Description:BACKGROUND
Technical Field
The embodiment herein generally relates to an OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division MultipleAccess)based communicationsystem providing broadcast services, and more particularly to a system and a method for providing broadcast transmitter specific pilots for performing channel estimation corresponding to a desired transmitter and interfering transmitters, in the frequency reuse one based broadcast communicationsnetworks.
Description of the Related Art
A pilot signal (reference signal) is commonly used incommunication systems to enable a receiver to perform several critical functions, including but not limited to, the acquisition and tracking of timing and frequency synchronization, the estimation, and tracking of desired channels for subsequent demodulation and decoding of the information data, the estimation, and monitoring of the characteristics of other channels for handoff, interference suppression, etc.
In a broadband communication/unicast communication, traditionally, each base station is equipped with a unique pilot pattern and/or pilot sequences called as reference signals. The base station specific pilots can be generated using Base station specific ID (BSID). The receiver can then use this BSID for obtaining local reference signals for channel estimation. This idea is incorporated in standards such as LTE. In Broadcast networks, the equivalent of BSID is the Transmitter ID (TxID). However, in broadcast standard,with synchronized broadcast communication as in Single Frequency networks (SFN), reference pilots in each subframearenot transmitter specific as they are not generated based on TxID, and hence they are common, both in terms of modulation value and position, across all the broadcast transmittersin a coverage area.
Communication of transmitter specific data using existing synchronized broadcast frameworks will lead to severe co-channel interference and hence cannot support the co-existence of SFN and Reuse-1 communication and/or reliable reception at the intersection of two or more SFN networks.
FIG. 1 illustrates anexample communication scenariowith co-channel interference, according to a prior art. According to FIG. 1, the co-channel interference is experienced by areceiver 102, due to reuse of the same frequency band across all the seven adjacent broadcast transmitters104A-104F. Interference aware receiver strategies require knowledge of channel frequency response (CFR) of the desired channel and interfering channels. Without accurate knowledge of the individual channel impulse and/or frequency responses, there will be severe degradation in the demodulation performance. The pilot-aided channel estimation strategies used in interference scenarios rely on the orthogonality or cross-correlation between pilot patterns of the desired and interfering frames. However, wireless standards like ATSC 3.0, DVB-T2, eMBMS/FeMBMS for MBSFN, etc., do not facilitate broadcast transmitterspecific orthogonal scatter pilots, for individual channel estimation, as they operate in Single Frequency Network (SFN) mode. In the frequency reuse-onescenario, each transmitter/SFN cluster in a network can have interference from neighboring transmitters/clusters 104b-104g. The channel estimation using the existing pilots of broadcast standards (including the pre-distorted) willresult in the estimation of the composite channel frequency response. This will result in the performance degradation at the receiver, even in the presence of more robust modulation and coding (MODCOD).
FIGS. 2A-2Care block diagrams of a broadcast exciter of the broadcast transmitter chain, according to a prior art illustration.The broadcast exciter is a system of signal processing modules that are responsible for the formation of broadcast frames according to the protocol. Here FIG. 2A represents broadcast exciter (transmitter)chain according to ATSC 3.0,FIG. 2b represents broadcast exciter (transmitter)chain as per the DVB-T2 standard. FIG.2C represents the broadcast transmitter chain as per the 3GPP eMBMS/FEMBMSstandard.Referring to FIGS. 2A, 2Band 2C, the main blocks in the exciterchain are categorized into the following modules. An input formatting module 202, a BICM (Bit-interleaved coding and modulation) module 204,anLDM combining module 206 (Layer Mapper in eMBMS), a MIMO precoding module 208, and a Waveform generation module 212.A Framing and Interleaving Module 210 that is specific to broadcasting standards like ATSC, DVB. The BICM module 204 includes forward error correction modules, related bit-interleaving, and a symbol mapping module. eMBMS/FeMBMS uses rate 1/3 Turbo codes and DVB-T2, ATSC 3.0 uses LDPC and BCH and/or CRC as the forward error correction methods. LDPC code word lengths of 64800 or 16200 are supported. ATSC 3.0 Symbol mapping uses non-uniform constellation and supports mapping from QPSK to 4096 QAM. Unlike DVB-T2 and FeMBMS,ATSC 3.0 supports layer division multiplexing. The LDM combining module 206 combines two coded and mapped user payloads into a single stream. The MIMO Precoding module 208 is an optional technology block to support MIMO. The Framing and Interleaving module 210 consists of three parts, Time interleaving, Framing, and Frequency interleaving.
The time interleaverspreads mapped payload symbols across time, thus providing time diversity. The frequency interleaver shuffles mapped symbols within anOFDM symbol, providing frequency diversity and the framing allocates user symbols to OFDM subcarriers resulting in OFDM symbols. Further, it groups OFDM symbols to form a frame or subframe. Sub carrier cell allocation can be TDM, FDM, LFDM, FLDM, etc.
Further, referring to FIGS. 2a, 2b, and 2c, the modules 212 (after the frequency interleaver block in 2a,2b, and after Precoding in Fig 2c) can be considered as part of waveformgeneration.The waveform generation module 212 typically includes Pilots, IFFT, Guard interval insertion modules as major submodules. Pilots’ insertion block inserts different types of pilots, each intended to serve different functionsin the receiver.Pilot location, subcarrier index, and the modulation values are predefined/obtained from spacing parametersthat are communicated to the receiver. To facilitate the ease of communication in SFN mode, scatter/reference pilot location and modulation values are designed to be independent of the broadcast transmitter or and hence they are same across all the transmitters.The IFFT converts frequency domain data to time domain.
Broadcast standards like ATSC 3.0, DVB-T2, etc., support the use of MISO precoding to avoid potential destructive interference at the receiver in SFN mode. However, the conventional precoding filters do not guarantee orthogonality of pilots in the frequency domain.
Accordingly, to support the coexistence of a single frequency network (SFN) and frequency reuse-one in broadcast networks and to facilitate accurate individual channel estimation, there isa need for generation and communication ofbroadcast transmitterspecific pilot signals(SFN group specific pilot signals)for channel estimation in interference-free and interference limited regions without making changes to the existing broadcast standard framework.
The above information disclosed in this background section is only for enhancement of understanding the background of the present disclosure, and therefore it may contain information that does not form the prior art.

