Technical Field

The present invention relates to a method for encoding information in a wireless communication system, or more particularly a method according to the preamble of claim 1. The invention also relates to a method in a transmit node and a method in a receive node, and a transmit node and a receive node thereof.

Background of the Invention

In a wireless communication system, increasing system bandwidth is a way to improve system performance, such as peak data rate, system throughput, capacity, etc. Although some advanced techniques, such as Multiple Input Multiple Output (MIMO), high order modulation and Hybrid Automatic Retransmission Request (HARQ) can be used to further increase system performance in terms of spectral efficiency, the system bandwidth is still a bottleneck for increasing system performance. Also, to meet the International Telecommunication Union (ITU) requirements of International Mobile Telecommunications (IMT) advanced, wireless communication systems will have to support larger bandwidths than what is done today.

In the Long Term Evolution (LTE) Release-8 (Rel-8) communication system, the supported maximum system bandwidth is up to 20 MHz for fulfilling Downlink/Uplink (DL/UL) 100 Mbs/50 Mbps peak data rate requirements. The LTE-Advanced (LTE-A) communication system ( 3GPP TR 36.913 vδ.0.1) is supposed to be an evolution of the LTE Rel-8 system, and up to 100 MHz system bandwidth is required for obtaining 1 Gbps/500 Mbps peak date rate for DL/UL, respectively.

In order to obtain wider system bandwidth in LTE-A, aggregating several component carriers has been considered, and the corresponding operation has been referred to as carrier aggregation. The aggregated component carriers could be located either contiguously or non- contiguously in frequency within one or multiple frequency bands. In LTE, only one component carrier is used, which is a contiguous frequency spectrum with a certain bandwidth. An important requirement for the LTE-A system is the issue of backwards compatibility, which in this case means that LTE ReI- 8 User Equipments (UEs) should be able to function in a LTE-A communication system, i.e. an LTE-A communication system shall so to speak be transparent for LTE ReI- 8 UEs.

In an LTE Rel-8 system, the supported system bandwidth modes include 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz, and further carrier aggregation is not supported in the LTE Rel-8 standard. In order for a LTE-A system employing aggregated carriers to be backwards compatible with LTE Rel-8 UEs, at least one, but preferably each, of the aggregated component carriers in the LTE-A system should be accessible to LTE Rel-8 UEs. Figure 1 shows an example of a LTE-A system bandwidth with 100 MHz by aggregating five contiguous 20 MHz LTE Rel-8 component carriers.

In a LTE-A system it is envisaged that asymmetric carrier aggregation will be supported, which means that the number of component carriers in DL and UL will be different. Typically, more component carriers will be aggregated in the DL than in the UL. This is motivated by the foreseen applications, which means that the DL traffic load is usually higher than the UL traffic load. It is also desirable for UE transmitter complexity reasons to utilize rather few uplink component carriers.

In an LTE-A system, aggregating different number of component carriers with different bandwidth between DL and UL, i.e. asymmetric carrier aggregation is not precluded. For example, two 20 MHz component carriers can be aggregated in the DL, while only one 20 MHz component carrier is used in the UL, an example of which is shown in Figure 2.

Regarding the relation between LTE Rel-8 UL and DL carrier in Frequency Division Duplex (FDD), there is a fixed default UE TX-RX (transmitter-receiver) carrier centre frequency separation, i.e. the distance between DL carrier centre frequency and UL carrier centre frequency is fixed. In other words, the UL and DL carriers that the LTE Rel-8 UEs identify should be paired with the fixed default separation. In Figure 2, only one of the DL component carriers has the fixed default separation with the UL carrier, and therefore LTE Rel-8 UEs can only work on this pair of carriers. However, for the other DL carrier, in Figure 2, LTE Rel-8 UEs can not access this component carrier as there is no corresponding UL carrier. Hence, this component carrier is thus non-backwards compatible to LTE Rel-8 UEs.

LTE Rel-8 UEs should not be able to access a non-backwards compatible carrier, while at the same time a LTE-A UE should be able to identify and access such a carrier. It is thus a problem to block LTE Rel-8 UEs from accessing non-backwards compatible carriers, and at the same time enable LTE-A UEs to work on both backwards compatible and non-backwards compatible carriers.

