Improved use of subframes in a cellular communications system

p00001Improved use of subframes in a cellular communications system.

p00002Technical field

p00003The present invention describes a method for use in a cellular communications system, in which system traffic within a cell is sent in frames. Each frame comprises a first number of subframes, and a second number of said subframes is available for at least either uplink traffic or downlink traffic.

p00004Background

p00005In cellular wireless systems, both in current systems such as, for example, UTRA systems (UMTS Terrestrial Radio Access, UMTS terrestrial radio access), and in future systems, such as LTE systems (Long Term Evolution, long-term evolution ), one of the principles used is the so-called TDD (Time Division Duplex, time division duplex), that is, a principle according to which uplink traffic and downlink traffic occur during different periods of time, called subframes, which are comprised within a larger frame. Typically, in a TDD system uplink traffic and downlink traffic use the same carrier frequency.

p00006Due to the fact that in a TDD system uplink traffic and downlink traffic share the same frequency, interference problems between different system cells can occur. In particular, downlink traffic from one cell can cause interference in other cells.

p00007In addition to interference between different cells of the same TDD system, interference may also occur between different cells of different, but co-located or adjacent systems, for example systems managed by different operators.

p00008One way to reduce inter-cell interference problems in TDD systems is to establish what is called "guard periods" in transitions between downlink traffic and uplink traffic, that is, periods during which no Traffic may occur. Guard periods can also be established in uplink to downlink transitions.

p00009Document CN 101 005 305A discloses a solution in which in a transition between uplink and downlink subframes three special subframes are located, one for downlink traffic, another that is a guard period, and another for the uplink traffic, the duration of the three special subframes being equal to a normal traffic subframe.

p00010Co-existence, that is, the ability to avoid interference between cells of the same system, as well as between adjacent or co-located cells of different systems, is an important factor.

p00011However, the frame structures of some of the current UTRA and LTE TDD standards offer few opportunities for coexistence. Preferably, in order to make efficient coexistence possible, the frame structure should make it possible to have great flexibility in configuring it to overcome interference problems, both from interference from "own" system cells, and from co cells. -located or adjacent to other systems.

p00012Compendium

p00013Therefore, as can be seen from the previous description, there is a need for a solution whereby coexistence can be increased in the form of reducing the risk of interference between cells of the same wireless cellular system or of different systems, in particularly in systems that use the TDD principle.

p00014Such a solution is offered by the present invention in that it discloses a method for use in a cellular communications system, in which system the traffic is sent in frames, where each frame comprises a first number of subframes and where a second number of subframes for at least either uplink traffic or downlink traffic.

p00015According to the method of the invention, at least one of the second number of subframes is made to comprise three parts, as follows:

<dl><dt>• </dt><dd>A part that is used for uplink traffic, </dd></dl>

<dl><dt>• </dt><dd>A part that is used for downlink traffic, </dd></dl>

<dl><dt>• </dt><dd>A part that is used as a guard period. </dd></dl>

p00016The guard period part is located between the uplink and downlink portions, and, according to the invention, the duration of at least two of said three parts can be modified to suit the current needs of the system.

p00017Thus, the present invention offers a solution whereby a subframe can be made to comprise a guard period of variable length, so that it can be adapted in order to overcome the interference problems of a specific system, and so that the remaining part of the subframe can be made to comprise uplink and downlink traffic in varying proportions, since, according to the invention, The remaining part can be divided between uplink and downlink addresses, thus ensuring maximum efficiency with respect to the use of available resources.

p00018In one embodiment, the method of the invention can be applied to a system using the so-called TDD, or time division duplex, that is, a system with what is called a missing spectrum, in which uplink traffic and downlink traffic in at least a first plurality of system cells occurs during different subframes, but on the same frequency. In another embodiment, the method of the invention can also be applied to a system using the so-called half-duplex FDD (Frequency Division Duplex), such that uplink traffic and downlink traffic for a The same user in at least a first number of system cells occurs during different subframes, and on different frequencies.

p00019Conveniently, a subframe of the invention is placed in a transition between uplink and downlink, either in a transition from downlink to uplink, or in a transition from uplink to downlink.

p00020The invention also describes a transceiver for use as a controlling node in a cell of a system of the invention, and a transceiver for use as a user terminal in a system of the invention.

