Mohammed Zafar Ali Khan

Bio: Mohammed Zafar Ali Khan is an academic researcher from Indian Institute of Technology, Hyderabad. The author has contributed to research in topics: Cognitive radio & Split-radix FFT algorithm. The author has an hindex of 11, co-authored 76 publications receiving 471 citations. Previous affiliations of Mohammed Zafar Ali Khan include Indian Institute of Science & Indian Institutes of Technology.

Space-time block codes from co-ordinate interleaved orthogonal designs

Abstract: We present space-time block codes called 'co-ordinate interleaved orthogonal designs' (CIOD). These codes have low decoding complexity; the same as that of the codes from complex orthogonal designs (COD). Rate 1 CIOD exist for two, three and four transmit antennas and rate 3/4 CIOD exist for five, six, seven and eight transmit antennas while COD exists only for two antennas and generalized COD (GCOD) of rate 3/4 are known to exist for three and four transmit antennas only. The maximum mutual information of these codes is also calculated.

Rectangular co-ordinate interleaved orthogonal designs

Abstract: Space-time block codes (STBC) from orthogonal designs (OD), quasi-orthogonal designs (QOD) and co-ordinate interleaved orthogonal designs (CIOD) have been attracting wider attention due to their amenability for fast (single-symbol decoding for OD, CIOD and double-symbol decoding for QOD) ML decoding, and rate-one with full-rank over quasi-static fading channels. The importance of CIOD is due to the fact that, rate-one, full-rank, square ODs for arbitrary complex constellations exist only for 2 transmit antennas while such a CIOD exists for 2,3 and 4 transmit antennas with a slight restriction on the complex constellations (Zafar Ali Khan and B. Sundar Rajan, Proc. IEEE ISIT 2002, p.275, 2002; DRDO-IISc Tech. Report No. TR-PME-2002-17, 2002). These limitations motivate study of rectangular (non-square) designs. One way of obtaining rectangular designs is by deleting columns from square or non-square ODs or CIODs. We present a new construction of rectangular single-symbol decodable designs that have higher maximum mutual information than those obtained by deleting columns of CIODs and has lower peak-to-average-power ratio (PAPR). Simulation results are presented for three and five transmit antennas and compared with that of OD, QOD, CIOD to demonstrate the superiority of the proposed rectangular designs.

The Achievable Rate of Interweave Cognitive Radio in the Face of Sensing Errors

Abstract: Cognitive radio (CR) systems are potentially capable of mitigating the spectrum shortage of contemporary wireless systems. In this paper, we provide a brief overview of CR systems and the important research milestones of their evolution, along with their standardization activities, as a result of their research. This is followed by the detailed analysis of the interweave policy-based CR network (CRN) and by a detailed comparison with the family of underlay-based CRNs. In the interweave-based CRN, sensing of the primary user’s (PU) spectrum by the secondary user’s (SU) has remained a challenge, because the sensing errors prevent us from fulfilling the significant throughput gains that the concept of CR promises. Since missed detection and false alarm errors in real-time spectrum sensing cannot be avoided, based on a new approach, we quantify the achievable rates of the interweave CR by explicitly incorporating the effect of sensing errors. The link between the PU transmitter and the SU transmitter is assumed to be fast fading. Explicitly, the achievable rate degradation imposed by the sensing errors is analyzed for two spectrum sensing techniques, namely, for energy detection and for magnitude squared coherence-based detection. It is demonstrated that when the channel is sparsely occupied by the PU, the reusing techniques that are capable of simultaneously providing low missed detection and false alarm probabilities cause only a minor degradation to the achievable rates. Furthermore, based on the achievable rates derived for underlay CRNs, we compare the interweave CR and the underlay CR paradigms from the perspective of their resilience against spectrum sensing errors. Interestingly, in many practical regimes, the interweave CR paradigm outperforms the underlay CR paradigm in the presence of sensing errors , especially when the SNR at the SU is below 10 dB and when the SNR at the PU is in the range of 10–40 dB. Furthermore, we also provide rules of thumb that identify regimes, where the interweave CR outperforms the underlay CR.

Localization and Activity Classification of Unmanned Aerial Vehicle Using mmWave FMCW Radars

Abstract: In this article, we present a novel localization and activity classification method for aerial vehicle using mmWave frequency modulated continuous wave (FMCW) Radar. The localization and activity classification for aerial vehicle enables the utilization of mmWave Radars in security surveillance and privacy monitoring applications. In the proposed method, Radar’s antennas are oriented vertically to measure the elevation angle of arrival of the aerial vehicle from ground station. The height of the aerial vehicle and horizontal distance of the aerial vehicle from Radar station on ground are estimated using the measured radial range and the elevation angle of arrival. The aerial vehicle’s activity is classified using machine learning methods on micro-Doppler signatures extracted from Radar measurements taken in an outdoor environment. To evaluate performance, various light weight classification models such as logistic regression, support vector machine (SVM), Light gradient boosting machine (GBM), and a custom lightweight convolutional neural network (CNN) are investigated. Based on the results, the logistic regression, SVM, and Light GBM achieve an accuracy of 93%. Furthermore, the custom lightweight CNN can achieve activity classification accuracy of 95%. The performance of the proposed lightweight CNN is also compared with the pre-trained models (VGG16, VGG19, ResNet50, ResNet101, and InceptionResNet). The proposed lightweight CNN suits best for embedded and/or edge computing devices.

