# US 2008/0304586 A1 · Reduced Lattice Demodulation Method and Apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0304586 A1 - Document ID: US20080304586A1 - Status: Published application - Kind: A1 - Application number: 11/760,285 - Filed: 2007-06-08 - Published: 2008-12-11 - Earliest claimed: 2007-06-08 - Assignees: Telefonaktiebolaget LM Ericsson (publ) - Inventors: Karl Molnar - Web page: https://patentgrep.com/patent/US20080304586A1 ## CPC - H04L 25/0212: {of impulse response} - H04B 1/7105: Joint detection techniques, e.g. linear detectors - H04B 1/7115: Constructive combining of multi-path signals, i.e. RAKE receivers - H04L 25/0204: {of multiple channels} - H04B 2201/709727: GRAKE type RAKE receivers - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract RAKE-based receivers utilize lattice reduction for improving symbol estimation accuracy. Channel response estimates and received signal streams are transformed from a constellation lattice basis to an integer lattice basis to increase the orthogonality of symbol estimation decision regions. In one embodiment, received signal streams are processed by generating despread signal samples from received signal streams transmitted using different spreading codes. Channel response associated with the different received signal streams is estimated and transformed from a first lattice basis to a second lattice basis having greater orthogonality between decision regions than the first lattice basis. The despread signal samples are aligned to the second lattice and combining weights generated based on the transformed channel response estimate. Symbol estimation decision statistics are generated based on the combining weights and the aligned despread signal samples. Soft bit values are generated for decoding based on the symbol estimation decision statistics. ## Claims ### Claim 1 A method of received signal processing, comprising: generating despread signal samples from received signal streams transmitted using different spreading codes; estimating channel response associated with the different received signal streams; transforming the channel response estimate from a first lattice basis to a second lattice basis having greater orthogonality between decision regions than the first lattice basis; aligning the despread signal samples to the second lattice; generating combining weights based on the transformed channel response estimate; generating symbol estimation decision statistics based on the combining weights and the aligned despread signal samples; and generating soft bit values for decoding based on the symbol estimation decision statistics. ### Claim 2 (depends on 1) The method of claim 1, wherein generating combining weights based on the transformed channel response estimate comprises generating the combining weights as a function of the transformed channel response estimate and a data covariance estimate derived from the received signal streams. ### Claim 3 (depends on 1) The method of claim 1, wherein generating combining weights based on the transformed channel response estimate comprises generating the combining weights as a function of the transformed channel response estimate and an impairment covariance estimate. ### Claim 4 (depends on 1) The method of claim 1, wherein generating the soft bit values comprises: identifying symbols located on the second lattice nearest the symbol estimation decision statistics; and generating the soft bit values based on the identified symbols. ### Claim 5 (depends on 4) The method of claim 4, wherein generating the soft bit values based on the identified symbols comprises: transforming the identified symbols to the first lattice; and generating the soft bit values from the transformed symbols. ### Claim 6 (depends on 4) The method of claim 4, wherein identifying symbols located on the second lattice nearest the symbol estimation decision statistics comprises: mapping valid constellation symbols located on the first lattice to the second lattice; and restricting quantization of the symbol estimation decision statistics to the mapped constellation symbols located on the second lattice. ### Claim 7 (depends on 6) The method of claim 6, wherein restricting quantization of the symbol estimation decision statistics to the mapped constellation symbols located on the second lattice comprises, for each received signal stream, restricting quantization of the symbol estimation decision statistics associated with the received signal stream to the mapped constellation symbols associated with the received signal stream. ### Claim 8 (depends on 6) The method of claim 6, wherein restricting quantization of the symbol estimation decision statistics to the mapped constellation symbols located on the second lattice comprises jointly restricting quantization of the symbol estimation decision statistics associated with each of the received signal streams to the mapped constellation symbols associated with the received signal streams. ### Claim 9 (depends on 1) The method of claim 1, wherein generating soft bit values based on the symbol estimation decision statistics comprises: identifying points located on the second lattice nearest the symbol estimation decision statistics; and determining the soft bit values based on the distance between the identified points and neighboring points located on the second lattice. ### Claim 10 (depends on 9) The method of claim 9, wherein determining the soft bit values based on the distance between the identified points and neighboring points located on the second lattice comprises determining the soft bit values based on the distance between points identified on the second lattice corresponding to valid constellation symbols and neighboring points located on the second lattice corresponding to valid constellation symbols. ### Claim 11 (depends on 1) The method of claim 1, wherein aligning the despread signal samples to the second lattice comprises shifting and scaling the despread signal samples based on the modulation scheme associated with the received signal streams. ### Claim 12 A wireless receiver comprising a baseband processor configured to: generate despread signal samples from received signal streams transmitted using different spreading codes; estimate channel response associated with the different received signal streams; transform the channel response estimate from a first lattice basis to a second lattice basis having greater orthogonality between decision regions than the first lattice basis; align the despread signal samples to the second lattice; generate combining weights based on the transformed channel response estimate; generate symbol estimation decision statistics based on the combining weights and the aligned despread signal samples; and generate soft bit values for decoding based on the symbol estimation decision statistics. ### Claim 13 (depends on 12) The wireless receiver of claim 12, wherein the baseband processor is configured to generate the combining weights as a function of the transformed channel response estimate and a data covariance estimate derived from the received signal streams. ### Claim 14 (depends on 12) The wireless receiver of claim 12, wherein the baseband processor is configured to generate the combining weights as a function of the transformed channel response estimate and an impairment covariance estimate. ### Claim 15 (depends on 12) The wireless receiver of claim 12, wherein the baseband processor is configured to: identify symbols located on the second lattice nearest the symbol estimation decision statistics; and generate the soft bit values based on the identified symbols. ### Claim 16 (depends on 15) The wireless receiver of claim 15, wherein the baseband processor is configured to: transform the identified symbols to the first lattice; and generate the soft bit values from the transformed symbols. ### Claim 17 (depends on 15) The wireless receiver of claim 15, wherein the baseband processor is configured to: map valid constellation symbols located on the first lattice to the second lattice; and restrict quantization of the symbol estimation decision statistics to the mapped constellation symbols located on the second lattice. ### Claim 18 (depends on 17) The wireless receiver of claim 17, wherein for each received signal stream, the baseband processor is configured to restrict quantization of the symbol estimation decision statistics associated with the received signal stream to the mapped constellation symbols associated with the received signal stream. ### Claim 19 (depends on 17) The wireless receiver of claim 17, wherein the baseband processor is configured to jointly restrict quantization of the symbol estimation decision statistics associated with each of the received signal streams to the mapped constellation symbols associated with the received signal streams. ### Claim 20 (depends on 12) The wireless receiver of claim 12, wherein the baseband processor is configured to: identify points located on the second lattice nearest the symbol estimation decision statistics; and determine the soft bit values based on the distance between the identified points and neighboring points located on the second lattice. ### Claim 21 (depends on 20) The wireless receiver of claim 20, wherein the baseband processor is configured to determine the soft bit values based on the distance between points identified on the second lattice corresponding to valid constellation symbols and neighboring points located on the second lattice corresponding to valid constellation symbols. ### Claim 22 (depends on 12) The wireless receiver of claim 12, wherein the baseband processor is configured to shift and scale the despread signal samples based on the modulation scheme associated with the received signal streams.