1,721,226 research outputs found
Dynamic code assignment in hybrid MC-CDMA/TDMA systems
No full text[[abstract]]In the past decade, the market for wireless mobile communications has been growing at a rapid pace. A future wireless mobile network is desired to support integrated services, including voice, data, video, etc. A well-designed multiple access control (MAC) protocol is crucial in supplying a satisfactory level of performance, such as delay or throughput. A dynamic code assignment in hybrid multi-code CDMA/TDMA is proposed in this paper. The code assignment scheme is designed to follow the time-varying traffic characteristics of mobile users. The base station (BS) assigns more codes to mobiles during congestion, but releases them when congestion subsides. Congestion is estimated from the queue lengths of mobiles. A queueing model is established for performance analysis, in which the traffic source is taken to be a Markov-modulated Poisson process (MMPP). Copyright (C) 2003 AEI.[[note]]SC
Per connection delay analysis of a frame-based TDMA/CDMA MAC protocol
No full text[[abstract]]A hybrid of TDMA and CDMA or the so-called time slotted CDMA is a popular mainstream multiple access technique in coordinating resource to accommodate a number of traffic connections/sources. The purpose of this paper is to conduct thorough delay analysis for a specific connection in such a hybrid TDMA/CDMA MAC protocol. The arrival process of this connection is assumed to be the Markov modulated Poisson process (MMPP) and can be generalized to the batch Markov arrival process (BMAP). The service that can be rendered to this connection in time and code is made general to fit any service pattern that one may configure. Past works on the delay analysis of a TDMA system are special cases of this paper. The results obtained in this paper can be used to evaluate the performance of many contemporary quality of service (QoS) oriented frame-based MAC protocols. (C) 2003 Published by Elsevier B.V.[[note]]SC
Per connection performance analysis of a frame-based TDMA/CDMA MAC protocol containing both reservation and contention slots
No full text[[abstract]]A mixture of reservation plus contention data slots is now widely implemented in TDMA/CDMA systems to make a system flexible enough to suit various kinds of packets but preserve the good nature of frame-based protocols. We conducted performance analysis for an arbitrary connection in such a system under the assumption of MMPP (Markov-modulated Poisson process) arrivals. Accessible slot locations of this connection in a frame are made general. Success probability in accessing a contention slot is also made general. We have obtained the system size distribution which can be used to evaluate the performance of various frame-based MAC protocols. The MMPP arrival pattern can be generalized to the BMAP (batch Markovian arrival process) family to further accommodate a broader set of traffic sources.[[note]]SC
Sharing of ARQ slots in Gilbert-Elliot channels
No full text[[abstract]]This letter treats the problem of m transmission slots sharing a pool of n automatic repeat request slots. Two cases are treated. In one, these m slots belong to the same basestation-terminal pair, i.e., a frequency-division multiplexing channel. In the other, they are used by m different basestation-terminal pairs, i.e., a time-division multiplexing channel. The smallest n to satisfy loss and delay requirement is determined.[[note]]SC
An ACK buffering method to improve TCP performance in mobile computing environments
No full text[[abstract]]In mobile computing environments, a problem may exist between loss recovery mechanisms employed by the TCP (transmission control protocol) and RLP (radio link protocol). It is because that local retransmissions performed by the RLP could interfere with the TCP end-to-end error recovery when there are long and correlated packet losses due to bursty channel errors. That is, a spurious timeout [1], [2] would occur at the transport layer. In this paper, a new method is proposed to effectively suppress the occurrence of TCP spurious timeouts. In this new method a small number of ACKs (acknowledgements) is buffered at the base station prior to the emergence of every bad state period in the wireless channel, and these ACKs are henceforth released by the base station one at a time to reset the TCP sender's retransmission timer. Comprehensive comparisons between the proposed method and a baseline method are conducted through simulations to show that the improvement in throughput performance can be as large as 22%.[[note]]SC
Quality-of-service based link control scheme for wireless integrated service communications
No full text[[abstract]]A quality-of-service based link control scheme to counteract correlated channel errors for wireless multimedia communications is proposed in this paper. Both the medium access (MAC) and data link control (DLC) layers are treated. The performance of the proposed scheme is evaluated using both analysis and simulation. The delay and jitter behaviors are examined for both the constant bit rate (CBR) traffic and variable bit rate (VBR) traffic. The throughput performance is also obtained for the available bit rate (ABR) traffic. Through numerical experiments, the proposed scheme is demonstrated to be not only robust against channel impairments but also capable of providing the desired QoS for wireless multimedia communications.[[note]]SC
