MXPA96006519A - Intracellular control with antennas direct - Google Patents

Abstract

The present invention relates to an intracellular control method in a cellular communication system having adaptive antenna arrangements, comprising the steps of: measuring spatial information within a sector with an array of antennas, determining whether an intracellular control is desirable for a mobile station, based on the measured spatial information, control the mobile station from a first channel to a second channel, within the same sector, when desired and compute spatial filters in transceivers for the mobile station and other mobile stations operating in the first and second channels, based on the spatial information media

Description

INTRACELLULAR CONTROL WITH DIRECTIONAL ANTENNAS Field of the Invention The present invention relates to an intracellular control method for use in a cellular communications system and, more particularly, to an intracellular control method which uses spatial information from a directional antenna. Background of the Invention Current digital cellular systems employ base stations, which distinguish between different mobile stations using frequency orthogonality and time. The signals from a mobile station are propagated to the base station. The signals are received in a single antenna or, sometimes, two antennas, to gain diversity of effects. The receiver processes the signal using the frequency orthogonality and the time to separate signals from different users. The control between channels within a base station, the intracellular control, is based on quality measurements from the mobile station and the base station. Intracellular control is used, for example, to avoid channels with strong interference. The allocation of channels, that is, the selection of the new channel, is done, in most cases, according to a frequency plan. The adapted allocation of channel, that is to say the assignment of a mobile station to a channel, based on the measured quality information, has been proposed by the developed TDMA systems and is used in the digital, wireless DECT system. Space filters are known in the art and are used to create spatial selectivity, that is, to reject interferences from certain directions and amplify desired signals from other directions. A spatial filter can be realized with, for example, a passive circuit with a radio frequency, a set of phase shifters of analog signals or by a signal process in a basic band. The term spatial information is used to denote information about how a spatial filter can process signals. Spatial information can, for example, consist of spatial filters that, in some sense, are optimal for processing signals from mobile stations. The spatial information may also consist of the direction of arrival of the power from the mobile stations. It is convenient to improve the spectral efficiency of such systems. One way to improve the spectral efficiency of the system is to use directional antennas, for example, to use a number of spatially separated antenna elements. It is then possible to distinguish between spatially separated users, using narrow lobes of adapted antennas.

This can be seen as a way to use orthogonality in the spatial dimension. Current digital cellular systems employ base stations, which use antennas with wide antenna lobes of approximately 120 or 360 degrees. The base station receives / transmits for all mobile stations within the lobe. Thus it is not necessary to know the position of the mobile station. On the other hand, it is not possible to suppress mobile stations that transmit from other angles. Thus there is no spatial information to be taken into account and control has to be done without such spatial information. A system using an adapted directional antenna can use a narrow antenna lobe to receive / transmit the desired signals and suppress unwanted signals. This adds a new dimension to control strategies, since spatial information can be used to adapt mobile stations into an appropriate channel.

It is necessary to take into account the spatial disturbance situation when assigning channels, in order to increase the spectral efficiency and avoid an excessive number of controls. A mobile station must "adjust" a channel in the sense that it is not unduly disturbed by the mobile stations already present in the channel in the cells of its own or of a joint channel. At the same time, it is important to choose a channel where the new mobile station does not disturb the mobile station that already uses the channel. It is also important that the characteristics of the transceiver for mobile stations in its own cell must sometimes be modified, as a new mobile station is assigned to the channel. The new mobile station may otherwise greatly disturb the other mobile station and cause lost cells or poor quality. Thus, there is new information that must be taken into account in order to carry out a correct control. In addition, the power levels in the system must also be adjusted so that the power levels of the base station (reception / transmission) are approximately equal to all mobile stations. A too large power difference, in practice, would destroy spatial orthogonality and create problems very similar to the "near-far" problem that occurs in CDMA systems.

