PRIORITY CLAIM

[0001] This application claims priority from Singapore Patent Application No. 10202011842U filed on 27 November 2020.

TECHNICAL FIELD

[0002] The present invention generally relates to 5G communication, and more particularly relates to methods and communication apparatuses for 5G-based positioning.

BACKGROUND OF THE DISCLOSURE

[0003] The fifth generation of mobile technology (5G) is designed to provide enhanced mobile broadband (eMBB), ultra-reliable low latency communications (URLLC) and massive machine type communications (mMTC). According to IMT- 2020, 5G is supposed to perform ten to a hundred times better in terms of peak data rate, latency and connection density. Due to the ubiquity of communication networks, 5G also provides an added value on positioning services even in some Global Navigation Satellite System (GNSS)-denied or constrained environments, such as indoors or in urban canyons. The fundamental positioning techniques of cellular networks are classified as trilateration, triangulation, proximity, scene analysis and hybrid, among which time of arrival (TOA) based trilateration is one of the most common methods utilized from 2G to 5G.

[0004] A Positioning Reference Signal (PRS) was first defined in Long-Term Evolution (LTE) as pilot signals to perform TOA measurement. Another candidate of pilot signals in LTE for TO A measurements is the cell- specific reference signals (CRS). In 5G standards, the CRS is removed. Taking on the legacy of LTE, 5G utilizes Orthogonal Frequency Division Multiplexing (OFDM) waveform with flexible numerology. The first commercial 5G network was launched in 2019 based on the Release 15 specifications. Only since Release 16, 5G new radio (NR) downlink (DL) PRS was defined in 3rd generation partnership project (3GPP) Technical Specification (TS) 38.211 and TS 38.214. Until March 2020, corresponding positioning procedures and 5G NR DL PRS configurations were finalized in TS 37.355. These specifications pave the way for further verifying the performance of 5G PRS based positioning services.

[0005] 5G NR PRS has flexible configurations and patterns, which are different from that of LTE CRS or other pilot signals adopted in OFDM system. Thus, there is a requirement of having proper timing recovery solutions for 5G standard-compliant pilot signals, such as 5G NR DL PRS, to obtain accurate timing estimate.

[0006] Thus, there is a need in the current 5G systems to provide methods and communication devices which can provide accuracy-improved carrier phase measurements and velocity estimations to enable highly accurate 5G-based positioning. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

SUMMARY

[0007] According to at least one aspect of the present embodiments, a communication apparatus is provided. The communication apparatus includes a 5G carrier phase receiver for receiving a 5G-compliant signal modulated on a 5G carrier wave. The 5G carrier phase receiver includes a 5G code phase receiver and a phase-locked loop. The 5G code phase receiver is configured for continuous phase change tracking of the 5G carrier wave and includes a phase rotation module configured to generate pilot symbols in response to one or more 5G-compliant reference signals extracted from the 5G- compliant signal. The phase-locked loop is coupled to the 5G code phase receiver to receive the pilot symbols and is configured to generate carrier phase measurements and velocity estimations in response to the pilot symbols.

[0008] According to another aspect of the present embodiments, a method for generating accuracy -improved carrier phase measurements and velocity estimations is provided. The method includes receiving a 5G-compliant signal modulated on a 5G carrier wave, continuously phase change tracking the 5G carrier wave, and extracting one or more 5G-compliant reference signals from the 5G-compliant signal. The method further includes generating pilot symbols in response to the one or more 5G-compliant reference signals and generating the carrier phase measurements and velocity estimations in response to the pilot symbols.

BRIEF DESCRIPTION OF THE DRAWINGS [0009] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments and to explain various principles and advantages in accordance with present embodiments.

[0010] FIG. 1 depicts a schematic illustration comparing 5G NR Downlink (DL) Positioning Reference Signal (PRS) symbol patterns to symbol patterns of pilot symbols. [0011] FIG. 2 depicts a graph of 5G NR DL PRS in OFDM symbols

[0012] FIG. 3 is a block diagram of a 5G NR DL PRS code phase-based receiver in accordance with the present embodiments.

[0013] FIG. 4 depicts a graph of normalized S-curve functions of different pilot symbol patterns.

[0014] FIG. 5 depicts a block diagram of a delay-locked loop (DLL) in accordance with the present embodiments.

[0015] FIG. 6 depicts a block diagram of a 5G carrier phase-based receiver in accordance with the present embodiments.

[0016] FIG. 7 depicts graphs depicts dense allocation of 5G NR DL PRS into OFDM symbols for carrier phase tracking in accordance with the present embodiments, wherein FIG. 7A depicts carrier phase offset of the OFDM symbols and FIG. 7B depicts PLL tracking error of the OFDM symbols.

[0017] FIG. 8 depicts an illustration of a simplified exemplary pilot symbol frame structure for use in code and carrier phase receivers in accordance with the present embodiments.

[0018] FIG. 9 depicts an illustration of a synchronisation signal block (SSB) is allocated to a pilot symbol frame structure in accordance with the present embodiments. [0019] FIG. 10 depicts a first illustration of 5G NR DL PRS patterns allocated to a frame structure in accordance with the present embodiments.

