Patent Application
20090232059
The present invention relates to wireless communications. More especially it relates to wireless packet data communications. Particularly it relates to latency reduction when setting up an uplink communications channel.
Multiplexing of a plurality of users on a common resource is well known in prior art. FDM (Frequency Division Multiplex), TDM (Time Division Multiplex) and CDM (Code Division Multiplex) are well known examples of multiplexing principles.
Also a number of queuing disciplines are known for scheduling traffic on the multiplexed resource.
Kenth Fredholm, Kristian Nilsson, ‘Implementing an application for communication and quality measurements over UMTS networks,’ LiTH-ISY-EX-3369-2003, Linköping 2003, describes simulations of voice over IP (Internet Protocol) in a UMTS (Universal Mobile Telecommunications System) system. The master thesis includes concepts such as QoS (Quality of Service), AMR (Adaptive Multi Rate), RTP (Real-time Transport Protocol), RTCP (Real-time Transport Control Protocol) and SIP (Session Initiation Protocol).
AMR can operate at various bit rates including, e.g., 12.2 and 4.75 kbit/s. Background noise is produced at 1.8 kbit/s. An AMR frame comprises an AMR header, AMR auxiliary information and an AMR core frame.
Comfort noise is transmitted in Class A bit field. Speech data classified in Class A bits are bits considered most important and Class C bits least for a resulting (decoded) speech quality. In UMTS, SCR (Source Controlled Rate) operation is mandatory for AMR and controls transmission data rate.
RTP supports various lower level protocols but typically runs over UDP (User Datagram Protocol) as illustrated in
Hossam Fattah, Cyril Leung, ‘An Overview of Scheduling Algorithms in Wireless Multimedia Networks, ’ IEEE Wireless Communications, pp. 76-83, June 2002 describes a plurality of scheduling algorithms and among other things scheduling in CDMA networks. One algorithm, Scheduled CDMA, reveals data exchange between BS and MS in fixed-size unit called capsule, comprising one or more packets. For uplink scheduling, a capsule transmission request is sent to base station by mobile station whenever the MS has new packets to transmit. For each time slot the scheduler selects capsule transmission requests from a common queue ordered according to priority or delay sensitivity. The base station sends transmission permission capsules to selected mobile stations to inform them of their capsule transmission times and power levels.
3rd Generation Partnership Project (3GPP): Technical Specification Group Core Network, Mobile radio interface layer 3 specification, (Release 1998), 3GPP TS 04.08 v7.21.0, France, December 2003, specifies procedures for Radio Link Control, RLC, and specifies the procedures used at the radio interface for Call Control, CC, Mobility Management, MM, Radio Resource, RR, management and Session Management, SM. Paragraph 3.5.2.1.2 describes initiation of packet access procedure and channel request. A mobile station initiates a packet access procedure by scheduling sending of CHANNEL REQUEST messages on RACH and leaving the packet idle mode. The RR entity of the mobile station schedules CHANNEL REQUEST messages on RACH.
3rd Generation Partnership Project (3GPP): Technical Specification Group GSM/EDGE Radio Access Network, General Packet Radio Service (GPRS), Mobile Station (MS)—Base Station System (BSS) interface, Radio Link Control/Medium Access Control (RLC/MAC) protocol, (Release 1999), 3GPP TS 04.60 v7.21.0, France, December 2003, specifies the procedures used at the radio interface (Reference Point Um) for the General Packet Radio Service, GPRS, Medium Access Control/Radio Link Control, MAC/RLC, layer. The present document provides the overall description for RLC/MAC layer functions of GPRS and EGPRS (General Packet Radio Service and Enhanced General Packet Radio Service) radio interface Um. Within this TS the term GPRS refers to GPRS and EGPRS unless explicitly stated otherwise. Paragraph 7.1.2.1.1 relates to access persistence control on PRACH. The PRACH Control Parameters IE contains the access persistence control parameters and shall be broadcast on PBCCH (Packet Broadcast Control Channel) and PCCCH (Packet Common Control Channel). The parameters included in the PRACH Control Parameters IE are:
The mobile station shall make maximally M+1, where M is received value of parameter MAX_RETRANS for a particular priority, attempts to send a PACKET CHANNEL REQUEST (or EGPRS PACKET CHANNEL REQUEST) message. After sending each PACKET CHANNEL REQUEST (or EGPRS PACKET CHANNEL REQUEST) message, the mobile station shall listen to the full PCCCH (corresponding to its PCCCH_GROUP).
