WO2008147910A1

WO2008147910A1 - Adaptive-gain transmitter

Info

Publication number: WO2008147910A1
Application number: PCT/US2008/064574
Authority: WO
Inventors: Aliazam Abbasfar
Original assignee: Rambus Inc.
Priority date: 2007-05-25
Filing date: 2008-05-22
Publication date: 2008-12-04

Abstract

A communication circuit includes an input node to receive two adjacent blocks of data symbols. A modulator, coupled to the input node, encodes these blocks of data symbols using an encoding technique into corresponding encoded data symbols. Moreover, a detector is coupled to the modulator. This detector determines peak values for each of the encoded data symbols. Furthermore, an amplifier is coupled to the detector, and an output node is coupled to the amplifier. This amplifier amplifies a given encoded data symbol in the encoded data symbols using an associated symbol-dependent gain prior to transmitting this encoded data symbol. Note that the associated symbol-dependent gain is based on an peak value associated with the given encoded data symbol.

Description

ADAPTIVE-GAIN TRANSMITTER

Inventors: Aliazam Abbasfar

FIELD

[0001] The present embodiments relate to techniques for communicating information. More specifically, the present embodiments relate to circuits and methods for using adaptive gain during transmission to transmit signals which carry the information.

BACKGROUND

[0002] Multi-tone signaling is an increasingly popular communication technique.

During multi-tone signaling, a usable range of frequencies in a communication channel is divided into a series of frequency bands or sub-channels. Next, data, which is to be communicated via the communication channel, is modulated using a transform operation and is then up-converted using one or more carrier frequencies associated with the frequency bands.

[0003] Multi-tone signaling typically has a high peak-to-average power ratio (PAPR). Unfortunately, a high PAPR can reduce the efficiency of power amplifiers in communication systems. For example, if there is clipping in the power amplifiers, spectral re-growth (i.e., nonlinearities) will occur. Furthermore, while the PAPR can be reduced by adding redundancy (for example, through additional power amplifiers), this redundancy also increase the complexity and cost of the communication system.

[0004] Hence, what is needed are circuits and techniques which can be used in communication systems that overcome the problems listed above. BRIEF DESCRIPTION OF THE FIGURES

[0005] FIG. 1 is a graph illustrating amplifier efficiency as a function of average power for an embodiment of a power amplifier.

[0006] FIG. 2A is a graph illustrating probability as a function of symbol peak power for an embodiment of a power amplifier.

[0007] FIG. 2B is a graph illustrating probability as a function of symbol peak power for an embodiment of a power amplifier.

[0008] FIG. 3 A is a block diagram illustrating an embodiment of a communication circuit. [0009] FIG. 3B is a block diagram illustrating an embodiment of a communication circuit.

[0010] FIG. 4 is a graph illustrating encoded data symbols for an embodiment of a communication system.

[0011] FIG. 5 is a graph illustrating bit error rate (BER) as a function of signal-to- noise ratio (SNR) for an embodiment of a communication system.

[0012] FIG. 6 is a flow chart illustrating an embodiment of a process for communicating data.

[0013] FIG. 7 is a flow chart illustrating an embodiment of a process for communicating data. [0014] Note that like reference numerals refer to corresponding parts throughout the drawings.

DETAILED DESCRIPTION

[0015] The following description is presented to enable any person skilled in the art to make and use the disclosed embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present description. Thus, the present description is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. [0016] Embodiments of a first communication circuit, a first integrated circuit that includes the first communication circuit, and a first technique for communicating between devices in a first communication system are described. This first communication circuit includes an input node which receives a first block of data symbols and a second block of data symbols, where the first block of data symbols and the second block of data symbols are adjacent to each other. A modulator, coupled to the input node, encodes the first block of data symbols into a first encoded data symbol using an encoding technique and encodes the second block of data symbols into a second encoded data symbol using the encoding technique. Moreover, a detector is coupled to the modulator. This detector determines a first peak value of the first encoded data symbol and determines a second peak value of the second encoded data symbol. Furthermore, a first amplifier is coupled to the detector, and an output node is coupled to the first amplifier. This amplifier amplifies the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and amplifies the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol. Note that the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value.

[0017] In some embodiments, gain of the first amplifier is varied on an encoded-data- symbol basis. Moreover, in some embodiments a given symbol-dependent gain in the first symbol-dependent gain and the second symbol-dependent gain is based on a nonlinear amplitude threshold of the first amplifier. And in some embodiments the first symbol- dependent gain is different from the second symbol-dependent gain.

[0018] In some embodiments, the first symbol-dependent gain and the second symbol-dependent gain decrease a variation in the average power of signals at the output node, where the signals correspond to the first encoded data symbol and the second encoded data symbol. Moreover, in some embodiments the first symbol-dependent gain and the second symbol-dependent gain decrease a peak-to-average power ratio (PAPR) of the signals at the output node.

