Hi Dialog,
We've done same GAP_GEN_DISCOVERY scan tests. When set the transmitted ADV packet interval great than 111 us , almost 100% ADV packets can be scanned, however, if set the packet interval to 111 us, only about 60% packets can be scanned.
Is there any way to support more shorter interval such as 50 us?
谢谢你,彼得
Device:
Hi Peter Luo,
According to the Bluetooth LE core specifications, the advertising interval (advInterval) shall be an integer multiple of 0.625ms in the range of 20ms to 10485s. Can you please share the advertising interval configuration (user_adv_conf structure)?
Thanks, PM_Dialog
Hi Dialog,
Yes, according to the Bluetooth LE core specifications, you are right, but when two or more advertisers send advertising packets randomly, something will be changed.
For example,
当只有一个广告商发送每秒31个字节有效载荷的广告数据包时，传输的空气时间为47 * 8 = 376，最小和最大数据包间隔约为1,000,000-376 = 999,624次，这是所有扫描仪的足够的时间正确接收所有广告数据包。
When two advertisers both send an advertising packet with 31 bytes payload per second, the minimal packet interval will change to a range from 0 us to (1,000,000-376-376)/2= 499,624 us when luckily no overlying happened.
When three or more (such as 100) advertisers send advertising packets randomly, the situation becomes more complex.
Obviously, the scanner with lower packet interval (such 50 us) support will get good performance, the scanner with only higher packet interval (such as 1000 us) support will get poor performance.
In order to simulate two or more advertisers, we’ve made a DIY device, its RF radio provides a parameter to change packet interval, it can be set very short value.
We want to make an ideal cheap scanner to scan all packets without loss, and try to recover the packets with CRC error. Although some expensive SDR devices can do this very well, it is out of our consideration.
DA14XXX对我们来说是一个很好的选择，目前的112美国最小的数据包间隔支持也是可接受的，但我们仍希望RF接收器可以支持较短的数据包间隔。
谢谢你,彼得
Hi Peter Luo,
I am reading again your initial post and you had mentioned that the packet interval to 111 us. What do you mean the packet interval? Do you mean the interval between the Tx of each advertising channel? Or do you mean the connection interval? How did you calculate the min and the max interval?
Thanks, PM_Dialog
Hi Dialog,
The packet interval discussed in here is a time between two continuous packets in air in a same channel (such as 37).
When our DIY device, not a standard BLE, just a simulator for a lot of BLEs in a same place at same time, transmits adv packets with a 112us interval on channel 37, the DA14585 scanner can receive almost 100% packets from DIY device. If change the interval from 112us to 111us, just 1 us decreased, the performance of DA14585 scanner drops quickly, only 60% packets can be received. Some other similar BLE under same condition, can receive almost 100% packets from DIY device even the interval was set to a value under 100us.
About min and max interval, please kindly see the attachment.
Because of some unique advantages, we still want to use DA14xxx.
谢谢你,彼得
Hi Peter,
Can you please indicate how you changed the packet interval that you have mentioned? Are you using the device under DTM (Direct test Mode) and you are testing the Continues Tx in Channel #37 ?
Thanks, PM_Dialog
Hi Dialog,
Yes, we are testing the Continues Tx in Channel #37 with a user defined packet interval parameter through our self-software, the transmitted packet is standard advertising packet with 31 bytes payload.
The low-level hardware of our DIY device provides a register for definition of time interval between two consecutive packets, it includes the time needed to turn on and turn off the radio, and the time needed to keep the radio in idle status.
In order to emulate the worst situation may happened in reality, we not obey the Bluetooth specification strictly, try to set the packet interval as short as possible.
谢谢你,彼得