Description:TECHNICAL FIELD
[0001] The present disclosure generally relates to the field of wireless communications. In particular, the present disclosure relates to imbalance parameter estimation and compensation for wireless communications.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Wireless communication channels are doubly dispersive channels in nature, i.e., they are dispersive in both time and frequency domains. The 4G Long term evolution (LTE) waveform, i.e., cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM) waveform can combat time dispersion effectively, but not frequency dispersion. Due to very high-speed movement between transmitter (Tx) and receiver
[0004] (Rx) (e.g., high speed bullet trains, V2X communication), a time varying Doppler shift occurs, which disturbs the orthogonality among sub-carriers in an OFDM system, thereby degrading its performance. The performance in an OFDM system is also degraded by high carrier frequencies between Tx and Rx. The proposed variants of OFDM (e.g., Windowed OFDM, filtered OFDM, coded-OFDM etc.), linear filter bank multi carriers (FBMC), and circular FBMC (e.g., Generalized frequency division multiplexing (GFDM)) waveforms are also not robust to Doppler shift.

OBJECTS OF INVENTION
[0005] An object of the present invention is to provide a method and system for wireless communication.
[0006] Another object of the present invention is to provide a method for two-level threshold-based technique for estimating channel parameters, IQ imbalance parameters for an OFDM based OTFS system under time varying wireless communication channels.

SUMMARY
[0007] The present disclosure generally relates to the field of wireless communications. In particular, the present disclosure relates to imbalance parameter estimation and compensation for wireless communications.
[0008] In a first aspect, the present disclosure provides a method for wireless communication including receiving, at a computing device coupled to a receiver, sample symbols; initializing, at the computing device, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. Responsive to convergence of symbol synchronization, the method further includes: removing, at the computing device, cyclic prefix; computing, at the computing device, Wigner transform to convert the symbols from time domain to frequency domain; computing, at the computing device, symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and computing, by the computing device, absolute values of the received sample symbols in the delay-Doppler domain.
[0009] In some embodiments, the method further includes determining, at the computing device, if the absolute values of the symbols exceed a first threshold value; and determining, responsive to the absolute values of the symbols exceeding the first threshold value, at the computing device, if the absolute values of the symbols exceed a second threshold value. A mirror path is deemed to exist if the absolute values of the symbols exceed the second threshold value.
[0010] In some embodiments, if the absolute values of the symbols do not exceed the first threshold value, it is deemed that no delay-Doppler path exists.
[0011] In some embodiments, if the absolute values of the symbols do not exceed the second threshold value, it is deemed that no mirror path exists.
[0012] In some embodiments, the method further includes determining, at the computing device, responsive to the absolute values of the symbols exceeding the second threshold value, channel coefficients.
[0013] In some embodiments, the method further includes determining, at the computing device, IQ imbalance coefficients.
[0014] In some embodiments, the method further includes compensating, at the computing device, the symbols for the IQ imbalance coefficients to obtain the symbols without IQ imbalance.
[0015] In some embodiments, the method further includes detecting, by the computing device, the data using any one of a message passing based detector, and minimum mean square error-based detector.
[0016] In some embodiments, the method further includes storing, at the computing device, the data.
[0017] In a second aspect, the present disclosure provides a system for wireless communication including a computing device configured to receive, at a receiver, sample symbols; initialize, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. Responsive to convergence of symbol synchronization, the computing device is further configured to remove cyclic prefix; compute Wigner transform to convert the symbols from time domain to frequency domain; compute symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and compute absolute values of the received sample symbols in the delay-Doppler domain.
