Adaptive Coded Modulation (acm)

The paper proposes a simple scheduling algorithm based on adaptive embedded modulation (EM) for the downlink in urban wireless networks. Embedded modulation allows multiple users to share a single downlink channel simultaneously. The proposed EM scheduling algorithm embeds the user which has the largest carrier-to-interference ratio (C/I) with each of the lower C/I users in turn. Simulation results show that the EM scheduler, employing adaptive coded modulation, can improve the average throughput of a given downlink by up to 33% over a round robin scheduler, while still maintaining acceptable fairness amongst the system users.

This paper presents a user-friendly learning software using MATLAB and its Graphical User Interface (GUI) to help student in achieving a better understanding in electrical engineering subjects. Currently, this educational software is designed for three subjects; electromagnetic, digital communication and power engineering. The m user interfaces (GUIs) are designed for ease of use. The standalone program is also developed; thus, user does not need to install MATLAB in their Personal Computer (PC) in order to use this educational software.

. Modulaţia cu simbol pilot(PSAM) este o metodă eficientă pentru a reduce efectul fadingului într-un sistem de comunicaţii mobile. În sistemele PSAM emiţătorul înserează periodic în fluxul de date simboluri pilot cunoscute, din care receptorul extrage amplitudinea şi faza semnalului recepţionat. În procesul de simulare am folosit o secvenţă de date generată aleator uniform distribuite şi o anumită secvenţă pilot (secvenţă Barker), care apoi au fost mapate într-un set de date 16-QAM. S-au simulat efectele zgomotului şi influenţa fadingului în componentele semnalului.

. Modulaţia cu simbol pilot(PSAM) este o metodă eficientă pentru a reduce efectul fadingului într-un sistem de comunicaţii mobile. În sistemele PSAM emiţătorul înserează periodic în fluxul de date simboluri pilot cunoscute, din care receptorul extrage amplitudinea şi faza semnalului recepţionat. În procesul de simulare am folosit o secvenţă de date generată aleator uniform distribuite şi o anumită secvenţă pilot (secvenţă Barker), care apoi au fost mapate într-un set de date 16-QAM. S-au simulat efectele zgomotului şi influenţa fadingului în componentele semnalului.

In this contribution, we propose an adaptive Turbo Trellis Coded Modulation (TTCM) aided Distributed Space-Time Trellis Coding (STTC) scheme for cooperative communication over quasi-static Rayleigh fading channels. An adaptive TTCM (ATTCM) scheme is employed by the source node during the first transmission period for reliably conveying the source bits to N number of relay nodes by appropriately adjusting the coderate and modulation mode according to the near-instantaneous channel condition. The TTCM switching thresholds are chosen to ensure that the Bit Error Ratio (BER) at each relay node becomes lower than 10 -6 in order to minimise the potential error propagation imposed by the relay nodes. During the second transmission period, an N -antenna assisted Distributed STTC (DSTTC) scheme is created with the aid of the aforementioned N single-antenna relay nodes. More specifically, the N relay nodes are utilised to form STTC codewords based on the re-encoded TTCM symbols of the relays for transmission to the destination node. At the destination node, iterative extrinsic information exchange is performed between the STTC and TTCM decoders for recovering the original source bits. It is shown that the proposed ATTCM-DSTTC scheme requires 12 dBs less transmission power in comparison to a standard TTCM scheme when aiming for a frame error ratio of 10 -3 .

A low bit-rate video coding techniques using the H.26L standard codec for robust transmission in mobile multimedia environments are presented. For the sake of achieving error resilience, the source codec has to make provisions for error detection, resynchronization and error concealment. Thus a packetization technique invoking adaptive bit-rate control was used in conjuction with the various modulation scheme employed. In this contribution, we propose a Burst-by-Burst Adaptive Coded Modulation-Aided Joint Detection-Based CDMA (ACM-JD-CDMA) scheme for wireless video telephony and characterise its performance when communicating over the UTRA wideband vehicular fading channels. The coded modulation schemes invoked in our fixed modulation mode based systems are Low Density Parity Check code based Block Coded Modulation (LDPC-BCM) and Turbo Trellis Coded Modulation (TTCM). The performance of LDPC-BCM was evaluated and compared to that of TTCM in the context of the ACM-JD-CDMA system using a practical modem mode switching regime. Both schemes exhibited a similar transmission integrity, although the LDPC arrangement is capable of achieving this at a lower complexity.

