Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-01-26
2004-10-05
Appiah, Charles (Department: 2686)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C398S115000, C455S131000
Reexamination Certificate
active
06801767
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to wireless communications systems. More particularly, it relates to a novel method and system for distributing multiband wireless communication signals.
BACKGROUND ART
As wireless communications become a way of life in society, a challenge to wireless communications network operators is to transport and distribute multiband wireless communications signals in an efficient, flexible, and economical manner. And the challenge is particularly acute in areas that are not traditionally covered by macro-networks. Such areas reside mostly in indoor environments, including airports, malls, office buildings, tunnels, hotels, convention centers, and sports arenas.
Distributed radio systems are conventionally used in the art to provide the radio coverage to the indoor environments, employing an architecture of one distributed antenna system supporting one wireless radio frequency (RF) band. Such an architecture entails that in order to support multiple RF bands, separate distributed antenna systems must be installed in parallel, each accommodating a specific RF band. This is a rather inefficient, and at times, cumbersome undertaking.
The past few years have seen a few other approaches in the art, attempting to distribute multiband wireless communication signals in a more efficient manner. For example, U.S. Pat. No. 5,969,837 by Farber et al. describes a communications system in which multiple RF signals from multiple wireless communications networks are first combined at a base unit. The combined RF signal is then split into multiple outputs, which are subsequently converted to optical signals and transmitted to remote units by optical fibers. At each remote unit, the received optical signal is converted back to an RF signal. The RF signal is then split and routed to separate antennas, wherein each antenna is designated to a specific frequency band (e.g., PCS, GSM, or paging).
A notable disadvantage of the above prior art system is that each frequency band requires a dedicated antenna, which handles both downlink and uplink RF signals by way of a duplexer. (And it should be noted that the duplexer (84) as disclosed by Farber et al. cannot feasibly separate more than one frequency band, particularly intertwined bands such as cellular and iDEN bands.) Such a configuration can become considerably bulky and inefficient, especially when dealing with multiple (e.g., more than two) frequency bands. There are additional shortcomings common to the above and other prior art multiband distributed systems, summarized as follows:
1. The prior art systems typically employ a star architecture, in which each remote unit is connected to a main (or base) unit by a dedicated fiber-optic cable. Such an architecture is inflexible and inefficient for many applications.
2. Strong downlink RF signals transmitted by the main unit tend to interfere with the reception of weak uplink RF signals in a remote unit by saturating the front-end radio receivers.
3. Intermodulation products produced by the nonlinearities in the downlink amplifiers tend to fall into the uplink frequency bands, thereby desensitizing the uplink receivers.
4. Intermodulation products produced in one downlink frequency band often fall into other downlink frequency bands, thereby causing regulatory violations.
5. Adjacent and/or intertwined frequency bands (e.g., iDEN and cellular bands) cannot be feasibly separated and therefore effectively filtered and amplified.
6. The prior art systems cannot support Time Division Duplex (TDD) protocols, in which the downlink and uplink RF signals share the same frequency band but are interleaved in time.
7. The prior art systems are devoid of carrying out an end-to-end gain calibration, such that a prescribed gain for each of the frequency bands is established in each of the remote units.
In view of the forgoing, there is a need in the art for a multiband distributed wireless communications system that overcomes the prior art problems.
SUMMARY
The aforementioned need in the art is provided by a novel method and system for distributing multiband wireless communication signals according to the present invention. In a multiband distributed wireless communications system of the present invention, a main unit is linked to multiple remote units by optical fibers in a hybrid star/cascaded architecture. As a way of example, the main unit can be directly connected to individual remote units, and/or connected to one or more cascaded chains of remote units. The main unit can also be linked to some of the remote units via one or more expansion units in an hierarchical (or tree-like) structure. Such a hybrid star/cascaded architecture of the present invention provides a modular and flexible way of distributing multiband wireless communications signals, particularly in an indoor environment.
In the present invention, multiband wireless communications signals are transported and distributed as follows. On the downlink, a plurality of downlink RF-sets in a plurality of downlink frequency bands transmitted from a plurality of wireless communication networks are received at the main unit. The downlink RF-sets each contain downlink RF signals in one of the downlink frequency bands. Some of these downlink RF signals are frequency-division-duplexed (FDD), such that downlink and uplink RF signals are separate in frequency; while others are time-division-duplexed (TDD), such that downlink and uplink signals share the same frequency band but are separated in time.
The received downlink RF-sets are then combined into a combined downlink RF signal, which is subsequently split into multiple downlink RF-parts. Each downlink RF-part is essentially a “copy” of the combined downlink RF signal in that it contains the downlink RF signals from all of the downlink RF-sets. The downlink RF-parts are then converted to downlink optical signals in a one-to-one correspondence, which are subsequently transmitted to the remote units by way of optical fibers.
At each of the remote units, a delivered downlink optical signal is converted to a delivered downlink RF-part. The delivered downlink RF-part is then separated into a plurality of downlink RF-groups by frequency band. Individual downlink-signal-conditioning is subsequently performed on each of the downlink RF-groups, wherein the downlink-signal-conditioning includes one or more steps of RF-amplifying, gain-adjusting, and RF-filtering. By performing amplification on the downlink RF-groups separately, nonlinear intermodulation products amongst the downlink RF-groups can be effectively avoided. The individual-conditioned downlink RF-groups are then combined and transmitted to a downlink antenna. Note that in the present invention, each remote unit is in RF-communication with at least one downlink antenna dedicated to handle the downlink RF signals transmitted from the remote unit.
Likewise, each of the remote units is also in RF-communication with at least one uplink antenna dedicated to handle the uplink RF signals to be received by the remote unit. Having separate uplink and downlink antennae enables the reception of uplink RF signals and the transmission of downlink RF signals to occur with spatial separation in the present invention. Such spatial separation creates propagation loss between the transmit (uplink) and receive (downlink) antennae, which helps protect the sensitive uplink receiver from being desensitized by strong downlink RF signals and/or by downlink intermodulation products that fall into one or more uplink frequency bands.
On the uplink, multiple uplink RF signals in a plurality of uplink frequency bands are first received by the uplink antenna connected to the remote unit. The received uplink RF signals are then separated into a plurality of uplink RF-groups by frequency band. Individual uplink-signal-conditioning is subsequently performed on each of the uplink RF-groups, which includes one or more steps of RF-amplifying, gain-adjusting, and RF-filtering. The individual-conditioned uplink RF-groups are then combined into
Eisenberg John
Forth Peter
Hart David
Schwartz Adam L.
Appiah Charles
LGC Wireless Inc.
Lumen Intellectual Property Services Inc.
Mehrpour Naghmeh
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