SUMMARY
In view of the foregoing, the embodiments herein provideaSingle frequency-basedcommunication systemincludinga desired broadcast transmitterand one or more adjacent interfering broadcast transmittersthat are in communication with a receiver over a wireless communication channel. Each of the broadcast transmitters includesanexciter for transmitting broadcast transmitterspecific pilot signals to the receiver and the receiver for receiving a superimposed signal ofthe transmitted broadcast transmitterspecific pilot signals.The desired broadcast transmitteris one of the broadcast transmittersfrom which receiver intends to receive data. The desired broadcast transmitter and each adjacent interfering broadcast transmitter includesa pilot insertion module and a precoding filter module. The precoding filter module is adapted to generate a transmitter specific precoding sequence from a plurality of precoding sequences based on a computed location index for specific pilot signals in a time frequency domain. The precoding filter module is adapted to precode a reference pilot signal to obtain the broadcast transmitter specific pilot signal sequences, based on the plurality ofprecodedsequences.
In some embodiments, precoding of the reference pilot signal includesobtaining broadcast transmitterspecific pilot modulation values that are orthogonal or quasi-orthogonal to the other pre-coded pilot signals of adjacent broadcast transmittersin the frequency domain.
In some embodiments, the receiver on receiving the superimposed broadcast transmitterspecific pilot signal sequence transmitted from the desired broadcast transmitterand at least one of the adjacent interfering broadcast transmittersareadapted to (i) extract a sub-carrier location value from a computed location index of the broadcast transmitterspecific signal sequence, (ii) obtain one or more precoding filter coefficients based on the broadcast transmitterspecific pilot location value, (iii) compute an estimate of Channel Frequency Responses (CFR) corresponding to the desired broadcast transmitterand the one or more adjacent interfering broadcast transmitters, based on the extracted pilot sub carrier values and the broadcast transmitterspecific pilot sequences and (iv) compute anindividual channel estimate for the plurality of data sub carriers and obtain Channel Frequency Response (CFR) and a Channel Impulse Response (CIR) of desired and interfering channels.
In some embodiments, the receiver is adapted to estimate the channels corresponding to the desired broadcast transmitterandthe one or more adjacent interfering broadcast transmitters. The receiver includesa pilot extraction module, a channel estimation module, and a data-carrier channel estimation module. Thepilot extraction module is configured to extract the received pilot sequence from the pilot locations obtained for a specific time-frequency domain. The obtained pilot locations correspond to superimposed pilot values of the desired broadcast transmitterand the one or more adjacent interfering broadcast transmitters. The channel estimation module is configured to estimate a channel frequency response (CFR) of the desired broadcast transmitterand the one or more adjacent interfering broadcast transmitters, from the extracted pilot sequence. The data carrier channel estimation module is configured to obtain one or more channel estimates corresponding to data subcarriers based on a channel frequency response estimated at the pilot locations.
In some embodiments, the channel estimation module estimates the channel frequency responses of the desired broadcast transmitterand the one or more adjacent interfering broadcast transmittersbased on a location of one or more pre-distorted pilots in a time-frequency domain.
In some embodiments, the pilot sequence generation module of the transmitter is further adapted togenerate broadcast transmitterspecific pilot sequences using at least one of one or more sequence generators at different broadcast transmittersand Single Frequency Network (SFN) clusters.
In some embodiments, thebroadcast transmitter specific pilot sequences include one of orthogonal pilot sequences or uncorrelated pilot sequences between the first broadcast transmitterand the second broadcast transmitter. The orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials.
In some embodiments, thepilot sequence generation module of the transmitter is further adapted togenerate broadcast transmitterspecific pilot sequences using at least one of a pilot reference generator and a broadcast transmitterspecific transmitter identity (TxID) sequence, where the broadcast transmitterspecific pilot sequences are orthogonal pilot sequences or uncorrelated pilot sequences.
In one aspect, a method performed by a Single frequency-basedbroadcast communication system is provided.TheSingle frequency-basedbroadcast communication systemincludesone or more broadcast transmittersin communication with a receiver over a communication channel. Each of the broadcast transmitters includes a waveform generator for transmitting broadcast transmitter specific pilot signals to the receiver for receiving a superimposed broadcast transmitter specific pilot signal, characterized in that, a desired broadcast transmitter is one of the broadcast transmitters from which mobile station intends to receive data and each broadcast transmitter includes a pilot insertion module and a precoding filter module. The method includes (i) generating a transmitter specific precoding sequence from a plurality of precoding sequences based on a computed location index for specific pilot signals in a time frequency domainand (ii) precoding a reference pilot signal to obtain the broadcast transmitter specific pilot signal sequences, based on the plurality of precoded sequences.
