FIELD OF INVENTION
[0001] The embodiments herein relate a communication system, and more specifically to a channel estimation method in a Long Term Evolution (LTE) system.
BACKGROUND
[0002] Channel estimation is one of important functions in any cellular system (e.g., LTE system). A signal at a receiver is usually degraded due to path loss, multipath-fading, additive channel noise, etc. The channel estimation helps in equalizing these impairing factors (e.g., path loss, multipath-fading, additive channel noise, etc) before the received signal is decoded. Further, based on channel state information feedback from the receiver, a transmitter decides best coding and modulation schemes for achieving the maximal capacity.
[0003] In order to support high data rates and low system delay, the LTE system employs Orthogonal Frequency Division Multiplexing (OFDM) technology both in an uplink signal and a downlink signal. The OFDM makes the channel estimation in a frequency domain particularly interesting because of orthogonal subcarriers.
[0004] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.
OBJECT OF INVENTION
[0005] The principal object of the embodiments herein to provide a channel estimation method in a LTE system.
[0006] Another object of the embodiments herein is to compute a channel SNR based on received reference signals.

[0007] Another object of the embodiments herein is to compare the computed channel SNR with a threshold.
[0008] Another object of the embodiments herein is to perform one of: repetition of an estimated channel response at Resource Elements (REs)
> mapped with the received reference signals to neighboring REs in
neighboring subcarriers when the computed channel SNR is greater than
the threshold, and a linear interpolation to estimate channels at the
subcarriers located in-between two subcarriers carrying the received
reference signals when the computed channel SNR is lower than the
i threshold.
SUMMARY [0009] Embodiments herein disclose a channel estimation method in a LTE system. The method includes computing a channel SNR based on received reference signals. Further, the method includes comparing the
> computed channel SNR with a threshold. Further, the method includes
performing one of: repetition of an estimated channel response at REs
mapped with the received reference signals to neighboring REs in
neighboring subcarriers when the computed channel SNR is greater than
the threshold, and a linear interpolation to estimate channels at the
i subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0010] In an embodiment, the method further includes recomputing channel SNR while performing repetition of the estimated channel response
i at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. Further, the method includes determining that the channel SNR is lower than the threshold. Further, the method includes adaptively switching the channel estimation to the linear

interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0011] In an embodiment, the method further includes recomputing channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. Further, the method includes determining that the channel SNR is higher than the threshold. Further, the method includes adaptively switching the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0012] Embodiments herein disclose a User Equipment (UE) for performing a channel estimation in a LTE system. The UE includes a channel SNR computation unit configured to compute a channel SNR based on received reference signals. A comparison unit is configured to compare the computed channel SNR with a threshold. A channel estimation unit is configured to adaptively perform one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0013] Embodiment herein provides a computer program product including a computer executable program code recorded on a computer readable non-transitory storage medium. The computer executable program code when executed causing the actions including computing a channel SNR based on received reference signals. The computer executable program code when executed causing the actions including comparing the computed channel SNR with a threshold. The computer executable

program code when executed causing the actions including performing one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0014] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0015] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0016] FIG. 1 is an overview of a LTE system for channel estimation, according to the embodiments as disclosed herein;
[0017] FIG. 2 is a schematic of a LTE downlink frame structure;
[0018] FIGS. 3a and FIGS.3b are schematic illustration of reference signal mapping to REs corresponding to one transmitting antenna port and two transmitting antenna ports, respectively;
[0019] FIG. 4 is a schematic illustration of channel estimation at reference signal REs, according to the embodiments as disclosed herein;

[0020] FIG. 5 is a schematic illustration of repetition of channel estimation for flat fading, according to the embodiments as disclosed herein;
[0021] FIG. 6 illustrates various units of an UE for channel estimation, according to the embodiments as disclosed herein;
[0022] FIG. 7 is flow diagram illustrating a channel estimation method by the UE in a LTE system, according to the embodiments as disclosed herein; and
[0023] FIG. 8 illustrates a computing environment implementing a mechanism for the channel estimation in the LTE system, according to embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0025] Embodiments herein provide a channel estimation method in a Long Term Evolution system. The method includes computing a channel SNR based on received reference signals. Further, the method includes comparing the computed channel SNR with a threshold. Further, the method includes performing one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0026] Unlike the conventional methods, the proposed method performs the channel estimation with low complexity and more accurate manner.

