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; characterized in that the channel estimate generation component comprises a validation component arranged to: - receive unvalidated channel estimate information for the received signal; - 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; - select at least one channel estimate tap for which channel estimate validation information is to be generated based on the unvalidated channel estimate information; and - perform cross-correlation between at least a part of the validation sequence within the packet and at least a part of the generated validation pattern to generate channel estimate validation information for the at least one selected channel estimate tap, wherein, the validation component is either: (a) further arranged to determine whether the unvalidated channel estimate information for the at least one selected channel estimate tap is valid based at least partly on the generated channel estimate validation information for the at least one selected channel estimate tap, and to output to the timestamping module an indication of whether the generated channel estimate information for the at least one selected channel estimate tap is valid based on said determination; or (b) is further arranged to replace unvalidated channel estimate information for the at least one selected channel estimate tap with validated channel estimate tap values for the at least one selected tap and to output validated channel estimate information to the timestamping module comprising the validated channel estimate tap values for the at least one selected tap. 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; characterized in that the channel estimate generation component comprises a validation component arranged to: - receive unvalidated channel estimate information for the received signal; - 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; - select at least one channel estimate tap for which channel estimate validation information is to be generated based on the unvalidated channel estimate information; and - perform cross-correlation between at least a part of the validation sequence within the packet and at least a part of the generated validation pattern to generate channel estimate validation information for the at least one selected channel estimate tap, - receive unvalidated channel estimate information for the received signal; - 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; - select at least one channel estimate tap for which channel estimate validation information is to be generated based on the unvalidated channel estimate information; and - perform cross-correlation between at least a part of the validation sequence within the packet and at least a part of the generated validation pattern to generate channel estimate validation information for the at least one selected channel estimate tap, (a) further arranged to determine whether the unvalidated channel estimate information for the at least one selected channel estimate tap is valid based at least partly on the generated channel estimate validation information for the at least one selected channel estimate tap, and to output to the timestamping module an indication of whether the generated channel estimate information for the at least one selected channel estimate tap is valid based on said determination; or (b) is further arranged to replace unvalidated channel estimate information for the at least one selected channel estimate tap with validated channel estimate tap values for the at least one selected tap and to output validated channel estimate information to the timestamping module comprising the validated channel estimate tap values for the at least one selected tap.