Communications and Network, 2013, 5, 286-291
http://dx.doi.org/10.4236/cn.2013.53B2053 Published Online September 2013 (http://www.scirp.org/journal/cn)
Research on Channel Codec of DCR System Based on
CMX7141
Yufeng Li1,2, Jun Yang1, Qing yan g Guan1
1College of Electronic and Information Engineering, Shenyang aerospace university, Shenyang, China
2National Mobile Communications Research Laboratory, Southeast University, Nanjing, China
Received July, 2013
ABSTRACT
This article introduces a digital pr ivate network of mobile communication dedicated chipset CMX7 141 that used for the
4FSK modulation and demodulation in DCR system, and introduces the application of CMX7141 in the DCR system.
Focus research on the channel codec techniques of the chip and have a simulation on the channel coding and decoding.
The simulation results indicate that, th rough channel error correction technique in CMX7141, the BER of DCR system
reduces greatly and the transmission quality of DCR system is improved.
Keywords: DCR; CMX7141; Cyclic Redundan cy Check; Punctured Convolutiona l Coding
1. Introduction
With the development of the information age, people
urgently request the intercom have the function such as
voice encryption, data transmission, net dispatching and
so on. The traditional analog radio defect has been
gradually reflected. Private wireless communications
system is gradually transform from analog to digital.
Currently, digital intercom has received worldwide atten-
tion, research on digital intercom technology and the
standardized work is prompting forward.
Commonly used international communication standard
of digital radio such as: TETRA, DMR[1], dPMR[2] and
DCR standard[3], TETRA (Trans European Terrestrial
Trunked Radio) Digital trunking communication system
is professional mobile communication system based on
TDMA digital technology; Digital mobile radio standard
was released for professional radio users (PMR) by ETSI;
DPMR (digital private mobile radio) is a digital radio
protocol, it through provides user the low cost, use low-
complexity technology realizes the advanced function.
ICOM、KENWOOD and many other Japanese manu-
facturers promulgated DCR standard for digital commer-
cial interphone. It’s enacted based on digital Private Mo-
bile Radio (dPMR). Its present standard is ARIB STD-
98.
CMX7141[4] is the product of CML Semiconductor
Company using in the digital special network mobile
communication. It’s conforming to ARIB’s T98 Digital
Convenience Radio standard. It implements modulation
and demodulation, channel coding and decoding, framing
and frame disassembled, and many other key technolo-
gies in DCR standard.
Digital interphone working in the wireless environ-
ment will inevitably be affected by the variety interfer-
ences. Design of channel codec for DCR system has an
important impact on the performance. This paper focuses
research on codec design in DCR system and punctured
convolutional en coding and decoding analyze the BER of
different codec mode and gives the Matlab simulation
results.
2. The Introduction of DCR Protocol
The DCR protocol is a digital handset standard, which
was set for commercial digital interphone by Association
of Radio Industries and business (ARIB). The DCR pro-
tocol has the following characteristics:
 Using frequency division multiple access methods.
 Using the 400MHz frequency band and the channel
spacing is 6.25 kHz.
 Half-duplex communications.
 Using 4 FSK modulati on a n d demodulati on.
 The coding scheme is CRC [5], convolution codes,
interleaving and scrambling .
 The information was transmitted in frame format,
the length of a frame of 80 ms and a super frame consists
of 4 frames and so on.
3. Function and Internal Module
Introduction for CMX7141
CMX7141 is a high integration digital PMR processor.
C
opyright © 2013 SciRes. CN

