Current mobilecommunications facilities, such as cellular phone system s and wireless networks, can not help to support mobile Internet communications. As is known, digital cellular phone (e.g. GSM) can provide a point-to-point data link con nections. Although the mobile unit itself can obtain a local connection to a local base station, it can establish a link to the fixed Access Point of the Internet, w hich means the user may pay for expansive long-distance mobile connection on top of Internet access fee. Another problem is the speed. Currently GSM cellular phone unit can only provide datarate of 2400bps to 9600bps. Although the forthcoming data service for GSM network, called General Packet Radio Service (GPRS)3, is expected to be im plem ented in next two years and to support data transfer at a rate of up to 100Kbps, the radio communication services are still quite slower than Local Area N etw ork con nection (LAN), ISDN connection and even norm al m odem (33.6Kbps to 56Kbps). The problem w ith wireless LAN is the roaming area, though its speed is high (from sev eral hundred Kbps to 5Mbps). Usually, a wireless LAN covers a very small area, given the limits of its frequency usage and power. Currently, w hen a portable com puter is carried away from home network, the practical way to connect it back to the Internet is to make a connection to home Access Point through dial-up line, either w ired or wireless. Current telecommunications infrastructure is employed to link the portable systems back to their original home AP no m atter how far the users are aw ay from their office or home. Here a dedicated communication link is required for each user. In some cases, the cost of long distance telecommunication link can be prohibitively high and the low utilisation is not desired.
SAW filters play an important role in today’s front-end radio frequency designs of wireless communications. Requirements by mobile phones like increased data rates make it stringent on RF filters to satisfy these condi- tions. RF SAW filters meet the demands of increased bandwidth, frequency and higher data rates . Their high stop band rejection and in band insertion loss make their applications span across a variety of commercial and military products. In addition, their low cost make them an attractive choice for high volume products. They are based on acoustic wave technology where information is carried on the surface of the piezoelectric crystal.
WiMAX has been regarded as the next milestone of BWA(Broadband wireless access) technology. It does not only provide fixed access but also provide mobile access just like 3G does. WiMAX (Worldwide Interoperability for microwave access) is an emerging wireless communication system that is expected to provide highdataratecommunications in metropolitan area networks (MANs) . IEEE 802.16 working group has developed a number of standards for WiMAX in the last few years. The first standard was published in 2001, which aims to support the communications in the 10-66 GHz frequency band. In 2003 IEEE 802.16a was introduced to provide additional physical layer specification for the 2-11 GHz frequency band. These two standards were further revised in 2004 (IEEE 802.16-2004) has two additional physical modes . Recently, IEEE 802.16e has also been approved as the official standard for mobile applications. In the physical (PHY) layer, IEEE 802.16 supports four PHY specifications for the licensed bands. These four specifications are Wireless-MAN-SC (single carrier), -SCa, OFDM (Orthogonal frequency division multiplexing, OFDMA(Orthogonal frequency division multiple access).
Recently, in the UWB communication environment, user will utilize various communications at the various channel condition such as indoor, outdoor, highmobile speed and low mobile speed. Therefore, the UWB communication system should change their system reliability and datarate depending on dynamically changing user’s demand and channel condition. Therefore, there are many researches of adaptive technique for user demand and channel condition [14–18].
In the proposed turbo equalizer, we split the problem of a priori probabilities-based equalization into two distinct MMSE optimization problems. The first problem consists in the estimation of past and future symbols using a priori probabilities and channel output information, while the sec- ond problem is the estimation of the current symbol based on past and future symbols. The solution to the first prob- lem is to use an MMSE equalizer similar to the one devel- oped in , but modified appropriately so as to provide all the required symbols instead of computing only the current symbol estimate. For the second problem we suggest using an MMSE SIC which has been designed under the assump- tion that its input symbols are actually correct symbols (in practice they are provided by the aforementioned equalizer). As shown experimentally, the proposed approach, so-called conditional expectation-soft interference canceller (CE-SIC), exhibits similar performance to the exact MMSE solution of , at a similar computational cost. Although the exact im- plementation of the CE-SIC does not enjoy any advantage over the exact equalizer of , it leads to the derivation of an approximate version, so-called approximate conditional expectation-soft interference canceller (ACE-SIC), which has linear complexity. Simulation results have shown that the proposed algorithm exhibits very good performance charac- teristics that make it suitable for highdatarate wireless com- munications.
