US20090252241A1 - Spectral shaping for multiband OFDM transmitters with time spreading - Google Patents
Spectral shaping for multiband OFDM transmitters with time spreading Download PDFInfo
- Publication number
- US20090252241A1 US20090252241A1 US12/380,405 US38040509A US2009252241A1 US 20090252241 A1 US20090252241 A1 US 20090252241A1 US 38040509 A US38040509 A US 38040509A US 2009252241 A1 US2009252241 A1 US 2009252241A1
- Authority
- US
- United States
- Prior art keywords
- instance
- input
- recited
- signal
- input component
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Images
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/7163—Spread spectrum techniques using impulse radio
- H04B1/71635—Transmitter aspects
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03828—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2614—Peak power aspects
- H04L27/2623—Reduction thereof by clipping
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/26265—Arrangements for sidelobes suppression specially adapted to multicarrier systems, e.g. spectral precoding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload
Definitions
- Multiband orthogonal frequency division multiplexing is a modulation technique used in some wireless communication systems such as ultra-wideband (UWB).
- the MB-OFDM modulation technique combines OFDM modulation with frequency hopping. It is a modulation technique suitable for devices designed to comply with Federal Communications Commission (FCC) regulations relating to UWB devices.
- FCC Federal Communications Commission
- UWB devices are allowed to operate within a relatively wide frequency band provided that two criteria are met. First, the occupied bandwidth is required to meet a predefined minimum. Second, the radiated power measured over an integrating bandwidth anywhere within the signal band is required to be less than a predefined maximum. According to the current regulations, UWB devices are allowed to operate in the frequency band between 3.1 to 10.6 GHz. The occupied bandwidth is required to meet a minimum of 500 MHz and the radiated power, when measured over a bandwidth of 1 MHz anywhere within the signal band, is required to be less than ⁇ 41.3 dBm.
- FIG. 1A is a diagram illustrating a frequency spectrum of an ideal UWB signal.
- factors such as D/A converter pulse shape, non-ideal filter characteristics, component variations and data characteristics tend to affect the shape of the spectrum.
- FIG. 1B is a diagram illustrating the frequency spectrum of a typical UWB signal generated by an existing device. There are peaks and variations in the frequency spectrum. The transmit power is typically limited by the largest peak in the signal spectrum. It would be desirable to have a UWB MB-OFDM transmitter design that would generate a flat output spectrum over the operating frequency range of the transmitter.
- FIG. 1A is a diagram illustrating a frequency spectrum of an ideal UWB signal.
- FIG. 1B is a diagram illustrating the frequency spectrum of a typical UWB signal generated by an existing device.
- FIG. 1C is a diagram illustrating the transmission of an OFDM-packet using multiple frequency hopping bands.
- FIG. 2A is a diagram illustrating the frequency spectrum of three hop bands generated by some transmitter embodiments.
- FIG. 2B is a diagram illustrating the frequency spectrum of three hop bands generated by a transmitter embodiment that compensates the effects shown in FIG. 2A .
- FIG. 3 is a block diagram illustrating an OFDM transmitter embodiment.
- FIG. 4A is a diagram illustrating a frequency spectrum of a set of uncompensated sub-carriers within a frequency hopping band.
- FIG. 4B is a diagram illustrating the frequency spectrum of the sub-carriers after the gain factors are applied.
- FIG. 5 is a block diagram illustrating an OFDM transmitter embodiment that adjusts the sub-carrier amplitudes.
- FIG. 6A is a diagram illustrating the frequency spectrum of a signal.
- FIG. 6B is a diagram illustrating the clipped frequency spectrum.
- FIG. 7 is a flowchart illustrating a frequency clipping process according to some embodiments.
- FIG. 8 is a block diagram illustrating another OFDM transmitter embodiment.
- FIG. 9 is a block diagram illustrating another OFDM transmitter embodiment that implements the phase shift.
- FIG. 10 is a diagram illustrating a transmitter embodiment that includes several spectrum shaping components.
- FIG. 11 is a diagram illustrating an embodiment of a frequency hopping transmission that employs time spreading.
- FIG. 12 is a flowchart illustrating an embodiment of a process for transmitting a subset of OFDM symbols with different instances.
- FIG. 13 illustrates an embodiment of a shifted pseudo random sequence used to select instances of OFDM symbols to modify.
- FIG. 14A illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the time domain.
- FIG. 14B illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the frequency domain.
- the invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links.
- these implementations, or any other form that the invention may take, may be referred to as techniques.
- a component such as a processor or a memory described as being configured to perform a task includes both a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task.
- the order of the steps of disclosed processes may be altered within the scope of the invention.
- Spectrum shaping techniques for transmitting OFDM signals are disclosed.
- a band gain control is used to determine a band gain for a selected band associated with the signal to be transmitted.
- a sub-carrier amplitude control is used to apply a gain factor to each of the sub-carrier frequency components of the modulated signal.
- modified synchronization sequences are used to reduce peaks in the frequency spectrum.
- a random phase shifter introduces random or pseudorandom phase shifts to the signal to reduce repetitive patterns in the signal and achieve flatter frequency spectrum. Combinations of these techniques can be used in various embodiments. For purposes of illustration, spectrum shaping of frequency hopping OFDM signals is discussed in detail below.
- multiple frequency hopping bands are used to transmit OFDM symbols to avoid symbol collision.
- An OFDM symbol waveform includes a number of modulated carrier waveforms, referred to as sub-carriers.
- Each sub-carrier is used to carry one data symbol, encoded as a phase shift or a combination of amplitude shift and phase shift.
- the sub-carrier frequency spacing is approximately equal to the inverse of the OFDM symbol duration, which means that the sub-carrier waveforms partly overlap in the frequency domain.
- FIG. 1C is a diagram illustrating the transmission of an OFDM packet using multiple frequency hopping bands. In the example shown, each rectangle corresponds to a synchronization symbol or an OFDM symbol.
- the initial part of the packet includes a sequence of identical packet synchronization (PS) symbols, followed by a small number of frame synchronization (FS) symbols.
- PS packet synchronization
- FS frame synchronization
- the synchronization symbols are used to aid the receiver in synchronizing to the received signal.
- the synchronization symbols include a specific sequence of binary phase shift keying (BPSK) symbols known as the synchronization sequence.
- BPSK binary phase shift keying
- the PS and FS symbols are identical except for a phase shift of 180°, making them easily distinguishable to the receiver. Detecting the location of the FS symbols allows the receiver to determine the boundary between the synchronization preamble and the header/data portion of the packet.
- FIG. 2A is a diagram illustrating the frequency spectrum of three hop bands generated by some transmitter embodiments.
- the frequency spectrum that includes hop bands 202 , 204 and 206 is uneven.
- the unevenness of the frequency spectrum is sometimes due to component gain difference (i.e. the gain difference introduced by transmitter components such as mixers, amplifiers, filters and the antenna). Variations in the manufacturing process and changes in the operating environment are some additional factors that may contribute to the gain difference.
- FIG. 2B is a diagram illustrating the frequency spectrum of three hop bands generated by a transmitter embodiment that compensates the effects shown in FIG. 2A .
- frequency hopping bands 252 , 254 and 256 each has a corresponding band gain used to compensate and adjust the signal strength to achieve a relatively flat frequency spectrum 260 .
- the adjustment is made by determining the frequency hopping band associated with the signal to be transmitted, determining the band gain that corresponds to the frequency hopping band and applying the band gain to the signal.
- the band gains are determined during the design process of the transmitter in some embodiments to correct any systematic gain deviations for different hop bands.
- an uncompensated output signal is measured to supply feedback information used to determine the band gain values and achieve the desired frequency spectrum characteristics.
- the feedback technique can be used during the manufacturing process, during the transmission operations of the transmitter or both.
- FIG. 3 is a block diagram illustrating an OFDM transmitter embodiment.
- transmitter 300 outputs a signal with a gain compensated frequency spectrum similar to 260 .
- Data bits are received on medium access control (MAC) interface 302 and then encoded by a forward error correction (FEC) encoder 304 .
- FEC forward error correction
- the encoded bits are optionally punctured, interleaved and repeated to provide better protection against multipath and interference.
- the bits are then mapped to modulation symbols by a symbol modulator 306 .
- Quadrature Phase Shift Keying (QPSK) or other appropriate modulation scheme may be used.
- the modulated symbols such as QPSK symbols are also referred to as sub-carriers.
- pilot tone inserter 306 adds pilot tones to the modulated symbols.
- An inverse Fast Fourier Transform (IFFT) component 308 is used to transform blocks of symbols from frequency domain into a time domain waveform (also referred to as an OFDM symbol).
