Aqdas Naveed Malik

Particle Swarm Optimization Assisted Multiuser Detection along with Radial Basis Function

In this work particle swarm optimization (PSO) aided with radial basis functions (RBF) has been suggested to carry out multiuser detection (MUD) for synchronous direct sequence code division multiple access (DS-CDMA) systems. The performance of the proposed algorithm is compared to that of other standard suboptimal detectors and genetic algorithm (GA) assisted MUD. It is shown to offer better performance than the others especially if there are many users.

QoS and rate enhancement in DVB-S2 using fuzzy rule based system

Adaptive Coding and Modulation (ACM) is one of the most promising features in many communication systems like WIFI, WiMAX and DVB-S2, in terms of throughput and link utilization. In this way the transmission parameters like power, code rate and modulation symbol are adapted according to the varying link conditions. In this paper we propose a Fuzzy Rule Based System (FRBS) for an efficient ACM in DVB-S2 standard. We have taken it as a constrained optimization problem in which the link reliability and throughput is maximized, while power constraint is satisfied. To do so we have selected the standard transmission Modulations and Codes (MODCODs) optimally using FRBS, according to the DVB-S2 downlink channel state information (CSI) at different sites. The FRBS module can easily be embedded in the ACM management module (AMM) which is a software module. Significance of the proposed scheme over other schemes is shown through simulations.

Recovery of Failed Element Signal with a Digitally Beamforming Using Linear Symmetrical Array Antenna.

An antenna array element failure problem is one of the practical and challenging issues in the field of adaptive beamforming. The complete radiation pattern of the array is distorted when any one of the elements fails. Sidelobes level increases, nulls are shifted and null depth is also decreased tremendously. In order to mitigate the problem, we have given a new and easy approach coined as conjugate symmetry approach of the array. In this, the failed element is given a conjugate of the output from its symmetrical counterpart element in the array. The Classical Dolph-Chebyshev and Taylor pattern are taken as the test antenna. The simulation results of both patterns show the validity and presentation of the proposed approach.

A Novel Modulation Classification Approach Using Gabor Filter Network

A Gabor filter network based approach is used for feature extraction and classification of digital modulated signals by adaptively tuning the parameters of Gabor filter network. Modulation classification of digitally modulated signals is done under the influence of additive white Gaussian noise (AWGN). The modulations considered for the classification purpose are PSK 2 to 64, FSK 2 to 64, and QAM 4 to 64. The Gabor filter network uses the network structure of two layers; the first layer which is input layer constitutes the adaptive feature extraction part and the second layer constitutes the signal classification part. The Gabor atom parameters are tuned using Delta rule and updating of weights of Gabor filter using least mean square (LMS) algorithm. The simulation results show that proposed novel modulation classification algorithm has high classification accuracy at low signal to noise ratio (SNR) on AWGN channel.

Dynamic resource allocation in OFDM systems using DE and FRBS

Dynamic allocation of the resources for optimum utilization is one of the most important fields of study in engineering as well as other disciplines nowadays. In this process the available resources are allocated in such a way that these resources are maximally utilized to enhance the overall system throughput while satisfying certain constraints at the same time. In this paper a similar constrained optimization problem is focused for Orthogonal Frequency Division Multiplexing OFDM environment, in which the transmission parameters namely code rate, modulation scheme and power are adapted in such a way that overall system data rate is maximized with a constrained bit error rate and transmit power. This is a highly non-linear problem that cannot be solved by ordinary linear optimization techniques. A Fuzzy Rule Base System FRBS is proposed for adapting the code rate and modulation scheme while Differential Evolution is used for choosing the optimum power vector. The proposed scheme is compared with other schemes.

Sidelobe suppression for OFDM based cognitive radio systems using genetic algorithm for subcarrier weighting

Orthogonal frequency division multiplexing (OFDM), because of its different advantages, has been proposed as the enabling modulation technology for cognitive radios. However, the high sidelobes of the subcarriers are a major disadvantage that result in out-of-band radiation (OOB) causing interference to adjacent licensed users. Subcarrier weighting is an efficient technique for suppressing these sidelobes. This paper proposes the genetic algorithm to solve the subcarrier weighting techniques optimization problem that gives the optimum weight vector for sidelobe suppression. The genetic algorithm calculates the weights of the OFDM subcarriers in an optimized way such that the sidelobes of these subcarriers interfere destructively with each other, resulting in a smooth signal in the optimization range thus the sidelobes are suppressed and minimal interference is offered to adjacent users.

