WO2018179010A1

WO2018179010A1 - Wavelength-based modulation of orthogonal frequencies

Info

Publication number: WO2018179010A1
Application number: PCT/IN2018/050179
Authority: WO
Inventors: Vinod Kumar MADAIAH; Kumar Nellicherry Sivarajan
Original assignee: Tejas Networks Limited
Priority date: 2017-03-31
Filing date: 2018-03-28
Publication date: 2018-10-04

Abstract

The invention related to a method for transmitting a signal using wavelength-based modulation in a network. In one embodiment this can be accomplished by identifying a fundamental frequency (f0) of the signal provided by the network, and using the same to form one or more of higher harmonic frequencies. The identified frequencies are orthogonal to each other over a time interval of 1/f0 seconds. Identifying wavelength of each of the harmonic frequencies and modulating each of the identified wavelength with a symbol. Summing all the modulated harmonics and transmit over channel or store the same for further processing.

Description

Wavelength-bas ed Modulation of Orthogonal F requenc ies

F ield of the Invention

The present invention related to a wireless communication and, more particularly to a method for transmitting a signal using wavelength-based modulation in a network.

¾

Background of the Invention

In order to increase the information carrying capacity for any type of communications highway, requires an understanding of the basic theory underlying channel capacity as developed by C laude S hannon and Ralph

¾ Hartley. The S hannon-Hartley Theorem is an application of the noisy channel coding Theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes channel capacity, a bound on the maximum amount of error-free digital data (pulse based information) that can be transmitted over a

¾ communication link, with a specified bandwidth and in the presence of the noise interference. The theorem is based on the assumption that the signal power is bounded and the Gaussian noise process is characterized by a known power or power spectral density. To achieve this goal, conventional methods attempt to increase the number of bits per single modulating ttl frequency using efficient technology enhancements. The improvement is limited since noise on the channel remains the same.

C onsidering all possible multi-level and multi-phase encoding techniques, the S hannon-Hartley theorem states that the channel capacity C, meaning the theoretical upper bound on the rate of clean (error free) data that can be sent with a given average signal power S through an analog communication channel subject to additive white Gaussian noise of power N is given by C =B log₂(1 +S/N) where C is the channel capacity in bits per second, B is the bandwidth of the channel in hertz, S is the total signal power

¾ over the bandwidth, measured in watts, N is the total noise power over the bandwidth, measured in watts, and S/N is the signal-to-noise ratio (S NR) of the communication signal to the Gaussian noise interference, expressed as a straight power ratio.

The S hannon-Hartley Theorem has been applied to all conventional

¾ communications systems and provides maximum data rate supported given the bandwidth of the channel and the S ignal to Noise Ratio. The limitation in the S hannon-Hartley Theorem is to communicate more bits for same signal power :S ^"and same bandwidth :B ~

In view of the above, there is a need in the art for a method and

¾ system for transmitting a signal in a network which can provide surplus spectral efficiency.

S ummary of the Invention

An aspect of the present invention is to address at least the above- ttl mentioned problems and/or disadvantages and to provide at least the advantages described below.

Accordingly, an aspect of the present invention is to provide a method for transmitting an information signal in a network. The method including the steps of transmission of the signals in the form of bits (0,1 ) from a transmitter to a receiver. The method further identifies a fundamental frequency (f₀) of the signal provided by the network, and using the same to form a plurality of other higher harmonic frequencies (f_{1 (} f₂, fad .f_n), where the identified frequency are orthogonal to each other over a time interval of 1 f₀ seconds.

¾ The method furthermore identifies wavelength of each of the harmonic frequencies. Modulating each of the identified wavelength with a symbol, where the symbol includes binary or m-Ary. S umming all the modulated harmonics for further processing, including but not limited to transmission over channel or storing in memory for discrete-time signal processing.

¾ 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.

¾ Brief description of the drawings

F or a better understanding of the solution, embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which:

FIG . 1 is an exemplary block diagram depicting a wireless ttl communication system.

