Claims:STATEMENT OF CLAIMS
I claim:
1. An automatic gain control (AGC) method in OFDM systems, the method comprising:
receiving IQ samples in digital domain for predefined number of OFDM symbols;
determining whether the OFDM symbols associated with the IQ samples is reference signal resource element (RSRE);
computing average power for RSRE OFDM symbols and root mean square (RMS) values for RSRE OFDM symbols, in response to determining that the OFDM symbols is the RSRE;
computing average power for Non-RSRE OFDM symbols and RMS values for Non-RSRE OFDM symbols, in response to determining that the OFDM symbols is the Non-RSRE;
determining ratio of average RMS value of Non-RSRE OFDM symbols to average RMS value of RSRE OFDM symbols;
applying AGC scaling to at least one of RSRE OFDM symbols and Non-RSRE OFDM symbols, in accordance with the determination of presence of data in RSRE OFMD symbols and Non-RSRE OFDM symbols.
2. The AGC method as claimed in claim 1, wherein method includes applying AGC scaling only to RSRE OFDM symbols in response to determining that ratio is lesser than a threshold and absence of data in the Non-RSRE OFDM symbols.
3. The AGC method as claimed in claim 1, wherein method includes applying AGC scaling to RSRE OFDM symbols and Non-RSRE OFDM symbols in response to determining that ratio exceeds a threshold and presence of data in the Non-RSRE OFDM symbols.
4. The AGC method as claimed in claim 3, wherein the AGC scaling is applied after deriving scaling factors for corresponding OFDM symbols in a subframe, wherein the scaling factors are derived as a ratio of power level of a OFDM symbol to a reference power.
5. A terminal is configured to:
receive IQ samples in digital domain for predefined number of OFDM symbols;
determine whether the OFDM symbols associated with the IQ samples is reference signal resource element (RSRE);
compute average power for RSRE OFDM symbols and root mean square (RMS) values for RSRE OFDM symbols, in response to determining that the OFDM symbols is the RSRE;
compute average power for Non-RSRE OFDM symbols and RMS values for Non-RSRE OFDM symbols, in response to determining that the OFDM symbols is the Non-RSRE;
determine ratio of average RMS value of Non-RSRE OFDM symbols to average RMS value of RSRE OFDM symbols;
apply AGC scaling to at least one of RSRE OFDM symbols and Non-RSRE OFDM symbols, in accordance with the determination of presence of data in RSRE OFMD symbols and Non-RSRE OFDM symbols.
6. The terminal as claimed in claim 5, wherein the terminal is configured to apply AGC scaling only to RSRE OFDM symbols in response to determining that ratio is lesser than a threshold and absence of data in the Non-RSRE OFDM symbols.
7. The terminal as claimed in claim 5, wherein terminal is configured to apply AGC scaling to RSRE OFDM symbols and Non-RSRE OFDM symbols in response to determining that ratio exceeds a threshold and presence of data in the Non-RSRE OFDM symbols.
8. The terminal as claimed in claim 7, wherein the AGC scaling is applied after deriving scaling factors for corresponding OFDM symbols in a subframe, wherein the scaling factors are derived as a ratio of power level of a OFDM symbol to a reference power.

Dated this 31st Day of March, 2017 Signatures:

Arun Kishore Narasani
Patent Agent

, Description:FIELD OF INVENTION
[0001] The embodiments herein relate a digital communication system, and more specifically to a automatic gain control (AGC) method and terminal for digitally controlling the automatic gain for OFDM systems.
BACKGROUND
[0002] In a wireless communications, the received signal energy will vary over many orders of magnitude due to variations in the characteristics of the channel. Such communication systems employ an automatic gain control (AGC) loop and an adaptive equalizer to handle the variations in received signal strength. Transmitters may transmit their signals at the same or different power levels. Further, the transmitters may be located at different distances to the receiver. The receiver may receive the signals from one or more transmitters at different received power levels. The receiver will perform AGC and adjust its gain.
