WO2000008789A1

WO2000008789A1 - Method and device for allocating channels in a communication system with cdma subscriber separation

Info

Publication number: WO2000008789A1
Application number: PCT/DE1999/002410
Authority: WO
Inventors: Markus Dillinger
Original assignee: Siemens Aktiengesellschaft
Priority date: 1998-08-06
Filing date: 1999-08-02
Publication date: 2000-02-17
Also published as: JP2002522951A; DE19835643C2; DE19835643A1; EP1103109A1; KR20010072270A

Abstract

The invention relates to a method for allocating channels, wherein CDMA codes form the channels for communication links. The CDMA codes are represented by sequences of symbols in a tree structure and can be derived from each other. According to various allocation strategies, the position in the sequence of symbols is determined for nodes that are still available, beginning with the root of the tree structure, whenever a difference occurs in comparison with a node that is already engaged. The sum of the positions of the engaged nodes is determined and the channel with the CDMA node corresponding to the node with a pre-determinable sum, i.e. the largest or smallest sum, is allocated. As a result, it is possible to manage links with both a fixed and variable data rate in a W- CDMA mobile radio system without having to make any substantial changes in channel allocation.

Description

description

Method and device for channel allocation in a communication system with CDMA subscriber separation

The invention relates to a method and a device for channel allocation in a communication system with CDMA subscriber separation.

In a communication system, a channel describes a connection from a message source (transmitter) to a message sink (receiver). The information to be transmitted is usually coded, modulated and amplified on the transmission side, so that it can be evaluated on the reception side by means of measures corresponding to the transmission side after transmission, which usually results in attenuation and distortion.

A cable or a radio interface can be used as the transmission medium. In the latter case, one speaks of radio communication systems that have found widespread use in the form of mobile radio systems.

In radio communication systems, information (for example voice, image information or other data) is transmitted with the aid of electromagnetic waves via a radio interface between the transmitting and receiving radio station (base station or mobile station). The electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system. For future mobile radio systems with CDMA or TD / CDMA transmission methods via the radio interface, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, frequencies in the frequency band of approx. 2000 MHz are provided. FDMA (frequency division multiple access), TDMA (time division multiple access) or CDMA (code division multiple access) subscriber separation methods are used to differentiate the signal sources and thus to evaluate the signals. These separation processes can also be combined. In the CDMA subscriber separation method, the channels are differentiated on the basis of the individual CDMA codes.

Channel allocation procedures describe a strategy for how to make the best possible use of the radio resources of the

Radio interface, the channels are allocated to the individual connections, whereby it should be noted that future changes in the data rate of individual connections should result in the least possible adaptation effort when allocating the channels to the previous connections. An adjustment effort arises when an existing connection has to give up a CDMA code and another CDMA code is assigned to it. For a communication system with CDMA subscriber separation, this object is achieved by the present invention with the features of claims 1 and 14, respectively. Advantageous developments of the invention can be found in the subclaims.

In the method for channel allocation according to the invention, the CDMA codes form the channels for connections, the CDMA codes available for channel allocation being derived from one another in a tree structure. A chip sequence of a higher-order CDMA code is thus, for example, a subset of the chip sequence of a lower-order CDMA code. The CDMA codes are represented by nodes within the tree structure. Several knots come together in a node, which in turn lead to further nodes of lower order.

The nodes are represented for the method of channel allocation by a symbol sequence, the symbol sequences of two nodes differing in one place, which are within the distance of the two nodes from their union nodes corresponds to the tree structure. A small digit means that two nodes are very different and a difference already occurs close to the root of the tree structure. In other words, the union node (father node) is near the root in this case. A distinction is made between free nodes and assigned nodes, a free node designating an unassigned CDMA code and a busy node designating an assigned CDMA code. Only unassigned CDMA codes can be allocated.

For the allocation of a free CDMA code to a connection, in a first step all free nodes are selected which are not connected directly up or down in the tree structure to an already occupied node, i.e. differ from an already occupied node in at least one symbol. No CDMA code may be assigned, the chip sequence of which is an exact subset of an already assigned CDMA code or for which the chip sequence of an already assigned CDMA code forms a subset.

