HK1065912B

HK1065912B - A method for providing a communication channel in time division duplexing (tdd) mode between a tdd mobile and a tdd base station

Info

Publication number: HK1065912B
Application number: HK04108593.0A
Authority: HK
Inventors: 卢斯．洛佩斯
Original assignee: Motorola Mobility, Inc.
Priority date: 2001-06-15
Filing date: 2002-03-18
Publication date: 2006-02-17

Description

Method for providing communication channel in time division duplex mode between TDD mobile and TDD base station

Technical Field

The present invention relates to a method of providing a communication channel in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station, and more particularly, but not exclusively, to reducing interference to communications in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station from a mobile operating in Frequency Division Duplex (FDD) mode that is located in the vicinity of the TDD base station.

Background

In a Universal Mobile Telecommunications System (UMTS), such as a cellular telephone, communication between a mobile station and a base station requires both an uplink channel (from the mobile station to the base station) and a downlink channel (from the base station to the mobile station). It is useful to provide the channel as a Time Division Duplex (TDD) or frequency division duplex system. Typically, different operators (operators) within the same coverage area will have one or two systems available to their customers.

In TDD, a particular frequency channel is divided into time frames, each frame being in turn divided into a number of time slots. Some of the time slots in each frame are designated as uplink and some are designated as downlink, and a particular mobile station is assigned a particular uplink and downlink time slot for a particular communication session. Of course, typically different operators will have different frequency channels assigned to them.

In FDD, a number of frequency channels are available for use as communication channels, and for a particular communication session with a mobile station, the operator will allocate one frequency channel as an uplink channel and one frequency channel as a downlink channel. Those special frequency channels then remain available to the mobile station throughout the communication session.

When a mobile station operating in FDD mode moves around a particular base station coverage area, it is controlled to increase or decrease its transmission power depending on how close it is to the base station at any particular time. It can be seen that if the mobile station is relatively far from the base station, its transmission power will be high. If the mobile station is close to a base station operating in TDD mode, any frequency channel available for TDD communication that is close to the FDD uplink channel on which the mobile is communicating will have interference from the FDD mobile due to power leakage from adjacent frequency channels to the FDD uplink channel. Such leakage may desensitize the TDD base station by causing it to desensitize its reception in TDD frequency channels adjacent to FDD uplink channels, whereby it may no longer adequately receive TDD uplink communications in those frequency channels.

This problem may occur even when the FDD mobile is close to the FDD base station if co-located or located near the TDD base station and the FDD uplink channel has a wide transmission spectrum. One way to overcome this problem is to use a very steep (sharp) RF filter to eliminate or reduce any overlap from the FDD uplink channel to the adjacent channel, but such a filter is very expensive.

Disclosure of Invention

Accordingly, the present invention seeks to provide a method for providing a communication channel in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station that will overcome or at least reduce the above-mentioned problems of the prior art.

Accordingly, in a first aspect, the present invention provides a method for providing a communication channel in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station, the method comprising the steps of:

designating a plurality of frequency channels available for TDD communications, each frequency channel having a plurality of uplink time slots and a plurality of downlink time slots defined in a frame;

assigning an uplink channel for a communication session between a TDD mobile and a TDD base station as a series of uplink timeslots, one uplink timeslot being assigned for each frame during the communication session;

assigning a downlink channel for a communication session between a TDD mobile and a TDD base station as a series of downlink time slots, one downlink time slot for each frame during the communication session;

the TDD base station determines which uplink and downlink channels are available at the beginning of a communication session; and

a TDD base station transmits to a TDD mobile at the beginning of a communication session which uplink and downlink channels are allocable for the communication session;

wherein the time slots forming the uplink and downlink channels are assigned on different frequency channels in different frames.

According to a second aspect, the present invention provides a method for reducing interference to communications in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station, the method comprising the steps of:

designating a plurality of frequency channels available for TDD communication, each frequency channel having a plurality of uplink time slots and a plurality of downlink time slots defined within a frame;

Drawings

An embodiment of the invention will now be described more fully hereinafter by way of example, with reference to the accompanying drawings, in which:

fig. 1 shows a schematic diagram of frequency channel and time slot allocation for FDD and TDD in a known communication system;

fig. 2 shows a schematic diagram of frequency channel and time slot allocation for FDD and TDD channels in a communication system according to an embodiment of the invention;

fig. 3 shows a schematic diagram of a communication system using the frequency channel and time slot assignments of fig. 2.

