EP2870704A1

EP2870704A1 - Rank selection for data transmissions in a wireless system

Info

Publication number: EP2870704A1
Application number: EP12753078.0A
Authority: EP
Inventors: Karri Markus Ranta-Aho; Alexander Sayenko
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2012-07-04
Filing date: 2012-07-04
Publication date: 2015-05-13
Also published as: WO2014005630A1

Abstract

A method comprises determining if at least one of a candidate primary or secondary block size for a rank n MIMO transmission is below a certain size and if so, selecting a rank m MIMO transmission, where m is less than n.

Description

RANK SELECTION FOR DATA TRANSMISSIONS IN A WIRELESS SYSTEM

This disclosure relates to data transmission in a wireless communication system, and in particular but not exclusively to data transmission in the uplink.

A communication system can be seen as a facility that enables communication sessions between two or more entities such as fixed or mobile communication devices, base stations, servers, machine type communication devices and/or other communication nodes. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how various aspects of communication such as access to the communication system and feedback messaging shall be implemented between communicating devices. The various development stages of the standard specifications are referred to as releases.

A communication can be carried on wired or wireless carriers. In a wireless communication system at least a part of communications between stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A wireless system can be divided into cells or other radio coverage or service areas provided by a station. Radio service areas can overlap, and thus a communication device in an area can send and receive signals within more than one station. Each radio service area is controlled by an appropriate controller apparatus. Higher level control may be provided by another control apparatus controlling a plurality of radio service area.

A wireless communication system can be accessed by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a communication device is used for enabling receiving and transmission of communications such as speech and data. In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station and/or another user equipment.

In this specification term mobile station (MS) is used for referring to a user equipment, the term base station (BS) is used for referring to a network radio access point including at least some control functionality and the term RNC (radio network controller) is used for referring to a network element that performs control functions over, typically but not necessarily, a number of base stations.

A method to improve the capacity of a cellular system is one based on spatial diversity or spatial multiplexing. In this system, the data rate can be increased by transmitting independent information streams using multiple transmit antennas but using the same channel as defined by frequency, time slot and/or spreading code. These systems are also referred to as multiple input multiple output (MIMO) systems.

According to an aspect, there is provided a method comprising: determining if at least one of a candidate primary or secondary block size for a rank n MIMO transmission is below a certain size; and if so, selecting a rank m MIMO transmission, where m is less than n.

In some embodiments, n is 2 and m is 1 .

The method may comprise receiving information indicating that an n M IMO transmission is to be made, prior to said determining.

The method may comprise determining comprises comparing at least one of said primary block size to a first threshold and said secondary block size to a second threshold.

The first and second thresholds may be the same.

At least one of said first and second thresholds may be dependent on a value which takes into account a number of bits in an interval, said number of bits being adjusted to take into account one or more processing steps.

The one or more processing steps may comprise cyclic redundancy check, puncturing and adding of tail bits. The adjusted number of bits may be quantised to a closest defined transport block size.

At least one threshold may be defined as a function of a network configured parameter.

The network configured parameter may comprise a puncturing limit parameter.

A computer program comprising program code means adapted to perform the methods may also be provided.

The method may be performed in a user equipment.

According to another aspect, there is provided an apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: determine if at least one of a candidate primary or secondary block size for a rank n M IMO transmission is below a certain size; and if so, selecting a rank m M IMO transmission, where m is less than n.

In some embodiments, n is 2 and m is 1 .

The at least one memory and the computer code may be configured with the at least one processor to cause the apparatus to receive information indicating that an n MIMO transmission is to be made, prior to said determining.

The at least one memory and the computer code are configured with the at least one processor to cause the apparatus to_compare at least one of said primary block size to a first threshold and said secondary block size to a second threshold.

The first and second thresholds may be the same.

The one or more processing steps may comprise cyclic redundancy check, puncturing and adding of tail bits.

The adjusted number of bits may be quantised to a closest defined transport block size. The at least one threshold may be defined as a function of a network configured parameter.

The network configured parameter may comprise a puncturing limit parameter.

According to another aspect, there is provided an apparatus comprising: means for determining if at least one of a candidate primary or secondary block size for a rank n M IMO transmission is below a certain size; and if so, means for selecting a rank m MIMO transmission, where m is less than n.

In some apparatus, n is 2 and m is 1 .

