Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-01-26
2004-04-20
Tran, Congvan (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S439000, C370S331000, C370S382000
Reexamination Certificate
active
06725038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a wireless communication systems, and more particularly to a method and apparatus for speeding up AAL
2
connection setup during handover in advanced cellular networks.
2. Description of Related Art
The demand by consumers all over the world for mobile communications continues to expand at a rapid pace and will continue to do so for at least the next decade. Over 100 million people were using a mobile service by the end of 1995, and that number is expected to grow to 300 million by the year 2000. Several factors are contributing to the exciting growth in the telecommunications industry. For example, a combination of technology and competition bring more value to consumers. Phones are smaller, lighter, had a longer battery life, and are affordable now for the mass market. Operators are providing excellent voice quality, innovative services, and roaming across the country or world. Most important, mobility is becoming less expensive for people to use. Around the world, as well as in the United States, governments are licensing additional spectrum for new operators to compete with traditional cellular operators. Competition brings innovation, new services, and lower prices for consumers.
The basis for any air interface design is how the common transmission medium is shared between users, that is, the multiple access scheme. In frequency division multiple access (FDMA), the total system bandwidth is divided into frequency channels that are allocated to the users. In time division multiple access (TDMA), each frequency channel is divided into time slots and each user is allocated a time slot. In CDMA, multiple access is achieved by assigning each user a pseudo-random code (also called pseudo-noise codes due to noise-like auto-correlation properties) with good auto- and cross-correlation properties. This code is used to transform a user's signal into a wideband spread spectrum signal. A receiver then transforms this wideband signal into the original signal bandwidth using the same pseudo-random code. The wideband signals of other users remain wideband signals. Possible narrowband interference is also suppressed in this process. TDMA and CDMA usually use FDMA to divide the frequency bank into smaller frequency-channels, which are then divided in a time or code division fashion.
There are several ways to classify CDMA schemes. The most common classification scheme is based on the modulation method used to obtain the wideband signal. This division leads to three types of CDMA: direct sequence (DS), frequency hopping (FH), and time hopping (TH). In DS-CDMA, spectrum is spread by multiplying the information signal with a pseudo-noise sequence, resulting in a wideband signal. In the frequency hopping spread spectrum, a pseudo-noise sequence defines the instantaneous transmission frequency. The bandwidth at each moment is small, but the total bandwidth over, for example, a symbol period is large. Frequency hopping can either be fast (several hops over one symbol) or slow (several symbols transmitted during one hop). In the time hopping spread spectrum, a pseudo-noise sequence defines the transmission moment. Furthermore, combinations of these techniques are possible.
Nevertheless, DS-CDMA is the technique that is being used for third generation wideband CDMA (WCDMA) proposals. Recently, extensive investigations have been carried out into the application of a code division multiple access (CDMA) system as an air interface multiple access scheme for IMT-2000/UMTS (International Mobile Telecommunications System 2000/Universal Mobile Telecommunications System). It appears that CDMA is the strongest candidate for the third generation wireless personal communication systems. As a result, many research and development (R&D) projects in the field of wideband CDMA have been going on in Europe, Japan, the United States, and Korea.
Wideband CDMA has a bandwidth of 5 MHz or more. The nominal bandwidth for all third generation proposals is 5 MHz. There are several reasons for choosing this bandwidth. First, data-rates of 144 and 384 Kbps, the main targets of third generation systems, are achievable within 5 MHz bandwidth with a reasonable capacity. Even a 2-Mbps peak rate can be provided under limited conditions. Second, lack of spectrum calls for reasonably small minimum spectrum allocation, especially if the system has to be deployed within the existing frequency bands occupied already by second generation systems. Third, the 5-MHz bandwidth can resolve (separate) more multipaths than narrower bandwidths, increasing diversity and thus improving performance. Larger bandwidths of 10, 15, and 20 MHz have been proposed to support higher data rates more effectively.
Several wideband CDMA proposals have been made for third generation wireless systems. These have all been proposed to provide advanced properties such as provision of multirate services, packet data, complex spreading, a coherent uplink using a user dedicated pilot, additional pilot channel in the downlink for beam-forming, seamless inter-frequency handover, fast power control in the downlink, and optional multi-user detection.
Today's transmission protocols of many telecommunication networks are based on pulse code modulation (PCM), and mobile radio systems are no exception. The switching is also based on the switching of 64- or 56-Kbps PCM connections. ATM technology has received lot of attention during recent years as the next major transport technology. ATM has also been proposed for wireless applications (i.e., ATM cells are transmitted over the air interface).
ATM provides not only the multiplexing gains of packet switching, but also the guaranteed delay characteristics of circuit switching. The fundamental strategy behind ATM is to split the information into small fixed size units that are easy to handle. The fixed size of the cell allows efficient switching. ATM networks are high-speed switching systems offering large bit pipes, which allow statistical multiplexing (i.e., multiplexing of many connections with variable rate characteristics), which altogether reduces the overall bandwidth requirements. Since ATM is based on the transmission of fixed size cells, it can be easily evolved for future services.
The basic unit in an ATM is a cell of 53 bytes. The ATM cell consists of a header (5 bytes) and information fields (48 bytes). The header consists of a field for Generic flow control (GFC), Virtual path identified (VPI) and Virtual channel identifier (VCI). The VPI and VCI are used to identify the virtual path and virtual channels identified with that path to route the ATM cells from the source node to the destination node.
The ATM and the ATM adaptation layer (AAL) form the data link layer. AAL converts the arbitrarily formatted information supplied by the user into ATM cells. Various forms of AAL protocols are necessary to handle the different types of traffic. AAL
0
provides direct access to the ATM layer. AAL
1
assumes constant bit rate traffic, which is intolerant of mis-sequenced information and variation in delay. It offers the following function: segmentation and reassembly (SAR) handling of delay variation handling, handling of lost and mis-inserted cells, source clock recovery, monitoring for bit errors, and handling those errors.
AAL
2
is used, for example, for voice and video. It assumes that traffic is bursty and intolerant of mis-sequencing and that a time stamp is needed for packet reassembling. It offers the following functions: multiplexing, SAR, handling delay variation, handling cell lost/error, and source clock recovery. AAL
2
will be used for compressed speech in third generation mobile radio systems in the network infrastructure.
AAL
3
/
4
and AAL
5
are geared to traffic that has bursty characteristics with variable frame length. Furthermore, delay is not critical and packets can be resequenced based on sequence numbers. AAL
5
is expected to supersede AAL
3
/
4
since it has lower overhead and TCP/IP acknow
Nokia Corporation
Squire Sanders & Dempsey L.L.P.
Tran Congvan
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