Design and implementation of address generator for wi max deinterleaver on fpga

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 139
DESIGN AND IMPLEMENTATION OF ADDRESS GENERATOR FOR
WiMAX DEINTERLEAVER ON FPGA
Mallikarjun Naykodi1
,G.S. Biradar2
1
Dept. of VLSI Design & Embedded System, VTURC Gulbarga, Karnataka, India
2
Dept. Of Electronics and Communication, PDA College Of Engineering, Gulbarga, Karnataka, India
Abstract
This Paper enumerates efficient method of address generator for WiMAX Deinterleaver using verilog coding. It is a low-complex,
high speed and resource efficient method because it eliminates the requirement of floor function. The use of an internal multiplier of
FPGA and the sharing of resources for quadrature phase-shift keying (QPSK),16-quadrature-amplitude modulation (QAM), and 64-
QAM modulations along with all possible code rates makes our approach to be novel and highly efficient when compared with
conventional look-up table-based approach. The proposed approach exhibits significant improvement in the use of FPGA resources.
Keywords: Digital circuits, error correction, field programmable gate arrays (FPGAs), wireless systems
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1.INTRODUCTION
BROADBAND wireless access (BWA) is continuously
becoming a more challenging competitor to the conventional
wired last mile access technologies [1]. IEEE has developed
standards for mobile BWA (IEEE 802.16e) popularly referred
to as mobile WiMAX [2]. The channel interleaver employed
in the WiMAX transreceiver plays a vital role in minimizing
the effect of burst error. In this brief, a novel, low-complexity,
high-speed, and resource-efficient address generator for the
channel deinterleaver used in the WiMAX transreceiver
eliminating the requirement of floor function is proposed [2].
Fig:1 Block diagram of the WiMAX transreceiver.
The mandatory blocks of a WiMAX transreceiver are shown
in Fig. 1. Data stream received from a source is randomized
before being encoded by two forward error correction (FEC)
coding techniques, namely, Reed–Solomon (RS) and
convolutional coding (CC). The channel interleaver permutes
the encoded bit stream to reduce the effect of burst error.
When convolutional turbo code (CTC) is used for FEC, being
optional in WiMAX, the channel interleaver is not required,
since CTC itself includes an interleaver within it[5].
Modulation and construction of orthogonal frequency-division
multiplexing symbols are performed by the two subsequent
blocks, namely, mapper and inverse fast Fourier transform of
Fig. 1. In the receiver, the blocks are organized in the reverse
order enabling the restoration of the original data sequence at
the output.
Fig:2 Block diagram of interleaver/deinterleaver structure.
Two-dimensional block interleaver/deinterleaver structure,
which is used as a channel interleaver/deinterleaver in the
WiMAX system, is described in Fig. 2.Hardware Structure for
Address Generator for WiMAX Using Different modulation
techniques
2.INTERLEAVING IN WiMAX SYSTEM
The block interleaver/deinterleaver exploits different
depthsNcbps to incorporate various code rates and modulation
schemes (see Table I) for IEEE 802.16e. The data stream
received from the RS-CC encoder is permuted by using the
two-step processes described by (1) and (2). These steps
ensure mapping of coded bits onto nonadjacent subcarriers

