Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-03-24
2004-02-17
Ngo, Ricky (Department: 2697)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S347000, C370S442000, C370S468000
Reexamination Certificate
active
06693885
ABSTRACT:
The present invention relates to a method and an arrangement for burst mode control to achieve effective radio transmission of data between a fixed station and at least one mobile station at one of a plurality of carrier frequencies, this data is transmitted in active time slots using a time-division multiplex method (TDMA), these slots each being followed by an inactive time slot.
DESCRIPTION OF THE RELATED ART
The DECT Digital Enhanced Cordless Telecommunication Standard was adopted at the start of the 1990's in order to replace the various existing analogue and digital Standards in Europe. This was the first common European Standard for cordless telecommunications. A DECT network is a microcellular, digital mobile radio network for high subscriber densities. It 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 will be 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 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 in each case 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 (TDD) is used for on the carriers. Once the base stations has transmitted twelve channels (channels
1
-
12
), it switches to received, and receives twelve channels in the opposite direction (channels
13
-
24
).
A time-division multiplex frame thus comprises 24 channels (see FIG.
2
). In this case, 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 104 bits of control data (synchronization, signalling and error check) as well as 56 bits of so-called guard (protection) field are transmitted in this time. The useful bit rate for a subscriber (channel) results from the 320 bits of information within 10 ms. It is thus 32 kilobits per second.
Integrated modules have been developed to carry out the DECT functions for fixed and mobile stations. In this case, the fixed station and the mobile station carry out similar functions. One of these integrated modules is the RF module, i.e., the module which carries out the actual function of receiving and transmitting the RF band.
It is known for so-called fast hopping RF modules to be used, (RF modules which can carry out a carrier frequency change very quickly, for example from one tome slot or channel to the next). These fast hopping RF modules are intrinsically very complex and costly. Thus, in practice, so-called slow hopping RF modules are mainly used, (RF modules which require a certain amount of time to program the carrier frequency for the next time slot). In practice, the time period which the slow hopping RF module requires to program the carrier frequency corresponds essentially to the time period of a time slot in the DECT Standard. This means that, after each active time slot, (in which data are transmitted), a so-called inactive time slot (blind slot) in which no data can be transmitted, must follow. This means that, 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. The organization to reuse physical channels is carried out by means of dynamic channel selection. Meaning that 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 was 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. Alternatively, the carrier frequency change can also be carried out after each frame.
As a further option, a carrier frequency change may always take place after a predetermined time period, such as a time slot or a frame, (designated “frequency hopping spread spectrum”.)
In other countries, the transmission conditions and standards may differ. 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 the 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=)1,152,000 bits/s. A data rate at this level is pointless in the American ISM band, since the bandwidth required per usable channel would be too large.
The problem thus exists of using components which have been developed for the DECT Standard in other transmission conditions as well, for cost reasons, while at the same time making it possible to use the available bandwidth efficiently.
EP-0 767 551 discloses a method for increasing the load and, thus, the capacity of the DECT system, whereby the ISM frequency band in the 2.4 GHz range is used for information transmission in addition to the DECT frequency band between 1.880 and 1.900 GHz, and the FHSS method (Frequency Hopping Spread Spectrum) or the DSSS method (Direct Sequence Spread Spectrum) is also applied.
GB-2 295 930 discloses a TDMA radio system based on the frequency hopping method wherein a frequency change is implemented in the guard period between two time slots. Radio devices of the TDMA radio system respectively comprise two RF modules (synthesizers) for this frequency change in the guard period between two time slots. While
Kockmann Juergen
Sydon Uwe
Terglane Hermann-Josef
Bell Boyd & Lloyd LLC
Ha Yvonne Q.
LandOfFree
Method, mobile station and base station for transmitting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method, mobile station and base station for transmitting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method, mobile station and base station for transmitting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3349014