Centralized synchronization for wireless networks
First Claim
1. A method of synchronizing a base station with a remote terminal, in which the base station has a base oscillator, the base oscillator having a base sample period, and in which the remote terminal has a remote oscillator, the remote oscillator having a remote sample period, the method comprising the steps of:
- transmitting a training sequence from the remote terminal to the base station over a channel;
upon receipt of the training sequence at the base station, transmitting a first vernier signal from the base station to the remote terminal over the channel, in which the first vernier signal comprises successive time segments, each time segment being offset in time from a multiple of the remote sample period by different multiples of a fraction of the remote sample period;
identifying a time segment in the successive time segments that upon receipt by the remote terminal most closely matches the remote oscillator;
determining a first time offset between the base oscillator and the remote oscillator from the identified time segment; and
advancing signals transmitted from the base station to the remote terminal by the first time offset.
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Accused Products
Abstract
This invention synchronizes the sample clocks of an entire wireless network from a single central base station. Unlike a conventional digital radio network where every terminal must have a synchronization circuit in its receiver to adjust the sample clock, each of the radio terminals in this network is clocked from an independent free-running oscillator. For each terminal, the base station learns the frequency and phase of the oscillator by exchanging a special set of signals: first a vernier signal to determine the initial time and frequency offset, and then an early-late signal to track changes in the oscillator. Once the base station is synchronized to the terminal'"'"'s oscillator, it can determine the absolute path delay between itself and the terminal and correct for the delay using an equalizer. Signals received from the terminal are corrected after the signal arrives at the base station. Signals sent to the terminal are corrected within the base station before they are transmitted so they arrive at the terminal at the precise time that the terminal'"'"'s free running oscillator takes a sample.
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Citations
17 Claims
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1. A method of synchronizing a base station with a remote terminal, in which the base station has a base oscillator, the base oscillator having a base sample period, and in which the remote terminal has a remote oscillator, the remote oscillator having a remote sample period, the method comprising the steps of:
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transmitting a training sequence from the remote terminal to the base station over a channel; upon receipt of the training sequence at the base station, transmitting a first vernier signal from the base station to the remote terminal over the channel, in which the first vernier signal comprises successive time segments, each time segment being offset in time from a multiple of the remote sample period by different multiples of a fraction of the remote sample period; identifying a time segment in the successive time segments that upon receipt by the remote terminal most closely matches the remote oscillator; determining a first time offset between the base oscillator and the remote oscillator from the identified time segment; and advancing signals transmitted from the base station to the remote terminal by the first time offset. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A base station for synchronizing a telecommunications network, the telecommunications network incorporating a remote terminal having a remote oscillator, the remote oscillator having a remote sample period, the apparatus comprising:
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a transmitter comprising a digital to analog converter and a pre-equalizer filter; a receiver comprising an analog to digital converter and a post-equalizer filter; a base oscillator, the base oscillator having a base sample period, the base oscillator being connected to supply a clock signal to the digital to analog converter and to the analog to digital converter; a frame counter connected to receive a clock signal from the base oscillator; an equalization controller connected to the pre-equalizer filter to provide radio channel corrections and a timing advance to signals transmitted from the base station and connected to the post-equalizer filter to provide radio channel corrections and a timing advance to signals received from the terminal; a synchronization controller connected to receive frame position information from the frame counter, the synchronization controller being connected to receive signals from the receiver and being configured to determine a timing advance required to adjust the base oscillator to be synchronized to the remote oscillator, the synchronization controller being connected to supply the timing advance to the equalization controller; and the synchronization controller being configured to generate a vernier signal, in which the vernier signal comprises successive time segments, each time segment being offset in time from a multiple of the remote sample period by different multiples of a fraction of the remote sample period. - View Dependent Claims (11, 12, 13, 14, 15)
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16. A base station for synchronizing a telecommunications network, the telecommunications network incorporating a remote terminal having a remote oscillator, the remote oscillator having a remote sample period, the apparatus comprising:
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a transmitter comprising a digital to analog converter and a pre-equalizer filter; a receiver comprising an analog to digital converte; a base oscillator, the base oscillator having a base sample period, the base oscillator being connected to supply a clock signal to the digital to analog converter and to the analog to digital converter; a frame counter connected to receive a clock signal from the base oscillator; an equalization controller connected to the pre-equalizer filter to provide a timing advance to signals transmitted from the base station; a synchronization controller connected to receive frame position information from the frame counter, the synchronization controller being connected to receive signals from the receiver and being configured to determine a timing advance required to adjust the base oscillator to be synchronized to the remote oscillator, the synchronization controller being connected to supply the timing advance to the equalization controller; and the synchronization controller being configured to generate a vernier signal, in which the vernier signal comprises successive time segments, each time segment being offset in time from a multiple of the remote sample period by different multiples of a fraction of the remote sample, the time segments uniformly covering the sample period. - View Dependent Claims (17)
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Specification