Y. F. LI ET AL. 287
CMX7141 is a 4FSK modulation and demodulation chips
that compatible with ARIB STD - 98 DCR standard.
Much of the ARIB STD - 98 DCR standard air interface
protocol is embedded within the CMX7141 operation
namely:
Air Interface – Physical Layer 1:
 4FSK modulation and demodulation
 Bit and symbol definition.
 Frequency and symbol synchronization.
Transmission burst building and splitting.
Air Inte r f a c e – D a t a Li n k Layer 2:
 Channel coding (FEC, CRC).
 Interleaving, de-interleaving and bit ordering.
 Frame building and synchronizing.
 Burst and parameter definition.
 Link addressing (source an d destination).
 Interfacing of voice applications (voice data)
with the Physical Layer.
 Data bearer services.
 Exchanging signaling and/or user data with the
Call Control Layer.
 Automatic Own-ID detection.
In addition to the above fun ction, CMX7141 ha s many
other functions and Auxiliary Functions.FI (functional
image file) defines the functions and features of CMX-
7141, before use needs to download FI to CMX7141
chip.CMX7141 internal function module shown in Fig-
ure 1.
Figure 1 show that the CMX7141 has fully realized
the channel coding and decoding technology specified in
DCR Protocol, including cyclic redundancy check,
Punctured convolutional coding, interweave and scram-
bling. In addition to channel coding and decoding were
completed by CMX7141, frames building and splitting
were also done by CMX7141, Two frame types are
defined by the standard: “Synchronous Burst 0” (SB0)
and “Service Channel” (SC) frames. The two types of
frame structure are shown in Figure 2.
“P” indicate preamble, it’s some particular symbols’
periodic sequence and its length can be defined. “SW”
means synchronization word; its length is 20 bits. Both
types of frame start with a 20-bit Sync Word, followed
by a 16-bit Radio Information Channel (RICH) block and
a 60-bit Slow Associated Control Channel (SACCH)
block.
RICH can control log ical channel identifi cation, commu-
nication pattern recognition and work pattern recog nition.
RICH raw data is 7-bit, insert a parity check at the tail
and then handle the data with double bit transform. We
can get 16-bit RICH data.
SACCH used to transmit control information, the
SACCH raw data is 36-bit.The former 8-bit is an M se-
quences and the last 18-bit is control information. Firstly,
the SACCH raw data has a CRC（32，26）processing,
insert four bits zero at the end of the data. Then, carries
on the punctured convolutional coding and interweave,
finally can get 60-bit SACCH data.
SC frames contain two144-bit Traffic Channel (TCH)
blocks. These can carry either “speech”, uncoded “non-
speech” or FEC coded “non-speech” payload data. TCH
raw data is 80-bit.The data generation process is similar
to SACCH. The difference is TCH use CRC(92，80),
interweave depth is also different.
SB0 frames also contain a single 144-bit parameter
information channel (PICH) block and 144-bit of pad-
ding.
The PICH block contains the 36-bit Call Sign (CSM)
field, which is the transmitting radio’s unique nine-digit
serial number encoded in binary-coded decimal (BCD)
format. The data generation process is same with TCH.
Figure 1. CMX7141 internal module diagram.

Y. F. LI ET AL.
288
Figure 2. Two kind of frame transfer in CMX7141.
A DCR call start with one (or more) SB0 frames fol-
lowed by a stream of SC frames carrying payload data.
Figure 2 shows that the length of each frame is 384-bits,
the duration is 80ms.Four frames can compose a super
frame.CMX7141 can achieve frame synchronization
automatically.
4. Channel Coding and Decoding
Technology in CMX7141
4.1. CRC
Cyclic Redundancy Check (CRC) code is a common type
of error checking code. The error detection capability is
as follows:
 Burst error lengthnk.
 Majority of burst error length 1nk , the pro-
portio n of su ch errors that cannot be d etected is () 2nk

.
 Majority of burst error length nk, the ratio of
the error cannot be detect is () 2nk

.
 The error of all the code distance of the allow code
group 1d.
min
 All odd number of errors.
The two kind of CRC are CRC-6 and CRC-12 in the
DCR standard. The expression of cyclic redundancy
check code is (n, k). “n” indicate the length of the en-
coded; “k” means the length of the original information.
CRC coding processing is:
() ()
()
() ()
nk
x
mx rx
Qx
g
xg


x
(1)
In this formula, “m(x)” represent the code polyno-
mial, “g(x)” represent the generate polynomial, “Q(x)” is
quotient and “r(x)/g(x)” is the remainder. The remainder
is also a polynomial, and then we can get the coding is:
()() ()
nk
Cxx mxbx