On the throughput maximization of Cognitive Radio using cooperative spectrum sensing over erroneous control channel

Abstract: In this paper, we consider optimization of number of secondary users (M) by maximizing average channel throughput of the cognitive radio (CR) network for a given fusion rule (k-out-of-M) at the fusion center (FC) over erroneous control channel. For a given arbitrary positive integer value n, we obtain the mathematical expressions for optimal M for k = 1 + n and k = M − n rules at FC. Considering energy detector as an example for the analysis, following observations are made: 1) In the interval n ∈ [0, ⌈M/2⌉ − 1], as n increases optimal M increases. If FC uses k = 1 + n or k = M − n fusion rule, average channel throughput improves as n increases. 2) For a given n, average channel throughput obtained using k = M − n fusion rule is better compared to k = 1 + n fusion rule.

Full-diversity, high-rate space-time block codes from division algebras

Abstract: We present some general techniques for constructing full-rank, minimal-delay, rate at least one space-time block codes (STBCs) over a variety of signal sets for arbitrary number of transmit antennas using commutative division algebras (field extensions) as well as using noncommutative division algebras of the rational field /spl Qopf/ embedded in matrix rings. The first half of the paper deals with constructions using field extensions of /spl Qopf/. Working with cyclotomic field extensions, we construct several families of STBCs over a wide range of signal sets that are of full rank, minimal delay, and rate at least one appropriate for any number of transmit antennas. We study the coding gain and capacity of these codes. Using transcendental extensions we construct arbitrary rate codes that are full rank for arbitrary number of antennas. We also present a method of constructing STBCs using noncyclotomic field extensions. In the later half of the paper, we discuss two ways of embedding noncommutative division algebras into matrices: left regular representation, and representation over maximal cyclic subfields. The 4/spl times/4 real orthogonal design is obtained by the left regular representation of quaternions. Alamouti's (1998) code is just a special case of the construction using representation over maximal cyclic subfields and we observe certain algebraic uniqueness characteristics of it. Also, we discuss a general principle for constructing cyclic division algebras using the nth root of a transcendental element and study the capacity of the STBCs obtained from this construction. Another family of cyclic division algebras discovered by Brauer (1933) is discussed and several examples of STBCs derived from each of these constructions are presented.

Cognitive Radio: An Information-Theoretic Perspective

Abstract: Cognitive radios have been proposed as a means to implement efficient reuse of the licensed spectrum. The key feature of a cognitive radio is its ability to recognize the primary (licensed) user and adapt its communication strategy to minimize the interference that it generates. We consider a communication scenario in which the primary and the cognitive user wish to communicate to different receivers, subject to mutual interference. Modeling the cognitive radio as a transmitter with side-information about the primary transmission, we characterize the largest rate at which the cognitive radio can reliably communicate under the constraint that (i) no interference is created for the primary user, and (ii) the primary encoder-decoder pair is oblivious to the presence of the cognitive radio.

Single-symbol maximum likelihood decodable linear STBCs

Abstract: Space-time block codes (STBCs) from orthogonal designs (ODs) and coordinate interleaved orthogonal designs (CIOD) have been attracting wider attention due to their amenability for fast (single-symbol) maximum-likelihood (ML) decoding, and full-rate with full-rank over quasi-static fading channels. However, these codes are instances of single-symbol decodable codes and it is natural to ask, if there exist codes other than STBCs form ODs and CIODs that allow single-symbol decoding? In this paper, the above question is answered in the affirmative by characterizing all linear STBCs, that allow single-symbol ML decoding (not necessarily full-diversity) over quasi-static fading channels-calling them single-symbol decodable designs (SDD). The class SDD includes ODs and CIODs as proper subclasses. Further, among the SDD, a class of those that offer full-diversity, called Full-rank SDD (FSDD) are characterized and classified. We then concentrate on square designs and derive the maximal rate for square FSDDs using a constructional proof. It follows that 1) except for N=2, square complex ODs are not maximal rate and 2) a rate one square FSDD exist only for two and four transmit antennas. For nonsquare designs, generalized coordinate-interleaved orthogonal designs (a superset of CIODs) are presented and analyzed. Finally, for rapid-fading channels an equivalent matrix channel representation is developed, which allows the results of quasi-static fading channels to be applied to rapid-fading channels. Using this representation we show that for rapid-fading channels the rate of single-symbol decodable STBCs are independent of the number of transmit antennas and inversely proportional to the block-length of the code. Significantly, the CIOD for two transmit antennas is the only STBC that is single-symbol decodable over both quasi-static and rapid-fading channels.

Cooperative Spectrum Sensing in Cognitive Radio Networks

Abstract: Cognitive users need to detect primary users continuously and rapidly.Cooperative spectrum sensing in cognitive radio(CR) networks is analyzed.Cooperative spectrum sensing in the ideal network with two cognitive users can reduce the mean detection time.Detection probability to primary users can be improved by multi-cooperative users in multi-user networks.Finally,the realization of multi-user networks is considered.