48 research outputs found
A characterization of the performance of Bluetooth 2.x + EDR technology in noisy environments
Bluetooth (BT) is by far the most popular shortrange
technology for the development of wireless personal
area networks and body area networks. Nowadays, BT 2.0
and 2.1 ? EDR are the most extended and implemented
versions of BT standard. This article presents an analytical
model that computes the packet delay of transmissions that
utilize this version of BT in noisy environments. The
model, which takes into account the packet retransmissions
caused by noise, is particularized to calculate the mean
packet delay as a function of the signal-to-noise ratio for
the different enhanced data rates provided by BT 2.0 and
2.1 specifications. Thus, the model permits evaluating the
efficiency of using these enhanced rates in the presence of a
certain noise level.Ministerio de Ciencia e Innovación TEC2009-13763-C02-01Ministerio de Ciencia e Innovación TEC2013-42711-
Non-coherent successive relaying and cooperation: principles, designs, and applications
Cooperative communication is capable of forming a virtual antenna array for each node (user) in a network by allowing the nodes (users) to relay the messages of others to the destination. Such a relay aided network may be viewed as a distributed multiple-input multiple-output (MIMO) system relying on the spatially distributed single antennas of the cooperating mobiles, which avoids the correlation of the antenna elements routinely encountered in conventional MIMO systems and hence attains the maximum achievable diversity gain. Therefore, the family of cooperative communication techniques may be regarded as a potential solution for future wireless networks. However, constrained by the half-duplex transmit/receive mode of most practical transceivers, the cooperative networks may impose a severe 50% throughput loss. As a remedy, successive relaying can be employed, which is capable of mimicking a full-duplex relay and thereby recovering much of the 50% throughput loss. Furthermore, for the sake of bypassing power-hungry and potentially excessive-complexity channel estimation, noncoherent detection techniques may be employed for multiple-antenna aided systems, because estimating all the associated channels may become unrealistic. Explicitly, the mobile-stations acting as relays cannot be realistically expected to estimate the source-to-relay channels. In order to motivate further research on noncoherent successive relaying aided systems, a comprehensive review of its basic concepts, fundamental principles, practical transceiver designs and open challenges is provide
Shuttle Communications and Tracking Systems Modeling and TDRSS Link Simulations Studies
An analytical simulation package (LinCsim) which allows the analytical verification of data transmission performance through TDRSS satellites was modified. The work involved the modeling of the user transponder, TDRS, TDRS ground terminal, and link dynamics for forward and return links based on the TDRSS performance specifications (4) and the critical design reviews. The scope of this effort has recently been expanded to include the effects of radio frequency interference (RFI) on the bit error rate (BER) performance of the S-band return links. The RFI environment and the modified TDRSS satellite and ground station hardware are being modeled in accordance with their description in the applicable documents
Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application
With the explosive growth of bandwidth requirement in optical fiber communication
networks, optical code division multiple access (OCDMA) has witnessed tremendous
achievements as one of the promising technologies for optical access networks over the
past decades. In an OCDMA system, optical code processing is one of the key
techniques. Rapid optical code reconfiguration can improve flexibility and security of
the OCDMA system. This thesis focuses on advanced optical modulations and
en/decoding techniques for applications in fast reconfigurable OCDMA systems and
secure optical communications.
A novel time domain spectral phase encoding (SPE) scheme which can rapidly
reconfigure the optical code and is compatible with conventional spectral domain phase
en/decoding by using a pair of dispersive devices and a high speed phase modulator is
proposed. Based on this scheme, a novel advanced modulation technique that can
simultaneously generate both the optical code and the differential-phase-shift-keying
(DPSK) data using a single phase modulator is experimentally demonstrated. A
symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using
a similar setup for both the transmitter and receiver is further proposed, based on which
a bit-by-bit optical code scrambling and DPSK data modulation technique for secure
optical communications has been successfully demonstrated. By combining optical
encoding and optical steganography, a novel approach for secure transmission of time
domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over
public wavelength-division multiplexing (WDM) network has also been proposed and
demonstrated.
To enable high speed operation of the time domain SPE/SPD scheme and enhance the
system security, a rapid programmable, code-length variable bit-by-bit optical code
shifting technique is proposed. Based on this technique, security improvements for
OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable
optical codes of up to 1024-chip have been achieved.