In some embodiments, precoding of one or more pilot signals comprises obtaining broadcast transmitterspecific pilot modulation values that are orthogonal or quasi-orthogonal to the other pre-coded pilot signals of adjacent broadcast transmittersin a frequency domain.
In some embodiments, the method further includesextracting, by the receiver, a sub-carrier location value ata computed location index of the broadcast transmitterspecific signal sequence,obtaining, by the receiver, one or more precoding filter coefficients based on the broadcast transmitterspecific pilot location value, computing, by the receiver, channel estimatescorresponding to the desired broadcast transmitterand the one or more adjacent interfering broadcast transmitters, based on the extracted sub carrier values and the broadcast transmitterspecific pilot sequences, andperforming, by the receiver, a channel estimation of desired channel and one or more interfering channels for the one or more data subcarriers by computing, by the receiver, an individual channel estimates for one or more data sub carriers.
In some embodiments, the method of performing channel estimation of one or more interfering channels includesextracting, by a pilot extraction module of the receiver, the received superimposed pilot sequence values from one or more pilot locations obtained for a specific time-frequency domain, where the pilot locations correspond to received superimposed pilot values of a desired broadcast transmitterand an interfering channel, estimating, by a channel estimation module of the receiver,channel estimates of the desired broadcast transmitterand the interfering channels at the extracted pilot location andobtaining, by a data carrier channel estimation module of the receiver, one or more channel estimates corresponding to data subcarriers based on channel estimates at reference pilot location.
In some embodiments, estimating the channel response of desired base station and anadjacent interfering broadcast transmitterisperformed based on a location of the one or more pre-distorted pilots in the time-frequency domain.
In alternate embodiments, the method includes generating, by the pilot sequence generation module, the broadcast transmitternetwork)specificpilot sequences using at least one of one or more sequence generators at different broadcast transmittersand Single Frequency Network (SFN) clusters.
In someembodiments, the broadcast transmitterspecific pilot sequences includeone of orthogonal pilot sequences or uncorrelated sequences between a first adjacent interfering broadcast transmitter and a secondadjacent interfering broadcast transmitter. In alternate embodiments, the orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials.
In alternateembodiments, the method includesgenerating, by the pilot sequence generation module, the broadcast transmitterspecific pilot sequences using at least one of a pilot reference generator and a broadcast transmitterspecific transmitter identity (TxID) sequence, where the broadcast transmitterspecific pilot sequences are orthogonal pilot sequences or uncorrelated pilot sequences.
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 THE DRAWINGS
The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
FIG. 1 illustrates an OFDM based Single frequencycommunication system with co-channel interference, according to a prior art;
FIGS. 2A-2C are block diagrams of a broadcast exciter chain, according to prior art;
FIG. 3 is a block diagram of aSingle frequency-based broadcast communication system that utilizes pilot transmissions, according to some embodimentsherein;
FIG. 4is a block diagram illustrating a precoding filter module, according to someembodimentsherein;
FIG. 5 is a block diagram of a channel estimation module, according to some embodiments herein.
FIG. 6 is a flow chart illustrating a method performed by a Single frequency basedbroadcast communication system that includes a desired broadcast transmitter and one or more adjacent interfering broadcast transmitters in communication with a receiver over a communication channel according to someembodiments herein;
FIG. 7 is a flow chart illustrating an operation of areceiver, according to someembodiments herein;
FIG. 8 is a flow chart illustrating a method of performing channel estimation, according to the embodiments herein; and
FIG.9 is a graphical representation of four different precoding frequency responses, according to the embodiments herein.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
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 to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein are adapted to generate broadcast transmitterspecific pilot signals for channel estimation in interference-free and interference-limited regions to address the issue of orthogonality or quasi-orthogonality of pilot sequences in frequency domain, in a broadcasting framework.
The embodiments herein are intended for standards that do not support broadcast transmitterspecific pilots for channel estimation in SFN. This includes the broadcast standards such asATSC, DVB-T2, eMBMS/FeMBMS for MBSFN, etc., In particular, the solution is intended for broadcast in frequency reuse-onemode in SFN network (Coexistence of SFN and Frequency Reuse-One). Moreover, the embodiments herein are applicable to any wireless standard that does not support broadcast transmitternetwork)specific pilots in synchronized broadcast communications based SFN.
According to an embodiment herein, the description is provided considering the wireless standards such as ATSC, DVB-T2, eMBMS/FeMBMS, etc., where broadcast transmitter network)specific pilots are not transmitted in each subframe in SFN mode.