p00021Brief description of the drawings

p00022The invention will be described in more detail below, with reference to the accompanying drawings, in which

p00023Figure 1 shows a schematic view of a system in which the invention can be applied, and

p00024Figures 2 and 3 show frames of the prior art, and

p00025Figure 4 shows a subframe of the invention, and

p00026Figure 5 shows a flow chart of a method of the invention, and

p00027Figure 6 shows a block diagram of a first transceiver of the invention, and

p00028Figure 7 shows a block diagram of a second transceiver of the invention.

p00029Detailed description

p00030Figure 1 shows a schematic view of a wireless cellular system 100 in which the present invention can be applied. In the following, the invention will be described in terms of the so-called LTE (long-term evolution) systems, but it should be noted that this should not be construed as limiting the scope of the protection requested for the present invention; LTE terminology is used only for the purpose of facilitating the understanding of the present invention by the reader, and the invention can also be used in other types of wireless cellular systems.

p00031In addition, the word "traffic" is used in this text. It should be noted that the word "traffic" in this text is understood as meaning any communication that is sent in the downlink and uplink, for example, both the so-called "payment data" and the control signals, etc.

p00032Returning now to the system 100 shown in Figure 1, the system comprises several cells, one of which is presented as 130 in Figure 1. A cell of the system can house various users, one of which is presented as 120 in Figure 1, and, using the LTE terminology, the user is identified as a "UE", ie "User Equipment" or "user equipment".

p00033In the system 100 there is also a controller node, presented as 110 in Figure 1, which has as one of its functions the control of traffic to and from the UEs 120 of cell 130. In LTE, the controller node is called " eNodeB ", that is, NodeB evolved.

p00034Traffic from UEs 120 to eNodeB 110 is called uplink traffic, in English "uplink traffic", abbreviated UL, and traffic from eNodeB to UEs is called downlink traffic, in English "downlink traffic", abbreviated DL.

p00035Both UL traffic and DL traffic are sent in so-called frames, and currently an LTE TDD system has two different frame structures, called type 1 and type 2. Type 1 will be described with reference to Figures 2 and 3: as shown in Figure 2, a type 1 frame comprises 10 of the so-called "subframe" sub-frames, abbreviated SF, presented as 201-210.

p00036As indicated by arrows in subframes 201-210, a subframe can be used for DL ​​traffic, or for UL traffic. However, as also indicated above, in systems in which a multitude of cells are synchronized with respect to the subframes that are used for UL or for DL ​​in, for example, a transition from DL to UL, it is possible produce inter-cell interference in neighboring cells due to "persistent" DL traffic.

p00037Such interference can be reduced, or even eliminated, by means of the so-called guard periods, which are periods during which transmissions cannot be made, and which are created by "silencing" the last part of a DL subframe, as shown. in Figure 3.

p00038In addition, it can also be mentioned that TDD systems can use a frame of a type known as type 2, which differs slightly from type 1, but which basically also uses the principle of guard periods in order to save interference problems.

p00039It is a purpose of the present invention to offer a new frame structure that can be used to replace existing type 1 and type 2 frames, since it is also desirable to reduce the number of options, and have only one type of frame.

p00040A basic idea behind the present invention is to allow a subframe to comprise three parts, one of which is used for uplink traffic, another of which is used for downlink traffic, and another of which be used as a guard period. Conveniently, the "guard period part" is located between the "uplink part" and the "downlink part".

p00041By means of the invention, as will be apparent from the more detailed description that follows, it will be possible that an LTE system using TDD or FDD half-duplex coexists better than before with other LTE TDD systems as well as with 3G TDD systems such as TD-SCDMA, or with WiMax systems.

p00042Unlike the UTRA and TDD LTE TDD systems, in which uplink or downlink subframes can be assigned, the present invention makes it possible, for example, to assign the first part of a subframe to the downlink transmission and the last part of a subframe to the uplink transmission. The DL part of a subframe of the invention will be called DwPTS, and the UL part of the subframe of the invention will be called UpPTS.

