Claims:
1. A method of diversity combining for a wireless communication receiver, the method comprising:
receiving and converting a plurality of RF Signals at each diversity branch to a baseband signal by mixing it with a local oscillator signal by a mixer 201;
digitizing the baseband analog signal by an analog to digital converter (ADC) 202 coupled to the mixer;
converting a serial digital baseband signal to parallel digital baseband signal by a serial to parallel convertor 203 coupled to the ADC and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver;
multiplying the transformed output of each diversity branch from transform block with the adaptive weights computed by a corresponding weight estimation block 212 by a weight application block 205; and
combining an adaptively weighted transformed signals of each of the diversity branches by a combiner 206 which mitigates the effects of channel fading and reduces the ISI, ICI and noise.

2. The method as claimed in claim 1, wherein the adaptive weights (weighting coefficients) are computed by using a stochastic gradient descent method.

3. The method as claimed in claim 1, wherein the adaptive weights are computed based on the error calculation, where the error is calculated by taking the difference between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain.

4. The method as claimed in claim 1, wherein the channel effects are corrected using a transform domain equalizer and the weighting coefficients are determined without the apriori estimate of the channels.

5. The method as claimed in claim 1, wherein the weight updation is done dynamically by computing error in the inverse transform domain.

6. The method as claimed in claim 1, wherein the channel equalization is achieved by the appropriate weighting of the transformed signal which mitigates the effects of channel fading and reduces the ISI, ICI and noise.

7. The method as claimed in claim 1, further comprises obtaining an inverse transform of the signal by an inverse transform block 207 coupled to the combiner, where the inverse transform block 207 obtains the inverse transform of the signal input to the transform block.

8. The method as claimed in claim 1, wherein the computing error in inverse transform domain speeds up the convergence of stochastic gradient descent method.

10. The method as claimed in claim 1, wherein for data segment, error is calculated by finding the difference between combiner output and the decision taken by Detector 209 on Combiner output in their inverse transform domain.

10. An optimal diversity combiner for a wireless communication receiver with multiple diversity branches, the optimal diversity combiner comprising:
a mixer 201 receives and converts RF signals at the diversity receivers to baseband by mixing it with local oscillator signal;
an analog-to-digital converter (ADC) 202 coupled to the mixer 201 which digitizes the baseband signal;
a serial to parallel converter module 203 coupled to the analog-to-digital converter (ADC), wherein the serial to parallel converter module is used to convert a serial digital baseband signal to parallel digital baseband signal and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver;
a weight application block 205 coupled to the transform block 204, wherein the weight application block 205 is used to receive the transformed output of each diversity branch and multiply the transformed output with the adaptive weights computed by a corresponding weight estimation block 212; and
a combiner 206 coupled to the weight application block 205, wherein the combiner 206 effectively combines the adaptively weighted transformed signals of each of the diversity branches which mitigates the effects of channel fading and reduces the ISI, ICI and noise.

11. The combiner as claimed in claim 1, wherein the weight estimation block 212 estimates the weight adaptively by using stochastic gradient descent method, where the adaptive weights are calculated based on the error calculation, where the error is calculated by taking the difference between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain.

12. The combiner as claimed in claim 1, further comprises an inverse transform block 207 coupled to the combiner, wherein the inverse transform block 207 takes the inverse transform of the signal input to the block, where the error is calculated by taking the difference 208 between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain.

13. The combiner as claimed in claim 1, wherein the weight updation of equalizer in transform domain is done dynamically by computing error in the inverse transform domain.

14. The combiner as claimed in claim 1, wherein the computing error in inverse transform domain speeds up the convergence of stochastic gradient descent method.