- IFFT inverse Fast Fourier Transform
- a synchronization preamble that includes repeated PS and FS synchronization symbols is added to the beginning portion of each data packet by preamble inserter 310 .
- the preamble may be inserted before the IFFT (i.e., in the frequency domain).
- a guard interval and a cyclic prefix or zero prefix are added to the OFDM symbol by prefix and guard inserter 312 .
- band gain control 314 applies a time varying band gain factor on its input to counter the effects of gain variations in different hop bands to achieve a more uniform frequency spectrum. Depending on the value of the gain factor that is applied, the signal gets amplified, attenuated or remains unchanged as appropriate.
- Band gain control 314 is controlled by a hop timing signal and a band select signal. Gain values that correspond to different hop bands are stored in a lookup table or other appropriate storage.
- the hop timing signal determines when the band gain factor should change according to the timing of the OFDM symbol generation.
- the band select signal determines the value of the band gain factor used for a given hop band. In some embodiments, signal strength is measured during operation and an appropriate gain is determined according to the measurement.
- the inphase (I) and quadrature (Q) components of the gain compensated baseband OFDM signal are converted from digital to analog by digital to analog converters (DACs) 316 and 318 , respectively.
- the analog signals are sent to a radio transmitter 320 to be up-converted to the desired carrier frequency, amplified and then transmitted via antenna 324 .
- the local oscillator (LO) signal used by radio 320 is generated by frequency synthesizer 322 , which is also controlled by the control signals.
- Frequency synthesizer 322 has the ability to switch its output frequency at the start of each OFDM symbol period so that different transmitted OFDM symbols may occupy different hop bands. In some cases, the LO frequency is switched every symbol period.
- the LO frequency remains the same for several symbol periods before it is switched again. It is also possible that the LO frequency is never switched during the transmission of an entire packet.
- the timing of the frequency switch is controlled by the hop timing signal.
- the appropriate LO frequency to be synthesized for a given symbol period is determined by the band select signal.
- FIG. 4A is a diagram illustrating a frequency spectrum of a set of uncompensated sub-carriers within a frequency hopping band.
- the sub-carriers should have equal amplitude and form a flat frequency envelope.
- uncompensated sub-carriers such as 402 , 404 and 406 have different amplitudes and form a frequency envelope 400 with amplitude variations.
- the signal amplitudes near the edges of the envelope are significantly weaker than those near the center of the envelope.
- the amplitude variations are partly attributed to the transmitter's DACs, which introduce a sin(x)/x shaping of the signal spectrum and cause the reduction in signal amplitude near the band edges.
- the various filters in the transmitter's signal path have a similar effect as the DAC. In some embodiments. these filters also cause a ripple in the signal spectrum.
- the effects of the DACs, the filters as well as other components are offset using gain compensation.
- a plurality of sub-carrier gain factors are applied to the uncompensated sub-carriers to make the amplitudes of the resulting gain compensated sub-carrier approximately equal.
- the corresponding uncompensated sub-carrier amplitude may be amplified, attenuated or unchanged.
- FIG. 4B is a diagram illustrating the frequency spectrum of the sub-carriers after the gain factors are applied. Each sub-carrier is multiplied with an appropriate sub-carrier gain factor.
- the values of the gain factors are selected such that when multiplied with corresponding sub-carriers in signal 415 , the resulting compensated sub-carriers have approximately the same amplitude.
- the sub-carriers near the band edges receive greater gain boost than the sub-carriers near the band center.
- the resulting sub-carrier envelope 430 is substantially more even compared to 406 .
- the amplitudes of uncompensated sub-carrier frequency components are measured to supply feedback information used to determine the sub-carrier gain factors. The measurement may take place during the manufacturing process, during the transmission operations of the transmitter or both.
- FIG. 5 is a block diagram illustrating an OFDM transmitter embodiment that adjusts the sub-carrier amplitudes.
- Transmitter 500 additionally includes a sub-carrier gain control 502 that adjusts the amplitudes of the sub-carriers by applying appropriate gain factors to the corresponding sub-carriers.
- a different set of gain factors is used for each frequency hopping band.
- a different gain factor may be applied to the Inphase and Quadrature components of each sub-carrier.
- the frequency hopping band associated with the signal is determined and the appropriate set of gain factors is selected and applied. The application of the gain factors compensates the spectral distortion introduced by the DACs and various filters in the transmit signal path.
- a substantially flat baseband signal similar to signal 430 is thus obtained.
- FIG. 6A is a diagram illustrating the frequency spectrum of a signal.
- the signal includes several peaks (such as peak 602 ) in its frequency spectrum.
- the signal is clipped at a level 604 to create a frequency spectrum that is more even.
- FIG. 6B is a diagram illustrating the clipped frequency spectrum. Details of the clipping process are discussed below.
- FIG. 7 is a flowchart illustrating a frequency clipping process according to some embodiments.
- frequency components of an input are limited to a predetermined clip level in order to reduce or eliminate the peaks and achieve a flat frequency spectrum.
- the original data sequence is first Fourier transformed to obtain its complex-valued spectral representation ( 702 ).
- a spectral component is then selected ( 704 ).
- the spectral component also referred to as the Fourier coefficient
- the clip level is selected ( 705 ).
- the clip level which controls the flatness of the generated signal spectrum, is chosen relative to the selected spectral amplitude in some embodiments.
- the amplitudes of the spectral components are then clipped according to the clip level ( 706 ). In other words, spectral components with amplitude exceeding the clip level are given a new amplitude value equal to the clip level. Other spectral components with amplitudes less than or equal to the clip level are unchanged. Finally, an inverse Fourier transform is applied to the clipped spectrum to transform the signal back to the time domain ( 708 ).
- the clipping operation can affect the auto-correlation and cross-correlation properties of the synchronization sequence.
- a moderate clip level for example, 3 dB below the maximum spectral amplitude
- the clip level is further reduced until all the spectral components in the modified synchronization sequence have approximately equal amplitude, thus creating a spectrum that is substantially flat.
- the clip level is set to a value less than or equal to the smallest spectral amplitude.
- several outputs generated by using different clip levels are compared to select an appropriate clip level that offers flat spectrum without significantly degrading the output sent to the receiver.
- FIG. 8 is a block diagram illustrating another OFDM transmitter embodiment. Like components of transmitter 800 and transmitter 300 perform like functions. In this example, modified synchronization sequences are stored in a lookup table 802 . When a preamble is to be generated, the modified synchronization sequence that corresponds to the preamble is retrieved and inserted into the signal stream. Other implementations are sometimes used in different embodiments. For example, the preambles can be inserted prior to the IFFT operation. The frequency domain components may be clipped and buffered before they are processed by the IFFT component.
- a random phase shifter that applies random or pseudorandom phase shifts to the OFDM symbols is used to randomize the signal and reduce peaks in the frequency spectrum.
- the amount of phase shift for each symbol may be determined according to a pseudo random sequence or other predefined sequence. If desired, the sequence of phase shifts can be reconstructed in the receiver, allowing the receiver remove the phase shift of each received OFDM symbol before other tasks such as channel estimation, phase estimation and data demodulation are carried out.
- FIG. 9 is a block diagram illustrating another OFDM transmitter embodiment that implements the phase shift.
- a random phase shifter 902 is used to introduce random or pseudo random phase shifts to the OFDM symbols.
- the phase shifts are limited to multiples of 90° (i.e. the phase shifts are restricted to 0°, 90°, 180°, 270°) so that the random phase shifter can be implemented via two basic operations: interchanging the I and Q signal components and reversing the sign of I and/or Q signal components.
- the random phase shift is shown to take place prior to analog to digital conversion in this example, the phase shift operation may also be performed elsewhere in the transmitter. For example, the phase of the QPSK symbols at the input of the IFFT may be shifted before the IFFT is applied.
- FIG. 10 is a diagram illustrating a transmitter embodiment that includes several spectrum shaping components.
- Transmitter 1000 shown in this example includes a sub-carrier amplitude control 1002 , a modified synchronization sequence lookup table 1004 , a random phase shifter 1006 and a band gain control 1008 .
- One or more of these components may be active at the same time to shape the output signal to achieve a more uniform output spectrum.
- FIG. 11 is a diagram illustrating an embodiment of a frequency hopping transmission that employs time spreading.
- OFDM symbols 1100 , 1102 , 1104 , 1106 , 1108 , and 1110 are part of a packet. Synchronization symbols for the packet are not illustrated and there may be more OFDM symbols in addition to those illustrated.
- time spreading two instances of each OFDM symbol are transmitted on the same hop band in this example.
- Time spreading is a process in which an OFDM symbol is input and multiple instances of the OFDM symbol are output. Instances may be unmodified (an identical copy of the original OFDM symbol) or may be modified.
