SPREAD SPECTRUM MODULATION TECHNIQUES
-spread spectrum - those modulation methods that are producing a signal whose
spectrum is more wider than of the data signal, the occupied frequency band being
independent by the signal of data band.
-The signals with spread spectrum of direct sequence type BPSK (BPSK-DS-SS)
-The signals with spread spectrum of direct sequence type QPSK – DS–SS
- Frequency hopping spread spectrum signals (FH-SS)
Frequency domain characterization of los nonfading indoor wireless LAN channel employing frequency and polarization diversity in the 63.4 to 65.4GHz band
The 4.0 kbit/s speech codec described in this paper is based on a
Frequency Domain Interpolative (FDI) coding technique, which
belongs to the class of prototype waveform Interpolation (PWI)
coding techniques. The codec also has an integrated voice
activity detector (VAD) and a noise reduction capability. The
input signal is subjected to LPC analysis and the prediction
residual is separated into a slowly evolving waveform (SEW) and
a rapidly evolving waveform (REW) components. The SEW
magnitude component is quantized using a hierarchical
predictive vector quantization approach. The REW magnitude is
quantized using a gain and a sub-band based shape. SEW and
REW phases are derived at the decoder using a phase model,
based on a transmitted measure of voice periodicity. The spectral
(LSP) parameters are quantized using a combination of scalar
and vector quantizers. The 4.0 kbits/s coder has an algorithmic
delay of 60 ms and an estimated floating point complexity of
21.5 MIPS. The performance of this coder has been evaluated
using in-house MOS tests under various conditions such as
background noise. channel errors, self-tandem. and DTX mode
of operation, and has been shown to be statistically equivalent to
ITU-T (3.729 8 kbps codec across all conditions tested.
High-Speed, Low-Power
Dual Operational Amplifier
The AD826 features high output current drive capability of
50 mA min per amp, and is able to drive unlimited capacitive
loads. With a low power supply current of 15 mA max for both
amplifiers, the AD826 is a true general purpose operational
amplifier.
The AD826 is ideal for power sensitive applications such as video
cameras and portable instrumentation. The AD826 can operate
from a single +5 V supply, while still achieving 25 MHz of band
width. Furthermore the AD826 is fully specified from a single
+5 V to ±15 V power supplies.
The AD826 excels as an ADC/DAC buffer or active filter in
data acquisition systems and achieves a settling time of 70 ns
to 0.01%, with a low input offset voltage of 2 mV max. The
AD826 is available in small 8-lead plastic mini-DIP and SO
packages.
The rapid growth in mobile communications has led to an increasing demand for wide-
band high data rate communications services. In recent years, Distributed Antenna
Systems (DAS) has emerged as a promising candidate for future (beyond 3G or 4G)
mobile communications, as illustrated by projects such as FRAMES and FuTURE. The
architecture of DAS inherits and develops the concepts of pico- or micro-cell systems,
where multiple distributed antennas or access points (AP) are connected to and con-
trolled by a central unit.
The next-generation wireless broadband technology is changing the way
we work, live, learn, and communicate through effective use of state-
of-the-art mobile broadband technology. The packet-data-based revolu-
tion started around 2000 with the introduction of 1x Evolved Data Only
(1xEV-DO) and 1x Evolved Data Voice (1xEV-DV) in 3GPP2 and High
Speed Downlink Packet Access (HSDPA) in 3GPP. The wireless broad-
band fourth-generation technology (4G) is an evolution of the packet-
based 3G system and provides a comprehensive evolution of the
Universal Mobile Telecommunications System specifications so as to
remain competitive with other broadband systems such as 802.16e
(WiMAX)
The first Third Generation Partnership Project (3GPP) Wideband Code Division
Multiple Access (WCDMA) networks were launched during 2002. By the end of 2005
there were 100 open WCDMA networks and a total of over 150 operators having
frequency licenses for WCDMA operation. Currently, the WCDMA networks are
deployedinUniversalMobileTelecommunicationsSystem(UMTS)bandaround2GHz
in Europe and Asia including Japan and Korea. WCDMA in America is deployed in the
existing 850 and 1900 spectrum allocations while the new 3G band at 1700/2100 is
expected to be available in the near future. 3GPP has defined the WCDMA operation
also for several additional bands, which are expected to be taken into use during the
coming years.
