A method for transmission by a transmitting node in a communication network using a plurality of non-orthogonal carriers, including obtaining, by a processor in the transmitting node, an information element data set comprised of a first number of elements, applying, by the processor, a transform matrix to the information element data set to obtain an output samples data set comprised of a second number of elements, the transform matrix being based on a non-linear function applied to a non-orthogonal frequency division matrix comprised of a plurality of columns wherein each column is associated one of the plurality of non-orthogonal carriers, and transmitting the output samples data set from a transmitter in the transmitting node.

FIELD OF THE INVENTION

The aspects described herein relate to an improvement over Orthogonal Frequency Division Multiplexing (OFDM), namely Root Non-Orthogonal Frequency Division Multiplexing (RNOFDM), for use in wireless communication systems such as, for example, Wi-Fi (IEEE 802.11 standards) and LTE (3GPP standards).

BACKGROUND

Orthogonal Frequency Division Multiplexing (OFDM) is a known technology for wireless communication that has the benefit of low equalization complexity. Currently, Wi-Fi utilizes OFDM for both its uplink and downlink transmissions, and LTE utilizes OFDM for its downlink transmissions.

One way to increase the transmission rate of an OFDM signal without increasing its equalization complexity is to relax the orthogonal nature of the signal; however, this increased rate may come at the expense of a more complex detection algorithm at the receiver. One way to achieve this increased transmission rate is by increasing the number of subcarriers in one OFDM symbol, while preserving its duration and bandwidth. Such a modulation technique is referred to herein as Non-Orthogonal Frequency Division Multiplexing (NOFDM). In an example of a NOFDM system, a plurality of non-orthogonal carriers is utilized for transmission. As used herein, a plurality of non-orthogonal carriers is a set of carriers in which at least some of the carriers are non-orthogonal to each other. In such a system, the plurality of non-orthogonal carriers may also include carriers which are orthogonal to each other.

Aspects of NOFDM are known to those skilled in the art; however, NOFDM has not been adopted in any standards due to its inability to deliver significant improvement in capacity over the capacity delivered by OFDM. There is a need for a NOFDM technique that provides an improvement in capacity over the capacity delivered by OFDM, while maintaining a low equalization complexity.

SUMMARY

Systems, devices and methods for Root Non-Orthogonal Frequency Division Multiplexing (RNOFDM) are provided herein.

In an aspect, a method is provided for method for transmission by a transmitting node in a communication network using a plurality of non-orthogonal carriers. The method includes obtaining, by a processor in the transmitting node, an information element data set comprised of a first number of elements, applying, by the processor, a transform matrix to the information element data set to obtain an output samples data set comprised of a second number of elements, the transform matrix being based on a non-linear function applied to a non-orthogonal frequency division matrix comprised of a plurality of columns wherein each column is associated with one of the plurality of non-orthogonal carriers, and transmitting the output samples data set from a transmitter in the transmitting node.

Other features and advantages of the present invention should be apparent from the following description which illustrates, by way of example, aspects of the invention.

DETAILED DESCRIPTION

Systems, devices and methods for conducting interference resolution in a communication system are provided.

The systems and methods disclosed herein can be applied to various types of communication systems, including wireless communication systems and wired communication systems. For example, the systems and methods disclosed herein may be used with Cellular 4G (including Long Term Evolution (LTE), LTE Advanced, and WiMAX), 5G, cellular backhaul, Wi-Fi, Ultra Mobile Broadband (UMB), and other point-to-point or point-to-multipoint wireless technologies, including communication systems used in wireless personal area networks (WPAN), wireless local area networks (WLAN), wireless metropolitan area networks (WMAN) and wireless wide area networks (WWAN). The systems and methods disclosed herein may also be implemented in wired communication systems including, but not limited to, hybrid fiber-coax cable modem systems. For concise exposition, the descriptions provided herein use terminology and aspects of particular communication technologies and standards; however, the devices, systems and methods described herein are also broadly applicable to other communication technologies and standards, both wired and wireless.

