Signaling data link for a GSM-CDMA air interface

Details Signaling data link for a GSM-CDMA air interface Signaling data link for a GSM-CDMA air interface

1999-09-30

2004-11-02

Nguyen, Chau (Department: 2663)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S337000, C370S467000

Reexamination Certificate

active

06813256

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to wireless telecommunications, and specifically to advanced cellular telephone networks.
BACKGROUND OF THE INVENTION
The Global System for Mobile (GSM) telecommunications is used in cellular telephone networks in many countries around the world. GSM offers a useful range of network services and standards. GSM standards define protocol stacks that are used in conveying signaling and user traffic between elements of the network, including subscriber units (also known as mobile stations—MSs), base station subsystems (BSSs) and mobile switching centers (MSCs).
FIG. 1
is a block diagram schematically illustrating the GSM standard protocol stack used in signaling over dedicated control channels between an MS and the network, as is known in the art and defined by GSM standards, particularly the GSM 04.xx series of standards. The term “dedicated” refers to communication channels used during a call to or from the MS, as opposed to when the MS is in an idle, or standby, state. The lowest protocol layer is the physical layer of the air interface, which in existing GSM networks is based on time-division multiple access (TDMA) digital communications technology. The data link layer provides data link services and functionality, as defined in particular in GSM standards 04.05 and 04.06, which are incorporated herein by reference. The GSM data link layer supports both acknowledged and unacknowledged messaging operation modes. In the acknowledged mode, the data link layer provides reliable transmission of upper layer messages, with services including: (1) message ordering, (2) priority and fragmentation, and (3) suspension and resumption of communications.
A radio interface layer, which in one embodiment includes three sublayers, controls and passes signals through the data link layer and physical layer. It will be understood by those skilled in the art that the terms Layer 1 and physical layer are commonly used interchangeably. Similarly, Layer 2 and the data link layer are commonly used interchangeably. Furthermore, the terms Layer 3, RIL3, and radio interface layer are commonly used interchangeably by those skilled in the art. In the present case, the terms physical layer, data link layer, and radio interface layer are used throughout, merely for the sake of clarity.
The lowest sublayer of the radio interface layer is a Radio Resource (RR) management sublayer. The RR management sublayer supports Mobility Management (MM) and Call Management (CM) sublayers above it. The CM sublayer supports signaling for call processing, as well as GSM supplementary services. The MM sublayer supports signaling required for locating the MS, authentication and encryption key management. It should be noted that any protocol that may be used to transmit messages through the physical layer and the data link layers, such as protocols associated with GSM short message service (SMS), would be considered to be a radio interface layer protocol for the purpose of this description.
Code-division multiple access (CDMA) is an improved digital communications technology, which affords more efficient use of radio bandwidth than TDMA, as well as a more reliable, fade-free link between cellular telephone subscribers and base stations. The leading CDMA standard is TIA/EIA-95 (commonly referred to as IS-95), promulgated by the Telecommunications Industry Association (TIA). IS-95 defines its own protocol stack for transmission of signaling over traffic channels, including a physical layer and a data link layer. Because the IS-95 CDMA air interface is based on fundamentally different technology from the GSM TDMA interface, there are substantial differences between the conventional IS-95 and GSM protocol stacks. Furthermore, the standard IS-95 data link layer does not provide some of the data link layer services defined by GSM standards for signaling over traffic channels, particularly services associated with acknowledged mode operation. For example, IS-95 data link layer does comply with GSM requirements for signaling on overhead (e.g., paging and access) channels.
International Patent Application Number PCT/US96/20764, which is incorporated herein by reference, describes a wireless telecommunications system that uses a CDMA air interface to implement GSM network services and protocols. Using this system, at least some of the TDMA base stations and subscriber units of an existing GSM network would be replaced or supplemented by corresponding CDMA equipment. CDMA BSSs (base station subsystems) in this system are adapted to communicate with GSM mobile switching centers (MSCs) via a standard GSM A-interface. Core GSM network services are thus maintained, and the changeover from TDMA to CDMA is transparent to users.
Hybrid cellular communications networks, incorporating both GSM and CDMA elements, are also described in International Publication Numbers WO 95/24771 and WO 96/21999, and in an article by Tscha, et al., entitled “A Subscriber Signaling Gateway between CDMA Mobile Station and GSM Mobile Switching Center,” in Proceedings of the 2nd International Conference on Universal Personal Communications, Ottawa (1993), pp. 181-185, which are incorporated herein by reference.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide methods and apparatus for conveying signaling over dedicated channels of an air interface between mobile stations and base station subsystems in a hybrid Global System for Mobile (GSM)/Code Division Multiple Access (CDMA) cellular communications network.
It is a further object of some aspects of the present invention to provide communications protocols that enable the use of GSM-compatible signaling over dedicated channels of a CDMA air interface.
In preferred embodiments of the present invention, a mixed GSM/CDMA cellular communications system includes one or more CDMA base station subsystems (BSSs), controlled by a GSM mobile switching center (MSC). A mobile station (MS) and one of the BSSs communicate over a CDMA air interface (i.e., physical layer) using a protocol stack including a data link layer that is modified so as to support a GSM-CDMA radio interface layer that is based on a GSM radio interface layer. Preferably, at least the Radio Resource (RR) sublayer of the GSM radio interface layer is also modified so as to interact with the CDMA air interface (i.e., physical layer), as described further in a U.S. patent application Ser. No. 09/119,717, entitled “Base Station Handover in a Hybrid GSM/CDMA Network,” filed Jul. 20, 1998, which is assigned to the assignee of the present patent application and is incorporated herein by reference. This modified RR is referred to as a GSM-CDMA RR.
The system thus enables the use of GSM signaling in dedicated traffic channels over the CDMA air interface. The modifications to the protocol stack provide functionality required to support substantially all of the GSM dedicated channel signaling services that are not provided by CDMA communications industry standards.
In some preferred embodiments of the present invention, the mixed GSM/CDMA cellular communications system includes both TDMA and CDMA base stations, jointly controlled by a mobile switching center (MSC). Systems of this type are described generally in the above-mentioned international applications and the above referenced U.S. patent application entitled “Base Station Handover in a Hybrid GSM/CDMA Network”. The MS is capable of communicating with both types of base stations, by appropriately switching between TDMA and CDMA air interfaces, while preferably using GSM network and signaling protocols over both types of interface. This use of GSM protocols over the CDMA air interface is enabled by the modified data link layer and by suitable modification of the GSM-RR sublayer. The Mobility Management (MM) and Call Management (CM) sublayers are preferably substantially unmodified relative to GSM standards.
In some preferred embodiments of the present invention, the modified data link layer comprises two sublaye

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