Transmitter and method for transmitting soft pilot symbols in a digital communication system   

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/073,264 filed Jun. 17, 2008, the disclosure of which is incorporated herein by reference in its entirety.

NOT APPLICABLE

NOT APPLICABLE

The present invention relates to digital radio communication systems. More particularly, and not by way of limitation, the present invention is directed to a transmitter and method for transmitting a sequence of transmitted symbols in a digital communication system utilizing soft pilot symbols.

In digital communication systems, the receiver must estimate some parameters in order to correctly demodulate the transmitted data. The receiver may also need to estimate a measure of signal quality to feed back to the transmitter. The estimation of parameters/signal quality generally falls into three categories:

(1). Blind estimation. Generally this approach relies on some signal or channel property/characteristic that is known a priori or learned in a slow manner (for example, second-order statistics). The biggest problem with blind estimation is performance. Blind estimation generally underperforms other approaches by a significant margin. Also, blind estimation algorithms may be more complex.

(2). Pilot-aided. This approach includes known (i.e., pilot) symbols in the transmitted signal. Pilot symbols can be embedded in the data sequence (for example, the midamble of GSM) or allocated a separate resource such as the pilot code in WCDMA, so long as the pilot symbols experience the same effective fading channel as the data. The pilot-aided approach generally offers the best performance. However, pilot symbols consume resources that might otherwise be devoted to transmitting useful data. Typically there is a tradeoff between having sufficient pilots for good estimation and maximizing data throughput.

(3). Data-aided. This approach uses demodulated data symbols as “extra” pilot symbols. Generally this approach is used in conjunction with either blind estimation or the pilot-aided approach. There are two problems associated with the data-aided approach. First, blind estimation or pilot-aided estimation (or both) is typically required as a first receiver step. Therefore, data-aided approaches require extra receiver complexity. Second, data-aided approaches can degrade receiver performance due to the effect of errors in demodulating data. In data-aided approaches, the demodulated data symbols are assumed to be correct and are used as additional pilot symbols. However, if the data symbols are incorrect, the parameter/signal quality estimation algorithms can produce incorrect results. The effects of incorrect symbol decision(s) can persist for more than one estimation interval, so data-aided approaches may need special mechanisms to avoid the effect of error propagation.

The data-aided approach has been utilized in a number of existing communication systems. For example, in Wideband Code Division Multiple Access (WCDMA) systems, the control channel on the uplink is demodulated/decoded, and the symbol decisions are used as effective pilots. This has also been proposed for the WCDMA control channel on the downlink. In the Digital Advanced Mobile Phone System (D-AMPS), the channel is first estimated over a synchronization word and then tracked over data during equalization. In the equalizer, early temporary unreliable decisions are fed to the tracker, and delayed better decisions are fed to the decoder. Also in D-AMPS and GSM, multi-pass (turbo) demodulation/decoding uses decoded/re-encoded symbols as effective pilots in a second pass.

SUMMARY

The present invention overcomes the disadvantages of the prior art by transmitting some symbols with higher reliability than others. These so-called “soft pilots” are demodulated first and then used as known symbols for use in channel estimation and demodulation of higher-order modulation symbols (amplitude reference). These soft pilot symbols are more robust than the surrounding symbols, thereby enabling reliable decision-directed parameter estimation. Additionally, inserting a “constant envelope” modulation symbol among higher order modulation symbols is particularly helpful in establishing the amplitude reference essential in demodulating the higher order modulation symbols.

In one embodiment, the soft pilot symbols are modulated with a simpler, lower order modulation (for example, BPSK or QPSK) compared to the rest of the symbol sequence, which is likely a higher order modulation (for example, 16 Quadrature Amplitude Modulation (16 QAM) or 64 QAM). By using these soft pilots, the symbol can still carry some data, contrasted to a fixed pilot symbol, which allows no data throughput for the symbol. These specified soft symbol locations (time/frequency/code) and the modulation type(s) are shared with the receiver. The receiver may know the information a priori or through signaling.

Soft pilots provide an alternative to explicit data pilots for future releases of WCDMA. With soft pilot symbols, explicit pilot symbols are not necessary. With knowledge of the modulation type and the location of the soft pilots in time, frequency, and code, the receiver can maximize performance. This allows for better data rates than would otherwise be possible with explicit pilot symbols.

