HK1113872A - Method and system for channel equalization - Google Patents

Description

Method and system for channel equalization

Priority requirements under U.S.C. § 119

The present application claims priority from provisional application No.60/650,042 entitled "FREQUENCY DOMAIN EQUALIZATION IN THEPRESENCE OF HIGH DOPPLER" filed on 4.2.2005 and assigned to the assignee OF the present invention and hereby expressly incorporated by reference herein.

Background

FIELD

The present invention relates to wireless communication methods and systems, and more particularly, to frequency domain equalization methods and systems.

Background

In a communication system having a higher data rate, e.g., a data rate in the range of 50-200Mbps, errors in the received signal may result in retransmission delays that prevent full utilization of the available bandwidth. One way to reduce retransmission delay is to reduce the Bit Error Rate (BER) in the received signal.

More specifically, during communication over a wireless channel, the channel behavior changes over time, thereby affecting (e.g., increasing errors in) signals transmitted over the channel. There is a need to predict or characterize time-varying channel behavior to compensate for such variations in channel characteristics when receiving a transmitted signal. In some systems, channel equalization is performed in the time domain to more accurately estimate the transmitted signal. However, equalization in the time domain requires significant computational power in the receiver and complicates the circuitry. In addition, the presence of noise, such as white noise on the channel, further complicates the correction in the time domain. Therefore, there is a need to simplify the computational complexity in computing channel behavior and correcting signals transmitted over the channel.

SUMMARY

One aspect of the invention includes a method of processing a signal. The method includes receiving a signal transmitted over a channel. The signal comprises an information signal and at least a portion of a known signal. The method further includes determining at least one indicator of a channel characteristic based at least in part on the portion of the known signal. The method further includes generating a first value indicative of the information signal based at least in part on the at least one indicator of the channel characteristic. The first value comprises an error signal. The method further includes removing the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

Another aspect of the invention includes an apparatus configured to receive a signal transmitted over a channel. The signal comprises an information signal and at least a portion of a known signal. The apparatus includes a first circuit configured to determine at least one indicator of a channel characteristic based at least in part on the portion of the known signal. The apparatus further includes a second circuit configured to generate a first value indicative of the information signal based at least in part on the at least one indicator of the channel characteristic. The first value comprises an error signal. The apparatus further includes a third circuit configured to cancel the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

Another aspect of the invention includes an apparatus configured to receive a signal transmitted over a channel. The signal comprises an information signal and at least a portion of a known signal. The apparatus includes means for determining at least one indicator of a channel characteristic based at least in part on the portion of the known signal. The apparatus further includes means for generating a first value indicative of the information signal based at least in part on the at least one indicator of the channel characteristic. The first value comprises an error signal. The apparatus further includes means for removing the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

Brief Description of Drawings

Fig. 1 illustrates an overview of an exemplary wireless communication system.

Fig. 2 is a block diagram illustrating an exemplary data frame structure for transmission in one embodiment of the system of fig. 1.

Fig. 3 is a block diagram illustrating the exemplary wireless communication system of fig. 1 in greater detail.

FIG. 4 is a flow chart illustrating one embodiment of a method of communicating data in the exemplary system shown in FIG. 3.

Fig. 5 is a flow chart illustrating an exemplary method of estimating channel characteristics, such as in a portion of the method illustrated in fig. 4.

Fig. 6 is a flow chart illustrating an exemplary method of performing frequency domain equalization, such as in a portion of the method illustrated in fig. 4.

Fig. 7 is a flow diagram illustrating an exemplary method of canceling residual intersymbol interference (ISI), such as in a portion of the method illustrated in fig. 4.

Detailed description of the invention

The following detailed description is directed to certain specific embodiments of the invention. The invention may, however, be embodied in many different forms as defined and covered by the appended claims. In this description, reference is made to the drawings wherein like parts are designated with the same reference numerals throughout.

In one embodiment, a receiver receives a signal transmitted over a Radio Frequency (RF) channel. These signals include a known signal, such as a pilot signal, and an unknown signal, such as a data signal. The receiver estimates a characteristic of the communication channel based at least in part on at least a received portion of the known signal. The receiver generates a first estimate of the unknown signal based at least in part on the estimated channel characteristics. The first estimate of the unknown signal comprises an error signal such as residual inter-symbol interference (ISI). The receiver determines an estimate of the error signal based at least in part on the known signal. The receiver cancels the error signal from the first estimate of the signal based at least in part on the error signal estimate.

