International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 3, March 2013
ISSN 2319 - 4847
Optical Interleave Division Multiple Access
(OIDMA) System-A Review
Arpana Thakur1, Himanshu Sharma2
1
M.tech student, M.M Engineering College, Mullana (Ambala), Haryana, INDIA
2
Asstt. Prof. ECE Deptt. M.M Engineering College, Mullana (Ambala), Haryana, INDIA
ABSTRACT
As the bandwidth and power become scarce to support the ever increasing throughput requirements, more efficient techniques
play more important roles in future communication systems. The need of faster and more reliable communication systems has
been felt these last years and the sharing of the huge optical bandwidth between users needs appropriate access techniques. In
order to meet these requirements, Optical IDMA (OIDMA) presents an attractive solution.
Keywords: Interleave Division Multiple Access (IDMA), Multiple Access Interference (MAI), Interleaver, Bit Error
Rate (BER).
1. INTRODUCTION
In Interleave division multiple access (IDMA), users are assigned with specific interleavers instead of PN-sequences as
in case of Code Division Multiple Access (CDMA) systems to differentiate amongst users. The scheme considered is a
special case of CDMA in which bandwidth expansion is entirely performed by low-rate coding. An interleaver-based
multiple access scheme gives high spectral efficiency, improved performance and low receiver complexity. IDMA
scheme shows an interleaver as the only means to distinguish the signals amongst users, and hence called as Interleave
division multiple access (IDMA). This scheme inherits many advantages from CDMA such as dynamic channel
sharing, mitigation of cross-cell interferences, asynchronous transmission, ease of cell planning, and robustness against
fading. It also allows a low complexity multiple user detection techniques applicable to systems with large numbers of
users in multipath channels. IDMA allows the use of low rate forward error correction (FEC) codes to maximize coding
gain. Furthermore, it allows a very simple chip-by-chip (CBC) iterative multiuser detection (MUD) strategy. The
normalized MUD cost (per user) is independent of the number of users, that is, its computation cost is very low.
2. INTERLEAVERS
Interleavers are the key component in designing of IDMA systems. Interleaver is the only means to separate users in
IDMA system. Because Once the interleaver is assigned to the user, it is fixed so, it is important that the interleaver
used in IDMA system should be efficient and least complex. It not only provides decorrelation between adjacent bit
sequences but also provide a means for decorrelating various users. The correlation between interleavers should
measure how strongly signals from other users affect the decoding process of a specific user .
3. OPTICAL IDMA (OIDMA)
Interleave Division Multiple Access (IDMA) is a recently proposed multiple access scheme which relies on an iterative
multiuser detection. With the increasing number of users it is required to get the higher transmission capacity to
support the projected growth in traffic levels, and the exponential use of the Internet together with an increase in the
number and range of new services. All optical fiber networking is considered to be the central solution for higher
capacity. The huge inherent bandwidth of single mode optical fiber has already been one of the major transmission
media for long distance Telecommunication with very low losses. To fully utilize the single mode optical fiber
bandwidth, optical multiplexing techniques have been deployed. There are three multiplexing alternatives: wavelength
division multiple access (WDMA), optical time division multiple access (OTDMA) and optical code division multiple
access (OCDMA). The need of faster and more reliable communication systems has been felt these last years and the
sharing of the huge optical bandwidth between users needs appropriate access techniques. In order to meet these
Volume 2, Issue 3, March 2013
Page 325
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 3, March 2013
ISSN 2319 - 4847
requirements, Optical IDMA (OIDMA) presents an attractive solution. This scheme inherits many advantages such as
flexibility of asynchronous and decentralized networking, potentially secure and uncongested high-rate data
transmission, total bandwidth utilization by all network users, both high rate and low rate transmission achieved,
reduced multiple access interference (MAI), better bit error rate (BER).
4. SYSTEM MODEL OF OIDMA SCHEME
4.1 Transmitter Structure
The upper portion of Figure 1, demonstrates the transmitter structure of the optical IDMA scheme with K simultaneous
users. The input data sequence dk of user-k is encoded based on a low-rate code C which generates a coded sequence Ck
≡ [Ck(1)…..Ck(j)…..Ck(J)]T, where J is the frame length. The elements in Ck are referred to as “coded bits”. Then Ck is
permutated by an interleaver , producing Xk ≡ [Xk(1)…. Xk(j)….. Xk (J)]T. The elements in Xk is called “chips”. It
can be an FEC code, or a spreading sequence (spreading is also a special form of coding), or a combination of the two.
From a performance point of view, it is advantageous to use a low-rate FEC code that can provide an extra coding gain.
The key principle of IDMA is that the interleavers {opted for user separation, should be orthogonal for all users. It
is assumed that the interleavers are generated independently and randomly. These interleavers disperse the coded
sequences so that the adjacent chips are approximately uncorrelated, which facilitates the simple chip-by-chip
detection.
Figure 1: System model of OIDMA.
After the interleavers electrical-to-optical convertor (E/O) is used to get optical pulses, which are combined in a
combiner and then pass through an optical fiber.
4.2 Receiver Structure
Lower portion of figure 1 shows optical IDMA receiver. The receiver consists of an optical-to-electrical convertor
(O/E), an elementary signal estimator (ESE) and K single-user decoders (DECs). At the receiver front we used optical
detectors (P-I-N or avalanche photo detector (APD)). Optical detectors must have a wide bandwidth and sharp response
to achieve the high bit-rate which is required by such a system. The interleaved data is arranged back into the original
sequence with the help of de-interleaver which is then decoded and original data of user-k can be reproduced.
Volume 2, Issue 3, March 2013
Page 326
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 3, March 2013
ISSN 2319 - 4847
5. MODULATION SCHEMES
Modulation schemes which are famously used are QPSK and BPSK. Binary data are represented by two signals with
different phases in BPSK. Typically these two phases are 0 and these signals are called antipodal. The reason that
they are chosen is that they have a correlation coefficient of -1, which leads to the minimum error probability for the
same Eb/No.
Among all MPSK schemes, QPSK is the most often used scheme since it does not suffer from BER degradation while
the bandwidth efficiency is increased. Other MPSK schemes increase bandwidth efficiency at the expenses of BER
performance.
6. CONCLUSION
OIDMA is well suited for modern communication system. Main features are robustness against interference, high
spectral efficiency as well as power efficiency. Interleaving is used to overcome correlated channel noise such as burst
error or fading, improve efficiency and performance in OIDMA systems. In this paper, we have presented the system
model of optical IDMA (OIDMA) scheme that reduces Multiple Access Interference (MAI) and provides better Bit
Error Rate (BER).
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