The apparatus may comprise means for receiving information indicating that an n M IMO transmission is to be made, prior to said determining.

The determining means may be for comparing at least one of said primary block size to a first threshold and said secondary block size to a second threshold.

The first and second thresholds may be the same.

One or more processing steps may comprise cyclic redundancy check, puncturing and adding of tail bits.

The adjusted number of bits may be quantised to a closest defined transport block size.

The network configured parameter may comprise a puncturing limit parameter.

A user equipment may comprise an apparatus as discussed above.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.

Embodiments will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which: Figure 1 shows a schematic diagram of a system where certain embodiments are applicable;

Figure 2 shows a schematic diagram of a mobile communication device according to certain embodiments;

Figure 3 shows a schematic diagram of a control apparatus according to some embodiments;

Figure 4 shows a precoded physical channel structure of an uplink MIMO with rank 2 transmission;

Figures 5 shows a E-DCH transport channel processing chain; and Figures 6 shows a method of an embodiment.

Certain exemplifying embodiments are explained below with reference to a wireless or mobile communication system serving mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system mobile devices or user equipment (UE) are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. A mobile device may be located within an area of, and thus communicate with, one or more base stations and the communication devices and stations may have one or more radio channels open at the same time and may send signals to and/or receive signals from more than one source. The example of Figure 1 shows two mobile stations MS1 and MS2 in communication with a base station BS. It shall be understood that the sizes and shapes of radio service areas provided by base stations can vary. A base station site can provide one or more cells. A base station can also provide a plurality of sectors, for example three radio sectors, each sector providing a cell or a subarea of a cell. All sectors within a cell can be served by the same base station.

Base stations are typically controlled by at least one appropriate controller apparatus so as to enable operation thereof and management of mobile communication devices in communication with the base stations. In Figure 1 control apparatus 8 is provided. It is noted that more than one base station may be controlled e.g. by a control apparatus. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity 10 and at least one data processor 12. The control apparatus and functions may be distributed between a plurality of control units. The term base station is used and is intended to cover base stations, Node Bs, evolved node Bs (eNBs) or the like.

Figure 2 is a schematic, partially sectioned view of a possible mobile device or station 200 for communication with the base station. Such a device is often referred to as user equipment (UE) or terminal. An appropriate mobile device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) such as a mobile phone or what is known as a 'smart phone', a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. A mobile device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Non-limiting examples of the content include various downloads, television and radio programs, videos, advertisements, various alerts and other information. The mobile device 200 may receive signals in the downlink 207 via appropriate apparatus for receiving and may transmit signals in the uplink 209 via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device. The wireless communication device is provided with a Multiple Input / Multiple Output (MIMO) antenna system. A mobile device is also typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications, such as communication of data and control signals with access systems and other communication devices and actions according to the embodiments described in more detail below. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling stations of an access system or to a radio network controller (RNC). In some embodiments, the control apparatus may be part of the base station. The control apparatus 300 can be arranged to provide control on communications in a service area of the system. The control apparatus can be configured to provide control functions in association with generation and communication of instructions to relevant nodes and processing of responses from the nodes and other related information by means of the data processing facility in accordance with certain embodiments described below. For this purpose the control apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of a base station. The control apparatus can be configured to execute an appropriate software code to provide the control functions. It shall be appreciated that similar component can be provided in a control apparatus provided elsewhere in the system for controlling reception of sufficient information for decoding of received information. A non-limiting example is described in relation to 3GPP High Speed Uplink Packet Access (HSUPA).

Some embodiments relate to a method and apparatus and, in particular not exclusively to apparatus and methods for use in multiple input multiple output M IMO modes. Some embodiments may be used for uplink MIMO for HSUPA.

With M IMO in uplink, two separate transport blocks are transferred by two separate spatial streams when rank 2 transmission is used. With rank 2 transmission, independent adaptation of data rates on each stream is possible. One ACK/NACK is transmitted per transport block. This means that there are double the number of HARQ (hybrid automatic repeat request) processes that are used in dual stream operation when compared to non-M IMO operation.

Reference is made to figure 4 which shows a pre-coded physical channel structure for uplink MIMO with rank 2 transmission. For rank 2 transmission, the primary transport block is carried over four E-DPDCH channels (enhanced dedicated physical data channel). To simplify the representation, the E-DPDCH block shown in figure 4 represents the set of four E-DPDCHs 104. The E- DPCCH 105 (enhanced dedicated physical control channel) is used to indicate the format which is used to transmit the primary transport block on the E- DPDCHs.

