In the paper, we present simulation results for the 13 channel DS CDMA WATM LAN utilising optimized complex spreading signatures based on Walsh-Rademacher functions. The method to obtain those optimized spreading signatures, as well as the full set of the coefficients giving the minimum level of cross-correlation between any pair of the channels is shown. The resultant system BER and the distribution of errors within encapsulated WATM cells is given. The obtained results indicate that with the application of a hybrid ARQ scheme, capable of correcting 10 errors, the number of WATM cells which would require retransmission is in the order of I-2%

Wysocki, Beata J

Wysocki, Tadeusz

Zepernick, Hans J

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Faculty Publications in Computer & Electronics 
Engineering (to 2015) 
Electrical & Computer Engineering, Department 
of 
1998 
Error Performance of the 13-Channel DS CDMA WATM LAN 
Beata J. Wysocki 
University of Nebraska-Lincoln 
Tadeusz Wysocki 
University of Nebraska-Lincoln, wysocki@uow.edu.au 
Hans J. Zepernick 
Curtin University of Technology 
Follow this and additional works at: https://digitalcommons.unl.edu/computerelectronicfacpub 
 Part of the Computer Engineering Commons 
Wysocki, Beata J.; Wysocki, Tadeusz; and Zepernick, Hans J., "Error Performance of the 13-Channel DS 
CDMA WATM LAN" (1998). Faculty Publications in Computer & Electronics Engineering (to 2015). 29. 
https://digitalcommons.unl.edu/computerelectronicfacpub/29 
This Article is brought to you for free and open access by the Electrical & Computer Engineering, Department of at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications in 
Computer & Electronics Engineering (to 2015) by an authorized administrator of DigitalCommons@University of 
Nebraska - Lincoln. 
Error Performance of the 13-Channel DS CDMA WATM LAN 
Beata J. Wysocki, Tadeusz A. Wysocki, Hans J. Zepernick 
Cooperative Research Centre - Broadband Telecommunications and Networking 
Curtin University of Technology 
GPO Box U1987, Perth WA6845, Australia 
email: tad@atri.curtin.edu.au 
tel: +618 9266 7892 
fax: +618 9266 3244 
Abstract: In the paper, we present simulation results 
for the 13 channel DS CDMA WATM LAN utilising 
optimized complex spreading signatures based on 
Walsh-Rademacher functions. The method to obtain 
those optimized spreading signatures, as well as the 
full set of the coefjicients giving the minimum level of 
cross-correlation between any pair of the channels is 
shown. The resultant system BER and the 
distribution of errors within encapsulated WATM 
cells is given. The obtained results indicate that with 
the application of a hybrid ARQ scheme, capable of 
correcting 10 errors, the number of WATM cells 
which would require retransmission is in the order of 
I-2%. 
I. INTRODUCTION 
ATM (Asynchronous Transfer Mode) is the commonly 
accepted standard for the broadband networks, and is also 
becoming accepted as a common nominator for all types 
of services and networks. Also, there has been widespread 
use of wireless communications to support users’ 
requirements for wireless access and terminal mobility in 
such scenarios as cellular telephony networks and 
narrowband wireless LANs. As a further advancement, 
users are now beginning to require broadband services and 
terminal mobility to be provided together through wireless 
access to ATM networks. 
A major challenge in the design of WATM networks 
is the need to overcome the severe degradation of channel 
bit error rate resulting from impairments to the wireless 