15. The combiner as claimed in claim 1, wherein the channel equalization is achieved by the appropriate weighting of the transformed signal which mitigates the effects of channel fading and reduces the ISI, ICI and noise.
, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)

“A diversity combiner and a method of diversity combining for a wireless communication receiver”

By
BHARAT ELECTRONICS LIMITED
Nationality: Indian
Address: OUTER RING ROAD, NAGAVARA, BANGALORE- 560045,
KARNATAKA, INDIA

The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention

The present invention mainly relates to a digital receiver for wireless communication and more particularly to a diversity combiner with adaptive channel estimation and signal processing in the transform domain for a wireless communication receiver and a method thereof.

Background of the invention

Wireless communications systems are generally exposed to fading conditions which causes degradation to the signal resulting in loss of information. In multipath transmission systems, such as those which employ troposcatter communication links, fading is a commonly observed phenomenon.
Multipath fading causes signal degradation because of the rapid and deep changes in the signal level that might be created in the transmission frequency band. Further, transmitted data may undergo phase distortion and intersymbol interference due to multipath fading.
Diversity combining techniques like spatial diversity, frequency diversity, etc. tends to smooth out the multipath fading effects by reducing the depth of fading and reducing the percentage of time the combined signal will fade below a given fade depth. In other words, diversity reception combat multipath fading by appropriately weighting and combining the signals received at the diversity branches using suitable signal processing technique and recover the original transmitted signal. However, achieving flat transmission frequency band in the presence of frequency selective fading is a major challenge in today’s wireless communications systems especially troposcatter systems while maintaining good performance, delivering high speed data rate even with diversity receiver. Non-line-of-sight / multi-path conditions are the factors which degrade the performance of tropo-systems. Multicarrier modulation (MCM) technique along with diversity receivers can improve the performance of wireless communication systems.
In multi-carrier modulation scheme, requisite data is sent over many sub- channels / sub-carriers. All the sub-carriers are made orthogonal to one another, preventing interference between the closely spaced sub-carriers. Data is then transmitted over these orthogonal sub-carriers simultaneously. MCM assures high resistance to Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) with high spectral efficiency. Multi-carrier modulated data/signal received by diversity branches has to be appropriately weighted by suitable signal processing methods to mitigate the effects of channel fading.
Various techniques for diversity combining have been suggested in the prior art in order to extract the original transmitted signal in the presence of fading by improving the SNR of the received signals.
For example, one of the conventional methods disclose a method and apparatus for controlling an antenna array to achieve directional reception in a wireless communication system. The method employed can suppress co-channel interference and can be used in conjunction with multi-carrier modulation signalling. Diversity combining weight vectors are calculated based on correlation estimates of an unwanted signal and channel responses.
Further, conventional system discloses a high-speed digital communication receiver system with pre-detection diversity combiner. The signals received at the diversity branches are weighted using forward adaptive filter equalizer prior to combining. The diversity combiner output, after demodulation is passed through a detector to recover the original data. The generated error signal after modulation is used in adaptive control circuitry which provides appropriate adaptive weighting signals in the processing of the received diversity signals at each of the forward filter equalizers. The backward adaptive filter equalizer utilizes detector output and unmodulated error signal to generate a cancellation signal that removes the intersymbol interference and source correlation effects from the demodulated diversity combiner output signal. An automatic gain control system is also described which reduces the dynamic range requirements of the forward filter weight components.
Another, conventional receiver describes a troposcatter modem receiver with diversity antennas which uses pre-detection linear maximal ratio combiner for diversity combining. Signals received by diversity antennas are then incoherently combined at RF level. The maximal ratio combiner output is further demodulated and filtered to obtain the baseband signal. This baseband signal is then equalized using a decision feedback equalizer (DFE) and provided to a detector circuit, the output of which is fed back as secondary input to the equalizer. The error between the detector input and output is then calculated by a difference circuit which is used to determine adaptive tap weight signals of equalizer so as to mitigate the effects of fading.
Another conventional method discloses a method and apparatus for combining signals at wireless receivers in the absence of channel gain estimation” discloses a method and an apparatus for combining signals at the diversity receiver after their processing in individual branches, which includes estimation of the phase changes induced by the channel at each received signal with reference to the transmitted signal, and weighting of each signal by a co-phasing coefficient based on said estimation, so that all received signals are co-phased. Weighting coefficients are calculated from the mean value and variance of signal to noise ratio (SNR) in each branch.
Another diversity combiner discloses an optimal diversity combiner which enhances the signal reception at the receiver by exploiting multipath faded signals received at the diversity receivers. Here combining is performed at the baseband level which makes use of Decision Feedback Equalizer (DFE) for compensating the channel effects. The weights of DFE are estimated adaptively using stochastic gradient descent method. All the estimations and processing are performed on the time domain signal not on transformed domain signal.
Therefore, there is a need in the art with a diversity combiner for a wireless communication receiver to solve the above-mentioned limitations.

