Patent Application
20050207396
The present invention relates to wireless communication, and more particularly to packet switching and circuit switching for wirelessly communicating with a mobile terminal.
The first Global System for Mobile (GSM) communication networks were designed for voice services rather than for data services. When the use of GSM data services started, it soon became evident that the Circuit Switched (CS) bearer services were not well-suited for certain types of applications with a bursty nature. Therefore the new Packet Switched (PS) data transmission service GPRS (General Packet Radio Service) was developed for packet services. GPRS is a packet radio network utilizing the GSM network, and GPRS endeavours to optimize data packet transmission by means of GPRS protocol layers on the air interface between a mobile station (hereinafter also called a mobile terminal) and a GPRS network.
A GPRS mobile station (MS) can operate in one of three modes of operation, as described in 3GPP TS 23.060, “Service description; Stage 2,” Section 5.4.5. The three modes are Class-A Mode, Class-B Mode, and Class-C Mode. According to the Class-A mode of operation, the MS is attached to both GPRS as well as other GSM services, and therefore Class-A Mode corresponds to Dual Transfer Mode (DTM) Mode (hereinafter also called dual mode). The mobile user in Class-A Mode can make and/or receive calls on the two services simultaneously, for example having a normal GSM voice call and receiving GPRS data packets at the same time. According to the Class B mode of operation, the MS is attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. According to the Class C mode of operation, the MS can only be attached either to the GSM network or the GPRS network; the selection is done manually and there are no simultaneous operations.
Based on the current standard (3GPP TS 44.018, “Radio Resource Control Protocol”), when the MS is in packet transfer mode and a CS connection (also referred to as a radio resource or RR connection) is needed, then all packet resources must first be aborted, then an RR connection is established, and finally packet resources may be requested. This process occurs, for example, when the MS initiates a call. This prior art system is illustrated in
The main problem with these prior art techniques is that the MS is not allowed to immediately enter a combined CS mode 212 and PS mode 216 (which together comprise a dual mode) until the MS has performed various time-consuming steps. Thus, the mobile station will be forced to idle its packet switching capabilities, while it sets up the circuit switching session 212.
The present invention enhances the change from the packet transfer mode to the dual transfer mode by streamlining the transition and making it more direct. The solution is to employ a radio link control or multiple access control (RLC/MAC) message using a packet associated control channel (PACCH) in order to produce a dual transfer mode (DTM) assignment command, without any need to idle packet resources. The mobile station (MS) maintains packet switched (PS) resources during this process, and the MS thus gains better quality of service for a packet application. The RLC/MAC message uses the PACCH either to request the DTM assignment from the network, or alternatively to convey the DTM assignment from the network without any need for the request.
While in packet transfer mode, either the MS or a network may initiate the CS connection. In the latter case (i.e. the MS-terminated case), a network can provide CS resources immediately, using either a DTM ASSIGNMENT COMMAND or an IMMEDIATE ASSIGNMENT message. Since there is no need to send a PACKET PAGING REQUEST or a PACKET CS REQUEST message, the MS can get CS resources even faster when those messages are not included.
An efficient way to establish the CS connection 212 in
The MS makes a maximum of M+1 attempts to send this PACKET CS REQUEST message 310 on the PACCH. In addition to the maximum number of transmissions, the MS will also spread the transmission of this request message. The spreading factor is based on the BS_CV_MAX parameter. The spreading factor could be, for example, BS_CV_MAX+x radio blocks, where x is a further new parameter.
Having made M+1 attempts to send a PACKET CS REQUEST message 310, the MS starts a new RLC/MAC timer 350 (Tx). At expiration of the timer Tx, the dual mode access procedure is aborted, packet resources are released as in the prior art, and the mobile station initiates random access by sending the CHANNEL REQUEST message on the RACH as specified in 3GPP TS 44.018, “Radio Resource Control Protocol.”
It is possible that the MS can use existing Max retrans and T3126 (currently used with the CHANNEL REQUEST message 211 when M+1 requests are sent) parameters, as specified in 3GPP TS 44.018, “Radio Resource Control Protocol,” or alternatively new parameters can be specified.
In the MS-terminated case illustrated in
The “CS Channel Request Description IE” is specified in sub-clause 9.1.8 of 3GPP TS 44.018, “Radio Resource Control Protocol.”
A network can reply to the MS by using existing radio resource management messages. These messages are encapsulated in one or more new RLC/MAC control messages. For example, a PACKET CS COMMAND can encapsulate all the RR messages. Another approach would be to add a new RLC/MAC message for each of the replies from the network.
A network will be able to allocate both PS and CS resources, or it will not be able to allocate PS resources, or it will not be able to allocate CS resources. Each of these three alternative situations will now be addressed. All three situations are possible in both the MS-originated or MS-terminated cases.
If a network can allocate both PS and CS resources, then it sends the DTM ASSIGNMENT COMMAND message 215. When the MS receives this message it starts CS connection establishment and finally enters the dual transfer mode. Note that the DTM ASSIGNMENT COMMAND message 215 is very large, especially the size of the conditional Frequency List parameter (the length is 4-132 octets), and it is possible that the size of this Frequency List parameter might somehow be limited.
If, however, a network cannot allocate PS resources, then it sends an IMMEDIATE ASSIGNMENT message 213. When the MS receives this message it releases the PS connection and starts establishment of a CS connection. In the CS dedicated mode, the MS may ask for PS resources by using the procedures of the prior art.
If, alternatively, a network cannot allocate CS resources, then it sends an IMMEDIATE ASSIGNMENT REJECT message. When the MS receives this message it continues in packet transfer mode normally.
As shown in
In both the DTM ASSIGNMENT COMMAND 215 and also the IMMEDIATE ASSIGNMENT message 213, a new parameter is needed to indicate that the message is sent because of paging. In addition, an indication that the MS supports this feature is needed in the MS Radio Access Capability information element (IE).
There are at least two possibilities for the message transfer on PACCH. First, it is possible to use a single RLC/MAC message for encapsulating all the RR messages already described herein. This possible approach has the advantage that only one RLC/MAC message definition is needed, which makes the present invention simpler, and uses only one RLC/MAC message type code point. This first solution would be in line with the provision of SI message on PACCH, specified for the Network Assisted Cell Change procedure introduced in 3GPP Release 4. The message, according to this first possibility, could be called for example PACKET CS COMMAND. A second possibility is to use separate RLC/MAC messages. The merits of this second solution are not as great as those of the first solution. In either of these two possible embodiments, an indication that a network supports this RLC/MAC message feature is needed in the GPRS Cell Options information element (IE).
It is to be observed that, in both
Referring now to the flowchart of
It is to be understood that all of the present figures, and the accompanying narrative discussions of best mode embodiments, do not purport to be completely rigorous treatments of the method, terminal, and system under consideration. A person skilled in the art will understand that the steps and signals of the present application represent general cause-and-effect relationships that do not exclude intermediate interactions of various types, and will further understand that the various steps and structures described in this application can be implemented by a variety of different combinations of hardware and software, in various configurations and sequences, which need not be further elaborated herein.