- OFDM symbol A 1100 and OFDM symbol A′ 1102 are transmitted on the hop band with center frequency f 1 , where OFDM symbol A′ 1102 is a modified instance and OFDM symbol A 1100 is an unmodified instance.
- OFDM symbol B 1104 and OFDM symbol B 1106 are transmitted on the hop band with center frequency f 3 and OFDM symbol C 1108 and OFDM symbol C′ 1110 are transmitted on the hop band with center frequency f 2 .
- all transmitted instances in a packet are unmodified.
- the two instances may be the output of a duplication block that outputs two identical instances for every OFDM symbol input.
- OFDM symbols A, A, B, B, C, and C of a packet may be transmitted.
- one or both of the transmitted instances in a packet are a modification of the original OFDM symbol.
- OFDM symbols A, A′, B, B′, C, and C′ of a packet may be transmitted.
- OFDM symbols A′, A′′, B′, B′′, C′, and C′′ of a packet may be transmitted, where OFDM symbol A′′ is another modification of OFDM symbol A that is a different modification compared to OFDM symbol A′.
- a combination of methods is employed in the same packet.
- the method of generating the two instances of an OFDM symbol is random.
- the frequency hopping scheme varies from that illustrated. For example, there may be more or less than three hop bands. The sequence of hops may vary from that shown. In some embodiments, the hop band changes at a different rate than that illustrated. For example, the hop band may change after every four OFDM symbols transmitted instead of every two OFDM symbols. In some embodiments, frequency band hopping is not employed and all synchronization symbols and OFDM symbols are transmitted on the same band. For example, OFDM symbols A 1100 , A′ 1102 , B 1104 , B 1106 , C 1108 , and C′ 1110 may be transmitted on band f 1 .
- the order of the OFDM symbols varies from that illustrated.
- the modified instance is transmitted before the unmodified instance.
- the two instances are not transmitted successively.
- the modification of the OFDM symbol is inversion.
- the modification may be swapping the I and Q signals or the modification may be the complex conjugation of the OFDM symbol.
- Another example modification is phase shifting. A combination of methods may also be employed.
- the transmitted spectral shape may be flatter than if the instances are the same. Rather than having the two instances of an OFDM symbol repeat each other on the same band (and thus repeat the same spectrum), two different instances may have different spectrums and contribute to a flatter spectrum overall.
- a process may be applied to select a subset of OFDM symbols in a packet. For the OFDM symbols not selected, the instances of each unselected OFDM symbol are the same. In some embodiments, the instances are both unmodified instances. For the subset of selected OFDM symbols, two different instances of each selected OFDM symbol are transmitted. In some embodiments, one instance is an unmodified instance and the other is a modified instance of the original OFDM symbol. When the spectrum is measured (perhaps over multiple OFDM symbols or multiple packets) a flatter spectral shape is produced.
- FIG. 12 is a flowchart illustrating an embodiment of a process for transmitting a subset of OFDM symbols with different instances.
- a modified instance or an unmodified instance is transmitted after an unmodified instance of the OFDM symbol.
- a pseudo random sequence PRS
- PRS pseudo random sequence
- the pseudo random sequence may be the sequence of pilot tones inserted into each OFDM symbol.
- a pseudo random generator may also be used.
- the elements of the pseudo random sequence are either 1 or ⁇ 1.
- An example of such a pseudo random sequence is [1 ⁇ 1 ⁇ 1 1 ⁇ 1] where each of the elements are generated using a random process.
- a pseudo random number generator already included in the design is used to generate the random number multiple times. Logic is reused and die size and manufacturing costs are kept low.
- the elements in the random sequence take on different values than those illustrated.
- the elements may take on more than two values.
- the values of the elements are discrete values such as integer values. In some embodiments, the elements are continuous values.
- the pseudo random sequence is shifted by K (PRS K ) at 1204 .
- K PRS K
- PRS K [ ⁇ 1 1 ⁇ 1 ⁇ 1 1 ⁇ 1].
- i is initialized to 0; i is used to track the current OFDM symbol and the current index of the shifted pseudo random sequence.
- the current OFDM symbol (OFDM[i]) is transmitted at 1208 .
- PRS K [i mod n] ⁇ 1 where n is the length of the pseudo random sequence. If the shifted pseudo random sequence is equal to ⁇ 1 then the current OFDM symbol is modified before it is transmitted at 1212 . Control is then transferred to step 1216 . If the shifted pseudo random sequence is not equal to ⁇ 1, then the current OFDM symbol (OFDM[i]) is not modified before it is transmitted at 1214 . Control is then transferred to step 1216 .
- FIG. 13 illustrates an embodiment of a shifted pseudo random sequence used to select instances of OFDM symbols to modify.
- Shifted pseudo random sequence 1304 is used to determine which input components of input signal 1300 to modify.
- the input signal may represent a packet and the input components are the OFDM symbols of the packet.
- Output signal 1304 represents the sequence of time spread instances transmitted.
- Shifted pseudo random sequence 1304 is used to determine whether output signal 1306 includes a modified instance or an unmodified instance for the second instance of each OFDM symbol.
- the first input element in input signal 1300 OFDM symbol A
- FIG. 14A illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the time domain.
- Pilot insertion block 1400 and time spreading block 1402 perform spectral shaping using time spreading.
- Time spreading block 1402 is after IFFT 1408 and processes time domain signals. For every OFDM symbol that is passed to time spreading block 1402 , two instances are output to DACs 1404 and 1406 .
- the first instance output by time spreading block 1402 may be an unmodified copy of the input OFDM symbol.
- the second instance is either a modified instance or an unmodified instance of the input OFDM symbol.
- pilot sequence from pilot insertion block 1400 is used as a pseudo random sequence and it (or a shifted version of it) is used to determine which OFDM symbols to modify.
- Time spreading block 1402 decides which OFDM symbols to modify using the pilot sequence and performs the appropriate modification or duplication.
- FIG. 14B illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the frequency domain.
- corresponding modules perform the same functions as those described in FIG. 3 .
- Time spreading block 1452 is before IFFT 1454 and processes frequency domain signals rather than time domain signals.
- Time spreading block 1452 outputs two instances of an OFDM symbol for every OFDM symbol passed to it. The first instance is an unmodified instance and the second is either a modified instance or an unmodified instance.
- time spreading block 1452 is coupled to pilot insertion block 1450 .
- the pilot sequence from pilot insertion block 1450 may be shifted and used to decide which OFDM symbols to modify. Time spreading block 1452 performs this decision making and the appropriate copying/modifying of OFDM symbols passed to it.
- time spreading block 1402 may consume less power compared to time spreading block 1452 . Since time spreading block 1452 is before IFFT 1454 , IFFT 1454 must process both instances of each OFDM symbol generated. IFFT 1408 , which precedes time spreading block 1402 , does not process both instances. This results in less power consumed by the transmitter to run IFFT 1408 using time spreading block 1402 .
- time spreading is performed at other points within the transmitter than those illustrated. Design complexity, die size, and power consumption may be considered when deciding where in the transmitter block diagram to perform time spreading. In some embodiments, it may be simpler to combine spectral shaping using time spreading with other modules.
- the time spreading block is implemented as multiple modules. For example, a first module may duplicate each OFDM symbol passed to it. A subsequent block may decide which duplicate OFDM symbols to modify and performs the modification.
Abstract
A method of shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum of a transmitted signal is disclosed. An input signal including an input component is received and a first instance of the input component is generated. The method also includes determining that a second instance of the input component is to be different than the first instance. The second instance of the input component that is different from the first instance is generated. An output signal to be transmitted is generated and includes the first instance and the second instance of the input component.
Description
- This application claims priority to U.S. Provisional Patent Application No. 60/560,948 (Attorney Docket No. AIELP024+) entitled SPECTRAL SHAPING FOR MULTIBAND OFDM TRANSMITTERS WITH TIME SPREADING filed Apr. 8, 2004 which is incorporated herein by reference for all purposes.
- Co-pending U.S. patent application Ser. No. 10/960,431 (Attorney Docket No. AIELP015) entitled SPECTRAL SHAPING IN MULTIBAND OFDM TRANSMITTER filed Oct. 6, 2004 is incorporated herein by reference for all purposes; co-pending U.S. patent application Ser. No. 10/960,430 (Attorney Docket No. AIELP030) entitled SPECTRAL SHAPING IN MULTIBAND OFDM TRANSMITTER WITH CLIPPING filed Oct. 6, 2004 is incorporated herein by reference for all purposes; and co-pending U.S. patent application Ser. No. 10/960,432 (Attorney Docket No. AIELP031) entitled SPECTRAL SHAPING IN MULTIBAND OFDM TRANSMITTER WITH PHASE SHIFT filed Oct. 6, 2004 is incorporated herein by reference for all purposes.