Objective of the invention

The main objective of the present invention is to provide a method for optimal combining of signals received by the diversity receivers in their transform domain for combating the channel effects like fading, ISI, ICI and noise.
Another objective of the present invention is to exploit the multipath faded signals at multiple diversity receivers and enhance the signal reception at the receiver with the techniques of equalization and diversity combining being performed in transformed domain.
Further objective of the present invention mitigates the effects of multipath fading, where equalizer weights are computed based on the transform of error in the inverse transform domain.
Furthermore, objective of the present invention provides a method of channel estimation in the transform domain performed together with diversity combining thereby combating the multipath fading effects. The present invention efficiently uses the preamble and the decision on data for channel estimation in a novel fashion.
Summary of the Invention

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.
Accordingly, in one aspect of the present invention relates to a method of diversity combining for a wireless communication receiver, the method comprising: receiving and converting a plurality of RF Signals at each diversity branch to a baseband signal by mixing it with a local oscillator signal by a mixer 201, digitizing the baseband signal (analog signal) by an analog to digital converter (ADC) 202 coupled to the mixer, converting a serial digital baseband signal to parallel digital baseband signal by a serial to parallel convertor 203 coupled to the ADC and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver, multiplying the transformed output of each diversity branch from transform block with the adaptive weights computed by a corresponding weight estimation block 212 by a weight application block 205 and combining an adaptively weighted transformed signals of each of the diversity branches by a combiner 206 which mitigates the effects of channel fading and reduces the ISI, ICI and noise.
Another aspect of the present invention relates to an optimal diversity combiner for a wireless communication receiver with multiple diversity branches, the optimal diversity combiner comprising: a mixer 201 receives and converts RF signals at the diversity receivers to baseband by mixing it with local oscillator signal, an analog-to-digital converter (ADC) 202 coupled to the mixer 201 which digitizes the baseband signal, a serial to parallel converter module 203 coupled to the analog-to-digital converter (ADC), wherein the serial to parallel converter module is used to convert a serial digital baseband signal to parallel digital baseband signal and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver, a weight application block 205 coupled to the transform block 204, wherein the weight application block 205 is used to multiply the transformed output with the adaptive weights computed by a corresponding weight estimation block 212 and a combiner 206 coupled to the weight application block 205, wherein the combiner 206 effectively combines the adaptively weighted transformed signals of each of the diversity branches which mitigates the effects of channel fading and reduces the ISI, ICI and noise.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
Brief description of the drawings

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates the block diagram of a method and apparatus to achieve directional reception in a wireless communication system and suppress co-channel interference thereby controlling antenna array with statistical characteristics of the received signal noise according to the prior art.
Figure 2 illustrates the block diagram of wireless communication receiver with adaptive channel estimation and optimum diversity combining in the transform domain according to one embodiment of the present invention.
Figure 3 shows the constellation diagram of the received signal (Fig. 3a) at the diversity branches at an SNR of 15dB and the constellation diagram of output combiner (Fig. 3b) obtained as an outcome according to one embodiment of the present invention.
Figure 3c shows the error curve according to one embodiment of the present invention.
Figure 4 shows a method of diversity combining for a wireless communication receiver according to one embodiment of the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

