Decision feedback equalizer for portable communication devices

Decision feedback equalizers are known and used. Regular equalizers are designed for long-term static or quasi-static multipath delays in terrestrial environments. This type of equalizer is unsuitable for portable and mobile applications such as notebooks and netbooks. Compared to rooftop antennas, which primarily go through static multipath, portable environments often go through time-varying multipath in addition to static multipath. Current demodulators utilize an equalizer with a relatively large number of taps to equalize high delay precursor echoes and postcursor echoes. However, this type of equalizer is unsuitable for long-term static and short-term dynamic echo equalization applications.

The features of the embodiments of the claimed subject matter will become apparent by reading the following detailed description with reference to the drawings. Similar reference numbers are added to similar parts.

<figref num="1">An example of an equalization method according to a time-varying channel in a portable environment according to an embodiment of the present technology is shown.</figref>

<figref num="2">An exemplary communication system according to an embodiment of the present technology is shown.</figref>

<figref num="3">An example of a dynamic multipath delay profile specified by the channel estimator of the communication system of FIG. 2 according to the embodiment of the present technology is shown.</figref>

<figref num="4">An example of a profile of equalizer error variance regarding the adaptation constant of the least squares average algorithm according to the embodiment of the present technology is shown.</figref>

<figref num="5">An exemplary position of the equalizer tap in FIG. 2 according to an embodiment of the present technology is shown.</figref>

<figref num="6">An embodiment of a computer system is shown.</figref>

The following detailed description refers to exemplary embodiments of the claimed subject matter, many of which are apparent to those skilled in the art. Therefore, the subject matter claimed should be construed in a broad sense and is intended to be defined solely by the appended claims.

As detailed below, embodiments of the present invention serve to provide deterministic feedback equalization techniques for time-varying channels in a portable environment. In particular, analyze the signal received by the receiver to identify static and dynamic multipath delays. In addition, the equalizer is constructed based on the identified static and / or dynamic multipath delay.

References such as "one embodiment," "one embodiment," and "exemplary embodiment" herein include all, although the described embodiments may include specific features, structures, or properties. It does not mean that the embodiments must include those particular features, structures, or properties. Moreover, such wording does not necessarily mean the same embodiment. Furthermore, if a particular feature, structure, or property is described in the context of an embodiment, those skilled in the art will be able to describe such particular feature, structure, or property, even if not specifically stated. , It should be understood that it can be modified in the context of other embodiments.

FIG. 1 shows an exemplary method 10 for equalization according to time-varying channels in a portable environment. At block 12, the carrier signal is received. In this embodiment, the carrier signal is received via the antenna of the receiver of the communication module. In an exemplary embodiment, the carrier signal includes an ATSC (advanced television systems committee) signal. In another exemplary embodiment, the carrier signal includes a DMB-T / H (digital multimedia broadcast-terrestrial / handheld) signal.

At block 14, the received carrier signal is analyzed to identify at least one of the signal's static and dynamic multipath delays. In one exemplary embodiment, the received pseudo-random noise (PM) sequence is compared to the reference sequence to identify at least one of the static and dynamic multipath delays. However, other techniques for identifying static and dynamic multipath delays may also be included.

In this exemplary embodiment, the static multipath delay corresponds to the delay caused by reflections from multiple static objects. In addition, the dynamic multipath delay corresponds to the delay caused by reflections from multiple moving objects located near the antenna. In one exemplary embodiment, the dynamic multipath delay corresponds to the delay caused by reflections caused by a mobile vehicle near a portable digital television (DTV) receiver platform. In one exemplary embodiment, the static multipath delay corresponds to reflections caused by remote static objects such as buildings and / or mountains.

In block 16, the communication module equalizer is configured based on at least one of static and dynamic multipath delays. In this exemplary embodiment, the equalizer comprises a sparse determination feedback equalizer. In an exemplary embodiment, the number of taps required by the equalizer to equalize at least one of static and dynamic multipaths is estimated. Further, the required number of taps is divided into a first tap set and a second tap set. The first tap set is provided to equalize the static multipath delay and the second tap set is provided to equalize the dynamic multipath delay. In one exemplary embodiment, the position of each of the first tap set and the second tap set is determined.