- This application is a continuation of co-pending U.S. patent application Ser. No. 11/099,224 (Attorney Docket No. AIELP024), entitled SPECTRAL SHAPING FOR MULTIBAND OFDM TRANSMITTERS WITH TIME SPREADING filed Apr. 4, 2005 which is incorporated herein by reference for all purposes.
- Multiband orthogonal frequency division multiplexing (MB-OFDM) is a modulation technique used in some wireless communication systems such as ultra-wideband (UWB). The MB-OFDM modulation technique combines OFDM modulation with frequency hopping. It is a modulation technique suitable for devices designed to comply with Federal Communications Commission (FCC) regulations relating to UWB devices.
- Unlike most other wireless systems in which the transmit power limit is typically set with respect to the total power integrated over the entire signal band, UWB devices are allowed to operate within a relatively wide frequency band provided that two criteria are met. First, the occupied bandwidth is required to meet a predefined minimum. Second, the radiated power measured over an integrating bandwidth anywhere within the signal band is required to be less than a predefined maximum. According to the current regulations, UWB devices are allowed to operate in the frequency band between 3.1 to 10.6 GHz. The occupied bandwidth is required to meet a minimum of 500 MHz and the radiated power, when measured over a bandwidth of 1 MHz anywhere within the signal band, is required to be less than −41.3 dBm.
- Since in UWB the integrating bandwidth (1 MHz) is much smaller than the bandwidth of the UWB signal itself (500 MHz), the shape of the spectrum is an important issue. In order to maximize the output power of a MB-OFDM transmitter, the spectrum of the generated signal should be made as flat as possible.
FIG. 1A is a diagram illustrating a frequency spectrum of an ideal UWB signal. In practice, factors such as D/A converter pulse shape, non-ideal filter characteristics, component variations and data characteristics tend to affect the shape of the spectrum.FIG. 1B is a diagram illustrating the frequency spectrum of a typical UWB signal generated by an existing device. There are peaks and variations in the frequency spectrum. The transmit power is typically limited by the largest peak in the signal spectrum. It would be desirable to have a UWB MB-OFDM transmitter design that would generate a flat output spectrum over the operating frequency range of the transmitter. - Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
-
FIG. 1A is a diagram illustrating a frequency spectrum of an ideal UWB signal. -
FIG. 1B is a diagram illustrating the frequency spectrum of a typical UWB signal generated by an existing device. -
FIG. 1C is a diagram illustrating the transmission of an OFDM-packet using multiple frequency hopping bands. -
FIG. 2A is a diagram illustrating the frequency spectrum of three hop bands generated by some transmitter embodiments. -
FIG. 2B is a diagram illustrating the frequency spectrum of three hop bands generated by a transmitter embodiment that compensates the effects shown inFIG. 2A . -
FIG. 3 is a block diagram illustrating an OFDM transmitter embodiment. -
FIG. 4A is a diagram illustrating a frequency spectrum of a set of uncompensated sub-carriers within a frequency hopping band. -
FIG. 4B is a diagram illustrating the frequency spectrum of the sub-carriers after the gain factors are applied. -
FIG. 5 is a block diagram illustrating an OFDM transmitter embodiment that adjusts the sub-carrier amplitudes. -
FIG. 6A is a diagram illustrating the frequency spectrum of a signal. -
FIG. 6B is a diagram illustrating the clipped frequency spectrum. -
FIG. 7 is a flowchart illustrating a frequency clipping process according to some embodiments. -
FIG. 8 is a block diagram illustrating another OFDM transmitter embodiment. -
FIG. 9 is a block diagram illustrating another OFDM transmitter embodiment that implements the phase shift. -
FIG. 10 is a diagram illustrating a transmitter embodiment that includes several spectrum shaping components. -
FIG. 11 is a diagram illustrating an embodiment of a frequency hopping transmission that employs time spreading. -
FIG. 12 is a flowchart illustrating an embodiment of a process for transmitting a subset of OFDM symbols with different instances. -
FIG. 13 illustrates an embodiment of a shifted pseudo random sequence used to select instances of OFDM symbols to modify. -
FIG. 14A illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the time domain. -
FIG. 14B illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the frequency domain. - The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. A component such as a processor or a memory described as being configured to perform a task includes both a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. In general, the order of the steps of disclosed processes may be altered within the scope of the invention.
- A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
- Spectrum shaping techniques for transmitting OFDM signals are disclosed. In some embodiments, a band gain control is used to determine a band gain for a selected band associated with the signal to be transmitted. In some embodiments, a sub-carrier amplitude control is used to apply a gain factor to each of the sub-carrier frequency components of the modulated signal. In some embodiments, modified synchronization sequences are used to reduce peaks in the frequency spectrum. In some embodiments, a random phase shifter introduces random or pseudorandom phase shifts to the signal to reduce repetitive patterns in the signal and achieve flatter frequency spectrum. Combinations of these techniques can be used in various embodiments. For purposes of illustration, spectrum shaping of frequency hopping OFDM signals is discussed in detail below.
- In some MB-OFDM systems, multiple frequency hopping bands (also referred to as hop bands or transmission bands) are used to transmit OFDM symbols to avoid symbol collision. An OFDM symbol waveform includes a number of modulated carrier waveforms, referred to as sub-carriers. Each sub-carrier is used to carry one data symbol, encoded as a phase shift or a combination of amplitude shift and phase shift. In some embodiments, the sub-carrier frequency spacing is approximately equal to the inverse of the OFDM symbol duration, which means that the sub-carrier waveforms partly overlap in the frequency domain.
FIG. 1C is a diagram illustrating the transmission of an OFDM packet using multiple frequency hopping bands. In the example shown, each rectangle corresponds to a synchronization symbol or an OFDM symbol. The initial part of the packet, referred to as the synchronization preamble, includes a sequence of identical packet synchronization (PS) symbols, followed by a small number of frame synchronization (FS) symbols. The synchronization symbols are used to aid the receiver in synchronizing to the received signal. In the example shown, the synchronization symbols, include a specific sequence of binary phase shift keying (BPSK) symbols known as the synchronization sequence. The PS and FS symbols are identical except for a phase shift of 180°, making them easily distinguishable to the receiver. Detecting the location of the FS symbols allows the receiver to determine the boundary between the synchronization preamble and the header/data portion of the packet. - For the purpose of illustration, three frequency hopping bands are used in the examples below, although any number of frequency hopping bands may be used as appropriate.
FIG. 2A is a diagram illustrating the frequency spectrum of three hop bands generated by some transmitter embodiments. In this example, the frequency spectrum that includeshop bands -
FIG. 2B is a diagram illustrating the frequency spectrum of three hop bands generated by a transmitter embodiment that compensates the effects shown inFIG. 2A . In this example,frequency hopping bands flat frequency spectrum 260. The adjustment is made by determining the frequency hopping band associated with the signal to be transmitted, determining the band gain that corresponds to the frequency hopping band and applying the band gain to the signal. The band gains are determined during the design process of the transmitter in some embodiments to correct any systematic gain deviations for different hop bands. In some embodiments, an uncompensated output signal is measured to supply feedback information used to determine the band gain values and achieve the desired frequency spectrum characteristics. The feedback technique can be used during the manufacturing process, during the transmission operations of the transmitter or both. -
FIG. 3 is a block diagram illustrating an OFDM transmitter embodiment. In this example,transmitter 300 outputs a signal with a gain compensated frequency spectrum similar to 260. Data bits are received on medium access control (MAC)interface 302 and then encoded by a forward error correction (FEC)encoder 304. In some embodiments, the encoded bits are optionally punctured, interleaved and repeated to provide better protection against multipath and interference. The bits are then mapped to modulation symbols by asymbol modulator 306. Quadrature Phase Shift Keying (QPSK) or other appropriate modulation scheme may be used. The modulated symbols such as QPSK symbols are also referred to as sub-carriers. Optionally,pilot tone inserter 306 adds pilot tones to the modulated symbols. An inverse Fast Fourier Transform (IFFT)component 308 is used to transform blocks of symbols from frequency domain into a time domain waveform (also referred to as an OFDM symbol). A synchronization preamble that includes repeated PS and FS synchronization symbols is added to the beginning portion of each data packet bypreamble inserter 310. Alternatively, the preamble may be inserted before the IFFT (i.e., in the frequency domain). A guard interval and a cyclic prefix or zero prefix are added to the OFDM symbol by prefix andguard inserter 312. - In this example,
band gain control 314 applies a time varying band gain factor on its input to counter the effects of gain variations in different hop bands to achieve a more uniform frequency spectrum. Depending on the value of the gain factor that is applied, the signal gets amplified, attenuated or remains unchanged as appropriate.Band gain control 314 is controlled by a hop timing signal and a band select signal. Gain values that correspond to different hop bands are stored in a lookup table or other appropriate storage. The hop timing signal determines when the band gain factor should change according to the timing of the OFDM symbol generation. The band select signal determines the value of the band gain factor used for a given hop band. In some embodiments, signal strength is measured during operation and an appropriate gain is determined according to the measurement. - The inphase (I) and quadrature (Q) components of the gain compensated baseband OFDM signal are converted from digital to analog by digital to analog converters (DACs) 316 and 318, respectively. The analog signals are sent to a
radio transmitter 320 to be up-converted to the desired carrier frequency, amplified and then transmitted viaantenna 324. The local oscillator (LO) signal used byradio 320 is generated byfrequency synthesizer 322, which is also controlled by the control signals.Frequency synthesizer 322 has the ability to switch its output frequency at the start of each OFDM symbol period so that different transmitted OFDM symbols may occupy different hop bands. In some cases, the LO frequency is switched every symbol period. In other cases, the LO frequency remains the same for several symbol periods before it is switched again. It is also possible that the LO frequency is never switched during the transmission of an entire packet. The timing of the frequency switch is controlled by the hop timing signal. The appropriate LO frequency to be synthesized for a given symbol period is determined by the band select signal. - Variations in frequency spectrum exist among frequency hopping bands as well as among sub-carriers.