[0003] Conventionally, AGC of a receiver is performed in mixed signal domain such that the gain computed in the baseband is fed back to RF amplifier to adapt the gain according the input control signal. The dependence of baseband input to RF is a complex process, the OFDM symbols would undergo non-linear distortion if the gain input to the RF amplifier is distorted.
[0004] One unit of data is contained in the subframe which has 14 OFDM symbols in the case of normal cyclic prefix (NCP) and 10 OFDM symbols in the case of extended cyclic prefix (ECP). The power control has to be adapted to all the 14 OFDM symbols after computing the power levels of the OFDM symbols.
[0005] Thus, there is a need in the art for a AGC method in digital domain and avoids the feedback mechanism to the RF amplifier.
[0006] 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
[0007] The principal object of the embodiments herein to provide an automatic gain control method in RSRE and/or Non-RSRE OFDM symbols.
[0008] Another object of the embodiments herein is to provide a method for computing AGC based on the presence of data in Non-RSRE OFDM symbols.
[0009] Another object of the embodiments herein is to provide a method to apply AGC scaling to RSRE OFDM symbols and/or Non-RSRE OFDM symbols based on the presence of data.
[0010] Another object of the embodiments herein is to provide the AGC method to normal cyclic prefix (NCP) and extended cyclic prefix (ECP) of the LTE OFDM symbols.
SUMMARY
[0011] Embodiments herein disclose an automatic gain control (AGC) method in OFDM systems. The method includes receiving IQ samples in digital domain for predefined number of OFDM symbols and determining whether the OFDM symbols associated with the IQ samples is reference signal resource element (RSRE). Further, the method includes computing average power for RSRE OFDM symbols and root mean square (RMS) values for RSRE OFDM symbols, in response to determining that the OFDM symbols is the RSRE and computing average power for Non-RSRE OFDM symbols and RMS values for Non-RSRE OFDM symbols, in response to determining that the OFDM symbols is the Non-RSRE. Furthermore, the method includes determining ratio of average RMS value of Non-RSRE OFDM symbols to average RMS value of RSRE OFDM symbols and applying AGC scaling to at least one of RSRE OFDM symbols and Non-RSRE OFDM symbols, in accordance with the determination of presence of data in RSRE OFMD symbols and Non-RSRE OFDM symbols.
[0012] 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
[0013] 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:
[0014] FIGS. 1a and 1b depict transmission from single and multiple transmitters to a terminal, according to embodiments as disclosed herein;
[0015] FIG. 2 is the block diagram of the terminal receiver performing AGC computation, according to embodiments as disclosed herein;
[0016] FIG. 3 is a block diagram corresponding to the proposed method of AGC computation of OFDM symbols in digital domain, according to the embodiments as disclosed herein;
[0017] FIG. 4 illustrates various units of the terminal for computing AGC, according to the embodiments as disclosed herein;
[0018] FIG. 5 is flow diagram illustrating the proposed AGC method, according to the embodiments as disclosed herein; and
[0019] FIG. 6 illustrates a computing environment implementing a AGC method in OFDM systems, according to embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0020] 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.
[0021] Embodiments herein provide an automatic gain control (AGC) method in OFDM systems. The method includes receiving IQ samples in digital domain for predefined number of OFDM symbols and determining whether the OFDM symbols associated with the IQ samples is reference signal resource element (RSRE). Further, the method includes computing average power for RSRE OFDM symbols and root mean square (RMS) values for RSRE OFDM symbols, in response to determining that the OFDM symbols is the RSRE and computing average power for Non-RSRE OFDM symbols and RMS values for Non-RSRE OFDM symbols, in response to determining that the OFDM symbols is the Non-RSRE. Furthermore, the method includes determining ratio of average RMS value of Non-RSRE OFDM symbols to average RMS value of RSRE OFDM symbols and applying AGC scaling to at least one of RSRE OFDM symbols and Non-RSRE OFDM symbols, in accordance with the determination of presence of data in RSRE OFMD symbols and Non-RSRE OFDM symbols.