In systems using an adapted directional antenna, both transmission and reception are adapted for the base station arrangement, which implies that the addition of a new mobile station can modify the antenna patterns of both transmission and reception for the base stations surrounding. Another difference is the fact that multiple users on a channel at the base station, using an adapted directional antenna, are not automatically orthogonal. Spatial orthogonality is something that should be created with a spatial filter adapted and with the appropriate location of the channel. SUMMARY OF THE INVENTION The present invention describes an intracellular control method, which extends the known control algorithms, using the spatial information from a directional antenna. In addition, the present invention provides a solution for the allocation of a decentralized adapted channel, where each base station assigns mobile stations to suitable channels, taking into account the interference situation. Also, the present invention describes a method for modifying the transceiver of the array, that is, a method for linking a mobile station to a channel already used, when a new mobile station is introduced. The present invention has at least three major advantages over the prior art. First, the capacity of the cellular system is increased, since the mobile stations are distributed in an appropriate manner between the channels. Second, the signaling of the network is minimized, since the solution of the invention is off center for each base station. Finally, all the transceivers using a channel are modified directly, in order to take the new disturbance situation into account. As a result, the quality for the old stations Mobile phones are not degraded when a new mobile station is introduced. According to one embodiment of the present invention, a decision as to whether an intracellular control should be made, is based on conventional information and / or a prediction of the increased spatial disturbance. If it is determined that the power level deviates too much from a nominal value, an intracellular control is performed, in which the mobile station is transferred to a channel, where it does not unduly disturb other connections. However, for all channels, where the quality is above a predetermined level, a relative uplink disturbance in the new mobile station is calculated from the measurements. Then, a relative uplink disturbance in the mobile stations that are already present in the channel from the new mobile station are calculated using the measurements. The downlink disturbance from the transfer measurements, assisted by the mobile station, is then calculated to check the existing downlinks. The best channel is then selected taking into account the conventional intracellular control information, together with the previously calculated information. Finally, all the transceivers that use the selected channel and the old channel are modified, according to the new disturbance situation.