In a further step, the position in the symbol sequence is determined for the selected nodes, beginning with the root of the tree structure, in which a difference to an already occupied node occurs. The location is therefore a measure of the distinctive character of two CDMA codes.

If two CDMA codes differ greatly, the data rate for one of the two CDMA codes can be increased without a collision with the second CDMA code occurring. Furthermore, a sum of the positions for all occupied nodes is determined and the channel with the CDMA code is allocated which corresponds to the node of the predeterminable sum. The allocation strategy is thus based on the distinctive character of all other CDMA codes, i.e. on the sum of the distinctions.

The tree structure is advantageously such that the distance of a node from the root increases hung of the spreading factor of the CDMA code and thus corresponds directly to a reduction in the data rate for the connection. The data rate can only be increased without changing the allocation of the other CDMA codes by changing a CDMA code by assigning a new node in the tree structure starting from the previous node in the direction of the root, giving up the previous one.

An advantageous development of the allocation strategy provides that the predeterminable sum is the smallest of the sums. It is thereby achieved that the CDMA codes differ very greatly and thus the connection with the newly assigned CDMA code is made possible for the future to increase the data rate as much as possible without adapting the remaining allocation.

The goal is different if for some connections no and only a limited increase in the data rate is possible or wanted, e.g. for participants with a fixed basic data rate. It is advantageous here that the predeterminable sum is the largest of the sums. CDMA codes that do not differ greatly are thus allocated, that is to say parts of the tree structure are kept free for further connections with possibly higher data rates.

A mixed form for the previous two strategies provides that an increase possibility for a data rate of the connection is determined and a node with a difference to an already occupied node is selected at a certain position, the position corresponding to the increase possibility. The possibility of increasing the data rate can be found in the tree structure in the number of nodes that can be moved in the direction of the root (one node before the union node with an already occupied node) without a collision with an already assigned CDMA code. If the potential for improvement is known in advance, can That is, exactly a sufficient part of the tree structure must be reserved, ie not too much and not too little.

When selecting the node, an additional possibility of increasing the connections for the nodes already occupied is advantageously taken into account. This does not affect the potential for increasing the existing connections.

The process can also be carried out in several stages. An advantageous further development of the invention provides that several channels with different CDMA codes are allocated, a desired data rate resulting from the total of the individual data rates of the CDMA codes. The free nodes of the tree structure can with a high load, i.e. Allocation of the nodes, nevertheless be used well.

For the widespread digital systems, the symbols are digital values. One branch branches off from each node in the direction of the root and two branches in the opposite direction. A particularly easy to implement mapping of the CDMA codes onto the tree structure provides that, starting from the root of the tree structure, the two following nodes of the outgoing branches are represented by an additional “0” or “1” in the symbol sequence, the number the bits of the symbol sequence correspond to the spreading factor. Regardless of the exact nature of the CDMA codes, the digital tree structure is very clear. The CDMA codes are, for example, orthogonal codes (OVSF) with a variable spreading factor. This simplifies the detection on the receiving side, since such CDMA codes constantly support the best possible decorrelation.

Although a channel assignment according to the invention can be used in a wide variety of communication systems, use for the downward direction of a radio interface in a broadband radio communication System particularly advantageous. Such a radio interface is set up for the 3rd generation of mobile communications and can support a large number of channels. The larger the number of channels, the more important a good assignment strategy is.

According to further advantageous features of the invention, a desired data rate and / or possibility of increasing the data rate of the connection is derived from an identifier and / or from a signaled request from a mobile station. The potential for increase can thus be determined precisely for the mobile stations and in accordance with the current connection and service profiles, and thus only the necessary and not useless free spaces in the tree structure can be reserved in the assignment strategy.

In the following, the invention is explained in more detail with reference to an exemplary embodiment with reference to graphic representations.

