Muhammad Ajmal Khan

Performance analysis of MRC-chirp system over independent and correlated fading channels

In this paper, chirp modulation is proposed to employ in Maximal Ratio Combining (MRC) diversity, referred to as MRCChirp system. Moment generating function (MGF) approach is used to derive easy-to-compute expressions for average bit error probability (ABEP) for two fading situations. Firstly, independent fadings with Rayleigh and Nakagami-m statistics are considered. Next, an exponentially correlated fading environment with Nakagami-m statistics is considered. The ABEP performance of the proposed system is illustrated using analytical expressions and using extensive Monte Carlo simulations. Numerical results show close agreement of analytical work with those of simulations. A discussion of numerical results on the performance of MRC-Chirp system as a function of diversity order L, chirp modulation parameters, and fading parameters is presented.

Closed-form error probability for M-ary chirp modulation in frequency-selective and -nonselective fading channels

A class of chirp signals for M-ary data transmission, referred to as M-ary chirp modulation (MCM), is considered. The performance analysis of this MCM over frequency-selective and -nonselective fading channels is carried out and closed-form error probability results that are easy for numerical computation are derived. The parameters that affect error performance are identified and illustrated. These analytical results are then compared using extensive Monte Carlo simulations. Specifically, the results are presented over Rayleigh and Nakagami-m flat fading and over Nakagami-m frequency-selective channels. It is shown that analytical results compare well with simulations.

Non-linear trigonometric and hyperbolic chirps in multiuser spread spectrum communication systems

Novel non-linear trigonometric and hyperbolic chirp waveforms are introduced in multiuser spread spectrum communication environment for binary data transmission. Three subclasses of non-linear trigonometric and hyperbolic chirp signals namely sinusoidal (sine-CSS), hyperbolic arc sinusoidal (asinh-CSS) and hyperbolic tangent (tanh-CSS) are described and their properties are given. Cross-correlations of these trigonometric and hyperbolic chirp signals are derived and presented as closed-form expressions. Moreover, the chirp rates in these signals are derived as a function of user in the multiuser environment using the orthogonal structure inherent in nonlinear chirp signals. A generic multiuser communication system model that employs non-linear chirp signals is presented and its bit error rate (BER) performance is analyzed in additive white Gaussian noise (AWGN) channel, and Rayleigh and Nakagami-m fading environments as a function of the number of users in the system, signal-to-noise ratio (SNR), and multiple access interference (MAI). Numerical results demonstrate that these proposed chirp signals with proper chirp rate assignment are very effective in reducing MAI.

Dual-hop signal space cooperative systems using multiple DF relays

In a dual-hop relaying system without a direct link between the source and the destination, the source broadcasts information signal to the relay and relay broadcasts it to the destination, thus it uses two phases to transmit one symbol. This study proposes a novel scheme to incorporate signal space diversity into a dual-hop relaying system with multiple decode-and-forward (DF) relays to enhance its spectral efficiency. The proposed dual-hop signal space cooperative relaying scheme transmits two symbols in three phases while the conventional dual-hop DF relaying system uses four phases to transmit the same two symbols. Therefore, the proposed scheme improves the spectral efficiency without additional complexity, bandwidth or transmit power. The proposed scheme is analysed over Rayleigh fading channel and error probability performance is derived. Moreover, an asymptotic approximation for the error probability is obtained to illustrate the impact of different system parameters and diversity gain. In addition, this study discusses the power allocation optimisation, relay position optimisation and the joint optimisation of both. Furthermore, closed-form expression for the average channel capacity is derived. In the end, analytical results are compared and validated through Monte Carlo simulations.

Low-Complexity PAPR Reduction Technique for OFDM Systems Using Biased Subcarriers

A peak-to-average power ratio (PAPR) reduction technique using biased subcarriers is proposed and investigated. A known time-domain reference sample (Dref) is used to bias the subcarriers at the transmitter, and the same bias is used at the receiver to recover the sequence of original subcarrier samples. A closed-form analytical expression for complementary cumulative distribution function for PAPR has been derived and is illustrated as a function of the introduced bias. The effectiveness of the proposed technique is evaluated both analytically and numerically. Analytical and simulation results confirm that significant reduction in PAPR can be achieved. For example, it is shown that nearly 9.45-dB reduction in 0.1% PAPR can be achieved for a 16-QAM orthogonal frequency division multiplexing system with 1024 subcarriers. Numerical results show that the average bit error rate performance of the proposed system does not degrade relative to the original system. It is found that the proposed technique has the lowest complexity among the various available techniques for PAPR reduction.

PAPR reduction in OFDM systems using differentially encoded subcarriers

A peak-to-average power ratio (PAPR) reduction technique that exploits the principle of differential encoding of subcarriers is proposed and investigated. The absolute maximum sample of the time-domain OFDM symbol is chosen as the reference to carry out the differential encoding process at the transmitter. A real multiplier (??) is applied to this reference to achieve appropriate PAPR level. Information about the proposed reference, however, is required to be communicated to the receiver, which performs the reverse effect to obtain back the original sequence of samples. The effectiveness of the proposed technique is evaluated through extensive computer simulations and complementary cumulative distribution function (CCDF) are obtained as a function of number of subcarriers and modulations. Numerical results confirm that significant reduction in PAPR can be achieved. For example, the proposed technique reduces the 0.1 percent PAPR to 1.5 dB for a 1024 subcarrier OFDM system, resulting in 10.3 dB reduction. Moreover, error performances of the OFDM system before and after applying the proposed technique are investigated using Monte Carlo simulations. Numerical results show that the average bit error rate performance of the proposed system does not degrade relative to the un-encoded system. An investigation of the complexity of the proposed technique with other techniques show that it is quite low complex.

Adaptive modulation for OFDM system with varying speed receiver

Adaptive modulation exploits the channel conditions to improve spectral efficiency of the wireless communication system. Moreover, channel characteristics also depend upon Dop-pler shift, due to the motion of the mobile station. In this paper, a new technique of adaptive modulation is proposed which takes into account the effect of varying speed receiver. For the purpose, mapping between channel correlation and instantaneous signal-to-noise ratio is obtained based on varying speed receiver and is used to select the best suitable modulation scheme. The system performance is obtained over frequency-selective fading channel and Kalman-filter based method is used to predict the frequency domain channel coefficients. The numerical results shows the improved performance of the proposed adaptive scheme to keep required bit error rate with varying speed receiver compared to the adaptive schemes with static receiver.