SimTX API/Packets/IqStreamDescriptor

IqStreamDescriptor

Frame	ServerFrame, field 11
Member	iq_descriptor
Direction	Server → client
Session	Receiver
Roles	ROLE_RECEIVER.
Permission	None
Answered by
Answers	ReceiverStart
Defined in	session.proto

IqStreamDescriptor states the parameters of the IQ stream a receiver is about to get. The server sends it once, after SessionStatus BOUND and before the first IqBlock. Its values are authoritative and may differ from the request.

Definition

message IqStreamDescriptor {
  int32 sample_rate = 1;           // complex samples per second
  double center_frequency_hz = 2;
  int32 chunk_samples = 3;         // complex samples per IqBlock
  SampleFormat sample_format = 4;
  bool timestamped = 5;
}

Fields

#	Field	Type	Description
1	sample_rate	int32	Negotiated sample rate, complex samples per second.
2	center_frequency_hz	double	Centre frequency in Hz.
3	chunk_samples	int32	Complex samples in every following IqBlock.
4	sample_format	SampleFormat	Format of IqBlock.samples.
5	timestamped	bool	True when every IqBlock carries a first-sample timestamp.

Usage

• Size buffers from chunk_samples and sample_format: each IqBlock carries exactly chunk_samples × 2 × bytesPerComponent sample bytes, where bytesPerComponent is 2 for INT16 and 1 for INT8.
• No second descriptor is sent after a ReceiverRetune. Track the frequency from the retune confirmations.

Example

Complete frames, including the varint length prefix, from the protocol's golden test vectors (protocol/simtx/v25/testdata/frames.json).

iq_descriptor_timestamped (server to client, 21 bytes):

14                            frame length 20
5A 12                         iq_descriptor (IqStreamDescriptor), 18 bytes
  08 80 F7 02                 sample_rate = 48000
  11 00 00 00 00 34 FC 5A 41  center_frequency_hz = 7074000.0
  18 80 20                    chunk_samples = 4096
  28 01                       timestamped = true

See also

• Negotiation