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Motivated by the possibility of decreasing the intersymbol interference (ISI) which is due to large delays of a multipath mobile radio channel, orthogonal frequency division multiplexing (OFDM) became very popular. However, the timevariance of the mobile radio channel induces intercarrier interference (ICI) yielding substantial channel estimation errors and thereby tremendous transmission impairments...
In this paper, the packet combining technique in the downlink OFDMA system is introduced in conjunction with frequency diversity to enhance the reliability of retransmissions and thus reduce the large time delay caused by retransmissions. The novel retransmission technique aims to reduce the maximum number of retransmissions for failed packets, while maximizing the throughput. A suboptimal algorithm...
The relative theory of improved form BDPSK modulation is analyzed. The discussion focuses on the influences of system performance made by delay module during the process of BDPSK differential coherent demodulation. The system demodulation expression between precision delay and error delay is compared. Through improving demodulation system, theoretically, the accuracy of delay units is improved. The...
We investigate the use of impulsive ultrawide band (I-UWB) modulation over medium voltage (MV) power line channels for low data rate communications. In particular, we consider a MV network where a channel measurement campaign has been carried out. In this paper, we firstly describe the MV test network. We study the statistics of the MV channels in terms of both root-mean-square delay spread (RMS-DS)...
Orthogonal frequency division multiplexing (OFDM) is effective method for transmitting high speed data at frequency selective channel. But OFDM is sensitive to the carrier frequency offset (CFO) and sample timing offset (STO). As these effects, inter-carrier interference (ICI), inter-symbol interference (ISI) and common phase noise error (CPE) occur. And these effects cause degradation of performance...
Mobile ad-hoc networks (MANETs) are dynamic in nature. Links between nodes may constantly change due to mobility. The performance of the transmission control protocol (TCP) degrades in such an environment mainly due to its inability to differentiate between congestion and link failures which are frequent in MANETs. Several TCP variants were proposed to adapt TCP to a mobile environment. In addition,...
For the poor error-correcting performance of traditional channel codes in shortwave channel, Low Density Parity Check Codes (LDPCC) with a optimal check-up matrix and a suitable decoding algorithm is introduced. Combined with Multi-Carrier-Code Division Multiple Access (MC-CDMA) technology which can inhibit multipath interference remarkably, the LDPC+OFDM+DSSS scheme is proposed. Then the effect of...
Traditional transmitted reference (TR) systems for Ultra-Wideband (UWB) communications separate the reference and data-modulated signals in the time domain, thus requiring at the receiver a delay component which is difficult to implement. To circumvent this drawback, frequency-shifted reference (FSR-TR) systems employ an analog carrier to make the reference and data-modulated signals orthogonal with...
To deal with the problem that cognitive information and queuing information are not both taken into account when performing Resource Allocation (RA), we have proposed a cross-layer RA scheme in a multiuser cognitive system with Orthogonal Frequency Division Multiple Access (OFDMA). In this scheme, we assume that several crucial factors influence the RA decision, including subchannel occupancy state,...
This paper evaluates the impact of using outdated channel estimates due to feedback delay for relay selection and signal amplification on the performance of partial relay selection with amplify-and-forward (AF) relays. Both variable and fixed gain AF schemes are considered. Expressions for the system's outage probability and the average bit error rate, and their high signal-to-noise ratio (SNR) approximations...
This paper presents the performance analysis of a realistic Smart Utility Network (SUN) system with low duty signaling design. The main focus of this paper is to evaluate the performance of the SUN system based on the specifications in an on-going industrial standardization activity, the IEEE 802.15.4g. For this purpose, a theoretical framework is constructed to model the transceiver with low duty...
In downlink Multiuser Multiple-Input Multiple-Output (MU-MIMO) systems, the zero-forcing (ZF) transmission is a simple and effective technique for separating users and data streams of each user at the transmitter side, but its performance depends greatly on the accuracy of the available channel state information (CSI) at the transmitter. Due to the existence of the CSI delay and channel estimation...
Ultra-wideband (UWB) serves the high bandwidth demand for high definition video transmission over short-range wireless networks. Nevertheless, bursty errors due to harsh channel conditions during video transmission greatly deteriorate video quality. In order to improve the quality of video transmission over UWB, we propose the use of a subpacket based hybrid automatic repeat request (HARQ) scheme...
An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. A number of routing protocols such as Dynamic Source Routing (DSR), Ad Hoc on-Demand Distance Vector Routing (AODV) and Destination-Sequenced Distance-Vector (DSDV) have been implemented. In this paper, an attempt has...
Recently, a novel single user weighted-transmitted reference (WTR) system has been proposed for high data rate ultra-wideband (UWB) communications. The WTR system not only achieves a superior performance but also supports high data rates and is robust to variations of both weighting coefficient and integration interval. Furthermore, it extremely reduces the sampling rate in comparison to the existing...
Increasing demands of ubiquitous services in wireless networks and evolution towards heterogeneous solutions has driven the necessity of developing efficient QoS aware vertical handoff (handoff between different networks) mechanisms. This paper proposes a QoS aware fuzzy rule based vertical handoff mechanism that makes a multi-criteria based decision, found to be effective for meeting the requirements...
A simple non-coherent solution to UWB-IR communication has been presented here. An all digital differential transmitter, developed in a 65 nm CMOS technology and a simple receiver, developed in a 180 nm CMOS technology, for detecting the received differential signal are demonstrated in the work. Though the transmitter and the receiver have been developed in two different technologies, the main objective...
A noval signal transmission method of asynchronous code division multiple access (CDMA) is proposed to improve the utilization of uplink timeslots for the time division duplexing (TDD) satellite communication systems. The terminals at different positions within a beam of the satellite antenna transmit their data blocks at different moments in the uplink timeslot window according to a certain rule...
This paper presents research status on public broadband wireless communication (PBB) system. The PBB system uses VHF band between 170 MHz and 205 MHz that is available after termination of analogue TV broadcasting service on July 24, 2011. This paper summarizes the transition of television service from analogue to digital and fundamental specification on spectrum usage, physical and MAC layers.
In this paper, a diversity scheme with imaging components on a separated channel for a fractional sampling (FS)-OFDM receiver is proposed. Cognitive radio is an emerging technology to utilize frequency spectrum flexibly through dynamic spectrum access. As one of the dynamic spectrum access scheme, here, the transmission of the imaging components of the desired signal over a separated channel is investigated...
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