[0020] FIG. 11 depicts a second illustration of 5G NR DL PRS patterns allocated to a frame structure in accordance with the present embodiments.

[0021] FIG. 12 depicts a table of user equipment (UE) positioning methods according to 3GPP Technical Specifications. [0022] FIG. 13 depicts an illustration of a configuration of a LTE Positioning Protocol (LPP) system which can be utilized by the methods and communication apparatuses in accordance with the present embodiments.

[0023] FIG. 14, comprising FIGs. 14A, 14B and 14C, depict graphs and a table of operation of the 5G NR code phase-based receiver of FIG. 3 in accordance with the present embodiments for different pilot symbol patterns, wherein FIG. 14A depicts graphs of 5G timing recovery of the 5G NR code phase-based receiver receiving a first pilot symbol pattern (Pattern A), FIG. 14B depicts graphs of 5G timing recovery of the 5G NR code phase-based receiver receiving a pilot symbol second pattern (Pattern B), and FIG. 14C depicts a table comparing kinematic and static timing recovery for both patterns on Additive White Gaussian Noise (AWGN) channels and/or multipath Rician fading channels.

[0024] FIG. 15, comprising FIGs. 15A, 15B and 15C, depicts graphs of operation of different portions of the 5G NR carrier phase-based receiver of FIG. 6 in accordance with the present embodiments, wherein FIG. 15A depicts a graph of 5G timing recovery for the PLL velocity estimation, FIG. 15B depicts graphs of 5G timing recovery and tracking results for the DLL, and FIG. 15C depicts graphs of 5G timing recovery and tracking results for the PLL.

[0025] FIG. 16, comprising FIGs. 16A,16B, 16C and 16D, depicts code and graphs of operation of different parts of the 5G NR carrier phase-based receiver of FIG. 6 in accordance with the present embodiments, wherein FIG. 16A depicts settings for the Rician channel of the carrier phase-based receiver, FIG. 16B depicts a graph of 5G timing recovery for the PLL velocity estimation, FIG. 16C depicts graphs of 5G timing recovery and tracking results for the DLL, and FIG. 16D depicts graphs of 5G timing recovery and tracking results for the PLL. [0026] FIG. 17, comprising FIGs. 17A,17B, 17C and 17D, depicts pilot symbol frame structures and graphs comparing operation of the NR carrier phase-based receiver of FIG. 6 in at two bandwidths in 5G and LTE systems in accordance with the present embodiments, wherein FIG. 17A depicts a pilot symbol frame structure at a first bandwidth, FIG. 17B depicts graphs of 5G timing recovery and tracking results for the DLL for the pilot symbol frame structure of FIG. 17A, FIG. 17C depicts a pilot symbol frame structure at a smaller bandwidth than FIG. 17A, and FIG. 17D depicts graphs of 5G timing recovery and tracking results for the DLL for the pilot symbol frame structure of FIG. 17C.

[0027] And FIG. 18, comprising FIGs. 18A,18B, 18C, 18D, 18E and 18F, depicts graphs of operation of the NR carrier phase-based receiver of FIG. 6 in accordance with the present embodiments for different pilot symbol patterns, wherein FIG. 18A depicts graphs of 5G timing recovery and tracking results for the DLL for a first pilot symbol pattern, Pattern A, FIG. 18B depicts graphs of 5G timing recovery and tracking results for the PLL for the first pilot symbol pattern, FIG. 18C depicts a histogram of PLL velocity estimation for the first symbol pattern, FIG. 18D depicts graphs of 5G timing recovery and tracking results for the DLL for a second pilot symbol pattern, Pattern B, FIG. 18E depicts graphs of 5G timing recovery and tracking results for the PLL for the second pilot symbol pattern, and FIG. 18F depicts a histogram of PLL velocity estimation for the second symbol pattern.

[0028] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale. DETAILED DESCRIPTION

[0029] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. It is the intent of present embodiments to present methods and communication apparatuses accuracy-improved carrier phase measurements and velocity estimations for 5G-based positioning.

[0030] For measuring timing error introduced by path time delay and asynchronous sampling clock, some pilot symbols are needed. However, the pilot symbols are transparent to 5G communication receivers. Therefore, in accordance with the present embodiments a code-phase and carrier phase-based timing recovery method is proposed which aims at estimating the timing error and obtaining accurate time of arrival of a communication signal.

