Frame structure, system and method for OFDM communications

• US 20070066362A1
• Filed: 09/29/2006
• Published: 03/22/2007
• Est. Priority Date: 10/17/2001
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Tong, Wen, Ma, Jianglei, Zhu, Peiying, Jia, Ming
• Granted Patent: US 8,085,814 B2
• Time in Patent Office: Days
• US Class Current: 455/562.100
• 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.

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24. A transmitter adapted to transmit a packet data frame structure comprising:

a superframe having a length corresponding to a synchronization period of a network;

the superframe containing a plurality of radio frames;

each radio frame containing a plurality of TPS (transmission parameter signalling) frames corresponding to an adaptive coding and modulation period;

each TPS frame containing a plurality of slots corresponding to an air interface slot size;

each slot containing a plurality of OFDM symbols.

25. A transmitter according to claim 57 wherein the header OFDM symbols have a header OFDM 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.

26. A transmitter according to claim 57 wherein the header OFDM symbols contain multiplexed pilot channel sub-carriers and common synchronization channel sub-carriers for each of the plurality of antennas.

27. A transmitter according to claim 57 wherein the header OFDM symbols further contain multiplexed broadcasting channel sub-carriers for each of the plurality of antennas.

28. A transmitter according to claim 24 adapted to transmit in a plurality of different modes by transmitting a different number of OFDM symbols per slot with an unchanged slot duration and with no change to the frame structure above the slot.

29. A transmitter according to claim 28 wherein modes with an increased number of OFDM symbols per slot are realized by shortening OFDM symbol duration, and shortening FFT size, but not changing sampling frequency.

30. A transmitter according to claim 24 adapted to transmit to a respective set of users for each TPS frame and to signal for each TPS frame which users should demodulate the entire TPS frame.

31. A receiver adapted to receive and process OFDM frames transmitted by the transmitter of claim 24.

57. A transmitter according to claim 24 wherein the first two symbols of the first slot of the first TPS frame of each OFDM frame are used as header OFDM symbols.

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58. A transmitter adapted to transmit using:

a first mode of operation in which OFDM symbols are constructed from N time domain samples;

a second mode of operation in which OFDM symbols are constructed from N/2 time domain samples.

59. The transmitter of claim 58 adapted to perform switches between the first and second mode subject to a frame size constraint.

60. The transmitter of claim 58 further adapted to, for each first mode OFDM symbol, transmit an M sample prefix, and for each second mode OFDM symbol, transmit an M/2 sample prefix.

61. The transmitter of claim 60 wherein N=1024 and M=32.

62. The transmitter of claim 58 wherein a sampling rate for the first mode of operation is equal to a sampling rate for the second mode of operation such that OFDM symbols in the second mode are twice as long as OFDM symbols in the first mode of operation.

63. A transmitter adapted to transmit using:

a first mode of operation in which OFDM symbols are constructed using a first FFT size;

a second mode of operation in which OFDM symbols are constructed using a second FFT size.

64. The transmitter of claim 63 wherein an increased number of OFDM symbols per slot are realized by shortening OFDM symbol duration for the second OFDM mode by setting the second FFT size smaller than the first FFT size, but not changing sampling frequency.

65. The transmitter of claim 63 further comprising a prefix inserter that inserts a prefix before each symbol, the prefixes for the first mode of operation having a first number of samples, and the prefixes for the second mode of operation having a second number of samples, with a ratio of the first number of samples to the first FFT size being equal to a ratio of the second number of samples to the second FFT size.

66. A transmitter comprising:

a first FFT element that has a first FFT size and generates first OFDM symbols with a first duration, each first OFDM symbol having a respective first cyclic prefix;

a second FFT element that has a second FFT size that is smaller than the first FFT size that generates second OFDM symbols with a second duration that is shorter than the first duration, each second OFDM symbol having a respective second cyclic prefix, a duration of each second cyclic prefix being shorter than a duration of each first cycle prefix;

the transmitter being adapted to transmit a series of slots with fixed duration, the slots containing first OFDM symbols and second OFDM symbols.