Dynamic link adaption for time division duplex (tdd)

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DESCRIPTION

Dynamic Link Adaptation for Time Sharing Duplex (TDD).

Background

The present invention relates to the field of wireless communications. More particularly, the present invention relates to a time-sharing duplex (TDD) communication system that uses dynamic link adaptation for transmissions between user equipment (UE: User equipment) and a base station (BS: Base station) for adjustment to change propagation conditions.

These third-generation (3G) cellular systems are capable of transmitting a wide range of services, from high-frequency data services, such as video and Internet downloads, to low-data-frequency services, such as speech. Referring to Figure 1, a plurality of user services are shown as individual data streams. These individual data streams are assigned to transport channels A, B, C, by which the data streams are encoded and multiplexed. Each transport channel A, B, C is assigned a specific coding rate and a specific Transmission Time Interval (TTI). The coding rate determines the number of transmitted bits of the physical layer, and the TTI defines the delivery period of the data block to be transmitted. For example, the TTI can be either 10, 20, 40, or 80 ms.

Multiple transport channels A, B, C are multiplexed together into a coded composite transport channel (CCTrCh: Coded Composite Transport Channel). Since the CCTrCh is made up of a plurality of transport channels A, B, C, it can have a plurality of different coding regimes and different TTIs.

For example, transport channel A may have a TTI of 20 ms and transport channel B may have a TTI of 40 ms. Therefore, you can change the formatting of transport channel A in the first 20 ms and the formatting of transport channel A in the second 20 ms. In contrast, since transport channel B has a TTI of 40 ms, the formatting, and therefore the number of bits, are the same for each 20 ms period in the TTI duration of 40 ms. It is important to note that all transport channels A, B, C are mapped for CCTrCh on a TTI basis, using the minimum TTI within CCTrCh. The transmission power is ultimately determined on the basis of the combination of transport formats applied to the minimum TTI within the CCTrCh.

Those skilled in the art should note that each individual data stream will have an associated data rate or frequency and each physical channel will have an associated data rate. Although these data regimes are related to each other, they are distinctly different data regimes.

Once the minimum TTI has been established within the CCTrCh, it must be determined how many data bits will be transmitted and what transport channels will be supported within a given TTI. This is determined by formatting the data.

A Transport Format Combination (TFC) is applied to each CCTrCh based on the minimum TTI. This essentially specifies for each transport channel how much data is transmitted on a given TTI and which transport channels will coexist in the TTI.

A set of TFCs is the set of all possible TFCs. If the propagation conditions do not allow all the TFCs within the set of TFCs to be supported by the UE, a reduced set of TFCs that are supported by the UE is created. This reduced set is called a subset of TFCs. TFC selection is the process used to determine what data and how much data to map for each transport channel A, B, C for the CCTrCh. A Transport Format Combination Indicator (TFCI) is an indicator of a particular TFC, and is transmitted to the receiver to inform the receiver which transport channels are active for each current bit series. The receiver, based on the reception of the TFCIs, will be able to interpret which physical channels and which time slots have been used. Therefore, the TFCI is the vehicle that provides coordination between the transmitter and the receiver in such a way that the receiver knows which physical transport channels to use.

In TDD, the UE normally calculates the required transmit power based on a Signal to Interference Ratio (SIR) target that is received from the base station. Knowing the TFC used, the UE calculates the required transmit power. If the RF propagation conditions are optimal, an RFC will be selected in such a way that the maximum number of bits are transmitted in each time slot. However, when propagation conditions deteriorate and the UE calculates a required power that is greater than the maximum allowable power of the UE in order to transmit all the desired information, a different set of TFCs must be selected (i.e. the aforementioned subset of TFCs) that will be supported by the maximum allowable power of the UE. This ultimately reduces the amount of data that the physical layer has to support, and reduces the power requirement.

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In short, the system chooses, on a TTI basis, which transport channels will be active and how much data will be transmitted on each. The TFC selection process takes into account physical transmission difficulties (one being the maximum allowable power), and reduces the physical transmission requirements for a certain duration.