[0031] A 5G NR downlink (DL) Positioning Reference Signal (PRS) has been introduced to assist localization services, making NR DL PRS a proper candidate for pilot symbol in the actual 5G networks as suggested in TS 38.305 (V16.0.0). Therefore, in accordance with the present embodiments, a code phase receiver and a carrier phase receiver are proposed which are suitable for 3GPP 5G standard-compliant localization service and signals, i.e. utilizing the NR DL PRS. In addition, a generalized path time delay estimation method is proposed in accordance with the present embodiments to adapt to the more generalized pilot symbol patterns, including 5G NR DL PRS. And further, based on the proposed code phase receiver, a 5G carrier phase receiver is proposed which can provide carrier phase measurements and velocity estimate. The receiver is able to continuously track the phase change of the 5G carriers due to relative movement between the receiver and the transmitter. [0032] While similar timing recovery schemes can be found in the prior art, the methods and communication receivers in accordance with the present embodiments are different than and an improvement over prior art schemes in several respects. First, 5G standard-compliant reference signals such as 5G synchronization signals (i.e., the primary synchronization signal (PSS) and the secondary synchronization signal (SSS)), PBCH block (SSB) signals, and NR DL PRS signals are adopted as pilot symbols in accordance with the present embodiments, in improvement over prior art solutions which utilized pilot symbols unavailable in 5G standards. In addition, at stage two of the three- stage timing recovery scheme, our timing recovery method in accordance with the present embodiments (i.e., the generalized path time delay estimation method in accordance with the present embodiments) is 5G-standard complaint unlike prior art schemes such as rotational invariance techniques (ESPRIT) algorithms.

[0033] In addition, at stage three of the three-stage timing recovery scheme, a delay- locked loop (DLL) and a phase-locked loop (PLL) are used to conduct phase rotation in ways different from prior art use. The relationship between the DLL and the PLL in the communication devices in accordance with the present embodiments and there use is also different from the prior art. For example, a PLL feedback ‘phase rotation’ module is directly used to track timing error instead of a PLL-aided DLL as described in some prior art techniques.

[0034] Also, the 5G NR DL PRS includes different patterns within the frame which requires a new path time delay estimation method. The generalized path time delay estimation method in accordance with the present embodiments is designed to address the different patterns of 5G NR DL PRS. Referring to FIG. 1, a schematic illustration 100 depicts the 5G NR DL PRS symbol patterns 110 as compared to pilot symbol patterns 120. While some prior art systems require an even allocation of pilot symbols and/or a condition that the pilot symbol occupies the entire Fast Fourier transform (FFT)/inverse FFT (iFFT) size or useful subcarrier size, in accordance with the present embodiments, neither is required. This enables the generalized path time delay estimation method in accordance with the present embodiments to advantageously be highly configurable and suitable for 5G NR DL PRS.

[0035] Further, the 5G carrier phase receiver in accordance with the present embodiments is able to continuously track the phase change of 5G carriers. Consequently, the 5G carrier phase receiver in accordance with the present embodiments is able to provide more accurate carrier phase measurements and additional velocity estimate, having a potential ranging accuracy at the millimetre level, an improvement over prior art phase receivers.

[0036] The code-phase timing recovery solution in accordance with the present embodiments is advantageously suitable for generalized pilot signal patterns including 5G NR DL PRS. It can be integrated with current 5G NR commercial networks directly. The positioning process in accordance with the present embodiments complies with that of 3 GPP 5G standards and the 5G carrier phase receiver in accordance with the present embodiments is able to advantageously provide highly accurate carrier phase measurements and additional velocity estimates. In addition, the 5G code phase receiver and 5G carrier phase receiver in accordance with the present embodiments can provide a more accurate localization service in 5G networks than current 5G technology.

[0037] Referring to FIG. 2, a graph 200 of 5G NR DL PRS in OFDM symbols indicates that for different OFDM symbols there are different PRS symbol patterns allocated on varied subcarriers in the frequency domain. To adapt 5G NR DL PRS as pilot symbols for the methods and communication receivers in accordance with the present embodiments, instead of requiring pilot symbols to be evenly inserted on N subcarriers, the requirements are loosened and, in accordance with the present embodiments, the pilot symbols T _m are only inserted in Nsc subcarriers and have the following pattern where a, c and b are known positive integers. That is, the pilot symbols are assumed to have certain patterns but are not necessarily allocated evenly into the entire Fast Fourier Transform (FFT)/inverse FFT (iFFT) size. In addition, for a particular symbol period i, if there is PRS it is defined in accordance with the standard-compliant configurations in TS 38.211 (V16.1.0).

[0038] In OFDM modulation, let Nsc denote the number of valid subcarriers and N denote the point of FFT/iFFT where denote N subcarrier symbols where i denotes the OFDM symbol number in the time domain and n represents the FFT/iFFT point in the frequency domain. As a result, when n -

[0039] At the transmitter, the Nsc symbols are modulated into N iFFT point locations and the rest points are zero-padding. To avoid intersymbol interference (ISI) introduced by multipath propagation, 5G NR adopts Cyclic-Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) modulation, which adds a guard interval T _g between adjacent symbol intervals. Accordingly, the continuous-time baseband signal output of the transmitter can be represented as where denotes a useful symbol interval, and T _s denotes a symbol interval including guard interval.

[0040] Over one useful symbol interval, there are N samples implemented by sampling at time t = n x T, where n = 0; ... , N - 1 , and T denotes the sample interval.

