Abstract: A method is provided which improves reliability of channel estimation in a digital communication system by reducing the ambiguity in the recognition of received symbols evaluated for the channel estimation. A data word transmitted according to a first mapping of data word values to modulation states is re-transmitted at least once with a second, re-arranged mapping of data word values to modulation states. The second mapping and possible further mappings are generated from the first mapping in a way that the number of different results which can be obtained from combining the transmitted original data symbol and the re-transmitted counterpart data symbol(s) is lower than the number of original modulation states in the first mapping.

Abstract: The present invention is directed to a transmitter and method for transmitting data in a digital communication system, the method comprising generating an original symbol by mapping the bits of the original bit sequence using a modulation constellation, generating at least one counter part symbol from the original symbol or from at least one counter part bit sequence generated from the original bit sequence where a combination of the original symbol and the at least one counter part symbol forms a quasi pilot symbol.

Abstract: A method sends uplink control information from a user equipment to a serving node of a radio communications system by first encoding uplink control information bits into symbols. The encoded symbols are split into at least two groups of symbols for use to achieve diversity transmission. Each of the at least two groups of symbols are cyclically repeated to generate a repeated group for each of the at least two groups of symbols. Then the repeated groups are mapped each to different transmission ports of the user equipment for diversity transmission as uplink control information through a plurality of uplink transmission slots of an uplink subframe.

Abstract: A digital phase shifter suitable for high power RF applications is disclosed. A plurality of MEMs switches selectively couple delay lines into the RF signal path providing adjustable phase shift under digital control. 90 degree hybrid combiners on either side of the MEMs switches allow two signal paths to be used in combination to provide a desired number of phase shift steps with a reduced number of delay lines and switches and with lower power level on each path.

Abstract: An approach is provided for minimizing co-channel interference in a communication system is disclosed. A header of a first frame is scrambled based on a first unique word. A header of a second frame is scrambled based on a second unique word. The first frame including the corresponding scrambled header and the second frame including the corresponding scrambled header are transmitted, respectively, over adjacent co-channels of the communication system. Each of the frames further includes a payload and a pilot block. The payload and the pilot block of the first frame are scrambled based on a first scrambling sequence. The payload and the pilot block of the second frame are scrambled based on a second scrambling sequence. The above arrangement is particularly suited to a digital satellite broadcast and interactive system.

Abstract: Certain aspects of the present disclosure relate to a method for demodulating CPM modulated signals transmitted in a wired or wireless communication system using a linear modulation model consisting of a linear superposition of time pulses modulated using pseudo-PSK pulses.

Abstract: A method is provided which improves reliability of channel estimation in a digital communication system by reducing the ambiguity in the recognition of received symbols evaluated for the channel estimation. A first plurality of bits is mapped to a modulation state according to a given Gray mapping of binary numbers to modulation states and transmitted. The plurality of bits is re-transmitted at least once, with a sub-set of bits contained in the plurality of bits inverted, and mapped to further modulation states according to the same Gray mapping. The bits to be inverted are determined in a way that the number of different vector sum results obtainable, for all combinations of bit values within the first plurality of bits, by adding vectors representing complex values of the first and further modulation states in a complex plane, is lower than the number of different modulation states within the Gray mapping.

Abstract: Methods and apparatus for constructing a pilot symbol for a communication frame transmitted in a wireless communication system, such as an OFDM system, are disclosed. In particular, the methods and apparatus generate at least one pseudo-random noise sequence having at least a predetermined length, where the at least one pseudo-random noise sequence represents a system configuration of a wireless system. A time domain symbol sequence is modulated with the at least one pseudo-random noise sequence to create a timing acquisition pilot symbol. The modulated acquisition pilot symbol is further masked to a prescribed frequency profile and placed in a frame for wireless transmission.

Abstract: A method and system is disclosed for shifting the phase of a PN long code for access attempts by an access terminal in a wireless communication network. An access terminal may seek to acquire access from a base station that is detected by the access terminal above a threshold power level, even if the access terminal is further away from the base station than a threshold distance beyond which access is not normally granted. According to one embodiment, the access terminal will, upon determining that it is beyond the threshold distance, embed in an access request message an apparent distance that is smaller than the threshold distance, by phase-shifting a timing signal and encoding the access request message with the phase-shifted timing signal. The access terminal will then transmit the access request message on an air interface communication link to the base station.

