José P. Carvalho

Asynchronous sequential symbol synchronizers based on pulse comparison by positive transitions at half bit rate

This work studies the asynchronous sequential symbol synchronizers based on pulse comparison by both transitions at rate (atx). Their performance will be compared with the reference synchronous synchronizers based on pulse comparison by both transitions at rate (stx). For the reference and proposed variants, we consider two versions which are the manual (m) and the automatic (a). The objective is to study the four synchronizers and evaluate their output jitter UIRMS (Unit Interval Root Mean Square) versus input SNR (Signal Noise Ratio).

Carrier Wave Phase Synchronizers

This work study four carrier wave phase synchronizers (CWPS) or carrier wave Phase Lock Loop (CWPLL).The VCO (Voltage Controlled Oscillator) output of the phase synchronizer synchronizes directly with the input carrier wave.We consider four carrier synchronizers namely the analog, hybrid, combinational and sequential. The difference between them is in the phase detector.The objective is to study the synchronizers and evaluate their output jitter UIRMS (Unit Interval Root Mean Square) as function of the input SNR (Signal to Noise Ratio).

High data rate synchronizers operating at low speed

This paper presents a new technique which allows high baud rate with low operation speed of the synchronizer. This technique is based on parallel processing. What is done by only one clock operating at the baud rate can be done by two clocks operating only at half rate. By generalizing we propose versions of clock recovery circuits operating at the ratio 1/2/sup n/ of the data rate. Thus we obtain circuits transmitting at very high data rate but operating at very low frequency. The proposed circuits which are transition sensitive (digital) are compared with the traditional level sensitive (analog).

Groups of synchronizers for communications by fiber optic

This work studies a digital transmission system by fiber optic. We give special relevance to the synchronism block. The fiber is a transmission medium with large bandwidth and low attenuation. These characteristics allow high speed and long distances. The transmission, instead asynchronous, it is synchronous what provides a big efficiency of 100%. However, the synchronous transmission needs a synchronizer. The objective is to study the synchronizers and their performance of output jitter Unit Interval Root Mean Square (UIRMS) versus input Signal Noise Ratio (SNR).

Laboratory performance measurements of IEEE 802.11 a WEP PTMP links

Wireless communications using microwaves are increasingly important, e.g. Wi-Fi. Performance is a very crucial issue, improving reliability and efficiency in communications. Security is also critically important. Laboratory performance measurements are presented for Wi-Fi IEEE 802.11 a WEP point-to-multipoint links. Our study contributes to performance evaluation of this technology under WEP encryption, using available equipments (HP V-M200 access points and Linksys WPC600N adapters). The paper gives new results from TCP, UDP and FTP experiments in terms of TCP throughput, jitter, percentage of datagram loss and the FTP transfer rate for OSI layers 4 and 7, which are compared with the data from WEP point-to-point, Open point-to-multipoint links and WPA. Conclusions are drawn about the comparative performance of the links.

Prefilter bandwidth effects in asynchronous sequential symbol synchronizers based on pulse comparison operating by positive transitions at half bit rate

This work investigates the prefilter bandwidth effects in four asynchronous sequential bit synchronizers. The prefilter bandwidth is changed between three discrete values, namely B1=∞, B2=2.tx and B3=1.tx, where tx is the bit rate. The synchronizers distinguish 2 variants, one asynchronous by both transitions at rate and other asynchronous by positive transitions at half rate. Each variant has two versions which are the manual and the automatic. The objective is to study the three prefilter bandwidths with the four synchronizers and to evaluate their output jitter UIRMS (Unit Interval Root Mean Square) as function of the input SNR (Signal Noise Ratio).

EXTENDED RESEARCH ON PREFILTER BANDWIDTH EFFECTS IN ASYNCHRONOUS SEQUENTIAL SYMBOL SYNCHRONIZERS BASED ON PULSE COMPARISON BY BOTH TRANSITIONS AT HALF BIT RATE

I. INTRODUCTION This work studies the asynchronous sequential symbol synchronizer based on pulse comparison operating by both transitions at half bit rate (ab/2). Their jitter is compared with the reference asynchronous synchronizers operating by both transitions at bit rate (ab) [1, 2]. For both, reference and proposal variant, we consider the versions manual (m) and automatic (a) [3, 4, 5, 6, 7]. The difference between the reference and proposal synchronizer is in the symbol phase comparator since the others blocks are similar. The phase comparator compares the input variable pulse duration Pv with the intern reference fixed pulse duration Pf and the error pulse Pe synchronizes the VCO (Voltage Controlled Oscillator) [8, 9]. The synchronizer regenerates the data, recovering a clock (VCO) that samples and retimes the data [10, 11, 12, 13]. Fig.1 shows the blocks of the general symbol synchronizer.

Prefilter bandwidth effects in asynchronous sequential symbol synchronizers based on pulse comparison by hybrid transitions at half bit rate

This work studies the effects of the prefilter bandwidth in four sequential symbol synchronizers. We consider three prefilter bandwidths namely B1=∞, B2=2.tx and B3=1.tx, where tx is the bit rate. The synchronizer has two variants one synchronous by both transitions at rate and other asynchronous by both transitions at rate. Each variant has two versions namely the manual and the automatic. The objective is to study the prefilter with the four synchronizers and to evaluate their output jitter UIRMS (Unit Interval Root Mean Square) versus input SNR (Signal Noise Ratio).

Experimental performance studies of laboratory WPA IEEE 802.11b, g PTMP links

Wireless communications using microwaves are increasingly important, e.g. Wi-Fi. Performance is a very crucial issue, resulting in more reliable and efficient communications. Security is equally very important. Laboratory measurements are made about several performance aspects of Wi-Fi IEEE 802.11b, g WPA point-to-multipoint links. A contribution is given to performance evaluation of this technology under WPA encryption, using available equipments (DAP-1522 access points from D-Link and WPC600N adapters from Linksys). Detailed results are presented and discussed, namely at OSI levels 4 and 7, from TCP, UDP and FTP experiments, permitting measurements of TCP throughput, jitter, percentage datagram loss and FTP transfer rate. Comparisons are made to corresponding results obtained for point-to-point links. Further comparisons are made to corresponding results obtained for WEP links. Conclusions are drawn about the comparative performance of the links.

Comparative performance studies of laboratory WPA IEEE 802.11g point-to-point links

Wireless communications using microwaves are increasingly important, e.g. Wi-Fi. Performance is a very important issue, resulting in more reliable and efficient communications. Security is equally very important. Laboratory measurements are made about several performance aspects of Wi-Fi IEEE 802.11g WPA point-to-point links. A contribution is given to performance evaluation of this technology under WPA encryption, using available wireless routers from Linksys (WRT54GL). Detailed results are presented and discussed, namely at OSI levels 4 and 7, from TCP, UDP and FTP experiments, permitting measurements of TCP throughput, jitter, percentage datagram loss and FTP transfer rate. Comparisons are made to corresponding results obtained for, mainly, open links. Conclusions are drawn about the comparative performance of the links.