[0019] In some embodiments, the first symbol-dependent gain and the second symbol-dependent gain improve a performance metric associated with communication of the first encoded data symbol and the second encoded data symbol. [0020] In some embodiments, the modulator includes an inverse fast Fourier transform (IFFT). For example, the modulator may include orthogonal frequency division multiplexing (OFDM). Thus, a given encoded data symbol in the first encoded data symbol and the second encoded data symbol may corresponds to an OFDM symbol. [0021] In some embodiments, the first communication circuit includes a partitioner coupled between the input node and the modulator. This partitioner divides a given block of data symbols in the first block of data symbols and the second block of data symbols into subgroups of data symbols. Note that the subgroups of data symbols may be encoded in parallel. However, in some embodiments data symbols in a given block of data symbols in the first block of data symbols and the second block of data symbols may be encoded in series.

[0022] In some embodiments, the modulator encodes the first encoded data symbol and the second encoded data symbol without intersymbol interference between the first encoded data symbol and the second encoded data symbol. [0023] In some embodiments, the first block of data symbols is associated with a first time interval and the second block of data symbols is associated with a second time interval, where the second time interval is after the first time interval. Moreover, there may be a time spacing between the first time interval and the second time interval.

[0024] In some embodiments, data symbols in a given block of data symbols in the first block of data symbols and the second block of data symbols are phase modulated.

[0025] In some embodiments, the first peak value is an extremum of the amplitude of the first encoded data symbol and the second peak value is an extremum of the amplitude of the second encoded data symbol.

[0026] In some embodiments, the signals at the output node are transmitted via a wireless communication channel.

[0027] In some embodiments, the first communication circuit includes a frequency up-conversion element coupled to the output node. This frequency up-conversion element up-converts signals at the output node to an associated band of frequencies.

[0028] In some embodiments, the first block of data symbols and the second block of data symbols include data symbols which are modulated using: time division multiple access (TDMA), frequency division multiple access (FDMA), and/or code division multiple access (CDMA). [0029] In some embodiments, the first communication circuit includes a buffer coupled to the modulator and the detector.

[0030] Another embodiment provides a first system that includes a first device and a second device. This first device includes the first communication circuit. Furthermore, the second device: receives signals from the first device via a wireless communication channel; demodulates the received signals; and detects the first block of data symbols and the second block of data symbols.

[0031] Another embodiment provides a first method for communicating data. During this method, a first block of data symbols is modulated using an encoding technique and a second block of data symbols is modulated using the encoding technique. This modulating technique generates first encoded data symbols associated with the first block of data symbols and second encoded data symbols associated with the second block of data symbols. Moreover, the first block of data symbols and the second block of data symbols are adjacent to each other. Then, a first peak value of the first encoded data symbol and a second peak value of the second encoded data symbol are determined. Next, the first encoded data symbol is amplified using a first symbol-dependent gain prior to transmitting the first encoded data symbol and the second encoded data symbol is amplified using a second symbol-dependent gain prior to transmitting the second encoded data symbol. Note that the first symbol- dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value.

[0032] Additional embodiments provide a second communication circuit, a second integrated circuit that includes the second communication circuit, and a second technique for communicating between devices in a second communication system. This communication circuit includes the input node and the modulator coupled to the input node. Furthermore, a second amplifier is coupled to the modulator and the output node is coupled to the second amplifier. This amplifier amplifies the first encoded data symbol using a first gain pattern prior to transmitting the first encoded data symbol and amplifies the second encoded data symbol using a second gain pattern prior to transmitting the second encoded data symbol. Note that gain during a given gain pattern in the first gain pattern and the second gain pattern varies for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol. In addition, the given gain pattern is selected based on a pattern of elements in the given encoded data symbol. [0033] In some embodiments, the second communication circuit includes control logic coupled to second amplifier. This control logic selects the given gain pattern. Moreover, in some embodiments the control logic provides the given gain pattern to a third communication circuit that receives signals corresponding to the given encoded data symbol from the second communication circuit.

[0034] Another embodiment provides a second system that includes a third device and a fourth device. This third device includes the second communication circuit. Furthermore, the fourth device: receives signals from the third device via the wireless communication channel; demodulates the received signals; and detects the first block of data symbols and the second block of data symbols.

[0035] Another embodiment provides a second method for communicating data. During this method, the first block of data symbols is modulated using an encoding technique and the second block of data symbols is modulated using the encoding technique. This modulating generates the first encoded data symbols associated with the first block of data symbols and the second encoded data symbols associated with the second block of data symbols. Moreover, the first block of data symbols and the second block of data symbols are adjacent to each other. Then, a first gain pattern associated with a first pattern of elements in the first encoded data symbol is selected and a second gain pattern associated with a second pattern of elements in the second encoded data symbol is selected. Next, the first encoded data symbol is amplified using the first gain pattern prior to transmitting the first encoded data symbol, and the second encoded data symbol is amplified using the second gain pattern prior to transmitting the second encoded data symbol. Note that gain during a given gain pattern in the first gain pattern and the second gain pattern varies for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol.

[0036] The aforementioned embodiments may be used in a wide variety of applications, including: serial or parallel wireless links, wireless metropolitan area networks (such as WiMax), wireless local area networks (WLANs), wireless personal area networks (WPANs), and systems and devices that include multiple antennas. For example, the embodiments may be used in conjunction with ultra- wide-band (UWB) communication and/or a communication standard associated with the Multi-Band OFDM Alliance (MBOA). Furthermore, the aforementioned embodiments may be used in: desktop or laptop computers, hand-held or portable devices (such as personal digital assistants and/or cellular telephones), set-top boxes, home networks, and/or video-game devices.