[0018] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS
[0019] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0020] FIG. 1 illustrates a schematic representation of data multiplexing in a delay-Doppler domain;
[0021] FIG. 2 illustrates a schematic representation of a system for OFDM based single input single output (SISO) OTFS considered with receiver IQ imbalance, in accordance with an embodiment of the present disclosure;
[0022] FIG. 3 illustrates a schematic flow diagram for a process for receiver side IQ imbalance parameter estimation and compensation, according to an embodiment of the present disclosure;
[0023] FIG. 4 illustrates a schematic flow diagram for a method for wireless communication, according to an embodiment of the present disclosure;
[0024] FIG. 5 illustrates a schematic block diagram of a computing device for implementing the method for wireless communication, according to an embodiment of the present disclosure; and
[0025] FIG. 6 illustrates an exemplary schematic block diagram of a hardware platform for implementing the computing device of FIG. 5.

DETAILED DESCRIPTION
[0026] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0027] In a first aspect, the present disclosure provides a method for wireless communication including receiving, at a computing device coupled to a receiver, sample symbols; initializing, at the computing device, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. Responsive to convergence of symbol synchronization, the method further includes: removing, at the computing device, cyclic prefix; computing, at the computing device, Wigner transform to convert the symbols from time domain to frequency domain; computing, at the computing device, symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and computing, by the computing device, absolute values of the received sample symbols in the delay-Doppler domain.
[0028] In some embodiments, the method further includes determining, at the computing device, if the absolute values of the symbols exceed a first threshold value; and determining, responsive to the absolute values of the symbols exceeding the first threshold value, at the computing device, if the absolute values of the symbols exceed a second threshold value. A mirror path is deemed to exist if the absolute values of the symbols exceed the second threshold value.
[0029] In some embodiments, if the absolute values of the symbols do not exceed the first threshold value, it is deemed that no delay-Doppler path exists.
[0030] In some embodiments, if the absolute values of the symbols do not exceed the second threshold value, it is deemed that no mirror path exists.
[0031] In some embodiments, the method further includes determining, at the computing device, responsive to the absolute values of the symbols exceeding the second threshold value, channel coefficients.
[0032] In some embodiments, the method further includes determining, at the computing device, IQ imbalance coefficients.
[0033] In some embodiments, the method further includes compensating, at the computing device, the symbols for the IQ imbalance coefficients to obtain the symbols without IQ imbalance.
[0034] In some embodiments, the method further includes detecting, by the computing device, the data using any one of a message passing based detector, and minimum mean square error-based detector.
[0035] In some embodiments, the method further includes storing, at the computing device, the data.
[0036] In a second aspect, the present disclosure provides a system for wireless communication including a computing device configured to receive, at a receiver, sample symbols; initialize, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. Responsive to convergence of symbol synchronization, the computing device is further configured to remove cyclic prefix; compute Wigner transform to convert the symbols from time domain to frequency domain; compute symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and compute absolute values of the received sample symbols in the delay-Doppler domain.
[0037] FIG. 1 illustrates a schematic representation of data multiplexing in a delay-Doppler domain. The delay Doppler plane is discretized to an MxN information grid. Here, T, M and N represent time duration, delay, and Doppler bins, respectively. The time frequency plane is discretized to MxN grid by sampling time and frequency.
[0038] Orthogonal time frequency space modulation (OTFS), which is very robust to doubly dispersive channels under high mobility, is an emerging waveform for 5G cellular applications. An object of the present disclosure is to use a two-level threshold-based technique for estimating channel parameters, IQ imbalance parameters for an orthogonal frequency division multiplexing (OFDM) based OTFS system under time varying wireless communication channels. Asymmetrical IQ imbalances at the receiver are considered. A pilot-based transmission is used at the transmitter and a two-level threshold-based detection, estimation and compensation is done at the receiver. The modulated OTFS symbols occupy a time duration of NT seconds and bandwidth of M times the subcarrier spacing. At the transmitter side, the information symbols which are residing in the delay-Doppler domain are converted to time frequency domain. Subsequently, the symbols which are residing in the time frequency domain are converted to time domain through certain transformations. The signal is transmitted through a linear time varying channel.
[0039] At the receiver side, the information symbols in the time domain are converted back to time-frequency domain through certain transformations. The symbols in the time frequency domain are converted back to delay-Doppler domain through some other transformation. Finally, the information symbols are analyzed in the delay-Doppler domain. These transformations convert a time varying channel into a nearly time invariant one, thereby making equalization less complex. This OTFS modulation is highly suited for high-speed communications where the Doppler frequencies are relatively higher.
