US20180343654A1

US20180343654A1 - Method and Apparatus for Asynchronous OFDMA/SC-FDMA

Info

Publication number: US20180343654A1
Application number: US15/992,860
Authority: US
Inventors: Javad Abdoli; Ming Jia; Jianglei Ma
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2014-03-31
Filing date: 2018-05-30
Publication date: 2018-11-29
Also published as: US10701685B2; US20160192353A1

Abstract

Various disclosed embodiments include methods and systems for communication in a wireless communication system. A method comprises receiving a signal corresponding to a plurality of modulated signals, each of the plurality of modulated signals corresponding to a unique electronic device. The method comprises filtering the received signal with a plurality of filters, each of which is matched to a corresponding filter in a respective electronic device to obtain a filtered signal for the respective electronic device. The method comprises performing a fast Fourier transform (FFT) operation on the filtered signal to obtain demodulated data corresponding to the respective electronic device.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No. 14/836,538, filed on Aug. 26, 2015 and entitled “Method and Apparatus for Asynchronous OFDMA/SC-FDMA,” which is a continuation in part (CIP) of U.S. application Ser. No. 14/231,217, now U.S. Pat. No. 9,419,770, filed on Mar. 31, 2014 and entitled “Method and Apparatus for Asynchronous OFDMA/SC-FDMA,” which are hereby incorporated by reference herein as if reproduced in its entirety.

TECHNICAL FIELD

The present disclosure is generally directed to asynchronous communication in a wireless communication system.

BACKGROUND

Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) systems are prevalent today. Typically, in an OFDMA system, the signals of several different users (i.e., entities that wish to communicate over the communication system) will each be assigned one or more unique subcarriers. Each subcarrier is generated and transmitted in a manner that allows all of the subcarriers to be transmitted concurrently without interfering with one another. Therefore, independent information streams can be modulated onto each subcarrier whereby each such subcarrier can carry independent information from a transmitter to one or more receivers.
Conventional OFDMA/SC-FDMA systems use a rectangular pulse shape, i.e., sinc in frequency, which has high side lobes. As a result, there are stringent synchronization requirements to maintain orthogonality. Timing advance signaling is required for synchronous multiple access, causing overhead. This overhead increases with the number of transmitters, which is a consideration in applications such as machine-type communication where a plurality of machines communicate with a base station. Moreover, OFDMA/SC-FDMA is highly sensitive to carrier frequency offset (CFO) mismatch between different electronic devices.
One way to avoid the aforementioned issues is to use Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation (OFDM/OQAM), which has become popular in the wireless community recently. However, using OFDM/OQAM has issues such as peak to average power ratio (PAPR), Multiple-Input Multiple-Output (MIMO) transmission, and time domain tails.
It would therefore be desirable to be able to provide a system that enjoys the benefits of OFDMA/SC-FDMA as its core waveform and yet offers the capability of asynchronous communication.

SUMMARY

According to one embodiment, there is provided a method of data transmission in a wireless communication system. The method comprises generating a signal corresponding to resource blocks assigned to an electronic device. The method comprises filtering the signal that corresponds to the resource blocks assigned to the electronic device with a spectrum shaping filter to reduce side lobe leakage in an adjacent frequency band to produce a filtered signal. The method comprises transmitting the filtered signal to a receiver in the communication system in a timeslot provided by a scheduler coupled to the receiver, the timeslot being independently determined with respect to other electronic devices communicating with the receiver.
In another embodiment, there is provided an electronic device for transmitting data in a wireless communication system. The electronic device comprises a modulator operative to generate a signal corresponding to resource blocks assigned to the electronic device. The electronic device comprises a spectrum shaping filter operative to filter the signal that corresponds to the resource blocks assigned to the electronic device to reduce side lobe leakage in an adjacent frequency band to produce a filtered signal. The electronic device comprises a transmitter operative to transmit the filtered signal to a receiver in the communication system in a timeslot provided by a scheduler coupled to the receiver, the timeslot being independently determined with respect to other electronic devices communicating with the receiver.
In another embodiment, there is provided a method of receiving a data transmission in a wireless communication system. The method comprises receiving a signal corresponding to a plurality of modulated signals, each of the plurality of modulated signals corresponding to a unique electronic device. The method comprises filtering the received signal with a plurality of filters, each of which is matched to a corresponding filter in a respective electronic device to obtain a filtered signal for the respective electronic device. The method comprises performing a fast Fourier transform (FFT) operation on the filtered signal to obtain demodulated data corresponding to the respective electronic device.
In another embodiment, there is provided an apparatus for receiving a data transmission in a wireless communication system. The apparatus comprises at least one processing device configured to receive a signal corresponding to a plurality of modulated signals, each of the plurality of modulated signals corresponding to a unique electronic device. The at least one processing device is configured to filter the received signal with a plurality of filters, each of which is matched to a corresponding filter in a respective electronic device to obtain a filtered signal for the respective electronic device. The at least one processing device is configured to perform a fast Fourier transform (FFT) operation on the filtered signal to obtain demodulated data corresponding to the respective electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:

FIG. 1 illustrates an example communication system for asynchronous communication according to one embodiment;

FIGS. 2A and 2B illustrate example devices that can implement asynchronous communication according to one embodiment;

FIG. 3 illustrates an example of a topology or system for implementing asynchronous communication according to one embodiment;

FIG. 4 illustrates the effect of down sampling on the spectrum of a band-pass signal;

FIG. 5 illustrates an example of a topology or system for implementing asynchronous communication according to another embodiment;

FIG. 6 illustrates an example of a topology or system for implementing asynchronous communication according to yet another embodiment;

FIGS. 7-9 illustrate BLER curves for various modulations compared with synchronous OFDMA;

FIG. 10 illustrates a flow diagram illustrating a method of operating an electronic device according to one embodiment; and

FIG. 11 illustrates a flow diagram illustrating a method of operating a receiver according to one embodiment;

FIG. 12 illustrates a diagram of an OFDM frame carrying OFDM symbols;

FIG. 13 illustrates graphs of a filtering signal and signals used to obtain the filtering signal; and

FIG. 14 illustrates a diagram of an embodiment fast-OFDM (f-OFDM) channel.

