Performance analysis of IDMA and CODED IDMA system

Anurag Yadav Department of E.C.E

G.L.A. University Mathura,India

anuuragyadav@gmail.com

Aasheesh Shukla Department of E.C.E

G.L.A. University Mathura,India

aasheesh.shukla@gla.ac.in

Abstract-At the present time, an alternative multiple access schemebaptizedinterleave-division multiple access (IDMA) has enticed greatly devotion, in which interleavers are recycled as the onlymeans for user parting. It has been displayed that the IDMAcan accomplish near single user presentation in multi-usersurroundings with very truncated receiver complexity. In this broadsheetWeequate the presentation of interleave-division multiple-access (IDMA) technique which deeds the interleaving as resources of user parting instead of by different marks as in a conventional code-division multiple-access (CDMA) pattern and coded IDMA arrangement where we use dissimilar codes to diminish bit error rate(BER).This technique take over many compensations from CDMA, such as diversity against fading and mitigation of the wickedest-case user interference problem. This paper offeringsangeneral idea of IDMA and deliberates the main features and regions of application. Keywords: IDMA, iterative decoding, multiuser detection.

I. INTRODUCTION

Lately, ainnovative approach to extent spectrum mobile systems called Interleave division multiple access (IDMA) has been offered. In CDMA users are illustrious by different signatureorders, while IDMA differentiates users by chip level interleaving procedure. IDMA receives many advantages from CDMA particularly, chip- by –chip interleaving can be in contrast to fading and mitigation of further cell user interference [1].In the transmitter of IDMA scheme, a chip glassy interleavers is trailed by spreading procedure which is dissimilar from conventional CDMA scheme [1-3]. The fundamental principle of IDMA arrangement is dissimilarinterleavers for dissimilar users. Numerousinterleavers have been already proposed. Once the interleaveris allotted to the user, it is immovable so, it is essential that the interleaverrecycled in IDMA organization should be effective and tiniestmultifaceted. In IDMA, data streams are divided by different interleaversinstead of by different spreading codes. All data stream is encrypted by the identical low-rate channel encoder. The data rate can be modified by cover upnumerous encoded and interleaved data streams at the receiver. And it can be done in aniterative, low complication way. In this broadsheet we equate the results of dissimilarinterleavers and underliningon their relative performance. We also indicate the benefits and application of interleavers at the most recent of the broadsheet.

II. WHYIDMA? The keydrawback with conventional CDMA organizations [3] is multiple access interference (MAI), andintersymbol interference (ISI). CDMA systems are having great degree of complication andmulti-user detection (MUD) isconstantly a greatproblematic. The procedure of signature sequences for user parting is a typical feature for a conventional CDMA organization. Interleaving is generally placed in the middle of forward error correction (FEC) coding and spreading and is conventionally employed to fight the fading result.[5] A conventional random waveform CDMA (RWCDMA) organization (such as IS-95) containsdistinct coding and spreading procedures. Theinvestigation shows that the ideal multiple access channel (MAC) capacity is attainable only when the whole bandwidth extension is dedicated to coding. This proposesmerging the coding and spreading procedureswith low-rate codes to exploit coding gain. But parting of users without spreading procedure is not achievable in CDMA [5]. ProbableExplanation for User Separation: • Narrow band coded-modulation scheme by means of

trellis code constructions. [4] • To employ chip-level interleavers. [3][4][5][6] Individually the methods are useful for the presentation. But hiringdissimilarinterleavers to dissimilar users [5] [6]enhanced the presentation of CDMA organization. So theprobableexplanation to this problematic is to engage chip-level interleavers for user parting. Its possiblebenefits have been established[7] viewing the probability of engaging interleaving for user parting in coded organizations.Ref. [9] deliberate a chip interleaved CDMA arrangement and a maximal-ratio-combining (MRC) procedure for ISI MACs. It visiblyverified the advantages of presenting chip-level interleavers. An interleaver-based multiple access arrangement has also been deliberated in [10],[11] for great spectral efficiency, enhanced error performance and truncated receiver complexity.

III.OVERVIEW TO IDMA IDMA standpoints for Interleave division multiple access.This arrangement is used for spreadspectrum mobile communication organizations, wherein users are illustrious by dissimilar chip-level interleaversas an alternative of by dissimilar signatures as in a conventional CDMA organization[2][11]. The arrangementmeasured is a distinct case of CDMA in which bandwidth development is

2013 5th International Conference on Computational Intelligence and Communication Networks

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DOI 10.1109/CICN.2013.60

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completelyachieved by low-rate coding. For suitability, it may be denoted as interleave-division multiple-access (IDMA) [10][11]. This arrangementreceives many benefits fromCDMA such as dynamic channel sharing, mitigation of cross-cell interferences ,asynchronous transmission, easiness of cell planning, and robustness in contrast to fading. It also permits a low complexity multiple user detection methodsappropriate to organizations with greatamounts of users in multipath channels. .

