M-level Quadrature Amplitude Modulation Research Articles

Moment-Generating Function Based Symbol Error Probability Comparison of M-ary Modulation Techniques in Fading Environment

This paper analyses and compare Symbol Error Probability (SEP) of M-ary modulation in different fading environment. Maximal ratio combining (MRC) technique with N branch receiver diversity is taken into consideration for the analysis. Expression for probability of symbol error for M-ary frequency shift keying/M-ary phase shift keying/M-ary differential phase shift key/and M-Level Quadrature Amplitude Modulation are obtained through moment-generating function (MGF) approach. Conventional integration process has probability of uncertainty and erroneousness because of composite mathematical calculations and infinite integration bounds. MGF method is used to avoid complex numerical computation for calculation of SEP. Comparison of SEP for diverse values of Rician factor “K”, Nakagami-M factor, modulation order “M” and diversity order “N” has been carried out.

Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi-Viterbi carrier phase estimation

We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation. Compared with conventional feed-forward CPE for square QAM signals, the simulated results show an enhanced tolerance of linewidth symbol duration product (ΔνTs) at a low sensitivity penalty by using feed-forward CPE structure with C-mQAM. This scheme can be easily upgraded to higher order modulations without inducing considerable complexity.

Simulation Implementation and Analysis of the Performance of M-QAM by Using MATLAB

For the implementation of digital multimedia communication, an efficient, reliable, deterministic transmission system plays a vital role. Quadrature amplitude modulation (QAM) is commonly used in digital communication systems. We focuses on simulation and analysis of M-level QAM by using MATLAB in this paper.

Adaptive Modulation in Spectrum-Sharing Channels Under Delay Quality-of-Service Constraints

We propose a variable-rate variable-power M-level quadrature amplitude modulation (MQAM) scheme employed under delay quality-of-service (QoS) constraints over spectrum-sharing channels. An underlay cognitive radio system, with one primary user and a secondary user, with constraints on interference leakage imposed by the primary receiver is considered. The transmission parameters of the secondary user are set optimally such that the successful communications for the primary user in terms of a minimum rate to be supported is satisfied, irrespective of co-existence with the secondary user. We obtain interference constraints that, when satisfied by the secondary users, is sufficient to satisfy the service outage requirement of the primary user. We further study the performance of the secondary user's link employing an adaptive MQAM scheme when, on top of the aforementioned interference constraint, the secondary user is also required to satisfy a statistical delay QoS constraint. Considering two modulation schemes, i.e., continuous MQAM and discrete MQAM with restricted constellations, we obtain the effective capacity of the secondary user's link and derive the optimum power allocation that maximizes the effective capacity of the secondary user.

Design and Analysis of Digitized RF-Over-Fiber Links

In this paper, we present a performance analysis of microwave signal transmission by deploying digitized RF transport over a standard optical fiber link. The bandpass sampling technique is used to digitize the RF signal. An analytical model, which is transparent to any modulation format, was developed to assess the transmission performance of a digitized RF signal in M-level quadrature amplitude modulation (M-QAM) format. Using this analytical model, key design parameters such as bit resolution, link bit rate, receiver sensitivity, and link signal-to-noise ratio (SNR) were analyzed for a digitized 2.475 GHz RF signal with 16-QAM data modulation format and 6 MSymbols/s baud rate over a 20-km optical link. The analytical results show that the link SNR is predominantly determined by the performance of the analog-to-digital converter (ADC). We experimentally demonstrated the digitized RF transmission over a 20-km optical link. The analytical model and experimental results show that the performance of the link SNR is governed by jitter noise beyond 7 bits of resolution of the ADC. Using an ADC with 8-bit resolution, a 2.475 GHz RF signal with 16-QAM 6 MSymbols/s data was successfully transmitted and recovered with very good error vector magnitude of 1.77.