[0037] We now describe embodiments of a communication technique for use in wireless communication devices and systems. FIG. 1 presents a graph 100 illustrating an embodiment of amplifier efficiency 110 as a function of average power 112 in a power amplifier. In this graph, the slope decreases when symbols are transmitted using an average power that exceeds a threshold 114. This change in the slope may be associated with clipping in the power amplifier. Unfortunately, nonlinearities such as the change in slope can result in spectral re-growth, and thus can degrade one or more performance metrics in a communication system, such as: a signal strength (such as a signal amplitude or a signal intensity), a mean square error (MSE) relative to a target (such as a detection threshold, a point in a constellation diagram, and/or a sequence of points in a constellation diagram), a signal-to-noise ratio (SNR), a bit-error rate (BER), a timing margin, and/or a voltage margin. [0038] Consequently, to maintain the one or more performance metrics the average power 112 may be reduced to avoid or reduce spectral re-growth. Furthermore, deviations from the average power 112 (as measured by the PAPR) may be similarly constrained. This is shown in FIG. 2A, which presents a graph 200 illustrating an embodiment of probability 210 as a function of symbol peak power 212. In this example, a data sequence (such as a sequence of symbols) is to be transmitted in a communication system and the symbol peak power 212 varies from symbol to symbol. Moreover, the probability 210 of a given symbol having a particular symbol peak power is characterized by a probability distribution.

[0039] To reduce spectral re-growth, the gain of the power amplifier has been set so that an average power 214 is well below a maximum peak power 216 (which is associated with spectral re-growth). In particular, back-off 218 may be selected so that 99% of the symbols (non-clipping probability 220) have a symbol peak power less than the maximum peak power 216, and thus 1% of the symbols (clipping probability 222) have a symbol peak power greater than the maximum peak power 216.

[0040] Unfortunately, many sequences of symbols (such as OFDM symbols) have high PAPRs (such as 10 dB), which constrains the gain of the power amplifier (and thus the average power 214). In communication systems where the SNR is limited by noise at the receiver, these constraints on the gain of the power amplifier in the transmitter may reduce the one or more performance metrics (such as the BER). Moreover, large PAPRs may also waste power in the transmitter, because the power amplifier is configured to provide peak power

(such as the maximum peak power 216) even though this is a rare occurrence. Thus, based on this discussion, the one or more performance metrics and/or power consumption may be improved by reducing the PAPR. [0041] A solution to this challenge is shown in FIG 2B, which presents a graph 250 illustrating an embodiment of probability 210 as a function of symbol peak power 212. In this example, the PAPR is reduced by dynamically adjusting the transmitter gain (for example, on a symbol-by-symbol basis) using an adaptive gain stage. Consequently, average power 260 is close to the maximum peak power 216, i.e., back-off 262 is much less than back-off 218 (FIG. 2A). As described further below with reference to FIG. 5, the resulting increase in the average gain (and the average power) of the transmitter in communication systems limited by noise at the receiver results in an improvement in BER, as well as other performance metrics.

[0042] We now describe embodiments of a transmitter that implements adaptive gain on a symbol-by-symbol basis. In the discussion that follows, multi-tone signaling is used as an illustrative example of modulation of blocks of data symbols in the transmitter.

[0043] FIG. 3 A presents a block diagram illustrating an embodiment of a communication circuit 300, which includes a transmitter 310. This circuit may be used to: perform baseband encoding and modulation of data x(n) 312, including partitioning one or more subgroups of the data x(n) 312 among a set of frequency tones; dynamically amplifying the encoded data symbols (for example, on a symbol-by-symbol basis), RF up-convert the data in the one or more subgroups into signals 330 corresponding to one or more subchannels; and to transmit these signals (for example, using one or more antennas). Note that signals 330 carried on these sub-channels may be time-multiplexed, frequency multiplexed, and/or encoded. Thus, in some embodiments the signals 330 are encoded using: TDMA, FDMA, and/or CDMA. In an exemplary embodiment, signals 330 use discrete multi-tone communication (such as OFDM).

[0044] Signals 330 are communicated by the communication circuit 300 (in a first device) via a communications channel with another communication circuit (in a second device). In an exemplary embodiment, the data is communicated using wireless communication (for example, using a 7 GHz frequency band centered on 60 GHz or using a frequency band between 50 and 90 GHz). However, in other embodiments the data is communicated using wireline communication and/or optical communication.

[0045] Note that communication of data between the first device and the second device may be unidirectional and/or bidirectional. For example, the communication between the devices may be simultaneous (i.e., full duplex communication in which both devices may transmit and receive information at the same time) or the communication direction may alternate (i.e., half -duplex communication in which, at a given time, one device transmits information and the other device receives information).

[0046] When the transmitter 310 receives the data x(n) 312, this data may be at least partially encoded. As an illustrative example, in the discussion that follows data x(n) 312 includes blocks of data symbols. However, as discussed further below, note that at least a portion of the data encoding is performed in sections of the communication circuit 300 that are associated with the sub-channels (including inverse Fast Fourier Transform (IFFT) circuit 318, amplifier 324, and modulator 308). In some embodiments, optional control logic 332 controls at least the portion of the data encoding. For example, optional control logic 332 may select at least the portion of the data encoding from look-up tables stored in optional memory 334.