Detailed description of the invention
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.
By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.
Figs. 1 through 4, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged communications system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.
The present invention relates to an optimal diversity combiner with adaptive channel estimation and signal processing in the transform domain which mitigates the effects of multipath fading and utilizes the multipath faded signals at the diversity receivers to enhance the signal to noise ratio (SNR) of the received signal. The present invention method can be applied to antenna arrays which are diversified in space or frequency or combination of both. The method utilizes the signals at the diversity branches which are uncorrelated to enhance the SNR at the receiver. The diversity combiner with appropriate method steps for channel estimation in the transform domain is capable of recovering the original transmitted signal by nullifying the effects of multipath fading and eventually improving SNR. The method step performs equalization jointly with the combiner in the transform domain. This method can be used in conjunction with multicarrier modulation signalling in a fading environment to improve the data rate. Weight vectors of the channel estimator for all diversity branches are estimated adaptively based on stochastic gradient descent method with the combiner output rather than individual channel outputs in the transform domain. Optimal recovery of transmitted data at the receiver can be achieved with the combiner by mitigating the effects of multipath fading, ISI, ICI and noise. The method can also be used for Troposcatter communication where Line-of-Sight doesn’t exist.
Figure 1 illustrates the block diagram of a method and apparatus to achieve directional reception in a wireless communication system and suppress co-channel interference thereby controlling antenna array with statistical characteristics of the received signal noise according to the prior art. This figure illustrates a multi-antenna receiver with an OFDM diversity combiner as described in the prior art, where the signals received by ‘K’ antenna elements receive signals are appropriately weighted and combined to give ‘N’ logic level outputs for an OFDM signal of ‘N’ subcarriers. The ‘K’ antenna elements provide input to ‘K’ Fast Fourier transform (FFT) processors 101-1 to 101-K respectively. Each of the FFT processors produces N frequency Samples for each OFDM symbol. The ‘N’ frequency domain contents of each of the ‘K’ diversity channels are fed to a Channel Estimation Unit 102 that computes the channel response Hnk for each antenna element k, k = 1,2…. K and each subcarrier n, n = 1, 2……N on the basis of a sequence of training symbols. The channel estimates Hn1, Hn2…. HnK are fed to nth Weight Extractor 103- n which also takes the correlation matrix R as input. The weight vector Wn extracted from the nth Weight Extractor unit is provided to the Decision maker unit 104- n which is then applied to the input sample vector En and the logic level is extracted. The output of the diversity combiner comprises the logic levels produced by the Decision-Making units 104-1 to 104-N, as well as the weight vectors produced by the Weight Extractor units 103-1 to 103-N.
The present invention relates to an optimal diversity combiner for a wireless communication receiver with multiple diversity branches where the optimal diversity combining is performed in the transform domain in conjunction with channel estimation and retrieves the data effectively from multipath faded environment. The present invention relates to an optimal diversity combiner where signal processing method steps for channel estimation are done in transform domain which includes a weight estimation unit that makes use of stochastic gradient descent method to estimate the channel and thereby combat the effects of channel fading. The optimal diversity combiner of the present invention does not require any apriori knowledge of the channel for mitigating the effects of multipath fading.
The optimal adaptive weights are calculated based on the error calculation and then applied on the received signals. These weighted signals are then summed by the combiner. The error is calculated by taking the difference between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain. Likewise, for data segment, error is calculated by finding the difference between combiner output and the decision taken on Combiner output in their inverse transform domain.
As an embodiment of present invention, OFDM signals, which use multicarrier modulation signalling, can be optimally combined using the said adaptive weight estimation algorithm where weights are updated stepwise by minimizing the error for each subcarrier.
The present invention depicts a diversity combiner for optimal combining of received signals with effective channel estimation that mitigates the fading effects in a wireless communication receiver. The present invention depicts a diversity combiner where signal processing method steps are performed on the transform domain. Signals received by multiple antennas have an organized frame structure where each frame consists of preamble and blocks of data symbols separated by pilot symbols. Signals received by the antennas are amplified and their gains are adjusted with the help of an ADC which is further digitized.