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and alternate less/more significant bits of the modulation
constellation, respectively. Thus,
mk=(Ncbps/d).(k%d)+[k/d] (1)
jk=s.[mk/s]+(mk+Ncbps – [d.mk/Ncbps])%s (2)
Here, the number of columns is represented by d (= 16/12for
WiMAX); mk and jk are the outputs after the first and second
steps, respectively; and k varies from 0 to Ncbps− 1. sisa
parameter defined as s = Ncpc/2, where Ncpc is the number of
coded bits per subcarrier, i.e., 2, 4, or 6 for QPSK, 16-QAM,or
64-QAM, respectively [9]. Modulo and floor functions are
signified by percent and _ _, respectively. The deinterleaver,
which performs the inverse operation, is also defined by two
permutations, i.e., (3) and (4). Let mj and kj define the first
and second level of permutations for the deinterleaver, where j
is the index of received bits within a block of Ncbps bits. As
per [10], (3) and (4) perform inverse operation of (2) and (1),
respectively. Thus
mj=s.[j/s]+(j+[d.j/Ncbps])%s (3)
kj=d.mj-(Ncbps-1).[d.mj/Ncbps] (4)
3. ALGORITHM FOR DEINTERLEAVER
Here, the proposed algorithm for address generator of the
WiMAX deinterleaver along with its mathematical
background has been described. A MATLAB program is
developed using(3) and (4) for all modulation schemes and
code rates. Due to the presence of a floor function in (3) and
(4), their direct implementation on an FPGA chip is not
feasible. Table shows the deinterleaver addresses for the first
four rows and five columns of each modulation type. As d =
16 is chosen, the number of rows are fixed (= d) for all Ncbps,
whereas the number of columns are given by Ncbps/d.
Table-1: Address generation of different schemes
A close examination of the addresses in Table reveals that the
correlation between them. The mathematical foundation of the
correlation between the addresses, as derived in this brief, is
represented by (5)–(7), i.e.,
Where j = 0, 1, . . . , d − 1 and i = 0, 1, . . . , (Ncbps/d) –
1represent the row and column numbers, respectively,
inTable-1[5]. In addition, kn represents the deinterleaver
addresses. General validity of (5)–(7) to represent the
correlation between addresses of Table has formally been
proven using the algebraic analysis, which lacks the
involvement of(5)–(7). The outcome of this analysis using
(5)–(7) provides the same result, as shown in Table. Thus, (5)–
(7) play the pivotal role in establishing formal mathematical
foundation of our proposed algorithm.
4.PROPOSED MODEL
Fig:3aThe address generator for QPSK.

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Fig:3bThe address generator for 16-QAM.
Fig:3cThe address generator for 64-QAM.
In order to test the proposed algorithms for the address
generator of the WiMAX deinterleaver with all modulation
schemes, transformation of these algorithms into digital
circuits are made and are shown in Fig. 3(a)–(c). The QPSK
hardware shown in Fig. 3(a) has a row counter RWC0 to
generate row numbers between 0 and d − 1. A column counter
CLC0 with multiplexer M0 and comparator C0 generate the
variable column numbers to implement permissible Ncbps. A
multiplier ML0 and an adder A0 perform the desired
operations to implement (5). The address generator for 16-
QAM follows a similar structure, such as that of QPSK with
few additional modules. These modules are designed with an
incrementer, a decrementer, two modulo-2 blocks, and two
multiplexers, as shown in Fig. 3(b). As per in the 64-QAM
modulation scheme, the address generator has to implement
three different progressive patterns for the column numbers.
The design procedure used in 16-QAM is extended in 64-
QAM to meet this requirement with the use of additional
hardware[6] and is shown in Fig. 3(c). A simple up counter
generates the read addresses for the 2-D deinterleaver.
Fig 4:Top-level view of complete deinterleaver address
generator.
The top-level structure of the deinterleaver address generator
is shown in Fig. 4. Logic circuits shown inside the dashed line
in Fig. 3(a)–(c) are presented here as QPSK block, 16-QAM
block, and 64-QAM block, respectively. Our design is
optimized in the sense that common logic circuits such as
multiplier, adder, row counter, and column counter are shared
while generating addresses for any modulation type. In
addition, the design also shares the incrementer and the
decrementer required in 16-QAM and 64-QAM blocks.
5.FPGA IMPLEMENTATION RESULT
The Verilog program developed for the proposed WiMAX
deinterleaver address generator is downloaded on the
XilinxSpartan-3 (Device XC3S400) FPGA. The two blocks,
namely, MO0 and MO1of Fig. 3(b), are implemented using
the mod 2n function of Verilog. The requirement of imod 3
(MO2) and j mod 3 (MO3)functions in 64-QAM circuit are
fulfilled by designing two small ROMs of dimension 16 × 3-
bit and 64 × 3-bit, respectively, as the MOD 3 function is not
supported in Verilog. The use of the rest of the logic circuits is
obvious in the design. As the FPGA-based implementation of
the WiMAX deinterleaver address generator has not been
found in the literature, direct comparison of the results of our
proposed work could not be carried out. However,
implementation of the conventional LUT-based technique of
address generation for the WiMAX2-D deinterleaver on the
same FPGA. In the latter case, the LUTs are modeled using
FPGA’s embedded memory, i.e., block RAM, to reduce the
memory access time. For fairness of comparison, three block
RAMs are used, i.e., one for each modulation scheme to house
the address LUT of various interleaver depths[7].Efficient use
of block RAMs is made possible by exploring the feature that,
within a modulation scheme, the address LUTof a smaller
Ncbps is the subset of the address LUT of the larger Ncbps. In
spite of the smart use of block RAM in LUT-based approach,
this brief results in a significant reduction in occupancy of
FPGA slices(by 80.24%), flip flops (by 35.9%), and four input
LUTs (by80.47%). This comparison clearly proves the low

