MXPA00002096A - A method for assigning spreading codes - Google Patents

Abstract

The present invention relates to methods for assigning spreading codes to forward-link connections with variable bit-rate in DS-CDMA communication systems. A first connection is assigned a first number of codes (x) from a first set (S1) of orthogonal codes. A second connection is assigned a second number of codes (y). A first part (y-k1) of the second number of codes (y) is taken from the first set (S1) of orthogonal codes. A second part (k1) of the second number of codes (y) is taken from a second set (S2) of orthogonal codes which is non-orthogonal to the first set (S1).

Description

METHOD FOR ASSIGNING EXTENSION CODES TECHNICAL FIELD OF THE INVENTION The present invention relates to methods for assigning extension codes to forward link connections of type DS-CDMA. DESCRIPTION OF THE RELATED TECHNIQUE CDMA (Multiple Access by Code Division) is a well-known method for multiple access in a radio communication system. The CDMA method uses the extension spectrum technique where many users simultaneously occupy the same frequency band with their radio channels. In a DS-CDMA (Direct Sequence CDMA) system which is a particular type of CDMA techniques, each user receives a specific extension code by which the user is separated from the other users of the system. Another name for an extension code is an extension sequence or extension code sequence. The information transmitted in the radio signal is encoded (extended) by a specific extension code in the transmitter. On the receiving side the encoded information is decoded (concentrated) by correlation with the same specific extension code again or by filtering the information received in a corresponding filter.

An extension code of the same length as the symbol interval is called a short extension code. Orthogonal codes are codes that have zero cross-correlation for zero time offset. The use of orthogonal codes will reduce intracellular interference, that is, the interference of other forward link signals in the same cell. Normally, intracellular interference is not totally eliminated since the time dispersion partially destroys the orthogonality between signals encoded with orthogonal codes. In general, a set of orthogonal codes contains only a finite number of codes, where the number of codes is always less than or equal to the length of the codes. Accordingly, there is only a finite number of orthogonal extension codes available, extension codes that are almost orthogonal or non-orthogonal have to be used to increase the number of simultaneous users or increase the bit rate of the system. In a DS-CDMA forward link (transmission from a base station to a radio unit), orthogonal extension codes are frequently used to separate different radio channels. When a connection through a radio channel uses more than an extension code, it is said to employ what is known as multiple code transmission. For connections of variable bit rates, that is, a connection where the bit rate varies during a call, the number of extension codes actually used for each connection varies in time and between different connections. A high bit rate uses more extension codes than a lower bit rate. An example of a scheme for assigning extension code to a connection with a variable bit rate in a radio communication system is the static assignment. A static assignment means that for a connection, when a call is established, it receives as many extension codes as is necessary to be able to transmit at a maximum bit rate required. This means that a small number of connections with a variable bit rate connection can receive all available extension codes if they do not use all these codes simultaneously. Another example of a scheme for assigning extension codes to a connection is dynamic allocation. A dynamic allocation means that all connections share a common set of extension codes that are continuously redistributed by a base station, in accordance with the instantaneous need of each connection.

