Omar A. Nasr

Proposed relay selection scheme for physical layer security in cognitive radio networks

In this study, the physical layer security for cognitive radio network (CRN) will be investigated in which a secondary user transmitter (SU-Tx) sends confidential information to a SU receiver (SU-Rx) on the same frequency band of a primary user (PU) in the presence of an eavesdropper receiver. Moreover, relay selection scheme is proposed for the security constrained CRNs with single eavesdropper, multiple eavesdroppers and PUs. The proposed scheme selects a trusted decode and forward relay to assist the SU-Tx and maximise the achievable secrecy rate that is subjected to the interference power constraints at the PUs for the different number of eavesdroppers and PUs under available channel knowledge. The SU cooperates with relays only when a high secrecy rate is achieved. Secrecy rate and secrecy outage probability are the two performance metrics that are used to verify the effectiveness of the proposed scheme although asymptotic approximations of the secrecy outage probability are also derived. Simulation and analytical results demonstrate that the performance improvement of the proposed scheme reaches to the double relative to the conventional scheme for the secrecy capacity.

An Efficient Adaptive Technique with Low Complexity for Reducing PAPR in OFDM-Based Cognitive Radio

Cognitive radio (CR) is considered nowadays as a strong candidate solution for the spectrum scarcity problem. On standards level, many cognitive radio standards have chosen Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) as their modulation scheme. Similar to OFDM, NC-OFDM suffers from the problem of having a high Peak to Average Power Ratio (PAPR). If not solved, either the transmitted signal will be distorted, which will cause interference to primary (licensed) users, or the effeciency of the power amplifier will be seriously degraded. The effect of the PAPR problem in NC-OFDM based cognitive radio networks is worse than normal OFDM systems. In this paper, we propose enhanced techniques to reduce the PAPR in NC-OFDM systems. We start by showing that combining two standard PAPR reduction techniques (interleaver-based and selective mapping) results in a lower PAPR than using them individually. Then, an “adaptive number of interleavers” will be proposed that achieves the same performance of conventional interleaver-based PAPR reduction while reducing the CPU time by 41.3%. Finally, adaptive joint interleaver with selective mapping is presented, and we show that it gives the same performance as conventional interleaver-based technique, with reduction in CPU time by a factor of 50.1%.

Interference-aware energy-efficient cross-layer design for healthcare monitoring applications

Body Area Sensor Networks (BASNs) leverage wireless communication technologies to provide healthcare stakeholders with innovative tools and solutions that can revolutionize healthcare provisioning; BASNs thus promotes new ways to acquire, process, transport, and secure the raw and processed medical data to provide the scalability needed to cope with the increasing number of elderly and chronic disease patients requiring constant monitoring. However, the design and operation of BASNs is challenging, mainly due to the limited power source and small form factor of the sensor nodes. The main goal of this paper is to minimize the total energy consumption to prolong the lifetime of the wireless BASNs for healthcare applications. An Energy-Delay-Distortion cross-layer framework is proposed in order to ensure transmission quality for medical signals under limited power and computational resources. The proposed cross-layer framework spans the Application-MAC-Physical layers. The optimal encoding and transmission energy are computed to minimize the total energy consumption in a delay constrained wireless BASN. The proposed framework considers three scheduling techniques: TDMA, TDMA-Simultaneous Transmission and dynamic frequency allocation scheduling. The TDMA-ST scheme schedules the weakly interfering links to transmit simultaneously, and schedules the strongly interfering links to transmit at different time slots. The dynamic frequency allocation scheme allocates the time-frequency slots optimally based on the applications requirements. Simulation results show that these proposed scheduling techniques offer significant energy savings, compared to the algorithms that ignore cross-layer optimization.

A CORDIC-friendly FFT architecture

Fast Fourier Transform (FFT) is one of the basic building blocks in signal processing and communications systems. The butterflies-based structure of the FFT is the main reason for the reduced number of arithmetic operations required to implement the transform. From implementation point of view, the complex rotations used in butterflies can be implemented by using COordinate Rotation DIgital Computer (CORDIC). This implementation strategy reduces the hardware complexity compared to the direct implementation of the butterflies using complex multipliers. In this paper, we introduce a restructure of the butterflies of the radix-2 FFT to be more CORDIC friendly. This algorithm-level modification of the FFT is friendly towards all CORDIC types, including those introducing non-fixed gain. Compared with the conventional radix-2 FFT algorithm, the proposed algorithm introduces a substantial increase in performance. For example, it achieves superior signal to quantization noise ratio (SQNR), with around 14 dB gain for 8 to 1024 points FFT. In addition, in pipeline architectures the modification leads to an improvement in latency or a reduction in the total area, with an improvement in either of 38% for 1024 points FFT.

Energy-aware routing for delay-sensitive applications over wireless multihop mesh networks

In this paper, a cross-layer algorithm that aims at minimizing the end-to-end transmission energy subject to a packet delay deadline constraint is proposed. The optimal transmission energy and rates, and the optimal route are computed to minimize the end-to-end total transmission energy in a delay constraint wireless mesh network. A cross-layer optimization framework is proposed under a constraint that all successfully received packets must have their end-to-end delay smaller than their corresponding delay deadline. In addition to the optimal solution, a suboptimum solution is also proposed. This solution has close-to-optimal performance with lower complexity. The simulation results show that, for the same delay constraint and bit error rate (BER), the optimum proposed algorithm has less energy consumption than routing algorithms that consider delay constraint only.