 (2)
CRC was widely used in data storage and data com-
munication, making in the disk driver and the corre-
spondence product (such as modulator and demodulator)
in hardware form. Its hardware implementation is shown
in Figure 3.
The decoding process of CRC is: (1) Using the re-
ceiving code polynomial r(x) divided by generate poly-
nomial g(x) and obtain adjoin polynomial s(x);(2) Ac-
cording to s(x) to determine the error pattern e(x); (3)
, Correct the mistakes.
() ()rx gx
Figure 3. (n-k) level feedback shift register code electric
circuit.
4.2. Punctured Convolutional Coding
If the system uses (n, 1, m) convolutional coding, the
maximum rate we can obtain is 1/2. For many applica-
tions, they need a higher coding rate. This can be
achieved by punctured convolutional[6-8] code. Punc-
turing process in fact is deletes part of elements in the
encoder output symbol stream, the number of deleted
symbols determining the final coding rate. The main ad-
vantage is using the same encoder, by changing the de-
lete code number can make a wide range of different in
coding rate. In the realization of puncturing, it must de-
termine puncturing pattern. “P” is a puncturing matrix
and it’s an n × p order ma trix.
1) The coding of Punctured convolution code
In DCR protocol, using the punctured convolutional
code of (2,1,5) convolutional code. The generating poly-
nomial is:
34
1
2
2
()1
()1
GDD D
GDD DD
 
 4
0
1
2
2
3
2
4
2
5
2
(3)
The output information according to order of G 1, G 2,
they are alternating readout.
Take the SACCH channel data as an example, the raw
data is 36-bit, Supposes the encoder initial state is zero.
Along with time t recursion and information
012 333435
(,,......., , )mmmm m m
input constantly, code output con-
tinuously.
0123
( , ,,......)CCCC
At the time t=0,
000
01
()CmAGG
101
CmAmA 2
1
10 1
()GG
201
CmAmAmA
At the time t=1,
2
32
210 1
()GG At the time t=2,
At the time t=3,
301233
3210 1
()CmAmAmAmAGG
At the time t=4,
4012344
432101
()CmAmAmAmAmA GG
At the time t=5,
5012345
54321 1
()CmAmAmAmAmA GG
Written in matrix form
012 3435 1363636
( , ,......,)CCCC CCmA




Y. F. LI ET AL. 289
012 3435
01234
012 34
0123
012
4
( , ,.....,)
... ...0
0... 0
00... 0
000... 0
... ... ... ... ... .........
000000...
mmmm m
AAAAA
AAAAA
AAAA
AAA
A





















(4)
12
Represents the output at the time t,
tt
GG
j
A
Repre-
sents the matrix coefficient.
We can obtain the coefficient matrix by the generate
polynomial:
01 2 34
(11),(01), (01),(10), (11)AAAAA  
After convolution encoding, the data from 36-bit be-
co ring, for different traffic channel provides
a


(5)
And the TCH/PICH data puncturing pattern is:

(6)
Take the TCH channel data as the example, Convolu-
tio
) (7)
After puncturing process, the output is:
(8)
Punctured convolution codes can implemen
ra
red convolution code lgebra
de
red convolution codes using Viterbi decoder for
de
ncturing positions. n
co computations as the
re
lution code sequence C is the convolution of
in
dding method in the puncturing positions.
in the trellis di
mes 72-bit.
Then punctu
different puncturing pattern. The puncturing pattern of
SACCH channel data is:
11

