2814 suwadi paper of icast2009
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Enhancement of Link Availability and Channel Capacity of
Millimeter-Wave Fixed Cellular Systems Using Adaptive
Coded Modulation and Equal Gain Combining
under the Impact of Rain in Indonesia
Suwadi
#1
, G. Hendrantoro
#2
and Wirawan
#3
Department of Electrical EngineeringInstitut Teknologi Sepuluh Nopember, Surabaya, Indonesia, [email protected],
Abstract- This paper presents the effects of tropical rain on theperformance of millimeter-wave fixed cellular system. The system is
local multipoint distribution service (LMDS) system that will be
implemented in Surabaya, Indonesia. Performance parameters of the
system are link availability and channel capacity. The system operates
at 30 GHz frequencies. Adaptive coded modulation (ACM) and
Equal Gain combining (EGC) are methods to increase link
availability and channel capacity for the system. The results of
simulation study by using ACM and EGC show that performance of
the LMDS system is guaranteed to have signal reception quality with
maximum BER 10
-11
in 2 km link length. The performance alsoshows that the link availability is 99.99% and the channel capacity is
3.63 bps/Hz. At 4 km link length, ACM and EGC can increase 0.45%
link availability if they are compared with fixed transmission mode
(for example, 64 QAM). The results also show that the channel
capacity can to increase from 0.318 bps/Hz to 3.448 bps/Hz for the
ACM and EGC. Furthermore, the simulation study shows that the
ACM and EGC can enhance link availability and channel capacity of
the LMDS system.
Index Terms- Link availability, Channel capacity, Millimeter-
wave, Adaptive coded modulation and Equal gain combining.
I. INTRODUCTION
HE demand for broadband communication for high speed,high quality, and multimedia transmission is driving the
use of the higher radio frequency spectrum. A local multipoint
distribution service (LMDS) [1] is a line of sight (LoS) point-
to-multipoint wireless access system operating at the Ka-band
millimeter wave frequency. They are designed to deliver
broadcast services (multimedia, video, internet, etc) from a
central transmitter to individual subscriber within its cell size.
The frequency bands allocated by ITU R and CEPT are
usually above 20 GHz. In this band, rain attenuation is the
most influential propagation factor to determine the system
availability [2], [3]. The cell-site diversity technique has been
proposed in order to reduce the outage time due to the above
reason [4], [5].In many tropical countries, as Indonesia, its rainfall
intensities are very high that cause significant rain attenuation
in Ka Band communication channel [6]. Analysis of diversity
gain using various combining techniques, i.e. combining (SC),
equal gain combining (EGC), and maximal-ratio combining
(MRC), in dual link millimeter wave communication systems
has been proposed by Wijayanti et al. [7]. There are several
rain fading compensation techniques, i.e. power control,
adaptive coded modulation (ACM), diversity and relay. In this
research, ACM and EGC have been applied.
This paper presents the results of simulation study about link
availability evaluation and channel capacity in LMDS system
at 30 GHz frequency using ACM and EGC diversity. The
evaluation is done based on rainfall intensities measurement in
Surabaya Indonesia and adopts ITU-R P.530 recommendation
for calculating rain attenuation [8].
II. SYSTEMMODEL
LMDS system model in this paper uses adaptive coded
modulation and equal gain combining (EGC) to increasemaximally channel capacity and link availability. The system
uses M-QAM with various modulation levels, i.e. 4, 16, 64
QAM. Its coding uses code rate variation of convolution code
CC(k/n) and Reed Solomon code RS(n,k). The system has to
be maintained so that performance of the system has high
signal quality with maximum bit error rate BER 10-6 and 10-11.
Probability of error of the M-QAM system and ACM can
be obtained [9]. It can be obtained thresholds of signal to noise
ratio reception for determining modulation level.
Adaptation scenario based on for maximum bit rate 10-6
and
10-11
for M-QAM and ACM. Channel capacity is an important
factor for evaluating the performance of the LMDS system inIndonesias rain environment. For our purpose, the channel-
capacity, as defined by Shannon [9], it is a good measure of
the merit of any communication system, since it gives the
maximum rate of transmission signal over the channel.
III. RAIN RATE AND ATTENUATION
For rain measurement, two kinds of instruments were used
to record, i.e. rain gauges and disdrometer. They have been
placed at the campus of Institut Technologi Sepuluh
Nopember (ITS) Surabaya, Indonesia since 2007. They were
used to record rain rate data with sampling period 10 s. In this
research, it uses rain rate measurement data for 2 years. The
R0.01 means that the rain rate at 0.01% of time in measuredperiod that the rain-rate value is exceeded. Surabaya
Indonesias R0.01 is 140 mm/h, larger than that of 100 mm/h
suggested by ITU-R.