channel such as those caused by multi-path propagation 
[l]. Spread spectrum techniques, such as direct sequence 
code division multiple access (CDMA), can be effective in 
combating multi-path effects, while also providing good 
tolerance to interference from other devices operating in 
the same frequency band. However, only a small 
processing gain is achievable due to the total available 
bandwidth of tens of MHz and the high data rate of several 
Mbps. Consequently, in-band jammers, like other channels 
of the same WLAN acquired by means of code division 
multiple access (CDMA) cause severe multiple access 
interference (MAI), which may block the communication. 
In theory, cancellation of that type of interference is 
possible if each of the users utilise orthogonal signals to 
transmit the data [2]. If the delays between transmitters 
and receiver are anyhow different, as is generally the case 
of terminal to base station (BS) transmission, the signals 
received by the BS cannot be regarded as orthogonal. Even 
within a 50 m coverage area those differences may be in 
the order of a few spreading code symbols (chips) 
depending on the data rate. This effect is particularly 
critical for very short spreading sequences, like 16-bits 
Walsh-Rademacher functions. 
In [3], we have proposed the method to reduce the IS1 
and MA1 for DS CDMA wireless networks, and in this 
paper, we consider application of this method to derive the 
spreading signatures based on the 16-bits Walsh- 
Rademacher functions [4] for the DS CDMA ATM 
WLAN. 
The paper is organized as follows. In Section 11, we 
briefly discuss the method of designing the complex 
multilevel spreading signatures based on the known set of 
binary codes. Section 111 deals with the practical 
implementation of the design method, and optimization of 
parameters for the set of complex signatures. In Section 
IV, we present simulation results for the 13 channel ATM 
WLAN utilizing these signatures, and Section V 
concludes the paper. 
11. DESIGN METHOD 
In [3], we have described the method to reduce IS1 and 
MA1 for non-synchronized CDMA signals by means of a 
modification to the carrier waveform. The modified carrier 
has been obtained by a regular distortion to the frequency 
of the original carrier, resulting in the ith user line signal 
si( t )  expressed by: 
where w i ( t )  - frequency distorting function which can be 
optimized to achieve minimum value of cross-correlation 
among all users, and to minimize the off-peak auto- 
0-7803-5106-1/98/$10.00 @ 1998 IEEE 
1295 
Published in Universal Personal Communications, 1998. ICUPC '98. IEEE 1998 International Conference on
Volume 2,  5-9 Oct. 1998 Page(s):1295 - 1298 vol.2
Digital Object Identifier 10.1109/ICUPC.1998.733703 
correlation of the ith line signal, $i( t )  - information 
carrying phase component. 
To simplify simulation process, we have applied here 
a base-band equivalent of the method. If follows from the 
fact that for the real spreading code g i ( t ) ,  equation (1) can 
be rewritten in the exponential .form as: 
The complex envelope [2] o(t) of such a signal is given 
by: 
Hence, the function 
(4) 
can be regarded as an analogue spreading waveform, 
leading, without any changes to the cosinusoidal carrier, to 
the same line signal s i ( t ) ,  as the original binary spreading 
code gi( t )  together with the previously described 
modification to the carrier waveform. 
Because signal is usually processed using digital 
signal processing (DSP) technology in the receiver, 
instead of the analogue spreading waveform g i ( t ) ,  one 