Abstract: Provided is a wireless communication apparatus wherein channel estimation accuracy is improved while keeping the position of each bit in a frame, even when a modulation system having a large modulation multiple value is used for a data symbol. In the wireless communication apparatus (100), an encoding section (101) encodes and outputs transmitting data (bit string) to a bit converting section (102), and the bit converting section (102) converts at least one bit of a plurality of bits constituting a data symbol to be used for channel estimation, among the encoded bit strings, into ‘1’ or ‘0’ and outputs it to a modulating section (103). The modulating section (103) modulates the bit string inputted from the bit converting section (102) by using a single modulation mapper and a plurality of data symbols are generated.

Abstract: A transmitter comprises a channel encoder to encode data bits; a modulator to modulate the encoded data bits, wherein the modulator selects one of a first modulation scheme and a second modulation scheme for each of a plurality of time slots; wherein, for each time slot, the channel encoder: includes a prefix and a suffix at the beginning and end, respectively, of the encoded data bits corresponding to the respective time slot, the prefix and the suffix being selected based on the selected modulation scheme for the respective time slot; and passes the prefix, the encoded data bits, and the suffix to the modulator; wherein, for each time slot, the modulator: modulates the prefix, the encoded data bits, and the suffix received from the channel encoder according to the selected modulation scheme for the respective time slot; and applies a window function to the prefix and the suffix.

Abstract: A method is provided for enhancing a legacy satellite digital radio audio service (SDARS) by overlaying a hierarchically modulated data stream on a base layer (legacy) data stream and improving the synchronization of the received signal in which an overlay layer frame is synchronized to a base layer frame. The base layer frame includes additional data that is used to synchronize the receivers to demodulate and decode the overlay layer and the base layer. The additional data is modulated using a technique that aids the receiver in synchronizing the received signal that is different from the overlay layer.

Abstract: Certain aspects of the present disclosure relate to a method for modulating single carrier signals using constant envelope 2-CPM modulation and quasi-constant envelope filtered continuously rotated pseudo-PSK modulation in a wireless communication system.

Abstract: The radio transmitting apparatus includes a first initial phase value setting circuit that sets, in the first modulator, an initial value of the phase of the first modulated signal, which is a value at the start of the modulation according to the first modulation scheme. The radio transmitting apparatus includes a second initial phase value setting circuit that sets, in the second modulator, the phase stored in the phase storing circuit as an initial value of the phase of the second modulated signal, which is a value at the start of the modulation according to the second modulation scheme. The radio transmitting apparatus includes a signal gathering circuit that selects and outputs the first modulated signal output from the first modulator and then selects and outputs the second modulated signal output from the second modulator.

Abstract: The present invention provides a method and an apparatus for controlling a phase delay offset point of a modulator. The method comprises: acquiring backlight detection current signals output from a modulator in different working states, and determining harmonic amplitude values of the backlight detection current signals corresponding to the different working states; determining a detection value of a phase delay offset point corresponding to the modulator according to the determined harmonic amplitude values; comparing the detection value with a set target value of the phase delay offset point, and controlling a position of the phase delay offset point corresponding to the modulator according to the comparison result. The accuracy of controlling the position of the phase delay offset point of the modulator and the performance of the Differential Quadrature Phase Shift Keying (DQPSK) modulation system are improved through the technical solution.

Abstract: A radio transmission device includes a modulation unit that maps a transmission bit sequence to a symbol corresponding to any one signal point by using a constellation in which a plurality of congruent equilateral triangles having a signal point as an apex are formed in each of four quadrants of an IQ plane representing an in-phase component and a quadrature component of a signal, two arbitrary neighboring equilateral triangles share one side, and signal points closest to an original point in the four quadrants form two neighboring equilateral triangles that share one side. The radio transmission device also includes a transmission unit that transmits the symbol obtained by mapping performed by the modulation unit.

Abstract: A circuit for providing AM/PM modulation is described. The circuit includes a signal generator, which provides two phase modulated (PM) signals used to form two drive signals which are later combined in a constructive/destructive fashion. The combination of the two phase modulated signals form a signal for driving a load. When the load is driven, the resulting signal is AM/PM modulated.

