MXPA00000219A - Channelization code allocation for radio communication systems - Google Patents

Abstract

Variable spreading factors and multi-code transmissions are flexibly accomodated by assigning spreading codes in accordance with the described techniques. Spreading codes are assigned so that the control channel is orthogonal to all physical channels in the composite spread spectrum signal. Power balance between in-phase (I)and quadrature (Q) branches in the transmitter is also provided by assigning physical channels to appropriate branches and splitting physical channels, where necessary.

Description

ALLOCATION OF THE CANALIZATION CODE FOR RADIOCOMMUNICATION SYSTEMS BACKGROUND This invention relates, in general, to transmissions at a variable data rate and, more specifically to the techniques for efficiently allocating spreading codes for data transmissions at a variable rate. Recently, cellular radiocommunication systems have been developed that use Discrete Spectrum Modulation and Code Division Multiple Access (CDMA) Modulation Techniques In a common, direct sequence CDMA system, an information data stream to be transmitted is superimposed on a data stream at symbol rate Much more often known as a scatter sequence, each scatter sequence symbol is commonly referred to as a chip.Each information signal is' assigned to a unique scatter code that is used to generate the scatter sequence commonly by periodic repetition The information signal and the dispersion sequence are commonly combined by In a process sometimes called coding or dispersion of the information signal. A plurality of scattered information signals are transmitted as modulations of the radio frequency carrier waves and ~~ are received together as a composite signal in a receiver. Each of the scattered signals is superimposed on all other coded signals, as well as the signals related to noise, in frequency and time. By correlating the composite signal with one of the unique scattering sequences, it is possible to isolate and decode the corresponding information signal. As radiocommunication is more widely accepted, it will be desirable to provide different types of radiocommunication services to meet consumer demand. For example, support for facsimile, e-mail, video, access to the Internet, etc., is possible through radiocommunication systems. In addition, it is expected that users may wish to have access to different types of services. For example, a videoconference between two users will include support for spoken language and video. Some of these_ different services will require relatively high data rates compared to the spoken language service that has traditionally been provided by radiocommunication systems, although other services will require service at a variable data rate. Thus, it is anticipated that future radiocommunication systems will need to be able to support communications at a high data rate as well as communications at a variable data rate. Various techniques have been developed to perform variable rate communications in CDMA radiocommunication systems. From the perspective of transmitting data at variable rates, these techniques include, for example, discontinuous transmission (DTX), variable dispersion factors, multi-code transmission and coding for early error correction (FEC). For systems that use DTX, the transmission occurs only during a variable portion of each frame, that is, a defined period of time to transmit a block of data of a certain size. The relationship between the portion of the frame used for transmission and the total frame time is commonly known as the occupation cycle?. For example, when it is transmitted at the highest possible rate, that is, throughout the frame period,? = 1, while for transmissions at rate 0, for example, during a pause in the conversation, = 0. DTX is used, for example, to provide transmissions at a variable data rate in systems designed in accordance with the United States standard. entitled "Compatibility Standard Mobile Station-Base Station for Broadband Broadband Spectrum Cell System", TIA / EIA Interim Standard TIA / EIA / IS-95 (July 1993) and its TIA / EIA Interim Standard TIA / EIA / revision IS-95-A (May 1995). These standards that determine the characteristics of the cellular communications systems of the United States are promulgated by the Association of Telecommunications Industries and the Association of Industries.

