Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2002-07-16
2004-08-17
Ton, Dang (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S312000, C370S328000, C370S349000, C455S422100, C455S503000
Reexamination Certificate
active
06778518
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to distributed radio systems and, more particularly, to an indoor system with multiple transceivers for simulcasting and selective processing of received signals.
BACKGROUND OF THE INVENTION
Wireless (e.g., cellular) operators are faced with the continuing challenge of expanding the coverage areas of their systems, while at the same time adhering to cost, power, and frequency limitations. One area for expanding coverage is in indoor environments. However, it is also desired that such systems not interfere with the existing macrocellular environment, even if operating in the same frequency band for a given cellular standard.
The present invention is directed to providing a system and method that can be operated at low power levels and which cause minimal interference with the existing macrocellular environment. More specifically, the present invention is directed to a system and method in which multiple transceivers are utilized in an indoor system and which are able to each effectively transmit signals to a mobile unit at low power levels by utilizing a simulcasting technique.
SUMMARY OF THE INVENTION
A distributed radio system with multiple transceivers for communicating with mobile units via simulcasting and selective processing of received signals is disclosed. In accordance with one aspect of the invention, the system transmits at very low power levels. Due to the use of the low power levels, the system does not tend to interfere with the existing macrocellular environment.
In accordance with another aspect of the invention, the system utilizes relatively few frequency channels. The system is able to provide large geographical coverage with relatively few channels, while transmitting at low power levels, by simulcasting identical radio frequency signals from several different radio transmitters distributed within a building or similar area using the limited number of frequency channels. This allows the system to cover a relatively large indoor installation. Furthermore, as noted above, the system interferes very little with the existing macrocellular environment, even though the same frequency band for a given cellular standard is being used, given that the system is able to operate at very low power levels by utilizing the simulcast technique.
In accordance with another aspect of the invention, in one embodiment the distributed radio system includes a plurality of processing elements and radio frequency transmitter elements interconnected by an Ethernet network (e.g., the IEEE 802). The distributed radio system simulcasts a common modulating signal on a common radio frequency carrier, using at least two radio frequency transmitter elements. A set of radio frequency transmitter elements, which simulcast a common modulated radio frequency signal, are designated as a radio frequency simulcast set. In operation, the elements of a radio frequency simulcast set are configured to receive Ethernet sampled signal packets and transmit the information contained in the packets by modulating their radio frequency carrier.
In accordance with another aspect of the invention, in one embodiment the simulcast method designates a number of particular radio frequency transmitter elements to be elements of a radio frequency simulcast set. A first set of Ethernet packets is transmitted to be received by the elements of the radio frequency simulcast set. The first set of Ethernet packets is used to program the elements of the radio frequency simulcast set with a multicast address. The elements of the radio frequency simulcast set are thereafter responsive to Ethernet packets containing the multicast address as the designation media access control (MAC) address. A second set of Ethernet packets is transmitted to be received by the elements of the radio frequency simulcast set. The second set of Ethernet packets is used to program the elements of the radio frequency simulcast set to operate using a particular common radio frequency carrier. In addition, Ethernet sampled signal packets are periodically transmitted. The Ethernet sampled signal packets contain a designation address, which is equivalent to the programmed multicast address. The elements of the radio frequency simulcast set are configured to receive the Ethernet sampled signal packets. The elements of the radio frequency simulcast set modulate the common radio frequency carrier in accordance with sampled data included in the Ethernet sampled signal packets.
In accordance with another aspect of the invention, the processing elements of the system include at least one central processing unit and a plurality of airlink processing units. The central processing unit is responsible for interfacing the system to external environments, such as a macrocellular environment, or to a public switched telephone network, as well as for network management of the overall system. In one embodiment, the central processing unit may be a network chassis unit. The central processing unit is coupled to several airlink processing units through an Ethernet network. Each airlink processing unit is coupled to several radio transceivers, also through the Ethernet network. In one embodiment, the airlink processing units may be airlink chassis units.
In accordance with another aspect of the invention, the data link layer may be centralized. For the transmission of data to the mobile units, it is important that the data, which is simulcast by several transmitters, be identical. If each simulcast radio frequency transmitter element does not transmit identical signals, co-channel interference can result, thus degrading the signal received by the mobile unit. To ensure that the transmitted data is identical, the layer 2 (data link layer) is centralized at the central processing unit. Layer 2 Ethernet packets are sent by the central processing unit to several airlink processing units, which further process the layer 2 information into waveforms, which are finally transmitted by each simulcast radio transmitter.
In accordance with another aspect of the invention, transmissions may be implemented by a two-level multicast technique. In an embodiment that utilizes this technique, the transmit data is sent by the central processing unit to multiple airlink processing units in layer 2 format as multicast Ethernet packets. Then, the transmit data is sent by each airlink processing unit to associated multiple radio transceivers in layer 1 format (sample waveforms), also as multicast Ethernet packets.
In accordance with another aspect of the invention, when signals transmitted from a mobile unit are detected by multiple radio receivers, the system is able to select a desired radio receiver signal for processing. The multiple radio receivers simultaneously provide detected data into the system. The detected data includes identical information, but at different quality levels. The system is able to select a desired signal for processing.
In accordance with another aspect of the invention, when selecting a received signal for processing, a distributed processing technique is utilized that performs a process of gradual selection. A given mobile device may be located in relatively close proximity to several possible wireless receivers. It is desired to select and process only the signal that is provided by the receiver having the strongest signal from the mobile unit. A selection decision is made by a process that has visibility to all of the relevant receivers in the system.
In accordance with another aspect of the invention, in a preferred embodiment, the system is interconnected via Ethernet links having limited bandwidth. This configuration would generally make it impractical to forward data from every receiver in the selective decision process because such would tend to rapidly exceed the network capacity. The solution provided by the present invention is to utilize a distributed processing technique that results in gradual selection. More specifically, the selection process may be performed at several different levels, in
Heinonen Jari
Hoole Elliott
Jesse Mary
Schladetzky Brian
Veintimilla Greg
Christensen O'Connor Johnson & Kindness PLLC
Hom Shick
RadioFrame Networks, Inc.
Ton Dang
LandOfFree
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