Shawki Shaaban

Frequency-hopped multi-user chirp modulation (FH/M-CM) for multipath fading channels

The multi-user chirp modulation (M-CM) technique was introduced previously by the author as an efficient multiple-access technique using chirp modulation spread-spectrum signals. To further improve the performance of M-CM in multipath dispersive channels we suggest the application of frequency hopping (FH) to M-CM. The band of M-CM multiplexed signals is frequency-hopped within the allowed channel bandwidth. The application of FH is shown to highly improve the performance of M-CM signals in multipath fading dispersive channels. The considered channel model is a generalized channel model that allows dispersion and flat fading due to multipath propagation. Closed form expressions for the upper bound on the error probability for FH/M-CM is derived and investigated for different cases of channel dispersion and multiple-access parameters.

Frequency hopped-chirp modulation (FH-CM) for multi-user signaling in multipath dispersive media

Chirp signals are categorized as spread-spectrum signals and have good advantages in interference rejection. The use of matched chirp modulation (MCM) for efficient digital signaling in dispersive communication channels has also been considered by El-Khamy et al. (1980, 1988). Chirp modulation has also been considered for multi-user applications. New forms of multi-user chirp modulation (M-CM) signals that are characterized by the same power as well as the same bandwidth have also been introduced previously by the authors. In this paper, we investigate the combination of frequency-hopping (FH) spread-spectrum techniques with M-CM to produce a multiple-access technique that is characterized by good performance in dispersive and fading propagation media. The considered frequency-hopped chirp modulation (FH-CM) is investigated in detail and its performance is shown to outperform that of M-CM.

Multi-user chirp modulation signals (M-CM) for efficient multiple-access communication systems

We present a novel technique for a multi-user communication system utilizing binary chirp modulated (CM) signals. This suggested technique is motivated by the inherent interference rejection capability of such spread-spectrum type system, specially in circumstances where immunity against Doppler shift and fading due to multipath propagation are important. The chirp signals used are selected such that they all have the same power as well as the same bandwidth. Closed form expressions, as well as approximate analytical expressions, for the cross-coherence functions between the different forms of considered chirp signals are derived. The performance of a suggested coherent receiver structure is investigated and the corresponding error rates are presented. The results show that the proposed multi-user chirp signaling technique is efficient and promising as a multiple-access technique.

Novel cell selection algorithm for improving average user's effective data rate in LTE HetNets

Cell selection algorithms are considered one of crucial features in LTE-Heterogeneous Networks (HetNets). Due to different downlink transmit power levels and randomness deployment of femtocells, achieving better user throughput and reducing the necessity of dynamic load balancing techniques require appropriate algorithms for selecting optimum serving cell. In this work, a new cell selection algorithm is proposed to enable new user to select best serving cell that achieves maximum effective achievable data rate. A new prediction algorithm is designed within the new proposed cell selection algorithm to predict the performance of Proportional Fair (PF) scheduling algorithm without running it after every Resource Block (RB), to calculate the expected degradation in theoretical new users achievable data. The numerical results show that the new cell selection proposed algorithm achieves higher average cell throughput than conventional cell selection methods and maintains better balanced load between different adjacent cells.

Wavelet Packet Modulation for Multi-carrier CDMA Communications

MC-CDMA inherits the interference rejection capability of CDMA, and the potential of mitigating multipath propagation effects of orthogonal frequency division multiplexing (OFDM). MC-CDMA with its frequency diversity is an attractive modulation scheme for multi-user high data rate wireless communication system. However on OFDM and MC- CDMA sub-channel decomposition cannot be achieved without adding guard band or cyclic prefix, where a copy of the end part of the data symbol block is transmitted. Due to the relationship between circular and linear convolutions in discrete Fourier transform (DFT), the residual inter symbol interference (ISI) is eliminated by dropping the guard interval part in the receiver. This method needs transmitting extra guard interval signals that introduces overhead and thus leads to spectral inefficiency and performance degradation. An efficient scheme which not only counters the degrading effects of ISI but also conserves the bandwidth is the application of discrete wavelet packet transform (DWPT) based MC-CDMA. in this paper we replace Fourier based complex exponential carriers of MC-CDMA with an orthonormal wavelets packets, such as daubechies, haar, biorthogonal, discrete meyer and coiflets to compare the performance of MC-CDMA based discrete fourier transform (DFT) and MC-CDMA based discrete wavelet packet transform(DWPT).