Detailed Description

Fig. 1 shows a schematic diagram 1 illustrating different frequency channels f and time slots t that may be used for communication. Known communication systems have special frequency channels which are allocated for use as communication channels between base stations of the network and mobile stations using the network. As described above, the network operator typically provides Frequency Division Duplex (FDD) mode or Time Division Duplex (TDD) mode services to the mobile station. Typically, different frequency channels to be used for TDD communication channels are allocated to different operators.

For example, as shown in FIG. 1, frequency channel f₁、f₂、f₃And f₄Assigned for TDD communications, may be assigned to multiple operators. Frequency channel f₆、f₇、f₈、f₉、f₁₀、f₁₁And f₁₂Allocated for FDD communication, frequency channel f₆、f₇And f₈For uplink channels, frequency channels f₁₀、f₁₁And f₁₂For the downlink channel. Frequency channel f₉Providing a guard band between uplink and downlink channels, frequency channel f₅A guard band is provided between the FDD and TDD frequency channels. It will be appreciated that the guard bands need not have the same bandwidth. In fact, in general, the bandwidth of the guard band between the FDD uplink and downlink channels is much larger than the bandwidth of the guard band between the FDD uplink channel and the TDD channel. Thus, for example, frequency channel f₁₀Downlink channel 2, frequency channel f usable by an FDD operator for communication sessions with a particular mobile station₆May similarly be used for a communication session as upstream channel 3. Frequency channel f₇And f₁₁May be similarly used by different mobile stations as the downlink channel 4 and uplink channel 5 for a communication session. Of course, a large number of mobile stations may share the same frequency band well by using different codes (for FDD communication) or different time slots and codes (in TDD communication).

In TDD communications, an operator with a frequency channel may allocate different time slots within frame F to different mobile stations for different communication sessions. Each frame F is typically divided into two parts, one for the uplink channel and one for the downlink channel. E.g. with assigned frequency channel f₄May be operative to transmit a first frame F₁First time slot t in the uplink part of (1)₁Assigned to the first mobile station as a corresponding time slot t in the uplink channel 6, downlink part₆Similarly assigned to the same mobile station as downlink channel 7. Obviously, the second frame F₂Of corresponding time slot t₁₁And t₁₆And in subsequent framesWill be assigned to the same mobile station until the communication session is completed. In fig. 1, a first frame F₁Time slot t in₃And t₈And a second frame F₂Time slot t in₁₃And t₁₈Are allocated to the second mobile station as uplink and downlink channels 8 and 9, respectively, a first frame F₁Time slot t in₄And t₉And a second frame F₂Time slot t in₁₄And t₁₉Are assigned to a third mobile station as uplink and downlink channels 10 and 11, respectively. Similarly, in frequency channel f₃Upper, first frame F₁Time slot t in₃And t₈And a second frame F₂Time slot t in₁₃And t₁₈Is allocated to a fourth mobile station as uplink and downlink channels 12 and 13, respectively, on frequency channel f₂And f₁In the above, the first and fifth and first, fourth and fifth time slots in each portion of each frame are shown as being allocated to different mobile stations as uplink and downlink channels 16, 18, 20, 22 and 17, 19, 21, 23, respectively.

It should be appreciated, of course, that the frequency channel f is not defined as steeply as shown in the figure. Conversely, signals on any particular frequency channel are likely to overlap into one or more adjacent channels, particularly at higher powers, as described above. Therefore, although the guard band f₅And f₉Attempting to provide the necessary division to prevent unwanted overlap, e.g. from frequency channel f₆To the frequency channel f₄(even in the protective tape f₅Above) may also occur, particularly when, for example, the frequency channel f₆The signal above is at a relatively high power because the mobile using the channel is quite far from the FDD base station with which it is communicating, although it may be relatively close to the TDD base station. As mentioned above, in this case, at frequency channel f₄TDD base station communicating on it may be due to the fact that it is from frequency channel f₆The interference on the frequency channel of FDD communication on is relatively insensitive, thereby adversely affecting the quality of TDD communication on the frequency channel. If the frequency channel f₄Has already been used forAn adverse effect on quality may be particularly undesirable for operators that may not have been assigned any or many other frequency channels.

Thus, according to the first embodiment of the present invention, the amount of communication interference in Time Division Duplex (TDD) mode between a TDD mobile and a TDD base station can be reduced by changing at least the frequency channel or preferably also the time slot allocated to a particular TDD communication channel. Therefore, a special frequency channel is not assigned to a special operator for TDD communication, but a frequency channel used by any special operator for TDD communication can be changed from frame to frame. For example, the operator may be assigned to a particular frequency channel that changes order, so that, from a certain reference moment, the frequency channel used may change every frame in a preset order. The time slots within a frame on a frequency channel may remain intact or may also change. Thus, from one frame to the next, no particular communication channel is reserved on the same frequency channel, or on the same time slot within a frame, so that no channel will have persistent interference from FDD or indeed any other interference source, but all communication channels will have interference shared between them.