FIG . 2 is a flow chart of a method for transmitting an information signal in a network, according to one embodiment of the present invention.

FIG . 3 is an implementation at the transmitter of wavelength- modulation, according to one embodiment of the present invention. FIG . 4 shows example illustration of the implementation of wavelength modulation of F igure 3.

FIG . 5 shows an implementation of matched filter at the Receiver.

P ersons skilled in the art will appreciate that elements in the figures ¾ are illustrated for simplicity and clarity and may have not been drawn to scale. F or 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 ¾ used to depict the same or similar elements, features, and structures.

Detail description of the Invention

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of ¾ 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 ttl 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.

¾ It is to be understood that the singular forms a, _ an, _ and ttie _ 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,

¾ 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 was intended to provide.

¾ F igures, 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 ttl 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.

A wireless communication system regarding one example

¾ environment of the invention will be set forth by referring to FIG . 1 . A transmitter 1 1 0 has one or more transmit antenna and a receiver 120 has one or more receive antenna. A system in FIG . 1 is typically used for a cellular communication system, but it is not limited to such a system. It is also possible for the system in FIG . 1 to be applied to a wireless LAN, a fixed

¾ wireless access network, etc. The transmitter has a function to modulate user data to convert it into a radio frequency (R F) signal in order to transmit the user data to the receiver wirelessly. The R F signal transmitted from the one or more transmit antennas arrives at the receive antenna of the receiver through one or more channels 130 (propagation paths). The receive antenna

¾ receives a signal in which the signal transmitted from the one or more antenna are mixed. The receiver performs a demodulation process to the received signal from the receive antenna to reproduce the user data. Often modulation and demodulation may be performed in multiple stages for implementation ease and low cost.

ttl FIG . 2 is a flow chart of a method for transmitting an information signal in a network, according to one embodiment of the present invention. At step 210, the method transmit one or more signals, where each signal is in the form of bits (0,1 ). At step 220, the method identifies a fundamental frequency (fo) of the transmitted signal provided and uses the same to form a plurality of other higher harmonic frequencies (f_{1 (} f₂, fad .f_n). The identified frequencies are orthogonal to each other over a time interval of 1 /f₀ seconds, and the higher harmonic frequencies are for example f1 = 2*f0 (Hz), f2=3*f0 (Hz), etc. Assuming, the total orthogonal frequencies may be N. At step 230, the

¾ method identifies wavelength of each of the harmonic frequencies (i.e.) identifying each wavelength of the N frequencies. The identified wavelength of each frequency are used to send bit or symbol such that each bit or symbol are sent on sequential number of wavelengths. At step 240, the method modulates each of the identified wavelength with a symbol, where

¾ the symbol includes binary or m-ary. In an example embodiment, the modulating wavelength including multiplying each bit or symbol with a single wavelength of frequency fO and transmit a waveform of Xo(t). The subsequent wavelength is multiplied by one bit with first wavelength of a frequency f1 =2*f0 and multiply another bit with second wavelength of the

¾ same frequency f1 and transmit a waveform X 1 (t), and so on. F urthermore, the fundamental period is based on inverse of fundamental orthogonal frequency, fO, so that modulation of one symbol per wavelength is achieved. The time-duration for which each symbol is applied on any particular input- line is equally distributed between all the bits in that particular input-line. At ttl step 250, the method sums all the modulated harmonics and store the same for further processing. Adding of all the modulated harmonics (all cycles) i.e. all the waveforms X0(t), X 1 (t), ϋ X N(t) and summing the same to transmit onto the channel to one or more receiver. Assuming if there are N orthogonal frequencies, then there are N*(N+1 )/2 wavelengths and therefore N*(N+1 )/2 symbols can be transmitted over time-interval of 1 /fO seconds. F urther, if each wavelength had S ignal-to-Noise-Ratio as value of S NR, then the capacity of the channel is given by i.e. C = N*(N+1 )/2*f0*log(1 +S NR), where fO is the fundamental frequency. It can be appreciated that this capacity is ¾ (N+1 )/2 times more than S hannon Hartley Theorem for the same S NR . If N takes a value of 1000, then this new capacity is about 500 times more.

