A processing module for a communication receiver device arranged to receive a signal transmitted by a transmitter device; the processor module comprising: a channel estimate generation component arranged to output channel estimate information for the received signal; and a timestamping module arranged to determine a Time-of-Arrival, ToA, measurement for a packet within the received signal based at least partly on the channel estimate information for the received signal generated by the channel estimate generation component; wherein the channel estimate generation component comprises a validation component arranged to: derive a validation pattern for the packet within the received signal for which a ToA measurement is to be determined; identify a section of the packet containing a validation sequence; and perform cross-correlation between at least a part of the received signal of the validation sequence within the packet and at least a part of the validation pattern to generate validated channel estimate information, and characterised in that the validation component is configured to compensate for non-ideal auto-correlation properties of the validation sequence by one or more of: modifying a result of the cross-correlation between at least a part of the validation sequence within the packet and at least a part of the validation pattern; using unvalidated channel estimate information, wherein the unvalidated channel estimate information is generated by the channel estimate generation component using synchronisation symbols within received signal; or modifying the validation pattern and thereby modifying the cross-correlation of the received signal of the validation sequence with the validation pattern in order to generate the validated channel estimate information. a channel estimate generation component arranged to output channel estimate information for the received signal; and a timestamping module arranged to determine a Time-of-Arrival, ToA, measurement for a packet within the received signal based at least partly on the channel estimate information for the received signal generated by the channel estimate generation component; wherein the channel estimate generation component comprises a validation component arranged to: derive a validation pattern for the packet within the received signal for which a ToA measurement is to be determined; identify a section of the packet containing a validation sequence; and perform cross-correlation between at least a part of the received signal of the validation sequence within the packet and at least a part of the validation pattern to generate validated channel estimate information, and characterised in that the validation component is configured to compensate for non-ideal auto-correlation properties of the validation sequence by one or more of: modifying a result of the cross-correlation between at least a part of the validation sequence within the packet and at least a part of the validation pattern; using unvalidated channel estimate information, wherein the unvalidated channel estimate information is generated by the channel estimate generation component using synchronisation symbols within received signal; or modifying the validation pattern and thereby modifying the cross-correlation of the received signal of the validation sequence with the validation pattern in order to generate the validated channel estimate information. derive a validation pattern for the packet within the received signal for which a ToA measurement is to be determined; identify a section of the packet containing a validation sequence; and perform cross-correlation between at least a part of the received signal of the validation sequence within the packet and at least a part of the validation pattern to generate validated channel estimate information, and characterised in that the validation component is configured to compensate for non-ideal auto-correlation properties of the validation sequence by one or more of: modifying a result of the cross-correlation between at least a part of the validation sequence within the packet and at least a part of the validation pattern; using unvalidated channel estimate information, wherein the unvalidated channel estimate information is generated by the channel estimate generation component using synchronisation symbols within received signal; or modifying the validation pattern and thereby modifying the cross-correlation of the received signal of the validation sequence with the validation pattern in order to generate the validated channel estimate information. modifying a result of the cross-correlation between at least a part of the validation sequence within the packet and at least a part of the validation pattern; using unvalidated channel estimate information, wherein the unvalidated channel estimate information is generated by the channel estimate generation component using synchronisation symbols within received signal; or modifying the validation pattern and thereby modifying the cross-correlation of the received signal of the validation sequence with the validation pattern in order to generate the validated channel estimate information.