Finally, a novel tunable two-dimensional coherent optical en/decoder which can
simultaneously perform wavelength hopping and spectral phase encoding based on
coupled micro-ring resonator is proposed and theoretically investigated. The techniques
included in this thesis could be potentially used for future fast reconfigurable and secure
optical code based communication systems
M-ary Chirp Modulation for Data Transmission
M-ary chirp modulations, both discontinuous- and continuous-phase, for M-ary data transmission are proposed and examined for their error rate performances in additive, white, Gaussian noise (AWGN) channel. These chirp modulated signals are described and illustrated as a function of time and modulation parameters. M-ary chirp modula tion with discontinuous phase is first proposed and then the M-ary Continuous Phase Chirp Modulation (MCPCM) is considered. General descriptions of these modula tion systems are given and properties of signals representing these modulations are given and illustrated. Optimum algorithms for detection of these signals in AWGN are derived and structures of optimum receivers are identified. Using the minimum Euclidean distance criterion in signal-space; upper bounds on Signal-to-Noise Ratio (SNR) gain relative to Multiple Phase Shift Keying (MPSK) are established for 2-.
*4-, and 8-ary MCPCM systems. It is observed that the maximum likelihood coherent and non-coherent receivers for MCPCM are non-linear and require multiple-symbol observations. Since symbol error probability performance analyses of these receivers are too complex to perform, union upper bounds on their performances are derived and illustrated as a function of SNR, number of observation symbols, and modulation parameters for MCPCM. Optimum 2-, 4-, and 8-ary modulation schemes that mini mize union upper bound on symbol error rates have been determined and illustrated. Our results show that 2-, 4-, and 8-ary optimum coherent MCPCM systems, with 5-symbol observation length, offer 1.6 dB, 3.6 dB, and 8 dB improvements relative to 2-ary, 4-ary, and 8-ary PSK systems, respectively. Also, it is shown that opti mum 2-ary and 4-ary non-coherent MCPCM systems can outperform 2-ary and 4-ary coherent PSK systems, respectively
Modulation Format Conversion in Future Optical Networks
Projecte realitzat en col.laboració amb el centre DTU(Technical University of Denmark)The signal generation and receiver schemes of different modulation formats such as
on off keying (OOK) in either non‐return to zero (NRZ) or return to zero (RZ),
correlative coding and phase‐shift keying (PSK) are described and numerically
simulated. Their receiver sensitivities for back to back structure are numerically
simulated at 40 Gb/s and compared. The results show how using balanced reception,
DPSK has the benefit of approximately 3 dB. We demonstrate that duobinary
modulation is characterized by a higher tolerance to the chromatic dispersion in
comparison with NRZ. Conversion techniques between modulation formats are
described. Different all optical format conversion based on the mentioned method are
discussed. Finally, format conversion from RZ‐OOK to RZ‐DPSK based on HNLF
nonlinearities is investigated in great detail and numerically simulated at 40 Gb/s.
Some converter requirements such as powers, wavelengths, bandwidths, pulse widths
and pulse shapes among other are studied. The results show that shorter pulse widths
in control signal for the case of walk‐off presence provide worse conversion. Sensitivity of converted RZ‐DPSK is compared with a conventional 33RZ‐DPSK signal showing a
penalty close to 4 dB. Finally, the effect of the control wavelength variation at the
input of the converter is investigated when the probe signal corresponds with
conventional 33%RZ, 50%RZ and 67%RZ duty cycle
Constant-Envelope Multi-Level Chirp Modulation: Properties, Receivers, and Performance
Constant envelope multi-level chirp modulations, with and without memory, are considered for data transmission. Specifically, three sub-classes referred to as symbol-by-symbol multi-level chirp modulation, full-response phase-continuous multi-level chirp modulation and full-response multi-mode phase-continuous multi-level chirp modulation are considered. These modulated signals are described, illustrated, and examined for their properties. The ability of these signals to operate over AWGN is assessed using upper bounds on minimum Euclidean distance as a function of modulation parameters. Coherent and non-coherent detection of multi-level chirp signals in AWGN are considered and optimum and sub-optimum receiver structures are derived. The performance of these receivers have been assessed using upper and lower bounds as a function of SNR, modulation parameters, modulation levels, decision symbol locations, and observation length of receiver. Optimum multi-level chirp modulations have been determined using numerical minimization of symbol error rate. Closed-form expressions are derived for estimating the performance of multi-level chirp signals over several practical fading channels. Finally, spectral characteristics of digital chirp signals are presented and illustrated
Empirical analysis of polarization division multiplexing-dense wavelength division multiplexing hybrid multiplexing techniques for channel capacity enhancement
This paper exemplifies dense wavelength division multiplexing combined with polarization division multiplexing with C-band frequency range-based single-mode fiber. In the proposed link, 32 independent channels with 16 individual wavelengths are multiplexed with two different angles of polarization. Each carrying 130 Gbps dual-polarization data with 200 GHz channel spacing claiming a net transmission rate of 4.16 Tbits/s with spectral efficiency of 69% with 20% side-mode-suppression-ratio (SMSR) and optical signal to noise ratio (OSNR) 40.7. The performance of the proposed techniques has been analyzed using optimized system parameters securing a minimum bit error rate (BER) 10-9 at a transmission distance up to 50 km