[0022] Unlike the conventional methods, the proposed AGC method is performed in baseband domain post ADC without any feedback to RF amplifiers. AGC is computed intelligently using RSRE OFDM symbols and non-RSRE OFDM symbols when the data is present in the non-RSRE OFDM symbols, else AGC is computed only by using the RSRE OFDM symbols.
[0023] Unlike conventional gain control method, the proposed method controls the gain by controlling the power of each OFDM symbol. The power adaptation maintains uniform power levels for all or part of the group of OFDM symbols in a subframe so that the data received by QAM4, QAM16, QAM64 and beyond will be maintained by the AGC with uniform constellation.
[0024] Referring now to the drawings, and more particularly to FIGS. 1 through 6, there are shown preferred embodiments.
[0025] FIGS. 1a and 1b depict transmission from single and multiple transmitters to a terminal 100, according to embodiments as disclosed herein. As depicted in FIG. 1a, the transmitter sends the signals to the terminal 100. The RF front-end receives the signals through antenna and the Analog-to-Digital convertor (ADC) converts the signal in analog domain to digital domain. The output of the ADC is the IQ samples. The AGC computation unit process the IQ samples in digital domain to determine the Reference Signal Resource Element (RSRE) OFDM symbols and Non-RSRE OFDM symbols. The proposed AGC computation determines the presence of data in the 0, 4, 7, 11 RSRE OFDM symbols and accordingly compute the AGC. Further, the proposed method determines the presence of data in 1,2,3,5,6,8,9,10,12,13 Non-RSRE OFDM symbols and accordingly determines to compute AGC for those Non-RSRE OFDM symbols which comprise data.
[0026] FIG. 1b depicts multiple transmitter scenario sending multiple signals to the terminal 100. The AGC method is performed at the terminal 100 is in the same manner as explained in FIG. 1a.
[0027] FIG. 2 is the block diagram of the terminal receiver performing AGC computation, according to embodiments as disclosed herein. The terminal receiver includes RF amplifier and the ADC. The digitally converted IQ samples are processed to compute AGC. Among 14 OFDM symbols in a subframe only 4 cell reference symbols (CRS) of every subframe carry the pilot carriers, referred as RSRE. The OFDM symbols are numbered in a subframe as 0,1,2,3,...,13 in one subframe of 1 millisecond. The OFDM symbols 0, 4, 7 and 11 are the RSRE symbols. The OFDM symbol 0 mandatorily carries RSRE including the control data. The OFDM symbols 1 and 2 may or may not carry the control data. The OFDM symbols other than the RSRE are 12 OFDM symbols which may or may not carry any data, therefore, the data among these OFDM symbols is not guaranteed, if no data then only noise would be present in those symbols. Computing the AGC based on the non-RSRE symbols would result in wrong gain estimation when there is no data present in those symbols.
[0028] The proposed method determine gains based on the RSRE OFDM symbols and optionally computing the gain for non-RSRE OFDM symbols. Here, optionally means when the data is present in the non-RSRE OFDM symbols then the power levels for AGC controlling is computed followed by the gain adaptation of the symbols, if no data is present in the non-RSRE OFDM symbols then the power computation in those OFDM symbols is skipped, and only the power from the RSRE based OFDM symbols is only considered.
[0029] The average power of all the 14 OFDM symbols are computed. Then, the Root mean square (RMS) values of the RSRE and Non-RSRE OFDM symbols are computed. After computing the RMS values, the ratio of the RMS value of Non-RSRE to the RMS value of the RSRE is determined. Further, a threshold is applied to the determined ratio. If the ratio is lesser than the threshold, then the Non-RSRE OFDM symbols do not carry the data. In this case, no AGC is applied to the non-RSRE OFDM symbols. The AGC scaling is applied to only RSRE OFDM symbols.
[0030] If the ratio is greater than and equal to threshold, then the Non-RSRE OFDM symbols carry the data and AGC is applied to the non-RSRE OFDM symbols. In this case, the AGC scaling is applied to both RSRE and non-RSRE OFDM symbols.
[0031] In an embodiment, the threshold is predetermined by the terminal.
[0032] In another embodiment, the threshold is informed by the base station.
[0033] The AGC scaling is based on the scaling factors derived for respective OFDM symbols.