FIG. 3 is a block diagram of aSingle frequency-basedbroadcast communication system 300 that utilizes pilot transmissions, according to someembodiments herein. The Single frequency-based broadcast communication system300 includesa desired broadcast transmitter304 and one or more adjacent interfering broadcast transmitters302A-302Fin communication with areceiver 316over a communication channel. The desired broadcast transmitter 304 includes a waveform generator306 for transmitting broadcast transmitterspecific pilot signals to a receiver 316 for receiving superimposed transmitted broadcast transmitter specific pilot signals. The desired broadcast transmitter304 is one of the transmitters from which the mobile station 312 intends to receive transmitter specific data. Each adjacent interfering broadcast transmitter 302A-302F includesa pilot insertion module 303a-303f and a precoding filter module 305A-305F. Each adjacent interfering broadcast transmitter 302a-302f further includesIFFTs 307A-307F and cyclic prefix adding modules 309a-309f. The desired broadcast transmitter 304 includes a pilot insertion module 308 and a precoding filter module 310. The desired broadcast transmitter 304 further includes an IFFT 312 and a cyclic prefix adding module 314. The IFFT module 312 is used to realize the OFDM modulation, at the transmitter. The cyclic prefix module 314 is used to prefix the OFDM symbol generated at the output of IFFT module 312. This is done to overcome inter-symbol interference (ISI) due to multipath propagation environment. Conventionally, the prefix samples are the last N_cp samplesof the OFDM symbol resulting in cyclic extension of an OFDM symbol.The precoding filter module 310 of the desired broadcast transmitter 304 generates a transmitter specific precoding sequence from one or more precoding sequences based on a computed location index for specific pilot signals in a time frequency domain. The precoding filter module 310 further precodes a reference pilot signal to obtain the broadcast transmitter specific pilot signal sequences, based on theone or moreprecodedsequences.
The precoding of the reference pilot signal includesobtaining broadcast transmitterspecific pilot modulation values that are orthogonal or quasi-orthogonal to the other pre-coded pilot signals of the one or more adjacent broadcast transmitters302A-302Fin a frequency domain.
The receiver 316 receives the broadcast transmitter specific pilot signal sequence transmitted from the desired broadcast transmitter 304 and at least one of the adjacent interfering broadcast transmitters 302A-302F,extracts a sub-carrier location value from a computed location index of the broadcast transmitterspecific signal sequence. The data subcarrier location information is obtained from the D_X and D_Y values of a pilot pattern. From the D_X and D_Y values, a relative carrier k of a particular OFDM symbol lshall be a pilot carrier if it satisfies:
k mod (DXDY) = DX (lmod DY)
In some embodiments, the values of D_X and D_Y are conveyed to the receiver 316 using bootstrap orpreamble of aframe. The receiver 316may decode the bootstrap/preamble to understand the D_X D_Y values of subframes.
Further, the receiver 316obtainsone or more precoding filter coefficients based on the reference pilot location value. The receiver 316then computes Channel estimatescorresponding to the desired broadcast transmitter304 and theone or more adjacent interfering broadcast transmitters 302A-302F, based on the extracted sub carrier values and the broadcast transmitterspecific pilot sequences. The receiver 316 then computes channel estimates corresponding to the data subcarriers and then obtainsindividual Channel Frequency Response (CFR) and a Channel Impulse Response (CIR).
The receiver316includesa pilot extraction module 318, a channel estimation module 320, and a data carrier channel estimation module 322. The pilot extraction module 318is configured to extract the received pilot sequence from the pilot locations obtained for a specific time-frequency domain. The pilot extraction module318 extracts the pilot sequence from pilot locations based on one or more spacing parameters. Here the one or more spacing parameters include a frequency-direction spacing; anda time-direction spacing.The obtained pilot locations correspond to superimposed pilot values of the desired broadcast transmitter304 and the one or more adjacent interfering broadcast transmitters 302A-302F.
The channel estimation module 320 is configured to estimate a channel frequency response (CFR) of the desired broadcast transmitter 304 and the one or more adjacent interfering broadcast transmitters 302A-302F from the extracted pilot sequence. The data carrier channel estimation module 322 is configured to obtain one or more channel estimates corresponding to data subcarriers based on a channel frequency response at the reference pilot location.
In some embodiments, the waveform generator 306 further includesa pilot sequence generation module that is adapted to generate broadcast transmitter reference pilot sequences using the pilot spacing parameters broadcast transmitterbroadcast transmitter
In some embodiments, the orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials. The pilot insertionmodule 306 of the desired broadcast transmitter 304 is further adapted to generate broadcast transmitter specific pilot sequences using at least one of a pilot reference generator and a broadcast transmitter specific transmitter identity (TxID) sequence. The broadcast transmitter specific pilot sequences are orthogonal pilot sequences or uncorrelated pilot sequences.