According to a proposed prior art solution some changes to synchronization and/or reference signal sequences on non-backwards compatible carriers can be performed to make these carriers totally non-detectable for LTE Rel-8 UEs. This solution implies that backwards compatible carriers and non-backwards compatible carriers should use different synchronization signal and/or reference signal sequences, and further that synchronization signals or reference signals on non-backward compatible carriers can not be identified by LTE Rel-8 UEs. In this manner, LTE Rel-8 UEs can not access these non-backwards compatible carriers.

However, a drawback with this proposed solution would be the increase in complexity for eNodeB and LTE-A UEs, as multiple synchronization signals have to be either generated or detected. This would prevent e.g. cost-efficient solutions taking off-the-shelf chips already developed for Rel-8 synchronization. Introducing changes in the synchronization signal as proposed also means that additional complexity of the communication system architecture is needed.

Summary of the Invention

An object of the present invention is to solve the aforementioned backwards compatibility problems. Another object of the invention is to provide a solution to the above problems which is easy and simple to implement in a wireless communication system.

According to one aspect of the present invention the aforementioned objects are achieved by a method for encoding information about a first or a second type of component carrier in a wireless communication system, in which at least one physical channel is transmitted on each component carrier, and wherein a number of bits are conveyed on said at least one physical channel. Said method comprises the steps of: scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said first type of component carrier, with a sequence belonging to a first set of sequences so as to encode a first type of component carrier; and/or

- scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said second type of component carrier, with a sequence belonging to a second set of sequences, wherein said sequence belonging to said second set of sequences is different from said sequence belonging to said first set of sequences so as to encode a second type of component carrier; and transmitting said at least one physical channel on a corresponding component carrier.

Various embodiments of the method in a wireless communication system above are disclosed in the dependent claims 2-14.

According to another aspect of the present invention the aforementioned objects are achieved by a method in a transmit node for encoding information about a first or a second type of component carrier in a wireless communication system, in which at least one physical channel is transmitted on each component carrier provided by said transmit node, and wherein a number of bits are conveyed on said at least one physical channel. Said method comprises the steps of: scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said first type of component carrier, with a sequence belonging to a first set of sequences so as to encode a first type of component carrier; and/or

- scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said second type of component carrier, with a sequence belonging to a second set of sequences, wherein said sequence belonging to said second set of sequences is different from said sequence belonging to said first set of sequences so as to encode a second type of component carrier; and transmitting said at least one physical channel on a corresponding component carrier. According to yet another aspect of the present invention the aforementioned objects are achieved by a method in a receive node for obtaining information about a first or second type of component carrier in a wireless communication system, in which at least one physical channel is transmitted on each component carrier, and wherein a number of bits are conveyed on said at least one physical channel. Said method comprises the steps of:

- receiving said at least one physical channel transmitted on a component carrier;

- decoding said number of bits conveyed on said at least one physical channel; and

- determining by descrambling at least one of said number of bits whether said at least one bit was scrambled with a sequence belonging to a first set of sequences corresponding to a first type of carrier, or with a sequence belonging to a second set of sequences corresponding to a second type of carrier.

According to an embodiment of the method in a receive node, the method further comprises the step of:

- determining by descrambling said at least one of said number of bits a number of antenna ports for said component carrier.

According to yet another aspect of the present invention the aforementioned objects are achieved by a transmit node for a wireless communication system, for encoding information about a first or a second type of component carrier, in which at least one physical channel is transmitted on each component carrier provided by said transmit node, and wherein a number of bits are conveyed on said at least one physical channel. Said transmit node being: configured for scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said first type of component carrier, with a sequence belonging to a first set of sequences so as to encode a first type of component carrier; and/or

- configured for scrambling at least one of said number of bits conveyed on said at least one physical channel to be transmitted on each of said second type of component carrier, with a sequence belonging to a second set of sequences, wherein said sequence belonging to said second set of sequences is different from said sequence belonging to said first set of sequences so as to encode a second type of component carrier; and further configured for transmitting said at least one physical channel on a corresponding component carrier. According to yet another aspect of the present invention the aforementioned objects are achieved by a receive node for a wireless communication system, for obtaining information about a first or second type of component carrier, in which at least one physical channel is transmitted on each component carrier, and wherein a number of bits are conveyed on said at least one physical channel. Said receive node being:

