Massive multiple-input multiple-output (MIMO) is a breakthrough technology equipped with a large number of antennas and radio frequency (RF) chains, which increases complexity and circuit power consumption at the RF front-ends. Power utilisation of analog-to-digital converters is a major concern in RF chains, so one-bit massive MIMO systems are seen as one of the potential solutions to this problem. Further, channel state information (CSI) accuracy at the base station is one of the crucial needs for realising the benefits of one-bit massive MIMO. The existing pilot based estimators demand additional pilots for enhancing the CSI accuracy which in turn reduces the spectral efficiency of the system. To address this limitation, we propose an iterative semi-blind based channel estimator for one-bit massive MIMO systems in a pilot contaminated scenario. The proposed algorithm consists of two stages namely, initialisation and iteration. The initial channel estimate is obtained from pilot based initialisation stage, which is further refined in iteration stage with the help of both pilot and a few data symbols. The proposed semi-blind algorithm improves estimation accuracy with minimum number of pilot symbols. Through simulations, we show that the proposed scheme achieves a considerable improvement in mean square error and bit error rate against the existing pilot based estimators at the cost of a nominal increase in computational complexity. Moreover, the proposed algorithm attains convergence in two iterations for all the considered scenarios. The proposed estimator is spectral and power-efficient in comparison to the pilot based algorithms. To the best of our knowledge, it is the first attempt of channel estimation in pilot contaminated one-bit massive MIMO systems.

In this work, we study the performance of a decode and forward relay assisted secondary user pair co-existing with a primary network under wireless energy harvesting scenario. The locations of primary transmitters and receivers are modeled using two independent Poisson point processes (PPPs). In this network model, we consider that the secondary transmitter scavenges energy from primary transmitters and transmits its data towards secondary destination via a secondary relay. The direct link between the secondary transmitter and secondary destination is assumed to be unavailable. We find an analytical expression for the probability of successful one way data communication between the secondary transmitter and secondary destination through the secondary relay considering, (i) maximum interference power constraint imposed by primary receivers, (ii) interference from primary transmitters and (iii) additive white gaussian noise. Trade-off between the benefit of energy harvesting at secondary transmitter and the adverse interference effect (both at secondary relay and destination) due to primary transmission is shown through numerical analysis. The analytical expression is validated through computer simulation.

In this paper, we propose a method for detecting the vowel onset points (VOPs) for low bit rate coded speech. VOP is the instant at which the onset of the vowel takes place in the speech signal. VOP plays an important role for the applications, such as consonant-vowel (CV) unit recognition and speech rate modification. The proposed VOP detection method is based on the spectral energy present in the glottal closure region of the speech signal. Speech coders considered to carry out this study are Global System for Mobile Communications (GSM) full rate, code-excited linear prediction (CELP), and mixed-excitation linear prediction (MELP). TIMIT database and CV units collected from the broadcast news corpus are used for evaluation. Performance of the proposed method is compared with existing methods, which uses the combination of evidence from the excitation source, spectral peaks energy, and modulation spectrum. The proposed VOP detection method has shown significant improvement in the performance compared to the existing method under clean as well as coded cases. The effectiveness of the proposed VOP detection method is analyzed in CV recognition by using VOP as an anchor point.

In this paper we present the closed form expression of bit-error-rate (BER) of a convolution coded MB-OFDM Ultra-Wideband (UWB) system. The analysis considers the log-normal fading statistics of UWB channels and captures the estimation error variances of timing and carrier frequency offset (CFO) estimation by our already published synchronizers ATS [1] and MBAFS [2] respectively. The derivation invokes moment generating function (MGF) for log-normal fading statistics and the Gauss-Hermite quadrature integration to deliver average BER expression for rate Rc coded QPSK modulated MB-OFDM system with ATS and MBAFS synchronizers and least square (LS) channel estimator. The analytical result is validated with simulation in the high delay spread UWB channel model CM3. This analysis helps in thorough understanding on the performance of an OFDM based communication system in an Ultra-Wideband environment.

A cross-correlation function (CCF) based timing synchronization algorithm of low complexity, applicable for single-band transmission is presented. Novelty of the synchronizer lies in utilization of specific preamble structure of the Multi-band OFDM frame format. This threshold based algorithm also takes care of the fact that stronger multipath components frequently appear on the later clusters. Performance of the algorithm is measured in terms of mean-squared-error and synchronization probability. Performance is compared with another single-band based timing algorithm by Yak et al. [2]. The probability of correct detection is analyzed mathematically to verify the experimental results.

A DS-CDMA system is said to be Overloaded if the number of users supported is more than the spreading factor N. Overloading is an attractive candidate for next generation cellular telephony that calls for a higher user capacity than that supported by conventional DS-CDMA systems. This work derives an accurate analytical model for Overloaded DS-CDMA system under imperfect synchronization. The Model also takes care of the degradation in signal energy due to the loss in Autocorrelation value at the matched filter receiver. BER expressions for Individual users are also derived for uniformly distributed synchronization errors that happen to be the case in practical scenario. Monte-Carlo simulations verify the presented analysis.

