System access and synchronization methods for MIMO OFDM communications systems and physical layer packet and preamble design

• US 7,548,506 B2
• Filed: 01/08/2002
• Issued: 06/16/2009
• Est. Priority Date: 10/17/2001
• Status: Expired due to Fees

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Ma, Jianglei, Tong, Wen, Jia, Ming, Zhu, Peiying
• Primary Examiner(s): Mattis, Jason E
• Application Number:
  US10/038,915
• Publication Number:
  US 20030072255A1
• Time in Patent Office: 2,716 Days
• Field of Search: 370/208, 370/324, 370/511
• US Class Current: 370/208
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/04 using two or more spaced independent antennas
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0667 of delayed versions of same signal using space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04J 11/0069 Cell search, i.e. determining cell identity [cell-ID] design of multiplexing codes H04J13/00; processing access restriction or access information H04W48/16; discovery of network devices for network data management H04W8/005; sounding signals for channel estimation H04L25/0226; structure of reference signals in multicarrier modulation systems H04L27/2613; frame, time or carrier synchronisation in multicarrier modulation systems H04L27/2655
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/26025 Numerology, i.e. varying one or more of symbol duration, subcarrier spacing, Fourier transform size, sampling rate or down-clocking allocating sub-channels of the transmission path H04L5/003
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2627 Modulators
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 27/2672 Frequency domain
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04W 36/08 Reselecting an access point

Abstract

A method and apparatus are provided for performing acquisition, synchronization and cell selection within an MIMO-OFDM communication system. A coarse synchronization is performed to determine a searching window. A fine synchronization is then performed by measuring correlations between subsets of signal samples, whose first signal sample lies within the searching window, and known values. The correlations are performed in the frequency domain of the received signal. In a multiple-output OFDM system, each antenna of the OFDM transmitter has a unique known value. The known value is transmitted as pairs of consecutive pilot symbols, each pair of pilot symbols being transmitted at the same subset of sub-carrier frequencies within the OFDM frame.

Claims

1. A MIMO-OFDM transmitter configured to transmit a header symbol format in which sub-carriers of a header OFDM symbol are divided into a non-contiguous set of sub-carriers for each of a plurality of antennas, with each antenna transmitting the header OFDM symbol only on the respective set of sub-carriers;

wherein the header symbol contains a frequency multiplexed dedicated pilot channel on dedicated pilot channel sub-carriers and common synchronization channel on common synchronization channel sub-carriers for each of the plurality of antennas;

wherein the common synchronization channel is used to transmit a complex sequence which is different for each transmit antenna of one transmitter, but which is common for respective transmit antennas of each transmitter within a communications network.

2. A transmitter according to claim 1 wherein there are N antennas and a different set of sub-carriers separated by N sub-carriers is assigned to each of the plurality of antennas.

3. A transmitter according to claim 1 wherein the header OFDM symbol further contains multiplexed broadcasting sub-carriers for each of the plurality of antennas.

4. A transmitter according to claim 1, that transmits a preamble having a prefix, followed by two identical OFDM symbols having said header OFDM symbol format.

5. A transmitter according to claim 4 wherein the prefix is a cyclic extension of the two identical OFDM symbols.

6. A transmitter according to claim 1 wherein the pilot channel sub-carriers have a BTS specific mapped complex sequence allowing efficient BTS identification.

7. A transmitter according to claim 1 wherein the common synchronization channel is designed for fast and accurate initial acquisition.

8. A transmitter according to claim 1 wherein the common synchronization channel is used for course synchronization and fine synchronization and the pilot channel is used for fine synchronization.

9. A transmitter according to claim 1 that transmits OFDM frames beginning with said header, and having scattered pilots throughout a remainder of OFDM symbols in each OFDM frame.

10. A transmitter according to claim 1 wherein during the header, for each of N transmit antennas, dedicated pilot channel sub-carriers are transmitted and common synchronization channel sub-carriers are transmitted and broadcasting channel sub-carriers are transmitted.

11. A transmitter according to claim 1 wherein the sub-carriers of the header OFDM symbol are organized as a repeating sequence of dedicated pilot channel sub-carriers for each of N transmit antennas and common synchronization channel sub-carriers for each of N transmit antennas, arranged in a predetermined order.

12. A transmitter according to claim 3 wherein the sub-carriers of the header OFDM symbol are organized as a repeating sequence of at least one dedicated pilot channel sub-carrier for each of N transmit antennas, at least one common synchronization channel sub-carrier for each of N transmit antennas and at least one broadcast channel sub-arrier, arranged in a predetermined order.

13. A MIMO-OFDM receiver configured to receive a header symbol format in which sub-carriers of a header OFDM symbol are divided into a non-contiguous set of sub-carriers for each of a plurality of transmit antennas, with each antenna transmitting the header OFDM symbol only on the respective set of sub-carriers;

wherein the header symbol contains frequency multiplexed dedicated pilot channel sub-carriers and common synchronization channel sub-carriers for each of the plurality of transmit antennas;

wherein the common synchronization channel is used to transmit a complex sequence which is different for each transmit antenna of one transmitter, but which is common for respective transmit antennas of each transmitter within a communications network.

14. A receiver according to claim 13 that receives from N transmit antennas with a different set of sub-carriers separated by N sub-carriers assigned to each of the plurality of transmit antennas.

15. A receiver according to claim 13 wherein the header OFDM symbol further contains multiplexed broadcasting carriers for each of the plurality of transmit antennas.

16. A receiver according to claim 13 that receives a preamble having a prefix, followed by two identical OFDM symbols having said header OFDM symbol format.

17. A receiver according to claim 13 wherein the dedicated pilot channel has a BTS specific mapped complex sequence, the receiver performing BTS identification on the basis of the dedicated pilot channel.

18. A receiver according to claim 16 wherein the dedicated pilot channel has a BTS specific mapped complex sequence, the receiver performing BTS identification on the basis of the dedicated pilot channel.

19. A receiver according to claim 18 wherein the header OFDM symbol contains multiplexed dedicated pilot channel sub-carriers and common synchronization channel sub-carriers for each of the plurality of transmit antennas, the receiver performing course synchronization on the common synchronization channel by looking for a correlation peak between consecutive OFDM symbols which are identical.

20. A receiver according to claim 19 that performs fine synchronization on the basis of the common synchronization channel sub-carriers and/or the dedicated pilot channel sub-carriers.