[0027] Referring now to the drawings, and more particularly to FIGS. 1 through 8, there are shown preferred embodiments.
[0028] FIG. 1 is an overview of a LTE system 100 for channel estimation, according to the embodiments as disclosed herein. The LTE system 100 includes a UE 102 and a cell 104. The UE 102 may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, or the like. The UE 102 can be, for example but not limited to, a cellular phone, a Personal Digital Assistant (PDA), a wireless communication device, a handheld device, a laptop computer, or the like.
[0029] The UE 102 is configured to compute a channel Signal-to-Noise Ratio (SNR) based on received reference signals. Further, the UE 102 is configured to compare the computed channel SNR with a threshold. Further, the UE 102 is configured to perform one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0030] In an embodiment, the UE 102 is configured to re-compute channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. Further, the UE 102 is configured to determine that the channel SNR is lower than the threshold. Further, the UE 102 is configured to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0031] In an embodiment, the UE 102 is configured to re-compute channel SNR while performing the linear interpolation for estimating

channels at the subcarriers located in-between two subcarriers carrying the received reference signals. Further, the UE 102 is configured to determine that the channel SNR is higher than the threshold. Further, the UE 102 is configured to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
r00321LTE Downlink Frame Structure: The LTE system 100 specifies two types of radio frame structures: Type 1 (also called Frequency Division Duplex (FDD)) and Type 2 (also called Time Division Duplex (TDD)). Both structures are specified over the radio frame timing of 10 msec. Each radio frame consists of 20 slots numbered from 0 to 19, and one slot duration is 0.5 msec. Alternatively, the radio frame consists of 10 subframes, where each subframe spanning two slots or 1 msec. Each slot consists of 7 OFDM symbols or 6 OFDM symbols depending on whether the cyclic prefix is of type normal or extended, respectively.
[0033] In the frequency domain, the signal in each slot is described by a resource grid of the subcarriers. 12 subcarriers make a Resource Block (RB). The subcarriers have a spacing of 15 KHz, thus each RB spans 180 KHz in the frequency domain. The RBs consist of resource elements. Each resource element corresponds to one subcarrier in the frequency domain and one OFDM symbol in the time domain. The LTE radio frame structure in a time domain and a frequency domain is shown in the FIG. 2
[0034] Cell-specific Reference Signals in LTE: The LTE specification mandates that the cell-specific reference signals is transmitted in all downlink subframes on one or several of antenna ports 0 to 3. The cell-specific reference signals are defined for subcarrier spacing of 15 kHz only.
[0035] The reference signal sequence rjn (ra)is defined by

1 ( 1 ^
rins(m)=-j=\l-2*c(2m)) + j-j={l-2*c(2m + iy))m = 0,l,...2*AC-l where yi is the slot number within the radio frame, / is the OFDM symbol
number within the slot, and ACT 1S tne maximum number of resource
blocks allowable. c(i) is a pseudorandom sequence defined by the standard and is given in section 7.2 of the specification. The pseudo-random sequence generator shall be initialized with C;nit given as
c,mt = 210 * (7 * (/i, +1)+/+1)* (2 * AC+1)+ (2 * AC + Nj
Cell
where ]\f denotes the physical layer ID of the cell, and NCP is equal to 1
for normal CP and 0 for the extended CP.
[0036] From the above equations indicate that the reference signal sequences are different in different OFDM symbols in the frame, but they are repeated at every frame. Further, the number of reference signals is two times the number of RBs, indicating that each OFDM symbol carrying a reference signal will have only two REs per RB reserved for the reference signals. Further, the reference signal values belong to the QPSK constellation. Therefore, they have unit norms.
[0037] Mapping to resource elements: The reference signal mapping to the resource elements depends on the number of transmitting antenna ports. In case of one transmitting antenna, they are transmitted on the 1st and 5th OFDM symbols of each slot for normal CP and on the 1st and 4* OFDM symbols of each slot for extended CP. Out of 12 sub carriers in the RB, only 2 subcarriers are used for transmitting the reference signals. These two subcarriers are placed 6 REs apart. The reference signal RE locations in 5* OFDM symbol (or 4* OFDM symbol) are staggered by 3 REs from the reference signal REs in the 1st OFDM symbol. The location

of the first reference signal RE is offset from the 1st RE in the RB by
Cell
number given as d= ]\[ mod 6. Therefore, every sixth cell will have the
same REs for the reference signal mapping.
[0038] For two transmitting antenna ports, the reference signals transmitted by the two antennas are the same, but their RE mappings are different. The reference signal REs in 1st and 5* OFDM symbols (or the 4* ODFM symbol for extended CP) for the first antenna are swapped in the second antenna. That is, the reference signal REs in 1st OFDM symbol for the first antenna are the same as the reference signal REs in 5* OFDM symbol for the second antenna, and the reference signal REs in the 5* OFDM symbol for the first antenna are the same as the as the reference signal REs in 1st OFDM symbol for the second antenna. The LTE specifies that the resource elements used for reference signal transmission on any of the antenna ports in the slot shall not be used for any transmission on any other antenna port in the same slot and is set to zero. Therefore the REs used by the 2n antenna port are reserved by the 1st antenna and vice versa.
[0039] As shown in the FIG. 3a and FIG. 3b, for four transmitting antenna ports, the RE mapping of the reference signals in the 1st and 2n antenna ports are identical to those in the case of two antenna ports. In the 3r and 4* antenna ports, the reference signals are transmitted on only the 2n OFDM symbol of each slot. The REs in the even numbered slots correspond to the same subcarriers as the REs in the 1st OFDM symbol of the 1st antenna whereas the REs in the odd-numbered slots correspond to the same subcarriers as the REs in the 5* OFDM symbol. The RE locations in the 3r antenna port are swapped in the 4* antenna port.
[0040] Frequency-domain Channel Estimation: The LTE standard uses the OFDMA in the downlink. In OFDMA, the eNodeB maps the data and control signals to different REs in the OFDM symbol before applying the inverse FFT. The OFDM symbol in the time domain consists of output

