The Universal Mobile Telecommunication System (UMTS) is the third generation mobile communications system being developed within the IMT -2000 framework. UMTS will build on and extend the capability of today's mobile technologies (like digital cellular and cordless) by providing increased capacity, data capability and a far greater range of services.
a) Umts Structure
B. BLUETOOTH Bluetooth operates in the unlicensed 2.4--GHz ISM (industrial, scientific and medical) band and uses a frequency- hopping spread spectrum (FHSS) technique to minimise interference. A Bluetooth unit has a nominal range of approximately 10 meters (in the Class 3 defined in the standard, but which can be enlarged by amplifying the transmit power in Class 2 and Class 1 up to 100 m.). Two or more Bluetooth units sharing the same channel form a piconet. Each piconet consists of a master unit and up to seven active slave units. Furthermore, two or more piconets can be interconnected to form a scattemet. To be a part of more than one piconet a unit called inter-piconet unit (gateway) is required.
c. IEEE802.11b Wireless local area networking (WLAN) radio technology provides superior bandwidth compared to any cellular technology. The IEEE 802.11 b standard offers a maximum throughput of II Mbps (typical 6.5 Mbps) working in the same 2.4- GHz ISM band as B1uetooth by the use of direct sequence spread spectrum (DSSS). WLANs were originally intended to allow local area network (LAN) connections where premises wiring systems were inadequate to support conventional wired LANs, but they were later identified with mobility. A WLAN cell is formed by an AP and an undefined number of users in a range from approximately 20 to more than 300 m ( 100 m. in indoor environments) that access the AP through network adapters (NAs ), which are available as a PC card that is installed in a mobile computer.
Table 1 summarizes the main parameters of each standard, where only Class 3 of the Bluetooth standard has been considered, as long as the Bluetooth version 1.0 specification focuses primarily on the 10- meter ranger standard radio. Notice that the coverage range in the UMTS case is capacity dependent and it can vary from 200 m. up to 1.4 Km., a phenomena known as "cell breathing"
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5. SERVICE INTEGRATOR
The different wireless access services of UMTS, W-LAN and Bluetooth require an integration of the services over the satellite. The central part of the service portfolio provisioning is the service integrator (SI), cf. Figure 3. The service integrator will provide the interfaces for the wireless and wired service access points in the cabin, as well as the interface to the terrestrial networks at aircom provider site. All services will be bundled and transported between a pair of Service Integrators. It performs the encapsulation of the services and the adaptation of the protocols.
The SI multiplexer is envisaged to assign variable capacities to the streams, controlled by a bandwidth manager that monitors also the QoS requirements of the different service connections. Changes in capacity assignment must be signaled to the SI at the other communication end. The heterogeneous traffic stream is then sent to streaming splitter/combiner. This unit is envisaged to support several satellite segments and to perform handover between them. Asymmetrical data rates in inbound and outbound directions can be managed here. Adaptation to the supported satellite segments are done by medium access controllers (MAC) in a modular manner. Towards the terminal side, the interfaces of the wireless access standards need to interwork with the transport streaming of the SI by specific adaptation layers (AL). These ALs have to be designed according to the analysis of the impact of delay, jitter and restricted / variable bandwidth on the protocol stack. Buffering (to compensate delay jumps at handover) and jitter compensation for real-time services (e.g., voice) must be also provided here.
Fig. 3 Service Integrator
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6. SERVICE DIMENSIONING
This section provides an overview of key issues and steps for the systematic system dimensioning of Wireless Cabin aircom satellite communications system. We will tackle the satellite constellations as potential candidates for aircom services as well as the gross traffic calculation and assignment process.
Different market entry options and reference business cases must be taken into account in an initial stage of a system design. The evolutionary path leads from existing L-band systems such as inmarsat GAN (see Figure 5) or B-Gan in few years up to C/Ku band and existing GEO transponders, whereas the “revolutionary” path may target from the beginning at advanced K/Ka band technology and the design of a tailor-made, potentially non-GEO system.
The system dimensioning process can be structured in several steps:
· Determination of gross traffic per aircraft using the multi-service model
· Determination of the timely and locally varying traffic, depending on the flight path and flight schedule, assuming also a service rool-out scenario for different airlines and aircraft types.
· Identification of potential serving satellites and their coverage areas.
· Mapping and traffic allocation of the aircom traffic to the satellite systems.
Two key observations concerning the “geographic market” are 1) the pronounced asymmetry of market opportunities between northern and southern hemisphere (partly just a result of our earth’s “continental layout”), and the fact that a significant share of the addressable market is at higher (northern ) latitudes, especially with the important long-haul intercontinental flight routes between the European, North American and East Asian regions. Both observations are illustrated in figure 6, although its view is Europe-centric; the underlying flight route investigations have been performed within the European ACTS project ABATE and have been used for design and dimensioning studies of an aeronautical subsystem of the EuroSkyWay satellite communications system
7. INTERFERENCE
Once the above described measurements finish. four types of interferences within the CMHN have to be studied: the co-channel interference among the terminals of the same wireless access segment, the inter- segment interference between terminals of different wireless networks, the cumulative interference of all simultaneous active terminals with the aircraft avionics equipment and the interference of the CMHN into terrestrial networks.
From the co-channel interference analysis the re-use distance and the re-use frequency factor for in-cabin topology planning will be derived. For this reason it is important to consider different AP locations during the measurements.
It is not expected to have major problems due to interference from UMfS towards WLAN and Bluetooth, thanks to the different working frequency. On the other hand, particular interest has to be paid in the interference between Bluetooth and WLAN .Due to the market acceptance of Bluetooth and WLAN, there is a special interest of designers and portable data devices manufacturers to improve the coexistence of the two standards. There are many studies showing the robustness and the reliability of Bluetooth in presence of WLAN and vice versa.
A description of the electromagnetic behaviour of conventional aircraft equipment is necessary to analyse the interference and the EMC of the new wireless network with the avionics systems. The allowed radiated field levels are regulated and must be respected if certification is desired. So far, GSM telephony is prohibited in commercial aircraft due to the uncertain certification situation and the expected high interference levels of the TDMA technology.
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