FIG. 4is a flow diagram illustrating the functions of a precoding filter module, according to an embodiment herein. The precoding filter is initialized with a set of N number of bipolar all-pass sequencesX_j,0=j=N-1each of length N_p=?NoC/(D_X D_Y )?, at step 402. Here N is the number of broadcast transmitters(networks)in tier 1. This corresponds to the maximum number of transmitters that are in communication with the receiver 316 and transmitting individual data. Each vector is then passed through a multiplier andmultiplied with pilot signals obtained for particular D_X,D_Y, at step 404. This will result in pre-distorted pilot vectors Y_j,0=j=N-1.Then the orthogonality of the pre-distorted pilot signals is checked at step 406. Each vectorX_j is then interpolated to obtain N_FFT-length vectorsX ^_j with elements of magnitude 1, at step 408. The interpolation is a non-linear mapping function such that X ^_j (p)=X_j (i). Here p represents pilot location index obtained from D_X D_Y and i?[0,N-1]. This ensures that the data is left undistorted due to precoding. The precoding filter generator then checks if the correlation matrix of interpolated signal set X ^^(N_FFT ), given by R_(X ^^(N_FFT ) X ^^(N_FFT ) )=X ^^(N_FFT ) ?((X) ^^(N_FFT ))?^' ,is diagonally dominant or not, at step 410. This will facilitate the use of minimum mean square estimators for joint estimation of desired and interfering data. If the correlation matrix is diagonally dominant, then obtain the time domain filter x ^_j ,0=j=N-1 at step 412. If the correlation matrix is not diagonally dominant, thenmodify the filter set at 402and then proceed with steps 404-410. Further, if the correlation matrix is diagonally dominant, then consider the dominant paths (paths above defined threshold) for each filter and check if the maximum filter length is less than N_MISO=N_cp/3 or not, at step 416. Here N_cpis the length of cyclic prefix. If maximum filter length is less than N_MISO, then compute Peak Side lobe level for each vector 418.At step 418, computes the Peak Side lobe level for each vector if PSL=Th else the process is stopped at 422.If the maximum peak side lobe level of the set is less than the threshold, then go back to step 402, modify the filter, and repeat the process from step 404.
The output of aprecoding filter generator modulewill be a set of N precoding vectors, that are uncorrelated/orthogonal in bothtime and frequency. The length of filters is in accordance with the standard, supporting the legacy receivers in SFN mode.
In SFN mode, the precoded OFDM symbols will be uncorrelated in time. In addition to this, in the reuse-1 mode the precoded OFDM symbols will have orthogonal pilots in frequency domain. Each vector is assigned to individual broadcast transmitters in SFN cluster or individual SFN clusters. The precoding filter of the embodiments herein facilitates the use of advanced receivers that work in co-channel interference regime supporting coexistence of SFN and Reuse-1.
FIG. 5 is a block diagram of the channel estimation module320, according to the embodiments herein. The channel estimation module 320includes a broadcast transmitterspecific pilot extraction module 502, a joint channel estimation module 504, and a broadcast transmitterspecific data carrier channel estimation module 506 as shown in FIG. 5. The broadcast transmitterspecific pilot extraction module 502extracts the pilots from the ATSC pilot locations obtained for specific D_X D_Y. The obtained pilot locations correspond to superimposed pilot values of desired broadcast transmitterand the interferers. To obtain channel estimation at these sub carriers joint channel estimation technique is used. The Joint Channel Estimation module 504 estimates the desired channel and the one or more adjacent interfering channels. The broadcast transmitterspecific data carrier channel estimation module 506 uses these channel estimates to obtain the channel estimates corresponding to the data subcarriers. Since the time domain precoding filter length is maintained as per the standard, existing receivers may be able to equalize this distortion using linear equalizers.
FIG. 6 is a flow chart illustrating a method performed by the Single frequency based communication system 300includesthe desired broadcast transmitter 304 and the one or more adjacent interfering broadcast transmitters 302A-302F in communication with the receiver 316 over a communication channelaccording to the embodiments herein.At step 602,a transmitter specific precoding sequence is generated from one or more precoding sequences based on a computed location index for specific pilot signals in a time frequency domain. At step 604,a reference pilot signal is precoded to obtain the broadcast transmitter specific pilot signal sequences, based on the plurality of precoded sequences.
According to alternate embodiments herein, the pilot sequence generation module generates thebroadcast transmitterspecific pilot sequences using at least one or more sequence generators at different broadcast transmittersand/orSingle Frequency Network (SFN) clusters. Wherein the broadcast transmitterspecific pilot sequences includeone of orthogonal pilot sequences or uncorrelated sequences between the first broadcast transmitterand the second broadcast transmitter. The orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials. The pilot sequence generation module further generatesbroadcast transmitterspecific pilot sequences using at least one of a pilot reference generator and a broadcast transmitterspecific transmitter identity (TxID) sequence. Thebroadcast transmitterspecific pilot sequences herein are orthogonal pilot sequences or uncorrelated pilot sequences.
FIG. 7 is a flow chart illustrating anoperation of the receiver316, according to the embodiments herein. At step 702,a sub-carrier location value is extracted by the receiver 316from a computed location index of the broadcast transmitter specific signal sequence. The receiver 316extracts the received pilot sequence values from one or more pilot locations based on one or more spacing parameters. Here the one or more spacing parameters include a frequency-direction spacing andtime-direction spacing.