IV. IDMAORGANIZATION A.TRANSMITTER CONFIGURATION

The upper portionof Fig.1indicate the transmitter configuration of an IDMA organization. The coder block of a low-rate code C is engaged to produce a coded

arrangement ( )Kc = { ( )Kc , j=1, 2, ..J}, whereverJ is the frame length,

monitored by a chip level interleaver ( )mΨ that draws ( )Kc to ( )Kx ={ ( )Kx , j=1, 2, ..J}.

We monitor the CDMAconvention and call the undeveloped

elements in ( )Kc and ( )Kx “chips”. Coderblockcan be either the similar or dissimilar for altered users. It can be a spreading code (spreading is also a distinct form of coding) or an FEC code or a grouping of the two [11]. From a presentationstandpoint, it is beneficial to use a low-rate FEC code [9][10] that can afford an additional coding gain. The

strategic principle of IDMA is that the interleavers { ( )KΨ } should be dissimilar for separate users. We assume that the interleavers are producedautonomously and arbitrarily. For straightforwardness, we first study time-invariant single-path channels with real channel coefficients and BPSK signaling. Later sampling at chip rate, the signal that is received from K users can be written as

( ) ( )

1

mK K

j j jr h x n= +� ,{j=1, 2…j} (1)

Wherever ( )Kjx is the Kth usertransmittedchipof jth,the

channel coefficient for theKth user is h(k)and jn is the

samples of a zero-mean additive white Gaussian noise

(AWGN) with 2σ =N0/2, where � is variance.

Figure 1. IDMA Transmitter and Receiver

B. RECIEVER CONFIGURATION The lower portion of Fig. 1, displays the receiver unit of IDMA organization. The iterative multiuser detector services a low-cost chip-by-chip detection scheme and escapes conventional MAP. The receiver portion containsElementary Signal Estimator (ESE)andaposteriori probability (APP) decoder (DEC). The Elementary Signal Estimatorinteract information with the Decoder in a turbo-

type manner [8]. On the information bits { Kd }, the hard

decisions { Krxd } also produced bythe Decoder (DEC)in the

final repetition. The operation of the receiver is based on the received signal

r,where { jr , j = 1…J}, the channelcoefficients h [ (1)h ,…,

( )kh ,…., ( )Kh ]. It is usually prohibitively very complicated to find the best solution. Now we consider a sub-optimal methodology by first sorting out the conditions, i.e., r, hand C, and after this we combine the results using an iterative or repetitive process. This significantlydecreases the complexity which is involved in it. In detail, the limitation of Coderis unnoticed in the Elementary Signal Estimator (ESE). TheESE output is well-defined by the logarithm likelihood ratio (LLR)

( | ( ) 1, ){ ( ( ))} log

( | ( ) 1, )j K

ESE Kj K

p r x j he x j

p r x j h

� �= += � �

= −� �� �,K j∀

(2) The Decoder (DEC) of the receivercomprises of K local APP decoders. AnAPP decoding of Coder for the kth useris

performed by the kth local APP decoderusing ESEe,afterward suitabledeinterleaving, as its input. The output is the pretended extrinsic LLR [8].

252

( ( ) 1| ( ( )), ){ ( ( ))} log ( ( ))

( ( ) 1| ( ( )), )r K ECE K

DEC K ECE Kr K ECE K

p x j e x j Codere x j e x j

p x j e x j Coder

� �=+= −� �

=−� �

,K j∀ ( 3) In the Decoder (DEC), we will not discussthe APP decoding it indetail because it is a standard function [8]. We will only focus on the ESE in the following. C. Explanations of the ESE

The ESE functioncreatesrough estimates of { ( )Kx j , j =

1,…,J, K = 1,..k,.., K}. Now to preserve low complexity,we ignorethe constraint of Coder. Now,under BPSK modulation,we consider the jth chip of the kth user with

( )Kx j ∈{+1, -1}. We treat ( )Kx j as a random variable

and use ( ( ))DEC Ke x j (initialized to zero) to approximate

the a priori LLR of ( )Kx j ,

( ( ) 1{ ( ( ))} log

( ( ) 1r K

DEC Kr K

p x je x j

p x j

� �= +≈ � �

= −� �(4)

Based on (4), we have

exp( ( ( ))) 1( ( ))) tanh(( ( ( )))/2)

exp( ( ( ))) 1DEC K

K DEC KDEC K

e x jE x j e x j

e x j

−= =

+

………… (5)

and 2Var( ( )))=1- ( ( )))K Kx j E x j , (6)

Algorithm 1: Chip-by Chip Detection in a single path Channel

Step (i): Estimation of Interference Mean and Variance

Set

Then

( )k jξ is the distortion (including interference-plus-noise)

in received signal with respect to user-k.