Fig. 1 illustrates an overview of an exemplary wireless communication system 100. In the exemplary embodiment, communication system 100 includes one or more base stations 102 and one or more user terminals 104. In the exemplary embodiment, the communication system is configured to operate as a cellular radio network. A cellular radio network comprises one or more base stations 102. Each base station 102 provides communication to different areas ("cells") (which may overlap) to provide radio coverage over an area greater than that of one cell. The location of the user terminal 104 may be fixed or mobile. Various handover techniques may be used to allow a moving user terminal 104 to communicate with different base stations 102, such as when entering or traversing cells. In other embodiments, the communication system 100 may include point-to-point communications or unidirectional communication links between the user terminals 102. Additionally, certain embodiments herein are discussed with reference to wireless communications using a Radio Frequency (RF) carrier. However, in other embodiments, the communication network may include other communication media, such as optical signals or communications over wired connections.

Various embodiments of system 100 may communicate over one or more channels in one or more RF bands, for example, bands commonly referred to as 800MHz, 850MHz, 900MHz, 1800MHz, 1900MHz, or 2000 MHz. Embodiments of the communication system 100 include an air interface that determines how the communication system operates a radio link between a base station 102 and a user terminal 104. For example, communication system 100 may use a Code Division Multiple Access (CDMA) based air interface or a Time Division Multiple Access (TDMA) air interface. In an exemplary embodiment, communication system 100 includes a wideband CDMA (W-CDMA) air interface that uses a 5MHz channel in the 1900MHz band. Typically, only 3.84MHz of this 5MHz band is available.

Certain types of data transmission may be sensitive to retransmission delays, such as voice and common internet protocols such as TCP (transmission control protocol). For example, if the transmission time (including the time to retransmit lost data in lower communication layers) is too large, the TCP connection typically does not fully utilize the available channel bandwidth. For example, in one embodiment, a data rate in the range of 50Mbps with a TCP SER (segment error rate) of 2 × 10 may be achieved^-5To 5X 10^-6Within the range. In one embodiment, by performing channel equalization on the received signal, the Bit Error Rate (BER) of communication system 100 is reduced, and thus ultimately the segment error rate of higher layer protocols such as TCP.

A channel refers to a communication medium over which signals may be transmitted. In general, a channel is not ideal, e.g., a channel typically has time and/or frequency dependent characteristics that affect the signal transmitted over the channel. Mathematically, a channel may be represented or characterized by a channel impulse response h (t) that correlates a signal input, e.g., transmitted, to the channel with a signal output, e.g., received, from the channel. Channel equalization generally refers to the process of adjusting a received signal in response to the dynamics of the channel over which the signal is transmitted.

Equalization may be performed in the time domain or the frequency domain. However, time-domain equalizers can be computationally complex. In addition, finite length time domain equalizers are prone to performance loss under certain channel conditions. In one embodiment, the present invention provides an apparatus comprising a frequency domain equalizer that is computationally efficient and compensates for the doppler effect.

In one embodiment, which will be described in further detail below, system 100 performs channel equalization by transmitting a known signal to the receiver along with a data signal. The data signal may contain one or more forms of data, such as voice or other data. For example, the data signal may comprise TCP data transmitted at least in part over an IP (internet protocol) network. The receiver identifies the known signal and uses it to estimate the characteristics of the channel. This channel estimate is used to perform channel equalization in the frequency domain.

Inter-symbol interference (ISI) generally refers to interference between pulses of a signal (corresponding to different symbols in the data), which can occur if adjacent pulses are dispersed in time so as to overlap one another. When this overlap becomes too large, the receiver may no longer be able to correctly distinguish or identify each pulse. In one embodiment, the equalized signal may contain intersymbol interference (ISI) that has not been equalized. In one such embodiment, the residual ISI is removed by estimating the residual ISI using the difference between the known signal and the received version of the known signal.

Fig. 2 is a block diagram illustrating an exemplary data frame structure for transmission in one embodiment of communication system 100, e.g., a High Speed Downlink Packet Access (HSDPA) system. HSDPA is a packet-based data service in a wideband code division multiple access (W-CDMA) system, in which data is transmitted to a receiver during a time slot 110. In one embodiment, the data comprises "chips" representing one or more bits of user data, such as voice, image, video, or other data. For example, a forward error correction code may be used to encode user data bits into symbols. Each of these symbols may be further encoded into a larger number of chips by applying a "spreading" code. Spreading codes are used in air interfaces such as CDMA to create spread spectrum signals, e.g., signals transmitted in a frequency band significantly wider than the frequency content of the user data.

