Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-31
2003-04-01
Appiah, Charles N. (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S524000, C455S525000, C370S332000
Reexamination Certificate
active
06542742
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the problem of cell selection, for e.g. cell handover, in mobile telecommunication systems, and more particularly to the problem of selecting the optimum cell among cells with differing capabilities due to different air interface modes.
RELATED ART
In
FIG. 1
is shown a view of a typical mobile system with many cells and a number of mobile stations (“MS”). Each of these cells has an associated base station (“BS”) which is responsible for radio communication over the air interface to mobile stations in that cell. For a given MS at a given time there is usually one serving cell which is the cell with the base station that the MS is receiving service from so that the MS may receive and transmit communication via the serving base station.
It is characteristic of modern cellular systems that it is possible to switch a call from one base station to another while the mobile station is moving from one cell to another within the mobile communication system. This is termed handover or handoff. In mobile communication systems, the handover process uses measurements made by the mobile station, the serving base station, and/or by surrounding base stations, using these measurements in the handover decision-making process. These measurements can be taken of the quality of the connections, or links, between the MS and the base station or surrounding base stations. “Link quality” measurements include e.g. the raw bit error rate (“BER”) and the received signal strength of the various links between the MS and its serving base station or between the MS and the surrounding base stations.
For example, in the mobile communication system known as GSM (“Global System for Mobile Communications”), a mobile station monitors the link quality (e.g. raw BER estimate and received signal strength) of the signal (downlink signal) received from the base station of the serving cell, as well as the link quality in terms of reception level, i.e. the received signal strength, of the downlink signal from the base stations in cells adjacent to the serving cell. In addition, the base station of the cell monitors the quality of the signal (uplink signal) received to the base station from every mobile station that is served by that base station.
Handover then occurs when either the measurement of the MS/BS indicates that the link quality in the currently serving cell is low and a better quality can be obtained from an adjacent cell, or an adjacent cell allows communication with lower transmission levels.
The problem of handover in today's systems can be summed up by saying that the strategy is to keep the mobile station connected to the “best” cell. The problem of selecting the “best” cell is simple in today's systems compared with the new systems to be developed over the coming years. These future systems will be based on different radio interface modes (e.g. with different coding and modulation schemes).
An example of developments in these future systems is the gradual introduction of several modulation and coding schemes in existing systems like e.g. GSM. Modulation is essentially the function which imposes the characteristics of the electromagnetic field (e.g. amplitude and frequency) onto a set of rules and the data to be transmitted (which “modulates” the transmission). In the case of today's GSM it is the phase of the electromagnetic field which carries the information. It is usual to distinguish the modulation and demodulation on one hand, and the transmission and reception on the other. The first processes transform digital data to and from a low frequency modulated signal, and the second pair of processes transform this low frequency modulated signal to and from the electromagnetic field.
In current GSM systems the modulation method used is Gaussian Minimum Shift Keying (“GMSK”). GMSK provides a compromise between a fairly high spectrum efficiency and a reasonable demodulation complexity. In IS-136 today, the modulation scheme is &pgr;/4-Shift Differential Quaternary Phase-Shift Keying (DQPSK).
In the evolution of second generation cellular systems like GSM and D-AMPS, proposed changes have been made to the modulation scheme in order to provide higher bit rates within the same spectrum. There are several proposed schemes. One of these is Differentially-encoded Binary Continuous Phase Modulation (“DBCPM”). This is a family of modulation types, one example of which is &pgr;/4-DBCPM, with the advantage of high power amplifier efficiency. Another proposed scheme is Quaternary-Offset-Quadrature Amplitude Modulation (“Q-O-QAM”), also known as Offset-16QAM.
A key difference between these different modulation schemes is that they provide users with different data rates. The goal of the evolution of these systems is to increase user bit rate. The result is that the systems will be using different modulation schemes, often in neighboring cells, in order to provide different users more options for which data rate they will use. In addition, differing data rates will often require differing channel coding schemes. Also, several coding schemes may be used for one modulation. As a result, there will be a variety of coding and modulation schemes providing different data rates.
Current handover algorithms set up that link between base station and mobile station which provides the highest link quality. There do exist, though, numerous variations of this base scheme where additional criteria are used, like vehicle speed, as illustrated in WO-9702716 “Method for Determining Handover in a Multicellular Communications System”, or interference in other cells, as illustrated in WO-9528808 “Handover Method and Arrangement”. However, none of the existing methods address the problem which will exist in evolved cellular systems, e.g. the problem of selecting the best cell for handover between cells with different air interface modes (e.g. with different modulation and coding schemes).
SUMMARY OF THE INVENTION
The present invention relates generally to the problem of cell selection, for e.g. cell handover, in mobile telecommunication systems, and more particularly to the problems discussed above. The means of solving these problems according to the present invention are summarized in the following.
As has been seen above, there is a current problem because current handover methods don't consider the capabilities of different cells in terms of different air interface modes when deciding which cell to handover to. It should also be pointed out that the general problems of selecting the best cell during handover apply also to other situations where cell selection occur, e.g. during call set-up or when the mobile stations continuously select cells during idle mode.
In current mobile communications systems this cell selection is not a problem because current systems typically use only one modulation scheme and one coding scheme in addition to typically using only one carrier and slot. In comparison, new systems are being proposed and developed, e.g. evolutions of GSM. In these evolved systems there will simultaneously exist different systems and different cells, each with different modulation and/or coding schemes to provide different data rates to different users. Present cell selection methods are not optimally designed to select the “best” cell for handover in these evolved systems.
Accordingly, it is one object of the present invention to provide a method of selecting the best cell from the user's point of view, i.e. in terms of maximizing the Quality of Service (“QoS”). The maximum QoS can be given in terms of e.g. higher data/bit rate or throughput. This new method of selecting the best cell is done by extending the known algorithm for cell selection and handover, and then applying additional criteria that take into account the capabilities of mobile station and the base stations that are possible candidates. Preferably, achievable data rate (for “transparent” services) or throughput (for “non-transparent” services) is predicted for the differen
Müller Frank
Olofsson Håkan Gunnar
Schramm Peter
Appiah Charles N.
Telefonaktiebolaget LM Ericsson (publ)
LandOfFree
Cell selection in mobile radio systems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cell selection in mobile radio systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cell selection in mobile radio systems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3047802