GB2351632A - CDMA radio systems - Google Patents

Abstract

The invention relates to a method of manipulating physical channels having different spreading ratios in a CDMA radio system, and to a CDMA radio system using the method. The method comprising the steps; selecting as a basic presentation format a physical channel having a predetermined spreading ratio; if a channel to be manipulated has a different spreading ratio from the basic presentation channel format, transforming the channel to be manipulated into the basic presentation channel format; performing the manipulation on the transformed channel; re-transforming the transformed channel back into the format of the original channel after the manipulation.

Description

2351632 MANIPULATING PHYSICAL CHANNELS HAVING DIFFERENT SPREADING RATIOS

IN A CDMA RADIO SYSTEM

FIELD OF INVENTION

The invention relates to a method of manipulating physical channels having different spreading ratios in a CDMA (Code Division Multiple Access) radio system and to a radio system using the method.

BACKGROUND OF INVENTION

In a CDMA radio system there are several different types of physical channels. The distinguishing feature of the channel type is its data transfer capacity. The data transfer capacity is determined by the used spreading ratio: the smaller the spreading ratio, the higher the number of payload symbols. Usually the spreading ratio is equal to the length of the spreading code. An extreme case is the spreading ratio 'one', which equals to a spreading code whose length is one, i.e. there is only one chip in the spreading code.

The problem with such different physical channel types is that separate channel types need separate programs or processing implementations. For example in the GSM system such a problem does not basically exist, because for payload carrying channels there exists only one frame structure having a fixed amount of data transfer capacity.

BRIEF DESCRIPTION OF INVENTION

It is an object of the invention to provide a method, and a WMA radio system implementing the method, solving the above problems. This is achieved with a method of manipulating physical channels having different spreading ratios in a CDMA radio system, comprising: selecting as a basic presentation format a physical channel having a predetermined spreading ratio; if a channel to be manipulated has a different spreading ratio from the basic presentation channel format, transforming the channel to be manipulated into the basic presentation channel format, performing the manipulation on the transformed channel, re-transforming the transformed channel back into the format of the original channel after the manipulation.

The invention also relates to a CDMA radio system using physical channels having different spreading ratios, comprising: means for selecting as a basic presentation format a physical channel having a predetermined 2 spreading ratio, means for transforming the channel to be manipulated into the basic presentation channel format, if a channel to be manipulated has a different spreading ratio from the basic presentation channel format; means for performing the manipulation on the transformed channel; means for re transforming the transformed channel back into the format of the original channel after the manipulation.

The preferred embodiments of the invention are claimed in the dependent claims.

Several advantages are achieved with the invention. In the solution of the present invention, every channel type looks like a multicode channel of a fixed spreading ratio. The processing unit only needs to know how to treat a multicode channel of this one spreading ratio. This simplifies the implementation of the processing unit.

BRIEF DESCRIPTION OF FIGURES

In the following the invention will be described in greater detail by means of preferred embodiments and with reference to the attached drawings, in which Figures 1 A and 1 B illustrate an example of a CDMA radio system; Figure 2A illustrates a transmitter and a receiver; Figure 213 illustrates spreading and modulation carded out in the transmitter; Figure 3 illustrates a frame structure, Figure 4 illustrates a part of a spreading code tree; Figure 5A is a flow diagram illustrating a method according to the invention; Figure 5B is a flow diagram illustrating preferred embodiments of the method; Figure 6 illustrates a slot structure according to the invention', Figure 7 illustrates the handling required in the transmitter according to the invention.

DETAILED DESCRIPTION OF INVENTION

The present invention can be used in different mobile telephone systems. In the following examples, the use of the invention is described in the Universal Mobile Telephone System (UMTS) without restricting the invention to it- The examples illustrate the FDD (Frequency Division Duplex) operation of 3 the U1VITS, but do not restrict the invention to it.

With reference to Figures 1A and 1B, a typical mobile telephone system structure will be described. Figure 113 only comprises the blocks that are essential for the description of the invention, although it is apparent to a person skilled in the art that a common mobile telephone system also comprises other functions and structures which need not be discussed in greater detail here. The main parts of the mobile telephone system are: a core network CN, a U1VITS terrestflat radio access network UTRAN, and a user equipment UE, The interface between the CN and the UTRAN is called the lu interface, and the interface between the UTRAN and the UE is called the Llu interface.