FIG. 1is a block diagram of a communication network in which systems and methods disclosed herein may be implemented in accordance with aspects of the invention. A macro base station (access node)110is connected to a core network102through a backhaul connection170. In an embodiment, the backhaul connection170is a bidirectional link or two unidirectional links. The direction from the core network102to the macro base station110is referred to as the downstream or downlink (DL) direction. The direction from the macro base station110to the core network102is referred to as the upstream or uplink (UL) direction. Subscriber stations (terminal nodes)150aand150dcan connect to the core network102through the macro base station110. Wireless links190between subscriber stations150and the macro base station110are bidirectional point-to-multipoint links, in an embodiment. The direction of the wireless links190from the macro base station110to the subscriber stations150is referred to as the downlink or downstream direction. The direction of the wireless links190from the subscriber stations150to the macro base station110is referred to as the uplink or upstream direction. Subscriber stations are sometimes referred to as user equipment (UE), users, user devices, handsets, terminal nodes, or user terminals and are often mobile devices such as smart phones or tablets. The subscriber stations150access content over the wireless links190using base stations (access nodes), such as the macro base station110, as a bridge.

In the network configuration illustrated inFIG. 1, an office building120(1) causes a coverage shadow104. A pico station (access node)130can provide coverage to subscriber stations (terminal nodes)150band150ein the coverage shadow104. The pico station130is connected to the core network102via a backhaul connection170. The subscriber stations150band150emay be connected to the pico station130via links that are similar to or the same as the wireless links190between subscriber stations150aand150dand the macro base station110.

In office building120b, an enterprise femto base station (access node)140provides in-building coverage to subscriber stations (terminal nodes)150cand150f. The enterprise femto base station140can connect to the core network102via an internet service provider network101by utilizing a broadband connection160provided by an enterprise gateway103.

FIG. 2is a functional block diagram of a base station275in accordance with aspects of the invention. In various embodiments, the base station275may be a mobile WiMAX base station, an LTE evolved Node B (eNB or eNodeB), or other wireless base station or access node of various form factors. For example, the macro base station110, the pico station130, the enterprise femto base station140ofFIG. 1may be provided, for example, by base station275ofFIG. 2. Base station275includes a processor281that is coupled to a transmitter-receiver (transceiver)279, a backhaul interface285, and storage283.

Transmitter-receiver279is configured to transmit and receive communications wirelessly with other devices. Base station275generally includes one or more antennae for transmission and reception of radio signals. The communications of transmitter-receiver279may be with one or more terminal nodes.

Backhaul interface285provides communication between the base station275and a core network. This communication may include communications directly or indirectly (through intermediate devices) with other base stations, for example to implement the LTE X2 interface. The communication may be over a backhaul connection such as, for example, the backhaul connection170ofFIG. 1. Communications received via the transmitter-receiver279may be transmitted, after processing, on the backhaul connection via backhaul interface285. Similarly, communication received from the backhaul connection via backhaul interface285may be transmitted by the transmitter-receiver279. Although the base station275ofFIG. 2is shown with a single backhaul interface285, other embodiments of the base station275may include multiple backhaul interfaces. Similarly, the base station275may include multiple transmitter-receivers. In such a scenario, the multiple backhaul interfaces and transmitter-receivers may operate according to different protocols. Communications originating within the base station275, such as communications with other base stations, may be transmitted on one or more backhaul connections by backhaul interface285. Similarly, communications destined for base station275may be received from one or more backhaul connections via backhaul interface285.

Processor281can process communications being received and transmitted by the base station275. Storage283stores data for use by the processor281. Storage283may also be used to store computer readable instructions for execution by processor281. The computer readable instructions can be used by base station275for accomplishing the various functions of base station275. In an aspect, storage283, or parts of storage283, may be considered a non-transitory machine readable medium. For concise explanation, base station275or aspects of base station275are described as having certain functionality. It will be appreciated that in some embodiments, this functionality is accomplished by processor281in conjunction with storage283, transmitter-receiver279, and backhaul interface285. Furthermore, in addition to executing instructions, processor281may include specific purpose hardware to accomplish some functions.

FIG. 3is a functional block diagram of a terminal node355in accordance with aspects of the invention. In various embodiments, terminal node355may be a mobile WiMAX subscriber station, an LTE user equipment, or other wireless terminal node of various form factors. The subscriber stations150ofFIG. 1may be provided, for example, by terminal node355ofFIG. 3. Terminal node355includes a processor361that is coupled to a transmitter-receiver (transceiver)359, a user interface365, and storage363.

Transmitter-receiver359is configured to transmit and receive communications with other devices. For example, transmitter-receiver359may communicate with base station275ofFIG. 2via its transmitter-receiver279. Terminal node355generally includes one or more antennae (not shown) for transmission and reception of radio signals. Although terminal node355ofFIG. 3is shown with a single transmitter-receiver359, other embodiments of terminal node355may include multiple transmitter-receivers. In such a scenario, the multiple transmitter-receivers may operate according to different protocols.