of the IFFT operation. Since the symbols are always prefixed with CPs, the effect of the multipath channel can be seen as a circular convolution instead of the regular linear convolution. Therefore, in the frequency domain, the received signal will be the element-wise product of the actual data elements and the FFT of the channel filter. Any additive channel noise will result in an additive noise component in the frequency domain. The application of the forward FFT at the UE 102 therefore will result in the following received signal.
x(k) = H(k)S(k) + N(k\k = 0X-.,(NRB *NSC -1) where k denotes the index of the RE, H(k) denotes the Discrete Fourier Transform (DFT) of the channel filter at the k1 subcarrier, s(k) denotes the transmitted signal at the M* subcarrier and N (k) denotes the additive noise component.
[0041] The proposed method assumes that channel remains constant over one slot period (0.5 milliseconds). Therefore, the proposed method estimates the channel over only one OFDM symbol per slot. The method does it for the first OFDM symbol in each slot. The channel response estimated at one RE in the first OFDM symbol is used to equalize the channels corresponding to the same subcarriers in the other OFDM symbols in the same slot.
[0042] Proposed channel estimation procedure consists of two steps: estimation of channel response at reference signal REs (RS-RE) and estimation of channel response at the non-reference signal REs (NRS-RE).
[0043] Estimation of channel response at reference signal REs: Once the initial cell search is over, the cell ID is known to the UE 102. Thus the UE 102 can compute the indices of the REs on which the reference signals are mapped. Furthermore, the UE 102 can compute the reference signal values. For a normal CP, the reference signals are transmitted on the 1st and the 5* OFDM signals. The method collects the

signals received at the reference signal REs in these two symbols and arranges them in the order of their indices. The signals in the two OFDM symbols are offset by 3 REs, thus there are 4 REs per RB where the reference signals are mapped. The method estimates the channels at these REs as:
£=^,* = *0,*0+3,*o+6,...*m r(k)
where x(k) denotes the received signal at the k* RE and r(k) denotes the reference signal mapped to that RE. k0 denotes the index of the starting reference signal RE, and kmax denotes the last index for the reference signal. In the case of two transmitting antennas, the method utilizes the same reference signals REs but swap the 1st and fifth OFDM symbols.
[0044] Since the reference signals have unit norms, the estimation can be equivalently expressed
H = x(k)r(k)*
where * denotes the complex conjugate operator. This requires less complexity since the complex division operation requires more complexity than complex multiplication. Further, since the reference signals belong to the QPSK modulation constellation, this multiplication can be further simplified by addition and subtraction of the real and imaginary coefficients of x(k) together with only one multiplication. For example, let
x(k) = xr+ jxt and let r(k) = (1 + j) 142 .
then,
[0045] Estimation of channel response at the non-reference signal REs:
[0046] To estimate the channels corresponding to the remaining subcarriers, the method follows two approaches:

[0047] Repetition: In the context of OFDM applications, the channels are usually assumed to be flat-fading, that is, the channel response at the neighboring subcarriers are almost identical. This is typically true in the case of LTE where the number of multipaths can be much less compared to the size of the FFT/IFFT. Therefore, the method repeats the estimated channel response at the REs mapped with reference signals to the neighboring REs as shown in the FIG. 5:
[0048] The advantage of this estimation procedure is low complexity. In the case of two transmitting antennas and two receiving antennas (spatial multiplexing in MTMO), it has the further advantage of reducing the complexity of computing matrix inversion by three times since the method can use the same matrix at three REs.
[0049] Linear Interpolation: For a more accurate channel estimate, the method proposes a linear estimation method as follows:
For k = k0X+^k0+6,....krmK
H(k + l) = ^H(k) + ±H(k + 3)
H(k + 2) = ^H(k) + ^H(k + 3)
[0050] Clearly, interpolation requires more complexity than the simple repetition approach. Therefore, the proposed method utilizes the linear interpolation when the channel SNR is low. In the case of the high SNR, the proposed method utilizes the repetition approach.
[0051] Estimation of Channel SNR: The channel SNR can be estimated based on the received reference signals. Since the channel is assumed to be flat-fading, over a few consecutive RBS, the channel can be assumed to be constant. Let us divide the available RBs for an OFDM symbol into sets of consecutive RBs. Each set is called a subband. Over the i* subband, the received reference signal can be modeled as