1111
110110
P

11

01
P

n encoder output:
(1) (2) (
(,,CCCC1) (2) (1) (2) (1) (2)
0011 2233
,,,,,,......CCCCC
(1) (1) (2) (1) (1)
(, ,, , ,.C CCCCC01123 .....)
t different
te requirements, And in the premise of ensuring the
reliability, can improve the transmission efficiency. And
because the codec is relatively simple and the error cor-
rection performance is good, therefore it is widely used
in channel error correction.
2) The decoding of Punctu
The convolution code decoding mainly has the a
coding and the probabilistic decoding. The algebra
decoding uses the majority-lo gic deco din g m ethod, the
probabilistic decoding divides into the Viterbi decoding
and the sequential decoding. The Viterbi decoding algo-
rithm is a maximum-likelihood decoding algorithm that
makes the probability of decoding error minimum. It’s
the optimal algorithm. Viterbi decoding algorithm can
divide into the soft decision and the hard decision de-
coding.
Punctu
coding has the two major ways:
a) Zero padding method in the pu
b) According to the bit rate of equivalent convolutio
de to decoding after puncturing.
The second method needs large
quest of coding efficiency to be high, the hardware
realization complex and the versatility is bad. Currently,
usually uses the first method for decoding, zero padding
in the puncturing positions and then use the Viterbi de-
coding.
Convo
put sequences m and impulse response g. Convolution
code sequence C after signaling mapping result is y. Af-
ter modulation through the noise channel, Arrive at the
receiving end receives the sequence r. Viterbi decoding
algorithm is using the receive sequence r, according to
the maximum likelihood criterion to estimate the code
sequence y. The decoding algorithm can be implemented
as follows:
a) Zero pa
b) The ,kt S indicates the State k S at the time of t
agram, specify a metvalue , ()
kt
VS to
each state in the trellis diagram and initialization:at the
time 0t
ric

, 0,0 ()0VS

, other state ,0 ()
k
VS

 .
c) 1tt

, Calculate measuremee nt value of then-
tire path to the state k S in the time t. Firstly calculate
branch metric at t: 0() ()
n
1
(| )(|)
j
j, if use
tt t t
j
Mr yMry


soft decision through calculate the square of Euclidean
distance
distance 0()() 2
njj
, hard decision use hamming
1()
tt
j
ry



0() ()
1()
njj
tt
j
ry


. Then calculates metric value
of the partial path at time t: 1 (|)(| )
ii
i
t
t
M
ry Mry

,
|)
t t
r y
through calculates ,
() (
kt
VS M

to realize.
() as tto thed) Set the metric he best path value VS,kt
e more st
h metric and
th
ate k S at time t. If hav than one best part of
path mric, we can select any one of these.
e) Store the best part of the survivor pat
et
e corresponding status and path.
f) If 1tLm

, returns to the second step, Other-
wid-out surviv
thm finally obtains the surviving
pa
4.3. Interleaving
ed so that author affiliations are
se reaing path, the corresponding mark is
the decoding output.
The Viterbi algori
th in the trellis diagram is unique. That is also the
maximum likelihood p a th.
The template is design
not repeated each time for multiple authors of the same
affiliation. Please keep your affiliations as succinct as
possible (for example, do NOT post your job titles, po si-
tions, academic degrees, zip codes, names of build-

