1996 Oct 29
80
Philips Semiconductors
Objective specification
GSM signal processing IC
PCF5083
FB_search_fcb_init
Initialization of FB_search_fcb. This routine has to be called before a new
FB search is started. The following parameters are recommended:
The parameter len_obser_int indicates how many observation windows
belong to an observation interval. The parameter len_obser_int must be set
to 11 for a 26-frames and to 15 (or 7) for 51-frames multiframe structure. If
the parameter len_obser_int is omitted or set to zero, all successive calls of
FB_search_fcb perform only fast FB detection.
The FB search algorithm includes a match filter for FB detection. The
output of this matched filter is compared with the parameter threshold in
order to decide whether an FB has been found or not. If the parameter
threshold is omitted (or set to zero respectively) the recommended default
value of 400 is used.
The parameter hi_threshold is used to perform a fast FB detection under
good channel conditions. If the matched filter output exceeds hi_threshold,
the FB search is terminated immediately. If hi_threshold is not specified, a
default value of 667 is used.
The parameter n_samples indicates the length of a search window in bits,
i.e. the number of IQ samples. If n_samples is not specified, a default value
of 1404 bits is used, corresponding to 9 timeslots.
The parameter n_obser_int indicates the number of observation intervals to
be used. If the n_obser_int is not specified, a default value of 1 is used.
MP_audio_sync
68
len_obser_int
[threshold]
[hi_threshold]
[n_timeslots]
[n_samples]
[n_obser_int]
To start speech procedures in a regular way in full rate traffic channel mode
the speech frame timing has to be locked to the TDMA frame timing. Each
time a traffic channel is established or switched over (e.g. handover), a new
synchronization has to be performed.
MP_AUDIO_SYNC has to be started before the receive time slot. The
procedure synchronises speech and TDMA frame timing by waiting for the
first I and Q pair coming from the BBD and then immediately sets the
pointers of audio input and output FIFOs.
The parameter slip is normally set to zero indicating that an audio
synchronization should be performed. If slip is not equal to zero (valid
range 1 to 5), it is checked whether the audio frame timing is still locked to
the TDMA frame timing. If the deviation exceeds slip audio samples
(125
μ
s) a resynchronization is performed.
The parameter tch_frame_no has to be set to (
fn mod 26
) where fn is the
TDMA frame number of the first TDMA frame of the TCH block.
The parameters delta_rx_delay and delta_tx_delay are normally set to
zero. They may be used to increase or decrease the speech delay in
receive and transmit path in 125
μ
s units, e.g. delta_rx_delay = 1 increases
the delay in the RX path by 125
μ
s. Valid range for delta_rx_delay and
delta_tx_delay is
10 to +10. Note that MP_iom2_enable must be called
beforehand.
41
tch_frame_no
slip
delta_rx_delay
delta_tx_delay
DESCRIPTION
ID
PARAMETERS
RETURN
VALUES