After the multiple transport channels A, B, C have been combined into a single CCTrCh, the CCTrCh is then segmented and those segments are mapped separately over a number of physical channels. In TDD systems, the physical channels can exist in one, or a plurality of different time slots, and can use a plurality of different codes in each time slot. Although there are as many as 16 possible codes in a time slot on the downlink, it is more usual to have, for example, 8 codes in a particular downlink of a particular time slot. On the uplink, there are rarely more than two codes in a particular time slot. In either case, there are a number of physical channels defined by a plurality of codes in a plurality of time slots. The number of physical channels can vary.

In the time division duplex (TDD) mode of the Universal Mobile Telecommunication System (UTMS), see for reference ETSI TS 125 221 V. 3.7.0 (2001-06) Physical channels and transport channel mapping over physical channels (TDD), the CCTrCh is mapped over the physical channels by assigning the time slots and codes in consecutive order. For example, the first time slot is selected for map formation. The first code in the first time slot is assigned first, and then each of the remaining codes in the first time slot is assigned consecutively until the last code has been assigned. Once all the codes have been assigned from the first time slot, the second time slot is entered. The mapping process is repeated using each of the codes from the second time slot consecutively until all have been assigned.

The mapping process for specific user equipment (UE) under UMTS is shown in the example of Figure 2A, which has 12 time slots (S1-S12), 8 codes in each time slot (0-7) , and 12 codes in total (A₁-TO₁₂) to be allocated / configured. Codes and timeslots shown as "shaded" are considered, for illustration purposes, not assignable to the present UE (since they may have been allocated to other UEs).

The allocable portions of time slots S4-S7 will be assigned in consecutive order starting at time slot S4, and codes 0-4 of each time slot will also be assigned in consecutive order. Assuming 12 codes will be mapped in this manner, the result is a map formation shown in Figure 2A, with code Ai being assigned first and code A being assigned.₁₂ the last.

Although the prior art process shown in Figure 2A provides an option to map data from CCTrCh over physical channels, there are some drawbacks to this process when transmission problems are encountered within a single time slot, for example when the desired transmit power exceeds the maximum allowable UE power. The process of consecutive allocation of time slots and codes to map the CCTrCh over the physical channels as set forth in the UMTS-TDD standard, tends to exaggerate the problems when a transmission problem occurs. By way of illustration, due to the consecutive manner in which time slots are allocated / configured when a transmission problem occurs, this typically occurs in one or more of the above time slots. When the system detects a problem, for example when the desired transmit power exceeds the maximum allowable UE power for a certain TTI, the system selects new TFCs in such a way that the data requirements are reduced in all time slots. Since the UMTS-TDD standard specifies which timeslots are assigned consecutively, if the transmission problem is in one of the first several timeslots, the system will still begin to pack data into the previous timeslots, in which the The problem is at its worst, leaving the last few timeslots relatively empty, where there are no transmission problems.

As a result, the system exacerbates the problem, as data rate requirements are lowered in time slots where there is no problem, and time slots that have a problem will be packed with data. This is an inefficient use of radio resources.

Summary

The present invention is a TTD UE that performs dynamic link adaptation by adding or changing control information to notify the receiver which timeslots and codes are currently active and which timeslots are to be avoided. In this way, the UE provides synchronization such that the receiver knows what time slots and codes the UE has used to map the CCTrCh over physical channels. The UE tries to avoid the timeslots that are experiencing transmission difficulties, while trying to use the timeslots that are not experiencing transmission problems.

Brief description of the drawings

Figure 1 is a block diagram of individual data streams that are combined into one physical channel.

Figure 2A is the result of a prior art code mapping process.

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Figure 2B is a prior art data burst.

Fig. 3A is a data burst structure of the first embodiment having a control field located in data field 1.

Fig. 3B is a data burst structure of the first embodiment having a control field located in data field 2.

Fig. 3C is a data burst structure of the first embodiment having a control field located in the middle.

Figure 3D is a data burst structure of the first embodiment having a control field located in both data fields.

Fig. 3E is an example of time slot allocation / configuration in the first embodiment.

