Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1997-01-13
2001-05-29
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
Frequency hopping
Reexamination Certificate
active
06240125
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of radio communications and then particularly to frequency hopping and hop between time-divided channels in a mobile telecommunications system. The invention includes a method in which hopsequence for hops between channels are established for different connections, thereby enhancing channel utilization. Channel interference is used to construct the hopsequences. The invention also relates to an arrangement for carrying out the method.
TECHNICAL FIELD
Frequency hopping in radio communications systems is known to the art and, for instance, has been used in military contexts to escape tapping of transmissions. In this regard, communication is effected with hops between different frequencies at regular time intervals. The hopsequences are formed by pseudo-slump series that are known only to the transmitter and receiver.
In addition to hops between different frequencies, frequency hopping also refers to hops between different frequency/time slot combinations in a TDMA system. This latter should actually be named frequency/time slot combination hopping, but the collective term channel hopping is used in the following for practical convenience.
Channel hopping has also been used in radio communications systems for the purpose of reducing disturbances. The advantage afforded in this regard is that the energy in the system is distributed between the different channels. In this regard, a number of channels are allocated to one and the same connection. As communication proceeds, the system causes the connections to hop between the channels in accordance with a given hop rule, for instance through the medium of a predetermined pseudo-slump series. When using a purely frequency hopping procedure, the disturbances are spread in the system because the centre frequency at which transmission takes place is changed on a number of occasions with each second. However, the level of disturbance in a radio communications system becomes higher when this type of frequency hop is used than when using a purely frequency schedule. This is because when frequency hopping, the frequencies are not chosen in a relevant manner, but are instead chosen randomly.
U.S. Pat. No. 4,716,573 teaches a frequency hopping system in which the frequency hop is determined with the aid of random number generation. Different frequencies have different measured status values which decide whether or not a pseudo-randomly selected frequency shall be included in the hopsequence.
The German published specification DE 3415032 A1 teaches a frequency hopping system in which frequency hopping is effected pseudo-randomly. The frequencies used are monitored and excluded from further use when they no longer have an acceptable interference level.
U.S. Pat. No. 4,998,290 describes a radio communications system which utilizes frequency hopping. The system includes a central control station which allocates frequencies for communication with several participating local radio stations. The control station maintains an interference matrix which reflects the capacity requirement of the various radio stations and the interference on all connections.
U.K. Patent Application GB 2,261,141 A teaches a method which utilizes frequency hopping in a radio communications system. The method involves monitoring the channels included in the hop sequence and replacing with new channels those channels that do not fulfil a quality criterion.
A general problem related to mobile telecommunications systems is that allocation of the bidirectional connections between base stations and mobile stations is effected without adequate channel selection. Attention is paid only to a few parameters, for instance only to the C/I value when deciding whether or not the connection is satisfactory. This has caused the system to allocate a channel which has good quality properties to a connection. The connection continues to use the allocated channel over the entire communication period, without taking into account the consequences of the allocation, for instance its disturbing influence on other connections or to uneven distribution of radio resources between different base stations. This has stopped the optimization of mobile telecommunications systems, for instance with regard to radio resources and with regard to disturbance effects on other connections. Examples of radio communications systems in which the aforesaid problem occurs are mobile telecommunications systems which use frequency division (FDMA), time division (TDMA), coding (CDMA) and so-called DECT systems.
SUMMARY OF THE INVENTION
The invention is concerned with improving radio communications systems which utilize channel hopping, and solves the problem of selecting the radiochannels between which the connection hops in a relevant fashion.
An object of the present invention is to provide a radio communications system which utilizes channel hopping such that those channels which have high channel quality for a given connection are used more often than channels having lower channel quality for the same connection. Interference is a measurement of channel quality. According to the invention, other channel quality measurements may also be used, for instance the bit error rate, BER, or the quotient between useful and disturbing signal strengths, the so-called C/I value.
Another object of the invention is to optimize channel utilization in a radio communications system that uses frequency hopping.
Still a further object of the invention is to enable a radiochannel that has very high channel quality to be used for several connections in progress. Still another object is to enable a radiochannel that has very low channel quality to be used occasionally in the connections in progress.
Yet still another object of the invention is to provide orthogonality in a base station of a radio communications system. This means that two or more separate connections in one and the same base station will never use one and the same radio channels simultaneously.
Another object of the invention is to make new radio channels available to a connection in the process of communication, thereby improving connection quality, and to make other radio channels whose quality is too low unavailable.
These objects are achieved with a method in which separate radio channels are allocated separate weight values in accordance with the respective measured channel qualities of the channels. Separate hopsequences are then formed for separate connections in accordance with the weight values allotted. The weight values are used to decide which channels shall be included in the hopsequences, and how often they shall appear. The connections then hop between the channels in accordance with the respective hopsequences formed. The invention also relates to an arrangement for carrying out the method.
According to the inventive method, the interference or some other quality measurement of the channels in a radio communications system, for instance a mobile telecommunications system, is measured for separate connections between at least one first base station and a plurality of mobile stations. The connections are generally bidirectional, having an uplink from a mobile station to a base station and a downlink from the base station to the mobile station. Channel quality, for instance interference, is measured with respect to uplink connections and with respect to downlink connections. The measured interference values are then stored in an interference list for each of the connections in the radio communications system. Downlink interference is measured in respective mobile stations, while uplink interference is measured in the base station. The downlink interference values are sent to the base station, via a control channel.
The interference lists are converted to corresponding weight lists for each of the connections in both uplink and downlink in the base station. The weight lists are preferably normalized so that the sum of all weights in a weight list for one connection will equal the value 1 (one). The we
Almgren Knut Magnus
Andersson Claes Håkan
Burns Doane Swecker & Mathis L.L.P.
Chin Stephen
Liu Shuwang
Telefonaktiebolaget LM Ericsson (publ)
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