SYSTEM ACCESS AND SYNCHRONIZATION METHODS FOR MIMO OFDM COMMUNICATIONS SYSTEMS AND PHYSICAL LAYER PACKET AND PREAMBLE DESIGN

• US 20120027136A1
• Filed: 08/05/2011
• Published: 02/02/2012
• Est. Priority Date: 10/17/2001
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: MA, Jianglei, JIA, Ming, ZHU, Peiying, TONG, Wen
• Granted Patent: US 8,441,918 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• 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 method in an orthogonal frequency division multiplexing (OFDM) receiver, comprising at least one receive antenna, to perform fine synchronization, the OFDM receiver configured to communicate with a transmitter comprising at least one transmit antenna, the method comprising:

at each of the at least one receive antenna receiving OFDM symbols containing a respective received frequency domain training sequence for each of the at least one transmit antenna;

performing fine synchronization in the frequency domain by looking for maximum correlations between known frequency domain training sequences and the received frequency domain training sequences.

2. A method comprising:

converting a frequency domain representation of a common sync sequence into a time domain representation;

transmitting the time domain representation twice, preceded by a cyclic prefix of the time domain representation.

3. The method of claim 2 wherein converting a frequency domain representation of a common sync sequence into a time domain representation comprises mapping the common sync sequence to a set of non-adjacent orthogonal frequency division multiplexing (OFDM) sub-carriers and performing an inverse fast Fourier transform (IFFT).

4. The method of claim 2 wherein the common sync sequence is common to multiple base stations.

5. A method of performing synchronization at an orthogonal frequency division multiplexing (OFDM) receiver comprising:

at each of at least one receive antenna, sampling a received OFDM signal to produce a respective set of time domain samples, the received signal comprising a received training sequence;

performing synchronization based on correlations between the received training sequence and a local copy of the training sequence;

wherein performing synchronization based on correlations between the received training sequence and a local copy of the training sequence is done in the frequency domain,

wherein the received training sequence is a frequency domain training sequence located on selected sub-carriers of the received OFDM signal.