[0047] Note that encoding should be understood to include modulation coding and/or spread-spectrum encoding, for example, coding based on binary pseudorandom sequences (such as maximal length sequences or m-sequences), Gold codes, and/or Kasami sequences. Furthermore, modulation coding may include bit-to-symbol coding, in which one or more data bits are mapped together to a data symbol. For example, a group of two data bits can be mapped to: one of four different amplitudes of an encoded data signal; one of four different phases of a sinusoid; or a combination of one of two different amplitudes of a sinusoid and one of two different phases of the same sinusoid (such as in quadrature amplitude modulation or QAM).

[0048] In general, the modulation coding may include: amplitude modulation, phase modulation, and/or frequency modulation, such as pulse amplitude modulation (PAM), pulse width modulation, and/or pulse code modulation. For example, the modulation coding may include: two-level pulse amplitude modulation (2-PAM), four-level pulse amplitude modulation (A-PAM), eight-level pulse amplitude modulation (S-PAM), sixteen-level pulse amplitude modulation (Xd-PAM), two-level on-off keying (2-OOK), four-level on-off keying (4-OOK), eight-level on-off keying (S-OOK), and/or sixteen-level on-off keying (\6-OOK).

In addition, as noted previously, the data x(n) 312 may be encoded using TDMA, FDMA, and/ 'or CDMA.

[0049] In some embodiments, the modulation coding includes non-return-to-zero (NRZ) coding. Furthermore, in some embodiments the modulation coding includes two-or- more-level QAM. Note that different sub-channels in communication channel may be encoded differently and/or the modulation coding may be dynamically adjusted. Thus, in some embodiments the number of bits per symbol in the data x(n) 312 and/or in one or more of the sub-channels is dynamically adjusted, thereby modifying the corresponding data rate(s). [0050] In some embodiments, at least a portion of the data includes error-detection- code (EDC) information and/or error-correction-code (ECC) information. For example, signals 330 may be transmitted with pre-existing ECC information incorporated into at least a portion of the data x(n) 312 (such as in one or more data packets). Alternatively, ECC information may be dynamically generated (i.e., in real time) based on at least a portion of the data x(ή) 312, and this ECC information may then be included with the transmitted signals 330.

[0051] In some embodiments, the ECC includes a Bose-Chaudhuri-Hochquenghem (BCH) code. Note that BCH codes are a sub-class of cyclic codes. In exemplary embodiments, the ECC includes: a cyclic redundancy code (CRC), a parity code, a Hamming code, a Reed-Solomon code, and/or another error checking and correction code.

[0052] After receiving data x(n) 312, this data is partitioned into subgroups of data symbols using a partitioner, such as serial-to-parallel converter 316. Note that in the communication circuit 300 the partitioning may be fixed (i.e., the subgroups of data symbols corresponding to the sub-channels are fixed) or dynamically adapted (for example, on a symbol-by-symbol basis based on a look-up table stored in optional memory 334). Moreover, the subgroups may be regular (such as those in which a given subgroup includes even or odd data symbols in a given block of data symbols) or irregular (where the given subgroup includes non-consecutive data symbols in the given block of data symbols, and where at least two pairs of adjacent data symbols in the given subgroup have different inter-data-symbol spacings in the given block of data symbols).

[0053] Then, the subgroups are modulated in parallel using TV-sample IFFT circuit 318 (which is used as an illustration of a modulation transform) to generate encoded data symbols (such as OFDM symbols) for transmission. In an exemplary embodiment, N is between 32 and 2048. Note that in some embodiments each subgroup is modulated by a separate IFFT circuit.

[0054] Next a detector 322 determines an peak value (such as a peak amplitude) associated with each of the encoded data symbols. During this determining, the encoded data symbols may be stored in a buffer 320. After determining the peak values, amplifier 324 may dynamically amplify a given encoded data symbol using a symbol-dependent gain that is determined or selected (from a look-up table) based on the peak value for the given encoded data symbol. Furthermore, the symbol-dependent gain may also be based on a non-linearity threshold of the amplifier 324 (such as threshold 114 in FIG. 1). As noted previously, dynamically adjusting the gain on a symbol-by-symbol basis may reduce the PAPR (allowing the amplifier 324 to be more efficient) and/or may improve one or more performance metrics of the communication channel. In some embodiments, dynamically adjusting the gain allows the communication circuit 300 to be simplified (for example, by reducing or eliminating redundancy).

[0055] In an exemplary embodiment, the gain for each data symbol is determined or set as follows: If the peak value of the data symbol preceding the amplifier 324 is P and the acceptable peak amplitude of the this amplifier is A, the gain is determined by dividing A over P (i.e., the gain equals AIP). In other words, the amplifier 324 attempts to amplify the data symbol so that the peak value of the data symbol after amplification becomes A. In some embodiments, the gain for at least two adjacent data symbols in a sequence of data symbols changes by at least 5 %.

[0056] Amplified encoded data symbols may then be converted to analog signals using digital-to-analog converter (DAC) 326 and RF up-converted to one or more appropriate frequency bands using one or more carrier frequencies/ 328 associated with the subchannels. For example, the up-conversion may use frequency-conversion elements, such as one or more heterodyne mixers or modulators, such as modulator 308.