In view of the above, the C hannel Capacity Limit Formula is: m

R is bit rate, C is channel capacity, #gis number of cycles in i-th orthogonal frequency, i^¾¾is max. S NR of i-th orthogonal frequency; i is from 0 to N-1

¾ (or 1 to N). One can transmit N*(N+1 )/2 complex symbols per transmission opportunity. This is order of (approx.) 1000-fold increase in spectral efficiency if N is 1024. There are 2^A( M*{ M+ '\ )/2 ) distinct transmissions possible. If B is available Bandwidth, then if we split this band into N orthogonal frequencies, then as per existing definition of spectral efficiency,

¾ S E = R/B. However, we should define S E as symbols per sec per cycle and not symbols per second per Hz. Another version of C hannel Capacity Limit F ormula is:

E ach frequency is orthogonal to other so one should be able to demodulate or extract information individually. E ach wavelength of an orthogonal frequency is orthogonal to another wavelength of the same orthogonal frequency in time resources, e.g. as in Time Division Multiplexing (T DM), so one should be able to demodulate or extract information individually. Assuming using ideal filter (with roll off factor zero.). As per the

¾ Nyquist theorem one should be able to transmit 2 real symbols per cycle or Hz ^" one over cosine and another over sinusoidal waveform. Two real symbols are same as one complex symbol. S o using fundamental frequency one can transmit 2 real symbols. Then using second harmonics it is possible to transmit 2*2 real symbols. Then using N-th harmonics it is also possible to

¾ transmit N*2 real symbols. S um of all waveforms will provide the enormous capacity in the channel. S o the spectral efficiency can be given as :_N =(Total symbols)- (Total cycles).

E xample 1 : If T₀ = 1 s, B = 10 MHz, S NR₀ =63, then f₀=1 /T₀ =1 Hz, N= B fo = 10⁷ and C_T0 =1 = 10⁷ x (10⁷ +1 )/2xlog₂ (1 +63) ~= 3x10¹⁴ bps. Here :_T =

3& C/B = 3x10¹⁴/ 10⁷ = 3x10⁷ bps/Hz. Note: Though :_T= 3x10⁷ bps/Hz, we are transmitting :_N = 1 complex symbol per cycle.

E xample 2: If T₀ = 100s, B = 10 MHz, S NR₀ =63, then f₀=1 /T₀ =0.01 Hz, N= B/fo = 10⁹ and C_T0 =100= 10⁹ x (10⁹ +1 )/2xlog₂ (1 +63)/100 ~= 3x10¹⁶ bps. Here :_T = C/B = 3x10¹⁶/ 10⁷ = 3x10⁹ bps/Hz. This shows that as T₀ ttl increases :_T also increases. Note: Though :_T= 3x10⁹ bpspHz, we are transmitting :_N = 1 complex symbol per cycle.

F igure 3 is an implementation at the Transmitter of wavelength- modulation. A block of N*(N+1 )/2 bits (or symbols) are sent to Disparate S erial to Parallel C onverter (DS P C ). The DS PC will send bits (or symbols) disparately, meaning different number of bits are sent on each line (or input- line of wavelength-modulator), to a wavelength-modulator or cycle- modulator. For example, top or first input-line will send only one bit, second input-line will send two bits, and so on. The wavelength or cycle modulator

¾ performs the following: 1 ) modulate or multiply bit xO with a single wavelength of frequency fO and transmit a waveform X0(t). 2) multiply x1 with first wavelength of a frequency f1 =2*f0 and multiply x2 with second wavelength of the same frequency f1 and transmit a waveform X 1 (t). And so on till f_(N-1 ) = N*f0 to transmit a waveform X_ N-1 (t). These waveforms are

¾ summed up. A summer block can be a simple junction or node made of N wires to receive the N waveforms and one wire to transmit the summed waveform onto the channel. It can be appreciated that the time-duration for which each symbol is applied on any particular input-line is equally distributed between all the bits in that particular input-line. F or example, if

¾ there are two symbols in an input-line, as in the second input-line, then each is applied for 50% duration; whereas a symbol is applied for 100% duration in the first input-line. F undamental duration or period is based on inverse of fundamental orthogonal frequency, fO. S o in effect, we apply or modulate one symbol per cycle or wavelength. At the receiver, Matched filter operation is ttl performed. F igure 4 shows working example of F igure 3 using a block of bits of size 3.