Abstract: A transmitting device, a receiving device, and a communication method for transmitting and receiving data modulated on frequency subcarriers of an OFDM communication system. An OFDM burst includes a preamble part and payload data part, whereby the preamble includes a section of pilot symbols mapped onto every n-th frequency subcarrier and signaling data mapped onto the frequency subcarriers between the frequency subcarriers with the pilot symbols. A first channel estimation on the basis of the received pilot symbols is performed, the result of which is used to reconstruct the entire section of the received preamble as a training pattern for an accurate channel estimation, which is used for a channel equalization of the received payload part.

Abstract: A non-feedback pre-encoder for optical DQPSK modulation includes four differential encoders, two power splitters, two delay lines, one exclusive OR gate and a cross switch. Each of two data streams input to the pre-encoder is divided into two identical streams by one of the power splitter, called an upper stream and a lower stream, respectively. Every upper stream is differentially encoded by one of the differential encoders, and outputs of the differential encoders are fed into the XOR gate. An output of the XOR gate drives the cross switch as a control signal. Two lower input data stream are delayed in the delay lines, and fed into the cross switch. The outputs of the cross switch are differentially encoded, separately, where outputs of the pre-encoder are provided. The invention eliminates the speed limitation due to the electrical propagation by constructing an all-forward control signal.

Abstract: Methods and apparatus for conditioning communications signals based on detection of high-frequency in the polar domain. High-frequency events detected in a phase-difference component of a complex baseband signal in the polar domain are detected and used as a basis for performing hole-blowing on the complex baseband signal in the quadrature domain and/or nonlinear filtering either or both the magnitude and phase-difference components in the polar domain. Alternatively, high-frequency events detected in the phase-difference signal that correlate in time with low-magnitude events detected in a magnitude component of the complex baseband signal are used as a basis for performing hole-blowing on the complex baseband signal in the quadrature domain and/or nonlinear filtering either or both the magnitude and phase-difference components in the polar domain.

Abstract: A quadrature amplitude modulator is provided. An oscillator generates an in-phase carrier signal having a rectangular wave, a trapezoidal wave or a waveform similar to these, and a quadrature carrier signal, the phase of which is shifted by ¼ cycle relative to the in-phase carrier signal. A multi-level driver generates an in-phase modulated signal by amplitude modulating the in-phase carrier signal with an analog in-phase baseband signal having a discrete voltage level or current level in accordance with the in-phase baseband data. Likewise, the multi-level driver generates a quadrature modulated signal by amplitude modulating the quadrature carrier signal with an analog quadrature baseband signal having a discrete voltage level or current level in accordance with the quadrature baseband data The multi-level driver generates a modulated signal, the amplitude of which takes a discrete level, by combining the modulated signals together.

Abstract: Disclosed is a vector modulator. The vector modulator can control the amplitude and phase of an input signal, by not using amplitude variable attenuators but using phase shifters. Further, the vector modulator has a simple configuration and enables an input signal to be exactly modulated. Furthermore, the vector modulator can modulate the phase of an input signal throughout all areas in the polar coordinate system.

Abstract: A communication system using an OFDM includes a data creation section for coding data to be transmitted and mapping the data, a null symbol insertion section for filling a null symbol into a no-data subchannel if the number of subchannels containing the mapped data is small for the band assignment, and a symbol interleave section for performing symbol interleave in the whole user assignment band and inserting a known training symbol and pilot symbol into the determined symbol position of the user assignment band are included and symbols are placed such that signal phase change is continuous in the same subcarrier between symbols and carrier sense is executed at the positions of the symbols where the signal phase change is continuous.

Abstract: A transmitter which transmits information in transmission frame to a receiver, the transmission frame including multiple transmission symbols and guard intervals obtained by replicating a fixed time period of a transmission symbol, generates a transmission frame by making phases of one transmission symbol out of two transmission symbols and a guard interval thereof continuous with phases of the other transmission symbol and a guard interval thereof, when the two continuous transmission symbols are the same.

Abstract: A modulator performs data processing operations such as interpolation and fractional delay adjustment on amplitude and/or phase data by performing shift operations in lieu of multiplication operations. In selected embodiments, the modulator samples input data at a first rate, processes the sampled input data using the first rate, and then interpolates the processed data to produce interpolated data. The modulator then samples the interpolated data at a second rate higher than the first rate and generates output data at the second rate.