[0057] Note that a given sub-channel in the communication channel is associated with the one or more carrier frequencies/ 328. In addition, the given sub-channel has an associated: range of frequencies, a frequency band, or groups of frequency bands (henceforth referred to as a frequency band). In some embodiments, frequency bands for adjacent subchannels may partially or completely overlap, or may not overlap. For example, there may be partial overlap of neighboring frequency bands, which occurs in so-called approximate bit loading. Furthermore, signals on adjacent sub-channels may be orthogonal.

[0058] After the up-converting, signals 330 are coupled to one or more antennas (not shown). Each of these antennas may be used to transmit signals corresponding to a given sub-channel in the communications channel. For example, there may be multiple antennas, each of which is used to transmit signals corresponding to one of the sub-channels. Note that the one or more antennas may be: external to the communication circuit 300, on-chip, on the package or chip carrier, and/or on another integrated circuit (for example, in a chip stack).

[0059] In some embodiments, multiple antennas are used to provide spatial diversity (such as multiple -input multiple-output communication) and/or polarization diversity. For example, the antennas may provide directional gain over a range of transmit angles, thereby providing more robust communication between the devices when obstacles disrupt at least a portion of the communication channel. In some embodiments, signals transmitted by different antennas in the antennas are distinguished from each other based on: encoding (such as TDMA, FDMA, and/or CDMA), spatial diversity, and/or polarization diversity.

[0060] In some embodiments, multiple antennas are included in a multi-element antenna (such as a phased-array antenna). Moreover, in some embodiments beam forming is used to provide directional communication between the devices. For example, phase encoding of the signals transmitted by two or more of the antennas may be used to provide: a directional antenna pattern, shaped beams, and/or to change a transmit direction associated with one or more of the shaped beams.

[0061] As discussed previously, the transmitted signals 330 may be received by another communication circuit (such as a receiver) using one or more antennas. This receiver may perform: RF down-conversion, baseband demodulation (for example, using an TV-point FFT), data-symbol detection, and baseband decoding. Note that an automatic gain control (AGC) in the receiver may adjust the gain of a receiver amplifier on a symbol-by-symbol basis. This adjusting may be aided by the use of a cyclic prefix in the given block of data symbols and/or by the use of a guard time between blocks of data symbols (as is illustrated below in FIG. 4). Also note that the baseband decoding may include symbol-to-bit encoding that is the opposite or the inverse of the bit-to-symbol encoding performed prior to transmitting the signals. Moreover, in some embodiments the receiver implements error detection and/or correction. For example, errors may be detected by performing a multi-bit

XOR operation in conjunction with one or more parity bits in the transmitted signals 330.

[0062] Note that AGC and data- symbol detection at the receiver may be less complicated if adaptive gain in the transmitter is used in conjunction with an encoding technique that encodes the data 312 x(ή) with phase information, for example, by using 2- PAM, binary phase shift keying (BPSK), or quadrature phase shift keying (QPSK). In embodiments where a more complicated type of amplitude modulation is used, decision thresholds or slicers in the receiver may need to be adapted to accommodate the gain variation in the transmitter. In some embodiments, the slicers are adjusted on a symbol-by- symbol basis (or as discussed below, within a given encoded data symbol). For example, the slicers may be adjusted based on information that is provided by the communication circuit 300 with the signals 330 (in-band communication) and/or separately (such as by using out-of- band communication or a different link).

[0063] In some embodiments, a range of gain values used by the amplifier 324 to dynamically amplify symbols associated with one or more sub-channels (as well as the modulating and/or encoding) is adapted or adjusted. For example, optional control logic 332 may adjust the range of gain values, the encoding, and/or the modulating of the blocks of data symbols. This adjusting may be based one or more of the performance metrics (associated with one or more of the sub-channels) and/or control information that is exchanged with control logic in the receiver.

[0064] Furthermore, the control information may be exchanged using in-band communication (i.e., via the frequency bands used in the communication channel) and/or out- of-band communication (for example, using another communication channel). This other communication channel may include a separate link between the devices. This separate link: may be wireless or wired; may have a lower data rate than the data rates associated with one or more of the sub-channels; may use one or more different carrier frequencies than are used in the sub-channels; and/or may use a different modulation technique than is used in the subchannels. Note that in some embodiments the adjusting of the range of gain values, the encoding, and/or the modulating of the blocks of data symbols is performed: continuously; as need based on one or more of the performance metrics; and/or after a pre-determined time interval (such as a time interval associated with the blocks of data symbols). [0065] In some embodiments, the adjusting involves an auto-negotiation technique between the devices. During this auto-negotiation technique, receiver may provide feedback to transmitter 310 on the efficacy of any changes to the signals 330 on the communication channel. Based on this feedback, transmitter 310 may further modify the signals 330 (henceforth referred to as remedial action). Note that the remedial action may include: retransmitting previous data; transmitting previous or new data (henceforth referred to as data) using an increased transmission power than the transmission power used in a previous transmission; reducing the data rate in one or more of the sub-channels relative to the data rate used in a previous transmission; transmitting data with reduced intersymbol interference (for example, with blank intervals inserted before and/or after the data); transmitting data at a single clock edge (as opposed to dual-data-rate transmission); transmitting data with at least a portion of the data including ECC or EDC; transmitting data using a different encoding or modulation code than the encoding used in a previous transmission; transmitting data after a pre-determined idle time; transmitting data to a different receiver; transmitting data to another device (which may attempt to forward the data to receiver); changing the number of subchannels; and/or changing the partitioning of the blocks of data symbols among the subchannels.