DETAILED DESCRIPTION

FIG. 1 illustrates an example communication system 100. In general, the system 100 enables multiple wireless or wired users to transmit and receive data and other content. The system 100 may implement one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), or single-carrier FDMA (SC-FDMA).
In this example, the communication system 100 includes electronic devices (ED) 110 a-110 c, radio access networks (RANs) 120 a-120 b, a core network 130, a public switched telephone network (PSTN) 140, the Internet 150, and other networks 160. While certain numbers of these components or elements are shown in FIG. 1, any number of these components or elements may be included in the system 100.
The EDs 110 a-110 c are configured to operate and/or communicate in the system 100. For example, the EDs 110 a-110 c are configured to transmit and/or receive via wireless or wired communication channels. Each ED 110 a-110 c represents any suitable end user device and may include such devices (or may be referred to) as a user equipment/device (UE), wireless transmit/receive unit (WTRU), mobile station, fixed or mobile subscriber unit, cellular telephone, personal digital assistant (PDA), smartphone, laptop, computer, touchpad, wireless sensor, or consumer electronics device.
The RANs 120 a-120 b here include base stations 170 a-170 b, respectively. Each base station 170 a-170 b is configured to wirelessly interface with one or more of the EDs 110 a-110 c to enable access to the core network 130, the PSTN 140, the Internet 150, and/or the other networks 160. For example, the base stations 170 a-170 b may include (or be) one or more of several well-known devices, such as a base transceiver station (BTS), a Node-B (NodeB), an evolved NodeB (eNodeB), a Home NodeB, a Home eNodeB, a site controller, an access point (AP), or a wireless router. The EDs 110 a-110 c are configured to interface and communicate with the internet 150 and may access the core network 130, the PSTN 140, and/or the other networks 160.
In the embodiment shown in FIG. 1, the base station 170 a forms part of the RAN 120 a, which may include other base stations, elements, and/or devices. Also, the base station 170 b forms part of the RAN 120 b, which may include other base stations, elements, and/or devices. Each base station 170 a-170 b operates to transmit and/or receive wireless signals within a particular geographic region or area, sometimes referred to as a “cell.” In some embodiments, multiple-input multiple-output (MIMO) technology may be employed having multiple transceivers for each cell.
The base stations 170 a-170 b communicate with one or more of the EDs 110 a-110 c over one or more air interfaces 190 using wireless communication links. The air interfaces 190 may utilize any suitable radio access technology.
It is contemplated that the system 100 may use multiple channel access functionality, including such schemes as described above. In particular embodiments, the base stations and EDs implement LTE, LTE-A, and/or LTE-B. Of course, other multiple access schemes and wireless protocols may be utilized.
The RANs 120 a-120 b are in communication with the core network 130 to provide the EDs 110 a-110 c with voice, data, application, Voice over Internet Protocol (VoIP), or other services. Understandably, the RANs 120 a-120 b and/or the core network 130 may be in direct or indirect communication with one or more other RANs (not shown). The core network 130 may also serve as a gateway access for other networks (such as the PSTN 140, the Internet 150, and the other networks 160). In addition, some or all of the EDs 110 a-110 c may include functionality for communicating with different wireless networks over different wireless links using different wireless technologies and/or protocols. Instead of wireless communication (or in addition thereto), the EDs may communicate via wired communication channels to a service provider or switch (not shown), and to the internet 150.
Although FIG. 1 illustrates one example of a communication system, various changes may be made to FIG. 1. For example, the communication system 100 could include any number of EDs, base stations, networks, or other components in any suitable configuration.
FIGS. 2A and 2B illustrate example devices that may implement the methods and teachings according to this disclosure. In particular, FIG. 2A illustrates an example ED 110, and FIG. 2B illustrates an example base station 170. These components could be used in the system 100 or in any other suitable system.
As shown in FIG. 2A, the ED 110 includes at least one processing unit 200. The processing unit 200 implements various processing operations of the ED 110. For example, the processing unit 200 could perform signal coding, data processing, power control, input/output processing, or any other functionality enabling the ED 110 to operate in the system 100. The processing unit 200 also supports the methods and teachings described in more detail above. Each processing unit 200 includes any suitable processing or computing device configured to perform one or more operations. Each processing unit 200 could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit.
The ED 110 also includes at least one transceiver 202. The transceiver 202 is configured to modulate data or other content for transmission by at least one antenna or NIC (Network Interface Controller) 204. The transceiver 202 is also configured to demodulate data or other content received by the at least one antenna 204. Each transceiver 202 includes any suitable structure for generating signals for wireless or wired transmission and/or processing signals received wirelessly or by wire. Each antenna 204 includes any suitable structure for transmitting and/or receiving wireless or wired signals. One or multiple transceivers 202 could be used in the ED 110, and one or multiple antennas 204 could be used in the ED 110. Although shown as a single functional unit, a transceiver 202 could also be implemented using at least one transmitter and at least one separate receiver.
The ED 110 further includes one or more input/output devices 206 or interfaces (such as a wired interface to the internet 150). The input/output devices 206 facilitate interaction with a user or other devices (network communications) in the network. Each input/output device 206 includes any suitable structure for providing information to or receiving/providing information from a user, such as a speaker, microphone, keypad, keyboard, display, or touch screen, including network interface communications.
In addition, the ED 110 includes at least one memory 208. The memory 208 stores instructions and data used, generated, or collected by the ED 110. For example, the memory 208 could store software or firmware instructions executed by the processing unit(s) 200 and data used to reduce or eliminate interference in incoming signals. Each memory 208 includes any suitable volatile and/or non-volatile storage and retrieval device(s). Any suitable type of memory may be used, such as random access memory (RAM), read only memory (ROM), hard disk, optical disc, subscriber identity module (SIM) card, memory stick, secure digital (SD) memory card, and the like.