In another embodiment of the invention, the soft pilot symbols are generated by low-level puncturing of channel coded bits. The method includes inserting a set of soft pilot symbols by low-level puncturing of channel coded bits and replacing with known bit patterns, modulating the sequence, and transmitting the radio signal.

In a specific embodiment related to the High Speed Downlink Shared Channel (HS-DSCH), the soft pilot symbols are generated during the channel coding chain by low-level puncturing of channel coded bits after rearranging the modulation constellation and before mapping to a physical channel. In a specific embodiment related to the Enhanced Dedicated Channel (E-DCH), the soft pilot symbols are generated during the channel coding chain by low-level puncturing of channel coded bits after interleaving on the E-DCH and before mapping to a physical channel. With such a mechanism, the use of soft pilots requires no changes to the specification and implementation of the critical channel coding and rate matching procedures. This enhances compatibility with legacy equipment and allows reuse of existing transceiver implementations.

In another embodiment, the present invention is directed to a transmitter for transmitting a radio signal that includes a sequence of transmitted symbols. The transmitter includes means for inserting a set of soft pilot symbols by low-level puncturing of channel coded bits and replacing the punctured bits with known bit patterns; and means for modulating the sequence and transmitting the radio signal.

In another embodiment, the present invention is directed to a channel coder for channel coding a radio signal for a radio channel. The channel coder includes means for inserting soft pilot symbols by low-level puncturing of channel coded bits; and means for replacing the punctured channel coded bits with known bit patterns after channel interleaving. In a specific embodiment, the radio channel is an HS-DSCH. In another specific embodiment, the radio channel is an E-DCH.

According to another embodiment of the invention, the locations of the soft pilots in terms of time and code (or frequency) are designed to accommodate time-varying channel responses and to minimize undesirable impact on code performance and peak-to-average ratios.

In the following section, the invention will be described with reference to exemplary embodiments illustrated in the figures, in which:

FIG. 1 is a flow chart illustrating the steps of an exemplary embodiment of the method of the present invention;

FIG. 2 shows the data bit mapping to points in the constellation for 16 QAM in one exemplary embodiment of the present invention;

FIG. 3 shows the data bit mapping to points in the constellation for 16 QAM in another exemplary embodiment of the present invention;

FIG. 4 (Prior Art) illustrates the existing channel coding chain for the HS-DSCH;

FIG. 5 illustrates the channel coding chain for the HS-DSCH in an exemplary embodiment of the present invention;

FIG. 6 is a flow diagram illustrating an overview of a soft pilot generation process in an exemplary embodiment of the present invention;

FIG. 7 is a flow diagram illustrating a soft pilot generation process for the HS-DSCH in an exemplary embodiment of the present invention;

FIG. 8 is a flow diagram illustrating a soft pilot generation process for the E-DCH in an exemplary embodiment of the present invention;

FIG. 9 is a functional block diagram of an exemplary embodiment of an interleaver structure for the E-DCH;

FIG. 10 illustrates a first exemplary embodiment of soft pilot symbol location;

FIG. 11 illustrates a second exemplary embodiment of soft pilot symbol location;

FIG. 12 is a functional block diagram of an exemplary embodiment of a two-pass G-Rake receiver of the present invention; and

FIG. 13 is a flow chart illustrating an exemplary embodiment of a processing method performed by the two-pass G-Rake receiver of the present invention.

DETAILED DESCRIPTION

For high data rate communications, higher order modulations such as 16 QAM and 64 QAM are utilized to increase spectral efficiency. According to a first embodiment of the present invention, the transmitter designates certain symbols in the data sequence as so-called “soft pilot” symbols by using a specific alternative modulation for these symbols. The specific modulation order and the location of these symbols (in terms of time, code, and/or frequency) is known by or signaled to the receiver. The receiver utilizes the soft pilot symbols to obtain an initial estimation of signal parameters such as the channel taps and the correlation matrix. After a first demodulation, decided symbols may be utilized as effective pilots in a second pass of parameter estimation. By limiting the decided soft pilot symbols to a lower modulation than the remaining symbols in the sequence, their decisions are reliable enough to make them useful pilots. The soft pilots are different than traditional fixed pilots in that some data throughput is carried by these soft pilot symbols. Thus, replacing traditional fixed pilots with soft pilots improves data throughput.