can use a multilevel complex spreading signature gi( t )  . 
The length of the signature g i ( t )  equals to the length of 
the original signature g i ( t )  multiplied by the number of 
samples per chip used in the receiver, and its pulse levels 
are weighted by the factor 
Wi(t)  = exp j wi(z)dz  . (5)  rs I 
Such an approach allows for the baseband correlational 
detection of the signals, easier optimization of the 
functions wi( t )  for the given set of binary signatures, and 
facilitates implementation of the receivers. 
In order to optimize the spreading sequences for the 
use in a 13 channel DS CDMA ATM WLAN, we have 
chosen a subset of 13 orthogonal Walsh-Rademacher 
functions [ 2 ]  as a set of binary spreading codes gi ( t ) ,  
i = 1, 2, ..., 13 . These functions are listed in the Table 1. 
To minimize the cross-correlation between any pair of 
the spreading signatures, independently of the relative 
delay (for a delay different than zero the sequences are, in 
general, not orthogonal), we applied the described method 
with the functions w , ( t ) ,  i = 1, 2, ..., 13, being of the 
form: 
where c( t)  - the triangular wave defined as: 
and 
0, t < O  
4t - 1, 
- 4t + 3,  
0 5 t < 0.5 
0.5 I; t < 1 
0, t z l  
h(t)  = 
Table 1: Set of 13 spreading sequences. 
No. Binary spreading sequence 
1 
2 
3 
1 1 1  1-1 -1 -1 -1 1 1 1 1-1 -1 -1 -1 
1 1-1 -1 -1 -1 1 1 1 1-1 -1 -1 -1 1 1 
-1 -1 1 1 1 1-1 -1 1 1-1 -1 -1 -1 1 1 
I 4 I -1-111-1-11111-1-111-1-1 
5 
6 
1 1-1 -1 1 1-1 -1 1 1-1 -1 1 1-1 -1 
1-1 -1 1 1-1 -1 1 1-1 -1 1 1-1 -1 1 
7 
8 
9 
10 
11 
-1 1 1-1 -1 1 1-1 1-1 -1 1 1-1 -1 1 
-1 11  -1 1-1 -1 1 1  -1 -1 1-1 1 1-1 
1-1 -1 1-1 1 1-1 1-1 -1 1-1 1 1-1 
1-1 1-1 -1 1-1 1 1-1 1-1 -1 1-1 1 
-1 1-1 1 1  -1 1-1 1-1 1-1 -1 1-1 1 
I 12 1 -1 1-1 1-1 1-1 1 1-1 1-1 1-1 1-1 
13 1-1 1-1 1-1 1-1 1-1 1-1 1-1 1-1 
111. O P T I ~ I ~ A T I O ~  OF THE 
SIGNATURE SET 
Optimization problem in the considered case can be 
formulated as follows: 
e find the values of the coefficients ai, pi ,  and yi;  
i = 1, 2, ..., 13, minimizing the maximum value 
K ( A ) ,  
wi(E) = 2n[ai<(t/16) t p i t ( t / 8 )  + yit;(t/4)], (6) 
1296 
(9) 
No. a P 
of the cross-correlation coefficients between any pair of 
the spreading codes, independently of the relative delay 
between them. 
Due to the bandwidth limitations, we want to keep the 
magnitudes of these coefficients as low as possible. 
Therefore, one needs to impose constraints on the values 
of these coefficients. In our case, we required them to fulfil 
the following: 
Y 
Since the function to be minimized is highly irregular 
having many local maxima and minima, we have used the 
following algorithm to find the solution: 
1. 
11. 
In the first step of the optimization we set: 
ai = a ,  i = 1,2, ..., 13 
p i = P ,  i = 1 , 2  ,..., 13 (11) 
yi = y , i = 1, 2, ..., 13 I 
and calculated the values of K ( A )  for the area 
satisfying the condition (lo), with grid step being 
equal to 0.05 for each of the parameters a ,  P , and y . 
Next we perform optimization for all 39 variables 
using the Nelder-Meade simplex search [5] imple- 
mented in MATLAB as the function fmins [6]. For 
the starting point, we choose 
* *  
where; 0 denotes the Kronecker product, a , p , 
and y are the values of a ,  p , and y , respectively, 
for which the function K ( A )  reaches the minimum in 
the previous step. 
have been chosen randomly from the whole considered 
domain. However, even though the procedure have been 
repeated 10 000 times, no better solution has been found. 
lhble 2: Set of the optimized coefficients. 
Therefore, we have decided to use the solution given 