The UTRAN is composed of radio network subsystems RNS, The interface between two RNSs is called the fur interface. The RNS is composed of a radio network controller RNC and one or more node Bs B, The interface between the RNC and the node B is called the lub interface. The reception area of the node B, i.e. cell, is denoted in Figure 1A with a C.

As the presentation in Figure 1A is very abstract, it is clarified in Figure 1 B by setting forth the parts of the GSM system that correspond with the parts of the U1VITS. It is clear that the presented mapping is by no me ans a binding one but an approximation, because the responsibilities and functions of the parts of the UMTS are still under heavy planning.

Figure 1B illustrates a packet switched transmission via Intemet 102 from a 'computer 100 connected with the mobile telephone system to a portable computer 122 connected with an user equipment UE. The user equipment UE may be a fixedly mounted wireless local loop terminal, a vehicle-mounted terminal or a hand-held portable terminal, for example.

The infrastructure of the radio network UTRAN is composed of radio network subsystems RNS, i.e. base station subsystems. The radio network subsystem RNS is composed of a radio network controller RNC, i.e. a base station controller, and at least one node B, i.e. a base station, under the control of the RNC.

The base station B comprises a multiplexer 114, transceivers 116, and a control unit 118 which controls the operation of the transceivers 116 and the multiplexer 114. The multiplexer 114 arranges the traffic and control channels used by a plurality of transceivers 116 to a single transmission connection lub.

4 The transceivers 116 of the base station B have a connection to an antenna unit 120 which is used for providing a bi-directional (or sometimes one-way) radio connection Uu to a user equipment UE. The structure of the frames transmitted in the radio connection Uu is determined in detail and the connection is referred to as an air interface.

The base station controller RNC comprises a group switching field

I 10 and a control unit 112. The group switching field 110 is used for switching speech and data and for connecting signaling circuits. The base station B and the base station controller RNC form a base station subsystem which additionally comprises a transcoder, also known as a speech codec, or TRAU (Transcoder and Rate Adapter Unit) 108.

The division of functions and the physical structures of the base station controller RNC and the base station B may differ according to the actual realization of the base station subsystem. Typically, the base station B implements the radio connection. The base station controller RNC typically manages the following: radio resource control, inter-cell handover control, power control, timing and synchronization, and paging of user equipment.

The transcoder 108 is usually located as close to a mobile switching center 106 as possible because this allows speech to be transmitted between the transcoder 108 and the base station controller RNC in a cellular radio network form, which saves transmission capacity.

The transcoder 108 converts different digital speech coding modes used between a public switched telephone network and a cellular radio network, to make them compatible, for instance from the 64 kb_it/s fixed network form to another form (such as 13 kbit/s) of the cellular radio network, and vice versa. Naturally, the transcoding is carried out only for speech. The control unit 112 carries out call control, mobility management, collection of statistical data and signaling.

The core network CN is composed of the infrastructure belonging to the mobile telephone system not being part of the UTRAN. Figure 1B illustrEites two equipment, which are part of the core network CN, namely a mobile switching center 106, and a gateway mobile switching center 104, which handles mobile telephone systems interfaces towards the outside world, in this example towards the Internet 102.

The essential parts of the user equipment UE are: an interface to the antenna of the user equipment UE, a transceiver, a control part of the user equipment UE, an interface to the battery, and a user interface comprising a display, a keyboard, a microphone and a speaker.

Figure 2A illustrates the functioning of a radio trans m itter-rad io receiver pair. The radio transmitter may be located in the node B or in the user equipment. Correspondingly the radio receiver may be located in the user equipment or in the node B. The upper portion of Figure 2A illustrates the essential functionality of the radio transmitter. Different services placed in a physical channel are e.g.

speech, data, moving video, or still video picture, and the control channels of the system that are processed in the control part 214 of the radio transmitter.