FIG. 1 is a flow chart illustrating the steps of an exemplary embodiment of the method of the present invention. At step 11, a radio signal is transmitted with some symbols having higher reliability (for example, with a lower order modulation) than other transmitted symbols. At step 12, the radio signal is received and the higher reliability symbols are demodulated first to form soft pilot symbols. At step 13, the soft pilots are utilized as known symbols for channel estimation and demodulation of the higher order modulation symbols. At step 14, data is extracted from both the soft pilot symbols and the higher order modulation symbols.

An exemplary embodiment of the present invention specifies the modulation type and the location (time/frequency/code) of the soft pilot symbols within the data sequence. According to one embodiment of the invention, the constellation points of the soft pilots are taken as a subset of the higher order modulation constellation for the data transmission, such as 16 QAM or 64 QAM. The transmitter may utilize a specified lower order modulation for the pilot symbols such as Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK). For the rest of the symbol sequence, the transmitter may utilize a higher order modulation (for example, 16 QAM or 64 QAM). These specified soft symbol locations and the modulation type(s) are known by the receiver. The receiver may know the information a priori or through signaling.

Thus the present invention transmits lower order modulation symbols inserted among higher order modulation symbols, and the receiver performs associated actions to exploit the lower order modulation symbols as effective pilots. A symbol can carry a range of number of bits m: m=0 bit corresponds to a pure pilot; m=1 bit corresponds to BPSK; m=2 bits corresponds to QPSK; and so on, up to the maximum number M (=6 for 64 QAM). If it is assumed for simplicity that all symbols have the same energy, then the bit energy and the bit reliability decrease with m. Thus, the symbols can be used as pilots of various levels of reliability, and the receiver can perform parameter estimations in multiple passes.

FIG. 2 shows the data bit mapping to points in the constellation for 16 QAM in one exemplary embodiment of the present invention. The four corner points of the 16 QAM constellation (shown in the figure as starred points) are taken as the constellation for the soft pilots. Two features of this embodiment can be readily recognized. First, the soft pilot constellation is equivalent to a scaled QPSK constellation. It thus offers the benefits of constant envelope and higher average power. Second, the soft pilot constellation points can be easily addressed within the higher-order constellation by keeping a subset of the bit labels fixed. In the example shown in FIG. 2, the soft pilot constellation points are those with the last two bit labels fixed at “11”.

As noted, the use of soft pilot symbols causes the transmitted 16 QAM or 64 QAM symbols to have a higher average power. For example, if one in ten symbols for one channelization code is a soft pilot symbol, the average power is increased by 0.15 dB for 16 QAM and by 0.54 dB for 64 QAM. Alternatively, if there are fifteen channelization codes, and one in ten symbols for one of the fifteen channelization codes is a soft pilot symbol, the average power is increased by only 0.02 dB for 16 QAM and by 0.04 dB for 64 QAM. In practice, the transmitted power may have to be reduced by these amounts when utilizing soft pilots. It has been seen, however, that the net system performance is improved by the use of soft pilots.

FIG. 3 shows the data bit mapping to points in the constellation for 16 QAM in another exemplary embodiment of the present invention. In this embodiment, the soft pilot constellation size is enlarged to allow higher capacity for carrying data. However, the soft pilot constellation provides a constant quadrature amplitude feature which may be utilized to derive an amplitude reference. The soft pilot constellation points are addressed within the higher-order constellation by fixing the last bit label to “1.” It is clear to those skilled in the art that an alternative soft pilot constellation may be specified by fixing the third bit label to “1”, providing constant in-phase amplitude.

The introduction of soft pilots reduces the number of channel coded bits that can be carried by the transmission signal. The reduction in channel coded bits can be implemented by two different approaches. In a first approach utilizing high-level puncturing, the reduction in channel coded bits is explicitly handled by the entire channel coding chain. This approach may be adopted when designing a new communications system or protocol. However, backward compatibility is an important factor to consider when introducing soft pilot symbols into existing systems. For backward compatibility, it may be preferred to adopt a second approach utilizing low-level puncturing such that the majority of the channel coding chain is affected by the new feature. In the following, the HSPA examples are utilized to illustrate the two approaches in detail.

