5 research outputs found
Probability of symbol error for MPSK, MDPSK and noncoherent MPSK with MRC and SC space diversity in Nakagami-m fading channel
This paper derives analytically some simple closed form expressions for the average symbol error rate (SER) of M-ary phase shift keying (MPSK), M-ary differential phase shift keying (MDPSK) and noncoherent M-ary frequency shift keying (MFSK) over a Nakagami-m (1960) fading channel with L-fold maximal ratio combining (MRC) and selection combining (SC) space diversity reception. Numerical results demonstrate the error performance improvement by employing MRC and SC diversity reception in the above communications systems and show that MRC improves the error performance more significantly than does simple SC.published_or_final_versio
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Study of continuous-phase four-state modulation for cordless telecommunications. Assessment by simulation of CP-QFSK as an alternative modulation scheme for TDMA digital cordless telecommunications systems operating in indoor applications
One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.Higher Education Ministr
Performance analysis and algorithm design for distributed transmit beamforming
Wireless sensor networks has been one of the major research topics in recent years because
of its great potential for a wide range of applications. In some application scenarios, sensor
nodes intend to report the sensing data to a far-field destination, which cannot be realized by
traditional transmission techniques. Due to the energy limitations and the hardware constraints
of sensor nodes, distributed transmit beamforming is considered as an attractive candidate for
long-range communications in such scenarios as it can reduce energy requirement of each sensor
node and extend the communication range. However, unlike conventional beamforming,
which is performed by a centralized antenna array, distributed beamforming is performed by
a virtual antenna array composed of randomly located sensor nodes, each of which has an
independent oscillator. Sensor nodes have to coordinate with each other and adjust their transmitting
signals to collaboratively act as a distributed beamformer. The most crucial problem of
realizing distributed beamforming is to achieve carrier phase alignment at the destination. This
thesis will investigate distributed beamforming from both theoretical and practical aspects.
First, the bit error ratio performance of distributed beamforming with phase errors is analyzed,
which is a key metric to measure the system performance in practice. We derive two distinct
expressions to approximate the error probability over Rayleigh fading channels corresponding
to small numbers of nodes and large numbers of nodes respectively. The accuracy of both
expressions is demonstrated by simulation results. The impact of phase errors on the system
performance is examined for various numbers of nodes and different levels of transmit power.
Second, a novel iterative algorithm is proposed to achieve carrier phase alignment at the destination
in static channels, which only requires one-bit feedback from the destination. This
algorithm is obtained by combining two novel schemes, both of which can greatly improve the
convergence speed of phase alignment. The advantages in the convergence speed are obtained
by exploiting the feedback information more efficiently compared to existing solutions.
Third, the proposed phase alignment algorithm is modified to track time-varying channels. The
modified algorithm has the ability to detect channel amplitude and phase changes that arise over
time due to motion of the sensors or the destination. The algorithm can adjust key parameters
adaptively according to the changes, which makes it more robust in practical implementation