The mobile station shall start timer T3186 at the beginning of the Packet Access Procedure. At expiry of timer T3186, the packet access procedure shall be aborted, packet access failure shall be indicated to upper layers and the mobile station shall return to packet idle mode. The first attempt to send a PACKET CHANNEL REQUEST (or EGPRS PACKET CHANNEL REQUEST) message, may be initiated at the first available PRACH block on the PDCH defined by the PCCCH_GROUP for the mobile station. The mobile station shall choose one of the four TDMA frames within the selected PRACH block randomly with a uniform probability distribution. For each attempt, the mobile station shall draw a random value R with uniform probability distribution in the set {0, 1, . . . 15}. The mobile station is allowed to transmit a PACKET CHANNEL REQUEST message if P(i), where i is the radio priority of the TBF being established, is less or equal to R. After each attempt, the S and T parameters are used to determine the next TDMA frame in which it may be allowed to make a successive attempt. The number of TDMA frames belonging to the PRACH on the PDCH defined by the PCCCH_GROUP for the mobile station between two successive attempts to send a PACKET CHANNEL REQUEST (or EGPRS PACKET CHANNEL REQUEST) message excluding the TDMA frames potentially containing the messages themselves is a random value drawn for each transmission with uniform probability distribution in the set {S, S+1, . . . , S+T−1}. Paragraph 8.1.2.5 describes uplink TBF establishment during downlink RLC data block transfer. The mobile station may request establishment of an uplink transfer during a downlink TBF by including a Channel Request Description information element in the PACKET DOWNLINK ACK/NACK message. Initiation is triggered by a request from upper layers to transfer a LLC PDU. The request from upper layers specifies a Radio Priority to be associated with the packet transfer. Upon such a request,
The mobile station initiates the packet access procedure by sending the Channel Request Description information element in a PACKET DOWNLINK ACK/NACK message on the PACCH and starting a timer.
3GPP TS 44.060 describes an alternative to the procedure in specifications 3GPP TS 04.08 and 3GPP TS 04.60.
3rd Generation Partnership Project (3GPP): Technical Specification Group GSM/EDGE Radio Access Network, General Packet Radio Service (GPRS), Mobile Station (MS)—Base Station System (BSS) interface, Radio Link Control/Medium Access Control (RLC/MAC) protocol (Release 5), 3GPP TS 44.060 v5.13.0, France, September 2004, specifies procedures for Radio Link Control, RLC, layer and Medium Access Control, MAC, layer, including physical link control functions of the radio interface between GSM/EDGE Radio Access Network, GERAN, and Mobile Station, MS. An Uplink State Flag, USF, is used on Packet Data Channel(s), PDCH(es) to allow multiplexing of uplink radio blocks from different mobile stations. An RR (Radio Resource) connection is a physical connection established between a mobile station and the network to support exchange of information flows. A TBF (Temporary Block Flow) is, in A/Gb mode, a physical connection used by the two RR peer entities to support the unidirectional transfer of LLC (Logical Link Control) PDUs on packet data physical channels. (A/Gb mode is a mode of operation of the MS when connected to the Core Network, CN, via GERAN and the A and/or Gb interfaces; the A interface being the interface between a BSS (Base Station Subsystem) and a 2G MSC (Mobile Switching Center) and the Gb interface being the interface between a BSS and a 2G SGSN (Serving GPRS Support Node).) In Iu mode, a TBF is a logical connection offered by two MAC entities to support the unidirectional transfer of RLC PDUs on basic physical sub-channels. (Iu mode is a mode of operation of the MS when connected to the CN via GERAN or UTRAN and the Iu interface; the Iu interface being the interface between a BSS or an RNC (Radio Network Controller) and a 3G MSC or a 3G SGSN.) In extended uplink TBF mode, the uplink TBF may be maintained during temporary inactive periods, where the mobile station has no RLC information to send.
The mobile station shall initiate a packet access procedure by scheduling sending of PACKET CHANNEL REQUEST messages on PRACH (Packet Random Access Channel) corresponding to its PCCCH_GROUP (Packet Common Control Channel Group) and simultaneously leaving the packet idle mode. While waiting for a response to the PACKET CHANNEL REQUEST message, the mobile station shall monitor the full PCCCH (Packet Common Control Channel) corresponding to its PCCCH_GROUP. While monitoring the full PCCCH, the mobile station shall decode any occurrence of the PERSISTENCE_LEVEL parameter included in a message received on PCCCH. When the mobile station receives the PERSISTENCE_LEVEL parameter, the value of the PERSISTENCE_LEVEL parameter shall be taken into account at the next PACKET CHANNEL REQUEST attempt that follows. The parameter PERSISTENCE_LEVEL comprises a persistence level P(i) for each radio priority i (i=1, 2, 3, 4); where P(i)ε{0, 1, . . . 14, 16}. The first attempt to send a PACKET CHANNEL REQUEST (or EGPRS PACKET CHANNEL REQUEST) message, may be initiated at the first available PRACH block on the PDCH (Packet Data Channel) defined by the PCCCH_GROUP for the mobile station. The mobile station shall choose one of four TDMA frames within the selected PRACH block randomly with a uniform probability distribution. For each attempt, the mobile station shall draw a random value R with uniform probability distribution in the set {0, 1, . . . 15}. The mobile station is allowed to transmit a PACKET CHANNEL REQUEST message provided that P(i) is less than or equal to R. Consequently, the smaller P(i), the greater is the persistency.
