Int. J. Communications, Network and System Sciences, 2011, 4, 630-637
doi:10.4236/ijcns.2011.410077 Published Online October 2011 (http://www.SciRP.org/journal/ijcns)
Copyright © 2011 SciRes. IJCNS
Chip Interleaved Multirate and Multimedia Transmission
in Self-Encoded Communication System with Iterative
Detection over Fading Channels
Liang Chi, Won-Mee Jang, Lim Nguyen
Department o f C omputer an d El e ct ro ni c s E n gineering, University of Nebraska-Lincoln,
Omaha, USA
E-mail: lchi@unomaha.edu, {wjang1, lnguyen1}@unl.edu
Received July 26, 2011; revised August 26, 2011; accepted September 14, 2011
Abstract
In this paper, we investigate the self-encoded multirate and the multimedia (SEMM) transmission. In SEMM
system, multiple applications transmit their information simultaneously with different bit rate via
self-encoded spreading spectrum (SESS), where the spreading codes are derived from the previous bits rather
than the pseudorandom code generator. At the transmitter, a block chip interleaving is employed to combat
the deep fading over the wireless channels. At the receiver, a decorrelation scheme separates the combined
signals to reduce the crosstalk between different applications, and provides a better estimation for the de-
spreading sequence. In addition, interference cancelation (IC) is also adopted to improve both the correlation
detection and iterative detection (ID) performance. The simulation results show that the proposed scheme
significantly improves the performance over fading channels.
Keywords: Multirate, Multimedia, Decorrelation, Iterative Detection
1. Introduction
In previous work about the self-encoded multiple access
(SEMA) system, every application transmits data with
the same bit rate [1] and the chip interleaving SEMA
with iterative detection achieves a significant perform-
ance improvement [2].
In SEMM transmission, each application employs
SESS with different processing gain, where SESS is a
time-varying spreading scheme which must update the
despreading code with the detection bit. One challenge in
SEMM system is to separate the combined signal at the
receiver for each application. Another problem exists
that the detection bit affected by multi-application inter-
ference is not accurate especially at lower SNR. In our
paper, we employ a modified decorrelation scheme in
which an extended signature vectors (ESV) is proposed
for spreading signature [3] to overcome the two difficul-
ties.
Iterative detection has been shown to improve the bit
error rate (BER) performance for its time diversity [2].
The fundamental of the iterative detection is that the in-
formation bit exists in the next N spreading sequence
consequently, where N is the chip length of the spreading
spectrum. However, in SEMM system, the information
bits are merged by the multi-application interference
through the wireless channel. Therefore, an inference
cancellation (IC) scheme is introduced to remove the
multi application interference and realize the iterative
detection.
The rest of this paper is organized as follows: in sec-
tion 2, SEMM system model is introduced; in section 3,
the numerical results are shown and in section 4, we
make a conclusion for the scheme. The important nota-
tions in this paper are with following:
i
l
l: the length of spreading sequences in application i;
max : the maximum length of all the spreading se-
quence;
u: the total applications number in the SEMM sys-
tem;
i: the number of the spreading sequence of applica-
tion i in one transmission circle;
m
ik : the extend spreading sequence in applica-
tion i;
pth
k
r: the received vector from the row of the chip
interleaver;
th
j