[0066] While the communication circuit 300 illustrates parallel encoding of the given block of data symbols, in other embodiments the given block of data symbols is encoded in series. This is shown in FIG. 3B, which presents a block diagram illustrating an embodiment of a communication circuit 350, which includes transmitter 360. In this circuit, data x(n) 312 are modulated in series using TV-sample IFFT circuit 362. This circuit may be clocked using clock signal 368. Buffer 320 and/or amplifier 324 may be clocked using clock signal 370, which has a frequency that is M¹ times smaller than that of clock signal 368 (where Mis the number of frequency tones output by IFFT circuit 362). Then, the amplified encoded signals may be combined using a combiner (such as optional serial-to-parallel converter 364) and converted into analog signals using DAC 366. Note that optional serial-to-parallel converter 364 and/or DAC 366 may be clocked using clock signal 368.

[0067] Note that communication circuits 300 (FIG. 3A) and/or 350 may include fewer components or additional components. For example, signal lines coupling components may indicate multiple signal lines (or a bus). In some embodiments, communication circuits 300 (FIG. 3A) and/or 350 include pre-emphasis to compensate for losses and/or dispersion associated with one or more communication channels. Similarly, in some embodiments a receiver of the signals includes equalization. Note that pre-emphasis and/or equalization may be implemented using feed-forward filters and/or decision-feedback-equalization circuits.

[0068] In some embodiments, communication circuits 300 (FIG. 3A) and/or 350 include receiver circuitry. Thus, either or both of these circuits may include transceiver circuits.

[0069] Moreover, while not explicitly shown in communication circuits 300 (FIG. 3A) and 350, these circuits may include memory buffers for the transmit signals. In addition, clocking circuits are not explicitly illustrated in communication circuits 300 (FIG. 3A) and 350. Nonetheless, signals may be transmitted and/or received based on either or both edges in one or more clock signals. Note that in some embodiments transmitting and receiving may be synchronous and/or asynchronous.

[0070] Components and/or functionality illustrated in communication circuit 300 (Fig. 3A) and/or 350 may be implemented using analog circuits and/or digital circuits. Furthermore, components and/or functionality in either of these communication circuits may be implemented using hardware and/or software. In some embodiments, optional control logic 332 operates on physical-layer structures in the communication circuits 300 (FIG. 3A) and/or 350 (such as an RF front-end) without using information from baseband-processing components. [0071] Note that two or more components in communication circuits 300 (Fig. 3A) and/or 350 may be combined into a single component and/or the position of one or more components may be changed. In some embodiments, communication circuits 300 (Fig. 3A) and/or 350 are included in one or more integrated circuits on one or more semiconductor die. [0072] FIG. 4 presents a graph 400 illustrating amplitude 410 for encoded data symbols 414 that have been amplified using a fixed transmitter gain 416 or a transmitter gain 418 that is varied for each data symbol. In this example, the transmitter gain for data symbol 414-1 is 3.5 and for data symbol 414-2 is 2. Note that each data symbol includes multiple elements 412 (corresponding to multiple frequency tones) and that a time space or guard time 420 between the data symbols 414 eliminates intersymbol interference between these symbols. Also note that the adaptive gain is effective for sequences of data symbols that have a large dynamic range between adjacent encoded data symbols. [0073] FIG. 5 presents a graph 500 illustrating an embodiment of BER 510 as a function of SNR 512 (in dB) for a white-noise-limited communication channel having a fixed transmitter gain 514 or a transmitter gain that is adapted 516 (and, in general, varied) for each data symbol. In this simulation, OFDM with 32 elements or frequency tones and 10% guard time was used. Note that the adaptive gain improves the BER 510 as much as a 3-10 dB increase in SNR 512.

[0074] We now describe embodiments of a process for communicating data. FIG. 6 presents a flow chart illustrating an embodiment of a process 600 for communicating data. During this process, a first block of data symbols is modulated using an encoding technique and a second block of data symbols is modulated using the encoding technique (610). This modulating generates first encoded data symbols associated with the first block of data symbols and second encoded data symbols associated with the second block of data symbols. Moreover, the first block of data symbols and the second block of data symbols are adjacent to each other. Then, a first peak value of the first encoded data symbol and a second peak value of the second encoded data symbol are determined (612). Next, the first encoded data symbol is amplified using a first symbol-dependent gain prior to transmitting the first encoded data symbol and the second encoded data symbol is amplified using a second symbol-dependent gain prior to transmitting the second encoded data symbol (614). Note that the first symbol-dependent gain is based on the first peak value and the second symbol- dependent gain is based on the second peak value.

