Patent ID: 12213092

DETAILED DESCRIPTION

We are looking for Positioning based on Cell-ID (CID) which uses geographical knowledge of a UE's serving cell. To improve the accuracy, measurements made by the UE and/or the eNodeB can be utilized in addition.

Basic CID positioning estimates the location of a UE using only the coordinates of its serving eNodeB. Typically, basic CID positioning provides only coarse estimation of the UE location, with accuracy of roughly the same order as the cell radius.

Enhanced CID positioning uses additional information beyond the identity of the eNodeB that is serving the UE. The distance of a UE from its serving eNodeB or cell can be estimated from the Round Trip Time (RTT). Two measurements are defined in LTE Release 9 by which an eNodeB can indicate the RTT to the E-SMLC, namely ‘Timing Advance Type 1’ and ‘Timing Advance Type 2’. A diagram of type 1 and type 2 timing advance are shown inFIG.1A.

Type 1 and type 2 Timing Advance definition is mentioned in 3GPP spec 36.214 section 5.2.4, which is hereby incorporated by reference.

DefinitionType 1Timing advance (TADV) type 1 is defined asthe time differenceTADV= (eNB Rx − Tx time difference) +(UE Rx − Tx time difference).where the eNB Rx − Tx time difference corresponds to thesame UE that reports the UE Rx − Tx time difference.Type 2:Timing advance (TADV) type 2 is defined as the timedifferenceTADV= (eNB Rx − Tx time difference),where the eNB Rx − Tx time difference corresponds to areceived uplink radio frame containing PRACHfrom the respective UE

Physical Random Access Channel (PRACH) is used to achieve uplink time synchronization for a UE which either has not yet acquired, or has lost, its uplink synchronization. A successful PRACH attempt should allow subsequent UE transmissions to be inserted among the scheduled synchronized transmissions of other UEs. This sets the required timing estimation accuracy which must be achievable from the PRACH decoding at eNB

PRACH Transmitter

Most convenient implementation of PRACH transmitter in the UE is to generate the preamble using smallest possible IFFT and shifting the preamble to the required frequency location through time-domain up sampling and filtering (commonly known as hybrid frequency/time domain PRACH generation shown in theFIG.2). Given that the preamble sequence based on Zadoff-Chu of length is 839, the smallest IFFT size that can be used is 1024, resulting in a sampling frequency of 1.28 Msps. Both the CP and sequence durations have been designed to provide an integer number of samples at this sampling rate. The CP can be inserted before the up sampling and time-domain frequency Shift.

A PRACH Preamble structure is shown inFIG.1B.

PRACH Formats

Preamble formatTCPTSEQ03168 · Ts24576 · Ts121024 · Ts24576 · Ts26240 · Ts2 · 24576 · Ts321024 · Ts2 · 24576 · Ts4*448 · Ts4096 · Ts

As described above Type 2 Measurement report of LPPa protocol requires 2Ts/8Ts resolution timing advance to better locate UE positioning. Physical layer is responsible for decoding PRACH Preamble and its corresponding Timing Advance (TA) and report to higher layers. Traditional measurement report gets 16 Ts timing resolution from Physical layer (PHY) which boils down to approx. 80 meters range of UE positioning. As part of LPPa requirement, PHY is required to report Timing Advance with higher accuracy of 2Ts. This 2Ts resolution will give UE positioning accuracy up to 10 meters.

Solution to Problem

The current implementation of the PRACH detector estimates the timing advance with the accuracy of 16 Ts. The proposed method works in tandem with the existing implementation to estimate the TA with higher resolution of 2Ts. A key insight is that the timing offset can be determined from the correlation of the received PRACH preamble with the reference received preamble. In other words, the transmitted preamble is known to be an interpolated or upsampled version of the original short preamble sequence.

The processing steps required in the method are as follows, and are shown inFIG.3.

