HK1117321B - Apparatus and method for dynamically assigning orthogonal codes in a radio communication system - Google Patents

Description

Apparatus and method for dynamically allocating orthogonal codes in wireless communication system

Field of the invention

The present invention generally relates to communication networks. More particularly, but not by way of limitation, the present invention relates to apparatus and methods for assigning orthogonal codes to different information signals in a cellular radio communications system that utilizes spread spectrum modulation and Code Division Multiple Access (CDMA) techniques.

Description of the related Art

In a typical CDMA cellular wireless communication system, an information data stream to be transmitted is superimposed on a data stream having a much higher bit rate, sometimes referred to as a spreading code. Each symbol of the spreading code is commonly referred to as a chip. The information signal and the spreading code signal are typically combined by multiplication in a process sometimes referred to as encoding or spreading the information signal. Each information signal is assigned a unique spreading code. Different information signals may be separated into different codes that are orthogonal to each other within the same spreading code, or different information signals may be separated simply by using different spreading codes.

In the third generation partnership project, technical specification group radio access network, RRC protocol technical specification (3GPP TS 25308, UTRA High Speed Downlink Packet Access (HSDPA); general description; phase 2), a new downlink transport channel, i.e. the high speed downlink shared channel (HS-DSCH), is proposed. The HS-DSCH allows for more efficient transmission with higher capacity, higher bit rate, and reduced latency compared to DCH channels. A common name for this concept is High Speed Downlink Packet Access (HSDPA).

HSDPA is based on five main technologies:

1. a shared channel transmission;

2. higher order modulation;

3. link adaptation;

4. scheduling depending on the wireless channel; and

5. hybrid ARQ with soft combining.

The goal of HSDPA is to provide a common robust channel with means for probing channel quality variations for different users at different times and to optimize the transmission at each given instant in terms of coding, modulation, and selective receiving user conditions. Shared channel transmission is advantageous, especially for non-continuous services, in that it enables efficient use of resources. Higher order modulation schemes allow higher peak data rates and higher system capacity. Link adaptation can take into account instantaneous channel conditions when transmitting data. As such, radio-dependent scheduling allows a wireless communication system to make it more convenient for users in good radio wave conditions to use transmission resources than for users in poor radio wave conditions. Finally, the hybrid automatic repeat request protocol with soft combining reduces the number of retransmissions required and also provides higher capacity and more robust link adaptation functions.

Fig. 1 is a simplified block diagram showing the protocol stacks and interfaces used between a User Equipment (UE)11, a node B (i.e., radio base station) 12, a Controlling Radio Network Controller (CRNC)13, and a serving radio network controller (SRNA). For HSDPA, the physical layer becomes more complex because of the introduction of an additional MAC protocol, MAC-hs 15. On the network side, the MAC-hs protocol is implemented at the node B. The MAC-hs protocol includes retransmission protocol, link adaptation, and channel-dependent scheduling. The increased complexity with HSDPA is therefore mainly related to the introduction of this intelligent layer 2 protocol in the node B.

Fig. 2 is an illustration of a typical Orthogonal Variable Spreading Factor (OVSF) code allocation tree 21 and possible allocation of high speed physical link shared channel (HS-PDSCH) codes. The OVSF code tree shows a way to separate different transmission signals for a certain spreading code. The HS-PDSCH may utilize the same orthogonal code tree and the same spreading code as the dedicated channel, the control channel, and the pilot channel. The 3GPP specifies that the HS-DSCH allocation may have a maximum of 15 (HS-PDSCH) codes 22, each with a Spreading Factor (SF) -16. The transport channel HS-DSCH is mapped on one or several physical channels (HS-PDSCH), each using one SF-16 code. Likewise, the dedicated transport channel is mapped on a Dedicated Physical Channel (DPCH) which uses a certain SF in the range of SF256 to SF 4. The code tree contains 16 SF-16 codes, so when a maximum of 15 HS-PDSCH channels are allocated, only one SF-16 code 23 remains for the other channels. The SF-16 codes 23 allocated to other channels may be further spread for each channel, fig. 2 showing such spreading to SF-256.