As shown in FIG. 2B, the base station 170 includes at least one processing unit 250, at least one transmitter 252, at least one receiver 254, one or more antennas 256, at least one memory 258, and one or more input/output devices or interfaces 266. A scheduler 253, which would be understood by one skilled in the art, is coupled to the processing unit 250. The scheduler 253 could be included within or operated separately from the base station 170. The processing unit 250 implements various processing operations of the base station 170, such as signal coding, data processing, power control, input/output processing, or any other functionality. The processing unit 250 can also support the methods and teachings described in more detail above. Each processing unit 250 includes any suitable processing or computing device configured to perform one or more operations. Each processing unit 2500 could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit.
Each transmitter 252 includes any suitable structure for generating signals for wireless or wired transmission to one or more EDs or other devices. Each receiver 254 includes any suitable structure for processing signals received wirelessly or by wire from one or more EDs or other devices. Although shown as separate components, at least one transmitter 252 and at least one receiver 254 could be combined into a transceiver. Each antenna 256 includes any suitable structure for transmitting and/or receiving wireless or wired signals. While a common antenna 256 is shown here as being coupled to both the transmitter 252 and the receiver 254, one or more antennas 256 could be coupled to the transmitter(s) 252, and one or more separate antennas 256 could be coupled to the receiver(s) 254. Each memory 258 includes any suitable volatile and/or non-volatile storage and retrieval device(s). Each input/output device 266 facilitates interaction with a user or other devices (network communications) in the network. Each input/output device 266 includes any suitable structure for providing information to or receiving/providing information from a user, including network interface communications.
Additional details regarding the EDs 110 and the base stations 170 are known to those of skill in the art. As such, these details are omitted here for clarity.
FIG. 3 illustrates an example of a topology or system 300 for wireless transmission of data according to an embodiment of this disclosure. The system 300 comprises a plurality of electronic devices (EDs) 302 to 303 (e.g., ED #1 to ED #K) and at least one receiver 320. In some embodiments, each electronic device 302, 303 may comprise the electronic device 110 of FIG. 1 and the receiver 320 may comprise the base station 170 of FIG. 1. The techniques described herein may be used for an asynchronous system in which the receiver receives an asynchronous superposition of the signals of EDs. These techniques may also be used for a synchronous system in which the receiver receives a synchronous superposition of the signals of EDs.
Each ED 302, 303 comprises a respective OFDM modulator 306, 307 configured to receive respective data 304, 305 and a respective spectrum shaping filter 308, 309. The data 304, 305 may be a modulation data sequence, and the OFDM modulators 306, 307 include inverse fast Fourier transform (IFFT) blocks. The OFDM modulators 306, 307 may also include respective cyclic prefix (CP) generators (not shown).
During operation, each ED 302, 303 generates its modulated signal (which is the result of an IFFT operation on the modulation data sequence) corresponding to its assigned resource blocks. A resource block is a set of resource elements. Each resource element corresponds to a specific subcarrier in a specific OFDM symbol. For example, a resource block in LTE is defined as a set of 12×14=168 resource elements (e.g., 12 consecutive subcarriers in 14 consecutive OFDM symbols). The signal may be an OFDM signal, a DFTS-OFDM signal, or other signal. Thereafter, each ED 302, 303 passes its OFDM signal through its appropriately designed spectrum shaping filter 308, 309 in order to eliminate side lobe leakage to the adjacent electronic devices in frequency. One skilled in the art will appreciate that although reference is made to the elimination of a side lobe, the described methods and systems will also be applicable if the filter reduces or strongly attenuates the side lobes. Filtering makes the signal of each ED localized in frequency. The EDs are assigned to be beside each other in frequency so each signal after the filtering is localized to a certain level such that the amount of interference that EDs cause each other is negligible.
To illustrate, the spectrum shaping filter 308 is centered at the assigned resource blocks of ED #1, its bandwidth is equal to the total width of the resource blocks assigned to ED #1, and its time duration is equal to half of an OFDM symbol. Similarly, the spectrum shaping filter 309 is centered at the assigned resource blocks of ED #K, its bandwidth is equal to the total width of the resource blocks assigned to ED #K, and its time duration is equal to half of an OFDM symbol.
The spectrum shaping filters 308, 309 offer sharp side lobe leakage elimination so that the electronic devices 302, 303 do not cause interference to each other during asynchronous transmission. As an illustrative example, the spectrum shaping filter 308 may be a finite impulse response (FIR) filter or other suitable filter.
Each ED 302, 303 starts the transmission at any time—it does not need to be synchronized to other EDs. However, the receiver 320 needs to know when transmission occurs.
The modulated signals transmitted by each of the EDs 302, 303 pass through the communication channels and are received at the receiver 320 and combined, such that the receiver 320 receives a combined signal 310. As illustrated, the received signal 310 is passed through K chains of operations corresponding to the K EDs 302, 303. The output of each chain (e.g., 334, 335) is the demodulated sequence of the corresponding ED.
To illustrate, the receiver operation of the i'th chain includes filtering, where the received signal 310 is passed through a filter h_i*(−n), which is matched to the corresponding filter used at ED #i. The role of this matched filtering is twofold: firstly, it rejects the contributions of the other EDs from the signal 3100. This ensures that the OFDM receiver (i.e., the subsequent FFT block in the chain), does not grab any interference from the neighboring EDs. Secondly, the matched filtering maximizes the received signal-to-noise ratio of ED #i.
For example, the receiver operation of the first chain includes filtering, where the received signal 310 is passed through a filter h₁*(−n) 322, which is matched to the filter 308 used at ED # 1 302. Similarly, the receiver operation of the K'th chain includes filtering, where the received signal 310 is passed through a filter h_K*(−n) 323, which is matched to the filter 309 used at ED #K 303.
The receiver operation of the i'th chain includes per-ED time synchronization that is performed at a time synchronization block. For example, at the output of the filtering described above, the operational window is shifted appropriately to be time-synchronized to the corresponding ED. The appropriate time shift includes the delay of ED #i together with the aggregate delay of the end-to-end filter g_i(n)
h_i*(n)*j_i(−n), i.e., the delay of its strongest tap, which is typically its middle tap. The beginning and end tails of the signal, due to the end-to-end filter g_i(n), are truncated.