FIG. 2 shows an exemplary communication system 20. In an exemplary embodiment, the communication system 20 includes a transmitter 22 that transmits a plurality of carrier signals as indicated by reference numeral 24. Such a signal 24 is transmitted from the transmission channel 26 to the communication module 28. In this exemplary embodiment, the communication module 28 includes a receiver 30 that receives a plurality of signals 24. The communication module also includes an equalizer 32. The equalizer 32 virtually eliminates the distortion caused by the transmit channel 26 and front-end electronics.

In this exemplary embodiment, the output of the received signal 34 sampled by the receiver 30 in instant k is represented by the following equation.<maths num="1"><img file="JP4901940B2_D0001.tif" /></maths> x (t) is the transmission signal 24, h (t) is the channel impulse response of the transmission channel 26, y (t) is the reception signal 34, and y (t) is expressed by the following equation.<maths num="2"><img file="JP4901940B2_D0002.tif" /></maths>

Where * is a superposition operation and n (t) is noise or interference.

In this exemplary embodiment, the equalizer 32 equalizes the effects of the channels and restores the transmitted signal x (t) 24. The communication module 28 includes a channel estimator 36 that analyzes each of the plurality of received signals 34 to identify at least one of the static multipath delay and the dynamic multipath delay of the signal. The equalizer 32 is constructed based on at least one of static and dynamic multipath delays. In this exemplary embodiment, the equalizer 32 comprises a sparse determination feedback equalizer. Other suitable equalizers can also be used.

The channel estimator 36 analyzes each of the plurality of received signals to identify the main path (the path having the maximum power) and the multipath delay. In some embodiments, the received pseudo-random noise (PN) sequence in the field sync correlates with the reference pseudo-random noise sequence. Correlation may be improved, standardized, and thresholds may be determined. All peaks above the threshold may represent the path with the maximum value representing the principal (ie, the main path), with the one on the left side of the principal identified as the precursor and the one on the right side of the principal as the postcursor. ..

Once the main path and multipath delays such as static and dynamic multipath delays have been identified, the equalizer 32 can be configured to equalize such multipath delays. In particular, determine the number of taps the equalizer needs to equalize static and dynamic multipath. Further, the required number of taps is divided into a first tap set and a second tap set (not shown). The first tap set is provided to equalize the static multipath delay and the second tap set is provided to equalize the dynamic multipath delay. Such equalization technology promotes reduction of the silicon region of the equalizer and reduction of power consumption.

FIG. 3 shows an example of a dynamic multipath delay profile 50 identified by the channel estimator 36 of communication system 20 of FIG. In this event example, the effect of a moving object (not shown), such as a vehicle near a portable digital television (DTV) receiver platform, such as a laptop, is modeled using a birth-and-death event. In this embodiment, the horizontal axis 52 represents time and the vertical axis 54 represents the exemplary amplitude of the multipath component.

In this embodiment, the main route is represented by reference number 56 and the birth-death multipath event is represented by profile 58. It can be seen that the birth-death event 58 occurs with a delay of τ seconds compared to the main pathway 56. In this example event, the amplitude of birth increases from about -20 dB to about 3 dB in about 0.1 seconds, as indicated by reference number 60. In this embodiment, the Birth and Death Profile 58 is a radar cross-sectional analysis of a large moving vehicle reflector (eg, truck, bus, etc.) passing in front of a coffee shop window about 6 feet high at a vehicle speed of 40 mph. Is determined using. The birth-death rate is assumed to be about 2000 vehicles per hour per lane in 3 lanes.

As reference number 62 indicates, the amplitude remains stable at 3 dB for approximately 0.2 seconds. In addition, the amplitude of death drops from about 3 dB to about -20 dB in 0.3 seconds. In some embodiments, birth and death occurrences take the form of a Poisson distribution. In this exemplary embodiment, a birth-death delay of about 200 nsec is assumed in the indoor environment, which is about 60 meters from receiver 30 (see Figure 2) of communication system 20 (see Figure 2). Corresponds to reflective objects. For a symbol period of about 92.9 seconds at an ATSC signal rate of about 10.76 Msps, the equalizer 32 (see Figure 2) requires a relatively small number of taps.

