PRACH configuration index. The PRACH identifier identifies the PRACH slot and operates only those slots depending on configured PCI. Unlike Formats 0-3 where only one, time instance for PRACH is possible in any given subframe, for mm frequencies there could be multiple PRACH instances possible across time in a given PRACH slot. Total number of time instances may be specified by a parameter the PRACH identifier locates all the possible time instances and extract

time domain data from each of the instances .

[0039] In one embodiment, at a given time instance there may be one of single and multiple frequency multiplexed PRACH instances. Total number of PRACH frequency resources configured may be specified by parameter . Based on configured higher layer parameters such as, but not limited to and total number of PRBs the

receiver may precisely identify starting and end index of each FDM group and extract the PRACH subcarriers, using the subcarrier de-mapping module configured in the receiver.

[0040] The de-mapping unit 110, configured in the receiver 100, performs de-mapping of the plurality of PRACH resources associated with the input signal 118 to obtain a plurality of de- mapped frequency domain PRACH resources. The de-mapping is performed using a plurality of subcarriers. The start of the subcarrier index is calculated as follows: 1 Compute

2 Using below Table 1 fetch the variable k.

3 Using 1 & 2 subcarrier start is computed.

Table 1

[0041] The PDP estimation unit 112, also referred as PDP estimator or Frequency Domain correlation unit, configured in the receiver 100 performs frequency domain correlation and PDP computation for the plurality of de-mapped frequency domain PRACH resources. The PDP estimation unit 112 performs frequency domain correlation to estimate the PDP profile. Also, the PDP estimation unit 112 performs a method of detecting random access preamble, in accordance with an embodiment of the present disclosure. The detection of the random-access preamble is based on the cross-correlation of the de-mapped received signal using the root Zadoff-Chu sequences. The power delay profile (PDP) is represented by an equation as:

where * represents cross correlation

[0042] In another embodiment, the PDP estimation unit 112 is configured to compute a cross correlation in frequency domain using the below equations:

[0043] In which scaling for N _IFFT point IFFT with 139 point inputs, rest are zeros

[0044] PDP is given by

[0045] The threshold estimator 114, configured in the receiver 100, determines a threshold value by estimating noise variance for each of the plurality of PRACH resources. The threshold estimator 114 is also referred as threshold value estimator, determines a threshold value by one of estimating noise variance for each of the plurality of PRACH resources using at least one of estimating noise for the vacant resource blocks associated with input signal using data-aided noise estimation; statistical method of estimating using the received input signal; and estimating noise for the PDP excluding a plurality of peaks associated with the corresponding plurality of UE’s.

[0046] In one embodiment of the present disclosure is noise variance estimation by the threshold estimator 114. For the threshold setting, considering that the noise variance is exactly known. However, in practice it is not necessarily known and must be estimated.

a. One way is to estimate noise in another resource block and feed it to the PRACH module, which is possible as BS or gNB knows which resource block (RBs) of the PRACH resources are vacant.

[0047] Even if none of the RBs are vacant, gNB may do data-aided noise estimation after decoding data. This is performed by estimating noise variance, using one of the following: b. Estimating noise variance, for the received signal variance in the PRACH resource block.

[0048] Here (n) is the filtered version of y(n ) to limit the estimation to PRACH resource block. c. Removing N _r peaks in the PDP sequence for each possible UE and then estimating the noise based using the mean of the PDP of the rest of the subcarriers. By considering N _r = 40.

where N _a = N— N _u N _r . Here /Vis the FFT size, N _u is the possible number of UEs present. Also, i ^{s a} vector of length N where the PDP values are stored in sorted (increasing)

order.

[0049] The identifying unit 116, is configured in the receiver 100, to identify a plurality of preamble associated with the PRACH transmission from a plurality of UEs by comparing the PDP estimate with the threshold i.e. the correlated values of the PDP plot are compared with a threshold. For threshold setting, a Neyman-Pearson detector with a false alarm a, an approximate distribution of the peak-detection test statistic is found, under the assumption that noise variance is known or may be estimated.

[0050] The identifying unit 116 performs a peak detection from the PDP. In each zero correlation zone if preamble ID is detected then search for peak detection is performed. The difference between the start of ZCZ and location of peak determines the UEs transmission timing.

[0051] Thereafter, PRACH detection is performed by probability detection. The probability that UE has transmitted a PRACH preamble with a preamble ID and being detected at the receiver correctly. In another embodiment, a False Alarm Probability is used, that one of the possible preambles was not used by any of the multiplexed UEs but still being detected at the receiver.

[0052] In an embodiment, under only AWGN scenario, i.e., under HO, may be modeled as

a zero mean complex circular symmetric Gaussian random variable with variance with both real and imaginary components having variance Considering, z _u (L) is IFFT of the

product of T(/c) and a known sequence X(k), which may be Gaussian distributed. For a given X(k ), distribution of is also a zero mean complex circular symmetric Gaussian random

variable with variance s ² zero mean complex Gaussian as s ² as shown in Figures 3 A and 3B. [0053] Figures 3A and 3B shows a plot illustrating empirical and theoretical distribution of real and imaginary parts of under HO, in accordance with an embodiment of the present disclosure.