Fig. 2 shows a number of exemplary transport channels mapped to different positions of a code tree: primary common pilot channel (P-CPICH), broadcast control channel (BCH), Paging Channel (PCH), Paging Indicator Channel (PICH), Acquisition Indicator Channel (AICH), high speed shared control channel (HS-SCCH), and a number of low spreading factor dedicated channels known as associated dedicated channels (a-DCH). These ADCHs may be used with the HS-DSCH for dedicated signaling.

Of course, there may be a tradeoff in the number of spreading codes available for the HS-DSCH channel. Allocating a large number of codes to HS-DSCH channels will result in fewer channels being available for allocation to dedicated transport channels (DCH), such as voice connections or video connections. Thus, if there is a high demand for DCH, less codes are allocated to the HS-DSCH channels, which is advantageous from the point of view of service availability, whereas if there are a large number of users allocated to HSDPA transmission, a large number of HS-DSCH codes are preferably allocated, since this will provide a high bit rate connection and an increased end user experience.

The CRNC has control over the case of the entire code tree. Therefore, the CRNC provides the configuration of the HS-DSCH, i.e. how many (SF-16) codes should be used. CRNC by NBAP protocol specified by 3GPP by I_ubThe interface 16 controls this and the HS-DSCH is set up according to a configuration message sent to the node B12. However, the algorithm for making the allocation is not standardized and different methods may be utilized. For example, the allocation may be made in a static manner, where a fixed number of codes are allocated to HSDPA transmissions, and any changes to the allocation require reconfiguration by the system operator. The spreading code allocation may also be made dynamically by the CRNC based on measurements at the node B and RNC, for example.

Both existing methods for spreading code allocation have disadvantages. For a fixed configuration of the HS-PDSCH codes, a trade-off must be made. The allocation of HS-PDSCH codes must be large enough to handle the arriving HS-DSCH traffic. On the other hand, the allocation must be small enough to avoid high DCH blocking. Therefore, in a fluctuating traffic environment, a dynamic approach is required.

In dynamically allocating codes, the RNC preferably needs information from the node B about the capability of the node B and the utilization of HS-PDSCH codes. Furthermore, the dynamic allocation algorithm in the RNC has to take into account several criteria from the RNC, such as the blocking rate of DCH codes, and several criteria from the node B, such as the availability of power. In addition, if the algorithm changes the allocation of the number of HS-PDSCH codes too frequently (e.g., based on a single event trigger), the allocation and de-allocation may become too "bursty," at I_ubThere is an excessive amount of signaling on the interface. However, if the dispense rate is too slow, the process will suffer more than a fixed approachThere are many problems. Therefore, the algorithm must attempt to find the optimal allocation rate. Thus, the problem quickly becomes very complex.

Therefore, there is a need for an apparatus and method that efficiently optimizes the allocation of spreading codes between DCH channels and HS-PDSCH codes. The present invention provides such an apparatus and method.

Summary of The Invention

In one aspect, the present invention relates to an apparatus for dynamically allocating orthogonal codes to different information signals communicated between a node B (i.e., a radio base station) and a user terminal in a cellular radio communication system, wherein a plurality of codes are allocated between a dedicated transport channel (DCH) and a high speed downlink shared channel (HS-DSCH), and a radio network controller allocates codes for the HS-DSCH to the radio base station. The arrangement is characterized by an optional code allocation means in the radio base station which allocates and deallocates additional codes for the HS-DSCH in addition to the plurality of codes given by the radio network controller. The discretionary code allocation means treats the HS-PDSCH codes allocated by the radio network controller as the minimum number of HS-PDSCH codes allocated to the radio base station, and allocates and reallocates unused codes without communicating with the radio network controller.

