Abstract-The effect of the companding process on QAM signals
has been under investigation for the past several years. The
compander, included in the PCM telephone network to improve
voice performance, has an unusual affect on digital QAM data
signals which are transmitted over the same channel. The quantization
noise, generated by the companding process which is multiplicative
(and asymmetric), degrades the detectability performance
of the outermost points of the QAM constellation more
than that of the inner points.
The combined effect of the companding noise and the inherent
white gaussian noise of the system, leads us to a re-examination of
signal constellation design.
In this paper we investigate the detectability performance of a
number of candidates for signal constellations including, a typical
rectangular QAM constellation, the same constellation with the
addition of a smear-desmear operation, and two new improved
QAM constellation designs with two-dimensional warpi
ofdm信道特性
Channel transmission simulator
Channel transmission simulator
％
％ inputs:
％ sig2 - noise variance
％ Mt - number of Tx antennas
％ Mr - number of Rx antennas
％ x - vector of complex input symbols (for MIMO, this is a matrix, where each column
％ is the value of the antenna outputs at a single time instance)
％ H - frequency selective channel - represented in block-Toeplitz form for MIMO transmission
％ N - number of symbols transmitted in OFDM frame
％
％ outputs:
％ y - vector of channel outputs (matrix for MIMO again, just like x matrix)
％ create noise vector sequence (each row is a different antenna, each column is a
％ different time index) note: noise is spatially and temporally white
Process a binary data stream using a communication system that
consists of a baseband modulator, channel, and demodulator.
Compute the system s bit error rate (BER). Also, display
the transmitted and received signals in a scatter plot.
MPEG-4 標準文檔
access to visual objects in natural and synthetic moving pictures and associated natural or synthetic sound for
various applications such as digital storage media, internet, various forms of wired or wireless communication etc.
The use of ISO/IEC 14496 means that motion video can be manipulated as a form of computer data and can be
stored on various storage media, transmitted and received over existing and future networks and distributed on
existing and future broadcast channels.
GNU_Radio
GNU radio is a free/open-source software toolkit for and the content is controlled by a handful of organizations. Cell
building software radios, in which software defines the phones are a great convenience, but the features your phone
transmitted waveforms and demodulates the received supports are determined by the operator s interests, not yours.
waveforms. Software radio is the technique of getting code A centralized system limits the rate of innovation. Instead of
as close to the antenna as possible. It turns radio hardware cell phones being second-class citizens, usable only if
problems into software problems.
Digital Modulation Techniques are those echniques through which we convert digital signals into analog signal which can be transmitted through transmission medium...this program demostrate some of the basics techniques
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.
Mobile communication devices like smart phones or tablet PCs enable us to
consume information at every location and at every time. The rapid development
of new applications and new services and the demand to access data in real time
create an increasing throughput demand. The data have to be transmitted reliably
to ensure the desired quality of service. Furthermore, an improved utilization of
the bandwidth is desired to reduce the cost of transmission.
Cognitive radio has emerged as a promising technology for maximizing the utiliza-
tion of the limited radio bandwidth while accommodating the increasing amount of
services and applications in wireless networks. A cognitive radio (CR) transceiver
is able to adapt to the dynamic radio environment and the network parameters to
maximize the utilization of the limited radio resources while providing flexibility in
wireless access. The key features of a CR transceiver are awareness of the radio envi-
ronment (in terms of spectrum usage, power spectral density of transmitted/received
signals, wireless protocol signaling) and intelligence.
OSCILLATORS are key building blocks in integrated transceivers. In wired and
wireless communication terminals, the receiver front-end selects, amplifies and
converts the desired high-frequency signal to baseband. At baseband the signal can
then be converted into the digital domain for further data processing and demodula-
tion. The transmitter front-end converts an analog baseband signal to a suitable high-
frequency signal that can be transmitted over the wired or wireless channel.