In this paper, an Adaptive Code NonUniform Modulation with Orthogonal Frequency Division Multiplexing (OFDM) System was evaluated in the underwater acoustic communication channel. This system was adopted from the Subcarrier arrangement of the OFDM standard of IEEE 802.11a, and improved with some modifications. There are three schemes in the proposed adaptive system. The first is the Hamming code with Binary phase-shift keying (BPSK) modulated, which is mapped for 12-bit subcarrier data. The second is the Bose-Chaudhuri-Hocquenghem (BCH) code with Quadrature phase-shift keying (QPSK) modulation which is for the other 12-bit subcarrier data. And the third is the Reed Solomon code with 16-Quadrature Amplitude Modulation (16- QAM) modulation that is mapped for 24-bit subcarrier data. The system modeling was evaluated in the shallow water acoustic environments. Bit error rate (BER) and signal-to-noise ratio (SNR) were analyzed to evaluate the proposed system performance. The evaluation r...

This paper contains study and comparative analysis of OFDM-IDMA system using BPSK technique in Simulink environment. Orthogonal frequency division multiplexing technique reduces long delay spread due to low data rate of subcarriers and due to which Inter Symbol Interference (ISI) is eliminated. Also the orthogonality of subcarriers reduces Inter Carrier Interference (ICI).Interleaver division multiple access (IDMA) layer are used to randomize the data so that the effect of channel noise does not corrupt the data serially. The main objective of this papers to analysis the performance of the OFDM-IDMA system on the basis of Bit Error Rate (BER). This simulation was done in MATLAB/Simulink and results are exported with the help of bertool. Keyword: OFDM, IDMA, BPSK, BER, ICI.

M-ary Quadrature Amplitude Modulation (M-QAM) is an important technique for the modulation of digital signals in wireless communication systems. Due to the increasing demands for high-rate data outputs in wireless communications, it is essential to investigate methods of achieving high spectral efficiency which would take into account the wireless channel models. The bit error rate (BER) is a parameter which gives an excellent indication of the performance of a data link such as a radio or optic fibre system. Understanding the method of evaluating the BER will aid in the design of a more suitable modulation scheme that will best suit the channel quality, thus delivering the optimum and efficient data rate to the downlink terminal. This paper will focus on evaluation of BERs for MQAM modulation varying from 4 to 64 and for integer values of bit energy-to-noise power spectral density ratio (Eb/No) between 0 and 7 using the Matlab R2013a simulation tool in the AWGN channel.

Keywords: AWGN channel, Bit Error Rate and M-ary Quadrature Amplitude modulation

Due to the increasing demand for wireless communications, spectral efficiency of transmission schemes has gained a great concern recently. Also, achieving secure wireless communications is of high importance. Recently, physical layer security has been intensively investigated as an extra layer of protection for wireless communications. Directional modulation (DM) has been proposed as a mean to implement physical layer security. Antenna subset modulation (ASM) is a low complexity single beam DM technique suitable for millimeter-wave communications. The small wavelengths nature of millimeter-wave band is exploited to equip a transmitter with a large antenna array, and by randomly choosing few elements of this array for transmitting a symbol, secure communication in a single direction is obtained. This paper provides a study for the performance of broadcasting multi-beams antenna subset modulation (MASM) in which it is desirable to broadcast data streams to different receivers. A statistical model has been driven, and the symbol error rate of MASM using QPSK and secrecy capacity are obtained. Simulation results show that ASM can be used efficiently for multidirectional broadcasting communication, while maintaining its inherent security.

Integer codes, defined over integer rings, allow the correction of single cross errors with distance 1 in a signal point constellation on a two-dimensional lattice. Several construction methods support the construction of integer codes that give constellations that have a variety of shapes. In this paper, we characterize all constellations that can be obtained from a particular integer code. In particular, we determine those that minimize the average symbol energy. In addition, we evaluate the symbol error probability when using an integer code for coded QAM constellations.

Adaptive techniques are becoming demand of almost every modern communication system. In this technique, transmission parameters are adapted in such a way that the overall throughput of the system is maximized and certain constraints are satisfied. In this paper a similar constrained optimization problem is focused and a fuzzy rule based system (FRBS) is proposed for its solution. The transmission parameters being optimized are practical channel code, modulation symbol and the transmit power. FRBS suggests the optimal code rate and modulation symbol while water-filling algorithm suggests the power vector according to channel conditions at Orthogonal Frequency Division Multiplexing (OFDM) sub-channels, so that throughput can be maximized while bit error rate (BER) and power remain constrained. Comparison of two channel codes namely Product codes and Convolutional code is given while Quadrature Amplitude Modulation (QAM) as Modulation scheme is used under supervision of FRBS. Compariso...

