László Pap

General performance analysis of M-PSK and M-QAM wireless communications applied to OFDMA interference

Accurate technique is presented to analyze the symbol error rate of coherent M-QAM and M-PSK modulation schemes. Transmission happens in the presence of additive white Gaussian noise, different types of fading channels have effect on analyzed signal, and arbitrary number interference sources are modeled. M-QAM and M-PSK symbol error rate results are extended for OFDMA transmission with equally spaced subcarriers of interferers.

A Unified Framework for Interference Analysis of Noncoherent MFSK Wireless Communications

This paper presents a new unified analytical technique for accurate interference analysis of noncoherent M-ary frequency shift keying (MFSK) wireless communication systems in the presence of additive white Gaussian noise (AWGN) and multiple arbitrary interfering signals. New exact bit error rate expressions are derived for nonorthogonal noncoherent binary FSK in the presence of an arbitrary number of interfering signals having arbitrary spectral shapes at arbitrary frequency offsets. Furthermore, tight upper bounds for the symbol and bit error rates are given for noncoherent MFSK with arbitrary tone spacings. These results are extended to include MFSK signals experiencing Rayleigh, Nakagami-m or Rician fading. Some specific interference scenarios are analyzed in details, including jammers with a given Doppler-spread, direct sequence spread spectrum and orthogonal frequency division multiplexing signals, and a Poisson field of arbitrary interferers.

A Markovian queue with varying number of servers and applications to the performance comparison of HSDPA user equipment

Inspired by the need for performability models for HSDPA user equipment, a Markovian queue with varying number of servers is conceived. The arrival and the service processes, the number of allocated or active servers of the queue are inherently, and independently (or jointly) Markov modulated. Batch arrivals, batch services, autocorrelation of inter-arrival times, and autocorrelation of batch sizes can be accommodated in the queue, by a suitable use of Markov modulation and generalized exponential distribution. The queue has a provision for negative customers too. Transformations of the balance equations into a computable form are proposed in order to obtain the steady state probabilities with the Spectral Expansion method. This queue is used to model the High Speed Downlink Packet Access (HSDPA) wireless networks. The model is an integrated one with respect to HSDPA, capable of accommodating many of the intricate aspects of HSDPA such as, channel allocation policy, loss of packets due to channel fading, bursty and correlated traffic. Good agreement is observed between the numerical results of the proposed analytical model and those of an independent simulator of real HSDPA and radio channel behaviors. The comparison of the terminal categories specified by the 3rd Generation Partnership Project (3GPP) is also presented.

Multiple-Access Capability of Synchronous FHSS Wireless Networks: An Analysis of the Effects of the Spacing Between Hopping Carriers

This paper presents a new analytical performance analysis of slow frequency-hopped synchronous spread-spectrum multiple-access (FHSS-MA) networks employing nonorthogonal binary frequency-shift keying (BFSK) and having arbitrary spacing between the hopping carriers. Taking into account the crosstalk due to the nonorthogonality of both hopping carriers and BFSK tones, and based on an accurate interference analysis, we derive new expressions for the average probability of error of a reference signal subjected to a number of similar signals in the additive white Gaussian noise Rayleigh-faded channel. These are used to investigate the effect of carrier and tone spacing on the spectral efficiency of an FHSS-MA network. It is shown that the spectral efficiency depends primarily on the shape of the employed pulses, in addition to both carrier and tone spacing. Numerical results show that rectangular pulses give higher spectral efficiency as compared with the half-sine pulses. Furthermore, orthogonal tone spacing is shown to be more efficient in the case of rectangular pulses, whereas half-sine pulses become more efficient with the nonorthogonal signaling

Joint Application of Spread Spectrum and OFDM Modulation for Microwave Radio Communication Used for Unmanned Aerial Vehicle