Y. F. LI ET AL.
290
ing/street/district/province/state, etc.). This template was
designed for two affiliations .
1) For author/s of only one affiliation: To change the
de affiliation lines.
ic
iliation lines for
th more than two affiliations: To
ch es.
ic
es of affiliation 1
an hard return immediately after
th
5. The Simulation Results
ces the binary random
hanne
B
fault, adjust the template as follows.
a) Selection: Highlight all author and
b) Change number of columns: Select the Columns
on from the MS Word Standard toolbar and then select
“1 Column” from the selection palette.
c) Deletion: Delete the author and aff
e second affiliation.
2) For author/s of
ange the default, adjust the template as follows.
a) Selection: Highlight all author and affiliation lin
b) Change number of columns: Select the “Columns”
on from the MS Word Standard toolbar and then select
“1 Column” from the selection palette.
c) Highlight author and affiliation lin
d copy this selection.
d) Formatting: Insert one
e last character of the last affiliation line. Then paste
down the copy of affiliation 1. Repeat as necessary for
each additional affiliation.
The random signal source produ
sequence, after channel coding and interweaves carries
on the 4FSK modulation, through the multipath fading
channel. Then, carries on the demodulation, de-interleave
and channel decoding, use MATLAB simulate this proc-
ess, and draws Non-error correction channel BER curve
and Error correction coding channel BER curves:
Figure 4 shows that: Error correction coding cl
ER is much lower than the Non-error correction code
channel BER. And when the signal-to-noise ratio is same,
01234567
10
-5
10
-4
10
-3
10
-2
10
-1
Eb/N0 in dB
Pe
Mul t i pat h fading c hannel
Non-error correc ti on code
S oft-dec i si on dec odi ng
Hard-dec i si on dec odi ng
Soft-decision decoding is better than the hard-decision
decoding. Moreover CMX7141 can select soft decision
or hard decision according to the needs of users. This
ensures error-correcting performance of error-correcting
code. Thereby channel co ding can improve the quality of
voice communication.
6. Conclusions
Figure 4. The error correction performance of puncture
convolution code.
edicated chipset CMX7141 that
owledgements
y the National Natural Sci-
RENCES
[1] ETSITR 102. Electromagnetic
Compatibility tters (ERM); Digi-
ibility and Radio Spectrum Matters (ERM);
Radio Industries and Busi-
-T98v1_3.pdf.
CR Operation. CML Microcir-
tion in a Trellis Coded System with Bit
Communica-
des,” In-
d
This article introduces a d
apply to DCR standard. And in conjunction with DCR
standard analysis CMX7141 internal algorithm and
simulate these algorithms. Enable the people to have cer-
tain understanding to the digital intercom key technolo-
gies, it’s convenient for people to improve algorithm on
the basis of the original algorithm and provide a theo-
retical foundation for new intercom standard, at the same
time to promote the development of digital radio tech-
nology.
7. Ackn
This article was supported b
ence Foundation contract NSFC No.61171081, the Ji-
angsu Postdoctoral Sustentation Fund contract No.
1101077C and the Fund of Aeronautics Science contract
No. 20122654004.
REFE
398V1.1.2 (2008-05)
and Radio Spectrum Ma
tal Mobile Radio (DMR) General System Design. ETSI,
2008.
[2] ETSITR 102 490V1.2.1 (2006-08). Electromagnetic
compat
Peer-to-Peer Digital Private Mobile Radio (DPMR) using
FDMA with a Channel Spacing of 6,25 kHz with e.r.p. of
up to 500 mW. ETSI, 2006.
[3] Digital Convenience Radio Equipment for Simplified
Service V.1.3 Association of
nesses.
2012.12.18.http://www.arib.or.jp/english/html/overview/d
oc/1-STD
[4] CML Microcircuits. Datasheet of CMX7131/CMX7141
Digital PMR Processor D
cuits, 2011.
[5] R. Prevost, M. Coulon, D. Bonacci, et al., “CRC-assisted
Error Correc
Stuffing,” Statistical Signal Processing Workshop (SSP),
2011 IEEE. Nice: SSP, 2011.pp. 381-384.
[6] B. F. Uchoa-Filho, D. R. Souza, C. Pimentel, et al., “Gen-
eralized Punctured Convolutional Codes,”
tions Letters, IEEE. Sep. 2005. pp. 1070-1072.
[7] J. Geldmacher and J. Goetze “Syndrome Former Trellis
Construction for Punctured Convolutional Co
formation Theory and its Applications (ISITA), 2010 In-

Y. F. LI ET AL.
291
ternational Symposium on. Taichung: ISITA. 2010.
pp.478-483.
[8] A. Katsiotis and N. Kalouptsidis, “On (n,n-1) Punctured
Convolutional Codes and Their Trellis Modules,” Com-
munications, IEEE Transactions on, 2011, pp. 1213-1217.