F igure 4 shows simple illustration of F igure 3. We assume a block of 3 bits, say 1 ,1 and 0. These bits are BP S K encoded, meaning bit 1 is mapped to -1 Voltage level and bit 0 is mapped to +1 Voltage level. S o for this particular block we get -1 ,-1 , +1 as shown in the figure. These B PS K encoded bits or coded bits or just bits are disparately applied to the multipliers. Multiplier 1 will receive bit -1 , which after multiplication with a wavelength or cycle of frequency fO will output a waveform X0(t). Multiplier 2

¾ will receive bits -1 and +1 as shown. Multiplier 2 will perform two multiplications, that is, it will multiply first wavelength or cycle of frequency 2*f0 with bit +1 and then it will multiply the second wavelength of frequency 2*f0 with bit -1 . The output of Multiplier 2 will be X 1 (t). The waveforms X0(t) and X 1 (t) will be summed and transmitted towards the channel. It should be

¾ clear that we are transmitting 3 bits or symbols over two harmonics, fO and f1 . This same operation can be extended for other harmonics. If we had N linear harmonics, then we can transmit 1 bit over fO, 2 bits over f1 , three bits over f2, and so on upto N bits over f_(N-1 ) frequencies. The total transmitted bits is 1 +2+3+u + N = N*(N+1 )/2 bits in a time duration of 1 FO seconds. If

¾ each wavelength had S ignal-to-Noise-Ratio as value S NR, then capacity is equal to N*(N+1 )/2*fO*log(1 +S NR).

To demodulate the individual symbol at the receiver, one need to separate each of the received orthogonal frequencies and then demodulate the cycles from the separated frequencies and extract the estimate of ttl transmitted symbols. Alternatively, one has to first sample the waveform in discrete frequency-domain and then integrate and dump per cycle (using e.g. matched filters) in the time-domain. Other demodulation scheme (e.g. equalizer, correlation filter, phase-lock techniques, successive-interference- cancellation, MAP decoder, ML decoder, etc.) can also be employed. This operation can be extended to multiple access easily where a selected list of frequencies and cycles are allotted to each transmit receive pair. F urther, referring to telecommunication, the aspect can be used for storage and retrieval. The method further needs a plurality of corresponding match filters

¾ for detecting the transmitted symbols. If the number of unique symbols in a constellation is q, then each wavelength can be modulated in q unique ways. Therefore N*(N+1 )/2 wavelengths can be modulated in Matched_ F ilter_size = q^N^N+l )/!) different ways. At the receiver the number of Matched filters required is Matched_ F ilter_size (=q^A(N*(N+1 )/2)) to decode the transmitted

¾ symbols which is shown in figure 5. If the number of unique symbols in a constellation is 2, then q is equal to 2 (i.e. q=2) as in case of binary digits of bit 0 and bit 1 . In which case we could multiply a particular wavelength by either 0 volt or 1 volt (or in terms of BPS K we could multiply a particular wavelength by either -1 volt or +1 volt) per wavelength. F or q=2,

¾ Matched_, F ilter_size = 2^Λ(Ν*(Ν+1 )/2). In figure 5, the output of all matched filters is represented as Output of Matched-filter (OMF), e.g. OMF 1 , OMF2, ϋ , OMF(2^Acycles). O MF 1 is produced when received waveform is matched with, for a block of three bits of figure 3, X0(t). These OMF values are enough to detect the transmitted bits or may additionally be sent to ttl DE T E CTOR based on E uclidean distance in order to produce the estimate of transmitted bits.