In another aspect of the invention, the allocation of codes for the HS-DSCH (HS-PDSCH codes) and codes used for other transport channels is allocated in the radio network controller such that the increase of HS-PDSCH codes at the node B becomes as efficient as possible.

In another aspect, the present invention is directed to a method of dynamically assigning orthogonal codes to different information signals in a cellular radio communication system. The method comprises the following steps: monitoring code usage within the wireless base station to determine if there are unused codes within a plurality of codes that are not used as additional HS-PDSCH codes; allocating, by the radio base station, at least one unused code as an additional HS-PDSCH code after determining the at least one unused code; and after determining later that the additional HS-PDSCH codes have become required DCH codes, releasing the additional HS-PDSCH codes and making them available for DCH allocations.

In yet another aspect, the present invention relates to a system for dynamically assigning orthogonal codes to different information signals in a cellular wireless communication system. The system comprises HS-PDSCH code allocation means within the radio network controller for allocating a minimum number of HS-PDSCH codes to the radio base station; and discretionary code allocation means within the radio network controller for allocating and deallocating additional HS-PDSCH codes in addition to the plurality of codes allocated from the radio network controller without communicating such additions to the radio network controller.

Brief Description of Drawings

Fig. 1 (prior art) is a simplified block diagram showing protocol stacks and interfaces utilized between a User Equipment (UE) and an existing radio access network;

fig. 2 (prior art) is an illustration of a typical Orthogonal Variable Spreading Factor (OVSF) code allocation tree and possible allocation schemes for HS-PDSCH codes.

Fig. 3 is an explanatory diagram of an OVSF code allocation tree in which an aspect of the present invention is shown.

FIGS. 4A-4B are a portion of a flow chart showing steps of an embodiment of a method of the present invention; and

fig. 5 is a simplified block diagram of an embodiment of the apparatus of the present invention.

Detailed description of the embodiments

Fig. 3 is an explanatory diagram of an OVSF code allocation tree 31 showing an aspect of the present invention. In the present invention, the minimum number of HS-PDSCH codes are allocated in a chip. For example, 5 codes are allocated as the minimum number of HS-PDSCH codes in fig. 3. This allocation is preferably made by the RNC using a shared channel configuration message. Thus, the RNC controls the minimum number of HS-PDSCH codes allocated to each given chip. This allocation may be fixed, or it may be dynamically manipulated in the RNC via a code allocation algorithm.

However, if there is a space in the code tree and the node B has the capability to serve more than five chips of HS-PDSCH codes for a certain period of time, the node B may dynamically allocate additional HS-PDSCH codes without informing the RNC or requesting resources from the RNC. For example, if the RNC allocates DCHs occupying seven SF-16 code positions, the node B may dynamically increase the number of HS-PDSCH codes to eight over multiple transmission time periods. This procedure can be performed internally in the node B without informing the RNC.

The node B may almost immediately "de-allocate" the HS-PDSCH codes. If they are needed by the DCH. Thus, the node B can always "borrow" unused codes as long as they are not used, thereby improving the transmission efficiency of the HS-DSCH without having to allocate and deallocate HS-PDSCH codes in the RNC using a complex allocation algorithm. If the demand for DCH increases, the node B immediately reduces the allocation of added or borrowed HS-PDSCH codes to provide the required number of DCH's until a minimum of five HS-PDSCH codes is reached. For example, if the number of DCHs required rises to 10 SF16 level codes for DCHs, the node B immediately reduces the allocation of HS-PDSCH codes back to the minimum of five HS-PDSCH codes.

In a system where the RNC allocates a fixed number of HS-PDSCH codes, the node B may treat the fixed allocation of the RNC as the minimum allocation of HS-PDSCH codes. The node B dynamically allocates the additional HS-PDSCH codes when they are needed and available. When additional codes are needed for DCH, the node B then de-allocates additional HS-PDSCH codes.

