ADAPTIVE RADIO CHANNEL SWITCHING

FIELD OF THE INVENTION

The present invention relates to adaptive radio channel switching in a radio network in order to optimise the overall radio network capacity. Especially, the present invention relates to adaptive down and up switching between dedicated channels .

BACKGROUND

Data traffic speeds using packet switched transmission over cellular systems like WCDMA can differ due to various reasons like: a) round trip delay and error rate in the radio network; b) slow or no radio bearer change when having bursty traffic in the radio downlink or uplink.

The throughput for these cases can be improved using radio adapted TCP software and/or proxy servers or using HSDPA/HSUPA which reduces the round trip delay and radio bearer switching time.

From data download tests to various data servers on the Internet, the present inventors have discovered that the speed can also be limited due to the remote FTP server speed/access limitations. The maximum access speed per user may be limited at these servers as many users may try to access this server at the same time, e.g. during some broadcasting or in general the maximum access speed may be limited. When accessing these servers over LAN, the same low speeds have been noticed. For these cases the allocated dedicated channel DCH supported 384 kbps although the average throughput was approximately 100 kbps and a 128 kbps DCH would have been sufficient in order to achieve the same average download speed. Allocating the wrong dedicated

channel DCH for such medium data speeds results in: 1) Unnecessary digital line (Iub) capacity occupation. Depending on the allocated dedicated channel, DCH, digital line capacity is reserved for this dedicated channel and cannot be given to other users. Currently, most Node B's are connected via one El line to the Radio Network Controller, RNC. The rent and fee for El lines are an expensive part of the network.

2) Unnecessary lower spreading factor code occupations or higher bit rate DCH' s. From indoor load tests using a dedicated indoor Node B, code and digital line limitations have been seen. Dedicated indoor WCDMA systems can show good code orthogonality and high loads can be achieved.

Due to the unnecessary radio and digital line capacity occupation some Packet Switched, PS, users may get dropped or new users may not get granted admission or the bit rate of all PS users may get downgraded. Furthermore, for such PS users in soft-handover condition the code usage at the Node B's and required digital line capacity between Node B's and RNCs, i.e. Iub, and RNCs to RNCs, i.e. Iur, can get reduced.

The patent application US 2004/0097191 describes a method of switching, by monitoring the traffic, from a current common channel to a dedicated channel for a user equipment. The method is used in a UMTS Terrestrial Radio Access Network (UTRAN) .

The patent application US 2003/0012217 Al describes channel-type switching to a common channel based on common channel load and considers mainly optimized channel switching between common and control channels.

The prior art documents relate to switching algorithms for switching between control and dedicated channels and between dedicated and shared channels, wherein the switching is made in dependence of throughput, buffer load, etc. Further, these applications relate to bursty traffic and describe how to avoid ping pong effects in the switching between common and dedicated channels.

An object with the present invention is to provide down and up switching between dedicated channels (WCDMA) using e.g. measured data throughput and buffer load in e.g. the RNC as switching parameters .

Another object of the invention is to provide a down and up switching between shared dedicated channels as a function of the data throughput and buffer load in e.g. the RNC or Node B.

Yet another object of the invention is to provide digital line capacity allocation/reservation switching depending on the dedicated channel and therefore also depending on the user throughput and buffer load.

SUMMARY OF THE INVENTION The present invention relates to adaptive radio channel switching between dedicated channels for WCDMA and shared channels for HSDPA/HSUPA radio systems in order to adapt to the user end-to-end packet switched data traffic requirements and with this to optimise the overall radio network capacity. The inventive switching method adds new functionalities in the radio and transport network resource managements by monitoring the user/users buffer and throughput information as available in the Radio Network Controller, RNC, and/or Node B. The invention optimises the overall network capacity as unnecessary reserved codes and

digital line capacity, Iub and Iur, can get free for other users .

The present invention allows adapting the channel bit rate allocation to the user's experienced end-to-end PS data throughput by monitoring the data throughput and buffer condition in the RNC and/or node B and applying the appropriate radio channel configuration and Iub reservetions for this user. This will be beneficial to all users in the radio network as the total radio resource, i.e. available codes, and digital line capacity will be optimised and the total achieved network throughput will be higher.