Show

1 shows the structure of orthogonal CDMA codes with a variable spreading factor, FIG. 2 shows a tree structure for displaying the CDMA codes, FIGS. 3-5 allocation strategies for channel allocation, and FIG. 6 shows a schematic representation of a mobile radio system.

In communication systems with CDMA subscriber separation, the different connections can be distinguished on the basis of an individual CDMA code with which the signals of the connections are spread. An example of such a communication system is a digital radio communication system with broadband channels, which consists of the “UTRA Physical Layer

Descπption FDD parts ", vθ.4, from June 25, 1998 is known. For the downward direction, ie for a radio transmission from base stations to mobile stations, orthogonal codes with a variable spreading factor OVSF and with a fixed chip rate of 4,096 Mcps according to FIG. 1 are used. The orthogonal codes with variable spreading factor OVSF can be represented in a tree structure, the individual CDMA codes being derived from one another within the tree structure.

The level of the tree doubles the number of chips per CDMA code and thus the spreading factor SF. Starting from the CDMA code with the chip sequence (1,1), two CDMA codes of the next lower level (1,1,1,1) and (1,1, -1, -1) are derived. The first half (1,1) is adopted and the second half either adopted (1,1) or inverted (-1, -1). In this way, a code family is created across eight levels, for example. Within the eight levels there are 508 different CDMA codes with eight different data rates (2048 Kbit / s with spreading factor SF = 4, 1024 Kbit / s with SF = 8, 512 Kbit / s with SF = 16, 256 Kbit / s with SF = 32, 128 Kbit / s with SF = 64, 64 Kbit / s with SF = 128, 32 Kbit / s with SF = 256). A gross data rate of 32 kbit / s is used, for example, to encode voice information with a net data rate of 8 kbit / s and to transmit it in an error-protected manner via the radio interface.

Within the level with a spreading factor SF = 256 gbit there are 256 different CDMA codes, at the next higher level there are 128 CDMA codes etc. The CDMA codes are allocated according to the data rate desired by the connection. Are all CDMA codes still free, e.g. in the start-up phase, then one of the CDMA codes can be arbitrarily assigned. However, if some of the CDMA codes have already been assigned, then when assigning a CDMA code that is still free to a new connection, boundary conditions must be observed.

The CDMA codes used within a frequency band in a radio cell must be at least in a part of them Distinguish chip sequence. Furthermore, changes in the data rate of a connection should be taken into account in advance and CDMA codes of a higher level should not be blocked by the new allocation of a CDMA code of a lower level.

For the orthogonal codes with a variable spreading factor OVSF, a form of representation in the form of a tree structure according to FIG. 2 is chosen, which designates the nodes of the tree with a digital symbol sequence. Starting from a knot, e.g. 11, a "1" is added for the upper of the branches moving away from the root and a "0" is added for the lower branch. This simplifies an evaluation of the tree structure, since the number of digits of the symbol sequence corresponds directly to the level of the node (and the spreading factor SF) in the tree.

For a comparison of nodes that is required for the algorithms explained below, the root of the tree should be assumed. However, it is self-evident for the person skilled in the art that a correspondingly opposite evaluation is also possible.

For example, if nodes 1110 and

1101 compared with each other, a difference occurs at the third position starting from the left. Later differences are of no interest.

For 10 and 1101 it is the second digit. In extreme cases, the

Difference at the eighth position (comparison of 11111110 and 11111111). The comparison is therefore left-justified.

E.g. nodes 00 and

001 compared with each other, no difference can be determined. The two nodes at least do not differ in a symbol. If no difference can be determined, this corresponds to two CDMA codes which are connected to one another in the tree structure directly upwards or downwards.

For the allocation of a CDMA code, all nodes must be excluded that have no difference compared to one of the occupied nodes (Hamming distance is 0). In other words, a node (1111 in FIG. 3) blocks all nodes (111, 11, 11, 1) arranged in ascending order in the tree and vice versa.

All nodes that differ from all occupied nodes are therefore selected for the allocation. Furthermore, only the nodes that correspond to the desired data rate are considered. According to FIG. 3, 3 nodes are still available for a desired data rate of 1024 Kbit / s with SF = 8 (101, 010, 001). A selection must now be made between these nodes.