- configured for receiving said at least one physical channel transmitted on a component carrier;

- configured for decoding said number of bits conveyed on said at least one physical channel; and further configured for determining by descrambling at least one of said number of bits whether said at least one bit was scrambled with a sequence belonging to a first set of sequences corresponding to a first type of carrier, or with a sequence belonging to a second set of sequences corresponding to a second type of carrier.

According to an embodiment of the receive node, the receive node is further configured for:

- determining by descrambling said at least one of said number of bits a number of antenna ports for said component carrier.

The transmit node and receive node may further be configured in accordance with the different embodiments of the method in the wireless communication system according to the dependent claims 2-14.

The present invention makes it possible to have a similar channel structure for backwards and non-backwards compatible carriers, which will simplify the complexity of LTE-A eNBs and LTE-A UEs. At the same time, the two different types of component carriers can easily be distinguished by LTE-A UEs.

Other advantages and applications of the present invention will be apparent from the following detailed description of the invention.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain the present invention in which: Figure 1 illustrates contiguous carrier aggregation in a wireless communication system to obtain wider system bandwidth; and

Figure 2 illustrates asymmetric carrier aggregation in a wireless communication system.

Detailed Description of the Invention

As mentioned, the LTE-A communication system is supposed to be an evolution of the LTE Rel-8 system. It was also mentioned that up to 100 MHz system bandwidth is required for obtaining 1 Gbps/500 Mbps peak date rate for DL/UL, and this may among other things be achieved with the described technique of carrier aggregation, in which component carriers are continuously or non-continuously aggregated into a single aggregated carrier. It is also a requirement of a LTE-A communication system that it should be backwards compatible, e.g. for LTE Rel-8 UEs.

Furthermore, as new technical features are expected in LTE-Advanced (e.g., higher order MIMO, Co-operative Multipoint transmission, relays, etc) it may be motivated to consider non-backwards compatible carriers that could be fully optimized for these new transmission techniques. Such carriers may not have to be constrained by the reference signals, transmission modes and feedback mechanisms that are present in the LTE Rel-8 system, and therefore these carriers should not be accessed by Rel-8 UEs.

Also, in order to simplify the wireless communication system, it is desirable that difference in transmission structure between backwards compatible carriers (for LTE-A UEs and LTE UEs) and non-backwards compatible carriers (for LTE-A UEs only) is as small as possible. Otherwise, e.g. eNBs and LTE-A UEs need to be equipped with two sets of different transmitter/receiver structures for backwards and non-backwards compatible carriers, which means increased complexity and cost in system build up.

On backwards compatible carrier, during initial cell search procedure, a UE firstly uses synchronization signal (including primary and secondary synchronization signal) to acquire time and frequency synchronization with a cell, as well as the cell ID. Then the UE detects the Physical Broadcast Channel (PBCH) to obtain essential system information, such as system bandwidth, number of antenna ports, etc. After obtaining this information, the UE can detect other physical channels and establish uplink synchronization.

According to the invention, in order to make non-backwards compatible carriers non- detectable for LTE Rel-8 UEs, the LTE Rel-8 UE can be blocked during initial cell search procedure to avoid receiving essential system information of non-backwards compatible carriers. Other transmission structures such as Physical Downlink Shared Channel (PDSCH), Physical Downlink Control Channel (PDCCH), etc, could be similar or same for simplifying the system design and transmitter/receiver structure of eNB and LTE-A UEs.

