Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-11-24
2002-11-26
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S347000, C455S101000, C455S131000, C455S422100, C455S507000
Reexamination Certificate
active
06487187
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to wireless communication systems and in particular to a method of random access control channel synchronization compatible with time-slot synchronization and signal gain control for in-band translators deployed in peripheral cells of TDMA systems to extend the range of broadband Base Transceiver Systems (BTSs) in a cellular communication system.
BACKGROUND OF THE INVENTION
The demand for wireless communication services, such as Cellular Mobile Telephone (CMT), Personal Communication Services (PCS) and the like, typically requires the operators of such systems to serve an increasing number of users. As a result, a type base station equipment known as a MULTICARRIER broadband Base Transceiver Systems (BTS) has been developed which is intended to service a relatively large number of active mobile stations in each cell. Such broadband BTS equipment can typically service ninety-six simultaneously active mobile stations, at a cost of less than $2000 to $4000 per channel in 1998 dollars.
When coupled with efficient frequency reuse schemes, such as that described in U.S. Pat. No. 5,649,292 entitled “A Method For Obtaining Times One Frequency Reuse in Communication Systems” issued to John R. Doner and assigned to Air Net Communications Corporation, who is the assignee of the present application, maximum efficiency in densely populated urban environments is obtained. According to that arrangement, each cell is split into six radial sectors and frequencies are assigned to the sectors in such a manner as to provide the ability to reuse each available frequency in every third cell. Although this frequency reuse scheme is highly efficient, it requires at least two complete sets of MULTICARRIER transceiver equipment such as in the form of a broadband base transceiver system (BTS) to be located in each cell. Such a configuration results in dramatically increased hardware installation costs for each cell.
While this equipment is cost effective to deploy when a relatively large number of active mobile stations is expected in each cell, it is not particularly cost effective in most other situations. For example, during an initial system build-out phase, a service provider does not actually need to use large numbers of radio channels. It is therefore typically not possible to justify the cost of deploying complex MULTICARRIER broadband transceiver system equipment based only upon the initial number of subscribers. As a result, the investment in broadband MULTICARRIER radio equipment may not be justified until such time as the number of subscribers increases to a point where the channels are busy most of the time. Furthermore, many areas exist where the need for wireless communication systems is considerable, but where signal traffic can be expected to remain low indefinitely (such as in rural freeway locations or large commercial/industrial parks). Because only a few cells at high expected traffic demand locations (such as in a downtown urban location or a freeway intersection) will justify the initial expense of building out a network of high capacity broadband transceiver systems, the service provider is faced with a dilemma. He can build-out the system with less expensive narrowband equipment initially, to provide some level of coverage, and then upgrade to the more efficient equipment as the number of subscribers rapidly increases in the service area. However, the initial investment in narrowband equipment is then lost. Alternatively, a larger up front investment can be made to deploy the high capacity equipment at the beginning, so that once demand increases, the users of the system can be accommodated without receiving busy signals and the like. But this has the disadvantage of carrying the money cost of a larger up-front investment.
Some have proposed various techniques for expanding the service area of a master cell site. For example, the HPT Cell Site Expander product manufactured by 3 dbm, Inc., of Camarillo, Calif. consists of a base station translator which samples downlink signal traffic and translates it to a selected offset frequency. The offset carrier is transmitted to an expansion cell site via directional antennas. At the expansion cell site, the carrier is translated back to the original cellular channel and transmitted throughout the expansion cell site coverage area such as via an omnidirectional antenna. In the uplink direction, a cellular signal received, by the expansion cell site from a mobile unit is translated and then transmitted back to the base station translator, which in turn translates the signal back to its original carrier frequency.
However, such a device is designed only for use with analog-type cellular systems. A specific problem is encountered when attempting to extend the service area of a base station that uses Time Division Multiple Access (TDMA) signaling. Such a system makes use of a technique in which multiple voice or data channels are provided by dividing the access to each radio carrier frequency into carefully synchronized time slots. In order to properly demodulate a TDMA signal at the base station, a timing advance must be taken into consideration for each radio pulse received from the mobile stations. The timing advance serves to compensate for the differences in signal propagation time since the distance to the base station is different for each mobile station.
A TDMA signal transmitted in the uplink direction must therefore arrive at the Base Transceiver System with proper time alignment. If this is not the case, the signal pulses from the various mobile stations will collide, and it will not be possible for the Base Transceiver System to properly demodulate the signals. As such, it has in most instances been necessary to limit the nominal radius of a TDMA cell so that proper time alignment may be maintained.
An approach to extending the radius of a TDMA cell was disclosed in U.S. Pat. No. 5,544,171, issued to Goedecker and assigned to Alcatel N.V. This technique uses a fixed Base Transceiver System (BTS) that includes both a standard TDMA radio receiver and an additional auxiliary TDMA receiver. The auxiliary TDMA receiver receives and compensates the TDMA radio pulses from mobile stations located outside of the nominal cell radius. In this manner, interference between the TDMA signals received from a mobile station located outside of the nominal cell radius and a mobile station located within the nominal radius is avoided.
Unfortunately, the Goedecker technique is intended for use where both radio transceivers can be located entirely within the base station site. This permits the timing signals for the auxiliary TDMA receiver to be directly connected to the timing signals for the standard TDMA receiver. Thus, it would not be possible to directly apply the Goedecker technique to a remote repeater or translator arrangement, where the auxiliary TDMA receiver would have to be located many miles away from the base station site and such timing signal connection would not be possible.
Furthermore, while the HPT and Goedecker designs can be used to extend the radius of a single cell, they do not appear to suggest how to synchronize TDMA signals received from multiple mobile stations located in multiple cells simultaneously, nor do they suggest any form of random access control channel processing of initial uplink transmissions from mobile stations.
DESCRIPTION OF THE INVENTION
Objects of the Invention
It is an object of this invention to extend the available range in a cellular communication system beyond that which is normally available with Time Division Multiple Access (TDMA) air interfaces.
Another object is to provide for time delay compensation in TDMA systems without using multiple auxiliary receivers.
A further object is to compensate for the delay associated between a translating receiver deployed in a remote outlying cell and a host base station.
Yet another object is to provide for remote receiver time delay compensation in an uplink direction by measuring a delay observed in a d
Coons David D.
Komara Michael A.
Nuckols Jeffrey R.
Overton Roger L.
Schmutz Thomas R.
Airnet Communications Corporation
Akerman & Senterfitt
Chin Wellington
Tran Maikhanh
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