The mobile station generally operates with a sliding trans-mission window of RLC data PDUs. In the extended uplink TBF mode of Technical Specification 3GPP TS 44.060, if there is no RLC data block available within the window, the mobile station shall stop sending RLC data blocks. The mobile station shall continue sending RLC data blocks when an RLC data block becomes available in the window.
A UMTS correspondence of TBFs in GSM/GPRS and GSM/EGPRS are RABs (Radio Access Bearers).
3rd Generation Partnership Project (3GPP): Technical Specification Group GSM/EDGE Radio Access Network, Multiplexing and multiple access on the radio path (Release 5), 3GPP TS 45.002 v5.12.0, France, April 2004, defines the physical channels of the radio sub system required to support the logical channels. It includes a description of the logical channels and the definition of frequency hopping, TDMA (Time Division Multiple Access) frames, time-slots and bursts. In the uplink part for channels other than PACCH (Packet Associated Control Channel) transmitted as access bursts on PRACH (Packet Random Access Channel) or CPRACH (Compact Packet Random Access Channel), the logical channel type shall be indicated by the message type contained in the block header part. For PACCH transmitted as access bursts, the logical channel type is indicated by the corresponding polling message on the downlink. For the PRACH or CPRACH case the logical channel type is indicated by the USF, set on the downlink on a block-by-block basis.
The MAC layer is responsible for sharing of communications resource (the air interface) common to data and voice users, according to an allocation strategy.
In e.g. GSM/GPRS, MAC of BSS (Base Station Subsystem) is responsible for management of uplink and downlink scheduling of RLC blocks belonging to different TBFs over available time slots, resolving conflicts due to e.g. request collisions, assigning uplink TBFs to requesting MTs (Mobile Terminals) if there are time-slots available, notifying of uplink TBF deallocation if MT has been inactive during a predefined period, associating respective voice calls to a pair of time-slots and signaling as need be for deallocating of a TBF to render the time-slot pair available for speech communications. In uplink direction, MAC of MT is responsible for initiating transmission of requests of uplink TBFs to BSS for transfer of data for which no TBF is yet established. Once the TBF setup is acknowledged, MAC of MT forwards RLC PDUs, carrying one or more segmented LLC PDUs, over a time-slot allocated by BSS. MT continues sending until there is no more data to send, or it has transmitted a maximum number of RLC blocks allowed. The TBF is then released. Each TBF is assigned by the network a temporary flow identity, TFI, which is unique in both directions.
None of the cited documents above discloses scheduling of uplink packet data transmissions or uplink TBF establishment triggered by downlink session ending, unconditioned on whether the related user or user equipment has data to send or not.
A general problem of multiple access systems is to fulfill various requirements of a session as regards, e.g. QoS. Another problem is how to incorporate such requirements when allocating traffic to communications resources and scheduling of transmission instances.
In multi-user access, delay or latency is often of vital importance. The demand for short delay or low latencies are immediate when real-time applications, e.g. speech, are provided over packet switched connections. One such example application is Push-to-talk over Cellular, PoC.
Generally, this is particularly a problem in uplink direction when a user e.g. does not get any response of a button press until after a delay, or cannot get his voice message through during a conversation despite the other party has stopped talking waiting for a response. Remembering that in typical existing systems, it is the network side of a wireless connection that is responsible for the TBF establishment in GSM/GPRS or GSM/EGPRS, RAB establishment in UMTS and correspondingly in CDMA2000, the delayed establishment is less of a problem in downlink direction, where a base station transmits data to a plurality of users and resources efficiently can be allocated and scheduled in relation to information available at sender side (without propagation time delay to a wireless user equipment).
In uplink direction a base station receiving information from a plurality of user devices, the queue status of the mobile entity is not always available, at least not if limited time restrictions also need to be met. Further it may not be efficient to spend communication resources on communicating such information to a scheduling entity, such as a base station, BS, or base station controller, BSC.
Consequently, there is a need of efficiently providing uplink communications channel scheduling and establishment of packet data transmissions for users, temporarily being in inactive state in terms of wireless transmissions, entering active state.
An object of the invention is to reduce time required for uplink communications channel establishment when user equipment or user enters an active state.
Another object is to provide signaling independent of amount of data in sender buffer for initiating uplink communications channel scheduling and uplink communications channel establishment.
It is also an object to provide a method and system of efficient scheduling and establishment uplink TBF, or correspondingly for the various communications systems.