To illustrate, the receiver operation of the first chain includes time synchronization that is performed at a time synchronization block 324. At the output of the filter 322, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED # 1 302). The appropriate time shift includes the delay of ED # 1 302 together with the aggregate delay of the end-to-end filter g₁(n)
h₁(n)*h₁*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 326. Similarly, the receiver operation of the K'th chain includes time synchronization that is performed at a time synchronization block 325. At the output of the filter 323, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED #K 303). The appropriate time shift includes the delay of ED #K 303 together with the aggregate delay of the end-to-end filter g_K(n)
h_K(n)*h_K*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 327.
The receiver operation of the i'th chain includes down sampling that is performed at a down sampling block. For example, each OFDM symbol is down sampled with a factor of N/N_i, where N is the fast Fourier transform (FFT) size of each ED's OFDM symbol and N_i
2^[log ² ^M ⁱ ^], with M_ibeing the number of subcarriers assigned to the ED #i. Therefore, each resulting OFDM symbol has N_isamples. The down sampling is done for the sake of receiver complexity reduction. The down sampling factor is chosen to satisfy Nyquist sampling criterion for reconstruction, with the constraint of N_ibeing a power of 2 in order to enable the subsequent FFT.
For example, the receiver operation of the first chain includes down sampling that is performed at a down sampling block 328. Similarly, the receiver operation of the K'th chain includes down sampling that is performed at a down sampling block 329.
The receiver operation of the i'th chain includes scaling to account for the down sampling effect and the scaled signal is passed through an N_i-point FFT block (e.g., a “short” FFT) to transform each symbol to the frequency domain. For example, the receiver operation of the first chain includes scaling of the down sampled signal to account for the down sampling effect and the scaled signal is passed through an N₁-point FFT block 330. Similarly, the receiver operation of the K'th chain includes scaling of the down sampled signal to account for the down sampling effect and is passed through an N_K-point FFT block 331.
The receiver operation of the i'th chain includes a cyclic subcarrier shift that is performed at a cyclic subcarrier shift block to account for down sampling of the band-pass signals. For example, the receiver operation of the first chain includes a cyclic subcarrier shift that is performed at a cyclic subcarrier shift block 332. Similarly, the receiver operation of the K'th chain includes a cyclic subcarrier shift that is performed at a cyclic subcarrier shift block 333. The output of each chain (e.g., 334, 335) is the demodulated sequence of the corresponding ED.
Although FIG. 3 illustrates one example of a system 300 for wireless transmission of data according to an embodiment of this disclosure, various changes may be made to FIG. 3. For example, various components in FIG. 3 could be combined, further sub-divided, moved, or omitted and additional components could be added according to particular needs. Also, the system 300 could include any number of each component shown in FIG. 3.
FIG. 4 illustrates the effect of down sampling on the spectrum of a band-pass signal, where the spectrum of a band-pass signal is illustrated at 402. The band-pass signal repeated in frequency 1/T_sis illustrated at 404. As illustrated at 406, the spectrum of the down sampled signal with a sampling rate 1/T_scan be a cyclically shifted version of the original spectrum depending on the spectrum occupied by the band-pass signal and the down sampling rate. The role of the cyclic subcarrier shift illustrated in FIG. 3 is to compensate for this effect, since the OFDM signal of ED #i in FIG. 3 is band-pass in general.
Although FIG. 4 illustrates one example of the effect of down sampling on the spectrum of a band-pass signal, various changes may be made to FIG. 4. For example, the spectrum of the band-pass signal and the sampling rate 1/T_sare for illustration only.
FIG. 5 illustrates another example of a topology or system 500 for wireless transmission of data according to an embodiment of this disclosure. The system 500 comprises the plurality of electronic devices 302 to 303 (e.g., ED # 1 to ED #K) of FIG. 3 and at least one receiver 520. The differences between this example and the example illustrated in FIG. 3 are that in this example, there is no down sampling, no short FFT, and no cyclic subcarrier shifting. Instead, a full-size FFT is performed per ED.
The modulated signals transmitted by the EDs 302, 303 are combined such that the receiver 520 receives the combined signal 310. As illustrated, the received signal 310 is passed through K chains of operations corresponding to the K EDs 302, 303. The output of each chain is the demodulated sequence of the corresponding ED (e.g., 534, 535).
To illustrate, the receiver operation of the i'th chain includes filtering, where the received signal 310 is passed through a filter h_i*(−n), which is matched to the corresponding filter used at ED #i. For example, the receiver operation of the first chain includes filtering, where the received signal 310 is passed through a filter h₁*(−n) 522, which is matched to the filter 308 used at ED # 1 302. Similarly, the receiver operation of the K'th chain includes filtering, where the received signal 310 is passed through a filter h_K*(−n) 523, which is matched to the filter 309 used at ED #K 303.
The receiver operation of the i'th chain includes per-ED time synchronization that is performed at a time synchronization block. For example, at the output of the filtering described above, the operational window is shifted appropriately to be time-synchronized to the corresponding ED. To illustrate, the receiver operation of the first chain includes time synchronization that is performed at a time synchronization block 524. At the output of the filter 522, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED # 1 302). The appropriate time shift includes the delay of ED # 1 302 together with the aggregate delay of the end-to-end filter g₁(n)
h₁(n)*h₁*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 526.
Similarly, the receiver operation of the K'th chain includes time synchronization that is performed at a time synchronization block 525. At the output of the filter 523, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED #K 303). The appropriate time shift includes the delay of ED #K 303 together with the aggregate delay of the end-to-end filter g_K(n)
h_K(n)*h_K*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 527.
The receiver operation of the i'th chain includes a full-size FFT performed per ED at an FFT block to transform each symbol to the frequency domain. For example, the receiver operation of the first chain includes performing a full-size FFT at an FFT block 530 after the cyclic prefix is removed. Similarly, the receiver operation of the K'th chain includes performing a full-size FFT at an FFT block 531 after the cyclic prefix is removed. The output of each chain (e.g., 534, 535) is the demodulated sequence of the corresponding ED.
