Using CC85xx in a multiroom audio system with more than 4 receivers

Hi Ali, 

Only real solution to your 'problem' is, like you have figured out, to add more CC85xx masters in the transmitter unit. What you experience with the close range issues is most likely saturation issues (one radio in Tx and the other in Rx). We quite recently introduced what we call timeslot alignment to cope with this issue. This is where masters can be daisy chained to sync up their Tx and Rx periods. Please see the user guide (search for timeslot alignment) or PurePath Wireless configurator under 'Advanced Options'.

From the Configurators help system:

Timeslot alignment

When using multiple PurePath Wireless protocol masters in a base station to increase number of audio channels and/or protocol slaves supported, the difference in crystal frequency will cause the timeslot timings to drift. This causes periodically variable robustness, since at certain points in time one protocol master will perform RX while another performs TX. Even though these protocol masters do not operate at the same channel at that time, it will always have a negative impact on RF performance (ranging from short audio drop-outs to network drop-outs that last for several seconds).

The issue can be prevented by using timeslot alignment, where wire-based synchronization (using one GIO pin per device) ensures that all (non-USB) protocol masters perform TX simultaneously and RX simultaneously. This results in stable performance and allows protocol master antennas to be located closely. Protocol masters without any network connections will randomly, at short interval, listen for other protocol masters to avoid permanent collision (since identical TX timing makes regular listen-before-talk ineffective, and two protocol masters could potentially start with the same set of active RF channels).

One of the protocol masters functions timing master (i.e. outputs the synchronization signal), while the other protocol masters function as timing slaves (i.e. captures the synchronization signal). It does not matter which protocol master is timing master, but it is recommended to enable the timing master before or simultaneously with the timing slaves, since the initial timing adjustment normally causes network drop-out on the timing slaves. If the timing master is disabled, the timing slaves are free-running and the mechanism is ineffective.

To be able to use timeslot alignment, the protocol masters' device configurations must be identical for all settings that affect timeslot timing:

• Device Configuation: Network role, application role and operation.
• Audio Streaming: Streaming format, supported sample rates and latency.
• Radio: Maximum slave count.
• Advanced Options: Fade out when muting, RF data rate, protocol version, timeslot period.

Hi Ali, 

Unless the you have the chance to do any active frequency planning (know the exact interference situation in the 2.4 GHz band) then I will always recommend using all 18 channels for both TX1 and TX2.  Our adaptive frequency hopping protocol is written so that it can detect interference from other PPW networks and this is why you see little to no difference. If you split the band between the two, then you are more vulnerable in the presence of a strong wide band interferer like WiFi. 

Also, for you set-up I would recommend the longest possible latency in the system. This allows for more re-transmissions while keeping the audio drop-out free in heavy interference condition.

I would also recommend testing this set-up in a realistic environment. Signal-to-noise (distance) between WiFi and the different PPW networks will influence the performance.

Regards,
Kjetil