Step(ii): LLR Generation

Step (iii): Updating of data

Now, the repeatedsteps are depending on no. of repetitions and users. Algorithm 2: Chip-by-Chip detection in a Multipath

Channel, Now with memory length L-1, we consider the

Elementary Signal Estimator(ESE) function in a quasi-static

multi-path fading channel. Afterward chip matched filtering,

the received signal can be represented by

where

Step(i): Interference Mean and VarianceEstimation

Step (ii): Generation of LLR

and

Step (iii): Dataupdating

1

( ( ( ))) ( ( ( )))S

DEC k ESE kj

e x j l e x j lπ π=

+ = +�

Flowchart for iterative decoder

( ( )) 0DEC ke x j =

,

2

( ( )) ( ( )) ( ( ))

( ( )) ( ( )) ( ( ))

k l k k

k k k

E j E r j h E x j

Var j Var r j h Var x j

ξ

ξ

= −

= −

( ( )) ( ( ))k kk

E r j h E x j⇐� ,k j∀

,

2

( ( )) ( ( )) ( ( ))

( ( )) ( ( )) ( ( ))

k l k k

k k k

E j E r j h E x j

Var j Var r j h Var x j

ξ

ξ

= −

= −

( ( )) 1 ( ( ( )) / 2)k kVar x j E x j⇐ −

2

( ) ( ( )) ( ( ))( ( )) 2 .

( ) ( ( ))k k

ESE k k

j k k

r j E r j h E x je x j h

Var r h Var x j

− +=

−

1

( ( ( ))) ( ( ( )))S

DEC k ESE kj

e x j e x jπ π=

=�1,...,j S=

, ,( ) ( ) ( )k l k k lr j l h x j jξ+ = +

1,... 1j J L= + +

',,

( ( )) ( ( ))k l kk l

E r j h E x j l= −�2 2

,,

( ( )) ( ( ))k l kk l

Var r j h Var x j l σ= − +�

, ,( ( )) ( ( )) ( ( ))k l k l kE j E r j l h E x jξ = + −

2

, ,( ( )) ( ( )) ( ( ))k l k l kVar j Var r j l h Var x jξ = + −

,k j∀

,,

,

( ) ( ( ))( ( )) 2

( ( ))k l

ESE k l k lk l

r j l E je x j h

Var j

ξ

ξ

+ −=

1

0

( ( )) ( ( ))L

ESE k ESE k ll

e x j e x j−

=

=�

1,...,j S=

253

Figure 2: Flowchart of mechanism in iterative decoder

STRATEGY FACTORS

A. MODULATION PATTERNS: Modulation Patterns which are well used are QPSK & BPSK.

B. CODING: The data can be sending in the channel with coding or without coding after modulation. There are various types of codes commonly used for coding.

• Convolution codes • Gold codes, etc. Interleaver :We will discuss lots of available interleavers. PERFORMANCE DETAILS OF SOME INTERLEAVING SCHEMES IDMA WITH MODLATION SCHEMES: L. ping has studied the IDMA organization with BPSK and QPSK modulation arrangements, in [13]. In both the arrangement,it has been observed that BER is more improved in comparison to CDMA. The QPSK arrangement is every timefavored to BPSK arrangement in terms of improved bandwidth utilization although the BER performance is comparable to that of BPSK.Advantagetogether with low-cost MUD for organization for large users, high spectral efficiency and near limit presentation, has been reported by L. ping. INTERLEAVER DIVISION MULTIPLEXING :In paper [14], K. Y. Wu, W. K. Leung and Li Ping showa class of ST codes for interleaver division multiplexing (IDM). Interleaving is accepted as the simple means to distinct signals from dissimilar antennas. The proposed arrangement is appropriate to organizations with random numbers of transmit antennas. Aobvious feature of the offered scheme is its easiness without cultured structural design processes. Performance close to the theoretical limits can be achieved at moderate receiver complexity.

POWER INTERLEAVER:Inbroadsheet[12], Li. Ping has offered a new interleavertermed power-interleaver. With this technique, the interleaver assignment arrangement is cut down and cost of memory is significantly reduced without give up performance. Here, the only need is to store the power interleaverφ . Let

the power interleaverbe1π φ≡ . After implementing the

detection cycle for user 1, the interleaver can be updated from

1π φ≡ to 2( )φ π φ= . This process continues

recursively.The result of numerical shows that this new method of interleaver generation are called ‘power-interleavers’, that can take the place of random-interleavers without loss of performance. The drawback of this arrangement is to consume higher

access time for user securing nφ interleaver where n is the user number. The result of simulation shows that similar results have been found as that attained with Random Interleavers, but significant amount of memory space has been saved. BLOCK RANDOM INTERLEAVER:In paper [40], Maria kovaci, Horia G. Balta and Miranda M. Naformitapresenta block random interleaver and their BER & FER (Frame Error Rate) are compared with random interleaver, S-interleaver, block interleaver, pseudo random interleaver and Takeshita- Costello interleaver. The performances recommend the proposed interleaver as an alternative to the S-interleaver, which is the best at lengths superior to 1000.bits. The performances of the proposed BRL (Block Random in Line) interleaver are very close to the performance of the S-interleaver with maximum S (a minimum interleaving distance) but the design of the new interleaver is simpler.