In a system where the controlling RNC dynamically allocates multiple HS-PDSCH codes, the node B may treat the changed allocation from the RNC as an adjustment to the minimum number of HS-PDSCH codes. The node B may then dynamically allocate and de-allocate additional HS-PDSCH codes even when the RNC is dynamically allocating a minimum number of HS-PDSCH codes. The task of dynamically allocating the minimum number of HS-PDSCH codes is much simpler for the RNC than trying to allocate the exact number of codes possible correctly, since the latter requires a large amount of information from the node B to optimize its operation. The minimum set of HS-PDSCH codes is advantageously supervised by means of information already available in the RNC, such as DCH blocking information and traffic for different types of services.

It should be noted that the UE is not dependent on information from the RNC to be able to decode the HS-PDSCH. Information about those codes allocated for the HS-PDSCH is signalled on the HS-SCCH, including HS-PDSCH code information that is fully controlled by the node B.

The solution provided by the present invention requires: the node B can allocate the "borrowed" HS-PDSCH codes fast enough when the codes are needed for DCH. In one embodiment, to ensure that the node B can release resources quickly enough for the incoming DCH requirements, the node B may cache a predetermined code or codes that cannot be used for the HS-PDSCH regardless of whether they are to be used for DCH allocations or not. For example, the node B may cache SF8 code for this purpose.

In addition, in one embodiment of the invention, there may be a limit to the number of HS-PDSCH codes that the node B is permitted to increase. This can also be done with a parameter that indicates that the maximum number of HS-PDSCH codes in a chip should not exceed a certain value.

The HS-PDSCH codes are allocated consecutively from one side of the code tree. The present invention preferably allocates DCHs from the opposite end of the code tree from the HS-PDSCH codes. According to the 3GPP standard, the primary common pilot channel should have a certain position on the code tree, and the BCH should have another position on the code tree. All other channels are configurable. From the code increase of the HS-DSCH it is advantageous to separate the allocation of the HS-DSCH from the allocation of other channels as much as possible. This separation will increase the probability of finding unused codes adjacent to the existing HS-DSCH allocation in low load situations and can thus be appended to the HS-DSCH to increase the number of HS-PDSCH codes. In one embodiment, the RNC may utilize a reallocation strategy to actively reallocate users to increase the likelihood that codes adjacent to HS-PDSCH codes are released in succession.

Fig. 4A-4B show partial flow charts of steps of an embodiment of the method of the present invention. In step 41 the controlling RNC allocates a number of HS-PDSCH codes to the node B, which it considers as a minimum allocation. The algorithm for allocating additional codes in the node B may be triggered by certain events, e.g. a request for an additional DCH from the radio network controller or any other event that may affect the code availability. Alternatively, the algorithm for assigning additional codes in the node B may run in a round-robin fashion or a combination of repeating cycles and events. Thus, in alternative embodiments of the present invention, the node B may allocate additional HS-PDSCH codes in response to a triggering event or periodically (i.e., in a predetermined repetition pattern). The repetition pattern is preferably utilized in conjunction with an algorithm that immediately de-allocates HS-PDSCH codes based on a triggering event such as a request for codes (e.g., for DCH allocations) originating from the RNC. Thus, in one embodiment, the algorithm periodically appends codes to the HS-DSCH allocation, but reduces the codes for the HS-PDSCH allocation in an event-driven manner.

The allocation algorithm begins at step 42. In step 43, the node B determines whether there is an unused available code in the OVSF code tree. If not, the program process ends at step 45. However, if it is determined in step 43 that there are unused codes available at the SF-16 level in the OVSF code tree, the process moves to step 44 in which the node B allocates additional HS-PDSCH codes from the unused code locations in the code tree. Before the code is allocated, the node B may also check additional criteria, such as bandwidth available on the interface and hardware, so that the proposed addition is supported. At step 45, the program process ends.

