# US 7,609,752 B2 · Transmitter and transmission control method used in random access communication environment > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,752 B2 - Document ID: US7609752B2 - Status: Granted - Kind: B2 - Application number: 11/365,532 - Filed: 2006-03-02 - Published: 2006-09-07 - Granted: 2009-10-27 - Earliest claimed: 2005-03-02 - Assignees: Ntt Docomo, Inc. - Inventors: Hiromasa Fujii; Hitoshi Yoshino; Takatoshi Sugiyama - Web page: https://patentgrep.com/patent/US7609752B2 ## CPC - H04L 1/0006: {by adapting the transmission format} - 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 5/0058: {Allocation criteria} - H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT} - H04W 24/00: Supervisory, monitoring or testing arrangements - H04W 72/00: Local resource management - H04W 74/08: Non-scheduled access, e.g. ALOHA (hybrid access H04W74/02) - 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 A transmitter comprises a frequency utilization status detector configured to detect the utilization status of an allocated frequency band based on a received signal, a symbol placement determination unit configured to determine placement of pilot symbols based on the detected status of frequency utilization, and a symbol placement unit configured to place the pilot symbols according to the determined symbol placement. ## Claims ### Claim 1 A transmitter comprising: a frequency utilization status detector configured to detect utilization status of an allocated frequency band based on a received signal; a symbol placement determination unit configured to determine placement of pilot symbols based on the detected status of the frequency utilization; a symbol placement unit configured to place the pilot symbols according to the determined symbol placement; and a synchronization timing detector configured to detect a synchronization timing based on the received signal, wherein the frequency utilization status detector detects the utilization status of the allocated frequency band based on the synchronization timing. ### Claim 2 (depends on 1) The transmitter of claim 1, wherein when receiving signals from transmitters belonging to other communication groups, the synchronization timing detector detects a sync signal from a transmitter belonging to a communication group with a highest power level. ### Claim 3 (depends on 1) The transmitter of claim 1, wherein upon receiving signals from transmitters belonging to other communication groups, the synchronization timing detector detects a sync signal from a transmitter belonging to a communication group with the fewest users. ### Claim 4 (depends on 1) The transmitter of claim 1, further comprising: a transmission timing control unit configured to control transmission timing based on the detected synchronization timing so as to insert a non-transmission section every prescribed number of frames. ### Claim 5 (depends on 1) The transmitter of claim 1, wherein the symbol placement determination unit determines placement of the pilot symbols at prescribed subcarrier intervals. ### Claim 6 (depends on 5) The transmitter of claim 5, wherein the symbol placement determination unit changes the subcarrier interval to a value determined by adding one to a number of simultaneously accessing users. ### Claim 7 (depends on 6) The transmitter of claim 6, wherein the symbol placement determination unit changes the subcarrier interval after a prescribed number of frames have passed since a new transmitter started communicating. ### Claim 8 (depends on 6) The transmitter of claim 6, wherein the symbol placement determination unit changes the subcarrier interval according to a time determined through negotiation with a new transmitter. ### Claim 9 (depends on 6) The transmitter of claim 6, wherein the symbol placement determination unit changes the subcarrier interval to a value represented by 2n, where n is an integer, and greater than a number determined by adding one to a number of spatial multiplexing streams. ### Claim 10 (depends on 1) The transmitter of claim 1, wherein the symbol placement determination unit shifts a pilot symbol position to a one-subcarrier lower position when an unused subcarrier position is lower than the currently used subcarrier position. ### Claim 11 (depends on 1) The transmitter of claim 1, wherein the frequency utilization status detector is further configured to detect at least one of an interference power level and a number of spatial multiplexing streams as the utilization status of the allocated frequency band. ### Claim 12 (depends on 11) The transmitter of claim 11, further comprising: a subcarrier block determination unit configured to select a subcarrier block to be used from among multiple subcarrier blocks determined by dividing the allocated frequency band, based on the utilization status of the allocated frequency band; wherein the symbol placement determination unit determines placement of the pilot symbols for the selected subcarrier block. ### Claim 13 (depends on 12) The transmitter of claim 12, wherein the subcarrier block determination unit selects the subcarrier block to be used from among prescribed subcarrier blocks. ### Claim 14 (depends on 12) The transmitter of claim 12, wherein the subcarrier block determination unit selects the subcarrier block to be used such that a size of unused subcarrier blocks becomes the maximum. ### Claim 15 (depends on 12) The transmitter of claim 12, wherein the subcarrier block determination unit reduces a size of the subcarrier block to be used when the number of spatial multiplexing streams will differ between lower-level subcarrier blocks under the subcarrier block to be used. ### Claim 16 (depends on 15) The transmitter of claim 15, wherein the subcarrier block determination unit determines to use a subcarrier block on a higher frequency side when the leading pilot symbol is using a subcarrier located at a frequency higher than the lower-most frequency. ### Claim 17 (depends on 12) The transmitter of claim 12, wherein the symbol placement determination unit determines to place pilot symbols in subcarriers covering one or more transmitters depending on a size of the subcarrier block to be used. ### Claim 18 (depends on 12) The transmitter of claim 12, wherein when the number of spatial multiplexing streams exceeds a prescribed level in at least a part of subcarrier blocks to be used, the subcarrier block determination unit determines to stop using the subcarrier blocks with an excessive number of spatial multiplexing streams. ### Claim 19 (depends on 18) The transmitter of claim 18, wherein the subcarrier block determination unit determines to stop using the subcarrier blocks with the excessive number of spatial multiplexing streams, based on at least one of the number of subcarriers being used and subcarrier frequencies to which the pilot symbols are placed. ### Claim 20 (depends on 12) The transmitter of claim 12, wherein the frequency utilization status detector detects the utilization status of an adjacent subcarrier block, in addition to the utilization status of a currently used subcarrier block; and wherein the subcarrier block determination unit selects the adjacent subcarrier block depending on the utilization status of the adjacent subcarrier block. ### Claim 21 (depends on 20) The transmitter of claim 20, wherein the subcarrier block determination unit selects the adjacent subcarrier block when a subcarrier interval of the currently used subcarrier block is less than the subcarrier interval of the adjacent subcarrier block with a difference of two or more, and when positions of empty subcarriers in the adjacent subcarrier block correspond to the positions in the currently used subcarrier block. ### Claim 22 (depends on 20) The transmitter of claim 20, wherein the subcarrier block determination unit estimates a throughput to be obtained when the currently used subcarrier block and the adjacent subcarrier block are used, compares the estimation result with a throughput obtained using a currently used subcarrier band, and selects the adjacent subcarrier block depending on the comparison result. ### Claim 23 (depends on 1) The transmitter of claim 1, wherein the symbol placement determination unit stops placement of the pilot symbols if a measured interference power level exceeds a threshold level over N successive frames, where N is an integer, or if an error is detected over N successive frames. ### Claim 24 A transmission control method comprising: receiving a signal from a transmitter that is currently conducting radio communications nearby; detecting the utilization status of an allocated frequency band based on the received signal; determining placement of pilot symbols based on the detected utilization status; placing the pilot symbols based on the determination result; and detecting a synchronization timing based on the received signal, the detection of the utilization status of the allocated frequency band being carried out based on the synchronization timing.