Patent Application
20080063105
Features, aspects, and embodiments of the inventions are described in conjunction with the attached drawings, in which:
The embodiments described below provide for preamble channel encoding that can efficiently transmit preamble information bits. The embodiments use tail-biting convolutional coding and CRC (Cyclic Redundancy Check) coupled with modulation schemes such as BPSK (Binary Phase Shift Keying), QPSK (Quadrate Phase Shift Keying) or QAM (Quadrate Amplitude Modulation). The embodiments described below are generally described in terms of BPSK; however, it will be understood that this does not exclude the use of other modulation techniques and is simply done for convenience.
Further, after tail-biting convolutional encoding and modulation, the modulated symbols can be further transformed according to the air interface standard being implemented, e.g., CDMA or OFDM, for transmission. For example, the signal can be transformed into an OFDM subcarrier waveform, e.g., with or without multiple antennas MIMO or beam-forming.
Implementation of the embodiments described below result in a frame structure with reduced overhead symbols, which allows for increased capability and a more efficient design. Further, such a frame structure requires lower transmission power or a lower signal to noise (Eb/N0) ratio in the receiver to achieve similar false alarm and missing detection performance as conventional solutions. Additionally, in some embodiments, it is unnecessary to make any tradeoff between false alarm and missing detection probabilities, because the CRC bit, as well as the information bits in certain implementations, including user information, transmission format information, and/or subcarrier or channelization code, etc., can be used to check errors. In some embodiments, the factors influencing whether the tradeoff between false alarm rates and whether mission detection probabilities exist include the number of CRC bits and the required false alarm rate. If the number of CRC bits is too few to provide a low false alarm rate, the tradeoff still exists.
Thus, the encoder 100 of
The output of CRC block 104 will then comprise (b+c) bits and will be input to tail biting convolutional encoder 106. As will be understood, a convolutional encoder converts (k) input bits, in this case k=b+c, into a sequence of (n) bits. The n-bit sequence, or symbol, can then used to determine the k bits in the receiver. Thus, the effective rate (R) of encoder 102 is R=k/n.
It will be understood that in a conventional convolutional encoder 106, a tail sequence must be added to the end of the generated sequence in order to properly end the encoding process. The tail sequence is typically a series of “0's,” which add to the overhead associated with the data control channel. Tail biting means that the encoder starts in the state given by the (m) last bits of the information sequence, where m is the size of the memory, or length of the register included in the encoder. Hence, the encoder starts and ends in the same state and thus the loss in rate of the code associated with conventional convolutional encoders is eliminated. In other words, the need for the tail sequence can be eliminated, which reduces overhead.
The output of tail biting convolutional encoder 106 is then input to block interleaver 108. Interleaving is a way to arrange data in a non-contiguous way in order to increase performance. Interleaving is mainly used in digital data transmission technology to protect the transmission against burst errors. These errors overwrite a lot of bits in a row, but seldom occur. Interleaving is used to solve this problem. All data is transmitted with some control bits (independently from the interleaving), such as error correction bits that enable the channel decoder to correct a certain number of altered bits. If a burst error occurs, and more than this number of bits is altered, the codeword cannot be correctly decoded. So the bits of a number of codewords, or symbols are interleaved and then transmitted. This way, a burst error affects only a correctable number of bits in each codeword, so the decoder can decode the codewords correctly.
The output of block interleaver 108 can then be modulated, e.g., using BPSK, and then mapped to certain OFDM tones for transmission as described in more detail below.
In order to add the CRC bits, switches 208a, 208b, and 208c are moved to the down position, connecting inputs 205 and 207 with the encoder section 200. In this example, inputs 205 and 207 are configured to feed “0's” to encoder section 200. Encoder section 200 comprises 4 one-bit storage registers 202a, 202b, 202c, and 202d, which are configured to store the input to each register 202 for one clock cycle and then shift the input out to the right, and 3 modulo-2 adders 204a, 204b, and 204c. The output of adder 204c is then input to inverter 206, which is configured to invert the output of adder 204c and pass the inverted result to output 203. In the example of
The output of encoder 100 is input to BPSK block 304 where the output symbols are modulated and then scrambled in scrambling block 306. Scrambling randomizes the data bits, which can improve the peak-to-average power ratio for the transmitted signal. For example, if a long string of “1's” were to be transmitted, then the resulting peak-to-average power ratio would be high. By randomizing, or scrambling the data bits, the peak-to-average power ratio can be reduced.
The output of scrambling block 306 can then be passed to gain block 308a and then to OFDM mapping block 310 where the encoded and modulated rate indicator bits are mapped to the tiles assigned to the preamble channel. At the same time, the MAC identifier bits can undergo Reed-Solomon (RS) encoding in RS coding block 302. Reed-Solomon error correction is an error-correcting code that works by oversampling a polynomial constructed from the input bits. The polynomial is evaluated at several points, and these values are sent or recorded. By sampling the polynomial more often than is necessary, the polynomial is over-determined. As long as “many” of the points are received correctly, the receiver can recover the original polynomial even in the presence of a “few” bad points. Thus, in one embodiment, the 8-bit MAC identifier can be encoded into a 32 bit code. The encoded MAC identifier bits can then be mapped to the appropriate tones along with the encoded rate indicator bits.
In certain embodiments, the tile assignments provided in the 3GPP2 standard C30-20060731-046 can be used for the preamble channel. Thus, OFDM mapping block 310 can be configured to map the encoded rate indicator and MAC identifier bits to tiles assigned in accordance with the C30-20060731-046 standard.
The output can then be modulated, e.g., using BPSK, QPSK, QAM, etc., in step 610. Finally, the modulated output can then be further modulated for transmission, e.g., using CDMA or OFDM, in step 612.
As noted, the transmitter of
While certain embodiments of the inventions have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the inventions should not be limited based on the described embodiments. Rather, the scope of the inventions described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.
This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 60/825,527, entitled “Coding For Preamble In UHDR-DO,” filed on Sep. 13, 2006, which is incorporated herein in its entirety as if set forth in full.
| Number | Date | Country | |
|---|---|---|---|
| 60825527 | Sep 2006 | US |