The guard interval T _g is always a multiple of T. Therefore, over one guard interval, there are N _CP samples implemented by duplicating N _CP samples at the tail of N useful samples. Thus, over one symbol interval, there are N _CP + N samples in total. Finally, the modulation and up-conversion to the carrier frequency /o of the complex-valued OFDM baseband signal is given by where is the initial phase of the carrier wave at the transmitter.

[0041] Assuming the signal is transmitted over a multipath fading channel including line-of-sight (LOS), the channel frequency response at the subcarrier frequency is described as where ti denotes path time delays, hi(l) denotes path gains, L is the number of paths, and

[0042] If the receiver could successfully remove the cyclic prefix (CP) and set the FFT starting point within the FFT window covers samples only from the same symbol interval and includes N _CP samples if the starting point is in front of the first useful sample. A symbol timing error within this interval can result in a phase rotation of every subcarrier symbol given by where -N _CP £ eo < 0, and m _,n denotes channel noise. Equation (7) indicates that as long as the FFT window falls in the CP interval, the orthogonality between the different subcarriers will be maintained.

[0043] In the presence of a carrier frequency offset fa, assuming the FFT window falls in the CP duration, the received signal at the zth symbol can be written as is the total carrier frequency offset due to the Doppler frequency, the clock drift and the oscillators' mismatch, D/ is the subcarrier spacing, C is the received signal power due to the antenna gain and any implementation loss, and Wi _,n denotes additional noise.

[0044] A block diagram 300 of the structure of the 5G NR DF PRS code phase-based receiver 301 in accordance with the present embodiments is shown in FIG. 3. The OFDM signal 302 is digitized by an analog-to-digital converter (AD) 304 operating under control of a local oscillator (FO) 306. The resulting sample sequence 308 is provided to a Fast Fourier Transform (FFT) module 310 to identify samples within a defined FFT window, such as samples from a same symbol interval, to derive the 5G NR DF PRS signal 312. The 5G NR DF PRS signal 312 is provided to a phase rotation module 314 and then to a delay-locked loop 316. The 5G NR DF PRS signal 312 is also provided to a path time delay module 318 for determining a generalized path time delay estimate in accordance with the present embodiments.

[0045] The sample sequence 308 is also provided to a synchronization signal (SS) correlation module 320, which, after correlating the sample sequency with synchronization signals selected based on cell ID is provided to a first switch 324 which determines a selectable input to a FFT window controller 326 setting the start and end points to define the FFT window for the FFT module 310. The selectable input to the FFT window controller 326 can be an output from the SS correlation module 320, an Integer part (Int{ . }) of the generalized path time delay estimate from the path time delay module 318, or an Integer part (Int{ . }) of the output from the DLL 316 as selected by the first switch 324.

[0046] The DLL 316 includes a NR DL PRS generator 330 which, in response to NR DL PRS configurations 332, generates an early pilot symbol 334 and a late pilot symbol 336 such that a first correlation module 338 generates an early cross -correlation output R _e (i, 0 340 in response to the early pilot symbol 334 and a second correlation module 342 generates a late cross-correlation output R _t (i , x) 344 in response to the late pilot symbol 336 in order to determine an adjusted timing error of the PRS pilot symbol of the NR DL PRS signal 312 introduced by the phase rotation module 314. Squared absolute values 346, 348 of the early and late cross -correlation outputs 340, 344 are summed 350 and provided to an inverse S-curve slope k _d module 352, where k _d =-l/k _s (, k _s being the slope of the S-curve functions of different pilot symbols as discussed hereinafter) and where the timing error can be derived from a near linearity range of the S-curve functions. A lowpass filter (LPF) 354 filters the output of the k _d module 352 and the error is accumulated by an accumulator 356. An integral part (Int{ . }) of the output of the accumulator may be the selectable input to the FFT window controller 326 from the output from the DLL 316 as selected by the first switch 324.

[0047] A second switch 358 selects an input to the phase rotation module 314 to adjust for timing error of the PRS pilot symbol of the NR DL PRS signal 312 introduced by the phase rotation module 314. The second switch 358 selects the input to the phase rotation module 314 from a fractional part (Fra{.|) of the generalized path time delay estimate from the module 318 and a fractional part (Fra{.|) of the output from the accumulator 356. [0048] The method of operation of the 5G NR DL PRS code phase-based receiver 301 in accordance with the present embodiments includes three main steps, which represent three different timing recovery stages. The symbol timing error eg is defined as , where denotes the sample position of the first useful OFDM symbol and is the estimated symbol timing. are normalized by sampling interval T. If the estimated symbol timing is earlier than , then .