The present invention describes a novel method of diversity combining in the transform domain performed in conjunction with channel equalization which is capable of removing intersymbol interference, intercarrier interference and mitigates the effects of fading to a greater extent thereby improving the data recovering performance at the receiver.
The present invention describes a novel method of diversity combining wherein channel equalization is achieved by adaptive weighting of the received signals in the transformed domain where the weighting coefficients are updated based on stochastic gradient descent method. The present invention describes a novel method of diversity combining in the transform domain which doesn?t requires any apriori knowledge of the channel for weight estimation.
The invention, herein described, utilizes diversity combining with channel estimation in transform domain for mitigating the effects of fading like frequency selective fading, where the optimal adaptive equalizer weights are calculated based on the error calculation. These estimated weights are applied on the received signals. These weighted signals are then summed by the combiner. The error is calculated by taking the difference between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain. Likewise, for data segment, error is calculated by finding the difference between combiner output and the decision taken on Combiner output in their inverse transform domain.
Figure 2 illustrates the block diagram of diversity receiver that performs optimum combining of received signals with channel estimation for Wireless communication according to one embodiment of the present invention.
The figure illustrates block diagram of an optimal diversity combiner for wireless communication which is capable of eliminating the effects of intersymbol interference (ISI) and multipath fading and recover the data efficiently at the receiver with the signal processing algorithm like channel estimation performed in transform domain and then effectively combine the diversity signals in accordance with the present invention. Diversity combiner of the present invention consists of diversity receiver and the signals received by the diversity branches of the receiver are processed in the transform domain. Received signals consist of symbols organized into frames. Each frame constitutes preamble followed by blocks of data symbols separated by pilot symbols.
RF Signals received at each diversity branch is converted to baseband by a mixer 201 by mixing it with local oscillator signal, and then digitized by analog -to - digital converter (ADC) 202. These digital baseband signals are passed through a serial to parallel converter 203 and provided to the transform block 204 which takes transform of the signal received at each of the diversity branches of the receiver. Let ri1, ri2, …. riN denote the N parallel outputs of the transform block 204 and i=1,2, ………….M where M denotes the number of diversity branches. The transformed output of each diversity branch is then provided to the corresponding weight application block 205 which multiply the transformed output with the adaptive weights wi1, wi2,… wiN, i=1,2,………….M computed by corresponding weight estimation block 212. The weight estimation block 212 estimates the weight adaptively by using stochastic gradient descent method which doesn’t require any apriori knowledge of the channel. Channel equalization is achieved by the appropriate weighting of the transformed signal which mitigates the effects of channel fading and reduces the ISI and noise. Adaptively weighted transformed signals are then combined by the combiner 206. Weight updation is done by computing error in the inverse transform domain. Inverse Transform block 207 takes the inverse transform of the signal input to the block. The error is calculated by taking the difference 208 between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain. Likewise, for data segment, error is calculated by finding the difference between combiner output and the decision taken by Detector 209 on Combiner output in their inverse transform domain. Computing error in inverse transform domain speeds up the convergence of stochastic gradient descent method. Combined channel equalization and diversity combining as explained above will improve the data recovery performance at the receiver by mitigating the effects of fading and noise.
In one embodiment, the figure 4 of the present invention relates to a method of diversity combining for a wireless communication receiver, the method comprising: receiving and converting a plurality of RF Signals at each diversity branch to a baseband signal by mixing it with a local oscillator signal by a mixer 201, digitizing the baseband signal (analog signal) by an analog to digital converter (ADC) 202 coupled to the mixer, converting a serial digital baseband signal to parallel digital baseband signal by a serial to parallel convertor 203 coupled to the ADC and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver, multiplying the transformed output of each diversity branch from transform block with the adaptive weights computed by a corresponding weight estimation block 212 by a weight application block 205 and combining an adaptively weighted transformed signals of each of the diversity branches by a combiner 206 which mitigates the effects of channel fading and reduces the ISI, ICI and noise.
