Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-10-15
2002-05-21
Olms, Douglas (Department: 2732)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000
Reexamination Certificate
active
06393007
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to telecommunication systems and, more specifically to radio communication systems for both voice and data transmission between two or more telecommunication units, at least one of which can be mobile.
BACKGROUND OF THE INVENTION
In the past decade, various techniques and concepts of radio communication systems for mobile telephony and data transmission have been developed. In general, two types of mobile communication systems can be distinguished,
One is cellular communication, providing service to mobile subscribers which may move relatively fast through relatively wide areas, called cells. Analog cellular systems, such as designated AMPS, ETACS, NMT-450 and NMT-900 have been deployed throughout the world. Digital cellular systems are designated IS-54B, D AMPS in the Unites States, PDC in Japan and the pan-European GSM system.
Cordless radio communication is the other system, ranging from simple residential cordless telephones to business cordless systems capable of serving hundreds or even thousands of cordless communications units across (large) offices or production halls, etc. and local public communication. Analog cordless systems are designated CT
0
, CT
1
en CT
1
+. Digital cordless systems are designated CT
2
, CT
2
-CAI, CT
3
, PHS and DECT.
GSM, D-AMPS, PDC and CT
3
, PHS and DECT use a digital access technique known as TDMA (Time Division Multiple Access), wherein transmissions take place in time slots and a plurality of time slots are gathered in a frame. Some emerging digital communication systems use CDMA (Code Division Multiple Access) as their access technique for establishing radio communication between communication units of a system. In general, these mobile or cordless communication systems are arranged for providing service at Multiple Carriers (MC) in a radio transmission band. That is, transmission at a particular carrier is provided using either TDMA or CDMA.
In cellular systems, like GSM, one or a plurality of carriers are individual to a cell. Cells that are spaced sufficiently apart can re-use the same carriers, without distorting effect. This so-called frequency re-use scheme allows an operator to serve a wide coverage area with many users and only a limited spectrum.
Cordless systems such as DECT and PHS are not based on frequency re-use. Instead, all the carriers are available for each cell. The system determines which carrier and communication channel of such carrier can be used for communication purposes, with the least amount of interference. Carriers and communication channels are dynamically allocated before and/or during transmission, which is called DCA (Dynamic Channel Allocation). Accordingly, no frequency planning or the involvement of an operator which controls the frequency spectrum are required.
For application in the home, like a wireless extension of the PSTN (Public Switched Telephone Network), or for wireless extensions of a LAN (Local Area Network), so-called unlicensed radio transmission bands are used. That is, subscribers do not require a license for operating radio equipment in such a radio transmission band. However, rules imposed on unlicensed bands by regulatory bodies like ETSI in Europe and the FCC in the U.S. prevent a single user of claiming the entire transmission band. Such rules usually involve collision avoidance schemes or spreading. In the case of spreading, the transmission of a subscriber is spreaded over the entire transmission band. Since different transmissions are uncoordinated, a radio air interface has to be applied which is robust against interference.
A global unlicensed transmission band has been defined at 2.4 GHz. Radio communication systems that are deployed in this unlicensed band have to adhere to strict rules defined by ETSI and the FCC. In the 2.4 GHz ISM (Industrial Scientific Medical) transmission band, spreading is mandatory. This means that a DCA schema used for DECT is not permitted. Instead FH (Frequency Hop) spreading or DS (Direct Sequence) spreading has to be applied, for example.
International Patent Application WO 93/17507 of applicant, which is herein included by reference, discloses several FH schemes for a TDMA radio communication system, wherein radio communication units transmit at radio channels in accordance with pseudo-random channel hopping schemes.
International Patent Application WO 93/22850 discloses a method of increasing interference diversity in a TDMA radio communication system, wherein frequency hopping is used and interference diversity is further increased in that communication channels also hop in a time slot raster. That is, instead of a fixed time slot allocation, time slots hop in position between sequential frames, i.e. TH (time slot hopping).
The ISM band is open to all equipment that fulfills the FCC and ETSI rules. Coordination between systems, to reduce interference, is not allowed, This means that the air interface of a communication system has to cope with unknown interference and jammers.
By applying any or both FH and TH schemes, the transmission of information in both frequency and time is randomised. That is, during a session, a communication channel occupies different frequency and time positions, such that the interference encountered at a communication channel is an average of all the channels at the transmission band. This is of particular advantage for voice transmission.
In practice, cellular and cordless radio communication systems both support voice and data transmission. In the context of the present description, the term voice communication is used for real time transmission of speech, whereas the term data communication is used for the transmission of other information, inclusive non-real time speech.
To enable error free delivery of data, data transmission typically uses a retransmission scheme to retransmit data packets that have been received in error. In an ARQ (Automatic Retransmission Query) scheme, the sender of the data is notified by the recipient about the performance of the previous transmission. If the sender has been informed that the reception was in error, the erroneous data is automatically retransmitted. In TDMA system like DECT, asymmetric data links can be established in which most of the time slots of a TDMA frame are allocated for simplex data transfer, i.e. in one direction only. However, at least one return communication channel has to remain in force to provide the ARQ information. To minimize delay and, accordingly, maximize throughput, the return channel directly follows the data channels. As a consequence, the recipient can acknowledge all data immediately preceding the return channel.
However, using a time slot hopping scheme, due to the random character of the hopping scheme, the return channel in a particular frame may end up in front of the data packets. Accordingly, immediate acknowledgment of received data packets in the same frame is not possible, simply because the return channel is not available after receipt of the data packets. Absence of the ARQ information results in an automatic retransmission of the previously transmitted data by the sender. This, despite the fact that the data might have arrived correctly. Those skilled in the art will appreciate that the throughput of the system is considerably reduced, and on average only 50% of the maximum throughput capacity is achieved.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of and equipment for radio communication, applying time hopping of time slots of a TDMA frame, suitable for coexistence of various types of communication in the same frame.
It is in particular an object of the present invention to provide an optimized allocation of time slots of a TDMA frame to support voice transmission in error prone radio communication systems, such as the unlicensed ISM band.
These and other objects, advantages and features of the present invention are provided by a method of radio communication in a TDMA radio communication system, wherein a communica
Burns Doane Swecker & Mathis L.L.P.
Olms Douglas
Telefonaktiebolaget LM Ericsson (publ)
Vanderpuye Ken
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