For these three nodes 101, 010, 001, the sum of the positions is used at which the first difference from the left occurred in comparison with all nodes already occupied (at least all occupied nodes of a part of the tree structure). For node 101 the sum 9 = 2 + 2 + 3 + 1 + 1, for node 010 the sum 8 = 1 + 1 + 1 + 2 + 3 and for node 001 the sum 8 = 1 + 1 + 1 + 2 + 3.

The sums are now compared with a predeterminable sum. If the predeterminable sum is the maximum, node 101 is selected. If the predeterminable sum is the minimum, node 010 or 001 can be selected. The choice between the two nodes 010 or 001 is arbitrary.

The maximum is chosen if it is desired to group the occupied nodes, ie the allocated CDMA codes, closely together (see FIG. 4). This has advantages if there are no major changes in the data rates of the connections. are waiting. The minimum is chosen in order to achieve the most even possible distribution of all CDMA codes used in the tree. From a statistical point of view, this has the advantage that there is maximum flexibility for a later allocation of higher data rates. According to FIG. 3, this is not yet relevant since the data rate cannot be simply doubled for any of the nodes 101, 010 or 001. However, the connections are not permanent, so that if a previously occupied CDMA code is released, the probability for nodes 010 and 001 is greater than for node 110 that an increase in the data rate will be possible in the future.

4 shows connections to subscribers with a basic data rate of 32 Kbit / s, e.g. simple voice connections. No increases in the data rate are to be expected for these participants, so that the strategy with the maximum for the predeterminable sum is selected. The sum for the free node 11111101 is 34 = 7 + 7 + 8 + 6 + 6, for nodes 11111001 and 11111000 the sum is 32 = 6 + 6 + 6 + 7 + 7. The node 11111101 is therefore selected. This does not prevent a later new allocation of node 1111100 with a higher data rate of 64 Kbit / s.

An additional aspect for both strategies arises if one knows not only the desired data rate for the connection, but also a defined possibility of increasing the data rate. The desired data rate and / or possibility of increasing a data rate of the connection is derived from an identifier (e.g. a service class of the possible services or an identification of the mobile station) or from a signaled request from a mobile station for a service. These values can also be updated during a connection.

Allocation optimization is aimed at a window of data rates for a connection. 5 is again some of the nodes are already occupied. The assignment of a CDMA code for a connection with a data rate of 32 Kbit / s with an increase to a maximum of 64 Kbit / s is to be shown. A node with a difference to an already occupied node is selected exactly at a certain point, which corresponds to the possibility of increase. The possibility of increasing to 64 Kbit / s corresponds to the seventh digit.

This is for nodes 11111001 or 11111000 or

11110011 or 11110010 the case. The difference between these nodes and nodes 11111010 and 11110000 occurs exactly at the seventh position. Other free nodes have differences already at the sixth position (11110100) or only at the eighth position (11111111). Which of the two pairs of nodes

(11111001 or 11111000 or 11110011 or 11110010) is shortlisted again depends on the optimization to the maximum or minimum. The choice between 11111001 or 11111000 or 11110011 or 11110010 is arbitrary. As a boundary condition, it should also be noted that the data rate may also have to be increased for existing connections. If the possibility of increasing the node 11110000 to 128 kbit / s is noted, this is an exclusion criterion for nodes 11110011 and 11110010.

For example, if a connection is to be operated with a data rate of 96 Kbit / s, two CDMA codes must be assigned, either three - 32 Kbit / s or one for 32 Kbit / s and another for 64 Kbit / s. The allocation process is therefore multi-stage. The desired data rate results from the total of the individual data rates of the CDMA codes. For FIG. 5 this means, for example, that depending on the optimization criterion, one of the nodes 1111011, 1111010 or 1111001 is assigned for the 64 Kbit / s and then a remaining free node is selected for 32 Kbit / s. Allocation of a CDMA codes for the higher data rate should be given before the allocation of a CDMA code for the lower data rate.