Fig. 4A is a data burst structure of the second embodiment having the first TFCI field modified.

Fig. 4B is a data burst structure of the second embodiment having the second TFCI field modified.

Fig. 4C is a data burst structure of the second embodiment having both TFCI fields modified.

Fig. 4D is an example of time slot allocation / configuration of the second embodiment.

Fig. 5A is a data burst structure of the third embodiment having a bit pattern encoded in field 1.

Fig. 5B is a data burst structure of the third embodiment having a bit pattern encoded in data field 2.

Fig. 5C is a data burst structure of the third embodiment having a coded bit pattern in the middle.

Fig. 5D is a data burst structure of the third embodiment without TFCI fields, having a bit pattern encoded in data field 1.

Fig. 5E is a data burst structure of the third embodiment without TFCI fields, having a bit pattern encoded in data field 2.

Fig. 5F is a data burst structure of the third embodiment without TFCI fields, having a coded bit pattern in the middle.

Fig. 5G is an example of time slot allocation / configuration in the third embodiment.

Fig. 6A is a data burst structure of the fourth embodiment having an interference information field located in data field 1.

Fig. 6B is a data burst structure of the fourth embodiment having an interference information field located in data field 2.

Fig. 6C is a data burst structure of the fourth embodiment having an interference information field located in the middle.

Fig. 6D is an example of time slot allocation / configuration in the fourth embodiment.

Figure 7A is the data burst structure of a first example.

Fig. 7B is an example of time slot allocation / configuration in a first example.

Figure 8A is the data burst structure of a second example.

Fig. 8B is an example of time slot allocation / configuration in the second embodiment.

Fig. 8C is an example of time slot allocation / configuration in an alternative to the first example.

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Detailed description of the preferred embodiments

The present invention will be described with reference to the figures of the drawings, in which the same numbers represent similar elements throughout.

Referring to Figure 2B, a prior art data burst is shown. The data burst comprises two data fields separated by a middle part, which are followed by a guard period (GP: Guard Period). The TFCI is transmitted within one or both of the burst data fields. The number of TFCI bits encoded depends on the number of possible TFCs that are supported. Since the TFCI is transmitted within the data fields, each bit required to transmit the TFCI reduces the number of user data bits. Therefore, it is desirable to limit the number of bits in the TFCI.

The location of the TFCI adjacent to the middle part allows the best possible transmission, since the interference from the middle part and the most reliable channel estimate for bits adjacent to the middle part can be suppressed. As those skilled in the art will appreciate, the data fields comprise both user data and physical control fields, although these fields will not be described in more detail below.

The present invention comprises four different embodiments for performing dynamic link adaptation. The first embodiment, as shown in Figures 3A-3E, comprises adding a new control field to the data burst to indicate which particular time slots are active, and which time slots are to be avoided. For example, as shown in Figure 3A, a control field has been added to data field 1. Figure 3B shows the control field added to data field 2. Alternatively, Figure 3C shows the control field as part of the middle part. Figure 3D shows the control field added to both data field 1 and data field 2. Although the control field (s) are displayed in a particular position within the data fields, they can be located in any portion of the data field.

In any of the alternatives shown in Figures 3A-3B, it is important to note that the control field identifies the time slots that the receiver must look at for valid data. The data in the control field can refer to "active" timeslots that include valid data; they may include "idle" timeslots that have invalid data and are to be avoided (hereinafter, "idle" timeslots); or they can include both active and inactive time slots. Active or inactive timeslots can be individually identified, or the identifier can include a string of bits, with a one indicating an active time slot and a zero indicating an inactive time slot. It is also to be noted that the control field may comprise a separately delineated control field or it may simply reside in a portion of the data fields.

Referring to Fig. 3E, the allocation / configuration of time slots using the method of the first embodiment is shown. In this example, the control fields in Figures 3A-3D are assumed to indicate that time slots S4, S6, and S7 are active, and that S5 is inactive. Therefore, time slot S5 is not used, and codes A1-A12 are allocated / configured in time slots S4, S6 and S7. This allows the system to avoid an "offensive" timeslot, such as timeslot S5 in this example, which will not adequately support communication without essential increase in UE power output.