The secondary transport block is carried over four S-E-DPDCHs

(secondary E-DPDCH) 106. The S-E-DPCCH 107 is used to indicate the format which is used to transmit the secondary transport block on the set of four S-E- DPDCHs. The E-DPDCHs may be l/Q multiplexed in pairs of two. The S-E- DPDCH may be l/Q multiplexed in pairs of two. The E-DPDCHs and the S-E- DPDCHs may be spatially multiplexed by using different pre-coding vectors, a primary precoding vector for the set of E-DPDCHs and a secondary precoding vector for the set of S-E-DPDCHs. The S-E-DPCCH is only sent with rank 2 transmissions when the S-E-DPDCHs are present. Rank 2 transmissions require that both the E-DPDCH and the S-E-DPDCH are sent with the full set of four E- DPDCHs and S-E-DPDCHs, each set using two spreading factor two and two spreading factor four channels (2xSF2 + 2xSF4 code combinations) in the same TTI (transmission time interval). An SF2 code can carry twice the number of bits in a TTI than an SF4 code. The full code tree would be in use with a single SF1 code, two SF2 codes or 4 SF4 codes, but some room is required for control channels, and because of this the full code tree is not used for the DPDCHs. With l/Q multiplexing the code tree can be used twice to form QPSK signal rather than a BPSK one. Again with spatial multiplexing (MIMO) the code tree pair twice can be used.. So with MIMO there is one SF4 E-DPDCH in I and one SF4 E-DPDCH in Q, one SF2 E-DPDCH in I and one SF2 E-DPDCH in Q carrying the primary transport block, and a same setup of S-E-DPDCH codes carrying the secondary transport block using an orthogonal precoding vector.

In more detail, the uplink uses may uses BPSK modulation and scrambles the transmit signal with a rate of 3840000 chips/second, which for a 2 ms TTI is 7680 chips. The channelization code tree under the scrambling code can be seen as having 256 SF256 codes, 128 SF128 codes, and so on. With l/Q multiplexing the same code can be used twice to form a QPSK waveform. The control channels (DPCCH, E-DPCCH, HS-DPCCH, S-DPCCH and S-E-DPCCH) take their share of the code tree, hence it is not possible to use SF1 in both the I and Q branches, i.e. 2xSF1 (or 2x2xSF2 or 2x4xSF4) for data transmission. Hence for data there is room for 3xSF4 in I and another 3xSF4 in Q, but this 3xSF4 is represented as 1 xSF4+1 xSF2. When this is in both I and Q , this gives 2xSF4+2xSF2 as the maximum code configuration for data. In MIMO there are two orthogonal spatial streams. There is transmission of two sets of these 2xSF4+2xSF2 codes. The first set is the set of E-DPDCHs, and the second set the set of S-E-DPDCHs.

In the case of a rank 1 transmission, the transport block is carried over the set of E-DPDCHs as in uplink CLTD (closed loop transmit diversity). It should be appreciated that in the case of rank 1 transmission, the S-E-DPDCHs are not used.

Referring back to figure 4, the raw bits of the primary transport block after transport channel processing are transmitted over the set of E-DPDCHs 104.

A DPCCH 102 is provided for channel estimation of the first spatial beam. Each channel 102...106 to be transmitted with the first spatial beam is weighted with a scaling operation 0... 6 adjusting the channels' amplitude relative to the other channels before summing them to a composite signal 122, which is then multiplied with a primary precoding vector w1 , w2 126, 128 to form a first spatial beam.

A S-DPCCH 108 is provided for channel estimation of the second spatial beam. Each channel 107 to 108 to be transmitted with the second spatial beam is weighted with a scaling operation 1 18...120 adjusting the channels' amplitude relative to the other channels before summing them to a composite signal 124, which is then multiplied with a secondary precoding vector w3, w4 130, 134 to form a second spatial beam.

The parts of the first and second spatial beam to be transmitted over the first antenna are summed together 136, scrambled with a scrambling code 140, and forwarded for transmission over the first antenna 144.

The parts of the first and second spatial beam to be transmitted over the second antenna are summed together 138, scrambled with a scrambling code 142, and forwarded for transmission over the second antenna 146.