[0049] The pu rpose of stage one is to obtain coarse signal synchronization by cross correlation. One way of implementing stage one is to let the received sample sequence 308 correlate with local generated 5G PSS/SSS synchronization signals (SS) via the SS correlation module 320, the SS including the same cell ID 322 to the transmitter that has a peak value of cross -correlation. The coarse signal synchronization indicates the coarse estimate is an integer, and that is typically close to real symbol timing but could be either larger or smaller than

[0050] As discussed hereinabove, in order to avoid ISI the starting point of the FFT window should fall in the CP interval. Therefore, in the initial phase of stage two, node A of the switch 324 is connected to node 1 to obtain from the SS correlation module 320, and is preadvanced by v sample intervals to have

[0051] Then, the FFT window controller 326 conducts /V-point FFT according to the adjusted the resulting NR DL PRS 312, which includes the phase rotation error described in Equation (7), is fed into path time delay estimate module 318 in which a least square (LS) estimate is adopted. Without loss of generality, assume there is a certain NR DL PRS pilot symbol pattern (known i, a, b, c, M) at the ;th symbol as described hereinabove in regards to Equations (1) to (8), then the least square (LS) estimate of the channel frequency response at these pilot subcarrier frequencies are where denotes the received pilot subcarrier symbols over the zth OFDM symbol.

Substituting Equation (8) into Equation (10) gives where denotes channel noise. Equation (11) illustrates the time-shifting property of the Fourier transform which states that if a function is shifted along the time axis by an amount , the effect is equivalent to multiplying its Fourier transform by the factor

[0052] If it is assumed that does not change over one symbol period, then is a constant over the zth OFDM symbol. For the Additive White Gaussian Noise (AWGN) channels or the multipath Rician fading channels in which the first path signal predominates the channel impulse response, the estimated channel impulse response is given by

[0053] Equation (13) denotes a 2M-point iFFT with when Substituting Equations (2), (3), (11) and (12) into Eq. (13) gives

[0054] From Equation (14): [0055] Under the above assumptions, for a certain k' satisfying

Equation (15) gives

[0056] Finally, the first path time delay estimate is derived in Equation (16): where k' can be obtained from Equation (14) when reaches the peak value. An alternative way of estimating eg is to choose k' based on continuous symbol periods having known pilot symbol patterns.

[0057] From Equation (16), it is known that the estimated timing error is a negative real number. The integer part is fed back to node A of the switch 324 (FIG. 3) through node 2 to adjust the FFT starting point in the FFT window controller 326, and the readjusted 5G NR DL PRS symbol sequence 312 is subsequently obtained. Thereafter, the fractional part is fed into node B of the phase rotation module 314 through node 1 of the switch 358.

[0058] In the initial phase of stage three, the adjusted timing error of the PRS pilot symbol introduced by the phase rotation is supposed to be within one sample interval. Defining the normalized local generated early and late pilot symbols as respectively, the early and late cross-correlation outputs are given by where Y _{i m} is the received pilot symbol over the ith symbol interval after normalization. Thus, the normalized S-curve function over the ith symbol period is defined as [0059] Referring to FIG. 4, a graph 400 depicts the normalized S-curve function As shown in the graph 400, Pattern A and Pattern B denote two normalized S-curve functions with different pilot symbol patterns defined by Equation (1). For Pattern A, M = 432, a = 2, b = 160, c = 0, and x = 0:5; and for Pattern B, M = 72, a = 12, b = 160, c = 0, and x = 0:5. The S-curve function in the graph 400 indicates that the timing error could be represented by a range of near linearity. Therefore, the corresponding DLL discriminator output function can be defined as where k _d = — l/k _s and k _s is the slope of normalized S-curve function.

[0060] The derivation of the slope of normalized S-curve function k _s is presented hereafter. The local generated early reference pilots are given by

[0061] The conjugation of Equation (21) is given by

And the demodulated pilots are given by [0062] Therefore, the early cross-correlation branch output is given by

[0063] Given the fact that, for r ¹ 1, it has

Equation (24) can be written as

[0064] Applying Euler's Formula Equation (26) can be written as

The local generated late reference pilots are given by (28)

And the conjugation of Equation (28) is given by

Therefore, the late cross-correlation branch output is given by

[0065] Similar to Equations. (24), (26) and (27), Equation (30) can be written as

[0067] Further, if , Equation (32) defining the slope K _S can be described as

[0068] Referring to FIG. 5, a block diagram 500 depicts the DLL 316 in accordance with the present embodiments. The system transfer functions of the lowpass filter (LPF) 354 and the accumulator 356 are shown in the block diagram 500, where n and T2 are filter parameters, and can be given by where is the damping factor and is the undamped natural frequency. The difference equations of the LPF 354 and the accumulator 356 are given by where is the filter interval, is the LPF 354 output and is the LPF 354 input (i.e., the output of the discriminator 510) in the 77th filtering cycle. represents the estimated timing error, which is normalized by the sampling interval T.

[0069] Whenever the chosen NR DL PRS pattern occurs in the frame structure, the DLL updates. Finally, the timing adjustment based on estimated is conducted. If , the DLL 316 will adjust the starting point of FFT via the FFT window controller 326 and the leftover fractional timing error will compensate the received symbol phase through node 2 of the switch 358 being connected with the phase rotation module 314 in the next filter interval as follows

[0070] Over the three-stage 5G code phase-based reception process in accordance with the present embodiments, the receiver estimates that the interest of the OFDM symbol starts from the samples. Without loss of generality, it is assumed that the time of the sample is known and at time t _T0A . Therefore, the time of arrival of the interest of OFDM symbol, is given by where the unit of i _T0A is the second, and T denotes the sampling interval.