The received preamble signal r(n) has the sampling frequency of 30.72 Msps and is 24576 samples long. It must be conditioned before passing to the PRACH detector. The signal conditioning includes following operations:

At301, Cyclic prefix is removed, and only Preamble sequence is extracted;

The positioning of the signal in the frequency domain is determined by the factor n_PRB_Offset. The signal is shifted in frequency by n_PRB_Offset so that it is centered about DC;

Anti-aliasing filter followed by down sampling by a factor of 24. So, the preamble sequence length reduces to 1024 samples. The resulting sequence is y(n);

At302, a 1024-point FFT of y(n) is calculated, outputting y(k);

At303, the output y(k) is padded with zeroes to become Y_hat(k), which is 12288 samples long;

Separately, at304, a reference preamble c(n) is input to a 1024-point FFT, outputting c(k);

At305, the down sampled version of the received preamble is correlated with the reference preamble sequence c(n) using the FFT method, Ryc=ifft{Y(k).C*(k)}, where Y(k) and C(k) are 1024-point FFT of y(n) and c(n) respectively;

At306, the peak value P of the correlation output Ryc is used to detect the preamble ID and the Timing advance at a resolution of 24Ts;

At307, the sequence C(k) is zero padded so that its length becomes 12288. Let the resulting sequence be C_hat(k);

At308, a maximum likelihood estimation (MLE) is performed to estimate the timing offset. The MLE method is based on the correlation of the received preamble at Fs=30.72 Msps with the reference received preamble that is also at the same sampling rate. We perform 12288 point circular correlation at multiple positions in a timing hypothesis window L, e.g., compute the selective IDFT transformed outputs of R_hat(m)=IDFT{Y_hat(k).C_hat*(k)};

The values of m are determined by the value P:
(P*12−L/2)≤m≤(P*12+L/2)

To reduce the complexity involved in the computation of R_hat(m), we avoid using conventional IFFT. Instead we use ‘Grouped FFT algorithm for selective transformed outputs’ (see the paper of the same title by CP Fan, GA Su—APCCAS 2006-2006 IEEE Asia Pacific . . . , 2006—ieeexplore.ieee.org). This algorithm exploits the periodicity and symmetricity properties of DFT twiddle factor to compute IDFT only at selective indices m within the window L. In other words, we exploit the fact that the transmitted LTE preamble is the interpolated or upsampled version of the original short preamble sequence. In other words, the frequency components of the preamble is bounded to a narrow bandwidth of 1.4 KHz.

Further reduction in computation is achieved using the sparsity of the IDFT inputs (depicted inFIG.4). Only 839 out of 12288 input samples are non-zeros. So, by keeping track of the input indices in the computations, unnecessary zero multiplications and additions are avoided.

At309, the peak value out of the R_hat(m) is detected and the corresponding index Q501that falls within timing hypothesis window L502will provide the timing advance with an accuracy of 2Ts, as shown inFIG.5.

In various embodiments, this method can be designed to be performed at the base station or could be performed anywhere where sufficient processing power is available, including at a baseband unit colocated or remotely located relative to the base station. No modification is required to the UE.

It is noted that the PRACH preamble structure used in 5G NR (New Radio) is exactly the same as that used in 4G, so the methods disclosed herein could be used by one having skill in the art at a 5G base station or in a 5G network. It is noted that different PRACH preamble structures could be standardized and used, and, when used in combination with the presently disclosed methods and new RF technologies, could provide UE positioning with greater resolution than 2Ts.

The timing advance values derived using the presently described methods could be used, in some embodiments, for UE location/positioning; responding to UE paging requests; reporting UE location to the core network; plotting UE location on a map; using UE location for compliance with governmental requirements for location services and/or emergency services; optimizing beamforming for MIMO applications; optimizing UE location for purposes of assessing handover and inter-cell interference coordination (ICIC), etc. The timing advance values derived using the presently described methods could, in the case of a UE that is a smart watch or smart fob or smart tag, be used to locate the UE within a small radius.

