Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-06-05
2001-09-11
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
Reexamination Certificate
active
06289006
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a telecommunications process with time division multiple access (TDMA) between a first and a second station, in which process one station transmits and the other receives in at least one predetermined time slot of a frame.
This process is a telecommunications process with time division multiple access (TDMA) between a first and a second station, in which process one station transmits and the other receives in at least one predetermined time slot of a frame.
In the process with time division multiple access (TDMA), the time axis is subdivided, specifically into frames which are each of the same length and have a predetermined number of bits. For example, each of these frames may be subdivided into an even number of time slots of the same size. The first half of this number of time slots within a frame is used to transmit from the transmitting first station to the receiving second station. This transmission direction is usually referred to as downlink if the first station is a base station and the second station is a mobile station. Accordingly, the second half of the number of time slots within the frame is used to transmit in the opposite transmission direction. Here, the second station transmits while the first station receives. This is usually referred to as uplink if the transmitting station is the mobile station and the receiving station is the base station.
Each of the aforesaid time slots is thus used to set up a transmission channel whose parameters are the number of the time slot within the frame and the carrier frequency used. In order to transmit digital data, the carrier frequency is then frequency-modulated or phase-modulated.
In the European DECT Standard (Digital European Cordless Telecommunications Standard), there are 24 time slots available per frame, specifically 12 in the downlink and 12 in the uplink. In contrast, in the Japanese PHS Standard (Personal Handy Phone System Standard) there are only two times four time slots available per frame, so that the number of time slots per frame is generally not very large.
However, many tasks may require a plurality of transmission channels with different carrier frequencies to be set up. In this case, a plurality of time slots have to be made available per frame in order to carry out the same task, so that, in terms of the number of time slots per frame, a capacity limit is quickly reached. Moreover, if, for reasons of cost, only simple synthesizers are used, the number of usable time slots is reduced further by half since these synthesizers cannot change over from one carrier frequency to another carrier frequency within the very short time period between two time slots.
SUMMARY OF THE INVENTION
The invention is based on the object of developing a telecommunications process of the type mentioned at the beginning in such a way that it permits the number of transmission channels to be increased without simultaneously requiring the use of a larger number of time slots per frame.
The means of achieving the object set is a set of process steps wherein the carrier frequency is changed over in the predetermined time slot from frame (R
1
) to frame (R
2
), and this changing over of the carrier frequency is terminated upon fulfillment of an abort criterion.
A telecommunications process according to the invention with time division multiple access (TDMA) between a first and a second station, in which process one station transmits and the other receives in at least one predetermined time slot of a frame, is distinguished in that
the carrier frequency is changed over in this time slot from frame to frame and
this changing over of the carrier frequency is terminated given fulfilment of an abort criterion.
It is thus possible to use only one time slot to set up two or more transmission channels which operate with different carrier frequencies. In this way, tasks which require the use of different transmission channels with different carrier frequencies can be carried out even if the capacity limit in terms of the number of time slots per frame is reached, for example because, with the exception of one, all the other time slots are already occupied or other time slots are subject to interference, or the like.
Generally, the transmitting stations are capable of detecting when the capacity in terms of the number of time slots per frame is exhausted, so that the process according to the invention does not need to be carried out continuously but is rather used only when for example, with the exception of one, all the other time slots per frame are no longer available for whatever reasons.
The setting up of different transmission channels which relate to the same time slot in successive frames can be carried out, for example, for the purposes of controlling the receiving station if, for this purpose, transmission has to take place at different carrier frequencies. The abort criterion can then be the expiry of a predetermined time. However, it may also be the reception of a message specifying that the changing over of the carrier frequencies be terminated. This message can be transmitted from a third station, for example.
A very advantageous further development of the invention is distinguished in that the first station, in the predetermined time slot, and the second station, in a further predetermined time slot of the same frame, alternately transmit and receive, and in that the carrier frequency in the further predetermined time slot is treated in the same way as that in the predetermined time slot.
In this context, the further predetermined time slot can advantageously be offset by half a frame length with respect to the predetermined time slot.
In this exemplary embodiment, there is a so-called duplex link, which requires two physical channels and which permits the subscribers to speak and listen simultaneously. In the DECT system, a time slot separation is used for duplex links. This is also referred to as Time Division Duplex (TDD). For this, time slot pairs are formed. If the first station, or base station, uses a predetermined time slot for transmission (in the downlink), the second station, or mobile station, transmits (in the uplink) in a time slot which is offset with respect to the first mentioned time slot by half a frame length.
According to the invention, in the case of a capacity bottleneck in terms of the number of available time slots (in the uplink) when using TDD, this second time slot is then also treated in the same way as the time slot in the downlink, which relates to the changing over of frequencies from frame to frame. In other words, when TDD is used, both time slots which are associated with one another are changed over in terms of carrier frequency from frame to frame in the downlink and in the uplink, so that different transmission channels can be set up from frame to frame for both aforesaid time slots.
This may be necessary if, in the uplink and in the downlink, with the exception of one time slot in each case, all the other time slots are occupied or no longer available and, for example, an intracell handover is to occur or a further transmission channel is to be set up. An intracell handover takes place if the radio channel is changed within a cell and thus with the same base station being retained. A reason for carrying out an intracell handover is if the reception level of the base station to which a link is being made at a given time is sufficiently high but the link quality is worsening severely, for example as a result of common channel interference.
Here, too, the abort criterion may be the expiry of a predetermined time. If no transmission channel with a sufficient level of link quality is found within the predetermined time, the link between the two stations may be interrupted. On the other hand, if a good level of link quality is achieved at one of the aforesaid frequencies, the corresponding transmission channel is definitely selected and its carrier frequency set in a stable fashion. The abort criterion would therefore in this case be the
Kwoh Jasper
Nguyen Chau
Nokia Mobile Phones Limited
Perma & Green, LLP
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