[0075] While the preceding discussion has described adapting the transmitter gain on a symbol-by-symbol basis, in some embodiments the gain of the amplifier (such as the amplifier 324 and/or 364 in FIGs. 3A and 3B) in the transmitter is varied within a data symbol. For example, the gain may be varied for at least two elements within an encoded data symbol by using a gain pattern. This gain pattern may be selected by control logic (such as optional control logic 332 in FIGs. 3A and 3B). For example, the control logic may select a given gain pattern in a look-up table of pre-determined gain patterns that are stored in optional memory 334 (FIGs. 3 A and 3B) based on a pattern of elements in a given encoded data symbol. [0076] This technique may be useful when there is intersymbol interference in a communication channel and/or if a non-orthogonal encoding technique is used. Note that the gain pattern used for a given encoded data symbol may be communicated to a receiver. For example, information about the gain patterns may be included in the signals 330 (FIGs. 3A and 3B) and/or may be communicated to the receiver separately by using out-of-band communication or and additional link.

[0077] FIG. 7 presents a flow chart illustrating an embodiment of such a process 700 for communicating data. During this process, the first block of data symbols is modulated using an encoding technique and the second block of data symbols is modulated using the encoding technique (710). This modulating generates the first encoded data symbols associated with the first block of data symbols and the second encoded data symbols associated with the second block of data symbols. Moreover, the first block of data symbols and the second block of data symbols are adjacent to each other. Then, a first gain pattern associated with a first pattern of elements in the first encoded data symbol is selected and a second gain pattern associated with a second pattern of elements in the second encoded data symbol is selected (712). Next, the first encoded data symbol is amplified using the first gain pattern prior to transmitting the first encoded data symbol and the second encoded data symbol is amplified using the second gain pattern prior to transmitting the second encoded data symbol (714). Note that gain during a given gain pattern in the first gain pattern and the second gain pattern varies for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol.

[0078] Note that in some embodiments there may be additional or fewer operations in process 600 (FIG. 6) and/or process 700. Furthermore, the order of the operations may be changed, and two or more operations may be combined into a single operation.

[0079] The foregoing descriptions of embodiments have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present description to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present description. The scope of the present description is defined by the appended claims.

Claims

What is claimed is:

1. An integrated circuit, comprising: an input node to receive a first block of data symbols and a second block of data symbols, wherein the first block of data symbols and the second block of data symbols are adjacent to each other; a modulator coupled to the input node, wherein the modulator is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; a detector coupled to the modulator, wherein the detector is to determine a first peak value of the first encoded data symbol and is to determine a second peak value of the second encoded data symbol; an amplifier coupled to the detector, wherein the amplifier is to amplify the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol, and wherein the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value; and an output node coupled to the amplifier.

2. The integrated circuit of claim 1 , wherein gain of the amplifier is to vary on an encoded-data- symbol basis.

3. The integrated circuit of claim 1, wherein a given symbol-dependent gain in the first symbol-dependent gain and the second symbol-dependent gain is based on a nonlinear amplitude threshold of the amplifier.

4. The integrated circuit of claim 1, wherein the first symbol-dependent gain is different from the second symbol-dependent gain.

5. The integrated circuit of claim 1, wherein the first symbol-dependent gain and the second symbol-dependent gain decrease a variation in the average power of signals at the output node, and wherein the signals correspond to the first encoded data symbol and the second encoded data symbol.

6. The integrated circuit of claim 1 , wherein the first symbol-dependent gain and the second symbol-dependent gain are to improve a performance metric associated with communication of the first encoded data symbol and the second encoded data symbol.

7. The integrated circuit of claim 1 , wherein the first symbol-dependent gain and the second symbol-dependent gain are to decrease a peak-to-average power ratio of signals at the output node, and wherein the signals correspond to the first encoded data symbol and the second encoded data symbol.

8. The integrated circuit of claim 1 , wherein the modulator includes an inverse fast Fourier transform (IFFT) circuit.

9. The integrated circuit of claim 1, wherein the modulator includes orthogonal frequency division multiplexing (OFDM).

10. The integrated circuit of claim 1, wherein a given encoded data symbol in the first encoded data symbol and the second encoded data symbol corresponds to an OFDM symbol.

11. The integrated circuit of claim 1 , further comprising a partitioner coupled between the input node and the modulator, wherein the partitioner is to divide a given block of data symbols in the first block of data symbols and the second block of data symbols into subgroups of data symbols.

12. The integrated circuit of claim 11, wherein the subgroups of data symbols are to be encoded in parallel.

13. The integrated circuit of claim 1 , wherein data symbols in a given block of data symbols in the first block of data symbols and the second block of data symbols are to be encoded in series.

14. The integrated circuit of claim 1, wherein the modulator is to encode the first encoded data symbol and the second encoded data symbol without intersymbol interference between the first encoded data symbol and the second encoded data symbol.

15. The integrated circuit of claim 1, wherein the first block of data symbols is associated with a first time interval and the second block of data symbols is associated with a second time interval, and wherein the second time interval is after the first time interval.

16. The integrated circuit of claim 15, wherein there is a time spacing between the first time interval and the second time interval.

17. The integrated circuit of claim 1, wherein the first peak value is an extremum of the amplitude of the first encoded data symbol and the second peak value is an extremum of the amplitude of the second encoded data symbol.

18. The integrated circuit of claim 1 , wherein data symbols in a given block of data symbols in the first block of data symbols and the second block of data symbols are phase modulated.

19. The integrated circuit of claim 1, wherein signals at the output node are transmitted via a wireless communication channel.