MINIATURE 1.87-dB INSERTION-LOSS V-BAND CMOS BANDPASS FILTER WITH TWO ENHANCED FINITE TRANSMISSION ZEROS
No full text[[abstract]]In this article, we demonstrate a miniature low-insertion-loss V-band bandpass filter with two finite transmission zeros by standard 0.13-mu m CMOS technology. The proposed filter architecture has the following feature: the low-frequency transmission-zero and the high-frequency transmission-zero can be tuned by the series-feedback capacitor C(s) and the parallel-feedback capacitor C(p), respectively. Parallel LC circuits (i.e.. C(12) in parallel with L(C1)-C(11)-L(C2) and C(22) in Parallel with L(C3)-C(21)-L(C4)) are used for implementing C(1) and C(2) to improve the roll-off characteristic at high frequency and the depth of the upper notch. Besides, low-insertion-loss was achieved by adopting thick microstrip-line (MSL) with optimized ground-plane pattern as the needed inductors to minimize both the metal loss and the substrate loss. Over the frequency range of 49.5-82.5 GHz, the filter achieved insertion-loss (1/S(21)) lower than 3 dB, and input return loss (S(11)) and output return loss (S(22)) better than -10 dB. The minimum insertion-loss was 1.87 dB at 66.5 GHz, a state-of-the-art result for a V-band CMOS bandpass filter. The chip area was only 0.466 x 0.307 mm(2), i.e., 0.143 mm(2), excluding the test pads. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1830-1836, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25302[[note]]SC
0.99 mW 3-11 GHz common-gate CMOS UWB LNA using T-match input network and self-body-bias technique
No full text[[abstract]]A low-power 3-10 GHz common-gate CMOS ultra-wideband (UWB) low-noise amplifier (LNA) using a T-match input network and the selfbody- bias technique is demonstrated. Wideband input impedance matching was achieved by using the proposed T-match input network to improve the input matching at low frequencies. A low supply voltage of 1.1 V (for two V(DS) drops) was achieved by using the self-body-bias technique to reduce the threshold voltage (V(th)) of the transistors, which leads to a low power consumption (P(D)). At V(G) = 0.77 V, the LNA consumed 2.15 mW and achieved S(11) of -10.4 to -35.5 dB, S(21) of 10.4 dB, and an average NF of 4.9 dB over the 3-10 GHz band of interest. At V(G) = 0.63 V, the LNA consumed 0.99 mW and achieved S(11) of -10.7 to -35.8 dB, S(21) of 7.9 dB and an average NF of 6 dB. Both are the lowest P(D) ever reported for an UWB CMOS LNA with bandwidth greater than 6 GHz.[[note]]SC
DESIGN AND IMPLEMENTATION OF A HIGH-PERFORMANCE V-BAND CMOS BANDPASS FILTER
No full text[[abstract]]In this article, we demonstrate a low-insertion-loss V-band (50-75 GHz) bandpass filter with two finite transmission zeros by standard 0.13 mu m CMOS technology. The proposed filter architecture has the following feature: the low-frequency transmission-zero and the high-frequency transmission-zero can be tuned by the series-feedback capacitor C(s) and the parallel-feedback capacitor C(p) respectively. Besides, low-insertion-loss is achieved by adopting thick microstrip-line (MSL) with optimized ground-plane pattern as the needed inductors to minimize the metal and substrate loss. This filter achieved insertion-loss (1/S(21)) lower than 3 dB m,er the frequency range of 52.2-76.7 GHz. input return loss (S(11)) better than -10 dB over the frequency range of 50.2-80.6 GHz, and output return loss (S(22)) better than -10 dB over the frequency range of 50.2-77.3 GHz. The minimum insertion-loss was 2.18 dB at 63.5 GHz, an excellent result for a V-band CMOS bandpass filter. The chip area was only 0,466 x 0.307 mm(2), i.e., 0.143 mm(2), excluding the rest pads. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 309-316, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24935[[note]]SC
3-11 GHz low-power, low-noise CMOS distributed amplifier using splitting-load inductive peaking and noise-suppression techniques
No full text[[abstract]]A CMOS distributed amplifier (DA) with. at and low noise figure (NF), and. at and high gain (S(21)) is demonstrated. A. at and low NF was achieved by adopting a RL terminating network for the gate transmission line, and a slightly under-damped Q-factor for the second-order NF response. Besides, flat and high S(21) was achieved using the proposed cascade gain cell, which constitutes a cascode-stage with a low-Q RLC load and a splitting-load inductive-peaking inverter stage. In the high-gain (HG) mode, the DA consumed 27.6 mW and achieved S(21) of 17.5 +/- 1.23 dB with an average NF of 3.24 dB over the 3 - 10 GHz band, one of the best reported NF performances for a CMOS UWB DA or LNA in the literature. The measured IIP3 was 2.1 dBm (at 8 GHz). In the low-gain (LG) mode, the DA achieved S(21) of 10.74 +/- 1.2 dB and an average NF of 4.67 dB with a low power dissipation of 9 mW.[[note]]SC
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