Figure 4B shows a partial exemplary flow chart when the algorithm is triggered by an increase in DCH resources from the RNC. At step 46, it is determined that the "borrowed" code currently being utilized for the HS-PDSCH codes is needed for the DCH. In step 47, the node B de-allocates the "borrowed" HS-PDSCH code and reallocates it to every DCH code that is required. In this embodiment it is assumed that the node B only needs to maintain control over the additionally "borrowed" code (for which the radio network controller has no information). Thus, there is no need at all for the node B to request a change to the number of HS-PDSCH codes provided by the radio network controller as the minimum number of such codes. This means that when the number of HS-PDSCH codes has reached the minimum number of codes in the node B (i.e. the radio network controller believes that this number of codes has been allocated), the RNC does not request resources for the DCH.

If the number of HS-PDSCH codes has been dynamically allocated by the RNC, the allocation is communicated to the node via a new shared channel configuration message.

Fig. 5 is a simplified block diagram of an embodiment of the apparatus of the present invention. The apparatus includes a discretionary HS-PDSCH allocation algorithm (DHSAA)51 implemented within a modified node B52. When a request for a resource 53 for a connection such as a voice or video connection (DCH) arrives at the CRNC 55, an admission control function 54 is set up at the CRNC 55 and a check is made of the RNC code allocation function 56. The admission control function may also determine: whether there is power available. If the RNC code allocation function indicates that: DCH codes are available according to the current DCH load and the HS-PDSCH allocation 57 sent to the node B, the CRNC sends a request for DCH resources 58 via an establish request. Likewise, if the connection is released, the CRNC will pass this message to the node B. In one embodiment of the invention, these DCH resource control messages may constitute triggers to the DHSAA algorithm 51.

In addition, within the CRNC 55, the RNC code allocation algorithm function 56 may also determine the total number of HS-PDSCH codes that should be configured in the node B52. This may depend on measurements of ongoing or expected traffic. The HS-PDSCH allocation 57 determines the minimum HS-PDSCH allocation for the node B. The minimum HS-PDSCH allocation is sent to the DHSAA 51 in the node B where it is used as a basis for additional HS-PDSCH allocations. The DHSAA is provided with information about DCH needs and HS-PDSCH code allocation and based on this information the DHSAA adds HS-PDSCH codes according to the availability of codes and removes previously added HS-PDSCH codes if DCH requests so require.

Those skilled in the art will appreciate that the present invention may be implemented using hardware, or software, or both, and further that software implementations may vary using different languages and data structures. The present invention is not limited to a particular language and/or class of languages, nor to the provision of any separate data structure.

The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims (18)

1. An arrangement in a cellular radio communication system for dynamically allocating orthogonal codes to different information signals communicated between a radio base station (52) and a user terminal (11), wherein a plurality of codes are allocated to dedicated transport channels, DCHs, and a plurality of codes are allocated to high speed downlink shared channels, HS-DSCH, and a radio network controller (55) allocates codes for HS-DSCH physical channels, HS-PDSCH codes, to the radio base station, said arrangement being characterized by:

discretionary code allocation means (51) within the radio base station, said discretionary code allocation means allocating and de-allocating additional HS-PDSCH codes in addition to the minimum number of HS-PDSCH codes, without communicating with the radio network controller; and

wherein the discretionary code allocation means treats the HS-PDSCH codes allocated by the radio network controller as the minimum number of HS-PDSCH codes.

2. The apparatus of claim 1, wherein the discretionary code allocation means allocates HS-PDSCH codes adjacent to HS-PDSCH codes allocated by the radio network controller.

3. The apparatus of claim 1 wherein the discretionary code allocation means monitors code usage to determine if there are unused codes within codes that are not used as DCH codes or HS-PDSCH codes, wherein the discretionary code allocation means allocates additional HS-PDSCH codes from the unused codes.

4. The apparatus of claim 3, wherein the discretionary code allocation means comprises:

means for allocating at least one unused code as an additional HS-PDSCH code in response to a determination that there is at least one unused code; and

means for reallocating the additional HS-PDSCH codes as DCH codes in response to another determination that the additional HS-PDSCH codes are needed as DCH codes.