FIG.6is a flow diagram of a first embodiment of a method for providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH). The method includes receiving a preamble signal r(n) having a predetermined sampling frequency and a predetermined length (601); correlating a down sampled version of the received preamble with a reference preamble sequence c(n) using an IFFT method to provide correlation output Ryc (602); using a peak value P of the correlation output Ryc to detect a preamble ID and a timing advance at a resolution of 24Ts (603); zero padding sequences Y(k) and C(k) so that they have a predetermined length resulting in sequences Y_hat(k) and C_hat(k), wherein Y(k) and C(k) are 1024-point FFT of y(n) and c(n) (604); performing a maximum likelihood estimation (MLE) to estimate a timing offset (605); and detecting a peak value out of the R_hat(m) and using a corresponding index Q to provide a timing advance with an accuracy of 2Ts (606).

FIG.7is a flow diagram of another embodiment of a method for providing high resolution timing advance estimation based on Physical Random Access Channel (PRACH). The method includes receiving a preamble y(n) from a user equipment in a frequency domain (701); performing a Fourier transform on the received preamble y(n) to generate a received time-domain preamble y(k) (702); performing a Fourier transform on a reference preamble c(n) to generate a time-domain reference preamble c(k) (703); performing an inverse Fourier transform on a dot product of the received time-domain preamble y(k) and the reference time-domain preamble c(k) to generate a correlation function R (704); padding the received time-domain preamble y(k) and the reference time-domain preamble c(k) to a certain length with zeroes (705); using a peak value P of the correlation function R to detect a preamble identifier (706); performing an inverse discrete Fourier transform on the dot product of the received time-domain preamble y(k) and the reference time-domain preamble c(k) at a plurality of positions within a sparse timing hypothesis window L, the sparse timing hypothesis window L based on the preamble identifier, to generate a second correlation function R_hat (707); and using a peak value Q of the second correlation function R_hat to determine a timing advance value (708). These steps could be performed in various orders as would be understood by one having skill in the art, e.g.,702and703could be performed with either one being first, or both of them concurrently.

FIG.8is an enhanced eNodeB for performing the methods described herein, in accordance with some embodiments. Mesh network node800may include processor802, processor memory804in communication with the processor, baseband processor806, and baseband processor memory808in communication with the baseband processor. Mesh network node800may also include first radio transceiver812and second radio transceiver814, internal universal serial bus (USB) port816, and subscriber information module card (SIM card)818coupled to USB port816. In some embodiments, the second radio transceiver814itself may be coupled to USB port816, and communications from the baseband processor may be passed through USB port816. The second radio transceiver may be used for wirelessly backhauling eNodeB800.

Processor802and baseband processor806are in communication with one another. Processor802may perform routing functions, and may determine if/when a switch in network configuration is needed. Baseband processor806may generate and receive radio signals for both radio transceivers812and814, based on instructions from processor802. The steps described herein could be performed at the baseband processor806, or, in some embodiments, at processor802. In some embodiments, processors802and806may be on the same physical logic board. In other embodiments, they may be on separate logic boards.

Processor802may identify the appropriate network configuration, and may perform routing of packets from one network interface to another accordingly. Processor802may use memory804, in particular to store a routing table to be used for routing packets. Baseband processor806may perform operations to generate the radio frequency signals for transmission or retransmission by both transceivers810and812. Baseband processor806may also perform operations to decode signals received by transceivers812and814. Baseband processor806may use memory808to perform these tasks.

The first radio transceiver812may be a radio transceiver capable of providing LTE eNodeB functionality, and may be capable of higher power and multi-channel OFDMA. The second radio transceiver814may be a radio transceiver capable of providing LTE UE functionality. Both transceivers812and814may be capable of receiving and transmitting on one or more LTE bands. In some embodiments, either or both of transceivers812and814may be capable of providing both LTE eNodeB and LTE UE functionality. Transceiver812may be coupled to processor802via a Peripheral Component Interconnect-Express (PCI-E) bus, and/or via a daughtercard. As transceiver814is for providing LTE UE functionality, in effect emulating a user equipment, it may be connected via the same or different PCI-E bus, or by a USB bus, and may also be coupled to SIM card818. First transceiver812may be coupled to first radio frequency (RF) chain (filter, amplifier, antenna)822, and second transceiver814may be coupled to second RF chain (filter, amplifier, antenna)824.

