WO2017028019A1

WO2017028019A1 - Multiple antenna transmit schemes for new pucch format in feca

Info

Publication number: WO2017028019A1
Application number: PCT/CN2015/086984
Authority: WO
Inventors: Shaohua Li; Xinghua SONG
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-08-14
Filing date: 2015-08-14
Publication date: 2017-02-23

Abstract

A Physical Uplink Control CHannel (PUCCH) precoding method is provided. According to the method, different precoding vectors can be applied to different Orthogonal Frequency Division Multiplexing (OFDM) symbols, and all the subcarriers in the same OFDM symbol can use the same precoding to achieve spatial diversity gain. By means of the method, full spatial diversity gain can be achieved without any cubic metric increase.

Description

MULTIPLE ANTENNA TRANSMIT SCHEMES FOR NEW PUCCH FORMAT IN FeCA

TECHNICAL FIELD

Embodiments of the invention relate to the field of wireless communication； and more specifically, to multiple antenna transmit schemes for new physical uplink control channel (PUCCH) format in further enhancement carrier aggregation (FeCA) .

BACKGROUND

Carrier Aggregation

The use of long term evolution (LTE) carrier aggregation (CA) , introduced in Rel-10 and enhanced in Rel-11, offers means to increase the peak data rates, system capacity and user experience by aggregating radio resources from multiple carriers that may reside in the same band or different bands and, for the case of inter-band time division duplexing (TDD) CA, may be configured with different uplink/downlink (UL/DL) configurations. In Rel-12, carrier aggregation between TDD and frequency division duplexing (FDD) serving cells is introduced to support user equipment (UE) connecting to them simultaneously.

In Rel-13, LAA (Licensed-Assisted Access) has attracted a lot of interest in extending the LTE carrier aggregation feature towards capturing the spectrum opportunities of unlicensed spectrum in the 5GHz band. WLAN operating in the 5GHz band nowadays already supports 80MHz in the field and 160MHz is to follow in Wave 2 deployment of IEEE 802.11ac. There are also other frequency bands, such as 3.5 GHz, where aggregation of more than one carrier on the same band is possible, in addition to the bands already widely in use for LTE. Enabling the utilization of at least similar bandwidths for LTE in combination with LAA as IEEE 802.11ac Wave 2 will support calls for extending the carrier aggregation framework to support more than 5 carriers. The extension of the CA framework beyond 5 carriers was approved to be one work item for LTE Rel-13. The objective is to support up to 32 carriers in both UL and DL.

Compared to single-carrier operation, a UE operating with CA has to report feedback for more than one DL component carriers. Meanwhile, a UE does not need to support DL and UL CA simultaneously. For instance, the first release of CA capable UEs in the market only supports DL CA but not UL CA. This is also the underlying assumption in the 3GPP RAN4 standardization. Therefore, an enhanced UL control channel, i. e. PUCCH format 3 was introduced for CA during Rel-10 timeframe. However, in order to support more component carriers in Rel-13, the UL control channel capacity becomes a limitation.

PUCCH Format 3

In LTE Rel-8, PUCCH format 1/1a/1b and PUCCH format 2/2a/2b are supported for SR, HARQ-ACK and periodic CSI reporting. The PUCCH resource is represented by a single scalar index, from which the phase rotation and the orthogonal cover sequence (only for PUCCH format 1/1a/1b) are derived. The use of a phase rotation of a cell-specific sequence together with orthogonal sequences provides orthogonally between different terminals in the same cell transmitting PUCCH on the same set of resource blocks. In LTE Rel-10, PUCCH format 3 was introduced for carrier aggregation and TDD, when there are multiple downlink transmissions, (either on multiple carriers or multiple downlink subframes) but single uplink (either single carrier or single uplink subframe) for HARQ-ACK, SR and CSI feedback.

Similarly, the PUCCH format 3 resource is also represented by a single scalar index from which the orthogonal sequence and the resource-block number can be derived. A length-5 orthogonal sequence is applied for PUCCH format 3 to support code multiplexing within one resource-block pair [2] and a length-4 orthogonal sequence is applied for shorted PUCCH.

Denote the PUCCH format 3 resource as

the resource block number of the PUCCH format 3 resource m is determined by the following

The orthogonal sequence applied for the two slots are derived by the following

Where

and

are the length of the orthogonal sequence for the two slots respectively,

holds for both slots in a subframe using normal PUCCH format 3 while

holds for the first slot and second slot in a subframe using shortened PUCCH format 3.