Detailed Description of the Drawings The present invention will now be described in more detail with reference to the preferred embodiments of the invention, given only by way of example, and illustrated in the accompanying drawings, in which: Figure 1 illustrates a careful control decision , according to one embodiment of the present invention; Figure 2 illustrates a channel assignment, according to one embodiment of the present invention; and Figure 3 illustrates a channel link according to an embodiment of the present invention. Detailed Description of the Invention The present invention describes an intracellular control method, which can be divided into three main stages: ICHO decision; Channel assignment and channel link. In brief, the ICHO decision stage determines if an intracellular control is necessary. When a control is necessary, the channel allocation stage determines an appropriate channel for the mobile station. After the mobile station has been transferred to the new channel, the transceivers of the mobile stations, which are currently using the channel, are modified in the link stage of the channel, in order to take into account the new interference situation. The present invention can be combined with, for example, a conventional fixed frequency plan, a slow adaptive channel assignment or a random frequency jump. Each individual stage will be described in more detail below. The present invention describes several ways to increase capacity. The first way, which is more conventional, is to use the directional antenna to reduce the crowding size, ie the distance of frequency reuse. This implies that there is only one mobile station per channel in a cell and that the interference originates from the users in other cells. The second way is to allow multiple users on a channel where the directional antenna is used to orthogonalize users. The interference will then originate from the joint channel mobile stations within the cell and from other cells. The present invention also covers the ICHO decision in cases where combinations of the techniques are used. the ICHO decision can, for example, be made with known techniques based on scalar quality measurements, from the mobile station and the base station. An example of a known technique is described in the ETSI / GSM specification 05.08. Additionally, the algorithm can use a careful strategy where spatial information is used, to predict a deterioration in transmission quality. For example, it is possible to detect that two mobile stations MSI and MS2 move close to each other, as illustrated in Figure 1. Mobile stations can be connected to the same cell or can be connected to different cells. This detection is given directly from the spatial characteristics, ie the direction of arrival, spatial filters, of the mobile stations. For example, the algorithm may follow the angle from which the signal arrives and detects that an angle difference between the mobile stations is too small. As a result, an ICHO decision can be made to move any of the mobile stations MSI and MS2 to another channel. An ICHO decision can be made in order to free a broad lobe channel from a user, which can be processed in a narrow lobe channel. In GSM-type systems, for example, the BCCH bearer must be distributed over all the cells in a wide antenna lobe and thus the BCCH bearer is a wide lobe channel. A mobile station using the traffic slots of the BCCH carrier can then be moved to an ordinary carrier, where the downlink can be transmitted in a narrow antenna lobe, and thus the narrow-lobe channel notation. The ICHO decision can thus reduce the level of interference in the system. An ICHO decision can thus imply that the mobile station is linked to a channel together with the other mobile stations. The power of the mobile stations currently operating in the channel, ie the old mobile stations, should not be driving the signal from the new mobile stations and it is necessary for the mobile station to regulate its uplink power to a nominal value. The downlink power of the base station is set analogously to a nominal value. The channel assignment, ie the selection of an appropriate new channel, can then be done as follows. First, the uplink power level of the mobile station is checked. If the power level of a mobile station is diverted by at least a predetermined amount from a nominal value, the mobile station is labeled as "MS with extreme power level" and is maintained in a wide-lobed channel for the current time. The channel assignment must also take into account the stability of the spatial information, a mobile station that has time variations in the measured spatial information, can be maintained in a wide-lobed channel or generally treated with care in order to reduce the interference levels. The uplink characteristics can be measured by the base station. For each channel, the disturbance power that will affect the receiver of the base station for the new mobile station, caused by the disturbances existing in the channel, can be measured. This disturbance power is then compared with the power and loss of path of the new mobile station to form a signal-interference relationship. This amount is denoted as aj, where j is the channel number. Mobile stations connected to other base stations act as uplink disturbances and thus will affect a. For each channel, the power of the alteration that will affect the receivers of the base station for the old mobile stations, caused by the disturbance of the new mobile station, is measured. This disturbance power is compared to the power and path loss of the old mobile stations to form a signal-to-interference ratio for each old mobile station. This amount is denoted by Bij, where j is the channel number and i 'is the number of the mobile station. The downlink characteristics can not be measured at the base station. The algorithm must thus use measurements from the mobile station, such as the Mobile Assisted Handover measurements (Control Assisted by the Mobile Station). However, the disturbance situation is reciprocal in the sense that the channel where the uplink transmissions do not interfere in the base station is a channel where the downlink transmission from the base station to a mobile station will not disturb the other mobile stations significantly. In other words, a base station will see the mobile station as a station disturbing This fact is used in channel allocation and in the link to optimize performance and quality. The mobile stations will also see other base stations that the first base station can not take into account. The signals from these other base stations, on the other hand, will usually be weaker than the signal from the first base station. This implies that the parameters aj and ^ ij can be used to capture an appropriate channel. This should also be combined with the conventional channel assignment information, such as the interference measurements of the mobile station. The parameters aj and 6j will be calculated in the following. Figure 2 illustrates an example of channel allocation, according to an embodiment of the present invention. In Figure 2, a cell flange 50 separates two cells, 52 and 54. Each cell has a base station BS1 and BS2, respectively, which have directional antennas. In this example, a first mobile station MSI has service of the base station BS1 and can be assigned to an arbitrary channel Cl. In addition, a second mobile station MS2 has service of the base station BS1 and can be assigned to the same channel Cl, since that the directional antenna can make the orthogonal mobile stations in both uplink and downlink. As illustrated, a third mobile station MS3 has a second mobile station MS2 at the same angle of sector, as seen from the second base station BS2. As a result, the second base station BS2 will see the second mobile station MS2 as a disturbance in the channel Cl and thus assign to the third base station MS3 a different channel, such as C2. In this example, a fourth mobile station MS4 will act as an uplink disturbance for the first mobile station MSI in the uplink to the first base station BS1. When the fourth mobile station MS4 performs downlink measurements, the mobile station will determine that the Cl channel is disturbed by the first base station BS1. The fourth mobile station reports the measurements to the second base station-BS2, which will assign the fourth mobile station to a different channel of Cl. However, if the fourth mobile station MS4 is not able to make sufficient MAHO measurements, the second base station you can assign the fourth mobile station to a channel based only on the uplink measurements. As a result, the mobile station MS4 can be assigned to the Cl channel. The first base station BS1 will then detect a new disturber for the first mobile station in the Cl channel. As a result, the first mobile station MSI must then be reassigned to another channel by the first base station BS1, if the interference caused by the fourth mobile station is too high.