5. The apparatus of claim 1, further comprising means within the radio base station for receiving the modified minimum number of HS-PDSCH codes from the radio network controller.

6. The apparatus of claim 1, wherein the discretionary code allocation means within the radio base station allocates additional HS-PDSCH codes in response to a triggering event.

7. The apparatus of claim 1, wherein the discretionary code allocation means within the radio base station allocates additional HS-PDSCH codes in a predetermined repetition pattern and de-allocates the additional HS-PDSCH codes in response to a triggering event.

8. A method in a cellular radio communication system for dynamically allocating spreading codes to different information signals communicated between a radio base station (52) and a user terminal (11), wherein a plurality of codes are allocated to dedicated transport channels, DCHs, and high speed downlink shared channels, HS-DSCH, and a radio network controller (55) allocates codes for HS-PDSCH codes for HS-DSCH physical channels to the radio base station, said method being characterized by:

monitoring (43) the use of codes within the radio base station to determine whether there are unused codes that are not used as DCH codes or HS-PDSCH codes; and

upon determining that there is at least one unused code, allocating, by the radio base station, the at least one unused code as an additional HS-PDSCH code without communicating with the radio network controller, and treating the HS-PDSCH codes allocated by the radio network controller as a minimum number of HS-PDSCH codes allocated to the radio base station.

9. The method of claim 8, further comprising:

determining (46) at a later time that the additional HS-PDSCH code is required as a DCH code; and

the additional HS-PDSCH codes are reallocated (47) by the radio base station as DCH codes.

10. The method of claim 8, further comprising receiving within the radio base station the modified minimum number of HS-PDSCH codes from the radio network controller.

11. The method of claim 8, wherein the step of allocating by the radio base station at least one unused code as an additional HS-PDSCH code comprises allocating the additional HS-PDSCH code in response to a triggering event.

12. The method of claim 8, wherein the step of allocating by the radio base station at least one unused code as an additional HS-PDSCH code comprises allocating the additional HS-PDSCH code in a predetermined repetition pattern and de-allocating the additional HS-PDSCH code in response to a triggering event.

13. A system for dynamically allocating spreading codes to different information signals communicated between a radio base station (52) and a user terminal (11) in a cellular radio communications network in which a plurality of codes are allocated between dedicated transport channels, DCHs, and high speed downlink shared channels, HS-PDSCHs, and a radio network controller (55) allocates codes for HS-DSCH physical channels, HS-PDSCH codes, to the radio base station, said system being characterized by:

HS-PDSCH code allocation means (56) within the radio network controller (55) for allocating a minimum number of HS-PDSCH codes to the radio base station; and

a discretionary code allocation means (51) within the radio base station (52) that allocates and de-allocates additional HS-PDSCH codes from a fixed number of codes without communicating with the radio network controller, and treats the HS-PDSCH codes allocated by the radio network controller as a minimum number of HS-PDSCH codes.

14. The system of claim 13 wherein the discretionary code allocation means (51) monitors code usage to determine if there are unused codes within the plurality of codes that are not used as DCH codes or HS-PDSCH codes, wherein the discretionary code allocation means allocates and de-allocates additional HS-PDSCH codes from the unused codes.

15. The system of claim 14, wherein the discretionary code allocation means de-allocates the additional HS-PDSCH codes when the additional HS-PDSCH codes are needed as DCH codes.

16. The system of claim 13, further comprising:

means within the radio network controller for modifying a minimum number of HS-PDSCH codes that have been allocated to the radio base station; and

means within the radio base station for receiving the modified minimum number of HS-PDSCH codes from the radio network controller.

17. The system of claim 13, wherein the discretionary code allocation means within the radio base station allocates additional HS-PDSCH codes in response to a triggering event.

18. The system of claim 13, wherein the discretionary code allocation means within the radio base station allocates additional HS-PDSCH codes in a predetermined repetition pattern and de-allocates the additional HS-PDSCH codes in response to a triggering event.