In this letter, we derive the random coding error exponent for the time-independent flat fading channel with perfect knowledge of the channel state information (CSI) at both the receiver and the transmitter. That is, the CSI is feedback from the receiver to the transmitter. In such a situation, the transmitter is capable of optimizing the power allocation of the transmitted signal according to the fading state in order to obtain, for our case, the best error exponent. The power scheme obtained here is different from the water-pouring one, which is known to maximize the channel capacity.

In this paper we consider variable-rate transmission for time-correlated MIMO (multi-input multi-output) channels with limited feedback. The number of bits loaded on each subchannel of the MIMO system is dynamically assigned according to the current channel condition and fed back to the transmitter. As the channel is time-correlated, bit loading is a vector signal that is also time-correlated. We propose to feedback bit loading using predictive coding, which is known to be a powerful quantization technique when the underlying signal is correlated in time. Assuming the channel is a first-order Gauss-Markov random process, we derive the predictor for the bit loading to be coded and analyze the corresponding prediction error variance when the channel is varying slowly. By exploiting the prediction error variance, we adapt the quantizer of the prediction error to have a smaller quantization error. Furthermore we show that the prediction error variance is proportional to a term that depends only on the time-correlation coefficient. This leads to the conclusion that, a codebook that is designed for a particular time correlation coefficient can be easily modified to a codebook for a different correlation coefficient without redesign. Simulations are presented to demonstrate that the proposed predictive coding can achieve a very good approximation of the desired transmission rate with a very low feedback rate.

We consider the minimization of hit error rate (BER) for OFDM systems with orthogonal precoders. For low S N Q we show that the conventional OFDM system is the optimal solution and the optimal precoder is the identity matrix. For high SNR, corresponding to a relatively practical range of BER, there are channel independent solutions for optimal precoders. One such solution is the DFT matrix and the resulting optimal transceiver becomes the single carrier transmission system. Furthermore, in this case the conventional OFDM system has the largest BER among all OFDM systems with orthogonal precoders.

Light Fidelity (Li-Fi) is an Optical wireless communication (OWC) technology, which uses light from light emitting diodes(LEDs) as a medium to deliver network, mobile, high-speed communication in a similar manner to Wi-Fi. Li-Fi can be simply position to remain Wi-Fi but in its place of radio waves light is used as a medium. Now, data is transmit using light whose amount varies faster than human eye to capture. In its place of using modems, Li-Fi uses LED bulbs with transceiver. Data transmission in Li-Fi is about 100 times faster than Wi-Fi. OFDM stands and 4QAM,16 QAM ,32QAM,64QAM has been reported. BER v/s SNR curves are simulated to improve their performance using light fidelity network. IndexTerms Li-Fi, Simulink, OFDM, QPSK, 4QAM, 16QAM, 32QAM, 64QAM.

The limitations of channel bandwidth, time varying channel and fading are significant and fundamental problem in wireless communication, which leads to the difficulty of providing high Quality of Service. The traditional wireless communication systems are designed to provide good quality of services at the worst channel conditions. Wherein any attempts to increase the channel bandwidth, interference arises along with these attempts. And result in inefficient utilization of the full channel capacity. One of the efficient techniques to overcome to these problems is known as adaptive modulation and coding (AMC). This paper was prepared as simulation study of interference decreasing using AMC algorithm where a comparison between ordinary modulation techniques is compared to Multicarrier Modulation MCM and adaptive modulation, results of the simulation was observed and compared for above scenarios.

The next generation wireless communications systems demand higher data rates transmission in order to meet the high quality services. Orthogonal Frequency Division Multiplexing (OFDM) offers high data rate, high Spectral Efficiency (SE), and immunity against narrow band interference. Spectral efficiency is one of the major issues in wireless communication system. The spectral efficiency of a channel is a measure of the number of bits per second per Hz. The spectral efficiency is presented in many ways in the literature. In wireless communication system SE depends on Bit Error Rate (BER), coding rate and modulation technique. This study investigates the SE and Bit Error Rate (BER) performance OFDM system over AWGN channel with different QAM modulation techniques. Simulation results show that minimum SE obtained with the 16QAM modulation technique with coding rate ½ at lower Signal to Noise Ratio (SNR). The comparative show that minimum BER can be achieved with the 16QAM modulation te...