In some standards, it has been defined that when a user equipment transmits MIMO rank 2, the following rules need to be satisfied.

- Both transport blocks are transmitted with the full code configuration available for payload transmission, the primary transport block with a set of four

E-DPDCHs, a pair of l/Q multiplexed spreading factor two E-DPDCHs and a pair of l/Q multiplexed spreading factor four E-DPDCHs, and the secondary transport block with a set of four S-E-DPDCHs, a pair off l/Q multiplexed spreading factor two S-E-DPDCHs and a pair of l/Q multiplexed spreading factor four S-E- DPDCHs over the air.

- The primary transport block and the secondary transport block can be of different sizes.

- Both the primary and secondary transport blocks are transmitted using equal power.

After the user equipment selects the size for each transport block satisfying the transmit power requirements, the user equipment needs to fit the selected transport blocks to the E-DPDCH and S-E-DPDCH physical channels. In some standards, the user equipment is not permitted to transmit an arbitrary transport block size on a full 2xSF2 + 2xSF4 code configuration due to lack of repetition encoding in the E-DCH transport channel processing chain.

Reference is made to figure 5 which shows a processing flow which shows a transport block as an input and the raw bits to be transmitted over the physical channel.

In step S1 , the transport block is input. A CRC (cyclic redundancy check) is attached. The CRC information is used for error detection in the transport blocks. The entire transport block may be used to calculate CRC parity bits. These parity bits may be appended to the transport block.

In step S2, the output of step S1 is has code segmentation applied thereto. For example, in HSUPA (High speed uplink packet access) and in LTE, minimum and maximum sizes are specified so that the block sizes are compatible with supported block sizes. If the length of the input block is greater than the maximum code block size, the input block will be segmented. If a segmented one of the segmented blocks does not have sufficient bits, then that the bits may be added or any other technique used to ensure that the block has the minimum number of bits.

The next step is step S3 where the output of the code block segmentation undergoes channel coding. Channel coding may provide forward error correction and may improve channel capacity by adding redundant information.

The output of the channel coding is subject to a physical layer hybrid-ARQ functionality/ rate matching step, step S4. In this step, an output bitstream is provided with a desired code rate to match the number of bits coming out of the channel coding to the number of bits available in the physical channels. Effectively, either some bits are removed if there were too many bits in the channel encoder output to fit to the physical channel bits available, or some bits are repeated if there were too few bits in the channel encoder output to fill the physical channel bits available. In some standards, the bit repetition is desired to be avoided.

This is followed by step S5 where the data is interleaved and there is physical channel mapping. In a M IMO mode with rank 1 transmissions the UE is allowed to transmit the primary (the only) transport block with a fewer number of codes than 2xSF2 + 2xSF4, or use a larger spreading factor when a single code is used rather than use bit repetition in the rate matching step S4. That is, with rank 1 the physical layer raw bit rate can adapt to the required TB sizes.

In a M IMO mode with rank 2 transmissions the UE needs to transmit both the primary and the secondary transport block using the 2xSF2 + 2xSF4 code configuration for transmitting each transport block.

The Node B scheduler may control the UE's rank, i.e. the Node B can indicate to the UE that it is to transmit with rank 1 (one TB only) in the uplink, or that it is to transmit with rank 2 (two TBs) in the uplink, and only fall back to transmitting rankl if it is not able to transmit with rank2 for a set of predefined reasons.

Some embodiments define one or more rules or criteria for the UE to fall back to using rank 1 transmission if the rank 2 TB size selection (E-TFC (E-DCH Transport Format Combination) selection) does not meet the criteria required for rank 2 transmission.

When the UE is in uplink MIMO mode and the Node B has indicated that the UE should transmit with rank 2 (two parallel transport blocks, one with a set of E-DPDCHs, another with a set of S-E-DPDCHs) the UE runs the E-TFC selection (the TB size selection) for both the primary and the secondary transport blocks normally.

After that the UE will compare the primary TB size to one threshold and the secondary TB size to another threshold. The thresholds may be the same or different. If both the primary and the secondary TB sizes are not above the threshold the UE falls back to rank 1 transmission.

The UE will re-run the E-TFC selection for the primary stream only, select just one TB size and transmits using rank 1 over E-DPDCH(s).

Reference is made to figure 6.