[0034] In an embodiment, the IQ samples of OFDM symbols in the subframe are scaled by the respective scaling factors.
[0035] FIG. 3 is a block diagram corresponding to the proposed method of AGC computation of OFDM symbols in digital domain, according to the embodiments as disclosed herein. The OFDM symbols in a subframe post ADC are the time domain samples. Based on the LTE bandwidth the number of IQ samples per 1 millisecond subframe is determined. The bandwidths are 20MHz, 15MHz, 10MHz, 5MHz, 3MHz and 1.4 MHz. In an example, for 20MHz LTE the subframe consists of 30720 IQ samples distributed among 14 OFDM symbols as per the 3GPP standard reference. One subframe consisting of 14 OFDM symbols are defined as below.
[0036] The IQ samples output of ADC of the 1st OFDM symbol are defined as where are complex samples with real part as I and imaginary part Q.
[0037] The IQ samples output of ADC of the 2nd OFDM symbol are defined as where are complex samples with real part as I and imaginary part Q.
[0038] The IQ samples output of ADC of the 14th OFDM symbol are defined as where are complex samples with real part as I and imaginary part Q.
[0039] The IQ samples are buffered in a memory.



[0040] The average powers for the RSRE OFDM symbols are calculated as




where (*) indicates the complex conjugate of the sample, is the average power of the kth RSRE OFDM symbol, i corresponds to the subframe number in a given radio frame. The Root Mean Square (RMS) values of the RSRE OFDM symbols for ith subframe and kth OFDM symbol are computed as

[0041] The RMS values of non-RSRE OFDM symbols are computed in the same way:

[0042] The ratio of the averaged RMS values of RSRE OFDM symbols for ith subframe is calculated as follows

[0043] If then the non-RSRE OFDM symbols do not carry the data, no AGC is applied to the non-RSRE OFDM symbols. The AGC scaling is applied to only RSRE OFDM symbols.
[0044] If then the non-RSRE OFDM symbols carry the data, AGC is applied to the non-RSRE OFDM symbols. The AGC scaling is applied to RSRE and non-RSRE OFDM symbols as:
where
[0045] In an embodiment, the AGC method is applied to NCP of the LTE OFDM symbols.
[0046] In another embodiment, the AGC method is applied to ECP of the LTE OFDM symbols.
[0047] FIG. 4 illustrates various units of the terminal 100 for computing AGC, according to the embodiments as disclosed herein.
[0048] In an embodiment, the terminal 100 is a base station (eNB).
[0049] In another embodiment, the terminal 100 is a user equipment (UE).
[0050] As shown, the IQ samples determination unit 402 determines the IQ samples per 1 millisecond subframe based on the LTE bandwidth. One unit of data is contained in the subframe which has 14 OFDM symbols (in the case of normal cyclic prefix (NCP)) and 10 OFDM symbols in the case of extended cyclic prefix (ECP). The power control has to be adapted to all the 14 OFDM symbols after computing the power levels of the OFDM symbols. The OFDM symbols are sensitive to power variations, therefore, the gain should be controlled by controlling the power of each OFDM symbol. The power adaptation described by the proposed method maintains uniform power levels for all or part of the group of OFDM symbols in a subframe so that the data received by QAM4, QAM16, QAM64 and beyond will be maintained by the AGC with uniform constellation.
[0051] The average power computation unit 404 computes power levels for RSRE OFDM symbols in a subframe, averaged to derive the reference power level Pref. The Pref is computed as (P0+ P4+ P7+ P11 )/4.
[0052] The power levels for non-RSRE OFDM symbols in a subframe are computed, averaged over each non-RSRE OFDM symbol to derive the power levels P1, P2, P3, P5, P6, P8, P9, P10, P12 and P13.
[0053] The RMS computation unit 406 computes RMS values for both RSRE OFDM symbols and Non-RSRE OFDM symbols.
[0054] The ratio computation unit 408 computes ratio of averaged RMS values of Non-RSRE OFDM symbols to the averaged RMS values of RSRE OFDM symbols.