The PUCCH format 3 resource is determined according to higher layer configuration and a dynamic indication from the downlink assignment. In detail, the TPC field in the DCI format of the corresponding PDCCH/EPDCCH is used to determine the PUCCH resource values from one of the four resource values configured by higher layers, with the mapping defined in Table 1. For FDD, the TPC field corresponds to the PDCCH/EPDCCH for the scheduled secondary serving cells. For TDD, the TPC field corresponds to the PDCCH/EPDCCH for the primary cell with DAI value in the PDCCH/EPDCCH larger than ‘1’ . A UE shall assume that the same PUCCH resource values are transmitted in each DCI format of the corresponding PDCCH/EPDCCH assignments.

Table 1: PUCCH Resource Value for HARQ-ACK Resource for PUCCH

SORTD for PUCCH format 3

For format 3, in order to support multiple transmitted antennas, SORTD (Spatial orthogonal-resource Transmit Diversity) schemes are adopted. In SORTD, different PUCCH format 3 resources are transmitted on different antenna ports. For different antennas, it may use different resource-block, or it may use different orthogonal sequence.

New PUCCH format to support up to 32 DL CCs

In 3GPP up to Rel-12, the maximum supported downlink component carriers is 5. However, in Rel-13, maximum 32 downlink carriers can be configured for one UE and hence a new PUCCH format will be introduced to carry more HARQ-ACK bits due to the aggregation of 32 DL CCs.

Currently, there are two main design options to support larger payload size on PUCCH:

Opt 1: New PUCCH format design based on PUCCH format 3

Opt 2: New PUCCH format design based on PUSCH

For opt 2, since it is based on PUSCH, it is more flexible to support different information loads and different resource allocations. Hence, opt 2 may be preferred in 3GPP.

In 3GPP, up to now, there is no discussion on how to transmit the new PUCCH format on multiple antennas, since new PUCCH formats for a single antenna is not settled. For new PUCCH format with multiple antennas, three schemes may be referred. One is to reuse PUSCH MIMO schemes, and one is reuse PUCCH SORTD (Spatial Orthogonal- Resource Transmit Diversity) schemes. Yet another is to reuse downlink transmit diversity scheme (such as space frequency block code or cyclic delay diversity schemes) . However, for PUSCH-based MIMIO schemes, it is close-loop MIMO. It aims to achieve precoding gain but the transmit diversity gain cannot be fully achieved. Further, open loop is more suitable for control channel transmission. For PUCCH-based SORTD schemes, if the new PUCCH format is based on PUSCH-like design, there may be no multiple orthogonal-resources in the same PRBs (Physical resource blocks) . Hence, it has no means to reuse SORTD schemes. For the third options which are based on downlink open loop MIMO schemes, since the precoding is performed in frequency domain, it will increase the cubic metric for uplink if it is applied in uplink. The increase of cubic metric will decrease the cell coverage. In order to overcome the above limitation of the current available multiple antenna transmission methods, in this invention, we propose a new multiple antenna schemes for new PUCCH format.

SUMMARY

As described herein, different spatial precoding vectors can be applied to different OFDM symbols, and all the subcarriers in the same OFDM symbol can use the same precoding to achieve spatial diversity gain. With these methods, one can achieve full spatial diversity gain but without any cubic metric increase.

One of ordinary skill in the art would realize that various communication nodes (e.g., UE or other station) could perform various processes described herein. Other features and advantages will become obvious to one of ordinary skill in the art in light of the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which:

Figure 1 is a block diagram of a user equipment (UE) 12 (e.g., a mobile device) , according to one exemplary embodiment, that can be used in one or more of the non-limiting example embodiments described.

Figure 2 shows a base station 10 (for example a NodeB or an eNodeB) that can be used in example embodiments described.

Figure 3 shows the new transmit processing chain for new PUCCH format design.

Figure 4 shows the resource block mapping for new PUCCH format.

DESCRIPTION OF EMBODIMENTS

In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

References in the specification to “one embodiment, ” “an embodiment, ” “an example embodiment, ” etc. , indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

In the following description and claims, the terms “coupled” and “connected, ” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other. “Connected” is used to indicate the establishment of communication between two or more elements that are coupled with each other.