Electronics located in Arlington, Virginia. The variation of the scattering factor is another known technique for providing communication at a variable data rate. As already mentioned, DS-CDMA wide-spectrum systems scatter data signals across the available bandwidth by multiplying each of the data signals with scatter sequences. By varying the number of chips per data symbol, that is, the dispersion factor, while maintaining the fixed chip rate, the effective data rate can be varied - in a controllable manner. In common implementations of the variable dispersion factor approach, the dispersion factor is limited by the ratio SF-2 x SF ^ n, where Sfm? N is the minimum allowable dispersion factor corresponding to the highest user rate allowed. Another known technique for varying the rate of transmitted data is commonly known as multi-code transmission. According to this technique, the data is transmitted using a variable number of scatter codes where the exact number of codes used depends on the instantaneous user bit rate. Indeed, this means assigning a variable number of physical channels to a connection to provide variable bandwidth. An example of multi-code transmission is described in the application of US Patent Serial No. 08 / 636,648 entitled "Systems and Methods DS-CDMA in Compressed Mode, Multicode", filed on April 23, 1996, the description of which is incorporated in the present as a reference. Still another technique for varying the rate of data transmitted in radiocommunication systems includes the variation of the FEC. More specifically, the rate of forward error correction coding (FEC) is varied by using code drilling and repetition or by switching between different rate codes. In this way, the user rate varies while the bit rate of the channel is kept constant. Those skilled in the art will appreciate the similarities between the variation of the FEC and a variable dispersion factor as mechanisms for carrying out the transmission at a "variable rate." In the uplink and the downlink, it is desirable that any number of logical channels can They are transmitted simultaneously to support a single connection between a base station and a mobile station to support different data rates.To transmit these logical channels over the radio interface, a number of physical channels are assigned. separated using different spreading codes (channelization codes), that is, multi-code transmission is used.Each physical channel can have one of several possible data bit rates, that is, one of different possible spreading factors is used when they are dispersed data transmitted over the physical channel, however, to date it has not been provided a flexible solution that has assigned code words to the physical channels taking into account the codes that have already been assigned to other channels and power considerations associated with the transmitter branches in phase (I) and quadrature (Q). Therefore, it would be desirable to create new techniques and systems for assigning dispersion codes in a flexible form that supports multi-code transmissions and variable dispersion factors and that optimizes energy efficiency.

COMPENDIUM These and other problems associated with the previous communication systems are solved by the invention of the applicants, where dispersion codes are assigned for physical channels taking into account the dispersion codes already assigned to other physical channels that are to be transmitted in parallel with them. For example, if the physical channel that is being assigned with a spreading code is a control channel (PCCH), then the techniques according to the present invention investigate whether another physical channel in any of the IOQ legs of the transmitter has already been assigned a scatter code so that the PCCH can be assigned with a scatter code that makes the PCCH orthogonal to the other physical channels used in the composite signal of the spread spectrum. further, for physical data channels (PDCH), the techniques according to the present invention determine whether to any other channel has been previously assigned scatter codes on the same branch I or Q as the channel currently under investigation. If so, this PDCH is assigned with a dispersion code that makes the PDCH orthogonal to the other PDCHs in the same branch, as well as to the PCCH. In accordance with other exemplary embodiments of the present invention, in addition to assigning a dispersion code to each physical channel, the physical channels are also allocated between the branches and Q of the transmitter in a proposed manner to compensate for the power between the two branches and improve the operation of the power amplifier. For example, if the data rate associated with a connection to be established is relatively low, then the connection can be supported by a PDCH and a PCCH, one of which is assigned to the I branch of the transmitter and the other to the Q branch. However, if the data rate associated with a connection to be established is relatively high, then assigning the PDCH to one branch and the PCCH to the other creates a large power discrepancy between the two branches. In such a case, the data may be transmitted over two PDCHs, each of which is assigned to the I and Q branches of the transmitter, respectively, and the control channel may be assigned to the I or Q branch.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics and objectives of the invention of the applicants will be understood by reading this description together with the drawings, in which: Figure IA is a representation of the block diagram of an exemplary transmitter structure in the which the present invention can be implemented; Figure IB illustrates an alternative dispersion technique that can be performed on the transmitter of Figure LA; Figure 2 is an exemplary code tree; Figure 3 is a flowchart representing the allocation of the physical channels between the I and Q branches of a transmitter in accordance with an exemplary embodiment of the present invention; and Figure 4 is a flow diagram illustrating the assignment of the scatter codes to the physical channels according to the present invention.

