Patent Application
20060104341
The present invention generally relates to communication systems and in particular to systems and methods for providing training data.
Various types of distortion and noise are introduced into data signals that are transmitted wirelessly over a given communication path. The distortion and noise are due to interference with other signals within the same frequency range and also due to multipath dispersions. Multipath dispersions occur when signals propagate along different or reflected paths through a transmission medium to a receiving destination. Generally, a signal or beam travels along a main or direct line-of-sight transmission path, while reflected signals travel along various reflected paths. Each reflected path has an associated delay and the overall effects of all such signals are a combination of the main signal and a plurality of reflected or delayed signals. Therefore, the signal received is usually not the same as the original signal transmitted, and when the signal is demodulated and decoded, errors in the original transmitted data may often result.
The effect of the multipath scattering is to alter or distort the received signal spectrum when compared to the spectrum as transmitted. In general, the effects are different at various frequencies across the signaling band. At some frequencies, the multipath signals add constructively to result in an increased signal amplitude, while at other frequencies the multipath signals add destructively (out of phase) to cancel or partially cancel the signal, resulting in reduced signal amplitude.
Wireless communication systems have been designed to compensate for the deleterious effects of multipath dispersion. Many wireless systems and some wired systems employ a channel estimation procedure to determine the effects the transmission environment has on the transmitted data signals. The channel estimation procedure can utilize training signals of known magnitude and phase to compensate for signal changes due to the transmission environment. The training signals can be transmitted prior to transmission of the data signals or interspersed in the data signals. The training signals can be analyzed to determine the effects of the environment on the transmitted signal and this information utilized to adjust the data signals appropriately.
However, within a given cell of a wireless communication network, operating conditions can vary greatly from location to location. For example, multi-path, interference, obstructions and other factors can produce regions where channel conditions are better in some location than in others. These effects impact the signal-to-noise ratio (SNR) at the receiver, which in turn affects the ability of the receiver to decode the transmitted data.
Systems and methods are disclosed for determining training data to be provided in a packet for a given receiver. The systems and methods determine at least one receiver performance metric associated with operating conditions of a given receiver. The at least one receiver performance metric can be compared to at least one performance metric level to determine training data to be provided in at least one subsequent data packet to be transmitted to the receiver. The performance metric can be measured at a given receiver or an access point associated with the given receiver.
In accordance with an aspect of the present invention, a communication system is provided. The communication system comprises a metric analyzer that measures at least one performance metric associated with at least a portion of a received data packet. The communication system also comprises an additional training determination component that determines additional training data to be transmitted in at least one subsequent data packet based on the measured at least one performance metric.
In accordance with yet another aspect of the present invention, a packet structure is provided comprising a preamble portion having a plurality of short training symbols and a plurality of long training symbols, a header portion having a plurality of parameters defining the packet structure, and a data portion having a plurality of data symbols. The packet structure also includes an additional training data portion for providing a plurality of additional training data in the packet structure. The additional training data portion can be part of the preamble or the data portion of the packet structure.
In accordance with a further aspect of the present invention, a methodology is provided for determining training data to be provided in data packets transmitted to a receiver. The method comprises measuring at least one performance metric associated with data received at a receiver, comparing the at least one performance metric to at least one predetermined performance metric level, and determining training data to be provided in transmitted data packets to the receiver based on the comparison.
In accordance with yet a further aspect of the present invention, a methodology is provided for transmitting data packets with training data. The method comprises receiving an indication of training data to be provided in subsequently transmitted data packets for a given receiver, building a data packet to be transmitted to the given receiver with the determined training data embedded in the data packet, and transmitting the data packet with the determined training data to the given receiver.
The present invention will be described with reference to systems and methods for determining training data to be provided in a packet for a given receiver associated with a wireless communication system. The systems and methods determine at least one receiver performance metric associated with operating conditions of a given receiver. The at least one receiver performance metric can be, for example, signal-to-noise ratio (SNR), signal-to-interference plus noise ratio (SINR), frame error rate (FER), bit error rate (BER) or other receiver performance metrics. The at least one receiver performance metric is employed to determine the training data to provided in subsequent packets transmitted to the receiver.
