
VITA-49 Radio Transport Protocol
Table 23:
Receiver Context Field Definition and Values
Bit Name
Bit
Position
Context Field
# of Words in
Field
Period of
Validity
I
31
Context Field Change Indicator
0
N/A
IQ
3
IQ Swapped Indicator
0
Persistent
Sc
2
N/A
N/A
N/A
St
1
New Stream Start ID
1
Persistent
Sw
0
New Sweep Start ID
1
Persistent
Context Field Change Indicator
The Context Field Change Indicator is used to indicate when some context value of the
system has changed. One or more of the bits in the indicator field will then be set,
indicating which values have been changed and have their updated values in the context
field(s) that follow. It is possible that a context packet may be sent where the Context
Field Change Indicator is set to 0, indicating that no change has occurred.
IQ Swapped Indicator
The IQ Swapped Indicator is used to indicate whether the two ADC data channels has
been swapped due to the mixing of a high-side or low-side LO injection at a given center
frequency. When the value is 1, the channels are swapped and 0 if not. This swapping
is necessary to maintain the data output format to always be {I,Q} such that the spectral
inversion is not required at the user-end during data processing.
This information, however, matters only when operating in the ZIF mode. The ZIF mode
is a direct conversion receiver architecture that typically creates some artifacts, mainly
due to IQ gain and phase imbalances. The artifacts are compensated by using a specific
correction algorithm, which incorporates both time- and frequency-domain corrections.
Further information on the algorithm and its usage will be provided in a future release.
Contact ThinkRF's Support for more information if necessary.
New Stream Start ID
The New Stream Start ID indicator indicates a new stream capture has started, any
packets following this Context Packet belong to this new stream capture.
The value of the New Stream Start ID field shall use the 32-bit unsigned integer format
shown in
Table 24:
New Stream Start ID Field Format
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
New Stream Start ID
New Sweep Start ID
The New Sweep Start ID indicator indicates a new sweep has started, any packets
following this Context Packet belong to this new sweep.
36
ThinkRF WSA5000 Wireless Signal Analyzer Programmer's Guide