The present invention relates to a method and a Radio Network Controller for adaptive radio channel switching between dedicated channels in an UMTS network.

The invention is defined in the independent claims and preferred embodiments are set out in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail with reference to the drawings, in which: Figure 1 schematically illustrates a UMTS network, according to prior art, comprising a core network and a

UTRAN;

Figure 2 schematically shows an embodiment of a radio resource management with an adaptive channel switching (ACS) algorithm implemented in the RNC;

Figure 3 schematically illustrates a possible adaptive channel switching, ACS, implementation for WCDMA;

Figure 4 schematically shows how the buffer and throughput values vary over time for WCDMA; Figure 5 schematically illustrates a possible adaptive

channel switching, ACS, implementation for HSDPA; and Figure 6 schematically shows how the buffer and throughput values vary over time for HSDPA.

DETAILED DESCRIPTION

The following abbreviates and acronyms will be used in the description of the present invention.

AAL2 ATM Adaptation Layer 2

ACS Adaptive Channel Switching

ATM Asynchronous Transfer Mode

CRNC Controlling RNC, role an RNC can take with respect to a specific set of Node B's

DCH Dedicated CHannel

FACH Forward Access CHannel

FTP File Transfer Protocol

HSDPA High Speed Downlink Packet Access

HS-DSCH High Speed-Downlink Shared CHannel

HS-USCH High Speed-Uplink Shared CHannel

HSUPA High Speed Uplink Packet Access

IP Internet Protocol

Iub Interface between the RNC and the Node B

Iur Interface between two RNCs

LAN Local Area Network

MAC-hs Medium Access Control-high speed

Node B Base Transceiver Station, BTS. Logical node in the 3GPP RNS responsible for radio transmission/ reception in one or more cells to and from the UE. Terminates the Iub interface towards the RNC.

PS Packet Switched

RAB Radio Access Bearer

RACH Random Access CHannel

RAN Radio Access Network

RLC Radio Link Control (throughput = data channel + control channels

RNC Radio Network Controller

SF Spreading Factor

SRNC Serving RMC

TCP Transmission Control Protocol

UE ^• User Equipment, e.g. mobile terminal, phone and all peripherals

UMTS Universal Mobile Telecommunications System UTRAN Universal Terrestrial RAN. The Base Station, Base

Transceiver System etc. for WCDMA/UMTS WCDMA Wideband Code Division Multiplex Access

Further, in this specification, the term channel is applied to both DCH configurations and HSDPA/HSUPA (HS-DSCH/HS- USCH) configurations.

Figure 1 illustrates schematically a Universal Mobile Telecommunications System, UMTS, network 10 according to prior art. The UMTS network 10 comprises a core network 20 and a UMTS Terrestrial radio Access Network, UTRAN, 30. The UTRAN 30 comprises a number of Radio Network Controllers, RNCs, 32 each of which is coupled to a set of neighbouring Base Transceiver Stations, BTSs, 34, also called Node Bs. Each Node B 34 is responsible for a given cell and the controlling RNC 32 is responsible for routing user and signal data between that Node B 34 and the core network 20. All of the RNCs 32 are coupled to one another. In another case the RNCs can be all connected to each other but they do not have to be and normally they are not all directly connected to each other. Figure 1 also illustrates a mobile terminal or a user equipment 40. The core network 20 comprises a serving GPRS Support node, SGSN, 22 and a GPRS Gateway Support Node, GGSN, 24. The SGSN 22 and the GGSN 24 provide packet switched data services to the user equipment 40 via the UTRAN 30.

The invention relates to adaptive channel switching for

WCDMA and HSDPA/HSUPA. WCDMA is a 3G technology that increases data transmission rates compared to GSM systems by using the CDMA air interface instead of TDMA. The HSDPA/HSUPA is an enhancement to the WCDMA 3G technology that increases the downlink/uplink speed by applying different modulation and coding techniques as well as multiple antennas .

Figure 2 schematically shows an embodiment of a radio resource management with an adaptive channel switching,

ACS, algorithm implemented in the RNC. The adaptive channel switching, ACS, is an additional function that complements existing channel switching features within the serving RNC, SRNC.