The determined training data can be in the form of a number and/or type of additional training symbols. Additionally, the training data can be in the form of a number and/or type of additional training tones (e.g. pilot tones) embedded in data symbols. The different types of training tones or symbols can include, for example, time orthogonal, time switched, frequency orthogonal and frequency switched designs. The at least one metric can be determined at a given receiver or at an access point associated with the receiver.
The additional training data is employed to improve the channel estimates at a given receiver, since each receiver in a wireless communication system is exposed to different operational conditions. Therefore, to mitigate degradation of receiver performance caused by different operating conditions, the receiver can specify the additional training desired to improve the channel estimates. Channel estimate results are improved with more training data because additional training symbols enable more averaging for better channel estimation results and additional training tones enable improved channel tracking capabilities during data symbols.
The use of the term additional training is employed in the following illustrated examples to refer to training data that is in addition to a fixed amount of training of a given wireless communication standard. It is to be appreciated that additional training data can be dynamically modified to be less than or greater than the additional training data provided in previous packets as operating conditions of a receiver or communication device change. It is also to be appreciated that training data for a given standard can be variable, such that an initial amount of training data can be provided based on the given standard. Therefore, the initial amount of training data can be adjusted to be less than or greater than an initial amount of training data defined by the standard.
For example,
The header portion 54 includes a plurality of parameters that define the packet structure 50. The plurality of parameters include at least the coding rate, length, and parity associated with the packet structure 50. The data portion 56 includes a plurality of data symbols. The number of allowable data symbols can be fixed based on the wireless standard of the packet structure 50. Additionally, other information such as service data may reside in the data portion 56 of the packet structure 50.
Referring again to
The digitized signal output of the one or more A/D converters 16 is then provided to the digital preprocessor 18. The digital preprocessor 18 provides additional filtering of the digitized signals and decimates the samples of the digitized signal. The digital preprocessor 18 then performs a Fast Fourier Transform (FFT) on the digitized signal. The FFT on the digitized signal converts the signal from the time domain to the frequency domain so that the frequencies or tones carrying the data can be provided. The digital processor 18 can also adjust the gain of the LNA at the analog front end 12 based on the processed data, and include logic for detection of packets transmitted to the receiver 10. The exact implementation of the digital preprocessor 18 can vary depending on the particular receiver architecture being employed to provide the frequencies or tones carrying the data. The frequencies and tones can then be demodulated and/or decoded. However, the demodulation of the tones requires information relating to the wireless channel magnitude and phase at each tone. The effects of the dispersion caused by the channel need to be compensated prior to decoding of the signal, so that decoding errors can be minimized. This is achieved by performing channel estimation.
Therefore, the digital preprocessor 18 provides the frequencies or tones to a channel estimator 20. The channel estimator 20 determines a channel estimate employing training tones embedded in the long training symbols and/or training tones embedded in data symbols of the data packet. The channel estimator 20 employs the long training symbols and/or training tones to perform channel estimation and to determine the amount of phase rotation and magnitude perturbation applied to the tones by the channel. Since the training tones are transmitted with known magnitude and phase, the channel response at the training tones is readily determined. For example, the known channel response at the training tones can then be interpolated in the frequency domain to determine the channel response at the data tones. A cyclic interpolation procedure can be employed.
The channel estimate is provided to a data demodulator 22 for demodulation of the digital data signal. The demodulated data signal is then transferred to data postprocessing component 26 for further signal processing. The data postprocessing component 26 decodes the demodulated data signal and performs forward error correction (FEC) utilizing the information provided by the data demodulator in addition to providing block or packet formatting. The data postprocessing component 26 then outputs the data.
A metric analyzer 24 is employed to determine at least one performance metric associated with processing of the data signal. For example, the metric analyzer 24 can be associated with the channel estimator 20 or data demodulator 22 for determining SNR or SINR of the received data signal. Alternatively, the metric analyzer 24 can be associated with the data postprocessing 26 to determine FER or BER. The metric analyzer 24 provides the measured performance metric data to a training determination component 28.
