Frequency offset estimation for MB-OFDM-based UWB systems

We address low-complexity, highly-accurate frequency offset estimation for multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wide band systems in time-invariant as well as time-variant channels. We investigate the unique characteristics of MB-OFDM systems, namely, different frequency offsets, channel responses, received energies, and preamble structures in different frequency bands. Utilizing them, we develop frequency offset estimators based on the best linear unbiased estimation principle. If compared to the reference estimators, our proposed methods achieve significantly better estimation performance (4 to 6.4 dB (5 to 20 dB) estimation mean-square error advantage in the time-invariant (time-variant) channels) for all preamble patterns of the MB-OFDM system in [8].     

Multiple genetic aberrations including evidence of chromosome 11q13 rearrangement detected in pituitary adenomas by comparative genomic hybridization

OBJECT: This study was conducted to determine whether comparative genomic hybridization (CGH) is a more sensitive method for detecting genetic aberrations than other tests currently in use. METHODS: The authors used CGH to examine 40 primary and 13 recurrent adenomas obtained from 52 patients for loss and gain of genetic material. Copy number aberrations (CNAs) were detected in 25 (48%) of the 52 patients studied. The chromosomes affected were, in order of decreasing frequency, 11, 7, X, 1, 8, 13, 5, 14, 2, 6, 9, 10, 12, 3, 18, 21, 4, 16, 15, 19, 22, and Y. Endocrinologically active adenomas were more likely to contain (p = 0.009) and had a greater number (p = 0.003) of CNAs. Of 26 adenomas with CNAs, 18 showed multiple aberrations involving entire chromosomes or chromosome arms. The most frequent CNA involving a chromosome subregion, which was present in four (8%) of 53 adenomas, was the loss of all chromosome 11 material except for a preserved common segment containing 11q13. Immunoperoxidase staining did not detect cyclin D1 expression in those four cases, making cyclin D1 an unlikely target of this rearrangement. CONCLUSIONS: These findings indicate that genetic abnormalities are present in pituitary adenomas at a higher rate than previously reported, are associated with endocrinological activity, and often involve several chromosomes. Rearrangement at 11q13 may inactivate a tumor suppressor gene or activate an oncogene that is important in the initiation or progression of sporadic pituitary adenomas.     

Supporting rate guarantee and fair access for bursty data trafficin W-CDMA

This paper presents a new protocol for statistical multiplexing of bursty data traffic in the forward (base-to-mobile) link of a wireless wideband code division multiple access (W-CDMA) system using orthogonal variable spreading factor (OVSF) codes. At the heart of the protocol is an efficient scheduling algorithm that dynamically assigns an OVSF code to a mobile user on a timeslot-by-timeslot basis and allows many users with bursty traffic to share a limited set of OVSF codes. An important feature of our protocol is that it can provide a heterogeneous data rate guarantee to each mobile user and fully utilize the system capacity. Moreover, the unreserved bandwidth of the network can be shared fairly among competing mobile users     

Optimal periodic training signal for frequency offset estimation in frequency-selective fading channels

This paper addresses an optimal periodic training signal design for frequency offset estimation in frequency-selective multipath Rayleigh fading channels. For a fixed transmitted training signal energy within a fixed-length block, the optimal periodic training signal structure (the optimal locations of identical training subblocks) and the optimal training subblock signal are presented. The optimality is based on the minimum Cramer-Rao bound (CRB) criterion. Based on the CRB for joint estimation of frequency offset and channel, the optimal periodic training structure (optimality only in frequency offset estimation, not necessarily in joint frequency offset and channel estimation) is derived. The optimal training subblock signal is obtained by using the average CRB (averaged over the channel fading) and the received training signal statistics. A robust training structure design is also presented in order to reduce the occurrence of outliers at low signal-to-noise ratio values. The proposed training structures and subblock signals achieve substantial performance improvement.     

An Efficient ARQ Protocol for Adaptive Error Control over Time-Varying Channels

Wireless Personal Communications -     

On the peak factors of sampled and continuous signals

Motivated by a recent letter on an infinite difference between the peak-to-average power ratios (PAPRs) of samples (a series) and a band-limited function constructed from that series, we investigate the amplitude and variations of a band-limited function and present some relevant bounds. Related aspects on sampling theorems and sampling series are also discussed     

On timing offset estimation for OFDM systems

Two timing offset estimation methods for orthogonal frequency division multiplexing (OFDM) systems as modifications to Schmidl and Cox's method (see IEEE Trans. Commun., vol.45, p.1613-21, 1997) are presented. The performances of the timing offset estimators in additive white Gaussian noise channel and intersymbol interference channel are compared in terms of estimator variance obtained by simulation. Both proposed methods have significantly smaller estimator variance in both channel conditions     

A Distributed Opportunistic Access Scheme and its Application to OFDMA Systems

Multiuser systems can provide multiuser diversity gains by assigning channels to users with higher channel gains. To avoid the extensive information exchange with the access point for the uplink access in centralized approaches, we propose in this paper a distributed opportunistic access scheme. Through a judicious design of a novel backoff mechanism to utilize the channel information and reduce collisions, significant multiuser diversity gains are achieved. To a user, the higher the channel gain is, the smaller the backoff time-slot and, hence, the higher the access priority of that user is. In addition, for heterogeneous systems, our proposed scheme can realize multiuser diversity gains and achieve fairness among the users at the same time. Finally, we design two distributed opportunistic access schemes for OFDMA systems. Users contend on all sub-channels in the first scheme and only on several strongest sub-channels in the second scheme. Compared with traditional centralized OFDMA systems and other distributed access schemes, our proposed schemes reduce overhead and achieve a higher throughput.     

Tribological Properties of Ultra-Thin Functionalized Polyethylene Film Chemisorbed on Si with an Intermediate Benzophenone Layer

In this study, an ultra-thin (~20 nm) functionalized polyethylene (fPE) film is successfully attached to Si substrate via a reactive benzophenone (Ph₂CO) layer. The presence of fPE promotes wear durability of Si/Ph₂CO/fPE to 1,000 cycles compared with 100 cycles for Si/Ph₂CO and nearly zero wear life for bare Si in a ball-on-disk (4-mm-diameter Si₃N₄ ball) wear test under 40 mN applied normal load and 500 rpm sliding speed. As an enhancement to the wear life, perfluoropolyether (PFPE) is applied as a top mobile lubricant layer coated onto Si/Ph₂CO and Si/Ph₂CO/fPE. A significant improvement in the wear durability is observed as Si/Ph₂CO/PFPE fails at 250,000 cycles and Si/Ph₂CO/fPE/PFPE does not fail until one million cycles. Si/Ph₂CO/fPE/PFPE can withstand a minimum applied load of 150 mN at a sliding speed of 0.052 ms⁻¹ without failure, providing a PV (pressure x velocity) limit of greater than 106.6 MPa ms⁻¹.     

Induction and immunological characterization of the uridine diphosphate-glucuronosyltransferase conjugating 1-naphthol in the rat choroid plexus

In this experiment, rats were injected intraperitoneally with 6 mg/kg methamphetamine (MAP) hydrochloride or the same volume of saline once daily for 14 days. Rats were decapitated after a 1-day, 4-day or 10-day withdrawal period. The number and affinity of [3H]mazindol binding sites in the striatum were measured. Their number in the MAP group decreased as compared with controls after a 1-day withdrawal period, but returned to the control level after a 4-day and 10-day withdrawal period. These results are believed to show that the decrease in dopamine uptake sites after repeated administration of MAP is transient and does not contribute to MAP-induced behavioral sensitization.