[0055] Based on the comparison with a predetermined threshold, the AGC scaling is applied to RSRE OFDM symbols and/or Non-RSRE OFDM symbols in accordance to the presence of data in the Non-RSRE OFDM symbols.
[0056] In an embodiment, the scaling factors for each non-RSRE OFDM symbol is derived by the ratio of s1=P1/ Pref, s2=P2/ Pref, s3= P3/ Pref, s5=P5/ Pref, s5=P6/ Pref, s8=P8/ Pref, s9=P9/ Pref, s10=P10/ Pref, s12=P12/ Pref, and s13=P13/ Pref. The s0,s1, s2,..., s13 are the scaling factors for respective OFDM symbols in the subframe.
[0057] The IQ samples of OFDM symbols in the subframe are scaled by the respective scaling factors s0,s1, s2,..., s13.
[0058] Although FIG. 4 shows exemplary units of the terminal 100, in other implementations, the terminal 100 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 4. Additionally or alternatively, one or more components may perform functions described as being performed by one or more other components of the terminal 100.
[0059] FIG. 5 is flow diagram illustrating the proposed AGC method, according to the embodiments as disclosed herein. At step 502, the method includes receiving IQ samples in digital domain for predefined number of OFDM symbols. The number of OFDM symbols (based on the LTE bandwidth) is received. In an example, for 20MHz LTE the subframe consists of 30720 IQ samples distributed among 14 OFDM symbols. At step 504, the method includes determining whether the OFDM symbols are RSRE or Non-RSRE. In response to determining that the OFDM symbols are RSRE, at step 506, the method includes computing average power for the RSRE OFDM symbols such as 0,4,7,11. Then, at step 508, the method includes computing RMS value for OFDM symbols based on average power.
[0060] At step 510, the method includes determining that the OFDM symbols are non-RSRE, and computes average power for Non-RSRE OFDM symbols such as 1,2,3,5,6,8,9,10,12,13. At step 512, the method includes computing RMS value for OFDM symbols based on average power of the Non-RSRE OFDM symbols.
[0061] At step 514, the method includes computing ratio of the averaged power levels of the non-RSRE OFDM symbols to the averaged power levels of the RSRE OFDM symbols.
[0062] At step 516, the method includes determining whether the ratio is lesser than the threshold. In an embodiment, the threshold is predetermined by the terminal.
[0063] In response to determining that the ratio is lesser than the threshold, at step 518, the method includes declaring that the Non-RSRE do not contain data and at step 520, the method includes ignore to apply AGC scaling to the Non-RSRE OFDM symbols. The method includes applying AGC scaling to only RSRE OFDM symbols.
[0064] In response to determining that the ratio is not lesser (i.e., greater or greater than and equal to) the threshold, at step 522, the method includes declaring that the Non-RSRE OFDM symbols contain data. At step 524, the method includes applying AGC scaling to RSRE OFDM symbols and the Non-RSRE OFDM symbols.
[0065] The various actions, acts, blocks, steps, and the like in the flow diagram 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.
[0066] FIG. 6 illustrates a computing environment implementing a AGC method for OFDM systems, according to embodiments as disclosed herein. The computing environment 602 comprises at least one processing unit 608 that is equipped with a control unit 604, an Arithmetic Logic Unit (ALU) 606, a memory 610, a storage unit 612, a plurality of networking devices 616 and a plurality Input / Output (I/O) devices 614. The processing unit 608 is responsible for processing the instructions of the technique. The processing unit 608 receives commands from the control unit 604 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 606.
[0067] The overall computing environment 602 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 608 is responsible for processing the instructions of the technique. Further, the plurality of processing units 604 may be located on a single chip or over multiple chips.
[0068] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 610 or the storage 612 or both. At the time of execution, the instructions may be fetched from the corresponding memory 610 or storage 612, and executed by the processing unit 608.
[0069] [0085] In case of any hardware implementations various networking devices 616 or external I/O devices 614 may be connected to the computing environment 602 to support the implementation through the networking unit and the I/O device unit.
[0070] 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 6 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.
[0071] 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.