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In cognitive radio networks, spectrum sensing is a fundamental function for detecting the presence of primary users in licensed frequency bands. Due to multipath fading and shadowing, the performance of detection may be considerably compromised. To improve the detection probability, cooperative sensing is an effective approach for secondary users to cooperate and combat channel impairments. This approach,...
Since several years, communications between fixed and mobile units have been studied in areas in underground tunnels. The leaky feeder (LF) is one of the most useful results of these studies. The LF technology in combination with other communication systems allows us to reduce the transmission power of the mobile entities without sacrificing quality of service. Because the leaky feeder cables are...
This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions...
A single transmit antenna Broadcast Channel (BC) with large number of users in a Rayleigh fading environment is considered. It is assumed each user either receives a predetermined minimum rate constraint or remains silent. Recently, it is shown that by applying a proper power allocation strategy, one can maximize the maximum number of active users in such channel. The main contribution of this paper...
Wireless ad hoc networks are an emerging and popular technology to the world; however, the benefits of them are actually their fragility, too. Owing to mobile node movement, the link break problem always occurs in the network. The problem greatly influences the throughput, delay, jitter, and lots of performance issues of a routing protocol. Hence, this article is proposed to evaluate the influence...
A constant three-user interference channel wherein users are not symbol synchronous is considered. A novel practical interference alignment scheme for this channel is proposed wherein aligning interfering signals at each receiver is performed with the help of asynchronous delays which inherently exist among the received signals at each receiver node. Due to the existence of asynchronism among the...
A single-letter characterization is provided for the capacity region of finite-state multiple access channels, when the channel state is a Markov process, the transmitters have access to delayed state information, and channel state information is available at the receiver. The delays of the channel state information are assumed to be asymmetric at the transmitters. We apply the result to derive power...
In this paper we study a multiple access system without feedback supporting multiple carriers for delay critical applications with a small loss tolerance. In such a system, users transmits R times within the next N timeslots, in order to improve their success probability. In an earlier work, we considered the same problem in a single carrier system and demonstrated that the distribution of properly...
We study the problem of multiple packet bundling in multi-carrier cellular networks for VoIP and data traffic. In a time-slotted system such as the cdma2000 1xEV-DO downlink, part of a time-slot may not be fully utilized, if the packet sizes are small, as in the case of real-time VoIP traffic. Packet bundling can alleviate such a problem by sharing a time slot among multiple users, as proposed in...
Time-of-arrival (ToA) estimation technique used with ultra-wideband (UWB) transmission can be used for accurate indoor ranging. In the indoor multipath rich environment, these techniques often suffer from significant inaccuracy in ranging estimation. It is generally believed that the main cause of the ToA estimation error in the Line-of-sight (LoS) scenario is noise, usually modeled as white Gaussian...
Tropospheric scattering channel is a random channel. When the signal transmitted through the troposphere, the multi-path fading could cause signal waveform distortion. In this paper, based on a valid tropospheric scattering channel model, respectively, from the time domain and frequency domain the reasons why the signal waveform was distortion were analyzed. Radar pulse as the transmit signal, and...
Railway operations is closely related to people's livelihood, and the reliability, availability, maintainability and security of railway communication system are the focus and key issues of railway information construction. There are series of problems, such as the deterioration of communication performance (difficult to meet the needs of train control and train scheduling) because of the wireless...
To achieve multiuser diversity gains, resource allocation relies on accurate and timely feedback of the users' channel states. This feedback suffers from transmission errors and delay which can heavily degrade the sum capacity of a scheduled multiuser downlink. The order of this capacity loss and its interdependency to relevant scenario factors is characterized in this paper. From studying a simple...
Multi-hop wireless ad hoc networks suffer from temporary link error due to fading. In order to improve packet transmission reliability and achieve efficient transmission in fading environment, this paper proposes an integrated dynamic multi-hopping scheme based on a cross-layer approach and cognitive behavior of local nodes. The scheme provides two important functions, temporary bypassing and dynamic...
This paper proposes an OFDM based transmission scheme for asynchronous amplify-and-forward cooperative systems with two relay nodes over frequency-selective channels. To combat the inter-symbol interference from multi-path fading and timing errors, the cyclic prefix (CP) is used at both the source node and relay nodes. Unlike using IDFT and DFT modulation for two consecutive OFDM blocks respectively,...
In mobile radio communications there is an ever-increasing demand for high speed and high quality data transmission. Error correction and multi-channel reception are two promising techniques incorporated in the present-day cellular system to attain high-quality and high-speed communication is a multipath fading environment where the rapid variations of the channel gain degrades the transmission quality...
In a code-multiplexed transmitted-reference (CM-TR) ultra-wideband (UWB) system [8], the reference pulse trains are made orthogonal to the information-bearing signal by code-shifting. The receiver is simple because it avoids the use of an analog delay line. Moreover, the CM-TR UWB system outperforms the original TR-UWB system in terms of error rates. In this paper, we extend the CM-TR concept to transmit...
In this paper, a new blind symbol synchronization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems. The proposed algorithm extracts the timing which is not disturbed by delay spread within the guard interval by utilizing the cyclic prefix. A new timing function is introduced. By detecting the down-turn transition timing of the function, the symbol synchronization...
This paper investigates power control of CDMA wireless networked systems with random transmission time delays in both downlink and uplink wireless communication channels. To deal with the random time delays, a novel power control algorithm is presented based on the modified generalized predictive control (M-GPC). Different from the conventional generalized predictive control (GPC) in which only the...
Recently, several scheduling techniques to enable multihop communications in the beacon enabled mode of the IEEE 802.15.4 standard have been proposed. Using the beacon enabled mode allows node synchronization and hence energy savings which is an important concern in wireless sensor networks (WSNs). However, and to the best of our knowledge, current available scheduling techniques have not been formally...
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