Every time you must increase the bit rate in a connection, the base station must inform the radio unit what new extension codes to receive. This will require a significant expense in terms of communication between the base station and the radio unit. U.S. Patent No. 5,533,013 describes a method and system for assigning full orthogonal extension codes and radio channels in a combined CDMA / TDMA or TDMA / CDMA communication system. Said method comprises the step of assigning a selected orthogonal extension code within a set of full orthogonal extension codes. Said system comprises a device for assigning selected orthogonal extension codes within at least one set of complete orthogonal extension codes. If there is more than one set, the complete orthogonal extension code code sets have been selected in such a way that they are completely orthogonal to each other. U.S. Patent No. 5,452,328 describes a method for assigning separate sets of binary extension code sequences to different nodes in a multi-node communication network. Each node in the network receives selected extension code sequences within a family of almost "orthogonal" binary sequences. The patent also discloses an apparatus and method for generating said sequence family by combining a first multi-stage shift register and a second multi-stage shift register. As will be seen here, each of the methods presented in these patents is of a different constitution from the method of the present invention. The term "radio unit" includes all portable and non-portable equipment intended for radio communication, such as mobile telephones, vocedores, telex, electronic notebooks and communicators. These devices can be used in any type of radio communication system, such as cellular networks, satellite networks or small local networks. SUMMARY OF THE INVENTION The present invention solves related problems in that how to a forward link connection is assigned specific extension codes in the DS-CDMA communication system where only a finite number of orthogonal extension codes are available. A problem occurs when the system is using a static assignment for connections of variable bit rates. The system may suffer from a shortage of extension codes even if only a small number of extension codes are used simultaneously in reality. Each connection receives the amount of extension codes it requires for the maximum bit rate regardless of whether the maximum bit rate is required for only a short time. Another problem occurs when the system is using a mechanical assignment for variable bit rate connections. A significant expense in communication between the base station and the radio unit is required to inform the radio unit which new extension codes should be received each time the bit rate is increased. Taking into account the above, a primary object of the present invention is to provide methods and means for assigning extension codes for radio units in a DS-CDMA communication system with variable bit rate connections. Another object of the present invention is to offer a large number of extension codes which is not limited to the number of orthogonal extension codes available in a DS-CDMA communication system. A further object of the present invention is to avoid reassignment of extension codes during a call in a DS-CDMA communication system. In accordance with a first aspect of the present invention, extension codes are assigned to forward link connections from a first set of orthogonal extension codes insofar as extension codes are available in the first set. When all the extension codes in the first set are assigned, a second set of extension codes that are not orthogonal with the extension codes in the first set is used from which extension codes are assigned to forward link connections. Where applicable, more than two sets of extension codes are used. In accordance with a second aspect of the present invention, the extension codes assigned to the forward link connection are assigned from two different code sets. A first group of extension codes is assigned from the first code set and a second group of extension codes is assigned from the second set of codes. Where applicable, more than two sets of extension codes are used. The present invention includes methods for assigning extension codes to forward link connections of variable bit rates. The methods include the step of assigning extension codes from a first set of orthogonal extension codes. The method also includes the step of assigning extension codes from a second set of orthogonal extension codes that are not orthogonal with the extension codes in the first set. In accordance with the first aspect of the present invention, extension codes are first assigned from the first set of extension codes. The extension codes are then assigned from the second set of codes when all the extension codes in the first set of codes are assigned. The number of code sets can be extended to more than two sets of codes. In accordance with the second aspect of the invention, the extension codes are assigned from two different code sets. A first group of extension codes is assigned from the first set of codes and a second group of extension codes is assigned from the second set of codes. The first group of extension codes comprises the codes that are used most frequently. The second group comprises the remaining codes. More than two sets of codes can be used. An advantage with the present invention is that the number of extension codes assigned simultaneously is not strictly limited by the size of a set of codes. Another advantage is that each connection receives a number of extension codes when a call is established. No reassignment of additional extension code is required. BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned objects and other features of the present invention will be more readily apparent with reference to the following description when taken in conjunction with the accompanying drawings. Figure 1 is an illustration of a base station and four radio stations in a DS-CDMA communication system. Figure 2 is an illustration of an example of a group of code sets in accordance with the present invention. Figure 3 is a first part of a flow chart illustrating a first embodiment of a method in accordance with the present invention. Figure 4 is a second part of the flow chart of Figure 3. Figure 5 is an illustration of a set of code sets with extension codes assigned in accordance with the first embodiment in Figures 3 and 4. Figure 6 (a) is a first part of a flow chart illustrating a second embodiment of a method in accordance with the present invention. Figure 6 (b) is a second part of the flow chart of Figure 6 (a). Figure 7 is an illustration of four groups of extension codes. Figure 8 is an illustration of a set of code sets with extension codes assigned in accordance with the second embodiment in Figure 6 (a) - (b). DETAILED DESCRIPTION OF MODALITIES The present invention relates to methods for assigning extension codes to forward link connections in DS-CDMA communication systems. Forward link connections are radio connections where the bit rate (variable bit rate) can be varied during a call. The extension codes can be assigned when a call is established and, for example, at the time of the transfer and during the establishment of additional services. Figure 1 shows a base station B and four radio units U1-U4 in a DS-CDMA communication system. Each radio unit U1-U4 has a forward link connection C1-C4 with a variable bit rate, between the base station B and the respective unit U1-U4. When a first forward link connection Cl between the base station B and the unit Ul is to be established, a specified number of extension codes are assigned to the first forward link connection Cl through station B or to another part of the communication system. The extension codes assigned to this forward link connection Cl are not assigned to new forward link connections C2-C4 within the same cell as the first forward link Cl connection continues. The number of extension codes that are assigned to each of the connections is determined through the desired bit rate in accordance with the following: A connection with a high bit rate requires more extension code than a connection with a low bit rate. A connection with a multiple code transmission uses several codes in parallel to increase the bit rate. Figure 2 shows an example of a set of code sets Sl-Sn in accordance with the present invention. A first set of SI codes comprises a number of orthogonal extension codes i. A second set of SI codes also comprises several orthogonal extension codes m2. These extension codes are orthogonal in relation to each other but are not orthogonal in relation to extension codes in the first set of SI codes.

