PCF5083HSLASHF2 datasheet(11/136 Pages) PHILIPS

11 / 136 page

1996 Oct 29

Philips Semiconductors

Objective speciﬁcation

GSM signal processing IC

PCF5083

OVERVIEW OF THE GSM CHIP SET

7.1

General

The chip set’s high-level architectural modularity ensures

that it can be easily adapted to meet various market

requirements in terms of hardware and software. Figure 4

is a simplified block diagram of a GSM terminal using the

Philips Semiconductors chip set.

The receiver converts the antenna input signal from

890 to 915 MHz down into a complex baseband signal

consisting of an in-phase (I) and a quadrature

component (Q). In order to deal with the high dynamic

range from

−104 to −10 dBm, the receiver provides an

AGC input controlled by the layer 1 software in the System

Controller. The complex baseband signal is connected to

the input of the PCF5072 baseband interface IC. This IC

samples the I and Q components at the GSM bit clock

(270 kHz) with an accuracy of approximately 2

× 13 bits.

The equalizer is responsible for the following tasks:

• Channel impulse response estimation and bit

synchronization by means of the training sequence

• Adaptive channel equalization with a modified Maximum

Likelihood Sequence Estimation (MLSE) approach that

produces a bit-by-bit soft decision information (Channel

Measurement Information (CMI)

• Channel impulse response adaption and frequency

offset estimation.

After decryption the channel decoder performs

convolutional and block decoding. Depending on the

logical channel in use, there are decoding schemes for

TCH/F (FACCH/F), SACCH and SDCCH.

The speech decoder synthesises the audio signal from the

received bit stream. Updating of comfort noise parameters

occurs each time a valid Silence Descriptor (SID) is

received. Comfort noise is inserted during periods of

speech pauses. Substitution and muting of lost or bad

frames is implemented.

The full rate speech encoder collects speech samples of

13-bit uniform PCM format (104 kbits/s) and compresses

them to 13 kbits/s according to the linear predictive coding,

long term prediction, Regular Pulse Excitation (RPE-LTP).

Discontinuous Transmission (DTX) is available (voice

activity detection, background acoustic noise).

To protect the data from transmission errors, block and

convolutional coders form the channel encoder. The

encoding modules relates to the logical channels (e.g.

RACH, TCH/F (FACCH/F), SDCCH/SACCH).

After encryption the burst builder generates either Normal

Bursts (NB) or Access Bursts (AB). The bit-stream is then

modulated with a GMSK modulator (Gaussian Minimum

Shift Keying) and upconverted in a quadrature mixer to

890 to 915 MHz.

The on-chip GSM timer generates all power-down and

control signals for the receiver, the transmitter, the

P90CL301 System Controller and the PCF5072 baseband

interface IC.

The System Controller (P90CL301) services all HW

interfaces and performs the signalling software contained

in the GSM layer stack (with L1, L2, L3, O&M, UAP,

SIMAP etc).

The voiceband ADCs and DACs of the PCF5072 perform

the conversion between the analog audio signals and the

digital domain.

7.2

The role of the PCF5083

The PCF5083 is a dedicated VLSI circuit offering

baseband signal processing tasks for the Pan European

Global System for Mobile telecommunication (GSM). The

PCF5083 can be applied in GSM mobile stations or

hand-helds. The embedded DSP core is optimized for

GSM baseband functions and contains an on-chip

program ROM featuring the following tasks:

• Full rate speech coding/decoding including VAD/DTX

(

“GSM 06 series” )

• Encryption/decryption according to both A5/1 and A5/2

algorithms (

“GSM Rec. 3.20, 3.21” )

• Burst building supporting access burst and normal burst

(

“GSM Rec. 5.02”)

• Frequency Correction Burst (FCB) detection and

evaluation

• Synchronization burst (SCH) detection

• BCCH monitoring of neighbouring cells

• Channel coding/decoding and

interleaving/de-interleaving (

“GSM Rec. 5.03”) for:

– Broadcast Channels (BCH): SCH, BCCH

– Common Control Channels (CCCH): PCH, RACH,

AGCH

– Dedicated Control Channels (DCH): SDCCH,

SACCH

– Traffic Channels (TCH): TCH/FS, TCH/F2.4,

TCH/F4.8, TCH/F9.6, TCH/H4.8 and TCH/H2.4

– Associated Control Channels (ACCH): FACCH and

SACCH

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