The present invention may also use a stopping criterion, which indicates whether a channel is densely loaded, since the mobile station will not be aggregated if any of the users in the channel are too narrow to a quality limit, indicating a possible transfer. The channel link, the link of the new mobile station to the channel, can be realized as follows. It is necessary to modify the transceivers for the old mobile stations using the selected channel and the transceiver operative for the new mobile station will be introduced in the selected channel. The spatial filters used in the receivers and transmitters in the base station array are calculated with an information containing an address vector around the desired signal and using the information about the disturbance situation in the channel. As a new mobile station enters the channel, the disturbance situation is changed and all spatial filters can be recalculated to take into account the new information. Transceivers for mobile stations in the old channel must be modified as the disturber is removed. Figure 3 illustrates an example of the channel linker, according to one embodiment of the present invention. In this example, the mobile station MSI uses the Cl channel when the mobile station MS2 is assigned to the channel Cl. The spatial filters in the transceivers for the mobile stations MSl and HS2 must then be adapted so that they are spatially orthogonal. In other words, the spatial filter for the mobile station MSl must override the mobile station MS2 and vice versa. The present invention performs this override in an instantaneous step without executing measurements. When the mobile station MS3 begins to use the channel, the mobile station MS3 will be measured and viewed as a new disturber of the base station BS1. However, the cancellation of the mobile station MS3 can be performed based on the spatial interference measurements. According to one embodiment of the present invention, a single channel assignment method can be used. In this method, the mobile station can be classified into used power classes and space sectors. For example, mobile stations with approximately equal power levels and well separated spatial filters can share the same channel. According to another embodiment of the present invention, a single algorithm using fixed filters can be used to allocate the channel. In this example, suppose that a number of filters with filiform beams have been previously calculated and stored. For example the filters afGjJ, a (02), · · ·, 01 (625), can be used with filiform beams in the addresses of -600, -55a, ... (60fi The filter can, for example, be a Hamming window, multiplied with the direction vector of the desired direction, each filter is designated by the direction of its beam filiform, your arrival address (DOA) You can find an appropriate channel as follows: A DOA is considered as used by the mobile station if this DOA itself or one of its two closest neighbors has been used successfully during the last ten bursts All channels where the quality is good enough are scanned to find a channel where the DOAs used by the new mobile station are not disturbed by the mobile stations in other celas or used by the mobile stations in the cells themselves Typically, a DOA it is considered as disturbed if the filter output power is above a fraction of the nominal power level.The DOAs for the chosen channel are then occupied by the new mobile station and they link the mobile station to the channel. The spatial transceiver for the new mobile station is simply the set of filters that are used. Thus, there is no need to modify the transmitters-receivers of the mobile station in the channel. According to one embodiment of the present invention, an algorithm can be used for the channel assignment. The mobile station that will be reassigned can be characterized by a spatial filter matrix W, an R matrix of covariance and a power P. The accessible channels J are characterized by their spatial filter matrices, W ^ ji = 1, ... Mj, where Mj is the number of mobile stations in channel j, by their covariance matrices, Tj and by the power of mobile stations P¿j. The expected power of the disturbance in the new mobile station in relation to its useful power is daí trace - T- * ~ The disturbance power expected in the number i of the old mobile station, which uses channel j of the new mfiv station. ' ' is: 'i. and d * J trace [wi - > wi, j 3 A selection is then capture channel J0 where Jo '* H.j) Another solution is to measure the maximum disturbance that will affect any of the old mobile stations and allow Jg - arg min. { aj + n &xfiij) I You should also use the conventional scalar information. For example, a heavily disturbed channel should not be loaded further, according to the detention criteria, mentioned previously. According to one embodiment of the present invention, an advanced algorithm for the channel link can be used. This example shows how the spatial filters for the mobile stations currently using the JD channel and for the new mobile station can be modified. The spatial filter matrices for the mobiles M using the channel are denoted by Wj_, WM and the new mobile station is denoted WM + 1. First the average cross-correlation for the existing mobile stations is calculated, in which for notational simplicity the correlation matrix of the JQ channel is denoted by R0ld '* «f (¿) | * oIerW¿ 1 - 1 The average cross-correlation for the new mobile station, with an associated correlation matrix, denoted R, is & xá (M + 1) - The correlation matrix for the channel after the addition of the new mobile station can be approximately A.w - hear * * It is then possible to calculate new spatial filters as "i - * a" < «i i" 1,. ·., * + 1 I The previous treatment has involved a single Rj per channel, but it is directly to incorporate a dependency in the sample phase. While a particular embodiment of the present invention has been described and illustrated, it should be understood that the present invention is not limited thereto, since modifications can be made by persons skilled in the art. The present application considers any and all modifications that are within the spirit and scope of the preceding invention, herein described and claimed.