FIG. 4A is a diagram illustrating a frequency spectrum of a set of uncompensated sub-carriers within a frequency hopping band. Ideally, the sub-carriers should have equal amplitude and form a flat frequency envelope. In practice, uncompensated sub-carriers such as 402, 404 and 406 have different amplitudes and form afrequency envelope 400 with amplitude variations. In the diagram shown, the signal amplitudes near the edges of the envelope are significantly weaker than those near the center of the envelope. The amplitude variations are partly attributed to the transmitter's DACs, which introduce a sin(x)/x shaping of the signal spectrum and cause the reduction in signal amplitude near the band edges. The various filters in the transmitter's signal path have a similar effect as the DAC. In some embodiments. these filters also cause a ripple in the signal spectrum. - In some embodiments, the effects of the DACs, the filters as well as other components are offset using gain compensation. A plurality of sub-carrier gain factors are applied to the uncompensated sub-carriers to make the amplitudes of the resulting gain compensated sub-carrier approximately equal. Depending on the value of the gain factor used, the corresponding uncompensated sub-carrier amplitude may be amplified, attenuated or unchanged.
FIG. 4B is a diagram illustrating the frequency spectrum of the sub-carriers after the gain factors are applied. Each sub-carrier is multiplied with an appropriate sub-carrier gain factor. The values of the gain factors are selected such that when multiplied with corresponding sub-carriers insignal 415, the resulting compensated sub-carriers have approximately the same amplitude. For example, the sub-carriers near the band edges receive greater gain boost than the sub-carriers near the band center. The resultingsub-carrier envelope 430 is substantially more even compared to 406. In some embodiments, the amplitudes of uncompensated sub-carrier frequency components are measured to supply feedback information used to determine the sub-carrier gain factors. The measurement may take place during the manufacturing process, during the transmission operations of the transmitter or both. -
FIG. 5 is a block diagram illustrating an OFDM transmitter embodiment that adjusts the sub-carrier amplitudes. In this example, like components oftransmitter 500 andtransmitter 300 perform like functions.Transmitter 500 additionally includes asub-carrier gain control 502 that adjusts the amplitudes of the sub-carriers by applying appropriate gain factors to the corresponding sub-carriers. In some embodiments, a different set of gain factors is used for each frequency hopping band. Additionally, a different gain factor may be applied to the Inphase and Quadrature components of each sub-carrier. During transmission, the frequency hopping band associated with the signal is determined and the appropriate set of gain factors is selected and applied. The application of the gain factors compensates the spectral distortion introduced by the DACs and various filters in the transmit signal path. A substantially flat baseband signal similar to signal 430 is thus obtained. - The synchronization sequences are often chosen for their autocorrelation and cross correlation properties rather than their spectral properties. As a result, the synchronization data sequence sometimes introduces peaks in the frequency spectrum, making the frequency spectrum substantially non-flat.
FIG. 6A is a diagram illustrating the frequency spectrum of a signal. In this example, the signal includes several peaks (such as peak 602) in its frequency spectrum. In some embodiments, the signal is clipped at alevel 604 to create a frequency spectrum that is more even.FIG. 6B is a diagram illustrating the clipped frequency spectrum. Details of the clipping process are discussed below. -
FIG. 7 is a flowchart illustrating a frequency clipping process according to some embodiments. Duringprocess 700, frequency components of an input are limited to a predetermined clip level in order to reduce or eliminate the peaks and achieve a flat frequency spectrum. The original data sequence is first Fourier transformed to obtain its complex-valued spectral representation (702). A spectral component is then selected (704). In this example, the spectral component (also referred to as the Fourier coefficient) with the maximum amplitude is chosen. Next, the clip level is selected (705). The clip level, which controls the flatness of the generated signal spectrum, is chosen relative to the selected spectral amplitude in some embodiments. The amplitudes of the spectral components are then clipped according to the clip level (706). In other words, spectral components with amplitude exceeding the clip level are given a new amplitude value equal to the clip level. Other spectral components with amplitudes less than or equal to the clip level are unchanged. Finally, an inverse Fourier transform is applied to the clipped spectrum to transform the signal back to the time domain (708). - The clipping operation can affect the auto-correlation and cross-correlation properties of the synchronization sequence. In some embodiments, a moderate clip level (for example, 3 dB below the maximum spectral amplitude) is chosen to achieve a substantial improvement of the spectral flatness with only a small impact on the performance of the receiver. In some embodiments, the clip level is further reduced until all the spectral components in the modified synchronization sequence have approximately equal amplitude, thus creating a spectrum that is substantially flat. In some cases, the clip level is set to a value less than or equal to the smallest spectral amplitude. In some embodiments, several outputs generated by using different clip levels are compared to select an appropriate clip level that offers flat spectrum without significantly degrading the output sent to the receiver.
- It is not necessary to perform the computations described in
process 700 for each data sequence during transmission. In some embodiments, similar effects are achieved by using pre-computed, modified synchronization sequences that have reduced spectral peaks in the preamble waveform. One way to derive the modified synchronization sequences is to apply the computations ofprocess 700 to different synchronization sequences and store the results.FIG. 8 is a block diagram illustrating another OFDM transmitter embodiment. Like components oftransmitter 800 andtransmitter 300 perform like functions. In this example, modified synchronization sequences are stored in a lookup table 802. When a preamble is to be generated, the modified synchronization sequence that corresponds to the preamble is retrieved and inserted into the signal stream. Other implementations are sometimes used in different embodiments. For example, the preambles can be inserted prior to the IFFT operation. The frequency domain components may be clipped and buffered before they are processed by the IFFT component. - In some embodiments, a random phase shifter that applies random or pseudorandom phase shifts to the OFDM symbols is used to randomize the signal and reduce peaks in the frequency spectrum. The amount of phase shift for each symbol may be determined according to a pseudo random sequence or other predefined sequence. If desired, the sequence of phase shifts can be reconstructed in the receiver, allowing the receiver remove the phase shift of each received OFDM symbol before other tasks such as channel estimation, phase estimation and data demodulation are carried out.
-
FIG. 9 is a block diagram illustrating another OFDM transmitter embodiment that implements the phase shift. In this example, arandom phase shifter 902 is used to introduce random or pseudo random phase shifts to the OFDM symbols. In some embodiments, the phase shifts are limited to multiples of 90° (i.e. the phase shifts are restricted to 0°, 90°, 180°, 270°) so that the random phase shifter can be implemented via two basic operations: interchanging the I and Q signal components and reversing the sign of I and/or Q signal components. Although the random phase shift is shown to take place prior to analog to digital conversion in this example, the phase shift operation may also be performed elsewhere in the transmitter. For example, the phase of the QPSK symbols at the input of the IFFT may be shifted before the IFFT is applied. - The spectrum shaping techniques can be used in combination in some embodiments. For example, some transmitter embodiments include both a modified synchronization sequence lookup table for clipping preamble frequency spectrum and a random phase shifter for performing phase shift. Some transmitter embodiments use both a band gain control and a sub-carrier amplitude control.