A third set of codes S3 also comprises several orthogonal extension codes m3. These extension codes are orthogonal in relation to each other but are not orthogonal in relation to the extension codes in the first set of SI codes and in the second set of S2 codes. The number of sets of codes n with extension codes can be greater than 3. Figure 3 and Figure 4 show a flow chart of a first embodiment of a method according to the present invention where several extension codes correspond to a required bit rate is assigned to a variable bit rate forward link connection Cl. In a step 31 (a), the number of extension codes required to transmit at the required bit rate between a base station B and a radio unit Ul in the forward link connection Cl is determined. In a step 31 (b) the number of available extension codes (unassigned) is determined in all available code sets. If there are fewer extension codes available than the required extension codes, the method terminates, otherwise proceed to step 32. In step 32, the number of extension codes available (not assigned) in a first selected SI set of Orthogonal extension codes are determined. If there are no extension codes available IF of extension codes, the method follows with a step 35. If available extension codes are in the first set of extension codes YES, the method proceeds to step 33. In step 33 , several extension codes, which do not exceed the number of extension codes required in the forward link connection Cl, are assigned from the SI set of extension codes to the forward link connection Cl. In a step 34, the number of extension codes required is compared to the number of extension codes assigned from the first SI sets of extension codes. The method determines whether the number of extension codes required is equal to the number of extension codes assigned from the first SI set of extension codes, otherwise proceeds to step 35. In step 35, the number of extension codes is determined. extension codes available in a selected set S2 of orthogonal extension codes. If there are no extension codes available in the second extension code set S2, the method proceeds with a step 38. If extension codes are available in the second extension code set S2, the method proceeds with a step 36. In In step 36, several extension codes are assigned, without exceeding the extension code number required in the forward link connection Cl, to the forward link connection Cl. In a step 37, the number of extension codes required it is compared with the extension code number assigned from the first set and the second set of extension codes SI, S2, respectively. The method terminates if the number of extension codes required is equal to the number of extension codes assigned from the first set and second set of extension codes SI, S2, respectively, otherwise proceed to step 38. In step 38, illustrated in Figure 4, the number of sets of codes is determined. The method follows a step 39 if the number of code sets is 3, otherwise it ends. In step 39, the number of extension codes available in a third selected set S3 of orthogonal extension codes are determined. If no extension codes are available in the third sets S3 of extension codes, the method proceeds with a step 42. If extension codes are available in the third set S3 of extension codes, the method proceeds with a step 40. In step 40, a number of extension codes, without exceeding the number of extension codes required in the forward link connection Cl, are assigned from the third set S3 of extension code. In a step 41, the number of extension codes required is compared with the number of extension codes assigned from the first, second and third set of extension codes SI, S2, S3, respectively. The method terminates if the number of extension codes required is equal to the number of extension codes assigned from the first, second, and third set of extension codes SI, S2, S3, respectively, otherwise follows in step 42 In step 42 the number of code sets is determined. Its number of code sets is 3, the method determines, otherwise it follows with more steps similar to the previous steps 39-42 in that there are more numbers of extension codes to be assigned and more Sl-Sn sets of codes available. The method according to Figure 3 and Figure 4 is repeated each time a new forward link connection is to be established. Figure 5 shows an illustration of a set of code sets Sl-Sn comprising extension codes in accordance with the first embodiment. The first forward link connection Cl between the base station B and the radio unit Ul, see figure 1, has been assigned a first number of extension codes x, from the first set SI of extension codes. A second forward link connection C2 has received a second number of extension codes Y. A first part y-ki of the second number of extension codes and a first set SI of extension codes is taken and assigned to the second connection forward link C2. The first part y-ki of the second number of extension codes and comprises at least one full extension code. A second part ki of a second extension code number is taken from the second set S2 of extension codes and assigned to the second forward link connection C2. The second part ki of the second number of extension codes and comprises at least one full extension code. The number of extension codes not assigned in the first SI set of