DETAILED DESCRIPTION Although this description is written in the context of cellular communication systems that include portable or mobile radio telephones, those skilled in the art will understand that the invention of the applicants can be applied to other communications applications. In accordance with exemplary embodiments of the present invention, CDMA systems can support services at variable bit rates, such as spoken language, by providing control information in each frame specifying the instant data symbol rate for this plot. To do this in a normal time interval, the physical channels can be organized in frames of equal length (in time). Each frame carries a whole number of chips and a whole number of bits of information. Using this exemplary frame structure, the bit rate control information may be provided for each CDMA frame by transmitting this information on a separate physical channel. The physical channels carrying the data and the control information (for example, including the pilot / reference symbols for the channel estimation, the power control instructions and the data rate information) can be defined as the channel of control. physical data (PDCH) and physical control channel (PCCH), respectively. Each connection between a mobile station and a base station will be supported by a PCCH and at least one PDCH. The dispersion code, the symbol rate or the equivalent scattering factor of the PCCH are known a priori by the receiver. In this way, the receiver can determine the data rate of the PDCHs from the PCCH before demodulating / decoding the PDCHs. Exemplary techniques for handling BRI information are described in the co-pending, co-pending US Patent Application Serial No., _ __ entitled "low rate detection for variable rate communication systems" by Dahlman, et al., presented on the same date as the present one. Many of the potential advantages are attributable to variable rate transmission. For example, it is possible to reduce the interference for different users of the system since the chip rate is kept constant and a lower bitrate provides a dispersion factor of greater than: r, thus allowing a lower transmission power. Those skilled in the art will readily appreciate how this ability to vary the rate of information in a CDMA system can be advantageously used to vary other parameters. However, the techniques for efficiently assigning dispersion codes for different physical channels (ie, PCCH and PDCH) are necessary and are described below. - A physical channel is a bit stream of a certain rate, which is dispersed using a certain code and assigned to the branch in phase (I) or quadrature (Q) in a transmitter. Variable rate services are supported by dispersion with a variable dispersion factor as already described. A number of data streams are dispersed at the chip rate using alsh codes of different length, followed by the summation, if desired, randomization. The structure of an exemplary transmitter (usable, for example, in a base station or a mobile station) that performs these "scatter, sum, and scramble" operations is illustrated in Figure A. In this, a first I? supplied to the multiplier 10 with a data rate of Rj which is equal to the chip rate Rc divided by the scattering factor FFn for this data stream.This data stream is dispersed with a channelization codeword Cu having a length of 2 chips that is selected so that the result of the multiplier 30 has an Rc chip rate by selecting a value to be related to the desired data rate of the physical channel I ?. For example, a channel data rate 250 kbps physical is dispersed at a chip rate of 4 Mcps using a channeling code of 16 (2) long chips.More details coa regarding the assignment of a particular channelization code according to the present invention are described below. In the same way, additional data streams are supplied to multipliers 12, 14 and 16 (and other branches that are not illustrated) to disperse their respective data streams with channel code words having a length that is selected to originate at a rate of Rc chips. The rate of data flows may be "limited to a range such that the dispersion factors used are greater than or equal to a predetermined SFmin." Each physical channel is then weighted by the respective amplifiers 18, 20, 22, and 24. Weights can be chosen individually to assign power to each physical channel, so that the predetermined quality requirements are met, for example, the bit error rate of each physical channel.The physical channels in the "I" branch of the transmitter they are added in the adder 26. In the same way, the physical channels in the "Q" branch of the transmitter are summed in the adder 28. Then, if desired, randomization is performed in the overlapping physical channels. In at least two ways, the first, as shown in Figure IA, randomization can be done by forming the I and Q pairs as a complex number in blocks 30 and 32 and then multiplying the result with another complex number (that is, the scrambling code with complex value ca? eator = i = jcQ) in block 34. It is also possible to perform randomization on the I and Q branches separately as illustrated in Figure IB, multiplying I and Q with two scrambling codes with real value Ci and CQ in blocks 36 and 38. The scrambling code is synchronized to the chip rate. The resulting signal is sent, for example to the processing circuits of the transmission signal * (for example, a QPSK or O-QPSK modulator followed by, possibly, pulse-forming filters), it is amplified by a transmitter power amplifier. (not shown) and finally it is coupled to an antenna (it is not shown either). The Walsh codes used to scatter in multipliers 10-16 can be seen in a tree-like manner, as illustrated in Figure 2. The codes of the same level in the tree are orthogonal and have the same scattering factor. Thus, the codes c4.?, C4.2, c4.3 and C4.4 are orthogonal codes, each one of which has the same scattering factor, that is, the same number of chips. If a physical channel is scattered with a first code in the