In some embodiments, a plurality of taps (not shown) are provided to the equalizer 32 to equalize the dynamic multipath delay described above. In one exemplary embodiment, these multiple taps are provided to the feedforward and feedback sections of the equalizer 32 to equalize the dynamic multipath delay. In one exemplary embodiment, the number of taps is less than about 32. In another exemplary embodiment, the number of taps is about 10. Therefore, a desired number of taps are provided around the equalizer 32's principal taps (not shown) to compensate for time-varying short multipath delays from nearby moving objects such as cars, trucks, or people. .. In terms of behavior, when a birth-death event occurs, the tap corresponding to the birth-death delay increases from zero to a higher value than the principal depending on the birth-death event multipath, and then very little when the birth-death falls. become.

In one exemplary embodiment, the adaptive constants of the least squares mean squares (LMS) algorithm used by the equalizer 32 are estimated. Note that the adaptive constant of the least squares averaging algorithm is selected based on the number of taps on the equalizer 32 and the received signal power. For dynamic multipath delay events, the number of taps is increased and the range of adaptive constants is relatively narrow. As a result, above a certain value, the equalizer does not converge for the time-varying birth-and-death event (that is, the equalizer follows with a small error). Therefore, the total number of taps corresponding to dynamic multipath delay is relatively small. In this exemplary embodiment, several taps are provided around the principal tap to equalize the dynamic multipath delay.

In this exemplary embodiment, the equalizer 32 is constructed on the basis of a static multipath delay. In particular, a first tap set is provided to equalize static multipath delays, and the number of first tap sets is at least as many as the number of delays that need to be equalized. Furthermore, the adaptive constant of the least squares averaging algorithm is determined based on the number of major static multipath delays, not on the "length" of the static delay. In one embodiment, the adaptive constant for dynamic multipath delay is relatively larger than the adaptive constant for static multipath delay.

Figure 4 shows an exemplary profile 80 of the equalizer error variance for the adaptive constants of the least squares average algorithm. In the embodiments shown, the horizontal axis 82 represents the adaptive constant and the vertical axis 84 represents the equalizer error distribution (dB). The profile of a conventional equalizer with a large number of taps is indicated by reference number 86, and the profile of an equalizer designed for portable mobile channels with a relatively small number of taps is indicated by reference number 88. You will find that the equalizer profile for portable mobile channels requires a relatively high value of adaptation constants compared to traditional equalizers. In addition, traditional equalizers can have unacceptably increased error variance at the high portable adaptation constants required.

In this exemplary embodiment, a sparse determination feedback equalizer is utilized to allow larger values of adaptation constants with fewer non-zero taps. This is advantageous because the convergence of the equalizer is improved and the calculation is reduced. In this exemplary embodiment, only the pre-cursor, post-cursor, and taps at their cross term location are set to nonzero. In addition, some non-zero taps around the principal tap are provided to compensate for the dynamic multipath delay. In the absence of birth and death events, non-zero taps around the principal tap do not affect the overall performance of the equalizer.

In an exemplary embodiment, the equalizer response is expressed by the following equation.<maths num="3"><img file="JP4901940B2_D0003.tif" /></maths> Where H (z) is the channel transfer function. Furthermore, the equalizer response is expressed by the following equation in the example of one precursor path, one main path, and one postcursor path.<maths num="4"><img file="JP4901940B2_D0004.tif" /></maths>

Here, (β, τ_β) Is the precursor, and (α, τ)_α) Is a post cursor.

Therefore, the equalizer has a principal tap, a pre-cursor tap, a post-cursor tap, and an intersection term tap (the fourth term of equation (4)). In some embodiments, taps on the order of the second (fifth and sixth terms of equation (4)) and above may be ignored depending on the magnitude of the amplitudes α and β. In an exemplary embodiment, the intersection term of the precursor at about -25 μsecs and the postcursor at about 47 μsecs is estimated as follows.<maths num="5"><img file="JP4901940B2_D0005.tif" /></maths>

Where T is the 64-staggered quadrature amplitude modulation (QAM) interval,

T / 2 is about 92.9 nsecs.

In some embodiments, the pre-cursor, post-cursor, and intersection positions are placed in non-zero positions to compensate for the effects of static multipath delay birth-and-death events. Estimate the number of non-zero taps based on birth and death delays. In some embodiments, the number of non-zero taps is about 5.