In the exemplary structure of fig. 2, slot 110 includes two sub-slots of 1280 chips each. Each sub-slot includes three data blocks 112, two of 448 chips and one of 128 chips. The exemplary slot 110 also includes a 64-bit prefix 114 and a 64-bit suffix 116 separating the data blocks 112. A known or pilot signal xp (t) is transmitted in the prefix 114 and suffix 116 so that the transmitter 302 transmits the known signal xp (t) and the data signal xd (t) in each time slot. In one embodiment, the known signal is the same in each time slot. For example, the known signal may be selected to have a constant frequency response across the entire bandwidth. Such a sequence may comprise a multi-phase sequence,where P is a finite integer representing the length of the known or pilot sequence, e.g., 64 in the embodiment shown in fig. 2. In one embodiment, the pilot sequence comprises a signal without spectral nulls, e.g., Xp (f) (the form of Xp (t) in frequency space) is selected to be different from 0.

In another embodiment, the known signal xp (t) is a signal transmitted on a different code channel, such as a pilot channel signal of a CDMA system. A portion of the pilot signal received just before, just after, or concurrently with the data signal may be used as the known signal. In one embodiment, the pilot channel of a CDMA system is encoded with a pseudo-random number (PN) sequence. Thus, the known signal xp (t) in such an embodiment of the system 100 is time-varying and depends on the position within the PN sequence. In other embodiments, the pilot signal may comprise any known signal.

Fig. 3 is a block diagram illustrating an exemplary wireless communication system 100 in more detail. In various embodiments, the functional blocks shown in fig. 3 may be implemented by a processor executing software instructions, as digital circuitry, as analog circuitry, or by a combination thereof. This block diagram shows a portion of both a transmitter 302 and a receiver 304 in the system 100. In particular, in one embodiment, transmitter 302 may comprise blocks 122-124 and receiver 304 may comprise blocks 130-146. In one embodiment, receiver 304 includes one or more integrated circuits formed using semiconductor fabrication techniques. These integrated circuits may include at least one of a general purpose processor, an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), other suitable hardware, or a combination thereof. In one embodiment, two or more of blocks 130-146 are formed on a single integrated circuit. In one embodiment, the transmitter 302 comprises a base station 102 and the receiver 304 comprises a user terminal 104. In one embodiment, the communications in system 100 are asymmetric, e.g., only base station 102 includes the transmitter 302 portion of fig. 3 and only user terminal 104 includes the receiver 304 portion. In other embodiments, the communications in system 100 are symmetric, with both base station 102 and user terminal 104 including both the transmit and receiver functional blocks of fig. 3.

In one embodiment, the transmitter 302 includes a combiner 122 that combines a known signal xp (t) with a data signal xd (t) to form a signal x (t). In one embodiment, the combiner 122 combines the known signal xp (t) with the data signal xd (t) to form a data stream as shown in the time slot 110 of fig. 2. In another CDMA system embodiment, combiner 122 combines known signal xp (t) with data signal xd (t) by placing known signal xp (t) in one code channel, e.g., a pilot channel, and placing data signal xd (t) in another code channel, e.g., a data channel, in a compliant CDMA system.

The transmitter 302 further includes a pulse shaper 124, the pulse shaper 124 generating a bandwidth limited signal by effectively convolving the pulse shaped signal p (t) with the signal x (t). The bandwidth limited signal is transmitted over a channel represented by a channel impulse response h (t), and shown in fig. 3 as block 126. The effect of the channel may be represented as a convolution of the channel impulse response h (t) with the shaped signal x (t) × p (t), e.g., x (t) × p (t) × h (t).

In one embodiment, at the receiver, a matched filter 130 (matched to the pulse shaping block 124) is applied to the signal to receive the transmitted signal. The matched filter 130 applies the complex conjugate p of the pulse shaped signal to the signal x (t) × p (t) × h (t) received from the channel^*(-t) to produce a received signal y (t). Mathematically, the received signal y (t) output from the matched filter 130 can be expressed as:

y(t)＝x(t)*p(t)*h(t)*p^*(-t). (formula 1)

The reception signal y (t) includes a reception data signal yd (t) and a reception known signal yp (t) corresponding to the transmission data signal xd (t) and the transmission known signal xp (t).