Figure 2 illustrates a radio network controller, RNC, 32 comprised in a radio and transport network, such as a UTRAN 30. The RNC 32 comprises a congestion control means 50 communicatively connected to a radio admission control means 52, means for adaptive channel switching, ACS, 54.

The ACS means 54 is communicatively connected to the radio admission control means 52 and an Iub admission control means 56.

The congestion means 50, the radio admission control means 52, the ACS means 54 and the admission control means 56 are communicatively connected to a monitoring means 58.

An Iub 60 is provided as an interface between the RNC 32 and a Node B 34, whereby a channel set up request can be sent from the Node B 34 to the RNC 32.

The monitoring means is configured to monitor e.g. DL codes, throughput, buffer load, radio load, transmit power etc.

The congestion means is configured to imitate a channel switching from a dedicated channel to a common channel if congestion exists, i.e. if not enough bandwidth to support the current traffic load is available.

The admission control means is configured to estimate the load and fill up the system to its load limits. If, for example, the downlink or uplink limit threshold. is exceeded, a new RAB may not be admitted. The function can be located in radio resource control in the RNC. The admission control can be configured to decide on the RAB during setup and can also switch user/users in case resources need to be released for new users.

Embodiments of the invention may comprise means 62 for other dependencies, which means 62 can be communicatively connected to the Iub admission control means 56. All of the admission controls run in parallel. The ACS channel switch is approved by the radio/digital admission control. The ACS IuB admission control 56 although connected with the arrow "B" to the ACS 54 is or could be also connected directly to the Congestion Control 50 and/or Admission Control 52. For the present invention it is of importance that the ACS connects to 50, 52 and 56 directly in order to invoke channel switching in the radio and digital domain if necessary. Iub admission control means 56 could be also seen as some other future/existing function which allows channel switching after getting some channel switch request/indication from the ACS.

The radio resource management can further comprise means for soft and softer handover, and means for coverage triggered channel switching. The means for handover can be configured to imitate a channel switching if otherwise a

link cannot be established. The means for coverage triggered channel can be configured to reconfigure the radio bearer when the coverage limit for the current bearer is reached.

As indicated by the arrow A in figure 2, the ACS means 54 decides the best channel configuration depending on the monitored throughput and buffer condition for each PS connection. The decision can be supported by monitored measurements at the mobile terminal 40, e.g. through measurements at the mobile terminal 40. For example, throughput values at the mobile terminal 40 can be measured. If the throughput and buffer is below/above a predetermined threshold value, the ACS 54 indicates that down/up switching is required.

Every channel switch is approved by the radio/digital transport-network admission control means 52 and 56 before carried out, as indicated by the arrows B in figure 2.

The threshold values for switching the channel preferably include some hysteresis in order to avoid the so called ping pong effect, i.e. in order to avoid too early switches due to short bursty fluctuations. Moving averaging can be applied to the measured throughput and buffer values.

The ACS means 54 and the ACS algorithm are configured to operate in parallel to other radio resource management- means and algorithms which for example handles new packet transmission, handover control, power control, congestion control, etc. The actual switching of the channel is done by carrying out a radio bearer reconfiguration as described in 3GPP TS25.331, Technical Specification Group Radio Access Network; Radio Resource Control (RRC) ; Protocol Specification, and will therefore not be described in more

detail .

The present invention applies to UMTS networks, WCDMA, where different radio channels can be assigned in order to deliver different bit-rates to the user. In the uplink this considers mobiles which allow data rates larger than 64 kbps . Furthermore, the invention includes updates to HSDPA and HSUPA.