At step 704, one or more precoding filter coefficients are obtained by the receiver 316 based on the broadcast transmitter specific pilot location value. At step 706,Channel estimatescorresponding to the desired broadcast transmitter and the one or more adjacent interfering broadcast transmittersare computed by the receiver 314, based on the extracted sub carrier values and the broadcast transmitter specific pilot sequences. At step 708, a channel estimation of a desired channel and one or more interfering channels for the one or more data subcarriers is performed by computing individual channel estimates for a plurality of data sub carriers.
FIG. 8 is a flow chart illustrating a method of performing channel estimation, according to the embodiments herein.At step802, the pilot extraction module of the receiver316extracts the received superimposed pilot sequence values from one or more pilot locations obtained for a specific time-frequency domain. The pilot locations correspond to received superimposed pilot values of the desired broadcast transmitter 304 and an interfering channel. At step804, the channel estimation module320 of the receiver316 estimates a channel frequency response (CFR) of the desired broadcast transmitterand the one or more adjacent interfering channels at the extracted pilot location. Here estimation of thechannel response of desired base station and anadjacent interfering broadcast transmitteris performed based on a location of the one or more pre-distorted pilots in the time-frequency domain.At step 806, the data carrier channel estimation module322 of the receiver316obtains one or more channel estimates corresponding to data subcarriers based on a channel frequency.
FIG. 9 is a graphical representation of four different precoding filter frequency responses, according to the embodimentsherein.The precoding filter herein is all pass in nature and results in highly uncorrelated or orthogonal scattered pilots (in frequency domain) between broadcast transmitters. Further, the precoding filter hasa minimum peak sidelobe level (PSL) in time. The time domain filter lengths are within the standard supported lengths and support 7 or more broadcast transmitter cluster reuse.
Thus, the embodiments herein providebroadcast transmitter specific pilots without changes in thetransmitter frame structure of the current broadcast standards operating in SFN mode and also without significant impact on the performance of an existing receiver. This will facilitate the coexistence of receivers in SFN mode and also frequency reuse-1 mode.
The embodiments herein are adapted to facilitate the channel estimation of desired broadcast transmitter and individual adjacent interfering broadcast transmitterswith a high degree of accuracy. Existing broadcast communication uses same pilots across all broadcast transmitters. At the receiver316, the received signal captures the superimposed channel frequency response. If the same pilots are used at all the neighboring broadcast transmitters, then the receiver 316cannot estimate individual channel frequency response (Channel between a specific broadcast transmitter and the receiver 316. The pre-distorted pilots of neighboring broadcast transmitters will facilitate the estimation of individual channel frequency responses. This is important for estimating the desired data.
According to another embodiment herein, each broadcast transmittercan have a sequence generator that has a different generator polynomial, when compared with neighbouring broadcast transmitters. The sequence generator uses this generator polynomial and generates sequences of desired lengths. Thus, orthogonal (even length sequences)or uncorrelated sequences (odd length sequences). between two broadcast transmitters can be generated using sequence generators with different generator polynomials.
According to yet another embodiment herein, each broadcast transmittercan have a sequence generator with the same generator polynomial but a different initial sequence. Since the generator polynomial is same, the sequences obtained at different broadcast transmitters can be a shifted version of the sequences from neighbouring broadcast transmitters. However, the pilot sequences obtained from these reference signals can be orthogonal (even length) or highly uncorrelated (odd length). Furthermore, the initial sequence can be the TxID sequence defined in the standard. Each broadcast transmitterhas a TxID that is a 13-bit unique sequence. This can be considered as an initial sequence for the generation of reference signals such that the pilot sequences obtained from these reference signals are orthogonal or highly uncorrelated.
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/generic embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
, Claims:We Claim:
1. ASingle frequency basedbroadcast communication system (300) comprising:
a desired broadcast transmitter (304) and a plurality of adjacent interfering broadcast transmitters (302A-302F) that are in communication with a receiver(316) over a communication channel, wherein the desired broadcast transmitter (304)comprising a waveform generator (306) for transmitting broadcast transmitterspecific pilot signals to areceiver(316), wherein the receiver (316) receives a superimposed signal of the transmitted broadcast transmitter specific pilot signals,
characterized in that,
the desired broadcast transmitter (304) is one of the broadcast transmitters from which mobile station intends to receive data and each adjacent interfering broadcast transmitter (302a-302f) comprisesa pilot insertion module (303A-303F) and a precoding filter module (305A-305F) and the desired broadcast transmitter (304) comprises a pilot insertion module (308) and a precoding filter module (310), wherein the precoding filter module (310) isdesigned to:
generate a transmitter specific precoding sequence from a plurality of precoding sequences based on a computed location index for specific pilot signals in a time frequency domain; and
precode a reference pilot signal to obtain the broadcast transmitterspecific pilot signal sequences, based on the plurality ofprecodedsequences.