As shown in fig. 2, the communication system includes an FDD operator 24 coupled to control an FDD base station 25 and an FDD mobile 26 in communication with the FDD base station 25, as indicated by the dashed link 27. The communication system operating in TDD mode has two operators 28 and 29, each controlling three TDD base stations 30, 31, 32 and 33, 34, 35. A first TDD mobile 36 communicates with TDD base station 31, a second TDD mobile 37 communicates with TDD base station 34, and a third TDD mobile 38 communicates with TDD base station 35. As shown, the FDD mobile 26 is closer to the TDD base station 31 than to the FDD base station 25 and causes interference, as shown by its dashed link 39 with the TDD base station 31. As described above, if TDD operator a28 has only one frequency channel allocated, there is little way to mitigate the effect of interference from mobile 26 on communications from TDD mobile 36 to TDD base station 31 on that frequency channel.

However, in this embodiment, the two TDD operators 28 and 29 are connected to a coordinator 40, and the coordinator 40 allocates frequency channels to the operators. As shown in fig. 3, the uplink and downlink channels of each TDD channel pass through the available frequency channels and time slots within the frame in a preset order from one frame to the next. In fig. 3, the same elements as in fig. 1 are shown with the same reference numerals. However, for simplicity, the number of channels used is actually shown to be less than in fig. 1. Thus, in this case, only a single FDD communication session is shown, at frequency channel f₆Uplink channel 3 and on frequency channel f₁₀The uplink channel 4 represents communication between the FDD mobile 26 and the FDD base station 25. Only five separate TDD communication sessions are shown in fig. 3, instead of the nine sessions in fig. 1. In this case, a first mobile (e.g., TDD mobile 36 in fig. 2) has uplink 6 and downlink 7 channels allocated to it, and a second mobile (not shown in fig. 2) has uplink 8 and downlink 9 channels allocated to it. A third TDD mobile (also not shown in fig. 2) has an uplink channel 16 and a downlink channel 17 assigned to it, and fourth TDD mobiles (e.g., TDD mobiles 37 and 38 in fig. 2) have uplink channels 18, 22 and downlink channels 19, 23 assigned to them, respectively. For simplicity, looking now at the upstream channel alone, it will be seen that upstream channels 6 and 8 are located in frame F₁Frequency channel f in₄Time slot t in₁And t₃In (1), the uplink channel 16 is located in the frequency channel f₂Time slot t in₅In frame F, the upstream channels 18 and 22 are located₁Frequency channel f in₁Time slot t in₂And t₅In (1).

But in frame F₂All channels are not in the same time slot in the same frequency channel, but have been moved to different frequency channels according to a preset order. In this case, except for moving to frequency channel f₄Frequency channel f₁Except for the channel in (1), the other channels are shifted down by one frequency channel. Thus, the upstream channels 6 and 8 are now located in frame F₂Frequency channel f in₃Time slot t in₁And t₃In (1), the uplink channel 16 is located in the frequency channel f₁Time slot t in₅In frame F, the upstream channels 18 and 22 are located₂Frequency channel f in₄Time slot t in₂And t₅In (1). Similarly, F for the next frame₃The upstream channels 6 and 8 are now located in frame F₃Frequency channel f in₂Time slot t in₁And t₃In (1), the uplink channel 16 is located in the frequency channel f₄Time slot t in₅In frame F, the upstream channels 18 and 22 are located₃Frequency channel f in₃Time slot t in₂And t₅In (1). Although the order of frequency channel hopping is preset, the coordinator 40 may be used to provide a reference time to ensure that all TDD operators connected to the coordinator can be correctly synchronized at preset intervals.

Thus, all channels are not in frequency channel f₄Upper, frequency channel f₄Most likely to experience interference from the frequency channel f over all frames₆The FDD channel 3 above, but all uplink channels are spread over all available TDD frequency channels. Of course, the sequence of frequency channels need not be a simple rolling sequence as shown, but may be different. For example, there may be a pre-set pseudo-random sequence such that all operators receive the sequence of frequency channels to be hopped, rather than one or more sequences of frequency channels allocated for exclusive use by any particular operator. In this case, an important feature is that the operator is provided with information about the order of the frequency channels to be used, and of course, also with a reference time for synchronizing the frequency channel change. Although the sequences mentioned so far are considered to be periodic, in other words the frequency channel sequence is finite and then repeats itself, it should be appreciated that the coordinator may dynamically change the sequence depending on the prevailing circumstances (e.g. amount of traffic on the system, amount of interference, etc.), if desired. Thus, if there is little traffic on the system, it is possible that the sequence can be adjusted to completely avoid the frequency channel(s) where most of the interference occurs.