Terminal node355, in many aspects, provides data to and receives data from a person (user). Accordingly, terminal node355includes user interface365. User interface365includes functionality for communicating with a person. User interface365, in an aspect, includes a speaker and a microphone for voice communications with the user, a screen for providing visual information to the user, and a keypad for accepting alphanumeric commands and data from the user. In some aspects, a touch screen may be used in place of or in combination with the keypad to allow graphical inputs in addition to alphanumeric inputs. In an alternate aspect, user interface365includes a computer interface, for example, a universal serial bus (USB) interface, to interface terminal node355to a computer. For example, terminal node355may be in the form of a dongle that can be connected to a notebook computer via user interface365. The combination of computer and dongle may also be considered a terminal node. User interface365may have other configurations and include functions such as vibrators, cameras, and lights.

Processor361can process communications being received and transmitted by terminal node355. Processor361can also process inputs from and outputs to user interface365. Storage363stores data for use by processor361. Storage363may also be used to store computer readable instructions for execution by processor361. The computer readable instructions may be used by terminal node355for accomplishing the various functions of terminal node355. In an embodiment, storage363, or parts of storage363, may be considered a non-transitory machine readable medium. For concise explanation, terminal node355or aspects of terminal node355are described as having certain functionality. It should be appreciated that in some aspects, this functionality is accomplished by processor361in conjunction with storage363, transmitter-receiver359, and user interface365. Furthermore, in addition to executing instructions, processor361may include specific purpose hardware to accomplish some functions.

FIG. 4is a block diagram of transform module400that is used in implementing root non-orthogonal frequency division multiplexing (RNOFDM) according to aspects of the invention. Transform module400receives, or accesses, information element data set410that may be comprised of, for example, data elements that are to be transferred by a transmitter chain in a communication system. Information element data set410may be arranged in any type of known data arrangement or structure such as, for example, an array, a matrix, a record, an object, a data set, etc. Transform module400applies a data set transform to generate output samples data set420which may be transmitted in a communication system by a transmitter chain, thereby implementing root non-orthogonal frequency division multiplexing (RNOFDM). The data set transform that is applied by transform module may be a matrix, a table, or other known data structure. Output samples data set420may be arranged in any type of known data arrangement or structure such as, for example, an array, a matrix, a record, an object, a data set, etc.

FIG. 5is a block diagram of a transmitter chain501in accordance with aspects of the invention. Transmitter chain501is used herein to process and transmit an input stream of data according to aspects of the invention, implementing root non-orthogonal frequency division multiplexing (RNOFDM). Transmitter501comprises encoder510, scrambler511, a modulation mapper512, an FFT or DFT module514(optional), a resource mapper517, a transform518, a cyclic prefix (CP) adder module519and a filter520. Filter520may be one or more of various types of known filters, such as a raised-cosine time-domain window based filter, and filter520may be optionally applied. Scrambler510and encoder511may be optional. As seen inFIG. 5, the output of transmitter chain501is transmitted via antenna550. In the case of a wired communication system, the output of transmitter chain501is transmitted via a communication wire or cable. One skilled in the art would know how to apply the single-in-single-out (SISO) transmitter chain501illustrated inFIG. 5to a multiple-input-multiple-output (MIMO) application/environment (e.g., multiple “RNOFDM” SISO chains).

FIG. 6is a flowchart illustrating an exemplary method for generating a data set transform (such as the transform400ofFIG. 4) for use in implementing root non-orthogonal frequency division multiplexing (RNOFDM) according to aspects of the invention. It should be noted that, in an aspect, the generation of a data set transform may be performed before operation of the communication system, a priori, such as for example before implementation of the transmitter chain. In an aspect, multiple data set transforms may be generated beforehand and then an appropriate one of the data set transforms can be selected during operation of the communications system. In step601, a Non-Orthogonal Frequency Division Multiplexing (NOFDM) matrix, hNOFDM, is defined, wherein each column of the matrix is associated with one of a multiple of non-orthogonal subcarriers.