x(k) = Htr(k) + N(k) where Hi denotes the average channel response over all the RBs in the i* subband. An Maximum Likelihood (ML) estimate of Hi is given as
H S>(*)**(*)
[0052] Based on this estimate, the ML estimate of the channel SNR over the i* subband is given as
( Y \x(k)*r(k)\2 *)
SNR, =\0hgw — , ~k , ' dB
[0053] The average SNR over the entire bandwidth can be
estimated as the average of all the subband SNRs:
1 L_1 SNR = —YdSNRi
L i=o
where L denotes the total number of subbands
[0054] Let SNRth denotes the SNR threshold for selecting the channel estimation method. If SNR > SNRth, then the method applies the
repetition approach, else the method applies the linear estimation.
[0055] FIG. 6 illustrates various units of the UE 102, according to the embodiments as disclosed herein. In an embodiment, the UE 102 includes a SNR value computation unit 602, a SNR value comparison unit 604, and a channel information estimation unit 606. The channel SNR computation unit 602 is configured to compute the channel SNR based on the received reference signals. The SNR value comparison unit 604 is configured to compare the computed channel SNR with the threshold. Based on the comparison, the channel information estimation unit 606 is configured to adaptively perform one of: repetition of the estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater

than the threshold, and the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0056] In an embodiment, the SNR value computation unit 602 is configured to re-compute channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. The SNR value comparison unit 604 is configured to determine that the channel SNR is lower than the threshold. The channel information estimation unit 606 is configured to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0057] In an embodiment, the SNR value computation unit 602 is configured to re-compute the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. The SNR value comparison unit 604 is configured to determine that the channel SNR is higher than the threshold. The channel information estimation unit 606 is configured to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0058] Although FIG. 6 shows exemplary units of the UE 102, in other implementations, the UE 102 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 6. Additionally or alternatively, one or more components of the UE 102 may perform functions described as being performed by one or more other components of the UE 102.

[0059] FIG. 7 is flow diagram 700 illustrating the channel estimation method in the LTE system 100, according to the embodiments as disclosed herein. At step 702, the method includes computing the channel SNR based on the received reference signals. In an embodiment, the method allows the SNR value computation unit 602 to compute the channel SNR based on the received reference signals. At step 704, the method includes comparing the computed channel SNR with the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to compare the computed channel SNR with the threshold.
[0060] If the computed channel SNR is greater than the threshold, at step 706a, the method includes performing repetition of the estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers. In an embodiment, the method allows the channel information estimation unit 606 to perform the repetition of the estimated channel response at the REs mapped with the received reference signals to neighboring REs in neighboring subcarriers.
[0061] If the computed channel SNR is lower than the threshold, at step 706b, the method includes performing the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the channel information estimation unit 606 to perform the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0062] At step 708a, the method includes re-computing the channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. In an embodiment, the method allows the SNR value computation unit 602 to recompute the channel SNR while performing repetition of the estimated channel response at the REs mapped

with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0063] At step 710a, the method includes determining that the channel SNR is lower than the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to determine that the channel SNR is lower than the threshold.
[0064] At step 712a, the method includes adaptively switching the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the channel information estimation unit 606 to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0065] At step 708b, the method includes re-computing the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the SNR value computation unit 602 to recompute the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0066] At step 710b, the method includes determining that the channel SNR is higher than the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to determine that the channel SNR is higher than the threshold.
[0067] At step 712b, the method includes adaptively switching the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. In an embodiment, the method allows the channel information estimation unit 606 to adaptively switch the channel

estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0068] The various actions, acts, blocks, steps, and the like in the flow diagram 700 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions, acts, blocks, steps, and the like may be omitted, added, modified, skipped, and the like without departing from the scope of the invention.
[0069] FIG. 8 illustrates a computing environment 802 implementing a mechanism for channel estimation in the LTE system 100, according to the embodiments as disclosed herein. The computing environment 802 comprises at least one processing unit 808 that is equipped with a control unit 804, an Arithmetic Logic Unit (ALU) 806, a memory 810, a storage unit 812, a plurality of networking devices 816 and a plurality Input / Output (I/O) devices 814. The processing unit 808 is responsible for processing the instructions of the technique. The processing unit 808 receives commands from the control unit 804 in order to perform its processing. Further, any logical and arithmetic operations involved in the execution of the instructions are computed with the help of the ALU 806.
[0070] The overall computing environment 802 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 808 is responsible for processing the instructions of the technique. Further, the plurality of processing units 804 may be located on a single chip or over multiple chips.
[0071] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 810 or the storage 812 or both. At the time of execution, the instructions may be