Effect of Channel Estimation Errors on $M$-QAM With MRC and EGC in Nakagami Fading Channels

We study the effect of imperfect channel estimation (ICE) on the error probability performance of M-level quadrature amplitude modulation ( M-QAM) with maximal-ratio combining and equal-gain combining diversity formats in Nakagami fading channels. We provide a novel formulation of the bit-error rate (BER) of M-QAM with ICE in terms of the signal constellation-dependent effective signal-to-noise ratios (SNRs) or amplitudes, which allows us to derive the general, accurate, and easy-to-evaluate BER formulas for square and rectangular diversity M-QAM with channel estimation errors. Our result shows that the performance loss caused by ICE may be manifested by the signal decision space distortion and a scaling of the effective SNR. Using our analytical result, we evaluate the performance of M-QAM with pilot-symbol assisted modulation and present some insightful findings

Exact BER for M-QAM with MRC and Imperfect Channel Estimation in Rician Fading Channels

In this paper, we study the effect of imperfect channel estimation (ICE) on the performance of M-level quadrature amplitude modulation (M-QAM) with maximum ratio combining (MRC) and pilot-symbol assisted modulation (PSAM) in generalized Rician fading channels. By expressing the bit error rate (BER) of MRC diversity M-QAM in terms of the distribution of new decision variables, we derive novel, exact, and easy-to-evaluate BER expressions for diversity M-QAM with channel estimation errors. Our results include versatile system and fading channel parameters (e.g., arbitrary spatial and temporal correlation patterns among the diversity branches), and are valid for arbitrary linear channel estimators and square and rectangular M -QAM with different constellation sizes. In addition, we evaluate the performance of minimum mean-squared error (MMSE)- and sinc-interpolator-based channel estimators with PSAM, and provide some new insights into the performance of M-QAM with PSAM in generalized fading channels

Quasi-synchronous code-division multiple access with high-order modulation

Code-division multiple access (CDMA) is a multiplexing technique where a number of users simultaneously access a transmission channel by modulating and spreading their signals with preassigned codewords. This paper studies the performance of CDMA signals with orthogonal (Walsh-Hadamard) codewords and synchronization errors smaller than the chip time. Two high-order modulation techniques, M-level quadrature amplitude modulation (M-QAM) and M-level phase-shift keying (M-PSK) are compared with respect to bit-error rate (BER). The results are especially important for the return channel of cable TV networks and summarized as follows: 1) Synchronization errors between transmitters lead to interference noise, whereas synchronization errors between the transmitter and the receiver lead to a decreased amplitude of the received user signal. Both effects have significant impact on the system performance. 2) Closed expressions are obtained for the BER of a CDMA signal with M-PSK and M-QAM with a given maximum synchronization error. 3) The higher the modulation order, the more sensitive the system gets for synchronization errors. 4) The BER is highly dependent on the assigned codewords out of the Walsh-Hadamard code set. 5) The BER performance of M-QAM outperforms that of M-PSK.

A Simulation Study of Space Diversity and Adaptive Equalization in Microwave Digital Radio

In this paper we analyze the performance of M-level quadrature amplitude modulation digital radio systems subjected to microwave multipath fading. We consider two kinds of adaptive receiver techniques, either singly or in combination: dual space diversity and adaptive equalization. The space diversity is assumed to be of either the selection type or the continuous-combining type, and the equalization is assumed to be ideal. We describe a specific form of combining which is optimal when no post-combiner equalization is used. A primary aim of the study is to quantify the performance of this combining approach and to compare it with alternate strategies. The study uses Monte Carlo simulations of the dual-channel fading response functions based on a recently published statistical model. For each response pair generated, a receiver detection measure is derived analytically in terms of the system parameters and receiver approach. Probability distributions of this measure, obtained by simulating several thousand response pairs, are then computed. They can be interpreted as displaying the link outage probability as a function of the number of modulation levels (M). We find that the appropriate combining scheme can serve in some cases to avoid the need for adaptive equalization. Also, where post-combiner equalization is used, the same scheme, while no longer optimal, can sharply reduce the dispersion seen by the equalizer input.