Receiver-based computation of transmitter parameters and state for communications beyond design ranges of a cellular network protocol
A telecommunications receiver is adapted to communicate with mobile devices that operate according to a protocol where the telecommunications receiver operates outside of expected ranges for the protocol but modifies its communications with mobile devices to appear to those mobile devices as being within the expected ranges. To determine what modifications to make to transmissions, the telecommunication receiver processes signals from mobile devices to determine where a communications channel is relative to the expected ranges and uses that information to modify transmissions to mobile devices. The expected ranges might relate to maximum distance between telecommunications receiver and a mobile device, maximum relative velocity, power etc. Determining a relative velocity, and therefore a Doppler shift, can be done by determining a fractional frequency offset, determining an expected subchannel, and determining an integer frequency offset based on the expected subchannel carrier frequency and the measured carrier frequency.
1. In a telecommunications receiver that is adapted to communicate with a mobile device that is adapted to communicate according to a communications protocol, wherein the communications protocol includes constraints as to a relative distance between the telecommunications receiver and the mobile device and relative velocity of the telecommunications receiver to the mobile device, and wherein a deployment of the telecommunications receiver is such that the telecommunications receiver will be further from the mobile device than a maximum distance specified by the communications protocol and will be moving relative to the mobile device at more than a maximum relative velocity specified by the communications protocol, a method of processing received signals received by the telecommunications receiver to handle communications with the mobile device that appear to the mobile device to compliant with the communications protocol, the method comprising:
receiving a transmission from the mobile device according to the communications protocol;
sampling the transmission to derive an array of samples;
determining, at least in part from the array of samples, the relative distance between the telecommunications receiver and the mobile device;
determining, at least in part from the array of samples, the relative velocity of the telecommunications receiver to the mobile device;
generating a response to the transmission, wherein the response is compliant with the communications protocol;
modifying the response to form a modified response, wherein modification is based on a first adjustment corresponding to a first measure of how much the relative distance exceeds the maximum distance and a second adjustment corresponding to a second measure of how much the relative velocity exceeds the maximum relative velocity; and
sending the modified response from the telecommunications receiver to the mobile device such that the modified response, when received by the mobile device, appears to be compliant with the communications protocol.
2. The method of claim 1 , wherein determining the relative velocity comprises determining a Doppler shift indicated in the array of samples.
3. The method of claim 2 , wherein determining the Doppler shift comprises:
determining a nominal carrier frequency;
determining a fractional frequency offset from the array of samples;
generating an array of corrected samples from the array of samples and the fractional frequency offset;
determining an integer frequency offset from the array of corrected samples; and
computing the Doppler shift from the fractional frequency offset, the integer frequency offset, and the nominal carrier frequency.
4. The method of claim 3 , wherein determining the fractional frequency offset comprises:
performing a delayed auto-correlation; and
identifying an angle corresponding to a complex number output of the delayed auto-correlation.
5. The method of claim 4 , wherein generating the array of corrected samples comprises performing a complex multiplication of the array of samples by an output of a numerically controlled oscillator tuned based on the complex number output and a subcarrier spacing.
6. In a telecommunications receiver that is adapted to communicate with mobile devices that are adapted to communicate according to a communications protocol, wherein the communications protocol includes a first constraint as to a first condition and an operating state of the telecommunications receiver is outside the first constraint, a method of processing received signals received by the telecommunications receiver to handle communications with a mobile device that appears to the mobile device to be within the first constraint, the method comprising:
receiving a transmission from the mobile device according to the communications protocol;
determining, at least in part from the transmission, a first state of communications with the mobile device;
computing a relationship between the first constraint and the first state;
generating a response to the transmission, wherein the response is compliant with the communications protocol; and
modifying the response to form a modified response, wherein modification is based on the relationship and is configured to have a received signal at the mobile device of the response appear to be compliant with the communications protocol, at least when sending the response to the mobile device given the first state would appear to be, to the mobile device, outside of the first constraint and inconsistent with the communications protocol.
7. The method of claim 6 , wherein the first constraint is a maximum relative velocity, the first state corresponds to a relative velocity, the relationship is an indication of whether the relative velocity exceeds the maximum relative velocity, and the modification to form the modified response is a frequency shift countering an estimated Doppler shift that the relative velocity will impose on the modified response to receiving that the mobile device.
8. The method of claim 7 , further comprising determining the estimated Doppler shift by:
determining a nominal carrier frequency;
determining a fractional frequency offset from an array of samples that sample the transmission from the mobile device;
generating an array of corrected samples from the array of samples and the fractional frequency offset;
determining an integer frequency offset from the array of corrected samples; and
estimating the estimated Doppler shift from the fractional frequency offset, the integer frequency offset, and the nominal carrier frequency.
9. The method of claim 8 , wherein determining the fractional frequency offset comprises:
performing a delayed auto-correlation; and
identifying an angle corresponding to a complex number output of the delayed auto-correlation.
10. The method of claim 9 , wherein the modified response is generated from an array of corrected samples derived from the array of samples by performing a complex multiplication of the array of samples by an output of a numerically controlled oscillator tuned based on the complex number output and a subcarrier spacing.