AD20msp410
Softwar e
T he analog voice signal is sampled at 8 kHz, producing 13-bit
linear values corresponding to the magnitude of the input. T he
resulting data is passed to the ASP through a dedicated serial
port.
T he required Layer 1 software is supplied with the chipset. In
addition, an object code license for Layers 2 and 3 of the
protocol stack is available. T his exact package of Layers 1,2,3 of
software, coupled with the AD20msp410 chipset, is today in
phones that have passed European GSM Final T ype Approval.
Speech Encoding (ASP )
T he ASP receives the voice data stream from the BBC and
encodes the data from 104 kb/s to 13 kb/s. T he algorithm used
is Regular Pulse Excitation, with Long T erm Prediction (RPE-
LT P) as specified in the 06-series of GSM recommendations.
T he algorithm is tested and proven to be bit-exact against the
GSM test vectors including all VAD/DT X functions. After
encoding the data is transferred to the PLP through a parallel
port in discrete blocks of 260 bits at 20 ms intervals.
Ar chitectur e O ver view
A standard GSM Handset can be divided into five functional
areas:
• Analog and Digital Baseband Processing Subsystem
• (Voice to Radio)
• Layer 1 Software (Physical Layer)
• Protocol Stack Software (Layers 2 and 3)
• Radio Subsystem
Channel Coding (P LP )
T he information received from the ASP contains data values
and filter coefficients that have different levels of priority. T hese
are subsequently protected to different levels within the channel
coding. T he encode protection process incorporates block
coding and convolutional encoding. In addition to the normal
speech traffic channels, the channel coding function also
supports data transmission at full rate and half rate. After the
interleave process, if necessary, the data is encrypted using the
required A5/1 or A5/2 encryption algorithm. Data is then
formatted into bursts, with the required timing and training
sequences and sent to the BBC through a dedicated serial port.
• User Interface Software (MMI)
Analog Devices and T he T echnology Partnership (T T P)
provide a cost effective and proven method of attaining the
baseband processing subsystem and protocol stack software.
T his data sheet includes functional descriptions of the baseband
processing subsystem and the Layer 1 software. T he T echnol-
ogy Partnership can provide licenses to software and reference
designs in all the other areas of a GSM hand-portable terminal.
For detailed information about the individual chipset compo-
nents, please refer to the ADSP-2178 (ASP), AD7015 (BBC)
and ADPLP01 (PLP) data sheets for electrical characteristics
and timing information.
GMSK Modulation and D /A Conver sion (BBC)
T he BBC receives data at 270 kb/s. T he on-chip lookup-table
ROM modulates and spectrally shapes the data being sent. A
pair of 10-bit matched differential DACs convert the modulated
data from the digital domain to the analog domain and pass I
and Q data to the transmit section of the radio subsystem.
FUNCTIO NAL D ESCRIP TIO N
Figure 1 is a functional block diagram of the GSM baseband
processing chipset. T he chipset can be viewed as a functional
block that contains a number of discrete functional units. T he
electrical and functional interfaces to the rest of the system are
briefly described at the end of this section and described in
detail in the individual data sheets for each component.
D O WNLINK
T he downlink baseband processing functions include the
following operations:
Analog-to-D igital Conver sion (BBC)
T he receiver I and Q signals are sampled by a pair of ADCs at
270 kHz. T he resulting digital words are transferred to the ASP
through a dedicated receive path serial link and DMA control.
BBC
ASP
Equalization (ASP )
BASE-
T he equalizer recovers and demodulates the received signal and
establishes local timing and frequency references for the mobile
unit. T he equalization algorithm is a version of the Maximum
Likelihood Sequence Estimation (MLSE) using the Viterbi
algorithm. T wo confidence bits per symbol provide additional
information about the accuracy of each decision to the channel
codec’s convolutional decoder. T he equalizer outputs a
sequence of bits including the confidence bits. T his data is
transferred to the PLP through a dedicated parallel port on the
ASP. At this point, the training sequence and trailing bits,
contained within the burst, are discarded.
VOICE
ADC
SPEECH
ENCODE
CHANNEL
ENCODE
INTER-
LEAVE
ENCRYPT
DECRYPT
BAND
DAC
BASE-
BAND
ADC
VOICE
DAC
SPEECH
SPEECH
DECODE
ENCODE
CHANNEL DEINTER-
DECODE
EQUALIZER
LEAVE
PLP
CONTROL + MMI + I/O
Figure 1. Functional Description
UP LINK
Channel D ecoding (P LP )
T he uplink baseband processing functions include the following
operations:
T he A5/1 or A5/2 decryption algorithm is used, as required, to
recover the data that is ready for the deinterleave process. T he
deinterleave process is an exact inversion of the interleave
process used by the transmit section. Data can pass directly to
this function, without the A5/1 or the A5/2 decryption, con-
trolled by the Layer 1 processing. T he decode function then
performs convolutional decoding and parity decoding. T he
convolutional decoder uses a Viterbi algorithm, with two soft
Analog-to-D igital Voice Conver sion (BBC)
A conventional microphone, connected directly to the BBC,
provides an analog input signal to the ADC. T he voice ADC
function uses a sigma-delta converter to convert and noise shape
the input signal, achieving a Signal-to-Noise Ratio plus T otal
Harmonic Distortion (SNR+T HD) of greater than 62.5 dB.
REV. 0
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