Referring to Figures 4A-D, a second embodiment of the present invention is shown. In this embodiment, one or both of the TFCI fields are expanded and / or modified to include the additional data regarding which timeslots are active and which are inactive. Figure 4A shows the first TFCI field expanded and / or modified to include the additional data; Figure 4B shows the second TFCI field expanded and / or modified thereby; and Figure 4C shows both TFCI fields expanded and / or modified thereby.

Referring to Fig. 4D, the allocation / configuration of the time slots using the method of the second embodiment is shown. In this example it is assumed that the control fields shown in Figures 4A-4C indicate that time slot S6 is inactive and time slots S4, S5 and S7 are active. Therefore, the codes are assigned / set in such a way that time slot S6 is bypassed and time slots S4, S5 and S7 are assigned / set with the codes in consecutive order. Timeslot S4 will be filled first, followed by timeslots S5 and S7 consecutively.

Referring to Figures 5A-5F a third embodiment is shown. In this embodiment, a special encoded bit pattern is added to one or both of the data fields or to the middle portion within the data burst; for example data field 1, as shown in Figure 5A, data field 2, as shown in Figure 5B or the middle part, as shown in Figure 5C. By including this special encoded bit pattern within a data burst, the transmitter indicates that these are idle time slots, to be avoided. When the receiver detects the special bit pattern encoded in the data burst, the information associated with that time slot is discarded or otherwise ignored.

Figures 5D-5F are similar to Figures 5A-5C, except that the data burst does not include TFCI fields. As shown in Figure 5D, the encoded bit pattern can be included anywhere within data field 1. Alternatively, as shown in Figure 5E, the encoded bit pattern may be located

ES 2 269 747 T3 within data field 2 or, as shown in Figure 5F, may be located within the middle portion. Although the encoded bit pattern located within data field 1 or data field 2 is preferably located close to the middle portion, this is not required in the present embodiment or in any of the other embodiments. Additionally, the encoded bit pattern may be minimal, as shown in Figures 5A-5D and 5F, or it may comprise most or all of the data field, as shown in Figure 5E.

The length of the bit pattern is such that a high gain coding scheme can be used so that it can be received at reduced power. Thus, for example, if a sequence of 256 chips is used, then the power requirements are reduced relative to a dispersion factor of 16, by 12 dB. In an alternative, a sync-like sequence (Golay) that does not require channel estimation can be used.

Fig. 5G shows a time slot allocation / configuration using the method of the third embodiment. In this example, the data bursts shown in Figure 5F are assumed to have indicated that time slot S6 has been designated as inactive. Thus, the data burst associated with time slot S6 will include the special encoded bit pattern. As a result, time slots S4, S5 and S7 will be allocated / configured consecutively and time slot S6 will be bypassed.

The fourth embodiment of the present invention scales all active time slots in order of decreasing interference, and then channel allocation / configuration is done based on interference levels.

Preferably, the transmitter periodically performs interference measurements in each time slot for the amount of interference and sends this information to the receiver. Once the timeslots are ranked or graded based on the level of interference, the timeslots with the least interference are filled first and the timeslots with the worst interference are filled last. The interference information, or grading, can be transmitted from the transmitter to the receiver in one of the fields of the data burst, or a new field can be created; for example, data field 1 as shown in Figure 6A, data field 2 as shown in Figure 6B or the middle part as shown in Figure 6C.

The measurements used to grade the time slots are those well known to those skilled in the art, such as the CQ (Channel Quality) channel quality measurements that are flagged between the RNC, RNS, and Node B in a 3G. Node B may also use higher layer signaling with an acknowledgment to prioritize channel allocation / configuration.

Fig. 6D illustrates a time slot allocation / configuration using the method of the fourth embodiment. In this example, time slot S6 is assumed to have the smallest magnitude of interference, time slot S5 has the second smallest magnitude of interference, time slot S7 has the third smallest magnitude, and time slot S4 has the increased interference. Therefore, the time slots will be filled in the following order: S6, S5, S7 and S4, as shown in Figure 6D.