in Table 2 in the simulation of the system. 
Iv. SIMULATION OF DS CDMA 
WATM LAN 
In order to simulate the 13 channel DS CDMA WATM 
LAN we assumed the following: 
an encapsulated WATM cell consisted of 524 bits (424 
bits of an ATM cell plus 100 bits of an overhead), 
BPSK was used as a modulation technique, 
the contents of each WATM cell was random, 
relative delay between the signals corresponding to 
different channels was random with the delay step of 
0.25 of a chip duration, 
the received power was equal for all of the channels. The optimized values of the coefficients a , fi , and y 
are given in the Table 2. 
For this set of coefficients, the function 
K ( A ~ ~ , )  = K,,,~,, = 0.2733. 
Since we can regard this results as a local minimum 
only, we have also tried another optimization approach. 
The starting points for the MATLAB function fmins  
The receiver antenna was simulated as a sum of the 
signals arriving from different channels, and the detection 
was a correlational one. The simulation was repeated for 
500 cells for each of the channels. 
The obtained results show that the quality of 
transmission depends slightly on the signature used to 
1297 
spread the signal, so the achieved BER is not uniform for 
all of the channels, which is reflected by the number of 
errors occurring in the received WATM cells. As an 
example, in Figure 1 we present histograms of the number 
of transmission errors in a received cell for two of the 
channels. 
For all 13 channels, the obtained BER is equal to 
2 . 8 ~ 1 0 - ~ ,  ranging from 1 . 5 ~ 1 0 ‘ ~  to 3.9x10”, and the 
histogram presenting the distribution of errors in the 
received WATM cells is presented in Figure 2. 
Total No. of transmitled cells = 5w 
Channel NO. = 1 
0 
5 10 15 20 25 
NUMBER OF ERRORS IN A RECENED WATM CELL 
350 
Total No of lransmiued cells = 5w 
Channel No = 5 
“0 2 4 6 8 10 12 
NUMBER OF ERRORS IN A RECEIVED WATM CELL 
Figure 1: Histograms of the numbers of transmission errors 
in a WATM cell. 
V. CONCLUSIONS 
order of only 1-2%. Further research investigating the 
behaviour of the system without the perfect power control 
and incorporating the realistic indoor channel model is 
required. 
300: 
250: 
2001 
5 
% 
B 
15a 
I 3
loo( 
5M 
Total No of transmined cells = 65CQ 
All 13 channels 
Figure 2: Histograms of the numbers of transmission errors 
in a received WATM cell for all 13 channels. 
VI. 
[I] T.Phipps, et.al.; “Wireless ATM Physical Layer 
Requirements”, ATM Forum, Doc. 96-1004, 
Aug.1996. 
[2] J.G.Proakis; “Digital Communications”, 3rd ed., 
McGraw-Hill, New York, 1995. 
[3] B.Wysocki, T.Wysocki; “A Method to Partially 
Suppress IS1 and MA1 for DS SS CDMA Wireless 
Networks”, ICC’97, V01.2, pp.899-903, Montreal 
1997. 
[4] P. Fan, M.Darnell; “Sequence Design for 
Communications Applications”, John Wiley & Sons , 
New York, 1996. 
[5] J.A.Nelder, R.Mead; “A Simplex Method for 
Function Minimization”, Computer Journal, Vo1.7, 
[6] Anonymous; “MATLAB - Reference Guide”, The 
Math Works Inc., August 1992. 
171 S.G.Fischer, T.A.Wysocki, and H.-J.Zepernick; 
“MAC Protocol for a CDMA Based Wireless ATM 
LAN”, ICC’97, Vo1.3, pp.1202-1206, Montreal 1997. 
pp.308-313. 
In this paper, we presented the simulation results for the 
13 channel DS CDMA WATM LAN utilising optimized 
complex spreading signatures based on Walsh- 
Rademacher functions. The results are very promising, 
and indicate that with the application of a hybrid ARQ 
scheme, capable of correcting 10 errors [7], the number of 
WATM cells which would require retransmission is in the 
1298 