fetched from the corresponding memory 810 or storage 812, and executed by the processing unit 808.
[0072] In case of any hardware implementations various networking devices 816 or external I/O devices 814 may be connected to the computing environment 802 to support the implementation through the networking unit and the I/O device unit.
[0073] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in the FIGS. 1 through 8 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.
[0074] 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 embodiments as described herein.
Claims:STATEMENT OF CLAIMS
I Claim:
1. A channel estimation method in a Long Term Evolution (LTE) system, the method comprising:
computing a channel Signal-to-Noise Ratio (SNR) based on received reference signals;
comparing the computed channel SNR with a threshold;
performing one of: repetition of an estimated channel response at Resource Elements (REs) mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
2. The method of claim 1, wherein the method further comprises:
recomputing channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers;
determining that the channel SNR is lower than the threshold; and
adaptively switching the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals
3. The method of claim 1, wherein the method further comprises:
recomputing channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals;
determining that the channel SNR is higher than the threshold; and
adaptively switching the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
4. A User Equipment (UE) for performing a channel estimation in a Long Term Evolution (LTE) system, the UE comprising:
a channel Signal-to-Noise Ratio (SNR) computation unit configured to compute a channel SNR based on received reference signals;
a comparison unit configured to compare the computed channel SNR with a threshold;
a channel estimation unit configured to adaptively perform one of: repetition of an estimated channel response at Resource Elements (REs) mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
5. The UE of claim 4, wherein the UE further comprises:
the SNR computation unit configured to recompute channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers;
the comparison unit configured to determine that the channel SNR is lower than the threshold; and
the channel estimation unit configured to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
6. The UE of claim 4, wherein the UE further comprises:
the SNR computation unit configured to recompute the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals;
the comparison unit configured to determine that the channel SNR is higher than the threshold; and
the channel estimation unit configured to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.

Dated this 9th Day of February, 2017 Signatures:

Arun Kishore Narasani
Patent Agent
, Description:FIELD OF INVENTION
[0001] The embodiments herein relate a communication system, and more specifically to a channel estimation method in a Long Term Evolution (LTE) system.
BACKGROUND
[0002] Channel estimation is one of important functions in any cellular system (e.g., LTE system). A signal at a receiver is usually degraded due to path loss, multipath-fading, additive channel noise, etc. The channel estimation helps in equalizing these impairing factors (e.g., path loss, multipath-fading, additive channel noise, etc) before the received signal is decoded. Further, based on channel state information feedback from the receiver, a transmitter decides best coding and modulation schemes for achieving the maximal capacity.
[0003] In order to support high data rates and low system delay, the LTE system employs Orthogonal Frequency Division Multiplexing (OFDM) technology both in an uplink signal and a downlink signal. The OFDM makes the channel estimation in a frequency domain particularly interesting because of orthogonal subcarriers.
[0004] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.
OBJECT OF INVENTION
[0005] The principal object of the embodiments herein to provide a channel estimation method in a LTE system.
[0006] Another object of the embodiments herein is to compute a channel SNR based on received reference signals.
[0007] Another object of the embodiments herein is to compare the computed channel SNR with a threshold.
[0008] Another object of the embodiments herein is to perform one of: repetition of an estimated channel response at Resource Elements (REs) mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
SUMMARY
[0009] Embodiments herein disclose a channel estimation method in a LTE system. The method includes computing a channel SNR based on received reference signals. Further, the method includes comparing the computed channel SNR with a threshold. Further, the method includes performing one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0010] In an embodiment, the method further includes recomputing channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. Further, the method includes determining that the channel SNR is lower than the threshold. Further, the method includes adaptively switching the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0011] In an embodiment, the method further includes recomputing channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. Further, the method includes determining that the channel SNR is higher than the threshold. Further, the method includes adaptively switching the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0012] Embodiments herein disclose a User Equipment (UE) for performing a channel estimation in a LTE system. The UE includes a channel SNR computation unit configured to compute a channel SNR based on received reference signals. A comparison unit is configured to compare the computed channel SNR with a threshold. A channel estimation unit is configured to adaptively perform one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0013] Embodiment herein provides a computer program product including a computer executable program code recorded on a computer readable non-transitory storage medium. The computer executable program code when executed causing the actions including computing a channel SNR based on received reference signals. The computer executable program code when executed causing the actions including comparing the computed channel SNR with a threshold. The computer executable program code when executed causing the actions including performing one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0014] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0015] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0016] FIG. 1 is an overview of a LTE system for channel estimation, according to the embodiments as disclosed herein;
[0017] FIG. 2 is a schematic of a LTE downlink frame structure;
[0018] FIGS. 3a and FIGS.3b are schematic illustration of reference signal mapping to REs corresponding to one transmitting antenna port and two transmitting antenna ports, respectively;
[0019] FIG. 4 is a schematic illustration of channel estimation at reference signal REs, according to the embodiments as disclosed herein;
[0020] FIG. 5 is a schematic illustration of repetition of channel estimation for flat fading, according to the embodiments as disclosed herein;
[0021] FIG. 6 illustrates various units of an UE for channel estimation, according to the embodiments as disclosed herein;
[0022] FIG. 7 is flow diagram illustrating a channel estimation method by the UE in a LTE system, according to the embodiments as disclosed herein; and
[0023] FIG. 8 illustrates a computing environment implementing a mechanism for the channel estimation in the LTE system, according to embodiments as disclosed herein.
DETAILED DESCRIPTION OF INVENTION
[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term “or” as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0025] Embodiments herein provide a channel estimation method in a Long Term Evolution system. The method includes computing a channel SNR based on received reference signals. Further, the method includes comparing the computed channel SNR with a threshold. Further, the method includes performing one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0026] Unlike the conventional methods, the proposed method performs the channel estimation with low complexity and more accurate manner.
[0027] Referring now to the drawings, and more particularly to FIGS. 1 through 8, there are shown preferred embodiments.
[0028] FIG. 1 is an overview of a LTE system 100 for channel estimation, according to the embodiments as disclosed herein. The LTE system 100 includes a UE 102 and a cell 104. The UE 102 may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, or the like. The UE 102 can be, for example but not limited to, a cellular phone, a Personal Digital Assistant (PDA), a wireless communication device, a handheld device, a laptop computer, or the like.
[0029] The UE 102 is configured to compute a channel Signal-to-Noise Ratio (SNR) based on received reference signals. Further, the UE 102 is configured to compare the computed channel SNR with a threshold. Further, the UE 102 is configured to perform one of: repetition of an estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and a linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0030] In an embodiment, the UE 102 is configured to re-compute channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. Further, the UE 102 is configured to determine that the channel SNR is lower than the threshold. Further, the UE 102 is configured to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0031] In an embodiment, the UE 102 is configured to re-compute channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. Further, the UE 102 is configured to determine that the channel SNR is higher than the threshold. Further, the UE 102 is configured to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0032] LTE Downlink Frame Structure: The LTE system 100 specifies two types of radio frame structures: Type 1 (also called Frequency Division Duplex (FDD)) and Type 2 (also called Time Division Duplex (TDD)). Both structures are specified over the radio frame timing of 10 msec. Each radio frame consists of 20 slots numbered from 0 to 19, and one slot duration is 0.5 msec. Alternatively, the radio frame consists of 10 subframes, where each subframe spanning two slots or 1 msec. Each slot consists of 7 OFDM symbols or 6 OFDM symbols depending on whether the cyclic prefix is of type normal or extended, respectively.
[0033] In the frequency domain, the signal in each slot is described by a resource grid of the subcarriers. 12 subcarriers make a Resource Block (RB). The subcarriers have a spacing of 15 KHz, thus each RB spans 180 KHz in the frequency domain. The RBs consist of resource elements. Each resource element corresponds to one subcarrier in the frequency domain and one OFDM symbol in the time domain. The LTE radio frame structure in a time domain and a frequency domain is shown in the FIG. 2
[0034] Cell-specific Reference Signals in LTE: The LTE specification mandates that the cell-specific reference signals is transmitted in all downlink subframes on one or several of antenna ports 0 to 3. The cell-specific reference signals are defined for subcarrier spacing of 15 kHz only.
[0035] The reference signal sequence is defined by
(m)=
where is the slot number within the radio frame, l is the OFDM symbol number within the slot, and is the maximum number of resource blocks allowable. c(i) is a pseudorandom sequence defined by the standard and is given in section 7.2 of the specification. The pseudo-random sequence generator shall be initialized with Cinit given as