The adaptive weights (weighting coefficients) are computed by using a stochastic gradient descent method. The adaptive weights are computed based on the error calculation, where the error is calculated by taking the difference between combiner output and prior known sequence for preamble/pilot segment in their inverse transform domain.
The channel effects are corrected using a transform domain equalizer and the weighting coefficients are determined without the apriori estimate of the channels. The weight updation of equalizer in transform domain is done dynamically by computing error in the inverse transform domain.
The channel equalization is achieved by the appropriate weighting of the transformed signal which mitigates the effects of channel fading and reduces the ISI, ICI and noise. The present invention method further obtains an inverse transform of the signal by an inverse transform block 207 coupled to the combiner, where the inverse transform block 207 obtains the inverse transform of the signal input to the transform block. The computing error in inverse transform domain speeds up the convergence of stochastic gradient descent method.
In another embodiment, the present invention relates to an optimal diversity combiner for a wireless communication receiver with multiple diversity branches, the optimal diversity combiner comprising: a mixer 201 receives and converts RF signals at the diversity receivers to baseband by mixing it with local oscillator signal, an analog-to-digital converter (ADC) 202 coupled to the mixer 201 which digitizes the baseband signal, a serial to parallel converter module 203 coupled to the analog-to-digital converter (ADC), wherein the serial to parallel converter module is used to convert a serial digital baseband signal to parallel digital baseband signal and the converted signal is provided to a transform block 204 coupled to the serial to parallel convertor which takes transform of the signal received at each of the diversity branches of the receiver, a weight application block 205 coupled to the transform block 204, wherein the weight application block 205 is used to receive the transformed output of each diversity branch and multiply the transformed output with the adaptive weights computed by a corresponding weight estimation block 212 and a combiner 206 coupled to the weight application block 205, wherein the combiner 206 effectively combines the adaptively weighted transformed signals of each of the diversity branches which mitigates the effects of channel fading and reduces the ISI, ICI and noise.
In another preferred embodiment of the present invention, error computation is performed in the transform domain. The error is calculated by taking the difference 208 between combiner output and prior known sequence for preamble/pilot segment in their transform domain.
In another preferred embodiment of the present invention, diversity combining with channel estimation can be used in conjunction with multicarrier modulation signalling in a fading environment to improve the data rate.
Figure 3 shows the constellation diagram of the received signal (Fig. 3a) at the diversity branches at an SNR of 15dB and the constellation diagram of output combiner (Fig. 3b) obtained as an outcome in accordance with an embodiment of the present invention. Fig. 3c shows the error curve and we can see that the error has been converged. From Fig. 3b and Fig. 3c, it is clear that the data can be retrieved at the receiver without any loss of information.

Advantages of the present invention

The optimal diversity combiner with an appropriate channel estimation method in the transform domain retrieves the original transmitted information by mitigating the effects of channel fading and improves SNR.
The combiner provides better performance than the existing methods for wireless communication even when the channels are heavily multipath faded with low SNR. Further, the combiner with appropriate channel estimator improves SNR, BER (Bit Error Rate) and ISI mitigation performance.
The present invention utilizes multipath faded signals at diversity receivers to enhance the signal reception at the receiver with the diversity combiner and suppresses the noise.
The present invention of diversity combining is applicable for space diversity or frequency diversity or combination of these diversity input channels.
The present invention describes a method to enhance data recovery performance of digital communication receiver by mitigating the effects of multipath fading, ISI and noise with diversity combiner and channel estimation in transformed domain.
The present invention also describes a method of diversity combining and channel estimation that can be used with multicarrier modulation signalling in a multipath fading environment to improve the data rate. Error estimation in the inverse transform domain has been found to be better in decoding the data under low SNR conditions and this has been substantiated in the experimental result shown in fig. 3.
Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. Therefore, the scope of the invention shall be defined and protected by the following claims and their equivalents.
FIGS. 1-4 are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. FIGS. 1-4 illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the art.
In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.
It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.