Abstract: The invention relates to a method of estimating symbols carried by a digital signal that is received by a receiver over a communication channel (5), said symbols being multiplexed or orthogonal frequency sub-carriers. The inventive method comprises the following steps in relation to each symbol carried by the digital signal, consisting in: performing at least two transforms towards the frequency domain (8,9) on a portion of the received signal essentially corresponding to the symbol, said transforms being performed with a determined time lag (10) therebetween: estimating the parameters (r0, r1, . . . , rn, r?0, r?1, . . . , r?n) of the communication channel from pre-determined binary information contained in the digital signal; and estimating the symbol from a combination of the result of each of the transforms performed and the estimated communication channel parameters.

Abstract: A method for allowing a reception end to effectively detect a sequence used for a specific channel of an OFDM communication system, and apparatus for the same are provided. During the sequence transmission, a specific part of a Zadoff-Chu sequence corresponding to the frequency “0” is omitted from a transmitted signal. In addition, first 31 constituent components of the sequence are continuously mapped to frequency resource elements of “?31” to “?1”, and the last 31 constituent components of the sequence are continuously mapped to frequency resource elements of “1” to “31”.

Abstract: Techniques for producing an output signal using an outphasing transmitter are disclosed. In some examples, constant modulation (CM) signals may be produced from a digital input signal. The CM signals may be converted to an analog state and filtered. The signals may then be modulated to produce modulated signals, which may be amplified. The amplified signals may be combined to produce combined signals, which may further be combined to produce an output signal.

Abstract: I/Q data skew in a QPSK modulator may be detected by sending identical or complementary data streams to I and Q channel PSK modulators, setting the relative carrier phase between I and Q to zero or ?, and monitoring the average QPSK output power, where the data streams sent to the I and Q channels include streams of alternating ones and zeroes.

Abstract: I/Q data skew in a QPSK modulator may be detected by sending identical or complementary data streams to I and Q channel PSK modulators, setting the relative carrier phase between I and Q to zero or ?, and monitoring the average QPSK output power, where the data streams sent to the I and Q channels include pseudorandom streams of ones and zeroes.

Abstract: A system and method for substantially reducing average transmit power by omitting the transmission of a majority of pulses by using a modified run length coding to reduce signal power. By lowering the average power, an opportunity is presented to either decrease the total power drawn by the transmitter (battery life) or raise the peak power of all symbols (Eb/No), thereby increasing range of a RF transmission system.

Abstract: An apparatus for and method of transmitting and/or receiving a signal by using signaling point rotation in mutually cooperative relaying are provided.

Abstract: An input digital signal is periodically and alternately subjected to first modulation and second modulation, being thereby converted into a pair of a baseband I signal and a baseband Q signal. The first modulation and the second modulation are different from each other. The pair of the baseband I signal and the baseband Q signal are outputted. The first modulation may be at least 8-signal-point modulation while the second modulation may be phase shift keying.

Abstract: Communication systems are described that use geometrically shaped constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. In several embodiments, the geometrically shaped is optimized based upon a capacity measure such as parallel decoding capacity or joint capacity. In many embodiments, a capacity optimized geometrically shaped constellation can be used to replace a conventional constellation as part of a firmware upgrade to transmitters and receivers within a communication system. In a number of embodiments, the geometrically shaped constellation is optimized for an Additive White Gaussian Noise channel or a fading channel.

Abstract: A wireless short range transmission system comprises a controller, a first oscillator, a transmitter, and an antenna. The transmitter comprises a phase-lock loop frequency synthesizer for receiving a reference signal from the first oscillator and a first modulation signal. The phase-lock loop frequency synthesizer is configured to be turned on by the first modulation signal for generating a carrier signal based on the reference signal. The transmitter further comprises a power amplifier for receiving the carrier signal from the phase-lock loop frequency synthesizer and a second modulation signal. The power amplifier is configured to be turned on/off by the second modulation signal to generate a modulated signal based on the carrier signal. The power amplifier is turned on after the phase-lock loop frequency synthesizer is stabilized and the phase-lock loop frequency synthesizer is turned off with the power amplifier or after the power amplifier has been turned off.

