DATA MODULATION IN A COMMUNICATION SYSTEM

The present invention relates to communication of data and in particular to modulation of data transmitted between two entities of a communication system.

A communication system is a facility which facilitates communication between two or more entitles such as communication devices, network entities and other nodes. A communication system may be provided by one more interconnect networks. It is noted that although a communication sysgtem typically comprises at least one communication network, lor example a fixed line network or a wireless or mobile network, in its simplest form a communication system is provided by two entities communicating with each other. The communication may comprise, for example, communication of data for carrying Communications such as voice, electronic mail (email), text message, multimedia and so on.

A user may communicate by means of an appropriate communication device. An appropriate access system allows the communication device to access to a communication system. An access to the commuπicat-ons system may be provided by .means of a fixed line or wireless communication interface, or a combination of these. Examples of wireless access systems include cellular access networks, various wireless local area networks (WLANs), wireless personal area networks (WPANs), satellite based communication systems and various combinations of these.

A communication system typically operates in accordance with a standard and/or a set of specification and protocols which set out what the various elements of the system are permitted to do and how that should be achieved. For example, it is typically defined if the user, or more precisely user device, is provided with a circuit switched bearer or a packet switched bearer, or both. Also, the manner in which communication and various aspects thereof should be implemented between the user device and fhe various elements of the communication and their functions and responsibilities are typically defined by a predefined

In a radio or wireless system an entity in the form of a base station provides a node for communication with user communication devices, often referred to as mobile stations. Communications in the direction from the base station to the user device is seen as occurring on a "downlink" (OL). Communications in the direction from the user device to the base station is, then seen as occurring on an "uplink" (UL). It is noted that in certain systems a base station is called 'Node B.

Signalling between various entities may be divided between signalling of control data and actual data. The latter refers to the data content the users wish to communicate. Control signalling, in turn, associates to transfer of information that is not related as such to the data content the users may wish to be transferred. In flie following these two forms of signalling are separated by referring to control signalling and data signalling, where appropriate.

To ensure proper operation of the system, Ihe control signaling typically has higher quality requirements than the data signalling. On the other hand, the amount of information conveyed by control signalling such as by acknowledgement signalling is typically only one or two bits. This is less than what can be earned by data modulated symbols, for example Quadrature amplitude modulated (QMS) symbols. For example 16QAM carries 4 bus and 64 QAM carries 6 bus.

An example of control signaling is the transfer of positive and negative acknowledgement information signaling,, often referred 16 as ACK/NACK signalling. The acknowledgement signaling is used to provide feedback concerning previous fransmissions , for example if a previous data transmission such as a data packet is properly received.

Despite the advantages in signaling technologies,, there is still need to optimize the performance of communications between two devices, for example though reduction of errors in control signalling. Use of a single modulation method for control signalling and data signalling might be desired in various applications

The herein described embodiments aim to address one or several of the above mentioned shortcomings and/or desires.

According to an embodiment, there; is provided a modulator for a communication device, the modulator . being configured to multiplex control symbols and data symbols for transmission in a signal based on information of the distance between the positions of at least two control symbols in a representation of symbol positions in the signal

In accordance with another embodiment there is provided a modulation method, comprising multiplexing control symbols wiih data symbols for transmission in a signal based on information of the distance between positions of at least two control symbols in a representation of symbol positions in the signal.

In accordance with yet another embodiment there is prowled a communication system comprising a first communicaion device and a second communication device, wherein at least one of the devices is configured to multiplex cøntro! symbols and data symbols for transmission in a signal to the other device based on information of the distance between the positions of at least two control symbols an a representation of symbol positions in the signal receiving a transmission by a first communication device from a second communication device.

in accordance with a more specific embodiment the control symbols are multiplexed based on at least one Euclidean distance. At least two control symbols may be mapped into positions that have the largest distance between them or that are otherwise located at least a predetermined length apart from each other.

Information about the power on at least one position in the representation may also be utilised. Positions witi the highest power may be selected for use by control symbols. According to an embodiment, positions with a power that

exceeds a predefined power threshold are selected for use by the control symbols.

The control symbols may comprise an acknowledgement by a first communication device, of a transmission from a second communication device, wherein the acknowledgement is multiplexed with the data symbols into a signal for transmission from the first communication device. The acknowledgement may comprise ACK/NACK symbols.

The representation may comprise a constellation diagram. The modulation may comprise at least one of quadrature amplitude modulation and phase shift keying. .

The computations may be provided by a computer program comprising program code means adapted to perform the necessary steps when the program is run on a processor. The processor may be for a stafion of a communication system.

For a better understanding of the present invention and how the same may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which:

Figure 1 shows a schematic presentation of a communication system wherein the invention may be embodied;

Figure 2 shows a flowchart in accoπlanoe with an embodiment; Figure 3 shows a mapping scheme;

Figure 4 shows a table of values associated with the Figure 3 example,

Figure 5 shows another mapping scheme; and

Figures 6 and 7 shows tables of valises associated with the Figure 5 example.