The wireless communication system used by an Unmanned Aerial Vehicle has special requirements. Two separate data streams are used, one for telemetry and control of the vehicle, and one for payload. The first stream is of relatively low data rate, but must be very robust. The second stream requires high data rate, but a best effort approach is acceptable. Real-time remote control usage mandates low response time (turn around latency) of the system, which demands small frames and frequent direction changes over the half duplex channel. These two different requirements must be accounted for in the design of the modulation system. In this paper our solution based on the joint application of a chirp spread spectrum modulation with a correlator based demodulator for the telemetry and control data stream and a high data rate orthogonal frequency division multiplexing (OFDM) modulation for the payload is presented. The OFDM communication occupies the same bandwidth as the spread spectrum modulation, but - unlike the Chirp signal - utilizes its full bandwidth. By using a correlation detector for all timing recovery tasks and keeping the same timing for the OFDM part of the frame, all control loops normally needed for this task (symbol synchronization PLL, COSTAS loop) can be eliminated. This results in the whole signal processing path being a finite impulse response system which aids us in a highly pipelineable design implementation and makes it possible to create a high speed implementation with a low-end field programmable gate array (FPGA) circuit.

Adaptive near-optimal multiuser detection using a stochastic and hysteretic Hopfield net receiver

This paper proposes a novel adaptive MUD algorithm for a wide variety (practically any kind) of interference limited systems, for example, code division multiple access (CDMA). The algorithm is based on recently developed neural network techniques and can perform near optimal detection in the case of unknown channel characteristics. The proposed algorithm consists of two main blocks; one estimates the symbols sent by the transmitters, the other identifies each channel of the corresponding communication links. The estimation of symbols is carried out either by a stochastic Hopfield net (SHN) or by a hysteretic neural network (HyNN) or both. The channel identification is based on either the self-organizing feature map (SOM) or the learning vector quantization (LVQ). The combination of these two blocks yields a powerful real-time detector with near optimal performance. The performance is analyzed by extensive simulations.

General interference analysis of M-QAM transmission applied to LTE performance evaluation

An exact and general performance analysis has been introduced for M-QAM modulation in terms of bit error ratio (BER) and transmission rate assuming gray mapping. BER expressions have been derived for different fading channel types (Rayleigh, Rice and Nakagami). The analyzed transmission considers OFDM interference, which is influenced by Rayleigh fading channel. During the calculation, the spectral shapes of the victim and interfering signals are also considered. The BER expressions have also been applied for LTE, giving a tool for the evaluation of LTE physical layer performance in adjacent channel interference scenarios.

Exact BER Analysis of Binary and Quaternary PSK With Generalized Selection Diversity in Cochannel Interference

This paper proposes a new analytical method for computing the average error probabilities in binary and generalized quadriphase signals with diversity receivers in the presence of Rayleigh-faded cochannel interference. This leads to new expressions for the exact average bit-error rates and average combined signal-to-noise-plus-interference-ratio of binary phase-shift keying (PSK), quadrature PSK (QPSK), offset QPSK, and minimum shift keying with generalized selection diversity (hybrid selection/maximal ratio combining) in the presence of multiple Rayleigh-faded cochannel interferers of arbitrarily power levels.

Accurate evaluation of packet error probabilities considering bit-to-bit error dependence

This paper presents new accurate packet error rate analysis of ALOHA type networks that employ BPSK or QPSK modulation in a Rayleigh fading environment. Relying on a precise interference model, we derive new accurate expressions for the packet success probabilities that account for bit to bit error dependence, and are valid for unequal power levels. The accuracy of the new expressions is validated by simulation. These results are used to investigate the throughput performance of Aloha type networks in different local area environments

General interference analysis of M-QAM and M-PSK wireless communications

This work includes an accurate and general technique, which has been developed to analyze the symbol-error-rate (SER) of coherent M-Quadrature Amplitude Modulation (QAM) and Phase Shift Keying (PSK) schemes for various conditions of the transmission. A calculation scheme has been presented dealing with Additive White Gaussian Noise and different fading effects influencing the analyzed M-ary QAM or PSK signals. Furthermore, the authors have considered the effects of multiple interference signals embedded into a stochastic model having numerous parameters, which can be assumed as random variables with adjustable distributions. The resulted M-QAM and M-PSK SER expressions have been extended for multi-carrier transmission based on the analytical calculation of the stochastic interference model.