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In this paper, we study the overhead introduced by the advanced encryption standard cipher in the context of wireless LANs, specifically at the medium access control layer, as described in the 802.11 standard developed by the 802.11n task group. The advanced encryption standard is incorporated into existing aggregation schemes for 802.11 wireless LANs in order to achieve secure transmission of frames. We compute the maximum throughput, optimal frame, and fragment sizes which can be achieved in this context and compare them to the optimal values when encryption is not used. We evaluate the delay performance of such a scheme in the context of encryption and study asymptotic properties of the medium access control layer efficiency, expected frame size, and throughput.

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In this paper, we use a multiple recursive generator (MRG) to generate sequences of numbers with very long periods, i.e., pseudo-random sequences. The MRG effectively constructs a block cipher which satisfies important quality requirements such as security, long period, randomness, and efficiency. We compare our approach with another lightweight block cipher based on a linear congruential generator (LCG) and analyze the efficiency in terms of the number of basic operations that are being performed. We also study the effects of using special classes of MRG which hold certain portability and efficiency properties, and analyze their advantages in this context. The proposed cipher is a lightweight cipher, which is very useful for resource limited resources such as sensor nodes in sensor networks, radio frequency identification (RFID) tags, etc.A. Olteanu et al.Lightweight block cipher for WSNs and RFID work. In Section 3, we introduce our block cipher based on the MRG generator. We then give a detailed analysis of the number of operations necessary for both generating a pseudo-random number, and for the block cipher, in Section 4. In Section 5, we compare our results with the performance of the LCG-based cipher. In Section 6, we provide performance analysis. In Section 7, we introduce some special classes of MRGs and analyze their efficiency. Section 8 presents approaches of speeding MRGS. Section 9 presents applications in WSNs and RFID sensor networks while Section 10 concludes the paper.Note that the LCG-based cipher in Reference [11] does not use LCG as the cipher, but is a cipher utilizing LCG. Since the LCG-based cipher in Reference [11] has been compared with other ciphers, in this paper, we only compare our cipher with the LCG-based cipher in Reference [11]. Since in Reference [11], we discussed some issues about the key managements, we will not consider this aspect in this paper. Furthermore, the proposed block cipher may be more suitable for active RFID instead of passive RFID. The proposed MRG-based cipher may not only have usefulness as a cipher, but also it could be used in parts of other ciphers as random number generators instead of a standalone cipher.

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Wireless sensor networks consist of a large number of sensors and have been broadly used for intrusion detection in surveillance systems. To guarantee detection quality, such networks are usually over-engineered, i.e., more than required sensors are deployed and remain active in order to cover each point in the monitored field with a high probability at any time instance. Existing sensor scheduling schemes based on the point coverage model tightly weave a sensor "net" that is unnecessarily dense. Intuitively, when the size and the shape of intrusion objects are considered, any net with holes no smaller than the size of the intrusion object would work fine. With this design philosophy in mind, we build a new mathematical model to investigate the impact of size and shape of intrusion objects on network configuration. We derive analytical results that provide practitioners with insights on how to weave an effective sensor "net" for intrusion object detection with minimum number of active sensors.

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In this paper, we study the overhead introduced by the advanced encryption standard cipher in the context of wireless LANs, specifically at the medium access control layer, as described in the 802.11 standard developed by the 802.11n task group. We compute the maximum throughput, optimal frame, and fragment sizes which can be achieved in this context and compare them to the optimal values when encryption is not used. I. INTRODUCTIONNE of the main challenges in wireless LANs (WLANs) nowadays is to develop a medium access control (MAC) layer that will not decrease the efficiency of the MAC layer when PHY rates are increased since as studied by Xiao et al. in [17,18,14], a theoretical throughput upper limit exists, indicating that by simply increasing the data rate without reducing overhead, the enhanced performance, in terms of throughput and delay, is bounded even when the data rate goes into infinitely high. Of the existing models, we are particularly interested in Aggregation with Fragment Retransmission (AFR) scheme, which was initially proposed in the IEEE 802.11n task group [9], and then developed more comprehensively in [6]. In this work, multiple frames are aggregated into a larger frame before being transmitted to the physical layer (PHY). If the size of a frame is larger than a pre-established threshold, the frame is divided into fragments before being aggregated. Transmission errors are handled by retransmitting only the fragments of the frame that had been corrupted.However, the work in [6] does not consider security, i.e., encryption algorithm AES, which is used in IEEE 802.11i. In other words, when IEEE 802.11n and IEEE 802.11i are both adopted, AES over the high speed wireless LANs (WLANs) must be considered. With this motivation, in this paper, we analyze the overhead introduced by AES, when added to the aggregation scheme in [6]. We compute the optimal frame and fragment sizes which render the maximum throughput in this context, and compare the results to the optimal values from [6], where AES encryption is not used. We derive asymptotic results related to the MAC layer efficiency, expected frame size and saturation throughput.II. RELATED WORK With respect to increasing efficiency at the MAC layer, much of the previous work has focused on minimizing the contention time which contributes to the transmission overhead ([3], [8], [16], 19). However, Xiao et al. in [17,18,14] show that a theoretical throughput upper limit exists, indicating that by simply increasing the data rate without reducing overhead, the enhanced performance, in terms of throughput and delay, is bounded even when the data rate goes