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Adaptive thu phát không dây P15
Conclusions and Suggestions for Further Research In this brief chapter a summary of this monograph is presented and the corresponding conclusions that can be drawn are presented. This will be followed by a range of ideas set aside for futureresearch.
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CDMA truy cập và chuyển mạch P1
Introduction One of the basic concepts in communication is the idea of allowing several transmitters to send information simultaneously over a communication channel. This concept is described by the terms multiple access and multiplexing. The term multiple access is used when the transmitting sources are not co-located, but operate autonomously as a multipoint-to-point network, while when the transmitting sources are co-located, as in a point-to-multipoint network, we use the term multiplexing. ...
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CDMA truy cập và chuyển mạch P2
Overview In this chapter we study the structures and properties of orthogonal and pseudoorthogonal sequences. Firstly, we examine several types of pseudo-orthogonal (PN) and Quasi-Orthogonal (QO) sequences, and present their cross-correlation properties under synchronous and asynchronous conditions. Secondly, we survey basic methods of constructing orthogonal code sets. Orthogonal binary (Hadamard) codes may exist for lengths 1, 2 and 4k (for k = 1, 2, 3, ...). Methods for generating all lengths up to 256 are presented...
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CDMA truy cập và chuyển mạch P3
Overview Code Division Multiple Access (CDMA) has been widely accepted and used for wireless access in terrestrial and satellite applications. These applications often require switching of the CDMA traffic channels in order to establish connectivity between end users. In existing terrestrial wireless networks, while CDMA is used for access, connectivity and routing is achieved via the Public Switched Telephone Network (PSTN). It is often desirable, however, that access and switching is performed within the same network in many applications. An example of such an application is the Satellite Switched CDMA (SS/CDMA) system presented in [1]...
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CDMA truy cập và chuyển mạch P4
Code Division Switching In this chapter we present and analyze the switching architecture of the exchange node for switched CDMA networks. As we have discussed in the previous chapter, in such a network CDMA traffic channels will be routed by the exchange node from any input to any output link. If we consider a traditional switching approach, the exchange node can be implemented as shown in Figure 4.1.
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CDMA truy cập và chuyển mạch P5
The Satellite Switched CDMA Throughput Overview As we have discussed in Chapters 3 and 4, the satellite switched CDMA system provides on-board switching which operates with demand assignment control. This approach resolves both the multiple access and switching problems while it allows efficient utilization of the system resources. This is achieved with Traffic channel assignment algorithms which can maximize throughput and integrate the traffic of circuit calls and data packets.
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CDMA truy cập và chuyển mạch P6
The Spectrally Efficient CDMA Performance Overview As we have discussed in Chapter 3, the SS/CDMA Traffic channels are based on a spectrally efficient CDMA (SE-CDMA). The SE-CDMA is designed to reuse each frequency channel in every satellite beam (frequency reuse one), and also achieve a very low bit error rate (10−6 to 10−10 ) at a very low signal-to-noise ratio (Eb /No ). The low Eb /No value will allow the use of an Ultra Small Aperture Terminal (USAT) (antenna dish 26” in diameter), and provide a sufficient margin to mitigate the Output Back-Off (OBO) at the on-board downlink power...
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CDMA truy cập và chuyển mạch P7
Network Access and Synchronization Overview As we have described in Chapters 3 and 6, the SS/CDMA uses orthogonal CDMA in both uplink and downlink. The orthogonal CDMA can reject the interference between the user traffic channels and thus maximize the system capacity. However, the use of orthogonal CDMA in the uplink requires a network-wide synchronization of all satellite receptions (global synchronization). The accuracy of the synchronization at steadystate and the speed at which synchronization is acquired depends on the propagation environment, i.e. the channel condition, the mobility of the end user, the propagation delay, etc....
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CDMA truy cập và chuyển mạch P8
Carrier Recovery for ‘Sub-Coherent’ CDMA Overview In this chapter we examine possible methods of carrier recovery for the SECDMA presented in Chapter 6. In particular, we propose, evaluate and compare two techniques; namely Symbol-Aided Demodulation (SAD) and the Pilot-Aided Demodulation (PAD). The performance analysis of each scheme (SAD and PAD) includes both Rician and Rayleigh multipath fading channels, and thus are also useful (in addition to the satellite) in terrestrial mobile applications....
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CDMA truy cập và chuyển mạch P9
Nonlinear Amplification of Synchronous CDMA Overview As we have described in Chapter 3, the SS/CDMA uses orthogonal CDMA for both uplink and downlink transmission. On board the satellite, each CDMA channel is routed to a destination downlink beam by the Code Division Switch (CDS). All channels in the same output port of the CDS are combined and then amplified with a Traveling Wave Tube (TWT) amplifier for downlink transmission.
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CDMA truy cập và chuyển mạch P10
Optimization Techniques for ‘Pseudo-Orthogonal’ CDMA Overview The CDMA systems presented in the previous chapters were mainly based on the synchronous or orthogonal approach. As we have discussed, orthogonal CDMA achieves maximum capacity, but it requires synchronization of all transmitting users in a multipoint-to-point access network. Such a synchronization, however, may not always be possible in a high mobility environment. In such an enviroment, we use ‘Pseudo-Orthogonal’ (PO) CDMA.