The mobile radio system shown in FIG. 6 as an example of a radio communication system consists of mobile switching centers MSC which are networked with one another or which provide access to a fixed network PSTN. Furthermore, these mobile switching centers MSC are each connected to at least one device RNC (radio network controller) for radio resource management. Each of these devices RNC in turn enables a connection to at least one base station BS. Such a base station BS can connect to other radio stations, e.g. Set up MS mobile stations or other mobile and stationary terminals. 6 shows, by way of example, connections VI, V2, Vk for the transmission of useful information and signaling information between mobile stations MS and a base station BS. An operation and maintenance center OMC implements control and maintenance functions for the mobile radio system or for parts thereof.

The base station BS contains a storage device SP for storing the tree structure, the occupied nodes and the CDMA codes, as well as a program for carrying out the allocation process and a processing device BE for selecting an unused node with a corresponding CDMA code and for assigning a channel with the CDMA code to a connection according to one of the previous strategies.

Claims

claims

1. A method for channel allocation in a communication system with CDMA subscriber separation, CDMA codes forming the channels for connections in which

the CDMA codes available for channel allocation are derived from one another in a tree structure,

- for the tree structure, several knots unifying branches are represented by a symbol sequence, the

Distinguish symbol sequences of two nodes at a location that corresponds to the distance between the two nodes and their union nodes within the tree structure,

a free node denotes an unassigned CDMA code and a busy node denotes an assigned CDMA code,

- for the allocation of a CDMA code to a connection, all free nodes are selected which are not connected directly up or down in the tree structure to an already occupied node, i.e. differ in at least one symbol from an already occupied node,

- for the selected nodes, starting with the root of the tree structure, the position in the symbol sequence is determined, m that a difference to an already occupied node occurs and a sum of the positions to the occupied nodes is determined, and

- The channel with the CDMA code is assigned, which corresponds to the node with a predetermined sum.

2. The method according to claim 1, wherein the tree structure is such that the distance of a node from the root corresponds with an increase in the spreading factor (SF) of the CDMA code and thus with a decrease in the data rate for the connection.

3. The method of claim 1 or 2, wherein the predetermined sum is the smallest of the sums.

4. The method according to claim 2, wherein for a connection with a data rate which is not very variable, the predeterminable sum is the largest of the sums.

5. The method according to claim 4, in which an increase possibility for a data rate of the connection is determined and a node with a difference to an already occupied node is selected at a certain position, the position corresponding to the increase possibility.

6. The method according to claim 5, wherein when selecting the node, an additional possibility of increasing the connections for the nodes already occupied is taken into account.

7. The method according to claim 2, in which a plurality of channels with different CDMA codes are allocated, a desired data rate resulting from the total of the individual data rates of the CDMA codes.

8. The method according to any one of the preceding claims, wherein the symbols are digital values and branch off a branch in the direction of the root and two branches in the opposite direction from each node.

9. The method according to claim 8, in which, starting from the root of the tree structure, the two following nodes of the outgoing branches are represented by an additional “0” or “V” in the symbol sequence, the number of bits of the symbol sequence having the spreading factor (SF ) corresponds.

10. The method according to any one of the preceding claims, wherein the CDMA codes are orthogonal codes (OVSF) with a variable spreading factor.

11. The method according to any one of the preceding claims, in which the channel assignment for the downward direction of a radio interface is carried out in a broadband radio communication system.

12. The method according to any one of the preceding claims, in which a desired data rate and / or possibility of increasing a data rate of the connection is derived from an identifier of a mobile station (MS).

13. The method according to any one of claims 1 to 11, in which a desired data rate and / or increase possibility for a data rate of the connection is derived from a signaled request from a mobile station (MS).

14. Device for carrying out the method according to claim 1 for a communication system with CDMA subscriber separation, with a memory device (SP) for storing the tree structure, the occupied nodes and the CDMA codes, with a processing device (BE) for selecting one occupied node with a corresponding CDMA code and for assigning a channel with the CDMA code to a connection.