where denotes the physical layer ID of the cell, and NCP is equal to 1 for normal CP and 0 for the extended CP.
[0036] From the above equations indicate that the reference signal sequences are different in different OFDM symbols in the frame, but they are repeated at every frame. Further, the number of reference signals is two times the number of RBs, indicating that each OFDM symbol carrying a reference signal will have only two REs per RB reserved for the reference signals. Further, the reference signal values belong to the QPSK constellation. Therefore, they have unit norms.
[0037] Mapping to resource elements: The reference signal mapping to the resource elements depends on the number of transmitting antenna ports. In case of one transmitting antenna, they are transmitted on the 1st and 5th OFDM symbols of each slot for normal CP and on the 1st and 4th OFDM symbols of each slot for extended CP. Out of 12 subcarriers in the RB, only 2 subcarriers are used for transmitting the reference signals. These two subcarriers are placed 6 REs apart. The reference signal RE locations in 5th OFDM symbol (or 4th OFDM symbol) are staggered by 3 REs from the reference signal REs in the 1st OFDM symbol. The location of the first reference signal RE is offset from the 1st RE in the RB by number given as d= mod 6. Therefore, every sixth cell will have the same REs for the reference signal mapping.
[0038] For two transmitting antenna ports, the reference signals transmitted by the two antennas are the same, but their RE mappings are different. The reference signal REs in 1st and 5th OFDM symbols (or the 4th ODFM symbol for extended CP) for the first antenna are swapped in the second antenna. That is, the reference signal REs in 1st OFDM symbol for the first antenna are the same as the reference signal REs in 5th OFDM symbol for the second antenna, and the reference signal REs in the 5th OFDM symbol for the first antenna are the same as the as the reference signal REs in 1st OFDM symbol for the second antenna. The LTE specifies that the resource elements used for reference signal transmission on any of the antenna ports in the slot shall not be used for any transmission on any other antenna port in the same slot and is set to zero. Therefore the REs used by the 2nd antenna port are reserved by the 1st antenna and vice versa.
[0039] As shown in the FIG. 3a and FIG. 3b, for four transmitting antenna ports, the RE mapping of the reference signals in the 1st and 2nd antenna ports are identical to those in the case of two antenna ports. In the 3rd and 4th antenna ports, the reference signals are transmitted on only the 2nd OFDM symbol of each slot. The REs in the even numbered slots correspond to the same subcarriers as the REs in the 1st OFDM symbol of the 1st antenna whereas the REs in the odd-numbered slots correspond to the same subcarriers as the REs in the 5th OFDM symbol. The RE locations in the 3rd antenna port are swapped in the 4th antenna port.
[0040] Frequency-domain Channel Estimation: The LTE standard uses the OFDMA in the downlink. In OFDMA, the eNodeB maps the data and control signals to different REs in the OFDM symbol before applying the inverse FFT. The OFDM symbol in the time domain consists of output of the IFFT operation. Since the symbols are always prefixed with CPs, the effect of the multipath channel can be seen as a circular convolution instead of the regular linear convolution. Therefore, in the frequency domain, the received signal will be the element-wise product of the actual data elements and the FFT of the channel filter. Any additive channel noise will result in an additive noise component in the frequency domain. The application of the forward FFT at the UE 102 therefore will result in the following received signal.

