摘要:
This invention relates to apparatus, methods, processor control code and signals for channel estimation in OFDM (Orthogonal Frequency Division Multiplexed) communication systems with a plurality of transmitter antennas, such as MIMO (Multiple-input Multiple-output) OFDM systems. An OFDM signal is transmitted from an OFDM transmitter using a plurality of transmit antennas. The OFDM signal is adapted for channel estimation for channels associated with said transmit antennas by the inclusion of orthogonal training sequence data in the signal from each said antenna. The said training sequence data is derived from substantially orthogonal training sequences of length K for each said transmit antenna, said orthogonal training sequences being constructed such that a minimum required sequence length K needed to determine a channel estimate for at least one channel associated with each said transmit antenna is linearly dependent upon the number of said transmit antennas.
摘要:
In the GPRS, a method of decoding uplink status having reduced interleaving depth in a RLC/MAC block is proposed; for RT-EGPRS users, all of the uplink flag bits are provided in the first burst of the four bursts; and for EGPRS users, nine bits of the uplink status flags are provided in the first burst of the RLC/MAC block and the remaining bits in the next three bursts. On receiving the first nine bits, a mobile performs an autocorrelation to identify the USF whether it belongs to the EGPRS or to the RT-EGPRS group.
摘要:
In a MIMO system the bit error rate floor caused by time dispersion is reduced by employing a joint minimum mean square error (MMSE) equalizer for all of the respective transmit antenna—receive antenna pairings that are possible in the MIMO system. The resulting joint equalization compensates not only for the impact of the channel on the transmit antenna—receive antenna pairings but also for the interference of the other transmit antennas on any given receive antenna. The joint equalization outperforms simply replicating the prior art minimum mean square error (MMSE) equalizer for each transmit antenna—receive antenna pairings.
摘要:
In a lattice-reduction-aided receiver based wireless communications system, soft estimates of transmitted bit values are determined from a received signal by applying lattice reduction to the channel estimate and equalising the received signal in accordance with the reduced basis channel, and determining probabilities of transmitted bits having particular values by selecting a core candidate vector in the reduced basis, determining a set of mapping functions between the core vector in the reduced basis and transmitted symbol vectors from which a set of candidate transmitted symbol vectors can be generated, generating a set of transmitted symbol vectors based on the mapping functions and, on the basis of the received signal determining the probability of each transmitted bit value having been transmitted.
摘要:
Information is detected in a signal received from a transmission over a MIMO channel from a plurality of transmit antennas. The information is encoded as QAM symbols over space and time and/or frequency. A method of detection is provided, comprising arranging the available QAM symbols into a hierarchical tree structure, each level of the tree structure providing a greater level of granularity than the previous and, for each level of the tree structure from the least specific onwards, for each selected branch of the tree structure in said level, determining a branch likelihood measure, representing the approximated likelihood of a received signal containing a symbol in said branch, selecting one or more of said branches on the basis of their branch likelihood measures, said selected branches being selected for consideration in the next level of the tree structure, such that, at a last level, wherein each branch thereof corresponds to a symbol, said branch likelihood measure for a branch corresponds to a likelihood of said received signal containing the corresponding symbol. Corresponding detector apparatus is further provided.
摘要:
A method of estimating channel response in a communications system comprising a transmitting device having a plurality of transmit antennas and a receiving device having at least one receive antenna, the method comprising: (a) Superimposing training sequences onto transmit data to be transmitted by the transmit antennas in order to form a composite message, wherein the training sequences for each transmit antenna are arranged such that they are non-overlapping in the frequency domain; (b) Transmitting the composite message from step (a); (c) Receiving data at the receiving device and then performing the following steps across all channels i. Equalising received data to remove channel distortion; ii. detecting an estimate for the transmit data; iii. using the estimate of the transmit data from step (c)(ii) in order to derive an estimate of the received training sequences as modified by the channel response from the received data; iv. comparing the estimate of channel modified training sequences from step (c)(iii) with the original training sequences in order to estimate the channel response
摘要:
This invention is generally concerned with methods, apparatus and processor control code for decoding a signal received over a MIMO (multiple input-multiple output) channel.A method of decoding a signal encoded as a string of symbols over space and time and/or frequency, transmitted over a MIMO (multiple-input multiple-output) channel, and received at a plurality of receive antennas, each transmitted symbol having one of a plurality of values, said decoding comprising determining a probability distribution for each symbol of the transmitted string of symbols; the method comprising: determining an initial estimate of said transmitted string of symbols from said received signal using an estimate of a response of said MIMO channel; and determining from said initial estimate a probability distribution for each symbol of the transmitted string of symbols, the probability distribution representing the likelihood of a symbol of the string having each of its possible values when other symbols of the transmitted string are treated as noise.
摘要:
In a lattice-reduction-aided receiver based wireless communications system, soft estimates of transmitted bit values are determined from a received signal by applying lattice reduction to the channel estimate and equalising the received signal in accordance with the reduced basis channel, and determining probabilities of transmitted bits having particular values by generating a set of candidate vectors in the reduced basis based on nearest candidate vectors, determining a corresponding transmitted symbol vector for each candidate vector and, on the basis of the received signal determining the probability of each transmitted bit value having been transmitted.
摘要:
The invention relates to apparatus, methods, processor control code and signals for channel estimation in MIMO (Multiple-input Multiple-output) OFDM (Orthogonal Frequency Division Multiplexed) communication systems. An OFDM signal is transmitted from an OFDM transmitter using a plurality of transmit antennas but has one or more nulled subcarriers, corresponding to windowing in the frequency domain. The OFDM signal is adapted for channel estimation for channels associated with said transmit antennas by the inclusion of orthogonal training sequence data in the signal from each said antenna. The training sequence data is derived from substantially orthogonal training sequences for each said transmit antenna, the training sequences being constructed based upon sequences of values Xmk=exp(−j2πkm/M) where k indexes a value in a said sequence, m indexes a transmit antenna, and M is the number of transmit antennas. Embodiments of these techniques provide training sequences that are more robust to, inter alia, nulled subcarriers.
摘要:
In a wireless communications system, an inverse of a lattice reduction matrix can be obtained at the same time as performance of the LLL algorithm to determine the lattice reduction. This is achieved by interposing in the LLL algorithm corresponding steps applied to a running calculation of the inverse matrix. Similarly, a row-wise sum of the inverse matrix can be calculated, if this is all that is required in subsequent processing.