Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-01-22
2001-07-24
Vu, Huy D. (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S280000, C370S337000, C370S348000, C370S352000
Reexamination Certificate
active
06266330
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method by which radio capacity is divided dynamically between packet radio service and circuit switched service in a TDMA system in which two-way traffic between base stations and mobile stations takes place in time slots on predetermined channels. The invention also relates to a mobile system operating according to the method.
BACKGROUND OF THE INVENTION
Most present-day cellular networks offer circuit switched services for speech and data. The available frequency band is divided between these services, all having equal priority. The network does not take into account whether the capacity is used for the transmission of speech or data.
Considering burst-form data services, circuit switching does not exploit the channel optimally. Therefore packet radio services are used alongside existing circuit switched services in cellular networks. Since the existing radio band cannot be expanded, packet radio services must be fitted into the same band as circuit switched services. Thus a certain amount of capacity has to be taken from circuit switched services for packet radio services.
In TDMA cellular systems, a radio band is usually divided into multiple frequency bands (FDMA, Frequency Division Multiple Access), and each frequency band is further divided into multiple time slots. Logical channels are transmitted in the physical time slots of the radio interface. In circuit switched cellular systems, all time slots are used for control signaling and for circuit switched traffic.
Cases associated with this topic have been discussed previously in certain patent publications. One example of them is EP-26 11 27, which describes a time-sharing telecommunications system wherein the spectrum is exploited in a relatively efficient manner by dividing narrow-band radio frequency channels into at least two time slots, one to transmit coded speech signals and one to provide two-way transmission. However, this publication does not discuss the dynamic allocation of capacity, and it does not discuss packet radio services as such.
U.S. Pat. No. 4,887,265 discloses a packet radio switched cellular system. In this system, a plurality of data calls can be switched to one and the same radio channel, whereby radio spectrum is saved. However, the publication mainly discusses the criteria of handoff. It does not discuss the dynamic allocation of capacity to packet radio and circuit switched services.
SUMMARY OF THE INVENTION
The purpose of the invention is to indicate a method by which the capacity of a radio channel can be better exploited. The object is a method which is used in determining the number of time slots allocated, on the one hand, to packet radio service and, on the other hand, to circuit switched service. According to the invention, this is done by using the characteristics of Claim
1
by allocating dynamically more capacity, i.e. more time slots, to the form of service requiring it at a given time.
According to the present invention, some basic number of time slots are reserved for packet radio service and a number of time slots for circuit switched service. If, for example, the traffic need of packet radio service increases, information regarding this is obtained through a request flagged by a mobile station or through traffic measurement by the base station, whereupon this information is used as a criterion in the allocation of more time slots to this service. Such a request can be transmitted from a mobile station to a base station on a message or signaling channel (e.g. in call set-up signaling) or on a traffic channel, or it may be, for example, a short message output. The request may also be transmitted on a packet radio channel. The capacity required by each service is monitored in the base station system (BSS), which is in a known manner made up of base transceiver stations (BTS) and base station controllers (BSC), and from which information is transmitted to the mobile station regarding the channel configurations, i.e. the allocation of radio capacity (which channel is in the use of which service).
In the basic mode, all the time slots of the channel may be allocated to packet radio service when circuit switched service does not need capacity. In this case, one or several time slots are allocated to circuit switched service when a request for it is received, for example, from a mobile station in call set-up signaling. The base station controller (BSC) interprets the request from call set-up signaling and thereupon deallocates a channel which is in the use of packet radio service and allocates it to circuit switched service. Alternatively, a predetermined minimum number of time slots may be allocated in the basic mode to packet radio service, in which case more time slots will be allocated to packet radio traffic when it increases. When the number of time slots used for packet radio service is increased, the same number of time slots must be deallocated from circuit switched service in the same channel.
In a preferred embodiment of the invention, a certain minimum number of time slots are allocated in the basic mode to packet radio service, this minimum number being controlled on the basis of economic factors important for the traffic and/or the operator. The control can be coupled to the results of traffic measurement at the base transceiver station so that the control will be automatic. Alternatively, the operator may effect the control manually, and it may be based on historical information on traffic, etc.
In sparsely populated areas, or when the packet radio traffic of a TDMA cell is known to be very scanty or incidental, all of the time slots of the channel serving this cell may be allocated to circuit switched service. When an incidental need for packet radio traffic arises, information regarding this is transmitted to the base transceiver station, for example via the message channel of circuit switched service or via some other signaling channel, traffic channel or short-message output. For the purpose, also a specific message may be defined which the mobile station requesting the service will transmit to the base transceiver station. Preferably, however, existing messages are used for the request, for example a part of a call set-up message minimally modified, in which case also old services will function.
According to a preferred embodiment, more time slots for a service may be allocated in the same frequency band so that the maximum number of time slots allocated to the service will be equal to the number of time slots in the band. Alternatively, time slots may be additionally allocated to a service also in another channel.
The object is thus a method which is used in determining the number of time slots in use, on the one hand, for packet radio service and, on the other hand, for circuit switched service. The same mechanism can be used in parallel for FDMA bands and, on the other hand, also for only one frequency band. In downlink packet radio control channels, the radio channels allocated to packet switched use must be flagged very often in order to keep the mobile stations informed of the channels currently in force.
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Hamalainen Jari
Jokinen Harri
Posti Harri
Nokia Mobile Phones Limited
Perman & Green LLP
Phan M.
Vu Huy D.
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