Rain attenuation was estimated by using synthetic storm
technique (SST). The rain attenuations in Surabaya Indonesia
at 4 km link length for outage probability 0.01% are 86, 93, 97
and 102 dB with links direction are east (0o), north west
(135o), north east (45
O) and north (90
o), respectively. Rain
attenuation estimation results show that North direction link
has the largest attenuation.
T
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TABLE I
SIMULATION RESULS OF LINK AVAILABILITY (%) FOR IDENTICAL DUAL-LINK LENGTHS WITH SEPARATION ANGLE 900
IN THE PRESENCE OF RAIN FADING
Link length
1 km 2 km 3 km 4 kmTransmission Mode
10-6
10-11
10-6
10-11
10-6
10-11
10-6
10-11
4 QAM 99.99 99.99 99.94 99.93 99.89 99.88 99.85 99.83
16 QAM 99.99 99.98 99.92 99.90 99.85 99.82 99.79 99.75
64 QAM 99.97 99.96 99.87 99.84 99.79 99.71 99.67 99.504 QAM+RS(63,31)+CC(1/3) 99,99 99,99 99,99 99,99 99,97 99,97 99,95 99,95
16 QAM+RS(63,51)+CC(1/2) 99,99 99,99 99,98 99,98 99,96 99,95 99,93 99,93
64 QAM+RS(63,59)+CC(2/3) 99,99 99,99 99,97 99,96 99,94 99,92 99,91 99,89
ACM + EGC Diversity 99,99 99,99 99,99 99,99 99,97 99,97 99,95 99,95
TABLE II
SIMULATION RESULS OF CHANNEL CAPACITY (bps/Hz) FOR IDENTICAL DUAL-LINK LENGTHS WITH SEPARATION ANGLE 900
Link length
1 km 2 km 3 km 4 kmTransmission Mode
10-6
10-11
10-6
10-11
10-6
10-11
10-6
10-11
4 QAM 1.998 1.998 1.961 1.960 1.908 1.906 1.863 1.860
16 QAM 3.990 3.989 3.854 3.845 3.722 3.705 3.600 3.580
64 QAM 5.930 5.910 5.608 5.553 5.327 5.245 5.070 4.944
4 QAM+RS(63,31)+CC(1/3) 0.328 0.328 0.325 0.325 0.322 0.322 0.318 0.318
16 QAM+RS(63,51)+CC(1/2) 1.618 1.618 1.591 1.589 1.564 1.560 1.539 1.533
64 QAM+RS(63,59)+CC(2/3) 3.729 3.723 3.613 3.589 3.499 3.464 3.414 3.360
ACM + EGC Diversity 3.735 3.731 3.645 3.630 3.555 3.532 3.484 3.448
IV. SIMULATIONRESULTSANDDISCUSSION
One of the LMDS system performances is link
availability. The results of simulation are shown in Table I.
Adaptive transmission method of LMDS system uses ACM
and EGC in the presence of rain attenuation. System
configuration is evaluated in identical dual-link lengths with
separation angle 900(north and east). The system is guaranteed
with maximum BER 10-6
and it is also evaluated at maximumBER 10
-11. Base on simulation results, ACM and EGC
techniquein the LMDS system has 99.95% link availability for
4 km link length for maximum BER 10-11
. For the fixed
transmission method, i.e. the 64 QAM has 99.50% link
availability. Additionally, LMDS system can be increased its
link availability with using ACM and EGC diversity.
Simulation results show that ACM and EGC diversity can
enhance 0.45% link availability for maximum BER 10-11
at 4
km link.
Channel capacity is another important factor of the LMDS
system performance. Table II shows the simulation results of
the system channel capacity that it uses ACM and EGC
diversity. The LMDS system using adaptive transmissionmethod (ACM and EGC) is evaluated. The system produces
channel capacity about 3.448 bps/Hz for maximum BER 10-11
at 4 km link. If the system uses non adaptive transmission
4QAM+RS(63,31)+CC(1/3) has 0.318 bps/Hz.
VI.CONCLUSION
Based on the results of simulation study, it can be
concluded that LMDS system using 64-QAM transmission
mode without coding has 99.50% link availability. By using
ACM and EGC diversity can enhance 0.45% link availability
for maximum BER 10-11
at 4 km link length. Additionally, the
system also produces 3.448 bps/Hz channel capacity. Finally,
performance of the LMDS system can be enhanced with using
adaptive transmission technique, i.e. adaptive coded
modulation (ACM) and equal gain combining (EGC).
REFERENCES
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