tree, and another physical channel is dispersed with another code that is: (1) not the same as the first code, (2) not to the left of the first code on the way to the root of the tree, and (3) not to the subtree that has the first code as the root, then the two scattered physical channels will be orthogonal. For example, if the PCCH is assigned the code c.?, And a PDCH is assigned the code C8.5, then these two scattered channels would be orthogonal. However, if the PDCH was assigned with the code Cs.i or cs.2 / then the PCCH and PDCH would be non-orthogonal. Each physical channel is assigned with a dispersion code from the tree, with dispersion factors coinciding with the respective data rates. As the data rate varies for a particular PDCH, a code of a different level of the tree would be assigned. For example, the increase in data rates will cause the selection of the code to move to the left in the tree, while for the decrease of the data rates the code selection will move to the right. Thus, a common variable rate PDCH will normally move up and down along a certain path in the code tree as its data rate varies. The assignment of the physical channels to the I and Q branches of the transmitter, as well as the codes of the code tree in Figure 2 as scatter codes (for example, cu, cQ ?, etc, in Figure IA) can be made from according to the following rules in accordance with the present invention. Figure 3 is a flow diagram illustrating an exemplary technique for allocating physical channels between the I and Q branches of a transmitter in accordance with the present invention for the case where it is possible to use a single PDCH (i.e. band) to support a connection. Those skilled in the art will appreciate that this technique provides a relatively compensated transmission power for each of the I and Q branches which in turn provide better performance of the power amplifier.The flow begins in block 40, where it is determined if the power needed to transmit the single PDCH is significantly greater than that needed to transmit the PCCH, for example, if the PLCH is going to be transmitted at a much higher rate than the PCCH if the quality of service (QoS) requirements for In this case, the flow proceeds to block 42, where the data flow is divided into the lowest rate PDCHs.The three physical channels can then be assigned , for example, as illustrated in block 2, to branches I and Q in a way that will help to more evenly compensate the transmission power between these two branches. another part, in block 40 it is determined that the PDCH is not going to be transmitted at a power significantly greater than the PCCH, then the flow proceeds to step 44, wherein the control channel is assigned to one of the branches and the channel of data to the other. Note that the particular selection of Q and I in blocks 42 and 44 is only exemplary, and that these designations, of course, could be reversed. Having assigned the physical channels to one of the I and Q branches in the transmitter, the next assignment made in accordance with the present invention is the selection of a scatter code for each of the physical channels. According to the present invention, the dispersion code selected to disperse the PCCH must be such that the PCCH is orthogonal to all other physical channels that are to be transmitted in the composite spread spectrum signal, ie, orthogonal to all channels in the I and Q branches. This feature is desirable because the PCCH must first be modulated and decoded in the receiver to provide estimates of the channel that are used to process the data channels transmitted in the same spread spectrum signal. Accordingly, an exemplary technique for assigning scatter codes according to the present invention will now be described with respect to the flow chart of Figure 4. The flow begins in block 52, where it is determined whether the channel present that is being assigned with a dispersion code is a data channel or a control channel. If the channel what is currently being assigned with a dispersion code is a PDCH, then the flow continues to block 54. In this, the PDCH is, assigned with a scatter code that makes the PDCH orthogonal to the PCCH (if the PCCH has already been assigned with scatter code) and which makes the PDCH orthogonal to either of the other PDCHs that are in the same I or Q branch of the transmitter. For example, suppose that at the time this particular PDCH is being assigned with dispersion code that the PCCH has already been assigned, the code c4.? and to the other PDCH the code has already been assigned. In addition, suppose that this particular PDCH is going to be transmitted at a data rate that requires a code of level 3 with respect to the code tree of Figure 2. with the present invention, this particular PDCH could then have assigned any of the codes cß.3, cs.4, Cs. ß / cß.7 and Cs.ß- This PDCH could not be assigned to the codes cs.i or CQ .2 since such assignments would give rise to non-orthogonality with the control channel. However, this PDCH could have assigned code cs.s if it is assigned to the opposite branch of the transmitter of the PDCH which has already assigned this dispersion code. The flow then proceeds to block 56 where more codes are assigned if additional channels remain. Otherwise the process ends. If, in block 52, a control channel for dispersion code assignment is evaluated, then the flow continues to block 58. In this, a code is selected that orthogonally makes the control channel to all channels with previously assigned codes, so that the PCCH can be easily decoded and demodulated in the receiver to provide channel estimates for use and evaluation of the data channels. It will be understood that the invention of the applicants is not limited to the specific modalities described above and that modifications can be made by those skilled in the art. The applicants' scope of invention is determined by the following clauses, and any and all modifications that fall within the scope are proposed to be included in this.