The present invention solves the aforementioned problems by a method for encoding information about a first or a second type of component carrier in a wireless communication system. According to the invention, the first type of carrier corresponds to backwards compatible carriers while the second type of carrier corresponds to non-backwards compatible carriers, which means that LTE Rel-8 UEs can access the first type of carrier but not the second type. The method involves scrambling Cyclic Redundancy Check (CRC) bits of a transport block to be transmitted on a channel on each of the first type of component carriers with a sequence belonging to a first set of sequences, and/or scrambling CRC bits of a transport block to be transmitted on a channel on each of the second type of component carrier with a sequence belonging to a second set of sequences, and where the sequence belonging to the second set of sequences is different from the sequence belonging to the first set of sequences. That is, the first and second sets of sequences have no common elements. Also, on each component carrier, there is at least one physical channel such as PBCH, PDCCH or PDSCH transmitted.

According to an embodiment of the invention the problem of blocking non-backwards compatible carriers for LTE Re- 8 UEs is solved by modification of the PBCH that will prevent LTE Rel-8 UEs from detecting said channel, while it will be detectable by LTE-A UEs. On backwards compatible carriers, the PBCH transmission structure is described in the following. Firstly, the entire transport block of PBCH α ₀ , a _λ , • • ^■ a _A _ _λ is used to calculate the Cyclic Redundancy Check (CRC) parity bits p ₀ , p _λ , • • • p _L _ _λ , where A is the size of the transport block, i.e. the number of information bits, and L is the number of CRC parity bits which is set to be 16. Secondly, the CRC parity bits are scrambled by a sequence (CRC mask) with length 16 Jt ₀ , x" , • • • x" ₅ corresponding to a certain number of transmit antennas configured by a eNB, where n = 1 , 2 or 4. After scrambling, the masked CRC parity bits are C ₀ , C ₁ , • • • C ₁₅ , where C ₁ = (P ₁ + x" ) mod 2, / = 0,1, • • • ,15. The mapping relation between the three scrambling sequences and the number of antenna ports is shown in Table 1.

Table 1: CRC masks for PBCH

Then, the masked CRC parity bits are attached to the transport block of PBCH to obtain a number of bits as α ₀ , a _λ , • • • a _A _ _λ , C ₀ , C ₁ , • • • , C ₁₅ . Finally, all information bits including BCH transport block and CRC bits undergo channel coding, rate matching, modulation, antenna mapping and transmission. At receiver side, the UE performs blind detection of the PBCH, which means that the UE tries which of the three CRC masks that will result in correct decoding.

In addition to the current three CRC masks in the LTE ReI- 8 system, which could be seen to define a first set of sequences in the wording of the present invention, this invention also introduces a second set of sequences comprising at least one additional CRC mask to indicate the existence of non-backwards compatible carriers. When transmitting PBCH on non- backwards compatible carrier, one of the additional CRC masks belonging to the second set of sequences will be employed. As LTE ReI- 8 UEs can only identify the three sequences listed in Table 1 and use the three candidate sequences to perform blind detection, they would not correctly detect PBCH if the CRC bits are scrambled by these additional CRC masks. Hence, they will not detect the PBCH and not be able to access the corresponding component carrier.

LTE-A UEs on the other hand knows about the existence of both the original CRC masks and the new additional CRC masks. When an LTE-A UE detects the PBCH, it will demodulate the PBCH under different number of transmit antenna hypotheses, perform de-rate matching and decoding, and then test for each possible CRC mask hypothesis, which one that passes the CRC detection. If the detected CRC mask is not any of the three masks defined in the LTE Rel-8 system, the LTE-A UE will assume that it is a non-backwards compatible carrier, and otherwise assume that it is a backwards compatible carrier.

The minimum Hamming distance between the CRC masks in Table 1 is eight, and additional defined CRC masks should preferably have as large Hamming distances as possible to minimize the probability that a LTE Rel-8 UE erroneously identifies a non-backwards compatible carrier as being backwards compatible. For example, some additional CRC masks which maintain the minimum Hamming distance of eight are:

^AlAlAlAlAlAlAl^^ljaaaaajAOAOAOAO^

<0,0,0,0,0,0,0,0,l,l,l,l,l,l,l,l>, <l, 1,1, 1,0,0,0,0,1, 1,1, 1,0,0,0,0, 0,0,0,0,1,1,1, 1,0,0,0,0,1, 1, 1,1>, <1, 1,1, 1,0,0,0,0,0,0,0,0,1, 1,1, 1>, O,0,0,0,l,l,l,l,l,l,l,l,0,0,0,0>.