extension codes is less than and such that more extension codes were assigned from a second set S2 of extension codes. A third forward link connection C3 received a third number of extension codes z from the second set S2 of extension codes. A fourth forward link connection C4 received a fourth number of extension codes w. A first part -k2 of the fourth number of extension codes w is taken from the second set S2 of extension codes and assigned to the fourth forward link connection C4. The first part w-k2 of the fourth number of extension codes w comprises at least one complete extension code. A second part k2 of the fourth number of extension codes w is taken from the third set S3 of extension codes and assigned to the fourth forward link connection C4. The second part k2 of the fourth number of extension codes w comprises at least one full extension code. Figures 6 (a) - (b) show a flow chart of a second embodiment of a method according to the present invention where several extension codes corresponding to a required bit rate are assigned to a forward connection Cl with variable bit rates. In a step 61 (a), a total number of extension codes required for transmission at the required bit rate between the base station B and the radio unit ul in the forward link connection Cl is determined. In a step 61 (b), the number of available extension codes (one assigned) is determined in all available code sets. If there are fewer extension codes available than the total number of extension codes required, the method ends, otherwise follows step 62. In step 62 the total number of extension codes required is divided into a first group and a second group Xi, x2, respectively. The number of extension codes required in a first group xi corresponds to the number of extension codes that will be used most frequently in the forward link connection Cl. The number of extension codes required in the second group x2 corresponds to the number of extension codes that will be used less frequently in the forward link connection Cl. The first group and the second group Xi, x2, respectively, will include the total number of extension codes required for the forward link connection Cl. A step 63, the number of extension codes available (not assigned) in a first selected set SI of orthogonal extension codes is determined. If no extension codes are available in the first extension code SI set, the method proceeds with a step 70, see page 14. If extension codes are available in the first SI set of extension codes, the method proceeds with a step 64. In a step 64, extension codes, which do not exceed the number of extension codes required for the first group Xi, are assigned to the first group of extension codes xi from the first SI set of extension codes. In a step 65, the number of extension codes required in the first group xx is compared to the number of extension codes assigned from the first SI set of extension codes. If the number of extension codes required in the first group i is equal to the number of extension codes assigned from the first SI set of extension codes, the method proceeds with a step 66 for assigning extension codes to the second group x2, otherwise it proceeds to step 70, to assign more extension codes from the first group Xi. In step 66, illustrated in Figure 6 (b), the number of available extension codes (not assigned) in a second selected set S2 of orthogonal extension codes is determined. If there are extension codes available in the second set S9 of extension codes, the method proceeds with a step 69. If there are no extension codes available in the second set S2 of extension codes, the method proceeds with a step 67. In step 67, several extension codes, without exceeding the number of extension codes required for the second group x2, are assigned to the second group x2 from the first set S2 of extension codes. In a step 68, the number of extension codes required in the second groups x2 is compared to the number of extension codes assigned from the second set S2 of extension codes. The method terminates if the number of extension codes required in the second group x2 is equal to the number of extension codes assigned from the second set S2 of extension codes, thus proceeding to step 69 to assign more extension codes to the second group x2. In step 69, the code set number terminates. The method proceeds with steps similar to previous steps 63-69 if the number of code sets is greater than 2, otherwise it ends. In step 70, the number of extension codes available in the second selected set S2 of orthogonal extension codes is determined. If there are no extension codes available in the second S2 sets of extension codes, the method follows a step similar to step 69 to search for more sets of codes. If extension codes are available in the second set S2 of extension codes, the method follows a step in which extension codes are assigned to the first group Xi from the second set of codes S2. The extension codes for the second group x2 are then assigned from a third set S3 of extension codes. The method according to FIGS. 6 (a) - (b) follows steps similar to the previous steps 63-70 insofar as there are more extension codes to be assigned and more sets of Sl-Sn codes available. The method is repeated every time a new forward link connection with variable bit rate must be established.