Those skilled in this technology can make various alterations and modifications without departing from the scope and spirit of the invention. F or example, the sheer size of Matched_ F ilter_size makes implementation difficult for large N. However, improved and efficient matched filter is possible with N orthogonal sinusoidal matched filters with N voltage-threshold detectors and N orthogonal co-sinusoidal matched filters with N voltage- threshold detectors. Therefore, the scope of the invention shall be defined

¾ and protected by the following claims and their equivalents.

F igures are merely representational and are not drawn to scale. C ertain portions thereof may be exaggerated, while others may be minimized. F igures illustrate various embodiments of the invention that can be understood and appropriately carried out by those of ordinary skill in the

3ft 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

2¾ 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 t i 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-E nglish equivalents of the respective terms comprising_ and wherein, . respectively.

Claims

C laims

1 . A method for transmitting a signal in a network, the method comprising

¾ transmission of the signals in the form of bits (0,1 ) from a transmitter to a receiver;

identifying a fundamental frequency (f₀) of the signal provided by the network, and using the same to form a plurality of other higher harmonic frequencies (f_{1 (} f₂, fad .f_n) wherein the identified frequencies are orthogonal to ¾ each other over a time interval of 1 /f₀ seconds;

identifying wavelength of each of the harmonic frequencies; modulating each of the identified wavelength with a symbol, wherein the symbol includes binary or m-Ary; and

adding all the modulated harmonics for further processing which ¾ includes transmission over channel or demodulating/detecting at the receiver or storing in memory for discrete-time signal processing.

2. The method of claim 1 , further comprising:

detecting the transmitted symbols by a plurality of corresponding ttl matched filters.

3. The method of claim 2, wherein the matched filters includes improved and efficient matched filter with N orthogonal sinusoidal matched filters with N voltage-threshold detectors and N orthogonal co-sinusoidal matched filters t& with N voltage-threshold detectors.

4. The method of claim 1 , wherein the identified wavelength of each frequency are used to send bit or symbol such that each bit or symbol are sent on sequential number of wavelengths.

5. The method of claim 1 , wherein the step of modulating wavelength including multiplying each bit or symbol with a single wavelength of frequency fO and transmit a waveform Xo(t).

¾ 6. The method of claim 1 and 5, wherein multiplying one bit with first wavelength of a frequency |=2*f₀ and multiply another bit with second wavelength of the same frequency f-i and transmit a waveform X-i(t).

7. The method of claim 1 to 6, wherein the fundamental period is based ¾ on inverse of fundamental orthogonal frequency, f₀, so that modulation of one symbol per wavelength is achieved.

8. The method of claim 1 , wherein the step of adding all the modulated harmonics including receiving all the waveforms X₀(t), X-i(t), ϋ X_N(t) and ttl summing the same to transmit onto the channel.

9. The method of claim 1 , wherein the time-duration for which each symbol is applied on any particular input-line is equally distributed between all the bits in that particular input-line.

†

10. The method of claim 1 , wherein the total transmitted bits in a time duration of 1 /f₀ seconds is given by N*(N+1 )/2 bits, where N is the total number of orthogonal frequencies and if each wavelength had S ignal-to- Noise-Ratio as value of S NR, then the capacity of the channel is given by N*(N+1 )/2*fO*log(1 +S NR), where fO is the fundamental frequency.

¾ 1 1. A system for transmitting and receiving a signal in a network, the system comprising;

a transmitter including:

a Disparate S erial to Parallel C onverter (DS PC) for receiving a signal as input and disparately send a plurality of number of bits or ¾ symbols as an output wherein each line of output has a different number of bits or symbols;

a wavelength modulator coupled with the Disparate S erial to Parallel C onverter to receive each line of output of bits or symbols as input and modulate the same with a wavelength of hierarchy of harmonic frequencies;

a summer to add all the modulated harmonics and transmit over channel,

and

a receiver including a detector for detecting the transmitted symbols ttl by a plurality of corresponding match filters, wherein the plurality of match filters demodulate the individual symbol.