[0054] Normalizing

[0055] So that is a standard Gaussian random variable under HO. Therefore

is a chi-squared PDF with 2 degrees of freedom as shown in Figure 4A.

[0056] Figure 4A shows a plot illustrating empirical and theoretical distribution o

in accordance with an embodiment of the present disclosure.

[0057] Since T _max is maximum of W chi-squared random variable with two degrees of freedom, the distribution of T _max is given by

where is the CDF of chi-squared random variables with two degrees of freedom. The

theoretical and empirical CDFs under HO are approximately close as shown in Figure 4B.

[0058] Figure 4B shows a plot illustrating empirical and theoretical CDF of T _max for W=l44 are approximatel same specially for values of CDF which are close to 1, in accordance with an embodiment of the present disclosure.

[0059] Therefore, the false alarm can be written in terms of the threshold for the Neyman-Pearson detector as

As such, the threshold for a given

[0060] As shown in Figure 4B, the method of threshold calculation works very well for a < 0.1 as the theoretical and empirical CDFs are especially close in the range of 0.9-1. [0061] Figure 5 shows a flowchart illustrating a method of detecting physical random access channel (PRACH) transmission from a plurality of user equipment’s (UEs), in accordance with an embodiment of the present disclosure.

[0062] As illustrated in Figure 5, the method 500 comprises one or more blocks for a method of detecting PRACH transmission from a plurality of UEs. The order in which the method 500 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the spirit and scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or combination thereof.

[0063] At block 510, receiving an input signal is performed by the input unit 108, configured in the receiver 100, from the plurality of UEs. The input signal 118 is a multiplexed signal or a composite signal received from a plurality of UEs. In an embodiment, the input signal comprises a Zadoff-Chu sequence that is sent on a plurality of PRACH resources, data and control information sent on a plurality of data resources and a plurality of vacant resources. The Zadoff-Chu sequence that is sent on PRACH resources is dependent on at least one of preamble Id, PRACH information, and any other information associated with PRACH.

[0064] At block 520, de-mapping is performed by a de-mapping unit 110, configured in the receiver 100, a plurality of PRACH resources associated with the input signal to obtain a plurality of de-mapped frequency domain PRACH resources.

[0065] At block 530, obtaining a power delay profile (PDP) estimate by the PDP estimation unit 112, configured in the receiver 100, for the plurality of de-mapped frequency domain PRACH resources by performing frequency domain correlation

[0066] At block 540, determining a threshold value by the threshold estimator 114, configured in the receiver 100, by estimating a noise variance for each of the plurality of PRACH resources. [0067] At block 550, identifying a plurality of preamble identities associated with the PRACH transmission from a plurality of UEs by the identifying unit 116, configured in the receiver 100, by comparing the PDP estimate with the threshold

[0068] Symbols and Acronyms

[0069] The described operations may be implemented as a method, system or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. The described operations may be implemented as code maintained in a“non-transitory computer readable medium”, where a processor may read and execute the code from the computer readable medium. The processor is at least one of a microprocessor and a processor capable of processing and executing the queries. A non-transitory computer readable medium may comprise media such as magnetic storage medium (e.g., hard disk drives, floppy disks, tape, etc.), optical storage (CD-ROMs, DVDs, optical disks, etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, Flash Memory, firmware, programmable logic, etc.), etc. Further, non-transitory computer-readable media comprise all computer-readable media except for a transitory. The code implementing the described operations may further be implemented in hardware logic (e.g., an integrated circuit chip, Programmable Gate Array (PGA), Application Specific Integrated Circuit (ASIC), etc.).

[0070] Still further, the code implementing the described operations may be implemented in “transmission signals”, where transmission signals may propagate through space or through a transmission media, such as an optical fiber, copper wire, etc. The transmission signals in which the code or logic is encoded may further comprise a wireless signal, satellite transmission, radio waves, infrared signals, Bluetooth, etc. The transmission signals in which the code or logic is encoded is capable of being transmitted by a transmitting station and received by a receiving station, where the code or logic encoded in the transmission signal may be decoded and stored in hardware or a non-transitory computer readable medium at the receiving and transmitting stations or devices. An“article of manufacture” comprises non- transitory computer readable medium, hardware logic, and/or transmission signals in which code may be implemented. A device in which the code implementing the described embodiments of operations is encoded may comprise a computer readable medium or hardware logic. Of course, those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope of the invention, and that the article of manufacture may comprise suitable information bearing medium known in the art.

[0071] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention.

[0072] When a single device or article is described herein, it will be clear that more than one device/article (whether they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether they cooperate), it will be clear that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.

[0073] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention.

[0074] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.