Before explaining in detail a few exemplifying embodiments, a brief explanation of certain general principles of wireless communications in a system comprising a base station and a communication device such as a mobile station is given with reference to Figure 1.

A communication device, for example a user device, can be used for accessing various services and/or applications provided via a communications system. In wireless or mobile systems the access is provided via an access interface between a user device 1 and an appropriate wireless access system. The user device can typically access wirelessly a communication system via at least one base station 10 or similar wireless transmitter and/or receiver node. Non-limiting examples of access nodes are a base station of a cellular system and a base station of a wireless local ansa network (WLAN ). Each user device may have one or more radio channels open at the same time and may be connected to more than one base station.

The base station may be connected to other systems, for example a data network. A gateway function between a base station node and another network may be provided by means of any appropriate gateway node, for example a packet data gateway and/or an access gateway.

A base station is typically controlled by at feast one appropriate controller entity. The controller entity can be provided for managing of the overall operation of the base station and communications via the base station. The controller entity is typically prowled with memory capacity and at least one data processor. Functional entities may be provided in the controller by means of the data processing capability thereof. The functional entities provided in the base station controller may provide functions relating to radio resource control, access control, packet data content control and so forth.

Certain embodiments can be used, for example, for the uplink (UL) part of a long term evolution (LTE) radio system for transmission of downlink (OL) ACK/NACK with UL data. Therefore the non-limitng example of Figure 1 shows the concept of what is known as the long term evolution (LTE). The system provides an evolved radio access system that is connected is a packet data system. Such an access system may be provided, for example, based on architecture that is known from the Evolved Universal Terrestrial Radio Access (E-UTRA) and based

on use of the Evolved Universal Terrestrial Radio Access Networks (E-UTRAN) Node Bs (eNBs). An Evolved Universal Terrestrial Radio Access Network (E- UTRAN) consists of E-UTRAN Node Bs (eNBs) which are configured to provide base station and control functionalities. For example, the eNBs nodes can . - provide independently radio access network features such as user plane radio fink control/medium access control/physical layer protocol (RLC/MAC/PHY) and control, plane radio resource control (RRC) protocol terminations towards the user devices,

It is noted that Figure 1 shows this architecture only to give an example of a possible communication system where the embodiments described below may be provided and that other arrangements and architectures are also possible. For example, the user device may communicate with a different access system,

The user device 1 can be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content For example, a user device may access data applications provided via a data network. For example, various applications may be offered in a data network that is based on the Internet Protocol (IP) or any other appropriate protocol. An appropriate user device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS), a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capacilities, or any combinations of these or the like.

The mobile device may communicate via an appropriate radio interface arrangement of the mobile device. The interface arrangement may be provided for example by means of a radio part 7 and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile

A mobile device is typically provided with at least one data processing entity 3 and at least one memory 4 for use in tasks ft is designed to perform. The data processing and storage entities can be provided on an appropriate circuit board and/or in chipsets, This feature is denoted by reference 6.

Figure 1 shows further a modulator component 9 connected to the other elements. Examples for modulation functions thereof are described later in this specification. It is noted that tie modulator functions may be arranged to be : provide by the data processing entity 3 instead of a separate component.

The user may control the operation of the mobile device by means of a suitable user interface such as key pad 2, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 5, a speaker and a microphone are also typically provided. Furthermore, a mobile device may comprise appropriate connecters (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

The following discusses embodiments an acknowledgement of transmission in one direction and data sent in another direction are multiplexed in a symbol level, and more particularly, certain embodiments where downlink ACK/NACK and uplink data. are time-multiplexed in the symbol level In the following examples downlink ACK/NACK signalling is modulated for transmission with uplink data from a mobile station to a base sfation. It is noted that instead of a base station, fine communication can be sent e.g. to another mobile station and that the modulation may also take place in a base station.

An exemplifying embodiment of the method is now described with reference to the flowchart of Figure 2. In this embodiment control symbols are multiplexed at

102 with data symbols based on informatiokn on the distance between positions of at least two control symbols in a representation of symbol positions in the signal, as determined at step 100. The multiplexed symbols can then be transmitted at

In accordance wfth a more specrffc embodiment a particular ACK/NACK bit mapping rule is used when ACK/NACK symbols are multiplexed with data symbols at 102. The multiplexing may be based on time multiplexing.

The symbols can be mapped Into a signal space diagram to illustrated idea! positions of symbols in a signal . An example of such representation of a signal is a constellation diagram, or simply constellation. A constellation diagram is an example of the possibilities to visualise symbol positions In a signal, and the basis thereof that a transmuted symbol can be represented as a complex number. The symbols are represented as complex numbers and can thus be visualized as points on the complex plane.