The control part 214 is related to the control of the equipment itself and to the control of the connection. Figure 2A illustrates manipulation of the control channel and data 200. Different services call for different source encoding equipment, for example speech calls for a speech codec. Source encoding equipment is, however, not presented for the sake of clarity in Figure 2A.

Different channels are then channel encoded in blocks 202A and 202B. One form of channel coding are different block codes, of which one example is cyclic redundancy check, or CRC. Another typical way of performing channel coding is convolutional coding and its different variations e.g. punctured convolutional coding and turbo coding.

Having been channel encoded, the channels are interleaved in an interleaver 204A, 204B. The object of interleaving is to make error correction easier. In interleaving, the bits are mixed with each other in a predetermined fashion, so that a transitory fading in the radio path does not necessarily make the transferred information unidentifiable. Different signals are multiplexed in block 208 in order to be sent using the same transmitter.

Then the interleaved bits are spread with a spreading code, scrambled with a scrambling code and modulated in block 206, whose operation is described in detail in Figure 2B, Fina, Ily the combined signal is conveyed to the radio frequency parts 210, %hich may comprise power amplifiers and bandwidth restricting filters.

Analog 'radio signal is then transmitted through an antenna 212 to the radio path Uu, The lower portion of Figure 2A illustrates the typical functionality of 36 a radio receiver. The radio receiver is typically a Rake receiver. The analog radio signal is received from the radio path Uu by an antenna 234. The 6 received signal is conveyed to radio frequency parts 232 that comprise a filter which blocks frequencies outside the desired frequency band. A signal is then converted in a demodulator 228 into an intermediate frequency or directly into baseband, and in this form the signal is sampled and quantized.

Because the signal in question is a multipath propagated signal, efforts are made to combine the signal components propagated in different multipaths in block 228 which comprises several Rake fingers.

In the so-called rowing Rake finger, the delays for the different multipath propagated signal components are searched. After the delays have been found, different Rake fingers are allocated for receiving each of its multipath propagated signals by correlating the received signal with the used spreading code delayed with the found delay of that particular multipath- The different demodulated and despread multipaths of the same signal are then combined in order to get a stronger signal.

The received physical channel is then demultiplexed in a demultiplexer 224 into data streams of different channels. The channels are then directed each to a de-interleaver 226A, 226B, wherein the received physical channel is then de-interleaved. After that physical channels are handled in a specific channel decoder 222A, 222B, wherein the channel coding used in the transmission is decoded. Convolutional coding is advantageously decoded with a Viterbi decoder. Each sent channel 220A, 220B, can be further processed, for example by transferring the data 220 to the computer 122 connected with the user equipment UE. The control channels of the system are conveyed to the control unit 236 of -the radio receiver.

Figure 213 illustrates in more detail spreading of the channel with the spreading code and the scrambling code, and modulation of the channel. In Figure 213 from left comes the bit stream of the channel into the block S/P, wherein serial to parallel conversion is carried out for each two bit sequences, whereby one bit is conveyed into the I branch of the signal and the other bit is conveyed into the Q branch of the signal. Then the I and the Q branches of the signal are multiplied with the same spreading code cch, whereby relatively narrow-band information is spread into a wide frequency band. Each radio corinection Uu has its own spreading code with which the receiver recognizes the transmissions meant for itself. Then the signal is scrambled by multiplying it with the scrambling code Cscramb that is different for each user equipment and 7 each base station. The pulse form of the produced signal is filtered with a filter p(t). Finally the signal is modulated into a radio frequency carrier by multiplying the different branches with a carrier. There is a 90 degree phase shift between the carriers of the different branches. The branches are then combined into one carrier which is ready to be sent into the radio path, excluding possible filtrations and power amplifications. The described modulation is QPSK (Quadrature Phase Shift Keying).

In Figure 4 examples of different spreading codes are illustrated.

Each dot 400 represents one possible spreading code. The vertical broken lines represent different spreading factors (SF) SF=I, SF=2, SF=4, SF=8, SF=16, SF=32, SF=64, SF=128, SF=256. The codes being located on the vertical broken line are mutually orthogonal. Two hundred fifty-six mutually orthogonal spreading codes can then maximally exist. For example in the UMTS, when a 4.096 megachip carrier is used, the spreading factor SF=256 corresponds to a transmission rate of about 32 kilobits/second.