2. The system (300)as claimedin claim 1, wherein precoding of thereference pilot signalcomprises obtainingbroadcast transmitterspecific pilot modulation values that are orthogonal or quasi-orthogonal to the other pre-coded plurality of pilot signals of adjacentbroadcast transmitters in a frequency domain.

3. The system (300) as claimedin claim 1, wherein the receiver(316) on receiving the broadcast transmitter specific pilot signal sequence transmitted from thedesired broadcast transmitter (304) and at least one of the plurality of adjacent interfering broadcast transmitters (302A-302F) is adapted to:
extract a sub-carrier location value from a computed location index of the broadcast transmitterspecific signal sequence;
obtain a pluralityof precoding filter coefficients based on thebroadcast transmitterspecific pilot locationvalue;
compute channel estimatescorresponding to the desired broadcast transmitterand the plurality of adjacent interfering broadcast transmitters, based on the extracted sub carrier values and the broadcast transmitterspecific pilot sequences; and
compute anindividual channel estimate for a plurality of data sub carriers and obtain Channel Frequency Response (CFR) and a Channel Impulse Response (CIR) of desired and interfering channels.

4. The system (300) as claimedin claim 3, wherein the receiver (316) is adapted to estimate the desired broadcast transmitter (304) and the plurality of adjacent interfering broadcast transmitters (302A-302F), wherein the receiver (316) comprises:
a pilot extraction module (318) configured to extract the received pilot sequence from the pilot locations obtained for a specific time-frequency domain; where the obtained pilot locations correspond to superimposed pilot values of the desired broadcast transmitter(304) and the plurality of adjacent interfering broadcast transmitters (302A-302F);
a channel estimation module (320) that is configured to estimate a channel frequency response (CFR) of the desired broadcast transmitter(304) and the plurality of adjacent interfering broadcast transmitters (302A-302F), from the extracted pilot sequence; and
a data carrier channel estimation module (322) that is configured to obtain one or more channel estimates corresponding to data subcarriers based on a channel frequency response.


