Communications: directive radio wave systems and devices (e.g. – Directive – Including directive communication system
Reexamination Certificate
2001-04-20
2002-05-21
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including directive communication system
C455S025000, C455S517000, C455S562100
Reexamination Certificate
active
06392595
ABSTRACT:
The present invention relates to a method and apparatus for directional radio communication in which signals between a first station and a second station may be transmitted only in certain directions. In particular, but not exclusively, the present invention is applicable to cellular communication networks using an antenna array in an adaptive manner, for example space division multiple access (SDMA).
With currently implemented cellular communication networks, a base transceiver station (BTS) is provided which transmits signals intended for a given mobile station (MS), which may be a mobile telephone, throughout a cell or cell sector served by a base transceiver station. However, space division multiple access (SDMA) systems have now been proposed. In a space division multiple access system, the base transceiver station will not transmit signals intended for a given mobile station throughout the cell or cell sector but will only transmit the signal in the beam direction in which a signal from the mobile station is received so that the same frequency can be used in the same cell at the same time to support two different users. SDMA systems may also permit the base transceiver station to determine the direction from which signals from the mobile station are received.
One problem is that the direction in which a signal is to be transmitted by the base station to the mobile station is determined on the basis of the signals received by the base station from the mobile station. However, in a frequency division duplex mode of operation, the frequencies of signals transmitted from the base station to the base station are quite different from frequencies used for the signals transmitted by the base station to the mobile station. The difference in the frequencies used in the up and down link signals means that the behaviour of the channel in the up link direction may be different from the behaviour of the channel in the down link channel.
In a time division duplex mode, the frequency used in the up and down link channels may be the same. It should be noted that in the time division duplex mode, signals will not be transmitted at the same time in that the up and down link channels. It can be assumed that the characteristics of the up and down link channels are the same provided that the duplexing time is much shorter than the coherence time of the channel. The coherence time of the channel is the interval over which a transmitted symbol will be relatively undisturbed by channel fluctuations. Channel fluctuations may be caused by changes in the radio environment, for example caused by movement of the mobile station. Accordingly, for the assumption that the up and down link channels are the same to be valid, a signal should be sent on the down link channel within a time period from receipt of the up link signal which is less than the coherence time for the channel. If a mobile station is moving, it is less likely than if the mobile station is stationary that the signal to be transmitted in the down link direction will be transmitted within a time period which is legs than the coherence time. Even if the mobile station is not moving the time between the receipt and transmission of a signal may be greater than the coherence time.
The spatial characteristics of an up link or a down link channel, such as its impulse response, will vary greatly in dependence on the radio environment.
In one known system which attempts to deal with this problem is shown in
FIG. 1
, the radio environment is divided into macro cells A, micro cells B and/or pico cells C. Macro cells A are relatively large whilst micro and pico cells B and C are much smaller. Pico cells C are smaller than micro cells B. Micro and/or pico cells B and C can be contained in macro cells A, as shown in FIG.
1
. It is assumed that the radio signal will behave quite differently in macro cells A as compared to micro or pico cells B and C. Thus, this allows different types of strategy to be used in determining the parameters of the signal to be transmitted in the down link direction. However, with this system, the behaviour of the signals in the macro and micro or pico cells can be misleading. For example, the signal of a mobile station which is operating close to a base station in a macro cell A can be received by the base station with a wide angular spread. This type of behaviour is typical of micro or pica cells. Street channelling, which is caused by the presence of buildings, results in a signal being received with a narrow angular spread. If this type of behaviour occurs in a micro or pico cell, the base station will receive the signal with a narrow angular spread. This behaviour is more typical of macro cells. This model therefore does not always reflect the actual radio environment in a macro, micro or pica cell. Rather, the model relies on the expected radio environment given the position of the mobile station relative to the base transceiver station. Accordingly, this model will sometimes result in poor quality of signals.
It is an aim of certain embodiments of the present invention to provide a method and apparatus which avoids or at least mitigates this problem.
According to one aspect of the present invention, there is provided a method of directional radio communication between a first station and a second station, comprising the steps of determining from at least one signal received at the first station from the second station which of a plurality of different radio environment types is present between said first and second stations; and transmitting a signal from the first station to the second station, at least one parameter of said transmitted signal being dependent on the determined radio environment type.
As the radio environment type is determined in accordance with the at least one signal which is received, it reflects the actual radio environment and not the expected radio environment. Thus, the signal transmitted by the first station can better take into account the actual radio environment than with the system described hereinbefore.
Preferably, the radio environment types are determined from the angular spread of the signal received by the first station from the second station. This is a useful parameter of the received signal to use when determining the radio environment type in a directional radio system.
Preferably, a first radio environment type is determined to as be present when the at least one signal received by the first station from the second station has a relatively small angular spread and a second radio environment type is determined to be present when at the least one signal received by the first station from the second station has a relatively large angular spread. In embodiments of the present invention, there may be more than two types of radio environment. However, it is preferred that there only be two as this provides good results but is not overly complex.
Preferably, if the first radio environment is determined to be present, then the signal transmitted by the first station is transmitted with a relatively small beam spread and if the second radio environment is determined to be present then the signal is transmitted with a relatively large beam spread. Thus, the signal which is transmitted takes into account the characteristics of the determined radio environment type.
Preferably, the method further comprises the step of, if it is determined that the first radio environment type is present, determining if the beam spread of the signal to be transmitted by the first station is to be increased. Thus the method ensures that a narrow beam is used whenever it is appropriate. However, if there is any other indication that a wider beam spread should be used to avoid loss of communication or poor quality communication, then the beam spread can be increased.
The determining if the beam spread is to be increased step may comprise considering a parameter indicative of the distance between the first and second stations and increasing the beam spread of the signal to be transmitted to the second statio
Katz Marcos
Ylitalo Juha
Altera Law Group LLC
Issing Gregory C.
Nokia Network Oy
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