Correspondingly, the highest usable transmission rate of 2048 kbit/s is achieved with the spreading code having the spreading factor SF=4. The transmission rate that the user obtains depends -on the channel coding used, e.g. while using 1/3 convolutional coding the transmission rate visible to the user is about one third of the actual transmission rate of the channel. The spreading factor may indicate the length of the spreading code. For example the spreading code (1) corresponds with the spreading factor SF=I. On the spreading factor level SF=2 there are two mutually orthogonal spreading codes (1,11) and (1,0). The spreading factor level SF=4 has four.mutually orthogonal spreading codes (1,1,0,0), (1,0,1,0) and (1,0,0,1). So the formulabon of the spreading codes is continued while traveling towards the lower levels of the code tree. The spreading codes at a certain spreading factor level are usually mutually orthogonal, e.g. in Walsh-Hadamard code sets.

Figure 3 shows an example of a frame structure used on a physical channelFrames 340A, 34013, 340C, 340D are given a running number from one to seventy-two, and they form a 720-millisecond long super frame. The length of one frame 340C is ten milliseconds. The frame 340C is divided into sixteen slots 330A, 33013, 330C, 330D. The length of slot 330C is 0.625 milliseconds. One slot 330C corresponds typically to one power control period, during which the power is adjusted for example by one decibel up or down, 8 The physical channels are divided into different types, including common physical channels and dedicated physical channels.

The common physical channels are used to carry the following transport channels: PCH, BCH, RACH and FACH, The dedicated physical channels consist of dedicated physical data channels (DPIDCH) 310 and dedicated physical control channels (DPCCH) 312. The DPIDCHs 310 are used to carry data 306 generated in layer two of the OSI (Open Systems Interconnection) model and layers above it, i.e. dedi cated control channels (DCH). The DPCCHs 312 carry the control information generated in layer one of the 051 model. Control information comprises: pilot bits 300 used in channel estimation, feedback information (FBI) 308 transmit power-control commands (TPC) 302, and optionally a transport format combination indicator (TFCI) 304. The VC1 304 tells the receiver the transport formats of different transport channels, i.e. Transport Format Combination, used in the current frame.

As can be seen from Figure 3, the down-link DPIDCHs 310 and DPCCI-Is 312 are time multiplexed into the same slot 330C. In the up-link the channels are sent in parallel so that they are iQ/code multiplexed (1 = in phase, 0 = quadrature) into each frame 340C.

The method according to the invention for manipulating physical channels having different spreading ratios in a CDMA radio system is presented in Figure 5A. The performance of the method begins in block 500.

In block 502, a physical channel having a predetermined spreading ratio is selected as a basic presentation format. In essence, this means that all or almost all other channels will be internally presented by means of this basic presentation format. "Internally' means that the presentation is used inside the transmitter or the receiver, i.e. the interface towards the outside world remains intact.

In block 504 a test is performed: is the spreading ratio of the channel to be manipulated different from the basic presentation channel format? If not, then the channel will be manipulated normally in block 506, whereafter the method will end in block 522.

If the channel to be manipulated has a different spreading ratio from the basic presentation channel format, then in block 508 the channel to be manipulated is transformed into the basic presentation channel format. After this in block 510, the manipulation is performed on the transformed channel.

9 The operation of blocks 506 and 510 is actually the same.

Therefore the operation of these blocks can be implemented with the same means, for example the same software module.

As the basic presentation channel format is internal, the transformed channel must be transformed back into the format of the original channel in block 520. Therefore the knowledge that some channel is actually a transformed channel which needs the re-transformation process must be stored somewhere, for example in a variable present in the software, The method of the invention can be implemented, for example, in the physical layer of the protocol stack. A physical channel consists of frames, and a frame consists of slots, and the basic presentation channel format has a predetermined number of symbols in a slot, The number of the symbols is always the same in the internal basic presentation format, One advantage is that the buffers used in the software or in the ASIC (Application Specific Integrated Circuit) for storing the symbols are of one length.