Error Performance of the 13-Channel DS CDMA WATM LAN

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications in Computer & Electronics Engineering (to 2015) Electrical & Computer Engineering, Department of 1998 Error Performance of the 13-Channel DS CDMA WATM LAN Beata J. Wysocki University of Nebraska-Lincoln Tadeusz Wysocki University of Nebraska-Lincoln, wysocki@uow.edu.au Hans J. Zepernick Curtin University of Technology Follow this and additional works at: https://digitalcommons.unl.edu/computerelectronicfacpub  Part of the Computer Engineering Commons Wysocki, Beata J.; Wysocki, Tadeusz; and Zepernick, Hans J., "Error Performance of the 13-Channel DS CDMA WATM LAN" (1998). Faculty Publications in Computer & Electronics Engineering (to 2015). 29. https://digitalcommons.unl.edu/computerelectronicfacpub/29 This Article is brought to you for free and open access by the Electrical & Computer Engineering, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications in Computer & Electronics Engineering (to 2015) by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Error Performance of the 13-Channel DS CDMA WATM LAN Beata J. Wysocki, Tadeusz A. Wysocki, Hans J. Zepernick Cooperative Research Centre - Broadband Telecommunications and Networking Curtin University of Technology GPO Box U1987, Perth WA6845, Australia email: tad@atri.curtin.edu.au tel: +618 9266 7892 fax: +618 9266 3244 Abstract: In the paper, we present simulation results for the 13 channel DS CDMA WATM LAN utilising optimized complex spreading signatures based on Walsh-Rademacher functions. The method to obtain those optimized spreading signatures, as well as the full set of the coefjicients giving the minimum level of cross-correlation between any pair of the channels is shown. The resultant system BER and the distribution of errors within encapsulated WATM cells is given. The obtained results indicate that with the application of a hybrid ARQ scheme, capable of correcting 10 errors, the number of WATM cells which would require retransmission is in the order of I-2%. I. INTRODUCTION ATM (Asynchronous Transfer Mode) is the commonly accepted standard for the broadband networks, and is also becoming accepted as a common nominator for all types of services and networks. Also, there has been widespread use of wireless communications to support users’ requirements for wireless access and terminal mobility in such scenarios as cellular telephony networks and narrowband wireless LANs. As a further advancement, users are now beginning to require broadband services and terminal mobility to be provided together through wireless access to ATM networks. A major challenge in the design of WATM networks is the need to overcome the severe degradation of channel bit error rate resulting from impairments to the wireless channel such as those caused by multi-path propagation [l]. Spread spectrum techniques, such as direct sequence code division multiple access (CDMA), can be effective in combating multi-path effects, while also providing good tolerance to interference from other devices operating in the same frequency band. However, only a small processing gain is achievable due to the total available bandwidth of tens of MHz and the high data rate of several Mbps. Consequently, in-band jammers, like other channels of the same WLAN acquired by means of code division multiple access (CDMA) cause severe multiple access interference (MAI), which may block the communication. In theory, cancellation of that type of interference is possible if each of the users utilise orthogonal signals to transmit the data [2]. If the delays between transmitters and receiver are anyhow different, as is generally the case of terminal to base station (BS) transmission, the signals received by the BS cannot be regarded as orthogonal. Even within a 50 m coverage area those differences may be in the order of a few spreading code symbols (chips) depending on the data rate. This effect is particularly critical for very short spreading sequences, like 16-bits Walsh-Rademacher functions. In [3], we have proposed the method to reduce the IS1 and MA1 for DS CDMA wireless networks, and in this paper, we consider application of this method to derive the spreading signatures based on the 16-bits Walsh- Rademacher functions [4] for the DS CDMA ATM WLAN. The paper is organized as follows. In Section 11, we briefly discuss the method of designing the complex multilevel spreading signatures based on the known set of binary codes. Section 111 deals with the practical implementation of the design method, and optimization of parameters for the set of complex signatures. In Section IV, we present simulation results for the 13 channel ATM WLAN utilizing these signatures, and Section V concludes the paper. 