SIM card818may provide information required for authenticating the simulated UE to the evolved packet core (EPC). When no access to an operator EPC is available, a local EPC may be used, or another local EPC on the network may be used. This information may be stored within the SIM card, and may include one or more of an international mobile equipment identity (IMEI), international mobile subscriber identity (IMSI), or other parameter needed to identify a UE. Special parameters may also be stored in the SIM card or provided by the processor during processing to identify to a target eNodeB that device800is not an ordinary UE but instead is a special UE for providing backhaul to device800.

Wired backhaul or wireless backhaul may be used. Wired backhaul may be an Ethernet-based backhaul (including Gigabit Ethernet), or a fiber-optic backhaul connection, or a cable-based backhaul connection, in some embodiments. Additionally, wireless backhaul may be provided in addition to wireless transceivers812and814, which may be Wi-Fi 802.11a/b/g/n/ac/ad/ah, Bluetooth, ZigBee, microwave (including line-of-sight microwave), or another wireless backhaul connection. Any of the wired and wireless connections described herein may be used flexibly for either access (providing a network connection to UEs) or backhaul (providing a mesh link or providing a link to a gateway or core network), according to identified network conditions and needs, and may be under the control of processor802for reconfiguration.

A GPS module830may also be included, and may be in communication with a GPS antenna832for providing GPS coordinates, as described herein. When mounted in a vehicle, the GPS antenna may be located on the exterior of the vehicle pointing upward, for receiving signals from overhead without being blocked by the bulk of the vehicle or the skin of the vehicle. Automatic neighbor relations (ANR) module832may also be present and may run on processor802or on another processor, or may be located within another device, according to the methods and procedures described herein.

Other elements and/or modules may also be included, such as a home eNodeB, a local gateway (LGW), a self-organizing network (SON) module, or another module. Additional radio amplifiers, radio transceivers and/or wired network connections may also be included.

The system may include 5G equipment. 5G networks are digital cellular networks, in which the service area covered by providers is divided into a collection of small geographical areas called cells. Analog signals representing sounds and images are digitized in the phone, converted by an analog to digital converter and transmitted as a stream of bits. All the 5G wireless devices in a cell communicate by radio waves with a local antenna array and low power automated transceiver (transmitter and receiver) in the cell, over frequency channels assigned by the transceiver from a common pool of frequencies, which are reused in geographically separated cells. The local antennas are connected with the telephone network and the Internet by a high bandwidth optical fiber or wireless backhaul connection.

5G uses millimeter waves which have shorter range than microwaves, therefore the cells are limited to smaller size. Millimeter wave antennas are smaller than the large antennas used in previous cellular networks. They are only a few inches (several centimeters) long. Another technique used for increasing the data rate is massive MIMO (multiple-input multiple-output). Each cell will have multiple antennas communicating with the wireless device, received by multiple antennas in the device, thus multiple bitstreams of data will be transmitted simultaneously, in parallel. In a technique called beamforming the base station computer will continuously calculate the best route for radio waves to reach each wireless device, and will organize multiple antennas to work together as phased arrays to create beams of millimeter waves to reach the device.

The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. In some embodiments, software that, when executed, causes a device to perform the methods described herein may be stored on a computer-readable medium such as a computer memory storage device, a hard disk, a flash drive, an optical disc, or the like. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Various components in the devices described herein may be added, removed, split across different devices, combined onto a single device, or substituted with those having the same or similar functionality.

Although the present disclosure has been described and illustrated in the foregoing example embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosure may be made without departing from the spirit and scope of the disclosure, which is limited only by the claims which follow. Various components in the devices described herein may be added, removed, or substituted with those having the same or similar functionality. Various steps as described in the figures and specification may be added or removed from the processes described herein, and the steps described may be performed in an alternative order, consistent with the spirit of the invention. Features of one embodiment may be used in another embodiment. Other embodiments are within the following claims.