Figure 3: Simulation result of Block Random Interleaver with and without convolution or gold code

254

Helical Interleaver: The principle design rule of helical interleavers is to start off from a pre-defined interleaver as a master interleaver,from which the family of helical interleavers are generated byreading the interleaver indices in a deterministic order. Thegeneration process can be described as follows: 1. Generate a one-dimensional master interleaver

oflength Nc(e.g, a pseudo-random interleaver) and write theinterleaver indices of the master interleaver row-wise intoa matrix with Mrrows and Mccolumns, where Mr�Mc= Nc.

2. The 1st helical interleaver is generated from the masterinterleaver by reading the interleaver indices column-wise from the matrix

3. The remaining interleavers are generated by cycliclyreading the interleaver indices from the diagonals of thematrix.

Figure 6: Simulation result of Helical Interleaver TREE BASED INTERLEAVER : In paper [46], N. V. AnilKumar, M. K. Shukla and S. Tiwari, propose a new Tree Based Interleaver (TBI) to generate different chip-level interleaving sequences for different users in an IDMA system, which reduces computation complexity. This method of generation also solves the memory cost problem and reduces the amount of information exchange between mobile stations and base stations required to specify the interleaver.

Figure 6: Interleaving mask allocationfor the proposed TreeBased Interleaving Scheme In this paper the proposed interleaver generation method is implemented in FPGA for 6 users with having 8 bits/chip. Simulation result of Tree Based Interleaver without coding and with coding (using gold codes) Techniques for 2 users.

Figure 8: Simulation results of Tree Based Interleaver V. Current Trends in IDMA

The testing and improvements in IDMA scheme is being carried out by many researchers throughout the world. Simulation of IDMA scheme has been performed and is explained in [10}, [11], and [12]. The problem of memory requirement for user specific interleavers at the receiver and transmitter end, is also explored in [15] and a suggestion has been explained regarding use of master interleaver. The space time coding in IDMA system has been performed in [16] and near optimum results has been obtained.

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IDMA can be considered as a special case of conventional CDMA. In IDMA, each data stream is first encoded by a (very) low-rate encoder. Conceptionally, the same encoder can be used for each data stream (i.e., even different users use the same encoder). For convenience, each data stream is referred to as a layer. We assume that the encoder is binary; hence the layers are binary as well. Subsequently the coded bits usually referred to as chips in this context, are interleaved. The main difference between IDMA and conventionalCDMA is that in IDMA each layer is assigned a layerspecific interleaver, whereas in conventional CDMA a layer-specific spreader is applied. As a consequence, in IDMA chip-by-chip interleaving is done and no spreading code is used. Finally, the encoded and interleaved data streams of different layers of the same user are linearly superimposed (preferably with different phases and amplitudes) before transmission. The data rate can be adapted by superimposing a variable number of layers. In contrast to other system designs, channel coding is an integral part of the IDMA system design. A receiver-side separation of the layers can be done iteratively (“turbo processing”) by exploiting the different interleavers, the codeconstraints, and a multi-layer detector. These properties make IDMA an attractive candidate for the 4G uplink, but also for an evolution of existing conventional CDMA systems and other applications such as wireless local area networks (WLAN), ad-hoc networks, sensor networks, ultra wideband communications (UWB), and underwater communications [14].

VI. Future Scope of Work IDMA scheme has many stones to be turned in terms of research. Some of them are listed below, • Implementation of different coding schemes in

Interleave Division Multiple Access Technique (IDMA) with AWGN Channel

• To study the performance of different signaling schemes in IDMA using without/with coding with AWGN Channel

• Implementation of IDMA for different Channels with different coding schemes

• Modification in interleaver design • IDMA implementation in VHDL

VII. Conclusions

The novel concept of IDMA can generate some fruitful results. The common advantages of conventional DS -CDMA aremaintained, since IDMA is just a special formof DS-CDMA. As a consequence, existingCDMA systems may be enhanced byIDMA as well. Still, there are many horizons open for further improvements and testing of IDMA systems such as in interleaving scheme for memory optimization, improvement in coding schemes, automatic repeat request,synchronization

issues, and peak-to-averagepower reduction, and in modulation schemes. Apart from this, diversity techniques may also be tested and implemented in IDMA systems for superior performances in wireless communication.

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