Preferred embodiments of the method will be presented next with reference to Figures 5B and 6. The transforming performed in block 508 is carried out as follows. First, a test will be performed in block 514., if the channel to be manipulated has a lower spreading ratio than the presentation channel format, the process moves to block 516, where the symbols of the channel to be manipulated are divided to at least two separate imaginary multicode channels having the basic presentation channel format.

In Figure 6, point A, two multicode channels are presented. A slot 600 of the first multicode channel contains eight symbols AO-A7, and a slot 602 of the second multicode channel contains eight symbols 130-137. This type of channel having eight symbols in a slot is selected as the basic channel presentation format. A "multicode channel" refers to a structure where the data transmission capacity of one user is increased by providing the user with two channels with different spreading codes. This structure is flexible:

sometimes the. user has only one channel, sometimes more, If the user uses a channel having 16 symbols AO-A15 in a slot, as illustrated in Figure 6, point 8, then this can be internally presented by using two Multicode channels each having 8 symbols in a slot. This is illustrated in Figure 6, point C, where the first multicode channel 600 comprises the even symbols AO, A2, A4, A5, A8, A10, A12 and A14, and the second multicode channel 602 comprises the odd symbols Al, A3, A5, A7, A9, All, A13 and A15. This kind of oddleven separation is only one of several possibilities. In fact, any kind of separation is possible as long as the required number of symbols are available for each channel slot. This embodiment can be used both in the transmitter and in the receiver. In general terms, if the basic channel presentation format has a spreading ratio N, and channel X has a spreading ratio M, and M<N, then channel X can be treated as N/M multicode channels of spreading ratio N by feeding symbols evenly to these multicode channels.

Naturally, different implementations are also possible. One implementation could comprise four multicode channels having four symbols in a slot, another implementation could have eight mufticode channels with two symbols in a slot. The choice is made purely as optimization in the product development phase.

In the second embodiment of the invention the transforming is performed in block 508 as follows. Again a test is made in block 514. if the channel to be manipulated has a higher spreading ratio than the presentation channel format, then the symbols of the channel to be manipulated are multiplied in block 518A into as many symbols as required for a slot of the basic presentation channel format.

The second embodiment is illustrated in Figure 6, points D and E.

Assume again that a channel having eight symbols in a slot is selected as the basic channel presentation format. In point D there are only four symbols AO A3, which are therefore multiplied to eight symbols: AO, Al, A2, A3, again AO, again Al, again A2, and again A3. The second embodiment can be -used both 'in the transmitter and in the receiver.

An alternative for the second embodiment is the third embodiment wherein in block 518E the symbols of the channel to be manipulated are divided into as many parts as required for a slot of the basic presentation channel format. The result is shown in Figure 6, point F, which now comprises the first half of symbol AC), the last half of symbol AO, the first half of symbol Al, the last half of symbol Al, the first half of symbol A2, the last half of symbol A2, the first half of symbol A3, and the fast half of symbol A3. Because the spreading ratio of the original channel format was twice as long as that of the basic channel presentation format, the original symbol can be halved and the halves will be handled as symbols half the length of the original symbols.

11 The despreading unit can consider the channel to have the nominal spreading ratio of eight. The third embodiment can be used in the receiver.

In general terms, if the basic channel presentation format has a spreading ratio N, and channel X has a spreading ratio L, and L>N, then channel X can be treated as a channel of spreading ratio N by multiplying every symbol into UN symbols, or alternatively despreading and integrating every N chips separately and not summing these partial symbols into one symbol before the processing which needs this unifing Next, an example illustrating the implementation of the first embodiment in the transmitter will be explained in connection with Figure 7.

The functionality is in black 206, which was already explained in connection with Figure 2A. The transmitter comprises means 214 for selecting as a basic presentation format a physical channel having a predetermined spreading ratio. There are also means 700 for transforming a channel to be manipulated into the basic presentation channel format, if the channel to be manipulated has a different spreading ratio from the basic presentation channel format. In the example the means 700 perform splitting: the symbols are split into each channel.