5. The system (300) as claimed in claim 4, wherein the channel estimation module (318) estimates the channel frequency responses of the desired based station (304) and the plurality of adjacent interfering broadcast transmitters (302A-302F) based on a location of a plurality of pre-distorted pilots in a time-frequency domain.

6. The system (300) as claimed in claim 1, wherein the pilot sequence generation module (306) of the transmitter (306) is further adapted to:
generate broadcast transmitter specific pilot sequences using at least one of one or more sequence generators at different broadcast transmitters and Single Frequency Network (SFN) clusters.

7. The system (300) as claimed inclaim 1, wherein the broadcast transmitter specific pilot sequences comprise one of orthogonal pilot sequences or uncorrelated pilot sequences between the first broadcast transmitter and the secondbroadcast transmitter, wherein the orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials.

8. The system (300) as claimedin claim 1, wherein thepilot sequence generation module (310) of the transmitter (306) is further adapted to:
generate broadcast transmitter specific pilot sequences using at least one of a pilot reference generator and a broadcast transmitterspecific transmitter identity (TxID) sequence, where the broadcast transmitter specific pilot sequences are orthogonal pilot sequences or uncorrelated pilot sequences.

9. A method performed by a Single frequency based broadcast communication system (300) comprising a desired broadcast transmitter (304) and a plurality of adjacent interfering broadcast transmitters (302A-302F) in communication with a receiver (316) over a communication channel, wherein each of the broadcast transmitters comprising a waveform generator (306) for transmitting broadcast transmitter specific pilot signals to the receiver (316) for receiving a superimposed transmitted broadcast transmitter specific pilot signals, characterized in that, a desired broadcast transmitter (304) is one of the broadcast transmitters from which mobile station (314) intends to receive data and each broadcast transmitter (306) comprises a pilot insertion module (308) and a precoding filter module (310), wherein the method comprises:
generating a transmitter specific precoding sequence from a plurality of precoding sequences based on a computed location index for specific pilot signals in a time frequency domain; and
precoding a reference pilot signal to obtain the broadcast transmitter specific pilot signal sequences, based on the plurality of precoded sequences.

10. The methodas claimedin claim 9, wherein precoding of a plurality of pilot signals comprises obtainingbroadcast transmitterspecific pilot modulation values that are orthogonal or quasi-orthogonal to the other pre-coded plurality of pilot signals of adjacent broadcast transmitters in a frequency domain.

11. The methodas claimedin claim 9,wherein the method comprises
extracting (702), by the receiver (316), a sub-carrier location value from a computed location index of the broadcast transmitterspecific signal sequence;
obtaining (704), by the receiver (316),a pluralityof precoding filter coefficients based on thebroadcast transmitterspecific pilot locationvalue;
computing (706), by the receiver (316), Channel estimatescorresponding to the desired broadcast transmitter and the plurality of adjacent interfering broadcast transmitters, based on the extracted sub carrier values and the broadcast transmitterspecific pilot sequences;
;and
performing (708), by the receiver(316),a channel estimation of a desired channel and one or more interfering channels by computing anindividual channel estimate for a plurality of data sub carriers.

12. The method as claimedin claim 11, wherein performing the channel estimation of the one or more interfering channels comprises:
extracting (802), by a pilot extraction module of the receiver (316), the received superimposed pilot sequence values from a plurality of pilot locations obtained for a specific time-frequency domain; where the pilot locations correspond to received superimposed pilot values of a desired broadcast transmitter(304) and an interfering channel;
estimating (804), by a channel estimation module (318) of the receiver (316), channel frequency response (CFR) of the desired broadcast transmitterand the interfering channels at the extracted pilot location; and
obtaining (806), by a data carrier channel estimation module(320) of the receiver (316), one or more channel estimates corresponding to data subcarriers based on a channel frequency.

13. The methodas claimedinclaim 9,wherein the method comprises
generating,by thepilot sequence generation module, the broadcast transmitter specific pilot sequences using at least one of one or more sequence generators at different broadcast transmitters and Single Frequency Network (SFN) clusters.

14. The method as claimedin claim 13, wherein the broadcast transmitter specific pilot sequences comprise one of orthogonal pilot sequences or uncorrelated sequences between a first adjacent interfering broadcast transmitter (302A) and a secondadjacent interfering broadcast transmitter (302B),wherein the orthogonal pilot sequences or uncorrelated pilot sequences are generated using sequence generators with different sequence generator polynomials.

15. The method as claimed in claim 9, wherein the method comprises
generating, by the pilot sequence generation module, the broadcast transmitter specific pilot sequences using at least one of a pilot reference generator and a broadcast transmitterspecific transmitter identity (TxID) sequence, where the broadcast transmitter specific pilot sequences are orthogonal pilot sequences or uncorrelated pilot sequences.

Dated this 15thday of September,2022