The training determination component 28 compares the measured performance metric with one or more predetermined performance metric levels to determine the training data to be transmitted in subsequent packets transmitted to the receiver 10. The training data can be a number and/or type of additional training symbols, and/or a number and/or type of additional training tones to be provided in data symbols for subsequent data packets. The training data can be an adjustment to an initial amount of training data, such that the adjustment can be more or less training data than the initial amount. The training determination component 28 can be an algorithm executing in a processor, a hardware device or a combination of hardware and software. The training determination component 28 provides an indication of the determined training data to a transmitter (TX) associated with the receiver, such as a transmitter in a MCU with the receiver. The transmitter transmits the indication of the training data to be provided in subsequently transmitted packets by an associated access point or base station that is providing data packets to the receiver 10.
For example, different measured levels of a given performance metric can be employed to determine the training data to be provided in subsequent packets. The communication unit associated with the receiver then transmits a communication to the access point or base station indicating the training data to be provided in subsequent transmitted packets to the receiver. The access point or base station will then transmit subsequent packets to the receiver with a specified number and/or type of training symbols and/or tones indicated by the receiver 10, until a further communication is received from the communication device associated with the receiver 10. The specified number and/or type of training symbols and/or tones can be an adjustment of training data that is more or less than training data provided in a previous data packet. This process can occur at initialization or be dynamically performed, such that changes in performance metric measurements caused the number and/or type of training symbols and/or tones to be periodically modified.
The specifying of training data in accordance with an aspect of the invention can be employed on a variety of different communication methods and devices utilizing a channel estimation procedure. One particular communication method is referred to as multicarrier modulation. One special case of multicarrier modulation is referred to as Orthogonal Frequency Division Multiplexing (OFDM). In general, OFDM is a block-oriented modulation scheme that maps a number of data constellation points onto a number of orthogonal carriers separated in frequency by BW/N, where BW is the bandwidth of the OFDM symbol and N is the number of tones in the OFDM symbol. OFDM is a technique by which data is transmitted at a high rate by modulating several low bit rate carriers in parallel rather than one single high bit rate carrier. OFDM is particularly useful in the context of Wireless Local Area Network (WLAN), Digital Video Broadcasting (DVB), High Definition Television (HDTV) and also for Asymmetric Digital Subscriber Lines (ADSL) systems. OFDM can also be useful in satellite television systems, cable television, video-on-demand, interactive services, mobile communication devices, voice services and Internet services.
In transmission of a data signal, an OFDM modulator converts a serial data stream into a block of N complex carriers. These carriers, of which phase and amplitude can be modulated, correspond to a time domain waveform that is generated using an Inverse Fast Fourier Transform (IFFT). The data signal is then amplified and transmitted over a wireless channel to a receiver. At the receiver end, a data signal or data burst is received in the time domain and converted back into the frequency domain employing a FFT for extraction of the frequencies (e.g., tones) from the data burst. The frequency domain signal is comprised of a plurality of data tones, training tones and zero tones. The training tones are transmitted at known magnitude and phase and employed in determining the channel estimate for use in compensating the data tones due to the effects of the channel on the tones.
Additionally, the data symbol generator can build data symbols with training tones 58. Additionally, the packet builder 40 employs a plurality of training symbols 38 for embedding in transmission packets to the one or more receivers. The packet builder 40 provides training symbols in the data packet based on the communication format of the data packet. Additionally, the packet builder 40 can include additional training data requested by each of a plurality of receivers in the building the data packets. The additional training data can be in the form of additional training symbols and/or tones that can vary in number and/or type for each receiver, such that each training sequence can be similar or unique.