where k denotes the index of the RE, H(k) denotes the Discrete Fourier Transform (DFT) of the channel filter at the kth subcarrier, s(k) denotes the transmitted signal at the Mth subcarrier and N (k) denotes the additive noise component.
[0041] The proposed method assumes that channel remains constant over one slot period (0.5 milliseconds). Therefore, the proposed method estimates the channel over only one OFDM symbol per slot. The method does it for the first OFDM symbol in each slot. The channel response estimated at one RE in the first OFDM symbol is used to equalize the channels corresponding to the same subcarriers in the other OFDM symbols in the same slot.
[0042] Proposed channel estimation procedure consists of two steps: estimation of channel response at reference signal REs (RS-RE) and estimation of channel response at the non-reference signal REs (NRS-RE).
[0043] Estimation of channel response at reference signal REs: Once the initial cell search is over, the cell ID is known to the UE 102. Thus the UE 102 can compute the indices of the REs on which the reference signals are mapped. Furthermore, the UE 102 can compute the reference signal values. For a normal CP, the reference signals are transmitted on the 1st and the 5th OFDM signals. The method collects the signals received at the reference signal REs in these two symbols and arranges them in the order of their indices. The signals in the two OFDM symbols are offset by 3 REs, thus there are 4 REs per RB where the reference signals are mapped. The method estimates the channels at these REs as:
=
where x(k) denotes the received signal at the kth RE and r(k) denotes the reference signal mapped to that RE. k0 denotes the index of the starting reference signal RE, and kmax denotes the last index for the reference signal. In the case of two transmitting antennas, the method utilizes the same reference signals REs but swap the 1st and fifth OFDM symbols.
[0044] Since the reference signals have unit norms, the estimation can be equivalently expressed

where * denotes the complex conjugate operator. This requires less complexity since the complex division operation requires more complexity than complex multiplication. Further, since the reference signals belong to the QPSK modulation constellation, this multiplication can be further simplified by addition and subtraction of the real and imaginary coefficients of x(k) together with only one multiplication. For example, let and let .
then,

[0045] Estimation of channel response at the non-reference signal REs:
[0046] To estimate the channels corresponding to the remaining subcarriers, the method follows two approaches:
[0047] Repetition: In the context of OFDM applications, the channels are usually assumed to be flat-fading, that is, the channel response at the neighboring subcarriers are almost identical. This is typically true in the case of LTE where the number of multipaths can be much less compared to the size of the FFT/IFFT. Therefore, the method repeats the estimated channel response at the REs mapped with reference signals to the neighboring REs as shown in the FIG. 5:
[0048] The advantage of this estimation procedure is low complexity. In the case of two transmitting antennas and two receiving antennas (spatial multiplexing in MIMO), it has the further advantage of reducing the complexity of computing matrix inversion by three times since the method can use the same matrix at three REs.
[0049] Linear Interpolation: For a more accurate channel estimate, the method proposes a linear estimation method as follows:
For


[0050] Clearly, interpolation requires more complexity than the simple repetition approach. Therefore, the proposed method utilizes the linear interpolation when the channel SNR is low. In the case of the high SNR, the proposed method utilizes the repetition approach.
[0051] Estimation of Channel SNR: The channel SNR can be estimated based on the received reference signals. Since the channel is assumed to be flat-fading, over a few consecutive RBS, the channel can be assumed to be constant. Let us divide the available RBs for an OFDM symbol into sets of consecutive RBs. Each set is called a subband. Over the ith subband, the received reference signal can be modeled as

where denotes the average channel response over all the RBs in the ith subband. An Maximum Likelihood (ML) estimate of is given as