FIG. 4 illustrates the existing channel coding chain for the High Speed Downlink Shared Channel (HS-DSCH). In a first high-level puncturing approach for implementing the reduction in channel coded bits, the behavior of the overall channel coding chain is changed similarly to the one for the HS-DSCH. The impact, however, is not simply a different number of coded bits to be output by the “physical-layer HARQ functionality”, but rather a significant redesign and redefinition of several inter-connect and intricate physical-layer procedures in “physical-layer HARQ functionality”, “physical channel segmentation”, “HS-DSCH interleaving”, and “Constellation rearrangement”. Such significant redesign of the critical channel coding chain will render most of the existing implementation obsolete and will be difficult to co-exist with new and legacy equipment in a network.

FIG. 5 illustrates the channel coding chain for the HS-DSCH in an exemplary embodiment of the present invention. In a second, preferred approach for implementing the reduction in channel coded bits, the soft pilot symbols are preferably generated by low-level puncturing of channel coded bits before the “physical channel mapping” stages of the channel coding chain. The preferred embodiment thus makes the presence of soft pilot symbols transparent to the “physical-layer HARQ functionality”, “physical channel segmentation”, “HS-DSCH interleaving”, and “constellation rearrangement” stages.

FIG. 6 is a flow diagram illustrating an overview of a soft pilot generation process in an exemplary embodiment of the present invention. In HSDPA, the bit collection procedure in physical-layer HARQ functionality and the HS-DSCH channel interleaving are designed to map systematic turbo-coded bits, if present, to the first bit labels of the 16 QAM or 64 QAM as much as possible. The purpose of this design is to ensure the important systematic turbo-coded bits are transmitted over the channel with higher reliability. As shown in FIG. 6, this is accomplished in the channel interleaver by utilizing pair-by-pair bit multiplexing and independent rectangular interleavers. When the data modulation is based on QPSK, only the first rectangular interleaver branch is active. When the data modulation is based on 16 QAM, the first and the second rectangular interleaver branches are active. All three branches are active when the data is carried by 64 QAM. Coupled with the constellation labeling specified in 3GPP, “Technical Specification Group Radio Access Network; Spreading and Modulation (FDD),” TS 25.213 v8, the bits in the first branch are transmitted over the channel with highest reliability. The bits in the third branch are transmitted with lowest reliability. Hence, in initial transmissions, the systematic bits are normally transmitted through the first branch as much as possible. For initial transmissions, the HARQ parameters are generally set such that the “constellation rearrangement” is effectively by-passed. It should be obvious to those skilled in the art that soft pilot symbols can be inserted right after the channel interleaving. For retransmissions, HARQ parameters can be used to instruct the “constellation rearrangement” to effectively retransmit channel coded bits with different reliability. Soft pilot symbols may be inserted into the signal after the “constellation rearrangement” procedure.

FIG. 7 is a flow diagram illustrating a soft pilot generation process for the HS-DSCH in an exemplary embodiment of the present invention. The coded bit inputs are denoted by rp,k and the outputs are denoted by r′p,k. Normally, the input bits are passed to the output without modification: r′p,k=rp,k. If a scaled QPSK soft pilot symbol (such as that shown in FIG. 2) is inserted to replace a 16 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=1, and r′p,k+3=1. If a scaled QPSK soft pilot symbol is inserted to replace a 64 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=1, r′p,k+3=1, r′p,k+4=1, and r′p,k+5=1.

If a soft pilot symbol with constant quadrature amplitude (such as that shown in FIG. 3) is inserted to replace a 16 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=rp,k+2, and r′p,k+3=1. If a soft pilot symbol with constant quadrature amplitude is inserted to replace a 64 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=rp,k+2, r′p,k+3=1, r′p,k+4=rp,k+4, and r′p,k+5=1. If a soft pilot symbol with constant in-phase amplitude is inserted to replace a 16 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=1, and r′p,k+3=rp,k+3. If a soft pilot symbol with constant in-phase amplitude is inserted to replace a 64 QAM data symbol, then r′p,k=rp,k, r′p,k+1=rp,k+1, r′p,k+2=1, r′p,k+3, r′p,k+4=1, and r′p,k+5=rp,k+5.