Claims (22)

1. A transmitter with a branch in phase (I) and a branch in quadrature (Q) to transmit a composite signal of the scattered spectrum that includes at least two physical channels, the transmitter comprises: the medium, associated with the I branch, to disperse data associated with one of the at least two physical channels using a first scatter code to generate a first scattered physical channel; and the means, associated with the branch Q, to disperse data associated with another of the at least two physical channels using a second scatter code to generate a second dispersed physical channel; wherein the first and second scatter codes have a different number of chips and the first and second scatter codes are selected such that the first and second scattered physical channels are orthogonal to each other.

2. The transmitter of claim 1, wherein one of the at least two physical channels is a control channel (PCCH) and the other of the at least two physical channels is a data channel (PDCH).

3. The transmitter of claim 2, further comprising: means for balancing the power associated with the I and Q branches of the transmitter by selectively assigning the at least two physical channels to the I and Q branches based on the transmit power requirements

4. The transmitter of claim 3, wherein the at least two physical channels include a second PDCH that is dispersed using a third code to generate a third dispersed physical channel, and wherein the means for balancing the power allocates the second PDCH to the same transmitter branch as the PCCH, based on the transmission power requirement.

5. The transmitter of claim 4, wherein the second and third scattered physical channels are orthogonal. The transmitter of claim 4, wherein the second and third scattered physical channels are non-orthogonal 7. The transmitter of claim 4, wherein the second and third codes are the same codes. 8. A method for assigning scatter codes to a plurality of physical channels that are to be transmitted in a composite spread spectrum signal in a radio communication system, comprises the steps of: assigning a first scatter code with a first number of chips to a control channel, so that the control channel is orthogonal to the others of the plurality of physical channels in the composite, spread spectrum signal; and assigning a second spreading code having a second number of chips different from the first number of chips to a first data channel, whose second spreading code is selected so that the control channel and the first data channel are orthogonal to each other . 9. The method of claim 8, wherein the control channel carries usable reference information to make estimates of the channel. The method of claim 8 further comprises the step of: assigning a third dispersion code having a third bit length to a second data channel, the third dispersion code selected such that the control channel and the second channel of data are orthogonal to each other. The method of claim 10, wherein the first and second data channels are orthogonal. The method of claim 10, wherein the first and second data channels are non-orthogonal. The method of claim 10, wherein the second and third scatter codes are the same codes. The method of claim 10, further comprising the steps of: allocating the second data channel to a branch I or a Q branch in a transmitter; and assigning the third data channel to the other of the I or Q branches. 15. The transmitter of claim 1 further comprises: the means for scrambling the first and second scattered physical channels of the I or Q branches. 1

6. A method for assigning scatter codes to a plurality of physical channels that are to be transmitted in a spread spectrum signal, composed in a radio communication system, comprises the steps of: assigning a first scatter code having a first number of chips to a first data channel; and assigning a second spreading code having a second number of chips different from the first number of chips to a control data channel, whose second spreading code is selected so that the control channel and the first data channel are orthogonal between yes. 1

7. The method of claim 16, wherein the control channel carries usable reference information to make estimates of the channel. The method of claim 16, further comprising the step of: assigning a third dispersion code having a third length of -bit to a second data channel, the third dispersion code selected so that the control channel and the second data channel are orthogonal to each other. 19. The method of claim 18, wherein the first and second data channels are orthogonal. The method of claim 18, wherein the first and second data channels are non-orthogonal. The method of claim 18, wherein the second and third scatter codes are the same codes. 22. The method of claim 18, further comprising the steps of: assigning the second data channel to a I or Q branch in a transmitter; and assigning the third data channel to the other of the I or Q branches.