FIG. 10 is a diagram illustrating a transmitter embodiment that includes several spectrum shaping components.Transmitter 1000 shown in this example includes asub-carrier amplitude control 1002, a modified synchronization sequence lookup table 1004, arandom phase shifter 1006 and aband gain control 1008. One or more of these components may be active at the same time to shape the output signal to achieve a more uniform output spectrum. -
FIG. 11 is a diagram illustrating an embodiment of a frequency hopping transmission that employs time spreading. In the example shown,OFDM symbols OFDM symbol A 1100 and OFDM symbol A′ 1102 are transmitted on the hop band with center frequency f1, where OFDM symbol A′ 1102 is a modified instance andOFDM symbol A 1100 is an unmodified instance.OFDM symbol B 1104 andOFDM symbol B 1106 are transmitted on the hop band with center frequency f3 andOFDM symbol C 1108 and OFDM symbol C′ 1110 are transmitted on the hop band with center frequency f2. - In some embodiments, all transmitted instances in a packet are unmodified. The two instances may be the output of a duplication block that outputs two identical instances for every OFDM symbol input. For example, OFDM symbols A, A, B, B, C, and C of a packet may be transmitted. In some embodiments, one or both of the transmitted instances in a packet are a modification of the original OFDM symbol. For example, OFDM symbols A, A′, B, B′, C, and C′ of a packet may be transmitted. In another example, OFDM symbols A′, A″, B′, B″, C′, and C″ of a packet may be transmitted, where OFDM symbol A″ is another modification of OFDM symbol A that is a different modification compared to OFDM symbol A′. In some embodiments, a combination of methods is employed in the same packet. In some embodiments, the method of generating the two instances of an OFDM symbol is random.
- In some embodiments, the frequency hopping scheme varies from that illustrated. For example, there may be more or less than three hop bands. The sequence of hops may vary from that shown. In some embodiments, the hop band changes at a different rate than that illustrated. For example, the hop band may change after every four OFDM symbols transmitted instead of every two OFDM symbols. In some embodiments, frequency band hopping is not employed and all synchronization symbols and OFDM symbols are transmitted on the same band. For example, OFDM symbols A 1100, A′ 1102,
B 1104,B 1106,C 1108, and C′ 1110 may be transmitted on band f1. - In some embodiments, the order of the OFDM symbols varies from that illustrated. In some embodiments, the modified instance is transmitted before the unmodified instance. In some embodiments, the two instances are not transmitted successively.
- In some embodiments, the modification of the OFDM symbol is inversion. Some embodiments employ other modification techniques. For example, the modification may be swapping the I and Q signals or the modification may be the complex conjugation of the OFDM symbol. Another example modification is phase shifting. A combination of methods may also be employed.
- If for some OFDM symbols both instances are transmitted on the same band and the instances are different, the transmitted spectral shape may be flatter than if the instances are the same. Rather than having the two instances of an OFDM symbol repeat each other on the same band (and thus repeat the same spectrum), two different instances may have different spectrums and contribute to a flatter spectrum overall. For example, a process may be applied to select a subset of OFDM symbols in a packet. For the OFDM symbols not selected, the instances of each unselected OFDM symbol are the same. In some embodiments, the instances are both unmodified instances. For the subset of selected OFDM symbols, two different instances of each selected OFDM symbol are transmitted. In some embodiments, one instance is an unmodified instance and the other is a modified instance of the original OFDM symbol. When the spectrum is measured (perhaps over multiple OFDM symbols or multiple packets) a flatter spectral shape is produced.
-
FIG. 12 is a flowchart illustrating an embodiment of a process for transmitting a subset of OFDM symbols with different instances. In the example shown, either a modified instance or an unmodified instance is transmitted after an unmodified instance of the OFDM symbol. A pseudo random sequence (PRS) is obtained at 1200. For example, the pseudo random sequence may be the sequence of pilot tones inserted into each OFDM symbol. A pseudo random generator may also be used. In this example, the elements of the pseudo random sequence are either 1 or −1. An example of such a pseudo random sequence is [1 −1 −1 1 −1] where each of the elements are generated using a random process. In some embodiments, a pseudo random number generator already included in the design is used to generate the random number multiple times. Logic is reused and die size and manufacturing costs are kept low. - In some embodiments, the elements in the random sequence take on different values than those illustrated. The elements may take on more than two values. In some embodiments, the values of the elements are discrete values such as integer values. In some embodiments, the elements are continuous values.
- The pseudo random sequence is shifted by K (PRSK) at 1204. For example, if PRS=[1 −1 −1 1 −1] and K=2, then PRSK=[−1 1 −1 −1 1 −1]. At 1206 i is initialized to 0; i is used to track the current OFDM symbol and the current index of the shifted pseudo random sequence. The current OFDM symbol (OFDM[i]) is transmitted at 1208.
- At 1210 it is determined whether PRSK[i mod n]=−1 where n is the length of the pseudo random sequence. If the shifted pseudo random sequence is equal to −1 then the current OFDM symbol is modified before it is transmitted at 1212. Control is then transferred to step 1216. If the shifted pseudo random sequence is not equal to −1, then the current OFDM symbol (OFDM[i]) is not modified before it is transmitted at 1214. Control is then transferred to step 1216.
- At 1216, it is determined whether the current OFDM symbol is the last OFDM symbol of the packet. If the current OFDM symbol is the last one then the process ends. Otherwise, control is transferred to 1218 and i is incremented. Control is then transferred back to 1208 and the next OFDM symbol (OFDM[i]) is transmitted.
-
FIG. 13 illustrates an embodiment of a shifted pseudo random sequence used to select instances of OFDM symbols to modify. In the example shown, pseudorandom sequence 1302 is shifted by K=2 to created shifted pseudorandom sequence 1304. Shifted pseudorandom sequence 1304 is used to determine which input components ofinput signal 1300 to modify. The input signal may represent a packet and the input components are the OFDM symbols of the packet.Output signal 1304 represents the sequence of time spread instances transmitted. - Shifted pseudo
random sequence 1304 is used to determine whetheroutput signal 1306 includes a modified instance or an unmodified instance for the second instance of each OFDM symbol. The first input element ininput signal 1300, OFDM symbol A, is copied tooutput signal 1306. Since the first element in shifted pseudorandom sequence 1304 is −1, a modified instance (A′) is copied tooutput signal 1306. Otherwise an unmodified instance is copied. This process repeats for the rest of the input elements. If there are more OFDM symbols ininput signal 1300 than elements in shifted pseudorandom sequence 1304 the index wraps to the beginning of the shifted pseudorandom sequence 1304. Thus, both OFDM symbol A and OFDM symbol F use the first element in shifted pseudorandom sequence 1304, which is −1. -
FIG. 14A illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the time domain. In the example shown, corresponding modules perform the same functions as those described inFIG. 3 .Pilot insertion block 1400 andtime spreading block 1402 perform spectral shaping using time spreading.Time spreading block 1402 is afterIFFT 1408 and processes time domain signals. For every OFDM symbol that is passed totime spreading block 1402, two instances are output to DACs 1404 and 1406. The first instance output bytime spreading block 1402 may be an unmodified copy of the input OFDM symbol. The second instance is either a modified instance or an unmodified instance of the input OFDM symbol. The pilot sequence frompilot insertion block 1400 is used as a pseudo random sequence and it (or a shifted version of it) is used to determine which OFDM symbols to modify.Time spreading block 1402 decides which OFDM symbols to modify using the pilot sequence and performs the appropriate modification or duplication. -
FIG. 14B illustrates an embodiment of a transmitter which implements spectral shaping using time spreading in the frequency domain. In the example illustrated, corresponding modules perform the same functions as those described inFIG. 3 .Time spreading block 1452 is beforeIFFT 1454 and processes frequency domain signals rather than time domain signals.Time spreading block 1452 outputs two instances of an OFDM symbol for every OFDM symbol passed to it. The first instance is an unmodified instance and the second is either a modified instance or an unmodified instance. In this example,time spreading block 1452 is coupled topilot insertion block 1450. The pilot sequence frompilot insertion block 1450 may be shifted and used to decide which OFDM symbols to modify.Time spreading block 1452 performs this decision making and the appropriate copying/modifying of OFDM symbols passed to it. - The illustrated placement of
time spreading block 1402 in the transmitter may consume less power compared totime spreading block 1452. Sincetime spreading block 1452 is beforeIFFT 1454, IFFT 1454 must process both instances of each OFDM symbol generated.IFFT 1408, which precedestime spreading block 1402, does not process both instances. This results in less power consumed by the transmitter to runIFFT 1408 usingtime spreading block 1402. - In some embodiments, time spreading is performed at other points within the transmitter than those illustrated. Design complexity, die size, and power consumption may be considered when deciding where in the transmitter block diagram to perform time spreading. In some embodiments, it may be simpler to combine spectral shaping using time spreading with other modules. In some embodiments, the time spreading block is implemented as multiple modules. For example, a first module may duplicate each OFDM symbol passed to it. A subsequent block may decide which duplicate OFDM symbols to modify and performs the modification.
- Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.
Claims (22)
1. A method of shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum of a transmitted signal, comprising:
receiving an input signal including an input component;
generating a first instance of the input component;
determining that a second instance of the input component is to be different than the first instance;
generating the second instance of the input component that is different from the first instance; and
generating an output signal to be transmitted, wherein the output signal includes the first instance and the second instance.
2. A method as recited in claim 1 , wherein the input component is an OFDM symbol.
3. A method as recited in claim 1 , wherein the first instance and the second instance is are transmitted on a same transmission band.
4. A method as recited in claim 1 further comprising transmitting the output signal using frequency band hopping.
5. A method as recited in claim 1 , wherein the input signal includes a plurality of input components and all second instances of the plurality of input components are determined to be different than their corresponding first instance.
6. A method as recited in claim 1 , wherein generating the second instance of the input component includes inversion.
7. A method as recited in claim 1 , wherein generating the second instance of the input component includes swapping I and Q elements.
8. A method as recited in claim 1 , wherein generating the second instance of the input component includes complex conjugation.
9. A method as recited in claim 1 , wherein generating the second instance of the input component includes phase shifting.
10. A method as recited in claim 1 , wherein generating the second instance of the input component includes using a time domain representation.
11. A method as recited in claim 1 further comprising generating a pseudo random number, wherein the pseudo random number is used in determining that the second instance of the input component is to be different than the first instance.
12. A method as recited in claim 1 , wherein:
the input signal includes a plurality of input components; and
a pseudo random sequence is used in determining which of the second instances of the plurality of input components are to be different than their corresponding first instance.
13. A method as recited in claim 1 , wherein:
the input signal includes a plurality of input components;
a pseudo random sequence is used in determining which of the second instances of the plurality of input components are to be different than their corresponding first instance; and
in the event there are more input components than elements in the pseudo random sequence, the pseudo random sequence is reused.
14. A method as recited in claim 1 , wherein:
the input signal includes a plurality of input components; and
a sequence used in the generation of pilots is used in determining which of the second instances of the plurality of input components are to be different than their corresponding first instance.
15. A system for shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum of a transmitted signal, comprising:
an interface configured to receive an input signal including an input component; and
a signal processor configured to:
generate a first instance of the input component;
determine that a second instance of the input component is to be different than the first instance;
generate the second instance of the input component that is different from the first instance; and
generate an output signal to be transmitted, wherein the output signal includes the first instance and the second instance.
16. A system as recited in claim 15 , wherein the first instance and the second instance are transmitted on a same transmission band.
17. A system as recited in claim 15 , wherein generating the second instance of the input component includes inversion.
18. A system as recited in claim 15 , wherein:
the input signal includes a plurality of input components; and
a pseudo random sequence is used in determining which of the second instances of the plurality of input components are to be different than their corresponding first instance.
19. A computer program product for shaping an orthogonal frequency division multiplexing (OFDM) signal spectrum of a transmitted signal, the computer program product being embodied in a computer readable medium and comprising computer instructions for:
receiving an input signal including an input component;
generating a first instance of the input component;
determining that a second instance of the input component is to be different than the first instance;
generating the second instance of the input component that is different from the first instance; and
generating an output signal to be transmitted, wherein the output signal includes the first instance and the second instance.
20. A computer program product as recited in claim 19 , wherein the first instance and the second instance are transmitted on a same transmission band.
21. A computer program product as recited in claim 19 , wherein generating the second instance of the input component includes inversion.
22. A computer program product as recited in claim 19 , wherein:
the input signal includes a plurality of input components; and
a pseudo random sequence is used in determining which of the second instances of the plurality of input components are to be different than their corresponding first instance.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12/380,405 US20090252241A1 (en) | 2004-04-08 | 2009-02-25 | Spectral shaping for multiband OFDM transmitters with time spreading |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US56094804P | 2004-04-08 | 2004-04-08 | |
US11/099,224 US7519123B1 (en) | 2004-04-08 | 2005-04-04 | Spectral shaping for multiband OFDM transmitters with time spreading |
US12/380,405 US20090252241A1 (en) | 2004-04-08 | 2009-02-25 | Spectral shaping for multiband OFDM transmitters with time spreading |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/099,224 Continuation US7519123B1 (en) | 2004-04-08 | 2005-04-04 | Spectral shaping for multiband OFDM transmitters with time spreading |
Publications (1)
Publication Number | Publication Date |
---|---|
US20090252241A1 true US20090252241A1 (en) | 2009-10-08 |
Family
ID=40525175
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/099,224 Active 2026-07-31 US7519123B1 (en) | 2004-04-08 | 2005-04-04 | Spectral shaping for multiband OFDM transmitters with time spreading |
US12/380,405 Abandoned US20090252241A1 (en) | 2004-04-08 | 2009-02-25 | Spectral shaping for multiband OFDM transmitters with time spreading |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/099,224 Active 2026-07-31 US7519123B1 (en) | 2004-04-08 | 2005-04-04 | Spectral shaping for multiband OFDM transmitters with time spreading |
Country Status (1)
Country | Link |
---|---|
US (2) | US7519123B1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070147526A1 (en) * | 2005-12-27 | 2007-06-28 | Samsung Electronics Co., Ltd. | Sub-carrier diversity method on multi-band orthogonal-frequency-division-multiplexing symbol |
US20120008709A1 (en) * | 2007-03-30 | 2012-01-12 | Sony Deutschland Gmbh | Single carrier high rate wireless system |
Families Citing this family (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8982683B2 (en) * | 2006-11-07 | 2015-03-17 | Apple Inc. | Transmission method and related device |
KR101314254B1 (en) | 2007-02-16 | 2013-10-02 | 삼성전자주식회사 | OFDM transmitting and receiving systems and methods thereof |
US9137075B2 (en) * | 2007-02-23 | 2015-09-15 | Telefonaktiebolaget Lm Ericsson (Publ) | Subcarrier spacing identification |
GB2447080B8 (en) * | 2007-03-01 | 2011-08-03 | Artimi Inc | Signal decoding systems |
KR100857243B1 (en) * | 2007-03-02 | 2008-09-05 | 인하대학교 산학협력단 | Cognitive uwb system and method for cognitive uwb data communication |
EP2335182B1 (en) * | 2008-10-03 | 2015-10-28 | Bluechiip Pty Ltd | Ringup/ ringdown interrogation of rfid tags |
AU2009217407C1 (en) | 2008-10-09 | 2015-07-23 | Sony Corporation | New frame and data pattern structure for multi-carrier systems |
KR101518346B1 (en) | 2008-10-20 | 2015-05-08 | 삼성전자주식회사 | A method for receiving and transmitting preamble in a OFDM system and an apparatus thereof |
US9848342B1 (en) * | 2016-07-20 | 2017-12-19 | Ccip, Llc | Excursion compensation in multipath communication systems having performance requirements parameters |
Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5852630A (en) * | 1997-07-17 | 1998-12-22 | Globespan Semiconductor, Inc. | Method and apparatus for a RADSL transceiver warm start activation procedure with precoding |
US5974082A (en) * | 1996-10-28 | 1999-10-26 | Kokusai Denshin Denwa Co., Ltd. | Spread spectrum communications system |
US6574283B1 (en) * | 1997-08-19 | 2003-06-03 | Sony Corporation | Communication method, transmission and reception apparatuses, and cellular radio communication system |