[0052] Based on this estimate, the ML estimate of the channel SNR over the ith subband is given as
dB
[0053] The average SNR over the entire bandwidth can be estimated as the average of all the subband SNRs:

where L denotes the total number of subbands
[0054] Let SNRth denotes the SNR threshold for selecting the channel estimation method. If , then the method applies the repetition approach, else the method applies the linear estimation.
[0055] FIG. 6 illustrates various units of the UE 102, according to the embodiments as disclosed herein. In an embodiment, the UE 102 includes a SNR value computation unit 602, a SNR value comparison unit 604, and a channel information estimation unit 606. The channel SNR computation unit 602 is configured to compute the channel SNR based on the received reference signals. The SNR value comparison unit 604 is configured to compare the computed channel SNR with the threshold. Based on the comparison, the channel information estimation unit 606 is configured to adaptively perform one of: repetition of the estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers when the computed channel SNR is greater than the threshold, and the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals when the computed channel SNR is lower than the threshold.
[0056] In an embodiment, the SNR value computation unit 602 is configured to re-compute channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. The SNR value comparison unit 604 is configured to determine that the channel SNR is lower than the threshold. The channel information estimation unit 606 is configured to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0057] In an embodiment, the SNR value computation unit 602 is configured to re-compute the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. The SNR value comparison unit 604 is configured to determine that the channel SNR is higher than the threshold. The channel information estimation unit 606 is configured to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0058] Although FIG. 6 shows exemplary units of the UE 102, in other implementations, the UE 102 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 6. Additionally or alternatively, one or more components of the UE 102 may perform functions described as being performed by one or more other components of the UE 102.
[0059] FIG. 7 is flow diagram 700 illustrating the channel estimation method in the LTE system 100, according to the embodiments as disclosed herein. At step 702, the method includes computing the channel SNR based on the received reference signals. In an embodiment, the method allows the SNR value computation unit 602 to compute the channel SNR based on the received reference signals. At step 704, the method includes comparing the computed channel SNR with the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to compare the computed channel SNR with the threshold.
[0060] If the computed channel SNR is greater than the threshold, at step 706a, the method includes performing repetition of the estimated channel response at REs mapped with the received reference signals to neighboring REs in neighboring subcarriers. In an embodiment, the method allows the channel information estimation unit 606 to perform the repetition of the estimated channel response at the REs mapped with the received reference signals to neighboring REs in neighboring subcarriers.
[0061] If the computed channel SNR is lower than the threshold, at step 706b, the method includes performing the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the channel information estimation unit 606 to perform the linear interpolation to estimate channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0062] At step 708a, the method includes re-computing the channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. In an embodiment, the method allows the SNR value computation unit 602 to recompute the channel SNR while performing repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0063] At step 710a, the method includes determining that the channel SNR is lower than the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to determine that the channel SNR is lower than the threshold.
[0064] At step 712a, the method includes adaptively switching the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the channel information estimation unit 606 to adaptively switch the channel estimation to the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0065] At step 708b, the method includes re-computing the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals. In an embodiment, the method allows the SNR value computation unit 602 to recompute the channel SNR while performing the linear interpolation for estimating channels at the subcarriers located in-between two subcarriers carrying the received reference signals.
[0066] At step 710b, the method includes determining that the channel SNR is higher than the threshold. In an embodiment, the method allows the SNR value comparison unit 604 to determine that the channel SNR is higher than the threshold.
[0067] At step 712b, the method includes adaptively switching the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers. In an embodiment, the method allows the channel information estimation unit 606 to adaptively switch the channel estimation to repetition of the estimated channel response at the REs mapped with the received reference signals to the neighboring REs in the neighboring subcarriers.
[0068] The various actions, acts, blocks, steps, and the like in the flow diagram 700 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions, acts, blocks, steps, and the like may be omitted, added, modified, skipped, and the like without departing from the scope of the invention.
[0069] FIG. 8 illustrates a computing environment 802 implementing a mechanism for channel estimation in the LTE system 100, according to the embodiments as disclosed herein. The computing environment 802 comprises at least one processing unit 808 that is equipped with a control unit 804, an Arithmetic Logic Unit (ALU) 806, a memory 810, a storage unit 812, a plurality of networking devices 816 and a plurality Input / Output (I/O) devices 814. The processing unit 808 is responsible for processing the instructions of the technique. The processing unit 808 receives commands from the control unit 804 in order to perform its processing. Further, any logical and arithmetic operations involved in the execution of the instructions are computed with the help of the ALU 806.
[0070] The overall computing environment 802 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 808 is responsible for processing the instructions of the technique. Further, the plurality of processing units 804 may be located on a single chip or over multiple chips.
[0071] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 810 or the storage 812 or both. At the time of execution, the instructions may be fetched from the corresponding memory 810 or storage 812, and executed by the processing unit 808.
[0072] In case of any hardware implementations various networking devices 816 or external I/O devices 814 may be connected to the computing environment 802 to support the implementation through the networking unit and the I/O device unit.
[0073] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in the FIGS. 1 through 8 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.
[0074] 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 embodiments as described herein.