11. DESIGN METHOD In [3], we have described the method to reduce IS1 and MA1 for non-synchronized CDMA signals by means of a modification to the carrier waveform. The modified carrier has been obtained by a regular distortion to the frequency of the original carrier, resulting in the ith user line signal si( t )  expressed by: where w i ( t )  - frequency distorting function which can be optimized to achieve minimum value of cross-correlation among all users, and to minimize the off-peak auto- 0-7803-5106-1/98/$10.00 @ 1998 IEEE 1295 Published in Universal Personal Communications, 1998. ICUPC '98. IEEE 1998 International Conference onVolume 2,  5-9 Oct. 1998 Page(s):1295 - 1298 vol.2Digital Object Identifier 10.1109/ICUPC.1998.733703 correlation of the ith line signal, $i( t )  - information carrying phase component. To simplify simulation process, we have applied here a base-band equivalent of the method. If follows from the fact that for the real spreading code g i ( t ) ,  equation (1) can be rewritten in the exponential .form as: The complex envelope [2] o(t) of such a signal is given by: Hence, the function (4) can be regarded as an analogue spreading waveform, leading, without any changes to the cosinusoidal carrier, to the same line signal s i ( t ) ,  as the original binary spreading code gi( t )  together with the previously described modification to the carrier waveform. Because signal is usually processed using digital signal processing (DSP) technology in the receiver, instead of the analogue spreading waveform g i ( t ) ,  one can use a multilevel complex spreading signature gi( t )  . The length of the signature g i ( t )  equals to the length of the original signature g i ( t )  multiplied by the number of samples per chip used in the receiver, and its pulse levels are weighted by the factor Wi(t)  = exp j wi(z)dz  . (5)  rs I Such an approach allows for the baseband correlational detection of the signals, easier optimization of the functions wi( t )  for the given set of binary signatures, and facilitates implementation of the receivers. In order to optimize the spreading sequences for the use in a 13 channel DS CDMA ATM WLAN, we have chosen a subset of 13 orthogonal Walsh-Rademacher functions [ 2 ]  as a set of binary spreading codes gi ( t ) ,  i = 1, 2, ..., 13 . These functions are listed in the Table 1. To minimize the cross-correlation between any pair of the spreading signatures, independently of the relative delay (for a delay different than zero the sequences are, in general, not orthogonal), we applied the described method with the functions w , ( t ) ,  i = 1, 2, ..., 13, being of the form: where c( t)  - the triangular wave defined as: and 0, t < O  4t - 1, - 4t + 3,  0 5 t < 0.5 0.5 I; t < 1 0, t z l  h(t)  = Table 1: Set of 13 spreading sequences. No. Binary spreading sequence 1 2 3 1 1 1  1-1 -1 -1 -1 1 1 1 1-1 -1 -1 -1 1 1-1 -1 -1 -1 1 1 1 1-1 -1 -1 -1 1 1 -1 -1 1 1 1 1-1 -1 1 1-1 -1 -1 -1 1 1 I 4 I -1-111-1-11111-1-111-1-1 5 6 1 1-1 -1 1 1-1 -1 1 1-1 -1 1 1-1 -1 1-1 -1 1 1-1 -1 1 1-1 -1 1 1-1 -1 1 7 8 9 10 11 -1 1 1-1 -1 1 1-1 1-1 -1 1 1-1 -1 1 -1 11  -1 1-1 -1 1 1  -1 -1 1-1 1 1-1 1-1 -1 1-1 1 1-1 1-1 -1 1-1 1 1-1 1-1 1-1 -1 1-1 1 1-1 1-1 -1 1-1 1 -1 1-1 1 1  -1 1-1 1-1 1-1 -1 1-1 1 I 12 1 -1 1-1 1-1 1-1 1 1-1 1-1 1-1 1-1 13 1-1 1-1 1-1 1-1 1-1 1-1 1-1 1-1 111. O P T I ~ I ~ A T I O ~  OF THE SIGNATURE SET Optimization problem in the considered case can be formulated as follows: e find the values of the coefficients ai, pi ,  and yi;  i = 1, 2, ..., 13, minimizing the maximum value K ( A ) ,  wi(E) = 2n[ai<(t/16) t p i t ( t / 8 )  + yit;(t/4)], (6) 1296 (9) No. a P of the cross-correlation coefficients between any pair of the spreading codes, independently of the relative delay between them. Due to the bandwidth limitations, we want to keep the magnitudes of these coefficients as low as possible. Therefore, one needs to impose constraints on the values of these coefficients. In our case, we required them to fulfil the following: Y Since the function to be minimized is highly irregular having many local maxima and minima, we have used the following algorithm to find the solution: 1. 