Although FIG. 5 illustrates one example of a system 500 for wireless transmission of data according to an embodiment of this disclosure, various changes may be made to FIG. 5. For example, various components in FIG. 5 could be combined, further sub-divided, moved, or omitted and additional components could be added according to particular needs. Also, the system 500 could include any number of each component shown in FIG. 5.
FIG. 6 illustrates another example of a topology or system 600 for wireless transmission of data according to an embodiment of this disclosure. The system 600 comprises the plurality of electronic devices 302 to 303 (e.g., ED # 1 to ED #K) of FIG. 3 and at least one receiver 620. The differences between this example and the example illustrated in FIG. 5 are that in this example, there is only a single full-size FFT performed at the receiver 620.
The modulated signals transmitted by the EDs 302, 303 are combined such that the receiver 620 receives the combined signal 310. As illustrated, the received signal 310 is passed through K chains of operations corresponding to the K EDs 302, 303. The output of each chain is the demodulated sequence of the corresponding ED (e.g., 634, 635).
To illustrate, the receiver operation of the i'th chain includes filtering, where the received signal 310 is passed through a filter h_i*(−n), which is matched to the corresponding filter used at ED #i. For example, the receiver operation of the first chain includes filtering, where the received signal 310 is passed through a filter h₁*(−n) 622, which is matched to the filter 308 used at ED # 1 302. Similarly, the receiver operation of the K'th chain includes filtering, where the received signal 310 is passed through a filter h_K*(−n) 623, which is matched to the filter 309 used at ED #K 303.
The receiver operation of the i'th chain includes per-ED time synchronization that is performed at a time synchronization block. For example, at the output of the filtering described above, the operational window is shifted appropriately to be time-synchronized to the corresponding ED. To illustrate, the receiver operation of the first chain includes time synchronization that is performed at a time synchronization block 624. At the output of the filter 622, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED # 1 302). The appropriate time shift includes the delay of ED # 1 302 together with the aggregate delay of the end-to-end filter g₁(n)
h₁(n)*h₁*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 626
Similarly, the receiver operation of the K'th chain includes time synchronization that is performed at a time synchronization block 625. At the output of the filter 623, a delay compensated signal is obtained by shifting the operational window appropriately to be time-synchronized to the corresponding ED (e.g., ED #K 303). The appropriate time shift includes the delay of ED #K 303 together with the aggregate delay of the end-to-end filter g_K(n)
h_K(n)*h_K*(−n). The delay compensated signal is then divided into OFDM symbols, and the cyclic prefix (CP) is removed from each received OFDM symbol by the cyclic prefix removal block 627. The outputs of the cyclic prefix removal blocks 626, 627 are summed to form a combined output 628.
The receiver operation includes a single full-size FFT performed at an FFT block to transform each symbol to the frequency domain. For example, the receiver operation of the first chain includes performing a single full-size FFT on the combined cyclic prefix removed symbol at an FFT block 630. Similarly, the receiver operation of the K'th chain includes performing the single full-size FFT on the combined cyclic prefix removed symbol at the FFT block 630. The output of each chain (e.g., 634, 635) is the demodulated sequence of the corresponding ED.
Although FIG. 6 illustrates one example of a system 600 for wireless transmission of data according to an embodiment of this disclosure, various changes may be made to FIG. 6. For example, various components in FIG. 6 could be combined, further sub-divided, moved, or omitted and additional components could be added according to particular needs. Also, the system 600 could include any number of each component shown in FIG. 6.
FIGS. 7-9 illustrate Block Error Rate (BLER) curves for various modulations using the proposed asynchronous OFDMA/SC-FDMA system compared with using synchronous OFDMA. FIG. 7 illustrates the BLER performance of the proposed asynchronous OFDMA/SC-FDMA system with Quadrature Phase Shift Keying (QPSK) and Forward Error Correction (FEC) rate 1/2 over an Additive White Gaussian Noise (AWGN) channel. As illustrated in FIG. 7, the asynchronous OFDMA shows substantially the same BLER performance as synchronous OFDMA for QPSK.
FIG. 8 illustrates the BLER performance of the proposed asynchronous OFDMA/SC-FDMA system with 16QAM and FEC rate 1/2 over an AWGN channel. As illustrated, the performance loss is less than 0.05 dB for 16QAM.
FIG. 9 illustrates the BLER performance of the proposed asynchronous OFDMA/SC-FDMA system with 64QAM and FEC rate 1/2 over an AWGN channel. As illustrated in FIG. 9, the performance loss is less than 0.2 dB for 64QAM.
In arriving at the results illustrated in FIGS. 7-9, an uplink asynchronous OFDMA system was simulated using the proposed scheme in the scenario where three EDs communicate with the receiver. Three resource blocks were assigned to each ED and one guard subcarrier was reserved between each pair of EDs that are adjacent in frequency. An FIR filter was used with time duration T/2, where T is the OFDM symbol duration without CP. The ED FFT size was N=1024 and the receiver FFT sizes were N_i=64, 1≤i≤3. The transmission bandwidth was 10 MHz and the signals were passed through an Additive White Gaussian Noise (AWGN) channel with random delays uniformly distributed between 0 and T.
For the sake of comparison, a modified receiver is also simulated wherein the outputs of the per-ED time synchronization blocks are added together and passed through a single OFDM demodulator with FFT size 1024 (as illustrated in FIG. 6). The simulation result for each modulation level is also shown in FIGS. 7-9 as “Filtered, 1 Sbcr Spacing, Single FFT”. As illustrated, this receiver has a performance gap which is more significant for higher modulation levels. The performance loss is due to the residual inter-ED interference which remains in the demodulated signal after the single FFT operation. This illustrates the benefit of separate ED processing in the proposed asynchronous OFDMA/SC-FDMA decoder as opposed to single FFT operation.
FIGURE to is a flow diagram illustrating a method 1000 of operating an electronic device in accordance with disclosed embodiments that may be performed, for example, by an electronic device such as the electronic device 110 of FIG. 1 or the electronic devices 302, 303 of FIGS. 3, 5 and 6.
The method 1000 includes generating a signal corresponding to resource blocks assigned to the wireless device, at step 1002. For example, each ED 302, 303 generates its modulated signal (which is the result of an IFFT operation on the modulation data sequence) corresponding to its assigned resource blocks.
The method 1000 includes filtering the signal that corresponds to the resource blocks assigned to the wireless device with a spectrum shaping filter and producing a filtered signal that eliminates side lobe leakage to a second wireless device adjacent to the wireless device in frequency, at step 1004. For example, each ED 302, 303 passes its OFDM signal through its appropriately designed spectrum shaping filter 308, 309 in order to eliminate side lobe leakage to the adjacent electronic devices in frequency.