ACS implementation for WCDMA

Figure 3 schematically illustrates how an embodiment of the inventive ACS algorithm may be implemented in order to switch the data rate between dedicated channels, e.g. 384 kbps DCH » 128 kbps DCH • 64 kbps DCH, and down to lower bit rate common channels, Random Access Channel RACH /

Forward Access Channel FACH, during an active data session. The physical channel and the transport channel parameters of the radio bearer are reconfigured using the standardised Radio Resource Control, RRC, procedure. The allocated / reserved digital line (AAL2) capacity for this connection is also reconfigured. Transport network switching is possible with ATM AAL2 layer. The ACS algorithms for the downlink and uplink are independent of each other. For mobile terminals which only support 64 kbps in the uplink, the uplink uses a fixed Radio Access Bearer, RAB, configuration. The threshold values for the buffer and throughput in order to activate channel down or up switching should consider:

- higher and upper threshold values for the buffer depending on the actual channel configuration. If the buffer size would be fixed, the buffer will reach faster the full condition for higher throughputs and this has to be considered with a larger safety margin in the buffer threshold values. - For the throughput, the upper and lower threshold

values also, like for the buffer, depend on the currently allocated DCH (throughput) .

In general, a moving average may be applied to the monitored throughput and buffer values in order not to switch too early due to some short bursty fluctuation in the traffic, whereby the so called ping pong effect can be avoided. The threshold values may be set relative to the upper throughput values of the current channel, e.g. upper threshold value 90% of maximum throughput value of current channel. If the highest / fastest channel has been reached no switching will occur.

An embodiment of the inventive method implemented for WCDMA comprises the steps of (cf . figure 3) :

100 initiating and admitting a new PS connection (Serving

RNC, SRNC) ;

102 checking if buffer and throughput value is below a lower threshold value; 104 if buffer and throughput value is below a lower threshold value, increasing the channel and repeating from step 102;

106 if buffer and throughput value is not below a lower threshold value, checking if buffer and throughput is above an upper threshold value,-

108 if buffer and throughput is above an upper threshold value, decreasing the channel and repeating from step 106;

110 if buffer and throughput is not above an upper threshold value, repeating from step 102; and 112 terminating or releasing the PS connection.

Fig 4 schematically shows how the buffer and throughput values vary over time for WCDMA.

ACS implementation for HSDPA/HSUPA

For HSDPA/HSUPA, the users in a cell can get allocated a HS-PDSC (high Speed Physical Downlink Shared Channel) at the Controlling RNC, CRNC. The Medium Access Control-high speed, MAC-hs, scheduler (not shown) is located in the Node B, which serves the corresponding cell. This allows fast resource sharing in the code domain and time domain for the users accessing the same HS-DPSCs. This allows users with bursty/constant, high or medium throughputs to get the correct high average throughput with optimised radio resource sharing. However, for example for HSDPA, the CRNC has to decide which HS-PDSCH has to be setup as there are 12 different classes, modulation schemes and maximum numbers of codes, available. Applying a too high HS-PDSCH class would block unnecessary codes and digital line capacity which could be used for other users.

Figure 5 schematically illustrates how an embodiment of the inventive ACS algorithm may be implemented in order to switch the HS-PDSCH to different classes, e.g. Class 1 • Class 5 • Class 12, and down to WCDMA transmission rate. The allocated/reserved digital line capacity for his connection will depend on the allocated HS-PDSCH. The threshold values for the buffer and throughput, moving average, etc., in order to activate HS-PDSCH down or up switching should consider, like for WCDMA, the actual speed of the HS-PDSCH but also the individual speed and buffer size usage of the individual users within the shared channel. This information may be available in the RNC and/or Node B and/or reported from the mobile terminals. In order to activate the switching, the algorithm will have to consider more input parameters than for WCDMA as users with different profiles in their throughputs are sharing the same channel .

An embodiment of the inventive method implemented for HSDPA

comprises the steps of (cf . figure 5) :

200 initiating and admitting a new PS connection (SRNC) ;

202 checking if buffer and throughput value is below a lower threshold value; 204 if buffer and throughput value is below a lower threshold value, increasing the HS-PDSCH and repeating from step 202;

206 if buffer and throughput value is not below a lower threshold value, checking if buffer and throughput is above an upper threshold value;

208 if buffer and throughput is above an upper threshold value, decreasing the HS-PDSCH and repeating from step 206;

210 if buffer and throughput is not above an upper threshold value, repeating from step 202; and 212 terminating or releasing the PS connection.

Figure 6 Figure 6 schematically shows how the buffer and throughput vary over time for HSDPA.

The present invention has been described with exemplifying embodiments. However it should be understood that modifications can be made without departing from the scope of the invention.