Claims (15)

1. REIVTNPICTICIDES 1. An intracellular control in a cellular communications system, which has adapted directional antennas, this method includes the steps of: measuring the spatial information with a directional antenna; determining whether an intracellular control is convenient for the mobile station, based on the measured spatial information; and controlling the mobile station from a first channel to a second channel, when convenient.
2. 2. An intracellular control method, according to claim 1, wherein the measured spatial information is used to forecast an interference situation that would result from various channel location decisions.
3. 3. An intracellular control method, according to claim 1, wherein the measured spatial information is used to modify the transceivers for the mobile station and other mobile stations operating in the first and second channels.
4. 4. An intracellular control method, according to claim 1, wherein the measured spatial information is used to modify the transceivers of the mobile stations using the first channel.
5. 5. An intracellular control method, according to claim 2, further comprising the steps of: measuring the power level of the mobile station; and assigning a channel to the mobile station, based on the measured power level and the measured spatial information.
6. 6. An intracellular control method according to claim 2, further comprising the step of: calculating the relative uplink interference in the mobile station.
7. 7. An intracellular control method according to claim 6, further comprising the step of: calculating the relative uplink interference in other mobile stations, caused by the first mobile station.
8. 8. An intracellular control method according to claim 2, further comprising the step of: calculating the downlink disturbance to check the existing downlinks.
9. 9. An intracellular control method, according to claim 7, further comprising the step of: calculating the downlink disturbance to check the existing downlinks.
10. 10. An intracellular control method, according to claim 2, wherein the second channel is selected using the calculated information.
11. 11. An intracellular control method, in a cellular communications system, having adapted directional antennas, this method comprises the steps of: determining if an intracellular control is necessary; measure the power level of the mobile station, which needs to be transferred; assigning to the mobile station a channel based on the level of the measured power; calculating the relative disturbance of the uplink in the mobile station; calculating the relative uplink disturbance in other mobile stations, from the first mobile station; calculate the downlink disturbance, to check the existence of downlinks; select the best channel, using the calculated information; modify the spatial filters of all the transceivers, using the selected channel and the old channel, according to the new disturbance situation.
12. 12. An intracellular control method, according to claim 11, wherein the downlink disturbance is calculated using the measurements from the mobile station.
13. 13. An intracellular control method, according to claim 11, wherein the scalar quality measurements are used when determining whether control is necessary.
14. 14. An intracellular control method, according to claim 11, wherein a control is carried out when two mobile stations, using the same channel, move too close together.
15. 15. An intracellular control method, according to claim 11, wherein the uplink disturbance in the base station is measured. REBDHEK OF INVENTION An intracellular control method is disclosed in a cellular communications system, which uses spatial information from a directional antenna. This spatial information is measured with the directional antenna. Then a determination is made as to whether an intracellular control from a mobile station is convenient, based on the measured spatial information. The mobile station is then controlled from a first channel to a second channel, when convenient.