In step T1 , the UE is configured in MIMO mode in the uplink by the RNC. In some embodiments the UE may be configured by the base station. In other embodiments, the control of the MIMO mode may be determined by the RNC and the base station. Where no RNC is provided, a control entity or apparatus may configure the UE to the in the MIMO mode.

In step T2, the UE is allowed it to transmit rank 2. This may be controlled in any suitable way. For example the UE may have received a 'rank-2 grant' by the base station. It should be appreciated that the UE may receive alternatively or additionally any other signal from or via the base station indicating that the UE should transmit rank 2 MIMO.

In step T3, the UE runs the E-TFC selection procedure or any other suitable procedure to select the size for the first or primary TB. This provides a candidate size for the primary TB.

In step T4, the UE runs the E-TFC selection procedure to select the size for the second or secondary TB. This provides a candidate size for the secondary TB. In step T5, the UE compares the size of the first TB to a first threshold.

In step T6 the UE compares the size of the second TB to a second threshold.

In step T7, if both TB sizes do not meet the thresholds, the UE falls back to rank 1 transmission, re-runs the E-TFC selection for one TB size only and transmits that using rank 1 .

The first threshold is in respect of the primary TB which is sent on the E- DPDCH and the second threshold is in respect of the secondary TB which is sent on the S-E-DPDCH.

In some embodiments, the order of the steps may be changed. For example, in some embodiments, steps T3 and T4 may take place at the same time or step T4 for may take place before step T3. In some embodiments, step T5 may take place before step T4. In some embodiments, steps T5 and T6 may take place at the same time. In some embodiments, if in step T5 it is determined that the size does not meet the threshold, then for example step T6 may be omitted. It should be appreciated that steps T6 and T5 can take place in any suitable order. It should be appreciated that whilst some examples of different orders for the steps have been given, this is not exhaustive and in alternative embodiments, the steps may take place in any suitable order. Some steps may be omitted. In some embodiments, the first and the second thresholds are set equal and the TB size should be at least N if the rank 2 mode is to be used.

N may be defined as follows:

• The full code combination of 2xSF2+2xSF4 has 1 1520 physical layer bits per 2 ms TTI (7680 chips/2 ms, 2*(7680/2) + 2*(7680/4) = 1 1520

• The CRC attachment and channel coding steps of the transport channel processing chain results with (TBsize + 24 bits for CRC) * 3 + 12 tail bits, after which puncturing (removal of bits) can be applied to fit the encoder output bits to the physical channel. Thus a minimum TB size of 3812 bits is required for transmitting 2xSF2+2xSF4. A smaller TB size is not able to fill all the 1 1520 bits available on the physical channels to transmit the TB.

• The value of 3812 bits may be quantized to the closest bigger TB size of the valid TB sizes defined in the TB size table in for example TS25.321 . There may be multiple TB size tables, each having at most 128 valid sizes.

The advantage of some of these embodiments is that it allows for transmitting with rank 2 with as small transport blocks as is possible without introducing repetition encoding to fill all the bits on the physical channels for arbitrarily small TB size.

In an alternative embodiment, the first threshold is set to M bits where M is a function of a network configured parameter (such as PLnon_max) puncturing limit, and the second threshold is set to N bits. This may be as defined in the relevant standard. In some embodiments, N may be as defined previously. The puncturing limit determines how many bits can be removed (punctured) in the rate matcher at maximum.

In some embodiments, M may be defined according to the above criteria, but in addition applying a puncturing limit in the minimum TB size calculation so that the minimum TB size allowed would be scaled up with a parameter PL_non_max so that TB size satisfying the equation below would be set as the first threshold. For example with PL_non_max = 1 the first threshold = second threshold = 3812 bits

• PL_non_max * [(TBsize + 24) * 3 + 12] = 1 1520 • In other words, the TB sizes meeting the criteria PL_non_max * [(TBsize + 24) * 3 + 12]≥ 1 1520 would be allowed and those not meeting this criteria would force the UE to fall back to rank 1 .

The advantage of some of these embodiments is that the TB to physical channel mapping follows the same rules for rank 1 and rank 2 transmission (the switch point in TB size between 2xSF2 and 2xSF2+2xSF4 is controlled by the PLnon_max parameter), and the secondary TB can be as small as possible without needing to introduce repetition.

In another embodiment, the first threshold is set to M 1 bits and the second threshold is set to M2 bits and each is a function of at least one network configured parameter (such as PLnon_max).