An electronic device (e.g., an end station, a network device) stores and transmits (internally and/or with other electronic devices over a network) code (composed of software instructions) and data using machine-readable media, such as non-transitory machine-readable media (e.g., machine-readable storage media such as magnetic disks； optical disks； read only memory； flash memory devices； phase change memory) and transitory machine-readable transmission media (e.g., electrical, optical, acoustical or other form of propagated signals –such as carrier waves, infrared signals) . In addition, such electronic devices includes hardware such as a set of one or more processors coupled to one or more other components, such as one or more non-transitory machine-readable media (to store code and/or data) , user input/output devices (e.g., a keyboard, a touchscreen, and/or a display) , and network connections (to transmit code and/or data using propagating signals) . The coupling of the set of processors and other components is typically through one or more busses and bridges (also termed as bus controllers) . Thus, a non-transitory machine-readable medium of a given electronic device typically stores instructions for execution on one or more processors of that electronic device. One or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware.

As used herein, a network device or apparatus (e.g., a router, switch, bridge) is a piece of networking equipment, including hardware and software, which communicatively interconnects other equipment on the network (e.g., other network devices, end stations) . Some network devices are “multiple services network devices” that provide support for multiple networking functions (e.g., routing, bridging, switching, Layer 2 aggregation, session border control, Quality of Service, and/or subscriber management) , and/or provide support for multiple application services (e.g., data, voice, and video) . Subscriber end stations (e.g., servers, workstations, laptops, netbooks, palm tops, mobile phones, smartphones, multimedia phones, Voice Over Internet Protocol (VOIP) phones, user equipment, terminals, portable media players, GPS units, gaming systems, set-top boxes) access content/services provided over the Internet and/or content/services provided on virtual private networks (VPNs) overlaid on (e.g., tunneled through) the Internet. The content and/or services are typically provided by one or more end stations (e.g., server end stations) belonging to a service or content provider or end stations participating in a peer to peer service, and may include, for example, public webpages (e.g., free content, store fronts, search services) , private webpages (e.g., username/password accessed webpages providing email services) , and/or corporate networks over VPNs. Typically, subscriber end stations are coupled (e.g., through customer premise equipment coupled to an access network (wired or wirelessly) ) to edge network devices, which are coupled (e.g., through one or more core network devices) to other edge network devices, which are coupled to other end stations (e.g., server end stations) . One of ordinary skill in the art would realize that any network device, end station or other network apparatus can perform the functions described herein.

Figure 1 is a block diagram of a user equipment (UE) 12 (e.g., a mobile device) , according to one exemplary embodiment, that can be used in one or more of the non-limiting example embodiments described. The UE 12 may in some embodiments be a mobile device that is configured for machine-to-machine (M2M) or machine-type communication (MTC) . The UE 12 comprises a processing module 30 that controls the operation of the UE 12. The processing module 30 is connected to a receiver or transceiver module 32 with associated antenna (s) 34 which are used to receive signals from or both transmit signals to and receive signals from a base station 10 in the network 2. To make use of discontinuous reception (DRX) , the processing module 30 can be configured to deactivate the receiver or transceiver module 32 for specified lengths of time. The user equipment 12 also comprises a memory module 36 that is connected to the processing module 30 and that stores program and other information and data required for the operation of the UE 12. In some embodiments, the UE 12 may optionally comprise a satellite positioning system (e.g.GPS) receiver module 38 that can be used to determine the position and speed of movement of the UE 12.

Figure 2 shows a base station 10 (for example a NodeB or an eNodeB) that can be used in example embodiments described. It will be appreciated that although a macro eNB will not in practice be identical in size and structure to a micro eNB, for the purposes of illustration, the base stations 10 are assumed to include similar components. Thus, the base station 10 comprises a processing module 40 that controls the operation of the base station 10. The processing module 40 is connected to a transceiver module 42 with associated antenna (s) 44 which are used to transmit signals to, and receive signals from, UEs 12 in the network 2. The base station 10 also comprises a memory module 46 that is connected to the processing module 40 and that stores program and other information and data required for the operation of the base station 10. The base station 10 also includes components and/or circuitry 48 for allowing the base station 10 to exchange information with other base stations 10 (for example via an X2 interface) and components and/or circuitry 49 for allowing the base station 10 to exchange information with nodes in the core network 4 (for example via the S1 interface) . It will be appreciated that base stations for use in other types of network (e.g. UTRAN or WCDMA RAN) will include similar components to those shown in Figure 2 and

appropriate interface circuitry

48, 49 for enabling communications with the other network nodes in those types of networks (e.g. other base stations, mobility management nodes and/or nodes in the core network) .