[0040] FIG. 2 illustrates a schematic representation of a system 100 for OFDM based single input single output (SISO) OTFS considered with receiver IQ imbalance, in accordance with an embodiment of the present disclosure. The model depicts the inner block corresponding with Time frequency modulation and outer block corresponding with OTFS modulation in the delay-Doppler domain. The information symbols in the delay-Doppler domain are assumed to be zero mean independent and identically distributed (i.i.d) Quadrature amplitude modulated (QAM) symbols. The OTFS signal of MN samples are transmitted in NT duration. (201) describes inverse symplectic finite Fourier transform and windowing which is together called as ISFFT transform. This is the pre-processing unit for OTFS based OFDM system 100. The symbols in the delay-Doppler domain are converted to time frequency domain using ISFFT transform (201). Heisenberg transform (202) is used for converting the symbols from time frequency domain to time domain. For the OFDM based OTFS system, it can be replaced with an inverse fast Fourier transform (IFFT). The pulse shaping that is used is a rectangular pulse shaping. A cyclic prefix (203) is added to eliminate the detrimental effects caused by the inter symbol interference (ISI). A linear time varying channel (TVC) is doubly dispersive in nature and almost all wireless channels are dispersive in either time domain or frequency domain or in both domains. (204) describes TVC for an OTFS based OFDM system. The IQ imbalance model is denoted in (205) where the output of the model is a sum of scaled component and a scaled conjugate component of the signal. Here K1 and K2 denotes IQ imbalance parameters which have to be estimated and compensated. The cyclic prefix (206) of the frame is removed and (207) is the Wigner transform which is used for converting a time domain signal to a time frequency domain signal. The signal is again converted to delay-Doppler domain through symplectic finite Fourier transform and windowing (208) which is together called a SFFT transform.
[0041] FIG. 3 illustrates a schematic flow diagram for a process 300 for receiver side IQ imbalance parameter estimation and compensation, according to an embodiment of the present disclosure. Once the symbols are received from analog to digital converter (ADC), the steps in the flowchart will be executed as follows. We start with (301). A frame of received samples are collected and stored in a buffer (302). At the transmitter, we transmit a start of frame (SOF) signal before OTFS frame transmission. At the receiver, we start checking for the SOF frame (303). Once the SOF is detected, we start symbol synchronization algorithm (304) which is used to find the optimal transmitted symbol. It will take few samples to converge. Once the SS algorithm is converged (305), then we start the actual process. We remove the cyclic prefix (306) which was transmitted to remove ISI. Once the CP is removed, we compute Wigner transform (307) which is used to convert a signal from time domain to time frequency domain. Next, we perform symplectic finite Fourier transform and windowing which is called as SFFT transform (308) to convert a signal from time frequency domain to delay-Doppler domain. Now the received symbols are in delay-Doppler domain. We compute the absolute values of the received symbols (309). Once the received absolute values exceed a pre-determined threshold T1 (310), we assume that there exists a delay-Doppler path which is caused not only by direct path from transmitter to receiver, but also by reflected, scattered, and diffracted paths. Then, we store the delay index and doppler index of the actual path (315). If the absolute values do not exceed a threshold T1, we ignore that symbol and start checking for the next symbol and we assume that delay-Doppler path does not exist (311). If the absolute values exceed threshold T1, then we also re-compute whether the received symbols exceed a threshold T2 (312), if the absolute value of symbols exceed threshold T2, then we assume that there exists a mirror path (314) which is caused by IQ imbalance. If the absolute values of the symbol do not exceed threshold T2, we assume that mirror path don’t exist (313). We store the mirrored delay index and mirrored Doppler index. From the actual delay-Doppler index and mirrored delay-Doppler index, we estimate the channel coefficients (316). Then, we estimate the IQ imbalance coefficients (317). We also compensate the IQ imbalance coefficients (318) from the pre-defined known model. Once the signal is free of IQ imbalance coefficients, we have known channel coefficients. We then use either message passing based detector or minimum mean square error-based detector for data detection (319), and we store the detected data symbols (320) and then we stop the Algorithm (321).