The receiver 304 further comprises a Fast Fourier Transform (FFT) module 132, which module 132 transforms the received signal Y (t) from the time domain into a frequency domain signal Y (f). By considering pulse shaping and matched filtering as constituting an effective transmission channel, the received signal in the frequency domain can be expressed as the product of the transmitted signal X (f) and the transfer function H (f) of the channel:

y (f) ═ X (f) · H (f), where "·" denotes multiplication. (formula 2)

In one embodiment, the estimation is based on channel characteristicsTo obtain an estimate of the transmitted signal. In particular, receiver 304 includes an estimate that determines channel characteristics based on the portions of received known signals yP (t) and yP (f) that correspond to transmitted known signals xP (t) and xP (f), respectivelyThe channel estimator 134. For example, in one such embodiment, the known signal xP (t) and the received version of the known signal yP (t) may be respectively denoted xP [ k ] in discrete frequency space]And YP [ k ]]. Similarly, the transfer function H (f) of a channel may be represented as H [ k ] k in discrete frequency space]. Suppose there is a presence in the system denoted as W [ k ]]And assuming the known signal XP k]Including a signal having P chips or pulses of integer length, the known signal YP k is received]Can be expressed in discrete form as:

(formula 3)

The known transmit signal (in discrete frequency space) XP [ k ] may be used]With known received signal (in discrete frequency space) YP [ k ]]To solve the equation to determine the channel characteristicsIs estimated. One method of solving this equation involves applying a statistical solution known as the Minimum Mean Square Estimation (MMSE) technique. In one embodiment, the channel estimates may be obtained in a discrete frequency spaceThe MMSE solution of (c) is as follows:

wherein the average channel statistic is represented as R_cc＝E{H[k]|²} (formula 4)

And the mean noise variance is represented as R_ww[k]＝E{W[k]|²}。

In one embodiment, the letterThe trace and noise variance statistics Rcc and Rww may be derived from previously received data. For example, Rcc may be derived fromSuch as averaging over several frames. Rww may be estimated based on the error in the lead = sample. In another embodiment, a Zero Forcing (ZF) (where the noise variance is taken to its zero limit) MMSE dispersion solution can be obtained as follows:

(formula 5)

Using the output of the channel estimator 134, the receiver 304 further includes an equalizer 136, the equalizer 136 using the channel estimateTo filter the received signal Y (f) to obtain an estimate of the transmitted data signalAs mentioned above, the received signal Y (F) is equal to the product of the transmitted signal X (F) and the channel transfer function H (F). Thus, by taking the complex conjugate H of the received signal Y (f) and the channel transfer function^*(f) The product of which yields a frequency domain estimate of the transmitted signal x (t)Considering the presence of additive white noise W (f), the estimated transmitted signal can be expressed as:

(formula 6)

Minimum Mean Square Estimation (MMSE) equalizer solution for this estimation of the received signalCan be expressed as:

(formula 7)

Wherein sigma²Representing the noise variance term associated with the noise term W (f).

Noise variance term σ in MMSE solution²Acts as a bias term to eliminate the possibility of introducing discontinuous zeros in this equation. In one embodiment, a signal is receivedThe above-represented discrete frequency space MMSE solution can be expressed as follows:

wherein R is_bb[k]＝E{X[k]|²And R_ww[k]＝E{W[k]|²And (formula 8)

Where W represents noise in the data signal.

In this embodiment, the data statistics Rbb and the noise statistics Rww may be derived from estimating the signal energy of the received data or from previously received data. Rbb may be derived from the received data signal constellation energy or from the ratio of traffic or data energy to pilot energy. Rww may be estimated based on the error in the pilot samples.

As mentioned above, the estimated signalContaining residual ISI after performing an inverse fast fourier transform.

In one embodiment, this residual ISI is corrected to obtain the transmitted data signal x_d(t) estimationIn particular, the receiver 304 further comprises an Inverse Fast Fourier Transform (IFFT) module 140, which module 140 transforms the equalized signalConversion into time-domain signalsReceiver 304 further comprises an ISI correction module 142, which module 142 corrects residual ISI to derive a data signal x_d(t) estimationIn one embodiment, discussed in further detail with reference to fig. 7, the ISI correction module 142 bases on the known signal and a received version of the known signal, e.g., x_P(t) andthe difference corrects for residual ISI. The receiver 304 further includes means for estimating the data signalA demodulator 144 for further processing. This processing may include, for example, recovering the signal from the modulated signal using a demodulation scheme such as QPSK, 16-QAM, 64-QAM, or any other suitable scheme.