The method 1000 includes transmitting the filtered signal to a receiver in the wireless communication system in a timeslot provided by a scheduler coupled to the receiver, the timeslot being independently determined with respect to other electronic devices communicating with the receiver, at step 1006. In one embodiment, the filtered signal is transmitted with a synchronization reference. The synchronization reference is, in one example, a known pattern that allows a transmitter and receiver to synchronize themselves. In another example, synchronization information from a third party source can be used to synchronize the ED with the receiver. For example, the modulated signal transmitted by the ED 302 of FIG. 3 is transmitted to the receiver 320 in a timeslot provided by the scheduler 253. The timeslot provided to the ED 302 is independently determined with respect to other electronic devices (e.g., the ED 303) communicating with the receiver 320. Similarly, the modulated signal transmitted by the ED 303 of FIG. 3 is transmitted to the receiver 320 in a timeslot provided by the scheduler 253. The timeslot provided to the ED 303 is independently determined with respect to other electronic devices (e.g., the ED 302) communicating with the receiver 320. Because the filtered signal transmitted by each of the EDs 302, 303 is transmitted to the receiver 320 in a timeslot provided by the scheduler 253 that is independently determined with respect to other electronic devices communicating with the receiver, and because the filtered signal transmitted by each of the EDs 302, 303 reduces or eliminates side lobe leakage in an adjacent frequency band, overhead with respect to timing advance signaling may be reduced.
Although FIGURE to illustrates one example of a method 1100 of operating an electronic device in accordance with disclosed embodiments, various changes may be made to FIG. 10. For example, while shown as a series of steps, various steps in FIG. 10 could overlap, occur in parallel, occur in a different order, or occur any number of times.
FIG. 11 is a flow diagram illustrating a method 1100 of operating a receiver in accordance with disclosed embodiments that may be performed, for example, by a base station such as the base station 170 of FIG. 1 or the receiver 620 of FIG. 6.
The method 1100 includes receiving a signal corresponding to a plurality of modulated signals, each of the plurality of modulated signals corresponding to a unique electronic device, at step 1102. For example, the received signal 310, which corresponds to the modulated signals transmitted by each of the EDs 302, 303 is received at the receiver 320.
The method 1100 includes filtering the received signal with a filter that is matched to a corresponding filter in a respective electronic device to obtain a filtered signal for the respective electronic device, at step 1104. For example, the receiver operation of the first chain includes filtering the received signal 310 with the filter h₁*(−n) 322, which is matched to the filter 308 used at ED # 1302.
The method 1100 includes performing a fast Fourier transform (FFT) operation on the filtered signal to obtain demodulated data corresponding to the respective electronic device, at step 1106. For example, as illustrated in FIG. 3, the receiver operation of the i'th chain includes scaling to account for the down sampling effect and the scaled signal is passed through an N_i-point FFT block (e.g., a “short” FFT) to transform each symbol to the frequency domain. As another example, as illustrated in FIG. 5, the receiver operation of the first chain includes performing a full-size FFT at the FFT block 530 after the cyclic prefix is removed. As yet another example, as illustrated in FIG. 6, the receiver operation of the first chain includes performing a single full-size FFT on the combined time synchronization output with the cyclic prefix removed at the FFT block 630.
Although FIG. 11 illustrates one example of a method 1100 of operating a receiver in accordance with disclosed embodiments, various changes may be made to FIG. 11. For example, while shown as a series of steps, various steps in FIG. 11 could overlap, occur in parallel, occur in a different order, or occur any number of times.
In some embodiments, some or all of the functions or processes of the one or more of the devices are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory.
Embodiments of this disclosure provide a method of data transmission in a wireless communication system. In this embodiment, the method includes generating a signal corresponding to resource blocks assigned to the electronic device, filtering the signal that corresponds to the resource blocks assigned to the electronic device with a spectrum shaping filter to reduce side lobe leakage in an adjacent frequency band to produce a filtered signal, and transmitting the filtered signal to a receiver in the communication system in a timeslot provided by a scheduler coupled to the receiver. The timeslot may be independently determined with respect to other electronic devices communicating with the receiver. In one example, the filtered signal is transmitted with a synchronization reference. In the same example, or in another example, the method further includes generating a second signal corresponding to resource blocks assigned to the second electronic device, filtering the second signal with a second spectrum shaping filter to reduce side lobe leakage in an adjacent frequency band to produce a second filtered signal, and transmitting the second filtered signal to the receiver in the communication system. In such an example, the second filtered signal may be transmitted with a second synchronization reference. In any one of the examples, or in another example, the signal that corresponds to the resource blocks is an orthogonal frequency division multiple access (OFDMA) based signal and wherein the spectrum shaping filter is centered at the resource blocks assigned to the electronic device. In such an example, a bandwidth of the spectrum shaping filter may correspond to a total width of the resource blocks assigned to the electronic device, and a time duration of the spectrum shaping filter corresponds to a portion of an OFDM symbol period. The synchronization reference may be a timing synchronization reference or a frequency synchronization reference. An apparatus for performing this method is also provided. In an embodiment, a method of receiving a data transmission in a wireless communication system is provided. In this example, the method includes receiving a signal corresponding to a plurality of modulated signals, each of the plurality of modulated signals corresponding to a unique electronic device, filtering the received signal with a plurality of filters each of which is matched to a corresponding filter in a respective electronic device to obtain a filtered signal for the respective electronic device, and performing a fast Fourier transform (FFT) operation on the filtered signal to obtain demodulated data corresponding to the respective electronic device. In one example, the method further includes obtaining a plurality of delay compensated signals by shifting an operational window at an output of