In order to make use of this flat spectral region during the implementation of the 2R regenerator, the filter was tuned towards longer wavelengths relative to the original signal wavelength. To optimise the regeneration performance further numerical simula- tions were carried out, since the filter offset has been shown to be a key parameter for obtaining the best performance. Fig. 8.7.a shows numerical transfer characteristics at different offset filterings. As well known, the higher the offset, the flatter the transfer curve becomes at the ”zero” level, although the power requirements to reach the curve peak increases and becomes more challenging experimentally. Fig. 8.7.a also shows that regeneration could be achieved in the instance that the filter was tuned towards shorter wavelengths relative to the original signal wavelength for the same amount of detuning, see grey dashed curve. Because of the asymmetry of the spectral broadening, the trans- fer functions observed either side of the central wavelength show different behaviour. In particular, for the same amount of peak power, the side of the spectrum towards shorter wavelengths broadens less and exhibits more pronounced ripple compared to longer wavelength operation. For these reasons, the corresponding curve is flatter for lower power levels, while the curve peak, reached at higher power levels, is sharper. In the experiment, the maximum average input power level available was used (∼31 dBm). Fig. 8.7.b shows a measurement of the transfer characteristic of the regenerator (circles) together with the numerical one (black curve) at a filter offset of 6.1 nm. The corre- sponding filtered spectrum is shown in Fig. 8.4.b (dashed curve). The relatively large offset wavelength, combined with the very flat SPM spectrum, ensures a clear two-level response between low and high powers. Despite the very good agreement, the reasons for the slight difference between the two curves could be linked to the high power amplifier used. Indeed, in the simulation the ASE noise induced by the amplifier and possible nonlinear effects with the amplifier were not accounted for. These effects are evident in the experimental spectral traces in Fig. 8.4 (for example see the visible ASE noise contribution at longer wavelengths for the lower power levels).
The IEEE 802.11 standards MAC supports two data packet transmission modes. The Distributed Coordination Function DCF whose implementation is mandatory for all IEEE 802.11 devices running in or out of infrastructure mode. The Point Coordination Function PCF used only in mode with infrastructure, offers an optional synchronous service . DCF is based on Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA), it abandons collision detection while strengthening mechanisms to avoid it . Each node competes with the other ones for access to the medium. The collisions are avoided by a random backoff procedure which ensures different waiting transmission times to the stations. For the signaling of the good reception of a frame, a mechanism of positive acknowledgment is deployed. Each time a frame is correctly received, an acknowledgment packet must be send to the source. The absence of this acknowledgment indicates a problem in the transmission of the frame. The frame must be retransmitted. This transmission takes place during the CP (Contention Period) . The medium access is managed only by means of a random procedure, that’s why DCF does not provide QoS support but supplies only best effort service. Figure 2
This phenomenon is primarily due to the way multicast data are delivered over the overlay net- work. In particular, the tree-based overlays may not utilize all available network links due to the single route from the sender to a receiver. Conse- quently, when the application data-rate approaches that of the link capacity, congestion will occur, leading to increased delay and loss. Even though the ALM protocol can detect and adapt to link quality degradations, such adaptation was designed primarily for recovering from peer and link failures rather than self-induced congestions. Thus the relocation of the congested overlay path to another network link will merely relocate the point of congestion.
The optical transmitter in our simulation consists of subsystem which isthe Pseudo Random Binary Sequence (P-RBS) generator, which is representing the data or information that need to transmit. The P-RBS generator output is the Return-to-Zero (RZ), where a bit stream of binary pulses; a sequence of“0”s (OFF) or“1”s (ON), of a reproducible and known pattern. The free space medium between receiver/transmitters has been considered as a free space optical channel. This free space medium (FSO channel) between an optical transmitter and an optical receiver consider to have an aperture diameter of (5 and 8) centimeter at each end respectively. At the same time, the beam divergence is set to (2mrad). The optical receiver composed of APD (an avalanche photodiode) followed by a low pass filter, front-end amplifier, and a 3R regenerator. The function of 3R regenerator is used to regenerate and modulated electrical as in the optical transmitter that have been used for analysis of BER (i.e. it normalized the signal waveform with Gigabit class transmission). This is with a view to allow transmissions of relay without retro gradation the quality of signal between buildings with distance more than 1 km apart or that do not provide a good LOS.In the steady model of simulation, we can set weather conditions Channel properties which described by item α atm. or due to visibility we can simulate different decreases of signal caused by Fog and smoke.
stepped microstrip line to the open slot. Two current nulls appear on the two vertical arms of the loop. Therefore, the current nulls of the two modes appear on diﬀerent arms. Then, the mechanism of high isolation between the dual modes is discussed. In Figure 2(a), It is shown that the current intensity on the stepped microstrip line is very small, which indicates few energy is coupled to port 2. In Figure 2(b), the current on the circular microstrip line is observed very weak, which indicates few energy is coupled to port 1. Therefore, high isolation is achieved between the two ports. In addition, small antenna footprint can be obtained by using the rectangular loop structure. This is because that the loop antenna operates at the one-wavelength-perimeter mode. Each arm of the loop has a length of about 0 . 25 λ , as the shape of the rectangular loop in the proposed design approaches to a square loop. In contrast, each arm of the slot antenna is about 0 . 5 λ , considering that the slot antenna operating at the half-wavelength mode.
