1. A method of obtaining precise absolute time transfer from a satellite, the method comprising:
receiving a precision time signal from a satellite, wherein the precision time signal comprises a periodic repeating code;
determining a timing phase of the code;
receiving aiding information through a network, wherein the network is provided by ground based infrastructure; and
using the timing phase and the aiding information to determine a precise absolute time.
2. The method of claim 1, wherein the network is a cellular network, a WiFi network, or an Internet network.
3. The method of claim 1, wherein the code alternates between a coarse timing code and a pseudorandom code.
4. The method of claim 1, wherein the satellite is a first satellite, the method further comprising:
using the precise absolute time to align positioning correlators of a receiver unit to determine a positioning signal from a second satellite in an attenuated or jammed environment.
5. The method of claim 4, wherein the second satellite is a Global Positioning System (GPS) satellite.
6. The method of claim 1, wherein the satellite is a Low Earth Orbit (LEO) satellite.
7. The method of claim 6, wherein the LEO satellite is an Iridium satellite or a Globalstar satellite.
8. The method of claim 1, wherein the aiding information is orbit information associated with the satellite, an approximate time within about 5 seconds, an approximate range between the satellite and a receiver unit within about 3000 meters, or clock offset information associated with a clock of the satellite.
9. The method of claim 1, further comprising determining the aiding information from a Doppler profile of the satellite.
10. A receiver unit adapted for use in attenuated or jammed environments comprising:
an antenna adapted to receive a precision time signal from a satellite and receive aiding information through a network, wherein the network is provided by ground based infrastructure, wherein the precision time signal comprises a periodic repeating code;
a processor; and
a memory adapted to store a plurality of computer readable instructions which when executed by the processor are adapted to cause the receiver unit to:
determine a timing phase of the code, and
use the timing phase and the aiding information to determine a precise absolute time.
11. The receiver unit of claim 10, wherein the satellite is a first satellite, the receiver unit further comprising:
system correlators adapted to be aligned based on the precise absolute time to perform navigation based on a positioning signal received from a second satellite.
12. The receiver unit of claim 11, wherein the system correlators are implemented by the processor.
13. The receiver unit of claim 10, wherein the satellite is a Low Earth Orbit (LEO) satellite.
14. The receiver unit of claim 13, wherein the LEO satellite is an Iridium satellite or a Globalstar satellite.
15. The receiver unit of claim 10, wherein the network is a cellular network, a WiFi network, or an Internet network.
16. The receiver unit of claim 10, wherein the code alternates between a coarse timing code and a pseudorandom code.
17. The receiver unit of claim 10, wherein the receiver unit is a cellular telephone, a handheld navigation device, a vehicle-based navigation device, or an aircraft-based navigation device.
18. The receiver unit of claim 10, wherein the precision time signal further comprises data and wherein the determining the timing phase of the code further comprises:
receiving the data over a frequency band of the satellite;
downconverting and sampling the received data;
capturing and storing the sampled data in appropriate blocks;
performing a coarse acquisition search of the sampled data;
screening for peaks in the sampled data;
performing a fine acquisition search at a location of a screened peak determined from the coarse acquisition search so that a best peak is determined; and
determining the timing phase of the code based on an identified message that generated the best peak and relative time.
19. The receiver unit of claim 18, wherein the performing the coarse acquisition search of the sampled data further comprises:
selecting a portion of the sampled data for detailed processing;
estimating Doppler of the portion of the sampled data using a known orbit model and estimated time;
digitally demodulating the portion of the sampled data with sine and cosine functions based on a known frequency sub band;
decimating the portion of the sampled data;
applying a Fast Fourier Transform to the decimated portion of the sampled data so that a highest peak and associated frequency are determined; and
continuing to a next portion of the sampled data and repeating the detailed processing.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A semiconductor device comprising:
a first oxide semiconductor film over an insulating surface;
a second oxide semiconductor film over the first oxide semiconductor film;
a source electrode and a drain electrode in contact with a side surface of the first oxide semiconductor film, a side surface of the second oxide semiconductor film, and a top surface of the second oxide semiconductor film;
a third oxide semiconductor film over the second oxide semiconductor film, the source electrode, and the drain electrode;
a gate insulating film over the third oxide semiconductor film; and
a gate electrode in contact with a top surface of the gate insulating film and facing the top surface and the side surface of the second oxide semiconductor film,
wherein the second oxide semiconductor film has a first length in a channel length direction,
wherein the source electrode and the drain electrode have a second length between the source electrode and the drain electrode, and
wherein a third length obtained by subtracting the second length from the first length is 0.2 times to 2.0 times as long as the second length.
2. The semiconductor device according to claim 1,
wherein the third length is longer than or equal to 30 nm and shorter than or equal to 60 nm.
3. The semiconductor device according to claim 1,
wherein the first length is shorter than or equal to 40 nm.
4. The semiconductor device according to claim 1,
wherein a channel width is shorter than or equal to 10 nm.
5. A semiconductor device comprising:
a first oxide semiconductor film over an insulating surface;
a second oxide semiconductor film over the first oxide semiconductor film;
a third oxide semiconductor film over the second oxide semiconductor film;
a source electrode and a drain electrode in contact with a side surface of the first oxide semiconductor film, a side surface of the second oxide semiconductor film, a side surface of the third oxide semiconductor film, and a top surface of the third oxide semiconductor film;
a gate insulating film over the third oxide semiconductor film, the source electrode, and the drain electrode; and
a gate electrode in contact with a top surface of the gate insulating film and facing a top surface and the side surface of the second oxide semiconductor film,
wherein the second oxide semiconductor film has a first length in a channel length direction,
wherein the source electrode and the drain electrode have a second length between the source electrode and the drain electrode, and
wherein a third length obtained by subtracting the second length from the first length is 0.2 times to 2.0 times as long as the second length.
6. The semiconductor device according to claim 5,
wherein the third length is longer than or equal to 30 nm and shorter than or equal to 60 nm.
7. The semiconductor device according to claim 5,
wherein the first length is shorter than or equal to 40 nm.
8. The semiconductor device according to claim 5,
wherein a channel width is shorter than or equal to 40 nm.