DWT-Based Antenna Selection for Correlated MIMO Channels

In this paper, we address the antenna selection problem in spatially correlated Multiple-Input Multiple Output (MIMO) channels. To reduce the severe performance degradation of the traditional antenna selection scheme in correlated channels, we propose to embed Discrete Wavelet Transform (DWT) operations in the RF chains. The resulting system shows a significant advantage for the capacity of spatial multiplexing schemes that reaching 5 b/s/Hz, while requiring only a minor hardware overhead and low computational complexity.

Partially coherent detection of continuous phase chirp (CPCM) signals

This paper treats the partially coherent detection of continuous phase chirp modulation (CPCM) signals. The optimum partially coherent receiver structures are described. Suboptimum receivers are also described and the corresponding bounds on error rate are calculated for optimum signal parameters. The optimum signal parameters are obtained for each degree of channel coherency by using a search program for the error probability versus the signal parameters.

Antenna Selection Algorithms in Correlated Fading MIMO Channels

This paper studies the performance of existing receive antenna selection algorithms in spatially correlated fading MIMO channels. The antenna subset is selected based on maximizing the channel capacity. First the most recently proposed algorithms, which are dedicated to i.i.d channel, are revisited and investigated. Then, we apply these algorithms to the case of correlated fading channel. The performance of each algorithm is evaluated and compared in terms of the outage characteristics for different scenarios regarding the angle spread and the required number of antenna elements. Finally, we compare between our results and another algorithm dedicated to correlated channels, namely the correlation selection algorithm

Hexagonal Two Tier Data Dissemination model for large scale wireless sensor networks

In wireless sensor networks new challenges appear when we target a large scale sensor network. The existing approaches suggest that each sink propagates its location continuously through the whole sensor field to keep the entire sensor modes updated with the direction of forwarding future data reports. The scalability problems appear when multiple mobile sinks send query request. This will lead to both increase of collisions in wireless transmission and excessive power consumption in battery operated sensor nodes. Hexagonal TTDD approach provides high efficiency in scalable data dissemination from multiple sources to multiple mobile sinks. Each source builds its own hexagonal grid structure and the sinks send their data query within local cells which will enable them to continuously receive data while moving. The performance of hexagonal TTDD evaluated through detailed analysis.

New trends towards speedy IR-UWB techniques

Wireless communications have been dominated by transmission schemes based on conventional narrowband technology. Therefore, narrowband systems are unable to increase higher data-rates in wireless communication applications, which cause Inter Symbol Interference (ISI) due to multipath fading phenomenon that can be resolved at the receivers. Several implementation schemes for Impulse-Radio (IR) Ultra-Wide Band (UWB) systems have been presented. These include methods such as Transmit Reference (TR) and Frequency-Shifted Reference (FSR), which can overcome the complexity of channel estimation by transmitting reference pulses separated by a shift in time and frequency, respectively. Code-Shifted Reference (CSR) has been proposed for IR-UWB transmission. The CSR scheme with UWB systems has been found to achieve a better performance than the previous schemes. In order to improve system performance, the CSR scheme was extended to the Differential CSR (DSCR) to reduce the power used to transmit the reference pulse sequence. This Paper includes the methods of Rake Receiver, TR, Frequency-Shift Reference (FSR), emerging CSR and DCSR. A brief discussion is given for each method followed by a performance comparison between DCSR and CSR, TR and FSR Rake methods.