Abstract: A method from transmitting data via multiple antennas. The method contemplates modulating data to be transmitted into a plurality of modulated symbols, encoding each pair of modulated symbols from among said plurality of symbols in accordance with a transmission diversity scheme to result in a plurality of 2 by 2 matrices, with each 2 by 2 matrix corresponding to each pair of modulated symbols, orthogonally spreading the plurality of 2 by 2 matrices to generate an output matrix, and transmitting the symbols in the output matrix via a plurality of antennas by using either a space time transmission diversity scheme, a space frequency transmission diversity scheme, or a combination of a space time transmission diversity scheme and a space frequency transmission diversity scheme.

Abstract: A method from transmitting data via multiple antennas. The method contemplates modulating data to be transmitted into a plurality of modulated symbols, encoding each pair of modulated symbols from among said plurality of symbols in accordance with a transmission diversity scheme to result in a plurality of 2 by 2 matrices, with each 2 by 2 matrix corresponding to each pair of modulated symbols, orthogonally spreading the plurality of 2 by 2 matrices to generate an output matrix, and transmitting the symbols in the output matrix via a plurality of antennas by using either a space time transmission diversity scheme, a space frequency transmission diversity scheme, or a combination of a space time transmission diversity scheme and a space frequency transmission diversity scheme.

Abstract: A system and method for data communication over a cellular communications network that allows the transmission of digital data over a voice channel using a vocoder that operates in different modes depending upon characteristics of the inputted signal it receives. To prepare the digital data for transmission, one or more carrier signals are encoded with the digital data using one of a number of modulation schemes that utilize differential phase shift keying to give the modulated carrier signal certain periodicity and energy characteristics that allow it to be transmitted by the vocoder at full rate. The modulation schemes include DPSK using either a single or multiple frequency carriers, combined FSK-DPSK modulation, combined ASK-DPSK, PSK with a phase tracker in the demodulator, as well as continuous signal modulation (ASK or FSK) with inserted discontinuities that can be independent of the digital data.

Abstract: A system, method of processing and method of manufacturing related to a signal processing scheme which receives multiple inputs and performs signal correlation to identify a predetermined signal based on a specific modulation type such as phase shift key or quadrature modulation related signal characteristics.

Abstract: A UWB transmission apparatus that, in a system using a mixture of amplitude and phase modulation schemes, can support both of the amplitude and phase modulation schemes, while preventing the signal powers of amplitude-modulated signals from degrading. In this UWB transmission apparatus, if the modulation mode is of QPSK, a mapping part (121) selects one of four signal points on the IQ plane in accordance with a 2-bit data, and outputs information related to the I- and Q-components of the selected signal point to a QPSK/ASK modulated signal forming part (122). If the modulation mode is of ASK, the mapping part (121) selects the origin point on the IQ plane when the data being ‘0’ and selects one of four signal points on the IQ plane, similarly to the case of QPSK modulation, when the data being ‘1,’ and outputs information, which is related to the selected signal point, to the QPSK/ASK modulated signal forming part (122).

Abstract: A method and apparatus for measuring channel quality over which has been transmitted a sequence of symbols produced by encoding and constellation mapping a source data element sequence. A sequence of received symbols is received over the channel. The sequence of received symbols is de-mapped based on a first channel quality indicator previously transmitted to a transmitter of the sequence of symbols. The de-mapped symbols are decoded to produce a decoded output sequence. In some embodiments, the decoding may be based on the first channel quality indicator. The decoded output sequence is re-encoded to produce a re-encoded output sequence. The de-mapped symbols are correlated with the re-encoded output sequence to produce a second channel quality indicator. The second channel quality indicator is transmitted to the transmitter to adaptively select a type of mapping based on the second channel quality indicator.

Abstract: Various embodiments are disclosed relating to techniques to transmit data rate control signals for multicarrier wireless systems. According to an example embodiment, a wireless apparatus may be adapted to transmit at least a first data rate control (DRC) value via an in-phase channel and at least a second DRC value via a Quadrature-phase channel. The first DRC value may be associated with a first forward link carrier and the second DRC value may be associated with a second forward link carrier. In this manner, DRC values may be transmitted over both the I and Q channels, for example.

Abstract: A wireless communication device including a controller communicably coupled to a transceiver. In one embodiment, the controller generates a QPSK sequence having multiple elements wherein each element includes real and imaginary parts. In another embodiment, the sequence is selected from a groups of sequences stored on a user terminal. Thereafter, the controller generates a reference signal based on the information representative of the selected QPSK sequence.