Study the effect of PAPR on wideband cognitive OFDM radio networks

Cognitive radio (CR) technology is viewed as a novel approach for maximizing the utilization of the radio electromagnetic spectrum. Spectrum sensing methods are often used for finding free channels to be used by CR. Recently, Orthogonal Frequency Division Multiplexing system (OFDM) has been suggested as a candidate technology for multicarrier-based CR systems. However, one problem that appears in OFDM systems is the high Peak to Average Power Ratio (PAPR). In this paper, the effect of PAPR reduction of the primary signal on the performance of the multiband joint detection for wideband spectrum sensing and the profit of the primary user will be investigated. Moreover, the optimal solutions for the multi-band joint detection for the non-cooperative and cooperative schemes will be analyzed by considering the primary user’s PAPR reduction. Also, the wideband cooperative spectrum sensing to improve the signal detection with high reduction in the PAPR will be suggested. Simulation results show that the PAPR reduction decreases the total price of the primary user and the aggregate opportunistic throughput of the secondary user. The cooperative scheme is effective in improving the performance in terms of the aggregate opportunistic throughput with PAPR reduction.

Proposed relay selection scheme for physical layer security in Cognitive Radio networks

Cognitive Radio (CR) technology is one of the strong candidate technologies to solve the spectrum scarcity problems. In this paper, we tackle the problem of secure data transmission between a secondary user transmitter and receiver through a relay in the presence of an eavesdropper in a cognitive radio network. The proposed scheme selects the best Decode-and-Forward relay among different relays to assist the transmitter, and to maximize the achievable secrecy rate without harming the primary user. Simulation results show that the secrecy capacity of the network using this scheme will almost be double the capacity when selecting the conventional scheme of relay selection.

Embedded reconfigurable synchronization & acquisition ASIP for a multi-standard OFDM receiver

Embedded reconfigurable architectures are currently attracting increasing attention in the wireless communications industry due to the escalating number of wireless standards in todays market. Application specific instruction-set processors (ASIPs) present a reconfigurable solution that offers a compromise between programmability and low power consumption. In this article, the design and implementation of an embedded synchronization and acquisition ASIP for OFDM based systems is proposed. The engine architecture is presented and the programming model is explained in details. The proposed engine is scalable and it can be configured to support a multitude of synchronization algorithms and OFDM standards. While applicable to many OFDM systems, the proposed architecture was successfully verified on long term evolution (LTE Rel. 8) and WiMAX 802.16e systems. A partial list of synchronization and acquisition algorithms are tested on the engine for the two standards, and the results highlight the capabilities of the engine. The processor has been synthesized with 0.18μ m standard cell CMOS library. It is estimated to occupy 1.1 mm2 and the projected power consumption is 7.9mW at 120 MHz, which meets the speed requirements of the tested standards. More results are included within the article.

ASIP design of a reconfigurable channel estimator for OFDM systems

Progress in wireless communications has led to an increasing number of standards such as WIMAX, 3GPP-LTE, DVB-T, DVB-H and more. This work presents a reconfigurable channel estimation engine for OFDM systems. The engine can support multiple channel estimation algorithms for many wireless standards. It can also support both 1D and 2D channel estimation algorithms. This is important because the large performance gain of 2D over 1D channel estimation algorithms, which can be up to 5dBs. Moreover, 1D algorithms are less complex than 2D algorithms and they are the best choice when there is a need to reduce the receiver processing power. The engine does not use any dividers for least square pilots estimation, and hence, the least square pilot estimator engine is less complex than other engines. Although the engine was designed and optimized for channel estimation algorithms, it can also be configured as an FFT engine, FIR engine and many more. The engine was synthesized on Altera Startix III EP3SC150 FPGA and performs the estimation process in 94 μsecond for the worst case parameters in all supported standards.

Fair allocation of backhaul resources in multi-cell MIMO coordinated beamforming

Coordinated beamforming in multipoint MIMO networks has been introduced to increase the overall capacity of wireless networks. In coordinated beamforming, the channel state information between the different MIMO access points/base stations in one hand, and the mobile stations on the other hand, needs to be shared among the MIMO nodes. A “backhaul” between different MIMO access points is used to transfer the channel state information. The channel state information of different links is quantized with different quantization steps according to a specific optimization criteria. This information is then shared through the backhaul. In this paper, we study the problem of allocating the backhaul bandwidth among users in coordinated beamforming MIMO multipoint networks. First, we prove through mathematical analysis, that there are many allocations that can provide “near maximum sum rate”. These different allocations vary significantly in fairness between users. A “fair” allocation is an allocation that provides a small variance between the rates of different users. Motivated by this finding, we introduce two novel, low complexity, backhaul bandwidth distribution schemes that can achieve a very close to maximum sum rate, and at the same time, offer throughput fairness among users. Simulation results show that, for the same sum-rate, the proposed schemes can achieve more fairness among users when compared to the conventional scheme, which gives all users the same share of bandwidth. Moreover, we show that one of the proposed schemes, namely the Equal SIR scheme, can achieve zero variance among users in a wide range of backhaul bandwidths while keeping a very close to maximum sum rate.