11. In the first step of the optimization we set: ai = a ,  i = 1,2, ..., 13 p i = P ,  i = 1 , 2  ,..., 13 (11) yi = y , i = 1, 2, ..., 13 I and calculated the values of K ( A )  for the area satisfying the condition (lo), with grid step being equal to 0.05 for each of the parameters a ,  P , and y . Next we perform optimization for all 39 variables using the Nelder-Meade simplex search [5] imple- mented in MATLAB as the function fmins [6]. For the starting point, we choose * *  where; 0 denotes the Kronecker product, a , p , and y are the values of a ,  p , and y , respectively, for which the function K ( A )  reaches the minimum in the previous step. have been chosen randomly from the whole considered domain. However, even though the procedure have been repeated 10 000 times, no better solution has been found. lhble 2: Set of the optimized coefficients. Therefore, we have decided to use the solution given in Table 2 in the simulation of the system. Iv. SIMULATION OF DS CDMA WATM LAN In order to simulate the 13 channel DS CDMA WATM LAN we assumed the following: an encapsulated WATM cell consisted of 524 bits (424 bits of an ATM cell plus 100 bits of an overhead), BPSK was used as a modulation technique, the contents of each WATM cell was random, relative delay between the signals corresponding to different channels was random with the delay step of 0.25 of a chip duration, the received power was equal for all of the channels. The optimized values of the coefficients a , fi , and y are given in the Table 2. For this set of coefficients, the function K ( A ~ ~ , )  = K,,,~,, = 0.2733. Since we can regard this results as a local minimum only, we have also tried another optimization approach. The starting points for the MATLAB function fmins  The receiver antenna was simulated as a sum of the signals arriving from different channels, and the detection was a correlational one. The simulation was repeated for 500 cells for each of the channels. The obtained results show that the quality of transmission depends slightly on the signature used to 1297 spread the signal, so the achieved BER is not uniform for all of the channels, which is reflected by the number of errors occurring in the received WATM cells. As an example, in Figure 1 we present histograms of the number of transmission errors in a received cell for two of the channels. For all 13 channels, the obtained BER is equal to 2 . 8 ~ 1 0 - ~ ,  ranging from 1 . 5 ~ 1 0 ‘ ~  to 3.9x10”, and the histogram presenting the distribution of errors in the received WATM cells is presented in Figure 2. Total No. of transmitled cells = 5w Channel NO. = 1 0 5 10 15 20 25 NUMBER OF ERRORS IN A RECENED WATM CELL 350 Total No of lransmiued cells = 5w Channel No = 5 “0 2 4 6 8 10 12 NUMBER OF ERRORS IN A RECEIVED WATM CELL Figure 1: Histograms of the numbers of transmission errors in a WATM cell. V. CONCLUSIONS order of only 1-2%. Further research investigating the behaviour of the system without the perfect power control and incorporating the realistic indoor channel model is required. 300: 250: 2001 5 % B 15a I 3loo( 5M Total No of transmined cells = 65CQ All 13 channels Figure 2: Histograms of the numbers of transmission errors in a received WATM cell for all 13 channels. VI. [I] T.Phipps, et.al.; “Wireless ATM Physical Layer Requirements”, ATM Forum, Doc. 96-1004, Aug.1996. [2] J.G.Proakis; “Digital Communications”, 3rd ed., McGraw-Hill, New York, 1995. [3] B.Wysocki, T.Wysocki; “A Method to Partially Suppress IS1 and MA1 for DS SS CDMA Wireless Networks”, ICC’97, V01.2, pp.899-903, Montreal 1997. [4] P. Fan, M.Darnell; “Sequence Design for Communications Applications”, John Wiley & Sons , New York, 1996. [5] J.A.Nelder, R.Mead; “A Simplex Method for Function Minimization”, Computer Journal, Vo1.7, [6] Anonymous; “MATLAB - Reference Guide”, The Math Works Inc., August 1992. 171 S.G.Fischer, T.A.Wysocki, and H.-J.Zepernick; “MAC Protocol for a CDMA Based Wireless ATM LAN”, ICC’97, Vo1.3, pp.1202-1206, Montreal 1997. pp.308-313. In this paper, we presented the simulation results for the 13 channel DS CDMA WATM LAN utilising optimized complex spreading signatures based on Walsh- Rademacher functions. The results are very promising, and indicate that with the application of a hybrid ARQ scheme, capable of correcting 10 errors [7], the number of WATM cells which would require retransmission is in the 1298 

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1033&amp;context=computerelectronicfacpub

Error Performance of the 13-Channel DS CDMA WATM LAN

Abstract

Similar works

Full text

Available Versions

UNL | Libraries

DigitalCommons@University of Nebraska