According to the invention, at least one additional CRC mask in a second set of sequences is needed to identify a non-backwards compatible carrier. However, multiple different CRC masks could also be defined to implicitly encode additional information e.g. number of antenna ports, etc. For example, on a non-backwards compatible carrier there may be:

• a set of LTE-A antenna ports,

• a set of LTE Rel-8 antenna ports, or

• a set of LTE-A and LTE Rel-8 antenna ports, where LTE Rel-8 antenna ports are defined by Common Reference Signals (CRS) according to the LTE Rel-8 standard, and LTE-A antenna ports are defined by Channel State Information-Reference Signal (CSI-RS) according to the LTE-A standard. At eNB or relay node side, a number of LTE ReI- 8 antenna ports and/or LTE-A antenna ports is configured for each component carrier.

Therefore, the additional CRC masks can also be used to encode information about the above combinations. That is, the use of a certain mask may also indicate a number of Rel-8 antenna ports on a non-backwards compatible carrier and/or a number of LTE-A antenna ports on a non-backwards compatible carrier, which means that the encoded information content using sequences in the second set of sequences may in one embodiment relate to more information.

In LTE Rel-8, the PBCH is transmitted either with one, two or four antenna ports and the CRC bits are scrambled with a corresponding mask. As diversity means, Space Frequency Block Coding (SFBC) is used for two antenna ports and Space Frequency Block Coding and Frequency Switching Transmit Diversity (SFBC+FSTD) for four antenna ports. In LTE-A, it might be sufficient to use up to four antenna ports for PBCH transmission, although a cell can support more antenna ports. The antenna ports for PBCH could be the ones from LTE Rel-8, or new defined antenna ports for the LTE-A system. Thus, in the LTE-A system it may be the case that the PBCH is transmitted with fewer antenna ports than what is available in a particular cell, e.g. eight antenna ports. This means that in contrast to the LTE Rel-8 system, we could consider having a CRC mask that encodes a number of antenna ports of the carrier being different (larger) from the number of antenna ports used for the PBCH transmission.

The number of antenna ports for PBCH transmission could be fixed or configurable. If the number of antenna ports is fixed to say two antenna ports, it would mean that a non- backwards compatible carrier always have to support at least two antenna ports. Therefore, embodiments of the invention when employing the PBCH cover the following cases for non- backwards compatible carriers:

• number of antenna ports for PBCH is fixed, o A set of LTE Rel-8 antenna ports is used for PBCH transmission o A set of LTE-A antenna ports is used for PBCH transmission

• number of antenna ports for PBCH is configurable, o A set of LTE Rel-8 antenna ports is used for PBCH transmission o A set of LTE-A antenna ports is used for PBCH transmission

In order to illustrate the invention more thoroughly non-limiting exemplary embodiments of the present invention are presented in different cases.

Case l

A number of transmit antennas used for PBCH transmission on non-backwards compatible carriers is fixed (e.g. pre-determined). For example, on each non-backwards compatible carrier, the PBCH is always transmitted using one (two, four or eight) transmit antenna(s). A new CRC mask is only used to indicate non-backwards compatible carrier. Hence additional signalling is needed for signalling the antenna port configuration for the carrier.

Exemplary embodiment 1:

It is configured that there is only one (two or four) LTE Rel-8 antenna port(s) on each non- backwards compatible carrier, and that the PBCH is transmitted using the LTE Rel-8 antenna port(s). In this case, only one new CRC mask is introduced for indicating non-backwards compatible carriers. If considering the current LTE Rel-8 three CRC masks, there will be a total of four CRC masks for the PBCH which is shown in Table 2 below.

Table 2: CRC mask for LTE-A PBCH

Exemplary embodiment 2:

It is configured that the PBCH on each non-backwards compatible carrier is transmitted using a fixed number of LTE-A antenna ports, which is a default value. For example, the default value could be one (two, four, or eight) which means that the PBCH is transmitted on one (two, four or eight) LTE-A antenna port(s). The CRC mask configuration for LTE-A PBCH is shown in Table 3.