each filter to be time-synchronized to the corresponding electronic device, dividing the delay compensated signals into orthogonal frequency division multiplexing (OFDM) symbols, and removing a cyclic prefix from each of the OFDM symbols to obtain a transformed symbol. In the same example, or another example, the method further includes after removal of the cyclic prefix, performing a down sampling operation on the transformed symbol to obtain a down-sampled transformed signal. In any one of the preceding examples, or in another example, the method further includes performing the FFT operation on the filtered signal comprises performing a short FFT operation on each down-sampled transformed symbol of each electronic device. In any one of the preceding examples, or in another example, after performing the short FFT operation, performing a cyclic shift operation based on the down sampling operation. In any one of the preceding examples, or in another example, performing the FFT operation on the filtered signal comprises: performing a full-size FFT operation on each transformed symbol of each electronic device. In any one of the preceding examples, or in another example, performing the FFT operation on the filtered signal comprises summing the transformed symbol of each electronic device to obtain a summed transformed symbol, and performing a full-size FFT operation on the summed transformed symbol. An apparatus for performing this method is also provided.
In accordance with an embodiment, a method for communicating orthogonal frequency-division multiplexing (OFDM) signals in a wireless communication system is provided. In this example, the method includes obtaining a cyclic prefix based OFDM (CP-OFDM) signal comprising a plurality of CP-OFDM symbols having a cyclic prefix comprising a repetition of an end of the corresponding CP-OFDM symbol; applying a digital filter to the obtained CP-OFDM signal to obtain a filtered CP-OFDM signal; and transmitting the filtered CP-OFDM signal over a radio interface.
In one example, a filter length of the digital filter exceeds a length of the cyclic prefix of at least one of the CP-OFDM symbols. In the same example, or in on another example, a duration of the filtered CP-OFDM signal is expressed by the following equation: M=N+L−1, where M is the duration of the filtered CP-OFDM signal, N is a duration of the CP-OFDM signal, and L is the filter length of the digital filter.
In any one of the preceding examples, applying the digital filter to the CP-OFDM signal may include generating a filtering signal, and convolving the filtering signal with the CP-OFDM signal to obtain the filtered CP-OFDM signal. In any one of the preceding examples, the digital filter may comprise a finite impulse response (FIR) filter or a infinite impulse response (IIR) filter. In any one of the preceding examples, applying the digital filter to the CP-OFDM signal may comprise applying, by a base station, a different digital filter to each sub-band of the CP-OFDM signal, wherein each sub-band is assigned to a group of one or more user equipments (UEs). In any one of the preceding examples, applying the digital filter to the CP-OFDM signal may include applying, by a user equipment, the digital filter to a specific sub-band carrying the CP-OFDM signal, the specific sub-band being assigned to the UE In any one of the preceding examples, a bandwidth of the digital filter may be variable. In such an example, the method may further include adjusting the bandwidth of the digital filter in accordance with a bandwidth of the CP-OFDM signal. In any one of the preceding examples, the CP-OFDM signal may be transmitted over a specific frequency sub-band. In any one of the preceding examples, applying the radio interface extends between a base station and a user equipment, and wherein the CP-OFDM signal is transmitted by the base station. An apparatus for performing this method is also provided.
In accordance with an embodiment, a method for receiving orthogonal frequency-division multiplexing (OFDM) signals in a wireless communication system is provided. In this embodiment, the method includes receiving a cyclic prefix based OFDM (CP-OFDM) signal over a radio interface, the CP-OFDM signal comprising a plurality of CP-OFDM symbols having a cyclic prefix comprising a repetition of an end of the corresponding CP-OFDM symbol, applying a digital filter to the obtained CP-OFDM signal to obtain a filtered CP-OFDM signal, and processing the filtered CP-OFDM signal.
In an example, a filter length of the digital filter exceeds a length of the cyclic prefix of at least one of the CP-OFDM symbols. In such an example, or in another example, a duration of the filtered CP-OFDM signal is expressed by the following equation: M=N+L−1, where M is the duration of the filtered CP-OFDM signal, N is a duration of the CP-OFDM signal, and L is the filter length of the digital filter. In an example, applying the digital filter to the CP-OFDM signal comprises applying the digital filter to a specific sub-band of the CP-OFDM signal, the specific sub-band being assigned to the UE. In an example, applying the digital filter to the CP-OFDM signal comprises applying a different digital filter to each sub-band of the CP-OFDM signal, wherein each sub-band is assigned to a group of one or more user equipments (UEs). An apparatus for performing this method is also provided
It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.
In accordance with an embodiment, a method of transmitting data is provided. In this example, the method includes performing a filtering operation on a signal corresponding to a first plurality of resource blocks with a spectrum shaping filter to produce a filtered signal, and transmitting the filtered signal to a receiver over a first plurality of subcarriers, wherein the first OFDM modulated signal is transmitted asynchronously with a second filtered signal, the second filtered signal being transmitted over a second plurality of subcarriers by a second wireless electronic device. In an example, bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks. In the same example, or in another example, a time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol. In an example,
the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks. In an example, each of the first spectrum shaping filter and the second spectrum shaping filter is a finite impulse response (FIR) filter. An apparatus for performing the method is also provided.
In accordance with an embodiment, a method of receiving data is provided. In this example, the method includes receiving a first filtered signal from a first wireless device over a first plurality of subcarriers, and receiving, by the receiver, a second filtered signal from a second wireless device over a second plurality of subcarriers, wherein the first filtered modulated signal is transmitted asynchronously with the second filtered signal. In one example, bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks. In the same example, or in another example, a time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol. In the same example, or in another example, the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks. In the same example, or in pectrum shaping filter is a finite impulse response (FIR) filter. An apparatus for performing the method is also provided.
While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.