In some embodiments, there may be no need to introduce repetition encoding in the E-DCH transport channel processing chain.

The advantage some of these options is that the primary and the secondary TB may follow the same rules as defined for rank 1 primary TB.

In some embodiments, the same steps may be used with a higher rank than rank 2. By way of example, the same rules apply for fall back from rank3 or rank4 to a smaller rank.

The required data processing apparatus and functions of a control apparatus in a network element and/or a mobile device for the causing configuration, signaling, determinations, and/or control of measurement and reporting and so forth may be provided by means of one or more data processor. The described functions may be provided by separate processors or by an integrated processor. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded or otherwise provided on an appropriate data processing apparatus. The program code product for providing the operation may be stored on, provided and embodied by means of an appropriate carrier medium. An appropriate computer program can be embodied on a computer readable record medium. A possibility is to download the program code product via a data network. In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large an automated process. Complex and powerful tools are available for converting a logic level design into a semiconductor circuit design ready to be formed on a semiconductor substrate.

It is noted that whilst embodiments have been described in relation to HSUPA, similar principles can be applied to any other communication system. Therefore, although certain embodiments were described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. Whilst the above embodiments have been described in relation to uplink communications, some embodiments may be used in downlink communications.

The foregoing description has provided by way of exemplary and non- limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. For example, a combination of one or more of any of the other embodiments previously discussed can be provided. All such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims.

Claims

1 . A method comprising:

determining if at least one of a candidate primary or secondary block size for a rank n MIMO transmission is below a certain size; and

if so, selecting a rank m MIMO transmission, where m is less than n.

2. A method as claimed in claim 1 , wherein n is 2 and m is 1 .

3. A method as claimed in any preceding claim, comprising receiving information indicating that an n MIMO transmission is to be made, prior to said determining.

4. A method as claimed in any preceding claim, wherein said determining comprises comparing at least one of said primary block size to a first threshold and said secondary block size to a second threshold.

5. A method as claimed in claim 4, wherein said first and second thresholds are the same.

6. A method as claimed in claim 4 or 5, wherein at least one of said first and second thresholds is dependent on a value which takes into account a number of bits in an interval, said number of bits being adjusted to take into account one or more processing steps.

7. A method as claimed in claim 6, wherein said one or more processing steps comprise cyclic redundancy check, puncturing and adding of tail bits.

8. A method as claimed in claim 6 or claim 7, wherein the adjusted number of bits is quantised to a closest defined transport block size.

9. A method as claimed in any of claims 4 to 8, wherein at least one threshold is defined as a function of a network configured parameter.

10. A method as claimed in claim wherein the network configured parameter comprises a puncturing limit parameter.

1 1 . A computer program comprising computer executable instructions which when run cause the method of any of claims 1 to 10 to be performed.

12. An apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to:

determine if at least one of a candidate primary or secondary block size for a rank n MIMO transmission is below a certain size; and

if so, selecting a rank m M IMO transmission, where m is less than n.

13. An apparatus as claimed in claim 12, wherein n is 2 and m is 1 .

14. Apparatus as claimed in claim 12 or 13, wherein the at least one memory and the computer code are configured with the at least one processor to cause the apparatus to receive information indicating that an n MIMO transmission is to be made, prior to said determining.

15. Apparatus as claimed in any of claims 12 to 14, wherein the at least one memory and the computer code are configured with the at least one processor to cause the apparatus to compare at least one of said primary block size to a first threshold and said secondary block size to a second threshold.

16. Apparatus as claimed in claim 15, wherein said first and second thresholds are the same.

17. Apparatus as claimed in claim 15 or 16, wherein at least one of said first and second thresholds is dependent on a value which takes into account a number of bits in an interval, said number of bits being adjusted to take into account one or more processing steps.

18. Apparatus as claimed in claim 17, wherein said one or more processing steps comprise cyclic redundancy check, puncturing and adding of tail bits.

19. Apparatus as claimed in claim 17 or claim 18, wherein the adjusted number of bits is quantised to a closest defined transport block size.

20. Apparatus as claimed in any of claims 15 to 19, wherein at least one threshold is defined as a function of a network configured parameter.

21 . Apparatus as claimed in claim 20, wherein the network configured parameter comprises a puncturing limit parameter.

22. A user equipment comprising an apparatus as claimed in any of claims 12