It should also be appreciated that the coordinator may assign batches of time slot and frequency channel hopping sequences to the operators to enable the operators to use these sequences in any manner the operators desire at a later time without having to reply to the coordinator with a new sequence for each individual communication session.

Although in the above embodiments the time slots allocated to the channels are not changed from frame to frame, but only their frequency channels, as described above, it is also possible to change the time slots within each frame to which a particular channel is allocated. Thus, different operators may be allocated different time slots on the same frequency channel, if desired. This obviously requires the coordinator to exercise more control over the operators than simply synchronizing them, but the control operation will in general be quite simple and will not be described further here. The operation of changing the time slot allocated to a particular channel may be performed in conjunction with any type of frequency channel changing operation of the above sequence. Thus, in addition to the simple case of rolling frequency channel changes described above, where time slots may change from frame to frame in a predetermined order, time slot changes may occur even if the frequency channel changes are pseudo-random or dynamic.

In the case of a preset frequency channel change, whether simple, rolling or pseudo-random, or some other preset order, if the operator sequence is given so that the operator can dedicate any particular frequency channel of a frame, the required time slot change is assumed by the operator without the coordinator providing a time slot change sequence. Of course, however, the coordinator may also provide a sequence of time slot and frequency channel changes, for example such that the operator is simply given a sequence of numerous changes, and then the operator assigns a particular order for a particular communication session. Of course, if the frequency channel change is dynamic, then preferably any time slot change will also be controlled by the coordinator, so that the coordinator then only needs to dynamically provide each operator with the changed sequence. The information provided to the operator about the changed sequence may be a relative change, such as changing the frequency channel by shifting up or down x frequency channels and changing the time slot by shifting up or down y time slots, or may be changed completely absolutely by providing the actual time slot frequency channel and timing for each frame.

It will be apparent that the operator will need to provide the mobile station with appropriate channel information at the beginning of each communication session, perhaps during the communication session, particularly when the sequence of frequency channels and, if applicable, time slots will change dynamically. This information may be provided to the mobile station in any known convenient manner and will not be described further herein.

It will be appreciated that although only a particular embodiment of the invention has been described in detail, various modifications and improvements can be made by those skilled in the art without departing from the scope of the invention.

Claims

1. A method for providing a communication channel in TDD mode between a time division duplex, TDD, mobile and a TDD base station, the method comprising the steps of:

assigning an uplink channel for a communication session between a TDD mobile and a TDD base station as a series of uplink time slots, one uplink time slot being assigned for each frame during the communication session;

designating, by an operator, a downlink channel for a communication session between a TDD mobile and a TDD base station on a frequency channel assigned to the operator as a series of downlink time slots, one downlink time slot being designated for each frame during the communication session;

the TDD base station determining which uplink and downlink channels are available at the beginning of a communication session; and

the TDD base station communicating to the TDD mobile at the beginning of a communication session which uplink and downlink channel allocations are for the communication session;

wherein the time slots forming the uplink and downlink channels are assigned on different frequencies in different frames.

2. A method of providing a communications channel according to claim 1, wherein the time slots forming the uplink and downlink channels are designated at different times in different frames.

3. A method of providing a communications channel according to claim 1 or 2, wherein the series of time slots forming the uplink and downlink channels are designated as a sequence of time slots on different frequency channels and at different time instants for different frames.

4. A method of providing a communications channel according to claim 3, wherein the sequence of time slots is predetermined, wherein the predetermined sequence is communicated to the TDD mobile at the start of the communications session.

5. A method of providing a communications channel as claimed in claim 3, wherein the sequence of timeslots is dynamically assigned, the frequency channel and the time of the subsequent timeslot being communicated to the TDD mobile in at least one preceding downlink timeslot.

6. A method of providing a communications channel according to any one of claims 3, 4 or 5, wherein the operator is provided with a sequence of time slots available to the operator on all frequency channels available to the operator, thereby enabling different operators to share the same frequency channels and time slots in different frames.

7. The method of providing a communication channel according to claim 6, wherein the sequence of timeslots available to an operator is dynamically specified.

8. A method of providing a communications channel according to claim 5 or 7, wherein the sequence of timeslots is changed during a communications session.