PERFORMANCE ANALYSIS OF MIMO-FREQUENCY DIVERSE ARRAY RADAR WITH VARIABLE LOGARITHMIC OFFSETS

Frequency diverse array (FDA) uses a small frequency increment at each antenna element to get a range, angle and time dependent beam pattern. Although linear frequency offset is used in most radar systems, nonlinear frequency offset is also very useful for analyzing FDA radar. A logarithmic frequency offsets based FDA (log-FDA) removes the inherent periodicity of FDA beam pattern to get a single maxima in area of interest. Multiple input multiple output frequency diverse array (MIMOFDA) radar has also been presented recently to provide some improvements compared to FDA radar. In this paper, a hybrid scheme has been proposed in which each subarray of MIMO-FDA uses a variable logarithmic offset. The resultant system, called MIMO-log-FDA, uses not only a different logarithmic offset, but also unique waveform in each subarray. Different logarithmic offsets have contributed in terms of getting more control on width of beam pattern, while the different waveforms have provided diversity, which can be exploited at the receiver of the proposed system. Some improvements in transmit beam patterns have been shown for MIMO-log-FDA, followed by detailed signal model for better estimation of target at the receiving side. Performance analysis has also been done in terms of signal to interference plus noise ratio (SINR) and Cramer-Rao lower bound (CRLB). Simulation and results have verified the effectiveness of proposed scheme by comparing it with Log-FDA and MIMO-FDA radar.

Sidelobe Suppression with Null Steering by Independent Weight Control

A uniform linear array of antenna elements can steer up to nulls. In situations where less than nulls are required to be steered, the existing algorithms have no criterion to utilize the remaining weights for sidelobe suppression. This work combines sidelobe suppression capability with null steering by independent weight control. For this purpose, the array factor is transformed as the product of two polynomials. One of the polynomials is used for null steering by independent weight control, while the second one is for sidelobe suppression whose coefficients or weights are determined by using convex optimization. Finally, a new structure is proposed to incorporate the product of two polynomials such that sidelobe suppression weights are decoupled from those of null steering weights. Simulation results validate the effectiveness of the proposed scheme.

Performance Analysis of Relay Subset Selection for Amplify-and-Forward Cognitive Relay Networks

Cooperative communication is regarded as a key technology in wireless networks, including cognitive radio networks (CRNs), which increases the diversity order of the signal to combat the unfavorable effects of the fading channels, by allowing distributed terminals to collaborate through sophisticated signal processing. Underlay CRNs have strict interference constraints towards the secondary users (SUs) active in the frequency band of the primary users (PUs), which limits their transmit power and their coverage area. Relay selection offers a potential solution to the challenges faced by underlay networks, by selecting either single best relay or a subset of potential relay set under different design requirements and assumptions. The best relay selection schemes proposed in the literature for amplify-and-forward (AF) based underlay cognitive relay networks have been very well studied in terms of outage probability (OP) and bit error rate (BER), which is deficient in multiple relay selection schemes. The novelty of this work is to study the outage behavior of multiple relay selection in the underlay CRN and derive the closed-form expressions for the OP and BER through cumulative distribution function (CDF) of the SNR received at the destination. The effectiveness of relay subset selection is shown through simulation results.

Spectrum Sharing in Cognitive Radio Using GSC with Suppressed Sidelobes

Cognitive radio system is an innovative technology in the wireless communication that has the capability to smartly communicate with each other by opportunistically exploiting the vacant spectrum of primary users. In this work we present a new idea of sidelobe suppression applicable for cognitive users on transmitter and receiver sides. In case of spectrum sharing with the primary users by suppressing the side-lobes at the transmitter and receiver side, the cognitive users will be able to increase the throughput without cooperating the permissible interference temperature limit of the license spectrum. We suggest two generalized sidelobe cancellers (GSCs) that operate in parallel. The first GSC planned to attain the two conflicting objective at the same moment: firstly maximize the cognitive users self throughput; secondly minimize the interference generated by cognitive users at each primary receiver. The second GSC generates two main beams at the positions of the highest amplitude sidelobes of the first one. The values of main beams are equal to the two sidelobe peaks. The subtraction of the outputs of the two GSCs, results in the suppression of the highest pair of sidelobes. This process is repeated iteratively to result in an adaptive algorithm. Simulation results are there to provide the effectiveness of the proposed algorithm.