Fig. 4 is a flow diagram illustrating one embodiment of a method 200 of transmitting data in the exemplary system 100 of fig. 3. Method 200 begins at block 202 where, for example, a transmitter of base station 102 identifies a data signal x to be transmitted_D(t) of (d). In one embodiment, the data signal is at least partially modulated, e.g., the data signal x_D(t) includes data, such as voice, video, speech, or other data, that has been encoded with one or more error correction codes. Moving to block 204, the transmitter 302 generates a known or pilot signal x_P(t) of (d). In one implementationIn this example, the pilot signal x_P(t) includes data pulses, chips, inserted as prefixes (e.g., preceding) or suffixes (e.g., following) to a data block to be transmitted during a slot. In one embodiment, the pilot signal is 64 chips in length.

Proceeding to block 206, the transmitter 302 transmits the data signal x over a channel_D(t) and a pilot signal x_P(t) is transmitted to the receiver, e.g., user terminal 104, as received signal y (t) yD (t) + yp (t). Next, at block 210, the receiver 304 performs an inverse fast fourier transform to convert the received signal Y (t) from the time domain into the frequency domain as Y (f).

Moving to block 212, the receiver 304 extrapolates a channel characteristic estimate in the pilot domain based on at least a portion of the known signal XP (f) and the corresponding Yp (f)This estimation process will be explained in more detail with reference to fig. 5. Next, at block 214, the receiver 304 estimates a channel based on the channelGenerating an estimate of a received data signal containing residual ISIThis process will be explained in more detail with reference to fig. 6.

Moving to block 216, the receiver 304 performs an inverse fast fourier transform to convert the frequency domain received signal Y (t) to a time domain signal Y (t). Next, at block 220, receiver 304 corrects for residual ISI to generate data signal x_d(t) estimated signalIn one embodiment, receiver 304 corrects for residual ISI based on the difference between at least a portion of the known signal xP (t) and the received signal yP (t) corresponding to the known signal. This process will be explained in more detail with reference to fig. 7. Proceeding to block 222, the receiver304 demodulate the received data signal by decoding the error correction or other encodingTo provide raw sound, video, voice or other data.

FIG. 5 is a block diagram illustrating one method of estimating channel characteristics, such as in a portion of method 200 shown in FIG. 4Is shown in the flowchart of exemplary method 212. At block 250, the receiver 304 identifies P samples of the pilot signal Yp (t) and performs an FFT to convert those samples to the frequency domain, e.g., Yp (f). Next at block 252, the receiver 304 derives a channel estimate based on the pilot signal Yp (f) as described above with reference to the channel estimator 134 of FIG. 3In one embodiment, equations 4 or 5 may be used to deriveIn discrete form

In general, the data block is much longer than the number P of pilot samples. For example, in the exemplary embodiment of fig. 2, the data block contains D448 or 128 chips, while the prefix or suffix block is only P64 chips long. Thus, channel estimationThere is a mismatch between the number of discrete data points or taps (tap) of the received signal Y (f). Thus, in one embodiment, which is further described with reference to blocks 254-258, the frequency domain channel estimates for the P-taps (e.g., having P discrete values)The frequency domain channel estimate converted to D-taps (e.g., with D discrete values) for use in the equalization block 214 of fig. 4. In particular, at block 254 of fig. 5, the receiver 304 performs an IFFT to estimate the channelConversion to the time domainNext, at block 256, the receiver 304 performs noise suppression (zero forcing) using a suitable threshold. In one embodiment, data points that fall below a threshold, e.g., 10-30% of the maximum in the data, are forced to zero or set to zero, or are removed from the channel estimate. Moving to block 258, the receiver 304 performs an FFT to estimate the channelConversion to D-tap (e.g., D-value 448 in one embodiment) frequency domain channel estimationThe channel estimationThereby being available for further processing of the received signal.