In a first example, even the distribution of data across all time slots is illustrated. In this example, referring to Figure 7A, a TFC is chosen, and the corresponding TFCs are transmitted in the TFCI fields, which reduce the data rate uniformly across all time slots to the point where offensive timeslots can support data transmission. This example is the simplest solution, since the TFCIs that are transmitted are the same as the prior art. However, the system allocates / configures time slots and encodes in such a way that the data is evenly distributed across all time slots.

The method of this example results in a time slot allocation / configuration shown in FIG. 7B. As shown, the codes are allocated in such a way that the data is evenly distributed across all time slots. This example has the additional advantages that new fields are not necessary and synchronization between the transmitter and receiver does not have to be performed, in order to effect a modification of active or inactive time slots, since all time slots are active. .

In a second example, shown in Figure 8A, the idle timeslot, and all the timeslots that follow it, are not used to send any information. The TFCI used to communicate which timeslots are to be used. However, when the UE calculates that the maximum allowable power will be exceeded in a certain time slot, such as time slot S5, that time slot and all subsequent time slots are not used.

The result of this example is an allocation / configuration shown in Figure 8B. In this example, time slot S5 is assumed to be the idle time slot. Therefore, since offensive time slots and all subsequent time slots are discarded, only time slot S4 will be used and only A1-A5 codes will be assigned / configured.

In an alternative, the idle timeslot can still be used, albeit at a lower capacity. As shown in Figure 8C, fewer codes can be assigned to that time slot to reduce the load on the time slot.

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A summary of the different embodiments and examples of the present invention is shown in Table 1 below.

TABLE 1

<td>REALIZATION/ EXAMPLES</td><td>FIGURES</td><td></td>

<td>First</td><td>3A-3E</td><td>A new control field is added to one or both data fields, or to the middle part, to indicate active and / or inactive time slots</td>

<td>Second</td><td>4A-4D</td><td>Modify one or both TFCI fields to indicate active and / or inactive time slots</td>

<td>Third</td><td>5A-5G</td><td>An encoded bit pattern is added to all time slots that are idle</td>

<td>Quarter</td><td>6A-6D</td><td>Time slots are graded in order of decreasing interference; the time slots with the least interference are used first</td>

<td>First Example</td><td>7A-7B</td><td>A TFC is chosen such that the "offending" timeslot can support a reduced data rate and resource allocations are averaged across all timeslots.</td>

<td>Second Example</td><td>8A-8B</td><td>The maximum power is determined for each specific time slot. Resource units are not applied to the time slot that exceeds the maximum allowable power and to all subsequent time slots.</td>

It should be noted that a drawback in the implementation of the present invention is the TFCI status and control information for active and inactive time slots (hereinafter "time slot information"). Since the TFCI normally exists only in certain time slots, it is possible to have a communication that uses five time slots, but designates only time slot 2, or time slots 1 and 4, to have the TFCI and / or time slot information. The TFCI and time slot information are necessary to synchronize the transmitter and receiver in data processing. However, there may be cases where the only timeslots that have the TFCI or timeslot information are timeslots that exceed the maximum allowable transmit power.

For the four embodiments of the present invention and described with reference to Figures 3A-6D, if the TFCI or time slot information is only in the time slots that have been designated as inactive, communication will fail.

One solution to this problem is to put the TFCI and time slot information in at least two time slots; and potentially every timeslot used when data loss is a major concern. This will ensure that if the receiver receives a timeslot, it also receives the TDCI and timeslot information.

For the first and second examples shown and described with reference to Figures 7A-8C, the TFCI problem does not exist. For the first example, the data rate is reduced, but all timeslots are still used and the TFCI and time-slot information will always be available. The second example will always include the TFCI and time slot information in the first time slot.

It should be noted that although the present invention has been described with reference to the uplink, it is equally applicable to the downlink; and using the teachings of the embodiments as described herein both uplink and downlink are contemplated herein as within the scope of the present invention.

Although the present invention has been described in terms of the preferred embodiment, other variations will be apparent to those skilled in the art that are within the scope of the invention as expressed in the claims that follow.