FIG. 8 is a flow diagram illustrating a soft pilot generation process for the E-DCH in an exemplary embodiment of the present invention. To accomplish reliability identification similar to that in HS-DSCH, the bit collection procedure in physical-layer HARQ functionality and the channel interleaving are designed to map systematic turbo-coded bits, if present, to the first bit labels of the 4 PAM as much as possible. According to the preferred embodiment, the soft pilot symbols are generated after the E-DCH channel interleaving.

FIG. 9 is a functional block diagram of an exemplary embodiment of an interleaver structure for the E-DCH. The channel interleaving is facilitated by two rectangular interleaver branches when the data is carried by 4 PAM. The coded bit inputs to the “soft pilot generation” are denoted by vp,k and the outputs are denoted by v′p,k. Normally, the input bits are passed to the output without modification: v′p,k=vp,k. If a scaled BPSK soft pilot symbol is inserted to replace a 4 PAM data symbol, then v′p,k=vp,k, v′p,k+1=1.

According to the preferred embodiment, the soft pilot symbols are generated by puncturing channel coded bits at fixed locations (in terms of time and code/frequency). On the receiver side, the soft values corresponding to the punctured bits are set to zero. With this, the use of the soft pilot symbols introduces no changes to the core rate-dematching and channel decoder implementation.

Note also that, according to this embodiment, the soft pilot symbols are generated by puncturing channel coded bits that are mapped to the least reliable bit labels. Since the soft values corresponding to these low-reliability bits are normally very small, setting them to zero introduces negligible impact to the overall channel coding performance.

Soft pilot symbols may be imbedded on the same code, on a single separate code, on different antennas in Multiple-Input-Multiple-Output (MIMO) systems, and the like. The placement may be coordinated so that the soft pilot symbols either coincide or do not coincide on different codes and/or antennas.

The soft pilot symbols can be inserted into the signal in several practical ways:

1. HSPA—one code assigned to the HSPA user utilizes soft pilot symbols while other codes assigned to the same user utilize a higher order modulation.

2. HSPA—certain data symbols within each code assigned to the HSPA user are soft pilot symbols while the remaining symbols in the codes are conventional data symbols. For example, symbols 0 through N−1 on code A, N through 2N−1, on code B, and so on may be soft pilot symbols.

3. HSPA—symbols N through 2N are soft pilot symbols on all codes assigned to the HSPA user while the remaining symbols in the codes assigned to the same user are conventional data symbols.

4. Long Term Evolution (LTE)—replace demodulation pilots with soft pilot symbols for some (or all) of the embedded demodulation pilots.

The following embodiments are designed with further consideration of (a) supporting time-varying channels, (b) minimizing coding performance impact, and (c) reducing impact on peak-to-average ratio (PAR).

FIG. 10 illustrates a first exemplary embodiment of soft pilot symbol location. The soft pilot symbols are spread out in time to provide a more reliable reference for time-varying channels. The exact locations of the symbols may be specified by periodic patterns. To allow for averaging for estimation noise reduction, the soft pilot symbols may be present in more than one code at the same spread-out locations. In contrast to concentrating the soft pilot symbols into only one (or very few codes), the spread-out pattern across codes minimizes the impact on overall channel decoding performance.

FIG. 11 illustrates a second exemplary embodiment of soft pilot symbol location. The embodiment previously illustrated in FIG. 10 is suitable only if the soft pilot symbols do not contribute to substantial increase in PAR. If the PAR increase is of concern, the embodiment of FIG. 11 can be adopted. The soft pilot symbol locations between different codes are offset to reduce PAR increase.

The use of soft pilot symbols provides several benefits. First, the soft pilot symbols are more robust than the surrounding symbols, thereby providing reliable decision-directed parameter estimation. Second, the soft pilot symbols may still carry some data, contrasted to fixed pilot symbols, which allow no data throughput for the symbol. Third, by making the soft pilot symbols “constant envelope” modulation symbols inserted among higher order modulation symbols, the soft pilot symbols become particularly helpful in establishing the amplitude reference essential for demodulating the higher order modulation symbols.

The use of soft pilot symbols is applicable to any wired or wireless communication system. Soft pilots provide higher data throughput than traditional pilot-aided schemes, and do not sacrifice performance as most blind estimation schemes do. The soft pilot approach requires that the receiver use a data-aided approach. However, as opposed to traditional data-aided approaches, the present invention specifies the modulation and location (in time/code/frequency) of the soft pilot symbols so that the receiver will know that there are certain high-quality symbols that can be used in a data-aided approach. Receiver estimation algorithms based on such symbols are less error-prone and provide consistently good parameter and/or signal quality estimates.