Fig. 6 is a flow chart illustrating an exemplary method 214 of performing frequency domain equalization, such as in a portion of method 200 shown in fig. 4. At block 270, the receiver 304 identifies a portion of the received signal X (f). In one embodiment, the estimated signal X (f) comprises a portion of the pilot signal XP (f). This portion of the pilot signal included is thus equalized for use in later processing steps as discussed with reference to fig. 6. Next, at block 272, the receiver 304 bases on the channel estimateDeriving estimates of transmitted data signals containing residual ISIFor exampleIn one embodiment, the estimated signalIncluding data signal partsAnd a pilot signal partIn one embodiment, as discussed above with reference to estimator 136 of fig. 3, receiver 304 derives the estimated signal using an MMSE or ZF-MMSE discrete solution of the following equation:

(formula 7)

Thereby providing an equalized signalFor further processing.

Fig. 7 is a flow chart illustrating an exemplary method 220 of canceling residual intersymbol interference (ISI), such as in a portion of the method 200 shown in fig. 4. At block 280, the receiver 304 identifies a portion of the pilot signal that has been equalizedAndthe receiver 304 uses the identified pilot signals at blocks 282 through 286To derive filter taps (data samples) and coefficients in order to perform a filtering from the equalized signalTime domain equalization to filter out residual ISI. In particular, at block 282, the receiver 304 is based at least in part on the channel estimateThe known pilot signal xP (t) (converted into the frequency domain to XP (f)) and the estimated pilot signalTo identify the filter tap positions (data points used in the filter). In one embodiment, the filter taps used in the time domain filter may be represented in discrete form as:

in the frequency domain(formula 9); and

in the time domain(formula 10).

In one embodiment, a suitable threshold is applied to these data points so that only the more significant data points are selected for use in the filter. In one such embodiment, the threshold is a predetermined threshold selected such that only those data points that fall within about 6db or 10% of the primary tap (the strongest, e.g., maximum value) are used. In another embodiment, the threshold is selected such that only those taps that fall within a threshold range between 1/10 and 1/4 of the main tap are used. In one embodiment, only the main tap is used.

Next, at block 284, the receiver 304 bases on the known pilot signal xp (t) and the estimated pilot signalThe difference determines the filter coefficients. Assuming an integer number k of different tap positions or data points, denoted as τ k, are selected in block 282, an MMSE or ZF-MMSE solution to the following optimization problem may be used to find the pilot signal indicative of the pilot signal xp (t) and the estimateFilter coefficient value a k with minimized value of difference]For example, a filter coefficient aopt [ k ] as shown in the following formula]To derive discrete-form filter coefficients a k]：

(formula 11)

Moving to block 286, the taps and coefficients are used to receive the signal fromThe residual ISI is filtered out. The discrete form of the data signal with residual ISI removed can also be derived using the following equation:

(formula 12)

The equalized and filtered signal is thus provided to a demodulator for further processing.

It will be recognized that some of the acts or events of the methods described herein can be performed in a different order, in accordance with the present embodiments, may be added, combined, or left out altogether (e.g., not all of the described acts or events are necessary for the performance of the respective methods) without departing from the scope of the present invention. Additionally, in some embodiments, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (36)

1. A method of processing a signal, the method comprising:

receiving a signal transmitted over a channel, said signal comprising an information signal and at least a portion of a known signal;

determining at least one indicator of a channel characteristic based at least in part on the portion of the known signal;

generating a first value indicative of the information signal based at least in part on the at least one indicator of channel characteristics, wherein the first value comprises an error signal; and

canceling the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

2. The method of claim 1, wherein the error signal is due at least in part to intersymbol interference.

3. The method of claim 1, wherein the known signal is characterized by a non-zero signal in the frequency domain.

4. The method of claim 1, wherein the known signal comprises a pilot signal.

5. The method of claim 1, wherein determining at least one indicator of a channel characteristic comprises determining an estimate of the channel characteristic in the frequency domain.

6. The method of claim 5, wherein determining the at least one indicator of channel characteristics further comprises transforming the estimate of channel characteristics from a signal comprising a first plurality of discrete values to a signal comprising a second plurality of discrete values, wherein the number of the second plurality of discrete values corresponds to the number of discrete values of the information signal.

7. The method of claim 1, wherein generating the first value comprises equalizing the received signal in a frequency domain based at least in part on the at least one indicator of channel characteristics.

8. The method of claim 1, wherein cancelling the error signal comprises determining a value indicative of the error signal based at least in part on a difference between the received portion of the known signal and the known signal.

9. The method of claim 8, wherein determining a value indicative of the error signal comprises determining coefficients of a filter based at least in part on a difference between the received portion of the known signal and the known signal.

10. The method of claim 9, wherein canceling the error signal comprises filtering the first estimate of the information signal.