p00043Figure 4 shows a subframe 420 of the invention, flanked by a DL 410 subframe and a UL subframe

p00044430 Therefore, and as shown in Figure 4, in subframe 420 of the invention, and between the two UL / DL periods, ie DwPTS and UpPTS, a guard period can be configured, called GP ("Guard Period" "), of variable length. The duration of the GP of the subframe of the invention will be based on different parameters, one of which may be the maximum round trip propagation time within a cell, called RTT ("Roundtrip Time", round trip time) , so that in this case the GP will be based on the size of the cell.

p00045Compared to the current situation, a subframe of the prior art (TDD of LTE type 2) can only contain DwPTS and GP. This may lead to significant losses of efficiency, which can be avoided by the subframe of the invention, since the invention allows the use of part of the subframe also for uplink transmissions, that is, the UpPTS part.

p00046The total sum of the durations of the DwPTS, the UpPTS and the GP constitutes the total length of the subframe, which makes a difference in comparison with the TDD frame structure of type 2 LTE, and also in comparison with the structure of frame used in systems that use TD-SCDMA (Time Division Synchronous Code Multiple Access, multiple access to synchronous code by time division).

p00047Another improvement of the invention with respect to the type 2 LTE TDD frame structure is that the length of the different parts can be modified, for example depending on the need for a guard period based on the maximum propagation time back and forth within the cell, and coexistence requirements with co-located or adjacent cells of other systems, as well as the need to adapt the capacity requirement between UL and DL to a finer scale than previously possible.

p00048Turning now to type 1 of LTE TDD frame structure, the fact that part of the subframe of the invention can be used for uplink transmission represents a difference with respect to the subframe of the invention. At present, in type 1 of LTE TDD frame, a subframe assigned to DL can only be used for DL ​​transmission, and may possibly also contain an "inactive" guard part, that is, a part that is not used for transmissions Therefore, it is a difference between the subframe of the invention and the TDD frame of LTE type 1 the fact that UL data can also be transmitted in the subframe of the invention.

p00049The subframe of the invention is conveniently located after a period of DL subframes and before a period of UL subframes, that is in a transition from DL to UL. In such an application, the DL part of the subframe of the invention is located first within the subframe.

p00050In another embodiment, the subframe of the invention may be located after a period of UL subframes and before a period of DL subframes, that is, in a transition from UL to DL. In such an application, the UL part of the subframe of the invention is located first within the subframe.

p00051Therefore, at least two of the three parts of the subframe of the invention can be modified to suit the needs of the system, since if two parts are modified, naturally the third part will be determined by what remains of the subframe.

p00052If the guard period, GP, is one of the parts that are modified, it can be modified based on at least one of the following parameters:

<dl><dt>1. </dt><dd>Interference from or with other cells of the same system, or other cells in other adjacent or co-located systems, </dd></dl>

<dl><dt>2. </dt><dd>The cell size, which determines the maximum round-trip propagation time, RTT, within the cell, </dd></dl>

<dl><dt>3. </dt><dd>The modulation scheme used for traffic within the cell. </dd></dl>

p00053In the preceding case 1, that is, when the guard period is modified depending on the interference from or with other system cells, the duration of the GP can be conveniently determined so that it is adapted to be at least equal to the propagation time of the signals coming from or sent to at least one controller node in another cell of the system.

p00054Conveniently, it is freely modified, that is, without discrete steps, at least one of the parts of uplink traffic, downlink traffic and guard period, according to the needs of the system. However, in the preceding case 3, that is, when the duration of the guard period is modified depending on the modulation scheme used for traffic within the cell, if the system is one that uses an OFDM (Orthogonal modulation method) Frequency Division Modulation, then at least one of the parts of uplink traffic, UpPTS, and downlink traffic, DwPTS, a duration corresponding to an integer number of OFDM symbols of the modulation method can be assigned. Conveniently, UpPTS and DwPTS are granted a length of 1 or 2 OFDM symbols, although other lengths of OFDM symbols can also be provided within the scope of the present invention.

p00055Accordingly, the invention will facilitate the harmonization of the two frame structures of the current LTE TDD systems into a single frame structure, which is harmonized with the LTE FDD frame structures, which will be beneficial at the current stage of 3GPP standardization, or at a later stage, as the LTE evolves into the so-called advanced IMT (International Mobile Telecommunications).

p00056The invention also solves some drawbacks of current LTE solutions, in particular because:

<dl><dt>• </dt><dd>it allows finer granularity when allocating resources to the UL and the DL, and greater flexibility when creating guard periods. </dd></dl>

<dl><dt>• </dt><dd>it allows greater flexibility in the creation of lengths of UL and DL periods, which is beneficial from the point of view of co-existence with TD-CDMA systems, as well as with TD-SCDMA and WiMAX systems. </dd></dl>

p00057Figure 5 shows an approximate flow chart of a method 500 of the invention. The steps that are options or alternatives are shown with dashed lines.

p00058As can be seen from the preceding description, the method of the invention is intended to be used in a cellular communications system, in which traffic within a cell is sent in frames, and where each frame comprises a first number of subframes

p00059A second number of the subframes is available for at least either uplink traffic or downlink traffic and, as shown in step 510, it is made that at least one of said second number of Subframes comprise at least three parts, as shown in step 515, as follows:

<dl><dt>• </dt><dd>A part that is used for uplink traffic, step 520, </dd></dl>

<dl><dt>• </dt><dd>A part that is used for downlink traffic, step 525, </dd></dl>

<dl><dt>• </dt><dd>A part that is used as a guard period, step 530. </dd></dl>

p00060The guard period part of step 525 is provided between the uplink and downlink portions and, as shown in step 532, the duration of at least two of the three parts of steps 520 can be modified, 525 and 530 to adapt to the current needs of the system.

p00061As indicated in step 540, the method of the invention can be conveniently applied to a TDD system,

p00062or time division duplex, that is, a system with a missing spectrum, so that uplink traffic and downlink traffic in at least a first plurality of system cells occurs during different subframes, but over the same frequency

p00063However, as indicated in step 535, the method of the invention can also be applied to a half-duplex system FDD, or frequency division duplex, such that uplink traffic and downlink traffic in the less a first plurality of system cells occurs during different subframes, and on different frequencies.

p00064As shown in step 550, in one embodiment of the method of the invention, the guard period is one of said at least two of three parts, and the guard period is modified according to at least one of the following parameters:

<dl><dt>• </dt><dd>Interference from or with other cells of the same system, or other cells of other adjacent or co-located systems, </dd></dl>

<dl><dt>• </dt><dd>The cell size, which determines the maximum round-trip propagation time, RTT, within the cell, </dd></dl>

<dl><dt>• </dt><dd>The modulation scheme used for traffic within the cell. </dd></dl>

p00065As shown in step 545, the guard period can also be modified depending on the interference from or with other cells of the system, so that the duration of the guard period is adapted to be at least equal to the time of signal propagation from at least one controller node in another cell of the system.

p00066In one embodiment, as shown in step 560, the method of the invention can be applied in a system in which an OFDM modulation method (orthogonal frequency division modulation) is used in at least one of the link addresses. uplink and downlink, at least one of the uplink and downlink traffic in said second number of subframes is assigned a duration corresponding to an integer number of OFDM symbols of the modulation method.

p00067In addition, in a further embodiment of the method of the invention, the subframe that has been made to comprise at least three parts is interposed after a subframe used for downlink traffic and is followed by a subframe used for uplink traffic, in where the downlink part is the first in said subframe.

p00068However, in an alternative embodiment, the subframe of the invention that is configured to comprise at least three parts is interposed after a subframe used for uplink traffic and is followed by a subframe used for downlink traffic, wherein the uplink part is the first in said subframe.

p00069As shown in step 570, the method of the invention can be applied to an LTE system (long term evolution).

p00070Figure 6 shows a block diagram of some parts of a first transceiver 600 that is intended for use as a controlling node in a system of the invention. Following the use of the illustrative LTE terminology, the transceiver 600 will be referred to as eNodeB. Since the eNodeB of the invention basically operates in accordance with the method described above, all the details of the operation of the eNodeB will not be repeated here.

p00071In a system of the invention, the decision or decisions regarding the details of subframe 420 of the invention, such as, for example, the duration of the three parts, the DwPTS, the GP and the UpPTS, can be taken in several different ways For example, the decision can be made by the system operator, and the system simply sends it to eNodeB 600. To be open to this possibility, the eNodeB will comprise means 610 of entry to receive such decisions. The input means 610 is conveniently an interface to another "superior" node of the system, through which the eNodeB communicates with the system.