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Nén Video thông tin liên lạc P1
Both the International Standardisation Organisation (ISO) and the International Telecommunications Union (ITU) standardisation bodies have been releasing recommendations for universal image and video coding algorithms since 1985. The first image coding standard, namely JPEG (Joint Picture Experts Group), was released by ISO in 1989 and later by ITU-T as a recommendation for still image compression. In December 1991, ISO released the first draft of a video coding standard, namely MPEG-1, for audiovisual storage on CD-ROM at 1.5—2 Mbit/s....
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Nén Video thông tin liên lạc P2
Since the digital representation of raw video signals requires a high capacity, low complexity video coding algorithms must be defined to efficiently compress video sequences for storage and transmission purposes. The proper selection of a video coding algorithm in multimedia applications is an important factor that normally depends on the bandwidth availability and the minimum quality required. For instance, a surveillance application may only require limited quality, raising alarms on identification of a human body shape, and a user of a video telephone may be content with only sufficient video quality that enables him to recognise the facial features of...
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Nén Video thông tin liên lạc P3
In multimedia communications, compressed video streams need to be transmitted over networks that have inconsistent and time-varying bandwidth requirements. To make the best use of available network resources at any time and guarantee a maximum level of perceptual video quality from the end-user’s perspective, a certain flow control mechanism must be introduced into the video communication system (Cote et al., 1998; Wang, 2000).
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Nén Video thông tin liên lạc P4
Compressed video streams are intended for transmission over communication networks. With the advance of multimedia systems technology and wireless mobile communications, there has been a growing need for the support of multimedia services such as mobile teleconferencing, telemedicine, mobile TV, distance learning, etc., using mobile multimedia technologies. These services require the real time transmission of video data over fixed and mobile networks of varying bandwidth and error rate characteristics....
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Nén Video thông tin liên lạc P5
The near future will witness the universal deployment of the third-generation mobile access networks that are expected to revolutionise the world of telecommunications. In addition to conventional voice communication services provided by the second-generation GSM networks, the third-generation mobile networks will support a greatly enhanced range of services due to the higher throughput made available by embracing a number of new access technologies. These include TDMA and a variety of CDMA radio access families such as the direct sequence Wideband-CDMA (WCDMA) and multi-carrier CDMA....
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Nén Video thông tin liên lạc P6
Due to the expansion and diversity of multimedia applications and the underlying networking platforms with their associated communication protocols, there has been a growing need for inter-network communications and media gateways. Eventually, these applications will encounter compatibility problems. Not only will asymmetric networks run different set of communication protocols, but they will also operate various kinds of incompatible source coding algorithms that are characterised by different target bit rates and compression techniques. ...
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DAV Nguyên tắc và các ứng dụng P1
Tài liệu hướng dẫn : DAV Nguyên tắc và các ứng dụng
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DAV Nguyên tắc và các ứng dụng P2
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p2', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P3
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p3', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P4
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p4', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P5
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p5', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P6
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p6', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P7
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p7', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P8
Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p8', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
8/29/2018 6:09:35 PM +00:00
DAV Nguyên tắc và các ứng dụng P9
Routing protocols in mobile and wireless networks Mobile and wireless networks allow the users to access information and services electronically, regardless of their geographic location. There are infrastructured networks and infrastructureless (ad hoc) networks. Infrastructured network consists of a network with fixed and wired gateways. A mobile host communicates with a Base Station (BS) within its communication radius. The mobile unit can move geographically while it is communicating. When it goes out of range of one BS, it connects with a new BS and starts communicating through it by using a handoff....
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DAV Nguyên tắc và các ứng dụng P10
Handoff in mobile and wireless networks Wireless data services use small-coverage high-bandwidth data networks such as IEEE 802.11 whenever they are available and switch to an overlay service such as the General Packet Radio Service (GPRS) network with low bandwidth when the coverage of a Wireless Local Area Network (WLAN) is not available. From the service point of view, Asynchronous Transfer Mode (ATM) combines both the data and multimedia information into the wired networks while scaling well from backbones to the customer premises networks....
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DAV Nguyên tắc và các ứng dụng P11
Signaling traffic in wireless ATM networks Handoff algorithms in terrestrial wireless networks focus on the connection rerouting problem. Basically, there are three connection rerouting approaches: full connection establishment, partial connection reestablishment, and multicast connection reestablishment. Full connection establishment algorithms calculate a new optimum route for the call as for a new call request. The resulting route is always optimal; however, the call rerouting delay and the signaling overheads are high....
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DAV Nguyên tắc và các ứng dụng P12
Two-phase combined QoS-based handoff scheme Wireless Personal Communication Services (PCS) and broadband networking for delivering multimedia information represent two well-established trends in telecommunications. While technologies for PCS and broadband communications have historically been developed independently, harmonization into a single architectural framework is motivated by an emerging need to extend multimedia services to portable terminals.
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DSP A Khoa học máy tính quan điểm P1
The reader is already an expert in signal processing, although possibly unaware of it. We are all remarkably complex signal processing systems, adaptively processing intricate audio and video signals every moment of our lives. While awake we input intricate signals from our environment, extract highlevel representations of information carried by these signals, make decisions based on this information, record some of the information for later recall and processing, and produce new signals to change our environment in real time....
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