An HSPA receiver that can utilize such soft pilots is fully described below in an exemplary embodiment consisting of a data-aided Generalized Rake (G-Rake) receiver. By way of background, the G-Rake receiver receives and processes WCDMA signals experiencing interference in dispersive channels. This interference is composed of self-interference (intersymbol interference), multiple access interference (interference due to non-zero code cross correlation), and other cell (downlink) or other user (uplink) interference. This interference must be suppressed in order to achieve good HSDPA throughput. In addition, the enhanced throughput requirements set by 3GPP for type 2 (single antenna terminal) and type 3 (dual antenna terminal) receivers cannot be met without interference suppression.

Linear methods for suppressing interference generally fall into the categories of chip level or symbol level equalization. Symbol level equalization follows the traditional Rake architecture where the received chip-level data is despread at multiple delays, and then the multiple images are combined. Chip level equalization reverses the order of these operations; the received chip data is first combined using a linear filter and then despread at a single delay. These techniques are generally equivalent from a performance perspective.

FIG. 12 is a functional block diagram of a G-Rake receiver 20 which may be modified to utilize the present invention. The receiver may be implemented, for example, in a mobile terminal or other wireless communication device. Spread-spectrum signals are transmitted through a radio channel and are received at one or more antennas of the receiver. A radio processor (not shown) generates a series of digitized baseband signal samples 21 from the received signal and inputs them to the G-RAKE receiver. In turn, the G-Rake receiver 20 demodulates the received signal samples to produce soft values or bit estimates 22. These estimates are provided to one or more additional processing circuits (not shown) for further processing, such as forward-error-correction (FEC) decoding and conversion into speech, text, or graphical images, and the like. Those skilled in the art will recognize that the particular information type(s) carried by the received signal and the particular processing steps applied by the receiver 20 are a function of its intended use and type.

A complete description of a G-Rake receiver suitable for use with the soft pilot symbols of the present invention is provided in co-owned U.S. Patent Application Publication No. 2005/0201447, the disclosure of which is incorporated herein by reference in its entirety.

Turning first to symbol level equalization, the G-Rake combining weights perform the coherent combining as well as interference suppression. The combining weights are given by:

w=Ru−1h,   (1)

where Ru is the impairment covariance matrix and h is a vector of net channel coefficients. It should be noted that the term “impairment” includes both interference and noise while the term “net channel coefficient” refers to a channel coefficient that includes the effects of the transmit and receive filters as well as the fading channel.

There are two general methods for implementing a G-Rake receiver. These methods are generally known as nonparametric and parametric. The nomenclature here focuses on the approach taken to obtain the impairment covariance matrix. Nonparametric method(s) are blind, and estimate Ru directly from observed data. The parametric method assumes an underlying model, and computes Ru from model parameters. Examples of both methods are provided below.

There are two ways that one can obtain a nonparametric estimate of the impairment covariance matrix. The first approach uses the pilot channel to estimate the slot-based quantities:

h ^ = 1 N p  ∑ k = 0 N p - 1  x p  ( k )  s *   R ^ u , slot = 1 N p - 1  ∑ k = 0 N p - 1  ( x p  ( k )  s * - h ^ )  ( x p  ( k )

Download full PDF for full patent description/claims.




You can also Monitor Keywords and Search for tracking patents relating to this Transmitter and method for transmitting soft pilot symbols in a digital communication system patent application.

Patent Applications in related categories:

20130121442 - Method and apparatus for mapping quadrature amplitude modulation symbol - A method and an apparatus for mapping a quadrature amplitude modulation (QAM) symbol. The QAM symbol mapping apparatus includes a frequency checker, which checks frequencies of sub-carriers in an orthogonal frequency division multiplexing (OFDM) symbol; and a data categorizer, which maps data coded for error correction and uncoded data to ...

20130121443 - Quadrature modulator balancing system - A method of balancing a quadrature modulator includes exciting an in-phase input of the quadrature module and sweeping a phase of an injection signal through a range of degrees, and determining a plurality of in-phase DC components. The method further includes exciting a quadrature input of the quadrature module and ...


###


Other recent patent applications listed under the agent :