11. An apparatus configured to receive a signal transmitted over a channel, the signal comprising an information signal and at least a portion of a known signal, the apparatus comprising:

a first circuit configured to determine at least one indicator of a channel characteristic based at least in part on the portion of the known signal;

a second circuit configured to generate a first value indicative of the information signal based at least in part on the at least one indicator of channel characteristics, wherein the first value comprises an error signal; and

a third circuit configured to cancel the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

12. The apparatus of claim 11, wherein the error signal is due at least in part to intersymbol interference.

13. The apparatus of claim 11, wherein the known signal is characterized by a non-zero signal in a frequency domain.

14. The device of claim 11, wherein the first circuit is configured to determine the estimate of the channel characteristic in the frequency domain.

15. The device of claim 14, wherein the first circuit is configured to transform the estimate of the channel characteristic from a signal comprising a first plurality of discrete values to a signal comprising a second plurality of discrete values, wherein a number of the second plurality of discrete values corresponds to a number of discrete values of the information signal.

16. The apparatus as recited in claim 11, wherein said second circuit is configured to equalize said received signal in the frequency domain based, at least in part, on said at least one indicator of channel characteristics.

17. The device of claim 11, wherein the third circuit is configured to determine a value indicative of the error signal based at least in part on a difference between the received portion of the known signal and the known signal.

18. The device of claim 11, wherein the third circuit is configured to determine coefficients of a filter based at least in part on a difference between the received portion of the known signal and the known signal.

19. The device of claim 18, wherein the third circuit is configured to filter the first estimate of the information signal.

20. The apparatus of claim 11, wherein at least a portion of the first, second, and third circuits are formed on an integrated circuit.

21. The apparatus of claim 11, wherein at least a portion of the first, second, and third circuits are further implementable as a processor.

22. An apparatus configured to receive a signal transmitted over a channel, the signal comprising an information signal and at least a portion of a known signal, the apparatus comprising:

means for determining at least one indicator of a channel characteristic based at least in part on the portion of the known signal;

means for generating a first value indicative of the information signal based at least in part on the at least one indicator of channel characteristics, wherein the first value comprises an error signal; and

means for removing the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

23. The apparatus of claim 23, wherein the error signal is due at least in part to intersymbol interference.

24. The apparatus of claim 23, wherein the known signal comprises a pilot signal.

25. The apparatus of claim 23, wherein the known signal is characterized by a non-zero signal in the frequency domain.

26. The apparatus of claim 23, wherein the means for generating comprises means for determining the estimate of the channel characteristic in the frequency domain.

27. The apparatus of claim 26, wherein the means for generating comprises means for transforming the estimate of the channel characteristic from a signal comprising a first plurality of discrete values to a signal comprising a second plurality of discrete values, wherein a number of the second plurality of discrete values corresponds to a number of discrete values of the information signal.

28. The apparatus of claim 23, wherein the means for generating comprises means for equalizing the received signal in a frequency domain based at least in part on the at least one indicator of channel characteristics.

29. The apparatus of claim 23, wherein the means for canceling comprises means for determining a value indicative of the error signal based at least in part on a difference between the received portion of the known signal and the known signal.

30. The apparatus of claim 23, wherein the means for canceling comprises means for determining coefficients of a filter based at least in part on a difference between the received portion of the known signal and the known signal.

31. The apparatus of claim 30, wherein said means for canceling comprises means for filtering said first estimate of said information signal.

32. A computer readable medium embodying a method of processing a signal, the method comprising:

receiving a signal transmitted over a channel, said signal comprising an information signal and at least a portion of a known signal;

determining at least one indicator of a channel characteristic based at least in part on the portion of the known signal;

generating a first value indicative of the information signal based at least in part on the at least one indicator of channel characteristics, wherein the first value comprises an error signal; and

canceling the error signal from the first estimate of the signal based at least in part on the portion of the known signal.

33. The method of claim 32, wherein generating the first value comprises equalizing the received signal in a frequency domain based at least in part on the at least one indicator of channel characteristics.

34. The method of claim 32, wherein the known signal is characterized by a non-zero signal in the frequency domain.

35. The method of claim 32, wherein determining at least one indicator of a channel characteristic comprises determining an estimate of the channel characteristic in the frequency domain.

36. The method of claim 32, wherein cancelling the error signal comprises determining a value indicative of the error signal based at least in part on a difference between the received portion of the known signal and the known signal.