[0071] Referring to FIG. 6, a block diagram 600 depicts a 5G carrier phase receiver 610 in accordance with the present embodiments. The 5G carrier phase receiver 610 consists of the 5G code phase receiver 301 (FIG. 3) and a phase-locked loop (PLL) 620. The PLL 620 has three main components: a carrier phase discriminator function which includes a discriminator module 625 and a NR DL PRS generator module 630, a carrier loop filter (LPF 635), and a numerically controlled oscillator (accumulator module 640).

[0072] Firstly, normalizing received pilot symbols to obtain when the DLL is successfully tracking the PRS pilot symbols Equation (8) can be written as where the phase rotation including the impact of residual With the NR DL PRS generator 630 providing which denotes the conjugate of the carrier phase discriminator function is defined as

[0073] In a multipath-free environment, Equation (41) gives

[0074] The PLL discriminator function for the ith received symbol can be written as

[0075] A second-order lowpass filter (LPF) is given by _ί undamped natural frequency for the PLL 630. Consequently, the difference equations of the LPF 635 and the accumulator 640 are given by where is the estimated phase, is the PLL filter interval, Lf (n) is the LPF 635 output and is the LPF 635 input (i.e., the discriminator 625 output) in the nth filtering cycle. Finally, the phase adjustment based on the estimated is conducted to compensate the received symbol phase through connecting node 2 of switch 650 to the phase rotation module in the next filter interval as follows

[0076] The communication receiver’s movement with respect to transmitter causes a Doppler shift and, as shown in FIG. 6, a velocity estimate V 660 in accordance with the present embodiments is the output of the LPF 635 of the PLL 620. Since the PLL filter interval 7/ is smaller than a 5G frame interval, assuming, without loss of generality, a 10 millisecond frame interval, there are z PLL LPF outputs over one frame, the average velocity V with respect to transmitter over one frame is given by where c is the speed of light in vacuum and f _c is the carrier frequency. In accordance with the present embodiments, the average velocity 660 can also be obtained in a similar manner every subframe or any given period of time.

[0077] As shown in the block diagram 600, a carrier phase measurement 670 in accordance with the present embodiments is the output of accumulator 640 of the PLL 620. In order to be able to track the carrier phase continuously in accordance with the present embodiments, the 5G NR DL PRS has to be densely allocated into the OFDM symbols. An example is illustrated in the graphs 700, 750 of FIGs. 7A and 7B respectively. The graph 700 depicts carrier phase offset of the OFDM symbols, where the square-shaped dots 710 are the ground truth over the OFDM symbols while the circle- shaped dots 720 are the carrier phase measurements 670 at the output of the accumulator 640 (FIG. 6). The graph 750 depicts tracking error by the PLL 620 of the OFDM symbols.

[0078] This example assumes that the subcarrier spacing is 30 kHz, the FFT size is 1024, and the phase rotation is caused by Doppler shift with a 6 GHz carrier. Therefore, a 30 meter/second velocity with respect to the transmitter causes a constant phase rate of change. The output 670 of the accumulator 640 is the tracking phase while the carrier phase measurement in the ;th symbol interval is given by where denotes the number of integer carrier phase cycle with respect to the first tracking time, is the fractional part of one carrier phase cycle, and the unit of is the cycle.

[0079] Finally, based on carrier phase measurement , the range measurement d(i) of the receiver with respect to the transmitter is given by

[0080] The unit of d(i) is meters. With a 6 GHz carrier frequency, one cycle represents meters and, in accordance with the present embodiments and as long as the PLL can successfully track the phase rotation, the ranging error of the carrier phase measurements 670 can advantageously be at millimetre-level as shown in the graphs 700, 750.

[0081] While 5G NR DL PRS 342 (FIG. 3 and FIG. 6) is the pilot symbol frame structure used for the code and carrier phase receivers 301, 610, this is not the only pilot symbol frame structure that can be used for the methods and communication receivers in accordance with the present embodiments. An example of a simplified pilot symbol frame structure for code and carrier phase receivers for use in accordance with the present embodiments is shown in the illustration 800 of FIG. 8 which depicts the primary synchronization signal (PSS), the secondary synchronization signal (SSS), the physical broadcast channel (PBCH), the PBCH demodulation reference signal DM-RS, and the DL PRS. For example, the synchronisation signal block (SSB) is allocated only in five to eight OFDM symbols as shown in the illustration 900 of FIG. 9, while the 5G NR DL PRS is allocated in selected OFDM symbols except for those allocated to the SSB. Examples of 5G NR DL PRS patterns are shown in the illustrations 1000, 1100 of FIGs. 10 and 11.

