Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary System description
Page 40 of 75
The sample-based voiceband processing is done on an interrupt level and its main task is to transfer the
voiceband samples from either analog audio front-end TX path or I2Sx RX path to the Voiceband Sample Buffer
and from the Voiceband Sample Buffer to the analog audio front-end RX path and/or I2Sx TX path.
First the TX path (uplink) is processed: the input sample is scaled, filtered and before it is copied into the
voiceband input buffer for the speech frame based processing and it is used to generate the sidetone for the RX
path processing. Furthermore the signal is mixed with the output of the circular buffer.
The frame-based voiceband processing consists of these operating parts: voice memo; echo cancellation and
auto gain control for hands free mode. The uplink path starts with output samples from voiceband buffer and
stops with speech encoding. The downlink path starts with output samples from speech decoder and stops with
output samples to voiceband buffer.
The circular buffer is a 3000 word buffer to store and mix the voiceband samples from external sources
(synthesizer data). The buffer has a circular structure, so that when the write pointer reaches the end of the
buffer, it is wrapped to the begin address of the buffer.
Two different sample-based sample rate converters are used: an interpolator, required to convert the sample-
based voiceband processing sampling rate of 8 kHz to the analog audio front-end output rate of 47.6 kHz; a
decimator, required to convert the circular buffer sampling rate of 47.6 kHz to the I2Sx TX or the uplink path
sample rate of 8 kHz.
1.9.3.1 Audio codecs
The following speech codecs are supported by firmware on the DSP:
GSM Half Rate (TCH/HS)
GSM Full Rate (TCH/FS)
GSM Enhanced Full Rate (TCH/EFR)
3GPP Adaptive Multi Rate (AMR) (TCH/AFS+TCH/AHS)
1.9.3.2 Echo cancelation and noise reduction
LEON-G100/G200 support algorithms for echo cancellation, noise suppression and automatic gain control.
Algorithms are configurable with AT commands (refer to the u-blox AT Commands Manual [2]).
1.9.3.3 Digital filters and gains
Audio parameters such as digital filters, digital gain, Side-tone gain (feedback from uplink to downlink path) and
analog gain are available for uplink and downlink audio paths. These parameters can be modified by dedicated
AT commands and be saved in 2 customer profiles in the non-volatile memory of the module (refer to the u-blox
AT Commands Manual [2]).
1.9.3.4 Ringer mode
LEON-G100/G200 modules support polyphonic ring tones. The ringer tones are generated by a built-in generator
on the chipset and then amplified by the internal amplifier.
The synthesizer output is only mono and cannot be mixed with TCH voice path (the two are mutually exclusive).
To perform in-band alerting during TCH with voice path open, only Tone Generator can be used.
Polyphonic standard format supported.