Synchronization in OFDM systems
Highly effective systems and methods for synchronizing OFDM receiver parameters to an OFDM transmitter are provided. These parameters may include carrier frequency, burst timing, and cyclic prefix length. These systems and methods incorporate special structural features into the OFDM signal to facilitate synchronization. In one embodiment, a supplemental cyclic prefix is added to an OFDM signal to facilitate synchronization. In an alternative embodiment, a synchronization burst with a periodic structure is used to facilitate synchronization. According to the present invention, synchronization may be maintained even if low cost analog oscillator components are used.
1 . (canceled)
2 . A method for transmitting an OFDM signal to facilitate receiver synchronization comprising:
forming a synchronization burst from a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least four frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
transmitting the synchronization burst.
3 . A method for synchronizing a receiver to an OFDM signal comprising:
receiving at least one synchronization OFDM burst, the synchronization OFDM burst formed of a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least two frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain;
evaluating a cost function that varies depending on burst timing alignment, the cost function measuring time domain periodicity of the synchronization OFDM burst; and
setting the burst timing alignment to optimize the cost function.
4 . A method as recited in claim 3 , further comprising:
computing a receiver frequency offset based on the burst timing alignment that is set to optimize the cost function in the step of setting.
5 . A method for synchronizing a receiver to an OFDM signal comprising:
receiving at least one OFDM synchronization burst, the synchronization OFDM burst formed of a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least two frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
determining burst timing alignment and frequency offset responsive to optimization of at least one cost function determined in response to content of the at least one OFDM synchronization burst.
6 . A system for transmitting an OFDM signal to facilitate receiver synchronization comprising:
a synchronization burst generation stage to generate a frequency domain synchronization burst formed of a set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least four frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
a transform processing stage that transforms the frequency domain synchronization burst into a time domain synchronization burst.
7 . A system as recited in claim 6 , wherein at least one of the periodically spaced frequency domain symbols carries data.
8 . A system for processing an OFDM signal comprising:
an OFDM receiver system that receives at least one synchronization OFDM burst, the synchronization OFDM burst formed of a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least two frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
a synchronization block that evaluates a cost function that varies depending on burst timing alignment, the cost function measuring time domain periodicity of the synchronization OFDM burst,
wherein the synchronization block is to set the burst timing alignment to optimize the cost function.
9 . A system as recited in claim 8 , wherein the synchronization system is further to compute a receiver frequency offset based on the burst timng alignment that is set by the synchronization system to optimize the cost function.
10 . A system for processing an OFDM signal comprising:
an OFDM receiver system to receive at least one OFDM synchronization burst, the synchronization OFDM burst formed of a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least two frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
a synchronization block that determines burst timing alignment and frequency offset burst timing alignment and frequency offset responsive to optimization of at least one cost function determined in response to content of the at least one OFDM synchronization burst.
11 . A system as recited in claim 10 , wherein at least one of the periodically spaced frequency domain symbols carries data.
12 . An apparatus for transmitting an OFDM signal to facilitate receiver synchronization, the apparatus comprising:
means for forming a synchronization burst from a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that ae spaced at least four frequency domain symbols apart, and only zero energy frequency domain symbols between the periodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain; and
means for transmitting the synchronization burst.
13 . An apparatus for synchronizing a receiver to an OFDM signal, the apparatus comprising;
means for receiving at least one synchronization OFDM burst, the synchronization OFDM burst formed of a set of frequency domain symbols, the set of frequency domain symbols including periodically spaced frequency domain symbols that can take on respective non-zero values and that are spaced at least two frequency domain symbols apart, and only zero energy frequency domain symbols between the perodically spaced frequency domain symbols, such that all the frequency domain symbols of the synchronization burst that can take on non-zero values are periodically spaced in the frequency domain;
means for evaluating a cost function that varies depending on burst timing alignment, the cost function measuring time domain periodicity of the synchronization OFDM burst; and
means for setting the burst timing alignment to optimize the cost function.