Figure 2 depicts an eNode B as a base station, but a WLAN AP could be substituted with similar functional elements.

Procedure for new PUCCH format design

In Figure 3, the new transmit processing chain for new PUCCH format design is given. The information bits are firstly encoded, and further adapted to a suitable final code rate by a rate matching process, which are included in the channel encoder block. The coded bits are then symbol-level channel interleaved and scrambled prior to serial to parallel transformation (corresponding to S->P block) , modulation mapping (corresponding to Bit->sym block) , DFT-spreading (corresponding to the DFT block) . The above procedure is very similar to the corresponding part of PUSCH, which is defined in 36.211. There may be some exceptions. As one example of the exceptions, the channel coding schemes may be different. When the length of information bits is smaller, the convolution encoder or Reed-Muller code may be used, rather than turbo code used in PUSCH. As another example of the exceptions, after DFT-spreading, some further spreading code may be employed to multiplex different UEs in the same resource blocks. Different UE may use orthogonal channels for transmission. The channels may be differentiated by different spreading code.

After modulation mapping and DFT-spreading, the symbols are further mapped to different subcarriers. For subcarrier mapping, a plurality of PRB pairs in each subframe is used to carry information bits. To increase the frequency diversity, in the first slot of one TTI (transmission time interval) , the PRB (s) are at or near one edge of the system bandwidth. In the second slot of the TTI, the paired PRB (s) are at or near the opposite edge of the system bandwidth. It is shown in Figure 4. This part is similar as resource allocation for PUCCH format 1a/1b, format 2 and format 3, which is defined in 36.211.

After OFDM modulation, spatial domain precoding is applied to map the OFDM symbol into different transmit antenna ports to achieve spatial diversity. Different OFDM symbols use different precoding vectors and all subcarriers in the same OFDM symbol use the same precoding. The precoding details are described below. It should be highlighted that the precoding is different from PUSCH precoding. In PUSCH, the precoding is the same for all OFDM symbols. The precoding is also different from downlink precoding for PDSCH. In the downlink precoding, the precoding may be different from one subcarrier to another subcarrier or from different PRBs to different PRBs.

It should be noted that the above order of the described procedure can be changed, according to certain embodiments. As one example, the spatial domain precoding can be performed after bit to symbol mapping and before DFT processing. As another example, the spatial domain precoding can be performed after DFT processing and before IFFT processing. In this example, the spatial domain is processed in frequency domain, since all the subcarriers use the same precoding； the processing in frequency domain is equivalent to the time domain processing. This order should not be construed as limiting to the embodiments herein, butmerely as an example made for illustrative purposes.

Precoding for the new PUCCH format

Assume there are P transmit antenna ports, L OFDM symbols which are not used for reference symbols, K samples in each OFDM symbols and Q subcarriers used for new PUCCH transmission. The transmitted signal with the precoding vector in time domain can berepresented by:

where z^(p)(l，k) (p＝0，…，P-1) is the kth (k＝0，…，K-1) samples of the lth (l＝0，…，L-1) OFDM symbols transmitted on the pth antenna ports, y(l，k) is the complex-valued symbols assigned to the kth samples of the lth OFDM symbols which is not used for reference symbols and resulted from a series of processing of information bits, as shown in Figure 3. W ^(p) (l) is the weighting on the lth OFDM symbols of the pth antenna port and W(l)＝[w⁽⁰⁾(l)，…，w^(p-1)(l)]^T .In the frequency domain, the signal can be represented by:

where

represents the transmitted signals on the pth antenna ports on the qth (q＝0，…，Q-1) subcarrier of the lth OFDM symbol and

denotes the transmitted signals on the qth subcarrier of the lth OFDM symbol.

For two antenna port case, assume there are N vectors in the weighting pool, the nth precoding vector

could be:

N is any integer number. In the specification, it can be predefined and can also be signaled. As two examples, one is with N＝4 and one is with N＝5, the details are shown as following:

Example 1: The number of vectors in the weighting pool is N＝4.

Table 2: code book for N＝4

In the above precoding, the elements of the precoding are 1, -1, j, -j. With the above precoding, the precoding does not need any multiplication. As a result, at the receiver, the handling of precoding does not need to have multiplication either. It will reduce a lot of complexity.

Example 2: The number of vectors in the weighting pool is 5:

Table 3: Code book for N＝5

With the above precoding, the granularity of precoding is smaller than the first example. It is expected to have better spatial coverage compared to the first example. But the element of the precoding is not simple 1, -1, j, -j. Both the complexity of precoding and decoding will be increased a bit.