Figure 7 shows an example of four groups of extension codes Gl, G2, G3, G4, respectively assigned to four different variable bit rate forward link connections C1-C4. Each group Gl, G2, G3, G4, respectively, comprises the total number of extension codes required in each forward link connection C1-C4. A total number of extension codes required in each forward link connection C1-C4 is divided into the first group and in the second group of extension codes xi, yi, Zi, wi, x2, y2, z2, w2 respectively, where each group i / yi zi, i, x2, y2, z2, w2 respectively comprise complete extension codes. Figure 8 shows an illustration of an assembly 80 of code sets Sl-Sn according to the second embodiment of the method of Figure 6. The first forward link connection Cl with variable bit rate between the base station B and the radio unit Ul, of figure 1, received extension codes of the first sets SI and second set S2 of code. The first extension code group Xi has been tuned from the first set of code Si and the second group x2 of extension codes has been assigned from the second set of code S2. The second forward link connection C2 with variable bit rates between the base station B and the radio unit U2, of figure 1, has been assigned extension codes from the first set SI and second set S2 of code. The first group yi of extension codes has been assigned from the first set of codes Si and the second group y2 of extension codes has been assigned from the second set of code S2. The third forward link connection C3 with variable bit rate between the base station B and the radio unit U3, of figure 1, has been assigned extension codes from the first set SI and second set 52 of code. The first extension code group Zi has been assigned from the first set of SI codes and the second group of extension codes z2 has been assigned from the following set of codes S2. The fourth forward link connection C4 with variable bit rate between base station B and radio unit U4, of figure 1 has been assigned extension codes from the first set SI and third set 53 of codes. The first group i of extension codes has been assigned from the first set of SI codes and the second extension code w2 has been assigned from the third set of S3 codes. There were no extension codes not assigned in the second set of codes S2 such that more extension codes were assigned from the third set of S3 codes.