The processor 32 builds a receiver table 42 based on communications from the receiver specifying the training data that the receiver is to receive in subsequent packet transmission to the receiver. Upon transmitting a packet to a given receiver, the processor 32 extracts an indicator from the receiver table 42 that is associated with the given receiver. The processor 32 then retrieves the training symbols 38 and/or training tones 58 for the given receiver based on the indicator. The packet builder 40 then builds the packet using the training symbols and/or tones. In this manner, specific training data associated with each receiver can be employed for transmissions to receivers. The receiver table 42 can be periodically updated or modified based on new communications received from the one or more receivers indicating that the one or more receivers require a different number and/or type of training symbols and/or tones.
The packet builder 40 combines the training symbols with the symbols from the header symbol generator 48 and the data symbol generator 34 to build the desired packet. Additionally, the data symbol generator builds the data symbols with or without training tones 58. If the built packet is represented in the frequency domain, the processor 32 performs an IFFT (Inverse Fast Fourier Transform) to convert it into a time domain representation. Once the built packet is represented in the time domain, the processor 32 appends a cyclic prefix to each symbol and then provides the built packet to a D/A converter (D/A) 36. The D/A converter 36 converts the digital data to the analog domain for transmission by an analog front end 46. The analog front end 46 includes upmixers, filters and one or more power amplifiers coupled to an antenna 44 for wireless transmission to one or more receivers.
An additional training definition field (AT) 66, and a plurality of additional training symbols (LSAT1-LSATN) 68 are embedded in the data portion 70 of the packet structure 60, where N is greater than or equal to one. In this manner, the additional training symbols 68 and/or training tones in the data symbols can be employed in current wireless standards without modification of the associated wireless standard. The additional training definition field (AT) 66 defines the number and/or type of additional training symbols and/or tones of additional training in the packet 60. Alternatively, the additional training definition field (AT) 66 can define a given sequence of training symbols and/or tones that includes a set number of additional training symbols and/or tones of the same or different type. Each receiver and access point in the wireless communication system can be operative to determine a desired sequence of training symbols and/or tones for a respective receiver, such that a given receiver receives packets with training symbols and/or tones based on a measured level of one or more performance metrics associated with the given receiver.
The header portion 90 includes a plurality of parameters that define the packet structure. The plurality of parameters include at least the coding rate, length, and parity associated with the packet structure. The data portion 92 includes data symbols associated with the packet structure 80. One or more data symbols can include embedded training tones. By providing additional training symbols in the preamble 82 and/or additional training tones in the data symbols, improved channel estimates can be obtained since more training symbols and/or tones can be employed during channel estimation.
The access point 100 includes a receiver portion that receives communications from one or more MCUs through an antenna 104 coupled to an analog front end 102. The analog front end 102 can include amplifiers, filters and mixers to provide a reliable received signal to an A/D converter 106. The A/D converter 106 digitizes the analog data signal to provide a digitized data signal to a digital preprocessor/demodulator/decoder 108. The digital preprocessor/demodulator/decoder 108 performs similar functions as discussed with respect to the receiver 10 in
The processor 110 performs one or more performance metrics on the decoded data signal to determine one or more metrics associated with the receiver associated with the MCU that transmitted the data signal. Although the metric analyzer 112 is illustrated at the processor 110, it is to be appreciated that performance metric measurements can be performed at one or more different receiver stages, as illustrated in
The transmitter portion of the access point 100 includes a packet builder 118. The packet builder 118 builds data packets for transmission to one or more receivers. The data packets can be data packets that conform to one or more wireless communication standards. Upon transmission of a data packet to a given receiver, the processor 110 employs the receiver table 116 to determine the training data to be associated with the given receiver.
The access point 100 includes a header symbol generator 124 that provides the packet builder 118 with a header symbol or symbols. The access point 100 also includes a data symbol generator 120 that receives a data input and builds data symbols to be provided to the packet builder 118. Additionally, the data symbol generator 120 can build data symbols with training tones 126. Additionally, the packet builder 118 employs a plurality of training symbols 114 for embedding in transmission packets to the one or more receivers. The packet builder 118 provides training symbols in the data packet based on the communication format of the data packet. Additionally, the packet builder 118 can include additional training data requested by each of a plurality of receivers in the building the data packets. The additional training data can be in the form of additional training symbols and/or tones that can vary in number and/or type for each receiver, such that each training sequence can be similar or unique. Furthermore, the training data can be an adjustment that is more or less than an initial amount of training data defined by a given standard.