Abstract: A coding unit for determining two different types of modulation to be applied to two carrier signals such that each modulated carrier signal represents a data symbol in accordance with a group of modulation points, each modulation point representing a modulation of the first type and a modulation of the second type that can be applied to one of the carrier signals, the coding unit being arranged to associate the data symbol with a first one of the modulation points by applying a first mapping function to that data symbol and associate the data symbol with a second one of the modulation points by applying a second mapping function to that data symbol, the first and second mapping functions being such that they each map two different data symbols to a respective common modulation point; and determine the modulation of the first and second types to be applied to the first carrier signal to be the modulation of the first and second types represented by the first modulation point and the modulation of the first an

Abstract: The present invention provides a method and device for generating and mapping a Channel State Information Reference Signal (CSI-RS) sequence, and the method includes: generating a pseudo-random sequence according to a pseudo-random sequence initial value, performing a Quadrature Phase-Shift Keying (QPSK) modulation on the pseudo-random sequence, and obtaining a first CSI-RS sequence according to maximum bandwidth of system; and cutting the first CSI-RS sequence according to the actual bandwidth of the system, obtaining a second CSI-RS sequence, and mapping the second CSI-RS sequence to a time frequency location of a CSI-RS antenna port. The CSI-RS reference signal sequence can be generated or obtained respectively at the UE terminal and eNB terminal in accordance with the stated methods for generating and mapping the reference sequence according to known parameters by the present invention, so that the calculated CSI-RS sequence can be utilized to measure the channel at the UE terminal.

Abstract: Disclosed are data transmission/reception apparatus and method that may be applied to a case where additional data is to be transmitted in a CE-OFDM modulation/demodulation scheme that satisfies an OFDM feature which is robust against multipath fading and simultaneously has a feature that amplitude is constant. Service channel information, modulation parameter information of a physical layer, and the like, may be transmitted by using an additionally secured information channel. If using this, a service search time may be saved, and power of a receiver may be reduced.

Abstract: A transmitter includes a monitoring circuit for monitoring phase transitions of in-phase and quadrature components of an input phase modulated signal. A filter is downstream from the monitoring circuit for generating a filtered phase modulated signal within an allocated bandwidth. A transmit gain controller is downstream from the filter for adjusting an amplitude of the filtered phase modulated signal based on a dynamic reference envelope control signal. A control circuit cooperates with the monitoring circuit and the transmit gain controller for generating the dynamic reference envelope control signal so that phase transitions are suppressed in the filtered phase modulated signal and so that the filtered phase modulated signal remains within the allocated bandwidth.

Abstract: The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for enabling a transmitter to transmit a sequence in a wireless communication system, and to an apparatus for the same. A sequence-transmitting method comprises the steps of: performing at least one of a complex conjugate operation and a reverse operation on a first sequence to generate a second sequence; mapping the second sequence to a plurality of subcarriers in an Orthogonal Frequency Division Multiple Access (OFDMA) symbol; and transmitting the OFDMA symbol to a receiver. The invention also relates to an apparatus for the sequence-generating method.

Abstract: A method and an apparatus for a transmitter to transmit data in a wireless communication system are provided. This method includes: generating a first signal field including at least one symbol; generating a second signal field configured by repeating at least one symbol of the first signal field; and transmitting a frame including the first signal field, the second signal field, and a data field and a first symbol of the second signal field is modulated through binary phase shift keying (BPSK) and symbols from a second symbol of the second signal field are modulated through Q-BPSK. According to the present invention, a service filed can be extended while maintaining compatibility with a wireless communication system in the related art by transmitting a frame using symbol repetition.

Abstract: A transmitting apparatus includes a modulation signal generating section that generates a modulation signal by modulating transmission data using one of a plurality of modulation schemes. The plurality of modulation schemes include a first modulation scheme, a second modulation scheme, and a third modulation scheme, where the first modulation scheme has maximum m-ary modulation value, the second modulation scheme has a lower m-ary modulation value than the first modulation scheme, and the third modulation scheme has a lower m-ary modulation value than the second modulation scheme. The transmitting apparatus also includes a pilot signal generating section that generates a pilot signal having one of a plurality of amplitudes, the pilot signal having a lower amplitude than a maximum amplitude of the first modulation scheme.