Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-12-02
2001-04-17
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S328000
Reexamination Certificate
active
06219346
ABSTRACT:
BACKGROUND
This invention relates to cellular telephony and, more particularly, to the use of packet techniques in cellular telephony.
The number of people that use cellular telephones is continually increasing. Because the available bandwidth is controlled by governmental regulations, providers of cellular telephony are meeting the increase in users by establishing smaller cell sizes. Smaller cell sizes accommodate larger numbers of mobile units within the same overall bandwidth because smaller cell sizes effectively increase the rate of bandwidth re-use per unit area. However, as cell sizes shrink, mobile units move between cells more frequently. In a circuit switched system, each move requires that one circuit be torn down and another one set up. Consequently, as cell sizes decrease, the work associated with handing off users between cells increases. In addition, when a mobile unit traverses more cells during its connection, it is more likely that the mobile unit will encounter a cell with more units than the bandwidth can support.
Packet switching, as compared to circuit switching, reduces the work required for hand off because addresses embedded within the packets are used to route individual packets rather than setting up and tearing down circuits. Packet switching was used in early military cellular systems. Those networks were designed to be rapidly deployed, were aimed primarily for wireless interconnection between mobile units, and were not connected to a wired backbone network.
Currently, the prevalent commercial cellular system in the United States is a circuit switched arrangement that employs Time Division Multiplexing (TDM). Another system, which is also a circuit switched system, employs Code Division Multiple Access (CDMA). These cellular systems can transmit data in the form of packets, but that does not constitute “packet switching,” either in the sense employed in the aforementioned military system or in the sense employed in this disclosure. Specifically, while the data may have a packet format, the switching within the cellular environment is not based on the explicit address information in the packets. For example, in TDM the address is implicit in the frequency and time slot at which the mobile unit operates.
The explicit addressing characteristic of packet switching is more flexible than implicit addressing. With explicit addressing, the capacity on the shared medium can be reassigned as required and the destination can be changed without advance notice. Because of that, it is beneficial to fashion a packet switching approach for cellular communication that interfaces effectively with a wired backbone network.
SUMMARY
Improved performance is achieved for cellular systems with an arrangement where mobile units transmit information in packet format. A base station routes received packets to switching agents identified by the packets, and the switching agents forward the information contained in the packets to a wired network. The switching agent thus forms the interface between the packet switched portion of the cellular system and the wired network, which may be a circuit switched network. The routing of packets to switching agents allows the system to dedicate one agent to each mobile unit known to the system. It also allows a mobile unit's switching agent to remain wherever it is hosted even when the mobile unit moves from cell to cell, causing different base stations to receive the mobile unit's packets.
The routing of packets is achieved with a routing network, which preferably is immune to single failures. In one illustrative embodiment, the routing network comprises a mesh network that interfaces a multiply connected routing network.
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AT&T Corp.
Olms Douglas
Pizarro Ricardo M.
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