Claims

What is claimed is:

1. A method of transmitting data, the method comprising:

performing, by a wireless electronic device, a filtering operation on a signal corresponding to a first plurality of resource blocks with a spectrum shaping filter to produce a filtered signal;

transmitting, by the wireless electronic device, the filtered signal to a receiver over a first plurality of subcarriers,

wherein the first OFDM modulated signal is transmitted asynchronously with a second filtered signal over a second plurality of subcarriers by a second wireless electronic device.

2. The method of claim 1, wherein bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks.

3. The method of claim 1, wherein time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol.

4. The method of claim 1, wherein the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks.

5. The method of claim 1, wherein each of the first spectrum shaping filter and the second spectrum shaping filter is a finite impulse response (FIR) filter.

6. A wireless electronic device comprising:

a processor; and

a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:

perform a filtering operation on a signal corresponding to a first plurality of resource blocks with a spectrum shaping filter to produce a filtered signal;

transmit the filtered signal to a receiver over a first plurality of subcarriers, wherein the first OFDM modulated signal is transmitted asynchronously with a second filtered signal over a second plurality of subcarriers by a second wireless electronic device.

7. The wireless device of claim 6, wherein bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks.

8. The wireless device of claim 6, wherein time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol.

9. The wireless device of claim 6, wherein the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks.

10. The wireless device of claim 6, wherein each of the first spectrum shaping filter and the second spectrum shaping filter is a finite impulse response (FIR) filter.

11. A method of receiving data, the method comprising:

receiving, by a receiver, a first filtered signal from a first wireless device over a first plurality of subcarriers; and

receiving, by the receiver, a second filtered signal from a second wireless device over a second plurality of subcarriers, wherein the first filtered modulated signal is transmitted asynchronously with the second filtered signal.

12. The method of claim 11, wherein bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks.

13. The method of claim 11, wherein time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol.

14. The method of claim 11, wherein the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks.

15. The method of claim 1, wherein each of the first spectrum shaping filter and the second spectrum shaping filter is a finite impulse response (FIR) filter.

16. A wireless electronic device comprising:

a processor; and

receive a first filtered signal from a first wireless device over a first plurality of subcarriers; and

receive a second filtered signal from a second wireless device over a second plurality of subcarriers, wherein the first filtered modulated signal is transmitted asynchronously with the second filtered signal.

17. The receiver of claim 6, wherein bandwidth of the first spectrum shaping filter is equal to the total width of the first plurality of resource blocks and bandwidth of the second spectrum shaping filter is equal to the total width of the second plurality of resource blocks.

18. The receiver of claim 6, wherein time duration of each of the first spectrum shaping filter and the second spectrum shaping filter is equal to half of an OFDM symbol.

19. The receiver of claim 6, wherein the first spectrum shaping filter is centered at the first plurality of resource blocks, and the second spectrum shaping filter is centered at the second plurality of resources blocks.

20. The receiver of claim 6, wherein each of the first spectrum shaping filter and the second spectrum shaping filter is a finite impulse response (FIR) filter.