Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
2000-05-09
2002-08-13
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Frequency hopping
C370S337000, C370S347000, C370S458000
Reexamination Certificate
active
06434183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for radio transmission of data between a fixed station and at least one mobile station at one of a plurality of carrier frequencies in time slots using a time division multiplex method and time division duplex method where the change from one carrier frequency to another for a subsequent time slot requires a predetermined time period in the order of magnitude of one time slot, and the data is transmitted in two successive active time slots followed by an inactive time slot in which no data are transmitted. The present invention is also directed to an arrangement for radio transmission of data having a fixed station and at least one mobile station where data is transmitted in time slots using the time-division multiplex method and time-division duplex method as well as at one of a plurality of carrier frequencies using the frequency-division multiplex method.
2. Description of the Related Art
The DECT (Digital Enchanced Cordless Telecommunication) Standard was adopted at the start of the 1990's in order to replace the various existing analog and digital Standards in Europe. This is the first common European Standard for cordless telecommunications. A DECT network is a microcellular, digital mobile radio network for high subscriber densities and, is primarily designed for use in buildings. However, it is also possible to use the DECT Standard outdoors. The capacity of the DECT network of around 10,000 subscribers per square kilometer provides, from the cordless standard, ideal access technology for network operators. According to the DECT Standard, it is possible to transmit both voice and data signals. Thus, cordless data networks can also be built on a DECT base.
The DECT Standard is explained in more detail in the following text with reference to
FIG. 2. A
digital, cordless telecommunications system for ranges of less than 300 m has been standardized for Europe under the designation DECT. In conjunction with the switching function of a telecommunications installation, this system is therefore suitable for mobile telephone and data traffic in an office building or on a commercial site. The DECT functions supplement a telecommunications installation, and thus make it the fixed station FS of the cordless telecommunications system. Digital radio links between the fixed station FS and a maximum of 120 mobile stations MS can be produced, monitored and controlled on up to 120 channels.
A maximum of ten different carrier frequencies (carriers) are used for transmission in the frequency range from 1.88 GHz to 1.9 GHz. This frequency-division multiplex method is called FDMA (Frequency Division Multiple Access).
Twelve channels are transmitted successively in time on each of the ten carrier frequencies using the time-division multiplex method TDMA (Time Division Multiple Access). Cordless telecommunication in accordance with the DECT Standard using ten carrier frequencies with twelve channels per carrier frequency provides a total of 120 channels. Since one channel is required, for example, for each voice link, there are 120 links to the maximum of 120 mobile stations MS. The duplex method (TTD) is used on the carriers. After the twelve channels (channels 1-12) have been transmitted, the systems switch to receive, and the twelve channels (1-24) in the opposite direction are received.
A time-division multiplex frame thus comprises 24 channels (see FIG.
2
). Channel 1 to channel 12 are transmitted from the fixed station FS to the mobile stations MS, while channel 13 to channel 24 are transmitted in the opposite direction, from the mobile stations MS to the fixed station FS. The frame duration is 10 ms. The duration of a channel (time slot) is 417 &mgr;s. 320 bits of information (for example voice) and 100 bits of control data (synchronization, signaling and error check) are transmitted in this time. The useful bit rate for a subscriber (channel) of 32 Kbits/s results from the 320 bits of information within 10 ms.
Integrated modules have been developed to carry out the DECT functions for fixed and mobile stations where the fixed station and the mobile station carry out similar functions. One of these in this case integrated modules is in this case the RF module, i.e. the module which carries out the actual function of receiving and transmitting the RF band.
It is known for fast hopping RF modules to be used, i.e. RF modules which can carry out a change in carrier frequency from one time slot or channel to the next. These fast hopping RF modules are intrinsically very complex and costly. Thus, in practice, slow hopping RF modules are mainly used, modules which require a certain amount of time to change the carrier frequency. In practice, the time period which the slow hopping RF module requires to change the carrier frequency corresponds essentially to the time period of a time slot. This means that, after each active time slot, (i.e., after each slot in which data are transmitted,) an inactive time slot (blind slot) must follow in which no data can be transmitted. Thus, in practice, only six links are available on one carrier frequency to the DECT standard instead of the twelve possible links.
A DECT channel is defined by its time slot and its carrier frequency. In this case, it should be noted that the organization to reuse physical channels in accordance with the DECT Standard is carried out by way of dynamic channel selection, so there is no need for any complex frequency planning, as in cellular systems. To set up a link, the signal levels of all the channels are measured continuously, and the interference-free channels are controlled in a channel list (channel map). While a link exists, the signal levels of all the channels and the reception quality continue to be monitored. If this monitoring indicates that the channel currently being used has been transmitted at a carrier frequency which is subject to interference (for example, as a result of the influence of a transmission at the same carrier frequency from or to another fixed station), another carrier frequency is automatically selected for the next active time slot and is entered in the channel list as being interference-free. This represents one option for the organization of the reuse of the channels.
Alternatively, for example, a so-called frequency hopping method can also be used, in which the carrier frequency is changed after a predetermined time period, for example, a transmission frame.
For nationals outside Europe, the DECT Standard may need to be modified and matched to local conditions. For example, in the USA, the normal DECT band between 1.88 and 1.90 GHz cannot be used for transmission, but the generally accessible 2.4 GHZ ISM band (Industrial, Scientific, Medical) is available instead. Furthermore, changes would have to be carried out for matching to the national Standards, such as the American Standard “FCC PART 15”(Federal Communications Commission). This American Standard describes the transmission method, transmission powers and available bandwidth allowed for the radio interface.
In the DECT Standard, in addition to the 320 information bits mentioned above, each time slot also contains another 104 bits required for signal transmission, as well as 56 bits in guard field, so that each time slot contains a total of 480 bits. This results in a data rate of (24×480 bits)/10 ms=)1.152 Mbits/s. A data rate at this level is unusable in the American ISM band, since the bandwidth required per usable channel would be too large.
The publication, IEEE Personal Communications 1 (1994), New York, No. 2, 2
nd
Quarter 1994, pages 36 through 35, P. D. Rasky et al., “Slow Frequency-Hop TDMA/CDMA for Macrocellular Personal Communications”, discloses a method for digital radio transmission of data between a fixed station and at least one mobile station on one of a plurality of carrier frequencies, in which the data are transmitted in time slots in a time-division multiplex method and a time-duplex method. The chan
Kockmann Juergen
Mueller Andreas
Schliwa Peter
Sydon Uwe
Bell Boyd & Lloyd LLC
Chin Stephen
Jiang Lenny
Siemens Aktiengesellschaft
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