[0042] FIG. 4 illustrates a schematic flow diagram for a method 400 for wireless communication, according to an embodiment of the present disclosure. At step 402, the method 400 includes receiving, at a computing device coupled to a receiver, sample symbols. At step 404, the method 400 further includes initializing, at the computing device, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. At step 406, the method 400 further includes responsive to convergence of symbol synchronization removing, at the computing device, cyclic prefix. At step 408, the method 400 further includes responsive to convergence of symbol synchronization computing, at the computing device, Wigner transform to convert the symbols from time domain to frequency domain. At step 410, the method 400 further includes responsive to convergence of symbol synchronization computing, at the computing device, symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain. At step 412, the method 400 further includes responsive to convergence of symbol synchronization; and computing, by the computing device, absolute values of the received sample symbols in the delay-Doppler domain.
[0043] FIG. 5 illustrates a schematic block diagram of a computing device 500 for implementing the method 400 for wireless communication, according to an embodiment of the present disclosure. The computing device 500 includes a processor 502 and a memory 504 communicably coupled to the processor 502. The memory 504 may store instructions executable by the processor 502 to implement the functions of the computing device 500. The computing device 500 further includes a processing engine 506. The processing engine 506 is configured to receive, at a receiver, sample symbols. The processing engine 506 is further configured to initialize, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol. Responsive to convergence of symbol synchronization, the processing engine 506 is further configured to remove cyclic prefix. Responsive to convergence of symbol synchronization, the processing engine 506 is further configured to compute Wigner transform to convert the symbols from time domain to frequency domain. Responsive to convergence of symbol synchronization, the processing engine 506 is further configured to compute symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain. Responsive to convergence of symbol synchronization, the processing engine 506 is further configured to compute absolute values of the received sample symbols in the delay-Doppler domain.
[0044] FIG. 6 illustrates an exemplary schematic block diagram of a hardware platform for implementing the computing device 500 of FIG. 5. As shown in FIG. 6, a computer system 600 can include an external storage device 610, a bus 620, a main memory 630, a read only memory 640, a mass storage device 650, communication port 560, and a processor 670. A person skilled in the art will appreciate that the computer system may include more than one processor and communication ports. Examples of processor 670 include, but are not limited to, an Intel® Itanium® or Itanium 2 processor(s), or AMD® Opteron® or Athlon MP® processor(s), Motorola® lines of processors, FortiSOC™ system on chip processors or other future processors. Processor 670 may include various modules associated with embodiments of the present invention. Communication port 560 can be any of an RS-232 port for use with a modem-based dialup connection, a 10/100 Ethernet port, a Gigabit or 10 Gigabit port using copper or fiber, a serial port, a parallel port, or other existing or future ports. Communication port 560 may be chosen depending on a network, such a Local Area Network (LAN), Wide Area Network (WAN), or any network to which computer system connects. Memory 630 can be Random Access Memory (RAM), or any other dynamic storage device commonly known in the art. Read-only memory 640 can be any static storage device(s) e.g., but not limited to, a Programmable Read Only Memory (PROM) chips for storing static information e.g., start-up or BIOS instructions for processor 670. Mass storage 650 may be any current or future mass storage solution, which can be used to store information and/or instructions. Exemplary mass storage solutions include, but are not limited to, Parallel Advanced Technology Attachment (PATA) or Serial Advanced Technology Attachment (SATA) hard disk drives or solid-state drives (internal or external, e.g., having Universal Serial Bus (USB) and/or Firewire interfaces), e.g. those available from Seagate (e.g., the Seagate Barracuda 7102 family) or Hitachi (e.g., the Hitachi Deskstar 7K1000), one or more optical discs, Redundant Array of Independent Disks (RAID) storage, e.g. an array of disks (e.g., SATA arrays), available from various vendors including Dot Hill Systems Corp., LaCie, Nexsan Technologies, Inc. and Enhance Technology, Inc.
