Deep WALE (4G-ALE) Async call utilizing PSK2

(for background http://i56578-swl.blogspot.com/search/label/4G-ALE)

Very interesting example of an asynchronous three-way Deep WALE handshake (4G-ALE, MS-141D App.G)(1) sent to me by my friend ANgazu; recordings credits to EA6AMM Gaspar. Although the common protocol exchange for 4G-ALE link establishment is the two-way handshake, it may occurs a traffic channel negotiation which requires a three-way handshake.
In figure 1 you can see the call which is formed by the "scanning call" (also known as "capture probe") + the actual Request, the call is then followed by the called & caller Confirm bursts. The scanning call is designed to capture asynchronously scanning receiver(s) so that they will halt scanning to receive the final Request. However, conversely of 2G and 3G ALE, the scanning call condition of the async WALE call is unaddressed: that is, the addresses of the stations are not sent during the capture probe and receivers are held unitl the reception of the ending Request.

Fig. 1 - Deep WALE async call

The scanning call consists of repeated blocks (known symbols) with an ACF value of 80 ms (Figure 2) that licence fast detection of the call, and so very short scanning dwell times. As in 2G and 3G ALE, the duration of the WALE scanning call dependes on the number of channels in the scan set and is as follows:

Tcapture ≥ Dmin(N+2)

where Dmin is the asynchronous-mode minimum dwell time (200 ms as default setting) and N is the number of channels. Since the capture probe lasts about 3500 ms, assuming the default setting is used, the number of channels is 15.

Fig. 2 - ACF value of scanning call (capture probe) portion

But the most crucial thing - see Figure 3 - is that the Deep WALE waveforms (call and confirms) usage PSK2 modulation(!) alternatively than PSK8 as required by MS-141B App.G standard.

Fig. 3

Once demodulated, the capture probe consists of a 192-bit series (originating the 80 ms ACF) which is repeated - in this example - 44 times (blocks):

0x [D1 38 6C BC 22 71 BD 65 B9 21 D6 F2 C6 FD FE 8F 49 D1 D9 FD 36 0D F1 80]
0x [2E C7 93 43 DD 8E 42 9A 46 DE 29 0D 39 02 01 70 B6 2E 26 02 C9 F2 0E 7F] other polarity

Fig. 4 - 192-bit sequences forming the scanning call blocks

These waveforms are not MS-141D App.G compliant at all; in fact, according to the standard:
- the modulation utilized shall be PSK8, while in the recorded samples is utilized PSK2;
- the scanning call blocks shall consist of 96 symbols, while here the blocks consist of 192 symbols, precisely double (obviously, the respective ACF values ​​are besides double);
- the duration of the Deep WALE Request (~ 622 ms) does not match the expected 1520 ms value (240 ms preamble + 1280 data ms).

Perhaps it is any circumstantial implementation of a fresh and more robust Deep WALE call, given that PSK2 is more robust than PSK8 especially in terms of mistake performance under the same sound conditions (2).

https://disk.yandex.com/d/GBKjZzt4q9509Q (recordings credits to EA6AMM Gaspar)

(1) The multiplicity of abbreviations and acronyms sometimes doesn't help, below what I used:
WB ALE (or WBALE), Harris implementation of 3GWB
WALE (or 4G ALE), wideband ALE as for MIL 188-141D App.G, 4th generation ALE
note that WB ALE is not synonymous with WALE since the second has its own PDUs and waveforms.

(2) In PSK2, the phase shift between the 2 possible symbols is 180°, which makes it very easy for the receiver to separate between them even in the presence of noise. In PSK8, the phase difference between adjacent symbols is only 45°, so even a tiny amount of sound can origin symbol errors.