04-09-2012, 02:38 PM
Efficient Resource Sharing Architecture for Multistandard Communication System
Efficient Resource.pdf (Size: 1.06 MB / Downloads: 29)
Introduction
Next generation wireless and mobile networks are all IPbased
heterogeneous networks that allow users to use
any system at anytime, anywhere, anyhow, and always-on
connectivity in a seamless [1] manner. Users carrying an
integrated open terminal can use a wide range of applications
provided by multiple wireless networks and access to various
air interface standards. The continuous evolution of wireless
networks and the emerging variety of different heterogeneous,
wireless network platforms with different properties
require integration into a single platform [2]. The handoff
mechanism allows a network connection on a mobile node
to operate over multiple wireless access networks in a way
that is completely transparent to end user applications. But
there is no single system that is good enough to support all
the wireless communication technologies. Instead of putting
efforts in developing new radio interfaces and technologies
for 4G [3] systems, we believe establishing 4G systems that
integrate existing and newly developed wireless systems into
one open platform is a more feasible option.
Wideband CodeDivisionMultiple
Access (WCDMA)
Wideband Code Division Multiple Access (WCDMA) is a
third-generation mobile wireless technology that is based on
an ITU standard derived from CDMA [14–16] technology.
WCDMA can support mobile/portable voice, images, data,
and video communications up to 2Mbps (local area access)
or 384 kbps (wide area access). One of the more demanding
functions on the WCDMA Baseband receiver module is the
Rake Receiver [17]. A Rake Receiver allows each arriving
multipath signal to be individually demodulated and then
combined to produce a stronger and more accurate signal.
Figure 1 shows the components of a Rake Receiver: a set of
fingers and a combiner block.
The actual number of Rake fingers is not specified
by WCDMA specifications but typically 4–8 fingers are
employed. The demodulation is performed in the Rake
fingers by correlating the received signal with a spreading
code over a period corresponding to the spreading factor.
Each Rake finger consists of two multipliers for applying
the spreading and scrambling codes and an accumulator
of length scrambling factor, input sample delay memory
block, downsampling block, scrambling and spreading code
generators. Figure 2 shows the schematic diagram of a Rake
finger.
Orthogonal Frequency Division
Multiplexing (OFDM)
Broadband WLAN standards (IEEE 802.11a/g, IEEE 802.16,
Digital Audio Broadcast (DAB), and HIPERLAN/2) are
based on the Orthogonal Frequency Division Multiplexing
(OFDM) [18–20]modulation scheme because of its superior
performance in various multipath environments, such as
indoor wireless networks and metropolitan area network.
OFDM can efficiently deal with multipath fading, channel
delay spread, enhanced channel capacity, adaptively modifies
modulation density and robust to narrowband interference.
Figure 3 shows the basic block diagram for OFDM Receiver
module. At the receiver, the received RF signal is downconverted
to baseband frequency, digitized, and fed to the
baseband section for further processing. Here the data is
first cleaved off the cyclic prefix, followed by Fast Fourier
Transform (FFT) [21, 22] operation and demodulated to
obtain the received data bits. The key kernel in an OFDM
receiver is the FFT processor. FFT-based processing is used to
convert the signals from time domain to frequency domain
and vice versa in OFDM modulation. The idea of using FFT
instead of DFT is that the computation can be made faster
where this is the main criteria for implementation. In direct
computation of DFT the computation for N-point DFT will
be calculated one by one for each point.
Conclusion
An architecture which can reconfigure itself to wireless
LAN OFDM and WCDMA standards, was presented in
this paper. While configuring these two standards, it was
also presented to implement FFT operation for OFDM
and Rake Receiver functioning for WCDMA efficiently. To
lower the number of multipliers in FFT and eliminate the
multipliers in Rake Receiver, we adopted Strength Reduction
Transformation technique and multiplier-less technique.
The proposed architecture was simulated using ModelSimSE
v6.5 and mapped onto a Xilinx Virtex 5 FPGA device and
synthesis report was generated. Substantial improvements
in terms of number of Slice LUTs used and the number of
gates utilized were achieved. Comparison results showed that
the proposed architecture can reduce large number of FPGA
resources, enhance efficiency of the hardware architecture,
and significantly reduce area and power consumption.
Moreover, the proposed architecture can be improved to
reconfigure to various other advanced wireless standards.