The present invention relates generally to wireless communication systems, and more particularly to ultrawideband orthogonal frequency division multiplexing communication systems.
Wireless communication systems, generally radio frequency (RF) communication systems, are widespread. Often such systems communicate using signals about a specific predetermined carrier frequency. Unfortunately, use of only a single carrier frequency may result in deleterious effects. Signals at specific frequencies may be particularly subject to disruption due to interference caused by multipath effects, other transmitters or other factors. Signals at specific frequencies may also dominate use of bandwidth about the specific frequencies, leaving less of the frequency spectrum available for use by others. Further signals at specific frequencies may provide insufficient bandwidth for particular communications.
Ultrawideband (UWB) communication systems generally communicate using signals over a wide band of frequencies. Use of a wide band of frequencies may allow for increased effective bandwidth between devices. Use of a wide band of frequencies also may minimize effects of interference about any particular frequency.
The use of orthogonal frequency division multiplexing (OFDM) methods by communication systems may also be beneficial for a number of reasons. Often in OFDM systems information is transmitted over a number of communication channels about different frequencies, with each channel including information transmitted over a number of sub-bands, each at slightly different frequencies.
UWB-OFDM communication systems, however, may require significant processing of transmitted and received information. Processing such information may pose difficulties, which may be compounded by the use of multiple transmit and/or receive antennas.
The invention provides ultrawideband transmitters and receivers, and associated methods. In one aspect the invention provides a method used in communication of data, comprising encoding a data stream; interleaving encoded symbols of the data stream; splitting the interleaved encoded symbols into a first data stream and a second data stream; and processing the first data stream and the second data stream independently.
In another aspect the invention provides a method used in communication of data, comprising receiving a data stream; separating the data stream into a first data stream and a second data stream, the first data stream including a first received orthogonal frequency division multiplexing (OFDM) symbol and every other OFDM symbol received thereafter and the second data stream including a second received OFDM symbol and every other OFDM symbol received thereafter; and separately performing processing on the first data stream and the second data stream.
In another aspect the invention provides a transmission processing system, comprising an encoder configured to provide encoded symbols; a plurality of processing chains, each of the plurality of processing chains data coupled with the encoder, each of the plurality of processing chains comprising an interleaver, a mapper coupled to the interleaver, and an inverse Fast Fourier Transform block coupled to the mapper.
In another aspect the invention provides a reception processing system, comprising a radio frequency (RF) receiver configured to receive radio frequency signals and convert the radio frequency signals to baseband signals; a plurality of processing chains, each of the plurality of processing chains data coupled with the RF receiver, each of the plurality of processing chains comprising a Fast Fourier Transform block, a demapper coupled to the Fast Fourier Transform block, and a deinterleaver coupled to the demapper.
These and other aspects of the invention are more fully comprehended upon review of this disclosure.
A symbol interleaver 113 receives the encoded symbols and interleaves the symbols. Interleaving of symbols is preferred so as to reduce effects of bursty errors, such as may occur during transmission over a channel of a communication medium.
Some of the interleaved symbols are provided to a first processing chain 115, and some of the interleaved symbols are provided to a second processing chain 117. The processing chains operate in parallel. Preferably, each processing chain receives every other symbol, for example the first processing chain receiving odd symbols of a sequence of symbols and the second processing chain receiving even symbols of the sequence of symbols. The use of two processing chains allows for reduction of effective clock rate used to drive the processing chains, with the use of two processing chains, for example, allowing for reduction of the clock rate by one-half of an expected clock rate for a single processing chain for processing data at similar data rates.
As illustrated, the processing chains each include a tone interleaver, a mapper 121a,b, and an inverse Fast Fourier Transform (iFFT) block 123a,b. The tone interleaver interleaves 119a,b bits of the symbols, preferably reducing possible effects of bursty errors over a particular subcarrier of a channel of a communication medium. The mapper performs a mapping of groups of bits, for example using a quadrature phase shift key (QPSK) or dual carrier modulation (DCM) (preferably corresponding to two shifted QPSK constellations over two subcarriers of a channel used for transmission of OFDM symbols) scheme. Preferably the mapper performs QPSK modulation for lower selected information rates and DCM for higher selected information rates. The iFFT transforms the mapped bits to the complex time domain.
The processing chains provide data to what is denoted in
In some embodiments, in operation the encoder receives a bit stream from a MAC and encodes the bit stream using an error correction code, for example a convolutional code of memory 6. The encoder is clocked, for example, at 66 MHz. Depending on a rate selection indication provided by the MAC, the encoder encodes the bit stream using a selected code rate, for example at a ½ code rate, a ⅝ code rate, a ¾ code rate, or a ⅘ code rate.
The encoded bit stream is interleaved by a symbol interleaver and then split into two separate bit streams, each bit stream receiving bits for every other OFDM symbol. Splitting the bit stream allow further processing, such as tone interleaving, mapping, and iFFTing, to be performed at a reduced clock rate, for example at 264 MHz instead of 528 MHz.
Each of the separate bit streams are separately tone interleaved and mapped. The mapping scheme used as either a QPSK or DCM scheme, with the use of QPSK or DCM based on a rate selection signal provided by the MAC.