[0082] As shown in clause 4.3.1, 3GPP TS 38.305 (V16.0.0), the current 5G network supports downlink time difference of arrival (DL-TDOA) positioning methods for localization services and the 5G NR DL PRS is the potential reference signal adopted by 5G standards for measuring reference signal time difference (RSTD) in DL-TDOA. In addition, 5G NR DL PRS is defined in Release 16 (3 GPP TS 38.214 (V16.1.0) and TS 37.355 (V16.0.0)). Accordingly, in the near future, the commercial 5G networks will support NR DL PRS-based positioning methods.

[0083] According to 3 GPP TS 37.355 (V16.0.0), LTE Positioning Protocol (LPP) is used point-to-point between a location server (E-SMLC, LMF or SLP) and a target device (UE or SET) in order to position the target device using position-related measurements obtained by one or more reference sources as shown in the table 1200 of user equipment (UE) positioning methods of FIG. 12. Internal LPP positioning methods and associated signalling content include NR DL-TDOA 1210. With the timing recovery scheme in accordance with the present embodiments, user equipment (UE) localization can advantageously be implemented using the NR DL PRS signals in the actual 5G commercial network through the NR DL-TDOA positioning method. [0084] Referring to FIG. 13, an illustration 1300 depicts a positioning protocol in LTE and 5G NR networks. A target device 1310 such as a UE receives reference signals from a first reference signal source 1320 such as satellite signals from the Global Navigation Satellite System (i.e., GNSS) and from a second reference signal source 1330 such as LTE/NR radio signals from a base station such as an eNodeB/NG-RAN. For positioning services, the UE 1310 communicates with a location server 1340 such as an E-SMLC/LMF/SLP using the LTE Positioning Protocol (LPP) by sending measurements (i.e., A, B, or A+B) or location data 1350 to the location server 1340 and receiving assistance data 1360 from the location server.

[0085] The methods and communication apparatuses in accordance with the present embodiments conform to the 5G NR standards and positioning protocol thereby providing improved compatible performance for 5G positioning. Once the localization service is initiated, the UE 1310 will receive NR DL PRS configurations from multiple base stations, i.e. NG-RAN 1330, through assistance data defined in 3GPP TS 37.355 (V16.0.0) including, but not limited to, NR-DL-TDOA Assistance Data 1360 supporting 5G positioning services in accordance with the methods described hereinabove of the present embodiments.

[0086] With the NR-DL-TDOA Assistance Data 1360, the UE 1310 obtains NR DL PRS reference signal configurations and patterns. Together with other system information including frequency bandwidth, the UE 1310 could receive and demodulate the expected NR DL PRS signals from the expected gNodeB. In addition, after sampling the received the NR DL PRS carried by the CP-OFDM waveform, the UE 1310 could apply the three-stage code and carrier phase receiver in accordance with the present embodiments to advantageously have an accurate estimate of timing error and obtain the resulting time of arrival (TO A).

[0087] Finally, as multiple gNodeBs result in multiple TOAs at the UE 1310, the multiple TOAs can be used to calculate the NR DL TDOA on either the UE 1310 side or the location server 1340 side. The measurements or location results could be sent back to the location server as measurements or location information 1350. [0088] Thus, it can be seen that the present embodiments provide methods and communication apparatuses compatible to current 5G systems to provide accuracy- improved carrier phase measurements and velocity estimations to enable highly accurate 5G-based positioning. The code and carrier phase receiver in accordance with the present embodiments can be integrated with current 5G NR commercial networks directly to present an improved, highly accurate positioning process which complies with 3GPP 5G standards, thereby delivering a more accurate localization service. [0089] Referring to FIGs. 14A, 14B and 14C, graphs 1410, 1420, 1430, 1440 and a table 1450 compare the timing recovery of the 5G NR code phase-based receiver 301 (FIG. 3) in accordance with the present embodiments for two different pilot symbol patterns (Pattern A and Pattern B). The 5G NR code phase-based receiver in accordance with the present embodiments advantageously has a software-defined radio (SDR) architecture design with flexible OFDM pilot symbol choice using 5G standard compliant numerologies and signals to achieve a sub-meter 5G positioning ranging accuracy.

[0090] The graphs 1410, 1420 depict DLL tracking results for 5G timing recovery of the 5G NR code phase-based receiver receiving a Pattern A, and the graphs 1430, 1440 depict 5G timing recovery of the 5G NR code phase-based receiver receiving a Pattern B pilot symbol pattern. The pilot symbol patterns, Pattern A and Pattern B, are received on an Additive White Gaussian Noise (AWGN) channel at 30dB with a S-curve function slope k _s of 3.24. The table 1450 compares kinematic and static timing recovery for both Pattern A and Pattern B on the AWGN channel and/or a multipath Rician fading channel.