The signals that had been encoded by short extension codes in the methods according to the present invention can be encoded. Signals in a forward link connection that have been encoded by short extension codes are encoded by a common (long) Pseudo Noise code (PN code). The coding randomizes the interference between the cells. The coding will not affect the orthogonality between the signals in a cell since all the signals use the same PN code. Neighboring cells use different PN codes.

Claims (1)

1. CLAIMS A method for assigning extension codes to a first corresponding forward link connection (Cl) between several forward link connections (C1-C4) in a DS-CDMA communication system having several radio units (U1-U4) ), which comprises the following steps: a) assigning extension codes (33) from a first set (SI) selected from extension codes orthogonal to said first forward link connection (Cl), characterized in that it has the additional step from: b) assigning (36) extension codes from a second selected set (S2) of extension codes orthogonal to said first forward link connection (Cl) if said first forward link connection (Cl) requires more extension codes than those available in said first set (SI) of orthogonal extension codes, where at least one of said extension codes of said second set (S2) of codes d The orthogonal extension is not orthogonal with at least one of said extension codes of said first set (SI) of extension codes. The method according to claim 1, characterized in that said assignment (33,36) in accordance with steps a) -b) involves the assignment of said extension codes to said first forward link connection (Cl), upon being established a call. A method according to claim 1, or according to claim 2, characterized in that said assignment (33, 36) in accordance with steps a) -b) involves assigning a number of verification codes to said first forward link connection (Gl), wherein said number of extension codes is determined through a requested maximum bit rate. A method according to any of claims 1-3, characterized in that said forward link connection (Cl) is a variable bit rate forward link connection (Cl). A method according to any of claims 1-4, characterized in that said DS-CDMA communication system provides multiple code transmission. A method according to any of claims 1-5, characterized in that said method further comprises the step of: c) assigning (40) extension codes from a selected third set (S3) of extension codes orthogonal to said first forward link connection (Cl), if said first forward link connection (Cl) requires more extension codes than those available in said first set (SI) and second set (S2) of orthogonal extension codes, where the minus one of said extension codes of said third set (S3) of orthogonal extension codes is not orthogonal in relation to at least one of said extension codes of said first set (SI) and second set (S2) of extension codes orthogonal A method for assigning extension codes to corresponding forward link connections (C1-C4) in a DS-CDMA communication system having a plurality of radio units (U1-U4), comprising the following steps: a) assigning (33) a first number of extension codes (x) from a first set (SI) of extension codes orthogonal to a first forward link connection (Cl); characterized by the following step of: b) assigning (33) a first part (y-ki) of full extension codes of a second number of extension codes (y) from said first set (SI) of extension codes to a second forward link connection (C2); c) assigning (36) a second part of complete extension codes (ki) of said second number of extension codes (y) from a second set (S2) of extension codes orthogonal to said second forward link connection (C2), wherein at least one of said extension codes of said second set (S2) is not orthogonal in relation to at least one of said extension codes of said first set (SI). A method for assigning several extension codes to a first forward link connection (Cl) corresponding between a plurality of forward link connections (C1-C4) in a DS-CDMA communication system having a plurality of radio units (U1-U4), characterized by the following steps: a) assigning (64) a first group (xi) of full extension codes to said first forward link connection (Cl) from a first selected set (SI) of orthogonal extension codes; b) assign (67) a second group (x2) of full extension codes to said first forward link connection (Cl) from a second selected set (S2) of orthogonal extension codes, wherein at least one of said extension codes of said second set (S2) is not orthogonal with respect to at least one of said extension codes of said first set (SI), and where said first group (xi), and said second group (x2) of codes extension include said number of extension codes required for said forward link connection (Cl). A method according to claim 8, characterized in that said assignment (64, 67) in accordance with step a) -b) involves assigning the extension codes to said first forward link connection (Cl) when a call is established. A method according to any of claims 8 or 9, characterized in that said number of extension codes required for said first forward link connection (Cl) is determined through a maximum bit rate required. A method according to one of claims 8-10, characterized in that said forward link connection (Cl) is a variable bit rate forward link connection (Cl). A method according to any of claims 8-11, characterized in that said DS-CDMA communication system provides multiple code transmission. A method for assigning a total number of extension codes to corresponding forward link connections (C1-C4) with variable bit rate in a DS-CDMA communication system having a plurality of radio units (U1-U4), characterized by the following steps: a) assigning (64) a first group (x) of full extension codes to a first forward link connection (Cl) from a first set (SI) of orthogonal extension codes; b) assigning (64) a first full extension code group (yi) to a second forward link connection (C2) from said first set (SI) of orthogonal extension codes; c) assign (67) a second group (x2) of full extension codes to said first forward link connection (Cl) from a second set (S2) of orthogonal extension codes, wherein at least one of said codes The extension of said second set (S2) is not orthogonal with respect to at least one of said extension codes of said first set (SI), and where said first group (xi) and said second set (x2) of extension codes for said first forward link connection (Cl) include the total number of extension codes required for said first forward link connection (Cl); assigning (67) a second group (y2) of full extension codes to said second forward link connection (C2) from said second set (S2) of orthogonal extension codes, wherein said first group (yi) and said second group (y2) of extension codes for said second forward link connection (C2) include the total number of extension codes required for said second forward link connection (C2).