The packet builder 118 combines the training symbols 114 with the header symbol or symbols and the data symbols with or without training tones 126 to build the packet with the selected training data. In this manner, a specific number and/or type of training symbols and/or tones can be employed for transmissions to receivers. The receiver table 116 can be periodically updated or modified based on new communications received from MCUs associated with the one or more receivers indicating that the one or more receivers require a different number and/or type of training symbols and/or tones. If the built packet is represented in the frequency domain, the processor 110 performs an IFFT (Inverse Fast Fourier Transform) to convert it into a time domain representation. Once the built packet is represented in the time domain, the processor 110 appends a cyclic prefix to each symbol and then provides the built packets to a D/A converter 122. The D/A converter 122 converts the digital data to the analog domain for transmission by the antenna 104 coupled to the analog front end 102.
It is to be appreciated that the present invention can be employed in wireless communication systems employing multiple input-multiple output (MIMO) systems in which base stations transmit data employing multiple transmitters and receivers receive transmission data using multiple receiving antennas. The data received in a multiple antenna receiver is typically transmitted using spatial diversity or time diversity. Multiple antenna receivers are more sensitive to environmental effects than are single antenna receiver systems. Additionally, good channel estimates are challenging when trying to keep the preamble length short in MIMO systems.
The noise variance estimator determines noise variances in the first and second receiver paths. The channel estimator extracts the long training symbols from the data signal and performs channel estimation for both the first and second receiver paths. The channel response determined at the training tones is employed to determine the channel response at the data tones. The channel estimates and the noise variance estimates are provided to the data demodulator 152 for demodulation of the digital data signal. The demodulated data signal is transferred to a data postprocessing component 154 for further signal processing. The data postprocessing component 154 decodes the demodulated data signal and performs forward error correction utilizing the information provided by the data demodulator. The data postprocessing component 154 then outputs the data.
A metric analyzer 156 is employed to determine at least one performance metric associated with processing of the data signal. For example, the metric analyzer 156 can be associated with the channel estimator/noise variance estimator 150 and/or the data demodulator 152 for determining SNR or SINR of the received data signal. Alternatively, the metric analyzer 156 can be associated with the data postprocessing component 154 to determine FER or BER. The measured performance metric is employed to determine an amount and/or type of training data to be provided subsequent data packets. For example, different measured levels of a given performance metric can be employed to define the number and/or type of training symbols and/or tones desired in subsequent transmission packets.
The metric analyzer 156 provides the measured performance metric to a training determination component 170. The training determination component 170 compares the measured performance metric with one or more predetermined performance metric levels to determine the training data to be provided in subsequent packets transmitted to the receiver 140. The training determination component 170 can be an algorithm executing in a processor, a hardware device or a combination of hardware and software. The training determination component 170 provides the determined number and/or type of training symbols and/or tones to a transmitter (TX) for transmitting to the device transmitting packets to the receiver 140.
In view of the foregoing structural and functional features described above, a methodology in accordance with various aspects of the present invention will be better appreciated with reference to
At 310, the amount and/or type of training data is determined for the one or more receivers. At 320, the access point or base station stores one or more indicators of the determined training data associated with one or more receivers in a receiver table. The indicators define a number of and/or type of training symbols and/or tones to be provided in subsequent packets of associated receivers. At 330, the access point or base station builds a transmission packet for a given receiver with the determined training data by employing the receiver table. At 340, the access point or base station transmits the transmission packet to the given receiver with the determined training data.
At 440, the access point or base station stores an indicator of the number and/or type of training symbols and/or tones for the given receiver in a receiver table. At 450, the access point or base station builds a transmission packet for a given receiver with the number and/or type of training symbols and/or tones employing the receiver table. At 460, the access point or base station transmits the transmission packet with the determined training data for the given receiver.
It is to be appreciated the methodologies of
What has been described above includes exemplary implementations of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.