In one embodiment, in the same subframes, the weighting W (l) can be different from symbol to symbol. As one example,

where l＝0，…，9 and N＝10.

In another embodiment, the weighting W (l) can be different from symbol to symbol in each slot, but in different slot, the weighting pattern may be the same. As one example,

where N＝5.

In another embodiment, the weighting may be cyclic selected from a predefined weight pool. As one example, N could be 4 and l＝0，…，9.

For four antenna ports, any precoding designed for transmitted diversity can be used for each OFDM symbol. As one example, the format of the nth precoding vector

could be:

Here, M is any integer number predefined or semi-statically configured by higher layers. n_k can be selected such that the minimum distance of any pair of precoding vector in the weighting pool is maximized. The distance can be chordal distance and it can be other distance which can be applicable for precoding optimization.

As a detailed example, M ＝ 4, the precoding vector

is given below

Receiver

At the receiver, assume the number of received antenna is M. The received signal in the frequency domain can be represented by:

r^(m) (l，q) is the received signal at the mth (m＝0，…，M-1) antenna on the qth subcarrier of the lth OFDM symbol. H^(m，p)(l，q) is the channel between the mth received antenna and the pth transmitted port on the qth subcarrier of the lth OFDM symbol. n is one vector with M dimension and denotes the additive white Gaussian noise.

To simplify the description, it can be further represented by

where

Hence, in the receiver, we can first estimate the row channel

H(l，q)(l＝0，…，L-1，q＝0，…，Q-1) for each antenna ports based on reference signal. Row channel H (l，q) are further multiplied by the precoding W (l) for each OFDM symbols to get the effective channel. Equalization is performed based on the effective channel.

In accordance with the foregoing, different spatial precoding vectors can be applied to different OFDM symbols, and all the subcarriers in the same OFDM symbol can use the same precoding to achieve spatial diversity gain. As a result, one can achieve full spatial diversity gain but without any cubic metric increase (i. e. , the cubic metric is the same as the single antenna case) .

With the proposed method, the precoding and decoding is very simple, since the precoding vector is composited by simple mathematic operation, such as simple rotation, or conjunction.

While processes in the figures may show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc. ) .

While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.

ABBREVIATIONS

Abbreviation Explanation

FeCA Further enhancement carrier aggregation

MIMO Multiple input and multiple output

PUCCH Physical uplink control channel

CA Carrier aggregation

LTE Long term evolution

TDD Time division duplex

UL Uplink

DL Downlink

FDD Frequency division duplex

UE user equipment

LAA Licensed-Assisted Access

SR Scheduling Request

HARQ Hybrid automatic repeat request

ACK Acknowledgement

CSI Channel state information

TPC Transmit power control

DCI Downlink control indicator

PDCCH Physical control channel

ePDCCH enhance downlink control channel

DAI Downlink assignment indicator

SORTD Spatial orthogonal-resource Transmit Diversity

CC Component carrier

PUSCH Physical uplink share channel

3GPP Third generation partnership project

CDD Cyclic delay diversity

OFDM Orthogonal frequency division multiplexing

DFT Discrete Fourier transform

PRB Physical resource block

TTI Transmission time interval

Claims

A Physical Uplink Control CHannel (PUCCH) precoding method comprising:

using different precoding vectors for different symbols to be transmitted on multiple antenna ports.
The method according to claim 1, wherein all subcarriers in the same symbol use the same precoding.
The method of claim 1 or 2, wherein the precoding vectors are different from symbol to symbol in each slot and the same in different slots.
The method of claim 1 or 2, wherein the precoding vectors are cyclic selected from a predefined weighting pool.
The method according to any of claims 1-4, further comprising obtaining the symbols by processing information bits.
The method of claim 5, wherein the processing of the information bits comprises channel encoding, serial to parallel transformation, modulating mapping and Discrete Fourier Transform (DFT) -spreading.
The method of claim 5, wherein the processing of the information bits comprises channel encoding, serial to parallel transformation and modulating mapping.
The method according to any of claims 1-6, wherein the symbols are Orthogonal Frequency Division Multiplexing (OFDM) symbols.
The method of any of claims 1-8, wherein the symbols are transmitted on the multiple antenna ports using new PUCCH format.
The method of claim 9, the new PUCCH format is based on PUCCH format 3 or Physical Uplink Share Channel (PUSCH) .