Patent Application
20110228886
The present disclosure relates generally to receiver synchronization for receiving wireless signals. More particularly, the present disclosure relates to receiver link re-synchronization for time-sliced orthogonal frequency-division multiplexing communication systems.
Wireless mobile communications devices such as mobile telephones are now increasingly used to receive and display digital video. Wireless communication technologies are being used to deliver this high-bandwidth content to the mobile devices. One such technology is orthogonal frequency-division multiplexing (OFDM). To conserve power in mobile receivers, some OFDM signals are time-sliced. These signals transmit data in bursts. A receiver can reduce power between bursts, and power up again to process each burst. To do this efficiently, the receiver needs knowledge of the start time for each burst. Determining these start times is referred to as link re-synchronization.
In general, in one aspect, an embodiment features a method comprising: receiving an estimated frame index, and an estimated symbol index, for a time-sliced OFDM signal; identifying a plurality of possible frame indexes, and a plurality of possible symbol indexes, based on the estimated frame index and the estimated symbol index; selecting a plurality of possible forward error correction code offsets based on the possible frame indexes and the possible symbol indexes; and selecting one of the possible frame indexes, and one of the possible symbol indexes, based on the possible forward error correction code offsets and a SYNC byte of the time-sliced OFDM signal.
Embodiments of the method can include one or more of the following features. Some embodiments comprise re-synchronizing a receiver of the OFDM signal based on the one of the possible frame indexes and the one of the possible symbol indexes. Some embodiments comprise displaying content of the OFDM signal based on the re-synchronizing. In some embodiments, the OFDM signal comprises a DVB-H signal. In some embodiments, selecting one of the possible frame indexes, and one of the possible symbol indexes, comprises: correlating the SYNC byte with a plurality of transport stream packets of the OFDM signal according to each of the possible forward error correction code offsets.
In general, in one aspect, an embodiment features an apparatus comprising: an input module to receive an estimated frame index, and an estimated symbol index, for a time-sliced OFDM signal; an index module to identify a plurality of possible frame indexes, and a plurality of possible symbol indexes, based on the estimated frame index and the estimated symbol index; an offset module to select a plurality of possible forward error correction code offsets based on the possible frame indexes and the possible symbol indexes; and a synchronization module to select one of the possible frame indexes, and one of the possible symbol indexes, based on the possible forward error correction code offsets and a SYNC byte of the time-sliced OFDM signal.
Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise a timing module to re-synchronize a receiver of the OFDM signal based on the one of the possible frame indexes and the one of the possible symbol indexes. Some embodiments comprise a display to display content of the OFDM signal based on the one of the possible frame indexes and the one of the possible symbol indexes. In some embodiments, the OFDM signal comprises a DVB-H signal. In some embodiments, the synchronization module comprises: a correlator to correlate the SYNC byte with a plurality of transport stream packets of the OFDM signal according to each of the possible forward error correction code offsets.
In general, in one aspect, an embodiment features computer-readable media embodying instructions executable by a computer to perform a method comprising: receiving an estimated frame index, and an estimated symbol index, for a time-sliced OFDM signal; identifying a plurality of possible frame indexes, and a plurality of possible symbol indexes, based on the estimated frame index and the estimated symbol index; selecting a plurality of possible forward error correction code offsets based on the possible frame indexes and the possible symbol indexes; and selecting one of the possible frame indexes, and one of the possible symbol indexes, based on the possible forward error correction code offsets and a SYNC byte of the time-sliced OFDM signal.
Embodiments of the computer-readable media can include one or more of the following features. In some embodiments, the method further comprises: re-synchronizing a receiver of the OFDM signal based on the one of the possible frame indexes and the one of the possible symbol indexes. In some embodiments, the method further comprises: displaying content of the OFDM signal based on the re-synchronizing. In some embodiments, the OFDM signal comprises a DVB-H signal. In some embodiments, selecting one of the possible frame indexes, and one of the possible symbol indexes, comprises: correlating the SYNC byte with a plurality of transport stream packets of the OFDM signal according to each of the possible forward error correction code offsets.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.