FIG. 5 shows an exemplary position 100 of the tap on the equalizer 32 of FIG. In this exemplary embodiment, the pre-cursor and post-cursor taps 102 and 104 are -25 μsecs and 47 μsecs, respectively. The feedforward section 106 has an interval of about T / 2, and the feedback section 108 has an interval of about T / 2. Further, as mentioned above, the crossing terms 110 are approximately 118.5T intervals.

The communication system 20 described above may be located in a computer system, a wireless communicator, and a handheld device. FIG. 6 shows an embodiment of the computer system 120. The computer system 120 includes a bus 122 in which various components are connected. Depending on the embodiment, the bus 122 includes an aggregate of a plurality of buses such as a system bus and a PCIe (Peripheral Component Interface Express) bus. These buses are represented as a single bus 122 for the sake of brevity, but the system 120 is not limited to this. Those skilled in the art will understand that the computer system 120 can include any suitable bus architecture and can include any number of bus combinations.

Processor 124 is connected to bus 122. Processor 124 includes microprocessors (eg, single-core or multi-core processors), network processors, application-specific ICs (ASICs), graphics processors (GPUs), or FPGAs (field programmable gate arrays), and any other similar device. , Any suitable processing device or system may be included. Although Figure 6 shows a single processor 124, it should be noted that the computer system 120 can include more than one processor.

The computer system 120 further includes a system memory 126 attached to the bus 122. The system memory 126 may include any suitable type and number of memories such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate DRAM (DDR DRAM), and the like. While the computer system 120 is running, the operating system and other applications may be in system memory 126.

The computer system 120 may further include a read-only memory (ROM) 128 attached to the bus 122. ROM128 can store instructions for processor 124. The computer system 120 may further include a storage device (s) 130 attached to the bus 122. The storage device 130 includes a suitable non-volatile memory such as a hard disk drive. The operating system and other programs may be stored on storage device 130. In addition, a device 132 (eg, a floppy® disk drive or CD ROM drive) that accesses the removable storage medium may be connected to the bus 122.

The computer system 120 may further include one or more input / output (I / O) devices 134 connected to bus 122. Common input devices include pointing devices such as keyboards and mice, and other data input devices. In addition, common output devices include video displays, printing devices, and audio output devices. It should be understood that these are just some examples of the types of I / O devices that can be coupled to the computer system 120.

The computer system 120 may further include a network interface 136 connected to the bus 122. The network interface 136 may include any hardware, software, or a combination of hardware and software that can connect the system 120 to a network (eg, a network interface card). The network interface 136 is an arbitrary suitable medium (wireless,) that supports information exchange via any suitable protocol such as TCP / IP (Transmission Control protocol / Internet Protocol), HTTP (Hyper-Text Transmission Protocol), and others. A link to the network can be built via copper wire, fiber optics, or a combination thereof).

The computer system 120 shown in FIG. 6 is intended to represent an embodiment of such a system and further indicates that the system may include any additional components omitted for the purpose of assisting understanding. By way of example, system 120 may include a DMA (direct memory access) controller, a chipset associated with processor 124, additional memory (eg, cache memory), and additional signal lines and buses. In addition, the computer system 120 may not include all of the components shown in FIG. The computer system 120 may include any type of computing device such as a desktop computer, laptop computer, server, handheld computing device, wireless communication device, entertainment system and the like.

In this embodiment, the computer system 120 may include a communication system as described in the embodiments described above. By way of example, computer system 120 analyzes each of a receiver receiving multiple carrier signals and each of the signals to identify at least one of the static and dynamic multipath delays of the signal. May include a channel estimator. The computer system 120 may further include an equalizer with multiple taps, which are constructed based on at least one of static and dynamic multipath delays.

The detailed description and accompanying drawings described above are for illustration purposes only and are not intended to be limiting. These are provided primarily for the purpose of facilitating a clear and comprehensive understanding of the disclosed embodiments and not for the purpose of deriving unnecessary limitations. Those skilled in the art will appreciate many additions, deletions, and modifications to the embodiments described herein, and alternative configurations, to the extent that they do not deviate from the spirit of the disclosed embodiments and the appended claims. Let's come up with it.