In this regard, in order to increase the transmission rate of OFDM, the orthogonality condition that is imposed on the OFDM subcarriers may be relaxed. Several techniques are known in the art to generate a non-orthogonal modulation based on OFDM. In one example, the number of subcarriers that are multiplexed (i.e., transformed) into one symbol is chosen, beyond the number, N, of orthogonal subcarriers. The increase in the number of subcarriers is denoted by a multiple M, which is selected for convenience to be a power of 2. In other words, one OFDM symbol, {right arrow over (y)}, of duration T and consisting of N multiplexed orthogonal subcarriers, is replaced by one NOFDM symbol, {right arrow over (y)}′, also of duration T and consisting of NM multiplexed subcarriers. In this case, the NOFDM symbol, {right arrow over (y)}′ may be represented as:
{right arrow over (y)}′=hNOFDM{right arrow over (x)}′(1)
Where

{right arrow over (x)}′≡NM×1 vector, is the input to the NOFDM multiplexer;

{right arrow over (y)}′≡N×1 vector, is the output from the NOFDM multiplexer; and

hNOFDM=N×NM matrix, is the NOFDM Matrix, defined as

Both output vectors, {right arrow over (y)} and {right arrow over (y)}′, respectively, may be oversampled by a multiple equal to M, or equivalently, to force the total number of samples for both {right arrow over (y)} and {right arrow over (y)}′ to equal NM using a sampling frequency, f′s, equal to Mfsfor both. The oversampling does not change the duration of the output vectors, {right arrow over (y)} and {right arrow over (y)}′ since the oversampling is still equal to

NMMfs=Nfs=T.
The choice of oversampling by a multiple equal to M forces hNOFDMto be square. In this scenario, oversampling the NOFDM symbol, {right arrow over (y)}′, by a multiple M corresponds to having a multiplexing matrix defined as:

ω⁢⁢e-j⁢2⁢πNM;
and

{right arrow over (y)}′≡NM×1 vector, is the output vector from the NOFDM multiplexer.

In this case, the lthcolumn of hNOFDM,hNOFDM,l, is a subcarrier which carries the information corresponding to the lthelement of {right arrow over (x)}′, and may be which is defined as:

In step602, the NOFDM matrix, hNOFDM, is multiplied by its complex conjugate transpose matrix (i.e. Hermitian) to obtain a matrix product hNOFDMhNOFDM*. In an aspect, in order to improve the spectral efficiency of NOFDM, in particular when the spectral threshold level is ≦−40 dBr, the variance between the eigenvalues of hNOFDMhNOFDM* may be reduced. One way to reduce the variance is by replacing hNOFDMwith

hNOFDM⁢hNOFDM*n,
or by replacing Equation (1) with:

y→′=hNOFDM⁢hNOFDM*n⁢⁢x→′(6)
where n is selected to be an integer. Such a modulation may be referred to as Root-NOFDM (RNOFDM). In an aspect, the product hNOFDMhNOFDM* corresponds to a square NM×NM matrix, and the duration of the RNOFDM symbol {right arrow over (y)}eis equal to that of the OFDM symbol {right arrow over (y)}, T.

In step603, a non-linear function (e.g., a root function such as an nthroot function

•n)
is applied to the matrix product to generate a data set transform (e.g., to generate

hNOFDM⁢hNOFDM*n).
The data set transform (e.g., transform module400ofFIG. 4, and transform518ofFIG. 5) may then be used to transform information elements (such as information element data set410ofFIG. 4, and output of resource mapper517ofFIG. 5) into an output samples data set (such as information element data set420ofFIG. 4, and output of transform518ofFIG. 5) for transmission according to RNOFDM, as described below with respect toFIG. 7according to aspects of the invention.

FIG. 7is a flowchart illustrating an exemplary method for applying a data set transform (such as transform module400ofFIG. 4) in the implementation of RNOFDM according to an aspect of the invention. In step701, an information element data set, {right arrow over (x)}′, is obtained or accessed, wherein the information element data set is comprised of a first number of elements.

A data set transform is applied to the information element data set in step702to obtain an output samples data set, {right arrow over (y)}″, comprised of a second number of elements M. The data set transform may, for example, be generated as described above with respect toFIG. 6.

In step702, a filter (such as filter520ofFIG. 5) may be optionally implemented. For example, in an aspect, a filter may be applied in which a raised-cosine time-domain window is used. A raised-cosine window is defined by its roll-off factor: the larger the roll-off factor of the window, the faster the rate of decay of its Fourier Transform. In an aspect, other types of windows may be used instead of the raised-cosine window. Examples of other windows include the Hamming window, the Hanning window, the Blackman-Harris window, and others. In addition, other techniques exist that may be used to speed the rate of decay of the power spectral density (PSD) of RNOFDM. Examples of such other techniques include the Filter Bank Multi-Carrier (FBMC) technique, which avoids using a Cyclic Prefix, and the Universal Filtered Multi-Carrier (UFMC) which is effective for short packets. FBMC performs a subcarrier filtering of the OFDM signal, while UFMC performs a sub-band filtering of the OFDM signal. Both techniques may be used for filtering the RNOFDM signal.