[0045] Bus 620 communicatively couples processor(s) 670 with the other memory, storage, and communication blocks. Bus 620 can be, e.g., a Peripheral Component Interconnect (PCI) / PCI Extended (PCI-X) bus, Small Computer System Interface (SCSI), USB or the like, for connecting expansion cards, drives and other subsystems as well as other buses, such a front side bus (FSB), which connects processor 670 to software system.
[0046] Optionally, operator and administrative interfaces, e.g., a display, keyboard, and a cursor control device, may also be coupled to bus 620 to support direct operator interaction with a computer system. Other operator and administrative interfaces can be provided through network connections connected through communication port 560. The external storage device 610 can be any kind of external hard-drives, floppy drives, IOMEGA® Zip Drives, Compact Disc - Read Only Memory (CD-ROM), Compact Disc-Re-Writable (CD-RW), Digital Video Disk-Read Only Memory (DVD-ROM). Components described above are meant only to exemplify various possibilities. In no way should the aforementioned exemplary computer system limit the scope of the present disclosure.
[0047] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprise” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0048] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF INVENTION
[0049] The present invention provides a method and system for wireless communication.
[0050] The present invention provides a method for two-level threshold-based technique for estimating channel parameters, IQ imbalance parameters for an OFDM based OTFS system under time varying wireless communication channels.
, Claims:1. A method (400) for wireless communication comprising:
receiving, at a computing device coupled to a receiver, sample symbols;
initializing, at the computing device, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol;
wherein, responsive to convergence of symbol synchronization, the method further comprises:
removing, at the computing device, cyclic prefix;
computing, at the computing device, Wigner transform to convert the symbols from time domain to frequency domain;
computing, at the computing device, symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and
computing, by the computing device, absolute values of the received sample symbols in the delay-Doppler domain.
2. The method (400) as claimed in claim 1, wherein the method (400) further comprises:
determining, at the computing device, if the absolute values of the symbols exceed a first threshold value; and
determining, responsive to the absolute values of the symbols exceeding the first threshold value, at the computing device, if the absolute values of the symbols exceed a second threshold value,
wherein, a mirror path is deemed to exist if the absolute values of the symbols exceed the second threshold value.
3. The method (400) as claimed in claim 2, wherein, if the absolute values of the symbols do not exceed the first threshold value, it is deemed that no delay-Doppler path exists.

4. The method (400) as claimed in claim 2, wherein, if the absolute values of the symbols do not exceed the second threshold value, it is deemed that no mirror path exists.
5. The method (400) as claimed in claim 2, wherein the method (400) further comprises determining, at the computing device, responsive to the absolute values of the symbols exceeding the second threshold value, channel coefficients.
6. The method (400) as claimed in claim 5, wherein the method (400) further comprises determining, at the computing device, IQ imbalance coefficients.
7. The method (400) as claimed in claim 6, wherein the method (400) further comprises compensating, at the computing device, the symbols for the IQ imbalance coefficients to obtain the symbols without IQ imbalance.
8. The method (400) as claimed in claim 7, wherein the method (400) further comprises detecting, by the computing device, the data using any one of a message passing based detector, and minimum mean square error-based detector.
9. The method (400) as claimed in claim 8, wherein the method (400) further comprises storing, at the computing device, the data.
10. A system (500) for wireless communication comprising:
a computing device configured to:
receive, at a receiver, sample symbols;
initialize, responsive to receiving a start of frame from a transmitter, symbol synchronization to find an optimal transmitted symbol;
wherein, responsive to convergence of symbol synchronization, the computing device is further configured to:
remove cyclic prefix;
compute Wigner transform to convert the symbols from time domain to frequency domain;

compute symplectic finite Fourier transform to convert the symbols from frequency domain to delay-Doppler domain; and
compute absolute values of the received sample symbols in the delay-Doppler domain.