WALE & wideband traffic, most likely RapidM proprietary WB-LDL & WB-RDL waveforms

My friend ANgazu and I are almost done going through nearly 30GB of recordings of broadband transmissions that took place in the portfion of 6.9-7 MHz band during October and November, monitoring was besides possible thanks to SM5TAH/Mats who made available its broadband SDR receiver (Airspy HF+, SDR-IQ). As already discussed in erstwhile posts, we think they were trial transmissions aimed at fixing the performance of modified waveforms with respect to the comparative mention standards (118-110D App.D and 188-141D App.G) especially with respect to the fourth-generation ALE. any of these tests were most likely conducted by Harris, as they more specifically afraid the 3GWB ALE (WBALE) and WHARQ broadband waveforms, although we did not find news or information about.

We besides found 188-141D 4G-ALE (WALE) waveforms that usage a modified/improved first preamble that are most likely traceable to trials by RapidM [1]: besides in this case no direct confirmation another than a presentation given at an HFIA Industries gathering on March 2020. The traffic waveforms following those WALE handshakes are totally "new" (or at least never meet before for me) and defintely not 188-110D App.G compliant. Obviously, since these waveforms are utilized in the WALE trials they are developed, along with the related modem, by the same manufacturer.

bandwidths. We could detect waveforms spreading from 3 Khz to 48 Khz, their allocation within a wideband channel is negotiated during the WALE link setup phase and follows the specifications required by 188-141D (1). The examples in Figures 1a,1b show the wideband channel allocations of any of the monitored waveforms.

Fig. 1a

Fig. 1b

paradigma. The first consideration to make is that the traffic segments look like a ARQ system, but after the last data transfers the responder' ACKs are missing (Figure 2), possibly they are forward/reverse traffic links or the latest ACK is not required/mandatory by the system. besides announcement that, although the wideband channel has been negotiated, the called station uses a different channel for its sendings, this channel is anyway "within" the 1 of the caller. most likely the responder announces it's own 16-bit sub-channel vector in the WALE confirm PDU.

Fig. 2

modulation. All the waveforms utilize eight-ary phase-shift keying (PSK8) constellation, the symbol mapping is the same utilized in 188-110D (Figure 3). As usual, the modulation rate varies according to the bandwidth.

Fig. 3

waveforms. According the utilized framing (ACF of 25.4 and 120 ms), we identified 2 families of waveforms, each consisting of 9 waveforms differing in bandwidth (3-24 and 48 KHz) and modulation rate (2400-19200 and 38400 Baud): unfortunately, the waveforms of the intermediate badwidths 30,36,42,.. KHz have not been found and therefore (hopefully at the moment) are missing.

25.4 ms framing. The frame structure consists of a "Tx Frame" consisting of a synchronization preamble followed by N "data packets" of fixed duration of 25.41 ms (except the 7200 Bd waveform), where N depends on the chosen waveform. Each data packet consists of alternating data (Unknown) and probe (Known) symbols. The frame structure is shown in Figure 4.

Fig. 4

A transmission consists of 1 or 3 Tx Frames separated by a "dead time" or a "guard interval", only the the first Tx Frame is preceeded by a TLC series (Figure 5).

Fig. 5

Main features of this household waveforms (so far seen) are sumarized in Table I.

Table I

The 25.4 ms periodicity of the data packets and their number N within each Tx frame can be seen in Figures 6 and 7 respectively.

Fig. 6

Fig. 7

However, I'm facing an unusual problem about the dimension of the (known symbols) probes; let's see for example the 2400 Bd data packet: as from Figure 8, the 9.996 ms probe makes a dimension of 24 PSK8 symbols but after its demodulation the bitstream shows 75-bit lenght patterns, i.e. 25 PSK8 symbols!

Fig. 8

The discrepancy is most likely due to the SA PSK demodulator. Indeed, it must be noticed that either the preamble sequences and the probes are characterized by the deficiency of the sub-carrier in their harmonic spectrum (Figure 9): this feature has already been found in the modified/enhanced WALE preambles discussed in the erstwhile post.

Fig. 9

120 ms framing. The frame structure consists of a TLC & synchronization preamble followed by fixed dimension 120 ms data packets, each data packet consisting of alternating data (Unknown) and probe (Known) symbols. The most interesting aspect is that the first TLC & preamble sections consist of the same Tx Frame of the correspondent 25.4 ms household waveforms (Figure 10): it could be said that both waveforms (25.4 ms and 120 ms) present the same "front-end" to the receiving modem.

Fig. 10

The complete frame structure is shown in Figure 11.

Fig. 11

Figure 12 shows the 120ms period of any waveforms, unfortunately not all the samples have a good quality.

Fig. 12

The main features of this household waveforms (so far seen) are sumarized in Table II. It's interesting to see what came up erstwhile comparing the values of Table II with the correspondent values of the Waveform Number 7 of 188-110D App.D: as you see, most of the framings (ie the number of the PSK8 symbols) match the ones of the correspondent 188-110D waveforms.

Table II

Although in any cases the durations are the same, the mini-probes series is different so there is no compatibilty between the observed waveforms and 188-110D. Figure 13 shows 2 frames of the 12 KHz 9600 Bd waveforms.

Fig. 13

RapidM Since these traffic waveforms are utilized together with the modified WALE waveforms seen in the erstwhile post, it is logical to presume that they besides are developed by the same manufacturer, i.e. - in our opinion - by fast Mobile (RapidM) [1]. A affirmative feedback comes from reading the method documentation of their RM10 modem [2] "In addition, the RapidM proprietary wideband HF packet data modems known as WB-RDL is offered in the RM10 as a software option. The WB-RDL waveforms and protocols are integrated with the WALE/4G ALE controller for link setup and dynamic forward/reverse traffic channel bandwidth negotiation. The combination of WALE/4G ALE with the WB-RDL supply data communication in challenged channel (e.g., SNR < 0 dB, high-latitude, advanced interference) conditions". More precisely, the documentation talks about the future WB-LDL & WB-RDL packet waveforms utilized with WALE: the acronyms could mean WideBand Low latency DataLink and WideBand Robust DataLink, that is the 2 families we have singled out (25.4 & 120 ms waveforms).

Fig. 12

We have rather quite a few assumptions and conjectures about it but at the minute we like to wait for "news" from RapidM on their authoritative website (new RM12 wideband modem?) and monitor the HF bands for (hopefully) specified fresh trials.

https://disk.yandex.com/d/CrBy3GAUjyaLdA

(1) the wideband channels are described in WALE PDUs utilizing 16-bit “sub-channel” vectors, each bit component of a sub-channel vector refers to a sub-channel within an assigned wideband channel and describes 1.5 kHz sub-channels, scope of 24 kHz, or 3 KHz sub-channels, scope up to 48 KHz

[1] https://i56578-swl.blogspot.com/2022/11/an-enhanced-design-for-deep-fast-wale.html
[2] https://www.rapidm.com/product/rm10-wideband-software-defined-modem/