Devices and methods employing hermetic transforms for encoding and decoding digital information in spread-spectrum communications systems
In a direct sequence spread-spectrum (DSSS) systems, such as CDMA, information is encoded in symbols using phase shift keying or quadrature amplitude modulation. Further, a transmitter applied a selected time shifted lag to each symbol to convey additional information. A receiver detects both the symbol data and the lag value. The receiver can use a hermetic matched filter matrix to identify the lag.
1. A receiver method comprising:
receiving a direct sequence spread spectrum (DSSS) signal with a combination of data symbols and a code;
deriving data from the data symbols;
determining one of a plurality of different time-shifted lag values of the received code relative to a known reference value;
deriving encoded data based on the lag value;
outputting data derived from both the data symbols and from the lag value,
wherein determining the lag value includes generating a plurality of vectors by shifting an input signal vector by a number N of time samples and applying a transform to produce a transformed signal; and
wherein determining the lag value further includes providing the transformed signal to a hermetic matched filter matrix to produce a hermetic matched filtered signal.
2. The method of claim 1 , wherein receiving the direct sequence spread spectrum signal with a combination of data symbols and a code includes oversampling the received signal.
3. The method of claim 1 , wherein the receiving includes quadrature demodulating and converting a received analog signal to a digital signal.
4. The method of claim 1 , wherein each symbol represents n bits, and wherein the lag value represents m bits, such that a lagged symbol represents n +m bits.
5. The method of claim 1 , wherein the DSSS signal is received by a mobile device.
6. The method of claim 1 , wherein the DSSS signal is received by a base station.
7. The method of claim 1 , wherein the receiving includes receiving symbols encoded with phase shift keying (PSK) or quadrature amplitude modulation (QAM).
8. The method of claim 1 , wherein determining the lag value includes determining one of at least 4 values, and determining encoded data includes deriving at least two bits from the lag value.
9. A receiver comprising an antenna for receiving RF signals:
memory for storing instructions; and
a processor for executing instructions, the receiver configured for: receiving a direct sequence spread spectrum (DSSS) signal with a combination of data symbols and a code;
deriving data from the data symbols;
determining one of a plurality of different time-shifted lag values of the received code relative to a known reference value;
deriving encoded data based on the lag value;
outputting data derived from both the data symbols and from the lag value,
wherein determining the lag value includes generating a plurality of vectors by shifting an input signal vector by a number N of time samples and applying a transform to produce a transformed signal; and
wherein determining the lag value further includes providing the transformed signal to a hermetic matched filter matrix to produce a hermetic matched filtered signal.
10. The receiver of claim 9 , wherein the receiver is part of a mobile device.
11. The receiver of claim 9 , wherein the receiver is part of a base station.
12. The receiver of claim 9 , wherein receiving the direct sequence spread spectrum signal with a combination of data symbols and a code includes oversampling the received signal.
13. A transmitter method comprising:
encoding data as symbols;
applying one of a plurality of possible sequence lag values to a spreading code to create a time-shifted spreading code relative to a reference value, wherein the lag value represents coded data;
combining the time-shifted spreading code and symbols to produce a spread spectrum signal that combines the symbols with the code at the applied lag value, where a spacing between lag values is less than 1 divided by a bandwidth of the spread spectrum signal; and
transmitting the combined signal to provide a signal including data represented by encoded symbols and data represented by the lag value.
14. The method of claim 13 , wherein the data symbols represent one of phase shift keyed data and quadrature amplitude modulated data.
15. The method of claim 14 , wherein the data symbol represent a number of bits n, and the lag value encodes a number of bits m, such that each lagged symbol represents n +m bits.
16. The method of claim 15 , wherein the transmitting is performed by a mobile device.
17. The method of claim 13 , wherein the transmitting is performed by a base station.
18. The method of claim 13 , wherein, the applying includes applying one of four lag values.
19. The method of claim 18 , wherein the lag value encodes at least two bits per symbol.