The transmitter also comprises means 702A, 702B for performing the manipulation on the transformed channel. Finally, as the basic channel presentation format is for internal use only, the transmitter comprises means 704 for re-transforming the transformed channel back into the format of the original channel after the manipulation. In the example the means 704 operate as a kind of a multiplexer. they multiplex the symbol streams of separate channels back into one stream. t The control unit 214 controls the blocks that are connected to it with a broken arrow-headed line. The invention is preferably implemented by software, but also ASIC (Application Specific Integrated Circuit) of some other HW implementation is of course possible. The means 214 for selecting, the means 700 fo transforming, the means 702A, 702B for performing, and the means 704 for re-transforming can consequently be software modules of the protocol stack residing in the user equipment UE, and in the radio network subsystem RNS.

In the receiver the invention is implemented in block 228, wherein despreading of a channel, channel estimation, and multipath combining are done, as was already explained in connection with Figure 2A 12 Even though the invention is described above with reference to an example shown in the attached drawings, it is apparent that the invention is not restricted to it, but can vary in many ways within the inventive idea disclosed in the attached claims.

13

Claims (11)

CLAIM$

1. A method of manipulating physical channels having different spreading ratios in a CDMA radio system, comprising:

(502) selecting as a basic presentation format a physical channel having a predetermined spreading ratio; (504) if a channel to be manipulated has a different spreading ratio from the basic presentation channel format, (508) transforming the channel to be manipulated into the basic presentation channel format; (510) performing the manipulation on the transformed channel; (520) re-transforming the transformed channel back into the format of the original channel after the manipulation.

2. A method as claimed in claim 1, wherein a physical channel consists of frames, and a frame consists of slots, the basic presentation channel format having a predetermined number of symbols in a slot.

3. A method as claimed in claim 2, wherein the transforming (508) is performed as follows: (514) if the channel to be manipulated has a lower spreading ratio than the presentation channel format, (516) dividing the symbols of the channel to be manipulated into at least two separate imaginary multicode channels having the basic presentation channel format.

4. A method as claimed in claim 2, wherein the transforming (508) is performed as follows: (514) if the channel to be manipulated has a higher spreading ratio than the presentation channel format, (518A) multiplying the symbols of the channel to be manipulated into as many symbols as required for a slot of the basic presentation channel format.

5. A method as claimed in claim 2, wherein the transforming (508) is performed as follows: (514) if the channel to be manipulated has a higher spreading ratio than the presentation channel format, (518B) dividing the symbols of the channel to be manipulated into as many parts as required for a slot of the basic presentation channel format.

6. A CDMA radio system using physical channels having different spreading ratios, comprising:

means for selecting as a basic presentation format a physical channel having a predetermined spreading ratio; 14 means for transforming a channel to be manipulated into the basic presentation channel format, if the channel to be manipulated has a different spreading ratio from the basic presentation channel format, means for performing the manipulation on the transformed channel; means for re-transforming the transformed channel back into the format of the original channel after the manipulation,

7. A CDMA radio system as claimed in claim 6, wherein a physical channel consists of frames, and a frame consists of slots, the basic presentation channel format having a predetermined number of symbols in a slot.

8. A CDMA radio system as claimed in claim 7, wherein the means for transforming comprise means for dividing the symbols of the channel to be manipulated into at least two separate imaginary multicode channels having the basic presentation channel format, if the channel to be manipulated has a lower spreading ratio than the presentation channel format.

9. A CDMA radio system as claimed in claim 7, wherein the means for transforming comprise means for multiplying the symbols of the channel to be manipulated into as many symbols as required for a slot of the basIc presentation channel format, if the channel to be manipulated has a higher spreading ratio than the presentation channel format.

10. A CDMA radio system as claimed in claim 7, wherein the means for transforming comprise means for dividing the symbols of the channel to be manipulated into as many parts as required for a slot of the basic presentation channel format, if the channel to be manipulated has a higher sprea.ding ratio than the presentation channel format.

11. A method of manipulating physical channels having different spreading ratios in a CDMA radio system substantially as herein described and illustrated in the accompanying drawings.

12, A CDMA radio system substantially as herein described and illustrated in the accompanying drawings.