
VITA-49 Radio Transport Protocol
IQ
measured
= as shown in the formula above. The IQ
measured
formula, however, is a
simplified example as it doesn't include any corrections, such as IQ imbalance,
DC offset or windowing
I
fft
= the real component of the FFT (Fast Fourier Transform) computation applied
on the VRT I data, which is normalized by dividing each Q by 2
bit_size – 1
Q
fft
= the imaginary component of the FFT computation applied on the VRT Q
data (when used), which is normalized by dividing each Q by 2
bit_size – 1
The Reference Level field shall use the 32-bit format shown in Table 19 with the upper 16
bits reserved and shall be set to zero. The Reference Level field value shall be
expressed in signed two’s-complement format in the lower 16 bits of this field. This field
has an integer and a fractional part, with the radix point to the right of bit 7.
Table 19:
Reference Level 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
Reserved
Integer Ref. Level
Frac. Ref. Level
The value of the Reference Level field has a range of nearly ±256dBm with a resolution
of 1/128dBm (0.0078125dBm).
For examples, a Reference Level field value of:
•
0x0080 represents a reference level of +1dBm,
•
0xFF80 represents -1dBm,
•
0x0001 repr0.0078125dBm, and
•
0xFFFF represents -0.0078125dBm.
RF Frequency Offset
The RF Frequency Offset indicator specifies the amount of frequency in Hz the received
data has been shifted.
The RF Frequency Offset field shall use the 64-bit, two’s-complement format as shown in
. This field has an integer and a fractional part, with the radix point to the right of
bit 20 in the second 32-bit word. This gives the RF Reference Frequency a range of
±8.79THz with a resolution of 0.95μHz.
Table 20:
RF Frequency Offset Word 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
Integer RF Reference Value (43..12), Hz
Integer RF Ref. Value (11..0), Hz
Fractional RF Reference Value(19..0)
Extension Context Packet Class
This Packet Class conveys metadata concerning IF Data Packet Class that cannot be
communicated in the IF Context Packet Class. See
context packet class.
34
ThinkRF WSA5000 Wireless Signal Analyzer Programmer's Guide