Only Netsight OneView is able to collect history client data and even then I don't use that to troubleshoot voice client issues.
If you check the report > clients by AP you'd see the RSSI from the AP point of view.
Most of the time the voice client point of view is more important.
In case we are talking about a Ascom i62 just connect via https to the phone IP and go to > troubleshoot > log > syslog.
Here you'd see whether roaming is working and if you've enough coverage.
i.e. here a roaming event of the phone from AP X with signal -74 to AP Y with signal -56, the APs in the {...} show other APs that the client could "see" but have a lower signal = lower priority and are not used to roam to....
2015-08-25 13:47:18.076,750 - From AP: d8:84:66:0e:3f:10 - RSSI: -74 - Ch: 56 - To AP: d8:84:66:0e:37:c0 - RSSI: -54 - Ch: 44 {AP: d8:84:66:0e:2c:d0 - RSSI: 72 - Ch: 60} {AP: d8:84:66:0e:3e:90 - RSSI: 62 - Ch: 36} {AP: d8:84:66:36:f4:50 - RSSI: 64 - Ch: 36} {AP: d8:84:66:02:dd:90 - RSSI: 72 - Ch: 48} {AP: d8:84:66:0e:39:40 - RSSI: 74 - Ch: 108}
You'd recognize bad coverage if the "from AP" signal is very high as normaly the phone should roam at 70dBm, so if you'd see 75+ you know that the phone hasn't found a better AP/signal before the new AP was in reach.
If you setup a call it looks like this on the phone....
2015-08-25 14:04:22.126,625 - Incoming call
2015-08-25 14:04:22.212,500 - Setting WLAN power mode: active
2015-08-25 14:04:23.546,375 - Voice Tx IP DSCP: 0x2e UP: 6
2015-08-25 14:04:23.557,625 - Voice Rx IP DSCP: 0x0c UP: 0
2015-08-25 14:04:24.009,375 - Call start - AP: d8:84:66:0e:3e:90 - RSSI: -40 - Codec: G711A
2015-08-25 14:04:25.686,250 - From AP: d8:84:66:0e:3e:90 - RSSI: -44 - Ch: 36 - To AP: d8:84:66:36:f4:50 - RSSI: -35 - Ch: 36 {AP: d8:84:66:02:dd:90 - RSSI: 48 - Ch: 48} {AP: d8:84:66:0e:39:40 - RSSI: 64 - Ch: 108} {AP: d8:84:66:0e:37:c0 - RSSI: 70 - Ch: 44}
2015-08-25 14:04:38.926,000 - Call disconnected by user
2015-08-25 14:04:38.004,500 - Setting WLAN power mode: long doze
2015-08-25 14:04:39.014,250 - AP: d8:84:66:36:f4:50 - RSSI: -48 - Rx packet loss: 0% - Rx packet: 745 - Tx packet: 751 - Rx min pkt interval: 0 ms - Rx max pkt interval: 170 ms - Rx average jitter: 7 samples - Call ended
Here the last message is the interesting one, if you see a big difference in rx and tx packets you've one way audio, a lot of discarded packets in one direction.
You'd also do a remote AP wireshark trace...
https://gtacknowledge.extremenetworks.com/articles/How_To/Using-Real-Capture-to-capture-wireless-tra...
Another thing is to forward the station events to a syslog server so you'd keep older roaming events, controller GUI > controller > logs > Forward station session events as traps
-Ron