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Many duty cycling MAC protocols exploit preamble sampling technique to improve the energy efficiency. In this technique, all the devices periodically listen to the medium for a short duration and then go back to sleep if medium is found idle. When a device wants to send data it transmits a long preamble followed by data bits. When the receiver wakes up and detects the preamble it stays awake until...
The mobile WiMAX standard (802.16e) uses multiple-input multiple-output (MIMO) limited feedback linear precoding to exploit the channel state information at the transmitter. Although the performance of limited feedback linear precoding in relation to traditional open-loop MIMO-OFDM has been extensively studied in the literature, these studies commonly assume perfect channel estimation at the receiver...
In this work, we investigate secret key generation from channel states. We point out, by means of a packet-delay-based attack, that observing its own channel states is not the only way an adversary can learn about the channel states of the legitimate communicating parties. The attack suggests that it is not secure to transmit data via the channel whose states generate secret keys. However, not using...
Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square...
In wireless ad hoc networks, multiple access interference is the limiting factor for the overall system performance. The lack of any central control unit necessitates a careful joint design of both, the physical and the MAC layer. Two promising technologies that address this problem are power control based cross-layer design and multiuser detection based cross-layer design. While approaches in the...
The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rate-adaptation to select appropriate transmission rate according to variations in the channel quality. This paper proposes a novel rate-adaptation scheme where the decision of rate selection relies on the mutual feedback...
We consider a point-to-point, correlated and block fading multiple antenna channel where the receiver has a noisy channel estimation and the transmitter has the statistics of the channel. Although very high rates are promised when the receiver knows the channel perfectly, the capacity is not known when the receiver has a noisy channel estimation. In this paper, we will derive an upper bound to the...
This paper presents an efficient way for overcoming the inaccurate path error encountered in ray tracing for site-specific indoor propagation modeling. The source is modeled using triangular ray tubes each of which consists of three rays which do not lie in the same plane. Each possible source ray inside an arbitrary ray tube is expanded in terms of the three rays defining that ray tube. The variations...
Channel coherence time is commonly used to characterize the rate at which the channel changes. The recently introduced effective coherence time measures the channel change rate from an estimation perspective. It was shown that the effective coherence time is related to the capacity of the non-coherent channel, in which the receiver has no prior knowledge of the channel, and tries to estimate it from...
In the WIMAX (802.16e) standard several small medium access control (MAC) packets may be aggregated to form a MAC burst, forwarded to the physical (PHY) layer The burst transmission is a mechanism to allow multiple MAC protocol data units (PDUs) belonging to the same video channel to be transmitted / received in an aggregated way, in order to enable power saving at the mobile station, by putting the...
Bit-interleaved coded modulation with iterative decoding (BICM-ID) performs well under a variety of channel conditions. Based on a factor graph representation of BICM-ID, we propose a modification of the BICM-ID receiver that can reduce the computational complexity significantly without BER degredation. The basic idea is to avoid updates of code bit log-likelihood ratios whose magnitude is already...
Dynamic allocation of resources to the best link in large multiuser networks offers considerable improvement in spectral efficiency. This gain, often referred to as multiuser diversity gain, can be cast as double-logarithmic growth of the network throughput with the number of users. In this paper, we consider large cognitive networks granted concurrent spectrum access with license-holding users. The...
A 900 MHz direct-conversion receiver for UHF RFID readers with low power, high linearity, and low noise in UMC 0.18 ??m CMOS technology is proposed. This receiver possesses I/Q two paths and each path consists of a passive mixer, an IF amplifier, a RC low-pass filter and a comparator. It supports a LO frequency from 860 MHz to 960 MHz and a data rate from 40 kb/s to 1 Mb/s which are in accordance...
We consider the digital fingerprinting problem where colluders apply uniform linear averaging followed by AWGN. For each user, the receiver computes the correlation between the attacked signal and that user's fingerprint, and performs thresholding (focused detection). We model the fingerprinting problem as a multi-user communications problem and develop a detection theoretic framework. Assuming independent...
This paper presents an achievable rate region for a 2-user Gaussian Z-interference channel with a noiseless and bidirectional digital communication link between the receivers. The region is achieved by utilizing the rate-splitting encoding technique, and the decode-and-forward and compress-and-forward strategies. In the very strong interference regime, the capacity region is achieved. In the weak...
In this paper, we consider the problem of functional compression for an arbitrary tree network. Suppose we have k possibly correlated source processes in a tree network, and a receiver in its root wishes to compute a deterministic function of these processes. Other nodes of this tree (called intermediate nodes) are allowed to perform some computations to satisfy the node's demand. Our objective is...
The radio frequency identification (RFID) tags are an integral part of lives today, whether realized or not. Thousands of applications are currently using RFID tags and the number is growing. RFID finds its application in fields as diverse as race timing, transportation payments, passports, & animal identification. This paper aims at combining the ubiquitous applicability of RFIDs with high speed...
Integrated 60 GHz transmitter and receiver GaAs front-end MMICs as well as a packaged transceiver module used for wireless communication link are presented. The data transmission capacity of the chips is examined using binary ASK modulation. A broadband 60 GHz direct carrier quadrature modulator is proposed to be integrated with the transmitter for realizing complex modulation schemes to increase...
This paper describes design issues related to high linearity SiGe BiCMOS active mixers, which are primarily targeted for WCDMA base-station applications. The effect of different mixer components to overall mixer dynamic range is described, and the measurement results from four different implementations are given to support this discussion. The different mixers are implemented using the same process...
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