p00072The decision of the system operator may also be to let the eNodeB decide the details of the subframe of the invention in a more or less autonomous manner. For example, the eNodeB can be instructed to decide the details of the subframe of the invention in a completely autonomous manner based, for example, on interference measurements carried out by the eNodeB. To be open to this possibility, the eNodeB comprises measuring means 620 that can measure the interference within the cell.

p00073A third possibility is for the operator to instruct the eNodeB to decide the details of the subframe of the invention in a semi-autonomous manner, for example, based on interference measurements, but with certain conditions that are set by the operator, for example that The duration of one of the three parts, the DwPTS, the GP and the UpPTS, cannot exceed or be shorter than a certain period of time.

p00074Regardless of how the eNodeB 600 arrives at the details of the subframe of the invention, the eNodeB 600 will comprise means 630 for making the decision to arrive at those details. As shown in Figure 6, these decision-making means 630 can receive information from both the input means 610 and the measurement means 620. Conveniently, the decision means 630 will also perform the actual establishment of the details of the subframe of the invention in the eNodeB 600. Conveniently, the decision and establishment means will comprise a microcomputer or some similar calculating component.

p00075In addition, the eNodeB 600 will also need to communicate the details of the subframe of the invention to the UEs of the cell, as well as to UEs that are on their way to the cell, ie UEs that are in the so-called "handover procedure" ", and also to UEs that are activated within the cell, that is, UEs that have entered the cell while turned off, and are turned on within the cell. For this reason, the eNodeB 600 is represented as provided with communication means 640, which will conveniently comprise a transmitter and an antenna, which are normally already comprised in an eNodeB for it to communicate with the UEs of a cell.

p00076Thus, the information concerning the subframe of the invention that the eNodeB communicates to the UEs of the cell will comprise the duration of the different parts of the subframe of the invention, that is, the DwPTS, the GP and the UpPTS. A preferred method of transmitting this information to the UEs of a cell by signals is to use the channel known as BCH ("Broadcast Channel"), although in principle this information can be communicated to the UEs through other channels of system control

p00077Figure 7 shows a block diagram of some parts of a second transceiver 700 of the invention, which is intended for use as a user terminal (telephone / laptop, etc.) in a system of the invention. Continuing with the use of the illustrative LTE terminology, the UE 700, "user equipment", will be called the 700 transceiver. Since the UE of the invention basically works according to the method described above, all the details of the operation of the UE will not be repeated here.

p00078As indicated in Figure 7, the UE 700 of the invention is equipped with means for receiving instructions from the cell's eNodeB regarding the duration of the three parts of the subframe of the invention, that is, the DwPTS, the GP and the UpPTS. Conveniently, these instructions are received through the same means as other communications from the eNodeB, that is, through a receiver and an antenna of the UE.

p00079Next, the instructions received from the eNodeB are processed by the UE, that is, the UE conforms to those values ​​of DwPTS, GP and UpPTS. This is done by 720 media intended to configure or reconfigure the DwPTS, the GP and the UpPTS in the UE. Conveniently, the configuration and / or reconfiguration means will comprise a microcomputer or some similar calculating component.

p00080In conclusion, the invention facilitates the harmonization of the two frame structures in LTE for TDD into a single frame structure to which a subframe duration of 1 ms can be assigned. In addition, the invention also resolves various drawbacks of current solutions, for example:

<dl><dt>• </dt><dd>it allows greater flexibility in the creation of lengths of UL and DL periods, which is beneficial from the point of view of co-existence with TD-CDMA, as well as with TD-SCDMA and WiMAX. </dd></dl>

<dl><dt>• </dt><dd>it allows fine granularity when allocating resources to the UL and the DL, and greater flexibility when creating guard periods. </dd></dl>

p00081Another principle that can be used is the so-called half-duplex FDD, frequency division duplex, in which uplink and downlink transmissions from the same system terminal occur over different frequencies and during different time intervals, such as previously mentioned subframes. The invention can also be applied in such a system, that is, a half-duplex FDD system.

p00082The invention is not limited to the examples of embodiments that have been described above and are shown in the drawings, but may be freely varied within the scope of the appended claims.