[0091] Referring to FIGs. 15A, 15B and 15C, graphs 1500, 1510, 1520, 1530, 1540 the timing recovery for various portions of the 5G NR carrier phase-based receiver 610 in accordance with the present embodiments. The 5G NR carrier phase-based receiver 610 in accordance with the present embodiments advantageously builds upon the code phase-based receiver 301 to additionally provide precise carrier phase measurements 670 and velocity estimations 660. The graphs 1500, 1510, 1520, 1530, 1540 are derived from a simulation scenario where the nFFT is 1025, the subcarrier spacing (SCS) is 30kHz, the carrier frequency f _c is 6GHz, and the carrier wavelength /., is 5cm. The velocity of the receiver 610 with respect to the gNodeB is 30 meter/second and every 10ms (i.e., 1 frame or 280 symbols) the distance traveled is 0.3m representing 0.03 sample timing offset in the DLL 316 and a six-cycle phase change in the PLL 620. [0092] The graph 1500 depicts 5G timing recovery for the PLL velocity estimation 660, the graphs 1510, 1520 depict 5G timing recovery for the DLL 316 tracking, and the graphs 1530, 1540 depict 5G timing recovery for the PLL 620 tracking. The DLL tracking results in the graphs 1510, 1520 and the PLL tracking results in the graphs 1530, 1540 are for pilot symbol patterns received on an Additive White Gaussian Noise (AWGN) channel at 30dB with a S-curve function slope k _s of 3.24. From the graphs 1500, 1510, 1520, 1530, 1540, it can be seen that the code phase receiver advantageously has a ranging error of 0.77 meters and the carrier phase receiver has a ranging error in the millimeter range with a velocity estimation error of just two meters per second.

[0093] FIG. 16A depicts exemplary settings 1600 of the Rician channel of the 5G NR carrier phase-based receiver 610 in accordance with the present embodiments. FIGs. 16B, 16C and 16D, depict graphs 1610, 1620, 1630, 1640, 1650 of operation of different parts of the 5G NR carrier phase-based receiver 610 in accordance with the present embodiments. The graph 1610 depicts 5G timing recovery for the PLL velocity estimation 1660, the graphs 1620, 1630 depict 5G timing recovery and tracking results for the DLL 316, and the graphs 1640, 1650 depict 5G timing recovery and tracking results for the PLL 620. The DLL tracking results in the graphs 1610, 1620 and the PLL tracking results in the graphs 1630, 1640 are for pilot symbol patterns received on multipath Rician fading plus AWGN channel types with a S-curve function slope k _s of 3.24. It can be seen that even on channel multipath Rician fading plus AWGN channels, the code phase-based receiver in accordance with the present embodiments provides positioning within a low ranging error of 0.62 meters and the carrier phase-based receiver in accordance with the present embodiments provides positioning within a very low ranging error at the centimetre level and velocity estimations within an error range of 16.5 meters per second.

[0094] FIGs. 17A,17B, 17C and 17D depicts frame structure 1700, 1730 and graphs 1710, 1720, 1740, 1750 comparing operation of the NR carrier phase-based receiver 610 at two bandwidths in 5G and LTE systems in accordance with the present embodiments. The pilot symbol frame structure 1700 has a larger bandwidth than the pilot symbol frame structure 1730 and the graphs 1710, 1720 depict 5G timing recovery and tracking results for the DLL for the pilot symbol frame structure 1700. The graphs 1740, 1750 depict 5G timing recovery and tracking results for the DLL for the pilot symbol frame structure 1730 having the smaller bandwidth. 5G supports larger bandwidth than LTE systems and the larger bandwidth of 5G such as that shown in the pilot symbol frame structure 1730 means higher accuracy as shown in a comparison of the graphs 1720 and 1750.

[0095] Referring to FIGs. 18A,18B, 18C, 18D, 18E and 18F, graphs 1800, 1810, 1820, 1830, 1840, 1850, 1860, 1870, 1880, 1890 depict operation of the NR carrier phase- based receiver 610 in accordance with the present embodiments for different pilot symbol patterns: Pattern A and Pattern B. The graphs 1800, 1810 depict 5G timing recovery and tracking results for the DLL 316 for the Pattern A pilot symbol pattern and the graphs 1820, 1830 depict 5G timing recovery and tracking results for the PLL 620 for the Pattern A pilot symbol pattern. The histogram 1840 depicts PLL velocity estimation for the Pattern A pilot symbol pattern.

[0096] Similarly, the graphs 1850, 1860 depict 5G timing recovery and tracking results for the DLL 316 for the Pattern B pilot symbol pattern and the graphs 1870, 1880 depict 5G timing recovery and tracking results for the PLL 620 for the Pattern B pilot symbol pattern. The histogram 1890 depicts PLL velocity estimation for the Pattern B pilot symbol pattern.

[0097] 5G systems support a shorter symbol interval leading to more densely allocated pilot symbols. More densely allocated pilot symbols mean more accurate carrier phase tracking. Consequently, from the graphs 1800, 1810, 1820, 1830, 1840, 1850, 1860, 1870, 1880, 1890, it can be seen that the more densely allocated pilot symbols of 5G systems enable the methods and communication apparatuses in accordance with the present embodiments to obtain highly accurate velocity estimations 660 and determine 5G positioning within a millimeter-level ranging accuracy.

[0098] While exemplary embodiments have been presented in the foregoing detailed description of the present embodiments, it should be appreciated that a vast number of variations exist. It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of steps and method of operation described in the exemplary embodiments without departing from the scope of the invention as set forth in the appended claims.