A constellation diagram can be used to provide a representation of a signal modulated by a digital modulation scheme such as the quadrature amplitude modulation (QAM) or a phase-shift keying (PSK). Quadrature (Q) carriers can be provided by modulating a cosine and sine carrier signal with the real and imaginary parts of the complex number, respectively, the symbol can be sent with two carriers on a single frequency. The real and imaginary axes are often called the in phase, or l-axis and file quadrature, or Q-axis. :

The constellation diagram can be used for displaying a signal as a two- dimensional diagram in a complex plane at symbol sampling instants, or points. The constellation diagram can thus be used to provide a representation of the position of the symbols in. the modulation scheme, and allows for a straightforward visualization of the modulafion process. Examples of rectangular 16 QAM constellation diagrams 30 are shown in Figures 3 and 5.

ACK/NACK symbols to be transmitted can be mapped into same constellation diagram that is used by the data symbols. In accordance win an embodiment constellation points having file largest Euclidean distance can be selected for

ACK/NACK transmission. The Euclidean distance is commonly understood as being the distance between two points represented as the mot of the square of

difference between co-ordinates of a pair of objects. The Euclidean distance can be computed as

where k=[1,2...m], / =[1,2...ml presents the indexes of modulatkm constellations used for data symbols, and m is number of constellations used for data symbols. _

Another possibility is to use a predefined threshold for the distance. For example, any points with a Euclidean distance that is larger than a predefined threshold can be selected. In accordance with a yet another embodiment the selection rule allows selection amongst constellation points that provide the most promising candidates, for example, 2 or 3 largest Euclidean distances, or any other predefined number of largest Euclidean distances.

In accordance with a further embodiment the power levels of the constellations points are also taken into consideration in the selection process. For example, the points that have the largest Euclidean distance or large enough Euclidean distance and a high enough power are selected. Thus a point with a large enough distance but too low power may not be selected An optimised combination of distance thresholds and power thresholds may be employed. In some applications it may be desirable to select the points with the highest power levels even if they are not he points with the largest distances.

Figure 3 shows an example of one-bit ACK/NACK mapping into a constellation diagram 30, More particularly, in this specific example a 16 quadrature amplitude modulation (QMA) scheme is used for data symbols. Use black dots 32 denote the proposed constellation points for ACK/NACK transmission. The White dots 34 are then left for data. More detailed examples of possible mapping rules considering also 64 QAM modulation, and two-bit AGK/NACK transmission are considered below.

Table 1 shown an Figure 4 is an example for constellation mapping of ACK/NACK signalling into complex-valued modulated symbols, X=l+jQ, with different data modulation schemes. More particularly, in the examples shown in Table 1 one-bit ACK/NACK symbols are mapped with data modulations QPSK, 16QAM and 64 QAM. The complex-values of this example are based on 3 ^rd Generation Partnership Project; (3GFP) Technical Specification TS 36.211 "Physical Channels and Modulation', version 1 ,0.0 of 19 March 2007.

Figure 5 shows mapping of a two-bits ACK/NACK signalling Into a constellation diagram 30. Two-bits ACK/NACK signalling may be needed e.g., when dual- codeword Multiple-Input Multiple-Output (MIMO) transmlssiom is used in the downlink.

An example for constellation mapping of two-bit ACK/NACK signalling with 16 QAM modulation is shown in Table 2 and for 64 QAM is shown in Table 3, see

Figures 6 and 7, respectively In 16 QAM modulation a pak of ACK/NACK signaling bis is mapped into complex-valued modulation symbols, X=l+Q, according to Table 2. In 54 QAM modulation, pair of the bite is mapped into complex-valued modulation symbols, x=l+jQ, according to Table 3.

The required data processing instructions for the modulatio and/or the related decision making may be provided by means of one or more data processors, Data processing may be provided in a processing unit or module of a station, for example a user device or a base station. The above cdescribed functions may be provided by separate processors or by an integrated processor. An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded on an appropriated processor, for example in a processor of a base station controller or a controller of a user device. T he program code may for example, perform the generation and/interpretatiuon of information signalled between the various entities and control various operations. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier

disc, card or tape. A possibility is to download the program code product to the mobile device via a data network.

An advantage of the above described examples of mapping ACK/NACK symbols, or other control signalling symbols, into the data symbols in a constellation is that optimized performance can be obtained. This is because the control symbol signals can be provided to have the maximum Euclidean distance or a predefined Euclidean distance between each other, thereby reducing ihe risk for errors. The quality of control signaling can be improved. Use of the constellation points from the same constellation diagram for control and payload data in modulation is enabled. If maximum power or large enough power is used for signalling control symbols maximized Signal-to-Noise Ratio (SNR) without any significant effect to Peak-to-Average Ratio (PAR) can be achieved.

It is noted that whilst embodiments have been described in relation to modulation in user devices such as mobile stations and network devices such as base stations, embodiments of the present invention are applicable to any other type of apparatus suitable for data communication where modulation may be needed. Similar principles may be appled to any communication technologie where modulation of control and data symbols can be utilised.

It is also noted that although certain embodinents 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. It is also noted that the terrm access system is understood to refer to any access system configured for enabling wireless communication for user accessing applications.

It is also noted herein that while the a bove describes exemplifying embodimerds of the invention, there are several variations and modifications which may be made to the disclosed solution without depqarting from the scope of the present invention.