20. The integrated circuit of claim 1, further comprising a frequency up-conversion element coupled to the output node, wherein the frequency up-conversion element is to up- convert signals at the output node to an associated band of frequencies.

21. The integrated circuit of claim 1 , wherein the first block of data symbols and the second block of data symbols include data symbols which are modulated using time division multiple access (TDMA), frequency division multiple access (FDMA), or code division multiple access (CDMA).

22. The integrated circuit of claim 1 , further comprising a buffer coupled to the modulator and the detector.

23. A system, comprising: a first device, wherein the first device includes: an input node to receive a first block of data symbols and a second block of data symbols, wherein the first block of data symbols and the second block of data symbols are adjacent to each other; a modulator coupled to the input node, wherein the modulator is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; a detector coupled to the modulator, wherein the detector is to determine a first peak value of the first encoded data symbol and is to determine a second peak value of the second encoded data symbol; an amplifier coupled to the detector, wherein the amplifier is to amplify the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol, and wherein the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value; and an output node coupled to the amplifier; and a second device, wherein the second device is to receive signals from the first device via a wireless communication channel, and wherein the second device is to demodulate the received signals and is to detect the first block of data symbols and the second block of data symbols.

24. A method for communicating data, comprising: modulating a first block of data symbols using an encoding technique and modulating a second block of data symbols using the encoding technique, wherein the modulating generates first encoded data symbols associated with the first block of data symbols and second encoded data symbols associated with the second block of data symbols, and wherein the first block of data symbols and the second block of data symbols are adjacent to each other; determining a first peak value of the first encoded data symbol and a second peak value of the second encoded data symbol; and amplifying the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and amplifying the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol, wherein the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value.

25. An integrated circuit, comprising: an input node to receive a first block of data symbols and a second block of data symbols, wherein the first block of data symbols and the second block of data symbols are adjacent to each other; means for modulating coupled to the input node, wherein the means is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; a detector coupled to the modulator, wherein the detector is to determine a first peak value of the first encoded data symbol and is to determine a second peak value of the second encoded data symbol; an amplifier coupled to the detector, wherein the amplifier is to amplify the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol, and wherein the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value; and an output node coupled to the amplifier.

26. A communication circuit, comprising: an input node to receive a first block of data symbols and a second block of data symbols, wherein the first block of data symbols and the second block of data symbols are adjacent to each other; a modulator coupled to the input node, wherein the modulator is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; a detector coupled to the modulator, wherein the detector is to determine a first peak value of the first encoded data symbol and is to determine a second peak value of the second encoded data symbol; an amplifier coupled to the detector, wherein the amplifier is to amplify the first encoded data symbol using a first symbol-dependent gain prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second symbol-dependent gain prior to transmitting the second encoded data symbol, and wherein the first symbol-dependent gain is based on the first peak value and the second symbol-dependent gain is based on the second peak value; and an output node coupled to the amplifier.

27. An integrated circuit, comprising: an input node to receive a first block of data symbols and a second block of data symbols; a modulator coupled to the input node, wherein the modulator is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; an amplifier coupled to the modulator, wherein the amplifier is to amplify the first encoded data symbol using a first gain pattern prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second gain pattern prior to transmitting the second encoded data symbol, wherein gain during a given gain pattern in the first gain pattern and the second gain pattern is to vary for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol, and wherein the given gain pattern is selected based on a pattern of elements in the given encoded data symbol; and an output node coupled to the amplifier.

28. The integrated circuit of claim 27, further comprising control logic coupled to the amplifier, wherein the control logic is to select the given gain pattern.

29. The integrated circuit of claim 28, wherein the control logic is to provide the given gain pattern to another integrated circuit that is to receive signals corresponding to the given encoded data symbol from the integrated circuit.

30. A communication circuit, comprising: an input node to receive a first block of data symbols and a second block of data symbols; a modulator coupled to the input node, wherein the modulator is to encode the first block of data symbols into a first encoded data symbol using an encoding technique and is to encode the second block of data symbols into a second encoded data symbol using the encoding technique; an amplifier coupled to the modulator, wherein the amplifier is to amplify the first encoded data symbol using a first gain pattern prior to transmitting the first encoded data symbol and is to amplify the second encoded data symbol using a second gain pattern prior to transmitting the second encoded data symbol, wherein gain during a given gain pattern in the first gain pattern and the second gain pattern is to vary for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol, and wherein the given gain pattern is selected based on a pattern of elements in the given encoded data symbol; and an output node coupled to the amplifier.

31. A method for communicating data, comprising: modulating a first block of data symbols using an encoding technique and a second block of data symbols using the encoding technique, wherein the modulating generates first encoded data symbols associated with the first block of data symbols and second encoded data symbols associated with the second block of data symbols; selecting a first gain pattern associated with a first pattern of elements in the first encoded data symbol and selecting a second gain pattern associated with a second pattern of elements in the second encoded data symbol; and amplifying the first encoded data symbol using the first gain pattern prior to transmitting the first encoded data symbol and amplifying the second encoded data symbol using the second gain pattern prior to transmitting the second encoded data symbol, wherein gain during a given gain pattern in the first gain pattern and the second gain pattern is to vary for at least two different elements in a given encoded data symbol in the first encoded data symbol and the second encoded data symbol.