The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears.
Embodiments of the present disclosure provide fast re-synchronization for time-sliced orthogonal frequency-division multiplexing (OFDM) signals. One such signal is DVB-H (Digital Video Broadcasting—Handheld) in time-slice mode. Various embodiments are described with reference to DVB-H signals. However, the disclosed techniques apply to other OFDM signals as well, as will be apparent after reading this disclosure.
Referring to
Referring to
Input module 216 of re-synchronization module 210 receives estimated frame index 218 and estimated symbol index 220 (step 304). Based on estimated frame index 218 and estimated symbol index 220, index module 222 of re-synchronization module 210 identifies a plurality of possible frame indexes 224, and a plurality of possible symbol indexes 226 (step 306). Based on possible frame indexes 224 and possible symbol indexes 226, offset module 228 selects a plurality of possible forward error correction code offsets 230 (step 308).
These identifications and selections can be based on the known patterns of the forward error correction code used in OFDM signal 104. For example, Tables 1-9 at the end of this disclosure show the known relationships between the Reed-Solomon Code Block Index (#RS block) and Offset (#Offset) for DVB-H signals. Tables 1-3 show the known relationships for 8K mode for Quadrature phase-shift keying (QPSK), 16QAM (Quadrature amplitude modulation), and 64QAM, respectively. Tables 4-6 show the known relationships for 2K mode for QPSK, 16QAM, and 64QAM, respectively. Tables 4-6 show the known relationships for 4K mode for QPSK, 16QAM, and 64QAM, respectively. According to the pattern for the RS code offset within 0-67 symbols (that is, one frame) in Table 1, the minimum repeat period of the RS code is 17 symbols. The possible repeat periods are 17, 34, 68 symbols, etc. Because the scattered pilot pattern is repeated every 4 symbols, the correct RS code offset can be selected if estimated symbol index 220 in the frame (that is, the approximate wake up time) is within +/−34 symbols.
Synchronization module 232 selects one of possible frame indexes 224, and one of possible symbol indexes 226, based on possible forward error correction code offsets 230 and a SYNC byte 234 of OFDM signals 104 (step 310). In particular, correlator 240 correlates SYNC byte 234 with a plurality of transport stream packets 242 of OFDM signal 104 according to each of possible forward error correction code offsets 230. For example, with DVB-H signals, in order to decide to which possible symbol index 226 is correct, SYNC byte 234 is used to verify because different symbol indexes are mapped to different RS code bit offsets, as shown in Tables 1-9. The first byte from the estimated RS code bit offset is SYNC byte 234. An 8-bit correlation can be applied to all 17 possible RS code offsets, and the absolute correlation value can be accumulated over N times (that is, N transport stream (TS) packets, where each TS packet has one SYNC byte 234 at the head position). Considering time diversity, this N accumulated 8-bit correlation is repeated by M times for verification. An average value is calculated for each RS code offset position among the M accumulated correlation elements. The accumulated correlation elements with values larger than the average value are taken as effective elements for further processing. By doing so, the even/odd de-interleave pattern in 2K mode can be resolved. It should be noted that the N TS packet number is equal to the TS packet number in each OFDM symbol in 2K mode. Furthermore, the average value of the effective elements is calculated for all 17 RS code offset positions. Among the 17 average values of the effective elements, the maximum value is obtained to indicate the correct RS offset with a value larger than a threshold 5/8*8*N (meaning 5 bits correct among the 8 bits of SYNC byte 234). Based on this information, synchronization module 232 selects the correct frame index 224 and the correct symbol index 226.
Referring again to
Embodiments of the disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments of the disclosure can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the disclosure can be performed by a programmable processor executing a program of instructions to perform functions of the disclosure by operating on input data and generating output. The disclosure can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).
A number of implementations of the disclosure have been described.
Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 61078811 | Jul 2008 | US | national |
This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/078,811 filed Jul. 8, 2008, the disclosure thereof incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/49868 | 7/8/2009 | WO | 00 | 4/5/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61078811 | Jul 2008 | US |
