Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2001-06-18
2003-08-26
Nguyen, Steven (Department: 2665)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S352000, C370S328000
Reexamination Certificate
active
06611510
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to wireless Internet Protocol (IP) networks. More specifically, this invention relates to the soft handoff of mobile terminals in wireless Code Division Multiple Access (CDMA) IP networks.
BACKGROUND OF THE INVENTION
Modem wireless networks commonly employ CDMA techniques to communicate information between a mobile terminal and a base station. Modulating information using CDMA techniques provides an advantage over other modulation methods because CDMA techniques enable multiple base stations to simultaneously use the same channel space to communicate information. Thus, CDMA techniques permit channel overlap between base stations, which has a number of significant advantages in wireless communication systems, including the reduction of interference between mobile terminals and base stations, the exploitation of wireless network multipath components, and the simultaneous modulation and demodulation of information on multiple channels with multiple base stations.
Soft handoff is one method that uses these advantages to reduce error and increase the quality of service for wireless CDMA networks. Soft handoff is a steady-state condition wherein a mobile terminal simultaneously communicates identical information with a plurality of base stations. Soft handoff increases transmission and reception diversity at the mobile terminal, thereby increasing information capacity and quality of service while reducing the requisite signal to noise power ratio necessary to reliably communicate information. Soft handoff typically exists throughout a mobile terminal's network connection; nonetheless, the plurality of base stations that communicate with the mobile terminal may change as the mobile terminal physically changes location, thereby requiring the mobile terminal to switch the base stations with which it communicates.
In order to implement soft handoff within a wireless CDMA network, a mobile terminal and the plurality of base stations it communicates with must perform certain functions in order to maintain the plurality of mobile terminal-base station network connections. First, the mobile terminal must receive multiple redundant base station transmissions on the forward link from the plurality of base stations to the mobile terminal and combine these redundant transmissions to aggregate the information sent by the plurality of base stations. This aggregation reduces the information error rate and increases the quality of service for the mobile terminal. The base stations must use identical CDMA symbols to modulate information and synchronize their redundant transmissions to the mobile terminal on the forward link for the mobile terminal to accurately aggregate and demodulate the redundant transmissions received from the base stations.
In addition, the plurality of base stations receive multiple redundant mobile terminal transmissions on the reverse link from the mobile terminal to the plurality of base stations. A mobile switching center aggregates or selects appropriate transmissions from the multiple redundant transmissions received by the base stations in order to reduce the error rate and maintain a sufficient quality of service. Thus, the mobile terminal must also synchronously transmit information modulated with identical CDMA symbols to the plurality of base stations for the mobile switching center to aggregate or select the redundant transmissions received from the mobile terminal by way of the different base stations.
Modern wireless IP architectures use IP-based protocols to communicate messages in data packets between mobile terminals and base stations and specifically IP version 4 (“IP
v
4”) protocols. In these architectures, IP base stations are connected to a wireless IP backbone network through edge routers, which interface the IP base stations with the IP backbone network. Each IP base station performs dual functions as both an RF front end for base station-mobile terminal communications and as a real-time router for IP data packets communicated between the mobile terminals and the wireless IP backbone network. The wireless IP backbone network further includes an IP-based control plane to route messages to and from the IP base stations that communicate with the mobile terminals.
Variations of wireless IP architectures include architectures wherein each base station's coverage area defines an IP subnet. In these “all IP” architectures, each base station has its own IP subnet address, and each base station and mobile terminal requires layer 3 mobility management techniques to communicate messages between the base station and a mobile terminal as the mobile terminal crosses a cell boundary. Thus, a mobile terminal may require an IP subnet address change when it crosses from one cell site to another using Mobile IP, DHCP, DRCP, or other layer 3 mobility management techniques.
Supporting soft handoff of mobile terminals in “all IP” architectures is accomplished using IP multicasting to simultaneously communicate information between a mobile terminal and a plurality of base stations. IP multicasting is a method wherein a plurality of multicast group participants are part of a multicast group. Whenever a message is broadcast to the multicast group, the message is sent to every multicast group participant.
Soft handoff of a mobile terminal can be visualized as a layer 2 multicasting process, wherein identical information is transmitted to a mobile terminal from an IP network via a plurality of multicast participants that are members of the mobile terminal's multicast group. Each multicast participant is an IP network interface that resides at the mobile terminal. When the plurality of multicast participants are established at the mobile terminal, a corresponding number of multicast network connections are created between the IP network and the mobile terminal. The IP network and the mobile terminal simultaneously communicate identical information via these separate multicast network connections by sending and responding to messages multicast to the mobile terminal's multicast group. Thus, soft handoff of the mobile terminal is accomplished by establishing a multicast group corresponding to the mobile terminal, creating a plurality of multicast participants within the mobile terminal's multicast group located at the mobile terminal, and communicating information between the mobile terminal and the IP network as multicast messages to the mobile terminal's multicast group.
In the context of a wireless CDMA IP network, each multicast network connection corresponds to a communication channel between a mobile terminal and a base station. When a plurality of multicast participants are created at a mobile terminal, each multicast participant corresponds to a multicast network connection between a base station and the mobile terminal. Each multicast network connection originates at one of the base stations and ends at the mobile terminal as a multicast IP network interface. Thus, a plurality of wireless CDMA IP network connections exist between the mobile terminal and the IP network through the plurality of multicast network connections between the base stations and the mobile terminal.
Once the plurality of multicast participants and multicast IP interfaces are established at the mobile terminal, information is communicated between the mobile terminal and the base stations by broadcasting the information to the mobile terminal's multicast group. The mobile terminal's multicast group is identified by the IP multicast address assigned to the mobile terminal that associates the mobile terminal with its multicast group and group participants. Multicast messages between the base stations and the mobile terminal are modulated and demodulated using CDMA techniques, thereby allowing the mobile terminal and its multicast network connections to share channel space with other mobile terminals and their multicast network connections while maintaining a soft handoff condition with the wireless CDMA
Famolari David
Marples David J.
Giordano Joseph
Molinari Michael J
Nguyen Steven
Telcordia Technologies Inc.
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