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complexity and hardware efficiency of our design over the
conventional technique. Furthermore, to make the design more
hardware efficient, embedded multiplier of the Xilinx Spartan-
3 FPGA is used to implement the ML3 block of Fig. 4. In
addition, the address generator using the proposed technique
can work48.69% faster than the latter. Furthermore, based on
the equivalence drawn between FPGA and application
specified integrated circuit implementations , our work is
again compared with the FPGA-equivalent implementation.
This comparison also shows almost 48.69% improvement in
our work with respect to operating frequency over as FPGA-
equivalent maximum frequency of the latter is found to be
62.5 MHz. The reasons behind these improvements are low-
complexity, optimized, and shared hardware design and the
use of FPGA’s embedded multiplier, which, in turn, reduces
interconnection delay inside FPGA. Both CTC and long-term
evolution interleavers do not use floor function for FPGA
implementation, whereas this brief involves the use of floor
function for such realization in an efficient manner.
Fig 5 Simulation result
6. CONCLUSIONS
In this novel algorithm along with its mathematical
formulation, including proof for address generation circuitry
of the WiMAX channel deinterleaver supporting all possible
code rates and modulation patterns as per IEEE802.16e. The
proposed algorithm is converted into an optimized digital
hardware circuit. The hardware is implemented on the Xilinx
FPGA using Verilog. Comparison of our proposed work with
a conventional LUT-based method and also with a recent work
show significant improvement on resource utilization and
operating frequency.
REFERENCES
[1]. W.Konhauser,” Broadband wireless access solutions-
Progressive challenges and potential value of next
Generation”, Wirelesspers commun.,vol.37,no.3/4pp.243-
259,May 2006.
[2]. B. Li, Y. Qin, C. P. Low, and C. L. Gwee, “A survey on
mobile WiMAX”, IEEE Commun. Mag., vol. 45, no. 12, pp.
70–75, Dec. 2007.
[3]. Y. N. Chang and Y. C. Ding, “A low-cost dual mode in
de-interleaver design,” Proc Int. Conf. Consum. Electron.,
2007, pp. 1–2.
[4]. A. A. Khater, M. M. Khairy, and S. E.-D. Habib,
“Efficient FPGA implementation for the IEEE 802.16e
interleaver,” in Proc. Int. Conf. Microelectron., Marrakech,
Morocco, 2009, pp. 181–184.
[5]. B.K.Upadhyaya,I.S.Misra,andS.K.Sanyal,“Noveldesign of
address generator for WiMAX multimode interleaver, using
FPGA based finite state machine,” in Proc.13th
Int.Conf.Comput. Inf. Technol., Dhaka, Bangladesh, 2010,
pp.153–158.
[6]. R.Asghar and D.Liu,“2 Drealization of WiMAX channel
interleaver for efficient hardware implementation,”
inProc.WorldAcad.Sci.Eng.Field Programm. Gate Arrays,
Monterey, CA, USA, 2006, pp. 21–30.
[7]. XilinxSpartan3FPGAFamily:CompleteDataSheet,Xilinx,
Inc.,San Jose,CA,USA,2012.
[8]. B.K.Upadhyaya and S.K.Sanyal, “Animproved LUT
based reconfigurable multimode interleaver for WLAN
application,” Int.J.Recent Trends Eng.Tech., ACEEE,
vol.6,no.2,pp.183–188,2011.
9]. I.KuonandJ.Rose, “Measuring the gap between FPGAs,” in
Proc.Int.Symp. Field Programm. GateArrays, Monterey,
CA,US A, 2006,pp.21–30.

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