Figure 3: Signal strength over transmitting power In Figure 3 we illustrate the overall signal strength of FBSs in the cellular environment. Thus, the signal strength increases due to the positioning of the indoor base station at the right placed in the home. However, the functionality of FBSs is boosting signal where poor reception of coverage is experienced. The placement of FBSs ensures optimal network coverage. As the distance increases, the network performance experienced an update and it improved the system capacity for uploading data at the indoor. The estimation of the signal strength illustrates the optimal system with the deployment of the femtocell. The FBS 1 ,
Being a multicarrier system OFDM is highly prone to large envelope variations leading to high peak to average power ratio. Peak to average power ratio is the ration peak power of the OFDM signal to the average power of the carrier. When PAPR is on the higher side it creates distortion when pass through a device with nonlinear I/O characteristic e.g. a high power amplifier. Multiple signal representation technique are one of the widely employed distortion less technique where data is divided in to sub blocks or scrambles and phase shifted using different combinations of phase vector, thus generating several OFDM symbols for same data set the one with the minimum power value will be used for transmission. Selective mapping and partial transmit sequence techniques are two such techniques. Partial transmit technique requires less number of complex arithmetic so used widely for many applications. Figure 1 shows various functional blocks of a PTS system.
Abstract— Image compression is the technique of reducing the size of image file without degrading the quality of the image Bandwidth conservation is an important issue in case of multimedia communication. Uncompressed multimedia (graphical, audio and video) data requires considerable storage capacity and transmission bandwidth. Despite rapid progress in mass- storage density, processor speeds and digital communication system performance, it demands for data storage capacity and data-transmission bandwidth continuously to outstrip the capabilities of available technologies. So to solve this problem an efficient multimedia communication scheme is proposed which is based on Wavelet. This Paper shows Better image compression by using different wavelet with the help of Neural network. This paper shows the objectives and methodology used for compressing radiograph image with help of back propagation algorithm.
In this paper, the Box-Jenkins modelling procedure is used to determine an ARIMA model and go further to forecasting. The mobile cellular subscription data for the study were taken from the ad- ministrative data submitted to the Zambia Information and Communications Technology Authori- ty (ZICTA) as quarterly returns by all three mobile network operators Airtel Zambia, MTN Zambia and Zamtel. The time series of annual figures for mobile cellular subscription for all mobile net- work operators is from 2000 to 2014 and has a total of 15 observations. Results show that the ARIMA (1, 2, 1) is an adequate model which best fits the mobile cellular subscription time series and is therefore suitable for forecasting subscription. The model predicts a gradual rise in mobile cellular subscription in the next 5 years, culminating to about 9.0% cumulative increase in 2019.
GSM was designed with a moderate level of service security. The system was designed to authenticate the subscriber using a pre- shared key and challenge-response. Communications between the subscriber and the base station can be encrypted. The development of UMTS introduces an optional Universal Subscriber Identity Module (USIM), that uses a longer authentication key to give greater security, as well as mutually authenticating the network and the user – whereas GSM only authenticates the user to the network (and not vice versa). The security model therefore offers confidentiality and authentication, but limited authorization capabilities, and no non-repudiation.
This report has been prepared solely for the purposes of assisting Telenor ASA in quantifying the economic impact of the mobile industry in Serbia, Ukraine, Malaysia, Thailand, Bangladesh and Pakistan. The distribution of this document to other parties is subject to the restrictions on use speciﬁ ed in the Engagement Letter dated 26 September 2007. We have agreed that Telenor ASA may publish this report in its entirety or for a speciﬁ c country by deleting only the executive summary and ﬁ ndings chapters for the other 5 countries and inserting the liability notice provided as Annex 7 to this report. No other party other than Telenor ASA is entitled to rely on this document for any purpose whatsoever and we accept no responsibility or liability to any other party in respect of the contents of the Report. Deloitte & Touche LLP accepts no responsibility for any reliance that may be placed on this document should it be used by any party other than the Recipient Parties or for any purpose that is not in accordance with the terms of the Engagement Letter.