Table 3: CRC mask for LTE-A PBCH

Case 2

The number of transmit antennas used for PBCH transmission on non-backwards compatible carriers is fixed. The new introduced CRC masks are used to indicate both non-backwards compatible carriers and a number of configured antenna ports. This is similar to embodiments 1 and 2 with additional CRC masks. Exemplary embodiment 3:

There is only one (two or four) LTE Rel-8 antenna port(s) configured on non-backwards compatible carriers, and the PBCH is transmitted on those (alternatively according to embodiment 2, the PBCH is transmitted on a fixed number of LTE-A antenna ports). The new CRC masks are used to indicate the non-backwards compatible carriers and the number of LTE-A antenna ports. For example, the number of LTE-A antenna ports could be one, two, four or eight, and four additional CRC masks are introduced for indication as shown in Table 4.

Table 4: CRC mask for LTE-A PBCH

Case 3

The PBCH transmission structure on non-backwards compatible carriers are associated with a configured number of transmit antenna ports. For example, SFBC and SFBC+FSTD are used for PBCH transmission when there are two and four transmit antennas, respectively. For this case, the new CRC masks need to identify the non-backwards compatible carrier and the number of transmit antenna ports.

Exemplary embodiment 4:

The number of LTE ReI- 8 antenna ports on non-backwards compatible carriers can be one, two or four, and the PBCH is transmitted on the LTE Rel-8 antenna port with the corresponding transmission structure. When there is only one LTE Rel-8 antenna port on non- backwards compatible carrier, the PBCH is transmitted in the normal manner; when there are two and four LTE Rel-8 antenna ports, the PBCH will be transmitted in the form of SFBC and SFBC+FSTD, respectively. It can be observed that the PBCH has the same transmission structure as on backwards compatible carriers. In this case, the new introduced additional CRC mask should identify both non-backwards compatible carriers and the number of configured LTE Rel-8 antenna ports.

Table 5: CRC mask for LTE-A PBCH

Exemplary embodiment 5:

The only difference compared to embodiment 4 is that the number of configured LTE Rel-8 antenna ports on non-backwards compatible carriers is one or two, and two corresponding CRC masks are introduced to indicate the non-backwards compatible carrier and the number of configured LTE Rel-8 antenna ports.

Table 6: CRC mask for LTE-A PBCH

Exemplary embodiment 6:

On non-backwards compatible carriers, the PBCH is transmitted on LTE-A antenna ports, and the number of configured LTE-A antenna ports can be one, two, four or eight. Four additional CRC masks are used to identity the non-backwards compatible carriers and the number of LTE-A antenna ports.

Table 7: CRC mask for LTE-A PBCH

In the LTE-A system, relay is considered to be a potential scheme for extending cell coverage and improving cell edge performance, such as spectrum efficiency. When relay nodes are introduced in the system, there will be dedicated communication between LTE-A eNBs and relay nodes in addition to the standard communication between eNB and UEs. Therefore, some dedicated resources are needed for the information exchange between LTE-A eNBs and relay nodes, here 'dedicated' means that the resources can not be used by UEs.

Non-backwards compatible carriers can also be used for communication between LTE-A eNBs and relay nodes. When this occurs, neither LTE Rel-8 UEs nor LTE-A UEs can access these carriers configured for communication between eNB and relay nodes, which are dedicated for relay node backhaul. In order to block all the UEs from access this types of carriers, a special CRC mask, which not can be identified or used by UEs can be employed for PBCH, i.e. PBCH on carriers which are dedicated for relay node backhaul can use a special relay node CRC mask.

Another alternative embodiment of the invention is that some component carriers are dedicated for LTE-A UEs and relay nodes, and LTE Rel-8 UEs can not access these component carriers. For this scenario, a number of new CRC masks are needed, which can be identified by LTE-A UEs and relay nodes. The invention also relates to a method in a transmit node and a method in a receive node corresponding to the method in a wireless communication system described above.

Furthermore, as also understood by the person skilled in the art, methods for encoding information about a first and second type of carriers according to the invention may be implemented in a computer program, having code means, which when run in a computer causes the computer to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may consist of essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Finally, it should also be understood that the present invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.