PCF5083HSLASH5V2SLASHF3 datasheet(80/136 Pages) PHILIPS

80 / 136 page

1996 Oct 29

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.

len_obser_int

[threshold]

[hi_threshold]

[n_timeslots]

[n_samples]

[n_obser_int]

−

MP_audio_sync

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

µs) 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

µs units, e.g. delta_rx_delay = 1 increases

the delay in the RX path by 125

µs. Valid range for delta_rx_delay and

delta_tx_delay is

−10 to +10. Note that MP_iom2_enable must be called

beforehand.

tch_frame_no

slip

delta_rx_delay

delta_tx_delay

−

DESCRIPTION

PARAMETERS

RETURN

VALUES

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