US20050078598A1 (en) * | 2003-08-21 | 2005-04-14 | Anuj Batra | Enhancement to the multi-band OFDM physical layer |
US7184719B2 (en) * | 2002-02-20 | 2007-02-27 | Freescale Semiconductor, Inc. | Method for operating multiple overlapping wireless networks |
US7206317B2 (en) * | 2000-03-28 | 2007-04-17 | At&T Corp. | OFDM communication system and method having a reduced peak-to-average power ratio |
US20070217546A1 (en) * | 2002-09-26 | 2007-09-20 | Kabushiki Kaisha Toshiba | Transmission signals, method and apparatus |
Family Cites Families (25)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4015088A (en) | 1975-10-31 | 1977-03-29 | Bell Telephone Laboratories, Incorporated | Real-time speech analyzer |
IL84902A (en) | 1987-12-21 | 1991-12-15 | D S P Group Israel Ltd | Digital autocorrelation system for detecting speech in noisy audio signal |
US5029184A (en) | 1990-01-24 | 1991-07-02 | Harris Corporation | Low probability of intercept communication system |
US5271038A (en) | 1990-09-10 | 1993-12-14 | Hughes Aircraft Company | Distortion suppression using thresholding techniques |
DE69434353T2 (en) | 1993-12-22 | 2006-03-09 | Koninklijke Philips Electronics N.V. | Multi-carrier frequency hopping communication system |
DE19635813A1 (en) | 1996-09-04 | 1998-03-05 | Johannes Prof Dr Ing Huber | Process for reducing the peak value factor in digital transmission processes |
US6175551B1 (en) | 1997-07-31 | 2001-01-16 | Lucent Technologies, Inc. | Transmission system and method employing peak cancellation to reduce the peak-to-average power ratio |
JP4310920B2 (en) | 1998-07-13 | 2009-08-12 | ソニー株式会社 | Transmitter, transmission method, receiver, and reception method |
JP4287536B2 (en) | 1998-11-06 | 2009-07-01 | パナソニック株式会社 | OFDM transmitter / receiver and OFDM transmitter / receiver method |
DE19914600A1 (en) | 1999-03-30 | 2000-10-05 | Bosch Gmbh Robert | Synchronization method for orthogonal frequency division multiplexing (OFDM) radio receivers by inserting symbol sequence in data stream |
JP3662772B2 (en) | 1999-05-24 | 2005-06-22 | 東芝テック株式会社 | Wireless communication system |
US6584106B1 (en) | 1999-05-24 | 2003-06-24 | Advanced Micro Devices, Inc. | Backbone forwarding scheme for multiport network switch |
US6657949B1 (en) | 1999-07-06 | 2003-12-02 | Cisco Technology, Inc. | Efficient request access for OFDM systems |
US6587526B1 (en) | 1999-10-12 | 2003-07-01 | Lucent Technologies Inc. | Apparatus and method for timing synchronization in OFDM-based wireless systems |
US6807145B1 (en) | 1999-12-06 | 2004-10-19 | Lucent Technologies Inc. | Diversity in orthogonal frequency division multiplexing systems |
US6687307B1 (en) | 2000-02-24 | 2004-02-03 | Cisco Technology, Inc | Low memory and low latency cyclic prefix addition |
JP3801460B2 (en) | 2001-04-19 | 2006-07-26 | 松下電器産業株式会社 | Base station apparatus and wireless communication method |
US6912262B1 (en) | 2001-04-30 | 2005-06-28 | Maxim Integrated Products, Inc. | Wideband symbol synchronization in the presence of multiple strong narrowband interference |
KR100754621B1 (en) | 2001-11-09 | 2007-09-05 | 삼성전자주식회사 | Method and apparatus for the papr reduction using pre-emphasis method in ofdm wireless communication system |
JP3947915B2 (en) | 2002-03-11 | 2007-07-25 | 日本電気株式会社 | Frequency hopping spread spectrum communication apparatus, frequency shift control method thereof, and method for obtaining coefficient used for frequency shift control |
KR100754721B1 (en) | 2002-04-26 | 2007-09-03 | 삼성전자주식회사 | Apparatus and method for transmitting and receiving multiplexed data in an orthogonal frequency division multiplexing communication system |
US7177297B2 (en) | 2003-05-12 | 2007-02-13 | Qualcomm Incorporated | Fast frequency hopping with a code division multiplexed pilot in an OFDMA system |
US7103111B2 (en) | 2003-06-16 | 2006-09-05 | Motorola, Inc. | System and method for generating a spectral efficient root raised cosine (RRC) pulse for increasing spectral efficiency |
TWI277308B (en) | 2003-08-07 | 2007-03-21 | Nokia Corp | Method and apparatus for discrete power synthesis of multicarrier signals with constant envelope power amplifiers |
US7738545B2 (en) | 2003-09-30 | 2010-06-15 | Regents Of The University Of Minnesota | Pulse shaper design for ultra-wideband communications |
-
2005
- 2005-04-04 US US11/099,224 patent/US7519123B1/en active Active
-
2009
- 2009-02-25 US US12/380,405 patent/US20090252241A1/en not_active Abandoned
Patent Citations (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5974082A (en) * | 1996-10-28 | 1999-10-26 | Kokusai Denshin Denwa Co., Ltd. | Spread spectrum communications system |
US5852630A (en) * | 1997-07-17 | 1998-12-22 | Globespan Semiconductor, Inc. | Method and apparatus for a RADSL transceiver warm start activation procedure with precoding |
US6574283B1 (en) * | 1997-08-19 | 2003-06-03 | Sony Corporation | Communication method, transmission and reception apparatuses, and cellular radio communication system |
US7206317B2 (en) * | 2000-03-28 | 2007-04-17 | At&T Corp. | OFDM communication system and method having a reduced peak-to-average power ratio |
US7184719B2 (en) * | 2002-02-20 | 2007-02-27 | Freescale Semiconductor, Inc. | Method for operating multiple overlapping wireless networks |
US20070217546A1 (en) * | 2002-09-26 | 2007-09-20 | Kabushiki Kaisha Toshiba | Transmission signals, method and apparatus |
US20050078598A1 (en) * | 2003-08-21 | 2005-04-14 | Anuj Batra | Enhancement to the multi-band OFDM physical layer |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070147526A1 (en) * | 2005-12-27 | 2007-06-28 | Samsung Electronics Co., Ltd. | Sub-carrier diversity method on multi-band orthogonal-frequency-division-multiplexing symbol |
US7848437B2 (en) * | 2005-12-27 | 2010-12-07 | Samsung Electronics Co., Ltd. | Sub-carrier diversity method on multi-band orthogonal-frequency-division-multiplexing symbol |
US20120008709A1 (en) * | 2007-03-30 | 2012-01-12 | Sony Deutschland Gmbh | Single carrier high rate wireless system |
US8526522B2 (en) * | 2007-03-30 | 2013-09-03 | Sony Deutschland Gmbh | Single carrier high rate wireless system |
Also Published As
Publication number | Publication date |
---|---|
US7519123B1 (en) | 2009-04-14 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8391379B2 (en) | OFDM signal spectrum shaping device and method for OFDM signal spectrum shaping | |
US7519123B1 (en) | Spectral shaping for multiband OFDM transmitters with time spreading | |
KR100869198B1 (en) | Multi-carrier communication system | |
US7317750B2 (en) | Orthogonal superposition coding for direct-sequence communications | |
US7236747B1 (en) | Increasing OFDM transmit power via reduction in pilot tone | |
US20050249266A1 (en) | Multi-subband frequency hopping communication system and method | |
US20040151109A1 (en) | Time-frequency interleaved orthogonal frequency division multiplexing ultra wide band physical layer | |
KR20050008388A (en) | Apparatus for generating preamble sequences in an orthogonal frequency division multiplexing communication system using a plurarity of transmission antennas and method thereof | |
KR101324136B1 (en) | Dynamic interleaving method and device | |
EP2057809B1 (en) | Transmission methods and apparatuses for cancelling inter-carrier interference | |
EP1754313B1 (en) | A transmitter and receiver for ultra-wideband ofdm signals employing a low-complexity cdma layer for bandwidth expansion | |
US8804869B2 (en) | OFDM PAPR reduction using cancelation vectors | |
KR20080045202A (en) | Adaptive radio/modulation apparatus, receiver apparatus, wireless communication system and wireless communication method | |
KR20040048547A (en) | Apparatus for generating preamble sequence in communication system using orthogonal frequency division multiplexing scheme and method thereof | |
US7535819B1 (en) | Multiband OFDM system with mapping | |
JP4633054B2 (en) | Method and transmitter for communicating ultra-wideband signals using orthogonal frequency division multiplexing modulation | |
US20230336385A1 (en) | Method, transmitter, structure, transceiver and access point for provision of multi-carrier on-off keying signal | |
US20050018783A1 (en) | OFDM transmitter for generating FSK modulated signals | |
JP4538052B2 (en) | OFDM signal processing method and OFDM transmitter | |
RU2761280C1 (en) | Structure, method, transmission device, receiver-transmission device and access point suitable for implementation with low difficulty | |
EP2317715B1 (en) | Technique for adjusting a phase relationship among modulation symbols | |
JP4109136B2 (en) | Communication device | |
CN1860719B (en) | Multi-carrier OFDM uwb communications systems | |
KR100683168B1 (en) | UWB transmitter and method thereof | |
WO2009044176A2 (en) | Method and device of transmitting an ofdm signal |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |
|
AS | Assignment |
Owner name: TAHOE RESEARCH, LTD., IRELAND Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:INTEL CORPORATION;REEL/FRAME:061175/0176 Effective date: 20220718 |