After mapping each signal is separately grouped into 128 subcarriers forming an OFDM symbol and transformed from the frequency domain to the time domain using, for example, a 128-point iFFT. After iFFT the signal is paralyzed by a factor of four on the time-sample level for FIR-filtering, using a clock rate of 264 MHz instead of 1056 MHz, for example, with FIR-filtering preferably being accomplished by a 4× polyphase filter.
The signal processor provides one of the two time domain symbol streams to a first processing chain 213 and the other of the two time domain symbol streams to a second processing chain 215. Use of the two processing chains, operating in parallel, allows for processing at a reduced clock rate, as compared to a clock rate required by use of only a single processing chain.
As illustrated in
Each of the two processing chains provides a data stream to a symbol deinterleaver 223. The symbol deinterleaver merges the two data streams and deinterleaves symbols from the data streams. The symbol deinterleaver also provides data blocks to two Viterbi decoder blocks 225a,b, preferably after depuncturing the coded bits of the symbols. It should be noted that depuncturing, as well as merging of the data streams and separating data blocks for the Viterbi decoders, may not necessarily be considered as being performed by the symbol deinterleaver, but is illustrated as such in
The Viterbi decoders decode the data, with the output of the Viterbi decoders provided to a MAC (not shown). The data provided to the Viterbi decoders has partially overlapping windows, particularly for embodiments where the data has been encoded using a single encoder. The partially overlapping windows, with data blocks for each decoder including bits in common with data blocks provided to the other encoder, are used, for example, to pre-synchronize and post-synchronize the Viterbi decoders.
In some embodiments, in operation a signal received by the antenna is amplified and downconverted to baseband. Downconversion may be performed in a frequency hopping manner, in accordance with a time-frequency pattern indicated by a MAC. The baseband signal is processed by a signal processor, performing functions such as packet detection, frame synchronization, automatic gain control determination and other functions normally performed by a baseband signal processor. Preferably the signal processor separates the time domain sample stream into two streams, with each stream containing every other OFDM symbol. In such implementations the signal processor may largely, or entirely, incorporate parallel processing streams, with data received from analog-to-digital conversion circuitry split into two streams operated on separately by the signal processor, with every other OFDM processed by each parallel processing stream. In many embodiments, however, parallelization is accomplished after packet detection and after removal of a null prefix (which may be a postfix) in the time domain.
The parallel streams are each provided to a separate processing chain, including, for example, a 128-point FFT block, a demapper, and a tone deinterleaver. Each processing chain separately transforms their respective signals from the time domain to the frequency domain, demaps the OFDM symbols to obtain soft bit estimates, and deinterleaves using the tone deinterleaver. Each processing chain is for example clocked at 264 MHz, assuming an ADC of the receiver is clocked at 528 MHz. The bits provided by the separate processing chains, each providing every other OFDM symbol, are merged and deinterleaved by a symbol deinterleaver. Preferably the deinterleaved bits are decoded by parallel Viterbi decoders.
The transmitter of
The transmitter of
Referring to the QAM constellation of
Returning to
Returning again to
Each demapper demaps data, for example in accordance with the 16-QAM constellation of
Each of the first symbol deinterleaver and the second symbol deinterleaver are associated with two Viterbi decoders 343a-d. Operation of each group of symbol deinterleaver and two Viterbi decoders operate as discussed with respect to the symbol deinterleaver and two Viterbi decoders of the receiver of
Preferably, however, the output provided to a MAC (not shown) is provided in accordance with the receive frame structure of
In some embodiments the system of
In operation of some embodiments, data is received from and provided to a MAC over a two byte interface and the number of encoding/decoding and interleaving/deinterleaving elements are doubled. Accordingly, in some embodiments a high byte is encoded by a first encoder and low byte is encoded by a second encoder. A symbol interleaver, and dual tone interleavers, are associated with each encoder. Two mappers each separately map interleaved encoded bits associated with both encoders. Interleaved encoded bits associated with the first encoder are mapped to onto the I-channel of a 16 QAM constellation, and interleaved encoded bits associated with the second encoder are mapped onto the Q-channel of the 16 QAM constellation. Processing thereafter on the transmission side is performed as discussed with respect to operation of embodiments of
In some embodiments the receiver includes multiple receive antennas. For example,
Outputs of the FFT blocks are received by parallel maximum ratio combining (MRC) blocks 717a,b. For convenience indicating the outputs of the FFT blocks as either even or odd symbols, outputs of FFT blocks providing even symbols are received by a first MRC block 717a and outputs of FFT blocks providing odd symbols are received by a second MRC block 717b. Accordingly, each MRC block receives representations of the same signal as received by the different antennas. Each MRC block performs a diversity combining function, preferably summing the signals, and doing so weighting each of the signals to be summed by their respective signal-to-noise ratios.
Accordingly, the invention provides ultrawideband transceiver and transceiver component architectures. Although the invention has been described with respect to certain specific embodiments, it should be recognized that the invention comprises the novel and non-obvious claims supported by this disclosure and insubstantial variations thereof.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/655,648, filed Feb. 23, 2005, the disclosure of which is incorporated by reference herein.
Number | Date | Country | |
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60655648 | Feb 2005 | US |