In an aspect, the PSD of NOFDM may be forced to decay below a spectral threshold using a cyclic Step-wise Gaussian Band Pass Filter (BPF) with a baseband-equivalent Transfer Function, H(f), which may be expressed mathematically as:

In step703, the output samples data set, {right arrow over (y)}′, is transmitted over a communications channel. In this manner, RNOFDM as described herein is utilized to achieve improved performance as compared to OFDM or known NOFDM techniques.

In this regard,FIG. 8is a graph depicting the performance of RNOFDM in comparison to OFDM, according to aspects of the invention. InFIG. 8, the spectral efficiency, ηOFDM, for the non-filtered OFDM signal using a raised-cosine window with a 12.5% roll-off factor (blue curves) is compared with that of the filtered RNOFDM signal using the BPF described in Equation (7) with σf=0.022097 and using a raised-cosine time window with a 12.5% roll-off factor after taking into consideration their relative bandwidths,

WOFDMWNOFDM⁢❘-40⁢dBr,
defined at a spectral threshold level of −40 dBr, for NM=64, 128, 256, 512, M=8 and n=5. The relative improvements in spectral efficiency that NOFDM offers over OFDM are shown inFIG. 7, namely 11% at 10 dB SNR, 25% at 20 dB SNR and 36% at 30 dB SNR, for NM=64 subcarriers.

In one aspect, the performance results described above are obtained under the following example assumptions and constraints.

Example Assumptions:A1: The signal, {right arrow over (y)}′, is transmitted using one antenna over a channel that is contaminated by an Additive White Gaussian Noise (AWGN), and is received by one antenna;A2: The OFDM signals that are selected as bases to develop the RNOFDM signal have N=8, 16, 32 and 64 subcarriers;A3: RNOFDM uses a multiple M=8 where NM is the number of subcarriers in the initial NOFDM signal and its number of samples;A4: The duration, T, of the RNOFDM symbol is identical to the duration, T, of the OFDM symbol;A5: The total signal energy used in one OFDM signal is identical to the total signal energy used in one NOFDM signal, which is also equal to the total signal energy used in one RNOFDM signal; andA6: Results inFIG. 8are obtained for the spectral efficiency versus the received normalized signal-to-noise ratio (SNR) for the OFDM signal and the RNOFDM signal. The normalized signal-to-noise ratio (SNR) is obtained for both signals, the OFDM signal and the RNOFDM signal, by dividing their total SNR by N.

Example Constraint:C1: The spectral threshold level is set at −40 dBr.

A summary of the spectral efficiency ratios,

ηOFDMηNOFDM⁢❘-40⁢dBr,
is shown in Table III below with NM=64. From Table III, it may be seen that the improvements that Equation (6) offers over Equation (1) may reach a peak value when n=4

It should be noted that the above-described assumptions, constraints and performance data and comparisons are exemplary only and that aspects of the invention as described herein are not limited by such assumptions, constraints and performance data.

The foregoing systems and methods and associated devices and modules are susceptible to many variations. Additionally, for clarity and concision, many descriptions of the systems and methods have been simplified. For example, the figures generally illustrate one of each type of device (e.g., one access node, one terminal node), but a communication system may have many of each type of device. Similarly, descriptions may use terminology and structures of a specific wireless standard, such as WiFi or LTE. However, the disclosed systems, devices and methods are more broadly applicable to wireless and wired communication systems, including for example, to hybrid fiber-coax cable modem systems.

Those of skill will appreciate that the various illustrative logical blocks, modules, units, and algorithm steps described in connection with the embodiments disclosed herein can often be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular constraints imposed on the overall system. Skilled persons can implement the described functionality in varying ways for each particular system, but such implementation decisions should not be interpreted as causing a departure from the scope of the invention. In addition, the grouping of functions within a unit, module, block, or step is for ease of description. Specific functions or steps can be moved from one unit, module, or block without departing from the invention.

The various illustrative logical blocks, units, steps and modules described in connection with the embodiments disclosed herein can be implemented or performed with a processor. As used herein a processor may be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any portion or combination thereof that is capable of performing the functions described herein. A general purpose processor can be a microprocessor, but in the alternative, the general purpose processor can be any processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm and the processes of a block or module described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium. An exemplary storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC. Additionally, device, blocks, or modules that are described as coupled may be coupled via intermediary device, blocks, or modules. Similarly, a first device may be described as transmitting data to (or receiving from) a second device when there are intermediary devices that couple the first and second device and also when the first device is unaware of the ultimate destination of the data.