A further object is to provide a method and system of uplink communications channel and establishment rendering PoC useful.
Finally, it is an object to provide a method and system of uplink communications channel and establishment integrating SIP signaling.
These objects are met by a method and system of uplink scheduling or uplink communications channel establishment and associated signaling.
For delay sensitive applications it is important with low latency.
In multi-user access, delay or latency is often of vital importance. The demand for short delay or low latencies are immediate when real-time applications, e.g. speech, are provided over packet switched connections. One such example application is Push-to-talk over Cellular, PoC.
The invention identifies that for many applications scheduling of one or more temporarily inactive TBFs (temporarily carrying no data) initiated conditioned on downlink session ending, unconditioned on whether the related user or user equipment has data to send or not reduces delay and latency. If a user equipment or user does not utilize the established TBF (s), the TBF (s) are released according to release criteria, known in the art.
To further reduce delay and latency, according to the invention the transmission scheduling is preferably persistent. USF flags are then sent more frequently than with regular transmission scheduling, this increases the requirements on the mobile station to actively being capable of receiving the scheduling information, thereby to some extent increasing power consumption as compared to a case when the invention is applied with less preferred regular non-persistent scheduling, even if optimized. An advantage achieved is that an entity of user equipment or a user then can send a greater number of blocks at once, without having to wait for potentially other entities of user equipment.
Generally, the delayed uplink TBF establishment of prior art is particularly a problem in uplink direction. In downlink direction, a base station transmits data to a plurality of users and resources can efficiently be allocated and scheduled in relation to information available at sender side (without propagation time delay to a wireless user equipment).
A problem in prior art is also that in uplink direction, the queue status of the mobile entity is not always available to a base station receiving information from a plurality of user devices, at least not if limited time restrictions also need to be met. Further it may not be efficient to spend communication resources on communicating such information to a scheduling entity, such as a base station or base station controller.
When a user equipment or user becomes inactive, not transmitting data but possibly receiving data, an earlier established TBF for the transmission of data is released unless new data arrives during a time frame in order of seconds. If the user equipment or user becomes active after this time frame and data then arrives, the TBF needs be established anew. The establishment takes time. It is identified that delay can be reduced by approximately 0.2 s by TBF establishment and scheduling according to the invention. With two parties involved in a conversation over similar connections the perceived effect is doubled. The effect is clearly noticeable. This is particularly the case, e.g., for speech communication in PoC and when web-browsing over cellular.
An example of equal share splitting and regular scheduling of a resource is schematically illustrated in
In regular scheduling, such as the scheduling illustrated in
Uplink TBF scheduling and establishment could also be accomplished in accordance with the method and system described in International Patent Application No. PCT/SE2004/001592.
According to the invention, the uplink TBF is preferably established when a downlink dataflow finishes <<Over>>, at least temporarily, to reduce the perceived delay of the response. The uplink TBF scheduling and establishment of the second entity of user equipment UE2>> preferably corresponds to uplink TBF scheduling and establishment described for the first entity of user equipment <UE1>>, but is not included in the figure for reasons of clarity.
Toll quality of, e.g., PoC requires delay reduction. The invention provides such delay reduction. It will also improve e.g. web-browsing over cellular.
According to a first embodiment of the invention a base station controller or corresponding entity over which downlink data is routed to an entity of user equipment detects when a downlink data transfer is ended and a dataflow ends. Preferably, data transfers comprising more than a predefined number of data blocks, e.g. corresponding to floor idle burst size, are considered for triggering of uplink TBF establishment. According to the first embodiment of the invention, the TBF establishment does not require involvement of the user equipment to which the data transfer is destined for requesting TBF establishment. The BSC establishes the uplink TBF and sends USFs to the user equipment.
According to a second embodiment of the invention, an entity of user equipment detecting that a downlink data transfer is ended automatically, preferably not requiring user interaction, starts sending of dummy data in uplink direction, the dummy data filling the output buffer and thereby triggering TBF establishment. The session ending is preferably detected by monitoring of reception of a floor idle or corresponding signal.
When the invention is applied to establishment of one or more RABs of UMTS, establishment is preferably initiated by a received SIP_INVITE signal <<RePre>>, illustrated in the initial signaling received by <<UE2>> in
In this patent application acronyms such as IP, UDP, RTP, SIP, TBF, RAB, BSS, MT, MS, GSM, GPRS, EGPRS, UMTS or CDMA2000 are applied. However, the invention is not limited to systems with entities with these acronyms, but holds for all communications systems operating analogously.
The invention is not intended to be limited only to the embodiments described in detail above. Changes and modifications may be made without departing from the invention. It covers all modifications within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2004/001862 | 12/13/2004 | WO | 00 | 6/11/2007 |
