Telecommunications – Radiotelephone system – Usage measurement
Reexamination Certificate
1997-06-17
2001-02-06
Hunter, Daniel S. (Department: 2749)
Telecommunications
Radiotelephone system
Usage measurement
C455S414200
Reexamination Certificate
active
06185413
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mobile station to be used in mobile radio systems.
DESCRIPTION OF THE RELATED ART
Mobile communication is one of the fastest growing segments of the telecommunications industry. Until the end of the eighties, only some analog radio telephone systems were operated in Europe which essentially work within a frequency band of between 450 and 900 MHz. Because of the lack of a uniform technical standard and because of the rapid technical advances in the field of digital voice coders and digital signal processing, work was started on a uniform pan-European digital system, the GSM (Global System for Mobile Communication), which was taken into operation in western Europe in 1992. In the time following that, other digital mobile radio systems were developed which will be explained in the following paragraphs, referring to FIG.
2
.
The GSM was initially taken into operation only in western Europe and was then also successful in many countries outside of western Europe such as, for example, Australia, China, Russia, Singapore, etc. In Germany, the Federal Ministry for Post and Telecommunications issued two licenses for digital GSM networks which were obtained, on the one hand, by DeTeMobil GmbH and, on the other hand, by Mannesmann Mobilfunk. The GSM networks provided by the two operators are two physically separate mobile radio networks having their own transmitting stations. DeTeMobil GmbH operates its GSM network under the name “D1,” whilst the GSM network operated by Mannesmann Mobilfunk is known by the name “D2.” As can be seen from
FIG. 2
, digital data transmission in the GSM network takes place from a mobile station which can be, for example, a car telephone, a cordless telephone or a handheld telephone, to the stationary base station in the frequency band between 890 and 915 MHz. This direction of connection is known as the “uplink.” The “downlink,” i.e. the data transmission from the stationary base station to the mobile station, takes place in the frequency band between 935 and 960 MHz. The carrier frequencies modulated with the digital transmission information have a channel spacing of 200 kHz and it is possible to transmit eight individual channels per carrier frequency.
To make it possible for several subscribers to access a certain frequency spectrum simultaneously, care must be taken to ensure that the signals of the individual subscribers do not interfere with one another. To be able to separate the various subscriber signals from one another, there are in principle three fundamental methods, namely the frequency division multiplex method (FDMA, Frequency Division Multiple Access), the time division multiplex method (TDMA, Time Division Multiple Access) and the code division multiplex method (CDMA, Code Division Multiple Access). In the FDMA method, the frequency axis is subdivided into frequency channels, each subscriber being allocated a separate channel on which the subscriber may transmit without restrictions as long as the transmission remains within the predetermined channel bandwidth. The FDMA method was last used mainly in the analog mobile radio systems. In the TDMA method, the time axis is subdivided instead of the frequency axis, i.e. although each subscriber has access to the entire bandwidth, the subscriber only may transmit at certain times, i.e. in time slots. These slots have a width of, e.g., 0.577 ms in the GSM mobile radio system which, as can be seen from
FIG. 2
, uses the TDMA method as access method. In the CDMA method, each subscriber can use the entire frequency bandwidth as in the TDMA method but can also transmit over the entire time without having to adhere to certain time slots. To avoid a collision between individual subscriber signals in this case, nevertheless, the individual subscriber signals are separated by using orthogonal codes in the direction of the power axis, i.e. the individual subscriber signals are transmitted at different powers. Apart from these three basic types, combinations of the individual access methods are also conceivable, a combination of TDMA and FDMA being normally used in the GSM mobile radio system.
For the transmission of digital communication information, a large number of different transmission methods are known which are distinguished from one another by the modulation method used in each case. Modulation is generally understood as being the change of a carrier signal depending on the information signal to be transmitted. In principle, the modulation methods involve three possibilities of impressing an information signal (which is present in digital form in digital modulation) on the carrier signal, a distinction being made between amplitude, frequency or phase modulation depending on whether it is the amplitude, the frequency or the phase angle which is changed by the information to be transmitted. A widely used phase modulation method is the GMSK (Gaussian Minimum Shift Keying) method. The GMSK method has the advantages of the MSK (Minimum Shift Keying) method, but the break points occurring in the frequency and phase characteristic of the MSK signal as a result of a widening of the power density spectrum are eliminated in the GMSK method by using a Gaussian low-power variant. Another known phase modulation method is the &pgr;/4 DQPSK (Differential Quadrature Phase Shift Keying) method which is an advantageous variant of the QPSK (Quadrature Phase Shift Keying) method. In the QPSK method, the communication information present as digital signals is divided into bits of even and odd position with the aid of quadrature phase shift keying and then multiplied by the carrier frequency. In this process, dips can occur in the envelope curve of the quadrature phase modulated signal which can lead to adjacent-channel interference. To achieve as constant as possible an envelope curve, the QPSK method was developed further into the &pgr;/4 DQPSK method in which the 180° phase jumps leading to the amplitude dips in the QPSK method are avoided. In addition to these phase modulation methods, a number of other modulation methods are known which, however, will not be discussed in greater detail in the text following.
FIG. 2
shows the characteristics of the GSM mobile radio system. In addition to the D1 and D2 licenses, the Federal Ministry for Post and Telecommunications issued a third mobile radio license which relates to the DCS (Digital Cellular System) 1800 mobile radio system. The DCS 1800 mobile radio system has been operated in Germany since 1994 as the “E1” network. A modified version of the GSM system is called PCS-1900 in the United States.
As a rule, mobile radio systems which are aimed at a large number of subscribers have a cellular structure, i.e. the entire area to be supplied is subdivided into smaller radio zones, “radio cells.” The intentional limiting of the radio zones makes it possible to reduce the transmitting power needed for transmitting information so that the transmitting frequencies, which are actually scarce, can be reused at a sufficiently large distance without the individual transmission channels interfering with one another. Two mobile radio subscribers which are far enough apart from one another can use the same frequency channel simultaneously in this manner. Each radio cell is allocated a base station, the receiving range of which is limited to the relevant radio cell. If a mobile station moves out of the service area of its base station, the connection must be conducted via another base station, which is then carried out by an automatic change in radio zone without significantly impairing the quality of the continuing connection. This process is called “handover.” In contrast to the cellular systems, the PCS or PCN system comprises individual local networks which, in turn, can be structured as cellular networks. The individual local networks, however, are connected to one another by the landline network. This means that in the case of the PCS or PCN systems the entire area is not covered by radio zones, but mobile radio t
King Neal J.
Mueller Wilhelm
Sassin Michael
Hunter Daniel S.
Siemens Aktiengesellschaft
Wyche Myron K.
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