# US 2019/0173722 A1 · Preambles in OFDMA System > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0173722 A1 - Document ID: US20190173722A1 - Status: Published application - Kind: A1 - Application number: 16/249,672 - Filed: 2019-01-16 - Published: 2019-06-06 - Earliest claimed: 2004-06-24 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Jianglei Ma; Hang Zhang; Wen Tong; Ming Jia; Peiying Zhu; Mo-Han Fong - Web page: https://patentgrep.com/patent/US20190173722A1 ## CPC - H04B 7/02: Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas (RAKE receivers H04B1/7115) - H04B 7/0452: Multi-user MIMO systems - H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT} - H04L 5/0023: {Time-frequency-space} - H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)} - H04L 7/043: {Pseudo-noise [PN] codes variable during transmission (synchronisation of spread spectrum receivers H04B1/69)} - H04L 27/2613: {Structure of the reference signals} - H04L 27/265: {Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators (H04L27/26524 takes precedence)} - H04L 27/2655: {Synchronisation arrangements} - H04L 27/2686: {Range of frequencies or delays tested} - H04L 27/2692: {with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver} - H04W 24/02: Arrangements for optimising operational condition - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) ## Abstract The present invention provides a preamble that is inserted into an OFDMA frame and has a common sequence for all the base stations participating in a transmission. The subscriber station performs fine synchronization using the common sequence on the common preamble, and the resulting peaks will provide the locations of candidate base stations. The base station specific search is then performed in the vicinities of those peaks by using base station specific pseudo-noise sequences. With this two stage cell search, the searching window is drastically reduced. The preamble is matched to known values by a respective receiver to decode the signals and permit multiple signals to be transferred from the transmitter to the receiver. The preamble may comprise two parts, Preamble-I and Preamble-2, which may be used in different systems, including multioutput, multi-input (MIMO) systems. ## Claims ### Claim at position 1 1-58. (canceled) ### Claim 59 A method, comprising: at a base station in an orthogonal frequency division multiplexing access (OFDMA) system: constructing at least one OFDMA frame having a primary synchronization signal and a secondary synchronization signal, wherein the primary synchronization signal is based on a common sequence and including information pertaining to the configuration of the secondary synchronization signal and wherein the secondary synchronization signal is specific to the base station; and transmitting to a subscriber station the at least one OFDMA frame, wherein the at least one OFDMA frame is configured for use in synchronization. ### Claim 60 (depends on 59) The method of claim 59, wherein the length of the common sequence is scalable with a bandwidth of channel. ### Claim 61 (depends on 59) The method of claim 59, wherein the common sequence has a repeated time domain structure. ### Claim 62 (depends on 59) The method of claim 59, wherein the common synchronization channel is separated by null-subcarriers. ### Claim 63 (depends on 59) The method of claim 59, wherein the primary synchronization signal is at a flexible location that is indicated by a preceding zone in the at least one OFDMA frame. ### Claim 64 (depends on 59) The method of claim 59, wherein the primary synchronization signal and the secondary synchronization signal are located at a predefined location in the at least one OFDMA frame. ### Claim 65 (depends on 59) The method of claim 59, wherein the primary synchronization signal and the secondary synchronization signal coexist with a legacy preamble. ### Claim 66 A method comprising: at a subscriber station in an orthogonal frequency division multiplexing access (OFDMA) system: receiving at least one OFDMA frame from a base station, the OFDMA frame having a primary synchronization signal and a secondary synchronization signal, wherein the primary synchronization signal is based on a common sequence and including information pertaining to the configuration of the secondary synchronization signal and wherein the secondary synchronization signal is specific to the base station; and synchronizing based on the at least one OFDMA frame. ### Claim 67 (depends on 66) The method of claim 66, wherein the common sequence provides locations of candidate base stations and reduces a fine search window for the base station specific preamble. ### Claim 68 (depends on 66) The method of claim 66, wherein the length of the common sequence is scalable with a bandwidth of channel. ### Claim 69 (depends on 66) The method of claim 66, wherein the common sequence comprises pseudo-noise codes and results in a low peak-to-average power ratio (PAPR). ### Claim 70 (depends on 66) The method of claim 66, wherein the primary synchronization signal is located in a zone comprising a first dimension of subchannels and a second dimension of time division and multiplex OFDM symbols, the zone being defined by a subcarrier allocation method. ### Claim 71 (depends on 66) The method of claim 66, wherein the secondary synchronization signal is at a flexible location that is indicated by a preceding zone in the at least one OFDMA frame. ### Claim 72 (depends on 66) The method of claim 66, wherein the secondary synchronization signal comprises cell-specific synchronization subcarriers. ### Claim 73 (depends on 66) The method of claim 66, wherein the primary synchronization signal indicates a number of antennas corresponding to the secondary synchronization signal. ### Claim 74 (depends on 66) The method of claim 66, wherein the primary synchronization signal includes information specifying whether the secondary synchronization signal is for a partially utilized subchannel (PUSC) or a fully utilized subchannel (FUSC). ### Claim 75 (depends on 66) The method of claim 66, further comprising: downconverting a plurality of OFDM symbols to a baseband frequency signal, wherein the plurality of OFDM symbols are included in the at least one OFDMA frame. ### Claim 76 (depends on 66) The method of claim 66, further comprising: identifying candidate timing synchronization positions using a correlation of the common sequence. ### Claim 77 (depends on 66) The method of claim 66, further comprising: searching for the secondary synchronization signal using the candidate timing synchronization positions. ### Claim 78 A subscriber station, comprising: receive circuitry receiving at least one OFDMA frame having a primary synchronization signal and a secondary synchronization signal, wherein the primary synchronization signal is based on a common sequence and including information pertaining to the configuration of the secondary synchronization signal and wherein the secondary synchronization signal is specific to the base station; and a processor configured to perform synchronization using the common sequence of the primary synchronization signal.