Event-driven wireless sensor networks gain precedence over data-driven networks due to the effective manner in which they reduce the redundancy in data transmitted. In this paper, an attempt has been made to model the events of information generation and dissemination in an event driven wireless sensor network with uniformly distributed sensor nodes. Two existing definitions for the lifetime of sensor network have been used and a comparison of performance metrics like network lifetime, packet throughput and energy utilization have been made. Furthermore the concept of data aggregation has been incorporated into the developed model and the improvement in performance is observed.

In this paper we propose a new multiple access scheme using multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM). MSE-OFDM is a bandwidth efficient OFDM scheme, where a number of OFDM symbols are grouped together as a frame and protected by one single cyclic prefix. We wish to explore a multiple access MSE-OFDM, where each symbol of the frame is from a different user. Performance analysis of multi-user MSE-OFDM in AWGN and multipath fading channels has been done and the effects of carrier frequency offset and timing offset on its performance have been studied for downlink channel. The signals from multiple users are assumed to be synchronous in the downlink and the channel conditions are also assumed to be similar for each user. The multiple access interference (MAI) should be minimum if the orthogonality of subcarriers is maintained. However, due to carrier frequency offset and symbol timing misalignment, the orthogonality between users may be destroyed resulting in MAI. The MAI has been analyzed for the proposed scheme and can be reduced by using suitable methods for frequency and time synchronization. Expressions for probability of error for multi-user MSE-OFDM in presence of inter-channel interference (ICI) and inter-symbol interference (ISI) have been derived. Both analysis and simulation results are found to be in close agreement.

An Ultra-Wideband (UWB) channel exhibits frequency dependent delay characteristics in different bands of transmission. In [6] we studied and quantified the differences of delay parameters over frequency bands 3.1-4.6 GHz in several UWB channel models (CM). Based on this observation, we proposed an adaptive timing synchronization scheme (ATS) which estimates and maintains the timing delays of each band separately. In this paper, we modify our ATS algorithm [6] by optimal selection of the threshold for timing estimation to reduce the mean-squared-error (MSE) and increase the synchronization probability of the estimator. The performance of UWB Multi- band OFDM (MB-OFDM) system with modified ATS algorithm is studied through computer simulations. We show that modified ATS gives signal-to-noise ratio (SNR) improvement of 1.7 dB at Bit Error Rate (BER) of 2times10-2, 2.2 dB at BER of 7times10-3, and 1.1 dB at BER of 5times10-3for CM4, CM3, and CM2 respectively for uncoded MB-OFDM system over a non-adaptive synchronization scheme [5]. Also, algorithmic computational complexity analysis of modified ATS is provided for its usability evaluation.

This work explores theoretically the unique aspects of different signal processing stages in a Multi-Band (MB) Orthogonal Frequency Division Multiplexing (OFDM) based system in realistic Ultra-Wideband (UWB) channel. In the process of analysis, it emphasizes the significant aspects of signal processing steps in UWB receiver design comparing a narrow-band system. The analysis preliminary considers perfect timing and frequency synchronization which is extended later with a frequency offset error and its correction. Performance of the offset estimator in MB-OFDM system via computer simulation is provided in order to support the mathematical analysis.

Overloading is a scheme to accommodate more users than the spreading factor N. This is a bandwidth efficient scheme to increase the number of users in a fixed bandwidth. One of the efficient schemes to overload a CDMA system is to use two sets of orthogonal signal waveforms (O/O). The first set is assigned to the N users and the second set is assigned to the additional users. An iterative multistage detection (IMSD) technique is used to cancel interference between the two sets of users. The interference cancellation receiver uses hard decisions (HDIC) or soft decisions (SDIC) to estimate the interference. In this paper, the BER performance of a new overloading scheme using orthogonal Gold code (OG/OG) sets is evaluated with SDIC receiver. It is observed that this scheme provides 25% (16 extra users) channel overloading for synchronous DS-CDMA system in an AWGN channel, with an SNR degradation of about 0.35 dB as compared to single user bound at a BER of 10-5. We have also evaluated the overloading performance, when the two set are scrambled with set specific complex scrambling sequence. It is shown that the amount of overloading increases significantly from 25% to 63% (40 extra users) by using complex scrambling for N=64.

A frequency offset estimation scheme is presented for coarse frequency offset estimation of Ultra-Wideband (UWB) Multi-Band Orthogonal Frequency Division Multiplexing (MB- OFDM) systems. Cramer Rao Lower Bound (CRLB) for variance of the estimated frequency offset is derived and compared with the simulated results of the proposed scheme. Performance of the MB-OFDM system in terms of the Bit Error Rate (BER) with suggested frequency offset estimator is also reported. The algorithm is tested by computer simulation over multiple UWB channel models (CM), CM1: 0-4m line-of-sight, CM2: 0-4m non-line-of-sight (NLOS), CM3: 4-10m NLOS, and CM4: 25 nsec. delay spread as suggested by IEEE 802.15 Channel Modeling sub-committee. With higher number of iteration the algorithm shows improvement of the system performance by 8.8 dB in both CM1 and CM2; 7.6 dB for CM3 and 8.3 dB for CM4 at BER=10-4.